Adaptive Control Strategy of Parallel Cascaded H-Bridge PV-Battery Hybrid Inverters for Enhanced Power Balance Capability

In a single-phase cascaded H-bridge (CHB) photovoltaic (PV) inverter, the modulation index (MI) of the H-bridge module with large power generation is high and faces the risk of overmodulation. The overmodulated H-bridge module has to exit maximum power point tracking (MPPT) mode to maintain the system normal operation which undoubtedly results in power generation loss. To overcome this limitation, a CHB-based parallel PV-battery hybrid system and corresponding adaptive power balance control strategy are proposed in this article. A battery unit is added in parallel with each PV module through a bidirectional dc-dc converter, and its power is provided as a new degree of freedom to regulate the MI of the overmodulated PV module. With the proposed approach, all PV modules can maintain their MPPT operation, avoid overmodulation, and harvest more solar energy even under severe power unbalanced conditions. Experimental results are provided to validate the effectiveness of the proposed control strategy.