Switched Reluctance Drive

Running an SRD open loop is tricky, especially during the startup. While it is possible (I actually hold a few patents on methods to do it,) it is by no means simple. Here's a patent for a low cost way to run open loop.

There are more sophisticated ways to estimate the rotor angle from the phase current, but those are considerably more expensive.

Hi, just wondering I dont think that I have ever come across this type of motor, what applications are they used for? Is this an older version of a stepper motor?

Cheers

Joe

Hi Joe,

SRM's are similar in concept to VR stepper motors, but optimized for power and efficiency rather than stepping accuracy. They emerged as a "new" motor technology in the 1980's. They're actually a very old concept, but affordable power electronics for commutation make them much more practical today. They are a niche motor technology, but have real advantages for some applications. Some of their salient features are:

• Low cost. Nothing but iron laminations and windings.
• High efficiency. Can be in the 90%+ range at rated speed and power
• Low rotor inertia gives them very fast response for servo applications
• High temperature capability. Because of their simple construction, they can be designed to run at very high temperatures.
• High speed capability. The simple, rugged rotor construction allows for very high speed operation.
  
• They can be made very fault tolerant. We designed SR drive systems that would run pretty well with phases out. This works because each phase winding is electrically independent of the others.
• Full four-quadrant operation (yes, they can run as generators, quite effectively)
  

Some disadvantages:

• High torque ripple. They don't make very smooth servos.
• High noise (due the torque ripple)
• They require accurate rotor position sensing for good commutation. However due to the saliency of the rotor, the position can be estimated pretty accurately by looking at the phase current.
  

In my "previous career," we designed and built switched reluctance drive systems ranging from fractional horsepower for appliance applications, up to 120 hp @ 20,000 rpm for aircraft engine fuel pumps and starter-generators.