Device for generating electric energy in a motor vehicle by means of a fuel cell and method for operating such a device

• US 6,777,909 B1
• Filed: 09/17/2002
• Issued: 08/17/2004
• Est. Priority Date: 11/11/1999
• Status: Expired due to Fees

• Current Assignee: NuCellSys GmbH (Mercedes-Benz Group AG)
• Original Assignee: Ballard Power Systems Corporation (Siemens AG)
• Inventors: Sonntag, Josef, Aberle, Markus
• Primary Examiner(s): LUK, LAWRENCE W
• Application Number:
  US10/129,651
• Time in Patent Office: 700 Days
• Field of Search: 320/104, 320/103, 320/116, 320/139, 320/132, 361/86, 361/87
• US Class Current: 320/104
• CPC Class Codes: B60L 15/2045 for optimising the use of energy
• CPC Class Codes: B60L 58/30 for monitoring or controlling fuel cells
• CPC Class Codes: B60L 58/33 by cooling
• CPC Class Codes: B60L 58/34 by heating
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/72 Electric energy management in electromobility
• CPC Class Codes: Y02T 90/40 Application of hydrogen technology to transportation, e.g. using fuel cells

Abstract

In a device for generating electrical power with the fuel cell in a vehicle, a temporary power storage supplies power for a battery start, is charged when the fuel cell is operating, outputs power to connected loads of the fuel cell power system when there is an increased power demand, and absorbs power during braking.

Claims

1. A device for generating electrical power in a vehicle having a fuel cell, a drive motor, a driving converter and auxiliary or supplementary units for starting and continuous operation phases of the vehicle, said device comprising:

a first temporary power store;

at least one switching contact for connecting the auxiliary or supplementary units and a first end of a first bidirectional d.c./d.c. converter to electrical outputs of the fuel cell; and

a controller which controls a release and direction of a power flux via the first d.c./d.c. converter as a function of an operating state of the fuel cell and of the first temporary power store;

wherein,

the drive motor is connectable to the fuel cell via the drive converter;

the driving converter is connected to electrical outputs of the fuel cell via a switching contact;

the first temporary power store is connectable to a second end of the first d.c./d.c. converter via at least one further switching contact;

a first end of at least one second bidirectional d.c./d.c. converter is connectable to electrical outputs of the fuel cell via the switching contact;

a second end of the second d.c./d.c. converter is connected to an onboard power system of the vehicle, whose voltage is lower than a rated voltage of the fuel cell, and which includes a second temporary power store;

the switching contact is arranged outside a connection path of the first temporary power store to the drive motor;

a release and direction of a power flux via the second d.c./d.c. converter is controlled by the controller as a function of the operating state of the fuel cell and of one of the first and second temporary power stores; and

the release and direction of the power flux via the first d.c./d.c. converter is controlled by the controller as a function of an operating state of the second power store.

2. The device according to claim 1, further comprising a diode whose polarity is in the forward direction with respect to the polarity of the output current at rated operation of the fuel cell, which is arranged between at least one electrical output of the fuel cell and the switching contact.

3. The device according to claim 1, wherein:

the switching contact is arranged parallel to a series connection of a further switch and of a resistor, between a first electrical terminal of the first temporary power store and an input of the first d.c./d.c. converter; and

the switches can be activated by means of the controller.

4. The device according to claim 1, wherein a switch which can be activated by the controller is arranged between a second electrical terminal of the first temporary power store and ground, to which in each case a terminal of the first d.c./d.c. converter and of the auxiliary drives as well as of the converter (3) is connected.

5. The device according to claim 1, wherein both electrical outputs of the fuel cell are connected via one switching contact each to the power system containing the converter, and the switching contacts can each be activated independently by the controller.

6. The device according to claim 1, wherein the first temporary power store is one of a lead acid battery, a nickel cadmium battery, a nickel metal hydride battery, a lithium ion battery and a lithium polymer battery.

7. The device according to claim 1, wherein the first temporary power store is one of a double-layer capacitor, a super capacitor and an ultra capacitor.

8. The device according to claim 1, further comprising sensors for measuring voltage and temperature of the first temporary power store, which sensors are connected to the controller as users on a bus.

9. The device according to claim 1, wherein a control and regulation program for operation of the fuel cell, the first and second d.c./d.c. converters, the auxiliary units and the temporary power store is stored in a non-volatile memory.

10. The device according to claim 1, wherein the first bidirectional d.c./d.c. converter and the second bidirectional d.c./d.c. converter are disposed in a common housing.

11. The device according to claim 10, wherein:

the switches are arranged between the first temporary power store and the d.c./d.c. converter; and

the controller is arranged in the housing.

12. The device according to claim 10, wherein:

the first and second d.c./d.c. converters arranged in the housing and the controller are jointly connected to a supply voltage;

the first and second d.c./d.c. converters have a common coolant supply; and

the housing has a communications interface with the bus.

13. A method for operating a device for generating electrical power in a vehicle which has a fuel cell;

a controller;

at least one drive motor which is connected via a driving converter to the fuel cell;

auxiliary units for starting and subsequent continuous operation phases of the vehicle, the driving converter, the auxiliary and supplementary units and a first end of a bidirectional d.c./d.c. converter being connectable to electrical outputs of the fuel cell; and

a temporary power store, which is connected to a controller and to a second end of the d.c./d.c. converter via at least one switch;

said method comprising;

measuring fuel cell-end voltage and temporary power store-end voltage;

when the temporary power store is charged, predefining and monitoring a minimum fuel cell-end voltage value, a fuel cell-end setpoint current, a maximum temporary power store-end voltage value and a maximum temporary power store-end current;

when the minimum fuel cell-end voltage value or the maximum temporary power store-end voltage value or the fuel cell-end setpoint current or the power accumulator-end maximum current are reached, reducing the charge current of the d.c./d.c. converter so as to avoid undershooting the minimum voltage value, exceeding the maximum voltage value, and exceeding the setpoint current or the maximum current;

when the temporary power store is discharged, predefining and monitoring a maximum fuel cell-end voltage value, fuel cell-end setpoint current, a temporary power store-end minimum voltage value and a temporary power store-end maximum current value; and

when the maximum fuel cell-end voltage value, the minimum temporary power store-end voltage value or the setpoint current or the power accumulator-end maximum current value is reached, the d.c./d.c. converter reducing the discharge current of the temporary power store such that the maximum voltage value is not exceeded, the minimum voltage value is not undershot, and the setpoint current and the maximum current are not exceeded.

14. The method according to claim 13, further comprising:

when one of the minimum fuel cell-end voltage value and a predefined high voltage value is reached or undershot, setting the d.c./d.c. converter to a discharge mode in which the current is fed into a power system connected to the fuel cell;

when one of the maximum fuel cell-end voltage value and a predefined lower voltage value is reached or exceeded, setting the d.c./d.c. converter to a charge mode in which current from the power system connected to the fuel cell is fed into the temporary power store; and

the d.c./d.c. converter being inactive when the voltage of the fuel cell lies between the minimum voltage value and the maximum predefined voltage value.

15. The method according to claim 13, wherein:

to start the fuel cell, the temporary power store is first connected, by closing the switch, to the d.c./d.c. converter which makes available the power for the auxiliary or supplementary units that are connected to the power system connected to its output;

the fuel cell is activated by the auxiliary or supplementary units; and

after the predefined output voltage of the fuel cell has been reached, a switch upstream of the output of the fuel cell is closed.