Power conversion system and method of operating the same

1. A medium voltage direct current (MVDC) collector system for renewable power generation facilities, said MVDC collector system comprising:

at least one renewable energy generation device;

at least one direct current (DC)-to-DC (DC/DC) power converter coupled to said at least one renewable energy generation device, said at least one DC/DC power converter configured to shift a switching operation of said DC/DC power converter between full-wave conversion and half-wave conversion;

at least one controller coupled to said at least one DC/DC power converter, said at least one controller configured to regulate shifting the switching operation of said at least one DC/DC power converter between full-wave conversion and half-wave conversion;

wherein said at least one DC/DC power converter comprises a full-bridge converter comprising an input DC link;

wherein the full-bridge converter comprises a plurality of switching devices, each switching device of said plurality of switching devices is directly connected to either a positive terminal or a negative terminal of the same input DC link; and

wherein the MVDC collector system further comprises a distributed energy storage system having a plurality of distributed energy storage devices, each distributed energy storage device includes storage batteries and momentum devices and is coupled to the said at least one DC/DC power converter through a distributed DC/DC power converter.

2. The MVDC collector system in accordance with claim 1 , wherein each switching device of said plurality of switching devices is coupled to said at least one controller, said at least one controller further configured to maintain at least a first portion of said plurality of switching devices in an OFF status and a second portion of said plurality of switching devices in an ON status to facilitate shifting the switching operation of said at least one DC/DC power converter from full-wave conversion to half-wave conversion.

3. The MVDC collector system in accordance with claim 1 , wherein said at least one DC/DC power converter comprises a plurality of DC/DC conversion modules, each DC/DC conversion module of said plurality of DC/DC conversion modules comprising an input section coupled to said at least one renewable energy generation device and an output section.

4. The MVDC collector system in accordance with claim 3 , said each DC/DC conversion module of said plurality of DC/DC conversion modules coupled to said at least one controller, said at least one controller configured to regulate switching said plurality of DC/DC conversion modules between an ON status and an OFF status to facilitate shifting the switching operation of said at least one DC/DC power converter from full-wave conversion to half-wave conversion.

5. The MVDC collector system in accordance with claim 1 , wherein said full bridge converter comprises a single resonant converter further comprising a high-frequency (HF) transformer and at least one resonant capacitor coupled in series with said HF transformer, said HF transformer comprising at least one inductive device, said at least one inductive device and said at least one resonant capacitor define a resonant tank circuit.

6. The MVDC collector system in accordance with claim 1 , wherein said at least one controller is further configured to use maximum power point tracking (MPPT) to regulate power conversion through said at least one DC/DC power converter.

7. The MVDC collector system in accordance with claim 6 , wherein said at least one DC/DC power converter comprises a plurality of switching devices, each switching device of said plurality of switching devices coupled to said at least one controller, said at least one controller further configured to maintain at least a first portion of said plurality of switching devices in an OFF status and a second portion of said plurality of switching devices in an ON status to facilitate shifting the switching operation of said at least one DC/DC power converter from full-wave conversion to half-wave conversion, said at least one controller further configured to regulate the switching frequency of said plurality of switching devices.

8. The MVDC collector system in accordance with claim 7 , wherein said plurality of switching devices is configured to switch within a range of frequencies between approximately 5 kiloHertz (kHz) and approximately 100 kHz.

9. The MVDC collector system in accordance with claim 7 wherein said at least one controller is further configured to regulate a voltage gain of said at least one DC/DC power converter through regulation of the switching frequency of said plurality of switching devices.

10. The MVDC collector system in accordance with claim 9 , wherein said at least one controller is further configured to:

receive real-time values of electric power transmitted through said at least one DC/DC power converter;

regulate the switching frequency of said plurality of switching devices to regulate the voltage gain of said at least one DC/DC power converter as a function of the real-time values of electric power transmitted through said at least one DC/DC power converter;

shift the switching operation of said at least one DC/DC power converter between full-wave conversion and half-wave conversion as a function of the real-time values of electric power transmitted through said at least one DC/DC power converter; and

decrease the switching frequency of said plurality of switching devices to decrease the voltage gain of said at least one DC/DC power converter under fault condition, thereby facilitating isolation of said at least one DC/DC power converter.

11. The MVDC collector system in accordance with claim 6 , wherein said at least one controller is further configured to regulate a voltage gain of said at least one DC/DC power converter as a function of load on said at least one DC/DC power converter.

12. The MVDC collector system in accordance with claim 1 , wherein said at least one DC/DC power converter comprises a plurality of DC/DC power converters and said at least one renewable energy generation device comprises a plurality of renewable energy generation devices, each DC/DC power converter of said plurality of DC/DC power converters and each renewable energy generation device of said plurality of renewable energy generation devices define a string of a plurality of strings, said MVDC collector system further comprising a MVDC bus, wherein said plurality of strings are coupled to said MVDC bus, each string of said plurality of strings further comprising at least one diode positioned between and coupled to said each DC/DC power converter and said MVDC bus.

13. The MVDC collector system in accordance with claim 12 , wherein said plurality of strings are devoid of DC-to-alternating current (AC) (DC/AC) converters, step-up transformers, and circuit breakers.

14. The MVDC collector system in accordance with claim 1 further comprising at least one electric power storage device coupled to said at least one DC/DC power converter.

15. A renewable energy generation facility comprising:

a direct current (DC) bus;

a plurality of renewable energy generation devices;

a plurality of direct current (DC)-to-DC (DC/DC) power converters, each DC/DC power converter of said plurality of DC/DC power converters coupled to at least one renewable energy generation device of said plurality of renewable energy generation devices, said each DC/DC power converter configured to shift a switching operation between full-wave conversion and half-wave conversion, each DC/DC power converter of said plurality of DC/DC power converters is coupled to said DC bus via a diode stack, wherein the diode stack is directly connected to an output terminal of the DC/DC power converter of said plurality of DC/DC power converters and blocks electric power flow from the said DC bus to the DC/DC power converter of said plurality of DC/DC power converters and allows only unidirectional transmission of electric power from respective DC/DC power converter to the DC bus; and

at least one controller coupled to said at least one DC/DC power converter, said at least one controller configured to regulate shifting the switching operation of said at least one DC/DC power converter between full-wave conversion and half-wave conversion.

16. The renewable energy generation facility in accordance with claim 15 , wherein said at least one controller is further configured to use maximum power point tracking (MPPT) to regulate power conversion through the at least one DC/DC power converter.

17. The renewable energy generation facility in accordance with claim 16 , wherein the at least one DC/DC power converter includes a plurality of switching devices, and wherein said at least one controller uses MPPT by:

regulating the switching frequency of the plurality of switching devices; and

regulating a voltage gain of the at least one DC/DC power converter as a function of load on the at least one DC/DC power converter.

18. The renewable energy generation facility in accordance with claim 16 , wherein the at least one DC/DC power converter includes a plurality of switching devices, said at least one controller is further configured to regulate a voltage gain of the at least one DC/DC power converter by regulating the switching frequency of the plurality of switching devices.

19. The renewable energy generation facility in accordance with claim 18 , wherein said at least one controller regulates the voltage gain of the at least one DC/DC power converter by:

receiving real-time values of electric power transmitted through the at least one DC/DC power converter;

regulating the switching frequency of the plurality of switching devices to regulate the voltage gain of the at least one DC/DC power converter as a function of the real-time values of electric power transmitted through the at least one DC/DC power converter;

shifting the switching operation of the at least one DC/DC power converter between full-wave conversion and half-wave conversion as a function of the real-time values of electric power transmitted through the at least one DC/DC power converter; and

decreasing the switching frequency of the plurality of switching devices to decrease the voltage gain of the at least one DC/DC power converter under fault condition, thereby facilitating isolation of the at least one DC/DC power.

20. The renewable energy generation facility in accordance with claim 15 further comprising a medium voltage alternating current (MVAC) collector system coupled to the at least one electrical bus through a DC/AC power converter and a second diode stack, wherein the second diode stack blocks electric power flow from the DC/AC power converter to the at least one electrical bus.

21. A medium voltage direct current (MVDC) collector system for renewable power generation facilities, said MVDC collector system comprising:

at least one renewable energy generation device;

at least one direct current (DC)-to-DC (DC/DC) power converter coupled to said at least one renewable energy generation device, said at least one DC/DC power converter configured to shift a switching operation of said DC/DC power converter between full-wave conversion and half-wave conversion;

at least one controller coupled to said at least one DC/DC power converter, said at least one controller configured to regulate shifting the switching operation of said at least one DC/DC power converter between full-wave conversion and half-wave conversion; and

wherein said at least one DC/DC power converter comprises a first half-bridge resonant converter and a second half-bridge resonant converter coupled in series to said at least one renewable energy generation device;

wherein the first half-bridge resonant converter includes a first resonant capacitive device and a first high frequency transformer; and

wherein the second half-bridge resonant converter includes a second resonant capacitive device different than the first resonant capacitive device and a second high frequency transformer different than the first high frequency transformer.

22. The MVDC collector system in accordance with claim 21 , wherein said at least one controller is configured to alternate at least one first half-bridge converter of said plurality of half-bridge converters and at least one second half-bridge converter of said plurality of half-bridge converters between the OFF status and the ON status to facilitate shifting the switching operation of said at least one DC/DC power converter from full-wave conversion to half-wave conversion.

23. The MVDC collector system in accordance with claim 21 wherein said plurality of half-bridge resonant converters comprise a plurality of switching devices, each switching device of said plurality of switching devices coupled to said at least one controller, said at least one controller further configured to maintain said plurality of switching devices in switching operation during full-wave conversion and wherein the said at least one controller is further configured to maintain at least a first portion of said plurality of switching devices in an OFF status and a second portion of said plurality of switching devices switching operation during half-wave conversion.