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ST7 - 8-bit Microcontrollers
ST7MC three-phase AC induction motor control software library
Application Note
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Last Updated: 13/07/2007
Pages: 102
Related Data Briefs
Low voltage motor control demonstration kit based on the ST7MC2S4 and STS8DNH3LL
Related Datasheets
8-bit MCU with nested interrupts, Flash, 10-bit ADC, brushless motor control, five timers, SPI, LINSCI"
Related Information
Source file for ST7MC three-phase AC induction motor control software library
release note for ST7MC three-phase AC induction motor control software library
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AN1904 Application note
ST7MC three-phase AC induction motor control software library
Introduction
This Application Note describes a 3-phase induction motor control software library developed for the ST7MC. This 8-bit microcontroller contains a peripheral dedicated to 3phase brushless motor control, making it suitable for AC induction motors and permanent magnet DC/AC motors (PMDC/PMAC also called BLDC). The library described here is made of several C modules that contain a set of convenient functions for the scalar control of AC induction motors and is compatible with COSMIC (www.cosmic-software.com) and METROWERKS (www.metrowerks.com) compilers. The control of a Permanent magnet motor in Six-step mode is detailed in application note AN1905. The control of a PMAC motor in Sine wave mode with sensors is detailed in application note AN1947. This software allows users to quickly evaluate both the MCU and the available tools, and to have a motor running in a very short time when used together with the ST7MC starter kit (ST7MC-KIT/BLDC) and the demonstration AC motor (ST7MC-MOT/IND). It also eliminates the need for time consuming development of sine wave generation and speed regulation algorithms by providing ready-to-use functions that let the user concentrate on his application layer. The prerequisite for using this library is the basic knowledge of C programming, AC motor drives and power inverter hardware. In-depth know-how of ST7MC functions is only required for customizing existing modules and when adding new ones (grey modules in Figure 1) for a complete application development. Figure 1. Overall software architecture
APPLICATION LAYER
SLIP REGULATION AC MOTOR DRIVE 3-PHASE SINE WAVE GENERATION COMMUNICATION PROTOCOL
P WM A R T
W WD G
PO RTS
MCO[0..5] PWM outputs
MT C
ADC
SCI
16 -bit Timer
SPI
Emergency Stop input Speed feedback
July 2007
Rev 3
1/102
www.st.com
Contents
AN1904
Contents
1 2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Working environment set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1 Development tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1 2.1.2 2.1.3 2.1.4 Integrated Development Environments (IDE) . . . . . . . . . . . . . . . . . . . . . 6 Emulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Programmers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Star ter kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2
Library source code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.1 2.2.2 Download . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 File structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3
Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.1 2.3.2 2.3.3 lib.h file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Sine wave look-up table spreadsheet . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 HyperTerminal file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4
Technical literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3
Getting started with the library using the ST7MC-KIT/BLDC . . . . . . . 10
3.1 3.2 3.3 Running the motor with the ST7MC control panel . . . . . . . . . . . . . . . . . . 10 Library configuration file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Customizing the files for your ST7MC derivative . . . . . . . . . . . . . . . . . . . 13
3.3.1 3.3.2 3.3.3 Memory mapping with COSMIC toolchain . . . . . . . . . . . . . . . . . . . . . . . 13 Memory mapping with METROWERKS toolchain . . . . . . . . . . . . . . . . . 14 Hardware registers description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.4
How to define and add a C module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.4.1 3.4.2 Using STVD7 release 2.5.x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Using STVD7 release 3.x.x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4
Library functions per software module . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1 4.2 Function description conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Sine wave generation and speed feedback (MTC) . . . . . . . . . . . . . . . . . . 18
4.2.1 4.2.2 Over view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 List of available functions and interrupt service routines . . . . . . . . . . . . 19
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AN1904 4.2.3
Contents Detailed explanations and customization of MTCparam.h . . . . . . . . . . . 38
4.3
Induction motor scalar control (ACMOTOR) . . . . . . . . . . . . . . . . . . . . . . . 47
4.3.1 4.3.2 4.3.3 Over view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 List of available functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Detailed explanations and customization of ACMparam.h . . . . . . . . . . 58
4.4
Analog to digital converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 Module description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Caution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Customizing the ADC module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.5
I/O ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.5.1 4.5.2 Push button reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.6
PWM auto reload timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.6.1 4.6.2 Software timebases working principle . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Timebase use for the AC motor control library and demo program . . . . 75
4.7
Serial communication interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.7.1 4.7.2 4.7.3 4.7.4 4.7.5 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Changes vs ST7 library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Customization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Impor tant notice for hardware implementation . . . . . . . . . . . . . . . . . . . 78
4.8
Nested interrupt controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5
Running the demo programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.1 5.2 5.3 5.4 Open loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Closed loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Using the serial communication interface . . . . . . . . . . . . . . . . . . . . . . . . . 83 Mainparam.h file description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.4.1 5.4.2 5.4.3 Star t-up parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Brake parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Closed-loop slip control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6
Designing your application with the library . . . . . . . . . . . . . . . . . . . . . 85
6.1 Library maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
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Contents
AN1904
6.2
Incremental system build . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 Preliminar y notice on debugging tools . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Build step1: open loop, low voltage, no motor connected . . . . . . . . . . . 87 Build step2: open loop, rated voltage/power, motor connected . . . . . . . 88 Build step3: open loop, rated power, motor connected with speed feedback 88 Build step4: closed loop operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
6.3
Motor control related CPU load in the application . . . . . . . . . . . . . . . . . . 89
6.3.1 6.3.2 Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Adjustment guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Appendix A Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
A.1 Flowchar ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
A.1.1 A.1.2 A.1.3 A.1.4 A.1.5 A.1.6 A.1.7 A.1.8 A.1.9 A.1.10 A.1.11 MTC_U_CL_SO_IT interrupt routine . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 MTC_C_D_IT interrupt routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 MTC_GetRotorFreq function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 GetLastTachoPeriod function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 GetAvrgTachoPeriod function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 MTC_Star tBraking function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 MTC_Brake function state diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 MTC_StopBraking function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 ACM_InitSoftStar t function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 ACM_SoftStar t function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Open Loop motor control demo program . . . . . . . . . . . . . . . . . . . . . . . . 99
A.2
Selni motor characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
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AN1904
Features
1
Features
ST7MC Library Version 1.0.1 Overview (CPU running at 8 MHz):
Stator Frequency Range: From 0.2 Hz up to 680.0 Hz (see Section on page 44) with resolution depending on PWM frequency (typically ~0.1Hz) Voltage Resolution: 8-bit modulation index 9 to 10-bit PWM generation for sine wave (typical resolution in inaudible PWM range) PWM Frequency: can be set by default to 1.95, 3.9, 7.8, 12.5 and 15.66 kHz, with centred pattern PWM generation Brake capabilities (DC current injection) Speed reversal Tacho generator Speed acquisition Speed regulation and control routines for speed profile management CPU Load (sine wave generation only) around 20%, adjustable (see Section ). Total CPU load (including closed loop control) is typically around 30% for a standard application (see Section 6.3) Free C source code and spreadsheet for look-up tables
The 12.5 kHz switching frequency is proposed by default, providing a PWM resolution close to 10-bit with a 16-MHz CPU clock. In addition, this frequency is a good compromise between the reduction of switching losses and acoustic noise (rejected in the inaudible range due to centred mode PWM patterns). Note: These figures are for information only; this software library may be subject to changes depending on the use of the final application and peripheral resources. It must be noted that it was built using robustness-oriented structures, therefore preventing the speed or code size from being fully optimized. Table 1 below summarizes the memory required by the software library, as it is delivered. These metrics include non motor control related code, implemented for demo purposes (such as ADC management, software timebases, etc.). These must therefore be considered only as indicative figures, which will be lower in the final application. Table 1. Memory size metrics
ROM (bytes) Cosmic 5.2b Closed Loop Open loop 4943 3840 Metrowerks 1.1 5729 4361 RAM (bytes) Cosmic 5.2b 136 108 Metrowerks 1.1 161 130
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Working environment set-up
AN1904
2
Working environment set-up
This section presents the available material that is needed to start working with the ST7MC and the library discussed in this document.
2.1
2.1.1
Development tools
Integrated Development Environments (IDE)
This library has been compiled using Cosmic & Metrowerks C compilers, launched with STVD7 release 2.5.4 (ST Visual Debugger) and STVD7 release 3.x.x. A complete software package consists of:
An IDE interface: ST's proprietary STVD7 (free download available on internet: www.stmcu.com), or third party IDE (e.g. Softec Microsystems' STVD7 for InDARTSTX). A third party C-compiler: either Cosmic or Metrowerks (if needed, time limited evaluation versions can be get upon request).
The choice of the C Toolchain is left to the appreciation of the user. Both COSMIC and METROWERKS are fully supported, and the dedicated workspace (compatible with `STVD7' & `STVD7 for Indart') can be directly opened in the root of the library installation folder (AC_Metrowerks.wsp, AC_Cosmic.wsp, acmotor.stw).
2.1.2
Emulators
Two types of real-time development tools are available for debugging applications using ST7MC:
In-circuit debugger from Softec (sales type: STXF-INDART/USB). The inDART-STX from Softec Microsystems is both an emulator and a programming tool. This is achieved using the In-circuit debug module embedded on the MCU. The real-time features of the Indart include access to the working registers and 2 breakpoint settings. However trace is not available.
ST7MDT50-EMU3 emulator Full-featured emulator: real-time with trace capability, performance analysis, advanced breakpoints, light logical analyser capabilities, etc. It can also be a programming tool when used with the delivered ICC ADDON module (select STMC-ICC as hardware target in STVP7). This ICC-ADDON module allows In-Circuit-Debugging with STVD7.
2.1.3
Programmers
In order to program an MCU with the generated S19 file, you should also install the ST Visual Programmer software (please visit our internet web-site) and use a dedicated programming interface (stick programmer for example for In-Circuit-Programming). The Visual Programming tool provides an easy way to erase, program and verify the MCU content. Please note that the inDART-STX from Softec Microsystems is also a programming tool (installation of DataBlaze Programmer software is required).
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AN1904 Figure 2. STVisual Programmer software (STVP7)
Working environment set-up
2.1.4
Starter kit
The present software library was fully validated using the main hardware board (a complete inverter and control board) included in ST7MC-KIT/BLDC starter kit, and the demonstration AC motor from SELNI (Sales type ST7MC-MOT/IND). See Section A.2 on page 100 for electrical specifications of this motor. The ST7MC-KIT/BLDC starter kit also includes a lowcost inDART hardware emulator, making this tool an ideal set for starting a project and evaluating/using the library. Finally, the graphical user interface included in the starter kit (ST7MC Control Panel) is primarily intended to run motors from a PC for testing and demo purposes, and is also able to generate library configuration files, with defines corresponding to your own motor. This makes the first implementation of this library significantly easier. See Section 4 of this document for details. Therefore, for rapid implementation and evaluation of the software discussed in this application note, it is recommended to acquire the ST7MC-KIT/BLDC starter kit and one of the two compatible C-toolchain (or at least time limited evaluation versions).
2.2
2.2.1
Library source code
Download
The complete source files are available for free on ST website (www.stmcu.com), in the Technical Literature and Support Files section, as a zip file. This library is also copied by default on the hard-disk when installing the ST7MC Control Panel from Softec micro systems, or available on www.softecmicro.com, in the Downloads section, software part (AK-ST7FMC System Software).
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Working environment set-up Caution:
AN1904
It is highly recommended to check for the latest releases of the library before starting a new development, and then verify the release notes from time to time to be aware of new features that might be of interest for the project. Registration mechanisms are also available on the web sites of ST and Softec Microsystems to get automatically update information.
2.2.2
File structure
Once the files are unzipped, the following library structure appears, depending on the toolchain.
Library release 1.0.0 This release only supports STVD7 2.5.x workspace; this IDE does not provide C builder capabilities. All build information is provided in makefiles and linker command files, in dedicated folders: config\Cosmic and config\Metrowerks (see Figure 3). Object files are also provided in dedicated folders.
Figure 3.
Library structure for release 1.0.0
ACmotor \ config \ cosmic \ metrowerks \ object \ cosmic \ metrowerks \ source
Library release 1.0.1 This library contains the workspace for both the STVD7 2.5.x and STVD7 3.x IDEs. Two separate sets of folders are provided to differentiate object and configuration files, with a common set of source files (see Figure 4). This is to ensure the compatibility with STVD7 for inDART-STX, based on STVD7 2.5.3.
Figure 4.
Library structure for release 1.0.1
ACmotor_1.0.1 \ config \ cosmic \ metrowerks For STVD7_2.5.x \ object \ cosmic \ metrowerks \ Debug For STVD7_3.x \ Release \ Source \ Utilities
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AN1904
Working environment set-up
2.3
2.3.1
Utilities
lib.h file
The purpose of this header file is to provide useful macros and type re-definitions which will be used throughout the entire library:
Re-definition of data types using the following convention: a first letter indicating if a variable is signed (s) or unsigned (u), plus a number indicating the number of available bits (for instance: u8, s16, etc.), Defines for assembly mnemonics used in C source code: Nop(), Trap(),... Common macros used for bit-level access (SetBit, ClrBit,...), to get the dimension of an array (DIM[x]), etc.
2.3.2
Sine wave look-up table spreadsheet
A sine3.xls Excel file is provided with the library, in the \utilities folder. It contains the data and calculations necessary to re-generate the sine wave reference look-up table. This lookup table includes 3rd harmonics and is therefore not suitable as it is for bi-phase motor control. PWM frequency set-up on page 39.
2.3.3
HyperTerminal file
An AC Library.ht file is also provided in the \utilities folder to set-up the HyperTerminal software when the RS232 communication is enabled. Serial communication interface on page 76.
2.4
Technical literature
More information can be found on the ST website (www.st.com).
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Getting started with the library using the ST7MC-KIT/BLDC
A N 19 0 4
3
Getting started with the library using the ST7MCKIT/BLDC
There a two ways to get started with this software library.
The first method is to edit (with your motor specific features) and compile the modules described in Section 4 of this application note. Then program ST7MC and run your motor using the ST7MC-KIT/BLDC Starter-kit hardware or your own design. The second method is to use the ST7MC-KIT/BLDC Starter-kit and follow this process: run and fine tune motor parameters with the ST7MC Control Panel, generate *.h files and select/save manually key parameters, edit some of the .h files with run-time parameters collected with the GUI (see Section 4.2.3 and Section 4.3.3 for details), compile, link and program the ST7MC, run the motor.
This second method is highly recommended and is described below.
3.1
Running the motor with the ST7MC control panel
As a starting point, the open loop mode can be used for the first trials. Low voltage values can be used for safety and then increased smoothly step by step. Incremental system build on page 86 for details. Once the motor settings have been finely adjusted (whatever the driving mode, open or closed loop), the parameters have to be imported into the stand-alone library. Simply click on `Generate *.h Files' and select the source directory of the stand-alone library: see Figure 5
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AN1904 Figure 5.
Getting started with the library using the ST7MC-KIT/BLDC . ST7MC Control Panel: library header files generation
This interface generates 3 header files containing the motor and application parameters plus a file with conditional compilation keys for library re-build (see Section 3.2):
MTCparam.h contains parameters of routines directly related to the motor controller peripheral, mainly PWM, sine wave generation and speed feedback processing (see Section 4.2.3 on page 38), ACMparam.h contains parameters related to the motor and the load, such as V/f curve and speed regulation (see Section 4.3.3 on page 58), Mainparam.h contains some application/demo specific features (see Section 5.4 on page 84).
Once the above files have been generated, the whole library must be re-built. The library and its demo program will then include the new settings automatically. To launch the compilation, click on the 'rebuild all' icon of STVD7: see Figure 6 Figure 6. Rebuilding the whole application with STVD7
Rebuild
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Getting started with the library using the ST7MC-KIT/BLDC
A N 19 0 4
3.2
Library configuration file
The purpose of this file is to declare the compiler conditional compilation keys which will be used throughout the entire library compilation process, to:
define the AC motor driving mode: open / closed loop (see Section 5 and Section 5.3), define the PWM resolution (needed to define the PWM frequency range, see Section ), enable or disable the RS232 communication (see Using the serial communication interface on page 83), enable or disable the PI parameters tuning (see Regulation tuning procedure on page 62).
Below are the compilation key definitions in config.h:
// Define here the desired control type // 0 -> Open loop // 1 -> Closed loop #define CONTROL1 //------------------------------------------------------------------------// Define here the chosen PWM resolution (linked to PWM switching frequency) // 0 -> 9-bit: 1.95kHz, 3.9kHz, 7.8kHz, 15.66kHz: cf. "MTCparam.h" // 1 -> 10-bit: 12.5 kHz #define PWM_RESOLUTION 1 //------------------------------------------------------------------------// Define here the way the closed loop parameters (Kp, Ki) are set // if this label is commented, Kp and Ki are set according to a look-up table // defined in ACMparam.h. //#define PI_PARAM_TUNING //------------------------------------------------------------------------// Define here if you want to use the SCI interface to monitor some internal // variables during run time // IMPORTANT NOTE: As communication is done by polling, this will decrease // the sampling rate of the PI Speed controller #define ENABLE_RS232
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AN1904
Getting started with the library using the ST7MC-KIT/BLDC
3.3
Customizing the files for your ST7MC derivative
Figure 7.
0000h 007Fh 0080h
Memory map
HW Registers
0080h
Short Addressing RAM (zero page)
00FFh 0100h
RAM (1536/1024 768/384 Bytes)
067Fh 0680h
256 Bytes Stack
01FFh 0200h
1000h
60 KBytes
Reserved
0FFFh 1000h
16-bit Addressing RAM
01FFh or 037Fh or 047Fh or 067Fh
4000h
48 KBytes
8000h A000h E000h
32 KBytes 24 KBytes
Program Memory (60K, 48K, 32K, 24K, 8K)
FFDFh FFE0h FFFFh
Interrupt & Reset Vectors
8 KBytes
FFFFh
The ST7MC memory is shown on Figure 7. The memory arrangement may vary depending on the type of the MCU. Please refer to the ST7MC datasheet for more information. The library is dedicated by default to the ST7FMC2N6B6 MCU (SDIP56, 32KB Flash, 1K RAM). In order to target another ST7MC MCU, you may need to modify the C-toolchain configuration files. Here's a basic example of what has to be done prior to any other modifications. The above example is based on the ST7FMC2S4 MCU (TQFP 44, 16K Flash, 768 Bytes RAM).
3.3.1
Memory mapping with COSMIC toolchain
Go to \config\Cosmic, edit 32K.lkf and check the following lines, in `SEGMENT DEFINITION':
# SEGMENT DEFINITION (.text, .const,.data,.bss,.bsct,.ubsct are c compiler predefined sections) +seg .text +seg .const +seg .bsct +seg .ubsct -b0x8000 -m0x8000 -nCODE -sROM -aCODE -it -sROM # executable code # constants and strings
-b0x0080 -m0x007F -nZPAGE -sRAM #initialized variables in SHORT range -aZPAGE -nUZPAGE -sRAM # uninitialized variables in SHORT range
+seg .share -aUZPAGE -is -sRAM # shared segment (defined when using compact or memory models only) +seg .data +seg .bss -b0x0200 -m0x27F -nIDATA -sRAM # NO initialized variables -aIDATA -nUDATA -sRAM # uninitialized variables
This section contains the memory placement for the object files, listed just after this declaration. In order to enter the memory mapping of the ST7FMC2S4, the size of ROM and RAM memory have to be changed (32K -> 16K Flash, 1K RAM -> 768 Bytes RAM). For ROM:
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+seg .text -b0xc000 -m0x3fe0 -nCODE -sROM # executable code
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(where 0xc000 is the new starting address of the program memory and 0x3fe0 the size in bytes). For RAM:
+seg .bss -b0x0200 -m0x0180 -nUDATA -sRAM # uninitialized variables
(where 0x0180 is the new size of the 16 bit addressing RAM memory).
3.3.2
Memory mapping with METROWERKS toolchain
Go to \config\Metrowerks, edit acmotor.prm and check the following lines: SECTIONS ZRAM = READ_WRITE 0x0080 TO 0x00FF; RAM ROM = READ_WRITE 0x0200 TO 0x047F; = READ_ONLY 0x8000 TO 0xFFDF;
This part of the prm file contains the memory locations of pages declared at the end of the file. To modify the memory size for the ST7FMC2S4, ROM and RAM memory settings have to be changed (32K -> 16K Flash, 1K RAM -> 768 Bytes RAM): ROM = READ_ONLY 0xC000 TO 0xDFFF;
(where 0xc000 is the new starting address of the program memory), RAM = READ_WRITE 0x0200 TO 0x027F; // 16 bit addressing RAM
(where 0x027F is the end address of the 16 bit addressing RAM memory).
Caution:
The application layer has been written for the STMFC2NB6. Using a different ST7MC sales type can imply the need to do some modifications to the library, according to the available features (some of the I/O ports are not present on low-pin count packages). Please refer to the datasheet for details.
3.3.3
Hardware registers description
The library is based on the ST7FMC2N6.h file, which contains the hardware registers declarations and memory mapping for the ST7FMC2N6. It also contains most of the bit masks for the peripherals, at the exception of some Motor Controller bits and bitfields described in mtc_bits.h. The ST7FMC2N6.h is provided by default with the STVD7 release 3.x.x toolchain, usually in: C:\Program Files\STMicroelectronics\st7toolset\include All other ST7MC derivative descriptions can be found in this folder, from the ST7FMC1K2 to the ST7FMC2M9. The name of the corresponding header file will have to be changed in the config.h file.
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3.4
How to define and add a C module
This chapter describes how to define and declare a new module in a project based on the library. The example is based on the addition of 2 files: `my_file.c' and the corresponding header file `my_file.h'. The first step is the creation of these files. Existing files can be copied, pasted and renamed, or created by clicking on the `new files' icon and then saving them with the right extension (*.c or *.h). Three files (two source and one object) have to be declared in the toolchain configuration files.
3.4.1
Using STVD7 release 2.5.x
COSMIC compiler
COSMIC compiler is launched using a makefile (acmotor.mak) and the linker gets information from the linker command file 32K.lkf file. These two files need to be modified. In 32.lkf, the new object file has to be added in the common object file list, or apart from this object list with correct settings (for instance for interrupt vectors or constants that need to be at fixed location, see documentation of C compiler for details). # OBJECT FILES
..\..\object\cosmic\main.o ... ..\..\object\cosmic\my_file.o ...
# OBJECT FILES END In acmotor.mak, `my_file.c' has to be added in the C source file list: C_SRC = \ main.c \ acmotor.c \ ... \ my_file.c \ ... \ vector.c and the list of dependencies has to be updated accordingly: # RULES FOR MAKING THE OBJECT FILES: main.o: main.c lib.h ports.h adc.h pwmart.h Sci.h mtc.h acmotor.h config.h Mainparam.h ST7FMC2N6.h $(CC) ..\..\source\main.c
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METROWERKS compiler
For METROWERKS users, modifications have to be done in acmotor.prm and acmotor.mak files. In the makefile, the new object file my_file.o has to be added in the `Object file list' section and the corresponding dependencies have to be set in the `Application files' section:
# ----------------------------- OBJECT FILES LIST ----------------------------OBJ_LIST ... # --------------------------- APPLICATION FILES -----------------------------main.o : $(ENV) main.c lib.h ports.h adc.h pwmart.h sci.h mtc.h acmotor.h \ config.h MainParam.h ST7FMC2N6.h $(CC) main.c = main.o mtc.o ... my_file.o
my_file.o : $(ENV) my_file.c my_file.h lib.h ST7FMC2N6.h ... $(CC) my_file.c
In acmotor.prm the new object file has to be added in the `Project module list' section: /*** PROJECT MODULE LIST ***/
NAMES main.o mtc.o ... my_file.o ... start07.o ansi.lib END
3.4.2
Using STVD7 release 3.x.x
The procedure is far easier with STVD7 3.x.x, as the makefile and linking command files are automatically generated. In the workspace window, just right click on the selected project (either cosmic or metrowerks) and select "Add Files to Project". You'll be asked to select source file. When rebuilding the library, the configuration files will be updated accordingly.
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Getting started with the library using the ST7MC-KIT/BLDC Adding a source file using STVD7 3.x.x
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4
4.1
Library functions per software module
Function description conventions
The functions are described in the format given below: Synopsis Description Input Returns Caution Warning This section lists the required include files and prototype declarations. The functions are described with a brief explanation on how they are executed. In few lines, the format and units are given. Gives the value or error code returned by the function. Indicates the limits of the function or specific requirements that must be taken into account during library integration. Indicates important points that must be taken into account to prevent hardware failures.
Functions called Allows to prevent conflicts due to the simultaneous use of resources. Duration The approximate duration of the routine. This is performed using the maximum CPU clock frequency (8 MHz) without interrupts if not notified. Slight variations may be expected when changing compiler, options, memory models,... Indicates the proper way to use the function if there are certain prerequisites (interrupt enabled, etc.).
Code example
Some of these sections may not be included if not applicable (no parameters, obvious use, etc.).
4.2
4.2.1
Sine wave generation and speed feedback (MTC)
Overview
The "mtc.c" module is intended to handle all motor control functionalities directly linked to the motor control peripheral hardware (initialization or run-time accessed registers, interrupt service routine). It can be seen as an interface between the AC motor control specific module and the low level control routines having direct influence on the hardware (PWM outputs, speed sensor, Emergency Shutdown pin). It contains, among other functions:
basic setup / control functions for the Motor Controller Peripheral (MTC), Sine wave generation (through PWM interrupt processing), DC current braking, Direction reversal, speed acquisition related interrupts and functions.
The prototype functions are located in the "mtc.h" header file.
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4.2.2
List of available functions and interrupt service routines
The following is a list of available functions as listed in the mtc.h header file.
MTC_ResetPeripheral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_InitPeripheral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_InitSineGen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_EnableMCOutputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_DisableMCOutputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_CheckEmergencyStop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_ClearEmergencyStop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_StartBraking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_Brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_StopBraking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_Toggle_Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_Set_ClockWise_Direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_Set_CounterClockWise_Direction . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_GetRotationDirection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_GetVoltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_GetStatorFreq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_GetSlip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_InitTachoMeasure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_StartTachoFiltering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_ValidSpeedInfo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_GetRotorFreq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_UpdateSine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GetLastTachoPeriod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GetAvrgTachoPeriod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_U_CL_SO_IT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_C_D_IT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_R_Z_IT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MCES_SE_IT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SET_MTC_PAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ToCMPxL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ToCMPxH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_EnableClock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MTC_DisableClock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . on page 20 on page 20 on page 20 on page 21 on page 21 on page 22 on page 22 on page 23 on page 24 on page 25 on page 26 on page 26 on page 26 on page 26 on page 27 on page 27 on page 27 on page 28 on page 28 on page 29 on page 30 on page 31 on page 32 on page 32 on page 33 on page 34 on page 35 on page 36 on page 37 on page 37 on page 37 on page 37 on page 37
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MTC_ResetPeripheral MTC_InitPeripheral MTC_InitSineGen
Synopsis #include "mtc.h" void MTC_ResetPeripheral(void); void MTC_InitPeripheral(void); void MTC_InitSineGen(void);
Description
The purpose of these three functions is to set-up the Motor Controller peripheral and to initialize the software variables needed for sine wave generation. MTC_ResetPeripheral Resets the whole circuitry of the Motor Controller peripheral of the ST7MC, as it is found after a microcontroller RESET, with the sole exception of the MDTG and MPOL write-once registers (see datasheet for details). MTC_InitPeripheral Performs the initialization of the Motor Controller peripheral hardware registers, for the sine wave general parameters (such as PWM frequency, output polarity, deadtime, interrupts,...) and speed feedback processing (tacho input selection, edge sensitivity,...). It also starts the 12-bit PWM timer and the tacho dedicated timer (MTIM:MTIML). All required motor control related interrupts are unmasked upon completion of this routine. MTC_InitSineGen Initialization of software variables needed for sine wave generation and used in the PWM update interrupt routine. Ensures that once the PWM update interrupts will have been enabled, the sine wave generated will have a null voltage and that stator frequency change will be taken into account.
Duration Note:
2.75s for MTC_ResetPeripheral, 26s for MTC_InitPeripheral and 392s for MTC_InitSineGen.
These three functions do not need to be called by the user application, as they are managed by the ACM_Init function.
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MTC_EnableMCOutputs MTC_DisableMCOutputs
Synopsis #include "mtc.h" void MTC_EnableMCOutputs(void); void MTC_DisableMCOutputs (void);
Description
The purpose of these two functions is to configure the MCOx outputs of the ST7MC. MTC_EnableMCOutputs Enables the MCOx pins to output the PWM signals of the Motor Controller Peripheral. This function must be called to re-start PWM generation after an emergency shutdown (low state on MCES pin). MTC_DisableMCOutputs This function immediately disconnects the MCOx PWM outputs pins from the Motor Controller peripheral. It resets the MOE bit in the MCRA register, thus causing the MCOx pins to be in their reset configuration, as defined in the options bytes (high impedance or low impedance high/low state).
Duration
2.15 s
See also
ST7MC Datasheet: MTC chapter.
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MTC_CheckEmergencyStop MTC_ClearEmergencyStop
Synopsis #include "mtc.h" BOOL MTC_CheckEmergencyStop(void); void MTC_ClearEmergencyStop(void);
Description
The purpose of these two functions is to provide to the higher level control modules information regarding an Emergency Stop of the PWM operation. This information is returned by a function call once the related interrupt routine has been serviced. For users requiring immediate action taken as soon as the NMCES event occurs, the interrupt routine needs to be used directly (see MCES_SE_IT on page 36). MTC_CheckEmergencyStop Indicates if PWM outputs are enabled or not, and therefore if MOE bit (Main Output Enable) has been cleared by hardware, upon Emergency Stop event. MTC_ClearEmergencyStop Resets the boolean where the emergency Stop interrupt routine execution was recorded, regardless of the MOE bit state.
Returns
MTC_CheckEmergencyStop returns a boolean parameter, TRUE if an emergency Stop interrupt has been serviced, causing the PWM outputs to be disabled.
Duration
2.5 s
See also
ST7MC Datasheet: Motor Controller section, Emergency feature section. MCES_SE_IT on page 36.
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MTC_Star tBraking
Synopsis
#include "mtc.h" void MTC_StartBraking(u16 DutyCycle);
Description
The purpose of this function is to start the braking sequence by initializing the brake related flags, stopping the PWM interrupts generation, disabling the PWM outputs and starting the timebase needed for stator demagnetization. It also set the sine wave voltage to zero in case the braking sequence is interrupted and sine wave generation is re-started. Braking is obtained by sinking DC current in one motor winding. The braking torque is also defined in this function, in direct relation with the duty cycle applied to one of the motor winding, the other two phases being grounded (low side switches continuously ON).
Input
Duty cycle value is entered as a u16 variable without unit: to get the applied duty cycle, the value has to be compared to the CMP0 register value, defining the PWM frequency. For instance, for a PWM frequency of 12.5kHz, CMP0 = 639 (refer to the Section for details). If the DutyCycle variable is set to 32, this will lead to an applied duty cycle of 32/(639+1) = 10% (with center-aligned patterns). As the AC motor is driven in voltage mode, there's no way to define a relationship between this duty cycle, the braking torque and the current feed in the motor. This duty cycle will therefore have to be defined empirically.
Functions called MTC_UpdateSine, MTC_DisableMCOutputs, ART_SetSequenceDuration.
Duration
70 s
See also
MTC_Brake, MTC_StopBraking, flowchart on A.1.6 on page 95, Section 5.4 on page 84 and Section on page 45 for timings set-up.
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MTC_Brake
Synopsis
#include "mtc.h" void MTC_Brake(void);
Description
The purpose of this function is to handle the three phases of the braking sequence, as represented below in Figure 9 1. A waiting time for the Stator current to decrease down to zero (demagnetization), all PWM being OFF. 2. A smooth DC current increase up to expected value to avoid inrush current in the stator. 3. The sustaining of this current permanently up to the MTC_StopBraking function call.
Figure 9.
Current
. Current waveform during brake sequence
Motor running
Current Rotor demag. settle
Active brake
This function must be called as often as possible (typically from the main loop) to respect the required timings. Once the steady state current is attained, the brake continues permanently, until the MTC_StopBraking function is called. Caution 1 Independently from software timebase jitter (+/-1ms), the programmed duration may vary depending on the interval between two MTC_Brake function call (the lower the interval, the better the resolution). If the user stops calling this function, the current will be maintained to its last value (either null during rotor demagnetization or below the final expected value). 14 s average
Caution 2
Duration
Functions called ART_IsSequenceCompleted, ART_SetSequenceDuration, MTC_EnableMCOutputs, MTC_DisableMCOutputs See also MTC_Star tBraking, MTC_StopBraking, Section 5.4 on page 84 and Brake on page 45 for timings set-up, flowchart on A.1.7 on page 96.
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MTC_StopBraking
Synopsis
#include "mtc.h" void MTC_StopBraking(void);
Description
This function stops the active braking, whatever the current sequence (stator demagnetization, current settle, steady state). It disables the PWM outputs and re-starts the PWM Update interrupts generation.
Duration
41.5 s
Functions called MTC_DisableMCOutputs
Caution:
The PWM outputs are disabled when exiting this function. In order to resume motor operations, it is mandatory to call a start function (ACM_InitSoftStart, ACM_InitSoftStart_OL) or MTC_EnableMCOutputs.
See also
MTC_Star tBraking, MTC_Brake, flowchart on A.1.8 on page 96
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MTC_Toggle_Direction MTC_Set_ClockWise_Direction MTC_Set_CounterClockWise_Direction MTC_GetRotationDirection
Synopsis
#include "mtc.h" void MTC_Toggle_Direction(void) void MTC_Set_ClockWise_Direction(void) void MTC_Set_CounterClockWise_Direction(void) Direction_t MTC_GetRotationDirection(void)
Description
These functions are used to set, modify or get indication of the rotating direction. Rotation direction change is achieved by modifying the sign of the variable holding the phase shift between the three phases (either 120 or -120). The clockwise direction is defined randomly. The real direction will only depend on the physical connection of the motor.
Duration
2.25 s for MTC_Set_ClockWise_Direction and MTC_Set_CounterClockWise_Direction, 3.5s for the other two functions.
Returns
The Direction_t type is a public enumerated typedef defined in the mtc.h file: {CLOCKWISE, COUNTERCLOCKWISE}.
Caution:
No tests are performed on motor status (running or stopped) inside these functions. You must therefore be sure that motor is stopped before calling any of the three routines able to modify the rotation direction. On the contrary, if direction is changed while motor is running, it can immediately become generator, thus injecting reactive energy in the high voltage DC bus capacitor, causing the voltage to go above capacitor's maximum voltage rating.
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MTC_GetVoltage MTC_GetStatorFreq MTC_GetSlip
Synopsis
#include "mtc.h" u8 MTC_GetVoltage(void); u16 MTC_GetStatorFreq(void); u16 MTC_GetSlip(void);
Descr iption
MTC_GetVoltage This function returns the current modulation index, corresponding to the voltage applied on the motor winding. MTC_GetStatorFreq This function returns the current Stator frequency; if a stator frequency update (done in PWM Update interrupt) is on-going after a call to the MTC_UpdateSine function and it has not been completed, the previous value is returned. MTC_GetSlip This function returns the difference between the stator and rotor frequencies. This value will always be positive (unsigned variable) assuming that this software library is not designed to handle negative slip operations (i.e. motor used as a generator). However, if the slip is negative, the returned value will be zero.
Returns
Stator and slip frequencies are given in [0.1Hz] unit using 16-bit format: a returned value of 357 corresponds to 35.7Hz. The voltage is an 8-bit value; 0 to 100% modulation index is described within the 0 to 255 range; 255 corresponds to full voltage.
Duration
MTC_GetVoltage: 1.85 s MTC_GetStatorFreq: 3.5 s MTC_GetSlip: 620 s (including ~20% of CPU time spent in interrupt for sine wave generation)
See also
MTC_GetRotorFreq, MTC_UpdateSine.
Note:
MTC_GetSlip duration mainly comes from the Rotor speed calculation, done in MTC_GetRotorFreq; if MTC_GetRotorFreq and MTC_GetSlip have to be used in the same function of your own, it may be interesting to compute the slip directly from the Stator and rotor speed information to spare CPU processing time.
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MTC_InitTachoMeasure MTC_StartTachoFiltering
Synopsis
#include "mtc.h" void MTC_InitTachoMeasure(void); void MTC_StartTachoFiltering(void);
Descr iption
MTC_InitTachoMeasure The purpose of this function is to initialize the flags and variables associated with speed acquisition: the software FIFO stack where the last 4 speed acquisitions are stored, the tacho timer clock prescaler and the flag disabling rolling average. Upon completion of this routine, MTC_GetRotorFreq function call will return a speed calculated from the very last tacho capture only. MTC_Star tTachoFiltering Once called, this function enables the MTC_GetRotorFreq to return a speed corresponding to the average of the last four captured values. On the tacho event following this function call, the whole software FIFO stack is filled with the latest captured value to start the rolling average with values up to date.
Duration
MTC_InitTachoMeasure: 26 s MTC_Star tTachoFiltering: 2.75 s
Code example ... ... IMC_InitTachoMeasure();/*Must be called before motor start*/ ... /* Start routine */ if (MTC_ValidSpeedInfo(MinRotorFreq)) { MTC_StartTachoFiltering (); /* Must be called once we } are sure that we have reliable speed information */
See also
MTC_GetRotorFreq, MTC_ValidSpeedInfo.
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MTC_ValidSpeedInfo
Synopsis
#include "mtc.h" BOOL MTC_ValidSpeedInfo (u16 MinRotorFreq);
Description
The purpose of this function is to determine if the motor has actually started and if the rotor speed exceeds a given threshold above which the tachometer can be considered has providing reliable information. Two conditions are evaluated: - If the actual speed is higher than the defined threshold, - If the acceleration is positive: the very last speed captured is higher than the average of the four previous values. This is necessary to discard the parasitic information appearing at the beginning of motor rotation. This spurious tacho events are usually due to the tachogenerator technology, made of winding and magnet; at very low speed, the tacho output signal is in the range of hundreds of mV, with relatively low signal vs noise ratio.
Input
The input parameter is the minimum rotor speed at which the motor is considered as really being started, in tenth of Hz. For instance, MinRotorFreq=105 corresponds to 10.5Hz. The minimum Rotor speed has to be set inside the intrinsically stable tile of the motor's torque versus frequency characteristic (typically 10-20Hz), keeping in mind that it must not be too high: the higher this value, the bigger will be the stator voltage/current inrush current at start-up. Fur thermore it is recommended to set a value as close as possible to the target speed to be reached when exiting the start-up routine to ease the transition to the closed loop speed regulation. If the target frequency is too high, then a ramp function has to be implemented.
Returns
Boolean parameter, TRUE if both the above conditions are verified, FALSE otherwise. The function will also return FALSE if called with the MinRotorPeriod parameter set to 0 (incorrect value). 88 s maximum
Duration Caution:
There is no way to differentiate rotation directions using a tachogenerator. Take note that this routine may return TRUE in certain conditions, even if the motor is not started in the right direction. In this case, you should manage a minimum amount of time before restar ting (for instance with high inertia load). Obviously, this function may be ineffective if the start-up duration is far shorter than time needed to have at least few consecutive speed values. Functions called MTC_GetRotorFreq, GetAvrgTachoPeriod, GetLastTachoPeriod.
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MTC_GetRotorFreq
Synopsis
#include "mtc.h" u16 MTC_GetRotorFreq (void);
Description
The purpose of this function is to provide the rotor rotational frequency. The frequency is calculated using the period between two edges of the sensor signal (typically a tachometer), the [MTIM:MTIML] counter and the MPRSR prescaler. If the MTC_StartTachoFiltering function has been called previously to this function, the rotor frequency is computed as the average of the last four values and the speed value is up-to date whatever the motor speed and the tacho information rate (rolling average). On the contrary, the very last tacho period is used to do the computation; this is of interest during the start-up phase of the motor, when the tachogenerator signal is very weak.
Returns
Rotor frequency with [0.1Hz] unit; for instance a returned value of 357 corresponds to rotor mechanical frequency of 35.7Hz If the calculated speed is less than a minimum speed the returned value will be 0. This minimum speed is checked using the MPRSR prescaler value, which is automatically updated (refer to the ST7FMC datasheet for details): if its value is >= MAX_RATIO constant, the returned speed is zero. MAX_RATIO is defined in MTCparam.h; it is set by default to 7: if no tacho edges are detected within a period of 500 ms to 1 second, the motor is considered to be stopped. This time out period depends on the previous value of the MPRSR prescaler: see the equations below.
Figure 10. Time Out duration before having Freq=0, depending on MPRSR value
0xFFFF × 2 T i m e o u t = ---------------------------------- = 524 m s 16 M H z 0xFFFF × 2 0xFFFF × 2 ---x F F F F × 2 T i m e o u t = 0------------------------------- + ---------------------------------- + ---------------------------------- = 917 m s 16 M H z 16 M H z 16 M H z
5 6 7 7
MPRSR=7 MPRSR=5
Note on accuracyWith the 16-bit timer range and its automatically updated prescaler, the accuracy is better than 0.1Hz up to tacho input frequency of 1265Hz. This limit is lowered when having Fmtc below 16MHz. Duration 560 s (inc. ~20% CPU time spent in U interrupt for sine generation)
Functions called GetAvrgTachoPeriod, GetLastTachoPeriod. See also MTC_Star tTachoFiltering on page 28, MTC_C_D_IT on page 34, Customization hints in Rotor frequency computation on page 38, flowchart on A.1.3 on page 92
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MTC_UpdateSine
Synopsis
#include "mtc.h" BOOL MTC_UpdateSine (u8 NewVoltage, u16 NewFrequency);
Description
The aim of this function is to update the 3-phase sine wave parameters: the amplitude (voltage) and the frequency. This routine will limit the frequency within a range defined in the constants section of the MTCparam.h file (between LOWEST_FREQ and HIGHEST_FREQ limits). The new parameters are taken into account in the PWM Update interrupt following this function completion, thus with a maximum delay of two PWM periods, due to the PWM preload registers mechanism. NewStatorFrequency is given with [0.1Hz] unit. This unit does not correspond to the real frequency resolution, which varies with the PWM switching frequency (refer to Stator frequency resolution on page 43 for details). With the default PWM frequency of 12.5kHz, the resolution is around 0.1Hz. NewVoltage is the value of the modulation index, in 8-bit format. The 0 to 100% modulation index corresponds to the 0 to 255 range. 255 corresponds to full voltage.
Inputs
Retur n s Duration Warning
Boolean type variable. FALSE if the previous call to MTC_UpdateSine has not yet been taken into account in U interrupt. 630 s (inc. ~20% CPU time spent in U interrupt sine generation). No tests are performed in this function on the input parameters, except for the frequency range. You must therefore verify the following conditions before calling the function: voltage and frequencies must be compliant with the characteristics of the motor: over-voltage can cause motor flux saturation, excessive frequency is incompatible with motor mechanics (ball bearings or rotor may explode for instance). voltage and frequencies values should not vary too suddenly when the motor is running, to avoid over current conditions. This is usually handled by the AC motor control software layer, by means of smoothing functions and/or regulation loops. Stator frequency must not be set below the rotor frequency value: this would cause the motor to become a generator, thus injecting reactive energy in the high voltage DC bus capacitor, causing the voltage to go above the capacitor's maximum voltage rating. If this situation is foreseen in the final application, a dissipative brake has to be implemented on the three-phase power inverter. By correctly managing a PWM signal applied to a brake dedicated transistor, regenerative power can be dissipated in a power resistor.
Note:
MCOx outputs state (enabled/disabled) is not tested in this routine.
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GetLastTachoPeriod GetAvrgTachoPeriod
Synopsis
None (mtc.c module private functions).
Description
These functions provide the raw results of the tacho speed measurement, as a period between two capture events. Their result is converted by the MTC_GetRotorFreq function to get the speed of the motor in Hz.
Returns
The function returns a 32 bit variable corresponding to the time interval (averaged or not) between two tacho capture events. The unit is Tmtc, set by default to 62.5ns (1/16MHz). GetLastTachoPeriod returns the very last captured period, GetAvrgTachoPeriod returns the average of the four last captured values.
Duration
GetLastTachoPeriod: 32.6 s GetAvrgTachoPeriod: 115 s
Caution:
The GetAvrgTachoPeriod function disables the tacho capture interrupts for 5.5s (Fcpu=8MHz) to avoid the software FIFO stack being written in the capture interrupt while it is being read from the main program.
Note:
By default, these functions are defined as private to the module, assuming they are only used by MTC_GetRotorFreq function.
See also
Flowchar ts, on A.1.4 on page 93 and A.1.5 on page 94.
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MTC_U_CL_SO_IT
Synopsis
Not relevant (interrupt service routine).
Description
In this interrupt are the PWM duty cycles updated for the sine wave generation. This is done by loading the appropriate values in the MCPUx, MCPVx and MCPWx registers. This algorithm is extensively described in a dedicated application note. The Update (U) interrupt is triggered when the repetition counter is at zero value, corresponding to the loading of the values stored in the compare preload registers into the active registers. Using preload registers (with automatic hardware loading) decreases real time constraints, but as a consequence, introduces a delay: the values loaded in the current U interrupt will be used when the next one occurs.
Duration
34.1 s, including average interrupt latency of 13 cycles and IRET execution.
Caution
A software preload mechanism is implemented in the U interrupt to avoid potential problems if the interrupt is triggered during the 16-bit frequency variable update (SineFreq) in the MTC_UpdateSine function. Consequently, any change of stator frequency done by calling MTC_UpdateSine will be inactive as long as U interrupts are masked, and MTC_UpdateSine will return a boolean equal to FALSE.
Note:
No SO (Sampling Out) event is generated when running an induction motor. CL (Current Limit) interrupt can be used but is not handled in the software library as of today.
See also
Section Nested interrupt controller on page 78, flowchart on A.1.1 on page 90.
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MTC_C_D_IT
Synopsis
Not relevant (interrupt service routine).
Description
This interrupt is triggered after every active edge on the MCIx input pin. The time interval since the last event is captured in the [MZREG:MZPRV] registers and the [MTIM:MTIML] counter registers are cleared (by hardware). The purpose of this interrupt is to store this period, which will be used later to compute speed feedback by converting it into the frequency domain with the correct unit (0.1Hz). The last four acquired values are stored in a software FIFO stack which is useful to average the raw results and thus reduce errors due to noise, tachogenerator dissymmetry, etc. In this routine the FIFO stack is also initialized in a synchronous manner, if the MTC_StartTachoFiltering function has been called.
Duration
22 s, including average interrupt latency of 13 cycles and IRET execution (CPU running at 8 MHz)
Note:
No D event is generated when running an induction motor
See also
MTC_GetRotorFreq on page 30, flowchart on A.1.2 on page 91, section Nested interrupt controller on page 78.
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MTC_R_Z_IT
Synopsis
Not relevant (interrupt service routine).
Description
This interrupt occurs as soon as the prescaler of the MTIM timer is modified (this automatically updated prescaler allows to optimize the speed measurement resolution). Two flags are set in the MTCStatus byte to indicate that the prescaling ratio was increased or decreased (R+ or Revents). This information is mandatory when computing the period between two speed information in the MTC_C_D_IT interrupt service routine.
Duration
14 s, including average interrupt latency of 13 cycles and IRET execution.
Note:
No Z event is generated when running an induction motor.
See also
MTC_C_D_IT on page 34, section Nested interrupt controller on page 78, ST7MC datasheet, section 9.6.7.5 "Speed Measurement Mode".
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MCES_SE_IT
Synopsis
Not relevant (interrupt service routine).
Description
This routine is executed with top priority as soon as a low level is applied on the MCES input pin. It allows the passing of information that the MCOx PWM outputs have been disabled (this is done automatically by hardware) and stores the information in the MCES_Status variable. It also gives the possibility to add some application specific code to be processed immediately after a MCES event.
Duration
13.5 s, including average interrupt latency of 13 cycles and IRET execution.
Note:
This routine is also intended to handle Speed Error interrupts. No specific processing of this event is done in the current version of the library. Nevertheless, the corresponding SEI flag of the MCRC register is reset.
See also
MTC_CheckEmergencyStop on page 22, section Nested interrupt controller on page 78.
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SET_MTC_PAGE ToCMPxH ToCMPxL MTC_EnableClock MTC_DisableClock
Synopsis
#include "mtc_bits.h" SET_MTC_PAGE(x); (x = 0 or 1) ToCMPxL(MCPxL, 16-bit compare value); ToCMPxH(MCPxH, 16-bit compare value); MTC_EnableClock(); MTC_DisableClock();
Description
These macros are intended to ease the handling of motor control peripheral bits and specific registers. SET_MTC_PAGE selects the active peripheral register page. It must be set to page 0 once the peripheral initialization is done. ToCMPxL and ToCMPxH allow the two 8-bit PWM compare registers to be loaded without taking care of their left-alignment (bits 0..2 are not significant). MTC_EnableClock and MTC_DisableClock act directly on the motor control peripheral clock: it is not recommended to disable the clock while the motor is running, as this will freeze the PWM output state and may result in excessive current in the motor.
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4.2.3
Detailed explanations and customization of MTCparam.h
Rotor frequency computation
In order to process speed feedback with minimal CPU overhead, the MTC peripheral contains a dedicated timer. The method used to determine the rotor frequency is shown in Figure 11 (Tacho refers to the tachogenerator, a common low-cost speed sensor). Figure 11. Tacho Signal for rotor frequency calculation
Tacho pin input signal (after amplification)
TTACHO
T''
T'''
The basic principle is to have a clear on capture counter triggered by tacho signal edges. For this, a small conditioning stage may be needed to get a clean square wave signal from the sine wave generated by the tachogenerator, particularly at low speed. It is possible to have both edges sensitivity but this is not recommended to avoid problems that may arise due to a dissymmetry of the tacho magnets/coils. For the same reasons, it is also recommended to average the information over several periods, when possible (usually every time, at the exception of the starting phase where tacho information is not yet reliable enough): this is done by calling the MTC_StartTachoFiltering function. Note: Note: when using one or several Hall sensor(s) for speed feedback, signal conditioning is not necessary and the signal can be directly input on the MCIx pins. In order to minimize the CPU consumption, the only information stored during the capture interrupt routine are the register contents (MTC_C_D_IT on page 34). The conversion of the raw register's content into a convenient variable is then only done when needed, for instance every time the speed regulation task is executed (See flowchart on A.1.3 on page 92). Several parameters must be taken into account to compute the rotor frequency with a convenient unit (see Figure 12 for formula):
The number of pulses per rotor revolution (TachoPulsePerRev): this depends on the sensor (either position sensor: hall, etc. or velocity sensor: tacho generator with n number of poles, etc.), Input clock of the timer (Fmtc): the higher, the better the resolution, usually set to 16MHz, Number of motor poles pairs (PolesPairs).
To obtain the required accuracy (0.1 Hz) throughout the entire speed range, the dynamic range of a 16-bit capture registers (MZREG and MZPRV) is not enough. The tacho counter input clock is automatically prescaled according to the rotor frequency that is to be measured (see ST7MC datasheet for details on this mechanism); this is reported as a factor 2ST[3:0], where ST[3:0] are the prescaler bits from the MPRSR register. Figure 12. Equations giving rotor frequency with 0.1Hz unit
P o l e s P a i r s × F m t c × 10 1 -- -F r o t o r [ 0.1 H z ] = -------------------------------------------------------------- × ------------------------------------------3--0ST[ . ] TachoPulsePerRev Capture × 2 C a p t u r e = 256 × M Z R E G + M Z P R V
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Library functions per software module Customizing Rotor Frequency Acquisition
This parameter can be automatically modified by the ST7MC Control Panel. Depending on the system parameters (sensor characteristics, etc.), you can edit the following defines:
#define POLE_PAIR_NUM ((u8)1) /* Number of motor's pole pairs */ #define TACHO_PULSE_PER_REV ((u8)8) /* Number of pulses per revolution */ TACHO_PULSE_PER_REV is the number of logical pulses issued (directly or after amplification) by
the speed sensor after each mechanical revolution of the rotor.
POLE_PAIR_NUM
is necessary to compute a rotor frequency that ease slip frequency evaluation. Using P Pole Motors on page 71. For instance 4 pole motors (two pairs) will be coded as POLE_PAIR_NUM=2. Zero speed detection
This parameter is not modified by the ST7MC Control Panel but can be edited. MTC_GetRotorFreq on page 30 for details.
#define MAX_RATIO ((u8)7) /* Max MTIM prescaler ratio defining the lowest
expected speed feedback */
Acquisition FIFO size
The depth of the software FIFO stack where tacho information is stored can be modified in a define (this parameter is not modified by the ST7MC Control Panel): #define SPEED_FIFO_SIZE ((u8)4) Increasing this size will result in additional computing time to get the rotor frequency value. MTC_StartTachoFiltering on page 28 for details of use. Furthermore attention must be paid to the size of the FIFO, located in memory page 0 for speed optimization: each level of the stack uses 3 bytes.
PWM frequency set-up
This parameter can be automatically modified by the ST7MC Control Panel. Five values are proposed: 15.66kHz, 12.5kHz, 7.8kHz, 3.9 kHz and 1.95kHz. These five values are actually resulting from two base frequencies: 12.5kHz and 15.66kHz. The other values are derived by modifying the PWM timer prescaler (7.8kHz is 15.66kHz/2, 3.9kHz is 15.66KHz/4, etc.). For each of these two base frequencies, several parameters have to be modified:
PWM_PRSC is the value loaded in the PWM counter prescaler PWM_MCP0 is the value loaded in the Compare 0 register, which directly sets the PWM frequency; it is set to 639 for 12.5kHz (and thus linked to the PWM_10BIT key defined in config.h), while it is set to 511 for all the other frequencies (compiled with the PWM_9BIT key). OFFSET: this value is coding for the neutral point of the sine wave, where the PWM duty cycle is 50%; this value corresponds to the most significant byte only and has to be modified according to the MCP0 value. const u8 SINE3RDHARM[256]: this is the sine wave reference look-up table stored in Flash memory. As the maximum value of this table is also linked to the MCP0 value, it must be changed with the PWM switching frequency. This table can be easily recomputed with the Excel file provided with the library (sine3.xls).
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According to the above listed values, the preprocessor recomputes at compile time the conversion factors used to get the expected stator frequency with 0.1Hz unit (PWM_FREQ and STATOR_FREQ_RESOL, see Adjusting the CPU load related to sine wave generation on page 42 for details). Note: 1 The provided look-up tables contain 3rd harmonics by default, which allows around 15% more voltage to be obtained on a motor, out of a given DC bus, compared to pure sine, see Third harmonics modulation on page 40 for explanations. The sine wave generation method will be described in details in a dedicated Application note. Refer to it for implementation details. To summarize, PWM frequency can be manually modified by editing a conditional compilation key in config.h: // Define here the chosen PWM resolution (linked to PWM switching frequency) // 0 -> 9-bit: 1.95kHz, 3.9kHz, 7.8kHz, 15.66kHz: cf. "MTCparam.h" // 1 -> 10-bit: 12.5 kHz #define PWM_RESOLUTION 1 and the PWM counter prescaler in MTCparam.h: // Prescaler ratio defines PWM frequency in a rough way: // 0 -> 15.66kHz, 12.5 kHz (depending on CMP0 value) // 1 -> 7.8kHz // 3 -> 3.9kHz // 7 -> 1.95kHz #define PWM_PRSC ((u8)0)
2
Third harmonics modulation
To fulfil the basic AC induction motor voltage needs, the reference PWM modulating signal can be a pure sine wave (Figure 13 left), but this kind of modulation has the drawback that it makes poor usage of the DC bus voltage. Let's consider Vbus as the bus voltage after mains rectification. One can easily find that the maximum available voltage on a motor using a standard three-phase power inverter is around 86% of Vbus.
Vb u s Vb u s V p h a s e n e u t r a l = ----------- with V n e u t r a l = ----------2 2 Vp h a s e p h a s e = 3 3 V p k = ------ V b u s 2
Adding a third harmonic modulation to the reference sine wave fundamental decreases the overall amplitude of the resulting PWM modulation (PWM duty cycle never reaches either 0% or 100%, Figure 13 right). This is due to the fact that the minimum of the 3rd harmonic corresponds to the maximum of the fundamental and vice versa.
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Library functions per software module Figure 13. Pure sine wave modulation and equivalent with third harmonic added
Sinewave modulation
120 PWM duty cycle (full modulation)
PWM duty cycle (full modulation) 120 100 80 60 40 20 0 -20
Sine wav e modulation with 3rd harmonic injection e quiv ale nt to pure sinewave modulation
100 80 60 40 20 0 -20 P MM dulation Wo
PW M Modulation Third harmonic Unc ompens ated Fundamental
As a consequence, this allows the fundamental + 3rd harmonic resulting signal amplitude to be increased up to the point were the modulating signal reaches the DC bus limits (i.e. 100% PWM modulation): see Figure 14 It can be shown that by applying an appropriate coefficient to the third harmonic component, the fundamental amplitude can be increased by 15%. Figure 14. Third harmonic injection with increased fundamental amplitude
Sinewave modulation with 3rd harmonic injection
120 PWM duty cycle (full modulation) 100 80 60 40 20 0 -20 P MM dulation Wo Third harm nic o Fundam ntal + 15% e
Finally, when considering the phase to phase voltage on the motor, third harmonic components are mutually cancelled out (a 120-degree phase-shift on the fundamental corresponds to a 360-degree shift for the third harmonic) and we have on the motor winding:
Sinusoidal voltage (and therefore currents) on the motor, meaning no extra iron losses due to current harmonics, Phase to phase voltage 15% higher than with pure sine wave PWM modulation.
Figure 15 below shows on top the filtered PWM modulation on one of the three half-bridges and the corresponding currents in the three motor phases.
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Library functions per software module Figure 15. Third harmonic PWM modulation and corresponding currents
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To summarize, third harmonic injection allows:
a decrease in the diameter of the copper winding in the motor for a given power rating, an increase in the current in the motor for a given frequency, therefore providing more output power, an increase in the maximum reachable speed for a given motor, as long as mechanics (ball-bearings mainly) are suited for higher speed operations.
Adjusting the CPU load related to sine wave generation
The Motor controller peripheral has the built-in capability to avoid systematic generation of PWM compare registers update interrupts (so called U events). This is handled by a repetition counter (see ST7MC datasheet for details) which allows to finely adjust the CPU load related to the sine wave generation, for a given PWM frequency. The Figure 16 shows the time spent in ISR versus the Repetition counter (REP) settings (where Tpwm=1/Fpwm). Figure 16. Influence of the repetition counter on the interrupt processing load
Centred pattern PWM PMW Counter REP=0 REP=1 REP=2 REP=3 REP=4 Edged-aligned pattern PWM
Tp w m
Tp w m
PWM Update (U) Interrupt service routine
Knowing the duration of the U interrupt service routine (MTC_U_CL_SO_IT): 34,1s and the PWM frequency, it is easy to compute the CPU load, following the equation on Figure 16
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Library functions per software module Figure 17. CPU load vs switching frequency and repetition rate
Fp w m Fp w m 6 4 C P U l o a d = ------------------------------------ × 34.1 ×10 × 100 = ---------------------------------- × 34.1 ×10 (Centred patterns) RefreshRate (REP + 1) / 2 Fp w m Fp w m 6 4 C P U l o a d = ------------------------------------ × 34.1 ×10 × 100 = ---------------------- × 34.1 ×10 (Edge-aligned patterns) RefreshRate REP + 1
For instance, 12.5kHz PWM, REP=3, centred patterns will give: CPU load = (12500/2)x34.1x10-6x100 = 21.3%.
Repetition rate set-up with library release 1.0.0
This is done directly in the mtc.c file, in the MTC_InitPeripheral function: MREP = 1; // Preload registers are loaded every PWM cycle To maintain the correct conversion factor for the stator frequency, one must also modify a define in the MTCparam.h file (set by default for REP=1 with centred patterns): #define PWM_FREQ ((u16) (MTC_CLOCK / (u32)(PATTERN_TYPE * PWM_MCP0 * (PWM_PRSC+1)))) //Resolution: 1Hz */ For REP=2 with centred patterns, one must divide by 1.5: #define PWM_FREQ((u16) (MTC_CLOCK * 2 / (u32)(PATTERN_TYPE * PWM_MCP0 * (PWM_PRSC+1)*3))) For REP=2 with centred patterns, one must divide by 2: #define PWM_FREQ((u16) (MTC_CLOCK / (u32)(PATTERN_TYPE * PWM_MCP0 * (PWM_PRSC+1)*2))) And so on...
Repetition rate set-up with library release 1.x.x
A parameter has been added in the MTCParam.h file: REP_RATE, which has to be set to the desired refresh rate (the value loaded in the repetition counter). For instance, for REP=3: #define REP_RATE ((u8)3) The PWM_FREQ factor is now automatically adjusted according to this value: #define PWM_FREQ ((u16) (MTC_CLOCK * 2 / (u32)(PATTERN_TYPE * PWM_MCP0 * (PWM_PRSC+1)*(REP_RATE+1))))
Stator frequency resolution
With the current sine wave generation method, the Stator frequency resolution is constant and depends on the PWM frequency and on the repetition rate, as shown in the formula in Figure 18). Figure 18. Frequency resolution
Fp w m Fp w m R e s o l u t i o n = ------------------------------------ / 65536 = ---------------------------------- / 65536 ( REP + 1 ) / 2 RefreshRate Fp w m Fp w m R e s o l u t i o n = ------------------------------------ / 65536 = ---------------------- / 65536 REP + 1 RefreshRate (Centred patterns)
(Edge-aligned patterns)
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Library functions per software module For instance, with 12.5kHz PWM, REP=3, centred patterns, the resolution is: Res = 12500/1/65535 = 0.1Hz.
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Stator frequency range
This parameter can be automatically modified by the ST7MC Control Panel, and sets the stator frequency range for the motor, with 0.1Hz unit. MTC_UpdateSine on page 31. #define HIGHEST_FREQ ((u16)3400)// Sine wave Max Frequency (max theoretical: 65535) #define LOWEST_FREQ ((u16)30)// Sine wave Min. Frequency Caution: Sampling theorem constraints must be kept in mind when defining the maximum stator frequency. A minimum ratio of 15 to 30 between the stator frequency and the reference look up table sampling is mandatory to avoid sub-harmonics in the motor current (refer to the formula on Figure 19). For instance, with Fpwm = 12.5kHz, centred pattern PWM, REP = 3, Fmax = 12500 / 2 / 15 = 416Hz. Figure 19. Maximum Stator frequency
Fp w m / ( ( R E P + 1 ) / 2 ) F M a x --------------------------------------------------------15 Fp w m / ( R E P + 1 ) F M a x --------------------------------------------15 (centred pattern)
(Edge-aligned pattern)
Motor Control Peripheral Clock
This parameter is not modified by the ST7MC Control Panel but can be edited. It indicates the motor control peripheral input clock (in Hz) and is necessary to properly compute both:
the rotor frequency from the tachogenerator information, the stator frequency.
#define MTC_CLOCK ((u32)160 0 00) /* Resolution: 1Hz */
Deadtime
This parameter can be automatically modified by the ST7MC Control Panel, for values above 625ns in order to be compatible with the provided hardware. If needed, for lower values for instance, the value can be edited, keeping in mind that only the 6 least significant bits are coding for the deadtime value. The MDTG bits coding for six-steps / sine wave generation and deadtime enable/disable are managed directly in the MTC_InitPeripheral routine). #define DEADTIME ((u8)4)
Polarity
This parameter is not modified by the ST7MC Control Panel (polarity is a critical parameter linked to the gate drivers logic). It can be edited if needed. The polarity is the value loaded in the MPOL register, where bit 6 and bit 7 are not significant for AC motors. Two pre-defined polarity set-ups are provided, for drivers having the same logic for high and low-side switches:
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Library functions per software module #define L6386_POLARITY ((u8)0x3F)// Positive logic level for L6386D drivers #define NEGATIVE_POLARITY((u8)0x00)// Negative logic level drivers to be used for the set-up: #define DRIVERS_POLARITY L6386_POLARITY
Phase shift
The phase shift is set-up to get 120 for three-phase AC motors, knowing that 360 are represented by a 8-bit variable (256). We thus have Phase shift = 256 x (120/360) = 85. #define PHASE_SHIFT ((s8)85)// (85/256) * 360 = 120 degrees
Brake
Brake parameters are divided in two categories: some of them are application dependent and can be modified by the ST7MC control panel in the mainparam.h file: the braking current and duration (see Section 5.4.2 on page 84), the rest are system critical parameters directly coded in the mtc.c file. These last are: #define STATOR_DEMAG_TIME((u16)300)// Time in ms before applying DC current braking #define CURRENT_SETUP_TIME ((u8)5) // Time in ms between two consecutive values of duty cycle during braking current increase Figure 20 represents the current in a SELNI motor winding, with library default parameters, to show a normal current shape during braking. It must be noted that:
demagnetization time appears to be greater than the programmed value: this is due to the fact that current is negligible at the beginning of the current settle time (low duty cycles), using a current probe, motor standstill can be monitored by a little current spike on top of the DC current. Beware when setting up the braking torque that this can trigger the overcurrent protection if the DC braking current is too close from the current limitation threshold.
The above two mentioned parameters must be set prior to the others, by empirical tests, starting from high values (typically 500ms for demagnetization time and 5ms as the interval between current increase steps). They can then be reduced step by step, while monitoring the current wave form to avoid situations where the power stage can be damaged (see Figure 21):
if the demagnetization time is too short, a regenerative current will appear and the energy will be transferred to the DC bus capacitor, causing the bus voltage to increase, if the current settle is too steep, there will be a current overshoot.
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Library functions per software module Figure 20. Motor current in one phase when braking
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Current spike when motor reaches zero speed Demagnetization time
Figure 21. Over-current and regenerative energy hazard in case of wrong brake settings
Current overshoot when the current settle is too steep
Reactive current flowing from the motor to the bus capacitor if demagnetization time is too short
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4.3
4.3.1
Induction motor scalar control (ACMOTOR)
Overview
The purpose of this module is to provide the AC motor control specific routines, which will be called from the application software layer:
Voltage versus frequency characteristic of the motor, Star t-up management, Speed regulation if the speed sensor is available.
It handles the lower layer functions implemented in mtc.c and has no direct access on the motor control peripheral hardware registers and interrupts. Two kinds of control are possible:
In Open loop, classical V/f control can be easily implemented, where voltage is simply adjusted depending on the stator frequency. This solution is sufficient when no precise speed control is necessary, nor efficiency optimization. Typical application field is where loads are slowly varying and are known: pumps, fans,... In closed loop, an improved scalar control method is proposed, which allows good performance and avoids the drawbacks of the classical scalar control implementations: this method is based on a slip regulation which dynamically adjusts the motor voltage to maintain the best efficiency.
Among the set of functions described in the following pages, the following can be distinguished:
ACM_SustainSpeed is here just as an example, its structure must be modified to implement a state machine in the main program and avoid spending the complete speed ramp duration inside the related routine (to be able to return periodically in the main routine to refresh the watchdog for instance). ACM_Init, ACM_VoltageMaxAllowed, ACM_InitSoftStart, ACM_InitSoftStart_OL, ACM_SoftStart, ACM_SoftStartOL, ACM_InitSlipFreqReg, ACM_SlipRegulation, ACM_GetPIParam, ACM_GetOptimumSlip, are on the contrary ready-to-use functions: their duration is set to minimum for them to be used in a state machine (such as the one implemented in main.c for demo purposes).
The prototype functions are located in the "acmotor.h" header file.
4.3.2
List of available functions
As listed in the acmotor.h header file.
ACM_Init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_VoltageMaxAllowed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_InitSoftStart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_InitSoftStart_OL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_SoftStart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_SoftStartOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_SustainSpeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_InitSlipFreqReg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_SlipRegulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_GetPIParam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACM_GetOptimumSlip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . on page 48 on page 49 on page 50 on page 50 on page 51 on page 52 on page 53 on page 54 on page 55 on page 56 on page 57
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ACM_Init
Synopsis
#include "acmotor.h" void ACM_Init (void);
Descr iption
This function performs the initialization of the ACM module. It initializes the hardware related software layer (mtc.c module) and the sine wave generation with the variable Voltage = 0 to be sure that duty cycle on each phase is 50% (corresponding to a null motor voltage) when starting the PWM operation.
Duration
460 s.
Functions called MTC_InitPeripheral, MTC_InitSineGen, MTC_Set_ClockWise_Direction, ART_SetSpeedRegPeriod.
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ACM_VoltageMaxAllowed
Synopsis
#include "acmotor.h" u8 ACM_VoltageMaxAllowed(u16 StatorFrequency);
Description
This function returns an indicative voltage value corresponding to a given stator frequency. This is usually know as the V/f curve. The characteristic points of this curve are represented in the figure below and can be set in the ACMparam.h file. Refer to Section on page 58 for cautions and the procedure to set-up this curve. This function does not update the stator voltage; this has to be done with the MTC_UpdateSine function.
Figure 22. Standard Voltage/Frequency Characteristics and Set-points
Voltage (8-bit modulation index)
V_MAX
V_MIN VF_LOWFREQ_LIMIT
Frequency (Hz)
VF_HIGHFREQ_LIMIT
The use of ACM_VoltageMaxAllowed depends on the motor control type. In open loop, it can be used to maintain a constant voltage versus a frequency ratio throughout a given speed range (know as rated flux operating range). The curve must be set to have the nominal torque available on the rotor shaft. It can be set also to follow a specific load torque characteristic, such as a fan. In closed loop, it must be set for the maximum motor current (given by the motor manufacturer), before motor flux saturation.The returned value is then considered as the maximum voltage which cannot be exceeded. The voltage applied to the stator can be decreased if needed when running a load below the maximum motor torque, to limit ohmic losses in the winding (operation below the rated flux operation). Inputs Returns StatorFrequency is given with [0.1Hz] unit. Modulation index voltage (unsigned 8-bit variable). If the Frequency parameter is outside the linear interpolation domain, the returned value will be V_MIN or V_MAX (no error code returned). Duration 33.5 s maximum
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ACM_InitSoftStart ACM_InitSoftStart_OL
Synopsis
#include "acmotor.h" void ACM_InitSoftStart(u16 StatorFreq); void ACM_InitSoftStart_OL(u16 StatorFreq);
Description
These functions initialize the soft start procedure: it forces the voltage to be null, enable the PMW outputs and set-up the timebases required to smoothly increase voltage and have a start-up time out. They must be called from the upper software layer just before starting the motor.
Caution:
Before calling this function, you must have started the PWM ART timer to have access to the miscellaneous timebases (see Section 4.6 on page 74).
Duration
850 s for ACM_InitSoftStart 540 s for ACM_InitSoftStart_OL
Functions called MTC_UpdateSine, MTC_EnableMCOutputs, ART_Set_TimeInMs In addition, for ACM_InitSoftStart only: ACM_VoltageMaxAllowed, MTC_InitTachoMeasure, ART_SetSequenceDuration
See also
ACM_InitSoftStar t flowchart on A.1.9 on page 97, MTC_ValidSpeedInfo on page 29, customization hints in Section on page 68.
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ACM_SoftStart
Synopsis #include "acmotor.h" Star tStatus_t ACM_SoftStart(u16 MinRotorFreq); Description This function provides a soft start which limits the inrush current in the motor. It also monitors the speed feedback to stop the voltage increase when a given minimum rotor speed is reached. The function ramps up the stator voltage linearly while the stator frequency remains constant. The ramp ends when one of the following conditions occurs: the START_TIMEOUT duration is elapsed, the motor starts and the rotor speed reached MinRotorFreq. At the end of this ramp, if the rotor speed is too low, the tacho is monitored for an additional duration (user defined EXTRA_TIMEOUT constant); this may be needed when driving high inertia loads. At the end of this time period, if the rotor speed is still not high enough, the motor is stopped and PWM outputs are disabled. Tip: Comparing the maximum voltage and the current voltage at the end of ACM_SoftStart can give an indication of the motor load. Inputs MinRotorFreq is the minimum expected rotor frequency below which the motor will not considered as started (see MTC_ValidSpeedInfo description for details). Unit is [0.1Hz]. Variable StartStatus_t typedef-ed in acmotor.h: START_OK indicates that the motor successfully starts during the predefined period. START_FAIL indicates that the motor either did not start or its speed was too low during the defined period. This is also returned if the input parameter is not correct (minimum expected rotor frequency higher than the current stator frequency). START_ONGOING indicates that soft start procedure is not yet completed. Caution: Note: The function must be called as often as possible during the start-up phase to have a linear voltage profile and accurate Time out period. ACM_InitSoftStar t must have been called before using this routine. Duration 95 s
Returns
Functions called MTC_GetStatorFreq, MTC_GetVoltage, MTC_UpdateSine, ACM_VoltageMaxAllowed, MTC_ValidSpeedInfo, MTC_StartTachoFiltering, ART_IsSequenceCompleted, MTC_DisableMCOutputs, ART_Is_TimeInMsElapsed. See also MTC_ValidSpeedInfo on page 29, Customization hints in AC motor startup method on page 68, flowchart on A.1.10 on page 98.
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ACM_SoftStartOL
Synopsis
#include "acmotor.h" BOOL ACM_SoftStartOL(u8 TargetVoltage);
Description
This function provides a Soft Start which limits the starting torque and the inrush current in the motor, when driving the motor in open loop. The voltage on the stator winding is smoothly increased until it reaches the required value, providing this function is called as often as possible until it is completed. The duration of the Soft Start depends on the voltage at the end of the start-up and on the timebase set in ACM_InitSoftStart_OL. For instance, if VOLT_SLEWRATE has been set to 15ms and Target voltage is 50, then the total duration will be:
V O L T S L E W R A T E × T a r g e t V o l t a g e = 15 × 50 = 750 m s
Finally, once the soft start is completed, the minimal interval between two sine wave parameters changes (voltage, frequency) is set; this is usually needed to avoid steep current variation during motor run time (refer to Section 5.1 on page 81 for details). Input Returns Note: Caution: Target modulation index (voltage) in unsigned 8-bit format, to be reached at the end of the soft start. Boolean, FALSE until soft start completion
It is mandatory to call the ACM_InitSoftStart_OL function before calling this routine. The function must be called as often as possible (at least with an interval lower or equal to VOLT_SLEWRATE time) during the start-up phase. This will guarantee a linear voltage profile; on the contrary the time between voltage increment will be defined by the interval between two function calls. Duration 21 s
Functions called MTC_GetVoltage, MTC_UpdateSine, ART_Set_TimeInMs. See also Customization hints in AC motor start-up method on page 68.
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ACM_SustainSpeed
Synopsis
#include "acmotor.h" void ACM_SustainSpeed(u16 Time);
Description
This function maintains the actual speed on the motor for a given duration. This is achieved using a closed loop slip control that maintains the optimum voltage level in steady state conditions.
Input
Time is given in ms.
Duration
As defined by input parameter.
Functions used MTC_GetStatorFreq, ART_Set_TimeInMs, ART_Is_TimeInMsElapsed, ART_IsRegPeriodElapsed, ACM_GetOptimumSlip, ACM_SlipRegulation, MTC_UpdateSine.
Caution:
The two functions ACM_InitSlipFreqReg and ACM_Init must have been called before ACM_SustainSpeed to set-up the regulation properly.
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ACM_InitSlipFreqReg
Synopsis
#include "acmotor.h" void ACM_InitSlipFreqReg(u8 OptimumSlip);
Descr iption
This function must be called before calling the regulation routine (typically after completing the ACM_SoftStart function). It guarantees a smooth transition from open loop to closed loop operations. It performs the initialization of the integral term of the PI regulator (VoltageIntegralTerm) formula below and reset the PI regulator clamping flags.
Voltage = Integral + Proportional (Integral = CurrentVoltage Proportional )
Input
Optimum Slip value for the current stator frequency, with [0.1Hz] unit.
Caution:
Since OptimumSlip is expected with u8 format, its value must be within the 0 to 25.5 Hz range.
Duration
1.45 ms (inc. ~20% CPU time spent in U interrupt sine generation).
Functions called MTC_GetVoltage, MTC_GetSlip, ACM_GetPIParam.
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ACM_SlipRegulation
Synopsis
#include "acmotor.h" u8 ACM_SlipRegulation(u8 OptimumSlip);
Description
This function performs a closed loop slip control to maintain the optimum voltage on stator winding. It can be shown that the AC motor efficiency is related to the slip frequency, having a maximum between zero and maximum torque slip values. This function uses a PI (Proportional and Integral) regulation algorithm to determine the most appropriate voltage value to get the expected slip frequency. Maintaining this slip optimizes the motor efficiency.
Input
OptimumSlip with [0.1Hz] unit, in u8 format. Its value must thus be within the 0 to 25.5 Hz range. Data returned by ACM_GetOptimumSlip function can be directly used as input. Modulation index voltage (u8 variable).
Returns Caution: Caution:
1. This function is executed regardless of regulator sampling time; this period must be managed by the calling function. 2. The sine wave parameters are not modified in this routine; the MTC_UpdateSine function has to be called afterwards using the voltage value returned. Duration 2.7 ms 1) (including ~20% of time spent in interrupt for sine wave generation).
Functions called MTC_GetSlip, ACM_GetPIParam, ACM_VoltageMaxAllowed. See also Code example Figure 31 on Figure 31. on page 68, ACM_GetPIParam function description. PI regulator implementation and tuning on page 62.
Note:
1
This function uses 32-bit arithmetic to be compatible with the widest range of application and speed domains. In certain conditions, it is possible to use 16-bit, which will result in a shorter execution time (see Section 6.3.2 on page 89).
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ACM_GetPIParam
Synopsis
#include "acmotor.h" void ACM_GetPIParam(u16 StatorFrequency);
Description
This function updates the value of the proportional and integral coefficient (so called Kp and Ki) needed by the PI regulator. In some applications, these coefficients have to be adjusted depending on the motor stator frequency, to reflect system dynamic response changes. The higher the speed range of the application, the higher the chance to have to modify these coefficients. For instance, at high speed, some loads may become so inertial that the proportional term may be greatly reduced or cancelled. The Kp and Ki values are extracted from a characteristic curve with two set-points, between which linear interpolation is performed (see Figure 30 on Figure 30. on page 66 for details); the corresponding global variables (Kp and Ki) are updated accordingly.
Input Note:
Stator frequency with [0.1Hz] unit, in u8 format.
NoteThe Kp and Ki variables are declared as module global variables when using the ACM_GetPIParam function, to avoid returning a pointer to a structure. This also allows you to initialize these variables once only, in the ACM_Init function for instance, if the application does not need these parameters to be modified during run time. Duration See also 15 s Section for detailed explanations on how the Kp and Ki parameters have to be set-up.
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ACM_GetOptimumSlip
Synopsis
#include "acmotor.h" u8 ACM_GetOptimumSlip(u16 StatorFrequency);
Description
The purpose of this function is to return the most appropriate slip frequency, based on the stator frequency, if this value changes within the motor operating range. Set-points for this curve may be obtained either from the motor manufacturer or from empirical trials.
Figure 23. Optimum Slip Frequency Slip Frequency (Hz)
OPT_SLIP_LOWFREQ
OPT_SLIP_HIGHFREQ OPT_SLIP_LOWFREQ_LIMIT
Stator Frequency (Hz)
OPT_SLIP_HIGHFREQ_LIMIT
Inputs
StatorFrequency with [0.1Hz] unit.
Returns
OptimumSlip with [0.1Hz] unit, in u8 format, from 0 to 25.6Hz maximum.
Duration
31.5 s (CPU running at 8 MHz).
See also
Section on page 60.
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4.3.3
Detailed explanations and customization of ACMparam.h
Voltage vs frequency curve / ACM_VoltageMaxAllowed function
Theoretical background
The stator winding of an AC motor can be approximately represented as an inductance, whose impedance increases with the stator frequency. First order, the current in the motor is proportional to the voltage applied and the torque in direct relation with the current (indeed the magnetic flux). The torque can thus be maintained to its rated value by keeping a constant voltage versus frequency ratio. This is what is called scalar control, a method commonly used for basic AC motor drives. Above a certain frequency limit, this ratio will decrease as the voltage is limited by the inverter topology, practically when modulation is at 100% (i.e. voltage = 255). A minimum voltage must also be maintained at low speed in order to energize and compensate the ohmic losses in the stator winding, and maintain a minimum magnetic flux. This finally leads to the characteristic shape shown in Figure 24 Figure 24. Standard V/f Characteristics and corresponding torque
Voltage (8-bit modulation index)
V_MAX
V_MIN VF_LOWFREQ_LIMIT
Frequency (Hz)
VF_HIGHFREQ_LIMIT
Motor torque Motor current Tmax Im a x
Frequency (Hz)
Rated flux domain Field weakening region
Implementation
Voltage is calculated by the following equations:
( StatorFrequency × VF_COEFF ) VF_OFFSET Voltage = ------------------------------------------------------------------------------------------------------------------------------ + V_MIN 256 ( 256 × ( V _MAX V_MIN ) ) VF_COEFF = ----------------------------------------------------------------------------------------------------------------------------------( VF_HIGHFREQ_LIMIT VF_LOWFREQ_LIMIT ) VF_OFFSET = VF_COEFF × VF_LOWFREQ_LIMIT
Set-points can be entered directly in the ACMparam.h header file or using the ST7MC Control Panel. Both VF_COEFF and VF_OFFSET are re-computed by the preprocessor at
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Library functions per software module compile time (multiplication by 256 is used here to maintain a sufficient accuracy and to decrease quantization effects). Important: All variables used in this function are 16-bit. When modifying set-points, you must verify the following:
VF_OFFSET 0xFFFF ( ( VF_HIGHFREQ_LIMIT × VF_COEFF ) VF_OFFSET ) 0xFFFF
On the contrary, certain variables and constants may have to be declared as u32 instead of u16. (Buffer declared inside ACM_VoltageMaxAllowed, VF_OFFSET, etc.).
Tuning the V/f characteristic
The following method can be followed to determine the three V/f curve set-points empirically (a current probe is mandatory). This must be done in open loop, to be able to freely apply any voltage or frequency on the motor and a speed sensor may be helpful.
VF_LOWFREQ_LIMIT: this is the first parameter to be set, usually corresponding to the application's lowest operating frequency, or a value slightly above. V_MIN: to determine this point, slowly increase the voltage on the motor, while maintaining the frequency to VF_LOWFREQ_LIMIT. This will result in an increasing current in the stator winding. Stop when the current level in the motor reaches the max value indicated by the motor manufacturer. Without indication, stop when the current shape become distorted from a pure sine wave to a triangular waveform, indicating flux saturation. This is the first set-point (VF_LOWFREQ_LIMIT, V_MIN). VF_HIGHFREQ_LIMIT: in no-load conditions, accelerate the motor by sequential increasing the frequency and the voltage; the voltage must be increased when the torque is not sufficient: if a speed sensor is available, this is indicated by a rapidly growing slip. Once a sufficiently high speed has been reached (if not the application's highest speed), the voltage must be set to its highest value (V_MAX =255) without saturation effects. From this point, the stator frequency must be slowly decreased, keeping in mind that the stator frequency must never be below the rotor frequency value: this would cause the motor to become a generator, thus injecting reactive energy in the high voltage DC bus capacitor, causing the voltage to go above capacitor's maximum voltage rating. This is easy to ensure with a speed feedback; if not available, just slowly decrease the frequency while checking the bus voltage value to monitor regenerative current effects. While decreasing the frequency, the current will increase in the stator winding. Stop when the current level in the motor reaches the max value indicated by the motor manufacturer. Without indication, stop when the current shape becomes distorted from a pure sine wave to a triangular waveform, indicating flux saturation. This is the second set-point (VF_HIGHFREQ_LIMIT, V_MAX=255).
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Library functions per software module Figure 25. Determining empirically the two V/f curve set-points
Voltage Increase voltage maintaining the frequency
V_MIN
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Frequency (Hz)
VF_LOWFREQ_LIMIT
Transient operations domain (start-up only)
2. Decrease frequency while maintaining voltage to its max value
Voltage
V_MAX
V_MIN
1. Increase frequency and voltage up to max value
VF_HIGHFREQ_LIMIT
Frequency (Hz)
Induction motor Optimum Slip Characteristics
Theoretical background If the slip is close to zero, the efficiency tends to be null (no additional mechanical power available) If the slip is too high, the current in the rotor increases up to values where the ohmic losses in the rotor become significant, which in turns affects the motor efficiency.
It can be shown that an AC motor efficiency varies with the slip frequency (see Figure 26):
Figure 26. AC motor efficiency vs Slip frequency
Torque Max operating slip Zero slip
Efficiency
Speed Optimum slip
Speed
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Library functions per software module Implementation
The purpose of this function is to return the most appropriate slip frequency, based on stator frequency, providing this value changes the motor operating range inside. Set-points for this curve (see Figure 27) may be obtained either from the motor manufacturer or from empirical trials. In this case, it is possible to determine the values using the ST7MC Control Panel in closed loop mode, a three-phase power meter and a motor brake. By varying the regulated slip frequency and comparing the motor input power and the mechanical power, a value giving the best efficiency will be found. The same can be done using the ST7MC starter kit in stand-alone mode, modifying the slip frequency to be regulated with a trimmer. These optimum values will then have to be reported in the code to be used by the slip regulation algorithm. The proposed function (ACM_GetOptimumSlip) performs linear interpolation between two set-points and can be used in most of the cases, provided that the measured optimum slip frequencies can be linearized. On the contrary, a look-up table may be necessary. Figure 27. Example of linear function returning Optimal Slip Value
Optimum Slip Frequency [0.1 Hz]
OPT_SLIP_LOWFREQ
OPT_SLIP_HIGHFREQ
Stator Frequency (Hz)
OPT_SLIP_LOWFREQ_LIMIT OPT_SLIP_HIGHFREQ_LIMIT
To enter the set-points described above, some defines in the ACMparam.h file must be edited according to the collected parameters: #define OPT_SLIP_LOWFREQ_LIMIT ((u16)2000)// 0.1Hz unit
#define OPT_SLIP_HIGHFREQ_LIMIT ((u16)2500)// 0.1Hz unit
#define OPT_SLIP_LOWFREQ #define OPT_SLIP_HIGHFREQ
((u8)30)// 0.1Hz unit ((u8)80)// 0.1Hz unit
The equations used to obtain the optimum slip value are comparable to the one described for the ACM_VoltageMaxAllowed function (see Section ). Set-points can be entered in the ACMparam.h header file. Both SLIP_COEFF and SLIP_OFFSET are re-computed by the preprocessor at compile time (multiplication by 256 is used here to maintain a sufficient accuracy and to decrease quantization effects).
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Important: All variables used in this function are 16-bit. When modifying set-points, you must verify the following:
SLIP_OFFSET 0xFFFF ( ( OPT_SLIP_HIGHFREQ_LIMI T × SLIP_COEFF ) SLIP _OFFSET ) 0xFFFF
However, certain variables and constants may have to be declared as u32 instead of u16. (Buffer declared inside ACM_GetOptimumSlip, SLIP_OFFSET, etc.).
PI regulator implementation and tuning
PID regulator theory and tuning methods are subjects which have been extensively discussed in the technical literature. Here is a basic reminder on the theory and a proposal of the empirical tuning method.
Theoretical background
The implemented regulator is actually a Proportional Integral one (see the note below regarding the differential term). The purpose of the regulation loop (see equation 1) is to adjust the voltage on the stator winding depending on the slip frequency.
V S t a t o r = f(S l i p) VS t a t o r = VS t a r t + Kp × E r r o rS l i p + Ki × E r r o rS l i p
t
(1) (2)
The equation 2 corresponds to a classical PI implementation, where:
Vstar t is a constant corresponding to the voltage on the motor at the end of the soft start (see Section on page 68 for details), Kp is the proportional coefficient, Ki is the integral coefficient.
The tuning and respective actions of these three parameters are discussed below. Note: No differential correction is implemented in the current regulator. Practice shows that this term leads to increased noise in the regulation loop (high pass function), in particular with low cost speed sensors such as tachogenerator. As a result, the system may become unstable or difficult to tune. Additional software filtering can be implemented to get proper differential slip error, but may result in additional response delay.
Regulation tuning procedure sampling time, propor tional coefficient, integral coefficient.
To tune the PI regulator parameters, it is advised to proceed in the following order:
In order to modify in real-time the values of the coefficients, one can use the ST7MC Control Panel or operate the ST7MC starter kit hardware in stand-alone mode. For this, a conditional compilation key must be set in the config.h file (disabled by default): #define PI_PARAM_TUNING
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Library functions per software module When this mode is activated, the ST7MC starter kit's trimmers assignmentis as follows:
RV1 sets the target speed (by default between 10 and 266 Hz by 1Hz steps) RV2 sets the Ki parameter (8-bit value, [0..255] range). RV3 sets Kp parameter (8-bit value, [0..255] range).
For convenience, it is also advised to activate the RS232 communication interface using the following key, in config.h: #define ENABLE_RS232 This will allow to read directly the Target speed and the Kp and Ki values on a PC Hyperterminal software (see Section 4.7 on page 76); it is also possible to get the rotor speed, the voltage applied on the motor or the current slip value.
Adjusting the regulation sampling Time
The sampling time needs to be modified to adjust the regulation bandwidth. As an accumulative term (the integral term) is used in the algorithm, increasing the loop time will decrease its effects (accumulation will be slower and the integral action on the output will be delayed). Inversely, decreasing the loop time will increase its effects (accumulation will be faster and integral action on the output will be increased). This is why this parameter has to be adjusted prior to set-up the integral coefficient of the PI regulator. In theory, the higher the sampling rate, the better the regulation. In practice, one must keep in mind that:
the related CPU load will grow accordingly; for instance, a 2.6ms PI routine executed every 10ms gives a 26% CPU load. the inputs of the system are usually for discrete information: a usual tachogenerator just provides 8 pulses per rotor revolution.This gives one speed information every 12.5ms if the rotor speed is 10Hz: no need in that case to have a sampling time lower than 12.5ms. at high speed, in most of the cases, system inertia is such that system response is slow: in these conditions there is no need to have a high sampling rate.
This parameter must be reported in the ACMParam.h file, in a specific define, in ms (10ms in the example below): #defineSAMPLING_TIME((u8)10)
Tuning the Proportional coefficient Kp
The Kp parameter provides the instantaneous error correction and is independent from the sampling time value. The higher the Kp, the lower the speed error and the better the dynamic response. Nevertheless, a value too high will lead to instability (see Figure 28 for speed response vs Kp value).
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Library functions per software module Figure 28. Speed correction versus Kp value (with Ki =0)
Speed
Target
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Kp=20
Ki =0 during the Kp set-up
Static error for Kp=0
K p= 0 K p= 2 Kp=5 K p= 1 0 Time
0
Here is an empirical method to tune the Kp coefficient:
With Ki=0 and Kp=0, start the motor; this is corresponding to open loop drive. At a given speed, with some load, there will be an error respect to the target speed (so called static error); by slowly increasing the Kp value, the error will decrease. When the system becomes unstable (oscillations), stop increasing Kp (this is Kp limit). The appropriate value of Kp to start working with will then be Kp = Kp limit / 2 (this is to provide a reasonable phase and gain margin). Confirm this result by trying several load conditions (if any) and slight speed variations to verify the system's dynamic response. The Kp can be slightly adjusted if necessary, keeping in mind that the final static error cancellation will be handled by the integral part of the PI regulator. The only important points to be validated are the lack of unstable behaviour over the whole working domain and a correct dynamic response (this last point will be further improved by the integral term action). Repeat the procedure for several speeds to scan the entire speed range of the application; for large speed ratios, it is most likely that several Kp values will have to be used to get the best results. Tuning the Integral coefficient Ki
This parameter Ki provides remaining static error cancellation over time. In the current implementation, as mentioned above for sampling time set-up, the integral term effectiveness is linked to the time interval between two PI regulator execution. This is to decrease the PI execution time (it removes one run-time calculation). Consequently, when starting the parameter set-up, the sampling time Ts should be frozen; if it has to be modified after having tuned the Ki, the Ki parameter will have to be re-adjusted so that its influence remains constant. The higher the Ki, the faster the speed error cancellation and the better the dynamic response. Nevertheless, a value too important will lead to instability (see Figure 29 for speed response vs Ki value). During the set-up, Kp and Ts must be kept constant with the determined values below .
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Speed
Target
Library functions per software module
Ki=20
Ki=10
Kp= x, Ki=0 Ki=2
0
Ki =5 Time
Kp and Ts are constant during the Ki set-up
Here is an empirical method to tune the Ki coefficient:
With Ki=0 and Kp=x and Ts=y, start the motor. At a given speed, with some load, there will be a static error respect to the target speed; as soon as the Ki value is different from zero, the error will start to decrease. Contrar y to proportional term adjustment, one cannot slowly increase the Ki to evaluate properly its action: it is necessary to have dynamic conditions. This can be done by suddenly
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