Comparative Analysis of Non-Isolated and Isolated Type Partial-Power Optimizers for PV-Battery Series Inverter Architecture

A seamless battery integration with higher power conversion efficiency and lower system power rating can be achieved by adopting the DC-series battery integration topology into a photovoltaic (PV) string inverter system, the PV-battery series inverter. The PV-battery series inverter uses the partial-power processing technique to achieve flexible current control between PV string and battery. In the process of designing the partial-power DC-DC optimizer, different types of DC-DC converters and different size of batteries can be considered, and the system efficiency and the power rating vary based on the system design. This paper presents a comparative analysis of the different type partial-power optimizers for the PV-battery series inverter in residential rooftop applications (<;10kW PV output power, <; 500V DC-bus voltage), in consideration of the DC-DC converter topology. Non-isolated and isolated bidirectional DC-DC converters are considered and selection of battery voltage in each case is made to have the optimized system design. The operation of the designed DC-DC optimizer is verified through controller hardware-in-the-loop test.