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Discussion Starter · #1 · (Edited)
Hi everyone,

I've a question that I still can't find an answer to. I'm working on the design of an electric vehicle and I need to choose the most efficient PMSM motor for its traction based on a duty cycle. I won't put a gear box but only a reducer. So I'm changing the reducer ratio to put the load points in the "torque vs speed" motor map so that I get the higher possible average efficiency. But as you know in a electric motor map, there are two zones: one with a constant torque and the other one with a constant power. So my question is the following: what do I get if I put the load points in the "constant torque zone" and what do I get if I put them in the other zone. In other words, what is going to change in the operation of my car by putting the duty cycle points in one of the two zones. Because I get two excellent global efficiency in the two zones but I can't understand the difference between the two of them. I read many books about the electric motors but I couldn't manage to get useful answers from a technical point of vue. So I ask anyone who reads my question and who has a very good knowledge of electric motors to share with us and help me get an answer.
Thanks 😊
 

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Rather than thinking of the operating range of the motor as just those two zones, I suggest looking at the efficiency map of an actual motor. There are published examples for various motors, but the most common is the Nissan Leaf, because it is so common and has been so thoroughly studied.
Google image search for "nissan leaf motor efficiency map"
If you can't find this for your motor, you can at least guess that the general trend will be similar to other PM synchronous motors.

Whether the limit for a battery/controller/motor combination is current (or torque) or power for a given speed is not important to efficiency. On a full map you can choose the speed at which a given power level is most efficiently delivered.

The most efficient point for the motor will always be at moderate speed and relatively high load, but that point doesn't matter when you don't need that much power. For any given power level there is a trade-off between high speed and light load or low speed and high load, with a continuous range of choices between the extremes, and the most efficient point for that power won't be at either extreme.
 
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