Method and apparatus for multiple mode control of voltage from a fuel cell system

• US 7,144,646 B2
• Filed: 12/14/2001
• Issued: 12/05/2006
• Est. Priority Date: 12/14/2001
• Status: Expired due to Fees

• Current Assignee: Ballard Power Systems Corporation (Superior Plus Corporation)
• Original Assignee: Ballard Power Systems Corporation (Superior Plus Corporation)
• Inventors: Pearson, Martin T.
• Primary Examiner(s): Ryan, Patrick Joseph
• Assistant Examiner(s): Martin, Angela J.
• Application Number:
  US10/017,462
• Publication Number:
  US 20030113599A1
• Time in Patent Office: 1,817 Days
• Field of Search: 429/23, 429/9, 429/13, 429/22, 429/21, 320/101, 320/118, 320/122, 320/134, 320/152, 320/148, 320/151, 320/157, 320/149, 307/66
• US Class Current: 429/428
• CPC Class Codes: H01M 16/006 of fuel cells with rechargeable batteries
• CPC Class Codes: H01M 8/04007 related to heat exchange
• CPC Class Codes: H01M 8/04119 with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying
• CPC Class Codes: H01M 8/04373 of auxiliary devices, e.g. reformers, compressors, burners
• CPC Class Codes: H01M 8/04567 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/04589 of fuel cell stacks
• CPC Class Codes: H01M 8/04597 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/04888 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/0491 of fuel cell stacks
• CPC Class Codes: H01M 8/04917 of auxiliary devices, e.g. batteries, capacitors
• CPC Class Codes: H01M 8/04992 characterised by the implementation of mathematical or computational algorithms, e.g. feedback control loops, fuzzy logic, neural networks or artificial intelligence
• CPC Class Codes: H02J 1/082 Plural DC voltage, e.g. DC supply voltage with at least two different DC voltage levels
• CPC Class Codes: H02J 13/00012 using an auxiliary transmission line
• CPC Class Codes: H02J 13/00016 using a wired telecommunication network or a data transmission bus
• CPC Class Codes: H02J 13/00018 using phone lines
• CPC Class Codes: H02J 2300/20 The dispersed energy generation being of renewable origin
• CPC Class Codes: H02J 2300/30 The power source being a fuel cell
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: Y02E 40/70 Smart grids as climate change mitigation technology in the energy generation sector
• CPC Class Codes: Y02E 60/00 Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
• CPC Class Codes: Y02E 60/10 : Energy storage using batteries
• CPC Class Codes: Y02E 60/50 : Fuel cells
• CPC Class Codes: Y04S 10/12 : Monitoring or controlling equipment for energy generation units, e.g. distributed energy generation [DER] or load-side generation
• CPC Class Codes: Y04S 10/123 : the energy generation units being or involving renewable energy sources
• CPC Class Codes: Y04S 40/124 : using wired telecommunication networks or data transmission busses

Abstract

A fuel cell system determines each of a battery charging current error, a battery voltage error, and a stack current error. The fuel cell system regulates current through a series pass element in response to a greater of the determined errors. Thus, the fuel cell system operates in three modes: battery voltage limiting mode, stack current limiting mode and battery charging current limiting mode. Additionally, there can be a fourth “saturation” mode where the stack voltage V_S drops below the battery voltage V_B as the load pulls even more current. Individual fuel cell systems can be combined in series and/or parallel to produce a combined fuel cell system having a desired output voltage and current.

Claims

1. A control circuit for a fuel cell system having a fuel cell stack and a battery, the control circuit comprising:

a series pass element electrically coupleable between at least a portion of the fuel cell stack and a portion of the battery; and

a regulating circuit for linearly regulating current through the series pass element in response to a greater of a battery charging current error, a battery voltage error and a stack current error wherein the regulating circuit comprises;

a battery charging current error integrator having a first input coupled to receive a battery charging current signal proportional to a battery charging current, a second input coupled to receive a battery charging current limit signal proportional to a battery charging current limit, and an output to supply a battery charging current error signal proportional to a difference between the battery charging current and the battery charging current limit;

a battery voltage error integrator having a first input coupled to receive a battery voltage signal proportional to a battery voltage, a second input coupled to receive a battery voltage limit signal proportional to a battery voltage limit, and an output to supply a battery voltage error signal proportional to a difference between the battery voltage and the battery voltage limit;

a stack current error integrator having a first input coupled to receive a stack current signal proportional to a stack current, a second input coupled to receive a stack current limit signal proportional to a stack current limit, and an output to supply a stack current error signal proportional to a difference between the stack current and the stack current limit; and

an OR circuit coupled to the output of each of the error integrators to select a greater one of the error signals from the error integrators.

2. A control circuit for a fuel cell system having a fuel cell stack and a battery, the control circuit comprising:

a series pass element electrically coupleable between at least a portion of the fuel cell stack and a portion of the battery wherein the series pass element comprises a transistor having a first terminal, a second terminal and a control terminal, the first and the second terminals coupleable between the fuel cell stack and the battery; and

a regulating circuit for linearly regulating current through the series pass element in response to a greater of a battery charging current error, a battery voltage error and a stack current error wherein the regulating circuit comprises;

a level shifter coupled to receive the greater of the battery charging current error, the battery voltage error and the stack current error; and

a charge pump coupled to the control terminal of the transistor by way of the level shifter.

3. A control circuit for a fuel cell system, comprising:

a series pass element;

a blocking diode electrically coupled in series with the series pass element; and

a regulating circuit coupled to the series pass element to regulate a current through the series pass element in proportion to at least a greater of a difference between a battery charging current and a battery charging current limit, a difference between a battery voltage and a battery voltage limit, and a difference between a stack current and a stack current limit wherein the regulating circuit comprises;

a battery current integrator having a first input, a second input and an output, the first input coupled to receive a battery current value and the second input coupled to receive a battery current limit value;

a battery voltage integrator having a first input, a second input and an output, the first input coupled to receive a battery voltage value and the second input coupled to receive a battery voltage limit value;

a stack current integrator having a first input, a second input and an output, the first input coupled to receive a stack current value and the second input coupled to receive a stack current limit value; and

an OR circuit coupled to the output of each of the battery current integrator, the battery voltage integrator and the stack current integrator to select the greater of a value on each of the outputs.

4. A control circuit for a fuel cell system, comprising:

a series pass element;

a blocking diode electrically coupled in series with the series pass element; and

a regulating circuit coupled to the series pass element to regulate a current through the series pass element in proportion to at least a greater of a difference between a battery charging current and a battery charging current limit, a difference between a battery voltage and a battery voltage limit, and a difference between a stack current and a stack current limit wherein the regulating circuit comprises;

a battery current integrator having a first input, a second input and an output, the first input coupled to receive a battery current value and the second input coupled to receive a battery current limit value;

a battery voltage integrator having a first input, a second input and an output, the first input coupled to receive a battery voltage value and the second input coupled to receive a battery voltage limit value;

a stack current integrator having a first input, a second input and an output, the first input coupled to receive a stack current value and the second input coupled to receive a stack current limit value;

an OR circuit coupled to the output of each of the battery current integrator, the battery voltage integrator and the stack current integrator to select the greater of a value on each of the outputs;

a level shifter coupled to the OR circuit to receive the greater of the value on each of the outputs; and

a charge pump coupled to the series pass element through the level shifter.

5. A control circuit for a fuel cell system, comprising:

a battery charging current sensor;

a battery charging current error integrator having a first input coupled to the battery charging current sensor to receive a battery charging current signal proportional to a battery charging current, a second input coupled to receive a battery charging current limit signal proportional to a battery charging current limit, and an output to supply a battery current error signal proportional to a difference between the battery charging current and the battery charging current limit;

a battery voltage sensor;

a battery voltage error integrator having a first input coupled to the battery voltage sensor to receive a battery voltage signal proportional to a battery voltage, a second input coupled to receive a battery voltage limit signal proportional to a battery voltage limit, and an output to supply a battery voltage error signal proportional to a difference between the battery voltage and the battery voltage limit;

a stack current sensor;

a stack current error integrator having a first input coupled to the stack current sensor to receive a stack current signal proportional to a stack current, a second input coupled to receive a stack current limit signal proportional to a stack current limit, and an output to supply a stack current error signal proportional to a difference between the stack current and the stack current limit;

an OR circuit coupled to the output of each of the battery current error integrator, the battery voltage error integrator and the stack current error integrator; and

a series pass element having a pair of terminals for selectively providing a current path and a control terminal coupled to the OR circuit for regulating current through the current path in proportion to a greater of the battery current error signal, the battery voltage error signal and the stack current error signal.

6. The control circuit of claim 5 wherein the regulating circuit comprises a number of discrete integrators.

7. The control circuit of claim 5 wherein the regulating circuit comprises an analog OR circuit.

8. The control circuit of claim 5 wherein the regulating circuit comprises a microprocessor.

9. The control circuit of claim 5, further comprising:

a temperature compensation circuit coupled to the battery temperature sensor to produce a battery voltage limit that is compensated for temperature.

10. A control circuit for a fuel cell system, comprising:

integrating means for determining a difference between a battery charging current and a battery charging current limit;

integrating means for determining a difference between a battery voltage and a battery voltage limit;

integrating means for determining a difference between a stack current and a stack current limit;

means for determining a greater of the difference between the battery charging current and the battery charging current limit, the difference between the battery voltage and the battery voltage limit, and the difference between the stack current and the stack current limit; and

series pass regulating means for regulating a flow of stack current through a blocking diode in proportion to the determined greater difference.

11. A control circuit for a fuel cell system, comprising:

means for determining a difference between a battery charging current and a battery charging current limit;

means for determining a difference between a battery voltage and a battery voltage limit;

means for determining a difference between a stack current and a stack current limit;

means for selecting a greater of the determined differences; and

series pass regulating means for regulating a flow of stack current through a blocking diode in response to the greater of the determined differences.

12. A control circuit for a fuel cell system, comprising:

means for determining a difference between a battery charging current and a battery charging current limit;

means for determining a difference between a battery voltage and a battery voltage limit;

means for determining a difference between a stack current and a stack current limit;

means for selecting a greater of the determined differences;

series pass regulating means for regulating a flow of stack current through a blocking diode in response to the greater of the determined differences; and

means for applying a signal to a control terminal of the series pass regulating means proportional to the greater of the determined differences.