Load reduction limitation in high temperature operation
The fuel cell load is gradually reduced and cooled through the control device, which solves the problem of unstable fuel cell system in the vehicle when operating at low loads, and achieves safe, stable operation and wear reduction of fuel cells.
Patent Information
- Application Number
- CN202380053712.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-07-14
- Filing Date
- 2023-07-10
- Publication Date
- 2025-02-28
AI Technical Summary
In vehicles, the fuel cell system may enter an unstable state when operating at low loads, resulting in insufficient wetting of the membrane and insufficient drainage, which may cause water flooding or excessive drying of the membrane, which cannot ensure the stable operation of the fuel cell.
Through the control device, the load of the fuel cell is gradually reduced, from the first load to the third load, and then from the third load to the second load, while cooling the fuel cell to ensure safe operation of the second load at a lower second temperature.
It delays the load reduction process from high to low, ensures that the fuel cell operates safely at a lower load after cooling to the appropriate temperature, avoids unstable operating conditions, improves the operating safety of the fuel cell system and reduces wear.
Smart Images
Figure CN119547231A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for operating a fuel cell of a fuel cell system for a vehicle, in particular for a land vehicle, a water vehicle, an air vehicle, etc. The invention further relates to a fuel cell system for a vehicle. Background Art
[0002] Hydrogen-based ion exchange membrane fuel cell systems are seen as a future mobility solution because they emit only water as exhaust gas and enable fast refilling times.
[0003] In vehicles, the amount of heat that can be dissipated is limited by the low temperature level of the fuel cell and the limited radiator area. The normal operating temperature of the fuel cell is about 60°C, and the permissible temperature to avoid damage to the fuel cell is about 90°C. In some operating states, such as when a motor vehicle is driving downhill with high power demand and low radiator flow rate, thermal limitations result. In the case of thermal limitations, the heat generated by the fuel cells, which are sometimes combined to form a fuel cell stack, can no longer be completely dissipated. In extreme cases, the power of the fuel cells of the fuel cell stack must be reduced, which is called thermal derating.
[0004] Methods for operating fuel cells are known in which, in order to avoid or delay the degradation, the operating temperature is usually increased from about 60° C. to 90° C. A greater temperature difference with the surroundings can increase the heat flow that can be removed by means of a given cooler. If the operating pressure is increased at the same time, robust operation with adequate membrane wetting can be ensured at high current densities.
[0005] However, situations may arise in which, due to prolonged full-load operation with insufficient cooling power, the system temperature may increase and the power requirement may then decrease significantly. This may occur, for example, when a motor vehicle stops spontaneously after driving downhill, especially at relatively high ambient temperatures and relatively low inflow velocities.
[0006] Due to the thermal inertia of the fuel cell, the power reduction in principle takes place much faster than the temperature reduction. As a result, the fuel cell system can enter a very unfavorable state in which a relatively high operating temperature of the fuel cell is present at a relatively low load. This operating state is referred to below as an "unstable operating state".
[0007] When operating at relatively low loads, a collision of the two operating boundaries can occur. In the regulation of the gas supply to ensure that the membrane of the fuel cell has sufficient humidity, the flow rate in the channel can become so slow that it is no longer possible to ensure sufficient drainage of liquid water from the fuel cell. The difference between the two operating boundaries increases with increasing system temperature. Due to the stable intermittent operation of the fuel cell, the operating area is expanded in the direction of lower loads.
[0008] If a lower load is to be set at high temperatures at the coolant outlet, unstable operating conditions can sometimes no longer be avoided even in intermittent operation. In this case, the two boundaries are so far apart that intermittent operation with a typical air system is no longer possible. Depending on the combination of pressure and stoichiometry, either flooding can occur due to insufficient drainage of liquid water or excessive drying of the membrane can occur. As a result, a stable, for example static, operating condition of the fuel cell cannot be ensured. Summary of the invention
[0009] According to a first aspect of the present invention, a method for operating a fuel cell of a fuel cell system for a vehicle, in particular a land vehicle, a water vehicle, an air vehicle, etc. is provided. The method comprises:
[0010] - operating the fuel cell at a first load and a first temperature by means of a control device of the fuel cell system,
[0011] - receiving, by the control device, a load request for operating the fuel cell at a second load, wherein the second load is less than the first load,
[0012] - reducing the load of the fuel cell to a third load in a targeted manner by means of the control device, wherein the third load is less than the first load and greater than the second load,
[0013] - cooling the fuel cell to a second temperature, and
[0014] - Reducing the load of the fuel cell to a second load by the control device.
[0015] In the context of the present invention, the operation of a fuel cell can also be understood as the operation of a plurality of or all fuel cells of a fuel cell stack. For better understanding, only one fuel cell is mentioned below, wherein a plurality of or all fuel cells can also be referred to.
[0016] When carrying out the method, the fuel cell is first operated by means of a control device in such a way that an initial situation is achieved, which in conventional methods for operating a fuel cell would normally lead to an unstable or critical operating state of the fuel cell when reducing a set, relatively large load to a second load. For example, such an initial situation could be achieved when a fully loaded motor vehicle is driven uphill for a relatively long time at relatively high outside temperatures.
[0017] In this initial state, a first load is applied, which can be between 80% and 100% within the full load range of the fuel cell, for example. This load can be set, for example, by current intensity, electrical power, voltage level or hydrogen supply. In the following, the concept according to the invention is described by way of example with respect to current intensity. For example, the first load can be between 450A (amperes) and 500A. Preferably, the first load is about 480A. The first load is transmitted to the control device within this scope, for example as a load request for operating the fuel cell.
[0018] In addition, the fuel cell has a first temperature in the initial state. For example, the first temperature can be between 80% and 100% of the maximum permissible operating temperature of the fuel cell. For example, the first temperature can be between 75° C. and 90° C. Preferably, the first temperature is about 90° C. The control device preferably continuously or intermittently determines the temperature value of the fuel cell. The first temperature can be determined, for example, by measurement using a temperature sensor and / or by calculation or determination from one or more characteristic curve diagrams of the fuel cell system, the temperature sensor being arranged, for example, at the coolant outlet of the fuel cell stack and configured to measure the temperature of the coolant flowing out through the coolant outlet.
[0019] Now, the control device receives a load request for operating the fuel cell at a second load that is less than the first load. In conventional methods, the control device will reduce the load of the fuel cell to the second load and operate the fuel cell at the second load until a load request for a change is received. However, since the first temperature of the fuel cell is relatively high, the operation of the fuel cell at the second load may lead to an unstable operating state of the fuel cell. An unstable operating state is understood to be a state in which the function of the fuel cell cannot be guaranteed, such as sufficient membrane wetting, sufficient drainage, etc. As a result, the fuel cell may, for example, suffer from accelerated aging or may no longer be able to work as specified. For example, a reasonable second load may be between 40A and 60A. Preferably, the second load is about 50A.
[0020] In order to avoid such an unstable operating state of the fuel cell, the control device reduces the load of the fuel cell to a third load between the first load and the second load. In other words, a load reduction of the fuel cell is carried out in a targeted manner, which is lower than the load reduction achieved by the load request predefined by the load request, for example, by the motor vehicle driver. The third load is preferably selected in such a way that when the fuel cell is operated at the first temperature with the third load, a critical operating state is avoided. For example, the third load can be between 100A and 200A. Preferably, the third load is about 150A.
[0021] By operating the fuel cell at the third load, cooling of the fuel cell is facilitated. According to the invention, it can be provided that the fuel cell is additionally actively cooled, for example by a blower, a cooled coolant, etc. Thus, the fuel cell is cooled to the second temperature by the reduced load. For example, the second temperature can be between 50° C. and 70° C. Preferably, the second temperature is about 60° C.
[0022] When the fuel cell is cooled to the second temperature, the load of the fuel cell is reduced to the second load by the control device. By cooling the fuel cell, a lower second temperature is ensured, so that the fuel cell can be safely operated at the second load.
[0023] The method according to the invention for operating a fuel cell of a fuel cell system for a vehicle has the following advantages over conventional methods: safe operation of the fuel cell is ensured in a simple and cost-effective manner. By delaying the load drop from the first load to the second load via the third load, the fuel cell can be cooled to a temperature at which a load request for operating the fuel cell at the second load can be safely implemented. Thus, sufficient humidity of the membrane and sufficient drainage from the fuel cell are always ensured. In this way, the operating safety of the fuel cell system, for example the fuel cell of the fuel cell system, can be increased and the wear of the fuel cell system, for example the fuel cell of the fuel cell system, can be reduced.
[0024] According to a preferred embodiment of the invention, it can be provided in the method that the fuel cell is operated at a first load and a first temperature in a static operating state or a stable intermittent operating state. With these operating states, sufficient membrane humidity and sufficient drainage from the fuel cell are always ensured. This has the advantage that high operational safety and low wear during operation of the fuel cell are ensured in a simple and cost-effective manner.
[0025] According to the invention, it is preferred to accept such a second load that the fuel cell would be operated in an unstable operating state with the first temperature and this second load. In the case of such a load request for the second load, the advantages of the method according to the invention over the method according to the prior art are particularly prominent. Although according to the prior art, the operation of the fuel cell takes place in an unstable operating state, this (unstable) operating state can be avoided by reducing to the third load only after the second temperature is reached and then to the second load. This has the advantage that a high operating safety and low wear when operating the fuel cell are ensured in a simple and cost-effective manner.
[0026] Further preferably, the targeted reduction of the load is carried out in a stepwise manner, in a progressive stepwise manner or in a stepwise manner or in a stepwise manner. In the context of the present invention, a stepwise reduction in the load is understood as a sudden reduction of the load to a third load in a jump. The progressive reduction of the load to the third load can be carried out, for example, linearly, incrementally and / or decreasingly. A stepwise reduction is understood as a sudden reduction of the load to the third load in multiple stages, in the case of which the load state between the reduction jumps is temporarily kept constant, for example, so that further reduction is performed only after a certain cooling of the fuel cell, so as to avoid unstable operating conditions. A stepwise reduction is understood as a stepwise reduction, in the case of which the load state between the reduction stages is kept constant. Alternatively, the reduction of the load can also be realized as a combination of two or more of these variants. This has the advantage that a load reduction that meets the requirements as much as possible can be performed in a simple and cost-effective manner. This ensures high operational safety and low wear during operation of the fuel cell.
[0027] In a particularly preferred embodiment of the invention, it can be provided in the method that a targeted reduction in the load is carried out in such a way that, during the transition to an unstable operating state, the fuel cell is operated at least temporarily in a stable intermittent operating state. It is preferred here to avoid or only temporarily tolerate the operation of the fuel cell in an unstable operating state. By means of this reduction in load, a stable operation of the fuel cell at a particularly low load is ensured, so that the cooling rate of the fuel cell is particularly high. This has the advantage that, due to the relatively high cooling rate, the reduction to the second load can be carried out particularly quickly in a simple and cost-effective manner.
[0028] Preferably, the fuel cell is operated in a static operating state or in a stable intermittent operating state when the second temperature is reached. In order to have as wide a buffer as possible for unstable operating states, the fuel cell is operated in a static operating state when the second temperature is reached. If the second temperature is also selected to be particularly low, it is possible to operate the fuel cell in a static operating state even after the load has been reduced to the second load. In order to reduce the load to the second load as quickly as possible, the fuel cell is operated in a stable intermittent operating state when the second temperature is reached. This has the advantage that the operating safety of the fuel cell system is increased in a simple and cost-effective manner and / or the time required to carry out the method is shortened.
[0029] According to a preferred embodiment of the present invention, the fuel cell is cooled to such a second temperature that the fuel cell is operated with a second load in a static operating state or a stable intermittent operating state. This has the following advantages: the operating safety of the fuel cell system is increased in a simple and cost-effective manner and / or the time required to perform the method is shortened.
[0030] Particularly preferably, the load difference between the second load and the higher load is used to actively cool the fuel cell, at which the fuel cell is operated during the execution of the method. For this purpose, the fuel cell system preferably has a cooling device or is coupled to a cooling device. The load request to the second load specifies the desired state of the fuel cell to be achieved. Since the fuel cell is operated at a higher load than the second load when the method according to the invention is executed, the fuel cell generates more electrical energy than required. This excess electrical energy should be consumed to avoid overloading the system. Active cooling for cooling the fuel cell is particularly suitable for this, because in this way the cooling rate of the fuel cell can be increased, and thus the time for executing the method can be shortened. This has the advantage that the operational safety and economy of operating the fuel cell are improved in a simple and cost-effective manner.
[0031] According to a second aspect of the present invention, a fuel cell system for a vehicle, in particular for a land vehicle, a water vehicle, an air vehicle, etc. is provided. The fuel cell system has a fuel cell and a control device for controlling the fuel cell. According to the present invention, the control device is configured to perform the method according to the present invention.
[0032] According to the invention, the fuel cell system can have a plurality of fuel cells, which can be controlled individually, in groups or all together by the control device. The fuel cells are preferably assembled into a fuel cell stack. Preferably, the fuel cells are arranged in a cell housing of the fuel cell system. The control device is preferably arranged in a separate control housing.
[0033] In the fuel cell system according to the invention, all the advantages described for the method for operating a fuel cell of a fuel cell system according to the first aspect of the invention are obtained. Accordingly, the fuel cell system according to the invention has the advantage over conventional fuel cell systems that safe operation of the fuel cell is ensured in a simple and cost-effective manner. By delaying the load reduction from the first load to the second load via a third load, the fuel cell can be cooled to a temperature at which a load request for operating the fuel cell at the second load can be safely implemented. Therefore, sufficient humidity of the membrane and sufficient drainage from the fuel cell can always be ensured. In this way, the operating safety of the fuel cell system, such as the fuel cell of the fuel cell system, can be improved, and the wear of the fuel cell system, such as the fuel cell of the fuel cell system, can be reduced.
[0034] According to the invention, it is preferred that the fuel cell system has a temperature sensor for determining the temperature of the fuel cell. The temperature sensor is preferably arranged on the fuel cell or in a coolant channel, which is configured for the flow of a cooling fluid heated by the fuel cell. Preferably, the temperature sensor contacts the fuel cell, for example a wall, a frame, etc. of the fuel cell. Alternatively or additionally, the coolant temperature at the outlet of the fuel cell stack can also be determined, which is very close to the operating temperature of the fuel cell. The operating temperature of the fuel cell can be reliably determined by the temperature sensor and thus does not need to be calculated in a laborious manner. This has the advantage that the operating safety of the fuel cell system is improved in a simple and cost-effective manner. BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Below, a method for operating a fuel cell of a fuel cell system for a vehicle and a fuel cell system for a vehicle according to the present invention are explained in more detail with reference to the accompanying drawings. The accompanying drawings schematically show:
[0036] FIG. 1 shows a graph of operating characteristics of a fuel cell when operating a fuel cell according to the prior art;
[0037] Figure 2 A graph showing an operating characteristic curve of a fuel cell when operating a fuel cell according to a preferred embodiment of the present invention;
[0038] Figure 3 A cross-sectional view showing a preferred embodiment of a fuel cell system according to the present invention; and
[0039] Figure 4 A flow chart showing a preferred embodiment of the method according to the invention is shown.
[0040] Elements with the same function and mode of action are shown in Figures 1 to Figure 4The same reference numerals are used throughout. DETAILED DESCRIPTION
[0041] FIG. 1 shows an operating characteristic curve diagram of a fuel cell 1 according to the prior art when the fuel cell 1 is in operation (see Figure 3 ). The operating characteristic curve diagram has three operating regions, namely a first operating region I for a static operating state SB, a second operating region II for a stable intermittent operating state SIB, and a third operating region III for an unstable operating state IB, wherein the third operating region III should be avoided during operation of the fuel cell 1.
[0042] In the first operating state Z1' of the fuel cell 1, the fuel cell 1 operates at a first load L1 of about 480A and has a first temperature T1' of about 87°C. Therefore, the first operating state Z1' is a static operating state SB. Due to the reduced load request made with the second load L2', the load of the fuel cell 1 is reduced to the second load L2', so that the fuel cell 1 has a second operating state Z2'. In the second operating state Z2' of the fuel cell 1, the fuel cell 1 operates at a second load L2 of about 50A and still has a first temperature T1' of about 87°C. As a result, the operating point of the fuel cell 1 is shifted to the third operating region III, which is not conducive to the operation of the fuel cell.
[0043] Figure 2 The operating characteristic curve diagram of the fuel cell 1 when the fuel cell 1 according to a preferred embodiment of the present invention is operated is shown. In the first operating state Z1 of the fuel cell 1, the fuel cell 1 operates with a first load L1 of about 480A and has a first temperature T1' of about 87°C. Therefore, the first operating state Z1' is a static operating state SB and corresponds to the first operating state Z1' in Figure 1. Due to the reduced load request with the second load L2, the load of the fuel cell 1 is reduced to a third load L3 of about 140A, so that the fuel cell 1 has a second operating state Z2 arranged in the second operating region II, so that the fuel cell 1 operates in a stable intermittent operating state SIB at the boundary to the third operating region III. By maintaining the third load L3, the temperature of the fuel cell 1 is reduced to a third temperature T3 of about 77°C. The third operating state Z3 is achieved here, which is also in the second operating region II and has a greater distance from the third operating region III.
[0044] Starting from the third operating state Z3, the load is reduced from the third load L3 to the fourth load L4 of about 85A. Here, the fourth operating state Z4 of the fuel cell 1 is realized, which is arranged in the second operating region II, so that the fuel cell 1 is operated again in the stable intermittent operating state SIB at the boundary to the third operating region III. By maintaining the fourth load L4, the temperature of the fuel cell 1 drops to the second temperature T2 of about 60°C. Here, the fifth operating state Z5 is realized, which is arranged in the first operating region I, so that the fuel cell 1 is operated again in a static operating state at the boundary to the second operating region II.
[0045] Starting from the fifth operating state Z5, the load is further reduced from the fourth load L4 to the second load L2 according to the reduced load request. The sixth operating state Z6 of the fuel cell 1 is achieved, wherein the fuel cell 1 is operated at the second temperature T2 at about 50A in the stable intermittent operating state SIB.
[0046] exist Figure 3 In the figure, a preferred embodiment of a fuel cell system 2 according to the present invention is schematically depicted in a cross-sectional view. The fuel cell system 2 has a plurality of fuel cells 1 (cells), which are combined into a fuel cell stack (stack) and arranged in a battery housing 5. Temperature sensors 4 are arranged on each of these fuel cells 1. Alternatively, a temperature sensor 4 can be arranged for detecting the coolant temperature at the coolant outlet of the stack. In addition, the fuel cell system 2 for controlling the fuel cell 1 has a control device 3 arranged outside the battery housing 5.
[0047] Figure 4 A preferred embodiment of the method according to the invention is schematically shown in a flow chart. In a first method step 100, the fuel cell system 1 is operated by the control device 3 at a first load L1 at a first temperature T1 in a static operating state SB. The fuel cell 1 thus has a first operating state Z1. In a second method step 200, the control device 3 receives a reduced load request for operating the fuel cell 1 at a second load L2 that is less than the first load L1.
[0048] In a third method step 300, the load of the fuel cell 1 is reduced in a targeted manner from the first load L1 to the third load L3 by the control device 3, wherein the third load L3 is greater than the second load L2. The temperature of the fuel cell 1 initially corresponds substantially to the first temperature T1, so that the fuel cell 1 has a second operating state Z2 and is operated, for example, in a stable intermittent operating state SIB.
[0049] The fourth method step 400 is triggered by reducing the load of the fuel cell 1, wherein the fuel cell 1 cools down to a second temperature T2, at which the fuel cell 1 is operated, for example, in a static operating state SB. When the fuel cell 1 reaches the second temperature T2, in a fifth method step 500, the load is reduced from the third load L3 to the second load L2 by the control device 3. For example, the fuel cell 1 is then operated again in a stable intermittent operating state SIB.
Claims
1. A method for operating a fuel cell (1) of a fuel cell system (2) for a vehicle, the method comprising: - operating the fuel cell (1) at a first load (L1) and a first temperature (T1) by means of a control device (3) of the fuel cell system (2), - receiving a load request for operating the fuel cell (1) at a second load (L2) by the control device (3), wherein: The second load (L2) is smaller than the first load (L1), - reducing the load of the fuel cell (1) to a third load (L3) in a targeted manner by means of the control device (3), wherein the third load (L3) is smaller than the first load (L1) and larger than the second load (L2), - cooling the fuel cell (1) to a second temperature (T2), and - Reducing the load of the fuel cell (1) to the second load (L2) by means of the control device (3).
2. The method according to claim 1, characterized in that: The fuel cell (1) is operated at the first load (L1) and the first temperature (T1) in a static operating state (SB) or a stable intermittent operating state (SIB).
3. The method according to claim 1 or 2, characterized in that: A second load (L2) is received such that the fuel cell (1) operates in an unstable operating state (IB) at the first temperature (T1) and the second load (L2).
4. The method according to any one of the preceding claims, characterized in that The targeted reduction of the load takes place in a stepped, progressive or step-by-step manner or in a step-by-step manner.
5. The method according to any one of the preceding claims, characterized in that A targeted reduction in load is carried out so that during a transition to an unstable operating state (IB), the fuel cell (1) is at least temporarily operated in a stable intermittent operating state (SIB).
6. The method according to any one of the preceding claims, characterized in that When the second temperature (T2) is reached, the fuel cell (1) is operated in a static operating state (SB) or a stable intermittent operating state (SIB).
7. The method according to any one of the preceding claims, characterized in that The fuel cell (1) is cooled to a second temperature (T2) so that the fuel cell (1) is operated at the second load (L2) in a static operating state (SB) or a stable intermittent operating state (SIB).
8. The method according to any one of the preceding claims, characterized in that The load difference between the second load (L2) and a higher load at which the fuel cell (1) is operated during the execution of the method is used for active cooling of the fuel cell (1).
9. A fuel cell system (2) for a vehicle, the fuel cell system comprising a fuel cell (1) and a control device (3) for controlling the fuel cell (1), characterized in that: The control device (3) is designed to carry out a method according to one of the preceding claims.
10. The fuel cell system (2) according to claim 9, characterized in that: The fuel cell system (2) has a temperature sensor (4) for determining the temperature of the fuel cell (1).