Open Loop V/f Control of Multiphase Induction Machine Under Open-Circuit Phase Faults

One of the main advantages of multiphase induction machines is their higher fault-tolerant capability. Under phase(s) loss, the machine currents can be optimally controlled to satisfy certain optimization criteria. In this paper, a simple open loop controller based on the conventional V/f control scheme of a five-phase induction machine is introduced which can ensure equal phase currents and minimum torque ripples under one phase open. The presented approach can be extended to any number of phases with any number of open phases. The fundamental dq components of the stator voltage are decided as in conventional V/f control. The measured currents are decomposed to their sequence components. The fundamental sequence is used to calculate the optimum reference third sequence current components that ensure equal stator currents under phase(s) open. The third sequence stator voltage components, that ensure equal remaining phase currents, are obtained using Proportional-Resonant (PR) controllers. The input errors of these controllers represent the difference between the actual third sequence current components and its optimum reference values. A prototype five-phase machine is used for experimental verification.