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Permanent Magnet Synchronous Motor (PMSM) Overview

The Permanent Magnet Synchronous Motor (PMSM) is an AC synchronous motor whose field excitation is provided by permanent magnets, and has a sinusoidal Back EMF waveform.

  • With permanent magnets the PMSM can generate torque at zero speed
  • Higher torque density versus AC Induction Motors (ACIM), i.e., smaller frame size for same power
  • High efficiency operation
  • Requires digitally controlled inverter for operations 
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Recommended Products for PMSM Control and Drive
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Microchip offers a complete line of single chip three-phase brushless drivers and three-phase brushless motor MOSFET gate drivers for a broad range of motor applications. These products are designed to interface to any microcontroller or be used in a standalone configuration.

  • For Single-Chip Drivers for PMSM Motor Control Start with the: MTD6501
  • For MOSFET Gate Drivers for PMSM Motor Control Start with the: MCP8024

Microchip offers a complete line of single chip drivers designed for low voltage fan control. These fan controllers offer sinusoidal control for fans with sinusoidally wound motors. They can be easily interfaced to any microcontroller using a simple PWM input and FG input or used in a standalone configuration.

Because PMSM motors must be driven with sinusoidal waveforms, the complexity of the control increases. Microchip’s dsPIC® family of digital signal controllers (DSCs) offer DSP performance to execute the PMSM control algorithms and advanced motor control peripherals to generate the waveforms needed to control them.

Microchip offers both MIPS and ARM Cortex MCU's for high performance, 32-bit motor control. These devices feature high performance peripherals tailored for high speed, closed loop motor control.

PMSM Control Development Tools
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For Microchip's three-phase brushless gate driver and dsPIC33 solution - MCP8025 TQFP BLDC Motor Driver Evaluation Board (ADM00600)

For Microchip single-chip BLDC drivers - MTD6505 3-Phase BLDC Sensorless Fan Controller Demonstration Board

For 16-bit dsPIC DSCs - MCLV-2 Low Voltage Motor Control Development Board (DM330021-2)
MCHV-2 High Voltage Motor Control Development Board (DM330023-2)
Low Voltage Motor Control Development Bundle (DV330100)

For 32-bit ARM Cortex and MIPS MCU’s – PIC32MK Motor Control PIM for use with MCLV-2 Low Voltage Board (MA320024)
SAMD21 Low Voltage Motor Control Kit (compatible with SAM D2x and SAM C2x plug-in-modules)

Key Characteristics of the PMSM Motor
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  • No sparks → safer in explosive environments
  • Cleaner, faster, more efficient
  • Less noisy, more reliable
  • Designed for high-performance servo applications
  • Runs with/without position encoders
  • More compact, efficient and lighter than ACIM
  • Coupled with FOC control produces optimal torque
  • Smooth low- and high-speed performance
  • Low audible noise and EMI
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How it Works
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PMSM and BLDC motors can usually be driven with either six-step commutation or sinusoidal commutation. A motor must have the proper mechanical and electrical design to get the benefits of sinusoidal operation listed above. It is best to ask the manufacturer which drive method is best for a given motor.

Sinusoidal operation requires more precise rotor position feedback from the motor and a more complex inverter switching algorithm. The PMSM is best controlled with a high performance 8-bit MCU, 16-bit MCU or dsPIC® digital signal controller.

PMSM Control
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Input:

  • Typically torque, speed, position and/or direction
  • Inputs can be analog voltage, potentiometer, switches or digital communications
Sine PWM
SINE_PMSM

BLDC Motor Control:

  • Basic I/O for firmware bit-bang for 6-step
  • 3-phase PWMs for hardware PWM
  • Comparators for speed sensing in sensorless control,
    over-current detection
  • Capture/Compare/PWM or input captures for speed sensing
sixstepsinecontrol

Feedback:

  • Hall effect sensors, optical encoder or back-EMF voltage

Driver:

  • 3-phase inverter
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Click image to enlarge
PMSM Application: Field Oriented Control
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microstepping
Click image to enlarge
  • V/F Sinusoidal drive produces smooth control at low speed but is inefficient at high speeds
  • FOC provides smooth control at low speeds as well as efficient control at high speeds
  • Top of the line dynamic torque response and efficiency and the lowest system cost motor control solution
  • ADC supports sampling the motor voltage and currents
  • DSP supports Clark and Park transformations transform and two PI loops controlling torque and flux
  • DSP supports speed and position PI loops as determined by an estimator motor model rotor position output
  • The outputs of the PI loops are transformed using space vector modulation to drive the MCPWM outputs to the motor

FOC treats torque and flux time in variant variables by viewing rotating rotor field relative to the rotating stator field. 

Applications
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  • Air conditioner & refrigerator (AC) compressors
  • Direct-drive washing machines
  • Automotive electrical power steering
  • Machining tools
  • Traction control
  • Data storage