Synchronous Reluctance Motors 6

[JBUDA54]

I have done some research on SRM's and found that:

A Reluctance Motor is a type of synchronous electric motor which uses the phenomenon of reluctance to induce non-permanent magnetic poles on the rotor. A reluctance motor, in its various incarnations, may be known as a:

synchronous reluctance motor
variable reluctance motor
switched reluctance motor
variable reluctance stepping motor
Reluctance motors can have very high power density at low-cost, making them ideal for many applications. They do suffer from high torque ripple when operated at low speed, and may be noisy. Until recently, their use has been limited by the complexity inherent in both designing the motors and controlling them. These challenges are being overcome by advances in the theory, by the use of sophisticated computer design tools, and by the use of low-cost embedded systems for motor control. These control systems are typically based on microcontrollers using control algorithms and real-time computing to tailor drive waveforms by rotor position and current or voltage feedback.

Thanks to the Wikipedia!!! Now then... Who sells these motors and what are their applications? Any experts out there on this topic? TIA. JBUDA54

 

[gepman]

jbuda54
Is this the same thing as a written pole motor? I designed an MG set for a computer power system that had a written pole motor driving the written pole generator. On the other end of the common shaft with the MG set was a natural gas engine. The MG set had such high inertia that in case of a power failure it would engage a clutch with the natural gas engine to start turning the generator. The MG set could slow down at least 30% and not loose the frequency since it could "write" the number of poles that the generator needed for the speed that it was going until the natural gas engine kicked in. The system did not need any inverter, batteries, or other type of flywheel (except of course the flywheel effect of the MG set). It is still working after six years.

The company that sells them is

http://www.precisepwr.com/Default_home.asp?bhcp=1

 

[JBUDA54]

gepman, I went to that site and noticed that they are located in Palmetto, FL! My first job out of college was with Trilectron Industries in the same town. This is a small world! I was only there for 9 months. As to a write pole motor... I haven't come across this either in my illustrious 13 year career. Interesting concept, though.

http://www.meridiumpower.ca/C/body_c.html

The more I read about written pole motors it appears that PrecisePwr has trademarked this technology. The fact that it is single phase makes it different from SRMs.

http://en.wikipedia.org/wiki/Reluctance_motor

I going to have to say these are different.

 

[sreid]

SRM just have not caught on as general purpose motors. I believe that the Dyson Vacuum uses one and they are being used in some battery powered hand tools.

 

[gepman]

jbuda54
The units that I installed were 3 phase, both motor and generator. I think that they found a niche market for areas where there is only single phase power available. Apparently the three phase written pole motor can't compete with the three phase induction motor (at least given the tremendous volume of three phase induction motors).

 

[Clyde38]

As you have already stated, reluctance motors are not written pole motors. They are essentially large angle VR (Variable Reluctance) step motors. They have been around for about a hundred years. Large locomotives use reluctance motors for the drive power. Warner Electric, near Rockford IL used to make the VR motors for the large Hewlett Packard plotters. Warner's volumes were in the millions. Yes they can be noisy, and yes they can exhibit high torque ripple. Emerson Electric, in St. Louis MO purchased Lawrenson (England) some time ago and has tried to incorporate reluctance motors in appliances (washers, dryers, etc.) The University of Glasgow has a laboratory that has done a lot of work on the design and control of reluctance motors (S.P.E.E.D) under the directions of Prof. Tim Miller. Some jet engine applications use reluctance technology for starter/generators. There is much more but I'm sure your all bored by now.

 

[electricpete]

A related discussion:
thread237-158042

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Eng-tips forums: The best place on the web for engineering discussions.

 

[sreid]

The biggest hurdle for SRM's is cheap induction motors and cheap VFD's.

 

[JBUDA54]

Thanks to everyone that responded!!!

I now understand a little more about SRMs!

Jason

 

[cswilson]

Switched reluctance, variable reluctance, and switched variable reluctance motors are all basically the same beast, but synchronous reluctance motors are significantly different.

In the first class of motors, the number of stator and rotor poles is different. A rotation of the stator winding excitation produces a vernier effect, yielding a smaller rotation of the rotor in the opposite direction. This yields an effective "gearing down" of the motor, producing lower speed and higher torque.

The protruding rotor pole is attracted to the closest energized stator pole, "seeking" to minimize the magnetic reluctance by lining up with it. Because this is a reluctance effect, the direction of the magnetic field produced by the stator winding current does not matter, and therefore the direction of the current in the winding does not matter. The ramification of this (which may not be immediately obvious, as many people have trouble catching on to this) is that these are not AC motors -- current must be off in each phase during half of the cycle, or it will produce torque in the opposite direction of that desired.

Controlled as open-loop stepper motors, and called "variable reluctance" motors, these were used by the millions for things like the paper advance in dot-matrix printers. The motors were cheap, simple, and amenable to simple pulsed digital control from a unipolar supply.

Starting in the 1970s, folks like Lawrenson and Miller started looking at these motors for applications like VSDs and servos. While the principle of operation is exactly the same, optimization of the motor design for continuous motion instead of primarily holding position led to substantially different designs. Generally, these people used the term "switched reluctance" motors to distinguish them from the classic stepper-motors. A few people use the term "switched variable reluctance" motors instead.

Synchronous reluctance motors are substantially different. I don't have nearly as much experience with these, so I will be briefer. They do not have different pole spacing on rotor and stator, so they do not get the "vernier" gearing effect. They expect an AC input. If memory serves me right, they were used in high-end audio turntables in my youth. The last project I was even peripherally involved in to use these was a high-speed flywheel energy-storage device. Here they wanted the reluctance motor instead of a permanent magnet motor so the spinning rotor would not automatically produce terminal voltages due to back EMF.

Curt Wilson
Delta Tau Data Systems