Efficiency control of multi-string PV system considering switching losses analysis

Photovoltaic (PV) system with multi-strings can be efficiently operated since individual maximum power point tracking (MPPT) of each separated panel is performed by converters which are connected to each panel. For the MPPT, it causes continuous switching losses of the converters. This paper proposes new control operating method in multi-string PV system using parallel DC/DC converters and single DC/AC inverter. In proposed method, the DC-link voltage is regulated to the highest maximum power point (MPP) voltage among the panels in the condition where the voltage is high enough to deliver power to grid. The converter for PV of the highest voltage passes the power without any switching and the inverter performs MPPT instead of the converter. Also, more optimized MPP is newly decided by analyzing switching losses according to variation of the DC-link voltage and the method for the MPPT is proposed. Thus, the efficiency of the system can be improved in comparison with the conventional method. Experimental results present the feasibility of the proposed control operation and the improved efficiency.