Reverse current protection device

• US 20040125518A1
• Filed: 02/10/2003
• Published: 07/01/2004
• Est. Priority Date: 12/26/2002
• Status: Active Grant

• Current Assignee: Sheppard, Mullin, Richter & Hampton LLP
• Original Assignee: ISE Research Corporation
• Inventors: Moran, Brian Douglas, Wilk, Michael David, Quintana, Ailen Villegas
• Granted Patent: US 7,057,868 B2
• Time in Patent Office: Days
• US Class Current: 361/23
• CPC Class Codes: H02H 3/18 responsive to reversal of direct current

Abstract

A reverse current protection device for a fuel cell of a power circuit protects the fuel cell from damage caused by reverse current into the fuel cell caused by a faulty diode. The reverse current protection device includes a contactor for opening the power circuit to prevent current from flowing therethrough and for closing the power circuit to allow current to flow therethrough, means for measuring the voltage across the diode to determine if the diode is in a good condition or a fault condition, means for causing the contactor to be closed if the diode is in a good condition and open if the diode is in a fault condition so that current does not flow through the contactor, protecting the fuel cell from damage caused by reverse current through the diode and into the fuel cell.

Claims

1. A method of protecting a fuel cell of a power circuit from damage caused by reverse current into the fuel cell caused by a faulty diode, the power circuit powering an electric motor of a bus for propelling the bus, comprising:

providing one or more contactors in the power circuit that open to prevent current from flowing therethrough and close to allow current to flow therethrough;

measuring the voltage across the diode to determine if the diode is in a good condition or a fault condition;

causing the one or more contactors to be closed if the diode is in a good condition so that current flows from the fuel cell through the diode and the contactor to the electric motor to propel the bus; and

causing at least one of the one or more contactors to be opened if the diode is in a fault condition so that current does not flow through the contactor, protecting the fuel cell from damage caused by reverse current through the diode and into the fuel cell.

2. The method of claim 1, further including providing the one or more contactors in a closed condition for a predetermined period of time upon start up of the power circuit until the power circuit reaches a normal operating condition.

3. The method of claim 2, further including performing a start up sequence prior to providing the one or more contractors in a closed condition.

4. The method of claim 3, wherein the start up sequence includes preliminarily sensing at least one of other circuit voltages and impedance levels for abnormal conditions.

5. The method of claim 1, wherein the diode is a power diode of at least 30 amps.

6. The method of claim 1, wherein measuring the voltage across the diode to determine if the diode is in a good condition or a fault condition includes inverting the voltage across the diode with an impedance buffer, comparing the inverted voltage to a reference voltage with a threshold detector, and determining that the diode is in a good condition if the inverted voltage is greater than the reference voltage and determining that the diode is in a fault condition if the inverted voltage is less than the reference voltage.

7. The method of claim 1, wherein causing the one or more contactors to be closed if the diode is in a good condition includes causing an opto-isolator to drive a relay that causes the one or more contactors to close.

8. The method of claim 1, wherein causing the one or more contactors to be opened if the diode is in a fault condition occurs in 30 milliseconds or less of when a fault condition of the diode is determined and the contactor drive signal occurs in 1 millisecond or less of when a fault condition of the diode is determined.

9. The method of claim 1, further including more than one reverse current protection circuit undergoing the above steps to provide redundant protection of the fuel cell.

10. A reverse current protection device for a fuel cell of a power circuit for protecting the fuel cell from damage caused by reverse current into the fuel cell caused by a faulty diode, the power circuit powering an electric motor of a bus for propelling the bus, comprising:

means in the power circuit for opening the power circuit to prevent current from flowing therethrough and for closing the power circuit to allow current to flow therethrough;

means for measuring the voltage across the diode to determine if the diode is in a good condition or a fault condition;

means for causing the power circuit opening and closing means to be closed if the diode is in a good condition so that current flows from the fuel cell to the electric motor to propel the bus; and

causing the power circuit opening and closing means to be opened if the diode is in a fault condition so that current does not flow through the power circuit opening and closing means, protecting the fuel cell from damage caused by reverse current through the diode and into the fuel cell.

11. The reverse current protection device of claim 10, further including means for providing the one or more contactors in a closed condition for a predetermined period of time upon start up of the power circuit until the power circuit reaches a normal operating condition.

12. The reverse current protection device of claim 11, further including means for performing a start up sequence prior to providing the power circuit opening and closing means in a closed condition.

13. The reverse current protection device of claim 12, wherein said means for performing a start up sequence include means for preliminarily sensing at least one of other circuit voltages and impedance levels for abnormal conditions.

14. The reverse current protection device of claim 10, wherein the diode is a power diode of at least 30 amps.

15. The reverse current protection device of claim 10, wherein means for measuring the voltage across the diode to determine if the diode is in a good condition or a fault condition include means for inverting the voltage across the diode, comparing the inverted voltage to a reference voltage, and determining that the diode is in a good condition if the inverted voltage is greater than the reference voltage and determining that the diode is in a fault condition if the inverted voltage is less than the reference voltage.

16. The reverse current protection device of claim 10, wherein means for causing the power circuit opening and closing means to be opened if the diode is in a fault condition occurs in 30 milliseconds or less of when a fault condition of the diode is determined and the contactor drive signal occurs in 1 millisecond or less of when a fault condition of the diode is determined.

17. The reverse current protection device of claim 10, wherein the reverse current protection device includes one or more of the above means multiple times to provide redundant protection of the fuel cell.

18. A reverse current protection device for a fuel cell of a power circuit for protecting the fuel cell from damage caused by reverse current into the fuel cell caused by a faulty diode, the power circuit powering an electric motor of a bus for propelling the bus, comprising:

one or more contactors in the power circuit that open to prevent current from flowing therethrough and close to allow current to flow therethrough;

an impedance buffer to invert the voltage across the diode;

a threshold detector to compare the inverted voltage to a reference voltage to determine if the diode is in a good or fault condition;

an opto-isolator actuatable by the threshold detector when at least one of a good diode condition is determined and a fault diode condition is determined; and

a relay in communication with the opto-isolator to cause at least one of the one or more contactors to close in a good diode condition so that power is supplied to the electric motor to propel the bus and open in a fault diode condition for protecting the fuel cell from damage caused by reverse current into the fuel cell caused by a faulty diode.