Low Torque Pulsation and High Power Control of Parmanent Magnet Motor with Distorted Electromotive Force.

Abstract

This paper describes low torque pulsation and high power control of parmanent magnet synchro nous motor (PM motor) with distorted electromotive force (emf).The experimental model of PM motor is 40 kW, 190 r/min, salient-pole, six-phase machine. An individual single-phase transistor inverter is connected to each phase of PM motor as a power source. By adopting full pitch and concentrated winding in the armature of the motor, the rate of flux utilization and output torque per mass can be increased.This winding causes trapezoidal distortion in the phase voltage waveform at no load. For realization of high peformance control of PM motor, the current waveform should be determined so as to minimize torque pulsation and maximize the output torque of the motor under the rated current.This paper proposes the method to determine the optimum current waveform. The currents and emf's are expressed as N-dimensional vectors (N: the number of phase). Due to the characteristics of the paticular structure of the motor, the armature reaction is small enough to be neglected. In this case, the optimum current vector can be derived under two conditions; (1) the direction of the current vector always agrees with that of the emf vector, and (2) the scalar product of the two vectors is held constant. Supplying the optimum current vector provides no torque pulsation and the nearly maximum output torque under the rated current. This method also can derive the new optimum current corresponding to open-phase operation.