Asymmetric three-phase operation of fault-tolerant inverters for increased output torque of electric machines

Abstract:
Some fault-tolerant inverters require the reduction of the maximum current of only one of their three phases after a single failure. Normally, the maximum phase current of the two healthy phases is also reduced in order to achieve a symmetric system. Nevertheless, the two healthy phases can still deliver a higher maximum output current and thus enable an asymmetric three-phase operation. The effects on the characteristics of an electric drive system are a higher medium output torque than in degraded symmetric operation, however with an additional torque ripple. Depending on the mechanical drive train, this ripple may be tolerated.