APPARATUS FOR MONITORING THE CELL VOLTAGE

Abstract

The invention relates to an apparatus for monitoring the cell voltage of an individual cell (3), formed by a membrane electrode assembly (4) and bipolar plates (6), of a fuel cell stack (1), the apparatus having a measuring device (7) for each of the individual cells (3), which measuring device comprises an optical signal generator (9) which is controllable by the measuring device. The apparatus according to the invention is characterized in that the measuring device (7) is formed on a flexible circuit board that is connected to a frame (5) of a framed membrane electrode assembly (4, 5) or is formed as part of the frame.

Claims

1. An apparatus for monitoring the cell voltage of an individual cell, formed by a membrane electrode assembly and bipolar plates, of a fuel cell stack, having a measuring device for each of the individual cells, which comprises an optical signal generator which can be controlled by it, characterized in that the measuring device is formed on a flexible circuit board which is connected to a frame of a framed membrane electrode assembly or formed as part of the same.

2. The device apparatus according to claim 1, wherein the measuring device is electrically conductively connected to the two adjacent bipolar plates via flexible conductor elements and/or spring contacts.

3. The apparatus according to claim 1, wherein the measuring device comprises a step-up converter.

4. The apparatus according to claim 1, wherein the optical signal generator is formed in such a way that it can be controlled by the measuring device with at least three different states.

5. The apparatus according to claim 1, wherein the optical signal generator of each measuring device is formed by a light-emitting diode, which is set up to emit light in at least two light colors.

6. The apparatus according to claim 1, wherein the optical signal generator of each measuring device is formed by at least two light-emitting diodes.

7. The apparatus according to claim 6, wherein the at least two light-emitting diodes of each optical signal generator produce different colors of light.

8. The apparatus according to claim 1, wherein the optical signal generators of all measuring devices are connected to at least one optical sensor via at least one light guide.

9. The apparatus according to claim 8, wherein an evaluation electronics for evaluating the data of the at least one sensor is provided, which is set up to evaluate the detected signals with regard to the occurrence of specific colors and/or flashing frequencies.

10. The apparatus according to claim 6 or 7, wherein at least two light guides are provided, which connect the at least two light-emitting diodes of all optical signal generators separately, each with at least one optical sensor.

11. The apparatus according to claim 10, wherein the at least one light guide is formed of a strip-shaped light-guiding material which is arranged such that the optical signal generators couple their light into one of the longitudinal sides, wherein the at least one optical sensor is arranged on at least one end face of the light guide.

12. The apparatus according to claim 2, wherein the measuring device comprises a step-up converter.

13. The apparatus according to claim 2, wherein the optical signal generator is formed in such a way that it can be controlled by the measuring device with at least three different states.

14. The apparatus according to claim 3, wherein the optical signal generator is formed in such a way that it can be controlled by the measuring device with at least three different states.

15. The apparatus according to claim 2, wherein the optical signal generator of each measuring device is formed by a light-emitting diode, which is set up to emit light in at least two light colors.

16. The apparatus according to claim 3, wherein the optical signal generator of each measuring device is formed by a light-emitting diode, which is set up to emit light in at least two light colors.

17. The apparatus according to claim 2, wherein the optical signal generator of each measuring device is formed by at least two light-emitting diodes.

18. The apparatus according to claim 3, wherein the optical signal generator of each measuring device is formed by at least two light-emitting diodes.

19. The apparatus according to claim 2, wherein the optical signal generators of all measuring devices are connected to at least one optical sensor via at least one light guide.

20. The apparatus according to claim 7, wherein at least two light guides are provided, which connect the at least two light-emitting diodes of all optical signal generators separately, each with at least one optical sensor.

Description

[0026] Further advantageous designs of the apparatus according to the invention also result from the exemplary embodiment, which is represented in more detail with reference to the figures.

[0027] Thereby shows:

[0028] FIG. 1 a schematic representation of a fuel cell stack;

[0029] FIG. 2 a section of a fuel cell stack with the apparatus according to the invention;

[0030] FIG. 3 a representation analogous to that in FIG. 1 with a particularly favorable design of the apparatus according to the invention;

[0031] FIG. 4 a representation of a possible design of the apparatus according to the invention based on a section of the fuel cell stack and the apparatus in a first possible embodiment;

[0032] FIG. 5 a representation of a possible design of the apparatus according to the invention based on a section of the fuel cell stack and the apparatus in a second possible embodiment;

[0033] FIG. 6 a representation of a possible design of the apparatus according to the invention based on a section of the fuel cell stack and the apparatus in a third possible embodiment; and

[0034] FIG. 7 a representation of a possible design of the apparatus according to the invention based on a section of the fuel cell stack and the apparatus in a fourth possible embodiment.

[0035] In the representation of FIG. 1, a fuel cell stack denoted by 1 is shown in very general terms. Between two end plates, each denoted by 2, there is a plurality of individual cells denoted by 3, not all of which are represented here on the one hand and not all of those represented are provided with a reference numeral on the other hand. The structure of such a fuel cell stack 1 is known to a person skilled in the art. The fuel cell stack 1 represented here should be a low-temperature fuel cell with PEM individual cells, i.e. cells with a catalytically coated proton-conducting membrane.

[0036] In the representation of FIG. 2, a section of the fuel cell stack is shown in an enlarged representation. The middle individual cell 3 shown here, of which only an upper part is represented, comprises a so-called membrane electrode assembly 4, which comprises the catalytically coated membrane on the one hand and the gas diffusion layers and electrodes on the other hand. This membrane electrode assembly is glued to a frame 5 here. This structure is also referred to as a framed membrane electrode assembly or Membrane Electrode Frame Assembly (MEFA). This MEFA 4, 5 can be provided with its own seals, which are not represented here. It is then referred to as SMEFA. As an alternative to this, the seals can also be inserted when stacked or are arranged in the bipolar plates 6 arranged adjacent to the MEFA 4, 5 in each case. Two of these bipolar plates 6 are represented in the representation of FIG. 2. On one side they have a flow field which is not represented here for distributing hydrogen-containing gases and on the other side a flow field which is not represented here for distributing oxygen-containing gas to the two adjacent individual cells. A flow field for cooling medium is typically arranged in between in the interior of the bipolar plate 6. All of this is known to those skilled in the art of fuel cells. The bipolar plates 6 can be made of metal or of plastics provided with electrically conductive fillers or plastic materials with an electrically conductive coating. All of this is of secondary importance for the present invention, so that it will not be discussed further.

[0037] In connection with or as part of the frame 5, a flexible circuit board which is not represented here is formed, which carries a measuring device denoted by 7, which is represented here on the frame 5. This measuring device 7 comprises various components such as a step-up converter and a device for detecting the voltage of the individual cell 3 to whose frame 5 it is connected. The measuring device 7 arranged on the flexible circuit board connected to the frame 5 or formed by it is electrically contacted with the two adjacent bipolar plates 6 preferably via resilient electrical contacts 8, namely on the one side with the positive surface and on the other side with the negative surface of the corresponding bipolar plate 6. As a result, the voltage of the individual cell 3 of the fuel cell stack 1 assigned to it can be monitored via the measuring device 7.

[0038] For the operation of the fuel cell stack 1, it is now essential to distinguish between different voltage states. On the one hand, this is the normal state, a state with reduced cell voltage, which is referred to as “low cell,” a state with increased voltage, which is referred to as “high cell,” and a state in which a reversal of the electrical polarity of the individual cell 3 has taken place. This state is often referred to by the term “cell reversal.” For the control of the fuel cell stack 1, it is now of decisive importance whether all of its individual cells 3 are working normally or whether one or more of the individual cells have one of the critical states just described, wherein the low cell and high cell states are not quite as critical as the state of a cell reversal.

[0039] The measuring device 7 can now detect these states. In contrast to conventionally structured devices for monitoring the voltage of the individual cells 3 of the fuel cell stack 1, the measuring device 7 of the type described here with the integration on the frame 5 has the advantage that it is installed directly during the production of the cell and not installed later and does not have to be electrically contacted separately. In order to reliably transmit the signal in the area, which is also critical with regard to explosion protection due to possible hydrogen leaks from the fuel cell stack 1, the measuring device 7 has an optical signal generator 9. This optical signal generator 9 can now in particular represent the above-mentioned states of the voltage of the individual cell 3 accordingly, for example by remaining switched off when the voltage is normal and, in the simplest case, by lighting up in one of the other states.

[0040] In principle, the signals from the optical signal generator can then be detected and evaluated in the manner known from the prior art, for example via a series of detectors or by deflecting the light to a high-resolution detector. All of this is conceivable in principle, but it is relatively complex in terms of the installation space required and the costs. Frequently, particularly in vehicle applications, it is sufficient if it is known that at least one of the individual cells 3 of the fuel cell stack 1 has a corresponding problem. In this case, a response must be made, in case of doubt by shutting down the entire fuel cell stack 1 or by changing its media supply accordingly.

[0041] The simplest variant of the structure is now shown in the representation of FIG. 3 using a fuel cell stack 1 analogous to the one in FIG. 1. The individual cells 3 represented each have the measuring device 7 with the optical signal generator 9. A light guide 10, which is formed as a strip-shaped light guide, for example with the cross-sectional shape of a cuboid, runs in the stacking direction s along the entire fuel cell stack 1, in such a way that the optical signal generators 9 of all measuring devices 7 of all individual cells 3 couple their light laterally into a longitudinal side of the light guide 10. Optical sensors 11 are now arranged on at least one or optionally on two end faces, preferably in the area of the end faces which face the end plates 2 of the fuel cell stack 1 or end in their area. In principle, one optical sensor 11 is sufficient. However, with a correspondingly high number of individual cells 3 and thus a large length of the fuel cell stack 1 in the stacking direction s, it can be advantageous to provide a further optional optical sensor 11 in the area of the second end plate 2 in order to obtain a reliable result even in case only an individual cell 3 generates a signal via its optical signal generator 9 of the measuring device 7, which is relatively far away along the stacking direction s from only one optical sensor 11 and therefore cannot be reliably detected by it.

[0042] As already mentioned above, it can now be advantageous if it is known whether the problem of a low cell, a high cell and/or the problem of a cell reversal has been detected via the optical sensor 11. In principle, there are various possibilities for this, which are represented and explained accordingly in the following representations of FIGS. 4 to 7. A section of one of the end plates 2 with three individual cells 3 and their measuring devices 7 is represented in each case.

[0043] In the case of the representation in FIG. 4, each of the measuring devices 7 has a light-emitting diode 12 as an optical signal generator 9. This light-emitting diode 12 is formed as a multicolor LED, which can represent different colors. If the voltage of the respective individual cell 3 is normal, it remains switched off. With a low cell, it emits a first color, e.g. yellow, with a high cell, it emits a second color, e.g. blue, and with a cell with reversed polarity, i.e. a cell reversal, it emits a third color, e.g. red. The light emitted and collected by the light guide 10 and guided into the area of the sensor 11 is now received via the one or optionally two optical sensors 11 arranged on the two end plates 2 and evaluated accordingly by evaluation electronics 13. In particular, a Fourier analysis can be carried out in this evaluation electronics 13 in order to analyze different light colors in the light detected by the sensor 11. If the light is only one color, for example if yellow light is present, then the problem of one or more low cells can be reported further via the evaluation electronics 13. If the light contains only red light, the problem of one or more cell reversals could be reported accordingly. If the light contains only blue light, the problem of one or more high cells could be reported further. If the light contains all three light colors, then a corresponding message that both low cells and a cell reversal are present can be forwarded accordingly. With regard to the hardware, this requires the multicolor LED 12 and with regard to the software, a corresponding evaluation in the evaluation electronics 13.

[0044] As an alternative or in principle also in addition to different light colors, different flashing frequencies or sequences, i.e. sequences of specific flashing patterns, could also be used here in order to make the different states of at least one of the individual cells 3 in the fuel cell stack 1 detectable via the at least one optical sensor 11.

[0045] The structure can be changed in such a way that the multicolor LED 12 can be dispensed with entirely. The structure in FIG. 5, which is to be understood in principle analogously to the representation in FIG. 4, now provides two differently colored diodes 14, 15, for example, for each one of the optical signal generators 9. If there is sufficient installation space, this can be a more cost-effective variant than using a multicolor LED. In this variant, both LEDs 14, 15 of different colors couple their light into the light guide 10 in the same way as described above. The detection via the at least one sensor 11 and the evaluation in the evaluation electronics 13 then take place analogously. The two different LEDs 14, 15 shown here as an example can therefore pass on a total of three states together with the “switched off” state. For example, this can be the normal function where both LEDs 14, 15 are switched off, it can be the problem of a high cell or low cell where one of the LEDs, for example LED 14, is switched on and it can be the problem of a cell reversal where, for example, LED 15 is switched on. Of course, this structure could be correspondingly expanded with a third LED, in order to be able to distinguish between the high cell and low cell states in the signal arriving at the at least one optical sensor 11.

[0046] A further variant is also shown in the representation of FIG. 6. Instead of arranging the LEDs 14, 15, for example, adjacent in the stacking direction in each of the measuring devices 7 as optical signal generators, they can also be arranged offset transversely to the stacking direction in such a way that they, as can be seen in the representation of FIG. 6, couple their light into two light guides 10, 16 running parallel. They can be different colors, but LEDs of the same color can be employed as well. In this case, for example, the LEDs 14 shown above in the representation of FIG. 6 indicate a low cell or high cell if they are activated, the LEDs 15 of the optical signal generator 9 arranged in the area of the second light guide 16 in the representation of FIG. 6 below indicate a cell reversal. The problem of low cells can then be indicated directly via the optical sensor 11 in a manner known per se, without the need for further evaluation with regard to the light colors, and passed on to the corresponding control devices, and the problem of one or more cell reversals via an optical sensor 17 on the end face of the other light guide 16 accordingly.

[0047] This structure represented in FIG. 6 can now, as has already been described in principle above, be expanded by a third LED 18 in addition to the two LEDs 14, 15, and in this case also correspondingly by a further light guide 19 and a further optical sensor 20. This is represented accordingly in the representation of FIG. 7, which is otherwise to be understood analogously to the representation of FIGS. 4 to 6. With this structure, one of the states of interest could then be indicated in each individual one of the light guides 10, 16, 19.

[0048] Overall, the structure of all variants is extremely simple and requires only a few optical sensors 11, 17, 20, which in turn only have to detect the presence of light and possibly the light color, and which do not have any high requirements, for example with regard to a high pixel resolution or the like.

[0049] In principle, the structures are suitable for any type of fuel cell stack 1, in particular for PEM fuel cells. They are particularly favorable for vehicle use of such fuel cell stacks 1, since here the conditions relating to the installation space limitation on the one hand and a very strong cost pressure in the assembly and production of the fuel cell stack 1 on the other hand have to be met.

[0050] The apparatuses for monitoring the cell voltage in the possible embodiment variants described make this possible in an ideal manner.