Systems and methods for grid interactive UPS

1. A grid interactive uninterruptible power supply (UPS) comprising:

a first path comprising:

a rectifier;

an inverter coupled in series with said rectifier; and

a battery coupled in parallel with said inverter; and

a second path in parallel with said first path, wherein said grid interactive UPS is operable to supply power from said battery to a grid coupled to an input of said grid interactive UPS, wherein said grid interactive UPS is operable in a peak shaving operating mode in which said battery supplies power to a load coupled to an output of said grid interactive UPS, wherein said grid interactive UPS is configured to activate the peak shaving operating mode in response to a control signal received from a controller that is generated in response to determining that a present energy rate of the grid exceeds a predetermined threshold energy rate, and wherein said grid interactive UPS is further configured to selectively drive one of the rectifier or the inverter to operate as a virtual resistor to provide active damping of resonant oscillation effects while concurrently placing the other of the rectifier or the inverter in a standby state.

2. A grid interactive UPS in accordance with claim 1 , wherein said battery is configured to be recharged by receiving power from the grid.

3. A grid interactive UPS in accordance with claim 1 , wherein said second path comprises a semiconductor switching module.

4. A grid interactive UPS in accordance with claim 1 , wherein said battery is a rechargeable sodium battery.

5. A grid interactive UPS in accordance with claim 1 , wherein said second path is operable as a bypass path that bypasses operation of said rectifier and said inverter.

6. A grid interactive UPS in accordance with claim 1 , wherein said rectifier is configured to inject at least one of active and reactive power into the grid.

7. A power system comprising:

a grid;

a load; and

at least one grid interactive uninterruptible power supply (UPS) coupled between said grid and said load, said at least one grid interactive UPS comprising:

a first path comprising:

a rectifier;

an inverter coupled in series with said rectifier; and

a battery coupled in parallel with said inverter; and

a second path in parallel with said first path, wherein said at least one grid interactive UPS is operable to supply power from said battery to said grid and supply power from said battery to said load in a peak shaving operating mode; and

a controller in communication with said at least one grid interactive UPS, said controller operable to:

compare a present energy rate of said grid to a predetermined threshold energy rate;

cause said at least one grid interactive UPS to activate the peak shaving operating mode when the present energy rate exceeds the predetermined threshold energy rate; and

selectively drive one of the rectifier or the inverter to operate as a virtual resistor to provide active damping of resonant oscillation effects while concurrently placing the other of the rectifier or the inverter in a standby state.

8. A power system in accordance with claim 7 , wherein said battery is configured to be recharged by receiving power from said grid.

9. A power system in accordance with claim 7 , wherein said second path comprises a semiconductor switching module.

10. A power system in accordance with claim 7 , wherein said battery is a rechargeable sodium battery.

11. A power system in accordance with claim 7 , wherein said second path is operable as a bypass path that bypasses operation of said rectifier and said inverter.

12. A power system in accordance with claim 7 , wherein said rectifier is configured to inject at least one of active and reactive power into said grid.

13. A power system in accordance with claim 7 , wherein said at least one grid interactive UPS comprises a plurality of grid interactive UPSs.

14. A method of operating a power system comprising a grid interactive uninterruptible power supply (UPS) coupled between a grid and a load, wherein the grid interactive UPS includes a first path including a rectifier, an inverter coupled in series with the rectifier, and a battery coupled in parallel with the inverter, and a second path in parallel with the first path, the method comprising:

comparing a present energy rate of the grid to a predetermined threshold energy rate using a controller in communication with the grid interactive UPS;

operating the grid interactive UPS in a peak shaving operating mode when the present energy rate exceeds the predetermined threshold energy rate, wherein the battery supplies power to a load in the peak shaving operating mode;

supplying power from the battery to the grid; and

selectively driving one of the rectifier or the inverter to operate as a virtual resistor to provide active damping of resonant oscillation effects while concurrently placing the other of the rectifier or the inverter in a standby state.

15. A method in accordance with claim 14 , further comprising recharging the battery by receiving power from the grid.

16. A method in accordance with claim 14 , wherein coupling a grid interactive UPS comprises coupling a grid interactive UPS that includes a rechargeable sodium battery.

17. A method in accordance with claim 14 , further comprising injecting at least one of active and reactive power into the grid using the rectifier.

18. A grid interactive UPS in accordance with claim 1 , wherein to selectively drive one of the rectifier or the inverter to operate as a virtual resistor to provide active damping of resonant oscillation effects comprises to drive one of the rectifier or the inverter to provide active damping of resonant oscillation effects produced by a capacitor connected in parallel with the load coupled to the output of the grid interactive UPS.

19. A power system in accordance with claim 7 , wherein to selectively drive one of the rectifier or the inverter to operate as a virtual resistor to provide active damping of resonant oscillation effects comprises to drive one of the rectifier or the inverter to provide active damping of resonant oscillation effects produced by a capacitor connected in parallel with the load.

20. A method in accordance with claim 14 , wherein selectively driving one of the rectifier or the inverter to operate as a virtual resistor to provide active damping of resonant oscillation effects comprises driving one of the rectifier or the inverter to provide active damping of resonant oscillation effects produced by a capacitor connected in parallel with the load.