Hybrid energy storage device charge equalization system and method

• US 6,559,621 B2
• Filed: 08/22/2001
• Issued: 05/06/2003
• Est. Priority Date: 05/21/2001
• Status: Expired due to Fees

• Current Assignee: Cellex Power Products, Inc. (Plug Power Inc.)
• Original Assignee: Cellex Power Products, Inc. (Plug Power Inc.)
• Inventors: Corless, Adrian J., Leboe, David
• Primary Examiner(s): TOATLEY, GREGORY J
• Application Number:
  US09/935,076
• Publication Number:
  US 20020171397A1
• Time in Patent Office: 622 Days
• Field of Search: 320/103, 320/104, 320/126, 320/119, 318/139, 307/9.1, 700/297, 180/65.8
• US Class Current: 320/103
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H01M 16/003 of fuel cells with other electrochemical devices, e.g. capacitors, electrolysers
• CPC Class Codes: H01M 6/5033 used as charging means for another battery
• 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 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A system and method for improving the performance of a hybrid power supply apparatus comprising a power generating device, such as a fuel cell, and a primary energy storage device, such as a battery. The purpose of the invention is to provide an equalization charge to the battery from a source other than the fuel cell when the battery achieves a predetermined state of charge condition, thereby avoiding the need to operate the fuel cell in a low power output mode. When the predetermined state of charge condition is detected by a controller, the fuel cell is shut-down. In one aspect of the invention the equalization charge is provided to the battery by a secondary energy storage device, such as a plurality of capacitors or secondary batteries. The predetermined state of charge condition may be satisfied, for example, when the state of charge of the battery exceeds a predetermined threshold, such as 80% of the battery'"'"'s storage capacity, for a predetermined period of time. In some aspects of the invention, the secondary energy storage device may also be connectable to the load. Preferably the system also includes a DC/DC converter for regulating current flow between the fuel cell and the storage devices.

Claims

1. A hybrid power supply system for supplying electrical power to a load comprising:

(a) a power generating device;

(b) a first energy storage device chargeable by said power generating device and electrically connectable to said load;

(c) a first detector for measuring the state of charge of said first energy storage device;

(d) a second energy storage device chargeable by said power generating device and electrically connectable to said first energy storage device; and

(e) a controller for receiving input from said first detector, wherein said controller causes said second energy storage device to provide an equalization current to said first energy storage device when said controller detects a first predetermined state of charge condition.

2. The system of claim 1, wherein said power generating device is operable in alternating charging and shut-down modes and wherein said controller causes said power generating device to switch from said charging mode to said shut-down mode when said first predetermined state of charge condition is detected.

3. The system of claim 2, wherein said controller detects said first predetermined state of charge condition when the measured state of charge of said first energy storage device exceeds a first threshold value for a predetermined length of time.

4. The system of claim 2, wherein said power generating device comprises a fuel cell system.

5. The system of claim 2, wherein said second energy storage device delivers said equalization charge to said first energy storage device while said power generating device is in said shut-down mode until said first energy storage device is fully charged.

6. The system of claim 2, further comprising a DC/DC converter electrically connected between said power generating device and said first and second energy storage devices.

7. The system of claim 6, wherein said DC/DC converter draws energy from at least one of said first and second energy storage devices when said power generating device is in said shut-down mode.

8. The system of claim 2, wherein said controller causes said power generating device to switch from said shut-down mode to said charging mode when said controller detects a second predetermined state of charge condition.

9. The system of claim 8, wherein said power generating device delivers current to said load and said first and second energy storage devices in said charging mode.

10. The system of claim 9, further comprising a second detector for measuring the state of charge of said second energy storage device, wherein said controller receives input from said second detector.

11. The system of claim 10, wherein said controller detects said second predetermined state of charge condition when the measured state of charge of at least one of said first or second energy storage devices falls below a second threshold value for a predetermined length of time.

12. The system of claim 11 wherein said second energy storage device is electrically connectable to said load.

13. The system of claim 12, further comprising a pre-charge circuit to deliver a pre-charge to said second energy storage prior to electrically connecting said second energy storage device to said load.

14. The system of claim 12, wherein said controller causes said second energy storage device to deliver current to said load when said controller detects a third predetermined state of charge condition.

15. The system of claim 14, wherein said controller detects said third predetermined state of charge condition when the measured state of charge of said second energy storage device achieves a third threshold value for a predetermined length of time.

16. The system of claim 7, wherein said first energy storage device is a battery and said second energy storage device is a capacitor.

17. The system of claim 7, wherein said first and second energy storage devices are batteries.

18. The system of claim 17, wherein said batteries are connected in parallel with said DC/DC converter and said load.

19. The system of claim 3, wherein said first threshold value is a state of charge within the range of between approximately 75-95% of the full storage capacity of said first energy storage device.

20. The system of claim 11, wherein said second threshold value is a state of charge within the bulk charge region of one of said first or second energy storage devices.

21. The system of claim 20, wherein said second threshold value is a state of charge equal to approximately 70-80% of the full storage capacity of said primary energy storage device.

22. The system of claim 15, wherein said third threshold value is a state of charge approximately equal to the state of charge of said first storage device when said states of charge of said first and second energy storage devices are measured simultaneously.

23. The system of claim 19, wherein said second storage device is sized such that the storage capacity of said second energy storage device is equal to approximately 125% of the charge necessary to charge said first energy storage device from said first threshold to full storage capacity.

24. A method of operating a hybrid power supply apparatus including a power generating device adjustable between charging and shut-down modes and further including first and second energy storage devices chargeable by said power generating device, at least one of the first and second energy storage devices being connected to a load for delivering electrical power thereto, said method comprising:

(a) operating said power generating device in said charging mode to deliver charging current to said first and second energy storage devices;

(b) repeatedly measuring the state of charge of said first energy storage device;

(c) adjusting said power generating device from said charging mode to said shut-down mode when the measured state of charge of said first energy storage device satisfies a first predetermined state of charge condition; and

(d) providing an equalization current from said second energy storage device to said first energy storage device while said power generating device is in said shut-down mode until the measured state of charge of said first energy storage device reaches approximately its full storage capacity.

25. The method of claim 24, wherein said first predetermined state of charge condition is achieved when said measured state of charge of said first energy storage device exceeds a first threshold value for a predetermined period of time, wherein said first threshold value is a percentage of the full storage capacity of said first energy storage device.

26. The method of claim 25, further comprising:

(e) adjusting said power generating device from said shut-down mode to said charging mode when the measured state of charge of said first energy storage device is below a second threshold value for a predetermined period of time.

27. The method of claim 24, wherein both of said first and second energy storage devices are electrically connectable to said load for delivering electrical power thereto and wherein said method further comprises:

(e) adjusting said power generating device from said shut-down mode to said charging mode when the measured state of charge of said first energy storage device is below a second threshold value for a predetermined period of time;

(f) repeatedly measuring the state of charge of said second energy storage device;

(g) delivering a pre-charge current from said power generating device or said first energy storage device to said second energy storage device; and

(h) electrically connecting said second energy storage device to said load when the measured state of charge of said second energy storage device exceeds a third threshold value for a predetermined period of time.

28. The method of claim 27, wherein said third threshold value is a state of charge approximately equal to the state of charge of said first energy storage device when said states of charge of said first and second energy storage devices are measured simultaneously.

29. The method of claim 27, wherein said first and second energy storage devices are charged simultaneously.

30. The method of claim 29, wherein said first and second energy storage devices are discharged simultaneously.

31. The method of claim 24, wherein said power generating device comprises a fuel cell and said apparatus further comprises a DC/DC converter for delivering current from said fuel cell to at least said first energy storage device.

32. The method of claim 31, further comprising connecting the output of said second energy storage device to the input of said DC/DC converter when the measured state of charge of said first energy storage device exceeds said first threshold value for a predetermined period of time.

33. The method of claim 27, wherein said power generating device is adjusted from said charging mode to said shut-down mode when the combined states of charge of said first and second energy storage devices exceed a predetermined amount.

34. The method of claim 27, wherein said apparatus is operable in successive alternating first and second operating cycles, wherein said second energy storage device delivers an equalization current to said first energy storage device when said power generating device is in said shut-down mode in said first operating cycle, and wherein said first energy storage device delivers an equalization current to said second energy storage device when said power generating device is in said shut-down mode in said second operating cycle.

35. A hybrid power supply system for supplying electrical power to a load comprising:

(a) a power generating device operable in alternating charging and non-charging modes;

(b) a first energy storage device chargeable by said power generating device and electrically connectable to said load;

(c) a first detector for measuring the state of charge of said first energy storage device;

(d) a second energy storage device chargeable by said power generating device and electrically connectable to said first energy storage device; and

(e) a controller for receiving input from said first detector, wherein said controller causes said second energy storage device to provide an equalization current to said first energy storage device when said controller detects a first predetermined state of charge condition, and wherein said controller causes said power generating device to switch from said charging mode to said non-charging mode when said first predetermined state of charge condition is detected.

36. The system of claim 35, wherein said power generating device comprises a fuel cell and a fuel processor supplying fuel to said fuel cell, wherein at least said fuel cell is adjusted to a shut-down state when said power generating device is in said non-charging mode.

37. A method of operating a hybrid power supply apparatus including a power generating device adjustable between charging and non-charging modes and further including first and second energy storage devices chargeable by said power generating device, at least one of the first and second energy storage devices being connected to a load for delivering electrical power thereto, said method comprising:

(a) operating said power generating device in said charging mode to deliver charging current to said first and second energy storage devices;

(b) repeatedly measuring the state of charge of said first energy storage device;

(c) adjusting said power generating device from said charging mode to said non-charging mode when the measured state of charge of said first energy storage device satisfies a first predetermined state of charge condition; and

(d) providing an equalization current from said second energy storage device to said first energy storage device while said power generating device is in said non-charging mode until the measured state of charge of said first energy storage device reaches approximately its full storage capacity.