Increased Reliability Using Asymmetrical Six Phase Induction Motor with Double Isolated Neutral

Abstract

This work suggested the use of asymmetrical six phase induction motors instead of the conventional three phase motors for safety critical equipment to improve the overall system reliability. The rule of thumb is that a single fault should not be able to draw safety critical equipment out of service. Multi-phase machine in general and six phase machine in particular are able to continue running with one phase or more open circuit. The ability of multi-phase machines even to start under fault is another useful feature. Statistically, the main reason for losing one of the motor phases is the single open gate transistor fault. The defected phase is entirely disregarded, and then the current in the rest of phases which still functioning is optimized. Consequently, if minimum copper loss criterion is applied, the paid penalty is 50% additional losses that leads to motor derating, if not pre-designed with proper safety factor. This paper introduces an alternative post fault control strategy, which allows the usage of the entire healthy power electronic switches. An achievement of reducing the post fault increase in stator copper losses to 25% is realized.