Energy storage system and controlling method thereof

1. An energy storage system comprising:

a battery;

an inverter for receiving a first power from an external source and generating a second power; and

a converter coupled between the battery and both the external source and the inverter, the converter being configured to enter an off mode between a charge mode for charging the battery and a discharge mode for discharging the battery,

wherein the converter is configured to enter the off mode for a set period of time when a difference between a value of the first power and a value of the second power changes polarity.

2. The energy storage system of claim 1 , wherein, when the converter is in the off mode, the converter is configured to remain in the off mode for the set period of time regardless of variation of the difference between the value of the first power and the value of the second power.

3. The energy storage system of claim 1 , wherein the converter is configured to operate in the discharge mode or the charge mode according to the difference between the value of the first power and the value of the second power, after the set period of time has elapsed.

4. The energy storage system of claim 1 , wherein the second power varies in accordance with an amount of power consumed by a load coupled to the inverter.

5. An energy storage system comprising:

a battery;

an inverter for receiving a first power from an external source and generating a second power; and

a converter coupled between the battery and both the external source and the inverter, the converter being configured to enter an off mode between a charge mode for charging the battery and a discharge mode for discharging the battery,

wherein the converter is configured to enter the off mode when a value of the first power is between a first threshold value and a second threshold value that is lower than the first threshold value.

6. The energy storage system of claim 5 , wherein a value of the second power is between the first threshold value and the second threshold value.

7. The energy storage system of claim 5 , wherein the first threshold value and the second threshold value change by a same amount as the value of the second power.

8. The energy storage system of claim 5 , wherein, when the converter is in the off mode, the converter is configured to remain in the off mode when variation of the value of the first power is between the first threshold value and the second threshold value.

9. The energy storage system of claim 5 , wherein, when the converter is in the off mode, the converter is configured to exit the off mode when the value of the first power is above the first threshold value or below the second threshold value.

10. The energy storage system of claim 9 , wherein, after the converter exits the off mode, the converter is configured to operate in the discharge mode or the charge mode according to the value of the first power and the first and second threshold values.

11. The energy storage system of claim 5 , wherein

at least one of the first threshold value or the second threshold value is between an upper hysteresis value and a lower hysteresis value, and

the converter is configured to remain in the off mode while a variation of the value of the first power is between the upper hysteresis value and the lower hysteresis value.

12. The energy storage system of claim 5 , wherein the second power varies in accordance with an amount of power consumed by a load coupled to the inverter.

13. A method of operating an energy storage system comprising a converter coupled between a battery and both an external source and an inverter, the method comprising:

converting a first power from the external source to a second power by the inverter;

operating the converter to enter an off mode between a charge mode for charging the battery and a discharge mode for discharging the battery;

discharging the battery by the converter when a value of the first power is less than a value of the second power and charging the battery by the converter when the value of the first power is greater than the value of the second power; and

operating the converter to enter the off mode for a set period of time when a difference between the value of the first power and the value of the second power changes polarity.

14. The method of claim 13 , further comprising:

when the converter is in the off mode, maintaining the converter in the off mode regardless of variation of the difference between the value of the first power and the value of the second power.

15. The method of claim 13 , further comprising:

after the set period of time has elapsed, operating the converter in the discharge mode or the charge mode according to the difference between the value of the first power and the value of the second power.

16. The method of claim 13 , wherein the second power varies in accordance with an amount of power consumed by a load coupled to the inverter.

17. A method of operating an energy storage system comprising a converter coupled between a battery and both an external source and an inverter, the method comprising:

converting a first power from the external source to a second power by the inverter;

operating the converter to enter an off mode between a charge mode for charging the battery and a discharge mode for discharging the battery;

discharging the battery by the converter when a value of the first power is less than a value of the second power and charging the battery by the converter when the value of the first power is greater than the value of the second power; and

operating the converter to enter the off mode when the value of the first power is between a first threshold value and a second threshold value that is lower than the first threshold value.

18. The method of claim 17 , wherein the first threshold value and the second threshold value change by a same amount as the value of the second power.

19. The method of claim 17 , further comprising:

when the converter is in the off mode, maintaining the converter in the off mode when variation of the value of the first power is between the first threshold value and the second threshold value.

20. The method of claim 17 , further comprising:

when the converter is in the off mode, operating the converter to exit the off mode when the value of the first power is above the first threshold value or when the value of the first power is below the second threshold value.

21. The method of claim 20 , further comprising:

after the converter exits the off mode, operating the converter in the discharge mode or the charge mode according to the value of the first power and the first and second threshold values.

22. The method of claim 17 , wherein

at least one of the first threshold value or the second threshold value is between an upper hysteresis value and a lower hysteresis value, and

the method further comprising:

maintaining the converter in the off mode while variation of the value of the first power is between the upper hysteresis value and the lower hysteresis value.

23. The method of claim 17 , wherein the second power varies in accordance with an amount of power consumed by a load coupled to the inverter.