Reconfiguration of NPC Multilevel Inverters to Mitigate Short Circuit Faults Using Back-to-Back Switches

Abstract

The main focus of this paper is to propose a reconfiguration method to mitigate short circuit faults in a neutral point clamped multilevel inverter which is widely used as a power conversion system with distributed energy resources. Existing reconfiguration methods use either a redundant strategy or need a large number of additional devices pre-installed in the circuit; these will increase the bulk and complexity of the system. Most existing control-strategy-based methods distort the phase-toneutral voltage, which results in degradation of power quality. To maintain control-strategy-based reconfiguration, avoid significant change to the circuit topology, and avoid phase voltage distortion, a new and practical reconfiguration method is proposed in this paper. The proposed method is applicable to neural point clamped (NPC) multilevel inverters at any voltage level and can mitigate short circuit faults in any device. A technique of switching series connected switches is selected to combine with the proposed reconfiguration method since it's a practical design consideration for realistic implementation. MATLAB/Simulink is used to simulate a five-level NPC inverter with non-idealities to verify the proposed reconfiguration method. A five-level NPC is also built and tested to experimentally verify the proposed method. Short circuit faults are injected to different devices and the proposed method is verified to quickly and effectively recover the NPC inverter from these faulty conditions.