Strategy With Smooth Transitions and Improved Torque–Speed Region and Stator Copper Loss for Two-Level Asymmetrical Six-Phase Induction Motor Drives Under Switch Faults

Asymmetrical six-phase drives are very attractive to obtain fault tolerance. Most faults arise in the power electronics. Two conventional methods to handle switch/diode faults in two-level converters are keeping the corresponding phases open (in two-level multiphase drives) or connecting them to the dc-link midpoint (in two-level three-phase drives) through a bidirectional switch (e.g., triac/relay). However, the former yields larger stator copper loss (SCL) for given torque and smaller maximum torque, because of current constraints; on the other hand, the latter reduces the maximum speed, due to voltage constraints, and has not been considered for two-level multiphase drives. This article presents several proposals to improve fault-tolerant behavior in two-level asymmetrical six-phase induction motor drives. First, to adequately combine and alternate said two approaches in these particular drives, depending on the speed, neutral-point configuration, and faulty legs. In this manner, the SCL-per-torque decreases and the total torque-speed region of the drive is extended, i.e., the maximum torque and maximum speed rise compared with each of the aforementioned conventional strategies. Second, to also turn on/off a switch between stator neutral points for further improvement in this regard. Third, a pulsewidth modulation procedure to ensure smooth transitions between drive configurations. Experimental results confirm the theory.