Methods and systems for selectively coupling a power conversion system to an electrical grid

1. A power conversion system for providing power to an electrical grid comprising:

a power converter coupled to and configured to receive power generated by a direct current (DC) power source;

a contactor coupled to said power converter and said electrical grid and configured to selectively electrically couple said power converter to said electrical grid; and

a system controller communicatively coupled to said power converter and said contactor, said system controller comprising a memory device, said system controller configured to:

close said contactor to electrically couple said power converter to said electrical grid when a DC voltage provided to said power converter has remained higher than a predefined voltage level until a first timer expires after a first predefined length of time value stored within said memory device;

activate said power converter with said contactor closed when the DC voltage provided to said power converter has remained higher than the predefined voltage level for the first predefined length of time value;

deactivate said power converter, while maintaining said contactor in the closed position, when an alternating current (AC) power output of said power converter has remained lower than a predefined power level until a second timer expires after a second predefined length of time value stored within said memory device;

maintain said contactor in the closed position until a contactor open-delay expires after a third predefined length of time value stored within said memory device; and

open said contactor when the DC voltage provided to said power converter has remained lower than the predefined voltage level subsequent expiration of the third predefined length of time.

2. The power conversion system in accordance with claim 1 , wherein said DC power source comprises a photovoltaic (PV) array.

3. The power conversion system in accordance with claim 1 , wherein said system controller is further configured to determine if the DC voltage provided to said power converter is greater than the predefined voltage level.

4. The power conversion system in accordance with claim 1 , wherein said system controller is further configured to determine the AC power output of said power converter.

5. The power conversion system in accordance with claim 1 , wherein said power converter comprises a two-stage power converter.

6. The power conversion system in accordance with claim 1 , wherein said memory device further configured to store at least one of the predefined voltage level and the predefined power level.

7. The power conversion system in accordance with claim 6 , wherein said system controller is configured to monitor the third predetermined length of time value that defines the period of time said contactor is closed.

8. The power conversion system in accordance with claim 7 , wherein said system controller is further configured to open said contactor when the DC voltage provided to said power converter has remained lower than the predefined voltage level for the second predefined length of time value and the length of time said contactor has been closed exceeds the third predefined length of time value.

9. A method for operating a power conversion system, the power conversion system including a power converter and a contactor configured to selectively electrically couple the power converter to an electrical grid, said method comprising:

determining that a direct current (DC) voltage provided to the power converter has remained higher than a predefined voltage level until a first timer expires after a stored first predefined length of time value;

closing the contactor to electrically couple the power converter to the electrical grid when a DC voltage provided to the power converter has remained higher than a predefined voltage level for the first predefined length of time value;

activating the power converter to convert the DC voltage input to an alternating current (AC) voltage output with the contactor closed and when the DC voltage provided to the power converter has remained higher than the predefined voltage level for the first predefined length of time value;

determining an AC power output of the power converter;

discontinuing operation of the power converter comprising maintaining the contactor in the closed position and turning-off the power converter when the AC power output has remained lower than a predefined power level until a second timer expires after a stored second predefined length of time value;

monitoring a length of time the contactor is closed; and

opening the contactor when the DC voltage provided to the power converter has remained lower than the predefined voltage level for the second predefined length of time value and the length of time the contactor has been closed exceeds a stored contactor-open delay value.

10. The method in accordance with claim 9 , wherein:

determining that the DC voltage is higher than a predefined voltage level comprises measuring a DC bus voltage within the power converter; and

activating the power converter comprises activating a DC to AC inverter included within the power converter when the DC bus voltage is greater than the predefined voltage level.

11. A system controller coupled to, and configured to control operation of, a power conversion system that includes a power converter coupled to a photovoltaic (PV) array and a contactor configured to selectively electrically couple the power converter to an electrical grid, said system controller comprising a memory device, said system controller configured to:

determine that a direct current (DC) voltage provided to the power converter has remained higher than a predefined voltage level until a first timer expires after a first predefined length of time value stored within said memory device;

close the contactor to electrically couple the power converter to the electrical grid when a DC voltage provided to the power converter has remained higher than a predefined voltage level for the first predefined length of time value;

activate the power converter to convert the DC voltage input to an alternating current (AC) voltage output with the contactor closed and when the DC voltage provided to the power converter has remained higher than the predefined voltage level for the first predefined length of time value;

determine an AC power output of the power converter;

discontinue operation of the power converter, while maintaining the contactor in a closed position, when the AC power output has remained lower than a predefined power level until a second timer expires after a second predefined length of time value stored within said memory device;

maintain the contactor in the closed position until a contactor open-delay expires after a third predefined length of time value stored within said memory device; and

open the contactor when the DC voltage provided to the power converter has remained lower than the predefined voltage level subsequent the third predefined length of time.

12. The system controller in accordance with claim 11 , further configured to:

monitor the third predetermined length of time that defines the period of time the contactor is closed; and

open the contactor when the DC voltage provided to the power converter has remained lower than the predefined voltage level for the second predefined length of time value and the third length of time the contactor has been closed exceeds the third predefined length of time value.

13. The system controller in accordance with claim 11 , further configured to operate a two-stage power converter.

14. The system controller in accordance with claim 13 , further configured to:

measure a DC bus voltage provided to a DC to AC inverter included within the two-stage power converter; and

operate the DC to AC inverter when the DC bus voltage is above the predefined voltage level and the output of the DC to AC inverter is above the predefined power level.