[thingstodo]

Originally Posted by cajunfj40

Hello all,

Hi!

I have what may be a motor or controller theory question, and please keep in mind that I'm a Mechanical Engineer, not an EE.

I would like to run two Leaf motors off one controller

As far as I know, Field Oriented control is done per motor. HPEVS has a dual 35 KW motor, and it uses 2 Curtis controllers, one gets the throttle signal and the other follows in torque mode. I have no details - but if they could do it with one controller it would be much more competitive in price.

Theoretically, this can be done - at least, it is common in industry to run multiple AC motors off a single VFD.

In my experience, multiple induction motors on one controller are done in Volts per Hertz mode. Every output voltage has a corresponding frequency output. It gives you more than one motor`s output in vector mode, but less than a controller per motor.

To my knowledge (please - I`d love to be wrong on this one!) no one does sensored or sensorless vector control, Field Oriented Control, etc with more than one motor per controller.

However, the Leaf is an Interior Permanent Magnet type AC motor, thus if I understand correctly it is a synchronous type and operates without "slip", and this complicates the process of trying to parallel two motors.

Actually, it`s worse than that. The control is like permanent magnet for low speed, and has more contribution from reluctance as the speed rises, so the angle that the current is driven changes with speed and with load (!!) Lots of calculations done by the controller to figure out what signal to send out for maximum torque.

So making both motors put out full torque with the same signal when they are coupled is quite a challenge. I won`t say impossible .. but I will say much more math to prove one way or the other than I`m up for!

Thus one could "easily" make a longer shaft and press two rotor lamination stacks onto it, and expect them to be very well aligned.

I think this is the crux of the issue - figuring out what to measure to make sure that they are `well aligned`.

On the electrical side of things, once the two motors are aligned, do I just hook up the two stators in parallel - making sure the correct phases are connected so the unit doesn't fight itself? Do I need to carefully adjust the wiring resistance so they are equal, or is inductance more important, or both? How critical is this adjustment?

As I understand it ... to get full torque, the resistance (wire length, mostly), inductance (cross sectional area across steel, tightness of the wire coil, consistency of the laminations), and reluctance (resistance to magnetic flux .. sort of .. dependent on consistent laminations of the steel, thickness of the varnish between laminations, etc) would all have to match at the same time. I believe this would be a challenge.

Alternately, if the two motors cannot be paralleled on the same drive for electrical reasons, can the twinned motors be run from a pair of inverters in master-slave mode, assuming the motors are aligned well enough that the single resolver is accurate enough to provide rotor position information for both motors?

Yes.