Grid-connected power storage system and method for controlling grid-connected power storage system

1. A grid-connected power storage system for coupling a power generation system to a grid to supply power to a load system, comprising:

a main battery for discharging stored power to the load system;

at least one additional battery coupled to the main battery for discharging stored power to the load system;

a bidirectional converter coupled to the main and additional batteries, and comprising a plurality of switches for performing a conversion between a DC link voltage, between the power generation system and the grid, and a battery voltage, a first switch of the plurality of switches corresponding to the main battery and a second switch of the plurality of switches corresponding to the additional battery, wherein the first and second switches are connected to each other in parallel;

an integrated controller for selectively controlling operations of the first switch and the second switch based on an amount of power used by the load system; and

a bidirectional inverter for converting the DC link voltage output from the bidirectional converter into an AC voltage of the grid and the AC voltage of the grid into the DC link voltage,

wherein the bidirectional inverter is configured to supply power from the power generation system to the grid via the bidirectional inverter.

2. The grid-connected power storage system of claim 1 , wherein the integrated controller comprises:

a monitoring system for detecting an amount of power utilized by the load system to determine whether the detected amount exceeds a reference amount of power;

a battery controller for determining whether the additional battery is to be coupled to the main battery when the detected amount exceeds the reference amount of power; and

a switch controller for generating a control signal for controlling driving of the second switch.

3. The grid-connected power storage system of claim 1 , further comprising a battery management system coupled to the main battery and the additional battery to control charging and discharging of the main and additional batteries.

4. The grid-connected power storage system of claim 1 , further comprising a manual operating switch comprising a mechanical contact for coupling the additional battery to the bidirectional converter.

5. The grid-connected power storage system of claim 1 , wherein the power generation system comprises a solar cell.

6. A method of controlling a grid-connected power storage system which couples a power generation system to a grid to supply power to a load system, the method comprising:

determining whether an additional battery is to be coupled to a main battery based on an amount of power utilized by the load system;

outputting a control signal to a bidirectional converter when the additional battery is to be coupled to the main battery, wherein the bidirectional converter comprises a first switch corresponding to the main battery and a second switch corresponding to the additional battery, and wherein the first and second switches are coupled to each other in parallel;

comprising converting a DC link voltage of the bidirectional converter into an AC voltage of the grid; and

supplying power from the power generation system to the grid.

7. The method of claim 6 , wherein the determination whether the additional battery is to be coupled to the main battery comprises:

detecting an amount of power utilized by the load system;

determining whether the detected amount exceeds a reference amount of power; and

determining that the additional battery is to be coupled to the main battery when the detected amount exceeds the reference amount of power.

8. The method of claim 6 , wherein the power generation system comprises a solar cell.

9. The method of claim 6 , wherein the control signal operates the second switch.