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A power converting device for a renewable energy storage system includes rechargeable batteries, bidirectional converters respectively connected in parallel to the batteries, direct current (DC) links connected in parallel to the bidirectional converters, respectively, bidirectional inverters connec

A power converting device for a renewable energy storage system includes rechargeable batteries, bidirectional converters respectively connected in parallel to the batteries, direct current (DC) links connected in parallel to the bidirectional converters, respectively, bidirectional inverters connected in parallel to the DC links, respectively, and an electric power system connected to the bidirectional inverters. The bidirectional inverters are cascade H-bridge multi-level boost inverters. The DC links are charged by the bidirectional inverters connected to the battery and a charged voltage of the DC links is provided to the electric power system by the bidirectional inverters. In addition, the DC links are charged by the bidirectional inverters connected to the electric power system and a charged voltage of the DC links is provided to the battery by the bidirectional inverters.

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1. A power converting device for a renewable energy storage system, the power converting device comprising: a plurality of rechargeable batteries;a plurality of bidirectional converters respectively connected in parallel to the plurality of batteries;a plurality of direct current (DC) links connecte

1. A power converting device for a renewable energy storage system, the power converting device comprising: a plurality of rechargeable batteries;a plurality of bidirectional converters respectively connected in parallel to the plurality of batteries;a plurality of direct current (DC) links connected in parallel to the plurality of bidirectional converters;a plurality of bidirectional inverters respectively connected in parallel to the plurality of DC links;an electric power system connected to the plurality of bidirectional inverters, the plurality of bidirectional inverters being selectably connected in series to the electric power system and configured to provide power to the electric power system; anda switch unit between the plurality of bidirectional inverters and the electric power system, the switch unit selectively connecting the plurality of bidirectional inverters in series to each other in a first state and in parallel to each other in a second state,wherein during discharging of the plurality of rechargeable batteries, the switch unit is in the first state which connects the plurality of bidirectional inverters in series to each other, andwherein during charging of the plurality of rechargeable batteries, the switch unit is in the second state which connects the plurality of bidirectional inverters in parallel to each other. 2. The power converting device of claim 1, wherein: power from each of the plurality of rechargeable batteries is converted by the plurality of bidirectional converters and is provided to the plurality of DC links, andpower from each of the plurality of DC links is converted by the bidirectional inverters and is provided to the electric power system. 3. The power converting device of claim 1, wherein: power from the electric power system is converted by the plurality of bidirectional inverters and is provided to the plurality of DC links, andpower from each of the plurality of DC links is converted by the plurality of bidirectional converters and is provided to the plurality of rechargeable batteries. 4. The power converting device of claim 1, wherein the plurality of bidirectional inverters are cascade H-bridge multi-level boost inverters that convert DC power from the DC links into AC power and provide the converted power to the electric power system. 5. The power converting device of claim 1, wherein the plurality of rechargeable batteries are lithium-ion batteries or lithium polymer batteries. 6. The power converting device of claim 1, wherein the switch unit includes a plurality of three-terminal switches. 7. The power converting device of claim 6, wherein each of the three-terminal switches includes: a first terminal connected to one of the bidirectional inverters,a second terminal connected to another bidirectional inverter that is closest to the one bidirectional inverter connected to the first terminal, anda third terminal connected to a higher or lower potential line connected to the electric power system. 8. The power converting device of claim 1, wherein during discharging of the plurality of rechargeable batteries, the switch unit connects nearest adjacent pairs of the bidirectional inverters in series to each other. 9. The power converting device of claim 1, wherein during charging of the plurality of rechargeable batteries, the switch unit connects the plurality of bidirectional inverters in parallel to the electric power system. 10. The power converting device of claim 1, wherein during charging of the plurality of rechargeable batteries, the switch unit connects the plurality of bidirectional inverters to provide a same voltage to each of the plurality of DC links. 11. The power converting device of claim 1, wherein during charging of the plurality of rechargeable batteries, the switch unit connects the plurality of bidirectional inverters to provide a same voltage to each of the plurality of DC links, irrespective of a state of charge of each of the plurality of rechargeable batteries. 12. The power converting device of claim 1, wherein during charging of the plurality of rechargeable batteries, the switch unit connects the plurality of bidirectional inverters to provide a voltage of the electric power system to each of the plurality of DC links.