Method for operating energy storage system and energy storage system

An energy storage system comprising:

• an energy storage device;
• a current transformer, wherein the energy storage device is coupled to an external power grid with the current transformer disposed on a connection line between the energy storage device and the external power grid;
• and
• a control device configured to:
• control the energy storage device of the energy storage system to access the external power grid;
• determine a connection status of the current transformer based on a relative difference between an on-load electrical parameter and a static electrical parameter, wherein the static electrical parameter is obtained during a non-operating state of the energy storage device and the on-load electrical parameter is obtained during an operating state of the energy storage device;
• and
• set an operating mode of the energy storage system based on the connection status.

A control device for an energy storage system comprising an energy storage device and a current transformer, wherein the energy storage device is coupled to an external power grid with the current transformer disposed on a connection line between the energy storage device and the external power grid, and

• wherein the control device is configured to:
• control the energy storage device to access the external power grid;
• determine a connection status of the current transformer based on a relative difference between an on-load electrical parameter and a static electrical parameter, wherein the static electrical parameter is obtained during a non-operating state of the energy storage device and the on-load electrical parameter is obtained during an operating state of the energy storage device;
• and
• set an operating mode of the energy storage system based on the connection status.