Comparison of Open-Switch Fault-Tolerant Control Strategies for Three-Level NPC Inverters in Five-Phase Induction Motor Drives

In recent years, interest in multiphase converters has grown significantly, driven by the demand for higher efficiency and reliability in electric drives. Simultaneously, multilevel converter technology has matured, offering a practical solution for delivering high power from devices with limited voltage ratings. The integration of these two technologies, multiphase and multilevel converters, provides increased degrees of freedom, enabling the implementation of various fault-tolerant control strategies. However, the higher number of switching devices in multilevel converters also raises the likelihood of switch faults. To mitigate the effects of an open-switch fault, conventional strategies often aim to nullify the current in the faulty phase. Multilevel inverters, with their inherent flexibility, allow for more sophisticated fault-tolerant approaches. This paper presents a comparative analysis of four fault-tolerant control strategies for five-phase, three-level neutral-point clamped (NPC) inverters. Each method exploits the multiphase system's redundancy to reduce the impact of a single open-switch fault, focusing on minimizing voltage ripple across the DC bus capacitors within each switching cycle and throughout the fault duration.