Inverter of new and renewable energy storage system

PURPOSE: An energy storage system is provided to simplify a circuit structure and a device structure using a DC-DC converting part which is same with an unregulated DC-DC converter and to offer an inverter in which a turn off switching loss is small. CONSTITUTION: A DC-DC converting part(141) is connected a DC link(130). The DC-DC converting part is an unregulated DC-DC converter. An inverting part(142) is connected between the DC-DC converting part and an electric power system(170). The DC-DC converting part is operated by 50% fixing duty and fixing frequency. The DC-DC converting part comprises a half bridge switching part(141a), a resonant part(141b), a transformer(141c), and a full bridge diode rectifier(141d). A first switch is connected to the first electrode of a DC link. A second switch is connected to a second electrode of the DC link and the first switch.