Vector control of a multiphase induction motor with open circuit phases

In order to provide enhanced tolerance to phase faults applications with extremely critical loads are using isolated phase motors where each phase can be driven by a separate inverter bridge This paper derives a model of a multiphase induction motor where the number of phases can be selected at run-time. It has be used to observe the severe torque pulsations that occur with one or more phases open circuit and to evaluate the techniques for eliminating them. The multiphase motor was modelled in the time domain using Simulink and the direct on line responses of a 2-phase motor were proved to be identical to a 6-phase motor of the same power rating. When one phase was opened on load the amplitude of the torque pulsation was observed to be smaller with higher number of phases The torque and speed responses were plotted using a rotor-flux-oriented vector-controller with current regulators in the stationary frame to drive a pulse-width-modulated voltage-source inverter and are seen to be the same regardless of the number of phases chosen. By adjusting the phase angle and amplitude of the remaining phases the torque pulsations can be eliminated and the original vector control can be made to function without any changes.