Switching DC-DC power converter and battery charger for use with direct oxidation fuel cell power source

• US 6,590,370 B1
• Filed: 10/01/2002
• Issued: 07/08/2003
• Est. Priority Date: 10/01/2002
• Status: Expired due to Term

• Current Assignee: MTI MicroFuel Cells, Inc. (Soluna Holdings, Inc.)
• Original Assignee: MTI MicroFuel Cells, Inc. (Soluna Holdings, Inc.)
• Inventors: Leach, David H.
• Primary Examiner(s): Tso, Edward H.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US10/261,823
• Time in Patent Office: 280 Days
• Field of Search: 320/101, 320/103, 320/125, 320/136, 323/299-303, 323/906, 363/16, 363/95, 363/97, 307/64, 307/66, 307/23, 429/30, 429/33, 429/41, 429/46, 324/433
• US Class Current: 323/299
• CPC Class Codes: H01M 16/006 of fuel cells with rechargeable batteries
• CPC Class Codes: H02J 2300/30 The power source being a fuel cell
• 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: H02M 1/0022 the disturbance parameters being input voltage fluctuations
• CPC Class Codes: H02M 3/155 using semiconductor devices only
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

This invention presents a method and apparatus for controlling the operating point, i.e. the output voltage or current, of a fuel cell to a desired value, efficiently transferring the available fuel cell power to a rechargeable battery and load, and isolating the fuel cell from the battery and load. Active control of the operating point of the fuel cell allows for optimized power output and fuel cell efficiency. This invention uses feedback from the input to regulate the input voltage or current. The output of the DC-DC converter either charges the battery or helps the battery supply the load, and is maintained equal to the battery voltage as the output of the DC-DC converter is directly connected to the battery.

Claims

1. A high efficiency DC-DC power converter and battery charger system comprising:

a power source comprising a direct oxidation fuel cell means which generates an output voltage and an output current;

a DC-DC converter circuit having an input which is connected to receive said output voltage and current from said fuel cell means;

a re-chargeable battery connected to an output of said converter circuit; and

a controller, coupled to said fuel cell means and said converter circuit, which compares at least one operating parameter of said fuel cell means to a reference and, in response thereto, generates control signals for said DC-DC converter circuit, whereby at least one operating parameter of said fuel cell means is maintained at a desired level, as determined by said reference.

2. The system as in claim 1 wherein said direct oxidation fuel cell means comprises one of the following:

a direct methanol fuel cell stack wherein a fuel cell stack, comprises two or more cells that are electrically connected; and

an individual direct methanol fuel cell.

3. The system as in claim 1 wherein a load is connected in parallel with said re-chargeable battery and said converter circuit operates to charge said battery and/or supplement current to said load.

4. The system as in claim 1 wherein said output of said converter circuit is connected to said battery such that an output voltage of said converter circuit is equal to said battery voltage.

8. The system as in claim 1 wherein said reference is adjustable.

9. The system as defined in claim 8 further comprising a control system which adjusts said reference to adjust at least one operating parameter of said fuel cell means.

10. The system as in claim 9 wherein said control system controls one or more of said fuel cell means operating parameters to substantially optimize fuel cell means power output and/or efficiency over a desired range of operating conditions.

11. The system as defined in claim 9 wherein said control system controls one or more of said fuel cell means operating parameters to perform fuel cell means diagnostics.

12. The system as defined in claim 11, wherein said fuel cell means diagnostics include measuring said fuel cell means current at at least one voltage.

13. The system as defined in claim 11, wherein said fuel cell means diagnostics include measuring said fuel cell means voltage at at least one current.

14. The system as in claim 1 wherein said direct oxidation fuel cell means comprises one of the following:

a direct oxidation fuel cell stack wherein a fuel cell stack comprises two or more cells that are electrically connected; and

an individual direct oxidation fuel cell.

15. The system as defined in claim 9, wherein said fuel cell means is a fuel cell stack and said control system controls one or more fuel cell stack operating parameters to substantially prevent an individual fuel cell in said fuel cell stack from operating outside of a desired voltage range.

16. The system as defined in claim 1 wherein said controller is at least one of an analog controller, a digital controller or a mixed signal controller.

17. The system as defined in claim 1 wherein said control signals are drive waveforms for switches in said DC-DC converter circuit that adjust on/off times of said switches.

18. The system as defined in claim 1 wherein said DC-DC converter circuit includes at least one of the following:

(A) inductor-based converter;

(B) transformer-based converter;

(C) step up (boost) converter;

(D) step down (buck) converter;

(E) inverting converter; and

(F) capacitor-based converter.

19. The system as defined in claim 14 wherein said fuel cell means is a fuel cell stack and said fuel cell means operating parameters include:

fuel cell stack output voltage, fuel cell stack output current, fuel cell stack output power, and voltages, currents and power of an individual fuel cell in the stack.

20. The system as defined in claim 14 wherein said fuel cell means is an individual fuel cell and said fuel cell means operating parameters include:

fuel cell output voltage, fuel cell output current and fuel cell output power.

34. The system as defined in claim 1 wherein said power source comprises a plurality of direct oxidation fuel cells means.

35. The system as defined in claim 34 wherein each fuel cell means in said plurality of fuel cells means of said power source is coupled to its own DC-DC converter circuit having a controller associated therewith, and an output of each said associated DC-DC converter circuit is coupled to a single rechargeable battery.

5. A method of efficiently charging a re-chargeable battery comprising the steps of:

(1) using a direct oxidation fuel cell means to produce power which is supplied to an input of a DC-DC converter circuit;

(2) using an output of said converter circuit to charge a re-chargeable battery;

(3) using at least one operating parameter of said fuel cell means as a feedback signal;

(4) using said feedback signal to generate control signals for controlling said DC-DC power converter circuit; and

(5) applying said control signals to said converter circuit whereby at least one operating parameter of said fuel cell means is substantially maintained at a desired level, which is determined by said reference.

6. The method of claim 5 wherein said direct oxidation fuel cell means comprises one of the following:

a direct methanol fuel cell stack, wherein a fuel cell stack comprises two or more cells that are electrically connected; and

an individual direct methanol fuel cell.

7. The method of claim 5 wherein a load is connected in parallel with said re-chargeable battery and said converter circuit operates to charge said battery and/or supplement current to said load.

21. The method as defined in claim 5 wherein said reference is adjustable.

22. The method as defined in claim 21 including the further step of

adjusting said reference to adjust at least one fuel cell means operating parameter.

23. The method as defined in claim 22 including the further step of

adjusting at least one fuel cell means operating parameter to substantially optimize said fuel cell means power output and/or efficiency over a desired range of operating conditions.

24. The method as defined in claim 22 including the further step of

adjusting at least one fuel cell means operating parameter in order to perform fuel cell means diagnostics.

25. The method as defined in claim 24 including the further step of:

measuring said fuel cell means current at at least one voltage.

26. The method as defined in claim 24 including the further step of:

measuring said fuel cell means voltage at at least one current.

27. The method of claim 5 wherein said direct oxidation fuel cell means comprises one of the following:

a direct oxidation fuel cell stack, wherein a fuel cell stack comprises two or more cells that are electrically connected; and

an individual direct oxidation fuel cell.

28. The method as defined in claim 27 wherein said fuel cell means is a fuel cell stack, the method including the further step of:

adjusting at least one fuel cell stack operating parameter to substantially prevent an individual cell in said fuel cell stack from operating outside of a desired voltage range.

29. The method as defined in claim 5 wherein said DC-DC converter circuit includes at least one of the following:

(A) inductor-based converter;

(B) transformer-based converter;

(C) step up (boost) converter;

(D) step down (buck) converter;

(E) inverting converter; and

(F) capacitor-based converter.

30. The method as defined in claim 5 including the further step of

using said control signals as drive waveforms for switches in said DC-DC converter circuit to adjust on/off times of said switches.

31. The method as defined in claim 27 wherein said fuel cell means is a fuel cell stack and said fuel cell means operating parameters include:

fuel cell stack output voltage, fuel cell stack output current, fuel cell stack output power, and voltages, currents and power of an individual fuel cell in the stack.

32. The method as defined in claim 27 wherein said fuel cell means is an individual fuel cell and said fuel cell means operating parameters include:

fuel cell output voltage, fuel cell output current and fuel cell output power.

33. The method as defined in claim 5 including the further step of:

using a controller to generate said control signals; and

selecting as said controller, at least one of an analog controller, a digital controller or a mixed signal controller.