DE102017220360A1 - Method for determining the tightness of adjusting means of a fuel cell system, fuel cell system and vehicle - Google Patents

Abstract

In order to provide a method for determining the tightness of a first and a second actuating means (38, 39) for shutting off a fuel cell stack (10) of a fuel cell system (100), which slows down degradation of the fuel cells of the fuel cell system (100), it is proposed to the following steps are provided: a1) setting the compressor (33) to a predetermined rotational speed, b1) closing one of the two actuating means (38), c1) discharging the fuel cell stack (10) and determining the discharge time, d1) evaluating the determined discharge time, e1) transition to normal operation of the fuel cell system (100), and optionallya2) setting the compressor (33) to a predetermined speed, b2) closing the other actuator (39), c2) discharging the fuel cell stack (10) and determining the discharge time, d2 ) Evaluation of the specific discharge time, e2) transition to the normal operation of the fuel cell system (100). In addition, a Brennstoffze System (100) and discloses a vehicle.

Description

The invention relates to a method for determining the tightness of a first and a second adjusting means for shutting off a fuel cell stack of a fuel cell system, wherein in a cathode supply of the fuel cell system, a compressor for conveying oxygen-containing gas to the inlet of the fuel cell stack is provided, a fuel cell system, wherein the fuel cell system a Control device that is configured to perform the method, and a vehicle with the fuel cell system.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as a core component the so-called membrane electrode assembly (MEA for membrane electrode assembly), which is a microstructure of an ion-conducting (usually proton-conducting) membrane and in each case on both sides of the membrane arranged catalytic electrode (anode and cathode). The latter mostly comprise supported noble metals, in particular platinum. In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane-electrode arrangement on the sides of the electrodes facing away from the membrane.

As a rule, the fuel cell is formed by a multiplicity of stacked MEAs whose electrical powers add up. As a rule, bipolar plates (also called flow field plates or separator plates) are arranged between the individual membrane electrode assemblies, which ensure that the individual cells are supplied with the operating media, ie the reactants, and are usually also used for cooling. In addition, the bipolar plates provide an electrically conductive contact to the membrane-electrode assemblies.

During operation of the fuel cell, the fuel (anode operating medium), in particular hydrogen, is supplied to the anode via a flux field of the bipolar plate and electrochemically oxidized to protons with release of electrons (H ₂ → 2 H ⁺ + 2 e ^- ). About the electrolyte or the membrane, which gas-tight and electrically isolated from each other, the reaction chambers, a transport of protons from the anode compartment into the cathode compartment. The electrons provided at the anode are supplied to the cathode via an electrical line.

The cathode is supplied during operation of the fuel cell, oxygen or an oxygen-containing gas mixture (for example air) as a cathode operating medium, so that a reduction of O ₂ to O ^2- with absorption of the electrons takes place (½ O ₂ + 2 e ^- → O ^2-). At the same time, the oxygen anions in the cathode compartment react with the protons transported via the membrane to form water (O ^2- + 2 H ⁺ → H ₂ O).

In order to supply a fuel cell stack with the operating media, this has an anode supply and a cathode supply. The anode supply includes an anode supply path for supplying the anode operating medium into the anode chambers of the fuel cell and an anode exhaust gas path for discharging an anode exhaust gas out of the anode chambers. In addition, a recirculation line is arranged in the anode supply in order to feed unused and discharged from the fuel cell stack hydrogen in the stack again. The cathode supply includes a cathode supply path for supplying the cathode operating medium into the cathode chambers of the fuel cell and a cathode exhaust path for discharging a cathode exhaust gas out of the cathode compartments.

The degradation of the components of a fuel cell system is of course a problem, it should therefore be monitored and, if possible, to prevent or at least delay. Thus, the tightness of the two shut-off valves of the fuel cell stack is important because in their leakage at a start both on the anodes and on the cathode oxygen is present (air-air start), which significantly contributes to aging of the stack. If one of the two flaps leaks, e.g. Because there is damage to the seal, oxygen enters the fuel cell stack in an uncontrolled manner, so that air-air starts occur more frequently or even after the vehicle has had a short service life.

In the DE 102012000867 A1 a fuel cell system is described, which has a fuel cell stack and at least one additional fuel cell, wherein the anode chamber of the additional fuel cell, at least in standstill phases, hydrogen is supplied. By monitoring the electrical power generated by the auxiliary fuel cell, the leaktightness of the system can be monitored during the standstill phase.

DE 102005037408 A1 discloses a method for detecting leaks in a fuel cell system in which a fuel cell is material tightly shut off and a discharge of the fuel cell is measured.

A method for determining a chemical short circuit is disclosed in U.S. Patent No. 5,376,854 DE 112004002513 T5 disclosed. This is a Pressure gradient determined in the fuel cell and adjusted with a setpoint.

The object of the invention is to provide a method, a suitably configured fuel cell system and a vehicle with which a degradation of the fuel cell of the fuel cell system can be slowed down.

This object is achieved by a method for determining the tightness of adjusting means for shutting off a fuel cell stack, a fuel cell system which can be operated according to the method, and a vehicle having this fuel cell system having the features of the independent claims. Advantageous embodiments are characterized in the subclaims.

• a1) Einstellen des Verdichters auf eine vorgegebene Drehzahl,
• b1) Schließen eines der beiden Stellmittel,
• c1) Entladen des Brennstoffzellenstapels und Bestimmung der Entladezeit,
• d1) Bewertung der bestimmten Entladezeit in Abhängigkeit von Vergleichswerten,
• e1) Übergang in den Normalbetrieb des Brennstoffzellensystems,

und optional

• a2) Einstellen des Verdichters auf eine vorgegebene Drehzahl,
• b2) Schließen des anderen Stellmittels der beiden Stellmittel,
• c2) aktives Entladen des Brennstoffzellenstapels und Bestimmung der Entladezeit,
• d2) Bewertung der bestimmten Entladezeit in Abhängigkeit von Vergleichswerten,
• e2) Übergang in den Normalbetrieb des Brennstoffzellensystems.

According to the invention, a method for determining the tightness of a first and a second adjusting means for shutting off a fuel cell stack of a fuel cell system is provided, wherein in a cathode supply of the fuel cell system, a compressor for conveying oxygen-containing gas to the inlet of the fuel cell stack is provided, the following steps, in the Order to execute, comprising:

• a1) setting the compressor to a predetermined speed,
• b1) closing one of the two actuating means,
• c1) discharging the fuel cell stack and determining the discharge time,
• d1) evaluation of the specific discharge time as a function of comparative values,
• e1) transition to normal operation of the fuel cell system,

and optional

• a2) setting the compressor to a predetermined speed,
• b2) closing the other actuating means of the two actuating means,
• c2) actively discharging the fuel cell stack and determining the discharge time,
• d2) evaluation of the determined discharge time as a function of comparative values,
• e2) transition to normal operation of the fuel cell system.

The adjusting means for shutting off the fuel cell stack are preferably designed as shut-off valves, shut-off valves or the like. The selection of the actuating means takes place as a function of the respective fuel cell stack or fuel cell system.

The two adjusting means are preferably arranged directly on the fuel cell stack, it also being possible to deviate from this depending on the fuel cell system.

It is therefore necessary to provide an adjusting means in a cathode supply path and an adjusting means in the cathode exhaust path. Which of the two actuating agents is tested first is not important to the process according to the invention.

The discharge of the fuel cell stack can be active or passive, in the passive discharge is to provide a corresponding consumer.

Advantageously, can be examined by the inventive method within the vehicle operation, whether one of the two actuating means has a leak. That both actuating means are defective at the same time is generally not given, but can also be determined with the method according to the invention.

If at least one of the two actuating means is closed, no new oxygen enters the fuel cell stack when the actuating means are undamaged. Thus, the stack voltage during discharge decreases by the reaction of the oxygen in the fuel cell stack.

If there is a delay in the determination of the discharge times compared to the comparative measurements, this indicates a leakage in at least one of the two actuating means, since the post-flow of oxygen, the cell reaction lasts longer than if the actuating means are dense.

Preferably, both actuating means are checked according to the method. However, it is also possible to repeat the test of an actuating agent one or more times to exclude measurement errors.

The method according to the invention is preferably initiated from the normal operation of a fuel cell system. For this purpose, there is a request for a start / stop procedure. It is checked before their initiation, whether a predetermined test interval for testing the tightness of the actuating means is reached. The specification of the test interval is carried out as a function of the adjusting means used and optionally the fuel cell system.

If the interval has not yet been reached, a start-stop procedure is performed according to the status of Technology. When the interval is reached, the leakage test is carried out.

Between the partial tests for the actuating means, the fuel cell system is briefly operated in normal operation to set conditions defined before the partial tests.

After carrying out the method according to the invention, a transition to normal operation also takes place.

A deviation of the discharge time and accordingly the tightness of comparison values of up to 20% can be tolerated. If the deviation is between 20 and 30%, an error message is output and if it exceeds 30%, the fuel cell stack in question is also output

According to a preferred embodiment of the invention, the evaluation of the discharge takes place in dependence on the current conditioning of the fuel cell stack, preferably as a function of the moisture content of the fuel cell, a H ₂ concentration at the anode, the system pressure, the system temperature and / or the age of the fuel cell system.

1. a) Einstellen des Verdichters auf eine vorgegebene Drehzahl,
2. b) Schließen beider Stellmittel,
3. c) Entladen des Brennstoffzellenstapels und Bestimmung einer Entladezeit,
4. d) Bewertung der bestimmten Entladezeit anhand von Laborwerten,
5. e) Übergang in den Normalbetrieb des Brennstoffzellensystems.

According to a further preferred embodiment of the method according to the invention, the following steps are carried out before the steps a1) to e1) and the steps a2) to e2)

1. a) adjusting the compressor to a predetermined speed,
2. b) closing both actuating means,
3. c) unloading the fuel cell stack and determining a discharge time,
4. d) evaluation of the specific discharge time on the basis of laboratory values,
5. e) transition to normal operation of the fuel cell system.

As a result of these upstream steps, specific values for the discharge times can be determined for the fuel cell system, which values can then preferably be used for an evaluation of the discharge times for the individual flaps. Otherwise, the evaluation of these discharge times is also based on laboratory values.

The use of the discharge times in step c) is possible because it is unlikely that both actuating means are defective at the same time (double error). The advantage of using these values is that the current conditioning of the fuel cell stack can be taken into account.

Preferably, when closing one or both actuating means, a wastegate line arranged between a cathode supply line and a cathode exhaust path is opened, so that advantageously the compressor does not get into the pump and possibly damage this component.

• Ausgabe einer Fehlermeldung an den Nutzer des Brennstoffzellensystem und/oder in einen Fehlerspeicher und/oder
• Einleitung von Maßnahmen zum Schutz des Brennstoffzellenstapels, beispielsweise Einleiten von Wasserstoff während des Stillstandes oder Außerbetriebsetzen des betreffenden Brennstoffzellenstapels. Auch kann eine Abstellprozedur zur Erhöhung der Sicherheit aufgrund der höheren Klappenleackage geändert werden, wobei jedoch Stapellebenszeit reduziert wird.

After the assessment of the determined discharge times, the following measures are preferably provided, of which at least one is carried out:

• Output of an error message to the user of the fuel cell system and / or in a fault memory and / or
• Initiate measures to protect the fuel cell stack, such as introducing hydrogen during standstill or decommissioning of the relevant fuel cell stack. Also, a shutdown procedure may be changed to increase safety due to the higher flap lapse, but reduce stack life.

The invention also relates to a fuel cell system with a control device which is set up to carry out the method according to the invention.

In addition to the control device, the fuel cell system has a fuel cell stack with a first actuating means arranged on the cathode inlet and a second actuating means on the cathode outlet, wherein a compressor for supplying oxygen-containing gas to the inlet of the fuel cell stack is provided in a cathode supply of the fuel cell system.

In order to supply the fuel cell stack with the operating gases, the fuel cell system has an anode supply and said cathode supply. The cathode supply includes a cathode supply path, and a cathode exhaust path. For conveying and compressing the cathode operating medium, the compressor is arranged in the cathode supply path.

The cathode supply preferably has a wastegate line which connects the cathode supply line to the cathode exhaust gas line. An actuating means arranged in the wastegate line serves to control the quantity of the cathode operating medium bypassing the fuel cell stack.

The control device preferably has a voltage sensor for measuring the voltage U of the fuel cell or the fuel cell stack, preferably of the Fuel cell stack, as this is technically easier to implement. In addition, a timer is provided.

Preferably, a current sensor for the detected current I of the fuel cell, a temperature sensor, a pressure sensor for pressures p in the anode and / or cathode space and the like are also provided.

Another object of the invention is a vehicle that is equipped with a fuel cell system described above.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

• 1 ein Blockschaltbild eines Brennstoffzellensystems gemäß einer bevorzugten Ausgestaltung,
• 2 ein Blockdiagramm des erfindungsgemäßen Verfahrens, und
• 3 ein Blockdiagramm des erfindungsgemäßen Verfahrens nach einer weiteren Ausführungsform.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

• 1 FIG. 2 is a block diagram of a fuel cell system according to a preferred embodiment; FIG.
• 2 a block diagram of the method according to the invention, and
• 3 a block diagram of the inventive method according to another embodiment.

In 1 is a total with 100 designated fuel cell system according to a preferred embodiment of the present invention. The fuel cell system 100 is part of a not further illustrated vehicle, in particular an electric vehicle having an electric traction motor, by the fuel cell system 100 is supplied with electrical energy.

The fuel cell system 100 comprises as a core component a fuel cell stack 10 containing a plurality of stacked single cells 11 having. Every single cell 11 each includes an anode compartment 12 and a cathode compartment 13 , which of an ion-conductive polymer electrolyte membrane 14 are separated from each other (see detail). The anode and cathode compartment 12 . 13 each comprises a catalytic electrode, the anode or the cathode (not shown), which catalyzes the respective partial reaction of the fuel cell reaction. The anode and cathode electrodes comprise a catalytic material, such as platinum, supported on an electrically conductive high surface area support material, such as a carbon based material. Between two such membrane-electrode assemblies is also one each with 15 indicated bipolar plate arranged, which the supply of the operating media in the anode and cathode spaces 12 . 13 serves and also the electrical connection between the individual fuel cells 11 manufactures.

To the fuel cell stack 10 to supply with the operating gases, the fuel cell system 100 on the one hand, an anode supply 20 and on the other hand, a cathode supply 30 on.

The anode supply 20 includes an anode supply path 21 which feeds an anode operating medium (the fuel), for example hydrogen, into the anode spaces 12 of the fuel cell stack 10 serves. For this purpose, the anode supply path connects 21 a fuel storage, not shown, with an anode inlet of the fuel cell stack 10 , The anode supply 20 further includes an anode exhaust path 22 containing the anode exhaust gas from the anode chambers 12 via an anode outlet of the fuel cell stack 10 dissipates. The anode operating pressure on the anode sides 12 of the fuel cell stack 10 is via an unillustrated actuating means in the anode supply path 21 adjustable.

The cathode supply 30 includes a cathode supply path 31 which is the fuel cell stack 10 supplying an oxygen-containing cathode operating medium, in particular air which is drawn in from the environment. The cathode supply 30 also has a cathode exhaust path 32 on which the cathode exhaust gas from the cathode compartments 13 of the fuel cell stack 10 dissipates and optionally this feeds an exhaust system, not shown.

For conveying and compressing the cathode operating medium is in the cathode supply path 31 a compressor 33 arranged, which can be configured as a mainly electric motor driven compressor. In addition, it is optional in the cathode exhaust path 32 a turbine 34 located. However, it is also possible, for example, instead of providing a flap valve or the like.

The cathode supply 30 also has a wastegate line 35 on which the cathode supply line 31 with the cathode exhaust gas line 32 connects, so a bypass of the fuel cell stack 10 represents. The wastegate pipe 35 allows excess air mass flow at the fuel cell stack 10 to pass without the compressor 33 shut down. One in the wastegate pipe 35 arranged adjusting means 36 serves to control the amount of the fuel cell stack 10 immediate cathode operating medium.

The fuel cell system 100 also has a humidifier module 37 on. The humidifier 37 on the one hand is in the cathode supply path 31 arranged to be flowed through by the cathode operating gas. On the other hand, it is so in the cathode exhaust path 32 arranged so that it can be flowed through by the cathode exhaust gas.

In the cathode supply path 31 are at the cathode inlet an actuating means 38 and in the cathode exhaust path 32 at the cathode outlet also an actuating means 39 arranged. Corresponding further, not shown, adjusting means can in the lines 21 . 22 the anode supply 20 be arranged to the fuel cell stack 10 If necessary, to isolate from the environment.

These adjusting agents 38 . 39 have a special sealing system to ensure a high tightness, so after stopping the fuel cell system 100 no oxygen in the fuel cell stack 10 or to extend the time until this happens.

This is to prevent starting the fuel cell stack 10 , both in the anode compartment 12 as well as in the cathode compartment 13 Oxygen is present, which would result in a so-called air-air start, which is strong for the aging (lifetime loss) of the fuel cell stack.

If one of the two actuating means 38 . 39 leaking oxygen enters the fuel cell stack 10 so that the number of air-air starts increases and thus reduces the life of the fuel cell system.

In the prior art, a start / stop procedure of the fuel cell system 100 executed such that the compressor 33 is turned off and the actuating means 38 . 39 getting closed. As a result, the oxygen in the cathode compartment 13 when unloading the fuel cell stack 10 is degraded by the ongoing cell reaction. New oxygen will not enter the cathode compartment 13 promoted because of the compressor 33 is switched off.

The adjusting means 38 . 39 of the fuel cell system 100 can be designed as controllable or non-controllable valves or flaps and adjusting means 36 as a controllable flap or valve.

Various other details of the anode and cathode supply 20 . 30 are in the simplified 1 not shown for reasons of clarity. So can the anode supply 20 a fuel recirculation line, which the anode exhaust path 22 with the anode supply path 21 combines.

The fuel cell system according to the invention 100 furthermore has a control device, not shown, which controls the operation of the fuel cell system 100 , in particular its anode and cathode supply 20 . 30 controls. In addition, the method according to the invention is carried out hereby. For this purpose, the control device receives 60 various input signals, in particular those with the voltage sensor 41 detected voltage U of the fuel cell 11 or the fuel cell stack 10 , which is relevant to the process, with the current sensor 42 detected current I of the fuel cell 10 , Information about the temperature T of the fuel cell 10 , the pressures p in the anode and / or cathode compartment 12 . 13 , the state of charge SOC of an energy store and other input variables. In addition, a timer is provided.

Based on 2 and 3 the method according to the invention is shown below.

According to 2 will be out of normal operation 40 of the fuel cell system 100 out a start-stop procedure 60 requested and before its initiation, a check is made 50 , whether a test interval of the actuating means 38 . 39 is reached. If not, the start-stop procedure becomes 60 executed and when requested back to normal operation 40 passed. Once the test interval has been reached, a first sub-step takes place 80 the method in which a first actuating means 38 closed and the compressor 33 is downshifted to a predetermined speed. Subsequently, the discharge time and its evaluation are determined on the basis of values determined in the laboratory. It follows the transition to normal operation 40 and then a second sub-step 90 the inventive method in which a second adjusting agent 39 closed and the compressor 33 is downshifted to a predetermined speed. This is followed by the determination of the discharge time and its evaluation and again the transition to normal operation 40 , The unloading time is evaluated on the basis of values determined in the laboratory.

In the 3 illustrated variant of the method according to the invention differs from the in 2 illustrated variant in that after the review 50 , whether a test interval of the actuating means 38 . 39 reached is a step 70 takes place, in which both actuating means 38 . 39 closed and the compressor 33 is downshifted to a predetermined speed. This is followed by the determination of the discharge time and its evaluation and again the transition to normal operation 40 , where the evaluation of the discharge time is based on values determined in the laboratory. In the following sub-steps 80 . 90 will be used to evaluate the unloading times in step 70 determined unloading time used.

After the steps 70 . 80 . 90 may upon detection of leakage at least one of the two actuating means 38 . 39 an error message and / or a measure to protect the fuel cell stack can be initiated.

LIST OF REFERENCE NUMBERS

100

The fuel cell system

10

fuel cell stack

11

single cell

12

anode chamber

13

cathode space

14

Polymer electrolyte membrane

15

bipolar

20

anode supply

21

Anode supply path

22

Anode exhaust gas path

30

cathode supply

31

Cathode supply path

32

Cathode exhaust path

33

compressor

34

turbine

35

Waste gate line

36

actuating means

37

humidifier

38

actuating means

39

actuating means

40

normal operation

50

Checking the check interval

60

Start-stop procedure

70

Testing both actuating means

80

Testing the first actuating means

90

Testing the second actuating means

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012000867 A1 [0008]
• DE 102005037408 A1 [0009]
• DE 112004002513 T5 [0010]

Claims (10)

A method for determining the tightness of a first and a second adjusting means (38, 39) for shutting off a fuel cell stack (10) of a fuel cell system (100), wherein in a cathode supply (30) of the fuel cell system (100) comprises a compressor (33) for promoting oxygen-containing gas is arranged to the inlet of the fuel cell stack (10), comprising the following steps: a1) setting the compressor (33) to a predetermined speed, b1) closing the first actuating means (38) of the two actuating means (38, 39), c1) actively discharging the fuel cell stack (10) and determining the discharge time, d1) evaluation of the specific discharge time, e1) transition to normal operation of the fuel cell system (100), and optional a2) setting the compressor (33) to a predetermined speed, b2) closing the second actuating means (39) of the two actuating means (38, 39), c2) actively discharging the fuel cell stack (10) and determining the discharge time, d2) evaluation of the specific discharge time, e2) transition to normal operation of the fuel cell system (100). Method according to Claim 1 , characterized in that before the steps a1) to e1) and the steps a2) to e2) the following steps are carried out a) setting the compressor (33) to a predetermined speed, b) closing both actuating means (38, 39), c ) actively discharging the fuel cell stack (10) and determining a discharge time, d) evaluating the determined discharge time, e) transitioning to normal operation of the fuel cell system (100). Method according to Claim 1 or 2 , characterized in that the evaluation of the discharge time in steps d), d1) and d2) takes place in relation to a discharge time determined in the experiment or that the evaluation of the discharge time in step d) takes place in relation to a discharge time determined in the experiment and the evaluation the discharge time in steps d1) and d2) takes place in relation to the discharge time determined in step d), whereby the evaluation of the discharge time in at least one of steps d), d1) and d2) optionally takes into account the current conditioning of the fuel cell stack (10). Method according to one of Claims 1 to 3 , characterized in that when closing one or both actuating means (38, 39) in steps b, b1) and b2) between a cathode supply line (31) and a cathode exhaust gas path (32) arranged wastegate line (35) is opened. Method according to one of Claims 1 to 4 , characterized in that at least after one of the steps d), d1), and d2) an error message and / or a measure to protect the fuel cell stack (10). Method according to one of Claims 1 to 5 , characterized in that the method steps for testing an actuating means (38, 39) before the examination of the other actuating means (38, 39) is repeated once or several times. A fuel cell system (100), wherein the fuel cell system (100) comprises a controller that is arranged to perform a method according to any one of Claims 1 to 6 and a fuel cell stack (10) having two actuating means (38, 39) for shutting off a fuel cell stack (10) and having an anode supply (20) and a cathode supply (30), the cathode supply (30) having a cathode supply line ( 31) via which an oxygen-containing cathode operating medium is supplied to the fuel cell stack (10) and a cathode exhaust path (32) which discharges the cathode exhaust gas from the fuel cell stack (10), wherein a compressor (33) is disposed in the cathode supply line (31), via which an oxygen-containing cathode operating medium is supplied to the fuel cell stack (10). Fuel cell system (100) after Claim 7 , characterized in that the cathode supply (30) has a wastegate line (35) which connects the cathode supply line (31) with the cathode exhaust gas line (32) and in which an adjusting means is arranged. Fuel cell system (100) after Claim 7 or 8th , characterized in that the control device comprises a sensor for a voltage of the fuel cell (10) and a timer. Vehicle with a fuel cell system (100) according to one of Claims 7 to 9 ,

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