Current-source invertor-fed induction motor torque pulsations

The paper presents the derivation of new expressions which may be used without the aid of a computer to calculate the torque waveform produced by an induction motor supplied by an ideal current-source invertor. It is shown that they give more accurate results than the existing method, and one expression is particularly accurate at low motor operating frequencies where the mechanical effects of the torque pulsations could be most significant. Torque pulsation results for a 22kW motor, obtained from a computer program embodying an accurate system model, are used as a basis for comparing the results obtained from the new and existing expressions. In addition, it is shown that the motor torque pulsations can be made smaller by increasing the magnetising inductance, and by reducing the direct-current ripple when the motor is on no load or regenerating.