Research on optimal-torque control method of permanent magnet synchronous motor

The input current and voltage, at the control interface of permanent magnet synchronous motor (PMSM), are restricted by output ability from inverter. Focusing on PMSM vector control method, the paper analyzes the motor running status restricted by limit current and limit voltage from inverter under the dq coordinates. Combining with the control method of maximum torque per ampere (MTPA) and the flux-weakening control principle that eliminating back electromotive force (back-EMF), optimal-torque control method is developed. In the MTPA method, we can calculate the maximum output torque from the present speed. When the giving torque is bigger than the limit value, the voltage restriction will result that PMSM can not provide enough torque under the MTPA method. At this time, we adjust the current vector to make it reach the intersection point of voltage limit ellipse and the track of invariable output torque, which can take full advantage of output ability from inverter. The simulation results proved the superiority of optimal-torque control method in the case of high-speed and high-torque situation.