Cascaded H-bridge Converter-based Large-Scale Photovoltaic Systems : Power Imbalance and Topology Derivation

The cascaded H-bridge (CHB) multilevel converter is a promising topology for large-scale photovoltaic (PV) systems. However, the different PV panels may generate different power, which results in the inter-module and inter-phase power imbalance. Consequently, the over-modulation caused by the inter-module and inter-phase power imbalance is one of the key issues for the CHB-based PV system. This paper analyzes the theoretical constraints on system operation range caused by power imbalance and discusses the necessary and sufficient condition to achieve complete power balance in modular cascaded PV systems based on graph-theory model. According to the graph-theory model, several derivate topology structures are presented and the basic simulation and experimental results are shown to verify their power balancing ability.