Quote:
Originally Posted by P-hack
I don't know at what point one controller makes sense though, maybe if you have a lead on 2 or 4 small motors that are just enough power for your needs (leads have to be the same length) and are on a tight budget. But if you have 4 regular motors, you are going to need so much battery that the extra power sections aren't gonna be noticed in the budget (and your controllers might need a controller, conceptually anyway, if you are trying to do stuff like traction control).
You have multiple rotor positions here (using current sensors), if you want FOC on multiple motors, you need multiple switches (IGBTs) and signals at a minimum so that the stator coils fire at just the right angle for each motor (though you still need some slip with FOC, I think it is mostly when changing speeds that it targets the highest torque vector). But a slip algorithm can also set slip for max torque, just not on the very first pulse.
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This thread is about a FOC controller - that's why we're talking about it; it's not a "how to control induction machines as easily as possilbe" thread.
Again, I don't know what you're talking about when you say "regular motors." Given the variety of AC type motors available, the beauty of FOC is the software can be adapted to control quite different hardware. I am going to use this controller for a motor like the one in your Prius, not an induction machine. The control hardware is more or less the same.
Really, a well engineered system would use appropriate parts for ALL components. The reason to use small motors on all wheels is not merely to find a cheap motor solution. It can provide the opportunity for better control - that's my interest. Therefore, if one used 4 motors that are rated at 50kW, a 200kW single motor with gearboxes dividing the power to all 4 wheels would be an equivelent system.
Noting that the expensive stuff tends to be the batteries and the power electronics, the same thing applies. You still need to control 200kW, whether there are 4 sets of IGBT's in parallel controlling one motor or 4 sets of IGBT's controlling 4 motors. The cost of the control electronics is relatively small, and whether one uses FOC or simply VFD control algorithms doesn't effect the cost AT ALL. Same with the batteries. They need to supply 200kW. This could be split simply by running wires to individual motor controllers or running bigger wires to one motor controller. I see no reason why multiple motors means increased battery cost. In fact, there is a really good example of a 2 motor AWD car that uses one battery pack here:
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System efficiency was a high priority for the people who made this car, and they were very successful, winning closed circuit road races against ICE cars.