A Control Strategy for Achieving the Whole Operation Range Power Matching of Single-Phase Cascaded H-Bridge PV Inverter

The single-phase cascaded H-bridge (CHB) inverter can realize module-level MPPT. Its multilevel output voltage can reduce the volume of filter inductance and avoid using the power frequency transformer. Therefore, the single-phase CHB inverter has a significant advantage in household photovoltaic (PV) power generation. However, due to the change of illumination conditions or damage to PV panels, the output power of H-bridges (HBs) will be unbalanced and result in the HBs with higher output power being overmodulated, affecting the stable operation of the CHB system and the quality of grid current. In this article, a control strategy is proposed to extend the operation range of the single-phase CHB inverter. The modulation strategy and reference power of each HB are adjusted according to the HB modulation index to achieve the whole operation range power matching. Compared with the existing methods, the proposed strategy further expands the operation range of the single-phase CHB inverter and ensures the full utilization of the power transmission capacity of the system on the premise of stable operation and grid current quality. The simulation and experiment verify the effectiveness of the proposed strategy.