Open-circuit fault mitigation for multiphase induction motors with a unified control structure

Multiphase drives have advantages in high power transport applications, because of their inherent fault tolerance. It takes only two phases to create a fundamental mmf distribution rotating at the supply frequency, so a machine with m phases can continue to operate at reduced power in a controlled manner, with m-2 phases open circuit. However, if the faulty motor is represented by a reduced-order model, a different control structure is required for each combination of loss of phases, with careful matching of initial conditions in the controller at the onset of the fault. This paper retains the full-order motor model, but imposes additional constraints within the control to account for the zero current in the open-circuit phases, giving a single, unified control. Simulation results present strategies for detecting and responding to the onset of the fault. Simulation and experimental results are shown pre-and post-fault, for a six-phase machine.