Power slope targeting for DC generators

• US 7,087,332 B2
• Filed: 07/31/2002
• Issued: 08/08/2006
• Est. Priority Date: 07/31/2002
• Status: Expired due to Fees

• Current Assignee: Sustainable Living Systems
• Original Assignee: Sustainable Living Systems
• Inventors: Harris, Brent Earle
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US10/210,545
• Publication Number:
  US 20040021445A1
• Time in Patent Office: 1,469 Days
• Field of Search: 320/126, 320/124, 320/133, 320/134, 320/136, 320/33, 320/48, 320/101, 323/299, 323/295, 323/275, 323/222, 323/304, 363/95, 363/65, 363/71, 376/333, 376/210, 376/216, 429/13, 429/22, 429/23, 429/17, 429/9, 429/30, 429/19, 429/21, 429/34, 180/65.2, 180/65.5
• US Class Current: 429/432
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell

Abstract

A simple feedback control loop, in conjunction with an improved maximum power point tracking intermediate controller, can be used ensure efficient operation of a power generator. The improved maximum power point tracking controller operates the generator at its maximum allowable power point. A power output of the generator is measured and compared to a power output setpoint. Operating characteristics of the generator are then adjusted to cause the maximum allowable power point and measured power output to approximate the power output setpoint. Although applicable to all types of generators, this is particularly beneficial in fuel cell generator systems and other systems where damage to generator components can occur if operated above a maximum allowable power output level. In other systems, the maximum allowable power output may approach or equal a maximum power point (or maximum possible power point).

Claims

1. A method comprising:

determining a maximum allowable power output of a fuel cell by determining a point on a power curve of the fuel cell at which additional power output may cause damage to the fuel cell, a slope of the power curve at the point characterized as non-zero;

measuring a power output from the fuel cell;

adjusting one or more electrical parameters of the fuel cell to cause an actual power output of the fuel cell to approximate the maximum allowable power output by controlling a rate of fuel input into the fuel cell to control the power output thereof.

2. The method of claim 1, wherein adjusting one or more electrical parameters of the fuel cell comprises controlling a voltage of the fuel cell.

3. The method of claim 1, wherein determining the maximum allowable power output of the fuel cell comprises varying a voltage level of the fuel cell while measuring a power output thereof.

4. The method of claim 1, wherein determining the maximum allowable power output and adjusting one or more parameters of the fuel cell to obtain the maximum allowable power output comprises repeatedly decreasing a voltage level of the fuel cell until the measured power output begins to decrease at a rate greater than the target slope then increasing the voltage level of the fuel cell until the measured power output begins to increase at a rate less than the target slope.

5. The method of claim 1, wherein determining the maximum allowable power output comprises tracing a polarization curve of the fuel cell for a current set of operating conditions and identifying a point on the polarization curve having a target slope that corresponds to the maximum allowable power output.

6. The method of claim 1, wherein determining the maximum allowable power output comprises analyzing DC voltage and current ripple of the fuel cell.

7. The method of claim 1, wherein controlling the rate of fuel input into the fuel cell comprises increasing the rate of fuel input to increase power output and decreasing the rate of fuel input to decrease power output.

8. A method comprising:

identifying a maximum allowable power point (MAPP) for a fuel cell by determining a target slope of a power curve corresponding to a point above which damage to the fuel cell may result from increased power output, the MAPP representing a first power output from the fuel cell that is less than a second power output that corresponds to a maximum power point (MPP) of the fuel cell; and

operating the fuel cell to generate a third power output that is approximately equal to the first power output.

9. The method of claim 8, wherein operating the fuel cell to generate the third power output comprises measuring a slope of the power curve at a present operating point;

comparing the measured slope to the target slope; and

adjusting one of the fuel cell operating parameters to cause the measured slope to approximate the target slope.

10. The method of claim 9, wherein adjusting one or more characteristics of the fuel cell comprises adjusting the voltage of the fuel cell.

11. A method comprising:

determining the operating characteristics of a fuel cell system;

identifying a maximum allowable power point (MAPP) for the fuel cell system using the operating characteristics of the fuel cell system, the MAPP less than a maximum power point (MPP) where a maximum power output may be obtained from the fuel cell system, the MAPP representing a power output level above which damage would result to the fuel cell system; and

operating the fuel cell system at or about the MAPP.

12. The method of claim 11, further comprising measuring a power output from the fuel cell system.

13. The method of claim 12, further comprising controlling a rate of fuel delivery to the fuel cell system to control a power output of the fuel cell system.

14. The method of claim. 12, wherein the maximum allowable power point corresponds to a target slope on a power curve for a given set of operating characteristics.

15. A circuit comprising:

a power measuring device configured to measure a power output from a fuel cell system;

a comparison circuit configured to compare the power output with a maximum allowable power point (MAPP) of the fuel cell system, the MAPP less than a maximum power point (MPP) of the fuel cell system, the MAPP corresponding to a power level above which damage may result to the fuel cell; and

a fuel flow controller configured to control a feed rate of reactants to the fuel cell based on a difference between the power output and the power setpoint.

16. The circuit of claim 15, further comprising a power slope targeting controller configured to receive a power slope target corresponding to the MAPP.

17. The circuit of claim 15, wherein the comparison circuit comprises an output power controller configured to produce a control signal based on a power output error corresponding to a measured difference between the power output and the MAPP.

18. The circuit of claim 17, wherein the fuel flow controller operates in response to the control signal.

19. A method comprising:

evaluating characteristics of a fuel cell system to determine a target slope on a curve, the curve representing the characteristics of the fuel cell system, the target slope not necessarily zero, the curve selected from the group consisting of a power curve and a polarization curve;

using the target slope to determine a maximum allowable power point (MAPP) for a set of fuel cell system operating conditions, the MAPP representing the greatest power output that may be obtained from the fuel cell system without damaging or impairing the fuel cell system, the MAPP not necessarily equal to a maximum power point (MPP) for the fuel cell system; and

controlling the fuel cell system to generate a power output that approximates the MAPP.

20. The method of claim 19, wherein controlling the fuel cell system to generate a power output that approximates the MAPP comprises:

measuring the power output from the fuel cell system;

generating a control signal in response to a measured difference between the power output and the MAPP; and

adjusting the characteristics of the fuel cell system in response to the control signal to cause the power output to approach the MAPP.

21. The method of claim 19, wherein controlling the fuel cell system to generate a power output that approximates the MAPP comprises:

measuring the power output from the fuel cell system;

comparing the power output from the fuel cell system with the MAPP;

generating a control signal based on a measured difference between the power output and the MAPP; and

causing the power output to approach the MAPP by adjusting a rate of fuel flow through a fuel flow controller in response to the control signal.

22. The method of claim 21, wherein using the target slope to determine the MAPP comprises analyzing the characteristics of the fuel cell system to determine a point along the curve above which damage to the fuel cell system may result from a further increase in the voltage of the fuel cell system.

23. A generator comprising:

a power generating device that includes a fuel cell;

a power measuring device configured to measure a power output from the power generating device;

a power slope targeting controller configured to determine a maximum allowable power point (MAPP) for the generator based on a power slope target for the generator, the power slope target not necessarily zero;

a comparator configured to compare the power output with a power output setpoint and to generate a control signal based on a difference between the power output setpoint and the power output; and

a power controller configured to control the power output from the generator in response to the control signal from the comparator, the power controller including a flow controller configured to control a flow rate of fuel into the fuel cell based on the control signal.

24. The generator of claim 23, wherein the flow controller is configured to increase the flow rate of fuel into the fuel cell when the control signal indicates that the measured power output is below the power output setpoint.

25. The generator of claim 23, wherein the flow controller is configured to decrease the flow rate of fuel into the fuel cell when the control signal indicates that the measured power output is above the power output setpoint.

26. A fuel cell generator system comprising:

a fuel cell;

a power output measuring device configured to measure a power output from the fuel cell;

a power control system configured to operate the fuel cell at its maximum allowable power point (MAPP), the MAPP representing a power level above which damage may result to the fuel cell, the MAPP determined based on a target slope on a curve representing the fuel cell operating conditions, the target slope characterized as non-zero;

a comparator configured to compare the power output with a power output setpoint and configured to generate a control signal based upon the comparison; and

a flow controller configured to control a flow rate of fuel into the fuel cell in response to the control signal.

27. The fuel cell generator system of claim 26, wherein the fuel cell generator system is connected to a grid.

28. The fuel cell generator system of claim 26, wherein the flow controller is configured to increase the flow rate of fuel into the fuel cell when the power output is below the power output setpoint.

29. The fuel cell generator system of claim 26, wherein the flow controller is configured to decrease the flow rate of fuel into the fuel cell when the power output is above the power output setpoint.

30. The fuel cell generator system of claim 26, wherein the MAPP is determined by identifying a target slope on a power curve for a standard set of operating conditions corresponding to the MAPP and by determining a point on the power curve that corresponds to the target slope.