# Asymmetric H Bridge Controller



## Salty9 (Jul 13, 2009)

In reading about switched reluctance motors I came across: 

http://itee.uq.edu.au/~aupec/aupec03/papers/151%20Chancharoensook.pdf

Could a switched reluctance motor be used in an EV or could this control method be used on another type of motor?


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## EVfun (Mar 14, 2010)

This electric motor cycle used a switched reluctance motor. Unfortunately Zap bought them, and like most things they touch, it ceased to be successful.


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## Coulomb (Apr 22, 2009)

Salty9 said:


> Could a switched reluctance motor be used in an EV


Oh, yes, switched reluctance motors have been considered as good contenders for some time, but somehow BLDC, PMAC, and induction motors seem to always be a little more suitable.

I believe that the Chinese are doing research into this, and I think you can even get some EV sized 4-phase controllers now. This might be for permanent magnet AC (or BLDC) motors, though.



> or could this control method be used on another type of motor?


It would not work for induction motors, since the output can't approximate a sine wave, and induction motors don't commutate. However, I believe that you could use these controllers for PMAC/BLDC motors. Most of these are 3-phase, of course, so you'd use three of these asymmetrical half H-bridge circuits rather than the four shown in the paper.

I haven't read the article in detail, but I don't see the advantage of using two transistors per phase compared with one transistor per phase. I suppose it's the ability to effectively reverse the voltage across the coils, to get them to turn off their magnetic field faster.

[ Edit: Thinking about this for a moment, it occurs to me that PMAC/BLDC motors would not have such square back EMF curves, so this controller topology would be limited to switched reluctance motors after all, not those with permanent magnets. ]


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