[cajunfj40]

Hello all,

Been keeping up with the development of MPaulHolmes' "Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control" and the gears are spinning merrily in my head.

I'm still a ways off from being able to afford a conversion, but using 1 or more Nissan Leaf motors with this 200kW capable controller looks like a winner from a bang for the buck perspective.

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, based on my assumption that it doesn't seem likely that the Leaf motor is overbuilt enough to put out much more than 100kW without increasing the voltage above a stock Leaf battery pack level, due to hitting the current saturation limit (or something). A single motor is "enough" (80kW constant rating at 7000RPM will theoretically push my theoretical EV up a 6% grade at 60-70mph), but I want more, of course. If a single leaf motor can handle 200kw short term (or longer with additional cooling), then no need to pair up.

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

I have an idea of what I would need to do to make two IPM motors work on one drive, so please follow along and let me know where I made my mistakes, and correct them if possible.

Poking around on the web I found some quite good cutaway views of the Leaf driveline, one included a teardown of the motor itself, showing that the rotor lamination stack is keyed to the main shaft (more like two very long slots on the shaft, 180 degrees apart, and the laminations have an integral pair of tabs that fit into said slots). Thus one could "easily" make a longer shaft and press two rotor lamination stacks onto it, and expect them to be very well aligned.

The stator windings/lamination stack is press-fit into the cooling-channel equipped main motor housing - it is unclear whether there is any keying there. The "simplest" way to pair them up would be to machine an adapter that would connect the "front" of one stator housing to the "back" of the next housing, with the stator slots aligned. Obviously the stator spacing would need to match the spacing of the rotors on the new common shaft.

Re-assemble, and you have a double-length motor with two rotors on one shaft, two stators in paired housings, each with their own cooling jacket and stator wiring connections, and one can use a factory front and rear housing end-plate and bearing setup on the ends. Custom work can be done to add additional cooling to the end-turns if desired.

Is this sufficient to align the two motors well enough to achieve proper operation when the stators are connected in parallel to the controller, or do I need to set up my "stator housing coupler" to be adjustable and play with the alignment until I get some measurable electrical output from the two stator windings to match? If I need to play with it, what sort of electrical output do I look for? I thought I could set it up and spin the rotor and watch the AC waveforms from the two stators on a scope and adjust the two housings relative to each other until they match as closely as possible. Or, I could run the paired motors off the controller at a low current and adjust the relative position of the stators until max torque is reached - but this is a much harder setup.

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?

I would then use only one encoder/resolver for the paired motor.

Thoughts?

This seemed more straightforward than a custom gearbox to accept two Leaf motors and combine the output into a single output shaft - trying to align the two rotors through the gears adds the problem of slop and having to re-do it every time you pull a motor or strip a gear.

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? How about if two standalone motor/encoder/inverter sets are mechanically connected? What would be awesome is a way to run two stock Leaf inverters this way...

Note that both ideas can be extended to pair up two or more of virtually any available wrecked OEM EV motors and possibly their inverters, depending on motor mechanical setup and inverter electronics/control scheme.

Thanks!