Resilient Operation for Grid-connected Cascaded H-bridge Multilevel Inverter with Improving PV Source Stress

In distributed power systems increasingly dominated by PV generation and grid-connected converters, cascaded H-bridge (CHB) multilevel inverters are particularly well-suited for high-power, high-voltage applications. However, CHB topologies are prone to unbalanced conditions due to submodule faults, which can be triggered by factors such as extreme weather, equipment aging, or operational stresses. While redundant sub-modules are commonly employed to mitigate these issues, they lower efficiency and increase the costs and complexity of circuits. This paper addresses unbalanced grid currents caused by faulty submodules in CHB multilevel inverters through a source stress-improved control strategy based on a neutral offset approach. When a submodule is bypassed due to faults or hot-swapping, all remaining submodules, across both normal and faulty phases, share the voltage lost from the bypassed submodule. By distributing the voltage contribution across all submodules in both faulty and non-faulty phases, this method reduces system costs and downtime while alleviating voltage stress and enhancing the operation efficiency of the inverter system.