AT512622B1 - METHOD AND DEVICE FOR OPERATING A FUEL CELL UNIT - Google Patents

Abstract

The method is intended for operating a fuel cell unit (1) with a plurality of cells (4) connected in series. During a normal operating state, at least two reaction gases (2, 3) are supplied to the cells (4), and electrical energy is generated from the reaction gases (2, 3) by means of a chemical reaction. At a termination of the normal operating state, a discharge operating state is passed, in which the supply of at least one reaction gas (2, 3) is interrupted and a residual amount of gas of at least one of the cells (4) remaining reaction gases (2, 3) is consumed by one by the Reaction gases (2, 3) in the cells (4) generated electrical power via at least one discharge load (17) is dissipated. Each cell (4) is separately connected during the discharge operating state by means of its own self-conducting Entladeschaltelements (16) with its own discharge load (17), so that at the same time for all cells (4) Entladestromkreise (15) are formed, each of a cell (4) are assigned and each comprise a self-conducting Entladeschaltelement (16) and a discharge load (17).

Description

description

METHOD AND DEVICE FOR OPERATING A FUEL CELL UNIT

The invention relates to a method for operating a fuel cell unit having a plurality of cells connected in series, wherein at least two reaction gases are supplied to the cells during a normal operating state, and by means of chemical reaction from the reaction gases, electrical energy is generated, and wherein at a termination of the normal operating state a discharge operating condition is passed, in which the supply of at least one reaction gas is interrupted and a residual amount of gas is consumed at least one of the reaction gases remaining in the cells by an electric current generated by the reaction gases in the cells is discharged through at least one discharge consumer. In addition, the invention relates to a device for operating a fuel cell unit with a plurality of cells connected in series, wherein the device, the fuel cell unit, terminals for supplying the cells during a normal operating state with at least two reaction gases, wherein in the cells by means of chemical reaction from the reaction gases electrical energy can be generated and at least one discharge consumer for discharging an electric current generated by a residual amount of gas of the reaction gases in the cells after completion of the normal operating condition.

Such a method and apparatus are described in US 5,105,142. For consumption of remaining after a shutdown in the fuel cell unit residual gas amount of reaction gases, a discharge circuit is used with a discharge load in the form of a discharge resistor. The discharge resistor can be changed in its resistance value and connected via a discharge switching element to the output terminals of the fuel cell unit. The discharge switching element designed as a relay can be self-locking or self-conducting. In the case of a discharge circuit connected to the output terminals of the fuel cell unit, a different rate of consumption of the residual gases present in the individual cells may occur, in particular if the total amount of residual gases is unevenly distributed among the cells. The electric current flows in the discharge circuit but until the residual gases are consumed in all cells. It also flows through cells from the stream, the residual gases have already been consumed. Consequently, the electrical voltage conditions in these gas-depleted cells are reversed. This is on the one hand dangerous because then can use an electrolysis reaction with the formation of explosive gas. The cells can thus be damaged massively. On the other hand, a degradation of the affected cells can occur, whereby the efficiency and the life of the fuel cell unit deteriorate.

Furthermore, a discharge circuit for a fuel cell unit is described in WO 2009/117749 A1, in which a discharge resistor is switched successively to the individual cells. The switching of the discharge resistor to the next cell takes place as soon as the residual gas in the last connected cell has been consumed. Although this prevents the situation described above with a voltage reversal in individual cells. However, the complete gas consumption in all cells takes a relatively long time, so that the fuel cell unit can be put back into operation only with a certain time delay. Another disadvantage is that in case of failure of the power supply no discharge is possible.

The process of the invention, the task is now to provide a method of the type described above, which allows a safe and rapid consumption of remaining after completion of the normal operating state in the cells residual amount of gas.

To solve this problem, a method according to the features of claim 1 is given. In the method according to the invention, each cell is separately connected during the discharge operating state and / or emergency shutdown by means of its own self-conducting Entladeschaltelements with its own discharge, so that at the same time for all cells discharge circuits are formed, each associated with a cell and each have a self-conducting Entladeschaltelement and include a discharge consumer. The discharge consumer is designed as an integral part of the self-conducting Entladeschaltelements.

Characterized in that a separate discharge circuit is provided for each cell flows in each cell during the discharge operating state, in particular just as long an electric current until the residual amount of gas at least one of the remaining reaction gases in this cell is completely consumed. Thereafter, the cell in question is substantially free of electrical current, regardless of whether in other cells, the discharge process continues with the consumption of the gas remaining there. Consequently, the unwanted and possibly even dangerous voltage reversal in individual cells is safely excluded.

It preferably does not matter how it came to the end of the previous normal operating state. In particular, it may either be a deliberately caused shutdown, an emergency shutdown, or also a stoppage of the chemical reaction in the fuel cell unit due to an error, e.g. a failure of the mains supply voltage or operating voltage / system voltage act. In any case, all cells of the fuel cell unit are brought by means of the discharge circuits in a safe, preferably inerted state, which allows trouble-free restarting of the fuel cell unit, in particular without the risk of degradation.

The use of self-conducting Entladeschaltelemente also leads to a safe state in case of unforeseen events. By "self-conducting" is to be understood here that the respective discharge switching element is electrically conductive without external influence. The closed switch state is thus the normal state of such a self-conducting Entladeschaltelements. In order to block the self-conducting Entladeschaltelement, ie to transfer to the open switch state, on the other hand, a targeted action, e.g. a control with a non-zero control signal, done. In the event of a failure of a supply voltage required for the generation of the control signal, the normally-on discharging switching element automatically goes into its conducting state, so that the relevant discharging circuit is closed and the associated cell is transferred to its inerted state. All this is done without external intervention, so that an intrinsically safe operating procedure is given. There is thus an emergency stop function. This results in a significantly further advantage, namely that a resistor contained in the discharge circuit, for example, as a discharge load, preferably always remains connected to the series connection of the cells (= stack) of the fuel cell unit, so that a discharge always occurs, even if no operating voltage is present ,

Another advantage is that during the Entladebetriebszustands in all cells at the same time the residual amount of gas is consumed and thus all cells can be converted simultaneously in their inertized state. The fuel cell unit is therefore very quickly ready for a reboot.

Characterized in that the discharge load is designed as an integral part of the self-conducting Entla-deschaltelements, space and costs are saved. In particular, the discharge load may be a volume resistance of an electronic component, preferably a MOSFET.

Advantageous embodiments of the method according to the invention will become apparent from the features of the dependent claims of claim 1.

An embodiment in which all cells are separated from the discharge consumers at the beginning of the normal operating state is advantageous in that all the normally-conducting discharge switching elements are transferred into their opened switch state. In this way, the fuel cell unit can bring very quickly to its normal operating state. In addition, all cells are in a defined and in particular safe inerted state until the initiation of these switching operations.

According to another advantageous embodiment, the transfer of all normally-off Entladeschaltelemente in the open switch state is carried out simultaneously by means of a single common control signal. This is particularly efficient and reduces the required effort. In addition, it is thus ensured that the chemical reaction for converting the reaction gases into electrical energy begins in all cells of the fuel cell unit substantially at a uniform time and the transition to the normal operating state takes place.

According to a further advantageous embodiment, the discharge switching element is a self-conducting semiconductor switch, in particular a self-conducting MOSFET (= metal-oxide-semiconductor field-effect transistor, in English: "Metal Oxide Semiconductor Field-Effect Transistor"). These switching elements are freely available with a wide variety of specifications. They work very reliably. In particular, in a semiconducting switch, such as a semiconductor switch, e.g. a MOSFET, during the switching operation in contrast to other mechanically functioning switching elements, such. a relay, no sparking on. In this respect, a semi-conductive switch offers a particularly high degree of safety, especially in an environment with explosive gases or gas mixtures. In addition, semiconductor switches and, in particular, MOSFETs can preferably be realized in a self-conducting embodiment without further ado. Furthermore, they have a very small size, so that they are well suited for integration into another module or assembly and / or for use with low available installation volume.

According to a further advantageous embodiment, the discharge load and the self-conducting Entladeschaltelemente be housed together with the cells in a housing. This results in a very compact design. Possibly. may also be other units, such as. a cell voltage monitoring unit and / or a cell voltage tap unit, may be arranged in the common housing.

Another object of the invention is to provide a device of the type described be-recorded, which allows a safe and rapid consumption of remaining after completion of the normal operating state in the cells residual amount of gas.

To solve this problem, a device according to the features of claim 6 is given. In the apparatus, each cell is associated with its own discharge circuit with its own self-discharging and a separate discharge consumer, and each cell is connected by means of the associated self-conducting Entladeschaltelements with the associated discharge load, so that in the cell in question after completion of the normal operating state generated electrical current over the associated discharge consumer can be discharged. The discharge consumer is an integral part of the self-conducting discharge switching element.

The device according to the invention and its embodiments have essentially the same special properties and advantages that have already been described in connection with the method according to the invention and its embodiments.

Advantageous embodiments of the device according to the invention will become apparent from the dependent claims of claim 6.

According to a favorable embodiment, all the self-conducting Entladeschaltelemente for particular simultaneous change in their respective switch state, preferably for transfer to their respective open switch state, connected to a common control unit. This is efficient and saves individual components as well as costs.

According to a further advantageous embodiment, all the self-conducting Entladeschaltelemente simultaneously by means of a single common control signal generated by the control unit in their respective switch state can be changed. In particular, all discharge switching elements are connected to a single common control signal output of the control unit. Alternatively, however, the discharge switching elements can also be connected to a plurality of control signal outputs of the control unit. As a result, it is possible to very easily synchronize the starting of the discharge operating state and the normal operating state in all cells. It is also possible that a plurality of discharge switching elements in groups, e.g. to twelfth, are connected together, for this purpose preferably four groups are formed. Thus, in particular four control signals are provided, which are advantageously easy to synchronize.

Further features, advantages and details of the invention will become apparent from the following description of exemplary embodiments with reference to the drawing. 1 shows an embodiment of a fuel cell unit with its own discharge circuit provided for each cell, each comprising a self-conducting switching element, and FIG. 2 shows another embodiment of a fuel cell unit with for each

Cell provided own discharge circuit, each comprising a self-conducting MOSFET.

Corresponding parts are provided in Figs. 1 and 2 with the same reference numerals. Also details of the embodiments explained in more detail below may constitute an invention in itself or be part of an inventive subject matter.

In Fig. 1, an embodiment of a fuel cell unit 1 for generating electrical energy from at least two reaction gases, in particular from hydrogen 2 and from oxygen 3 or air, is shown.

A fuel cell is an electrochemical generator that generates an electrical current directly from a chemical reaction. The operating principle of a fuel cell is based in particular on the reversal of the electrolytic decomposition of water, in which the reaction gases hydrogen 2 and oxygen 3 are formed by a flow of current. A fuel cell is a galvanic cell that converts the chemical reaction energy of the reaction gases into electrical energy. It is therefore also referred to as an energy converter. The energy for power production is supplied in chemically bonded form with the reaction gases.

The fuel cell unit 1 comprises a plurality of cells connected in series. The overall structure with the series connection of all cells 11 forms a stack 5. In the individual cells 4 of the fuel cell unit 1, the reaction gases hydrogen 2 and oxygen 3 react with each other, whereby electric current is generated. Each cell 4 has an anode 7 provided with a first catalyst 6, a cathode 9 provided with a second catalyst 8, and an electrolyte 10. The anode 7 and the cathode 9 are separated from each other by the electrolyte 10. The catalysts 6 and 8 are respectively arranged on the side of the anode 7 or the cathode 9 facing the electrolyte 10. In particular, they each consist of platinum, which is applied to a carbon carrier layer. The electrolyte 10 is in particular a polymer layer.

Furthermore, 4 means not shown in detail for supplying the hydrogen 2 to the anode 7 and for supplying the oxygen 3 to the cathode 9 are provided in each cell. The catalysts 6 and 8 cause individual reactions of the supplied hydrogen 2 and oxygen 3 at the respective electrode, ie at the anode 7 and at the cathode 9, respectively.

In the reaction of the hydrogen 2 on the catalyst 6 of the anode 7, a hydrogen molecule is split into two hydrogen atoms in each case. A hydrogen atom has two components, a negatively charged electron and a positively charged proton. In the reaction, every atom of hydrogen releases its electron. The positively charged protons diffuse through the electrolyte 10, which is impermeable to the negatively charged electrons, and thus reaches the cathode 9.

In the simultaneous reaction of the oxygen 3 at the catalyst 8 of the cathode 9, oxygen molecules are divided into two oxygen atoms, which are deposited on the cathode 9.

Thus, at the cathode 9, the positively charged protons of hydrogen 2 and the oxygen atoms, and deposited at the anode 7, the negatively charged electrons of the hydrogen 2. As a result, there is an electron deficiency at the cathode 9 and an excess of electrons at the anode 7, so that the anode 7 is at a negative potential with respect to the cathode 9. Accordingly, the anode 7 forms a negative pole (-) and the cathode 9 a positive pole (+).

Connecting the two electrodes, so the anode 7 and the cathode 9, with an electrical conductor 11, the electrons migrate due to the potential difference across the electrical conductor 11 from the anode 7 to the cathode 9. It flows electrical DC through the Ladder 11 and by a possibly integrated in the conductor 11 load 12. The load 12 may be formed for example by a battery that stores the electrical energy generated, by an inverter, which converts the direct current into an alternating current, or by a load resistor. The circuit with the conductor 11 and the load 12 can be switched on and off by means of a load circuit breaker 13.

Two electrons, which have migrated via the electrical conductor 11 from the anode 7 to the cathode 9 are added to the cathode 9 each of an oxygen atom. There are two times negatively charged oxygen ions. These oxygen ions combine with the positively charged protons of hydrogen 2, which have been diffused through the electrolyte 10 from the anode 7 to the cathode 9, to form water 14. The water 14 is removed from the cathode 9 as a reaction end product.

For switching off the fuel cell unit 1, the supply of the reaction gas oxygen 3 or air is preferably interrupted. At least some of the reaction gases remain in the cells 4. Without further measures, this would have the consequence, at least in some types of fuel cells, that hydrogen 2 diffuses through the electrolyte 10 and forms an explosive gas mixture at the cathode 9 of the cells 4. Likewise, the remaining amount of gas in the cells 4 can lead to a degradation of the cells 4, in particular of the electrolyte 10 and the catalysts 6 and 8, and thus to a reduction in the efficiency and / or the life of the fuel cell unit 1. In order to prevent this, after a termination of the normal operating state of the fuel cell unit 1, a targeted discharging process is performed. During this discharge operating state, at least the proportion of the oxygen 3 in the residual gas remaining in the cells 4 of the reaction gases is consumed so far that the fuel cell unit 1 can be turned off safely when switched off and the stack 5 is in an at least substantially inertized state.

In the fuel cell unit 1, the practically complete consumption of the after the termination of the normal operating state, that is, e.g. after a shutdown of the fuel cell unit 1, in the cells 4 remaining amount of gas at least one of the reaction gases by means of each cell 4 switchable discharge circuits 15 reaches. Each cell 4 is associated with its own discharge circuit 15, which comprises, in addition to the relevant cell 4, in each case a self-conducting discharge switching element 16 and a discharge consumer 17 in the form of an electrical discharge resistor. As a result, in contrast to the coating of all cells 4 with a common resistance, no voltage reversal dangerous for the cells 4 can occur in the case of premature gas depletion in one of the cells 4. The consumption of the gas residual amount of the reaction gases in the cells 4 of the fuel cell unit 1 is also referred to as reacting the cells 4.

The self-conducting discharge switching element 16 and the discharge load 17 connected in series are connected between the anode 7 and the cathode 9 of the relevant cell 4. The discharge circuits 15 of adjacent cells 4 may share a part of the electric wires. The cathode 9 of a cell 4 is short-circuited to the anode 7 of the adjacent cell 4.

The discharge switching elements 16 are self-conducting, i. they are normally in the closed switch state. The discharge circuits 15 are therefore closed without targeted action from the outside and connected to the relevant cell 4. The discharge switching elements 16 are connected via dashed control lines shown in Fig. 1 to a control unit 18, in particular to a common control signal output 19 of this control unit 18. The control unit 18 is designed to generate a control signal SS and to supply the discharge switching elements 16 via the control signal output 19 and the control lines connected thereto. By means of the common control signal SS, which is present in particular during the normal operating state of the fuel cell unit 1, all discharge switching elements 16 and thus all discharge circuits 15 are opened and then kept open.

This opened state remains as long as the control signal SS is applied. If this is no longer the case for whatever reason, and / or if the absolute value of the control signal SS falls below a certain trigger threshold, and in particular even goes back to zero, the discharge switching elements 16 automatically fall back into their normal state with the switching path closed. In this state, the Abreaction begins in the cells 4, in order to convert the fuel cell unit 1 in a safe shutdown with inerted stack 5. This Abreaktion takes place advantageously in all cells 4 simultaneously, so that the discharge operating state can be completed very quickly. If the residual amount of gas consumed in one of the cells 4, the current flow in the associated discharge circuit 15 automatically stops, regardless of whether the Abreaction in the other cells 4 is still ongoing and in the discharge circuits 15 still current flows.

Preferably, the load 12, which is supplied with power during the normal operating state of the fuel cell unit 1, during the discharge operating state by opening the load circuit switch 13 is switched off. As a result, defined current flow conditions are created during the consumption of the residual amount of gas in reaction gases in the cells 4, which are determined exclusively by the current flow in the discharge circuits 15 via the discharge consumers 17.

FIG. 2 shows a further exemplary embodiment of a fuel cell unit 20 for generating electrical energy from at least two reaction gases. The fuel cell unit 20 also comprises the stack 5 with the cells 4, not shown in detail in FIG. 2, connected in series.

Each cell 4 is in turn assigned a separate discharge circuit 21. The discharge circuits 21 comprise, in addition to the relevant cell 4 in each case as discharging a discharge resistor 22 and as discharge a self-conducting MOSFET 23. Gate terminals 24 of the MOSFETs 23 are connected by means of the control lines respectively to the control signal output 19 of the control unit 18. By means of the control signal SS, the gate terminals can be brought to a negative gate potential, so that the MOSFETs 23 are each put in the non-conducting state. The discharge circuits 21 are then opened and de-energized.

In the embodiment shown in Figure 2 ohmic discharge resistor 22 are provided as separate components in the discharge circuits 21. But there are also alternative embodiments not shown with differently designed discharge consumers. Thus, the discharge consumers may also be protected by variable resistances, e.g. in the form of a transistor in linear operation, be formed. Their resistance values may then be e.g. be set or regulated by the control unit 18 according to the currently given requirements. Furthermore, the discharge resistor 22 may be part of the discharge switching element of the zugehö ring discharge circuit 21. In the case of a discharge switching element designed as a MOSFET 23, the discharge resistor 22 may in particular be the internal volume resistance of the MOSFET 23. This leads to a very compact construction with relatively few individual components.

In particular, when using MOSFETs 23, the space requirement of the discharge circuits 21 is very low. They can then preferably be placed together with the stack 5 and also the control unit 18 in a common housing 25. Such a common housing 25 is shown in the embodiment of FIG. 1 with.

Overall, allow the fuel cell units 1 and 20 due to the separate wiring of each cell 4 with its own discharge circuit 15 and 21, a safe and fast Abreagieren all cells 4 after switching off the fuel cell units 1 and 20. By using self-conducting Entladeschaltelemente 16 and MOSFETs 23 also achieve intrinsic safety. In the event of a system defect, in particular if the control signal SS fails, the normally-on discharging switching elements 16 or MOSFETs 23 close automatically and the fuel cell unit 1 or 20 is brought into a safe switch-off state.

Claims (10)

claims A method of operating a fuel cell unit (1; 20) having a plurality of cells (4) connected in series, wherein a) during a normal operating state the cells (4) at least two reaction gases (2, 3) are supplied, and by chemical reaction of the Reactive gases (2, 3) electrical energy is generated, b) at a termination of the normal operating state, a discharge operating state is passed, in which the supply of at least one reaction gas (2, 3) is interrupted and a residual amount of gas at least one of the remaining in the cells (4) Reaction gases (2, 3) is consumed by discharging an electric current generated by the reaction gases (2, 3) in the cells (4) via at least one discharge consumer (17; 22), characterized in that c) each cell (4 ) during the discharge operating state and / or in an emergency shutdown separately by means of a separate self-conducting Entladeschaltelements (16; 23) with its own discharge consumption r (17; 22), so that at the same time for all cells (4) discharge circuits (15; 21) are formed, which are each associated with a cell (4) and in each case a self-conducting Entladeschaltelement (16; 23) and a discharge load (17; 22) and d) the discharge consumer (17; 22) is implemented as an integral part of the self-conducting discharge switching element (16; 23). 2. The method according to claim 1, characterized in that at the beginning of the normal operating state all cells (4) are separated from the discharge consumers (17; 22) by all self-conducting Entladeschaltelemente (16; 23) are transferred to their open switch state. 3. The method according to claim 2, characterized in that the transfer of all normally-off Entladeschaltelemente (16; 23) takes place in the open switch state at the same time by means of a single common control signal (SS). 4. The method according to any one of the preceding claims, characterized in that the discharge switching element is a normally-on semiconductor switch, in particular a self-conducting MOSFET (23), is provided. 5. The method according to any one of the preceding claims, characterized in that the discharge load (17; 22) and the self-conducting Entladeschaltelemente (16; 23) are housed together with the cells (4) in a housing (25). Apparatus for operating a fuel cell unit (1; 20) having a plurality of cells (4) connected in series, comprising a) the fuel cell unit (1; 20), b) terminals for supplying the cells (4) during a normal operating state with at least two reaction gases (2, 3), wherein in the cells (4) by means of chemical reaction from the reaction gases (2, 3) electrical energy can be generated, and c) at least one discharge consumer (17; 22) for discharging one by one in the cells (4 ) after completion of the normal operating state residual amount of gas of the reaction gases (2, 3) generated electric current, characterized in that d) each cell (4) has its own discharge circuit with its own self-conducting Entladeschaltelement (16; 23) and its own discharge load (17; ), and each cell (4) can be connected to the associated discharge consumer (17; 22) by means of the associated self-conducting discharge switching element (16; an electrical current generated in the relevant cell (4) after termination of the normal operating state via the associated discharge consumer (17; 22), and e) the discharge consumer (17; 22) is an integral part of the self-conducting discharge switching element (16; 23). 7. Apparatus according to claim 6, characterized in that all the self-conducting Entladeschaltelemente (16; 23) are connected to change their respective switch state to a common control unit (18). 8. The device according to claim 7, characterized in that all the self-conducting Entladeschaltelemente (16; 23) at the same time by means of a single common generated by the control unit (18) control signal (SS) are variable in their respective switch state. 9. Device according to one of claims 6 to 8, characterized in that the discharge switching element is in each case designed as a self-conducting semiconductor switch, in particular as a self-conducting MOSFET (23). 10. Device according to one of claims 6 to 9, characterized in that the discharge load (17; 22) and the self-conducting Entladeschaltelemente (16; 23) are housed together with the cells (4) in a housing (25). For this 2 sheets of drawings