METHOD FOR SWITCHING GRID-TIED MODE AND OFF-GRID MODE, AND ENERGY STORAGE SYSTEM

Embodiments of this application provide an energy storage system, including a controller, an inverter, an on-grid/off-grid mode switch, and a load. The inverter is configured to: in response to determining that the energy storage system is in an islanding state, send an islanding state message to the controller, freeze an output frequency of the inverter based on a preset frequency, and control an output current of the inverter based on an association relationship that an output voltage of the inverter is negatively correlated with apparent power of the inverter. The controller is configured to send a disconnection instruction to the on-grid/off-grid mode switch. The controller is further configured to send a switching instruction to the inverter in response to receiving a disconnection complete message from the on-grid/off-grid mode switch. The inverter is further configured to switch to a voltage source mode when receiving the switching instruction and determining that the output voltage of the inverter meets the preset range of the rated voltage. In embodiments of this application, frequency distortion and voltage distortion events can be avoided, control efficiency of the inverter is improved, and operation stability of the load can be improved.