High efficiency power conditioner employing low voltage DC bus and buck and boost converters

• US 6,369,461 B1
• Filed: 09/01/2000
• Issued: 04/09/2002
• Est. Priority Date: 09/01/2000
• Status: Expired due to Term

• Current Assignee: ABB Incorporated (ABB Limited)
• Original Assignee: ABB Incorporated (ABB Limited)
• Inventors: Jungreis, Aaron M., Bapat, Vinod
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US09/653,663
• Time in Patent Office: 585 Days
• Field of Search: 429/12, 429/22, 307/66, 307/46, 307/23
• US Class Current: 307/46
• CPC Class Codes: H01M 16/003 of fuel cells with other electrochemical devices, e.g. capacitors, electrolysers
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A power conditioner interfaces a load to a fuel cell 10 that produces a low voltage that varies with the load. A dc-to-ac inverter 16 operates with a low voltage input provided by a dc bus 14. When a positive step load change occurs, a low voltage battery 22 provides power equal to the step change until the fuel cell 10 is able to provide enough power to support the entire load. The power from the battery 22 is supplied to the varying dc bus 14 through a boost converter 12. When very large positive load step changes occur, the battery can feed power to the dc bus through diode D1, rather than through the boost converter. Diode D1 does not need to be used, but its use allows the boost converter to be sized for common load changes rather than for the maximum possible load change (such as might be seen during a faulted output). A buck converter converts the variable voltage on the dc bus 14 to the appropriate float charging voltage of the battery. The buck converter also supplies power for auxiliary equipment when available from the fuel cell. If the fuel cell is unable to provide the auxiliary power (such as during startup or load transients), then the auxiliary power can come directly from the battery.

Claims

1. A power conditioner for conditioning electrical power provided by a fuel cell to a load through a dc-to-ac inverter, comprising:

(a) a dc bus coupled to the fuel cell and the dc-to-ac inverter;

(b) a battery operatively coupled to the dc bus;

(c) a buck converter coupled between the battery and the dc bus; and

(d) a boost converter coupled between the battery and the dc bus.

2. A power conditioner as recited in claim 1, wherein a low side of the buck converter is coupled to the battery and a high side of the buck converter is coupled to the dc bus.

3. A power conditioner as recited in claim 2, wherein a low side of the boost converter is coupled to the battery and a high side of the boost converter is coupled to the dc bus.

4. A power conditioner as recited in claim 3, further comprising a diode (D1) coupled between the battery and the dc bus.

5. A power conditioner as recited in claim 4, wherein the diode is configured such that, when very large positive load step changes occur, the battery can feed power to the dc bus through the diode rather than through the boost converter.

6. A power conditioner as recited in claim 1, wherein the dc-to-ac inverter is designed to operate with a low voltage input, and the low voltage input is provided by the dc bus.

7. A power conditioner as recited in claim 1, wherein, when a positive step load change occurs, the battery provides power, through the boost converter and dc bus, equal to the step change until the fuel cell is able to provide enough power to support the entire load.

8. A power conditioner as recited in claim 7, wherein the boost converter permits control of the battery power so that the power drawn from the fuel cell can be gradually increased as the ability of the fuel cell to produce the required load power gradually increases.

9. A power conditioner as recited in claim 8, wherein, when very large positive load step changes occur, the battery feeds power to the dc bus through a diode (D1) rather than through the boost converter.

10. A power conditioner as recited in claim 9, wherein, when the fuel cell has enough reserve power to both charge the battery and supply all of the load power, the buck converter provides charging current to the battery.

11. A power conditioner as recited in claim 10, wherein the buck converter converts a variable voltage on the dc bus to a float charging voltage of the battery.

12. A power conditioner as recited in claim 11, wherein the buck converter further supplies power for auxiliary equipment when available from the fuel cell.

13. A power conditioner as recited in claim 12, wherein a low side of the buck converter is coupled to the battery and a high side of the buck converter is coupled to the dc bus;

wherein a low side of the boost converter is coupled to the battery and a high side of the boost converter is coupled to the dc bus; and

wherein the diode is coupled between the battery and the dc bus.

23. A power conditioner as recited in claim 1, wherein the buck and boost converters are combined into a bi-directional converter.

24. A power conditioner as recited in claim 1, wherein the fuel cell is coupled in parallel with an energy storage medium and has a maximum operating voltage that is less than a minimum operating voltage of the storage medium.

25. A power conditioner as recited in claim 1, wherein the boost converter includes an air-core switching inductor, wherein the air-core inductor is able to pass high over-currents for short periods of time.

14. A power conditioner for conditioning electrical power provided to a load, comprising:

a dc-to-ac inverter having an output providing ac output power for the load;

a low voltage, variable dc bus coupled to a power generation device and the dc-to-ac inverter;

a low voltage energy storage medium operatively coupled to the dc bus;

a buck converter coupled between the low voltage energy storage medium and the dc bus; and

a boost converter coupled between the low voltage energy storage medium and the dc bus.

15. A power conditioner as recited in claim 14, wherein the energy storage medium is a member of a group consisting of a battery, electrolytic capacitor, super capacitor, and flywheel system.

16. A power conditioner as recited in claim 15, further comprising one or more energy storage media that are paralleled with the power generation device.

17. A power conditioner as recited in claim 16, wherein the energy storage media are directly paralleled and have identical voltage output.

18. A power conditioner as recited in claim 16, wherein the energy storage media are indirectly paralleled by coupling their respective output to a bus via an accompanying buck and boost converter to tie into the dc bus.

19. A power conditioner as recited in claim 18, wherein a fuel cell is coupled in parallel with one of an electrolytic capacitor and a flywheel system, and the fuel cell has a maximum operating voltage that is less than a minimum operating voltage of the electrolytic capacitor and flywheel system.

20. A power conditioner as recited in claim 14, wherein the buck and boost converters are combined into a bidirectional converter.

21. A power conditioner as recited in claim 14, wherein the low voltage power supply comprises a battery.

22. A power conditioner as recited in claim 14, wherein the boost converter includes an air-core switching inductor, wherein the air-core inductor is able to pass high over-currents for short periods of time.