- Motor Control With AVR®
- Release Notes
- Related Documentation
- Software Used
- Hardware Used
- Quick Start Guide
- Application Usage
- Motor Control Software Description
- Results
- Troubleshooting Guide
- Scenario 1: Can't program the board
- Scenario 2: The motor does nothing when the MPPB button is pressed
- Scenario 3: The motor starts spinning with vibrations and stops, then the red LED blinks five times
- Scenario 4: The motor starts, spins a few times, then stops or runs erratically
- Scenario 5: The motor is spinning, but it consumes a lot of current
- Scenario 6: Motor starts, then unexpectedly starts shaking, vibrating, then stops
- Scenario 7: Motor starts normally, but when turning the potentiometer it enters Stall mode, then stops
- Scenario 8: Console Interface doesn't display any data
- Scenario 9: DVRT tool doesn't display any data
- Scenario 10: Changes made in
mc_config.hhave no effect - Scenario 11: CNANO board is not recognised in MPLAB X IDE
- Summary
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This repository contains one bare metal source code example for a Motor Control application, using the new AVR EB family of devices. Check the Release Notes section to see all the available functionality on the current release. The approach for this application is focused on the dedicated hardware peripherals of the AVR16EB32 microcontroller (MCU), which reduce the amount of memory used and the Central Process Unit (CPU) overhead as some mathematical calculations are done in hardware by this device.
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AVR EB has two new peripherals, the Timer Counter type E (TCE) and a Waveform Extension (WEX), that have new hardware capabilities meant to takeover software functions usually used in motor control, as described in Getting started with TCE and WEX and in the AVR EB data sheet.
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The functionality of the application is to obtain a Trapezoidal (6-step block commutation) and a Sinusoidal drive method with motor synchronization, with support for both sensored and sensorless feedback types. The focus is on Brushless Direct Current (BLDC) motors and Permanent Magnet Synchronous Motors (PMSMs).
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The Sensored feedback and synchronization is achieved using Hall sensors. A software algorithm is used to overcome possible faulty transitions of Hall sensors, due to noise or mechanical misalignments, and thus correctly detecting the rotor's position and synchronize the motor with the driving signals.
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The Sensorless feedback and synchronization is achieved using the Zero-Cross Detection (ZCD) of Back-Electromotive Force (BEMF) of the three phases of the motor. Each phase of the motor is filtered to determine when to commutate the motor drive voltages. The position of the rotor sensing algorithm is the same as in the Sensored case, the only difference is the commutation timing, which differs from Hall sensors to BEMF.
Current version 1.1.1 features:
- Motor specification in configuration file
- Trapezoidal drive
- Sensored Sinusoidal drive (Space Vector Pulse-Width Modulation (SVPWM) profile, Saddle profile)
- Hall Sensor feedback support
- BEMF sensing
- Motor–Drive (Rotor-Stator) synchronization (Open loop)
- Phase Advance selection
- Start and stop ramps
- MPLAB® Data Visualizer Run Time (DVRT) communication support for plotting parameters in real time
- Proportional-Integral (PI) algorithm with fixed parameters for Closed Loop control over speed regulation
- Fault support for Hardware Peak Overcurrent Protection (Peak OCP) and Software Average Overcurrent Protection (Avg OCP), Overvoltage Protection (OVP), Undervoltage Protection (UVP), Overtemperature Protection (OTEMP), and Stall Detection
- Current, Voltage Bus, Temperature and Potentiometer analog measurements at run-time
Known issues and future improvements:
- Sinusoidal drive harmonic distortion in light load condition
- Stall detection doesn't work all the time in Sensorless mode
- Sinusoidal sensorless drive
- Configurable (PI) algorithm for Closed Loop control over speed regulation
- Profiler tool for motor self-commissioning
- PWM input for compatibility with radio-controlled receivers
More details and code examples on the AVR16EB32 can be found at the following links:
- AVR® EB Curiosity Nano
- Multi-Phase Power Board (MPPB)
- AVR EB Curiosity Nano Adaptor to MPPB
- BLDC Motor (Suggestion: ACT57BLF02)
- A Voltage power supply (6-50V and 5A limit, depending on the motor used)
The AVR16EB32 Curiosity Nano Development board is used along with the MPPB, AVR EB CNANO to MPPB Adaptor board, the BLDC Motor and a Voltage power supply.
Connections steps:
- Plug in the AVR16EB32 CNANO board in the connector present on the MPPB Adaptor board.
- Plug in the MPPB Adaptor board to the MPPB board.
- Connect the Voltage power supply wires to the V_SUPPLY conector from the MPPB.
- Connect motor phase wires to the PHASE connector from MPPB in this order:
- Motor PHASE A -> MPPB PHASE A
- Motor PHASE B -> MPPB PHASE B
- Motor PHASE C -> MPPB PHASE C
- If Sensored control is preferred, connect motor Hall wires to the HALL SENSOR connector from the MPPB in this order:
- Motor HALL A -> MPPB HALL A
- Motor HALL B -> MPPB HALL B
- Motor HALL C -> MPPB HALL C.
If the MPPB and the Adaptor boards are not used, the user can integrate the AVR EB into another hardware setup by using the following pinout:
All the pins can be configured in the mc_pins.h file.
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Connect the AVR EB CNANO board to the PC.
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Open the
mc_demo.Xproject in MPLAB X IDE. -
Right click the project and select Set as Main Project.
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Edit the
mc_config.hfile, found inmc_demo/Application/Configuration headers, with the utilized motor parameters and drive options. See Predefined Config Settings for examples. -
Edit the
mc_limits.hfile, found inmc_demo/Application/Configuration headers, with the hardware and motor used specifications. See Fault Limits for explanations. -
Build the
mc_demo.Xproject by clicking Clean and Build Project.
- Click Make and Program Device to program the project to the board.
This is a set of configuration settings, apart from the default values, needed to run the demo in Trapezoidal Sensorless/Sensored or Sinusoidal Sensored mode, with the motor ACT57BLF02. Overwrite the settings from mc_config.h file with the ones listed below:
/* possible values: MC_SENSORED_MODE, MC_SENSORLESS_MODE */
#define MC_CONTROL_MODE MC_SENSORLESS_MODE
/* possible values: MC_CONTINUOUS_MODE, MC_STEPPED_MODE */
#define MC_DRIVE_MODE MC_STEPPED_MODE
/* possible values: MC_SCALE_CENTER, MC_SCALE_BOTTOM */
#define MC_SCALE_MODE MC_SCALE_BOTTOM
/* motor specific settings */
#define MOTOR_PHASE_ADVANCE (15.00) /* degrees */
#define MC_MOTOR_PAIR_POLES (4) /* pole pairs */
#define MC_MIN_SPEED (400) /* RPM - minimum speed */For Sensorless mode, the MC_MIN_SPEED must be set to at least 10-15% of the nominal speed of the motor.
/* possible values: MC_SENSORED_MODE, MC_SENSORLESS_MODE */
#define MC_CONTROL_MODE MC_SENSORED_MODE
/* possible values: MC_CONTINUOUS_MODE, MC_STEPPED_MODE */
#define MC_DRIVE_MODE MC_STEPPED_MODE
/* motor specific settings */
#define MOTOR_HALL_DEVIATION (0.00) /* degrees */
#define MOTOR_HALL_INVERTED true /* true - inverted, false - non-inverted */
#define MOTOR_PHASE_ADVANCE (15.00) /* degrees */
#define MC_MOTOR_PAIR_POLES (4) /* pole pairs */
#define MC_MIN_SPEED (100) /* RPM - minimum speed */For Sensored mode, the MOTOR_HALL_INVERTED must be set to either true or false, depending on the motor manufacturing. If this parameter is set to the wrong value, it is probable that the motor will enter a stall condition, or the power consumption will be high. For more details see Sensored Mode.
/* possible values: MC_SENSORED_MODE, MC_SENSORLESS_MODE */
#define MC_CONTROL_MODE MC_SENSORED_MODE
/* possible values: MC_CONTINUOUS_MODE, MC_STEPPED_MODE */
#define MC_DRIVE_MODE MC_CONTINUOUS_MODE
/* motor specific settings */
#define MOTOR_HALL_DEVIATION (0.00) /* degrees */
#define MOTOR_HALL_INVERTED true /* true - inverted, false - non-inverted */
#define MOTOR_PHASE_ADVANCE (15.00) /* degrees */
#define MC_MOTOR_PAIR_POLES (4) /* pole pairs */
#define MC_MIN_SPEED (100) /* RPM - minimum speed */For Sensored mode, the MOTOR_HALL_INVERTED must be set to either true or false, depending on the motor manufacturing. If this parameter is set to the wrong value, it is probable that the motor will enter a stall condition, or the power consumption will be high. For more details see Sensored Mode.
After all the steps from Quick Start Guide are completed, turn the MPPB potentiometer to 50 and press the MPPB button to spin the motor in clockwise direction.
1. Short press the button present on the MPPB board. The motor starts spinning in clockwise (CW) direction and enters the Running state. The LED from MPPB turns on. Speed can be adjusted by using the potentiometer present on the MPPB board.
2. Short press the button from MPPB again. The motor spins down, stops and enters an Idle state. The LED from MPPB turns off.
3. Short press the button a third time. The motor starts spinning in counterclockwise (CCW) direction and enters the Running state. The LED from MPPB turns on. The Speed can be adjusted by using the potentiometer present on the MPPB board.
4. Short press the button a fourth time. The motor is spinning down, stops and enters Idle state. The LED from MPPB turns off.
5. Short press the button a fifth time. Go back to step 1.
Long press the button (more than 1.5 seconds) to restart the application.
If a Fault event occurs, the motor stops and enters the Idle state. The LED from MPPB blinks until the fault condition is cleared.
After the Quick Start Guide setup steps are done, the user can start spinning the motor using the button on the MPPB. By short-pressing the button (under 1.5 seconds) the motor will start spinning in the CW direction in Forced Commutation using a ramp-up to reach a threshold value of speed in a configurable amount of time. After the ramp-up is finished, the application switches to Synchronization mode, either with feedback coming from Hall sensors or BEMF ZCD, depending what is chosen in the mc_config.h file.
The speed of the motor is imposed from the potentiometer present on the MPPB. When the motor starts spinning and the synchronization and speed regulation algorithms start working, the LED from MPPB is turned ON. The motor can be stopped by short-pressing the button again. When the stop command is given, the application sets the three motor phases in Floating state; amplitude and speed are set to zero, and from then on the motor will stop naturally, depending on the rotor inertia and the load.
If the button is short-pressed a third time, the motor will start spinning again, but this time in the CCW direction, with the same functionality described above. The user can change the direction of rotation at run-time for as many times as needed, by two short presses of the button from the MPPB. The application can be restarted by long-pressing the button from MPPB for more than 1.5 seconds.
In case of a Fault event, the motor stops spinning and enters in an Idle state. The normal operation can only be restored if the fault condition is gone and the user short presses the button.
The main application functionality and overview flowcharts are shown below:
The application has two types of communication interfaces, only one enabled at a single moment of time:
- Console interface.
- DVRT tool interface.
To activate it, the MC_PRINTOUT_ENABLED must be set to true in mc_config.h file. Then simply open a PC software terminal, select the UART protocol, 8N1, with a baud-rate of 460800 bps.
The serial interface provides information about the Drive mode, PWM Scale mode, Sense mode, pole-pairs number, state of the motor, direction of rotation, speed in RPM, voltage, temperature, average current consumption and potentiometer percentage. The periodic interval for printing variables is given in milliseconds and can be configured from MC_PRINTOUT_REFRESH_INTERVAL parameter.
All the LED and button functionality are the same as in the basic functionality section.
To activate it, the MC_DVRT_ENABLED must be set to true in mc_config.h file. This tool provides capabilities to plot graph with variables in real time at run-time. Follow the steps below to get the DVRT running:
1. Build, compile and program AVR EB with DVRT support enabled.
2. MPLAB Data Visualizer has a stand-alone version or an MPLAB X IDE integrated version. The stand-alone tool can be downloaded and installed from this link.
To use the stand-alone version, open MPLAB Data Visualizer and start a new DVRT Session.
To use the MPLAB X integrated version, click the drop-down arrow of the green icon and select DVRT for Main Project, as shown in the image below:
3.The user can press the Load button and then go to avr16eb32-bldc-pmsm-motor-control-demo\Apps\mc_demo.X and load the mc_demo_eb_dvws file. This file has predefined baud, communication port settings and two variables added (potentiometer and speed).
4. *Optional: Change streaming tick to 1 ms and toggle the dark theme.
5. Click the play button, and plot all variables button.
Capture with dark theme enabled of potentiometer in percentage (green) and speed in RPM (yellow) at run-time:
If loading the mc_demo_eb_dvws file fails, the user can manually configure the DVRT tool following the next steps:
1. Start DVRT standalone version or MPLAB integrated plugin.
2. Select the AVR EB communication PORT
3. Set the baud rate to 460800 bps.
4. Manually load the ELF file. Click on the red marked icon, then navigate to the output folder and point to the elf file. This step is skipped in the MPLAB integrated plugin.
5. Add the potentiometer and speed variables
6. Click the play button, and plot all variables button.
All the LED and button functionality are the same as in the basic functionality section.
In case the application doesn't have the described behaviour from Application Usage, then check the Troubleshooting Guide.
The APIs from the Motor Control Stack found in motor_control.h are the following:
• MC_Control_Initialize() - Initialization function, needs to be called before any other function
• MC_Control_StartStop() - Starts or stops the motor depending on which state it is found in when the start-stop event is received
• MC_Control_DelayMs() - Performs a delay using a timer in the background
• MC_Control_ReferenceSet() - Sets the reference point for speed in closed loop, or the amplitude level in open loop synchronization
• MC_Control_PotentiometerRead() - Returns potentiometer value expressed in percentage
• MC_Control_FastPotentiometerRead() - Returns potentiometer value expressed in raw Analog-to-Digital (ADC) format
• MC_Control_VoltageBusRead() - Returns voltage bus value expressed in volts
• MC_Control_TemperatureRead() - Returns MOSFET transistors temperature expressed in degrees Celsius
• MC_Control_CurrentRead() - Returns mean application current consumption expressed in milliamperes
• MC_Control_Speed_Get() - Returns the rotational speed expressed in mc_speed_t
• MC_Control_PeriodicHandlerRegister() - Registers a custom software callback for the main application. This function must be called from main, not from interrupt context.
• MC_Control_StatusGet() - Returns the state of the motor (MOTOR_IDLE, MOTOR_RUNNING or MOTOR_FAULT), direction of the motor (MC_DIR_CW or MC_DIR_CCW), and the fault status (FAULT_UNDERVOLTAGE, FAULT_OVERVOLTAGE, FAULT_STALL, FAULT_OVERTEMPERATURE or FAULT_OVERCURRENT)
Users must use only the public APIs from the motor_control.h file so as not to alter the library functionality in any way.
The parameters from config file used to customize the application are the following:
MOTOR SETTINGS
• MOTOR_HALL_DEVIATION - Hall sensors are imperfect, and deviations can appear from mechanical placements or other various reasons. This parameter is expressed in electrical degrees.
• MOTOR_HALL_INVERTED - Some Hall sensors give 1 logic output when the magnet is near them, other sensors give 0 logic output when a magnet is near them
• MOTOR_PHASE_ADVANCE - Can range from 0 to 30 electrical degrees. This parameter is used to obtain greater speeds than the maximum the drive algorithm would normally be able to obtain and also to optimize the power consumption.
• MC_MOTOR_POLE_PAIRS - Can range from 1 to 28 pole pairs, usually suppplied by the motor manufacturer in the data sheet
• MC_MIN_SPEED - Used as target RPM speed by the ramp-up algorithm, spinning up from zero to target speed. This is the speed from where the switchover between forced commutation and synchronization loop starts. If Sensorless mode is used, this paramater must be set to at least 10-15% of the nominal speed of the motor.
• MC_RAMP_UP_DURATION - The desired duration for the Ramp-up algorithm, given in milliseconds
• MC_RAMP_DOWN_DURATION - The desired duration for the Ramp-down algorithm, given in milliseconds
• MC_STARTUP_VOLTAGE - The amount of voltage supplied to the motor phases during the start-up phase, given in volts. If the supply voltage is less than the start-up voltage, the application will throw an error message and the motor ramp-up will fail.
POWER BOARD SETTINGS
• MC_SHUNT_RESISTANCE - The current sense shunt resistance, given in ohms, dependent on the power board
• MC_CURR_SENSOR_GAIN - The current sense amplifier, dependent on the power board
• MC_VBUS_DIVIDER - The voltage divider, used to scale the VBUS to be able to measure it with the MC_VOLTAGE_REFFERENCE logic, dependent on the power board
• MC_VOLTAGE_REFFERENCE - The voltage reference (this application has a 3V3 logic)
• MC_TEMP_K1 - The temperature sensor coefficient, dependent on the power board
• MC_TEMP_K1 - The temperature sensor coefficient, dependent on the power board
PWM DRIVE SETTINGS
• PWM_DTH - The value of dead-time inserted at the left of one complementary PWM signals pair, given in nanoseconds
• PWM_DTL - The value of dead-time inserted at the right of one complementary PWM signals pair, given in nanoseconds
• PWM_PERIOD - The value of the PWM signals period given in microseconds
• MC_SCALE_MODE - Selects the scaling from PWM signals to start from 0% up to 100% duty cycle in MC_SCALE_BOTTOM mode
APPLICATION SETTINGS
• MC_DVRT_ENABLED - Enables or disables the communication DVRT tool
• MC_PRINTOUT_ENABLED - Enables or disables the information printing using a serial terminal software. The application can have only one of MC_DVRT_ENABLED and MC_PRINTOUT_ENABLED options available at the same time, otherwise an error will appear at compilation time
• MC_PRINTOUT_REFRESH_INTERVAL - Used by a periodic event to print various analog parameters and motor parameters like speed in RPM, voltage VBUS, etc.
CONTROL FUNCTIONALITY SETTINGS
• MC_SPEED_REGULATOR_EN - Enables or disables the closed loop over speed regulation
• MC_SYNCHRONIZED - Activates the synchronization loop. When the amplitude of the motor is modified or a load is applied to the motor's shaft, the speed will change accordingly so as not to lose synchronization. If the dynamic load change is too great, after a time-out, the application will detect a motor stall.
• MC_CONTROL_MODE - Selects between sensored with Hall sensors Control MC_SENSORED_MODE mode and sensorless with BEMF Control mode MC_SENSORLESS_MODE
• MC_DRIVE_MODE - Selects the drive method between Trapezoidal MC_STEPPED_MODE and Sinusoidal MC_CONTINUOUS_MODE
• MC_STALL_EVENTS_THRESHOLD - Number of misalignment events before throwing a stall error
• MC_STALL_ERROR_TOLERANCE - Angle error expressed in electrical degrees that conducts to a stall condition
• MC_FAULT_ENABLED - Enables or disables the fault handling mechanism
All these parameters are set to safe default values. With the initial values, the motor will spin, maybe not optimal, but it is a good starting point to start tunning for a custom application.
The configurable threshold values found in mc_limits.h file are the following:
• MC_OVER_CURRENT_PEAK_EVENT_LEVEL - The peak current limit, given in amperes. Used to protect the MOSFETS from irreversible damage
• MC_OVER_CURRENT_AVG_EVENT_LEVEL - The continuous average current limit, given in amperes. Used for overload protection, or if the phase advance difference between the stator and the rotor is too big
• MC_OVER_TEMPERATURE_LEVEL - The temperature limit, given in degrees Celsius. Used to protect the MOSFETS from irreversible damage
• MC_TEMPERATURE_RESTORE_LEVEL - The temperature restore value, given in degrees Celsius. OTEMP fault is cleared when this value is reached
• MC_OVER_VOLTAGE_EVENT_LEVEL - The voltage bus limit, given in volts. Used to protect the hardware setup from irreversible damage
• MC_OVER_VOLTAGE_RESTORE_LEVEL - The voltage bus restore value, given in volts. OVP fault is cleared when this value is reached
• MC_UNDER_VOLTAGE_RESTORE_LEVEL - The minimum voltage bus limit, given in volts. The motor will not start if this vaue is not reached
• MC_UNDER_VOLTAGE_EVENT_LEVEL - The minimum voltage bus restore value, given in volts. UVP fault is cleared when this value is reached
Set these values according to the hardware and motor used.
The layers of the Motor Control Stack are the following:
- Control Layer - The layer that integrates all the other layers (except the Communication Interface because it is independent) and is used by the User Layer
- Drive Layer - Achieves Force Commutation without getting any feedback from the motor
- Sense Layer - Gets information about the rotor's position from BEMF or HALL sensors, to synchronize the motor with the drive
- Analog Layer - Monitors the analog parameters
- Fault Layer - Handles the fault events, and stops the motor when needed to prevent irreversible damage
- Low-Level Drivers Layer - Drivers for low-level peripherals used by the application
The User Layer represents the application from the main file and it integrates the Control Layer and the Communication Interface.
The Control Layer is a wrapper for Drive Layer, Sense Layer, Analog Interface Layer, Fault Layer and its APIs can be used in the main.c file by the user. This layer is responsible for updating the values of the PWM driving signals from the Drive Layer based on the feedback it got from the Sense Layer. Also, this layer adjusts the driving sequence to follow the Hall/BEMF sequence to keep the synchronization, and to handle fault situations. Lastly, this layer is used to get more abstract and device independent APIs for monitoring the analog parameters.
All run-time functionality is done in a motor handler function called in an Interrupt Service Routine (ISR) that takes place every 50 µs. The time spent during this interrupt window can be observed from the image below:
The Control layer uses a state machine consisting of three states (MOTOR_IDLE, MOTOR_RUNNING and MOTOR_FAULT) to be aware at all times about the motor status and what action needs to be taken next. The START_STOP_EVENT coming from the main application starts or stops the motor. The FAULT_SET_EVENT and FAULT_CLEAR_EVENT are used to trigger and clear fault situations. The state machine flowchart is depicted in the image below:
This layer implements a rotor sensing position algorithm that can unify the two types of feedback sources (HALL or BEMF) and have the same approach and implementation. The goal of the algorithm is to keep the motor field in sync with the drive field, regardless of the type of feedback. Because the acquisition of BEMF and HALL data is affected by multiple factors like mechanical misalignment or noise, both of these feedback acquisition methods need a filtering algorithm to sense the correct transitions of sensors or BEMF Zero-Cross. The proposed algorithm takes the raw data from BEMF or HALL every complete PWM cycle. The sensing algorithm is called along with the drive update function every 50 μs.
The data from BEMF or sensors is in a 3-bit format, and it is checked to verify if the current value is different from the previous one. If the condition is true, then a new sector is reached, and the raw data is processed through a LUT of eight elements to calculate the angle of the rotor. The rotor angle is a 16-bit number that goes from 0 and up to 65536, equivalent to 0° to 359° when scaled in electrical degrees. If the current value of the data acquired from sensors or BEMF is the same as the previous value, then the rotor is still in the current sector.
There is also a time-out angle which is set to 0° at the start of a new sector. If the rotor is still in the current sector and the time-out angle is smaller than 90°, the drive sequence is updated with the value of the drive speed. The drive speed is also a 16-bit number that is used to increment a 16-bit counter that periodically overflows, and this counter specifies the current sector where the stator (drive sequence) is. The speed of the motor is basically the speed of scrolling through a simplified LUT of 256 elements.
The algorithm counts on the idea that between two transitions from sensors or the BEMF Zero-Cross there is no change in the motor’s speed, and the next drive sequence of the rotor and time-out angle can be interpolated with the value of drive speed. Note that the drive speed is measured in electrical degrees per sample. If the time-out angle is equal to or bigger than 90°, then a stall is detected and the motor is forcefully stopped.
Based on the calculations done by the sensing algorithm there are three possible cases:
1. The drive field is ahead of the motor field, so the drive speed must be reduced to keep synchronization.
2. The drive field is behind of the motor field, so the drive speed must be increased to keep synchronization.
3. The drive field and the motor field are in phase with one another, withing a range, so the drive speed must not be updated in this situation.
To summarize the synchronization method, the sensing algorithm basically estimates the rotor’s position and then calculates the difference between the stator (driving field) and the rotor (motor field). The result (in electrical degrees) represents how much the drive field is out of phase with the motor field. Based on this difference, the drive speed is updated to keep a constant phase shift between stator and rotor. The phase shift value can be configured by the user and it depends upon the load of the motor. If the phase shift is too small the torque might not be enough to keep the synchronization. If the phase shift is too big, the synchronization is also lost. An optimal value is determined to have enough torque produced and an efficient power consumption.
The motor's efficiency, from the power consumption point of view, can be increased by adjusting the phase advance angle or the “lead” angle. In order to have the best efficiency, the BEMF / HALL signals must be in phase with the current signals for each motor phase. Due to the motor’s inductance, the current signals lag the voltage BEMF/HALL signals, so phase advance is used for switching the driving sequence in advance. Because the voltage is switched in advance, the current has time to reach the maximum point until the signal from BEMF or HALL has a transition that marks a sector change. Phase advance angle is added in the speed adjusting algorithm and it is used when the difference between the stator field and the rotor field is calculated. Based on the difference, the speed is increased or decreased to keep synchronization.
Closed Loop control over speed regulation can keep a certain desired value of the speed, even if load variations may appear. Speed regulation is achieved using a software PI algorithm. The algorithm takes two inputs: the desired speed and the actual speed of the motor. Based on the Proportional and Integral parts, the error between the two inputs is calculated and the PWM duty cycle amplitude of the drive signals is changed to keep the desired value of speed while the motor is running. If the amplitude is set to maximum and the value of the desired speed still cannot be reached, then a time-out can be implemented to stop the motor. (This will be available in the next version)
The motor speed behavior using Close Loop for Speed Control is depicted in the illustration below. In this figure, the motor spins up to 1000 RPM and then keeps this value for speed by changing the amplitude level, if a load is applied to the motor’s shaft.
The Drive Layer generates the six PWM signals that are used to drive the motor using six-step block commutation. This layer is a wrapper for the low-level drivers of TCE and WEX. The signals' generation block diagram can be observed below.
WEX has a Pattern Generation mode (PGM) feature. It can take control of the output port pins from TCE without stopping the timer. PGM is very useful for Trapezoidal drive because it can stop the drive for any phase during the floating sectors.
The sector succession is faster or slower based on the motors' imposed speed.
Sinusoidal drive is generated in the same way as Trapezoidal. However, the difference is that for Sinusoidal drive, all three motor phases are constantly driven. There are never floating phases. One sinewave period represents 360 electrical degrees and the sinewave signals for the three phases are generated using a precalculated Look-up Table (LUT), to be able to emulate sinusoidal signals by modulating the Pulse-Width Modulation (PWM) signals. The frequency of the sinewaves increases or decreases based on the motors' imposed speed.
The values from the LUT are scaled based on the desired amplitude using TCE's hardware scaling feature. The three phases have a phase delay of 120 electrical degrees between each other all the time. At initialization, the first phase starts from 0 electrical degrees, the second one starts from 120 electrical degrees and the third one starts from 240 electrical degrees.
Example of a LUT used to generate sinewave signals:
The sinewave signals frequency increases if the speed of the motor is increased and decreases if the speed of the motor is decreased. The amplitude of the sinewave is changed by modulating the duty cycles of the PWM signals. AVR EB can change the amplitude of the sinewave signals in hardware by just changing the values written in a few registers without the need to recalculate the values from the LUT and add extra mathematical computation that adds to the CPU overhead.
Sinusoidal signal generated using PWM duty cycle signal modulation:
Controlling the amplitude of the sinewave with PWM duty cycle modulation, modifying only the AMP register:
The driving signals update happens in an Interrupt Service Routine (ISR) every 50 µs for both Trapezoidal and Sinusoidal drives. The Drive Layer functionality is shown below:
By using only the Drive Layer, the motor can be spun in Forced Commutation mode, updating the driving sequence blindly without using any feedback from the rotor's position. If a load is applied, Forced Commutation is not enough to stop the motor from entering a Stall state. In practice, it spins up a motor to a speed from where it is safe to start the synchronization loop. For example, BEMF is not detectable until the motor reaches at least 10-15% of the nominal speed, so the motor spins up using a ramp in Force Commutation mode, and only then the synchronization and Closed Loop control can start.
For sensored feedback, the data from Hall sensors is acquired using three General Purpose Input Output (GPIO) pins. The three pins are set as inputs to the HALL sensors and are sampled periodically during an interrupt window.
Sometimes, Hall sensors have mechanical misalignments due to manufacturing imperfections or due to user's intervention. Because of this, the data acquisition can be affected, resulting in non-optimal running or even bad behaviour of the motor. To compensate for these errors, the MOTOR_HALL_DEVIATION parameter can be adjusted using the following steps:
- Set the
MOTOR_HALL_DEVIATIONparameter to 0.00, compile and program. - Spin the motor CW then CCW and write down the reported speeds.
- If recorded speed in CW direction is higher than that in CCW direction, then
MOTOR_HALL_DEVIATIONparameter needs to be increased. As a rule of thumb, for every 100 RPM one degree is added to deviation.
E.g: If CW speed is 5200 RPM and CCW speed is 4800 RPM, the difference is 400 RPM then, the first tried value forMOTOR_HALL_DEVIATIONis 4 degrees. - If the recorded speed in CW direction is lower than that in CCW direction, then the
MOTOR_HALL_DEVIATIONparameter needs to be decreased. This parameter is allowed to have both a positive or a negative value. - Repeat the process from step 2 until the speed and current consumption have very close values in CW and CCW directions.
Another parameter that must be adjusted is MOTOR_HALL_INVERTED. Hall sensors can have different outputs, when a magnet is near them, as shown in the image below:
For Trapezoidal drive, the Hall combination read from the pins decides which sector follows next. Usually, these sensors are in number of three and are placed inside the motor, each sensor 120° apart from another one.
The Hall transitions are mapped using a state machine with six states (from ST0 up ST5) in a circular shape that repeats itself over and over. The rotation direction doesn't impact the order scrolling through the states. The order of scrolling through the states will always be ST0 -> ST1 -> ST2 -> ST3 -> ST4 -> ST5 -> ST0 and so on. The state machine implementation can be observed from the images below:
For Sinusoidal drive, all three motor phases are continuously driven so there are no sectors, but the sensing algorithm is the same as in the Trapezoidal drive case. Based on the combination read from the Hall sensors the motor's rotor position can be estimated roughly every 60 electrical degrees. In this way, the sensing and synchronization algorithms are unified for both Trapezoidal and Sinusoidal drive.
For sensorless feedback, the values for the BEMF signals for each motor phase are sampled with the Analog Comparator (AC) peripheral. During each sector one of the three motor phases will be in the Floating state and the BEMF can be read from that phase. All the PWM driving signals from that motor phase must be synchronously logically low, the coil is not driven and the signal measured after all the propagation delays is the motor’s BEMF.
The Analog Comparator is connected to the divided motor's phase signals at the positive input using a multiplexed input selection to switch from a motor phase to another and acquire the necessary data. The AC is connected to the motor summing neutral at the negative input. The neutral can be reconstructed either in software or using hardware components like a resistor star configuration. In this application, the hardware motor neutral reconstruction is used. The signals are divided to be in the range of 0 to 3.3V, to be readable by the MCU. The values for the voltage dividers used in this application are the ones present on MPPB.
The BEMF sensing algorithm has the same implementation as the Hall sensing algorithm. Based on the combination read from the BEMF signals the motor's rotor position can be estimated roughly every 60 electrical degrees.
The BEMF Zero-Crosses are mapped using a state machine with eight states dictated by the sector change and the polarity of the comparator output change events. The functionality is explained and can be observed in the images below:
• If the Odd Sector change event happens (S0), the comparator output will go from 0 logic to 1 logic to detect a positive ZCD. After the sector changes, the state machine enters in INIT0. When the sector is changed and the motor phases are put in a Floating state, the body diodes of the MOSFETS enter in Conduction mode and a positive spike is induced in the motor phase. This can interfere with the BEMF acquisition. If that spike is detected, the comparator output must be ignored because it would detect a 1 logic signal, a false ZCD, meaning the C1 event happens, and the state machine enters the PRE0 state to filter the output. If another sector change is happening during the PRE0 state, then the ZCD of BEMF is coming earlier than expected (LEAD case). When the comparator output goes back to 0 logic, the state machine enters in WAIT0 state, where the real ZCD transition is waited. If another sector change is detected during the WAIT0 state, then the ZCD of BEMF is coming later than expected (LATE case). If the real ZCD is detected and another sector changed didn't happen yet, the state machine moves to the END0 state, where it is waiting for another sector change.
• If the Even Sector change event happens (S1), the comparator output will go from 1 logic to 0 logic to detect a negative ZCD. After the sector changes, the state machine enters in INIT1. When the sector is changed and the motor phases are put in a Floating state, the body diodes of the MOSFETS enter in Conduction mode and a negative spike is induced in the motor phase. This can interfere with the BEMF acquisition. If that spike is detected, the comparator output must be ignored because it would detect a 0 logic signal, a false ZCD, meaning the C0 event happens, and the state machine enters the PRE1 state to filter the output. If another sector change is happening during the PRE1 state, then the ZCD of BEMF is coming earlier than expected (LEAD case). When the comparator output goes back to 1 logic, the state machine enters in WAIT1 state, where the real ZCD transition is waited. If another sector change is detected during the WAIT1 state, then the ZCD of BEMF is coming later than expected (LATE case). If the real ZCD is detected and another sector changed didn't happen yet, the state machine moves to the END1 state, where it is waiting for another sector change.
The Sense Layer takes feedback from Hall sensors or BEMF and processes that information to estimate the rotor position. The information obtained by this layer is used to synchronize the motor. The Sense Layer is a wrapper for the Analog Comparator (AC) low-level driver and for the GPIO pins used to get data from Hall sensors. The information obtained from both sensors or BEMF can estimate the rotor's position roughly every 60° (electrical degrees).
The Analog Layer is responsible of monitoring some of the Motor Parameters for fault protections or for providing useful information for the user at run-time. AVR EB implements this layer using the ADC in Averaging mode. The analog parameters measured with the ADC are:
- Voltage BUS - Provided at run-time and used for overvoltage and undervoltage fault triggering, if threshold values are reached
- Temperature - Provided at run-time and used for overtemperature fault triggering, if a treshold is reached
- Potentiometer - Provided at run-time as a percentage between 0% and 100% and used for imposing a Voltage Bus duty cycle to the motor in open loop synchronization, 0% meaning the minimum duty cycle and 100% meaning the maximum duty cycle. The potentiometer is used to impose a reference speed for the motor in closed loop control
- Current - Provided at run-time and used for displaying the mean power consumption of the motor
Voltage Bus, Temperature, Potentiometer and Current are converted using the Single-Ended Conversion mode of the ADC with over sampling burst accumulation (due to a feature of the ADC present on AVR EB, a 17-bit resolution can be achieved). Data provided by analog layer represents averaged and low pass filtered information. So, it is not time-accurate information, but the values obtained are smoother.
The Fault Layer provides Peak OCP, Avg OCP, OVP, UVP, OTEMP and stall detection. The peripherals used for the Fault Layer are the ADC, AC, Event System (EVSYS) and WEX. The Fault Layer is responsible for protecting the hardware setup from irreversible damage.
- Slow Acting Protection
- Fast Acting Protection
It is done in software and it is responsible for fault protection in case of OVP, UVP, OTEMP, average OCP and stall. The ADC samples the voltage, temperature, current, and potentiometer values and converts them from raw data into human-readable values that can be displayed during run-time. The converted values are then compared with some threshold values (limit values set by the user). If the measured values exceed the limit values, then all three motor phases are driven to a logical level 0.
To drive all the output signals low, AVR EB uses the WEX in Pattern Generation mode to take control of the output pins from TCE and sets them to 0. TCE is still running in the background while WEX takes control. If the fault condition is not valid anymore, the normal operation is restored , after the user short-presses the button, and the motor will restart with a ramp-up. When a threshold value is exceeded, the limit is temporarily modified to create a hysteresis effect. In this way, the motor will not restart spinning until the fault condition is over.
The hysteresis type of fault applies to OVP, UVP and OTEMP. In case of average/peak OCP and stall there is no hysteresis applied.
A stall of the motor is detected if the current motor state is MOTOR_RUNNING and if a new transition from either BEMF or Hall sensors has not come for more than a time-out angle expressed in electrical degrees. The time-out angle can be configured by changing the MC_STALL_ERROR_TOLERANCE parameter value. If stall conditions are met, the motor is stopped, and to restore the operation, short press the MPPB button.
The average OCP does not detect momentary high current spikes. This type of fault will trigger if the load slowly increases in time, until a limit is reached. The average OCP is shown in the image below:
It is done in hardware and is responsible for fault protection in case of peak OCP. This fault handling mechanism is implemented in hardware because the current can change very fast and the system needs a quick response to prevent damaging the hardware setup. The AC sets a threshold value on one of it’s two inputs. That value represents the limit value of current that is supported by the hardware setup. The other AC input is the measured current. If the measured current exceeds the threshold value, then a hardware fault is triggered and all motor phases are floating. In this case, the normal operation can be restored only by user intervention, and, in addition the fault condition must not be present anymore.
For AVR EB the hardware fault trigger is given by an WEX interrupt. WEX has one event input enabled that is connected to the output of the AC through the EVSYS peripheral. When the AC output is logic high 1, WEX drives all output signal low (or a user desired state) using the hardware fault handling feature. The fault handling response time in case of overcurrent is fairly short, usually two or three peripheral clock cycles.
The peak OCP is much faster than the average OCP because it is done in hardware. In case of a momentary high current spike, the peak OCP will trigger.
All the fault limit values are described in Fault Limits.
Below are some logic analyzer and oscilloscope captures, to have a better view about the waveforms of the three motor phases:
Yellow -> Current from driving board to the motor on Phase A
Blue -> Voltage (filtered) on driving board Phase A
Capture taken at 4800 mechanical RPM at 24V with 10 electrical degrees phase advance
Capture taken at 5200 mechanical RPM at 24V with 30 electrical degrees phase advance
Capture taken with SVPWM drive, 10 degrees phase advance. To use this type of drive, select MC_SCALE_MODE parameter to MC_SCALE_CENTER.
Capture taken with Saddle drive, 10 degrees phase advance. To use this type of drive, select MC_SCALE_MODE parameter to MC_SCALE_BOTTOM.
This is a list of possible scenarios with application erratic behaviours and how to fix them:
To fix this issue check the following steps:
- Go to mc_demo/Application/Platform/AVR16EB32/clkctrl.c
- Copy these instructions into the FUSES struct:
.reserved_1 = {0xFF, 0xFF},
.reserved_2 = {0xFF}
- The struct must look like in the image below:
* Note: This is a temporary fix and it will be solved in future versions.
To fix this issue check the following steps:
- Make sure the MPPB is connected to the power supply and the board is powered as mentioned in Hardware Setup. If the MPPB board is powered, the LEDs for 3v3, 5V, and 12V are on.
- Make sure the power supply voltage is at least double the value of MC_STARTUP_VOLTAGE and no less than 5V if the MPPB board is used, otherwise the start-up process fails and the motor will not start spinning
- Make sure the CNANO board is connected to the PC and is programmed with the mc_demo.X project
- Make sure that if multiple projects are open at the same time in MPLAB X IDE, the mc_demo.X project is set as main project, as specified in step three from Software Setup. Otherwise there is a risk to program the CNANO board with the wrong project.
To fix this issue check the following steps:
- Disable MC_SYNCHRONIZED and MC_SPEED_REGULATOR_EN, and the motor will stay forever in Forced Commutation mode and remove any load from the motor if it is present
- Make sure the MC_MIN_SPEED parameter is at least 10-15% of the nominal speed of the motor mentioned in the data sheet and reprogram the CNANO board
- If the motor is not spinning without vibrations, try to increase the MC_MIN_SPEED to 15% of the nominal speed
- If the motor is still not spinning accordingly, increase the MC_STARTUP_VOLTAGE parameter with increments of one volt per trial
- Tweak MC_STARTUP_VOLTAGE and MC_MIN_SPEED until the ramp-up spins the motor without vibrations
- Connect the load back, if it was removed for this troubleshoot, and spin the motor again. If it spins without vibrations, then the MC_SYNCHRONIZED and MC_SPEED_REGULATOR_EN can be enabled again. If not, try to increase the MC_STARTUP_VOLTAGE parameter a bit more and try again.
- MC_RAMP_UP_DURATION, given in milliseconds, can also be increased, to avoid an abrupt ramp-up
To fix this issue check the following steps:
- Set the initial value for MOTOR_PHASE_ADVANCE to zero and program the CNANO board again
- If the motor is not spinning, try to gradually increase the MOTOR_PHASE_ADVANCE with five electrical degrees starting from zero and reprogram the CNANO board until the motor starts spinning
- For some motors, the MOTOR_PHASE_ADVANCE can be below zero. If increasing the phase advance is not solving the issue, then gradually decrease the MOTOR_PHASE_ADVANCE with five electrical degrees starting from zero until the motor starts spininng, but this is not very common.
This issue is also fixed by tunning the MOTOR_PHASE_ADVANCE parameter until the power consumption is minimum. MOTOR_PHASE_ADVANCE must be increased and decreased by one electrical degree and the current consumption must be observed. If the current consumption is getting smaller when MOTOR_PHASE_ADVANCE is increased, continue to increase it until an optimal consumption in achieved. The procedure is the same if the current consumption is getting smaller for decreasing the MOTOR_PHASE_ADVANCE.
To fix this issue check the following steps:
- Increase MOTOR_PHASE_ADVANCE to increase motor torque and prevent stall
- Check if the power supply has dropped unexpectedly, this may cause a stall
- Check if the mechanical load on the motor shaft increased unexpectedly, this causes a stall
Scenario 7: Motor starts normally, but when turning the potentiometer it enters Stall mode, then stops
To fix this issue check the following steps:
- Check if the power supply has dropped unexpectedly, when the potentiometer is turned to left, towards the minimum value, this causes a stall
- Increase MOTOR_PHASE_ADVANCE to increase motor torque and prevent stall
This is usually due to a wrong baud rate value, or because the project has the MC_DVRT_ENABLED parameter enabled. Make sure the baud rate value is 460800 bps, MC_PRINTOUT_ENABLED parameter is enabled and MC_DVRT_ENABLED is disabled.
This is usually due to a wrong baud rate value, or because the project has the MC_PRINTOUT_ENABLED parameter enabled. Make sure the baud rate value is 460800 bps, MC_DVRT_ENABLED parameter is enabled and MC_PRINTOUT_ENABLED is disabled.
After changing some options in mc_config.h and reprogramming, the changes have no effect. This happens if the project is not built and compiled properly. After every change made in mc_config.h, the CNANO board must be reprogrammed using the steps five and six from Software Setup.
After plugging and unplugging the CNANO board from PC multiple times, there is a small chance that the CNANO board is not seen anymore by the MPLAB X IDE. If that happens, try unplugging and plugging the board again. If the issue is not fixed, close and restart MPLAB X IDE.
This project provides support for spinning a BLDC motor using Trapezoidal Drive or Sinusoidal Drive methods and feedback from HALL sensors or BEMF ZCD to achieve motor synchronization in an Open Loop and fixed Closed Loop for speed regulation. The control algorithm is fairly simple and robust. AVR EB's hardware capabilities for scaling the PWM duty cycle and generating complementary signals with dead-time using only one timer with its waveform extension, ensures the CPU doesn't have a substantial overhead and optimizes memory usage and resource consumption.
The demo has a user layer that offers customizations to adjust motor and power board parameters, making it suitable for multiple setups. There is a dedicated user layer that allows for full control without disturbing the AVR EB dedicated HW configurations.