Effects of flux derating methods on torque production of fault‐tolerant polyphase inductiondrives.

Fault‐tolerant drives have been gaining increasing attention due to the need to enhance the reliability and robustness of electric drive systems, particularly for safety critical applications. However, in postfault control, it is often necessary to derate the machine, that is to reduce the torque and/or flux currents, to satisfy the current constraints of the power electronic devices. For induction motors, there are different approaches to quantify the current components in postfault operation while maintaining a stable operation within the current constraints. The efficiency enhancement of a faulted drive through flux current reduction is one of the methods reported in literature, however, the details of power components, that is, achievable torque and speed, are not addressed. This study broadly investigates the effect of flux and/or torque current partitioning on postfault capability of polyphase (three and more phases) induction machines in terms of achievable torque and speed. It is demonstrated that the magnetising inductance characteristics, which depend on the machine design and its power rating, have a profound effect on the choice of postfault current partitioning, and hence the machine performance. Theoretical discussion is supported with experimental verification using three‐phase and symmetrical six‐phase induction motors. [ABSTRACT FROM AUTHOR]