Resilient Operation for Grid-Connected Cascaded H-Bridge Multilevel Inverter Based on Neutral Offset

In power systems increasingly dominated by renewable energy generations, cascaded H-bridge (CHB) multilevel inverters are well-suited for high-power applications. However, CHB topologies are prone to unbalanced conditions due to submodule faults. While redundant submodules are commonly employed to mitigate these issues, they lower efficiency and increase the costs and complexity of circuits. This article addresses unbalanced grid currents caused by faulty submodules in CHB inverters through a neutral point-shifting control strategy. When submodules are bypassed due to faults, all remaining submodules, across both normal and faulty phases, share the lost voltage of the bypassed submodules. The corresponding control strategy is presented in this article, constraints and source voltage stress reduction are analyzed, and the effectiveness is verified by simulation and experimental tests. The proposed method can reduce system costs and downtime, thus enhancing the resilient operation of the entire system.