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 be integrated into a traction or propulsion chain of a vehicle. Previous techniques

[0002] Vehicle traction or propulsion systems are known that include a fuel cell coupled to an electric machine. In these systems, the fuel cell and the electric machine generate the electrical power necessary to propel the vehicle. More precisely, the two energy sources can be used together or separately, or 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 simplify electrical safety by remaining in a very low voltage range, i.e. below 120V, and make it compatible with traction or propulsion chains, batteries or auxiliary systems which are very common and mostly operate 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 generate a sufficiently high current and power.

[0005] However, increasing the surface area of ​​a cell is not optimal from either a structural integrity standpoint or with respect to the desired homogeneity of the operating conditions of the fluids used for generating electricity. Furthermore, using cells with a larger surface area than standard cells can result in reduced availability and higher production costs. Description of the invention

[0006] The invention aims 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 equipped with a first air supply circuit, a second dihydrogen supply circuit, a third cooling circuit and a fourth electrical circuit returning an electrical charge produced.

[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 includes a diode connected in series with each stack so as to prevent any reverse current in the stacks.

[0009] Preferably, the system includes 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 includes a hydraulic device for balancing the voltage and / or current associated with each stack and / or the fourth electrical circuit includes an electronic device for balancing the voltage and / or current associated with each stack.

[0011] Preferably, the system includes an electronic control unit configured to control the balancing devices based on hydraulic air flow setpoints and electrical load setpoints.

[0012] Advantageously, the system includes a zeta topology DC-DC converter 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 includes a voltage boost-down converter associated with each stack for voltage and / or current balancing.

[0015] According to an advantageous feature, the system includes a proportional valve disposed upstream of each stack and intended to impose an air flow 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 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 objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying 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 the [Fig.1];

[0021] [Fig.3] illustrates a fourth electrical circuit of the system of the [Fig.1];

[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] Figure 1 illustrates a fuel cell system 2 according to the invention. The fuel cell system 1 can be integrated into a vehicle's traction or propulsion system. However, the proposed fuel cell system can be used for any stationary or mobile system that includes a fuel cell power source operating at very low voltage. For example, the proposed invention can find applications in the field of material handling equipment or be used as a supplementary power source to solar panels.

[0026] System 1 is equipped with a first air supply circuit 3 and a second dihydrogen supply circuit 4, a third cooling circuit 5 and a fourth electrical circuit 6 which returns the electrical charge produced. The system thus constitutes a generator set.

[0027] A fuel cell consists of two electrodes (anode and cathode) formed by a reaction zone and a diffusion layer, separated by an electrolyte. The potential difference available across such a cell is low, on the order of a volt. To achieve useful voltages, cells are stacked, that is, placed in electrical series. The stack thus created 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 inevitable 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 may result from a significant imbalance, the system 1 includes a diode 8 mounted in series with each stack 7 so as to prohibit any reverse current in the stacks.

[0031] Preferably, system 1 includes 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, system 1 may not be equipped with a voltage and / or current balancing device 9.

[0032] In the embodiment illustrated in [Fig. 1], the first air supply circuit 3 includes a hydraulic voltage and / or current balancing device 9 associated with each stack, and the fourth electrical circuit 6 includes a electronic device 9 for voltage and / or current balancing associated with each stack.

[0033] Alternatively, the balancing devices 9 may be provided only on the first air supply circuit 3. In this variant, the balancing devices 9 are hydraulic.

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

[0035] The system 1 also includes an electronic control unit 10 which includes a measuring module 11, a calculation module 12 and a control module 13. The electronic control 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 hydraulic air inlet flow setpoints and electrical outlet load setpoints based on system 1 parameters measured by the measurement module 11. The control module 13 is capable of controlling the balancing devices 9 based on the setpoints from the calculation module 12.

[0037] Figure 2 illustrates the first air supply circuit 3 of the system in Figure 1. In the figures, the same elements bear the same reference numerals.

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

[0039] The first air supply circuit 3 is equipped with voltage and / or current balancing devices 9. These devices 9 are located upstream of the inlet 18 of each stack 7 and each includes a proportional valve 20 for imposing an incoming airflow rate into each stack 7. The incoming airflow rate is controlled according to the setpoints from the electronic control unit.

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

[0041] Figure 3 illustrates the fourth electrical circuit 6 of the system of Figure 1. The fourth electrical circuit 6 includes 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 no more detailed here. With such an architecture, it is possible to independently control the electrical 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 DC mode, each zeta converter 25 regulates 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 onboard network it supplies. Thus, this topology is particularly suitable for onboard networks and very low-voltage stacks, typically 48V.

[0045] The electrical load setpoint of each stack 7 is derived from the electronic control 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. The configuration of such a voltage boost converter is known and is not described in further detail here. With such an architecture, it is possible to balance the current loads of each stack 7 or to balance the power delivered by each stack 7. Thus, the power supplied by the stack with the lowest bias 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 buck converter. The configuration of such a buck converter is known and is not described in further detail here. With such an architecture, the voltage delivered to the electrical load can only be lower than the voltage of the stack with the lowest voltage.

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

Claims

Demands

1. A fuel cell system (1) (2) having a first air supply circuit (3), a second hydrogen supply circuit (4), a third cooling circuit (5), and a fourth electrical circuit (6) returning an electrical charge produced, said system being characterized in that it comprises at least two stacks (7) of elementary cells operating at a voltage below 120V, 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), said system comprising at least one voltage and / or current balancing device (9) associated with each stack so as to reduce an imbalance between the stacks,said system comprising an electronic control unit (10) configured to control said balancing devices (9) based on hydraulic air flow setpoints and electrical load setpoints.

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

3. Fuel cell system according to claim 1 or 2, comprising a zeta topology DC-DC converter associated with each stack for voltage and / or current balancing.

4. Fuel cell system according to claim 1 or 2, comprising a voltage boost converter associated with each stack for voltage and / or current balancing.

5. Fuel cell system according to claim 1 or 2, comprising a voltage boost-step converter associated with each stack for voltage and / or current balancing.

6. Fuel cell system according to any one of claims 1 to 5, comprising a proportional valve (20) positioned upstream of each stack and intended to impose an airflow entering each stack (7).

7. Vehicle traction or propulsion system, comprising at least one electric machine capable of operating at least in generator mode and a fuel cell system (1) according to any one of claims 1 to 6.

8. Vehicle comprising a traction or propulsion system according to claim 7.

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