Solution of input double-line frequency ripple rejection for high-efficiency high-power density string inverter in photovoltaic application

One important type of power conditioning systems in photovoltaic (PV) application is the string inverter which requires small input voltage and current ripple. In addition, high-efficiency and high-power density are also the critical requirements for string inverter system. So the input voltage and current ripple cannot be easily rejected by paralleling large conventional electrolytic capacitors in the inverter input side only, since the huge electrolytic capacitors will limit the efficiency and power density. This paper presents a control strategy to limit the input double-line frequency ripple with a high-efficiency and high-power density front-end buck-type dc/dc converter. The double-line frequency energy is stored at the DC bus capacitor with the control strategy employed and the input current and voltage ripple are highly reduced compared with traditional electrolytic capacitor filter. Experimental results based on a 2-kW 6.6 inch3 hardware prototype with 99.6% peak efficiency are provided to validate the proposed double-line frequency ripple rejection control method.