Method and apparatus to regulate the supply of power to an electric drive using a hybrid energy supply system in a vehicle

• US 6,953,100 B2
• Filed: 05/23/2003
• Issued: 10/11/2005
• Est. Priority Date: 05/24/2002
• Status: Expired due to Fees

• Current Assignee: NuCellSys GmbH (Mercedes-Benz Group AG)
• Original Assignee: Ballard Power Systems Corporation (Superior Plus Corporation)
• Inventors: Schetter, Thomas, Blum, Joachim, Boehmisch, Mathias, Aberle, Markus
• Primary Examiner(s): FISCHMANN, BRYAN R
• Application Number:
  US10/445,270
• Publication Number:
  US 20040065489A1
• Time in Patent Office: 872 Days
• Field of Search: 477/7, 477/2, 477/3, 363/51, 180 651- 653, 180/65.8, 701/22, 429/22, 429/23, 290/40.C, 318/139, 320/101
• US Class Current: 429/432
• CPC Class Codes: B60L 58/40 for controlling a combination of batteries and fuel cells
• CPC Class Codes: B60W 10/26 for electrical energy, e.g. batteries or capacitors
• CPC Class Codes: B60W 20/00 Control systems specially adapted for hybrid vehicles hybrid vehicle design, B60K6/00; electric vehicles B60L
• CPC Class Codes: B60W 20/13 in order to stay within battery power input or output limits; in order to prevent overcharging or battery depletion
• CPC Class Codes: B60W 2510/244 Charge state
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 90/40 Application of hydrogen technology to transportation, e.g. using fuel cells
• CPC Class Codes: Y10S 429/90 Fuel cell including means for power conditioning, e.g. Conversion to ac

Abstract

Regulation of energy supplied to an electric motor from an energy supply system including a fuel cell and an energy storage buffer such as a battery, improves the dynamic response of the motor by adding current from the energy storage buffer to the current from the fuel cell during acceleration.

Claims

1. A method to regulate a supply of energy to an electric motor from a hybrid energy supply system that comprises at least one fuel cell, at least one energy storage buffer, a bi-directional converter electrically coupled between the fuel cell and the energy storage buffer, and a DC/DC converter electrically coupled between the bi-directional converter and the energy storage buffer, the method comprising:

producing a vehicle current request value based at least in part on a detected position of a throttle;

determining an output voltage of the fuel cell;

in a first operating mode,

current controlling the DC/DC converter if the output voltage of the fuel cell is between an upper limit value and a lower limit value so that the current supplied to the electric motor by the fuel cell is approximately equal to the vehicle current request value;

voltage controlling the DC/DC converter if the output voltage of the fuel cell is at or below the lower limit value to raise the output voltage of the fuel cell to a level of at least the lower limit value, and

voltage controlling the DC/DC converter if the output voltage of the fuel cell is at or above the upper limit value to lower the output voltage of the fuel cell, to a level not greater than the upper limit value.

2. The method of claim 1, further comprising:

in a second operating mode,

reversing the flow of current of the DC/DC converter and the bi-directional converter to charge the energy storage buffer;

current controlling the DC/DC converter;

current controlling the bi-directional converter if the output voltage of the fuel cell is at or below the upper limit value to reduce power to the electric motor to a set point value; and

voltage controlling the bi-directional converter if the output voltage of the fuel cell exceeds the upper limit value in order to limit the output voltage of the fuel cell to the upper limit value.

3. The method of claim 2 wherein the first operating mode corresponds to period of acceleration or constant power, and the second operating mode corresponds to a period of deceleration or regeneration.

4. The method of claim 2, further comprising:

determining the set point value based at least in part on the detected position of the throttle;

determining the vehicle current request value based at least in part on a voltage-current characteristic of the fuel cell;

providing the determined vehicle current request value from a vehicle controller to a fuel cell controller;

determining a fuel cell current request value based at least in part on an actual current delivered by the fuel cell, a current from the fuel cell available for the electric motor, and a charge state of the energy storage buffer;

providing the determined fuel cell current request value from the fuel cell controller to at least one actuator for at least one of an air metering system and a fuel metering system.

5. The method of claim 4 wherein determining a fuel cell current request value comprises:

summing the vehicle current request value with one of an energy storage buffer charge current value and an energy storage buffer discharge current value produced by an energy storage buffer controller;

modulating the sum of the vehicle current request value and the one of the energy storage buffer charge current value and the energy storage buffer discharge current value; and

subsequently combining the modulated sum with a fuel cell correction current value, the result comprising the fuel cell current request value.

6. The method of claim 5, further comprising:

determining a difference between the actual current delivered by the fuel cell and the current from the fuel cell available for the electric motor;

forwarding the determined difference to PID control; and

subsequently routing the resulting value with a time delay and a rate-of-change limitation as the fuel cell correction current value.

7. The method of claim 6, further comprising:

subtracting the fuel cell correction current value from the determined difference between the actual current delivered by the fuel cell and the current from the fuel cell available to the motor to produce an intermediate difference;

subtracting the intermediate difference with a time delay from the vehicle current request value; and

applying the intermediate difference to at least one of the energy storage buffer charge current request value and energy storage buffer discharge current request value of the energy storage buffer controller and to an energy storage buffer correction current value to generate a setting value of the currents for the DC/DC converter.

8. The method of claim 7, further comprising:

applying a difference between the setting value of the current for the DC/DC converter and a limit setting value to the vehicle current request value.

9. The method of claim 4 wherein the fuel cell and the energy storage buffer are operated efficiency-optimized according to the following equation:

η

_OPT=(η

_FC^SB)_OPT,

whereby η

_OPT is the overall efficiency, η

_FC is the efficiency of the fuel cell, and η

_SB is the efficiency of the energy storage buffer.

10. The method of claim 2, further comprising:

determining an actual current of the fuel cell by measuring a current supplied to the bi-directional converter and summing the measured current supplied to the bi-directional converter with a current supplied by the energy storage buffer.

11. The method according to claim 10 wherein determining an actual current of the fuel cell, further comprises:

subtracting estimates of currents required by at least one other load in addition to the motor from the measured current.

12. The method of claim 2, further comprising:

determining a charge state of the energy storage buffer;

determining a temperature of the energy storage buffer;

providing one of a charge current request, a discharge current request and no current request to a fuel cell controller based on at least one of the determined charge state and the determined temperature; and

providing a setting signal indicating one of the first and the second operating modes to control the DC/DC converter, wherein the setting signal is limited, based at least in part on the operating mode, to at least one of a preset maximum charge current value, a preset maximum discharge current value, and a preset maximum voltage value, where the maximum charge current value is subtracted from an the available current value produced by the fuel cell controller and is provided to a vehicle controller as a minimum available current value, and where a maximum discharge current value is added to the available current value and is provided to the vehicle controller as the maximum available current in the first operating mode.

13. The method of claim 12, further comprising:

generating the discharge current request from the energy storage buffer controller if the charge state of the energy storage buffer exceeds an upper charge state limit value;

generating the charge current request from the energy storage buffer controller if the charge state of the energy storage buffer is below a lower charge state limit value; and

generating no current request if the charge state of the energy storage buffer is between the upper and the lower charge state limit values.

14. The method of claim 13, further comprising:

if the discharge current request has been provided and a current that is required by the electric motor is higher than a current generated by the fuel cell at a highest efficiency, generating current at the highest efficiency by the fuel cell and delivering current from the energy storage buffer sufficient to make up the remainder of the vehicle current request value; and

if the current required by the electric motor is smaller than the current generated at the highest efficiency, not efficiency-optimized partitioning the current required for the electric motor between the fuel cell and the energy storage buffer.

15. The method of claim 13, further comprising:

if the charge current request has been produced and a current required by the electric motor is greater than zero but smaller than a current generated by the fuel cell at a highest efficiency, generating current at the highest efficiency by the fuel cell and charging the energy storage buffer with a current that corresponds to the difference between the vehicle current request value and the current generated by the fuel cell at the highest efficiency; and

if the electric motor requires a current that is higher than the current delivered by the fuel cell at the highest efficiency, generating current by the fuel cell approximately equal to the vehicle current request value and the charge current for the energy storage buffer without any efficiency-optimized setting.

16. The method of claim 13 wherein in a charge state of the energy storage buffer without charge current request or discharge current request, if the energy storage buffer is being charged by recovered energy, and if the sum of a product of the fuel cell current at an optimum efficiency of the fuel cell and the optimum efficiency of the fuel cell and the product of a difference between the requested fuel cell current and the fuel cell current at the optimum efficiency of the fuel cell, with an optimum efficiency of the fuel cell, an efficiency of the DC/DC converter, and a discharge efficiency of the energy storage buffer is higher than a product of the value of the requested fuel cell current and an efficiency of the fuel cell for the requested fuel cell current, and if the difference between the requested fuel cell current and the fuel cell current at the optimum efficiency of the fuel cell is greater than zero, then the fuel cell generates the current at a highest efficiency, and in all other cases the fuel cell current will be set to the fuel cell current request value.

17. The method of claim 13 wherein in a charge state of the energy storage buffer without the charge current request or discharge current request, if the energy storage buffer is being charged by the fuel cell, and if a sum of a product of the fuel cell current at an optimum efficiency of the fuel cell with an optimum efficiency of the fuel cell and a product of a difference between the fuel cell current request value and a fuel cell current at the optimum efficiency of the fuel cell, with an optimum efficiency of the fuel cell, a square of an efficiency of the DC/DC converter, and a charge efficiency and a discharge efficiency of the energy storage buffer is higher than a product of the fuel cell current request value and the efficiency of the fuel cell for the fuel cell current request value, the fuel cell generates the current at the highest efficiency, and that in all other cases the fuel cell current will be set to the fuel cell current request value.

18. The method of claim 1 wherein the upper limit and the lower limit values are non-critical values for the operation of the fuel cell.

19. The method of claim 1, further comprising:

determining if the output voltage of the fuel cell is between the upper and the lower limit values.

20. An apparatus to regulate the energy supply of an electric motor and further loads using a hybrid energy supply system that comprises a fuel cell stack and an energy storage buffer;

comprising;

a power bus electrically coupling the fuel cell stack to the electric motor;

a DC/DC converter electrically coupled between the power bus and the energy storage buffer;

a bi-directional converter electrically coupled between the power bus and the electric motor;

a voltage sensor electrically coupled across the fuel cell stack to determine a fuel cell stack output voltage;

a current sensor electrically coupled to the fuel cell stack to determine a fuel cell stack output current;

a throttle;

a position detector coupled to detect a position of the throttle;

a motor controller coupled to control the electric motor;

a vehicle controller configured to produce a current request value based at least in part on a position of the throttle and further configured to provide a setpoint to the motor controller;

a fuel cell controller coupled to receive the current request value from the vehicle controller, and to provide indications of an available vehicle current, a maximum vehicle current, and a minimum available vehicle current to the vehicle controller, the fuel cell controller further coupled to receive an indication of the fuel cell output voltage from the voltage sensor;

the motor controller, vehicle controller and fuel cell controller coupled and configured to,

in a first operating mode,

current control the DC/DC converter if the fuel cell stack output voltage is between an upper limit value and a lower limit value so that the current supplied to the electric motor by the fuel cell is approximately equal to the vehicle current request value;

voltage control the DC/DC converter if the fuel cell stack output voltage is at or below the lower limit value to raise the fuel cell stack output voltage to a level of at least the lower limit value, and

voltage controlling the DC/DC converter if the fuel cell stack output voltage is at or above the upper limit value to lower the fuel cell stack output voltage to a level not greater than the upper limit value; and

in a second operating mode,

reverse the flow of current of the DC/DC converter and the bi-directional converter to charge the energy storage buffer;

current controlling the DC/DC converter;

current controlling the bi-directional converter if the output voltage of the fuel cell is at or below the upper limit value to reduce power to the electric motor to the set point value; and

voltage controlling the bi-directional converter if the output voltage of the fuel cell exceeds the upper limit value in order to limit the output voltage of the fuel cell to the upper limit value.

21. The apparatus of claim 20, further comprising:

an energy storage buffer controller coupled to provide a charge state value to the fuel cell controller, the charge state value indicative of a charge state of the energy storage buffer, wherein the fuel cell controller executes a current-management program that processes values of the fuel cell stack output current and of an estimated available fuel cell current as well as the charge state value to determine values to control at least one function of fuel cell operation.

22. An apparatus to regulate a supply of energy to an electric motor from a hybrid energy supply system that comprises at least one fuel cell, at least one energy storage buffer and a DC/DC converter electrically coupled between the fuel cell and the energy storage buffer, comprising:

means for producing a vehicle current request value based on a detected position of a throttle;

means for determining an output voltage of the fuel cell;

in a first operating mode, means for;

current controlling the DC/DC converter if the output voltage of the fuel cell is between an upper limit value and a lower limit value so that the current supplied to the electric motor by the fuel cell is approximately equal to the vehicle current request value;

voltage controlling the DC/DC converter if the output voltage of the fuel cell is at or below the lower limit value to raise the output voltage of the fuel cell to a level of at least the lower limit value, and

voltage controlling the DC/DC converter if the output voltage of the fuel cell is at or above the upper limit value to lower the output voltage of the fuel cell to a level not greater than the upper limit value; and

in a second operating mode, means for;

reversing the flow of current of the DC/DC converter and the bi-directional converter to charge the energy storage buffer;

current controlling the DC/DC converter;

current controlling the bi-directional converter if the output voltage of the fuel cell is at or below the upper limit value to reduce power to the electric motor to a set point value; and

voltage controlling the bi-directional converter if the output voltage of the fuel cell exceeds the upper limit value in order to limit the output voltage of the fuel cell to the upper limit value.