Fuel cell system and shutdown control method thereof

Abstract

The present invention relates to a fuel cell shutdown control method, comprising: before the fuel cell is shut down, the anode and cathode of the fuel cell are purged; after the purging is completed, the current cathode pressure is adjusted to be equal to the target cathode pressure, and the cathode is closed; current is applied to the stack for fuel replenishment, and after completion, the anode is closed, and the discharge resistor is discharged to complete the shutdown of the fuel cell. The present invention can effectively prevent the hydrogen-air (hydrogen-oxygen) interface from appearing during startup, avoiding problems such as battery startup failure; at the same time, the present invention can balance the hydrogen content and pressure of the anode and cathode, minimize the generation of the hydrogen-oxygen interface, and ensure that the stack performance remains unchanged when the stack is started again.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a fuel cell system and a shutdown control method thereof. Background Art

[0002] Fuel cell vehicles are one of the important technical routes for new energy vehicles. The basic principle is that hydrogen and oxygen undergo an electrochemical reaction under the action of a proton exchange membrane or related catalysts, and the reaction process generates electrical energy and heat energy. The generated electrical energy can be used for battery storage or directly used as a driving force for the vehicle, and the generated heat energy can be used for waste heat utilization or directly discharged into the atmosphere. Since hydrogen fuel cells do not produce harmful substances during the electrochemical reaction of hydrogen and oxygen, they are recognized as one of the most promising clean power sources in the field of new energy vehicles.

[0003] Under cold conditions, if the water stored inside the fuel cell is not effectively discharged, the water content is too high, and ice formation at low temperatures will affect the reaction area on the electrode surface, which will be hindered by the freezing of residual water and generated water. Ice will fill the pores of the catalyst layer or diffusion layer, reducing or even stopping the electrochemical reaction, which can easily lead to cold start failure and affect the low-temperature start performance of the stack. In automotive applications, there are a large number of start and stop cycles during the service life of the fuel cell system, and after multiple starts and stops, the battery stack and membrane electrode will be permanently damaged. The hydrogen fuel cell engine will be purged after shutdown to blow out the residual water inside, and the reaction gas can reach the catalyst layer for reaction at the next cold start. During the startup process, part of the generated water is carried away by the airflow, and part condenses into ice and remains in the gas diffusion layer. When the condensed water does not completely block the gas diffusion layer, the temperature of the stack has risen above zero and it will no longer condense, and the condensed water will gradually melt.

[0004] In traditional technology, when the fuel cell is shut down, the cathode inlet and outlet shut-off valves are always open, and the cathode is purged in a manner that the purge pressure is the same as the atmospheric pressure. The anode purge pressure is greater than the cathode purge pressure, and the drain valve is purged at a certain switching frequency. This will cause the following problems: 1) Cathode normal pressure purge will cause negative pressure to form inside the cathode cavity of the stack after the system is shut down and the oxygen is consumed; 2) After the system is shut down, only the anode cavity of the stack is filled with hydrogen, and the cathode of the stack is not filled with hydrogen; 3) When the system is parked for a long time, oxygen will gradually accumulate inside the stack, and after being exposed to high potential, it will cause oxidation of the stack catalyst. It will take a long time for the stack to activate the next time it is turned on before the stack performance can be restored. Summary of the invention

[0005] Based on this, it is necessary to provide a shutdown control method and a fuel cell system to extend the service life of the fuel cell and ensure normal start and stop of the fuel cell in order to address the above problems.

[0006] In a first aspect, the present invention provides a fuel cell shutdown control method, comprising:

[0007] Before shutting down the fuel cell, purging the anode and cathode of the fuel cell;

[0008] Adjust so that the current cathode pressure is equal to the target cathode pressure;

[0009] closing the cathode;

[0010] Applying current to the battery stack to refuel;

[0011] sealing the anode;

[0012] The discharge resistor discharges; and

[0013] Complete shutdown of the fuel cell.

[0014] In one embodiment, before shutting down the fuel cell, the process further comprises:

[0015] de-loading the fuel cell from operating power to idle power;

[0016] The target purge temperature is calculated according to the environmental parameters, and the current purge temperature is adjusted to the target purge temperature.

[0017] In one embodiment, the method for determining whether the purge is completed includes:

[0018] Calculate the normal purge time according to the environmental parameters, the stack temperature parameters and the target purge temperature calculated according to the environmental parameters;

[0019] When the actual purge time exceeds the normal purge time, the purge is completed.

[0020] In one embodiment, the method for determining whether the purge is completed further includes:

[0021] Calculating the minimum EIS real impedance of the purge according to the target purge temperature;

[0022] Calculating a minimum purge time and a maximum purge time according to the environmental parameters, the stack temperature parameters and the target purge temperature;

[0023] When the actual impedance is greater than the minimum EIS real impedance, and the actual purge time is greater than the minimum purge time and less than the maximum purge time, the purge is completed;

[0024] When the actual impedance is less than or equal to the minimum EIS real impedance and the actual purge time is greater than or equal to the maximum purge time, the purge is completed;

[0025] When the fuel cell has no EIS, the actual purge time is greater than the normal purge time, and the purge is completed.

[0026] In one embodiment, the target cathode pressure is the ratio of the actual ambient pressure to the difference between 1 and the actual oxygen content in air.

[0027] In one embodiment, the fuel cell includes an outlet stop valve provided on the cathode side, an inlet stop valve, an air compressor provided upstream of the inlet stop valve, and a stack bypass valve provided in a bypass; the adjustment so that the current cathode pressure is equal to the target cathode pressure includes:

[0028] Slowly close the cathode outlet stop valve and the stack entry stop valve, and at the same time adjust the air compressor speed and the stack bypass valve so that when the outlet stop valve and the stack entry stop valve are fully closed, the current cathode pressure is equal to the target cathode pressure.

[0029] In one embodiment, the fuel cell includes a converter, an air compressor arranged on the cathode side, and a tail exhaust valve and a hydrogen shut-off valve arranged on the anode side; the fuel replenishment is hydrogen replenishment, and the hydrogen replenishment process includes oxygen consumption hydrogen replenishment and migration hydrogen replenishment.

[0030] In one embodiment, the oxygen consumption hydrogen replenishment comprises:

[0031] The converter applies a load current to the fuel cell stack, and when the average single-chip voltage is less than a preset value, the current application is stopped, and the air compressor and the tail exhaust valve are closed.

[0032] In one embodiment, the migration hydrogen replenishment includes:

[0033] Determine whether migration hydrogen replenishment is needed based on environmental parameters, downtime and catalyst degradation. If the conditions for migration hydrogen replenishment are met, migration hydrogen replenishment is performed.

[0034] The converter inputs a reverse load current;

[0035] When the current cathode pressure is greater than the target cathode pressure, or the current integral is greater than the current target integral, migration hydrogen replenishment is terminated.

[0036] In one embodiment, the fuel cell includes a converter, and the discharge resistor discharges until the converter voltage is less than a preset value, disconnecting the converter from the fuel cell to complete the shutdown of the fuel cell.

[0037] In a second aspect, the present invention proposes a fuel cell system, comprising: a fuel cell; and a processor for executing the above-mentioned fuel cell shutdown control method.

[0038] The above fuel cell shutdown control method avoids negative pressure at the cathode after the fuel cell is shut down by setting the target pressure of the cathode shutdown, so that after the oxygen consumption and hydrogen replenishment are completed, the oxygen inside the cathode is consumed, and the pressure inside the cathode cavity is just the atmospheric pressure, thereby preventing the hydrogen-air (hydrogen-oxygen) interface from appearing when the power is turned on again, and avoiding problems such as high potential, carbon corrosion, catalyst oxidation, and battery startup failure. The above fuel cell shutdown control method realizes the migration hydrogen replenishment process inside the fuel cell by using a bidirectional DC DCDC converter to load the fuel cell with current, and combines the external hydrogen replenishment and oxygen consumption process to balance the hydrogen content and pressure of the anode and cathode, and minimize the generation of the hydrogen-oxygen interface, so that the performance of the stack remains unchanged when the stack is started again. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the fuel cell shutdown process;

[0040] Figure 2 The structure diagram of the fuel cell system;

[0041] Figure 3 It is a schematic diagram of the overall shutdown control process of the fuel cell of the present invention;

[0042] Figure 4 Schematic diagram of the migration process of hydrogen from the anode to the cathode in a fuel cell;

[0043] Figure 5 It is a schematic diagram of the shutdown control flow of the fuel cell of the present invention. DETAILED DESCRIPTION

[0044] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0045] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0046] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0047] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0049] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0050] During the shutdown purge process of the conventional technology, the cathode inlet and outlet valves are always open, and the purge control method according to the atmospheric pressure is simple. However, after the inlet and outlet valves are closed, since the air contains a certain component of oxygen, the exhaustion of the cathode oxygen will cause a negative pressure to form inside the cathode cavity. This negative pressure will cause the pressure on both sides of the inlet and outlet valves to be unbalanced, reduce the valve sealing performance, and make it easier for external oxygen to enter the stack, thereby consuming the anode hydrogen through diffusion. Specifically, when the fuel cell system is shut down, there may be excess hydrogen or oxygen left in the fuel cell stack, or the system may try to consume both reactants at the same time. In the first case, the unreacted hydrogen stays on the anode side of the fuel cell stack. The hydrogen can diffuse through or pass through the membrane or catalyst to react with the oxygen on the cathode side of the fuel cell stack. When the hydrogen diffuses to the cathode side, the total pressure on the anode side of the fuel cell stack drops. A portion of the oxygen will remain in the cathode pipeline and will slowly re-enter the cathode flow field by convection or diffusion. Most of the oxygen will react with the hydrogen locally present in the battery. Eventually, the local hydrogen in the battery will be consumed, and the oxygen will begin to concentrate. Eventually, oxygen will locally permeate the membrane or catalyst and reach the anode. When the fuel cell is turned on again, air enters the anode side of the fuel cell stack, creating a hydrogen-air interface that causes a short circuit on the anode side, resulting in a lateral flow of hydrogen ions from the hydrogen-filled portion of the anode side to the air-filled portion of the anode side. This lateral current is combined with the high lateral ionic resistance of the membrane to produce a significant lateral potential difference across the membrane. A local high potential is generated between the air-filled portion on the cathode side and the opposite anode side, such as Figure 1 As shown in Figure 2, the high potential adjacent to the electrolyte membrane promotes rapid carbon corrosion and causes the electrode carbon layer to thin. This weakens the support for the catalyst particles, thereby reducing the performance of the fuel cell.

[0051] In this embodiment, the shutdown control process is described by taking a proton exchange membrane fuel cell (PEMFC) as an example. PEMFC is composed of a membrane electrode assembly (MEA), which includes a bipolar plate, a proton exchange membrane, i.e., an electrolyte, a catalyst, and a gas diffusion layer, etc. The gas diffusion layer, the catalyst layer, and the polymer electrolyte membrane are prepared by a hot pressing process to obtain the MEA. The proton exchange membrane in the middle plays multiple roles in conducting protons (H+), preventing electron transfer, and isolating cathode and anode reactions. The catalyst layers on both sides are the places where the fuel and the oxidant undergo electrochemical reactions; the main functions of the gas diffusion layer are to support the catalyst layer, stabilize the electrode structure, provide a gas transmission channel, and improve water management; the main functions of the bipolar plate are to separate the reaction gas, and to introduce the reaction gas into the fuel cell through the flow field, collect and conduct current, support the membrane electrode, and undertake the heat dissipation and drainage functions of the entire fuel cell. In PEMFC, the precious metal Pt or its alloy is generally used as a catalyst, and carbon is used as a carrier. Hydrogen fuel cells usually use organic fuels to reform hydrogen, so the hydrogen produced contains a small amount or trace amount of CO. CO has a strong adsorption capacity on Pt. After CO is adsorbed on the Pt surface, it will reduce the adsorption of H on platinum, thereby affecting the electrochemical reaction of H2. Only when the anode potential rises to ~0.6V (relative to the standard hydrogen electrode) will CO be oxidized to CO2, which will cause battery voltage loss and greatly reduce battery efficiency.

[0052] In this embodiment, see Figure 2 , Figure 2 The schematic diagram of the structure of the fuel cell system in one embodiment of the present invention is shown. The fuel cell system 1 includes a fuel cell stack 10, an anode side component 30, a cathode side component 20, a heat dissipation circuit 40 and a converter 50. The fuel cell stack 10 has an anode and a cathode, the cathode of the fuel cell stack 10 is externally connected to the cathode side component 20, and the anode of the fuel cell stack 10 is externally connected to the anode side component 30.

[0053] The cathode side assembly 20 includes a stack entry shutoff valve 21 and a stack entry pipeline, which is used to provide the fuel cell system 1 with oxygen / air required for the internal chemical reaction. A filter 24, an air compressor 25 and an intercooler 26 are provided upstream of the stack entry shutoff valve 21. In this embodiment, the upstream refers to the inlet direction of a certain component, that is, a pipeline is provided between the inlet of the component on the same pipeline or a connected pipeline and the outlet of another component, which is called the upstream of the other component. The cathode side assembly 20 also includes an outlet shutoff valve 23 and an outlet pipeline, which are used to discharge the gas on the cathode side. A bypass pipeline is also provided between the inlet of the stack entry shutoff valve 21 and the outlet of the outlet shutoff valve 23, and a stack bypass valve 22 is provided on the bypass pipeline.

[0054] The anode side assembly 30 includes a hydrogen shut-off valve 32 and an inlet pipeline. The hydrogen shut-off valve 32 may also be a hydrogen proportional valve or a hydrogen injector, etc., for adjusting the amount of hydrogen entering the anode of the fuel cell stack 10. At the outlet of the hydrogen shut-off valve 32, also on the inlet pipeline, a first pressure relief valve 33 is provided, and the outlet of the first pressure relief valve 33 is connected to the fuel cell stack 10 through the inlet pipeline. The outlet of the first pressure relief valve 33 is connected to a bypass, and a hydrogen circulation pump 34 is provided on the bypass. The first pressure relief valve 33 also has another outlet, which is connected to the outlet of the hydrogen circulation pump 34 through a pipeline. The outlet of the hydrogen circulation pump 34 and the above-mentioned pipeline merge into one pipeline and are connected to the inlet of the water vapor separator 35. The first outlet of the water vapor separator 35 is connected to the fuel cell stack 10 through a pipeline, and the second outlet of the water vapor separator 35 is connected to the tail valve 36. The water vapor separator 35 is used to separate the water vapor from the mixed gas and discharge the liquid water to prevent the liquid water from entering the fuel cell stack, causing the anode to be flooded, and increasing the workload of the hydrogen circulation pump 34 or the hydrogen shut-off valve 32. The outlet of the tail valve 36 is connected to the inlet of the hydrogen circulation pump 34 and the outlet of the first pressure relief valve 33 on the inlet pipeline through a pipeline, that is, the outlet of the tail valve 36 is connected to the inlet pipeline and the bypass connection near the anode through a pipeline, and the connection is provided with a second pressure relief valve 31.

[0055] The heat dissipation circuit 40 includes a pump 43, a thermostat 41 and a radiator 42. The thermostat 41 can be a three-way valve, the inlet of the thermostat 41 is connected to the stack 10 through a pipeline, the first outlet of the thermostat 41 is connected to the inlet of the pump 43 through a pipeline, and the second outlet of the thermostat 41 is connected to the radiator 42 through a pipeline and then connected to the inlet of the pump 43, so that the two pipelines are connected in parallel, that is, a small circulation pipeline and a large circulation pipeline. The large circulation passes through the radiator, and the higher heat is taken away by the radiator. The coolant with a lower temperature enters the stack from the radiator outlet, and returns to the cooling water pump inlet after the internal reaction heat of the stack is discharged; the small circulation does not pass through the radiator, and the coolant enters the stack directly from the thermostat outlet, discharges the reaction waste heat in the stack, and returns to the cooling water pump inlet again. The outlet of the pump 43 is connected to the stack 10 through a pipeline. The heat dissipation circuit 40 can also include a deionizer and a PTC heater, which are not shown in the figure.

[0056] In this embodiment, the converter 50 is a bidirectional DC / DC voltage converter, which is arranged between the fuel cell system 1 and the power device of the vehicle. The converter 50 converts the DC power output by the fuel cell stack into an adjustable DC power supply.

[0057] The above structure is only one of the structures of the fuel cell system used in the control method of the present invention. It should be known that the control method in the embodiment of the present invention is not limited to the structure of the above fuel cell system.

[0058] In traditional technology, the cathode inlet and outlet valve is always open, and the cathode is purged in the same way as the atmospheric pressure. The anode purge pressure is 20-30 kPa greater than the cathode purge pressure, and the drain valve is purged at a certain switching frequency. Cathode atmospheric pressure purge will cause negative pressure to form inside the cathode cavity of the stack after the system is shut down and the oxygen is consumed. This negative pressure will cause the pressure on both sides of the inlet and outlet valve to be unbalanced, reduce the sealing performance of the valve, and make it easier for external oxygen to enter the stack, and then consume the anode hydrogen through diffusion. After the hydrogen is exhausted, the next startup will cause the aforementioned hydrogen-oxygen interface to form. The amount of hydrogen in the anode is limited by the pressure difference that the MEA membrane can withstand, and the maximum amount of anode gas is about 20-30 kPa of cathode pressure difference. When the anode hydrogen is exhausted after a long shutdown, oxygen will slowly accumulate in the anode, resulting in the next hydrogen-oxygen interface. Under the action of high potential, the stack catalyst will be oxidized, and it will take a long time for the stack to activate the next startup to restore the performance of the stack. At the same time, when the system is running for a long time, a small amount of pollutants such as carbon monoxide and sulfur dioxide in the air are adsorbed on the surface of platinum, which can also lead to the poisoning of the aforementioned catalyst.

[0059] Based on this, combined Figure 3 , 4 As shown, Figure 3 A schematic diagram of the overall shutdown control process of a fuel cell in an embodiment of the present invention is shown. Figure 4 The shutdown control process of a fuel cell in one embodiment of the present invention is shown in FIG. The shutdown control method of the fuel cell in this embodiment includes the following steps:

[0060] S100. Before shutting down the fuel cell, purge the anode and cathode of the fuel cell.

[0061] S200. After the purging is completed, the current cathode pressure is adjusted to be equal to the target cathode pressure, and the cathode is closed.

[0062] S300. Apply current to the fuel cell stack to replenish hydrogen. After the hydrogen replenishment process is completed, close the anode, discharge the discharge resistor, and complete the shutdown of the fuel cell.

[0063] Furthermore, in step S100, the following steps are also included:

[0064] S101. Before executing the fuel cell shutdown, the fuel cell is derated from the operating power to the idle power. Specifically, the fuel cell system 1 includes a processor, and when the processor receives an input shutdown signal, the processor controls the fuel cell to derate from the operating power to the idle power.

[0065] S102. Calculate the target purge temperature based on the environmental parameters and adjust the current purge temperature to the target purge temperature T prg In this step, the environmental parameters include weather parameters, ambient temperature, etc.

[0066] S103. After a certain period of purging, determine whether the purging is completed. If it is completed, execute step S200. Specifically, the cathode is purged by compressed air delivered by the air compressor 25, and the cathode and anode are purged at the same time. The anode is purged by extending the opening time of the tail valve 36 so that the air passes through the proton membrane. The judgment step of the completion of purging includes: according to the environmental parameters, the temperature parameters of the stack and the target purging temperature T prg , calculate the normal purge time; when the actual purge time exceeds the normal purge time, the purge is completed. In this step, the environmental parameters include the humidity of the environment, and the stack temperature parameters include the stack air inlet temperature T cath Furthermore, the method for determining whether the purge is complete also includes:

[0067] S103a. According to the target purge temperature T prg , calculate the real impedance R of the minimum electrochemical impedance spectroscopy (EIS) under purge EIS The calculation method is: R EIS =f(T prg ), f is a table lookup function obtained by calibration of test data. According to the environmental parameters, stack temperature parameters and target purge temperature, the minimum purge time t min , Normal purge time t normal and maximum purge time t max , calculated as [t max ,t normal ,t min ]=f(RH,T cath ,T prg ), where f is a table lookup function obtained through calibration of test data. Furthermore, when there is no humidity sensor to obtain the ambient humidity, a value with a higher probability, such as 50%, can be given. Furthermore, when performing an EIS test, an excitation current input is required. When the excitation frequency is greater than 1KHz, the real impedance measured can represent the internal resistance of the MEA membrane. At the same time, in order to ensure the signal-to-noise ratio and the accuracy of the measurement, the excitation current needs to be greater than a certain value. Therefore, in this embodiment, it can be required that the excitation frequency be set greater than 1KHz, the excitation current be >3% and >10A, etc.

[0068] S103b. Obtain or calculate the actual impedance and actual purge time, and judge and compare the actual value with the calculated value of step S103a. When the actual impedance is greater than the minimum EIS real impedance, and the actual purge time is greater than the minimum purge time and less than the maximum purge time, the purge is completed; when the actual impedance is less than or equal to the minimum EIS real impedance, and the actual purge time is greater than or equal to the maximum purge time, the purge is completed; when the fuel cell has no EIS, the actual purge time is greater than the normal purge time, and the purge is completed.

[0069] In order to reduce the penetration of oxygen into the stack, increase the gas tightness of the stack, and avoid the hydrogen-air interface and catalyst poisoning mentioned above, it is necessary to balance the pressure inside and outside the stack as much as possible. Further, step S200 specifically includes the following steps:

[0070] S201. Calculate the target cathode pressure. The target cathode pressure P g It is the ratio of the difference between the actual ambient pressure P0 and 1 and the actual air oxygen content N, that is, P g =P0 / (1-N), for example, when the ambient pressure (atmospheric pressure) is 101 kPa, the cathode shutdown target pressure = 101 / 0.79 = 126.6 kPa.

[0071] S202. Adjust so that the current cathode pressure is equal to the target cathode pressure. Specifically, slowly close the cathode outlet stop valve 23 and the stack entry stop valve 21, and adjust the speed of the air compressor 25 and the stack bypass valve 22 at the same time, so that when the outlet stop valve 23 and the stack entry stop valve 21 are completely closed, the current cathode pressure is equal to the target cathode pressure P g It should be known that the goal of this step in controlling the shutdown of the fuel cell system 1 is to make the current cathode pressure equal to the target cathode pressure, but in the actual process, there are often certain differences. Therefore, the current cathode pressure equal to the target cathode pressure here also includes the situation where the current cathode pressure is close to the target cathode pressure, that is, in the actual control process, the current cathode pressure can be the target cathode pressure ±10kPa.

[0072] Oxygen that penetrates into the fuel cell stack due to the negative pressure at the cathode will react with hydrogen, slowly consuming hydrogen, causing the anode pressure of the fuel cell stack to slowly drop. In order to extend the storage time and service life of the fuel cell stack, in addition to ensuring the pressure at the cathode, it is also necessary to replenish more hydrogen inside the fuel cell stack. In this embodiment, the fuel cell system 1 uses a DC / DC as an exchanger, specifically a DC / DC with a bidirectional direct current function. After the fuel cell completes the oxygen consumption and hydrogen replenishment stage, the DC changes from a load to a voltage source, applying a portion of the voltage to the fuel cell stack. Under the action of the voltage, the hydrogen at the anode loses electrons and becomes hydrogen ions. The hydrogen ions pass through the proton exchange membrane, receive electrons at the cathode and become hydrogen again, thereby causing the hydrogen to migrate from the anode to the cathode, allowing more hydrogen to be filled into the fuel cell stack, such as Figure 4(A) Process. Since the hydrogen concentration at the anode is high and the hydrogen concentration at the cathode is low, hydrogen will also diffuse through the proton exchange membrane to the cathode, such as Figure 4 (B) process, but the transmission rate of process B is slow and it takes a long time to normalize the concentrations of the positive and negative electrodes.

[0073] Furthermore, in step S300, the following steps are also included:

[0074] S301. Determine the anode target pressure P according to the actual cathode pressure and shutdown time anod And the amount of hydrogen replenishment. Specifically, P anod =f(P cath, t stop ), f is a table lookup function.

[0075] S302. Perform a hydrogen replenishment process, which includes an oxygen consumption hydrogen replenishment process and a migration hydrogen replenishment process.

[0076] Specifically, S302a. The oxygen-consuming hydrogen replenishment process includes: the bidirectional direct current DC / DC converter applies a load current to the fuel cell stack, starts the hydrogen circulation pump 34, and consumes the oxygen in the pipeline. When the average single-chip voltage of the fuel cell is less than 50mv, stop applying the load current, and turn off the air compressor 25 and the tail exhaust valve 36. Specifically, applying the load current includes controlling the bidirectional direct current DC / DC to the operating mode, setting the bidirectional direct current DC / DC target input current of 5 to 10A, and the value of the current is adjusted according to the system power size and MEA membrane parameters.

[0077] S302b. The migration hydrogen replenishment process comprises the following steps:

[0078] S302b.1 According to environmental parameters, downtime t stop The environmental parameter is the ambient temperature T env . Determine whether to migrate and replenish hydrogen based on the ambient temperature and the expected downtime, M1=f(T env ,t stop ), M1 function returns the judgment value, if it is true, it is determined that hydrogen needs to be replenished, otherwise it does not need to be replenished, f is a table lookup function. According to the catalyst degradation situation, whether to perform migration and hydrogen replenishment for activation, M2 = f(α run ,t run ), f is the lookup function, where α run is the decay percentage of the polarization curve, t run is the fuel cell operating time. For example, run By scanning different operating times, the catalyst degradation can be detected and a standard can be established. When the degradation reaches a certain level, migration and hydrogen replenishment are performed.run , by scanning different α run , the catalyst degradation can be detected and the target value can be set. When the degradation reaches a certain level, migration and hydrogen replenishment will be carried out.

[0079] S302b.2 If the conditions for migration hydrogen replenishment are met, migration hydrogen replenishment is performed, and the converter inputs a reverse specific load current. If the conditions for migration hydrogen replenishment are not met, the process proceeds to step S304. The specific judgment method is as follows: When the current cathode pressure is greater than the target cathode pressure, the migration hydrogen replenishment process ends. The target cathode pressure P cath_migr =f(T env ,t stop ), f is a table lookup function. Alternatively, when the current integral is greater than the current target integral, the migration hydrogen replenishment is terminated, and the current target integral Q elec_migr =f(T env ,t stop ), f is a table lookup function.

[0080] S303. After the hydrogen replenishment is completed, determine whether the anode pressure reaches the target set pressure. If it does not reach the target set pressure, continue to replenish hydrogen. If it reaches the target set pressure, close the hydrogen stop valve 32, seal the anode, and turn off the converter 50.

[0081] S304. Perform discharge resistance discharge to determine whether the output voltage of the converter 50 is less than 48 V. If it is less than 48 V, disconnect the contactor to complete the shutdown process of the fuel cell system 1. If the output voltage of the converter 50 is not less than 48 V, continue to discharge.

[0082] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A fuel cell shutdown control method, characterized in that: include: Before shutting down the fuel cell, purging the anode and cathode of the fuel cell; Adjust so that the current cathode pressure is equal to the target cathode pressure; closing the cathode; Applying current to the stack to refuel; sealing the anode; Discharging through the discharge resistor; as well as Complete shutdown of the fuel cell.

2. The fuel cell shutdown control method according to claim 1, characterized in that: The fuel cell also includes before shutting down: de-loading the fuel cell from operating power to idle power; Calculate target purge temperature based on environmental parameters; Adjust the current purge temperature to the target purge temperature.

3. The fuel cell shutdown control method according to claim 1, characterized in that: The method for determining whether the purge is completed includes: Calculate the normal purge time according to the environmental parameters, the stack temperature parameters and the target purge temperature calculated according to the environmental parameters; When the actual purge time exceeds the normal purge time, the purge is completed.

4. The fuel cell shutdown control method according to claim 3, characterized in that: The method for determining whether the purge is completed further includes: Calculating the minimum EIS real impedance of the purge according to the target purge temperature; Calculating a minimum purge time and a maximum purge time according to the environmental parameters, the stack temperature parameters and the target purge temperature; When the actual impedance is greater than the minimum EIS real impedance, and the actual purge time is greater than the minimum purge time and less than the maximum purge time, the purge is completed; When the actual impedance is less than or equal to the minimum EIS real impedance and the actual purge time is greater than or equal to the maximum purge time, the purge is completed; When the fuel cell has no EIS, the actual purge time is greater than the normal purge time, and the purge is completed.

5. The fuel cell shutdown control method according to claim 1, characterized in that: The target cathode pressure is the ratio of the actual ambient pressure to the difference between 1 and the actual air oxygen content.

6. The fuel cell shutdown control method according to claim 1, characterized in that: The fuel cell comprises an outlet stop valve arranged on the cathode side, a stack stop valve, an air compressor arranged upstream of the stack stop valve, and a stack bypass valve arranged in a bypass; the adjustment so that the current cathode pressure is equal to the target cathode pressure comprises: Slowly close the cathode outlet stop valve and the stack entry stop valve, and at the same time adjust the air compressor speed and the stack bypass valve so that when the outlet stop valve and the stack entry stop valve are fully closed, the current cathode pressure is equal to the target cathode pressure.

7. The fuel cell shutdown control method according to claim 1, characterized in that: The fuel cell comprises a converter, an air compressor arranged on the cathode side, and a tail exhaust valve and a hydrogen shut-off valve arranged on the anode side; the fuel replenishment is configured to replenish hydrogen, and the hydrogen replenishment process comprises oxygen-consuming hydrogen replenishment and migration hydrogen replenishment.

8. The fuel cell shutdown control method according to claim 7, characterized in that: The oxygen consumption and hydrogen replenishment comprises: The converter applies a load current to the fuel cell stack, and when the average single-chip voltage is less than a preset value, the current application is stopped, and the air compressor and the tail exhaust valve are closed.

9. The fuel cell shutdown control method according to claim 7, characterized in that: The migration hydrogen replenishment comprises: Determine whether migration hydrogen replenishment is needed based on environmental parameters, downtime and catalyst degradation. If the conditions for migration hydrogen replenishment are met, migration hydrogen replenishment is performed. The converter inputs a reverse load current; When the current cathode pressure is greater than the target cathode pressure, or the current integral is greater than the current target integral, migration hydrogen replenishment is terminated.

10. The fuel cell shutdown control method according to claim 1, characterized in that: The fuel cell includes a converter, and the discharge resistor discharges until the converter voltage is less than a preset value, disconnecting the converter from the fuel cell to complete the shutdown of the fuel cell.

11. A fuel cell system, characterized in that: include: Fuel cells; A processor, configured to execute the fuel cell shutdown control method according to any one of claims 1 to 10.

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