View Single Post
Old 11-23-2015, 04:31 AM   #2348 (permalink)
e*clipse
Permanent Apprentice
 
Join Date: Jul 2010
Location: norcal oosae
Posts: 523
Thanks: 351
Thanked 296 Times in 213 Posts
Quote:
Originally Posted by P-hack View Post
well I know you have an idea for a solution in search of a problem, but lets focus on what you have to work with then.
How about if we try this - a little mutual respect. It will help considerably in keeping the conversation both productive and positive.

As a start, I've done a ton of research on this motor, including reading just about every paper published on it. I also have one in pieces on my workbench, so I have an excellent idea of it's physical details. I also made a spreadsheet that includes every detail of a car/battery/motor system that includes voltage sag, aerodynamic drag, tire drag, etc etc. This spreadsheet has real numbers based on real data, not guesses. This spreadsheet gets extremely close to real-world EV test results.
Quote:

the mgr is listed as 50kw, but you mentioned 75kw, assuming you get there with more current and not just revs, then at 360v you should be able to approach 41kw, which is only 114 amps per motor, or 456 amps, a comfortable margin below 600 amps.
That's fine - you're well on the way to proving why the last person who tried the MGR was dissappointed in it's performance. He used one MGR, a 360V pack and a motor controller designed for a BLDC motor. He gave up on it when the car couldn't exceed 45mph.
Quote:
Your units also have gearing fixed, which is a problem from a top speed perspective probably, but with all 4 units you should be able to exceed 3000 lbs of force, might even approach 1g off the line if the car is light enough (does your car weigh less than 3000 lbs?), but I don't know how you figured 75kw.
Yes, the car will weigh less than 3000lbs. No, single speed gearboxes aren't the main problem. Ask Tesla.
I based the 75kW on the fact that current is limited by the cooling requirements. The MGR relies entirely on whatever heat can be removed from the case. Providing better cooling would allow more power output. A real cooling system may allow a 25% increase in torque. I'm merely building in some controller/battery headroom to allow this improvement.

Quote:
If you go with stock 50kw mgr figures the breakdown speed can be interpolated from the lower voltage (360v leaf pack assumed, might have to charge it fully to account for voltage drop)

50kw * 360 / 650=27kw. 610 wheel rpm * 360 / 650= 337 rpm where the torque falls off. I dont know your wheel size, but if they are 2 feet rolling diameter, that is 24mph. And 75 amp per motor, 300 from the battery.
Again, you're just proving again why it's not a good idea to run with 360V. Also, ORNL tested the Prius motor (a very similar design) at 650VDC bus, 500VDC bus, and 225VDC bus. In short, the results show that you can't simply linearly interpolate that point where the torque falls off. At 650V, that point is 3800 rpm. At 500V, it's 3200 rpm. At 225V, it'sabout 1500 rpm.

In the start of this you stated that "well I know you have an idea for a solution in search of a problem."
Well, you're demonstrating what the problem is.

Quote:
Even with 650 volts, it will peak before 44mph.

But taking the simple case, 360v, does field weakening in a pmac take extra current? I.e. you have to "cancel out" the existing rotor field somehow to increase the rpm? Or are you able to somehow shift to a more reluctance based torque angle when the bemf rises?
Yes, you can "cancel out" the BEMF and use the reluctance torque using FOC. Quoting ORNL:
Quote:
Although the maximum PM torque is produced at a current angle of zero electrical degrees and the maximum reluctance torque is produced at 45 electrical degrees, the maximum total torque is produced at about 35 electrical degrees. This optimal current angle varies with many conditions such as current magnitude and speed.
So yes, I'm relying on this fact and the ability of this FOC controller to make it possible.

Quote:
Also, 650/360 is 1.8. The voltage change from wye/delta is 1.732, you should *really* make sure there isn't a trivial way to change it over to delta, because it would be nearly a perfect fit for the leaf battery then. you would be at 50kw * 4 @520 battery amps max (@375v).
The motor is wound wye. The common connection point for the wye is hard to get to, even for measurement purposes. I think Toyota knew what they were doing when they made these (understatement of the century ), so I'm attempting to match their control methods to obtain optimum performance. I think it would be a mistake to completely change the motor in an attempt to stick with a bus voltage that is far below the one the motor was designed for.

The numbers I posted were just examples of reasonable scenarios. I really don't want to hijack this thread talking about the MGR. Paul had expressed interest in building a motor controller with a built-in boost stage. I'm trying to help out with that and as a starting point figure out how much boost would be reasonable. I've found a combo that works for me; I'd like to know if this would be useful for others. If no one has any interest in this, I'll just build what works for me; it's much easier.

- E*clipse
  Reply With Quote