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Switched Reluctance (SR) Motor Controllers and Drivers

 Our Solutions for Switched Reluctance Motor Control

A Switched Reluctance (SR) or variable reluctance motor does not contain any permanent magnets. The tradeoff for this low-cost construction is a complex drive with more switches and complex control techniques to achieve a smooth torque operation. SR motors are an excellent choice for applications that require high-speed operation and power density in a compact form factor.

Permanent Magnet-less Switched Reluctance Motor

Typical Applications

  • Fuel pumps
  • Throttle controls
  • Oil pumps
  • Anti-Lock Braking Systems (ABS)
  • Vacuum cleaners
Products Field Oriented Control
Microcontrollers (MCUs),
Digital Signal Controllers (DSCs) and
Field-Programmable Gate Arrays (FPGAs)		 dsPIC33 DSCs
32-bit PIC32MK and SAM MCUs
IGLOO® 2 FPGAs
SmartFusion® 2 SoC FPGAs
Three-Phase Gate Drivers ATA6843
ATA6844
MIC4604
MIC4605

Some Basics About Switched Reluctance (SR) Motors

How a SR Motor Works

While SR motor control is simple to implement, this type of motor is not commonly available.  The stator is similar to that of a Brushless DC (BLDC) motor; however, the rotor is made only of iron laminates. The iron rotor is attracted to the energized stator pole, and the polarity of the stator pole does not matter. Torque is produced as a result of the attraction between the electromagnet and the iron rotor.

SR Motor Characteristics

  • Synchronous operation
  • Low-cost motor because of simple and magnet-free construction
  • More suitable for high-speed/high-power density applications
Switched Reluctance Motor Segment Diagram

Implementing SR Motor Control

The simple, inexpensive construction of an SR motor requires a microcontroller for speed control and to reduce torque ripple and audible noise. The rotor forms a magnetic circuit with the energized stator pole. The reluctance of this magnetic circuit is analogous to the resistance of an electric circuit, and it decreases as the rotor aligns with the stator pole. When the rotor is in line with the stator, the gap between the rotor and stator is very small. At this point, the reluctance is at its minimum. This is where the name switched reluctance comes from. The inductance of the energized winding also varies as the rotor rotates. When the rotor is out of alignment, the inductance is very low, and the current will increase rapidly. When the rotor is aligned with the stator, the inductance will be very high and the current decreases slowly, which results in torque ripple. This is one of the difficulties in driving a switched reluctance motor.

Microcontroller Features for SR Motor Control

Basic I/O Digital/analog signal for speed direction and torque
Capture/Compare/Pulse-Width Modulation (CCP) Generate independent PWMs for multiple MOSFET switches and tachometer input for speed sensing using input capture
Comparators Overcurrent detection and protection
Analog-to-Digital Converter (ADC) Measurement of phase current and DC bus voltage for speed and position sensing in sensorless control
Quadrature Encoding Interface (QEI) Optical encoder interfacing for position sensing
Communication Peripherals (I2C, SPI, CAN) Typically torque, speed, position and/or direction

Motor Control Hardware and Software Solutions

Motor Control Application Algorithm and Software Library

Sensor-Based Speed Control 

This code example outlines the setup requirements for operating a Switched Reluctance Motor (SRM) with the dsPIC33AK128MC106 DSC. For information about speed control, please refer to the "Switched Reluctance Motor Control” product brief in the Documentation section below.

Switched Reluctance Motor Control Demonstration Application

Our Switched Reluctance Motor (SRM) demonstration application features a dsPIC33AK128MC106 DSC, asymmetric H-bridge converter and additional analog ICs to implement precise motor operation under challenging conditions.

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Documentation

Title
Switched Reluctance Motor Control Solution Product Brief Download