Fuel cell system

Abstract

This fuel cell system (1) (2), equipped with a first air supply circuit (3), a second hydrogen supply circuit (4), a third cooling circuit (5), and a fourth electrical circuit (6) returning a generated electrical charge, comprises at least two stacks (7) of elementary cells operating at very low voltage, said stacks being identical and connected in parallel, said system comprising a diode (8) connected in series with each stack (7) so as to prevent any reverse current in the stacks (7). Figure for the abstract: [Fig 1]

Description

Title of the invention: Fuel cell system Technical field

[0001] The present invention relates to a fuel cell system intended to integrate a traction or propulsion chain of a vehicle. Previous techniques

[0002] Vehicle traction or propulsion systems are known which comprise a fuel cell associated with an electric machine. In these systems, the fuel cell and the electric machine generate the electrical power necessary for the vehicle to move forward. More precisely, the two energy sources can be used together or separately, or even the electric machine can be used to store energy produced by the fuel cell.

[0003] In such architectures, the possibility of having a fuel cell system operating at a limited maximum voltage, for example 48V, would make it possible to simplify electrical safety by remaining in a very low voltage range, i.e. less than 120V, and to make it compatible with traction or propulsion chains, batteries or very widespread auxiliary systems operating for the most part at 48V.

[0004] However, imposing a limited maximum voltage, for example 48V, means having to use elementary cells with a large surface area in order to allow the fuel cell to create a sufficiently high current and power.

[0005] However, enlarging the surface area of ​​a cell is not optimal either from a structural strength point of view or in relation to the desired homogeneity of the operating conditions of the fluids used for generating electric current. In addition, the use of cells having a larger surface area than standard cells can result in reduced availability and higher production costs. Statement of the invention

[0006] The aim of the invention is to overcome at least some of the aforementioned drawbacks and to propose a fuel cell system using standard elementary cells and operating at a maximum voltage limited to the very low voltage range, for example 48V.

[0007] The invention relates to a fuel cell system provided with a first air supply circuit, a second hydrogen supply circuit, a third cooling circuit and a fourth electrical circuit restoring a produced electrical charge.

[0008] The system comprises at least two stacks of elementary cells operating at very low voltage, the stacks being identical and connected in parallel. The system comprises a diode connected in series with each stack so as to prevent any reverse current in the stacks.

[0009] Preferably, the system comprises at least one voltage and / or current balancing device associated with each stack so as to reduce an imbalance between the stacks.

[0010] Advantageously, the first air supply circuit comprises a hydraulic device for balancing the voltage and / or current associated with each stack and / or the fourth electrical circuit comprises an electronic device for balancing the voltage and / or current associated with each stack.

[0011] Preferably, the system comprises an electronic control unit configured to control the balancing devices from incoming air hydraulic flow setpoints and outgoing electrical load setpoints.

[0012] Advantageously, the system comprises a direct-direct converter of zeta topology associated with each stack for voltage and / or current balancing.

[0013] For example, the system includes a voltage boost converter associated with each stack for voltage and / or current balancing.

[0014] For example, the system comprises a step-up / step-down converter associated with each stack for voltage and / or current balancing.

[0015] According to an advantageous characteristic, the system comprises a proportional valve arranged upstream of each stack and intended to impose a flow of air entering each stack.

[0016] According to another aspect, the invention relates to a traction or propulsion system for a vehicle comprising at least one electric machine capable of operating at least in a generator mode and a fuel cell system as described above.

[0017] According to another aspect, the invention relates to a vehicle comprising a traction or propulsion system as described above. Brief description of the drawings

[0018] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0019] [Fig-1] illustrates a fuel cell system according to the invention;

[0020] [Fig.2] illustrates a first air supply circuit of the system of [Fig. 1];

[0021] [Fig.3] illustrates a fourth electrical circuit of the system of [Fig.l];

[0022] [Fig.4] illustrates another embodiment of the fourth electrical circuit;

[0023] [Fig.5] illustrates another embodiment of the fourth electrical circuit; and

[0024] [Fig.6] illustrates another embodiment of the fourth electrical circuit. Detailed description of at least one embodiment

[0025] [Fig.l] illustrates a fuel cell system 1 2 according to the invention. The fuel cell system 1 can be integrated into a traction or propulsion chain of a vehicle. However, the proposed cell system can be used for any stationary or mobile system which comprises a fuel cell power source operating at very low voltage. For example, the proposed invention can find applications in the field of handling equipment or be used as a complementary source to solar panels.

[0026] The system 1 is provided with a first air supply circuit 3 and a second hydrogen supply circuit 4, a third cooling circuit 5 and a fourth electrical circuit 6 restoring the electrical charge produced. The system thus constitutes an electric generator.

[0027] A fuel cell consists of two electrodes (anode and cathode) formed of a reaction zone and a diffusion layer, separated by an electrolyte. The potential difference available at the terminals of such a cell is low, of the order of a volt. To achieve useful voltages, cells are stacked, that is to say placed in electrical series. The stack thus produced is commonly referred to by the English term "stack".

[0028] The system 1 comprises at least two stacks 7 of elementary cells operating at very low voltage, for example a voltage of 48V. All the stacks 7 are identical and connected in parallel.

[0029] The unavoidable imbalances and dispersions of the polarization curves between the stacks 7 necessarily lead to an imbalance of the currents generated by the stacks 7.

[0030] To avoid any damage that could result from a significant imbalance, the system 1 comprises a diode 8 connected in series with each stack 7 so as to prevent any reverse current in the stacks.

[0031] Preferably, the system 1 comprises at least one voltage and / or current balancing device 9 associated with each stack 7 so as to reduce an imbalance between the stacks. Alternatively, it is possible for the system 1 not to be equipped with a voltage and / or current balancing device 9.

[0032] In the embodiment illustrated in [Fig.l], the first air supply circuit 3 comprises a hydraulic device 9 for balancing the voltage and / or current associated with each stack and the fourth electrical circuit 6 comprises an electronic device 9 for balancing the voltage and / or current associated with each stacking.

[0033] Alternatively, it is possible for the balancing devices 9 to be provided only on the first air supply circuit 3. In this alternative, the balancing devices 9 are hydraulic.

[0034] According to another variant, it is possible for the balancing devices 9 to be provided only on the fourth electrical circuit 6. In this variant, the balancing devices 9 are electronic.

[0035] The system 1 also comprises an electronic regulation unit 10 which comprises a measurement module 11, a calculation module 12 and a control module 13. The electronic regulation unit 10 ensures both the regulation of the hydraulic flows which supply each stack 7 and the regulation of the outgoing electrical charge of each stack 7.

[0036] The calculation module 12 is configured to calculate incoming air hydraulic flow setpoints and outgoing electrical load setpoints as a function of parameters of the system 1 measured by the measurement module 11. The control module 13 is capable of controlling the balancing devices 9 from the setpoints from the calculation module 12.

[0037] [Fig.2] illustrates the first air supply circuit 3 of the system of [Fig.l]. In the figures, the same elements bear the same references.

[0038] The first supply circuit 3 comprises a filter 14, a compressor 15, a cooling unit 16 and a humidification unit 17. Each stack 7 is connected to the first air supply circuit 3 by an inlet 18 and an outlet 19 which respectively allow the entry and exit of air.

[0039] The first air supply circuit 3 is provided with voltage and / or current balancing devices 9. These devices 9 are arranged upstream of the inlet 18 of each stack 7 and each comprise a proportional valve 20 intended to impose an air flow entering each stack 7. The control of the incoming air flow is carried out according to the instructions from the electronic regulation unit.

[0040] The first circuit 3 further comprises an outlet valve 21 and a silencer 22 both arranged downstream of the outlets 19 of the stacks 7.

[0041] [Fig. 3] illustrates the fourth electrical circuit 6 of the system of [Fig. 1]. The fourth electrical circuit 6 comprises an electronic voltage and / or current balancing device 9 associated with each stack 7.

[0042] Preferably, each electronic balancing device 9 comprises a DC-DC converter 25 of zeta topology, as illustrated in [Fig.3]. The configuration of such a converter 25 of zeta topology is known and is not further detailed here. With such an architecture, it is possible to independently control the electric charge of each stack 7.

[0043] Thus, in parallel with the hydraulic regulation of each stack 7, the control of each zeta converter 25 allows the regulation of the current load of each stack 7. Such electronic regulation has the advantage of anticipating the slower dynamics of the hydraulic regulation.

[0044] In direct current mode, each zeta converter 25 makes it possible to regulate the output voltage of the associated stack 7 via the duty cycle applied to the switching of a transistor 26. It should be noted that the transistor 26 must withstand a voltage at least equal to the sum of the voltage of the associated stack 7 and that of the on-board network that it supplies. Thus, this topology is particularly relevant for an on-board network and stacks at very low voltage, typically 48V.

[0045] The electrical charge setpoint of each stack 7 comes from the electronic regulation unit 10 which also manages the hydraulic flows which supply each stack 7 as already indicated previously.

[0046] According to an embodiment illustrated in [Fig. 4], each electronic balancing device 9 comprises a voltage boost converter, commonly referred to by the English term “boost”. The configuration of such a voltage boost converter is known and is not detailed further here. With such an architecture, it is possible to balance the current charges of each stack 7 or to balance the powers delivered by each stack 7. Thus, the power supplied by the stack which has the lowest polarization curve is increased up to a limit of approximately 0.5V per cell.

[0047] According to an embodiment illustrated in [Fig.5], each electronic balancing device 9 comprises a voltage step-down converter, commonly referred to by the English term "buck". The configuration of such a voltage step-down converter is known and is not detailed further here. With such an architecture, the voltage delivered to the electrical load can only be lower than the voltage of the stack having the lowest voltage.

[0048] According to an embodiment illustrated in [Fig.6], each electronic balancing device 9 comprises a voltage step-up / step-down converter, commonly referred to by the English term “buck-boost”. The configuration of such a step-up / step-down converter is known and is not detailed further here. With such an architecture, it is possible to control the current of each stack regardless of its voltage.

Claims

Claims

1. Fuel cell (2) system (1) provided with a first air supply circuit (3), a second dihydrogen supply circuit (4), a third cooling circuit (5) and a fourth electrical circuit (6) restoring a produced electrical charge, said system being characterized in that it comprises at least two stacks (7) of elementary cells operating at a voltage lower than 120V, said stacks being identical and mounted in parallel, said system comprising a diode (8) mounted in series with each stack (7) so as to prevent any reverse current in the stacks (7).

2. System according to claim 1, comprising at least one voltage and / or current balancing device (9) associated with each stack so as to reduce an imbalance between the stacks.

3. Fuel cell system according to claim 1 or 2, wherein the first air supply circuit (3) comprises a hydraulic device (9) for balancing the voltage and / or current associated with each stack and / or the fourth electrical circuit (6) comprises an electronic device (9) for balancing the voltage and / or current associated with each stack.

4. Fuel cell system according to claim 2 or 3, comprising an electronic regulation unit (10) configured to control said balancing devices (9) from incoming air hydraulic flow setpoints and outgoing electrical charge setpoints.

5. A fuel cell system according to any one of claims 2 to 4, comprising a zeta topology DC-DC converter associated with each stack for voltage and / or current balancing.

6. A fuel cell system according to any one of claims 2 to 4, comprising a voltage boost converter associated with each stack for voltage and / or current balancing.

7. A fuel cell system according to any one of claims 2 to 4, comprising a voltage step-up / step-down converter associated with each stack for voltage and / or current balancing.

8. Fuel cell system according to any one of claims 2 to 7, comprising a proportional valve (20) arranged upstream of each stack and intended to impose a flow of air entering each stack (7).

9. Traction or propulsion system for a vehicle, comprising at least one electric machine capable of operating at least in a generator mode and a fuel cell system (1) according to any one of claims 1 to 8.

10. Vehicle comprising a traction or propulsion system according to claim 9.

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