BLDC and PMSM Control Using Sensorless FOC Algorithm Based on MSPM0 MCUs

Why is MSPM0 Considered for BLDC, PMSM, and FOC?

Texas Instruments' scalable M0+ MSPM0Gxx high-performance MCUs with advanced on-chip motor control peripherals provides a design for variety of motor control applications. The portfolio covers from 32 KB to 128 KB of flash with scalable analog integration, motor control peripherals, and CAN.

• 80-MHz M0+ CPU – Reduces processing time for FOC algorithms and sensing signal
• Integrated math accelerator
  • 32-bit hardware divider (8 cycles) for fixed point and IQ format numbers
  • Square root operation in 21 cycles
  • 24-bit trigonometric calculations (sin, cos, atan) in 29 cycles
• Two independent 4-Msps 12-bit ADC Module (up to 16 channels)
  • Up to 11 ENOB with SNR
  • Up to 4-Msps ADC boost motor phase current sensing within 250 ns
• Two "zero-drift" chopper op amps – Accurately amplifies 2-phase currents and calculate the 3rd phase current
• Three high speed comparators– Enables hardware low-side current limiting for motor with zero-wait
• Advanced motor control timers – Flexible 6 PWM control and cross triggers
  • Center-aligned PWM generate
  • Asymmetric PWM allows two center-aligned PWM signals to be generated with a controlled phase shift
  • Complementary PWM with dead band insertion
  • Cross trigger to generate ADC timing to capture 2-phase current
• Robust IO design with glitch filter – Provides a reliable system despite motor noise.
• Comprehensive communication interfaces – Including UART, I2C, SMBus, SPI and CAN-FD to meet all the communication requirements with the motor control system.
• FOC algorithm library – Accelerates time to market of motor control design.
• Scalable MCU portfolio – Pin-to-pin compatible devices across a wide range of flash memory options.
• Low cost and small footprint package – Options for space constrained designs.
• Wide operating temperature range (-40°C to +125°C)
• Automotive-Q100 qualified and functional safety options (up to ASIL-B) for system stability and reliability.

What can MSPM0 do in BLDC, PMSM, and FOC?

In BLDC, PMSM, and FOC applications, MSPM0 monitors the motor status and runs the FOC algorithm. Depending on the system architecture and motor voltage, there are two main topologies of analog integration used in FOC applications, especially in sensorless FOC applications where an observer is required to estimate the real-time position of the motor. The MSPM0G also provides an integrated hardware accelerator to calculate the computations for efficient FOC performance at 30 kHz PWM frequency or higher.

MSPM0 Analog Integration and Gate Driver

With the help of scalable analog integration, the MSPM0 can accurately sense the motor phase voltage, bus voltage, current, and speed quickly to provide feedback to the FOC algorithm. Two programmable gain amplifiers (PGAs) amplify the difference between phase currents sensed through two shunt resistors and a scaled DAC output voltage, and the output of the PGAs directly can be sampled by internal ADCs. This topology is designed for FOC applications that require high voltages, low-cost or high efficiency, such as servo drives, HVAC motors, and large appliances.

Figure 4 MSPM0Gx50x + Gate Driver Block Diagram for FOC

MSPM0 and Gate Driver with Analog Integration

In lower voltage motor applications, many gate driver or motor driver devices integrate up to three current sense amplifiers with programmable gain, which offloads analog requirements from the MSPM0Gx device. MSPM0Gx devices without analog integration are available in packages as small as 24-VQFN to reduce system size. MSPM0 can accurately sense the motor phase voltage, bus voltage, current, and speed quickly to provide feedback to the FOC algorithm using 12-bit simultaneous sampling 4-Mbps ADCs. This topology is designed for FOC applications that are small form factor, such as pumps, fans, blowers, and small appliances.

Figure 5 MSPM0Gx10x + Gate Driver Block Diagram for FOC

Design details

• Motor control designs in MSPM0-SDK
  • MSPM0 Sensorless FOC Library
    • Supports DRV830x, DRV831x, DRV832x, DRV834x, DRV835x devices with integrated current sense
    • Supports 3-phase gate driver designs using MSPM0Gx integrated analog for current sense up to 650 V
• FOC Algorithm Libraries
  • Hardware abstraction layer (HAL)
    • Used to make the device-specific peripherals (for example, PWM, ADC, and Timer) generic across the rest of the algorithm for easy porting.
  • Space vector modulation (SVM)
    • PWM control algorithm to create a continuously rotating space vector that generates appropriate gate signals for the gate driver every PWM period.
  • Clarke and Park transforms (and inverse)
    • Mathematical modules used in the algorithm to achieve direct-quadrature-zero transform, which is a crucial element of FOC theory. The module is applied here to control three-phase stator and rotor qualities to maximize torque.
  • Estimator
    • Used to measure rotor flux magnitude and angle in sensorless FOC systems.
  • PID controller
    • A typical proportional-integral-derivative controller can be used to stabilize closed loop performance.
  • User
    • A module containing all user tunable parameters to achieve desired performance.
• Timer and ADC
  • Generates six external PWM signals from one timer (TIMA0) and trigger 2 ADC module conversions to simultaneously sample phase currents, phase voltages, and bus voltage.
  • PWM: Center-aligned complementary PWM with deadband insertion.
    Figure 6 MSPM0Gx TIMA and ADC Sequence for FOC
• OPA – standard (STD) mode
  • 6-MHz GBW, 4-V/µs slew rate, and 6-µV/°C drift in STD mode
  • Figure 7 MSPM0Gx OPA Block Diagram for Current Sensing

• COMP – high-speed mode
  • The 8-bit DAC (1-µs settling time) inside COMP module enables a 40-ns response time for setting current limit thresholds
    Figure 8 MSPM0Gx COMP Block Diagram for Current Protection