Air supply device, fuel cell system, and vehicle

Abstract

The invention relates to an air supply device (28) for a fuel cell system with two-stage compression. The invention is characterized by the fact that a turbocompressor (15, 16) is provided for each of the fuel cell stacks (2, 3) for supplying the electrically parallel-connected fuel cell stacks (2, 3), which turbocompressors (15, 16) are mechanically connected with the exhaust turbines (17, 18) for the respective fuel cell stacks (2, 3), and at least one electric flow compressor (28) is provided in front of each turbocompressor (15, 16) in the flow direction of the compressed air, which flows and supplies air in parallel to at least two of the turbocompressors (15, 16). A fuel cell system with at least two fuel cell stacks (2, 3) including such an air supply can be used, for example, in a vehicle (1), in particular a commercial vehicle.

Description

[Technical field]

[0001] The present invention relates to an air supply device for a fuel cell system with two-stage compression. Furthermore, the present invention relates to a fuel cell system equipped with such an air supply device and to a vehicle equipped with such a fuel cell system. [Background technology]

[0002] The use of fuel cell systems for generating electrical power, for example for stationary applications or even in particular as an electric power source for vehicles, is largely known from the prior art. For this purpose, PEM fuel cells are often used, which are supplied with air as an oxygen source on the cathode side. In this case, a single-stage flow compressor is often used for the air supply. Particularly often, this flow compressor is combined with an exhaust turbine and an electric machine, forming a so-called electric turbocharger or a motor-assisted turbocharger. This means that the energy contained in the exhaust gas of the respective fuel cell can be at least partially recovered and used for the air supply.

[0003] The problem is always that such structures operate on a characteristic curve very close to the surge limit, so a so-called relief valve, also called wastegate valve, is typically present to ensure a reliable supply of the fuel cell during part-load operation without exceeding the surge limit.

[0004] This in fact limits the free choice of operating point on the one hand and, on the other hand, causes power losses if the already compressed supply air flows through the relief valve, since in the exhaust turbine only a part of the energy delivered during compression can be recovered again.

[0005] To address this problem, a fuel cell air supply system is known from DE 10 200 03 133 A1, which is configured as a two-stage system. This allows a high variability of volume flow and pressure to be achieved without being influenced by the surge limit. The design is such that the first stage is formed by an electrically operated flow compressor and the second compression stage by a turbocompressor. The turbocompressor is connected directly via a shaft to the exhaust turbine and is therefore realized as a free runner. In this case, the exhaust turbine has variable turbine guide vanes. In the design described there, a relief valve is still provided, which could, however, in principle not be necessary here. [Patent Document 1] WO 02 / 086997 A2

[0006] Fuel cell systems are now increasingly being used to provide a relatively large power output, for example for driving commercial vehicles, such as passenger buses, trucks or the like. In this regard, in order to achieve a simple and possibly scalable adaptation of the power output to different sizes of commercial vehicles, several fuel cell stacks are electrically combined in the fuel cell system. A typical construction provides, for example, two electrically parallel-connected fuel cell stacks in such a construction. Since both fuel cell stacks should be controlled independently of each other, both in terms of fuel supply and in terms of air supply, in the constructions known from the general prior art, typically two air supply systems are provided in parallel with each other. Most often, this is two separate electric turbochargers in the sense described at the beginning, which in this case require two relief valves, two converters, two electric motors and the like. Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is therefore to correspondingly simplify this design, which is known in principle from the prior art, and to improve the variability to be achieved in the air supply of a fuel cell system. [Means for solving the problem]

[0008] According to the invention, this problem is solved by an air supply device for a fuel cell system having the features of claim 1, here in particular the characterizing part of claim 1. Furthermore, a fuel cell system with such an air supply device solves this problem. A vehicle with such a fuel cell system can also solve this problem. Further advantageous configurations and variants of the air supply device and the vehicle are evident from the dependent claims.

[0009] The air supply device according to the invention comprises a turbocompressor for each of the fuel cell stacks operating electrically in parallel, which is mechanically connected to the exhaust turbine for the respective fuel cell stack, in which at least one electrically operated flow compressor is provided upstream of the turbocompressor in the flow direction of the compressed air, which flow compressor respectively supplies air in parallel to at least two of the turbocompressors.

[0010] The turbocompressors, which are each formed as free runners and directly mechanically coupled to the exhaust turbine, thus form the second compressor stage of the two-stage air supply system. Each of the turbocompressors is assigned to one of the fuel cell stacks, which operate in parallel in the overall system and are typically electrically connected in parallel, although an electrical series connection is also conceivable in principle.

[0011] Here, the first stage of compression in the air supply device is formed by one electric flow compressor for each at least two of the turbocompressors. That is, in the case of a typical configuration with two fuel cell stacks, one electric flow compressor as the first compression stage supplies two turbocompressors as the second compression stage, which in turn supply one assigned fuel cell stack each. The exhaust air from the cathode side of the fuel cell stack then reaches the surroundings via an exhaust turbine associated with the respective turbocompressor, so that the residual energy in the exhaust air drives the second compression stage for the respective fuel cell stack via the exhaust turbine. In this case, both turbocompressors have a common flow compressor, which supplies the turbocompressors with air on the low pressure side, thereby forming a first stage of compression common to both turbocompressors.

[0012] This structure therefore makes it possible to take advantage of the advantages of two-stage compression in order to have a high degree of freedom in the selection of the operating point without the risk of exceeding the surge limit. Moreover, this structure is compact and efficient, since in the area of ​​both turbocompressors as the second stage there is no electric machine, making it a simple and efficient free-runner. As the first stage of compression, this structure uses one equally simple flow compressor, which can have, for example, a compressor wheel with a larger circumference than both turbocompressors, in order to provide the required air volume in the case of moderate rotational speeds and a correspondingly simple and inexpensive drive motor.

[0013] Overall, this design requires only one electric motor with corresponding converter for both parallel fuel cell stacks and, due to the two-stage compression, it is possible to do away with relief valves, among other things, which results in considerable cost and installation space advantages in terms of saved components, in particular in terms of saved electrical components and their control.

[0014] According to a very preferred variant of the air supply device according to the invention, at least one of the exhaust turbines has variable turbine guide vanes. Preferably, according to an advantageous variant, all exhaust turbines may have variable turbine guide vanes. In order to achieve high variability in driving the turbocompressor in the second compression stage, the energy provided by the fuel cell via the exhaust to the respective exhaust turbine can be varied accordingly by means of such variable turbine guide vanes in the region of the exhaust turbine. Both fuel cell stacks operating in parallel can thus be controlled sufficiently independently of each other in terms of the amount of air supplied thereto. This allows a very advantageous and sufficiently independent operation of each fuel cell stack from the other fuel cell stacks in terms of the air supply of the fuel cell stacks. Thus, in conjunction with an easily controllable dosing valve for hydrogen on the anode side, each of the fuel cell stacks can be operated independently of the respective other fuel cell stacks.

[0015] A further very crucial aspect is that at least one variable turbine geometry and the electric motor of the flow compressor are controlled by a common controller, in order to also reduce the costs related to the controller, which can, among other things, also control the dosing of hydrogen to the anode side of each fuel cell stack, and thus can individually control the power delivered in at least two fuel cell stacks operating in parallel.

[0016] As already mentioned, according to one particularly preferred embodiment, the arrangement can have exactly one flow compressor and exactly two turbo compressors and can be provided for supplying air to two fuel cell stacks operating in parallel.

[0017] A further advantageous embodiment is in addition to this, a charge air cooler is respectively arranged behind the turbocompressor in the flow direction, so that the charge air, which is hot and typically dry after compression in the two-stage compression process, is correspondingly cooled and, if necessary, humidified via a humidifier connected to the charge air cooler or combined with it.

[0018] A fuel cell system according to the invention may comprise at least two fuel cell stacks and an air supply device in the manner described, so that the advantages described for and the possibilities opened up via the air supply may be ideally utilized for efficient operation and individual control of at least two fuel cell stacks in one fuel cell system.

[0019] Accordingly, the vehicle according to the invention comprises such a fuel cell system with at least two, preferably exactly two, fuel cell stacks and may be configured as a commercial vehicle, for example as a truck or a bus.

[0020] Further advantageous configurations of the air supply device according to the invention and of the fuel cell system and / or vehicle according to the invention are evident from the exemplary embodiments which are explained in more detail below with reference to the figures. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 shows a fuel cell system with two fuel cell stacks and two air supply systems according to the prior art. [Diagram 2] FIG. 2 is a view showing a structure equipped with an air supply device according to one possible embodiment of the present invention, following the structure in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In the representation of Fig. 1, a vehicle 1, for example a commercial vehicle, is very strongly schematically suggested. The vehicle 1 is to receive its electric power or at least a part of its electric power from two fuel cell stacks 2, 3. The fuel cell stacks 2, 3 are operated in parallel for this purpose and are in particular electrically connected in parallel. The arrangement has a common hydrogen source 4, which can be formed for example as a compressed gas reservoir, a cryo-reservoir or the like. The hydrogen source 4 directs hydrogen via two separate pressure regulating and dosing valves 5, 6 into the anode chambers 7, 8 of both fuel cell stacks 2, 3. Unused hydrogen reaches the environment together with the exhaust gases in the exemplary embodiment shown here.

[0023] This is merely a schematic diagram. It is clear to those skilled in the art that further components, such as an anode circuit, can be arranged here, or measures can be taken, such as feeding the exhaust gas into the exhaust, to dilute it accordingly. However, the anode side is incidental to the invention, and therefore will not be discussed further here.

[0024] In order to supply air to both cathode chambers 9, 10 of both fuel cell stacks 2, 3, in this configuration according to the prior art, an electric turbocharger 11, 12 is provided, respectively. Both electric turbochargers 11, 12 have an electric motor 13, 14 and a turbo compressor 15, 16. On a common shaft together with both components, furthermore, an exhaust turbine 17, 18 of this electric turbocharger, respectively, is arranged. In addition, the air supply pipes 19, 20 to the respective fuel cell stacks 2, 3 are provided with respective air supply coolers 21, 22. Furthermore, the air supply pipes 19, 20 to the respective fuel cell stacks 2, 3 are connected via so-called relief valves 23, 24, also called wastegate valves, to the respective exhaust pipes 25, 26 of the fuel cell stacks 2, 3, so that the compressed air after the respective turbo compressors 17, 18 can be discharged if necessary when the respective fuel cell stacks 2, 3 are operated in part-load operation. This is necessary to reliably prevent the surge limit at a certain operating point from being exceeded. This construction allows for independent air supplies for both fuel cell stacks 2, 3, but is relatively complex in terms of the components required and their control.

[0025] The representation of Fig. 2 thus shows a structure with an air supply device 27, which here offers a decisive advantage. Both fuel cell stacks 2, 3 with the supply and discharge pipes and both charge air coolers 21, 22 are shown and can be understood according to the representation in Fig. 1. We will not go into this structure, nor even into the entire anode side of the fuel cell system, which is again only shown exemplarily and diagrammatically.

[0026] Here, an air supply 27 serves for the mutually independent air supply of both fuel cell stacks 2, 3 and is configured as a two-stage air supply 27. The first stage is a flow compressor 28 with an electric motor 29, common to both fuel cell stacks 2, 3. This electric motor 29 is correspondingly controlled by a common control 30, as well as further components, which will also be mentioned later. In this case, the air flow of the flow compressor 28 is split into two parallel intake pipes 31, 32, which again supply two turbocompressors, again numbered 15, 16 according to the representation in FIG. 1. The two turbocompressors 15, 16 thus form a second compression stage, the air compressed by which is delivered as oxygen supply by the intake pipes 19, 20 via the intake air coolers 21, 22 to the cathode chambers 9, 10 of both fuel cell stacks 2, 3.

[0027] In contrast to the prior art design according to FIG. 1, both turbocompressors 15, 16 are configured as so-called free runners and are arranged on a common shaft with the respective exhaust turbines 17, 18. However, this design can be realized much more simply and efficiently without the electric machines of the two prior art electric turbochargers 12, 13. In addition to the design described so far within the context of FIG. 1, both exhaust turbines 17, 18 now each have variable turbine guide vanes 33, 34. In this connection, independent control of these turbine guide vanes 33, 34 is provided by a common control unit 30. This allows the air quantities fed via the two turbocompressors 15, 16 to the respective fuel cell stacks 2, 3 or to the cathode chambers 9, 10 to be adjusted independently of one another accordingly, when the first stage of compression by the flow compressor 28 is shared. Comparably to the prior art design according to FIG. 1, the air feeds of both fuel cell stacks 2, 3 can be controlled independently of one another, despite the relatively simple design with few components. Thus, a fully independent operation of the two fuel cell stacks 2, 3 is possible, together with the control of the dosing valves 5, 6, which in any case should be performed very simply and independently. Furthermore, this two-stage system makes it possible to dispense with the relief valves 23, 24, although in principle they could of course be provided, for example if required for reasons other than system bypass or similar.

Claims

1. 1. An air supply device (27) for a fuel cell system with two-stage compression, characterized in that a turbo compressor (15, 16) is provided for each of the fuel cell stacks (2, 3) electrically connected in parallel for supplying said fuel cell stacks (2, 3), said turbo compressors (15, 16) being mechanically connected with an exhaust turbine (17, 18) for each of said fuel cell stacks (2, 3), and in the compressed air flow direction, at least one electrically operated flow compressor (28) is provided before each of said turbo compressors (15, 16), said flow compressors (28) supplying air in parallel to at least two of said turbo compressors (15, 16).

2. 2. An air supply device (27) according to claim 1, characterized in that at least one of the exhaust turbines (17, 18) has variable turbine guide vanes (33, 34).

3. 3. An air supply device (27) according to claim 1 or 2, characterized in that each of the exhaust turbines (17, 18) has variable turbine guide vanes (33, 34).

4. 3. The air supply device (27) according to claim 1 or 2, characterized in that at least one variable turbine guide vane (33, 34) and the drive motor (29) of the flow compressor (28) are controlled by a common control unit (30).

5. 3. Air supply device (27) according to claim 1 or 2, characterized in that one flow compressor (28) and exactly two turbo compressors (15, 16) are provided.

6. 3. Air supply device (27) according to claim 1 or 2, characterized in that a charge air cooler (21, 22) is arranged behind each of the turbo compressors (15, 16) in the flow direction.

7. A fuel cell system comprising at least two fuel cell stacks (2, 3) and an air supply device (27) according to claim 1 or 2.

8. A vehicle (1) equipped with a fuel cell system according to claim 7.

9. 9. The vehicle (1) according to claim 8, characterized in that it is designed as a commercial vehicle.

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