Fuel cell system and method for controlling purging thereof

Abstract

The present application relates to a fuel cell system and a method for controlling purging thereof. Disclosed is a fuel cell system including: a purging valve that discharges hydrogen on a hydrogen supply line passing through a fuel cell stack; an operating state monitoring device that monitors an operating state of the fuel cell stack; and a controller that determines a purging frequency based on the operating state, and controls the purging valve with reference to the determined purging frequency.

Description

Technical Field

[0001] This disclosure relates to fuel cell systems and methods for controlling their purging. Background Technology

[0002] Fuel cell systems can generate electricity by using fuel cell stacks. For example, when hydrogen is used as fuel for fuel cell stacks, it can be a solution to global environmental problems, and therefore research and development of fuel cell systems has been ongoing.

[0003] A fuel cell system may include a fuel cell stack that generates electricity, a fuel supply device that supplies fuel (hydrogen) to the fuel cell stack, an air supply device that supplies oxygen from the air as an oxidant required for the electrochemical reaction of the fuel cell stack, a thermal management system (TMS) that performs water management functions, vents the reaction heat of the fuel cell stack to the outside, and controls the operating temperature of the fuel cell stack, and a fuel cell system controller that controls the overall operation of the fuel cell system.

[0004] Fuel cell systems generate electricity by reacting hydrogen (fuel) with oxygen from the air in a fuel cell stack, producing water and heat as byproducts. In a fuel cell system, cross-over occurs due to the difference in gas concentration between the hydrogen electrode and the air electrode in the fuel cell stack. Hydrogen diffuses from the hydrogen electrode to the air electrode, causing a decrease in the hydrogen concentration at the hydrogen electrode and consequently reducing the cell voltage. To address this, the fuel cell system purges residual hydrogen to maintain the hydrogen concentration at the hydrogen electrode within a specific range.

[0005] However, traditionally, because hydrogen is discharged during hydrogen purging, it is contained in the exhaust gas, which can reduce safety and fuel efficiency. To address this, the purging frequency is adjusted to account for fuel efficiency or the hydrogen content in the exhaust gas. However, due to aging of the purging valve or increases in differential pressure, the amount of fluid discharged at the same purging frequency changes, making it difficult to maintain constant fuel cell performance and efficiency. Summary of the Invention

[0006] This disclosure is made to solve the aforementioned problems in the related art, while maintaining the advantages achieved by the related art.

[0007] One aspect of this disclosure provides a fuel cell system and a method for controlling its purging, the fuel cell system enhancing the power generation efficiency of the fuel cell by adjusting the purging frequency according to changes in the voltage and power generation efficiency of the fuel cell during purging.

[0008] Another aspect of this disclosure provides a fuel cell system that, during its operation, searches for a purging frequency with maximum efficiency when the power generation efficiency of the fuel cell decreases, while simultaneously increasing or decreasing the purging frequency per unit time.

[0009] The technical problems to be solved by this disclosure are not limited to those described above, and any other technical problems not mentioned herein will be clearly understood by those skilled in the art to which this disclosure pertains through the following description.

[0010] According to one aspect of this disclosure, a fuel cell system includes: a purge valve that discharges hydrogen through a hydrogen supply line passing through a fuel cell stack; an operation status monitoring device that monitors the operation status of the fuel cell stack; and a controller that determines a purge frequency based on the operation status and controls the purge valve with reference to the determined purge frequency.

[0011] In an implementation, the operating status monitoring device can monitor at least one or a combination of the fuel cell stack's current, voltage, power generation efficiency, or hydrogen supply.

[0012] In one implementation, the operation status monitoring device can monitor the operation status based on an average value for the operation status.

[0013] In this implementation, the controller can determine the first purge frequency at which the power generation efficiency of the fuel cell stack reaches its maximum efficiency point.

[0014] In one implementation, the controller can, when the maximum efficiency point of the fuel cell stack changes during its operation, adjust the purging frequency in units of specific time periods while searching for a second purging frequency that reaches the changed maximum efficiency point.

[0015] In this implementation, the controller can increase or decrease the purging frequency in units of specific time periods based on changes in the efficiency and voltage of the fuel cell stack.

[0016] In one implementation, the controller can increase the purging frequency when the power generation efficiency and voltage of the fuel cell stack become higher than those of the previous time point.

[0017] In one implementation, the controller can reduce the purging frequency when the voltage of the fuel cell stack becomes lower than the voltage at the previous time point and at the same time the power generation efficiency of the fuel cell stack becomes higher than the power generation efficiency at the previous time point.

[0018] In one implementation, the controller can increase the purging frequency when the power generation efficiency and voltage of the fuel cell stack become lower than those of the previous time point.

[0019] In one implementation, the controller can reduce the purging frequency when the voltage of the fuel cell stack becomes higher than the voltage at the previous time point and at the same time the power generation efficiency of the fuel cell stack becomes lower than the power generation efficiency at the previous time point.

[0020] According to another aspect of this disclosure, a method for controlling the purging of a fuel cell system includes: monitoring the operating state of the fuel cell stack; determining a purging frequency based on the operating state; and controlling a purging valve with reference to the determined purging frequency, the purging valve discharging hydrogen through a hydrogen supply line passing through the fuel cell stack.

[0021] In an implementation, monitoring the operating status of the fuel cell stack may include monitoring at least one or a combination of the fuel cell stack's current, voltage, power generation efficiency, or hydrogen supply.

[0022] In one implementation, monitoring the operating status of the fuel cell stack may include: monitoring the operating status based on an average value for the operating status.

[0023] In one implementation, controlling the purge valve may include: determining a first purge frequency at which the power generation efficiency of the fuel cell stack reaches its maximum efficiency point.

[0024] In one implementation, controlling the purge valve may include: when the maximum efficiency point of the fuel cell stack changes during its operation, while adjusting the purge frequency in units of specific time periods, searching for a second purge frequency that reaches the changed maximum efficiency point.

[0025] In one implementation, searching for a second purging frequency may include adjusting the purging frequency by increasing or decreasing it in units of a specific time period, based on changes in the efficiency and voltage of the fuel cell stack.

[0026] In one implementation, adjusting the purging frequency may include increasing the purging frequency when the power generation efficiency and voltage of the fuel cell stack become higher than those of the previous time point.

[0027] In one implementation, adjusting the purging frequency may include reducing the purging frequency when the voltage of the fuel cell stack becomes lower than the voltage at the previous time point and at the same time the power generation efficiency of the fuel cell stack becomes higher than the power generation efficiency at the previous time point.

[0028] In one implementation, adjusting the purging frequency may include increasing the purging frequency when the power generation efficiency and voltage of the fuel cell stack become lower than those of the previous time point.

[0029] In one implementation, adjusting the purging frequency may include reducing the purging frequency when the voltage of the fuel cell stack becomes higher than the voltage at the previous time point and at the same time the power generation efficiency of the fuel cell stack becomes lower than the power generation efficiency at the previous time point. Attached Figure Description

[0030] The above and other objects, features and advantages of this disclosure will become clearer from the following detailed description taken in conjunction with the accompanying drawings:

[0031] Figure 1 This is a diagram illustrating a fuel cell system according to an embodiment of the present disclosure;

[0032] Figure 2 This is a block diagram illustrating the control of a fuel cell system according to an embodiment of the present disclosure;

[0033] Figure 3A and Figure 3B This is a graph illustrating the variation of voltage and efficiency of a fuel cell system according to an embodiment of the present disclosure with respect to the purging frequency;

[0034] Figure 4 This is a diagram illustrating the purge frequency adjustment conditions of a fuel cell system according to an embodiment of the present disclosure;

[0035] Figure 5 This is a diagram illustrating the purging frequency adjustment operation of a fuel cell system according to an embodiment of the present disclosure; and

[0036] Figure 6 This is a diagram illustrating the operation flow of a method for controlling the purging of a fuel cell system according to an embodiment of the present disclosure. Detailed Implementation

[0037] In the following, some embodiments of the present disclosure will be described in detail with reference to the exemplary accompanying drawings. When adding reference numerals to the components in the figures, it should be noted that identical or equivalent components are referred to by the same numerals even if they are shown in other figures. Furthermore, in describing embodiments of the present disclosure, detailed descriptions of related known configurations or functions will be omitted if it is determined that they interfere with the understanding of embodiments of the present disclosure.

[0038] In describing components according to embodiments of the present disclosure, terms such as first, second, A, B, (a), (b), etc., may be used. These terms are intended only to distinguish components from other components, and they do not limit the nature, order, or sequence of the components. Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will also be understood that terms such as those defined in a general dictionary should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and not in an idealized or overly formal sense, unless expressly defined herein.

[0039] Figure 1 This is a diagram illustrating a fuel cell system according to an embodiment of the present disclosure.

[0040] Reference Figure 1 The fuel cell system includes a fuel cell stack 10, and may also include a hydrogen supply line 11 connected to a hydrogen electrode of the fuel cell stack 10 and through which hydrogen is supplied to the fuel cell stack 10, an air supply line 21 connected to an air electrode of the fuel cell stack 10 and through which air is supplied to the fuel cell stack 10, and discharge lines 31, 33 and 35 for discharging moisture (water), unreacted gases and the like as reaction byproducts, and a purge line 41.

[0041] The fuel cell stack 10 (or "fuel cell") may have the following structure: electricity can be generated by the oxidation / reduction reaction of fuel (e.g., hydrogen) and oxidant (e.g., air).

[0042] As an example, the fuel cell stack 10 may include: a membrane electrode assembly (MEA) in which a catalyst electrode layer undergoing an electrochemical reaction is attached to opposite sides of the electrolyte membrane through which hydrogen ions flow; a gas diffusion layer (GDL) for uniformly distributing the reactant gases and transferring the generated electrical energy; gaskets and fastening devices for maintaining the sealing performance and appropriate fastening pressure of the reactant gases and cooling water; and a bipolar plate through which the reactant gases and cooling water flow.

[0043] In the fuel cell stack 10, hydrogen as fuel and air (oxygen) as oxidant are supplied to the anode and cathode of the membrane electrode assembly through bipolar plates, and hydrogen can be supplied to the anode as the hydrogen electrode and air can be supplied to the cathode as the air electrode.

[0044] Hydrogen supplied to the anode is decomposed into protons and electrons by a catalyst in electrode layers disposed on opposite sides of the electrolyte membrane. Of these, only hydrogen ions can selectively pass through the electrolyte membrane, which serves as a cation exchange membrane, and be transported to the cathode, while electrons can pass through a gas diffusion layer and bipolar plates. At the cathode, the hydrogen ions supplied through the electrolyte membrane and the electrons transported through the bipolar plates can encounter oxygen from the air supplied to the cathode via an air supply device, resulting in a reaction that produces water. Then, due to the flow of hydrogen ions, electrons can flow through external wires, and this flow of electrons generates an electric current.

[0045] A fuel flow rate sensor FF, a fuel shut-off valve FCV, a fuel supply valve FSV, and a fuel injector FEJ can be installed in the hydrogen supply line 11. The hydrogen supply line 11 can be connected to a hydrogen tank.

[0046] The fuel flow rate sensor FF is a sensor that measures the flow rate of hydrogen supplied from the hydrogen tank to the fuel cell stack 10.

[0047] A fuel shut-off valve (FCV) is located in the hydrogen supply line 11 between the hydrogen tank and the fuel supply valve (FSV) and is used to interrupt the supply of hydrogen discharged from the hydrogen tank to the fuel cell stack 10. The fuel shut-off valve (FCV) can be controlled to open in the start-up state of the fuel cell system and to close in its closed state.

[0048] A fuel supply valve (FSV) is located in the hydrogen supply line 11 between the fuel shut-off valve (FCV) and the fuel injector (FEJ) and is used to regulate the pressure of hydrogen supplied to the fuel cell stack 10. As an example, the fuel supply valve (FSV) can be controlled to open to supply hydrogen when the pressure in the hydrogen supply line 11 decreases and to close when the pressure in the hydrogen supply line 11 increases.

[0049] The fuel injector FEJ is located in the hydrogen supply line 11 between the fuel supply valve FSV and the fuel cell stack 10, and is used to supply hydrogen through the fuel supply valve FSV by applying pressure to the fuel cell stack 10.

[0050] The hydrogen supply line 11 defines the hydrogen circulation path by connecting the outlet of the fuel cell stack 10 and the fuel injector FEJ. Therefore, hydrogen discharged from the fuel injector FEJ can generate electricity while reacting with air in the fuel cell stack 10, and unreacted hydrogen can be reintroduced into the fuel injector FEJ through the outlet of the fuel cell stack 10. In this case, unreacted hydrogen can be reintroduced into the fuel injector FEJ to supply the fuel cell stack 10 again, thereby enhancing the hydrogen reaction efficiency.

[0051] During the recirculation of unreacted hydrogen in the hydrogen electrode of the fuel cell stack 10, moisture present in the hydrogen supply line 11 can be condensed. The condensate (condensate liquid) can then be discharged through a point connected to the first discharge line 31 of the air humidifier AHF via a point on the hydrogen supply line 11, through which the unreacted hydrogen in the hydrogen electrode of the fuel cell stack 10 flows to the fuel injector FEJ.

[0052] The fuel water receiver (FWT) and fuel discharge valve (FDV) can be installed on the first discharge line 31.

[0053] The fuel water receiver (FWT) is used to store the condensate that is introduced into the first discharge line 31 at a point on the hydrogen supply line 11.

[0054] The fuel discharge valve FDV is used to discharge condensate stored in the fuel water receiver FWT along the first discharge line 31 to the air humidifier AHF. Here, the fuel discharge valve FDV can be controlled to close until the condensate stored in the fuel water receiver FWT exceeds a certain level, and to open when the condensate stored in the fuel water receiver FWT exceeds the certain level, so that the condensate is discharged through the first discharge line 31.

[0055] Air compressor ACP, air humidifier AHF, air shut-off valve ACV, etc. can be installed in air supply line 21.

[0056] The air compressor ACP is located between the air intake port through which ambient air is drawn in from the air supply line 21 and the air humidifier AHF, and is used to draw in and compress ambient air and supply compressed air.

[0057] An air humidifier (AHF) is disposed in the air supply line 21 between the air compressor (ACP) and the air shut-off valve (ACV), and is used to adjust the humidity of the air drawn in and compressed by the air compressor (ACP) and supply the air to the air electrode of the fuel cell stack 10. When air compressed by the air compressor (ACP) is introduced through the inlet of the air humidifier (AHF), moisture can be supplied to the introduced air to adjust the humidity. As an example, the air humidifier (AHF) can humidify the air supplied from the air compressor (ACP) by using condensate introduced through the first discharge line 31 and moisture contained in the air discharged through the second discharge line 33, which connects the air electrode of the fuel cell stack 10 and the air humidifier (AHF).

[0058] The air humidifier AHF can be connected to the first discharge line 31. Therefore, the air humidifier AHF can supply moisture to the air supplied from the air compressor ACP by using the condensate introduced through the first discharge line 31.

[0059] Furthermore, the air humidifier AHF can be connected to the air outlet of the fuel cell stack 10 via a second discharge line 33, and air discharged from the air electrode of the fuel cell stack 10 can be introduced into the air humidifier AHF via the second discharge line 33. Here, because the air discharged from the air electrode of the fuel cell stack 10 contains moisture, the air humidifier AHF humidifies the air by exchanging moisture between the air discharged from the air electrode of the fuel cell stack 10 and the air supplied from the air compressor ACP. In this way, the air supplied with moisture by the air humidifier AHF is introduced into the air electrode of the fuel cell stack 10 to react with hydrogen and then produce water.

[0060] Furthermore, the air humidifier AHF is connected to an external outlet via a third discharge line 35, and exhausts the air introduced through the second discharge line 33 to the outside via the third discharge line 35. An exhaust valve AEV can then be installed in the third discharge line 35.

[0061] An air shut-off valve (ACV) can be installed on the air supply line 21 connecting the fuel cell stack 10 and the air humidifier AHF. It can interrupt the supply of air discharged from the air humidifier AHF to the air electrode of the fuel cell stack 10, or adjust the pressure of the air supplied to the air electrode of the fuel cell stack 10. As an example, the air shut-off valve (ACV) can be controlled to open in the start-up state of the fuel cell stack 10 and to close in its closed state.

[0062] In addition, the air shut-off valve ACV can be connected to a second discharge line 33, which connects the fuel cell stack 10 and the air humidifier AHF. The air shut-off valve ACV can interrupt the supply of air discharged from the air electrode of the fuel cell stack 10 to the air humidifier AHF through the second discharge line 33, or adjust the pressure of the air discharged from the air electrode of the fuel cell stack 10 to the air humidifier AHF.

[0063] although Figure 1 An example is shown where the air shut-off valve (ACV) is integrated into the air supply line 21 and the second discharge line 33. However, the first air shut-off valve (not shown) on the air supply line 21 and the second air shut-off valve (not shown) on the second discharge line 33 can be implemented separately.

[0064] In addition, the purge line 41 can be connected to a point on the hydrogen supply line 11 through which hydrogen from the fuel injector FEJ is supplied to the hydrogen electrode of the fuel cell stack 10, and the fuel line purge valve (FPV) 50 can be provided on the purge line 41.

[0065] The purge valve (FPV) 50 is a valve that opens and closes to manage the hydrogen concentration of the fuel cell stack 10, hydrogen supply line 11, etc., and is used to maintain the hydrogen concentration of the fuel cell stack 10 and hydrogen supply line 11 within a specific range.

[0066] The fuel cell stack 10 generates electricity by using hydrogen and air, and the fuel line purge valve (FPV) 50 is closed when the fuel cell stack 10 is operating under normal conditions.

[0067] Here, the air supplied to the fuel cell stack 10 contains nitrogen in addition to oxygen, and cross-contamination may occur due to the different nitrogen partial pressures in the hydrogen electrode and the air electrode, thereby reducing the cell voltage. Therefore, the fuel line purge valve (FPV) 50 can maintain stack performance by purging residual hydrogen to increase the hydrogen concentration in the hydrogen electrode and thus reduce the nitrogen concentration. When the charge calculated by integrating the current generated in the fuel cell stack 10 over a specific time period exceeds the target charge, the fuel line purge valve (FPV) 50 can open to purge hydrogen, thereby controlling the hydrogen concentration in the hydrogen electrode to remain at a specific value or higher.

[0068] Figure 2 This is a block diagram illustrating the control of a fuel cell system according to an embodiment of the present disclosure.

[0069] Reference Figure 2 The fuel cell system may include an operating status monitoring device 110 and a controller 120.

[0070] The operation status monitoring device 110 may be a hardware device such as a processor or central processing unit (CPU), or a program implemented by the processor, and may monitor the operation status of the fuel cell system while the fuel cell system is being operated.

[0071] As an example, the operating condition monitoring device 110 can monitor the current, voltage, and power generation efficiency of the fuel cell stack 10. Furthermore, the operating condition monitoring device 110 can monitor the amount of hydrogen and oxygen required for the reaction, the actual amount of hydrogen and air supplied, and the hydrogen concentration in the exhaust gas. Here, the operating condition monitoring device 110 can monitor the condition based on the average value of the operating conditions.

[0072] The controller 120 may be a hardware device such as a processor or central processing unit (CPU), or a program implemented by a processor. The controller 120 may be connected to the configuration of the fuel cell system to perform overall functions regarding the management and operation of the fuel cell stack 10 of the fuel cell system. As an example, the controller 120 may be a fuel cell control unit (FCU) that controls the overall functions of the fuel cell system.

[0073] The controller 120 can determine the purging frequency and control the fuel line purging valve (FPV) 50 based on the determined frequency. The controller 120 can determine the purging frequency at which the power generation efficiency (hereinafter referred to as "efficiency") of the fuel cell stack 10 reaches its maximum efficiency as an initial value (hereinafter referred to as the "first purging frequency"). The purging frequency refers to the number of purgings per unit time period, and the first purging frequency at which the efficiency of the fuel cell stack 10 reaches its maximum efficiency can be a preset value. Here, the fact that the efficiency of the fuel cell stack 10 reaches its maximum efficiency can mean that the efficiency of the fuel cell stack 10 is a reference value or greater, or reaches a preset maximum value.

[0074] During the operation of the fuel cell system, the maximum efficiency point at which the fuel cell stack 10 reaches its maximum efficiency can be indicated as follows: Figure 3A middle.

[0075] Figure 3A The graphs illustrate the relationships between the voltage and power generation efficiency of the fuel cell stack and the purging frequency, as well as the relationship between the hydrogen flow rate and the purging frequency, as defined during the operation of a fuel cell system.

[0076] Reference Figure 3A Reference numeral 311 indicates the efficiency change of fuel cell stack 10, reference numeral 321 indicates the voltage change of fuel cell stack 10, reference numeral 331 indicates the change in supplied hydrogen, and reference numeral 341 indicates the change in unreacted hydrogen. Here, the amount of hydrogen required for the reaction can be calculated by subtracting the amount of unreacted hydrogen from the amount of supplied hydrogen. Furthermore, the efficiency of fuel cell stack 10 can be calculated based on the value obtained by dividing the output of fuel cell stack 10 by the hydrogen supply.

[0077] Then, the efficiency of the fuel cell stack 10 reaches its highest value at point P1. Therefore, the controller 120 can determine the purging frequency corresponding to point P1 as the first purging frequency.

[0078] Therefore, the controller 120 can control the fuel line purge valve (FPV) 50 based on a previously determined first purge frequency during operation of the fuel cell system.

[0079] During operation of the fuel cell system, the operation status monitoring device 110 continuously monitors the operation status of the fuel cell system while controlling the fuel line purge valve (FPV) 50 based on the first purge frequency.

[0080] During the operation of the fuel cell system, the operating conditions can change due to various factors, thus the purging frequency at which the fuel cell stack 10 achieves maximum efficiency can be altered. For example, the membrane characteristics of the fuel cell stack 10 can change, the amount of nitrogen and vapor crossing from the air electrode to the hydrogen electrode can change, the purity of the hydrogen can change, or the amount of fluid discharged at a preset purging frequency can decrease due to aging of the fuel line purge valve (FPV) 50 or an increase in differential pressure. Therefore, the efficiency of the fuel cell stack 10 can gradually decrease. In this way, when the efficiency of the fuel cell stack 10 decreases, the purging frequency at which the fuel cell stack 10 achieves maximum efficiency can be changed.

[0081] The implementation method where the point at which the fuel cell stack 10 reaches its maximum efficiency changes with the operating state of the fuel cell system can be as follows: Figure 3B As shown.

[0082] Figure 3B The graphs illustrate the relationships between the voltage of the fuel cell stack and the power generation efficiency, as well as the relationship between the hydrogen flow rate and the purging frequency, as defined during the operation of a fuel cell system.

[0083] Reference Figure 3B Reference numeral 311 indicates the efficiency change of the fuel cell stack 10 during normal operation of the fuel cell system, while reference numeral 315 indicates the efficiency change that varies according to changes in operating conditions. Furthermore, reference numeral 321 indicates the voltage change of the fuel cell stack 10, while reference numeral 325 indicates the voltage change that varies according to changes in operating conditions. Additionally, reference numeral 331 indicates the change in the supplied hydrogen, and reference numeral 341 indicates the change in unreacted hydrogen. Here, the amount of hydrogen required for the reaction can be calculated by subtracting the amount of unreacted hydrogen from the amount of supplied hydrogen. Furthermore, the efficiency of the fuel cell stack 10 can be calculated based on the value obtained by dividing the output of the fuel cell stack 10 by the amount of hydrogen supplied.

[0084] However, as shown in reference numeral 315, the modified efficiency of the fuel cell stack 10 has its highest value at point P2. In this way, when the point at which the efficiency of the fuel cell stack 10 reaches its maximum efficiency changes from P1 to P2, the efficiency of the fuel cell stack 10 can gradually decrease as the controller 120 continuously performs purging control with reference to the purging frequency corresponding to point P1.

[0085] Therefore, when it is determined that the efficiency decreases during the operation of the fuel cell system, the purging frequency can be adjusted based on the monitoring results of the operating status monitoring device 110. Then, when it is determined that the efficiency of the fuel cell stack 10 decreases, the controller 120 searches for a second purging frequency at which the efficiency of the fuel cell stack 10 reaches its maximum efficiency, while increasing or decreasing the purging frequency in units of a reference time period, based on changes in the voltage and efficiency of the fuel cell stack 10.

[0086] The operation status monitoring device 110 continuously monitors the operation status of the fuel cell stack 10 while the controller 120 searches for the purging frequency. Therefore, the controller 120 can determine whether to increase or decrease the purging frequency based on the operation status monitoring results (e.g., the voltage and efficiency of the fuel cell stack 10) during the search for the purging frequency.

[0087] The operation of determining whether to increase or decrease the purging frequency based on the voltage and efficiency of fuel cell stack 10 will refer to... Figure 4 The implementation method.

[0088] Figure 4 This is a diagram illustrating the purging frequency adjustment conditions of a fuel cell system according to an embodiment of the present disclosure. (Refer to...) Figure 4 Reference numeral 311 indicates the efficiency change of fuel cell stack 10, reference numeral 321 indicates the voltage change of fuel cell stack 10, reference numeral 331 indicates the change in supplied hydrogen, and reference numeral 341 indicates the change in unreacted hydrogen.

[0089] The controller 120 can calculate the minimum and maximum hydrogen supply based on the information about the operating status from the operating status monitoring device 110, and can perform purging control taking into account the calculated minimum and maximum hydrogen supply.

[0090] Here, the minimum hydrogen supply is the minimum amount of hydrogen required to output the target current during the operation of the fuel cell system, and the formula for obtaining the minimum hydrogen supply will refer to Equation 1 below.

[0091] [Formula 1]

[0092]

[0093] In Equation 1, H min Indicates the minimum hydrogen supply, I represents the stack current, and N represents the minimum hydrogen supply. cell This represents the number of batteries stacked in the pile, while F represents the Faraday constant.

[0094] The maximum hydrogen supply can be calculated based on the hydrogen concentration in the exhaust gas. The hydrogen concentration in the exhaust gas can be calculated by dividing the amount of unreacted hydrogen by the value obtained by adding the amount of unreacted air and the amount of unreacted hydrogen. Here, the amount of unreacted hydrogen can be calculated by subtracting the amount of reacted hydrogen from the actual hydrogen supply. The actual hydrogen supply is obtained by compensating for the amount of hydrogen discharged due to purging within the minimum hydrogen supply. Furthermore, the amount of unreacted air can be calculated by subtracting the amount of reacted oxygen from the amount of supplied air.

[0095] The hydrogen supply rate at which the hydrogen concentration in the exhaust gas reaches the hydrogen emission limit can be the maximum hydrogen supply rate. Therefore, the formula for obtaining the maximum hydrogen supply rate will refer to Equation 2.

[0096] [Equation 2]

[0097]

[0098] In Equation 2, H max Indicates the maximum hydrogen supply, I represents the stack current, and N represents the maximum hydrogen supply. cell The number of cells stacked in the pile is represented by F, F represents the Faraday constant, H2′ represents the hydrogen concentration in the exhaust gas, and SR represents the number of cells stacked in the pile. air The stoichiometric ratio of air is represented by xO2, where xO2 represents the concentration of oxygen in the air. Here, the stoichiometric ratio of air can be predetermined during the design and operation of the fuel cell stack 10. Hydrogen emission limits for the hydrogen concentration in the exhaust gas can be determined based on the environmental factors and / or regulations to which the fuel cell system is applied or installed.

[0099] like Figure 4 As shown, at a point Q1 in the interval of the purge frequency lower than the maximum efficiency point, the voltage decreases and the efficiency decreases as it moves to the left (in the direction of low purge frequency), and the voltage increases and the efficiency increases as it moves to the right (in the direction of high purge frequency). Therefore, the controller 120 determines that the current purge frequency corresponds to the low interval relative to the maximum efficiency point when the voltage decreases and the efficiency decreases or when the voltage increases and the efficiency increases.

[0100] Furthermore, at a point Q2 in the range of purge frequencies where the maximum efficiency is relative to the efficiency of fuel cell stack 10, the voltage increases while the efficiency decreases as it moves to the right (in the direction of high purge frequency), and the voltage decreases while the efficiency increases as it moves to the left (in the direction of low purge frequency).

[0101] In other words, because foreign matter is more smoothly expelled with increasing purging frequency in the corresponding range, the partial pressure of hydrogen increases, thus increasing the voltage of the fuel cell stack 10. However, because hydrogen is also expelled during purging, the efficiency of the fuel cell stack 10 gradually decreases. Furthermore, during purging, the degree of danger can increase with increasing hydrogen concentration in the exhaust gas. Additionally, because hydrogen expulsion is suppressed with decreasing purging frequency in the corresponding range, the efficiency of the fuel cell stack 10 increases, but the partial pressure of hydrogen decreases, thus decreasing the voltage of the fuel cell stack 10.

[0102] Therefore, when the voltage increases while the efficiency decreases, or when the voltage decreases while the efficiency increases, the controller 120 determines that the current purging frequency corresponds to the high range relative to the point of maximum efficiency and reduces the purging frequency.

[0103] In this way, the controller 120 can search for the purge frequency corresponding to the point of maximum efficiency while increasing or decreasing the purge frequency according to changes in efficiency and voltage.

[0104] When the efficiency at the current time point remains the same as the efficiency at the previous time point, the controller 120 can determine that the current purging frequency is the purging frequency corresponding to the point of maximum efficiency, and can perform purging control while maintaining the purging frequency at the corresponding time point.

[0105] However, as the purging frequency continues to increase, the hydrogen concentration in the exhaust gas increases, which may lead to dangerous situations. In this case, the controller 120 adjusts the purging frequency within the range that does not exceed the upper limit of the purging range obtained due to the maximum hydrogen supply.

[0106] Therefore, the implementation method for the search operation regarding the purging frequency will refer to... Figure 5 .

[0107] Figure 5 This is a diagram illustrating the purging frequency adjustment operation of a fuel cell system according to an embodiment of the present disclosure. (Refer to...) Figure 5 The controller 120 can perform purge control at time point t(n-1) at a purge frequency corresponding to the point of reference mark 511. At this time, because the voltage increases with the efficiency of the fuel cell stack 10, the controller 120 adjusts the purge frequency according to... Figure 4 The conditions shown will increase the purging frequency by a specific value (e.g., "1").

[0108] Therefore, the controller 120 performs purge control at a purge frequency corresponding to the point of reference mark 515 at a later time point t(n). In this case, it can be identified that the efficiency at the point of reference mark 515 is higher than the efficiency at the point of reference mark 511 at the previous time point. Therefore, the controller 120 can increase the purge frequency by a specific value (e.g., "1") in units of specific time periods until the efficiency reaches the point of maximum efficiency.

[0109] As another example, controller 120 can perform purge control at time point t(m-1) at a purge frequency corresponding to the point of reference mark 521. At this time, because the voltage increases as the efficiency of fuel cell stack 10 decreases, controller 120 adjusts accordingly. Figure 4 The conditions shown will reduce the purging frequency by a specific value (e.g., "1").

[0110] Therefore, the controller 120 performs purge control at a later time point t(m) at a purge frequency corresponding to the point of reference mark 525. In this case, it can be identified that the efficiency at the point of reference mark 525 is higher than the efficiency at the point of reference mark 521 at the previous time point.

[0111] Therefore, the controller 120 can reduce the purging frequency by a specific value (e.g., "1") in units of specific time periods until the efficiency reaches the maximum efficiency point.

[0112] In this way, the controller 120 can perform purging control at the purging frequency when the efficiency reaches the maximum efficiency point during the operation of the fuel cell system. When the efficiency decreases during the operation of the fuel cell system, the controller can increase or decrease the purging frequency based on the changes in efficiency and voltage of the fuel cell stack 10 at the corresponding time point, while searching for and adjusting the purging frequency efficiency point corresponding to the maximum value, so as to maintain the performance of the fuel cell stack 10 constantly.

[0113] The operation of the fuel cell system configured in this manner according to the present disclosure will now be described in detail.

[0114] Figure 6 This is a diagram illustrating the operation flow of a method for controlling the purging of a fuel cell system according to an embodiment of the present disclosure.

[0115] Reference Figure 6 The fuel cell system performs operations on a unit time basis based on a pre-set purging frequency (S110). Here, the pre-set purging frequency can be the first purging frequency at which the efficiency of the fuel cell stack 10 reaches its maximum efficiency point. As another example, the first purging frequency can be the frequency at which the efficiency of the fuel cell stack 10 becomes a reference value or higher.

[0116] The operating status of the fuel cell system is monitored simultaneously during process "S110" (S120). In process "S120," the fuel cell system can perform monitoring based on average values ​​for each operating state. As an example, the fuel cell system can monitor its status based on average values ​​of the efficiency, voltage, and / or hydrogen supply of the fuel cell stack 10.

[0117] The fuel cell system calculates the maximum and minimum hydrogen supply based on the operating state of process "S120" (S130). The fuel cell system can then reflect the maximum and minimum hydrogen supply calculated in process "S130" for purging control.

[0118] During the operation of the fuel cell system, the maximum efficiency point can change due to various factors. When the maximum efficiency point does not change, the difference between the efficiency "k" identified in process "S120" at the current time point and the efficiency (k-1) identified at the previous time point becomes 0. Therefore, when the difference between the efficiency "k" identified in process "S120" at the current time point and the efficiency (k-1) identified at the previous time point is 0, the fuel cell system performs purge control while repeating processes "S110" to "S140".

[0119] Furthermore, when the maximum efficiency point changes due to various factors during the operation of the fuel cell system, the efficiency during operation based on the first purge frequency may not be the maximum efficiency. Therefore, when the difference between the efficiency "k" identified at the current time point and the efficiency (k-1) identified at the previous time point is not zero, the fuel cell system determines that the maximum efficiency point has changed and then begins searching for a purge frequency. The fuel cell system then adjusts the purge frequency based on the changes in the efficiency and voltage of the fuel cell stack 10.

[0120] In other words, when the difference between the efficiency "k" identified at the current time point and the efficiency (k-1) identified at the previous time point is greater than 0 (S150), the fuel cell system determines that the efficiency has increased. Furthermore, when the difference between the voltage "k" identified at the current time point and the voltage (k-1) identified at the previous time point is greater than 0 (S160), the fuel cell system determines that the voltage has increased.

[0121] Therefore, the fuel cell system determines the purging frequency below the maximum efficiency point when efficiency and voltage increase, and increases the purging frequency while keeping the hydrogen supply below the maximum hydrogen supply (S170 and S180). As an example, in process "S180", the fuel cell system increases the purging frequency by "1". Thereafter, the fuel cell system can perform operations per unit time based on the increased purging frequency in processing "S180" while executing the process after "S110". The fuel cell system monitors its operating status in real time while operating under the state of adjusted purging frequency.

[0122] Furthermore, when the difference between the efficiency "k" identified at the current time point and the efficiency (k-1) identified at the previous time point in process "S150" is greater than 0, the fuel cell system determines that the efficiency has increased. Conversely, when the difference between the voltage "k" identified at the current time point and the voltage (k-1) identified at the previous time point is not greater than 0 (S160), the fuel cell system determines that the voltage has decreased.

[0123] Therefore, when the voltage decreases while the efficiency increases, the fuel cell system determines that the purge frequency at the current time point is higher than the purge frequency at the maximum efficiency point, and reduces the purge frequency (S200). As an example, in process "S200", the fuel cell system reduces the purge frequency by "1". Furthermore, when the purge frequency adjusted in process "S200" is not greater than 0 (S210), the purge frequency remains at "1" (S220). Thereafter, the fuel cell system can perform operations per unit time based on the reduced purge frequency in process "S200" while executing the process following "S110". The fuel cell system monitors its operating status in real time while operating under the state of adjusted purge frequency.

[0124] As another example, when the difference between the efficiency “k” identified at the current point in process “S150” and the efficiency (k-1) identified at the previous time point is not greater than 0, the fuel cell system determines that the efficiency has decreased.

[0125] Then, when the difference between the voltage “k” identified at the current time point and the voltage (k-1) identified at the previous time point is not greater than 0 (S190), the fuel cell system determines that the voltage has decreased.

[0126] Therefore, when both efficiency and voltage decrease, the fuel cell system determines that the current purging frequency is below the maximum efficiency point and increases the purging frequency while keeping the hydrogen supply below the maximum hydrogen supply. As an example, in process "S180", the fuel cell system increases the purging frequency by "1". Thereafter, the fuel cell system can perform operations per unit time based on the increased purging frequency while executing the process following "S110". The fuel cell system monitors its operating status in real time while operating with the purging frequency adjusted.

[0127] Furthermore, in the fuel cell system, when the difference between the efficiency "k" identified at the current time point in process "S150" and the efficiency k-1 identified at the previous time point is not greater than 0, it is determined that the efficiency decreases, and when the difference between the efficiency "k" identified at the current time point in process "S190" and the efficiency k-1 identified at the previous time point is greater than 0, it is determined that the voltage increases.

[0128] Therefore, when the voltage increases while the efficiency decreases, the fuel cell system determines that the purge frequency at the current time point is higher than the purge frequency at the maximum efficiency point, and reduces the purge frequency (S200). As an example, in process "S200", the fuel cell system reduces the purge frequency by "1". Furthermore, when the purge frequency adjusted in process "S200" is not greater than 0 (S210), the purge frequency remains at "1" (S220). Thereafter, the fuel cell system can perform operations per unit time based on the reduced purge frequency in process "S200" while executing the process following "S110". The fuel cell system monitors its operating status in real time while operating under the state of adjusted purge frequency.

[0129] In this way, the fuel cell system repeats the process from "S140" to "S220" while increasing or decreasing the purging frequency, until the purging frequency reaches the purging frequency at the maximum efficiency point.

[0130] The operational status monitoring device 110, controller 120, and other devices, apparatuses, units, modules, and components described herein are implemented by hardware components. Examples of hardware components that can be used to perform the operations described herein, where appropriate, include controllers, sensors, generators, drivers, memories, comparators, arithmetic logic units, adders, subtractors, multipliers, dividers, integrators, and any other electronic components configured to perform the operations described herein. In other examples, one or more hardware components performing the operations described herein are implemented by computing hardware, such as one or more processors or computers. A processor or computer may be implemented by one or more processing elements such as logic gate arrays, controllers and arithmetic logic units, digital signal processors, microcomputers, programmable logic controllers, field-programmable gate arrays, programmable logic arrays, microprocessors, or any other means or combination of means configured to respond to and execute instructions in a defined manner to achieve desired results.

[0131] The methods for performing the operations described in this application are executed by computing hardware, such as one or more processors or a computer, which are implemented as described above to execute instructions or software to perform the operations described in this application performed by the methods. For example, a single operation or two or more operations may be performed by a single processor, or two or more processors, or a processor and a controller. One or more operations may be performed by one or more processors, or a processor and a controller, and one or more other operations may be performed by one or more other processors, or another processor and another controller. One or more processors, or a processor and a controller, may perform a single operation, or two or more operations.

[0132] As described above, according to the fuel cell and the method for controlling the fuel cell according to the present disclosure, the power generation efficiency of the fuel cell can be enhanced by adjusting the purging frequency according to the changes in the voltage and power generation efficiency of the fuel cell during purging, and when the power generation efficiency of the fuel cell decreases during its operation, the purging frequency with maximum efficiency can be searched while increasing and decreasing the purging frequency on a unit time basis.

[0133] According to embodiments of this disclosure, the power generation efficiency of a fuel cell can be enhanced by adjusting the purging frequency according to changes in the voltage and power generation efficiency of the fuel cell during purging.

[0134] In addition, when the power generation efficiency of the fuel cell decreases during its operation, the purging frequency with maximum efficiency can be searched while increasing or decreasing the purging frequency per unit time.

[0135] The above description is a simple example of the technical spirit of this disclosure, and those skilled in the art to which this disclosure pertains can make various modifications and alterations to this disclosure without departing from its essential characteristics.

[0136] Therefore, the embodiments disclosed herein are not intended to limit the technical spirit of this disclosure, but rather to describe it, and the scope of the technical spirit of this disclosure is not limited by the embodiments. Therefore, the technical scope of this disclosure should be interpreted by the appended claims, and all technical spirit within the equivalent scope falls within the scope of this disclosure.

[0137] Cross-references to related applications

[0138] This application claims priority to Korean Patent Application No. 10-2022-0074134, filed with the Korean Intellectual Property Office on June 17, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. A fuel cell system, the fuel cell system comprising: A purge valve configured to discharge hydrogen from a hydrogen supply line passing through the fuel cell stack; An operation status monitoring device, configured to monitor the operation status of the fuel cell stack; as well as A controller configured to determine a purging frequency based on the operating state and to control the purging valve with reference to the determined purging frequency. The controller is further configured as follows: Determine the first purge frequency at which the power generation efficiency of the fuel cell stack reaches its maximum efficiency point, and When the maximum efficiency point of the power generation efficiency of the fuel cell stack changes during the operation of the fuel cell system, while adjusting the purging frequency in units of specific time periods, a second purging frequency that reaches the changed maximum efficiency point is searched.

2. The fuel cell system according to claim 1, wherein, The operation status monitoring device is configured as follows: Monitor at least one or a combination of the current, voltage, power generation efficiency, or hydrogen supply of the fuel cell stack.

3. The fuel cell system according to claim 2, wherein, The operation status monitoring device is also configured to: The operating status is monitored based on the average value for the operating status.

4. The fuel cell system according to claim 1, wherein, The controller is also configured to: The purging frequency is increased or decreased in units of the specific time period based on changes in the efficiency and voltage of the fuel cell stack.

5. The fuel cell system according to claim 4, wherein, The controller is also configured to: When the power generation efficiency and voltage of the fuel cell stack become higher than those of the previous time point, the purging frequency is increased.

6. The fuel cell system according to claim 4, wherein, The controller is also configured to: When the voltage of the fuel cell stack becomes lower than the voltage at the previous time point, and the power generation efficiency of the fuel cell stack becomes higher than the power generation efficiency at the previous time point, the purging frequency is reduced.

7. The fuel cell system according to claim 4, wherein, The controller is also configured to: When the power generation efficiency and voltage of the fuel cell stack become lower than those of the previous time point, the purging frequency is increased.

8. The fuel cell system according to claim 4, wherein, The controller is also configured to: When the voltage of the fuel cell stack becomes higher than the voltage at the previous time point, and the power generation efficiency of the fuel cell stack becomes lower than the power generation efficiency at the previous time point, the purging frequency is reduced.

9. A method for controlling the purging of a fuel cell system, the method comprising the following steps: Monitor the operating status of the fuel cell stack; The purging frequency is determined based on the aforementioned operating status; as well as The purge valve is controlled with reference to the determined purge frequency and is configured to discharge hydrogen from the hydrogen supply line passing through the fuel cell stack. The step of controlling the purge valve includes the following steps: Determine the first purge frequency at which the power generation efficiency of the fuel cell stack reaches its maximum efficiency point, and When the maximum efficiency point of the power generation efficiency of the fuel cell stack changes during the operation of the fuel cell system, while adjusting the purging frequency in units of specific time periods, a second purging frequency that reaches the changed maximum efficiency point is searched.

10. The method according to claim 9, wherein, The steps for monitoring the operating status of the fuel cell stack include the following: Monitor at least one or a combination of the current, voltage, power generation efficiency, or hydrogen supply of the fuel cell stack.

11. The method according to claim 10, wherein, The step of monitoring the operating status of the fuel cell stack further includes the following steps: The operating status is monitored based on the average value for the operating status.

12. The method according to claim 9, wherein, The steps for searching the second purge frequency include the following: Based on the changes in the efficiency and voltage of the fuel cell stack, the purging frequency is adjusted by increasing or decreasing the purging frequency in units of the specific time period.

13. The method according to claim 12, wherein, The steps for adjusting the purging frequency include the following: When the power generation efficiency and voltage of the fuel cell stack become higher than those of the previous time point, the purging frequency is increased.

14. The method according to claim 12, wherein, The steps for adjusting the purging frequency include the following: When the voltage of the fuel cell stack becomes lower than the voltage at the previous time point, and the power generation efficiency of the fuel cell stack becomes higher than the power generation efficiency at the previous time point, the purging frequency is reduced.

15. The method according to claim 12, wherein, The steps for adjusting the purging frequency include the following: When the power generation efficiency and voltage of the fuel cell stack become lower than those of the previous time point, the purging frequency is increased.

16. The method according to claim 12, wherein, The steps for adjusting the purging frequency include the following: When the voltage of the fuel cell stack becomes higher than the voltage at the previous time point, and the power generation efficiency of the fuel cell stack becomes lower than the power generation efficiency at the previous time point, the purging frequency is reduced.

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