DIY Electric Car Forums banner

Switched Reluctance Motor

156K views 142 replies 19 participants last post by  cts_casemod 
#1 ·
I "rediscovered" this motor in my searches and it seems to be making a comeback because electronic controls are now ubiquitous and the design has many advantages and few downsides. As a point of reference this was touched upon here:
http://www.diyelectriccar.com/forums/showthread.php?t=75088&highlight=reluctance

Here are some links I posted elsewhere but I'll consolidate them here:

http://machinedesign.com/article/the-switch-to-switched-reluctance-1211
http://www.youtube.com/watch?feature=player_embedded&v=jt4Fa4H43Iw (simple VR motor)
http://www.youtube.com/watch?v=nQ8G5wnH5sc&feature=player_embedded (variable reluctance test motor 3p stator 4p rotor)
http://www.youtube.com/watch?v=b3hmkehrcUg&feature=player_embedded (SRM test)
http://www.youtube.com/watch?v=G2qS2TxU9KY&feature=player_embedded (first run)

I made a drawing of a proposed design for a switched reluctance motor:



Here is a video of a simple SR motor and controller I just made:


From the description:

This is an experimental switched reluctance motor which uses only external electromagnets in the stator, and no windings or permanent magnets in the rotor. Thus it is a very simple, rugged, and low cost design. The expense and complexity may be in the controller. The principle is essentially using electromagnets to align a piece of steel and then switching the excitation to adjacent magnets to achieve motion. I think I need to work on the design of the rotor and the pole pieces so that the force aligns the rotor at an exact point of rotation, which means wider stator pole pieces or more narrow rotor tips.

I may make some changes and see if I can get significant improvement, especially for self-starting. I think I will need to use a full three-phase H-bridge so the pole pairs can be driven both positive an negative (N and S). I also found that it helps to drive two sets of poles together to get higher torque and smoother transitions.
 
See less See more
1 1
#141 · (Edited)
But my question is on the repurposing of a DC 4 pole motor stator using 2 phases (and a 3 phase inverter topology) and a 2 or 3 pole rotor. i.e. what is wrong, if anything, with this picture? And do you need a custom inverter topology to maintain good efficiency? assymetrical rotor poles so they can self start. Are the extra wide dc stator poles a deal breaker for instance? Seems like it would be murder on the Ld/Lq if the next phase already has rotor iron under it when it fires.


Admittedly I've still a lot of head scratching to do, and there are plenty of perfectly useable as-is motors out there, so this is very much academic.
 
#143 · (Edited)
The problem I see with that topology is torque ripple. Even if one were to assume 4 poles that's quite a large distance between them, since DC motors normally have 'flat' poles. What happens if the motor stops in between? One might not have enough torque to restart, due to the large distance.

Induction motors, on the other hand are composed of 36 slots. It's much easier to machine a rotor, also with 36 slots, and energyse/de-energise the stator coils at the right time to 'pull' the rotor (or push to regenerate). The torque will be pulsating, but at 360/36 = 10degree steps, the motor inertia tends to smooth the output very well (just like PWM in an electrical circuit).
 
#142 · (Edited)
What I have on my mind is to re-purpose the motor with a suitable inverter and a new stator, rather than using the original as that will always tend to generate it's own "induction" field, which again may be convenient if one plans to make it start across the mains, but for us EVer's there's not much point in doing so. It will negatively impact efficiency. The point in going SR is so that the motor can operate synchronously.

I may try that using a car alternator with some hall sensors, which again is a more wise choice as the stator can remain unchanged if you wish so (only the rotor needs to be machined (for testing) or reconstructed (for final use at full torque).

Paul, did you finish your prototype?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top