ST STM32 Nucleo User manual

November 2016
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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:
1
download the X-CUBE-SPN7 or X-CUBE-SPN8 firmware packages from
www.st.com.
2
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.
3
change the motor and drive parameters
4
compile the firmware
5
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.

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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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3.3.2 Voltage mode control
In the voltage mode driving method, the loop generates the output through a PI regulator
which compares the speed reference to the actual speed motor feedback. No ETR function
is needed because the output calculates the new duty cycle value of PWM signals.
Figure 5: Voltage mode control
The six-step firmware library v.1.1 supports both current and voltage modes, the
v.1.0 only supports the current mode.

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3.3.3 Rotor speed measurement
The sinusoidal and the trapezoidal motor structures are mentioned in this document. The
motor structure can be recognized by rotating the motor by hand and connecting a probe to
two motor phases.
The figures below show the signal acquired through an oscilloscope.
Figure 6: Sinusoidal construction

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Figure 7: Trapezoidal construction
The rotor magnetic field produces a BEMF signal in the stator windings. If the motor is
intrinsically sinusoidal or trapezoidal, the induced BEMF signals are periodic and their
frequency is proportional to the frequency of the motor turns. The proportional coefficient is
the number of motor pole pairs; this number is used to calculate the mechanical speed of
the motor: for instance, with 1000 Hz and 10 pole pairs (or 20 poles) the mechanical
frequency is equal to 100 Hz.
The motor speed in rpm can consequently be calculated by measuring the electrical
frequency of the motor:
Equation 1
()=60
× () × 6
where, steptime is the duration (in seconds) of a low frequency timer that regulates the
length of each step. It is multiplied by the number of steps and converted in rpm. The new
value of steptime is managed by the zero crossing calculation function and it is updated at
the frequency of the step generation (Step_N to Step_N+1).

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Figure 8: High and low frequency timer signals
3.3.4 Commutation, demagnetization delay and zero crossing event
Since the BLDC is a synchronous motor, the drive main objective is to ensure the rotor
position synchronization with the stator magnetic field. It is possible to demonstrate that the
drive maximum efficiency is obtained by keeping the stator magnetic field with a 90-degree
spatial advance with respect to the rotor magnetic field, achieved by keeping the zero
crossing in the middle of each step (see Figure 9: "BEMF signal and zero crossing
detection").
Since each motor has different inductance values, the current could reach zero with a delay
at each step commutation. This event called demagnetization determines the starting point
for zero crossing detection. The delay is a percentage of the step time (see Figure 10:
"Demagnetization time"). The BEMF signal can be measured when the current reaches the
zero value in the floating phase after the demagnetization delay time.

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Figure 9: BEMF signal and zero crossing detection
Figure 10: Demagnetization time
This method is managed through firmware (see Figure 11: "Demagnetization: delay time
(N=3)"). Two different modes have been implemented, one is based on look-up-table and
one is based on the current step time duration multiplied by a constant. The first is
implemented in FW version 1.0, the other one only in version 1.1.0 (Please refer to the next
section for further information). Figures Figure 11: "Demagnetization: delay time (N=3)" and
Figure 12: "Demagnetization: delay time (N=2)" show the commutation delay at different N
values: for instance, for N = 3 the delay time is 2 * T (switching period).

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Figure 11: Demagnetization: delay time (N=3)
Figure 12: Demagnetization: delay time (N=2)

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3.3.5 Zero crossing detection method
In order to synchronize the BLDC motor with the driver, when the BEMF signal becomes
equal to the motor neutral voltage a zero crossing point occurs.
There are two different scenarios that depends on the high frequency PWM signal
generated to modulate the high-side devices that change the way of measuring the BEMF
value, in particular:
1. during PWM T-on time applied to the high-side switch, the motor neutral voltage
becomes equal to the bus voltage divided by 2.
2. During PWM T-off time applied to the high-side switch, the motor neutral voltage
becomes 0 V.
The zero crossing can be detected during both the on and the off time of the PWM signal.
The six-step fw library v.1.0 and v.1.1 are only based on T-off mode and the detection of
the zero crossing point is performed by comparing the BEMF converted value to a fixed
threshold. Figure 13: "BEMF measuring during the OFF-time and ADC sampling" shows
the BEMF measuring during the T-OFF of T1 switch when the phase C is floating and the
ADC sampling method measures the BEMF signals, Vbus, temperature, motor current etc.
Figure 13: BEMF measuring during the OFF-time and ADC sampling
3.3.6 Startup procedure
To perform a sensorless control on the BLDC motor, the BEMF must reach an appreciable
value to be readable. Since the BEMF amplitude depends on the rotor speed, it requires
the motor to rotate at the speed above a specific threshold. Thus, it is important to
implement an asynchronous startup strategy.
The following phases are necessary to start the motor up and begin the closed loop control
with BEMF detection:
•alignment phase
•ramp generation phase

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3.3.6.1 Alignment phase
During the alignment phase, the rotor is forced at a specified position through a specific
switch configuration. A fixed current (managed by firmware) is maintained to move the rotor
at the closest pole pair position. The alignment is performed through the choice of a
specific step number (for instance, if the step number 1 is the starting point, the choice is
step number 6).
3.3.6.2 Ramp generation phase
To perform a good BEMF control, start the motor with a ramp profile of speed: a fixed and
controlled current (current mode) is maintained to run and accelerate the motor. The
control system monitors the motor speed and check if this value reaches a specified
threshold (managed by the firmware: red circle). In case of a positive check, the counter of
zero crossing events starts and at a specific value (managed by the firmware: green circle)
determines the starting point of the closed loop operation (see the figure below). This
condition is reached if the number of zero crossing events reach a threshold (set through
the firmware).
Figure 14: Alignment and ramp-up generation

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4 X-CUBE-SPN7 and X-CUBE-SPN8 software
expansion for STM32Cube
4.1 Firmware package architecture overview
The firmware example in X-CUBE-SPN7 and X-CUBE-SPN8 is provided for three different
IDE tools, IAR EWARM, Keil MDK-ARM, AC6 Workbench. In this case the IAR IDE
workspace appears as shown in the following figure.
Figure 15: Project workspace on IAR IDE
The firmware solution is built around three independent levels that can easily interact with
each other as described in Figure 16: "X-CUBE-SPN7 software architecture" and Figure
17: "X-CUBE-SPN8 software architecture".

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Figure 16: X-CUBE-SPN7 software architecture
Figure 17: X-CUBE-SPN8 software architecture
The software architecture is mainly composed by:
•Middleware
•Examples
•Driver (BSP/Component).
Since the X-NUCLEO-IHM07M1 contains the L6230 driver and the X-NUCLEO-IHM08M1
contains the L6398 driver, in the firmware package, inside BSP/Components, the specific
driver is provided according to the power board used (see Figure 18: "X-CUBE-SPN8
folder contents").