Torque Characteristic With Respect to the Load Angle of a Permanent Magnet Motor

Abstract

This paper deals with a simple and effective method of calculating average torque and torque ripple with respect to load angle for reluctance motors and permanent magnet motors. In a vector inverter, these motors are generally controlled by sine wave currents. When the position of the rotor is rotated relative to the stator, and the three phase currents have a fixed value, a torque curve can be plotted with reference to the load angle. Load angle refers to the difference in angle between the magnetic flux axis of a stator current and the magnetic flux axis of a permanent magnet within a rotor. The process is repeated using several different electrical angles for the three phase currents. The results are then overlapped, using the same load angle curve. Finally, the average torque and torque ripple can be plotted as a function of the load angle. The advantage of this proposed method is that both the average and ripple torques can be determined over a wide range of load angles simply by performing several torque analyzes with a simple static finite element method rather than using a transient method. This proposed method has been experimentally verified. The torque characteristics of permanent magnet motors with different rotor structures, with respect to the load angle, are analyzed and compared for the purpose of application.