Operating method for an electric energy system of a motor vehicle comprising a fuel cell system, an accumulator and an electric motor

• US 9,688,160 B2
• Filed: 03/25/2014
• Issued: 06/27/2017
• Est. Priority Date: 09/26/2011
• Status: Active Grant

• Current Assignee: Bayerische Motoren Werke AG
• Original Assignee: Bayerische Motoren Werke AG
• Inventors: Goetz, Georg, Burckhardt, Sylvester, Bauer, Michael, Buchner, Andreas, Pfattrisch, Florian
• Primary Examiner(s): Shin, Jeffrey
• Application Number:
  US14/224,824
• Publication Number:
  US 20140203636A1
• Time in Patent Office: 1,190 Days
• CPC Class Codes: B60L 2240/423 Torque
• CPC Class Codes: B60L 50/72 Constructional details of fuel cells specially adapted for electric vehicles
• CPC Class Codes: B60L 58/13 Maintaining the SoC within a determined range
• CPC Class Codes: B60L 58/40 for controlling a combination of batteries and fuel cells
• CPC Class Codes: B60L 7/10 Dynamic electric regenerative braking B60L7/22 takes precedence
• CPC Class Codes: H01M 10/46 Accumulators structurally combined with charging apparatus circuits for charging H02J7/00
• CPC Class Codes: H01M 16/006 of fuel cells with rechargeable batteries
• CPC Class Codes: H01M 8/04097 with recycling of the reactants H01M8/04119, H01M8/04104 take precedence
• CPC Class Codes: H01M 8/04201 Reactant storage and supply, e.g. means for feeding, pipes
• CPC Class Codes: H01M 8/04395 of cathode reactants at the inlet or inside the fuel cell
• CPC Class Codes: H01M 8/04544 Voltage
• CPC Class Codes: H01M 8/04798 of fuel cell reactants
• CPC Class Codes: H01M 8/0488 of fuel cell stacks
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• 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

Abstract

A method of operating an electric system of a motor vehicle, consisting of a fuel cell system, an accumulator and an electric driving motor is provided. Without implementing an electric voltage conversion and therefore without an electric voltage converter, as a function of the level of the electric voltage made available by the fuel cell system and by the accumulator and the electric power demanded by the electric motor, a first switching element in the connection between the fuel cell system and a node point electrically connected with the accumulator and the electric motor, as well as a second switching element in the connection between the accumulator and this node point are opened or closed as needed. This is done such that the power requirement of the electric motor is met primarily from the fuel cell system, and in an auxiliary fashion, additionally from the accumulator. If the electric power offered by the fuel cell system exceeds the electric power demanded by the electric motor, the excess power will be fed to the accumulator for as long as its permissible charging current is not exceeded and the accumulator still has a defined residual storage capacity.

Claims

1. A method of operating an electric system of a motor vehicle equipped with a fuel cell system, an accumulator, and an electric motor operable as a vehicle drive motor, the fuel cell system, accumulator and electric drive motor being electrically coupled to allow the fuel cell system to supply electric energy to the electric motor and the accumulator, and to allow the accumulator to supply electric energy to the electric motor, the method comprising the acts of:

designing the electric system, without an electric voltage converter and without an electric voltage conversion, such that the accumulator is essentially chargeable completely by the fuel cell system alone as well as also by the electric motor alone when operating as a generator;

depending on the electric voltage level made available by the fuel cell system and by the accumulator, and on the power required by the electric motor;

opening and closing a first switching element as needed, the first switching element being arranged between the fuel cell system and a node point that is electrically coupled to the accumulator and to the electric motor, and

opening and closing a second switching element as needed, the second switching element being arranged between the accumulator and the node point, wherein

the opening and closing of the first and second switching elements is such that the power requirement of the electric motor is met primarily by the fuel cell system and additionally in an auxiliary manner by the accumulator, and

if the electric power made available by the fuel cell system exceeds the power demanded by the electric motor, the excess power of the fuel cell system resulting from a difference between the power made available and the power demanded is fed to the accumulator as long as an admissible charging current of the accumulator is not exceeded and the accumulator still has a defined residual storage capacity, the defined residual storage capacity being at least in an amount of a kinetic energy of the motor vehicle feedable to the accumulator in a current driving state of the vehicle by recuperation via the electric motor operating as the generator.

2. The method according to claim 1, wherein

in cases in which a voltage level provided by the fuel cell system is significantly higher than a voltage level processable by the electric motor and the accumulator, or significantly lower than the voltage level demanded by the electric motor or accumulator, adapting the voltage level of the fuel cell system to the demand by modulating an oxygen content on a cathode side of fuel cells of the fuel cell system, which fuel cell system has at least one hydrogen (air) oxygen fuel cell.

3. The method according to claim 2, wherein the act of adapting the voltage level of the fuel cell system to lower the voltage level of the fuel cell system as needed is carried out by:

changing a rate of exhaust gas returned to the cathode side of the fuel cell, and/or

changing an air throughput at the cathode side of the fuel cell.

4. The method according to claim 2, wherein the act of adapting the voltage level of the fuel cell system to raise the voltage level of the fuel cell system as needed is carried out by:

increasing an oxygen content of an airflow flow fed to the cathode side of the fuel cell.

5. The method according to claim 3, wherein the act of adapting the voltage level of the fuel cell system to raise the voltage level of the fuel cell system as needed is carried out by:

increasing an oxygen content of an airflow flow fed to the cathode side of the fuel cell.

6. The method according to claim 4, wherein the increasing of the oxygen content of the airflow fed to the cathode side of the fuel cell is carried out by:

adding oxygen to the airflow, which oxygen was obtained in advance from fed air and stored in a suitable storage material, and/or

reducing a nitrogen fraction in the airflow fed to the cathode side of the fuel cell, said reduction being carried out via a molecular sieve.

7. The method according to claim 5, wherein the increasing of the oxygen content of the airflow fed to the cathode side of the fuel cell is carried out by:

adding oxygen to the airflow, which oxygen was obtained in advance from fed air and stored in a suitable storage material, and/or

reducing a nitrogen fraction in the airflow fed to the cathode side of the fuel cell, said reduction being carried out via a molecular sieve.

8. The method according to claim 1, wherein the fuel cell system has a plurality of individual fuel cells, the method further comprising the act of:

continuously monitoring the electric voltage of all the individual fuel cells in order to maintain permissible limit values, and

preventing an exceeding or falling-below of the permissible limit values by changing a quantity of reaction gas fed to the individual fuel cells.

9. The method according to claim 2, wherein the fuel cell system has a plurality of individual fuel cells, the method further comprising the act of:

continuously monitoring the electric voltage of all the individual fuel cells in order to maintain permissible limit values, and

preventing an exceeding or falling-below of the permissible limit values by changing a quantity of reaction gas fed to the individual fuel cells.

10. The method according to claim 3, wherein the fuel cell system has a plurality of individual fuel cells, the method further comprising the act of:

continuously monitoring the electric voltage of all the individual fuel cells in order to maintain permissible limit values, and

preventing an exceeding or falling-below of the permissible limit values by changing a quantity of reaction gas fed to the individual fuel cells.

11. The method according to claim 4, wherein the fuel cell system has a plurality of individual fuel cells, the method further comprising the act of:

continuously monitoring the electric voltage of all the individual fuel cells in order to maintain permissible limit values, and

preventing an exceeding or falling-below of the permissible limit values by changing a quantity of reaction gas fed to the individual fuel cells.

12. The method according to claim 6, wherein the fuel cell system has a plurality of individual fuel cells, the method further comprising the act of:

continuously monitoring the electric voltage of all the individual fuel cells in order to maintain permissible limit values, and

preventing an exceeding or falling-below of the permissible limit values by changing a quantity of reaction gas fed to the individual fuel cells.