ST STM32 Nucleo User manual

November 2016

DocID029868 Rev 1

1/39

www.st.com

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User manual

Getting started with the six-step firmware library for

STM32 Nucleo boardsbased on STM32F microcontrollers

Introduction

The six-step (trapezoidal) firmware is an easy-to-use and low requirement brushless scalar software

library for three phase permanent magnet (PMSM) and brushless DC motors (BLDC) developed for

STM32 microcontrollers.

The procedure to configure the six-step firmware library for STM32F microcontrollers and drive a BLDC

motor in both open and closed loop is described in the following sections.

The current control method is based on sensorless mode but it is compatible with hall and encoder

speed sensor modes.

The rotor position is reconstructed by BEMF detection.

The six-step library is written in the C programming language and it is based on STM32Cube library.

The IDE tools supported are IAR Workbench, Keil and AC6. The core of this control algorithm is

embedded inside the X-CUBE-SPN7 and X-CUBE-SPN8 firmware package available on the ST web

site.

A prerequisite for using this library is basic knowledge of the C programming language, three phase

motor drives and power inverter hardware. In-depth knowledge of STM32 functions is only required for

customizing existing modules and for adding new ones for complete application development.

Contents

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Contents

1Acronyms and abbreviations ......................................................... 5

2Features ........................................................................................... 6

2.1 Six-step software library in X-CUBE-SPN7 and X-CUBE-SPN8

packages........................................................................................................6

2.2 Development tools ............................................................................7

2.3 Toolchains......................................................................................... 7

2.3.1 Programming tools ............................................................................. 7

3Implementation of six-step motor control algorithm in STM32

Nucleo microcontroller............................................................................ 8

3.1 Introduction to BLDC theory..............................................................8

3.2 Rotor synchronization .......................................................................9

3.3 Motor driver control ...........................................................................9

3.3.1 Current mode control.......................................................................... 9

3.3.2 Voltage mode control........................................................................ 11

3.3.3 Rotor speed measurement ............................................................... 12

3.3.4 Commutation, demagnetization delay and zero crossing event....... 14

3.3.5 Zero crossing detection method ....................................................... 17

3.3.6 Startup procedure............................................................................. 17

4X-CUBE-SPN7 and X-CUBE-SPN8 software expansion for

STM32Cube ............................................................................................ 19

4.1 Firmware package architecture overview........................................ 19

4.2 How to identify the six-step library version ...................................... 22

5Getting started with the STM32 six-step firmware library .......... 23

6Designing an application at user level using the firmware library32

6.1 Run a different BLDC motor............................................................ 32

6.2 DAC settings for debug ................................................................... 36

6.3 How to use the API function for application development ............... 36

7Revision history ............................................................................ 38

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List of tables

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List of tables

Table 1: List of acronyms............................................................................................................................5

Table 2: Six-step firmware library version...................................................................................................6

Table 3: ROM and RAM requirements .......................................................................................................6

Table 4: Main mapped peripherals ...........................................................................................................24

Table 5: Header file basic parameters......................................................................................................24

Table 6: Header file advanced parameters (open loop control) ...............................................................24

Table 7: Six-step advanced parameters for motor driving (current mode) ...............................................26

Table 8: Six-step advanced parameters for motor driving (voltage mode)...............................................27

Table 9: Six-step general parameters for motor driving ...........................................................................27

Table 10: Six-step firmware library not exported functions.......................................................................28

Table 11: Six-step firmware library exported functions (APIs)..................................................................28

Table 12: Document revision history ........................................................................................................38

List of figures

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List of figures

Figure 1: BLDC motor control sequence ....................................................................................................8

Figure 2: six-step phase voltage with BEMF sequence and PWM modulation ..........................................8

Figure 3: Current mode control.................................................................................................................10

Figure 4: ETR function on current mode control.......................................................................................10

Figure 5: Voltage mode control.................................................................................................................11

Figure 6: Sinusoidal construction..............................................................................................................12

Figure 7: Trapezoidal construction ...........................................................................................................13

Figure 8: High and low frequency timer signals........................................................................................14

Figure 9: BEMF signal and zero crossing detection .................................................................................15

Figure 10: Demagnetization time..............................................................................................................15

Figure 11: Demagnetization: delay time (N=3) .........................................................................................16

Figure 12: Demagnetization: delay time (N=2) .........................................................................................16

Figure 13: BEMF measuring during the OFF-time and ADC sampling ....................................................17

Figure 14: Alignment and ramp-up generation .........................................................................................18

Figure 15: Project workspace on IAR IDE ................................................................................................19

Figure 16: X-CUBE-SPN7 software architecture......................................................................................20

Figure 17: X-CUBE-SPN8 software architecture......................................................................................20

Figure 18: X-CUBE-SPN8 folder contents................................................................................................21

Figure 19: six-step library version.............................................................................................................22

Figure 20: Acceleration rate and number of steps....................................................................................25

Figure 21: six-step firmware library component overview ........................................................................30

Figure 22: six-step main firmware routines: low priority task....................................................................30

Figure 23: six-step main firmware routines: medium priority task ............................................................31

Figure 24: six-step main firmware routines: high priority task ..................................................................31

Figure 25: New motor running ..................................................................................................................33

Figure 26: Motor successful initialization ..................................................................................................34

Figure 27: Motor successful initialization zoom ........................................................................................34

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Acronyms and abbreviations

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1 Acronyms and abbreviations

Table 1: List of acronyms

Acronym Description

ACC acceleration constant

API application programming interface

ARR autoreload register

BEMF back electromotive force

BLDC brushless DC motor

DAC digital to analog converter

DC direct current

ETR external trigger

IDE integrated development environment

PMSM permanent magnet synchronous motor

PWM pulse-width modulation

UART universal asynchronous receiver transmitter

Features

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2 Features

2.1 Six-step software library in X-CUBE-SPN7 and X-CUBE-

SPN8 packages

The BLDC software library source code is available on www.st.com.

The six-step library is included in two different firmware packages called X-CUBE-SPN7

(tailored for X-NUCLEO-IHM07M1) and X-CUBE-SPN8 (tailored for X-NUCLEO-IHM08M1)

which provide the compliance with STM32 ODE in STM32 Nucleo expansion platforms.

The main library features are:

•supported trapezoidal six-step method

•sensorless mode: BEMF (back electromagnetic force) voltage on the non-energized

phase is monitored and used to trigger the commutation events

•voltage mode: PWM duty cycle is set directly via a PWM 16-bit timer

•current mode: the inner current loop and an external speed loop are used to control

motor winding current. The output of a speed PI regulator becomes the input of the

current loop that generates the PWM signal.

•DC bus voltage measurement

•fault handling (overcurrent)

•one channel virtual DAC functionality for debugging.

Table 2: Six-step firmware library version

Configuration Version

X-CUBE-SPN7 1.0.0

X-CUBE-SPN8 1.1.0

Table 3: ROM and RAM requirements

Configuration ROM (Kbytes) RAM (Kbytes)

Six-step algorithm 7 0.5

X-CUBE-SPN7(1) 24 1

X-CUBE-SPN8(1) 24 1

Notes:

(1)It includes the STM32Cube library (ROM size: 12Kbytes). The remaining memory size is for the compliance with

ST - STM32 ODE

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2.2 Development tools

The BLDC firmware library is specific to some hardware platforms, in particular the X-

CUBE-SPN7 with X-NUCLEO-IHM07M1 and the X-CUBE-SPN8 with X-NUCLEO-

IHM08M1.

For evaluation purposes or new user development, it is recommended to use these

hardware platforms together with STM32 Nucleo development board.

The X-CUBE-SPN7 is compatible with the following boards:

•NUCLEO-F030R8

•NUCLEO-F103RB

•NUCLEO-F302R8

•NUCLEO-F401RE

•P-NUCLEO-IHM001

•X-NUCLEO-IHM07M1

The X-CUBE-SPN8 is compatible with the following boards:

•NUCLEO-F302R8

•NUCLEO-F401RE

•X-NUCLEO-IHM08M1

2.3 Toolchains

The library has been compiled through different integrated development environment (IDE)

interfaces: IAR EWARM 7.4, Keil MDK-ARM v.5 and AC6 Workbench.

In the X-CUBE packages, it is possible to choose the right project workspace based on the

MCU.

2.3.1 Programming tools

The six-step firmware library is preloaded in the motor control Nucleo pack (P-NUCLEO-

IHM001).

For the other cases:

download the X-CUBE-SPN7 or X-CUBE-SPN8 firmware packages from

www.st.com.

open the project workspace from the IDE tool available (IAR EWARM, Keil MDK-

ARM v.5 or AC6 Workbench) choosing the right STM32 Nucleo development

board.

change the motor and drive parameters

compile the firmware

upload the binary

When using the STM32 Nucleo development boards no additional

programming tool (for instance external ST-Link, J-Link or equivalent) is

needed as it is already embedded.

Implementation of six-step motor control

algorithm in STM32 Nucleo microcontroller

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3 Implementation of six-step motor control algorithm

in STM32 Nucleo microcontroller

3.1 Introduction to BLDC theory

A brushless three phase motor is made of a fixed part (a three winding set called "stator")

and a mobile part (containing a permanent magnet called "rotor").

In BLDC motor control, the electrical cycle is subdivided into six commutation steps. For

each step, the bus voltage is applied to one of the motor three phase windings whereas the

ground is applied to a second winding. The third winding remains open. The successive

steps are executed in the same way except that the motor phase winding changes to

generate a rotating stator field (see Figure 1: "BLDC motor control sequence"): the red

arrow shows the stator flux vector rotation of and the blue arrow shows its direction.

A BLDC motor has a trapezoidal BEMF (back electromagnetic force) induced into the

motor phase windings. The BLDC drive is also called trapezoidal control because of the

phase current shape. This control method allows having the maximum performance in

terms of efficiency and minimum torque ripple since the motor is intrinsically built as BLDC.

Figure 2: "six-step phase voltage with BEMF sequence and PWM modulation" shows the

voltage applied to a phase (BEMF waveform and PWM modulation).

Figure 1: BLDC motor control sequence

Figure 2: six-step phase voltage with BEMF sequence and PWM modulation

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3.2 Rotor synchronization

The BLDC drive is a synchronous control drive: the maximum efficiency is achieved if the

commutation between two consecutive steps is performed only when the rotor is in the right

spatial position, which occurs when the BEMF signal and the phase current are

synchronized.

The following methods can be implemented to perform the rotor synchronization:

•sensored drive, which uses position, Hall or encoder sensors to measure the rotor

position.

•sensorless drive, based on the BEMF detection. It analyzes the zero crossing of the

floating phase BEMF signal to establish the commutation point. The match between

the floating phase BEMF signal with respect to the ground point is used to generate

the commutation between two consecutive steps in order to achieve the rotor

synchronization.

The six-step firmware library v.1.0 or v.1.1 is only based on sensorless mode, no position

sensor is supported. The BEMF signal is analyzed for each step and a new commutation

point is calculated step by step. This method allows rotor position synchronization with the

drive control.

3.3 Motor driver control

The BLDC drive is performed modulating the phase voltage through a PWM sequence that

is generated by two different control methods:

•current mode (peak control): two control loops are needed, one inner and one outer.

The inner loop generates, by hardware (with analog comparator), the PWM sequence

for motor current regulation starting from an analog reference signal; this signal is

generated by the outer loop that contains a digital PI regulator that compares the

speed reference with the motor speed real feedback. It provides the torque control and

inherent current limitation in the windings.

•voltage mode: only one loop is needed, the PI regulator directly generates the PWM

regulating the duty cycle value.

3.3.1 Current mode control

Figure 1: "BLDC motor control sequence" shows the current mode (peak current) driving

method. The inner loop contains all the components to acquire the motor current, amplify

and conditioning the signal to be compared with a reference value. This block output is

directly connected to the ETR timer function (MCU features) that regulate the duration of

the PWM signals. In this case, PWM Ton are managed by the ETR.

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Figure 3: Current mode control

Figure 4: "ETR function on current mode control" shows how the ETR works during the

normal operation. The red line is the motor current regulated at a fixed current reference

(green). In blue the PWM signals managed by the ETR, each time the motor current

reaches the current reference threshold, the ETR turns PWM signals off.

Figure 4: ETR function on current mode control

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