Application Notes | Industrial | Motor Control | 8-bit Microcontrollers | ST7 - 8-bit Microcontrollers

ST7MC three-phase BLDC motor control software library

Application Note

Format: (1786 kb)

Last Updated: 13/07/2007

Pages: 77

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 BLDC sensor motor stand alone library

Source file for ST7MC three-phase BLDC sensorless motor stand alone library

release note for ST7MC ST7MC three-phase BLDC sensorless motor stand alone library

release note for ST7MC three-phase BLDC sensor motor stand alone library

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AN1905 APPLICATION NOTE
ST7MC THREE-PHASE BLDC MOTOR CONTROL SOFTWARE LIBRARY
INTRODUCTION
This application note describes one of the software libraries available for the ST7MC MCU. The ST7MC microcontroller comes with a dedicated motor control cell (MTC) and can drive both permanent magnet DC/AC motors (PMDC/PMAC also called BLDC) and induction AC motors. This application note describes the ST7MC software library required to control a BLDC motor with a trapezoidal 6-step drive in sensor or sensorless mode, open or closed loop, and in current or voltage mode. The control of a PMAC motor in Sinewave mode with sensors is detailed in application note AN1947. The control of an AC induction motor in Sinewave mode is detailed in application note AN1904. The library is made of different C modules, compatible with both COSMIC (www.cosmic-software.com) and METROWERKS (www.metrowerks.com) toolchains. The functions are grouped into several families, making this library an easy way to go through any BLDC project development. Used in conjunction with the ST7MC starter kit (ST7MC-BLDC-KIT), evaluation can be achieved in a very short time, as the library eliminates the need to study the MCU in detail. A basic knowledge of C Language, PMDC motor drives and power inverter hardware is requ ired.

AN1905

Rev 2

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Table of Contents
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 OVERALL SOFTWARE ARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1 GETTING STARTED WITH TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1 WORKING ENVIRONMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2 SOFTWARE TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2.1 PROGRAMMERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2.2 Emulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.3 LIBRARY SOURCE CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3.1 Download . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.3.2 File structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.4 UTILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4.1 lib.h file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2 CUSTOMIZING THE WORKSPACE FOR YOUR ST7MC DERIVATIVE . . . . . . . . . 11 2.1 USING STVD7 RELEASE 2.5.X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.1 Memory mapping with the COSMIC toolchain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.1.2 Memory mapping with the METROWERKS toolchain . . . . . . . . . . . . . . . . . . . . . . . 12

2.2 USING STVD7 RELEASE 3.X.X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3 "VERSION.H" FILE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.4 ADDITIONAL OR UP-TO-DATE TECHNICAL LITERATURE . . . . . . . . . . . . . . 15 3 GETTING STARTED WITH THE LIBRARY USING THE ST7MC-KIT/BLDC . . . . . . 16 3.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.2 RUNNING THE MOTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.3 STANDALONE MODE AND CLOSED LOOP OPERATION . . . . . . . . . . . . . . . 18 3.4 NOTE ON DEBUGGING TOOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.1 Low voltage applications (below 30V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.4.2 Medium-high voltage application (above 30V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.5 USING YOUR OWN POWER STAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.6 CHECKING THE CURRENT SENSOR RESISTOR VALUE . . . . . . . . . . . . . . . 21
77 3.6.1 Maximum current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.6.2 Interpreting the current feedback/settings in the GUI . . . . . . . . . . . . . . . . . . . . . . . 23

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4 MODULES PRESENTATION, LIBRARY ROUTINES . . . . . . . . . . . . . . . . . . . . . . . . 25 4.1 LIBRARY REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.2 MTC SOFTWARE LAYER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2.1 List of available routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 4.2.2 List of MTC interrupt routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.3 APPLICATION LAYER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.3.1 4.3.2 4.3.3 4.3.4 regul.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . adc.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . it_ST7MC.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ports.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.4.1 Push button reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.4.2 LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 45 46 47 47 47

4.3.5 spi.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 4.3.6 LinSCI.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5 HOW TO DEFINE AND ADD A MODULE (STVD7 2.5.X) . . . . . . . . . . . . . . . . . . . . . 49 5.1 COSMIC TOOLCHAIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 5.2 METROWERKS TOOLCHAIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 6 CODE EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 7 PMDC (PMAC) MOTOR CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 7.1 PHYSICAL CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
7.1.1 Checking the number of pair poles of the motor . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 7.1.2 Connecting the sensor outputs to the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

7.2 CONTROL STRATEGY CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 55
7.2.1 Voltage versus current mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 Choosing a demagnetization type (Sensorless mode only) . . . . . . . . . . . . . . . . . . . 7.2.3 The 4 Z event sampling methods (Sensorless) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3.1 At the end of the PWM low state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3.2 At PWM On, with delay once . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3.3 At PWM On, with delay, at fSCF frequency . . . . . . . . . . . . . . . . . . . . . . . 7.2.3.4 At fSCF frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 56 57 57 58 58 58 59

7.2.4 Setting the PWM distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

7.3 SOFTWARE SETTING CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
7.3.1 PI regulator implementation and tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 7.3.2 Adjusting falling/rising Bemf settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 7.3.3 Completion of Fine Tuning and Other Software Considerations . . . . . . . . . . . . . . . 75

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8 REVISION HISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

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OVERALL SOFTWARE ARCHITECTURE

APPLICATION LAYER
PI REGULATION COMMUNICATION PROTOCOL

PMDC MOTOR DRIVE

WDG

I/Os
PWM outputs
MCO[0..5]

MTC

ADC

LIN SCI

16-bit SPI Timer

MCES MCIx (Optional hall effect sensors)

ST7MC Library Version 1.0 Characteristics (CPU running at 16 MHz)
- BLDC (trapezoidal 6 step method) modes available:

1. Sensorless : Back EMF voltage on the non-energized phase is monitored and used to trigger the commutation events Sensor : Hall effect sensors trigger the commutation events. 2.Voltage : PWM duty cycle is set directly via 12-Bit PWM Generator. Current : Internal current loop and external voltage reference are used conjointly to set the maximum current in motor windings. PWM duty is automatically set according to current feedback loop output. 3.Open loop operation. Closed loop operation : PI regulation, 1 to 255 ms sampling time.
- 12-bit PWM generation frequencies:

Current mode, Voltage mode: fixed 390Hz, 625Hz, 961Hz, 1.25Khz, 1.56Khz, 3.13Khz, 6.25Khz, 10Khz, 12.5Khz, 15.4Khz, 18.1Khz, 20Khz, 25Khz, 33.33Khz, 40Khz, 50Khz. (Voltage mode PWM frequency can be manually adjusted up to 50Khz in the library)

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- Required ROM/RAM:
ROM (bytes) Cosmic 4.5A Metrowerks 1.1 3400 4500 4700 6000 2370 3200 3500 4600 RAM (bytes) Cosmic 4.5A Metrowerks 1.1 100 115 130 150 85 90 120 125

Sensorless open loop Sensorless closed loop Sensor open loop Sensor closed loop

These metrics include non motor control related code, implemented for demo purposes (such as ADC management, software time bases, etc.). Depending on the chosen memory model, the code size produced can be smaller or larger. This must therefore be considered only as indicative figures.

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1 GETTING STARTED WITH TOOLS
1.1 WORKING ENVIRONMENT 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. The ST7MC-KIT/BLDC starter kit also includes a low-cost INDART hardware debugger, making this tool an ideal set for starting a project and evaluating/using the library. 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-toolchains. 1.2 SOFTWARE TOOLS This library has been compiled using COSMIC and Metrowerks C-toolchains, running under STVD7 release 2.5.4 (ST Visual Debugger) and STVD7 release 3.x.x. Free IDE and demo versions of third party toolchains can be found at http://www.st.com/mcu/ (then select Downloads). A complete software package consists of: - An IDE interface: STVD7 (free download available on internet), or third party IDE (e.g. SOFTEC Indart STX for ST7). - A third party C-compiler: either Cosmic or Metrowerks (if needed, time-limited evaluation versions can be obtained upon request. A free 4K COSMIC version can compile all stand alone firmware configurations). 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' and `STVD7 for Indart') can be directly opened in the root of the library installation folder (BLDC_Sensorless_Metrowerks_STVD2_5_4.wsp,BLDC_Sensorless_Cosmic_STVD2_5_4. wsp,BLDC_Sensor_Metrowerks_STVD3_x.wsp, BLDC_Sensor_Cosmic_STVD3_x.wsp). In addition, the GUI included in the ST7MC-KIT/BLDC starter-kit allows customization of these libraries with variables prepared for your own motor. This makes the first implementation of this library significantly easier. See Section 3 of this document. 1.2.1 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 programming interface (STICK programmer for example for In-Circuit-Programming). The Visual Programmer tool provides an easy way to erase, program and verify the MCU content. Please note that the INDART STX kit from SOFTEC (see next chapter) is also a programming tool (installation of DataBlaze Programmer is required).

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Figure 1. STVisual Programmer software

1.2.2 Emulators Two types of real-time development tools are available for debugging applications using ST7MC: - In-circuit debugger from Softec (salestype : STXF-INDART/USB) The INDART from SOFTEC features an emulation 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 real-time registers and 2 break-point settings. However, trace is not available. - ST7MDT50-EMU3 emulator Fully-featured emulator: real-time with trace capability, performance analysis, advanced breakpoints, light logical analyser capabilities, etc. It can also function as 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.

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1.3 LIBRARY SOURCE CODE 1.3.1 Download The complete source files are available for free on the ST website (http://www.st.com/mcu), in the Downloads 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 in the Downloads section of www.softecmicro.com, software part (AK-ST7FMC System Software). Important Note: It is highly recommended to check for the latest releases of the library before starting any new development, and then verify from time to time all release notes to be aware of any 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 automatically obtain update information.

1.3.2 File structure Once the files are unzipped, the following library structure appears, depending on the toolchain.

Library release 1.0

This library contains the workspace for both the STVD7 2.5.4 and STVD7 3.x IDEs. Four separate folders are provided (see Figure 2).

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Figure 2. Library structure for release 1.0 BLDCmotor_1.0 \ BLDC sensor \ config \ cosmic \ metrowerks \ object \ cosmic \ metrowerks \ source \ debug \ release \ BLDC sensorless \ config \ cosmic \ metrowerks \ object \ cosmic \ metrowerks \ source \ debug \ release \ Pair poles chk \ config \ cosmic \ metrowerks \ object \ cosmic \ metrowerks \ source \ debug \ release \ sci

1.4 UTILITIES 1.4.1 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(), etc. Common macros used for bit-level access (SetBit, ClrBit, etc.), to get the dimension of an array (DIM[x]), etc.

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2 CUSTOMIZING THE WORKSPACE FOR YOUR ST7MC DERIVATIVE
2.1 USING STVD7 RELEASE 2.5.X Figure 3. Memory Map
0000h 007Fh 0080h

HW Registers

0080h

Short Addressing RAM (zero page)
00FFh 0100h

RA M (1536/1024 768/384 Bytes)
067Fh 0680h

256 By tes S tac k
01FFh 0200h

1000h

60 KBytes

Reserved
0FFFh 1000h

16-bit Addressing RA M
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 3. The memory arrangement may vary depending on the type of the MCU. Please refer to the datasheet in order to get 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. This example is based onto the ST7FMC2S4 MCU (TQFP 44, 16K Flash, 768 Bytes RAM) 2.1.1 Memory mapping with the COSMIC toolchain Go into the ..\BLDC sensorless\config\Cosmic\ folder ( ..\BLDC sensor\config\Cosmic\ for sensor driving mode).
Edit the "BLDC_Cosmic.lkf" file and check the following lines, in `SEGMENT DEFINITION':
# SEGMENT DEFINITION (.text, .const, .data, .bss, .bsct, .ubsct, .eeprom are c compiler predefined sections) +seg .text -b0x8000 -m0x7f00 -nCODE -sROM # executable code +seg .const -aCODE -it -sROM # constants and strings +seg .bsct -b0x0080 -m0x007F -nZPAGE -sRAM # initialized variables in SHORT range +seg .ubsct -aZPAGE -nUZPAGE -sRAM # uninitialized variables in SHORT range +seg .share -aUZPAGE -is -sRAM # shared segment +seg .bss -b0x0200 -m0x0280 -nUDATA -sRAM # uninitialized variables +seg .data -aUDATA -nIDATA -sRAM # initialized variables

This section contains the memory placement for the object files, listed just after this declaration. In order to target the memory size of the ST7MC2S4, the sizes of ROM and RAM memory have to be changed (32K -> 16K Flash, 1K RAM -> 768 Bytes RAM)

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+seg .text

-b0xc000 -m0x3f00 -nCODE -sROM

# executable code

where 0xc000 is the new starting address of the program memory and 0x3fe0 the size in bytes. +seg .bss -b0x0200 -m0x0180 -nUDATA -sRAM # uninitialized variables

where 0x0180 is the new 16-bit addressing RAM memory in bytes. 2.1.2 Memory mapping with the METROWERKS toolchain
Go into ..\BLDC sensorless\config\Metrowerks ( ..\BLDC sensor\config\Metrowerks\ for sensor driving mode). Edit the "BLDC_Metrowerks.prm" file
SECTIONS ZRAM = READ_WRITE 0x0080 TO 0x00FF; // zeropage RAM = READ_WRITE 0x0200 TO 0x047F; // 16 bit adressing RAM ROM_SEC_2 = READ_ONLY 0x8000 TO 0xDFFF; // sector 2 ROM_SEC_1 = READ_ONLY 0xE000 TO 0xEFFF; // sector 1 ROM_SEC_0 = READ_ONLY 0xF000 TO 0xFEFF; // sector 0 - 0xFF00 to 0xFFDF reserved for ICC

This Section contains the memory locations of pages declared at the end of this file. To target the memory size of the ST7MC2S4, ROM and RAM memory settings have to be changed (32K -> 16K Flash, 1K RAM -> 768 Bytes RAM). ROM_SEC_2 = READ_ONLY 0xC000 TO 0xDFFF; // sector 2

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 ending address of the 16-bit addressing RAM memory Important Note: The application layer has been written for the STMFC2NB6. Using a different ST7MC sales type can imply the need for 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 data sheet for details.

2.2 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 the source file.

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When rebuilding the library, the configuration files will be updated accordingly.

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2.3 "VERSION.H" FILE The purpose of this file is to declare the compiler options which will be used throughout the entire library compilation process. Define the PMDC driving mode: voltage/current, open/closed loop In sensorless mode, 3 more options are added for the demagnetization type: hardware, hardware with software backup, software. Special care has to be taken for the demagnetization type, since the value range is 1, 2 and 3, corresponding respectively to hardware, hardware with software backup, software demagnetization type (HW, HSW, SW). Other compiler options can be disabled/enabled by writing 0 or 1 in front of each declaration (0 for disable, 1 for enable). Figure 4 gives an example when setting the current/closed loop/alternate hard soft demagnetization in sensorless mode. Figure 4. Settings for current/closed loop/alternate hard soft demagnetization (sensorless)
. . . /* Demagnetization type parameters */ #define HW 1 // 1 -> Hard demag only #define HSW 2 // 2 -> Hard with soft backup #define SW 3 // 3 -> Soft Demag only /* Driving mode parameters */ #define CURRENT_MODE 0 #define VOLTAGE_MODE 1

// 0 -> Current mode // 1 -> Voltage mode

/* Regulation type parameters */ #define OPEN_LOOP 0 // 0 -> Open loop #define CLOSED_LOOP 1 // 1 -> Closed loop .... /* * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ****/ /* Option settings used throughout the compilation process */ #define SENSOR_TYPE 0 // no use in sensorless mode #define DEMAG_TYPE 2 // no use in sensor mode #define DRIVING_MODE 1 #define FEEDBACK_TYPE 1

After choosing the desired compiler options, the whole library has to be rebuilt. To launch the compilation, click on the 'rebuild all' icon.

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2.4 ADDITIONAL OR UP-TO-DATE TECHNICAL LITERATURE More information can be found on the ST website (http://www.st.com/mcu). More specifically, the latest documents and software can be found directly at: http://www.st.com/mcu in the Downloads section In addition, FAQ and Forums can be found directly at : http://www.st.com/stonline/products/support/micro/st7/st7mc.htm

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3 GETTING STARTED WITH THE LIBRARY USING THE ST7MC-KIT/BLDC
3.1 INTRODUCTION There are two ways to get started with this software library. The first way is to edit (with your motor specific features), compile and assemble the modules described in Section 5 and Section 6 of this application note. Then, program ST7MC and run your motor on hardware like the one provided in the ST7MC-KIT/BLDC Starter-kit. The second way is to use the ST7MC-KIT/BLDC Starter-kit and follow this process: - run and fine-tune the motor parameters with the GUI - generate the *.H files and manually select/save the key parameters - edit mtc.h file with key parameters - compile, link, program ST7MC - run the motor If you are new to the BLDC environment or to the ST7MC product, the second method is highly recommended and is described below. 3.2 RUNNING THE MOTOR As a starting point, the open loop mode shall be used for the first trials. Low-duty cycle values should be used also (alignment, ramp and real time settings) and then increased smoothly step by step. Once the motor settings have been finely adjusted (whatever the driving mode, sensor/sensorless), the parameters have to be `injected' into the stand-alone library. Simply click on `Generate *.h Files' and select the source directory of the stand-alone library.

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The GUI will generate 1 dedicated header file containing the settings of the motor (mainly the MTC peripheral settings) and another one containing the compiler options (see Figure 5). Figure 5. Files generated in sensorless and sensor mode

SENSORLESS MODE
"MTC_Settings_Sensorless.h"

SENSOR MODE
"MTC_Settings_Sensor.h"

"Version.h"

"Version.h"

Once previous files have been generated, launch a new compilation. Firmware will then be compiled according to the new settings/compiler options automatically.

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3.3 STANDALONE MODE AND CLOSED LOOP OPERATION To run a BLDC motor in standalone closed loop, the approach should be, for a given target mechanical speed, to fine tune all the realtime parameters most adequate for this speed. For each target speed, these values should be recorded in the form of a table, which will be used by the ST7MC standalone firmware. You should collect data for 4 speeds: the min and max speeds specified in the GUI advanced screen, and 2 intermediate speeds of your choice. The ST7MC standalone firmware will then make a linear extrapolation of realtime parameters in between the 4 specified speeds to ensure smooth operation. Once the data is collected, edit the `mtc.h' file and fill in the field dedicated to the Rising/Falling Bemf, Ki, Kp coefficient calculation (see Figure 6). Figure 6. `mtc.h' field for coefficient computation
// See 'Mtc_Settings_Sensorless.h' for Freq_Min & Freq_Max values //Fmin #define Rising_Fmin 20 // Frequency min coefficient settings #define Falling_Fmin 30 #define Ki_Fmin 10 #define Kp_Fmin 30 //F_1 #define #define #define #define #define //F_2 #define #define #define #define #define //Fmax #define #define #define #define

F_1 Rising_F_1 Falling_F_1 Ki_F_1 Kp_F_1

1000 50 40 20 10

// 100 Hz // Intermediate frequency 1 coefficient settings

F_2 Rising_F_2 Falling_F_2 Ki_F_2 Kp_F_2

2000 30 10 50 40

// 200 Hz // Intermediate frequency 2 coefficient settings

Rising_Fmax Falling_Fmax Ki_Fmax Kp_Fmax

10 16 13 18

// Frequency max coefficient settings

Once the motor runs, rising/falling Back-EMF and proportional/integer coefficients are computed following a linear curve between F_min and F_1, F_1 and F_2, F_2 and F_max (see Figure 7). Note that F_min, F_1, F_2, F_max are electrical frequencies, with 0.1 Hz resolution (for example F_1 = 1234 means F_1 = 123.4Hz).

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Figure 7. Linear curve for coefficient computation
Rising/Falling Bemf Ki, Kp

Rising_F_2, Falling_F_2 Ki_F_2, Kp_F_2 Rising_Fmax, Falling_Fmax Ki_Fmax, Kp_Fmax

Rising_F_1, Falling_F_1 Ki_F_1, Kp_F_1 Rising_Fmin, Falling_Fmin Ki_Fmin, Kp_Fmin

F_min

F_1

F_2

F_max

Target rotor electrical frequency

3.4 NOTE ON DEBUGGING TOOLS 3.4.1 Low voltage applications (below 30V) For these voltage levels, the real-time emulator can be connected to the application, taking care to connect the protective boards provided with the MDT50 emulator (refer to the emulator datasheet for details). It offers trace and advanced breakpoint capabilities, as well as the possibility to automatically disable the PWM outputs on a breakpoint to avoid any DC current injection in the motor (see Figure 8). This emulator is delivered with a set of three boards to protect some of the motor control dedicated I/Os from voltages greater than 5V. It is highly recommended to have them connected during the development. A neutral board is also provided in case the protection networks impedance (1K series resistor plus 5V3 zener diode) is an issue for the application. Refer to the ST7MDT50-EMU3 Probe user guide Section 3.1 for details. An In-Circuit Debugging tool can also be directly connected, as long as an ICC connector is available on the application. Important Note: When using ICD, during a breakpoint, the clock circuitry is not disabled: a permanent DC current may flow in the motor as the PWM outputs are enabled. It is thus recommended to use a power supply with fast current limitation capabilities or if possible to disable the PWM outputs (by inserting MTC_DisableMCOutputs function) before the breakpoint.

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Figure 8. Configuring the Motor Controller clock state on breakpoint with MDT50

3.4.2 Medium-high voltage application (above 30V) Here the real-time emulator use is not recommended, even if protective boards are inserted. Important Note: In the event of high voltage applications connected to the mains, the application ground may be at a dangerous voltage; so too then would be the MDT50 emulator (the protective boards do not provide galvanic isolation).

For voltages above 30V, it is highly recommended to use only programmed devices. ICD debugging can be used in conjunction with an ICC isolation board, as the one provided with the ST7MC-KIT/BLDC starter kit, but the limitations mentioned in Section 3.4.1 nevertheless apply, and are even emphasized by the high voltage levels. Good practice for real-time application debugging is to use "diagnostic tools" such as: RS232 communication which can be easily isolated, Standalone DAC (serial SPI-based model for instance) to be able to monitor signals on an oscilloscope, Debug outputs of the ST7MC itself (MCDEM and MCZEM pins), to monitor the D, Z and C events (refer to datasheet for details). Refer to the application note AN438 (Safety Precautions for Development Tool Triac + Microcontroller) for further details when working with the mains supply.

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3.5 USING YOUR OWN POWER STAGE In order to configure the standalone library to match any kind of power stage, care should be taken to observe the logic input diagrams of the drivers. The starter kit uses three L6386 highvoltage high and low side drivers; other devices may require adjustments, depending on whether their logical inputs are active low or high. The `MPOL' register has then to be set manually in the firmware. Modifications can be done in the `MTC_InitPeripheral' routine (see Figure 9). It has to be noted also that the option byte has to be updated accordingly (MCO output states during reset). Figure 9. MPOL register configuration
void MTC_InitPeripheral(void) { MTC_ResetPeripheral(); // Initialize registers in page 1 first SET_MTC_PAGE(1); MCONF = mem_MCONF; MPWME = (u8)(mem_MPWME | DG_MSK); //Force output of debug signal MPOL = ALL_ACTIVE_HIGH; device characteristics // (L6386D) <-- to be updated according to your own // ZVD bit=0; Z and D have opposite edge

The starter kit can also be connected directly to an external power stage using the socket J6 (26 pins). 3.6 CHECKING THE CURRENT SENSOR RESISTOR VALUE The starter kit comes with a current sensor resistor of 0.047 Ohm (R21 on the schematic, see Figure 10). The current limiter of the MTC cell relies on a comparator that turns off the PWM when the voltage on this resistor has reached a limit (see Section 7.2.1 Voltage versus current mode for more details). This voltage is amplified by a factor of 11 by the internal OPAMP configured as a non-inverter amplifier (see R66 and R67 values).

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Figure 10. Starter kit: zoom on the power stage

`R21' 47 milli-ohm resistor acting as a current sensor

3.6.1 Maximum current The saturation voltage of the internal comparator is 5 Volts. Figure 11 summarizes the hardware configurations when the winding current is set to maximum.

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Figure 11. Configuration at max. current
clock PWM freq. comparator
MCCREF

HV
Set R

+

T1

5 Volts

OAZ/MCCFI1

A

T4
Uout OPAMP X11 Usense 47 milli-Ohm

Therefore, the maximum current can be calculated: Imax = Vsaturation / (OPAMPgain x Rsense) Previous formula applied to the starter kit leads to: Imax = 5 / (11 x 0.047) = 9.67 amperes The current sense resistor value has to be adjusted when a different working range is needed. It is then necessary to decrease it when the current requirement is higher, or to increase it when the current requirement is lower. It is also possible to adjust the OPAMP gain, but it has to be remembered that: A High-gain OPAMP configuration may decrease EMC performance. A low-gain OPAMP combined with a high current sense resistor value will induce higher power loss (into the resistor). The power stage of the starter kit has been designed to handle power up to 1KW. For higher power, a bigger heat sink and current capability IGBTs or MOSFETs may be required. 3.6.2 Interpreting the current feedback/settings in the GUI Settings related to current values on the GUI are treated as if the current sensor value were a 47 milli-Ohm type (with OPAMP gain equal to 11). When using a different resistor value, settings concerning current can't be read/written directly but have to be calculated manually using a proportional coefficient equal to: K = 47 milli-Ohm / new value The actual current information is the one shown on the GUI multiplied by the proportional coefficient `K' (See Figure 12 & Figure 13).

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Figure 12. Using a 20 milli-Ohm resistor, K = 2.35 (47/20)
Actual value: 3x2.35 = 7.05 A 1x2.35 = 2.35 A 8.7x2.35 = 20.45 A

Figure 13. Using a 100 milli-Ohm resistor, K = 0.47 (47/100)

Actual value: 1.97x0.47 = 0.93 A

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4 MODULES PRESENTATION, LIBRARY ROUTINES
4.1 LIBRARY REFERENCES Functions are described in the format given below: Synopsis D escription Input Returns Caution Warning Functions called Code example This section lists the referenced include files and prototype declarations. The functions are specifically described with a brief explanation of how they are executed. This section gives the format and units. Gives the value returned by the function, including when an input value is out of range or an error code is returned. Indicates the limits of the function or specific requirements that must be taken into account before implementation. Indicates important points that must be taken into account to prevent hardware failures. Used to prevent conflicts due to the simultaneous use of resources. Indicates the proper way to use the function if there are certain prerequisites (interrupt enabled, etc.).

Some of these sections may not be included if not applicable (no parameters, obvious use, et c.).

4.2 MTC SOFTWARE LAYER The software related to the MTC peripheral is part of a module which is call `mtc.c'. This module refers to all the routines needed to initiate and run the peripheral properly. The dedicated MTC hardware registers declaration are also grouped into a module named `mtc_hr.c'. This module provides: - Basic setup - Control routines - Related interrupt handling routines - Speed acquisition for closed loop operation Routine prototypes can be found in the `mtc.h' header file.

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4.2.1 List of available routines The following is a list of available functions as listed in the mtc.h header file. MTC_InitPeripheral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 27 MTC_StartMotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 28 MTC_StopMotor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 29 Set_Duty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 30 Set_Target_Electrical_Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 31 active_brake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 32 Get_Motor_Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 33 Set_Motor_Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 34 Chk_Motor_Stalled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 35 MTC interrupt handling routines are described in the next chapter.

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MTC_InitPeripheral
Synopsis #include "mtc.h" void MTC_InitPeripheral(void) D escription The purpose of this function is to (re-)initialize the MTC cell. A reset of this peripheral is done first, and the hardware registers are then set with appropriate values. It must be noted that part of MPOL and MDTG registers are written once, meaning they cannot be modified any further once the MTC_InitPeripheral() function has been executed MTC_Re setPerip heral() ST7MC Datasheet: MTC chapter.

Caution

Functions called See also

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MTC_StartMotor
Synopsis D escription #include "mtc.h" void MTC_StartMotor(void) This function Initializes HW registers and SW variables needed in real time for the motor drive. To ensure a proper start-up, the bootstrap capacitors of the high side switch drivers are refreshed. Finally, this function performs the alignment of the rotor in a known position, and sets the flags of expected MTC interrupt events. Init_PI (closed loop only), MTC_EnableDirectAccess, MTC_DisableDirectAccess, MTC_EnableOutputs, RefreshBootstrap, MTC_EnableClock, MTC_DisableClock, AlignRotor ST7MC Datasheet: MTC chapter.

Functions called

See also

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MTC_StopMotor
Synopsis D escription #include "mtc.h" void MTC_StopMotor(void) This function disables all motor control related interrupts and switches off all transistors. This puts the windings in floating state once they are completely demagnetized. MTC_EnableDirectAccess, MTC_DisableDirectAccess

Functions called

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Set_Duty
Synopsis #include "mtc.h" void Set_Duty(u16 duty) D escription Input This function is used to refresh the MCPUH/L register contents (MCPVH/L in current mode). The `duty' is a u16 variable, and has to be set according to the PWM frequency (MCPOH/L registers) for both voltage or current mode. The desired duty cycle is set using this formula: Duty = desired duty (0 to 100%) x MCPOH/L (voltage mode') Duty = desired current limitation (Amp) x MCPOH/L / 9.7(current mode) Caution In voltage mode, the `duty' variable is directly linked to the PWM duty cycle while in current mode, the `duty' variable sets the voltage reference (MCPVH/L, actually the current limitation) at the input of the MTC cell comparator (MCCREF pin, via a RC filter on the board). ST7MC Datasheet: MTC chapter. Voltage mode: 20 Khz PWM frequency (ratio between 12-bit PWM clock and PWM frequency, MCPOHL = 16 MHz/20kHz = 800), desired duty = 40%: duty = 40 x MCPOHL/100 = 320 -> Update_Duty(320); Current mode: *Fixed 10 Khz PWM frequency (MCPOHL = 1600), desired current limitation = 4 Amp: duty = 4 x MCPOHL/9.7 = 4 x 1600/9.7 = -> Update_Duty(660);

See also Code example

* hardware dependant. For other PWM frequencies, please check the RC filter value at the input of the MTC comparator cell (MCCREF pin).

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Set_Target_Electrical_Frequency
Synopsis #include "mtc.h" void Set_Target_Electrical_Frequency(u16 target_freq) D escription This function is used to refresh the MCPUH/L register contents (MCPVH/L in current mode). The output of the PI regulation loop routine is used to do so. The `target_freq' is a u16 variable, and has to be set according to the desired target frequency (0.1Hz resolution). The target electrical frequency is given by: target_freq = desired electrical frequency x 10 (0.1 Hz resolution) Caution Functions called See also Code example Frequency is given with 0.1Hz resolution. regul_PI ST7MC Datasheet: MTC chapter. desired electrical frequency : 100 Hz: target_freq = 100 Hz x 10 = 1000; -> Set_Target_Electrical_Frequency(1000) Reminder: Electrical frequency = number of pair poles x mechanical frequency RPM speed = 60 x Mechanical frequency (RPM: revolutions per minute) example: electrical frequency = 100 Hz, motor with 8 pair poles: 100Hz electrical <-> 100/8 =12.5Hz mechanical <-> 12.5 x 60=750 RPM

Input

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active_brake
Synopsis D escription Input Returns Caution #include "mtc.h" BOOL active_brake(u16 duty, u16 time) The purpose of this function is to switch the active brake of the motor, by sinking a DC current in 1 phase, another one being grounded. Duty cycle applied during active brake phase, with the Time given in milli-seconds TRUE if brake time elapsed or duty sets to 0. In voltage mode, the `Duty' variable is directly linked to the PWM duty cycle while in current mode, the `Duty' variable sets the voltage reference at the input of the MTC cell comparator (MCCREF pin, via a RC filter on the board). MTC_EnableDirectAccess, MTC_DisableDirectAccess ST7MC Datasheet: MTC chapter. The `duty' is a u16 variable, and has to be set according to the PWM frequency (MCPOH/L registers). Example: PWM frequency set at 10 Khz, MCPOH/L = 1600 (ratio between 12-bit PWM clock and PWM frequency 16 MHz/10kHz = 1600) Desired duty = 40% = 40 x MCPOHL/100 = 40 x 1600/100 = 640 Desired braking time : 2 sec = 2000 ms -> if (active_brake(640,2000) == TRUE) State = STOP; // stop motor

Functions called See also Code example

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GetMotorStatus
Synopsis #include "mtc.h" u8 GetMotorStatus(void) D escription This function returns the `MotorStatus' byte. Bit description:

MotorStatus Sensorless
EMERGENCY_STOP START_UP_FAILED HARD_FAILURE MOTOR_STALLED LAST_FORCED_SWITCH F IR S T _ A U T O _ S W I T C H AUTO_SWITCH

7

6

5

4

3

2

1

0

MotorStatus Sensor
EMERGENCY_STOP HARD_FAILURE MOTOR_STALLED Returns unsigned char

7

6

5

4

3

2

1

0

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SetMotorStatus
Synopsis D escription #include "mtc.h" void SetMotorStatus(u8 status) This function updates the `MotorStatus' byte according to the `status' byte parameter. Please see `GetMotorStatus' routine description for status byte definition. unsigned char

Input

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Chk_Motor_Stalled
Synopsis #include "mtc.h" void Chk_Motor_Stalled(void) D escription The purpose of this function is to check the ratio of the MTC cell set in the MPCR register. If the ratio is equal to the maximum ratio (15), then the bit `MotorStalled' of `Power_Motor_Status' is set. ST7MC Datasheet: MTC chapter.

See also

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4.2.2 List of MTC interrupt routines The following is a list of the MTC interrupt handling routines. These functions are all included in the `mtc.c' module. MTC_U_CL_SO_IT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 37 MTC_C_D_IT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 38 MTC_R_Z_IT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 42

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MTC_U_CL_SO_IT
Synopsis #include "mtc.h" void MTC_U_CL_SO_IT(void) D escription This interrupt routine is entered once there is a current limitation, PWM update or Sampling Out event. Only the current limitation event is processed in the library: status flag is reset, and the bit `OverCurrent' of `Power_Motor_Status' is set. ST7MC Datasheet: MTC chapter.

See also

Figure 14. CLI event processing (sensorless/sensor)

CLI interrupt request

Set overcurrent flag in Power_Motor_Status Disable CLI interrupt for 300 ms

Return from interrupt

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MTC_C_D_IT
Synopsis #include "mtc.h" void MTC_C_D_IT(void) D escription This function is dedicated to the Commutation and Demagnetization interrupt service routine. Figures 15,16,17,18 & 19 show the routine flowcharts. ST7MC Datasheet: MTC chapter.

See also

Figure 15. Commutation event processing (Sensor mode only)
C interrupt request?

Preload active phase on next C event: MPHST with phase, MCRB with comparator edge, PWM orientation Voltage mode: save MCPUHL and force duty cycle during demag if enabled MWGHT = RISING/FALLING delay

Return from interrupt

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Figure 16. Commutation event processing (Sensorless mode only)
Reset RPICounter StepIndex = StepIndex + 1 Preload active phase on next C event: MPHST with phase, MCRB with comparator edge, demagnetisation mode and PWM orientation Voltage mode: save MCPUHL and force duty cycle during demag if enabled

C interrupt request?

SW DEMAG
Adjust soft demag time according to RPICounter yes Preset soft demag time + MCOMP > 0xff no

HSW DEMAG HW DEMAG

MotorStatus? FORCED_SWITCH LAST_FORCED_SWITCH FIRST_AUTO_SWITCH
MWGHT = AUTO_DELAY Init PI buffer (Step_Z[ ]) Reset delay_counter MotorStatus= AUTO_SWITCH

AUTO_SWITCH

MDREG = MCOMP/(SWITCHED_SW_DEMAG) Wait for Z event (MCOMP=255) MWGHT = TRANSITION_DELAY Enable autoswitch and relevant interrupts MotorStatus= FIRST_AUTO_SWITCH

C_IT_ForcedSW Return from interrupt

C_IT_AutoSW

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Figure 17. Commutation event processing (Sensorless mode only) continued C_IT_ForcedSW

Update MCOMP& MPRSR with step time and ratio stored in RAMP[ ] Enable D event if RampIndex= 2

SW DEMAG HW DEMAG

HSW DEMAG
MDREG = MCOMP/(SWITCHED_SW_DEMAG)

Ramp finished without success? no

yes Stop motor

Bemf blanking over? (RampIndex = bemf_blank?) no Bemf are present and consecutive? (same number of C & Z event?) no Reset CeventCounter & BemfCounter

yes

Enable Z event

yes

CeventCounter++

Return from interrupt

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Figure 18. Commutation event processing (Sensorless mode only) continued
HSW DEMAG
C _ IT_A ut oSW
SDM bit set? (hard + soft demag ongoing?) yes no

SW DEMAG
C_IT_AutoSW

HW DEMAG
C_IT_AutoSW

RM event?
no no

yes

SoftDemagTime = SoftDemagTime*2 Update MDREG with user settings MDREG = preset demag time MCOMP+SoftDemagTime / 2^(RP_counter) > 0xff ? yes Adjust SoftDemagTime & RPICounter for correct MTIM timer overflow

MDREG = SoftDemagTime + MCOMP

delay_counter <= MAX_DELAY_COUNTER? no

yes

Increase delay_counter yes

delay_counter = AUTO_DELAY_STEP? MWGHT = RISING/FALLING delay no

MWGHT = MEDIUM_DELAY

Return from interrupt

Figure 19. Demagnetisation event processing (Sensorless mode only)
Voltage mode?
yes

D interrupt request?
no

SENSORLESS

Restore MCPUHL values if duty cycle has been forced during demag

HSW DEMAG
yes

SW DEMAG HW DEMAG

Autoswitchmode?

no

SoftDemagTime = 1.25 x (MDREG-MCOMP)

SoftDemagTime = 1.25 x MDREG

Return from interrupt

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MTC_R_Z_IT
Synopsis #include "mtc.h" void MTC_R_Z_IT(void) D escription This function is dedicated to the Zero-Crossing and Ratio Increment/ Decrement interrupt service routines. Figures 20, 21, 22, 23, 24 & 25 show the routine flowcharts. ST7MC Datasheet: MTC chapter.

See also

Figure 20. Z event processing (sensorless mode only)
Z interrupt request?
yes no

Autoswitchmode?

BemfCounter++ Save MZREG value and prescaler ratio into Step_Z buffer (save step time between two zero crossing events)

no

Correct number of Successive Bemf detected?

yes

Center last zerocrossing in the middle of 2 C events (MCOMP = MZREG x 2) MotorStatus = LAST_FORCED_SWITCH

Return from interrupt

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Figure 21. Z event processing (Sensor mode only)

Z interrupt request?

Save MZREG value and prescaler ratio into Step_Z buffer (save step time between two zero crossing events)

Return from interrupt
Figure 22. RP event processing (Sensorless mode only)
RP interrupt request?

HSW DEMAG HW DEMAG
yes

SW DEMAG
RPICounter = 0?
no

RPICounter = RPICounter-1

RPICounter = 0?
no

yes

MDREG = SoftDemagTime

Return from interrupt

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Figure 23. RP event processing (Sensor mode only)

RP interrupt request?

Return from interrupt

Figure 24. RM event processing (Sensorless mode only)

RM interrupt request?

Set RM_EVT Flag

Return from interrupt

Figure 25. RM event processing (Sensor mode only)

RM interrupt request?

Return from interrupt

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4.3 APPLICATION LAYER The application layer is split into modules; each module comes with a set of routines dedicated to a peripheral, event (interrupt routines), or are grouped by functionality. The following information summarizes the most important routines in the different modules. regul.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ad c.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . it_ST7 MC.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . po rts.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LinSCI.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 regul.c This module contains the code of the PI regulation loop, which is used for closed loop operation. The `u16 Period_To_Frequency(void)' routine converts the Step_Z buffer information into frequency (the Step_Z buffer contains the time elapsed between 7 zero-crossing events -> corresponds to the time of six (6) steps period of the electrical frequency). The `u16 regul_PI(u16 Target_Freq)' routine computes the PI output according to Ki, Kp, sampling time, and target electrical frequency. The returned value is a 10-bit long integer (0 to 1024). 4.3.2 adc.c This module starts and initializes the analog to digital converter, and launches upon request a conversion on a channel. It is able to provide ready-to-use values to the upper software layer. It was basically written to monitor signals that vary slowly, such as trimmers, since the returned results are averaged values of 8 successive conversions. The `u16 ADC_Get_10bits(u8 Channel)' and `u8 ADC_Get_8bits(u8 Channel)' functions return the ADC result on the selected channel. The `u8 Get_RV1(void)', `u8 Get_RV2(void)' and `u8 Get_RV3(void)' routines return the value read on the potentiometers connected to the MCU (RV1, RV2, RV3). The `BOOL Get_Temperature(void)' returns a boolean. This function returns `TRUE' if the voltage on the thermal resistor connected to channel AIN0 has reached the threshold level or if the voltage has not yet reached back the threshold level minus the hysteresis value after an overheat detection. I n order to set the temperature and hysteresis threshold, the `NTC_THRESHOLD' and `NTC_HYSTERIS' values can be adjusted in the adc.c file. page 45 page 45 page 46 page 47 page 48

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The `BOOL Get_HVBus(void)' returns a boolean. This function returns `TRUE' if the voltage of the HVBUS connected to channel AIN1 has reached the threshold level or if the voltage has not yet returned to the threshold level minus the hysteresis value after an over-voltage detection. I n order to set the voltage and hysteresis threshold, the `HVBUS_THRESHOLD' and `HVBUS_HYSTERIS' values can be adjusted in the adc.c file. 4.3.3 it_ST7MC.c Th is module contains all non-MTC related interrupt service routines. In the stand alone firmware, the timer B resource is the only one to be used. The output compare capability is used in order to decrease 2 different time bases, 10ms and 1ms (see `Timer.c' file for the timer B registers configuration). Basically, unless equal to 0, variables are decreased by one each timer B output compare interrupt event (every 10ms or 1ms for output compare 1 and 2 respectively). Therefore, a variable `VAR' is loaded with `50' in the main code and decreased by one every 10 ms, and will reach `0' after 500ms (490 to 500 ms if the initialization of `VAR' is done outside of the interrupt routine). Figure 26. Time base Principle: Timer B output compare 1 interrupt every 10ms
Main routine: VAR = 50 VAR = 49 VAR = 48 VAR = 47

int

int

int

int

int

10 ms

Clear Status flag, refresh timer B output compare registers, and update variables used for timing purpose

For more information regarding the configuration of this peripheral, please refer to the data sheet of the MCU, `16-bit timer' section.

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4.3.4 ports.c The purpose of the ports.c module is to centralize all information regarding the I/O ports (including the alternate functions) within the same file. It is intended to clarify the sharing of I/Os between the peripherals and the functions requiring standard input/outputs, such as LEDs and push button reading. I/Os are initialized at the beginning of the main program, using the `void PORTS_Init(void)' function. Two functions are handled by this module, needed when running the software library with the ST7MC starter kit hardware. 4.3.4.1 Push button reading The function `BOOL key_scan(void)' returns a boolean, TRUE if the push button (connected to PC0) has been pushed during a minimum duration. This duration can be programmed in ms, to debounce the button reading. This timing is verified using `it_ST7MC.c' module resources, in `void TIMB_Interrupt(void)' interrupt routine. The location of the push button (port and bit location) must be specified at the beginning of the ports.c file. The push button must be connected between ground and a pull-up resistor to get a low level on the input pin when it is pushed (refer to ST7MC starter kit schematics for details). 4.3.4.2 LEDs A set of functions can be called to switch ON, OFF or toggle the two LEDs present on the starter kit: PORTS_RedLedOn, PORTS_RedLedOff, PORTS_RedLedToggle, etc. It must be remembered that these two LEDs are powered using a single I/O (see schematics for details). Consequently: they cannot be turned ON simultaneously the I/O port state can be configured either as an output or as a floating input to switch OFF the LEDs. 4.3.5 spi.c This module contains the code related to the SPI peripheral. The initialization of this peripheral is made within the `void SPI_Init(void)' function. Care should be taken when configuring the SPI interface in accordance with the system (particularly operating frequency and polarity). Communication with a serial EEPROM can be done using the `Send_EEPROM(u8 address, u8 data)' and `Read_EEPROM(u8 address)' routines.

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4.3.6 LinSCI.c This module contains the code related to the LINSCI serial communication interface and gives a n example of configuration and usage (with the `void SCI_Config(void)' and `void SCI_Send_Data(u8 data)' routines) and the `TTY_7.exe' executable file. You can find the executable in the `SCI' folder of the stand alone firmware. Working TTY Settings with the stand alone firmware are as follow: - Baud Rate 38.4K, Data Bits 8, Parity none, Stop Bits 1, RTS/CTS enable, other options disabled. When running the code in: - Closed loop : the MCU feeds back respectively the rising, falling Bemf delay coefficients, integral, proportional coefficients, motor frequency (LSB then MSB), then `0' (decimal values). - Open loop : the MCU feeds back respectively the rising, falling Bemf delay coefficients, the motor frequency (LSB then MSB), then `0', `0', `0' (decimal values). Those settings can be changed in the `main.c' file, by modifying the values entered in the `Lin_Tx_Buffer[0...7]'. Figure 27. Running TTY_7.exe on a PC (open loop firmware)

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5 HOW TO DEFINE AND ADD A MODULE (STVD7 2.5.X)
This chapter describes how to define and declare a new module within the library. The exa m p le is based on the addition of 2 files: `my_file.c' and the corresponding header file `my_file.h'. Users of STVD7 3.x can refer to Section 2.3. The first step is the creation of two new files. You can either copy and paste existing files and rename them, or click on the `new files' icon and save it in the right format (*.c or *.h extension). The new files containing the user code will generate a new `my_file.o' object file that has to be declared in the toolchain configuration files. 5.1 COSMIC TOOLCHAIN F o r C O S M I C u s e r s , mo d i f i c a t i o n s h a v e to be do n e in B L D C _ C o s m i c . l k f a n d BLDC_Cosmic.mak files. In BLDC_COSMIC.lkf, the new object file has to be added to the main object file list (see Figure 28). However, if special options are required (for example, no optimization, or the forced placement of variables in memory), then it has to be declared in another section (e.g. after the main list) with the correct settings. See your C toolchain documentation for further details. Figure 28. BLDC_COSMIC.lkf
# OBJECT FILES ..\..\object\cosmic\main.o ..\..\object\cosmic\LinSCI.o . . . ..\..\object\cosmic\my_file.o

In BLDC_Cosmic.mak, `my_file.c' has to be added in the C source file list (see Figure 29) and the list of dependencies has to be updated accordingly (see Figure 30). Figure 29. BLDC_Cosmic.mak, C source list
C_SRC = main.c \ mtc.c \ vector.c \ opamp.c \ . . . my_file.c \

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Figure 30. BLDC_Cosmic.mak, dependencies
# RULES FOR MAKING THE OBJECT FILES: main.o: main.c version.h lib.h RAM_Sensorless.h $(CC) ..\..\source\main.c . . . my_file.o: my_file.c my_file.h $(CC) ..\..\source\my_file.c

5.2 METROWERKS TOOLCHAIN For METROWERKS users, modifications have to be done in BLDC_Metrowerks.prm and BLDC_Metrowerks.mak files; in BLDC_Metrowerks.prm the new object file has to be added in the `Project module list' section (see Figure 31). In BLDC_Metrowerks.mak, the new source file and the corresponding dependencies have to be set in the `Application Files' section (see Figure 32). Figure 31. BLDC_Metrowerks.prm
/*** PROJECT MODULE LIST ***/ NAMES main.o ST7MC_hr.o+ mtc_hr.o+ .... my_file.o ansi.lib END

Figure 32. BLDC_Metrowerks.mak
# --------------------------- APPLICATION FILES ------------------------------main.o : $(ENV) main.c version.h lib.h RAM_Sensorless.h $(CC) main.c ST7MC_hr.o : $(ENV) ST7MC_hr.c ST7MC_hr.h mtc_hr.h version.h lib.h $(CC) ST7MC_hr.c . . . my_file.o : $(ENV) my_file.c my_file.h $(CC) my_file.c

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6 CODE EXAMPLE
This section gives a very simple code example. Once an action on the start button is detected, the motor starts and runs in open loop voltage sensorless mode with a duty cycle of 25%; once an action on the stop button is detected, an active brake procedure is engaged for 2 seconds with a duty cycle of 17%, then the power stage is switched off.

Warn ing:

This code example assumes that correct settings have been entered for the alignment phase and ramp data. Modifications may be done using the Graphical User Interface provided with the demokit (by clicking on the `generate *.h files' icon).

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Figure 33. Code example
While(1) // main loop

//

{ if (Chk_Timer_WDG_Elapsed() == TRUE)WWD_Refresh(); Chk_Power_Motor_Status(); if ((u8)(GetMotorStatus() & FAULT_MSK) != 0) State = FAULT; // START_UP_FAILED // or MOTOR_STALLED // or HARD_FAILURE // or EMERGENCY_STOP? switch (State) { case IDLE: if (timer_10ms == 0) PORTS_RedLedOn(); // red LED back to normal after // overvoltage, overtemperature detection if (key_scan() == TRUE) State = START; break; case START: if (MTC_StartMotor() == TRUE) State = RUN; break; case RUN: if (GetMotorStatus() & AUTO_SWITCH) { if (ValBit(Flag_MTC,SAMP_EVT)) // update PWM? { Falling_bemf = (u8)(Get_RV3()); // read RV3 & set falling // Bemf coefficient accordingly Rising_bemf = (u8)(Get_RV2()); // read RV2 & set rising Bemf // coefficient accordingly Set_Duty((u16)(PWM_FREQUENCY*25/100)); } } Chk_Motor_Stalled(); if (timer_10ms == 0) PORTS_GreenLedOn(); if (key_scan() == TRUE) State = BRAKE; break; case BRAKE: if (active_brake((PWM_FREQUENCY*17/100),2000) == TRUE) State = STOP; // Brake_Duty = 17% break; case STOP: MTC_StopMotor(); PORTS_RedLedOn(); State = IDLE; break; case FAULT: default: MTC_StopMotor(); PORTS_RedLedOn(); if ((u8)(GetMotorStatus() & FAULT_MSK) == 0) State = IDLE; break; } } // 25% duty cycle

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7 PMDC (PMAC) MOTOR CONSIDERATIONS
7.1 PHYSICAL CONSIDERATIONS 7.1.1 Checking the number of pair poles of the motor In most cases, there is an easy way to check how many pair poles are present with the motor you are working with. This applies only to motors from which you can observe any mechanical effect (by looking at the axis for example). The trapezoidal driving method is based on 6 steps, and each step involves a particular low / high side driver configuration. 1 electrical cycle is then accomplished within 6 steps. The number of pair poles gives the link between electrical frequency and mechanical frequency:

mechanical frequency (hertz) = electrical frequency (hertz) / number of pair poles

Thus, by switching from one step to another at a very low frequency (e.g. 1Hz) and simply by controlling the mechanical effect by sight, we can determine the number of pole pairs by counting the number of steps within 1 mechanical cycle. It is given by:

number of pole pairs = total number of steps / 6

Example: assuming that 24 steps are needed to describe 1 mechanical cycle (e.g. 360 degrees on the axis of the motor), then the number of pole pairs is 24/6 = 4. The software package includes a workspace containing a firmware example in order to drive the motor step by step at a frequency of 1Hz. You can open it in the `Pair poles chk' folder and open the dedicated workspace to your toolchain. This folder contains also a s19 file (in `S19 file for EEPROMER') so that you can program a MCU directly and avoid the use of an emulator. RV1 potentiometer is used to set the PWM duty cycle. The Start/Stop push button launches/stops the procedure. Warn ing: Operations are made in voltage mode with a PWM frequency of 10Khz and duty cycle is set via RV1 potentiometer. Make sure that the duty cycle is not too high as the winding currents can increase very quickly in this particular mode of operation.

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7.1.2 Connecting the sensor outputs to the board Two configurations are commonly used: sensor 60 / sensor 120 degrees. The easiest and most time-efficient solution is to connect the motor cables into the demokit by trying all the connection style combinations. First you need to check which sensor distribution is used by connecting the sensor outputs to a scope and running the motor smoothly (by hand, for example). The consecutive events (in the time domain) have to be monitored (with a scope/multimeter): 3 successive rising/falling edges means a sensor 60 configuration, while an alternate rising/falling edge means a sensor 120 configuration. Now that the sensor distribution is known, you have to randomly connect the sensor outputs to the demokit (select the right sensor configuration in the GUI). As there are 3 phases (let's say P1,P2 and P3), that simply means we have 6 possibilities of connection: P1P2P3, P1P3P2, P2P1P3, P2P3P1, P3P1P2 and P3P2P1. For each connection, you may try to start the motor (with the GUI for example) and find out which 1 of the 6 cable connections is able to run the motor properly. If none of them is able to do so (wrong motor direction), then 2 sensor cables have to be swapped and the same procedure repeated. Warn ing: Make sure that the duty cycle is not set too high as the winding currents can increase very quickly, especially if the motor is stalled.

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7.2 CONTROL STRATEGY CONSIDERATIONS 7.2.1 Voltage versus current mode The motor control peripheral of the ST7MC allows voltage and current control modes. Both modes set the PWM duty cycle according to: - Voltage mode: the values of the MCPUH/L registers allow direct configuration of the duty cycle in accordance to the maximum allowed current thanks to the comparator cell (see Figure 34). - Current mode: the current threshold that will turn the PWM into off-state (see Figure 35). Figure 34. PWM duty cycle behaviour in voltage mode
MTC peripheral PWM

ST7MC Microcontroller

channel U

HV
set R

Max current reference

Max current reference

+

-

T1

I

t

A
MCCREF OAZ/MCCFI1

W12 Channel V 33K 100nF

Motor Voltage

Vdd

t
T4
Pot 1
OPAMP

step time
T1-T4

step time
T1-T6

MTC peripheral PWM

Figure 35. PWM duty cycle behaviour in current mode
ST7MC Microcontroller current reference
Channel V 33K
OAZ/MCCFI1

clock PWM freq.
MCCREF

HV
Set R

current reference

I + T1 clock

t t

A
Motor Voltage

MTC peripheral 100nF PWM T4
OP AM P

t
step time
T1-T4

step time
T1-T6

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Basically, the current sense circuit acts as a PWM duty cycle manager in current mode while it acts as a maximum current limiter in voltage mode. The current loop allows a fine control of the torque by imposing the current in the windings. Voltage mode can be used when there is a high torque variation. 7.2.2 Choosing a demagnetization type (Sensorless mode only) There are 3 methods in sensorless mode to detect the end of demagnetization: software, hardware with software backup and hardware demagnetization (no demagnetization event in sensor mode). A. Hardware Detection of the end of demagnetization is entirely done by hardware and no safety precaution is taken in order to manage a wrong event detection. Hardware demagnetization can be chosen for system running at low speed. Generally, this method doesn't have any advantage compared to the `Hardware with software backup', and therefore shouldn't be used. B. Hardware with software backup This method gives the advantage of an hardware detection combined with a software demagnetization used as a backup method when the system fails to detect the end of a demagnetization event. This allows the most accurate demagnetization time to be achieved and therefore permits the window timing to be opened for the Bemf detection as early as possible. If there is a problem with the end of demagnetization event detection (which could occur on a falling Bemf event detection while running at high speed), then a software demagnetization occurs after a pre-programmed amount of time. In the stand-alone library, the time is set to 125% of the last hardware demagnetization time (see `mtc.c' file, `MTC_C_D_IT' routine). Figure 36. Software backup demagnetization time update routine
{ if (MotorStatus == AUTO_SWITCH) temp_D = (u8)(MDREG - MCOMP); // Demag.time = MDREG - MCOM else temp_D = MDREG; // synchronous mode SoftDemagTime = (temp_D >> 2); // div/4 SoftDemagTime += temp_D; // next MDREG value = 1.25*(hard demag.time) RP_counter=0;//reset counter of RP event coming between Dhard and next C ClrBit(Flag_it,RM_EVT); }

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C.Software demagnetization All demagnetization events are simulated and the end of the demagnetization occurs after a pre-programmed amount of time (see `MTC_Settings_Sensorless.h' file, `Setting of demagnetization time in running mode' section). The demagnetization time is an arbitrary value that has to adjusted according to the motor specifications; it has to be kept in mind that very inductive motors will require longer demagnetization time, and therefore will require longer step times. This solution might be preferred when the `Hardware with software backup' demagnetization solution can't provide reliable motor operation. 7.2.3 The 4 Z event sampling methods (Sensorless) Below is the description of the 4 sampling types that can be used for Z event detection while running motors in sensorless mode (for further information on these methods, refer to the application note AN1946). Figure 37. Z event sampling methods as shown in the GUI

7.2.3.1 At the end of the PWM low state This is the ST patented method; it provides very good sensitivity on the full speed range, without the usage of any external components. This solution requires an OFF time during each PWM period in order to detect the zero-crossing event (PWM low state). Samples are taken after a time window configured with ZWF[3:0] bits in MZFR register. Therefore the dutycycle can't be set to its maximum. The maximum duty cycle will depend of the minimum PWM off time needed by the system in order to detect the Z event. Figure 38. Sampling during OFF time, at PWM frequency
TSampling PWM OFF time PWM signal ZWF[3:0] ZWF[3:0] Current sample New sample

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7.2.3.2 At PWM On, with delay once This method requires additional external components (resistor dividers, with/without RC filtering). Samples are taken once, each PWM ON time, after a delay programmed by DS[3:0] bits in MCONF register. Duty cycle variation induces jitter on the sampling clock; if the system stability is affected, sampling should then be done at fSCF frequency (see next section). True 100% duty cycle can be set. Figure 39. Sampling during ON time, at PWM frequency
TSampling New sample

DS[3:0] PWM signal PWM OFF time

DS[3:0]

C u rrent sample

7.2.3.3 At PWM On, with delay, at fSCF frequency This method requires additional external components (resistor dividers, with/without RC filtering). Samples are taken at fSCF frequency, during PWM ON time and after a delay programmed by DS[3:0] bits in MCONF register. True 100% duty cycle can be set. Figure 40. Sampling during ON time at fSCF
f SCF
during ON time

DS[3:0] PWM signal PWM OFF state

DS[3:0]

Current sample

7.2.3.4 At fSCF frequency This method requires additional external components (resistor dividers, with/without RC filtering). The sampling is done at a programmable frequency independent of the PWM state. Samples are taken at fSCF frequency. This type of sampling might be chosen when the motors are driven with Pulse Amplitude Modulation (PAM).

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Figure 41. Sampling at fSCF, Pulse Amplitude Modulation
fSCF

Phase voltage

7.2.3.5 Conclusion When setting up the system and unless working specifically in Pulse Amplitude Modulation, the easiest way to start is the ST patented method, providing a fast and effortless solution (no resistor dividers or RC filters to calculate). If the application requires a true 100% duty cycle (to bypass the speed limitation while sampling at end of the PWM low state), the sampling has then to be done during ON time, at PWM or fSCF frequency. 7.2.4 Setting the PWM distribution During each step, one can choose to apply the PWM signal on the low or the high side of the switches (1 of 3 IGBT/MOSFET legs). Even though this is not mandatory, it can greatly improve the system stability and efficiency. Changing the PWM distribution can decrease the demagnetization time and can reduce reactive currents in motor windings (see Figures 44, 45 & 46).

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Figure 42. Command sequence for 6-step mode
HV

T0

T2 B I1 I6

T4

Step
Step number
Current direction High Low

I4

1 A to B T0 T3

2 A to C T0 T5

3 B to C T2 T5

4 B to A T2 T1

5 C to A T4 T1

6 C to B T4 T3
A I5 I2

I3

C

T1

T3

T5

Figure 43. Voltage on phase B
. 1
HV

2 C2 D2

3

4

5

6

C4

HV/2

0V

Z2 Demagnetization Commutation delay

D5 Z 5 t PWM off pulses

Wait for BEMF = 0

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Figure 44. PWM applied on low/high side on a rising Bemf during demagnetizationf
HV T0 T2 B I1 T4

Step 1 T0-T3 with PWM applied on high side

A

C

T1

T3

T5

Step 2 T0-T5 with PWM applied on high side during demagnetization PWM ON
T0 T2 B T4

OR

Step 2 T0-T5 with PWM applied on low side during demagnetization

Id
HV
T0 T2

Id

PWM ON
HV

T4 B

Voltage on phase B 2 1
HV

M
A

M
A

I2

C

I2
T5

C

T1

T3

T5

HV/2

T1

T3

PWM OFF
T0

Id
HV

Id
0V
T4 B
T0 T2 B

PWM OFF
HV

T2

T4

t T0-T3 ->T0-T5 Com mutation Demagnetization

M
A C

M
A C T5

T1

T3

T5

Id: free wheeling
demagnetization current

T1

T3

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Figure 44 shows the freewheeling demagnetization current during the step 1 to step 2 transition. In order to minimize the demagnetization time in the freewheeling diode, it is easy to verify that the shortest time is achieved while lowering the M potential. If the PWM is applied on high side, the M potential is either equal to 2 x HV/3 (PWM ON), or equal to HV/3 (PWM OFF). The voltage applied on the winding B (potential difference between B and M) is then doubled when the PWM switches from ON to OFF state. If the PWM is applied on the low side, the M potential is either equal to 2 x HV/3 (PWM ON), or equal to HV (PWM OFF). The voltage applied on winding B switches from HV/3 to 0 (ON to OFF state). The demagnetization is effective only during the "ON" state of the PWM. It is then better to apply the PWM on the high side during the step 2 demagnetization process (C to D event).

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Figure 45. PWM applied on low/high side on a falling Bemf during demagnetizationf
HV T2 T0 T4 B

I4

Step 4 T2-T1 with PWM applied on high side

A

C

T1

T3

T5

Step 5 T4-T1 with PWM applied on high side during demagnetization PWM ON
HV T4 T0 T2 B

OR

Step 5 T4-T1 with PWM applied on low side during demagnetization PWM ON
HV

T0

T2 B

T4

Voltage on phase B 4
HV

5

M
A

M
A

I5

C

I5

C

Id
T1 T3 T5

T1 T3

Id
T5

HV/2

PWM OFF PWM OFF
T0 T2 B HV T4
HV

0V

T0

T2 B

T4

T2-T1 ->T4-T1 C o mmutation

t Demagnetization

M
A C

M
A C

Id
T1 T3 T5

Id
T1 T5 T3

Id: free wheeling demagnetization current

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Figure 45 shows the freewheeling demagnetization current during the step 4 to step 5 transition. In order to minimize the demagnetization time in the freewheeling diode, it is easy to verify that the shortest time is achieved while raising the M potential. If the PWM is applied on high side, the M potential is either equal to HV/3 (PWM ON), or equal to 0 (PWM OFF). The voltage applied on the winding B (potential difference between B and M) switches from HV/3 to 0 (ON to OFF state). The demagnetization is effective only during the "ON" state of the PWM. If the PWM is applied on low side, the M potential is either equal to HV/3 (PWM ON), or equal to 2 x HV/3 (PWM OFF). The voltage applied on the winding B is then doubled when the PWM switches from ON to OFF state. It is then better to apply the PWM on the low side during the step 5 demagnetization process (C to D event).

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Figure 46. Comparison: reactive currents, highly inductive motor windings (sensor 120)
Case 1 : PWM applied on high side during step 2, low side during step 5 (All other steps: high side)

Case 2: PWM applied on low side during step 2, high side during step 5 (All other steps: high side)

The reactive currents become negligible when PWM is applied on the appropriate switch

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The ST7MC allows any kind of PWM configuration. Based on previous examples, one can see the choice to be made when accelerating any reactive or demagnetization current time. When using the ST patented method, it must be noted that the PWM signal has to be applied on the high side switch between D and Z events (Bemf sampling is done during Toff time). To set the PWM distribution, click on `Advanced Settings', then double-click on the dedicated configuration bits. Figure 47. PWM distribution settings

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7.3 SOFTWARE SETTING CONSIDERATIONS 7.3.1 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 of the theory and a proposal of the empirical tuning method.

Theoretical background

The implemented regulator is actually a Proportional Integral one (see note below regarding the differential term). The purpose of the regulation loop (see equation 1) is to adjust the PWM duty cycle on the motor winding depending on the frequency. P W M D u t r = f(f r e q) P W MD u t r = P W MS t a r t + Kp × E r r o rf r e q + Ki × E r r o rf r e q
t

(1) (2)

The equation 2 corresponds to a classical PI implementation, where: PWMstart is a constant corresponding to the duty cycle on the motor windings when the ST7MC switches from synchronous to autoswitch mode in sensorless (exit of the ramp). In sensor mode, this constant is set to 0, but can be manually adjusted. See `Init_PI()' in `regul.c' file for more 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). As a result, the system may become unstable or difficult to tune. Additional software filtering can be implemented to get proper differential frequency error, but may result in additional response delay.

Regulation tuning procedure

To tune the PI regulator parameters, it is advised to proceed in the following order: sampling time, proportional coefficient, integral coefficient.

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 the

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integral action on the output will be increased). This is why this parameter has to be adjusted prior to setting-up the integral coefficient of the PI regulator. In theory, the higher the sampling rate, the better the regulation. In practice, you must keep in mind that: the related CPU load will grow accordingly. In the stand alone library (sensor/sensorless), the speed information is based on a 6-step time. There's absolutely no need to have a sampling time lower than this duration (for example, electrical frequency at max speed = 100 Hz -> T6_steps = 10ms). at high speed, in most cases, system inertia is such that the system response is slow: in these conditions there is no need to have a high sampling rate. This parameter must be reported in the mtc.h file, in a specific define (50ms in the example here below):
#define SAMPLING_TIME 50 // 50ms

Tuning the Proportional coefficient Kp

This parameter Kp 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 48 for speed response vs Kp value). Figure 48. Speed correction versus Kp value (with Ki =0)
Speed
Target

Kp=20

Ki=0 during the Kp set-up

Static error for K p = 0

K p=0 K p=2 K p=5 Kp = 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 (with oscillations), stop increasing Kp (this is Kp limit).

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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

The parameter Ki provides the 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 executions. 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 will be and the better the dynamic response. Nevertheless, a value too too high will lead to instability (see Figure 49 for speed response vs Ki value). During the set-up, Kp and Ts must be kept constant with the values determined below. Figure 49. Speed error versus Ki
Speed
Target

Ki=20

Ki=10

Kp= x, Ki=0 Ki=2
0

K i =5 Time

Kp and Ts are constant during the Ki set-up

Here is an empirical method to tune the Ki coefficient:

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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 with respect to the target speed; as soon as the Ki value will be different from zero, the error will start to decrease. Contrary to proportional term adjustment, you cannot slowly increase the Ki to evaluate properly its action: it is necessary to have dynamic conditions. This can be done by suddenly applying a given Ki coefficient (as represented on Figure 49). This can also be done by modifying the target speed or the load to verify that the speed settle time is correct and there's no or limited speed overshoot. A sharp variation as provided by dynamic brakes will represent the most difficult conditions and is usually not very representative of a real application. It is normally easier to work with the final application speed profile or load variations. When the system becomes unstable (big speed overshoot or with oscillations), stop increasing Ki (this is Ki limit). The appropriate value of Ki to start working with will then be Ki = Ki 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 Ki can be slightly adjusted if necessary to find the best trade-off between settle time and speed overshoot, keeping in mind that it is important to validate the lack of unstable behaviour over the whole working domain. 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 Ki values will have to be used to get the best results.

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Adjusting Ki and Kp vs the motor frequency

Depending on the application and/or the speed range, it might be necessary, as seen in the previous sections, to use different values of Kp and Ki parameters depending on motor frequency. These values will have to be reported in the code to feed the regulation loop algorithm. A function performing linear interpolation between four set-points (Set_Target_Electrical_Frequency) is provided as an example in the software library and can be used in most of the cases, as long as the coefficient values can be linearized (see Figure 7 on page 17 for details). On the contrary, a function with a larger number of set-points or a look-up table may be necessary. When running the starter kit in standalone mode, the RS232 communication interface might be used using the `tty_7.exe' windows program; this will allow the Kp and Ki values to be read directly on a PC; it is also possible to get the motor speed, the rising and the falling Bemf de lay. To enter the four set-points, some defines in the mtc.h file must be edited according to the collected parameters: (See 'Mtc_Settings_Sensorless.h' or 'Mtc_Settings_Sensor.h' for Min and Max frequency values)
//Fmin #define #define .. //F_1 #define #define #define .. //F_2 #define #define #define .. //Fmax #define #define Ki_Fmin Kp_Fmin 10 30

F_1 Ki_F_1 Kp_F_1

1000 20 10

// 100 Hz

F_2 Ki_F_2 Kp_F_2

2000 50 40

// 200 Hz

Ki_Fmax Kp_Fmax

13 18

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Tricks and traps When tuning the PI parameters you should look for the worst case conditions, which may be when the load quickly and unpredictably varies, when the inertia is at a minimum, or when the mains voltage is maximum for an off-line application. Frequency regulation output is a 10-bit variable. If the final application requires a different resolution (involving the PI routine to be rewritten), the output might be chosen as a power of 2 so that logical shift operations can be used as divisions (new duty = (max_duty x PIoutput)>>10 for 10-bit returned value). This will result in compact code and will reduce the CPU time consumption while processing the PI output. To give sufficient accuracy to the control algorithm, the returned data should not be less than an 8-bit value, and shouldn't be greater than 12 bits long (the same resolution as the MTC cell PWM timer). A regulation tuned in no-load condition (at the highest) will most probably be unresponsive in the final application, and vice versa: a regulation tuned in the application may become unstable in no-load conditions.

Implementing the closed loop regulation
... if (ValBit(Flag_MTC,SAMP_EVT)) // Sampling time elapsed? -> update PWM { ClrBit(Flag_MTC,SAMP_EVT); Set_Target_Electrical_Frequency((u16)(your_frequency)); } ...

Below is an example of the use of this regulation process.

Note: Whatever the declared number of pair poles is, the `Set_Target_Electrical_Frequency' routine needs to be fed with an electrical frequency input. The `Pole_Pair_Num' definition in `MTC_Settings_Sensorless.h' or `MTC_Settings_Sensor.h' file is just declared as a reference; it can be used for example in the final application in order to display the mechanical frequency instead of the electrical.

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Figure 50. Closed loop PWM duty cycle control
Current frequency Target frequency

Frequency error (signed 16 bit)
Clamp frequency error value to signed 16 bit Proportional = Kp x Slip Error

Is PI output saturated?

No

Integral = Integral + Ki x Sampling time x Slip Error

Integral term frozen Output = Proportional + integral (signed value)

Is Output<0 or >1024 (2^10)? No Reset Saturated Output Flag

Yes

Clamp Output value to unsigned [0..1024] domain]

Set Saturated Output Flag

Update PWM duty cyle

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7.3.2 Adjusting falling/rising Bemf settings Rising and falling Back-EMF coefficients allow the delay to be set up between a zero-crossing e ve n t (Z event) and the consecutive commutation event (C event). Once this `delay' is elapsed, the PWM is applied on the next switch configuration (one of the 6 steps, T0-T3, T0T5, etc.). With the help of this setting, fine tuning of the commutation `mechanism' is permitted: low coefficient values (early commutation) may make the system unstable, while high values may lower the maximum speed of the system. In order to match any system, and especially when motor windings are not mounted entirely symmetrically, 2 delay coefficients can be adjusted: rising (respectively falling) delay associated with rising (respectively falling) Back-EMF voltage (to further reduce dissymmetrical winding effects, the sensorless method allows to choose the previous MZPRV or current MZREG value for delay computation). It has to be noted that `rising' and `falling' definitions are meaningful only in sensorless mode. In sensor mode, the hall effect sensor outputs can be connected to the demokit in different ways, so the rising delay may then be associated to a falling-edge sensor output. Generally, the delay coefficients have to be set in order to run the motor properly at a desired frequency, and used to balance the step times (equal time duration of the 6 steps, see Figure 51). The final application layer could even allow greater flexibility (not implemented in the library): 6 independent delay coefficients (1 per step) in sensorless mode, or 3 delay coefficients in s e nso r mode (1 per sensor). This may be required especially when motor windings are strongly dissymmetrical or when the sensors are not set equally apart from each other (120 degrees in sensor 120 mode with 1 pair pole for example).

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Figure 51. Current shape in a well-balanced system (current mode)

7.3.3 Completion of Fine Tuning and Other Software Considerations If your motor works fine with the GUI, please refer to Section 3 GETTING STARTED WITH THE LIBRARY USING THE ST7MC-KIT/BLDC.

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8 REVISION HISTORY
Table 1. Document revision history
Date
10-Jan-2005 12-Jul-2007

Revision
1 2

Changes
Initial release Removed references to obsolete products

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