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.

中文翻译：

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开关故障下两电平非对称六相异步电动机驱动的平滑过渡和改进转矩-速度区域和定子铜损的策略

非对称六相驱动器对于获得容错非常有吸引力。大多数故障发生在电力电子设备中。处理两电平转换器中开关/二极管故障的两种传统方法是保持相应的相断开（在两电平多相驱动器中）或通过双向连接将它们连接到直流链路中点（在两电平三相驱动器中）开关（例如，双向可控硅/继电器）。然而，由于电流限制，前者在给定扭矩和较小的最大扭矩下产生较大的定子铜损 (SCL)；另一方面，由于电压限制，后者降低了最大速度，并且尚未考虑用于两电平多相驱动器。本文提出了几种改进两电平非对称六相感应电机驱动器容错行为的建议。第一的，根据速度、中性点配置和故障腿，在这些特定驱动器中充分组合和交替上述两种方法。以这种方式，SCL-per-torque 减小，驱动器的总转矩-速度区域扩大，即与上述每个传统策略相比，最大转矩和最大速度上升。其次，还要打开/关闭定子中性点之间的开关，以在这方面进一步改进。第三，脉宽调制程序，以确保驱动器配置之间的平滑过渡。实验结果证实了该理论。与上述传统策略中的每一个相比，最大扭矩和最大速度上升。其次，还要打开/关闭定子中性点之间的开关，以在这方面进一步改进。第三，脉宽调制程序，以确保驱动器配置之间的平滑过渡。实验结果证实了该理论。与上述传统策略中的每一个相比，最大扭矩和最大速度上升。其次，还要打开/关闭定子中性点之间的开关，以在这方面进一步改进。第三，脉宽调制程序，以确保驱动器配置之间的平滑过渡。实验结果证实了该理论。