Module Power Balance Control Strategy for Three-Phase Cascaded H-Bridge PV Inverter Under Unbalanced Grid Voltage Condition

In the field of high-voltage and high-power photovoltaic (PV) power generation, three-phase cascaded H-bridge (CHB) inverter has been attracting more and more attention because of its easy modularization and high output voltage. Compared with other structures, the three-phase CHB inverter based on common dc-bus structure has more advantages, which is capable of avoiding interphase and intermodule power imbalance problems. When the grid voltage is balanced, the total active power transmitted by each phase of the three-phase CHB inverter is the same, and because the number of modules in each phase is designed to be equal, the active power transmitted by all modules is the same. However, if the grid voltage is unbalanced or some modules fail, the module power in different phases may be unequal, which makes heat dissipation requirements and service life of each module significantly different. In this article, a module power balance control strategy is proposed, it ensures that all modules still transmit equal powers when the grid voltage is unbalanced, or some modules fail. Simulation and experimental results all verify the effectiveness of the proposed strategy.