Fuel cell system

Abstract

To quickly and accurately determine a misfire of a combustion unit regardless of a secular change of a system.SOLUTION: A fuel cell system includes: a fuel cell; a combustion unit configured to combust an off-gas from the fuel cell; a combustion catalyst unit configured to process an exhaust gas from the combustion unit with a combustion catalyst; a determination unit configured to determine whether or not a misfire has occurred in the combustion unit based on whether or not temperature of the combustion unit is lower than a first threshold value or whether or not temperature of the combustion catalyst unit is equal to or greater than a second threshold value; and a setting unit configured to set the first threshold value or the second threshold value based on at least one of an amount of increase in internal resistance of the fuel cell, an output current output from the fuel cell, an amount of increase in an oxidant gas supplied to the fuel cell, and cumulative operation time of the fuel cell.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This specification discloses a fuel cell system. [Background technology]

[0002] Conventionally, in a fuel cell system equipped with a combustion section that combusts exhaust gas discharged from a fuel cell cell and a combustion catalyst section that combusts the exhaust gas discharged through the combustion section using a combustion catalyst, a system has been proposed in which misfire in the combustion section is determined based on the temperatures of the combustion section and the combustion catalyst section (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-48091 Summary of the Invention [Problem to be solved by the invention]

[0004] In a system equipped with a fuel cell, the heat generated by the fuel cell increases as the fuel cell deteriorates, and the temperatures of the combustion section and the combustion catalyst section change depending on the heat generated by the fuel cell. Therefore, when determining whether a misfire has occurred based on the temperature of the combustion section or the combustion catalyst section, if a constant threshold value is used for the determination, there is a risk of misdetection of a misfire. To prevent this, it is possible to set the threshold value to a value far removed from the normal value, but in this case, it becomes impossible to quickly determine whether a misfire has occurred.

[0005] The main object of the fuel cell system of the present disclosure is to quickly and accurately determine misfire in the combustion section, regardless of aging of the system. [Means for solving the problem]

[0006] The fuel cell system of the present disclosure employs the following measures to achieve the above-mentioned main object.

[0007] The fuel cell system of the present disclosure comprises: a fuel cell that generates electricity using a fuel gas and an oxidant gas; a combustion unit that combusts off-gas from the fuel cell; a combustion catalyst section that treats exhaust gas from the combustion section with a combustion catalyst; a determination unit that determines whether a misfire has occurred in the combustion unit based on whether the temperature of the combustion unit is less than a first threshold value or whether the temperature of the combustion catalyst unit is equal to or greater than a second threshold value; a setting unit that sets the first threshold value or the second threshold value based on at least one of an increase in the internal resistance of the fuel cell, an output current output from the fuel cell, an increase in the amount of oxidant gas supplied to the fuel cell, and an accumulated operating time of the fuel cell; The gist of the project is to provide the following:

[0008] The increase in the internal resistance of the fuel cell, the output current output from the fuel cell, the increase in the amount of oxidant gas supplied to the fuel cell, and the cumulative operating time of the fuel cell are parameters directly related to the amount of heat generated by the fuel cell. In the fuel cell system disclosed herein, by setting the first and second thresholds based on these parameters, misfire in the combustion section can be determined quickly and accurately, regardless of deterioration of the system over time. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a fuel cell system according to an embodiment of the present invention; [Figure 2] 4 is a flowchart illustrating an example of an operation control routine. [Figure 3] 4 is a flowchart illustrating an example of a misfire determination process. [Figure 4] 2 is an explanatory diagram showing the relationship between stack current I and stack voltage V. FIG. [Figure 5] 1 is an explanatory diagram showing an example of the relationship between internal resistance R and cumulative power generation time, and an internal resistance increase amount ΔR. [Figure 6]FIG. 4 is an explanatory diagram showing the second misfire threshold Tref2 of the present embodiment and a comparative example. [Figure 7] 10 is a flowchart showing a misfire determination process according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present disclosure will be described with reference to the drawings.

[0011] Fig. 1 is a schematic diagram of a fuel cell system 10 of this embodiment. As shown in Fig. 1, the fuel cell system 10 of this embodiment includes a power generation module 20 including a fuel cell stack 21 that generates power through an electrochemical reaction between hydrogen in an anode gas and oxygen in a cathode gas, a raw fuel gas supply device 30 that supplies a raw fuel gas (e.g., natural gas or LP gas) that serves as a raw material for the anode gas to the power generation module 20, a reforming water supply device 40 that supplies reforming water necessary for reforming (steam reforming) the raw fuel gas to the power generation module 20, an air supply device 50 that supplies air as a cathode gas to the power generation module 20 (fuel cell stack 21), an exhaust heat recovery device 60 that recovers exhaust heat generated in the power generation module 20, and a control device 100 that controls the entire system.

[0012] The power generation module 20 includes a fuel cell stack 21, a vaporizer 22, a reformer 23, a combustor 24, and a heat exchanger 26, all of which are housed in a module case 29 having thermal insulation properties.

[0013] As shown in FIG. 1, in this embodiment, the fuel cell stack 21 is configured as a solid oxide fuel cell stack in which a plurality of unit cells are stacked. Each unit cell has an electrolyte and an anode and a cathode that sandwich the electrolyte. The reformer 23 is connected to the anode of each unit cell via an anode gas pipe 71. Furthermore, the air supply device 50 (air supply pipe 51) is connected to the cathode of each unit cell via a cathode gas pipe 72. A temperature sensor 111 is installed near the fuel cell stack 21. The temperature sensor 111 detects a temperature (stack temperature Ts) that correlates with the temperature of the fuel cell stack 21.

[0014] The vaporizer 22 and reformer 23 of the power generation module 20 are disposed above the fuel cell stack 21 inside the module case 29. In addition, a combustor 24 is disposed between the fuel cell stack 21 and the vaporizer 22 and reformer 23 to generate heat required for the operation of the fuel cell stack 21 and the reactions in the vaporizer 22 and reformer 23.

[0015] The vaporizer 22 heats the raw fuel gas from the raw fuel gas supply device 30 and the reforming water from the reforming water supply device 40 using heat from the combustor 24, preheating the raw fuel gas and evaporating the reforming water to generate steam. The raw fuel gas preheated by the vaporizer 22 is mixed with steam, and the mixed gas flows from the vaporizer 22 into the reformer 23.

[0016] The reformer 23 has a Ru-based or Ni-based reforming catalyst filled therein, and generates hydrogen gas and carbon monoxide by a reaction (steam reforming reaction) of the mixed gas from the vaporizer 22 with the reforming catalyst in the presence of heat from the combustor 24. The reformer 23 further generates hydrogen gas and carbon dioxide by a reaction (carbon monoxide shift reaction) between the carbon monoxide generated in the steam reforming reaction and steam. As a result, the reformer 23 generates anode gas containing hydrogen, carbon monoxide, carbon dioxide, steam, unreformed raw fuel gas, etc. The anode gas generated by the reformer 23 is supplied to the anode of each unit cell through the anode gas pipe 71.

[0017] Air as a cathode gas is supplied to the cathode of each unit cell through a cathode gas pipe 72. At the cathode of each unit cell, oxide ions (O 2- ) are produced, and the oxide ions pass through the electrolyte and react with hydrogen and carbon monoxide at the anode to generate electrical energy.

[0018] Anode gas (hereinafter referred to as "anode offgas") not used in the electrochemical reaction (power generation) in each unit cell is supplied to the combustor 24 through an anode offgas pipe 73, and cathode gas (hereinafter referred to as "cathode offgas") not used in the electrochemical reaction (power generation) in each unit cell is supplied to the combustor 24 through a cathode offgas pipe 74. The anode offgas is a combustible gas containing fuel components such as hydrogen and carbon monoxide, and is mixed with the cathode offgas containing oxygen in the combustor 24. The mixed gas is then burned to generate heat required for the operation of the fuel cell stack 21, preheating the raw fuel gas and generating steam in the vaporizer 22, and the steam reforming reaction in the reformer 23. The combustor 24 is equipped with an ignition device 25 for igniting the mixed gas of the anode offgas and cathode offgas introduced into the combustor 24. The combustor 24 is also equipped with a temperature sensor 112. The temperature sensor 112 detects a temperature (combustion section temperature Tb) that correlates with the temperature of the combustor 24.

[0019] The combustion exhaust gas generated by the combustion of the mixed gas in the combustor 24 passes through the reformer 23, heat exchanger 26, and vaporizer 22 in this order, supplying heat necessary for steam reforming, heat necessary for raising the temperature of the cathode gas (air), and heat necessary for generating steam, respectively, before being supplied to the condenser 62 through the combustion exhaust gas piping 75. The combustion exhaust gas supplied to the condenser 62 is cooled by the condenser 62 to remove at least a portion of the water vapor contained in the combustion exhaust gas, and then discharged into the atmosphere. A combustion catalyst 28 (oxidation catalyst) for combusting unburned fuel contained in the combustion exhaust gas is provided near the outlet of the combustion exhaust gas piping 75. A temperature sensor 113 is also provided near the combustion catalyst 28. The temperature sensor 113 detects a temperature (combustion catalyst part temperature Tc) that correlates with the temperature of the combustion catalyst 28.

[0020] The raw fuel gas supply device 30 includes a raw fuel gas supply pipe 31 that connects a raw fuel supply source 1 that supplies raw fuel gas to a vaporizer 22, and on-off valves (dual valves) 32 and 33 that are arranged in sequence from upstream to downstream on the raw fuel gas supply pipe 31, a flow sensor 39, a gas pump 34, and a desulfurizer 35. By operating the gas pump 34, the raw fuel gas is pressure-fed (supplied) from the raw fuel supply source 1 to the vaporizer 22 via the desulfurizer 35. The flow sensor 39 detects the flow rate per unit time (gas flow rate Fg) of the raw fuel gas flowing through the raw fuel gas supply pipe 31.

[0021] The reforming water supply device 40 has a reforming water tank 42 that stores reforming water, a reforming water supply pipe 41 that connects the reforming water tank 42 and the vaporizer 22, and a reforming water pump 43 installed in the reforming water supply pipe 41. By operating the reforming water pump 43, the reforming water in the reforming water tank 42 is pumped (supplied) by the reforming water pump 43 to the vaporizer 22.

[0022] The air supply device 50 includes an air supply pipe 51 connected to a cathode gas pipe 72 installed inside the module case 29, an air filter 52 installed at the inlet of the air supply pipe 51, and an air pump 53 and a flow sensor 54 installed at the air supply pipe 51. The flow sensor 54 detects the flow rate per unit time (air flow rate Fa) of air flowing through the air supply pipe 51. By operating the air pump 53, air as cathode gas is sucked into the air supply pipe 51 through the air filter 52 and is pressure-fed (supplied) to the fuel cell stack 21 (cathode) through the cathode gas pipe 72. A heat exchanger 26 is installed in the cathode gas pipe 72, and the air flowing into the heat exchanger 26 is heated to a required temperature by heat exchange with the high-temperature combustion exhaust gas discharged from the combustor 24 before being supplied to the cathode of the fuel cell stack 21.

[0023] The exhaust heat recovery device 60 includes a hot water storage tank 61 that stores hot water, a condenser 62 that exchanges heat between the hot water and anode off-gas flowing from the fuel cell stack 21 through an anode off-gas piping 73 and condenses the water vapor contained in the anode off-gas, a circulation piping 63 connected to the hot water storage tank 61 and the condenser 62, and a circulation pump 64 incorporated in the circulation piping 63. The hot water stored in the hot water storage tank 61 is introduced into the condenser 62 by operating the circulation pump 64, where it is heated by heat exchange with the anode off-gas and then returned to the hot water storage tank 61.

[0024] Furthermore, a condensed water pipe 44 and a combustion exhaust gas pipe 76 are connected to the passage outlet on the combustion exhaust gas side of the condenser 62, and the condensed water obtained by condensing the water vapor in the combustion exhaust gas through heat exchange with hot water from the hot water storage tank 61 is introduced into the reforming water tank 42 through the condensed water pipe 44. The reforming water tank 42 is equipped with a water purifier (not shown) that purifies the condensed water that has passed through the condensed water pipe 44. Furthermore, as described above, the combustion exhaust gas from which the water vapor has been removed in the condenser 62 is discharged into the atmosphere through the combustion exhaust gas pipe 76.

[0025] An input terminal of a power conditioner 80 is connected to an output terminal of the fuel cell stack 21, and the output terminal of the power conditioner 80 is connected to a power line 3 from the power grid 2 to a load 4 via a relay (not shown). The power conditioner 80 has a DC / DC converter that converts the DC power output from the fuel cell stack 21 into DC power of a predetermined voltage (e.g., DC 250 V to 300 V), and an inverter that converts the converted DC power into AC power of a voltage (e.g., AC 200 V) that can be connected to the power grid. This makes it possible to convert the DC power from the fuel cell stack 21 into AC power and supply it to a load 4 such as a home appliance. A current sensor 114 that detects the current flowing through the fuel cell stack 21 (stack current I) is attached to the output terminal of the fuel cell stack 21, and a voltage sensor 115 that detects the terminal-to-terminal voltage of the fuel cell stack 21 (stack voltage V) is attached between the output terminals of the fuel cell stack 21.

[0026] A power supply board 81 is connected to the power conditioner 80. The power supply board 81 converts DC power from the fuel cell stack 21 and AC power from the power system 2 into low-voltage DC power and supplies it to the drive circuits of the gas pump 34, the reforming water pump 43, the air pump 53, and the circulation pump 64, sensors such as flow rate sensors 39 and 54, temperature sensors 111, 112, and 113, current sensor 114, and voltage sensor 115, and the control device 100. In addition, cooling fans and ventilation fans (not shown) for cooling the power conditioner 80 and the power supply board 81 are disposed in the auxiliary machinery room where the power conditioner 80 and the power supply board 81 are disposed. The cooling fans send air to heat-generating parts of the power conditioner 80 and the power supply board 81, cooling the heat-generating parts through heat exchange with the air. The air that has been heated by cooling the heat-generating parts is discharged into the atmosphere by the ventilation fan.

[0027] The control device 100 is configured as a microprocessor centered around a CPU 101. In addition to the CPU 101, the control device 100 also includes a ROM 102 for storing processing programs, a RAM 103 for temporarily storing data, a timer 104, and input / output ports (not shown). Various detection signals from flow rate sensors 39 and 54, temperature sensors 111, 112, and 113, a current sensor 114, a voltage sensor 115, and the like are input to the control device 100 via input ports. The control device 100 also outputs various control signals to the solenoids of the on-off valves 32 and 33, the pump motor of the gas pump 34, the pump motor of the reforming water pump 43, the pump motor of the air pump 53, the pump motor of the circulation pump 64, and the like via output ports. A remote control (not shown) is connected to the control device 100 via a wireless or wired communication line. The control device 100 performs various controls based on signals from the remote control operated by a user of the fuel cell system 10.

[0028] Next, the operation of the fuel cell system 10 configured as described above will be described. When a system startup request is made, the CPU 101 of the control device 100 executes a fuel adsorption process to adsorb fuel components in the desulfurizer 35, a purging process to purge the inside of the power generation module 20 by supplying air, The system is started by sequentially carrying out an ignition process in which raw fuel gas and air are supplied to the combustor 24 to ignite the mixed gas, and a steam reforming process in which raw fuel gas and reforming water are supplied to the vaporizer 22 to cause a steam reforming reaction in the reformer 23.

[0029] Once system startup is complete, the CPU 101 starts power generation operation by controlling the supply rates of raw fuel gas, reforming water, and air so that the fuel cell stack 21 outputs a current (current command Ireq) corresponding to the required output Preq of the system. The supply rate of raw fuel gas is controlled by setting a gas flow rate corresponding to the current command Ireq to a target gas flow rate Fgtag so that the fuel utilization rate Uf matches the target utilization rate Uftag, and by controlling the gas pump 34 through feedback control so that the gas flow rate Fg detected by the flow sensor 39 matches the set target gas flow rate Fgtag. The fuel utilization rate Uf is the ratio of the amount of anode gas used for power generation to the amount of anode gas supplied to the anode. The supply rate of reforming water is controlled by setting a target reforming water flow rate Fwtag based on the target gas flow rate Fgtag so that the steam-to-carbon ratio SC in the reformer 23 matches the target ratio SCtag, and by controlling the reforming water pump 43 so that reforming water is supplied at the set target reforming water flow rate Fwtag. The steam-carbon ratio SC is the molar ratio of carbon contained in hydrocarbons in the raw fuel gas to steam added for steam reforming. The amount of air supplied is controlled by setting a target air flow rate Fatag through feedback control so that the temperature (stack-correlated temperature) Ts detected by the temperature sensor 111 matches the target temperature Tstag, and by controlling the air pump 53 through feedback control so that the air flow rate Fa detected by the flow rate sensor 54 matches the set target air flow rate Fatag. As deterioration of the fuel cell stack 21 progresses, the internal resistance increases and the amount of heat generated increases. For this reason, in this embodiment, the amount of air supplied to the fuel cell stack 21 is increased through the above-mentioned feedback control so that the temperature of the fuel cell stack 21 is maintained within an appropriate temperature range regardless of the degree of deterioration of the fuel cell stack 21.

[0030] When a request is made to shut down the system, the CPU 101 adjusts the supply amounts of raw fuel gas, reforming water, and air so that the fuel cell stack 21 and reformer 23 are cooled and the anode of the fuel cell stack 21 does not oxidize and deteriorate in a high-temperature atmosphere, and when cooling of the fuel cell stack 21, etc. is complete, it executes a system shutdown process to stop the supply of raw fuel gas, reforming water, and air.

[0031] Next, a description will be given of the operation of the fuel cell system 10 during power generation. Figure 2 is a flowchart showing an example of an operation control routine executed by the CPU 101 of the control device 100. This routine is executed after the system is started up.

[0032] In the operation control routine, the CPU 101 first executes the normal power generation operation described above (S100). Next, the CPU 101 executes a misfire determination process (S102) to determine whether a misfire has occurred in the combustor 24 (S104). In this embodiment, the misfire determination process is performed by determining whether either the combustion section temperature Tb is less than the first misfire threshold Tref1 or the combustion catalyst section temperature Tc is equal to or greater than the second misfire threshold Tref2, as will be described in detail later. If the CPU 101 determines that a misfire has not occurred, the process returns to S100 and continues the normal power generation operation. On the other hand, if the CPU 101 determines that a misfire has occurred, the CPU 101 executes misfire recovery control to recover from the misfire (S106). In this embodiment, the misfire recovery control is performed by sequentially executing a fuel increase control to increase the amount of anode gas supplied to the fuel cell stack 21, an output limit control to limit the power generation output of the fuel cell system 10, and an ignition control to activate the ignition device 25. This allows the combustor 24 to successfully recover from misfire. The CPU 101 then executes a misfire recovery determination process to determine whether the combustion unit temperature Tb is equal to or greater than a first recovery threshold that is a predetermined value greater than the first misfire threshold Tref1, and whether the combustion catalyst unit temperature Tc is less than a second recovery threshold that is a predetermined value less than the second misfire threshold Tref2. In this embodiment, the misfire recovery control involves sequentially executing fuel increase control, output limit control, and ignition control, and therefore the misfire recovery determination process is executed each time each misfire recovery control is executed. When the CPU 101 determines that the combustion unit has recovered from misfire through misfire recovery control (any of fuel increase control, output limit control, and ignition control), the process returns to S100 and resumes normal power generation operation. On the other hand, if the CPU 101 determines that the misfire has not been recovered from even through the misfire recovery control (either through fuel increase control, output limit control, or ignition control), it determines that some abnormality has occurred in the fuel cell system 10, stops the system (S110), and terminates this routine.

[0033] Next, the misfire detection process will be described in detail with reference to a flowchart of FIG.

[0034] In the misfire detection process, the CPU 101 receives inputs such as the combustion section temperature Tb from the temperature sensor 112, the combustion catalyst section temperature Tc from the temperature sensor 113, the stack current I from the current sensor 114, the internal resistance R of the fuel cell stack 21, and the air flow rate Fa from the flow rate sensor 54 (S200). Here, the internal resistance R is calculated by, for example, acquiring multiple stack currents I from the current sensor 114 and stack voltages V from the voltage sensor 115 at a predetermined sampling period after power generation begins each time the system is started, deriving an approximate line from the acquired multiple pairs of stack currents I and stack voltages V using the least squares method, and determining the slope of this approximate line (see FIG. 4). Note that the internal resistance R is correlated with the cumulative power generation time of the fuel cell system 21, and therefore, the internal resistance R may be calculated based on the cumulative power generation time by previously determining the relationship between the internal resistance R and the cumulative power generation time.

[0035] Next, the CPU 101 calculates the internal resistance increase amount ΔR (=R−Rini) by subtracting a predetermined initial resistance Rini from the input internal resistance R (S202), and sets first correction terms α1 and β1 by multiplying the internal resistance increase amount ΔR by positive correction coefficients A1 and B1 (S204). The first correction terms α1 and β1 take into consideration the influence that an increase in stack temperature Ts due to an increase in internal resistance R has on the combustion section temperature Tb and the combustion catalyst section temperature Tc.

[0036] Next, the CPU 101 sets second correction terms α2 and β2 by multiplying the input stack current I by positive correction coefficients A2 and B2 (S206). The second correction terms α2 and β2 take into consideration the influence that an increase in stack temperature Ts due to stack current I has on the combustion section temperature Tb and the combustion catalyst section temperature Tc.

[0037] Next, the CPU 101 calculates an air increase amount ΔFa by subtracting the initial flow rate Faini from the input air flow rate Fa (S208), and sets third correction terms α3 and β3 by multiplying the air increase amount ΔFa by positive correction coefficients A3 and B3 (S210). The initial flow rate Faini is determined in advance for each required output Preq. The air increase amount ΔFa is calculated by deriving the corresponding initial flow rate Faini based on the required output Pref and subtracting the derived initial flow rate Faini from the air flow rate Fa input in S200. Because heat from the fuel cell stack 21 is transferred to the combustor 24 and the combustion catalyst 28 as the air passes through the fuel cell stack 21, the third correction terms α3 and β3 take into account the effect of heat transfer due to an increase in the air flow rate Fa on the combustion section temperature Tb and the combustion catalyst section temperature Tc.

[0038] After setting the first correction terms α1 and β1, the second correction terms α2 and β2, and the third correction terms α3 and β3 in this manner, the CPU 101 uses the first correction term α1, the second correction term α2, and the third correction term α3 to set the first misfire threshold Tref1 according to the following equation (1) (S212). The first misfire threshold Tref1 is a threshold for determining whether a misfire has occurred in the combustor 24 based on the combustion unit temperature Tb. In equation (1), "Tini1" is an initial misfire threshold used for comparison with the combustion unit temperature Tb at the time of shipment of the fuel cell system 10, and is determined in advance through experimentation and analysis. As shown in equation (1), the first misfire threshold Tref1 is calculated by adding the first correction term α1, the second correction term α2, and the third correction term α3 to the initial misfire threshold Tini1.

[0039] Tref1=Tini1+α1+α2+α3 …(1)

[0040] The CPU 101 further sets a second misfire threshold Tref2 using the first correction term β1, the second correction term β2, and the third correction term β3 according to the following equation (2) (S214). The second misfire threshold Tref2 is a threshold for determining whether a misfire has occurred in the combustor 24 based on the combustion catalyst section temperature Tc. In equation (2), "Tini2" is an initial misfire threshold used for comparison with the combustion catalyst section temperature Tc at the time of shipment of the fuel cell system 10, and is determined in advance through experimentation and analysis. As shown in equation (2), the second misfire threshold Tref2 is calculated by adding the first correction term β1, the second correction term β2, and the third correction term β3 to the initial misfire threshold Tini2.

[0041] Tref2=Tini2+β1+β2+β3 …(2)

[0042] After setting the first misfire threshold Tref1 and the second misfire threshold Tref2 in this manner, the CPU 101 determines whether the combustion unit temperature Tb is less than the first misfire threshold Tref1 (S216) and whether the combustion catalyst unit temperature Tc is equal to or greater than the second misfire threshold Tref2 (S218). If the CPU 101 determines that the combustion unit temperature Tb is equal to or greater than the first misfire threshold Tref1 and that the combustion catalyst unit temperature Tc is less than the second misfire threshold Tref2, it determines that a misfire has not occurred in the combustor 24 and ends the misfire determination process. On the other hand, if the CPU 101 determines that the combustion unit temperature Tb is less than the first misfire threshold Tref1 or that the combustion catalyst unit temperature Tc is equal to or greater than the second misfire threshold Tref2, it determines that a misfire has occurred in the combustor 24 (S220) and ends the misfire determination process.

[0043] As the fuel cell stack 21 deteriorates, its internal resistance R increases, causing the amount of heat generated by the current (stack current I) to increase. The temperatures of the combustor 24 and the combustion catalyst 28 change due to the heat generated by the fuel cell stack 21. Therefore, when comparing the combustion section temperature Tb with the first misfire threshold Tref1 and the combustion catalyst section temperature Tc with the second misfire threshold Tref2 to determine whether a misfire has occurred in the combustor 24, setting the first misfire threshold Tref1 and the second misfire threshold Tref2 to constant values ​​may result in an erroneous misfire determination. However, if the first misfire threshold Tref1 and the second misfire threshold Tref2 are set to values ​​significantly different from the normal values ​​to prevent an erroneous misfire determination, the first misfire threshold Tref1 and the second misfire threshold Tref2 will deviate significantly from the combustion section temperature Tb and the combustion catalyst section temperature Tc during normal operation during initial shipment, making it difficult to quickly determine whether a misfire has occurred (see FIG. 6A). In contrast to this, in this embodiment, the first misfire threshold Tref1 and the second misfire threshold Tref2 are set by adding correction terms (first correction terms α1, β1, second correction terms α2, β2, and third correction terms α3, β3) that are set to increase as the deterioration of the fuel cell stack 21 progresses to the initial misfire thresholds Tini1, Tini2, so that it is possible to quickly and accurately determine whether a misfire has occurred in the combustor 24 at any time from the early stages of shipment to the end of durability (see Figure 6(b)).

[0044] In the above-described embodiment, the CPU 101 multiplies the stack current I by the positive correction coefficients A2 and B2 to set the second correction terms α2 and β2. However, as shown in S206B of the misfire determination process shown in FIG. 7, the square value of the stack current I (I 2 The second correction terms α2 and β2 may be set by multiplying the positive correction coefficients A2 and B2. The heat generation amount of the fuel cell stack 21 is calculated by multiplying the square value of the stack current I (I 2 ), the influence of the heat generation amount of the fuel cell stack 21 on the combustion section temperature Tb and the combustion catalyst section temperature Tc can be more appropriately reflected in the first misfire threshold Tref1 and the second misfire threshold Tref2.

[0045] In the above-described embodiment, the CPU 101 calculates the first correction term α1 proportional to the internal resistance increase amount ΔR and the stack current I or the square value (I 2 The first misfire threshold Tref1 is set by adding a second correction term α2 proportional to the air intake pressure ΔFa and a third correction term α3 proportional to the air increase amount ΔFa to the initial misfire threshold Tini1. However, one or two of the first correction term α1, the second correction term α2, and the third correction term α3 may be omitted.

[0046] In the above-described embodiment, the CPU 101 calculates the first correction term β1 proportional to the internal resistance increase amount ΔR and the stack current I or the square value (I 2 The second misfire threshold Tref2 is set by adding a second correction term β2 proportional to the air intake pressure ΔFa and a third correction term β3 proportional to the air increase amount ΔFa to the initial misfire threshold Tini2. However, one or two of the first correction term β1, the second correction term β2, and the third correction term β3 may be omitted.

[0047] In the above-described embodiment, the CPU 101 executes the fuel increase control, the output limit control, and the ignition control in this order as the misfire recovery control, but it is sufficient if it executes at least one of these three controls.

[0048] In the above-described embodiment, the fuel cell system 10 includes the vaporizer 22 that evaporates reforming water to generate steam, and the reformer 23 that uses the steam to reform the raw fuel gas into an anode gas. However, the fuel cell system 10 may omit the vaporizer 22 and the reformer 23, and supply hydrogen as an anode gas to the fuel cell stack 21 from a hydrogen supply source such as a hydrogen tank.

[0049] The above describes the forms for implementing the present disclosure using embodiments, but the present disclosure is not limited to these embodiments in any way, and it goes without saying that the present disclosure can be implemented in various forms within the scope that does not deviate from the gist of the present disclosure. [Industrial Applicability]

[0050] The present disclosure is applicable to the fuel cell system manufacturing industry. [Explanation of symbols]

[0051] 21 fuel cell stack (fuel cell), 24 combustor (combustion section), 25 ignition device (ignition section), 28 combustion catalyst (combustion catalyst section), 100 control device (determination section, setting section).

Claims

1. a fuel cell that generates electricity using a fuel gas and an oxidant gas; a combustion unit that combusts off-gas from the fuel cell; a combustion catalyst section that treats exhaust gas from the combustion section with a combustion catalyst; a determination unit that determines whether a misfire has occurred in the combustion unit based on whether the temperature of the combustion unit is less than a first threshold value or whether the temperature of the combustion catalyst unit is equal to or greater than a second threshold value; a setting unit that sets the first threshold value or the second threshold value based on at least one of an increase in the internal resistance of the fuel cell, an output current output from the fuel cell, an increase in the amount of oxidant gas supplied to the fuel cell, and an accumulated operating time of the fuel cell; A fuel cell system comprising:

2. 2. The fuel cell system according to claim 1, the first threshold value or the second threshold value is set by adding at least one correction term out of a first correction term proportional to an increase in the internal resistance, a second correction term proportional to the output current, and a third correction term proportional to an increase in the oxidant gas to an initial threshold value. Fuel cell system.

3. 2. The fuel cell system according to claim 1, the first threshold value or the second threshold value is set by adding at least one correction term out of a first correction term proportional to an increase in the internal resistance, a second correction term proportional to a square of the output current, and a third correction term proportional to an increase in the oxidant gas to an initial threshold value. Fuel cell system.

4. 4. The fuel cell system according to claim 1, a misfire recovery control unit that, when it is determined that a misfire has occurred in the combustion unit, executes misfire recovery control including at least one of fuel increase control for increasing the amount of fuel gas supplied to the fuel cell, output reduction control for reducing the power generation output of the fuel cell, and ignition control for activating an ignition unit provided in the combustion unit; A fuel cell system comprising:

Images