Power Balance of a Delta-Connected CHB Converter with MPC for Photovoltaic Systems

Cascaded H-Bridge (CHB) converters are attractive candidates for next generation photovoltaic (PV) inverters. The overall plant can be divided in several PV strings that can be connected to each H-bridge cell. However, due to variability on solar irradiance conditions, each PV string may present different maximum available power levels, which difficult the overall converter operation. In this work, both inter-bridge and inter-cluster power imbalance are directly considered into the optimal control problem by designing a suitable system reference. Thus, the inter-cluster power imbalance is tackled by enforcing the converter to operate with a proper circulating current component. Moreover, the inter-cell imbalance power is achieved by governing the duty cycles independently.