Method for charging a battery with maximum power tracking

• US 6,255,804 B1
• Filed: 03/24/2000
• Issued: 07/03/2001
• Est. Priority Date: 09/18/1998
• Status: Expired due to Fees

• Current Assignee: Fire Wind & Rain Technologies LLC
• Original Assignee: Fire Wind & Rain Technologies LLC
• Inventors: Schlanger, William J., Herniter, Marc E.
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/535,362
• Time in Patent Office: 466 Days
• Field of Search: 320/101, 320/123, 320/137, 320/139, 320/140, 320/143, 320/163, 320/DIG. 28, 320/DIG. 29, 323/299, 323/303, 323/906, 136/290, 136/291, 136/293
• US Class Current: 320/137
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

Apparatus and attendant methodology for extracting maximum power from an energy source, such as a photo voltaic panel, an array of photo voltaic panels, or a windmill and delivering that power to a battery or an array of batteries is disclosed. The apparatus determines the maximum operating point of the energy source, and circuits and circuit topologists are presented for extracting the energy. The apparatus eliminates the problem of finding local maximum points, and problems attendant variations of the absolute maximum power point as a function of temperature, insolation, array construction, and photo voltaic panel manufacturing tolerances. The energy source supplies power in the form of a voltage and charges the batteries with a controllable current source.

Claims

1. A method for charging a battery from an electrical energy source, comprising the steps of:

(a) tracing out substantially an entire I-V characteristic of the energy source to determine a voltage and current level that yield the maximum power which can be drawn from the energy source; and

(b) drawing the current level from the energy source that yields the maximum power to charge the battery.

2. The method as set forth in claim 1 wherein the energy source is a variable energy source.

3. The method as set forth in claim 2 wherein the energy source includes a photo voltaic panel.

4. The method as set forth in claim 1 wherein the step of tracing out the entire I-V characteristic of the energy source is performed periodically.

5. The method as set forth in claim 1 comprising the additional steps of:

(a) sensing for changes in the voltage level of the energy source during the step of drawing the current level from the energy source;

(b) tracing out a portion of the I-V characteristic of the energy source in response to sensing of a change in the voltage level of the energy source to determine a new voltage and current level that yield the maximum power which can be drawn from the energy source; and

(c) drawing the new current level from the energy source that yields the maximum power to charge the battery.

6. The method as set forth in claim 5 wherein the step of tracing out a portion of the I-V characteristic of the energy source in response to sensing of a change in the voltage level of the energy source includes the steps of:

(a) if the voltage level of the energy source is sensed to have increased, tracing out a portion of the I-V characteristic for increasing current levels starting at the current level being drawn from the energy source to charge the battery and ending when the energy source voltage goes below a preset minimum operating voltage; and

(b) if the voltage level of the energy source is sensed to have decreased, tracing out a portion of the I-V characteristic for decreasing current levels starting at the current level being drawn from the energy source to charge the battery and ending when the power produced by the energy source falls below a specified percent of the maximum power observed during the sweep.

7. A battery charger for charging a battery from an electrical energy source, comprising:

(a) means for tracing out substantially en entire I-V characteristic of the energy source to determine a voltage and current level that yield the maximum power which can be drawn from the energy source; and

(b) means for drawing the current level from the energy source that yields the maximum power to charge the battery.

8. The battery charger as set forth in claim 7 wherein the energy source is a variable energy source.

9. The battery charger as set forth in claim 8 wherein the energy source includes a photo voltaic panel.

10. The battery charger as set forth in claim 7 wherein the means for tracing out the entire I-V characteristic of the energy source includes means for tracing out the entire I-V characteristic of the energy source periodically.

11. The battery charger as set forth in claim 7 comprising additionally:

(a) means for sensing for changes in the voltage level of the energy source while drawing the current level from the energy source;

(b) means for tracing out a portion of the I-V characteristic of the energy source in response to sensing of a change in the voltage level of the energy source to determine a new voltage and current level that yield the maximum power which can be drawn from the energy source; and

(c) means for drawing the new current level from the energy source that yields the maximum power to charge the battery.

12. The battery charger as set forth in claim 11 wherein the means for tracing out a portion of the I-V characteristic of the energy source in response to sensing of a change in the voltage level of the energy source includes:

(a) means for determining if the voltage level of the energy source is sensed to have increased and for tracing out a portion of the I-V characteristic for increasing current levels starting at the current level being drawn from the energy source to charge the battery and ending when the energy source voltage goes below a preset minimum operating voltage; and

(b) means for determining if the voltage level of the energy source is sensed to have decreased and for tracing out a portion of the I-V characteristic for decreasing current levels starting at the current level being drawn from the energy source to charge the battery and ending when the power produced by the energy source falls below a specified percent of the maximum power observed during the sweep.

13. A method for charging a battery with a current mode feedback from an energy source providing electrical power, said method comprising the steps of:

(a) providing a first feedback signal commensurate with the instantaneous switch current of a switch having a controllable duty cycle;

(b) further providing a second feedback signal commensurate with the average current flowing to the battery; and

(c) generating a gate signal with a control circuit responsive to the first and second feedback signals, the voltage at the energy source and the voltage at the battery to control the duty cycle of the switch and maximize the power level delivered by the energy source to the battery.

14. The method as set forth in claim 13 including the step of passing the current generated by the energy source through an inductor to the switch.

15. The method as set forth in claim 13 including the step of producing the energy source from a plurality of photo voltaic panels.

16. The method as set forth in claim 13 including the step of producing the energy source from a photo voltaic array.

17. A method for charging a battery with constant current from an energy source providing electrical power, said method comprising the steps of:

(a) providing a first feedback signal commensurate with the instantaneous switch current of a switch having a controllable duty cycle;

(b) further providing a second feedback signal commensurate with the current drawn from the energy source; and

(c) generating a gate signal with a control circuit responsive to the first and second feedback signals, the voltage at the energy source, and the voltage at the battery to control the duty cycle of the switch and maximize the power level delivered by the energy source.

18. The method as set forth in claim 17 including the step of passing the current generated by the energy source through an inductor to the switch.

19. The method as set forth in claim 17 including the step of producing the energy source from a plurality of photo voltaic panels.

20. The method as set forth in claim 17 including the step of producing the energy source from a photo voltaic array.

21. A method for charging a battery from an energy source which energy source may have a voltage lower than the battery voltage, said method comprising the steps of:

(a) providing a first feedback signal commensurate with the instantaneous switch current of a switch having a controllable duty cycle;

(b) further providing a second feedback signal commensurate with the current drawn from the energy source drawn through a transformer having a primary coil in series with the energy source and the switch and a secondary coil in series with the battery; and

(c) generating a gate signal with a control circuit responsive to the first and second feedback signals, the voltage at the energy source and the voltage at the battery to control the duty cycle of the switch.

22. The method as set forth in claim 21 wherein said step of further providing includes the step of developing the second feedback signal with a current monitor.

23. The method as set forth in claim 21 including the step of producing the energy source from a photo voltaic array having a voltage less than the voltage of the battery.

24. The method as set forth in claim 21 including the step of producing the energy source from a plurality of photo voltaic panels connected in series and wherein the battery includes a plurality of batteries connected in series.

25. A method for charging a battery from an energy source which may have a voltage lower than the battery, said method comprising the steps of:

(a) connecting the energy source across the center tap of the primary coil of a transformer and ground;

(b) interconnecting one end of the primary coil with a first switch through a resistor to ground;

(c) further interconnecting another end of the primary coil with a second switch through the resistor to ground;

(d) further connecting the battery across the center tap of the secondary coil of the transformer and the opposed ends of the secondary coil through diodes;

(e) providing a first feedback signal commensurate with the instantaneous switch current;

(f) further providing a second feedback signal commensurate with the current flowing to the battery; and

(g) generating first and second gate signals with a control circuit responsive to the first and second feedback signals, the voltage at the energy source and the voltage at the battery to control the duty cycles of the first and second switches, respectively, and maximize the power level delivered by the energy source to the battery.

26. The method as set forth in claim 25 including the step of producing the energy source from a photo voltaic array having a voltage less than the voltage of the battery.

27. The method as set forth in claim 26 including the step of producing the energy source from a plurality of photo voltaic panels connected in series and wherein the battery includes a plurality of batteries connected in series.

28. The method as set forth in claim 25 wherein said step of further providing includes the step of developing the second feedback signal with a current monitor.

29. A method for charging a battery from an energy source which may have a voltage lower than the battery, said method comprising the steps of:

(a) connecting the energy source across the center tap of a primary coil of a transformer and ground;

(b) interconnecting one end of the primary coil with a first switch through a resistor to ground;

(c) further interconnecting another end of the primary coil with a second switch through the resistor to ground;

(d) further connecting the battery across the center tap of a secondary coil of the transformer and the opposed ends of the secondary coil through diodes;

(e) providing a first feedback signal commensurate with the instantaneous switch current;

(f) further providing a second feedback signal commensurate with the current flowing from the energy source; and

(g) generating first and second gate signals with a control circuit responsive to the first and second feedback signals, the voltage at the energy source and the voltage at the battery to control the duty cycle of the first and second switches, respectively, and maximize the power level delivered by the energy source to the battery.

30. The method as set forth in claim 29 including the step of producing the energy source with a photo voltaic array having a voltage less than the voltage of the battery.

31. The method as set forth in claim 29 wherein said step of further providing comprises the step of developing the second feedback signal with a current monitor.

32. A method for charging a battery from an energy source which may have a voltage lower than the battery, said method comprising the steps of:

(a) connecting the energy source across a center tap of a primary coil of a transformer and a ground common to the energy source and the battery;

(b) interconnecting one end of the primary coil with a first switch through a resistor to ground;

(c) further interconnecting another end of the primary coil with a second switch through the resistor to ground;

(d) connecting the battery to opposed ends of a secondary coil of the transformer through diodes and to the ground common with the energy source;

(e) providing a first feedback signal commensurate with the instantaneous switch current;

(f) further providing a second feedback signal commensurate with the current flowing to the battery; and

(g) generating first and second gate signals with a control circuit responsive to said first and second feedback signals, the voltage at the energy source and the voltage at the battery to control the duty cycles of the first and second switches, respectively, and maximize the power level delivered by the energy source to the battery.

33. The method as set forth in claim 32 including the step of producing the energy source with a photo voltaic array having a voltage less than the voltage of the battery.

34. The method as set forth in claim 32 wherein said step of further providing comprises the step of developing the second feedback signal with a current monitor.

35. A method for charging a battery from an energy source which may have a voltage lower than the battery, said method comprising the steps of:

(a) connecting the energy source across a center tap of a primary coil of a transformer and a ground common to the energy source and the battery;

(b) interconnecting one end of the primary coil with a first switch through a resistor to ground;

(c) further interconnecting another end of the primary coil with a second switch through the resistor to ground;

(d) further connecting the battery to opposed ends of a secondary coil of the transformer through diodes and to the ground common with the energy source;

(e) providing a first feedback signal commensurate with the instantaneous switch current;

(f) further providing a second feedback signal commensurate with the current flowing from the energy source; and

(g) generating first and second gate signals with a control circuit responsive to said first and second feedback signals, the voltage at the energy source and the voltage at the battery to control the duty cycles of the first and second switches, respectively, and maximize the power level delivered by the energy source to the battery.

36. The method as set forth in claim 35 including the step of producing the energy source with a photo voltaic array having a voltage less than the voltage of the battery.

37. The method as set forth in claim 36 wherein said step of further providing comprises a step of developing the second feedback signal with a current monitor.