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Why is Weak Magnetic Control Necessary for High-speed Motors?

01. MTPA and MTPV
Permanent magnet synchronous motor is the core driving device of new energy vehicle power plants in China. It is well known that at low speeds, permanent magnet synchronous motor adopts maximum torque current ratio control, which means that given a torque, the minimum synthesized current is used to achieve it, thereby minimizing copper loss.

So at high speeds, we cannot use MTPA curves for control, we need to use MTPV, which is the maximum torque voltage ratio, for control. That is to say, at a certain speed, make the motor output the maximum torque. According to the concept of actual control, given a torque, the maximum speed can be achieved by adjusting iq and id. So where is the voltage reflected? Because this is the maximum speed, the voltage limit circle is fixed. Only by finding the maximum power point on this limit circle can the maximum torque point be found, which is different from MTPA.