Equalizer system and method for series connected energy storing devices

• US 5,952,815 A
• Filed: 07/25/1997
• Issued: 09/14/1999
• Est. Priority Date: 07/25/1997
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company), Avestor (Bolloré SE), Bathium Canada Inc. (Bolloré SE)
• Original Assignee: 3M Company, HYDRO-Quebec Corporation
• Inventors: Knudson, Orlin B., Morin, Andre, Comte, Christophe, Ross, Guy, Rouillard, Jean, Hagen, Ronald A.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TOATLEY, GREGORY J
• Application Number:
  US08/900,607
• Time in Patent Office: 781 Days
• Field of Search: 320/116, 320/122, 320/162, 320/160, 320/139, 320/125
• US Class Current: 320/116
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]

Abstract

An apparatus and method for regulating the charge voltage of a number of electrochemical cells connected in series is disclosed. Equalization circuitry is provided to control the amount of charge current supplied to individual electrochemical cells included within the series string of electrochemical cells without interrupting the flow of charge current through the series string. The equalization circuitry balances the potential of each of the electrochemical cells to within a pre-determined voltage setpoint tolerance during charging, and, if necessary, prior to initiating charging. Equalization of cell potentials may be effected toward the end of a charge cycle or throughout the charge cycle. Overcharge protection is also provided for each of the electrochemical cells coupled to the series connection. During a discharge mode of operation in accordance with one embodiment, the equalization circuitry is substantially non-conductive with respect to the flow of discharge current from the series string of electrochemical cells. In accordance with another embodiment, equalization of the series string of cells is effected during a discharge cycle.

Claims

1. A method of charging series connected thin-film electrochemical cells, comprising:

supplying a charge current to the thin-film electrochemical cells to cause a voltage to increase in each of the series connected electrochemical cells; and

controlling, in response to the voltage of a particular series connected electrochemical cell reaching a voltage limit, the charge current through the particular electrochemical cell without interrupting the charge current supplied to other ones of the electrochemical cells.

2. The method of claim 1, wherein controlling the charge current comprises preventing overcharging of the particular electrochemical cell.

3. The method of claim 1, wherein controlling the charge current further comprises diverting the charge current from the particular electrochemical cell to the other electrochemical cells.

4. The method of claim 1, wherein controlling the charge current further comprises alternately directing the charge current between the particular electrochemical cell and a current path that bypasses the particular electrochemical cell.

5. The method of claim 1, wherein controlling the charge current further comprises modulating a switch connected in parallel with the particular electrochemical cell to direct the charge current between the particular electrochemical cell and a bypass current path in parallel with the particular electrochemical cell.

6. The method of claim 5, wherein controlling the charge current comprises modulating the switch using either a pulse width modulation or a frequency with modulation technique.

7. The method of claim 1, wherein supplying the charge current comprises:

supplying the charge current at a substantially constant level to the electrochemical cells until the particular electrochemical cell reaches the voltage limit; and

applying a substantially constant charge voltage at a first voltage level across the electrochemical cells in response to the particular electrochemical cell reaching the voltage limit.

8. The method of claim 7, wherein applying the substantially constant charge voltage comprises determining the first voltage level by summing the voltages of the electrochemical cells.

9. The method of claim 7, further comprising applying a substantially constant charge voltage at a second voltage level across the electrochemical cells prior to supplying the charge current at the substantially constant level to the electrochemical cells.

10. The method of claim 9, further comprising:

determining a voltage of each of the series connected electrochemical cells;

computing a voltage difference between a maximum voltage and a minimum voltage of the electrochemical cell voltages; and

setting the second voltage level to the maximum voltage in response to the voltage difference exceeding a pre-established limit.

11. The method of claim 1, further comprising:

determining a voltage of each of the series connected electrochemical cells;

determining a maximum voltage and a minimum voltage of the electrochemical cell voltages; and

applying a constant charge voltage at the maximum voltage across the electrochemical cells prior to supplying the charge current at the substantially constant level to the electrochemical cells.

12. The method of claim 1, further comprising providing the thin-film electrochemical cells in an enclosed housing, wherein controlling the charge current further comprises controlling, in-situ the enclosed housing, the charge current through the particular electrochemical cell without interrupting the charge current supplied to other ones of the electrochemical cells.

13. The method of claim 1, wherein controlling the charge current comprises digitally controlling the charge current through the particular electrochemical cell.

14. The method of claim 1, wherein the charge current is greater than 200 amperes.

15. A voltage equalization apparatus coupled to a charging unit that provides a charge current, the voltage equalization apparatus comprising:

a plurality of thin-film electrochemical cells connected in series;

a plurality of equalizer devices, each of the equalizer devices being coupled to one of the plurality of electrochemical cells and comprising;

a detector coupled to a corresponding one of the electrochemical cells that senses a voltage of the corresponding electrochemical cell, the detector producing an output signal related to the magnitude of the sense voltage;

a signal generator coupled to the detector that produces a control signal in response to the detector output signal; and

a bypass circuit coupled to the corresponding electrochemical cell and the signal generator, the bypass circuit, in response to the control signal, conducting at least a portion of the charge current so as to bypass the corresponding electrochemical cell without interrupting the charge current provided to other ones of the plurality of electrochemical cells.

16. The apparatus of claim 15, wherein the detector further comprises a comparator that determines a voltage difference between the voltage of the corresponding electrochemical cell and a reference voltage, the detector output signal being related to the voltage difference.

17. The apparatus of claim 15, wherein the signal generator comprises one of a frequency modulation circuit or a pulse width modulation circuit.

18. The apparatus of claim 15, wherein the signal generator further comprises a voltage controlled oscillator coupled to the detector and to a monostable device, the monostable device being coupled to the bypass circuit.

19. The apparatus of claim 15, wherein the signal generator further comprises:

a voltage controlled oscillator, coupled to the detector, that produces an output signal having a frequency that varies in relation to a magnitude of the detector output signal; and

a monostable device coupled to the voltage controlled oscillator and the bypass circuit that, in response to the output signal of the voltage controlled oscillator, produces the control signal having a fixed pulse width.

20. The apparatus of claim 15, wherein the bypass circuit is coupled in parallel with the corresponding electrochemical cell and comprises an inductor coupled to a transistor, the inductor and transistor defining a bypass current path through which the charge current portion is conducted in response to the control signal.

21. The apparatus of claim 15, wherein the plurality of electrochemical cells provides power for the voltage equalization apparatus.

22. The apparatus of claim 15, wherein the plurality of electrochemical cells comprises prismatic thin-film electrochemical cells.

23. The apparatus of claim 15, wherein the plurality of electrochemical cells comprises energy storing modules, each of the energy storing modules comprising a plurality of thin-film electrochemical cells.

24. The apparatus of claim 15, wherein the plurality of electrochemical cells comprises a plurality of electrochemical cells arranged in a parallel relationship to form a plurality of electrically independent cell packs, the plurality of electrically independent cell packs being arranged in a series relationship.

25. The apparatus of claim 15, further comprising an enclosed housing separate from the charge unit, wherein the thin-film electrochemical cells and the equalizer devices are respectively provided in the enclosed housing.

26. The apparatus of claim 15, wherein the charge current is greater than 200 amperes.

27. A voltage regulating apparatus coupled to a charging unit that provides a charge current, the voltage regulating apparatus comprising:

a plurality of thin-film electrochemical cells connected in series;

a plurality of regulating circuits, each of the regulating circuits being coupled to one of the plurality of electrochemical cells and comprising;

a sensor that senses a voltage of a corresponding one of the electrochemical cells, the sensor producing an output signal related to the magnitude of the sense voltage of the corresponding electrochemical cell;

a processor coupled to the sensor that determines a voltage difference between the sense voltage and a reference voltage, the processor producing a difference signal related to the magnitude of the voltage difference;

a signal generator coupled to the processor that produces a digital control signal in response to the difference signal; and

a bypass circuit coupled to the signal generator and the corresponding electrochemical cell, the bypass circuit, in response to the digital control signal, diverting at least a portion of the charge current to other ones of the plurality of electrochemical cells.

28. The apparatus of claim 27, wherein the signal generator produces one of a frequency varying control signal or a time varying control signal.

29. The apparatus of claim 28, wherein the bypass circuit comprises a bypass switch which modulates between a conducting state and a non-conducting state in response to the control signal, the bypass switch diverting the charge current portion to other ones of the plurality of electrochemical cells when in the conducting state.

30. The apparatus of claim 29, wherein the bypass switch diverts the charge current portion so as to prevent overcharging of the corresponding electrochemical cell.

31. The apparatus of claim 27, wherein the charge current is greater than 200 amperes.

32. A voltage regulating apparatus coupled to a charging unit that provides a charge current, the voltage regulating apparatus comprising:

a plurality of energy storing devices connected in series; and

a plurality of regulating circuits, each of the regulating circuits being coupled to one of the plurality of energy storing devices and comprising a frequency modulated switching circuit or a pulse modulated switching circuit, a particular one of the regulating circuits shunting at least a portion of the charge current from a corresponding energy storing device to other ones of the plurality of energy storing devices in response to the corresponding energy storing device reaching a voltage setpoint.

33. The apparatus of claim 32, wherein each of the regulating circuits operates autonomously relative to other ones of the plurality of regulating circuits.

34. The apparatus of claim 32, wherein each of the regulating circuits comprises a processor that controls shunting of the charge current portion from the corresponding energy storing device to the other ones of the plurality of energy storing devices.

35. The apparatus of claim 34, further comprising a system processor coupled to each of the regulating circuit processors.

36. The apparatus of claim 32, wherein the particular regulating circuit shunts the charge current portion from the corresponding energy storing device so as to prevent overcharging of the corresponding energy storing device.

37. The apparatus of claim 32, wherein the energy storing devices comprise one or more thin-film electrochemical cells.

38. A method of charging series connected energy storing devices, comprising:

supplying a charge current to the energy storing devices to cause a voltage to increase in each of the series connected energy storing devices; and

in response to the voltage of a particular series connected energy storing device reaching a voltage limit, modulating, using either a phase modulation technique or a frequency modulation technique, a switch connected in parallel with the particular energy storing device to direct the charge current between the particular energy storing device and a bypass current path in parallel with the particular energy storing device.

39. The method of claim 38, wherein the phase modulation technique comprises a pulse width modulation technique and the frequency modulation technique comprises a frequency with modulation technique.

40. The method of claim 38, wherein the energy storing devices comprise one or more thin-film electrochemical cells.

41. A method of charging series connected thin-film electrochemical cell devices, comprising:

determining a voltage of each of the series connected thin-film electrochemical cell devices;

computing a voltage difference between a maximum voltage and a minimum voltage of the thin-film electrochemical cell device voltages;

applying, in response to the voltage difference exceeding a pre-established limit, a substantially constant charge voltage at a first voltage level equivalent to the maximum voltage across the thin-film electrochemical cell devices;

supplying, subsequent to applying the substantially constant charge voltage at the first voltage level, a charge current at a substantially constant level to the thin-film electrochemical cell devices to cause a voltage to increase in each of the series connected thin-film electrochemical cell devices until the voltage of a particular series connected thin-film electrochemical cell device reaches a voltage limit; and

applying, in response to the voltage of the particular thin-film electrochemical cell device reaching the voltage limit, a substantially constant charge voltage at a second voltage level across the thin-film electrochemical cell devices.

42. The method of claim 41, further comprising determining the second voltage level by summing the voltages of the thin-film electrochemical cell devices.

43. The method of claim 41, wherein each of the thin-film electrochemical cell devices comprises one or more thin-film electrochemical cells.

44. A voltage equalization apparatus for an energy storing system, the voltage equalization apparatus coupled to a charging source that provides a charge current, the voltage equalization apparatus comprising:

a plurality of thin-film electrochemical cell devices connected in series;

a plurality of equalizer devices, each of the equalizer devices being coupled to one of the plurality of thin-film electrochemical cell devices and operating autonomously with respect to other ones of the plurality of equalizer devices, each of the equalizer devices comprising;

an analog monitor circuit including first and second voltage inputs coupled across a corresponding one of the thin-film electrochemical cell devices, the analog monitor circuit sensing a voltage of the corresponding thin-film electrochemical cell device; and

a power transistor having a gate coupled to an output of the analog monitor circuit, and a collector and an emitter coupled across the corresponding thin-film electrochemical cell device so as to define a bypass current path, the analog monitor circuit, in response to the sensed voltage, controlling the gate of the power transistor so as to moderate a flow of current through the bypass current path;

wherein power dissipated by the power transistor is linearly related to the sensed voltage of the corresponding thin-film electrochemical cell device and the charge current.

45. The apparatus of claim 44, wherein the power dissipated by the power transistor is directly proportional to the sensed voltage of the corresponding thin-film electrochemical cell device and the charge current of each of the equalizer devices.

46. The apparatus of claim 44, wherein substantially all heat associated with each of the equalizer devices is generated by the power transistor.

47. The apparatus of claim 44, wherein the analog monitor circuit controls the gate of the power transistor in accordance with a super zener diode characteristic curve in response to the sensed voltage.

48. The apparatus of claim 44, wherein the analog monitor circuit comprises a remote sensing voltage amplifier and a current amplifier.

49. The apparatus of claim 44, wherein each of the equalizer devices receives a setpoint control corresponding to a voltage setpoint from a controller.

50. The apparatus of claim 44, wherein each of the equalizer devices is powered by the corresponding thin-film electrochemical cell device.

51. The apparatus of claim 50, wherein:

offset voltages are induced between the equalizer devices; and

a voltage setpoint of each of the equalizer devices is transmitted from a common reference circuit by a current source which is independent with respect to the offset voltage.

52. The apparatus of claim 51, wherein the sensed voltage of each of the thin-film electrochemical cells is transmitted to a common measuring circuit using a current source that is proportional to the corresponding thin-film electrochemical cell device voltage.

53. The apparatus of claim 44, wherein each of the thin-film electrochemical cell devices comprises one or more thin-film electrochemical cells.

54. The apparatus of claim 44, wherein the charge current is greater than 200 amperes.