[aquabiologist]

Hmm

According to this:

http://www.fieldlines.com/index.php?topic=149371.0

It seems something like 18.46 rpm per volt?

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[dcb]

well, there may be things going on in the fancy leaf controller that are boosting the voltage output, come to think of it there has to be (it can regen a 400v pack down to a couple mph). Controllers are a buck converter when feeding the motor, so they can be boost converters going back the other way. I'm sure it has to be synced with the shaft magnetic position though.

 

[aquabiologist]

Thanks for your input on regen.

I was more thinking about max speed i get if the motor was run at lower voltage.

Doing some more thinking now i guess:

As torque is constant up to ca. 2730 rpm and torque drops at higher rpm i guess voltage @ motor increases from 0 to 360/sqrt(2) volts from 0 to 2730 rpm?

Above 2730 rpm more rpm is done with phase advance and thus torque drop?

So then: kv would be more like 10.6 rpm / motor volt

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[dcb]

you will probably be able to extract more useable power out of it using a controller fyi, like when it is spinning too slow for the pack, and better power factor. But you would need a buck converter feeding the pack also if the pack voltage is lower than the max anticipated output from the generator. Even if you just rectify the output of the generator you will want a buck converter, or at least something, to control the current and shut it off.

re: K/V, yah I was going to suggest looking at the torque graph. drops off at about 2700 rpm, and it is a 360v nominal pack, which figures to 7.777K/V but it is under a heavy load too with additional losses and interactions, so not exactly, K/V is a no-load measurement. The rest of the graph is field weakening, which seems unlikely to be much concern if you are considering a windmill, dunno what you have planned though. (edit, you did clarify, my bad)

If you just want to throw 180 volts at it I would scale it by 50% to the left and leave the grid numbers where they are and guess peak torque stops at ~1300 rpm (280nm).

edit: I don't know if the final taper on the right is representative, but if that is how it would drop off without field weakening, then KV could be as much as 5000rpm/360v.

edit2: I would imagine the efficiency part doesn't get scaled down in the attachment, but I was lazy.

 

[dcb]

here, this one might be more realistic, just guessing. Hopefully you get the idea. So where w/360v you could make 150nm, @5000 rpm at 94% efficiency, at 180v @5000 rpm you can make 75nm at maybe 93% efficiency? Probably not real accurate at the extremes there though so I wouldn't count on it.

 

[aquabiologist]

Thanks for the graphs, excellent!

Over the weekend I tried to excelify the leaf motor.

https://drive.google.com/file/d/0B6CR2c8c9UP-TjU2MGZBdE0yV21OSENfQzdMMnp2VUk5Vnc0/view?usp=drivesdk


Yellow fields are for input. Seems to match your predictions pretty well

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[dcb]

so one thing I forgot to mention, is with field weakening on a pm motor, since you can push it well past the pack k/v limit, you can't just shut off field weakening at high rpm.

Also I don't know how suitable it is for a leaf motor, but a somewhat common thing to do with induction motors is to reconfigure them for a lower voltage, i.e. open it up and switch it from wye to delta (sqrt(3)), or reconfigure the poles in each phase to be in parallel (div by 2 or whatever). Occasionally folks will rewind them for lower voltage too, but that is a little involved. And a second hand leaf pack is like $2000, so hard to justify except in space limited scenarios.

so paralleling fields increases the k/v by two (depending how much paralleling you do, depending on number of poles). but reduces the k/t by two, so you need twice as many motor amps for the same torque, but you doubled the number of conductors so it should be ok. With those constraints and a suitable battery/controller you can get back close to the original graph at a different voltage, though switching losses will be greater. rewinding has a similiar effect, increases conductor cross section and reduce number of effective turns, only a bit more precise about matching to a specific voltage instead of 360/2.

 

[aquabiologist]

Overvoltage at high rpm with regen seems to be a problem then. You say you cant just turn off field weakening. Why?

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[dcb]

well your standard inverter (or even your standard dc controller) doesn't regulate the current going back into the battery when the motor voltage output is higher than the battery (because you are over 5k rpm or so). Well, it does, but with field weakening, by using the stator field to "push back" against the rotor field, in sync with the rotor

It is just a bunch of diodes/solid state switches that control the application of voltage from battery to motor, and if motor voltage is higher...

I only mention this as you may have to look into a custom 3 phase controller, depending on how your component selection resolves. I think most folks are content just keeping 360v and using the stock controller these days (and the charger and the bms and etc) if on a budget and not space constrained, some have sorted out various other controllers, but they might not work with a PM motor, some don't have field weakening, some are completely homebrew or started with a kit. Some have even "hotrodded" the leaf controller, though you might consider rwd if you want it to hook up.

http://www.mynissanleaf.com/viewtopic.php?t=21335

 

[aquabiologist]

Would that be 'dynamic braking'?

Seems dangerous.

I would rather have a system that disconnects the motor while overvoltage. Even when the controller fails.

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[dcb]

Would that be 'dynamic braking'?

Not really, more like current control, if it is negative motor current then braking, positive current then motoring, zero current then coasting (basically just cancelling out the induced voltage in the stator, by focusing on the d-axis).

Seems dangerous.

Meh, it is a little more bleeding edge, but been around in cars since the first prius probably, and maybe 90% of the EV's on the road do it that way as well. You can see from the graph that field weakening really extends the useful range of a PM motor, without it the leaf would stall out at like 30mph!

I would rather have a system that disconnects the motor while overvoltage. Even when the controller fails.

Induction motors are good like that. A couple % less efficient than a PM and a bit heavier, but is more failsafe, and easier to find a controller for, and more voltage options usually, and usually pretty cheap. It can do regen and field weakening too, just rotate the field slower than the rotor for regen, and just keep increasing frequency once you hit the pack kv limit for field weakening. There are fancy algorithms for it to to optimize it better, but overall it is more forgiving. The rotating stator field creates the rotor field (with slip), and if the stator stops working, the rotor will shut down.

 

[dcb]

fyi if you are interested in this sort of thing, have a look at dave wilson's series "teaching old motors new tricks".

https://www.youtube.com/watch?v=fpTvZlnrsP0

 

[aquabiologist]

A lot of Informationen to take in
Thank you again for all the details!

I guess for now, i have plenty to think about. Maybe the new netgain hyper 9 might be my best option, as my engineering skills are not really up to the task for building my own controller or modifying a motor.

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[MPaulHolmes]

I wonder if the 18.46 volts you found was from 360v/(sqrt(3)*sqrt(2)) at 2730rpm. The highest duty that the the controller uses for each of the 3 phases is pack voltage / (sqrt(3)). then, /sqrt(2) to get rms. The Line to line voltage peak is 360v. So, the line to neutral peak is 360/sqrt(3), so the line to neutral RMS is 360/(sqrt(3)*sqrt(2))