Cell balancing method, cell balancing device, and energy storage system including the cell balancing device

1. A method of balancing a plurality of battery cells, the method comprising:

acquiring by a controller, an, open circuit voltage (OCV) of a battery cell of the plurality of battery cells connected in series;

determining, by the controller, a state of charge (SOC) of the battery cell based on the OCV of the battery cell;

determining, by the controller, a value (ΔOCV/ΔSOC) corresponding to a change in the OCV (ΔOCV) of the battery cell per a change of the SOC (ΔSOC) of the battery cell, in accordance with the SOC of the battery cell; and

activating, by the controller, cell balancing of the plurality of battery cells when the value (ΔOCV/ΔSOC) is greater than a reference value.

2. The method of claim 1 , further comprising:

determining, by the controller, a voltage difference between a maximum voltage and a minimum voltage among the open circuit voltages (OCVs) of the battery cells; and

activating, by the controller, cell balancing of the plurality of battery cells when the voltage difference is greater than a reference voltage.

3. The method of claim 2 , further comprising:

monitoring, by the controller, the voltage difference; and

inactivating, by the controller, the cell balancing of the battery cells when the voltage difference is less than or equal to the reference voltage.

4. The method of claim 1 , wherein activating cell balancing of the plurality of battery cells comprises performing selectively charging or discharging the battery cell.

5. A cell balancing device comprising:

a battery management unit electrically connected with a plurality of battery cells, wherein the battery management unit is configured to:

acquire an open circuit voltage (OCV) of a battery cell of the plurality of battery cells;

determine a state of charge (SOC) of the battery cell based on the OCV of the battery cell;

determine a value (ΔOCV/ΔSOC) corresponding to a change in the OCV (ΔOCV) of the battery cell per a change of the SOC (ΔSOC) of the battery cell, in accordance with the SOC of the battery cell; and

activate cell balancing of the plurality of battery cells when the value (ΔOCV/ΔSOC) is greater than a reference value.

6. The cell balancing device of claim 5 , wherein the battery management unit is further configured to:

determine a voltage difference between a maximum voltage and a minimum voltage among the open circuit voltages (OCVs) of the battery cells; and

activate cell balancing of the plurality of battery cells when the voltage difference is greater than a reference voltage.

7. The cell balancing device of claim 6 , wherein the battery management unit is further configured to monitor the voltage difference and to inactivate the cell balancing of the battery cells when the voltage difference is less than the reference voltage.

8. The cell balancing device of claim 6 , wherein the battery management unit comprises:

a controller; and

a cell balancing unit electrically connected to the battery cells and operatively connected to the controller, wherein the cell balancing unit is configured to selectively discharge the battery cell in accordance with control signals from the controller.

9. An energy storage system comprising:

a battery system for storing energy from an energy generation system or a power grid; and

a power conversion system for controlling power conversion among the battery system, the energy generation system, and the power grid,

wherein the battery system comprises:

a plurality of serially connected battery cells; and

a battery management unit electrically connected with the battery cells, wherein the battery management unit is configured to:

acquire an open circuit voltage (OCV) of a battery cell of the plurality of battery cells;

determine a state of charge (SOC) of the battery cell based on the OCV of the battery cell;

determine a value (ΔOCV/ΔSOC) corresponding to a change in the OCV (ΔOCV) of the battery cell per a change of the SOC (ΔSOC) of the battery cell, in accordance with the SOC of the battery cell; and

activate cell balancing of the plurality of battery cells when the value (ΔOCV/ΔSOC) is greater than a reference value.

10. The energy storage system of claim 9 , wherein the battery management unit is further configured to:

determine a voltage difference between a maximum voltage and a minimum voltage among the open circuit voltages (OCVs) of the battery cells; and

activate cell balancing of the plurality of battery cells when the voltage difference is greater than a reference voltage.

11. The energy storage system of claim 10 , wherein the battery management unit is configured to selectively charge or discharge the battery cell when cell balancing is activated.