Low torque pulsation and high‐power control of permanent magnet motor with distributed electromotive force

Abstract

This paper describes low torque pulsation and high‐power control of permanent magnet synchronous motor (PM motor) with distorted electromotive force (emf). The experimental model of PM motor is a 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‐performance control of PM motor, the current waveform should be determined so as to minimize torque pulsation and to maximize the output torque of the motor under the rated current. This paper proposes also the method to determine the optimum current waveform. The currents and emfs are expressed as N‐dimensional vectors (N: the number of phases). Due to the characteristics of the particular 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. The validity of the method is confirmed experimentally. The characteristics of the experimental model of PM motor also are described in this paper.