Fuel Cell Systems

Abstract

To determine the deterioration state of a fuel cell with good accuracy even when performing load following operation.SOLUTION: A fuel cell system that stops and starts to operate every time an operating time reaches a predetermined time includes a current sensor that detects an output current of a fuel cell, a voltage sensor that detects the output voltage of the fuel cell, and an internal resistance acquisition unit that acquires the internal resistance of the fuel cell. After starting the system, the internal resistance acquisition unit acquires the output current and output voltage of the fuel cell detected by the current sensor and the voltage sensor at the timing when the fuel cell starts to generate power, and acquires the internal resistance on the basis of the obtained output current and output voltage.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fuel cell system. [Background technology]

[0002] Conventionally, as this type of fuel cell system, there is known one that performs deterioration diagnosis of a cell stack. For example, Patent Document 1 discloses a system that uses a temperature detection means to detect a stable temperature state at a predetermined part of the cell stack, and while in the stable state, controls the supply amounts of raw fuel gas, reforming water, and oxidant gas to be constant, while controlling an inverter to change the output current of the cell stack, and diagnoses the deterioration state using the output voltage value at this time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-27580 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned fuel cell system, in order to reduce variation in deterioration diagnosis, the supply amounts of raw fuel gas and oxidant gas are intentionally kept constant, and the deterioration state is determined from the relationship between the output current and output voltage at that time. Therefore, it may not be possible to use this system for load-following operation, in which the required amounts of raw fuel gas and oxidant gas change, or even if it is used for load-following operation, the accuracy of the diagnosis may be degraded.

[0005] A main object of the present invention is to provide a fuel cell system capable of performing load following operation, which is capable of determining the degradation state of the fuel cell with high accuracy. [Means for solving the problem]

[0006] In order to achieve the above-mentioned main object, the fuel cell system of the present invention employs the following means.

[0007] The fuel cell system of the present invention comprises: A fuel cell system including a fuel cell, the system being stopped and started every time an operating time reaches a predetermined time, a current sensor for detecting an output current of the fuel cell; a voltage sensor for detecting an output voltage of the fuel cell; an internal resistance acquisition unit that acquires an output current and an output voltage detected by the current sensor and the voltage sensor at a timing when power generation of the fuel cell is started after the system is started, and acquires an internal resistance of the fuel cell based on the acquired set of output current and output voltage; The gist of the project is to provide the following:

[0008] The fuel cell system of the present invention stops and starts the system every time the operating time reaches a predetermined time. This system includes a voltage sensor, a current sensor, and an internal resistance acquisition unit, which acquires the output current and output voltage of the fuel cell detected by the current sensor and the voltage sensor at the timing when the fuel cell starts generating electricity after the system is started, and calculates the internal resistance based on the acquired output current and output voltage. This allows the output current and output voltage required to acquire the internal resistance to be acquired under the same conditions at all times, thereby suppressing variations in the acquisition of the internal resistance. As a result, it becomes possible to more accurately diagnose the state of the fuel cell based on the internal resistance of the fuel cell. The fuel cell system includes a reformer that reforms the raw fuel gas supplied via a gas microcomputer meter into a fuel gas, and the gas microcomputer meter is specified to cut off the supply of the raw fuel gas when the flow rate change of the raw fuel gas is equal to or less than a certain amount and continues for a certain period of time or more, and the fuel cell system can be applied to a system that stops and starts before the certain period of time has elapsed.

[0009] In the fuel cell system of the present invention, a temperature sensor is provided for detecting a temperature correlated with the temperature of the fuel cell, and the output current and output voltage detected by the current sensor and the voltage sensor are obtained multiple times at predetermined time intervals, and the internal resistance is obtained based on multiple sets of the obtained output current and output voltage, and if the amount of change in temperature detected by the temperature sensor from the start to the end of obtaining the output current and output voltage is equal to or greater than a predetermined amount, the internal resistance may not be obtained. In this way, variation in the obtained internal resistance can be further suppressed.

[0010] In the fuel cell system of the present invention, the internal resistance acquisition unit may repeatedly acquire the output current and output voltage detected by the current sensor and the voltage sensor a plurality of times at predetermined time intervals, calculate a degree of correlation based on a plurality of sets of the acquired output current and output voltage, and if the calculated degree of correlation is less than the predetermined level, not acquire the internal resistance. In this way, the variation in the internal resistance can be further suppressed.

[0011] Furthermore, the fuel cell system of the present invention may further include a deterioration diagnosis unit that determines a relationship between previously acquired internal resistances and corresponding operating times of the system, sets a threshold based on the determined relationship, and performs deterioration diagnosis of the fuel cell based on whether the currently acquired internal resistance exceeds the threshold. In this way, an abnormality in the fuel cell can be detected early and dealt with.

[0012] The fuel cell system of the present invention may further include a deterioration diagnosis unit that sets a threshold value by adding a predetermined value to the previously obtained internal resistance, and performs deterioration diagnosis of the fuel cell based on whether the currently obtained internal resistance exceeds the threshold value. In this way, an abnormality in the fuel cell can be found early and dealt with. [Brief description of the drawings]

[0013] [Figure 1]1 is a schematic diagram of a fuel cell system according to an embodiment of the present invention; [Diagram 2] 10 is a flowchart illustrating an example of an internal resistance calculation process. [Diagram 3] FIG. 4 is an explanatory diagram showing the relationship between a stack current and a stack voltage. [Figure 4] FIG. 4 is an explanatory diagram showing changes in internal resistance over time of accumulated power generation. [Diagram 5] 13 is a flowchart showing an example of a degradation diagnosis process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

[0015] 1 is a schematic diagram of a fuel cell system according to the present embodiment. As shown in the figure, the fuel cell system 10 according to the present embodiment includes a power generation module 20 including a fuel cell stack 21 that generates power by an electrochemical reaction between hydrogen in an anode gas (fuel gas) and oxygen in a cathode gas (oxidant gas), a raw fuel gas supply device 30 that supplies a raw fuel gas (e.g., natural gas or LP gas) that is a raw material for the anode gas to the power generation module 20, a reforming water supply device 40 that supplies reforming water required 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), and an exhaust heat recovery device 60 that recovers heat (exhaust heat) of the combustion exhaust gas generated in the power generation module 20.

[0016] The power generation module 20 includes a fuel cell stack 21, a vaporizer 22, and two reformers 23, which are housed in a thermally insulating module case 29. In this embodiment, the power generation module 20 has two fuel cell stacks 21, which are installed on a manifold 24 arranged in the module case 29 so as to face each other with a gap between them.

[0017] Each fuel cell stack 21 has an electrolyte such as zirconium oxide, an anode electrode and a cathode electrode sandwiching the electrolyte, and has a plurality of solid oxide type unit cells arranged in the left-right direction (horizontal direction) in FIG. 2. An anode gas passage (not shown) is formed in the anode electrode of each unit cell so as to extend in a direction perpendicular to the arrangement direction of the unit cells, i.e., in the vertical direction. In addition, a cathode gas passage (not shown) for circulating a cathode gas is formed around the cathode electrode of each unit cell so as to extend in a direction perpendicular to the arrangement direction of the unit cells, i.e., in the vertical direction. The anode gas passage of each unit cell is connected to the manifold 24, and the cathode gas passage of each unit cell is connected to an air passage in the module case 29. Furthermore, a temperature sensor 92 is installed between (near) the two fuel cell stacks 21 so as to be at the same distance from both of them. The temperature sensor 92 detects a temperature (stack-correlated temperature) T4 that correlates with the temperature of each fuel cell stack 21.

[0018] The vaporizer 22 and reformer 23 of the power generation module 20 are disposed above the two fuel cell stacks 21 in the module case 29 with a gap therebetween. In this embodiment, the vaporizer 22 and one of the reformers 23 are disposed above one of the fuel cell stacks 21, and the other reformer 23 is disposed above the other fuel cell stack 21. Furthermore, between the one of the fuel cell stacks 21 and the vaporizer 22 and one of the reformers 23, and between the other fuel cell stack 21 and the other reformer 23, combustion sections 25 are defined to generate heat required for the operation of the fuel cell stack 21 and the reactions in the vaporizer 22 and reformer 23. An ignition heater 26 is provided in each combustion section 25.

[0019] 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 with heat from the combustion section 25, preheats the raw fuel gas, and evaporates the reforming water to generate water vapor. The raw fuel gas preheated by the vaporizer 22 is mixed with water vapor, and the mixed gas flows from the vaporizer 22 into the reformer 23. The reformer 23 is also provided with a temperature sensor 91 that detects the temperature (vaporizer temperature) T1 of the mixed gas flowing into the reformer 23.

[0020] 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 combustion section 25. Furthermore, the reformer 23 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 an anode gas containing hydrogen, carbon monoxide, carbon dioxide, steam, unreformed raw fuel gas, and the like. The anode gas generated by the reformer 23 flows into the anode gas passage of each unit cell via piping and manifold 24, and is supplied to the anode electrode.

[0021] Air is supplied as a cathode gas to the cathode electrode of each unit cell of the fuel cell stack 21 through an air passage formed in the module case 29. In the cathode electrode of each unit cell, oxide ions (O 2- ) are generated, and the oxide ions pass through the electrolyte and react with hydrogen and carbon monoxide at the anode electrode to generate electrical energy. The anode gas (hereinafter referred to as "anode off-gas") and cathode gas (hereinafter referred to as "cathode off-gas") that were not used in the electrochemical reaction (power generation) in each unit cell flow out from the anode gas passage and cathode gas passage of each unit cell to the upper combustion section 25.

[0022] The anode offgas flowing from each unit cell into the combustion section 25 is a combustible gas containing fuel components such as hydrogen and carbon monoxide, and is mixed with the cathode offgas containing oxygen flowing from each unit cell into the combustion section 25. Hereinafter, the mixed gas of the anode offgas and the cathode offgas is referred to as "offgas." When the offgas is ignited by the ignition heater 26 and ignited in the combustion section 25, the combustion of the offgas generates heat required for the operation of the fuel cell stack 21, preheating the raw fuel gas in the vaporizer 22, generating steam, and the steam reforming reaction in the reformer 23. In addition, in the combustion section 25, a combustion exhaust gas containing unburned fuel and steam is generated, and the combustion exhaust gas is supplied to the heat exchanger 62 via the combustion catalyst 27. The combustion catalyst 27 is an oxidation catalyst for reburning the unburned fuel in the combustion exhaust gas.

[0023] 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 (two-valve) 32, 33, an orifice 34, a gas pump 35, and a desulfurizer 36 that are installed in the raw fuel gas supply pipe 31. The raw fuel gas is pumped (supplied) from the raw fuel supply source 1 to the vaporizer 22 via the desulfurizer 36 by operating the gas pump 35. The desulfurizer 36 is configured as, for example, a room temperature desulfurization type desulfurizer. In addition, between the on-off valve 33 and the orifice 34 of the raw fuel gas supply pipe 31, a pressure sensor 37 that detects the pressure inside the raw fuel gas supply pipe 31 and a flow rate sensor 38 that detects the flow rate per unit time of the raw fuel gas flowing through the raw fuel gas supply pipe 31 (gas flow rate Qg) are installed.

[0024] The raw fuel gas from the raw fuel supply source 1 is introduced into the raw gas supply pipe 31 via a gas microcomputer meter (hereinafter referred to as gas meter) 1a. The gas meter 1a has a cutoff function that cuts off the flow of gas when the amount of change in the gas flow rate remains below a certain amount for a certain period of time or more.

[0025] 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.

[0026] The air supply device 50 has an air supply pipe 51 connected to an air passage formed in the module case 29, an air filter 52 provided at the inlet of the air supply pipe 51, and an air pump 53 installed in 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 each fuel cell stack 21 (cathode electrode) via the air passage in the module case 29.

[0027] The exhaust heat recovery device 60 has a hot water storage tank 61 that stores hot water, a heat exchanger 62 that exchanges heat between the hot water and the combustion exhaust gas generated in the combustion section 25 of the power generation module 20, a circulation pipe 63 that connects the hot water storage tank 61 and the heat exchanger 62, and a circulation pump 64 incorporated in the circulation pipe 63. The hot water stored in the hot water storage tank 61 is introduced into the heat exchanger 62 by operating the circulation pump 64, and is returned to the hot water storage tank 61 after being heated by heat exchange with the combustion exhaust gas in the heat exchanger 62.

[0028] The exhaust heat recovery device 60 also has a radiator 66 incorporated in the circulation piping 63, a radiator fan that blows air to the radiator 66, and a heater 65 that heats the hot and cold water in the circulation piping 63 by using the electricity generated by the power generation module 20. The radiator 66 is installed in the circulation piping 63 so as to be located between the circulation pump 64 and the heat exchanger 62, and the heater 65 is installed in the circulation piping 63 so as to be located between the radiator 66 and the circulation pump 64.

[0029] Furthermore, the heat exchanger 62 of the exhaust heat recovery device 60 is connected to the reforming water tank 42 via a pipe 67, and the condensed water obtained by condensing the water vapor in the combustion exhaust gas through heat exchange with the hot water from the hot water storage tank 61 is introduced into the reforming water tank 42 via the pipe 67. Furthermore, the combustion exhaust gas passage of the heat exchanger 62 is connected to a combustion exhaust gas exhaust pipe 68. As a result, the exhaust gas from which moisture has been removed by the heat exchanger 62 is discharged into the atmosphere via the combustion exhaust gas exhaust pipe 68.

[0030] An input terminal of a power conditioner 71 is connected to an output terminal of the fuel cell stack 21, and an output terminal of the power conditioner 71 is connected to a power line 3 from the power system 2 to a load 4 via a relay (not shown). The power conditioner 71 has a DC / DC converter that converts the DC voltage output from the fuel cell stack 21 to a predetermined voltage (e.g., DC 250 V to 300 V), and an inverter that converts the converted DC voltage to an AC voltage (e.g., AC 200 V) that can be connected to the power system 2. A current sensor 73 that detects a current (stack current I) output from the fuel cell stack 21 is provided at the output terminal of the fuel cell stack 21, and a voltage sensor 74 that detects a terminal-to-terminal voltage (stack voltage V) of the fuel cell stack 21 is provided between the output terminals of the fuel cell stack 21.

[0031] A power supply board 72 is connected to a power line branched off from the power conditioner 71. The power supply board 72 converts the DC voltage from the fuel cell stack 21 and the AC voltage from the power system 2 into a DC voltage suitable for the operation of the auxiliary equipment and supplies it to the auxiliary equipment. In the embodiment, examples of the auxiliary equipment include the ventilation fan 14, the on-off valves 32 and 33, the gas pump 35, the reforming water pump 43, the air pump 53, the circulation pump 64, and the heater 65.

[0032] The control device 80 is configured as a microprocessor centered on a CPU 81, and includes, in addition to the CPU 81, a ROM 82 for storing a processing program, a RAM 83 for temporarily storing data, a non-volatile memory 84, a timer 85 for measuring time, and an input / output port (not shown). Various detection signals from the pressure sensor 37, the flow rate sensor 38, the temperature sensors 91 and 92, the current sensor 73, the voltage sensor 74, and the like are input to the control device 80 via the input port. In addition, the control device 80 outputs various control signals to the fan motor of the ventilation fan 14, the solenoids of the on-off valves 32 and 33, the pump motor of the gas pump 35, the pump motor of the reformed water pump 43, the pump motor of the air pump 53, the pump motor of the circulation pump 64, the heater switch of the heater 65, the DC / DC converter and inverter of the power conditioner 71, the power supply board 72, the ignition heater 26, and the like via the output port. In addition, a remote control (not shown) is connected to the control device 80 via a wireless or wired communication line. The control device 80 executes various controls based on signals from the remote control operated by the user of the fuel cell system 10. Furthermore, the control device 80 measures the accumulated power generation time by integrating the accumulated time measured by the timer 85 while the power generation module 20 is generating power.

[0033] Next, the operation of the fuel cell system 10 of this embodiment thus configured will be described. When the CPU 81 of the control device 80 is requested to start up the system, it sequentially executes a fuel adsorption process in which raw fuel gas is supplied to the desulfurizer 36 until the adsorption of the fuel components reaches a saturated state, and a purge process in which the inside of the combustion section 25 is purged by supplying air, and then transitions to a warm-up mode in which raw fuel gas and air are supplied to the combustion section 25 and the mixed gas is ignited in the combustion section 25 to warm up the power generation module 20. Then, when the stack correlation temperature T4 detected by the temperature sensor 92 reaches a predetermined power generation permission temperature or higher, the system starts up, and the amount of raw fuel gas and air starts to be increased, transitioning to a power generation mode.

[0034] In the power generation mode, power is generated by controlling the supply amounts of raw fuel gas, reforming water, and air so that a target current Itag corresponding to a required power generation output is output from the fuel cell stack 21. The supply amount of raw fuel gas is controlled by setting a target gas flow rate Qgtag so as to achieve a predetermined fuel utilization rate Uf based on the target current Itag, and controlling the gas pump 35 so that the gas flow rate Qg detected by the flow sensor 38 coincides with the set target gas flow rate Qgtag. The supply amount of reforming water is controlled by setting a target reforming water flow rate Qwtag based on the target gas flow rate Qgtag so that the steam carbon ratio SC (the molar ratio between carbon contained in the hydrocarbons in the raw fuel gas and the steam added for steam reforming) in the reformer 23 coincides with a predetermined target ratio SCtag, and controlling the reforming water pump 43 so that reforming water at the set target reforming water flow rate Qwtag is supplied. The amount of air supplied is controlled by setting a target air flow rate Qatag by feedback control so that the stack correlation temperature T4 detected by the temperature sensor 92 coincides with a predetermined target temperature T4tag, and by controlling the air pump 53 so that air is supplied at the set target air flow rate Qatag.

[0035] When a request to stop the system is made during the power generation mode, the gas pump 35 is controlled by setting the target gas flow rate Qgtag to a flow rate (constant flow rate) at which the fuel cell stack 21 (electrodes) will not be oxidized and deteriorated in a high-temperature atmosphere until the stack correlation temperature T4 detected by the temperature sensor 92 falls below a predetermined stop permission temperature, and the air pump 53 is controlled by setting the target air flow rate Qatag to a flow rate (constant flow rate) required to cool the fuel cell stack 21. Then, when the stack correlation temperature T4 falls below the stop permission temperature, the gas pump 35 and air pump 53 are stopped to shut down the system.

[0036] As described above, the fuel cell system 10 of this embodiment receives raw fuel gas from the raw fuel supply source 1 via the gas meter 1a, and repeats the operation of stopping the system and then starting the system each time the continuous operating time reaches a predetermined time (e.g., one month) that is slightly shorter than the operation time of the shutoff function of the gas meter 1a so as not to activate the shutoff function of the gas meter 1a.

[0037] Furthermore, the fuel cell system 10 of this embodiment calculates the internal resistance (stack resistance) R of the fuel cell stack 21, and diagnoses the state (deterioration) of the fuel cell stack 21 based on the calculated internal resistance R. Fig. 2 is a flowchart showing an example of an internal resistance calculation process executed by the CPU 81 of the control device 80. This process is executed when the fuel cell system 10 begins to start up. As described above, the fuel cell system 10 repeatedly stops and starts the system every time the continuous operation time reaches a predetermined time, so the internal resistance calculation process is periodically and repeatedly executed.

[0038] In the internal resistance calculation process, the CPU 81 of the control device 80 first waits for the operation mode to transition to the warm-up mode (step S100). When it is determined that the operation mode has transitioned to the warm-up mode, the CPU 81 acquires the stack correlation temperature T4 from the temperature sensor 92 (step S110), and determines whether the acquired stack correlation temperature T4 is less than the threshold value T4ref (step S120). Here, the threshold value T4ref is a threshold value for determining whether the state of the fuel cell stack 21 is suitable for calculating the internal resistance R. In this embodiment, when the system is started periodically, the stack correlation temperature T4 is usually less than the threshold value T4ref when the system transitions to the warm-up mode, and when the system is stopped and started at any timing by an operator's operation for maintenance or the like, the stack correlation temperature T4 may become equal to or greater than the threshold value T4ref. Step S120 is for determining whether the system is started periodically as a normal start. If it is determined that the acquired stack correlation temperature T4 is not less than the threshold value T4ref but is equal to or greater than the threshold value T4ref, it is determined that the state of the fuel cell stack 21 is not suitable for calculating the internal resistance R, and the internal resistance calculation process is terminated. On the other hand, if it is determined that the acquired stack correlation temperature T4 is less than the threshold value T4ref, it waits for the operation mode to transition to the power generation mode (step S130).

[0039] When it is determined that the mode has been changed to the power generation mode, the temperature (stack correlation temperature) T4 from the temperature sensor 92 is acquired (step S140), and the acquired stack correlation temperature T4 is set to the acquisition start temperature Ts (step S150). Next, during the increase in the amount of raw fuel gas and air accompanying the start of the power generation mode, the stack current I from the current sensor 73 and the stack voltage V from the voltage sensor 74 are acquired at a predetermined sampling period (several hundred msec) (step S160), and it is determined whether or not the number of acquisitions has reached a predetermined number (for example, 30 or 40) (step S170). When it is determined that the number of acquisitions has not reached the predetermined number, the process returns to step S160, and the acquisition of the stack current I and the stack voltage V for each sampling period is repeated. On the other hand, when it is determined that the number of acquisitions has reached the predetermined number, the stack correlation temperature T4 from the temperature sensor 92 is acquired (step S180), and the acquired stack correlation temperature T4 is set to the acquisition end temperature Te (step S190). Once the acquisition start temperature Ts and acquisition end temperature Te are set, the temperature change amount ΔT is calculated by subtracting the acquisition end temperature Te from the acquisition start temperature Ts to obtain the absolute value (step S200), and it is determined whether the calculated temperature change amount ΔT is less than a threshold value Tref (step S210). Here, the threshold value ΔTref is a threshold value for determining whether the stack correlation temperature T4 has changed to an extent that affects the calculation of the internal resistance R while the stack current I and the stack voltage V are being acquired. If it is determined that the temperature change amount ΔT is not less than the threshold value ΔTref but is equal to or greater than the threshold value ΔTref, it is determined that the acquired data is not suitable for calculating the internal resistance R, and the internal resistance calculation process is terminated.

[0040] On the other hand, if it is determined that the temperature change amount ΔT is less than the threshold value ΔTref, a correlation coefficient r is calculated based on a plurality of pairs of the acquired stack current I and stack voltage V (step S220). The correlation coefficient r can be calculated by dividing the covariance of the stack current I and stack voltage V by the product of the standard deviation of the stack current I and the standard deviation of the stack voltage V. Then, it is determined whether the absolute value |r| of the calculated correlation coefficient r is equal to or greater than a predetermined value rref (e.g., 0.8 or 0.9) (step S230). If it is determined that the absolute value |r| of the correlation coefficient r is not equal to or greater than the predetermined value rref, it is determined that the correlation between the acquired stack current I and stack voltage V is weak and the acquired data is not suitable for calculating the internal resistance R, and the internal resistance calculation process is terminated. On the other hand, if it is determined that the absolute value |r| of the correlation coefficient r is greater than or equal to the predetermined value rref, the internal resistance R is calculated based on multiple pairs of the acquired stack current I and stack voltage V (step S240), and the calculated internal resistance R is stored in the non-volatile memory 84 in association with the cumulative power generation time (step S250), and the internal resistance calculation process is terminated.

[0041] Fig. 3 is an explanatory diagram showing the relationship between stack current and stack voltage, and Fig. 4 is an explanatory diagram showing the transition of internal resistance for each accumulated power generation time. The internal resistance R can be calculated, for example, by finding an approximation line from a plurality of pairs of acquired stack current I and stack voltage V by the least squares method and finding the slope of this approximation line. As shown in the figure, the longer the accumulated power generation time, the greater the slope of the approximation line and the greater the internal resistance R.

[0042] In this embodiment, the internal resistance calculation process is executed every time the system is started up periodically, so that the internal resistance R is basically calculated every time the system is started up. This allows the internal resistance R to be always calculated under the same conditions, so that the accuracy of the internal resistance R can be further improved. On the other hand, even when the system is started up, if the temperature state of the fuel cell stack 21 is not suitable for calculating the internal resistance R or if the correlation between the acquired stack voltage V and stack current I is weak, the calculation of the internal resistance R for that round is skipped, so that it is possible to suppress the occurrence of variations in the calculation of the internal resistance R for each round.

[0043] Next, a description will be given of an operation for diagnosing the state (deterioration) of the fuel cell stack 21 based on the calculated internal resistance R. Fig. 5 is a flowchart showing an example of the deterioration diagnosis process. This process is executed every time the internal resistance R is calculated by the internal resistance calculation process.

[0044] When the deterioration diagnosis process is executed, the CPU 81 of the control device 80 first calculates a predicted value Rpre of the internal resistance R to be calculated this time from a plurality of internal resistances calculated in the past (step S300). The predicted value Rpre can be predicted, for example, based on an approximate straight line obtained by the least squares method from a plurality of pairs of the internal resistances calculated in the past and the corresponding cumulative operating times. Next, a value obtained by adding a predetermined value ΔR to the calculated predicted value Rpre is set as a threshold value Rref (step S310), and it is determined whether the internal resistance R calculated this time is greater than the threshold value Rref (step S320). If it is determined that the internal resistance R calculated this time is equal to or less than the threshold value Rref, it is determined that the fuel cell stack 21 has not deteriorated beyond the expected level, and the deterioration diagnosis process is terminated. On the other hand, if it is determined that the internal resistance R calculated this time is greater than the threshold value Rref, it is determined that the fuel cell stack 21 has deteriorated beyond the expected level, and the system is stopped (step S330), and a control signal is output so that a predetermined warning display is performed on the remote control (step S340), and the deterioration diagnosis process is terminated.

[0045] In the fuel cell system 10 of the present embodiment described above, the system is stopped and started at predetermined time intervals so that the shutoff function of the gas meter 1a is not activated, and after the system is started, the stack voltage V and stack current I detected by the voltage sensor 74 and current sensor 73 are obtained at the timing when the fuel cell stack 21 starts generating electricity, and the internal resistance R is calculated from the obtained set of stack voltage V and stack current I. This makes it possible to obtain the stack voltage V and stack current I used to calculate the internal resistance R under the same conditions (timing), so that the internal resistance R can be calculated with high accuracy. As a result, it becomes possible to more accurately diagnose the state of the fuel cell stack 21 based on the internal resistance R of the fuel cell stack 21.

[0046] Furthermore, in the fuel cell system 10 of this embodiment, if the stack correlation temperature T4 at the transition to warm-up mode is less than the threshold value T4ref, if the temperature change ΔT of the stack correlation temperature T4 while multiple pairs of stack voltage V and stack current I are acquired at a predetermined sampling period in the power generation mode is equal to or greater than the threshold value ΔTref, or if the absolute value |r| of the correlation coefficient r between the acquired stack voltage V and stack current I is less than a predetermined value rref, then the internal resistance R is not calculated, thereby more reliably suppressing variations in the calculation of the internal resistance R.

[0047] In this embodiment, a predicted value Rpre of the internal resistance to be calculated this time is calculated based on an approximate straight line obtained by the least squares method from a plurality of pairs of previously calculated internal resistances R and corresponding accumulated power generation times, and a value obtained by adding a predetermined value ΔR to the calculated predicted value Rpre is set as the threshold value Rref for diagnosing the deterioration of the fuel cell stack 21. However, the threshold value Rref is not limited to this, and a value obtained by adding a predetermined value to the internal resistance calculated last time may be set. Alternatively, a predetermined value may be set.

[0048] In this embodiment, when the internal resistance R is greater than the threshold value Rref, the system is stopped and a warning is displayed on the remote control. However, the present invention is not limited to this. For example, a limit may be set on the power generation output of the fuel cell stack 21 and power generation may be continued within a range not exceeding the limit, a limit may be set on the rate of increase of the power generation output of the fuel cell stack 21 and output may be taken within a range not exceeding the limit, or a limit may be set on the output current of the fuel cell stack 21 and current may be taken within a range not exceeding the limit. Furthermore, if the fuel cell system 10 is connected to a management server via a network, information indicating that deterioration has occurred in the fuel cell stack 21 may be transmitted to the management server.

[0049] The correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem will be described below. In the embodiment, the fuel cell stack 21 corresponds to the "fuel cell", the current sensor 73 corresponds to the "current sensor", the voltage sensor 74 corresponds to the "voltage sensor", and the CPU 81 of the control device 80 that executes the internal resistance calculation process corresponds to the "internal resistance acquisition unit". The temperature sensor 92 corresponds to the "temperature sensor". The CPU 81 of the control device 80 that executes the degradation diagnosis process corresponds to the "degradation diagnosis unit".

[0050] Note that the correspondence between the main elements of the embodiment and the main elements of the invention described in the Means for Solving the Problem column does not limit the elements of the invention described in the Means for Solving the Problem column, since the embodiment is an example for specifically explaining the form for implementing the invention described in the Means for Solving the Problem column. In other words, the interpretation of the invention described in the Means for Solving the Problem column should be made based on the description in that column, and the embodiment is merely a specific example of the invention described in the Means for Solving the Problem column.

[0051] The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment in any way, and it goes without saying that the present invention can be carried out in various forms without departing from the gist of the present invention. [Industrial Applicability]

[0052] The present invention can be used in the fuel cell system manufacturing industry and the like. [Explanation of symbols]

[0053] 1 raw fuel supply source, 1a gas microcomputer meter (gas meter), 2 power system, 3 power line, 4 load, 10 fuel cell system, 20 power generation module, 21 fuel cell stack, 22 vaporizer, 23 reformer, 24 manifold, 25 combustion section, 26 ignition heater, 27 combustion catalyst, 29 module case, 30 raw fuel gas supply device, 31 raw fuel gas supply pipe, 32, 33 opening and closing valve, 34 orifice, 35 gas pump, 36 desulfurizer, 37 pressure sensor, 38 flow sensor, 40 reforming water supply device, 41 reforming water supply pipe, 42 reforming water tank, 43 reforming water pump, 50 air supply device, 51 air supply pipe, 52 air filter, 53 air pump, 60 exhaust heat recovery device, 61 hot water storage tank, 62 heat exchanger, 63 Circulation piping, 64 circulation pump, 65 heater, 66 radiator, 67 piping, 68 combustion exhaust gas exhaust pipe, 71 power conditioner, 72 power supply board, 73 current sensor, 74 voltage sensor, 80 control device, 81 CPU, 82 ROM, 83 RAM, 84 non-volatile memory, 85 timer, 91, 92 temperature sensors.

Claims

1. A fuel cell system including a fuel cell which generates electricity by receiving a supply of a fuel gas and an oxidant gas, and a combustor which combusts gas which has passed through the fuel cell, the fuel cell system being stopped and started each time an operating time reaches a predetermined time, a current sensor for detecting an output current of the fuel cell; a voltage sensor for detecting an output voltage of the fuel cell; a temperature sensor for detecting a temperature correlated with a temperature of the fuel cell; an internal resistance acquisition unit that acquires multiple output currents and output voltages detected by the current sensor and the voltage sensor at predetermined time intervals while the amounts of the fuel gas and the oxidant gas supplied to the fuel cell are increased as the fuel cell starts to generate power, and acquires the internal resistance of the fuel cell from the slope of the relationship between the output current and the output voltage based on the multiple sets of the acquired output currents and output voltages; and A fuel cell system comprising:

2. 2. The fuel cell system according to claim 1, the internal resistance acquisition unit does not acquire the internal resistance when an amount of change in temperature detected by the temperature sensor from the start to the end of acquisition of the output current and the output voltage is equal to or greater than a predetermined amount of change. Fuel cell system.

3. 3. The fuel cell system according to claim 1, the internal resistance acquisition unit does not acquire the internal resistance when an absolute value of a correlation coefficient between the output current and the output voltage obtained based on a plurality of pairs of the acquired output current and output voltage is less than a predetermined value; Fuel cell system.

4. 4. The fuel cell system according to claim 1, a deterioration diagnosis unit that obtains a relationship between a previously obtained internal resistance and a corresponding operation time of the system, sets a threshold value based on the obtained relationship, and performs deterioration diagnosis of the fuel cell based on whether or not the currently obtained internal resistance exceeds the threshold value; Fuel cell system.

5. 5. The fuel cell system according to claim 1, a deterioration diagnosis unit that sets a threshold value by adding a predetermined value to the previously acquired internal resistance, and performs deterioration diagnosis of the fuel cell based on whether or not the currently acquired internal resistance exceeds the threshold value; Fuel cell system.

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