DE102011119307A1 - Method for detecting position of drain valve in anode circuit of fuel cell system, involves comparing anode circuit pressure change pattern detected over predetermined period of time, with reference pattern to recognize valve position - Google Patents

Abstract

The method involves detecting pressure change pattern of anode circuit (5) of fuel cell system (1) over predetermined period of time. The detected pressure change pattern is compared with reference pattern so as to recognize an opened position or closed position of a drain valve (11). The predetermined period of time is set lesser than 5 seconds.

Description

The invention relates to a method for detecting the valve position of at least one drain valve in an anode circuit of a fuel cell system.

Fuel cell systems are known from the general state of the art. They may be formed, for example, on the basis of so-called PEM fuel cells and may be used in particular for the provision of electrical power in vehicles. The fuel cell systems often have a so-called anode circuit. This anode circuit connects the input of an anode side of the fuel cell to the output of the anode side. The anode circuit also receives fresh fuel. In this case, the fresh fuel comes in the area of the anode compartment and is there only partially implemented. Product water, residual fuel and inert gases, in particular nitrogen, which diffuse through the membrane into the anode space, pass via the anode circulation back to the inlet of the anode chamber, to which they are fed again together with fresh fuel. This ensures a very good utilization of the available active area of the anode space. On the other hand, water and inert gas accumulate in the anode circuit with time. Since the anode circuit typically has a constant volume, this inevitably lowers the hydrogen concentration and the performance of the fuel cell deteriorates. It is therefore generally known and customary to discharge water and / or gas from the region of the anode circuit via at least one drain valve. This can be done for example via two separate valves for liquid and gas, or via a common valve. The discharge of liquid and / or gas takes place, for example, time-dependent or as a function of the hydrogen concentration or the nitrogen concentration in the anode circuit. Other triggers for the discharge, such as the simulation of a resulting amount of water or the like, are conceivable. Purely by way of example with regard to a possible structure on the WO 2008/052578 A1 to get expelled.

In particular, at the end of the discharge process, ie when closing the drain valve, it is crucial to know the valve position of the drain valve safely and reliably, so as not to drain too much hydrogen with the inert gases. On the one hand, this is important for reasons of efficiency, on the other for safety reasons.

From the general state of the art, it is known that there are valves which have a position feedback. However, these are expensive and not always 100% reliable, depending on the principle of the position feedback. Alternatively, it is possible to carry out the measurement of the hydrogen concentration at a point in which the gas is discharged from the anode circuit, for example in the exhaust gas of the fuel cell. However, such an additional hydrogen sensor is also expensive and not 100% reliable in practice.

The object of the present invention is now to provide a method for detecting the valve position of at least one drain valve in an anode circuit of a fuel cell system, which allows easy and efficient cost-effective way to safely determine the valve position.

This object is achieved by a method having the features in the characterizing part of claim 1. An alternative solution to this is for a fuel cell system in which the pressure in the anode circuit via a fuel supply by a pressure control valve to a predetermined - optionally load-dependent - value is controlled, indicated by the features in the characterizing part of claim 6. Advantageous embodiments of the method will become apparent from the respective dependent claims. In addition, a particularly preferred use of the method is given in claim 10.

In the inventive method according to claim 1, it is provided that a pressure curve over time in the anode circuit is detected for a predetermined period of time, after which the detected pressure change is compared with a reference value to an open position or a closed position of the drain valve detect.

The idea of the invention is to measure the pressure or its change over time, ie the pressure gradient, in the anode circuit and thereby to detect whether the discharge valve is open or closed. As a result, the position of the drain valve can be detected by means of a simple, very reliable pressure measurement to be carried out with reliable and cost-effective sensors. This is correspondingly safe and easy.

According to a particularly favorable and advantageous embodiment of the method according to the invention, it is further provided that the predetermined time period in the range of a few seconds, preferably less than 5 seconds, is specified. Already such a short period of time is enough for the review. The check is thus very fast and reliable. Ideally, the check is made so that the pressure curve during a constant load, preferably Zero load, the fuel cell is detected. This is particularly preferred since the anode pressure is usually load-dependent. Because fuel cell systems, especially when used in vehicles, usually. have a battery or an electrical energy storage, it is easily possible due to the short period of time for measuring a few seconds to set a constant load point of the fuel point and as long as to provide the required load on the energy storage. The measurement does not affect the fuel cell system.

In a particularly favorable embodiment of the method according to the invention, it is also provided that when the open position of the drain valve, if it is used for the discharge of liquid and then gas, is detected by a change in a pressure gradient, whether the drain valve still liquid or already flows through in gaseous form. In such a combined drain / purge valve, as is known, for example, from the prior art mentioned above, when the open position of the drain valve is detected, a further change in the pressure value, and here in particular the pressure gradient, that is, the pressure value over time , to be detected, whether still liquid flows through the drain valve or already gas. This is of crucial importance for the control of the amount of gas to be discharged, since in addition to the pure knowledge of the open position or closed position of the discharge valve, this time also plays a role in order to be able to influence the amount of gas to be discharged as precisely as possible.

Now it is also the case that fuel cell systems often have a pressure control in the anode circuit, in which the pressure in the anode circuit is controlled by a fuel supply by a pressure regulating valve to a predetermined value. The method according to the invention described can not be realized in such an embodiment readily. Therefore, it is provided according to a particularly favorable and advantageous development of the method according to the invention that during a pressure control in the anode circuit it is exposed during the period for detecting the pressure curve and a fuel supply is controlled to a constant value corresponding to the respective load. In the best case, the fuel supply for the period of detection even by closing the valve 7 completely interrupted. By the load-dependent control of the fuel supply during the period for detecting the pressure curve, ie a brief suspension of the pressure control in the anode circuit, the use of the method according to the invention for detecting the valve position of the drain valve is possible even in such fuel cell systems.

Alternatively, it is therefore provided in a sibling method for detecting the valve position of at least one drain valve in an anode circuit of a fuel cell system according to the preamble of claim 7 that the required at the respective load volume flow of fuel is determined by the pressure control valve, and that one with the Flow is the pressure control valve at least indirectly corresponding size with the required volume flow of fuel is compared, being closed to an open drain valve when the flow through the pressure control valve exceeds the required at the respective load volume flow of fuel by more than a predetermined reference value. This alternative possibility makes it possible, just as simply and reliably as with the method described above, to determine the position of the discharge valve on the basis of a variable corresponding at least indirectly to the flow through the pressure regulating valve, in particular a control signal for the pressure regulating valve. The pressure control does not have to be suspended for this.

In both methods according to the invention, the reference values can be calculated as a function of the respective load point. This may be useful, in particular for load-dependent reference values. For this purpose, a simulation of the system can be used, which precalculates, for example, the consumption and / or the pressure accordingly. If the methods according to the invention then determine deviating values using these reference values, it must be assumed that the valve is open.

Additionally or alternatively, it is of course also possible to previously calculate or measure the reference values and store them accordingly and to use for one of the inventive method.

Both methods of the invention make it very simple, reliable and inexpensive to determine whether the drain valve is open or not. They are therefore particularly suitable for fuel cell systems, which are produced in large quantities and therefore need to be realized in a particularly simple and cost-effective manner. Since they also ensure a very high level of security when determining the value to be determined, the inventive methods can nevertheless be used in fuel cell systems to which high safety requirements are to be placed, for example because people are often in the field of these fuel cell systems and explosive or flammable mixtures are therefore to be avoided in any case.

The two last described aspects of a simple and inexpensive fuel cell system, which is also very safe, predestine the inventive method for use in a fuel cell system, which is used in a vehicle for the provision of electrical power, in particular electrical drive power. Here are special requirements for safety and because of the high quantities are also very simple and inexpensive fuel cell systems of particular advantage.

Further advantageous embodiments of the method according to the invention emerge from the remaining dependent subclaims. Furthermore, advantageous embodiments of the method according to the invention and of a fuel cell system for carrying out the method according to the invention from the exemplary embodiment, which will be described in more detail below with reference to the figures.

Showing:

1 a detail of a fuel cell system for carrying out the method according to the invention in a first embodiment; and

2 a section of a fuel cell system for carrying out the method according to the invention in a second embodiment.

In the presentation of the 1 is a section of a fuel cell system 1 , as it is suitable for carrying out the method according to the invention to recognize. The fuel cell system 1 should in a principle indicated vehicle 2 be arranged. It can provide electrical power there. This can be used for example for secondary consumers or in particular as electrical drive power. The core of the fuel cell system 1 is a fuel cell 3 , which may be formed for example as a PEM fuel cell stack. The fuel cell 3 has a cathode compartment 4 and an anode room 5 , The cathode compartment 4 air is supplied as an oxygen supplier in a conventional manner, exhaust air passes out of the cathode compartment 4 back in the area. This process is known per se and usual. It can be realized via suitable compressors, compressors, electric turbochargers or the like.

The anode compartment 5 the fuel cell 3 Hydrogen is used as fuel from a compressed gas storage tank 6 fed. In the presentation of the 1 this hydrogen passes through a metering valve 7 from the compressed gas storage 6 in the area of the anode compartment 5 , Unused residual hydrogen passes through a recirculation line 8th and a recirculation conveyor 9 , which may be formed here, for example, as a hydrogen blower and / or as a gas jet pump, back to the anode compartment 5 and is fed again, mixed with fresh hydrogen. This structure is also known as a so-called anode circuit. In the area of the recirculation line 8th is an example of a water separator 10 arranged. This is about a drain valve 11 with an area in which water and gas can be discharged from the anode circuit, in conjunction. This can, for example, the supply air to the cathode compartment 4 or the exhaust air from the cathode compartment 4 be. Other areas in which gas and / or water are drained are known and conceivable. Since this does not play a significant role for the present invention, a detailed description has been omitted. Alternative to the combined drain valve 11 For water and / or gas of course, the division would be conceivable on two separate drain valves and pipes.

The fuel cell 3 provides, as already mentioned, electrical power available. It is in the embodiment shown here parallel to an electrical energy storage 12 , For example, a storage battery, a capacitor bank or a combination thereof, formed. This is followed by power electronics 13 , via which the electrical power in a basically indicated wiring system 14 is fed.

Now it is the case that in the known manner in the anode circuit of the fuel cell system 1 Inert gases accumulate over time, in particular nitrogen, which flows through the membranes from the cathode compartment 4 in the anode compartment 5 is diffused. In addition, water accumulates, which is typically in the water separator 10 is deposited. To the hydrogen concentration in the anode circuit on a for the functionality of the fuel cell 3 it is necessary to occasionally drain the inert gases and / or water. This is the already mentioned drain valve 11 intended. The deflation can be triggered from time to time, depending on the hydrogen and / or nitrogen concentration or by comparable and known per se methods. Here, the knowledge of the switching state of the drain valve 11 important to ensure that not too much hydrogen is released with the inert gases and / or water. On the one hand this is decisive for efficiency reasons, on the other hand, depending on the interconnection, also for security reasons, none critical hydrogen emissions in the environment of the fuel cell system 1 to cause.

At the in 1 described fuel cell system 1 should now a via a pressure sensor 15 detected pressure or its change over time in the anode circuit can be used to thereby detect whether the drain valve 11 open or closed. Since in the area of the pressure sensor 15 measured anode pressure is usually load-dependent, should be a check of the valve position of the drain valve 11 preferably at constant load of the fuel cell 3 respectively. However, the check is possible within a few seconds, so that via the energy storage device 12 in the fuel cell system 1 or the vehicle 2 at least briefly during the check of the valve position of the drain valve 11 a constant load condition can be set. The actual of the electrical system 14 required load can then as long as the energy storage device 12 to be provided. Checking the valve position of the drain valve 11 via a measurement of the time course of the pressure in the region of the pressure sensor 15 So it can be done at constant load. Ideal would be a load point in which there is no load, so there is no load. This is for example in fuel cell systems 1 with a start / stop operation during the stop phase possible. Otherwise it is possible to use the fuel cell 3 briefly to switch to idle, since, as already mentioned, the energy storage device 12 as long as the electrical energy supply of the electrical system 14 could take over alone.

If the pressure in the area of the pressure sensor is now at a stationary load point 15 measured for a certain period of time of a few seconds and the pressure drops faster than with the balance of flow through the metering valve 7 and consumption in the fuel cell 3 expected rate, it can be assumed that the drain valve 11 is open. Other leakage of the anode circuit can typically be excluded here, since this is generally not accompanied by as high a flow as the open drain valve 11 , The measured over the time pressure curve, so the pressure gradient, so it can be compared with a reference value, which is recalculated depending on the load in each case for the current case. Alternatively, the measured pressure gradient may also be with one in previous measurements or independently of the fuel cell system 1 pre-calculated reference values, which then in a control unit 16 are stored accordingly, are compared. Once the controller 16 determines that the detected pressure change deviates from the calculated or stored reference value, can via the control unit 16 an open position or a closed position of the drain valve 11 be recognized. This knowledge can then, for example, for driving the drain valve 11 be used.

If the draining as in the 1 illustrated fuel cell system 1 via only one drain valve 11 , which in particular in the area of the water separator 10 is arranged, then it can also be detected by a change in the pressure gradient when the open position of the drain valve, whether the drain valve 11 is still flowed through by liquid or gas. Since liquid is typically incompressible, the pressure gradient goes directly to the flow rate of the liquid through the drain valve 11 associated. Due to the compressibility of the gas and the anode circuit under an overpressure, the pressure drops significantly more at the moment, in which only the gas of the discharge valve is lowered 11 happens because it comes in addition to the outflow to an expansion of the gas. This time can be recorded and used to the drain valve 11 to control so that only a minimal amount of hydrogen is discharged.

The method can be used in a fuel cell system 1 with a control of the hydrogen supply in the anode circuit via the metering valve 17 realize. The control is typically done load-dependent, and, as is typical for a controller, without feedback of the actually metered value. In this case, the detection of a pressure gradient then allows the characteristic evaluation, which conclusions on the valve position of the drain valve 11 allows. Now it is often the case with fuel cell systems 1 an operating guide is provided, which provides a control of the anode circuit, wherein the pressure in the anode circuit via a pressure regulating valve 17 as it is in 2 is controlled by influencing the hydrogen supply to a constant value. Such a structure is the example of a fuel cell system 1 in the presentation of the 2 to recognize. Here are only the differences in comparison to 1 shown. On the representation of the electrical connection of the fuel cell 3 As well as the vehicle was omitted here, but these should of course also be available.

The pressure control valve 17 is about the pressure sensor 15 coupled to the anode or the anode circuit. Again with the reference numeral 16 provided control device should be a control of the anode circuit to a constant pressure.

In such a structure of the fuel cell system with controlled pressure of the anode circuit, there are now two ways that Valve position of the drain valve 11 to check. The first possibility is that the control of the pressure in the anode circuit is suspended during the check, ie during the period during which the pressure profile is measured. At the preferably constant load is then via the pressure control valve 17 set a predetermined volume flow of hydrogen in the manner of a control, or completely prevented in the ideal case of zero load, the supply of hydrogen. In this situation, the measurement can then be performed in the manner already described above. After the time span of a few seconds, within which the measurement is carried out, then the regulation of the pressure in the anode circuit can be reactivated.

An alternative way to detect the valve position of the drain valve 11 On the other hand, it provides that the verification is carried out in regulated operation. For this purpose, it is checked in controlled operation, whether the resulting drive signal and thus ultimately the flow through the pressure control valve 17 at the present load-dependent consumption by the reactions of the fuel cell 3 corresponds to the expected value for the respective load. This value can be calculated, for example, currently or from the electrical load of the fuel cell 3 be derived. Is the drive signal as with the flow through the pressure control valve 17 Corresponding size thereby by a predetermined reference value greater than the desired signal, which results from the expected value of the fuel consumption, it can be assumed that the drain valve 11 is open. The reference value, by which the deviation must be above the desired signal, can in turn currently be calculated as a function of the load or measured or calculated in advance and in the control unit 16 to save.

The method can be used both for gas-flowed drain valves 11 as well as for liquid-flow discharge valves 11 apply. The method is very simple and efficient in both possible embodiments. It allows the monitoring of the valve position of the drain valve 11 safe and reliable, without the need for elaborate valve technology and / or complex gas sensors.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• WO 2008/052578 A1 [0002]

Claims (10)

Method for detecting the valve position of at least one drain valve ( 11 ) in an anode circuit of a fuel cell system ( 1 ) characterized in that for a predetermined period of time, a pressure variation over time in the anode circuit is detected, after which the detected pressure change is compared with a reference value to an open position or a closed position of the drain valve ( 11 ) to recognize. Method according to claim 1, characterized in that the predetermined period of time is specified in the range of a few seconds, preferably less than 5 seconds, Method according to claim 1 or 2, characterized in that the pressure curve during a constant load of a fuel cell ( 3 ) of the fuel cell system ( 1 ), preferably during no load. A method according to claim 3, characterized in that during the detection of the pressure curve in the fuel cell system ( 1 ) required load via an energy storage device ( 12 ) provided. Method according to one of claims 1 to 4, characterized in that in a pressure control in the anode circuit, this is exposed during the period for detecting the pressure curve, and a fuel supply to a constant, the respective load corresponding value is controlled. Method according to one of claims 1 to 5, characterized in that when it is known open position of the drain valve ( 11 ), if this is used for the discharge of liquid and then gas, is detected by a change in a pressure gradient, whether the drain valve ( 11 ) is still liquid or gas flows through it. Method for detecting the valve position of at least one drain valve ( 11 ) in an anode circuit of a fuel cell system ( 1 ), wherein a pressure in the anode circuit via a fuel supply by a pressure regulating valve ( 17 ) is regulated to a predetermined value, characterized in that the required at the respective load volume flow of fuel through the pressure control valve ( 17 ) and that one with the flow through the pressure regulating valve ( 17 ) at least indirectly corresponding size is compared with the required volume flow of fuel, wherein an open drain valve ( 11 ) is closed when the flow through the pressure regulating valve ( 17 ) exceeds the volume flow of fuel required at the respective load by more than a predetermined reference value. A method according to claim 7, characterized in that as at least indirectly with the flow through the pressure regulating valve ( 17 ) corresponding size the drive signal for the pressure control valve ( 17 ) is being used. Method according to one of claims 1 to 8, characterized in that the reference value is calculated as a function of the respective load point. Method according to one of claims 1 to 9, characterized in that the reference value has previously been calculated and / or measured and stored.

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