ENERGY STORAGE SYSTEM, AND DEVICE FOR CONTROLLING GROUND STRUCTURE OF ENERGY STORAGE SYSTEM

Discussed is an energy storage system connected with a power grid, and including a photovoltaic (PV) system; a power conversion system to be connected with the power grid and selectively connected to the photovoltaic system; a first switch to selectively connect the photovoltaic system and a direct current (DC) link of the power conversion system; a first ground fault detector including a terminal connected to a ground; a second switch selectively to connect the photovoltaic system and another terminal of the first ground fault detector; and a switch controller to change a ground structure of at least one of the photovoltaic system, the power conversion system, and a battery system included in the energy storage system and to selectively connect the photovoltaic system and the DC link, by controlling the first switch and the second switch based on a power generation state of the photovoltaic system.