Improved Capacitor Voltage Balancing Method for CHB Inverter Based on Hybrid Modulation Strategy and Reference Voltage Reconfiguration

For the cascaded H-bridge (CHB) inverter, significant disparity in active power distribution among the submodules (SMs) may destabilize it. This paper presents an improved capacitor voltage balancing method for scenarios where some SMs are involved in zero active power input. A hybrid modulation strategy (HMS) is employed for the H-bridges to balance the dc-link capacitor voltages through voltage sorting. Furthermore, to prevent over-modulation of any H-bridge, the H-bridge reference voltages for these SMs with zero active power input are reconfigured. Importantly, the number of proportional-integral (PI)-based inner-phase voltage balancing controllers can be reduced to one. Finally, simulation results using MATLAB/Simulink for four SMs demonstrate the effectiveness of the presented method.