| CPC H02J 7/35 (2013.01) [G01R 31/52 (2020.01); H02J 3/32 (2013.01); H02J 2300/24 (2020.01)] | 21 Claims |

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1. An energy storage system connected with a power grid, the energy storage system comprising:
a photovoltaic (PV) system;
a power conversion system (PCS) configured to be connected with the power grid and selectively connected to the photovoltaic system;
a first switch configured 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 which is connected to a ground;
a second switch selectively configured to connect the photovoltaic system and another terminal of the first ground fault detector, wherein the second switch is located between the first switch and the photovoltaic system; and
a switch controller configured 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 of the power conversion system, by controlling the first switch and the second switch based on a power generation state of the photovoltaic system.
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