DE102021134201B3 - Method for operating a fuel cell system and fuel cell system - Google Patents

Abstract

The invention relates to a method for operating a fuel cell system (1) with a plurality of fuel cell stacks (2) equipped with auxiliary units (3) which can be activated and/or deactivated selectively, with each fuel cell stack (2) and each of the associated auxiliary units ( 3) the aging influences are determined individually using measured values or expected values, comprising the steps:
- Assignment of future operating times to one of the fuel cell stacks (2) with the ancillary units (3) whose degree of degradation, determined on the basis of the aging effects, is the lowest, and
- Uniform distribution of future operating times on the fuel cell stack (2) if the differences in the degree of degradation is below a predetermined or specifiable threshold value.
The invention also relates to a fuel cell system (1).

Description

• - Zuordnung von künftigen Betriebszeiten zu einem der Brennstoffzellenstapel mit den Nebenaggregaten, deren anhand der Alterungseinflüsse bestimmten Degradationsgrad am geringsten ist, und
• - gleichmäßige Verteilung künftiger Betriebszeiten auf die Brennstoffzellenstapel, wenn die Unterschiede des Degradationsgrades unterhalb eines vorgegebenen oder vorgebbaren Schwellenwertes liegt.

The invention relates to a method for operating a fuel cell system with a plurality of fuel cell stacks equipped with ancillaries that can be selectively activated and/or deactivated, with the aging effects being determined individually for each fuel cell stack and for each of the associated ancillary units by means of measured values or expected values, comprising the steps :

• - Assignment of future operating times to one of the fuel cell stacks with the ancillary units whose degree of degradation, determined on the basis of the effects of aging, is the lowest, and
• - Equal distribution of future operating times on the fuel cell stack if the differences in the degree of degradation is below a predetermined or specifiable threshold value.

The invention also relates to a fuel cell system.

A fuel cell is used to allow a suitable fuel, in particular hydrogen, to react in a controlled manner with oxygen, usually provided from the air, and to generate electricity in an electrochemical reaction. To increase performance, it is known to combine several fuel cells in a fuel cell stack, with ancillary units being used to supply this fuel cell stack with sufficient oxygen-containing air in the required conditioned state with regard to temperature and humidity. Auxiliary units are also used to recirculate unused fuel to achieve high efficiency. Such fuel cell devices with a fuel cell stack and associated ancillary units are also used in fuel cell vehicles to provide electric mobility.

If the power requirement is increased even further, for example in a truck, several fuel cell stacks can be used, which can also be supplied from common ancillary units, which then have to be very large and then sometimes only run at partial load, for example if the current power requirement is to be met only one fuel cell stack is activated and the others are kept on standby. Alternatively, there is also the possibility of providing a plurality of fuel cell devices, ie fuel cell stacks with associated ancillary units, which can then be dimensioned smaller and standard systems can be manufactured more cost-effectively in large numbers.

In the U.S. 2009/0305087 A1 describes a method and a fuel cell system that has a plurality of fuel cell stacks connected in parallel, with each module being able to be switched on or off, and thus activated or deactivated, according to the load requirement, with the accumulated operating time of each module being taken into account in order to achieve even wear .

In the DE 10 2020 200 249 A1 describes a fuel cell device with a fuel cell stack that includes at least one component that degrades, ages, or wears out during operation. An operating strategy is adapted in order to achieve the required service life of the component as a function of a currently expected service life based on the accumulated loads, i.e. in the case of a compressor, for example, operation is continued at a relatively low speed in order to prevent a start-stop process.

In the JP 2015-176737 A describes a fuel battery cell unit CS that generates power and supplies this power to a power load section via a power output circuit unit. The fuel battery cell unit CS is configured to be able to perform the supply and stop of oxidizing gas to a fuel electrode and the supply and stop of oxidizing gas to an air electrode for each of the plurality of cell blocks CB and the electrical connection state to a power output circuit unit for to switch each of the multiple cell blocks CB.

In the DE 10 2018 218 086 A1 a method for operating a fuel cell system with a stack arrangement is described. This stack arrangement comprises a plurality of fuel cell stacks which can be activated and/or deactivated selectively, it being possible for performance data of each individual fuel cell stack present in the stack arrangement to be recorded.

The problem with the use of a plurality of fuel cell stacks with associated ancillary units, which are activated and deactivated as fuel cell devices as required, is that the individual components of the fuel cell system are operated for different periods of time and the general conditions during operation can also be different, for example in the case of a fuel cell stack high number of frost starts accumulated is while another air-to-air launch was suspended.

It is therefore the object of the present invention to provide a method and a fuel cell system which take into account the disadvantages mentioned above.

This object is achieved with a method for operating a fuel cell system having the features of claim 1 and with a fuel cell system having the features of claim 10. Advantageous configurations with expedient developments of the invention are specified in the dependent claims.

The method according to the invention is characterized in that improved efficiency is achieved with reduced overall degradation of the fuel cell system, which also achieves a longer service life as a result. There is a more homogeneous overall system in which there is improved knowledge about the condition of the fuel cell units with the ancillary units. It is also favorable that a threshold value with regard to the differences is taken into account, i.e. it is avoided that fuel cell stacks are exchanged during operation due to minor differences, i.e. activation of one fuel cell stack and deactivation of another takes place, thus reducing the number of starts and stops.

It is particularly advantageous if, when an increased load requirement is detected, those inactive fuel cell stacks are activated one after the other in a sequence with increasing degree of degradation until the active fuel cell stack provides a power that meets the increased load requirement. This results in a sequence that leads to an improved allocation of future operating times. This also applies if, when a reduced load requirement is detected, those active fuel cell stacks are deactivated one after the other in a sequence with decreasing degree of degradation, until the still active fuel cell stacks provide a power that meets the reduced load requirement.

It is expedient if the aging influences with regard to the mechanical load on each fuel cell stack are recorded in order to determine the degree of degradation, namely with regard to the absolute pressure and/or the pressure across the membranes of the membrane electrode assemblies and/or the power gradient with regard to the fuel cells of the fuel cell stack and/or or the number of frost starts.

An improved level of knowledge with uniform aging can also be achieved if the aging influences with regard to the electrochemical load of each fuel cell stack are recorded in order to determine the degree of degradation, namely with regard to the current strength and/or the electrical voltage and/or the temperature and/or the relative humidity of the membranes the membrane electrode assemblies and/or the number of air/air starts.

Again, the achievement of the above advantages is that for the determination of the degree of degradation, the aging influences are taken into account with regard to the ancillaries, which are selected from a group of compressors, electric turbochargers for the compressors, fans for recirculation in an anode circuit of the fuel cell stack, thermostatic valves, humidifiers with humidifier membranes, DC/DC converter included.

The completeness of the inclusion of different parameters serves that for the determination of the degree of degradation the aging influences for the compressors and/or the fans with regard to the temperature and the speed, and/or for the electric turbochargers with regard to the temperature after the compressor and/or the speed and /or the starting frequency and/or the differential pressure between the compressor and the turbine of the electric turbocharger and/or the thermostatic valves with regard to the switching frequency and/or for the humidifier with regard to the temperature and/or the humidity of the humidifier membrane and/or for the DC/DC -Converter are detected in terms of current and / or temperature and / or temperature change.

Since the fuel cell stacks represent cost-intensive components whose maintenance and replacement affect the costs over the entire service life of the system, it is provided that the aging effects of the respective fuel cell stack are weighted more heavily than the associated ancillary units when determining the degree of degradation.

The improvement in service life by achieving uniform wear also serves to classify the individual fuel cell stacks with the assigned ancillary units in a control unit for prioritizing the assignment of future operating times when activated and with an inversion of the prioritization when deactivated.

The advantages and effects mentioned above also apply mutatis mutandis to a fuel cell system with a plurality of fuel cell stacks equipped with ancillary units can be selectively activated and/or deactivated, with the aging effects being detectable and/or predictable with regard to the expected value for each fuel cell stack and for each of the associated ancillaries using a measuring arrangement designed to record individual performance data, and with a control device that is designed to use the aging effects of each fuel cell stack with the associated ancillaries to allocate future operating times to each fuel cell stack in such a way that the fuel cell stack with the lowest degree of degradation is activated and an even distribution of future operating times to the fuel cell stack is achieved if the differences between the Degrees of degradation of the fuel cell stack are below a predetermined or specifiable threshold value.

In a further development of the invention, it has proven to be advantageous if at least one of the inactive fuel cell stacks is processed to reduce reversible aging effects, in particular by reducing its degree of degradation. Thus, the fuel cell stacks can be subjected to a recovery strategy during the inactive phase, ie in particular reversible aging effects in the inactive fuel cell stacks can be reduced or eliminated. For example, oxygen depletion can be carried out on the cathode side while maintaining the current flow above a predetermined or predeterminable minimum current intensity for a predetermined period of time. This causes the voltage potential of the individual fuel cell to drop, which is conducive to the reduction of the catalyst oxide. Since the fuel cell system is also operated in a sub-stoichiometric ratio due to the oxygen depletion, i.e. less oxygen is supplied to the cathode side than is required for the reaction with the hydrogen provided, the excess hydrogen reacts with the oxygen of the catalyst oxide, so that the catalyst is regenerated. The resulting lower degree of degradation can be taken into account in the aging effects.

The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown alone in the figures can be used not only in the combination specified in each case, but also in other combinations or on their own, without going beyond the scope of the leave invention. Embodiments are therefore also to be regarded as included and disclosed by the invention which are not explicitly shown or explained in the figures, but which result from the explained embodiments and can be generated by means of separate combinations of features.

• 1 eine schematische Darstellung eines Brennstoffzellensystems mit mehreren Brennstoffzellenvorrichtungen,
• 2 eine Darstellung der relativen Häufigkeit eines Betriebszustandes bei einer gegebenen elektrischen Spannung pro Brennstoffzelle, in der oberen Reihe für eine erste Brennstoffzellenvorrichtung und in der unteren Reihe für eine zweite Brennstoffzellenvorrichtung, bei der ein höherer Anteil am Niederlastbetrieb bei hohen Zellspannungen vorliegt, kenntlich gemacht durch die Ringe,
• 3 eine zeitabhängige Darstellung der generierten Leistung der ersten Brennstoffzellenvorrichtung (strichlierte Linie) und der zweiten Brennstoffzellenvorrichtung (gepunktete Linie) in der oberen Reihe mit den Ein- und Ausschaltvorgängen, mit der Temperatur nach dem Brennstoffzellenstapel (mittlere Reihe) und der Geschwindigkeit (strichlierte Linie) und der Steigung (gepunktete Linie) (untere Reihe), und
• 4 eine Abschätzung der zeitabhängigen elektrochemischen Degradation mit dem der Optimierung dienenden Verfahren (linke Darstellung) und ohne dem der Optimierung dienenden Verfahren (rechte Darstellung).

Further advantages, features and details of the invention result from the claims, the following description of preferred embodiments and from the drawing. It shows:

• 1 a schematic representation of a fuel cell system with several fuel cell devices,
• 2 a representation of the relative frequency of an operating state at a given electrical voltage per fuel cell, in the top row for a first fuel cell device and in the bottom row for a second fuel cell device, in which there is a higher proportion of low-load operation at high cell voltages, identified by the rings ,
• 3 a time-dependent representation of the generated power of the first fuel cell device (dashed line) and the second fuel cell device (dotted line) in the upper row with the switching on and off processes, with the temperature after the fuel cell stack (middle row) and the speed (dashed line) and the slope (dotted line) (bottom row), and
• 4 an estimation of the time-dependent electrochemical degradation with the optimization method (left diagram) and without the optimization method (right diagram).

In 1 a fuel cell system 1 is shown in highly schematic form, which consists of a plurality of fuel cell stacks 2, one of which is shown in FIG 1 only two are shown, but others may be added. The fuel cell stacks 2 are each provided with ancillary units 3 shown schematically, which are formed, for example, by compressors, electric turbochargers for the compressors, fans for recirculation in an anode circuit of the fuel cell stack, thermostatic valves, humidifiers with humidifier membranes, DC/DC converters, coolant pumps, jet pumps , intercooler.

• - Zuordnung von künftigen Betriebszeiten zu einem der Brennstoffzellenstapel 2 mit den Nebenaggregaten 3, deren anhand der Alterungseinflüsse bestimmten Degradationsgrad am geringsten ist, und
• - gleichmässige Verteilung künftiger Betriebszeiten auf die Brennstoffzellenstapel 2, wenn die Unterschiede des Degradationsgrades unterhalb eines vorgegebenen oder vorgebbaren Schwellenwertes liegt.

The fuel cell stacks 2 can be activated and/or deactivated selectively, with the aging effects being determined individually for each fuel cell stack 2 and for each of the associated ancillary units 3 by means of measured values or expected values. For example, for each fuel cell stack 2 and for each of the associated ancillary units 3 individually, the aging influences are recorded by means of a measuring arrangement that records individual performance data, as a result of which the degree of degradation can be determined. It is also conceivable to determine an expected value for the degradation on the basis of the operating time and the general operating conditions, for example associating an operating time of 100 hours for one of the components with a degradation of 20%; a different value may apply to a different component. Part of the fuel cell system is also a control unit 4, which is designed to assign future operating times to each fuel cell stack 2 based on the aging effects of each fuel cell stack 2 with the associated ancillary units 3 in such a way that the fuel cell stack 2 with the ancillary units 3 is activated with the lowest degree of degradation and an even distribution future operating times is reached on the fuel cell stack 2 when the differences in the degree of degradation of the fuel cell stack 2 is below a predetermined or specifiable threshold value. This fuel cell system 1 can therefore be used to carry out a method for operating the fuel cell system 1, which comprises the following steps:

• - Allocation of future operating times to one of the fuel cell stack 2 with the ancillary units 3, whose degree of degradation determined on the basis of the aging effects is the lowest, and
• - Even distribution of future operating times on the fuel cell stack 2 if the differences in the degree of degradation is below a predetermined or specifiable threshold value.

It is also possible that when an increased load requirement is detected, those inactive fuel cell stacks 2 are activated one after the other in a sequence with increasing degree of degradation until the active fuel cell stack 2 provides a power that meets the increased load requirement, and that when a reduced one is detected Load requirement those active fuel cell stacks 2 are deactivated one after the other in an order with decreasing degree of degradation until the still active fuel cell stack 2 provides a performance that meets the reduced load requirement. In the control unit 4, the individual fuel cell stacks 2 with the associated ancillary units 3 are classified for prioritizing the assignment of future operating times when activated and for inverting the prioritization when deactivated.

To determine the degree of degradation, the aging influences with regard to the mechanical load on each fuel cell stack 2 are recorded, namely with regard to the absolute pressure and/or the pressure across the membranes of the membrane electrode assemblies and/or the power gradient with regard to the fuel cells of the fuel cell stack 2 and/or the Number of frost starts.

The aging influences 2 with regard to the electrochemical load of each fuel cell stack are also recorded for determining the degree of degradation, namely with regard to the current intensity and/or the electrical voltage and/or the temperature and/or the relative humidity of the membranes of the membrane electrode assemblies and/or the number of air-to-air launches. 2 shows in the bottom row a higher load on the fuel cell stack due to more frequent operation in the low-load range at high cell voltages, which promote degradation. For the analysis and evaluation of the menu data, these are shown as a histogram.

Correspondingly, the aging influences with regard to the ancillary units 3 are taken into account for determining the degree of degradation, which are selected from a group consisting of the compressors, electric turbochargers for the compressors, fans for recirculation in an anode circuit of the fuel cell stack, thermostatic valves, humidifiers with humidifier membranes, DC/DC converter included.

It is also provided that for the determination of the degree of degradation, the aging influences for the compressors and/or the fans with regard to the temperature and speed, and/or for the electric turbochargers with regard to the temperature after the compressor and/or the speed and/or the starting frequency and/or the differential pressure between the compressor and the turbine of the electric turbocharger and/or the thermostatic valves with regard to the switching frequency and/or for the humidifier with regard to the temperature and/or the humidity of the humidifier membrane and/or for the DC/DC converter with regard to the Current and / or the temperature and / or the temperature change are detected.

The aging effects of the respective fuel cell stack are weighted more heavily than the associated ancillary units when determining the degree of degradation, since this serves to better preserve the fuel cell stack, the maintenance and replacement of which as the main component is more complex and expensive.

4 shows the estimation of the electrochemical degradation, where a value of 25 on the ordinate indicates the limit of the lifetime. The operation according to the invention leads to a service life of approx. 10,000 hours (left graphic) compared to only 7,000 hours without the optimization according to the invention (right graphic).

Claims (10)

Method for operating a fuel cell system (1) with a plurality of fuel cell stacks (2) equipped with auxiliary units (3) which can be activated and/or deactivated selectively, wherein for each fuel cell stack (2) and for each of the associated auxiliary units (3) the Aging influences are determined using measured values or expected values, comprising the steps: - Assignment of future operating times to one of the fuel cell stacks (2) with the ancillary units (3) whose degree of degradation, determined on the basis of the aging effects, is the lowest, and - Uniform distribution of future operating times on the fuel cell stack (2) if the differences in the degree of degradation are below a predetermined or specifiable threshold value. procedure after claim 1 , characterized in that when an increased load requirement is detected, those inactive fuel cell stacks (2) are activated one after the other in a sequence with increasing degree of degradation until the active fuel cell stack (2) provides a power that meets the increased load requirement. procedure after claim 1 or 2 , characterized in that when a reduced load requirement is detected, those active fuel cell stacks (2) are deactivated one after the other in a sequence with decreasing degree of degradation until the still active fuel cell stack (2) provides a power that meets the reduced load requirement. Procedure according to one of Claims 1 until 3 , characterized in that for the determination of the degree of degradation the aging influences with regard to the mechanical load of each fuel cell stack (2) are recorded, namely with regard to the absolute pressure and/or the pressure across the membranes of the membrane electrode assemblies and/or the power gradient with regard to the fuel cells of the Fuel cell stack and / or the number of frost starts. Procedure according to one of Claims 1 until 4 , characterized in that for the determination of the degree of degradation the aging influences with regard to the electrochemical load of each fuel cell stack (2) are recorded, namely with regard to the current intensity and/or the electrical voltage and/or the temperature and/or the relative humidity of the membranes of the membrane electrode locations and/or the number of air/air starts. Procedure according to one of Claims 1 until 5 , characterized in that for the determination of the degree of degradation, the aging influences with regard to the ancillaries (3) are taken into account, which are selected from a group consisting of compressors, electric turbochargers for the compressors, fans for recirculation in an anode circuit of the fuel cell stack, thermostatic valves, humidifiers with Humidifier membranes, DC/DC converter included. procedure after claim 6 , characterized in that for the determination of the degree of degradation, the aging influences for the compressor and/or the fan in terms of temperature and speed, and/or for the electric turbocharger in terms of temperature after the compressor and/or speed and/or starting frequency and/or the differential pressure between the compressor and the turbine of the electric turbocharger and/or the thermostatic valves with regard to the switching frequency and/or for the humidifier with regard to the temperature and/or the humidity of the humidifier membrane and/or for the DC/DC converter with regard to the Current and / or the temperature and / or the temperature change are detected. Procedure according to one of Claims 1 until 7 , characterized in that the aging effects of the respective fuel cell stack (2) compared to the associated ancillaries (3) are weighted more heavily when determining the degree of degradation. Procedure according to one of Claims 1 until 8th , characterized in that in a control unit (4) the individual fuel cell stacks (2) with the associated ancillaries (3) are classified for prioritizing the assignment of future operating times when activated and with an inversion of the prioritization when deactivated. Fuel cell system (1) with a plurality of auxiliary units (3) equipped Fuel cell stacks (2) that can be selectively activated and/or deactivated, with the aging effects being individually detectable and/or the expected value can be predicted on the basis of the operating time and the general operating conditions, and with a control unit (4) which is designed to assign future operating times to each fuel cell stack (2) based on the aging effects of each fuel cell stack (2) with the associated ancillary units (3) in such a way that the fuel cell stack (2) with the lowest degree of degradation is activated and future operating times are distributed evenly to the fuel cell stack (2) if the differences in the degree of degradation of the fuel cell stack (2) are below a predetermined or specifiable threshold value.

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