Fuel cell system, control method for fuel cell system, computer program, and recording medium

Abstract

In a circulation path (111), an anode off-gas discharge port (133) of a fuel cell (120), a discharge position (117), a supply position (118), and a hydrogen supply port (131) of the fuel cell (120) appear in this order. A supply path (112) is connected to the circulation path (111) at the supply position (118), and supplies hydrogen-containing gas (101) to the circulation path (111). A discharge path (113) is connected to the circulation path (111) at the discharge position (117). A controller (190) executes abnormality response control when an abnormality occurs in a detection result of a sensor (170) in the circulation path (111). In the abnormality response control, discharge processing for discharging an anode off-gas (105) from the anode off-gas discharge port (133) via the discharge path (113) is executed.

Description

Fuel cell system, fuel cell system control method, computer program, and recording medium

[0001] The present disclosure relates to a fuel cell system, a control method for a fuel cell system, a computer program, and a recording medium.

[0002] Various studies have been conducted on fuel cell systems. The fuel cell system disclosed in Patent Document 1 includes a hydrogen reflux path, a hydrogen circulation pump, a gas purge valve, a hydrogen mass flow rate estimation means, and a purge control means. The hydrogen reflux path returns hydrogen not used for power generation in the fuel cell to a passage that supplies hydrogen to the fuel cell. The gas purge valve is provided in the hydrogen reflux path. The hydrogen mass flow rate estimation means estimates the hydrogen mass flow rate in a hydrogen circulation system including the hydrogen reflux path. The purge control means opens the gas purge valve when the hydrogen mass flow rate falls below a threshold value.

[0003] The hydrogen mass flow rate estimation means of Patent Document 1 includes a volume flow rate detection means that detects the volume flow rate of the mixed gas based on the propagation time of ultrasonic waves through the mixed gas in the hydrogen circulation system.

[0004] Japanese Patent Application Laid-Open No. 2003-317752

[0005] The present disclosure provides a technique suitable for avoiding a situation in which control for discharging anode off-gas cannot be executed in the presence of an error factor that may affect the detection result of a sensor.

[0006] The present disclosure provides a fuel cell system comprising: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; a sensor provided in the circulation path; and a controller that executes abnormality response control when an abnormality occurs in the detection result of the sensor, wherein the abnormality response control executes a discharge process in which the discharge valve is set to an open state to discharge anode off-gas from the anode off-gas discharge port via the discharge path.

[0007] The technology according to the present disclosure is suitable for avoiding a situation in which control for discharging anode off-gas cannot be executed in the presence of an error factor that may affect the detection result of the sensor.

[0008] Schematic diagram of a fuel cell system according to an embodiment. Explanatory diagram of a sensor according to an embodiment. Explanatory diagram of a sensor according to an embodiment. Explanatory diagram of a sensor according to an embodiment. Explanatory diagram of a structure and posture of a sensor and a circulation path according to an embodiment. Flowchart for explaining transition between a first mode and a second mode. Graph showing an example of change over time in an estimated value of the mass flow rate of hydrogen. Explanatory diagram of a sensor according to a modified example. Explanatory diagram of a sensor according to a modified example.

[0009] (Knowledge and the like that forms the basis of the present disclosure) Consider a fuel cell system in which anode off-gas is discharged from the anode of a fuel cell, the anode off-gas is mixed with a hydrogen-containing gas, and the resulting mixed gas is supplied to the anode. In this fuel cell system, a circulation path is configured to return hydrogen in the anode off-gas to the fuel cell. The hydrogen returned to the fuel cell via the circulation path is used to generate electricity in the fuel cell. The hydrogen-containing gas is, for example, pure hydrogen gas.

[0010] Impurities may be introduced into a hydrogen circulation system that includes an anode and a circulation path. For example, a fuel cell includes a membrane electrode assembly (MEA) in which an electrolyte membrane is sandwiched between an anode and a cathode. Nitrogen may cross-leak from the cathode through the electrolyte membrane to the anode, and be introduced into the hydrogen circulation system as an impurity.

[0011] In a hydrogen circulation system, when impurities are introduced, the hydrogen concentration decreases and the mass flow rate of hydrogen decreases. This reduces the mass flow rate of hydrogen supplied to the fuel cell, which can lead to a decrease in the power generation efficiency of the fuel cell and deterioration of the fuel cell. To address this problem, it is possible to discharge anode off-gas with a reduced hydrogen concentration. By discharging anode off-gas while continuing to supply hydrogen-containing gas, it is possible to restore the mass flow rate of hydrogen in the hydrogen circulation system and the mass flow rate of hydrogen supplied to the fuel cell.

[0012] The timing of discharging the anode off-gas can be determined by providing a sensor in the circulation path and utilizing the detection results of the sensor. For example, the mass flow rate of hydrogen in the anode off-gas is estimated based on the detection results. The timing of discharging the anode off-gas is determined according to a decrease in the estimated value.

[0013] However, the detection results of the sensors installed in the circulation path are not always accurate. For example, the detection results of the sensors can be inaccurate due to the influence of water. For example, water can be generated by chemical reactions during power generation in the fuel cell. Also, for example, water can be generated by condensation from gas in the hydrogen circulation system that is humidified for supply to the fuel cell.

[0014] Inaccurate detection results can interfere with determining the timing of anode off-gas discharge. Therefore, the present inventors have investigated a technology suitable for avoiding a situation in which control of anode off-gas discharge cannot be executed in the presence of error factors that can affect the detection results.

[0015] 1 is a configuration diagram of a fuel cell system 100 according to an embodiment. The fuel cell system 100 includes a circulation path 111, a hydrogen supply path 112, a discharge path 113, an air supply path 114, a water discharge path 115, a fuel cell 120, a humidifier 140, a pump 150, gas-liquid separators 161 and 162, a sensor 170, a discharge valve 180, and a controller 190. In the embodiment, the pump 150 may also be referred to as a hydrogen circulation pump.

[0016] In an embodiment, the fuel cell 120 is a polymer electrolyte fuel cell (PEFC). The fuel cell 120 includes a membrane electrode assembly (MEA) 121. The membrane electrode assembly 121 includes an electrolyte membrane 125, an anode 126, and a cathode 127. The electrolyte membrane 125 is sandwiched between the anode 126 and the cathode 127.

[0017] 1 illustrates one membrane electrode assembly 121. However, in an actual fuel cell 120, a stack is configured. The stack is an assembly of multiple cells. Each cell includes a membrane electrode assembly 121.

[0018] The fuel cell 120 includes a hydrogen supply port 131, an anode off-gas discharge port 133, an air supply port 134, and a water discharge port 135. The hydrogen supply port 131 is a supply port for hydrogen used in power generation by the fuel cell 120. The anode off-gas discharge port 133 is a discharge port for anode off-gas 105 from the anode 126. The air supply port 134 is a supply port for oxygen-containing air 102 used in power generation by the fuel cell 120. The water discharge port 135 is a discharge port for water 106 produced by power generation by the fuel cell 120.

[0019] The circulation path 111 connects the anode off-gas discharge port 133 and the hydrogen supply port 131. In the circulation path 111, the anode off-gas discharge port 133, the gas-liquid separator 161, the pump 150, the gas-liquid separator 162, the discharge position 117, the sensor 170, the supply position 118, the humidifier 140, and the hydrogen supply port 131 appear in this order.

[0020] The hydrogen supply path 112 is connected to the circulation path 111 at a supply position 118. The hydrogen supply path 112 supplies the hydrogen-containing gas 101 to the circulation path 111. The hydrogen-containing gas 101 is supplied to the hydrogen supply path 112 from a supply source (not shown). The supply source is, for example, infrastructure, a tank, etc.

[0021] The concentration of hydrogen in the hydrogen-containing gas 101 is, for example, 70% by volume or more and 100% by volume or less, in one specific example, 80% by volume or more and 100% by volume or less, and in a more specific example, 90% by volume or more and 100% by volume or less.

[0022] In this embodiment, the hydrogen-containing gas 101 is pure hydrogen gas, which has a hydrogen concentration of 90% by volume or more and 100% by volume or less.

[0023] The discharge path 113 is connected to the circulation path 111 at a discharge position 117. A discharge valve 180 is provided in the discharge path 113. When the discharge valve 180 is set to an open state, the anode off-gas 105 is discharged to the outside of the fuel cell system 100 via the discharge path 113.

[0024] The air supply path 114 is connected to an air supply port 134. The water discharge path 115 is connected to a water discharge port 135.

[0025] The sensor 170 is provided in the circulation path 111. In an embodiment, the sensor 170 is an ultrasonic sensor that detects the mass flow rate of hydrogen in the gas using ultrasound. "Detecting" may include calculation. In an embodiment, in the context associated with the sensor 170, the gas flowing through the circulation path 111 is specifically the anode off-gas 105.

[0026] 2 to 4 are explanatory diagrams of a sensor 170 according to an embodiment. In the embodiment, the sensor 170 includes an ultrasonic vibrator 171 and an ultrasonic vibrator 172. In the circulation path 111, the ultrasonic vibrator 171 is provided upstream of the ultrasonic vibrator 172.

[0027] 2, the ultrasonic vibrators 171 and 172 face each other in a direction D1. At a position 119 between the ultrasonic vibrators 171 and 172 in the circulation path 111, the anode off-gas 105 flows in a direction D2. The deviation angle θ of the direction D1 with respect to the direction D2 is non-zero.

[0028] 3, an ultrasonic wave SG1 is transmitted by an ultrasonic transducer 171 and received by an ultrasonic transducer 172. The sensor 170 measures a propagation time t1 of the ultrasonic wave SG1 from transmission to reception. The ultrasonic wave SG1 may be an ultrasonic signal.

[0029] 4, an ultrasonic wave SG2 is transmitted by an ultrasonic transducer 172 and received by an ultrasonic transducer 171. The sensor 170 measures a propagation time t2 of the ultrasonic wave SG2 from transmission to reception of the ultrasonic wave SG2. The ultrasonic wave SG2 may be an ultrasonic signal.

[0030] Because the deviation angle θ is non-zero, a difference Δt occurs between the propagation time t1 and the propagation time t2 when the anode off-gas 105 is flowing at the position 119. The greater the volumetric flow rate (L / min) of the anode off-gas 105 at the position 119, the greater the difference Δt.

[0031] In this embodiment, the sensor 170 estimates the mass flow rate (g / min) of hydrogen in the circulation path 111 based on the propagation time t1 and the propagation time t2. As a result, the sensor 170 obtains an estimated value m of the mass flow rate of hydrogen in the circulation path 111. Specifically, the estimated value m is an estimated value of the mass flow rate of hydrogen in the anode off-gas 105 at the position 119 of the circulation path 111. For information on estimating the mass flow rate of hydrogen based on the propagation time t1 and the propagation time t2, see known documents such as Patent Document 1.

[0032] 5 is an explanatory diagram of the structure and posture of a sensor 170 and a circulation path 111 according to the embodiment. The sensor 170 includes a housing 175. The circulation path 111 passes through the housing 175. An ultrasonic vibrator 171 and an ultrasonic vibrator 172 are housed within the housing 175.

[0033] A portion 111a of the circulation path 111 that is upstream of the housing 175 is located vertically above the housing 175. A portion 111b of the circulation path 111 that is downstream of the housing 175 is located vertically below the housing 175. The portion 111a and the portion 111b are each formed of a pipe.

[0034] 5, the portion of portion 111a surrounded by dotted line DL is enlarged. As shown within the enlarged dotted line DL, condensed water 107 may flow due to gravity along the inner wall of the structure (specifically, the piping) that constitutes portion 111a and enter into housing 175. Alternatively, the flow of anode off-gas 105 in portion 111a may cause water droplets in portion 111a to enter into housing 175. Note that while FIG. 5 depicts condensed water 107 for ease of explanation, portion 111a may be transparent or non-transparent. The same applies to portion 111b.

[0035] A hole (not shown) is provided in the housing 175. Even if water enters the housing 175 from the portion 111a, it flows toward the hole inside the housing 175 and can be discharged vertically downward from the hole. In this way, the housing 175 has a drainage function due to the hole.

[0036] 1, the controller 190 controls the discharge valve 180, the pump 150, the fuel cell 120, etc. based on the detection results of the sensor 170. The "detection results of the sensor 170" will be described below.

[0037] In an embodiment, the detection result of the sensor 170 includes an estimate m.

[0038] In the embodiment, the ultrasonic vibrator 171 of the sensor 170 receives (hereinafter referred to as first reception) ultrasonic waves SG2 that are transmitted from the ultrasonic vibrator 172 of the sensor 170 and are affected by the gas flowing through the circulation path 111. The detection result of the sensor 170 includes a voltage value V1 that is generated in the ultrasonic vibrator 171 by the first reception.

[0039] In the embodiment, the ultrasonic vibrator 172 of the sensor 170 receives (hereinafter, referred to as second reception) ultrasonic waves SG1 that are transmitted from the ultrasonic vibrator 171 of the sensor 170 and are affected by the gas flowing through the circulation path 111. The detection result of the sensor 170 includes a voltage value V2 that is generated in the ultrasonic vibrator 172 by the second reception.

[0040] The controller 190 obtains an estimated value m of the mass flow rate of hydrogen in the circulation path 111 based on the detection result of the sensor 170. Hereinafter, the expression "the controller 190 obtains an estimated value m of the mass flow rate of hydrogen in the circulation path 111 based on the detection result of the sensor 170" will be described. This expression encompasses a first acquisition manner in which the detection result of the sensor 170 includes the estimated value m, and the controller 190 obtains the estimated value m by receiving the estimated value m from the sensor 170. This expression also encompasses a second acquisition manner in which the controller 190 receives the detection result of the sensor 170 from the sensor 170, and obtains the estimated value m by estimating the mass flow rate of hydrogen in the circulation path 111 based on the detection result.

[0041] In the embodiment, an estimated value m is acquired in a first acquisition manner. Specifically, the estimated value m is an estimate of the mass flow rate of hydrogen in a portion 111U of the circulation path 111 that is downstream of the anode off-gas discharge port 133 and upstream of the supply position 118. More specifically, the estimated value m is an estimate of the mass flow rate of hydrogen in a portion 111q of the circulation path 111 that is downstream of the discharge position 117 and upstream of the supply position 118.

[0042] The control modes of the controller 190 include a first mode and a second mode. In this embodiment, the first mode is a normal mode. The second mode is an exception mode. FIG. 6 is a flowchart for explaining the transition between the first mode and the second mode. In FIG. 6, "start" corresponds to, for example, the start of operation of the fuel cell system 100.

[0043] In step S1, the control mode of the controller 190 is set to the first mode. The controller 190 controls the various components of the fuel cell system 100 in the first mode.

[0044] Next, in step S2, the controller 190 determines whether the start condition for the second mode is met. If the start condition is not met, the controller 190 proceeds to step S1, where the first mode is continued. On the other hand, if the start condition is met, the controller 190 proceeds to step S3.

[0045] In step S3, the control mode of the controller 190 is set to the second mode. The controller 190 controls the various components of the fuel cell system 100 in the second mode.

[0046] Next, in step S4, the controller 190 determines whether the termination condition for the second mode is met. If the termination condition is not met, the controller 190 proceeds to step S3, where the second mode continues. On the other hand, if the termination condition is met, the controller 190 proceeds to step S1.

[0047] The first and second modes will be described in detail below. Note that in the description of the second mode, descriptions common to the first and second modes may be omitted.

[0048] 2. First Mode In the first mode, as shown in FIG. 1, hydrogen is supplied to the anode 126 of the fuel cell 120 from the hydrogen supply port 131. The catalyst in the anode 126 causes the hydrogen molecules to release electrons and become hydrogen ions. The released electrons are used as electrical energy. The hydrogen ions move to the cathode 127 through the electrolyte membrane 125.

[0049] Air 102 is supplied from air supply path 114 to cathode 127 of fuel cell 120 via air supply port 134. At cathode 127, hydrogen ions and electrons combine with oxygen molecules in air 102 to produce water 106. Water 106 is discharged to water discharge path 115 via water discharge port 135.

[0050] Anode off-gas 105 containing unreacted hydrogen is discharged from the anode 126 through an anode off-gas outlet 133 to the circulation path 111. The anode off-gas 105 is pressurized by a pump 150. The anode off-gas 105 is dehumidified by gas-liquid separators 161 and 162.

[0051] The anode off-gas 105 then passes through a sensor 170 and reaches a supply position 118. The anode off-gas 105 that has reached the supply position 118 is mixed with the hydrogen-containing gas 101 from the hydrogen supply path 112. In this way, a mixed gas 103 is generated. The mixed gas 103 is humidified by a humidifier 140 and then supplied to the anode 126 of the fuel cell 120 from a hydrogen supply port 131. In this way, hydrogen derived from the fresh hydrogen-containing gas 101 and hydrogen derived from the anode off-gas 105 are supplied to the anode 126.

[0052] As described above, air 102 is supplied to the cathode 127. The air 102 contains not only oxygen but also nitrogen. The nitrogen cross-leaks from the cathode 127 to the anode 126 through the electrolyte membrane 125. As a result, in the hydrogen circulation system 116 including the anode 126 and the circulation path 111, the nitrogen concentration increases, the hydrogen concentration decreases, and the mass flow rate of hydrogen decreases.

[0053] Therefore, the controller 190 executes a discharge process. The discharge process is a process in which the discharge valve 180 in the discharge path 113 is set to an open state, thereby discharging the anode off-gas 105 from the anode off-gas discharge port 133 via the discharge path 113. The discharge process reduces the nitrogen concentration in the hydrogen circulation system 116, and can restore (i.e., increase) the mass flow rate of hydrogen. This can restore the mass flow rate of hydrogen supplied to the fuel cell 120. This can ensure the power generation efficiency of the fuel cell 120 and suppress deterioration of the fuel cell 120.

[0054] In the first mode, the controller 190 executes the discharge process when the estimated value m of the mass flow rate of hydrogen in the circulation path 111 falls below the target value R. This configuration allows the discharge process to be executed in a timely manner. During the discharge process, hydrogen is discharged along with nitrogen. The timely discharge process makes it possible to reduce the nitrogen concentration while preventing excessive discharge of hydrogen.

[0055] 7 is a graph showing an example of how the estimated value m changes over time. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the estimated value m. The time during which the estimated value m decreases corresponds to the time during which the nitrogen concentration in the hydrogen circulation system 116 increases. The time during which the estimated value m recovers (i.e., increases) corresponds to the time during which the discharge process is being performed.

[0056] 7, in the first mode, the discharge process can be performed intermittently. In the first mode, the controller 190 performs feedback control using the detection result of the sensor 170 so as to prevent the estimated value m from continuing to be lower than the target value R.

[0057] [3. Second Mode] In the embodiment, the start condition for the second mode is set so that the control mode switches from the first mode to the second mode when an abnormality occurs in the detection result of the sensor 170. In the second mode, the controller 190 continues the abnormality response control triggered by the occurrence of an abnormality in the detection result. Therefore, the controller 190 executes the abnormality response control when an abnormality occurs in the detection result of the sensor 170. In the abnormality response control, a discharge process is executed. This configuration can avoid a situation in which control to discharge the anode off-gas 105 cannot be executed in the presence of an error factor that may affect the detection result.

[0058] In the abnormality response control of the embodiment, the discharge process is continuously executed. Therefore, in the second mode, the controller 190 continues the discharge process triggered by the occurrence of an abnormality in the detection result of the sensor 170. Specifically, in the second mode, the controller 190 maintains the discharge valve 180 in an open state.

[0059] In the embodiment, the abnormality in the detection result of the sensor 170 is an abnormality that appears due to the influence of water. This configuration can avoid a situation in which control to discharge the anode off-gas 105 cannot be executed in the presence of water that could affect the detection result. The water can be water droplets. The water that causes the abnormality can be water 106 generated by a chemical reaction during power generation in the fuel cell 120, water that is generated by condensation of gas in the hydrogen circulation system 116 that is humidified by the humidifier 140, or the like. In the example of FIG. 5 , the water that causes the abnormality can be condensed water 107 that has entered the housing 175, water droplets that have entered the housing 175 due to the flow of the anode off-gas 105, or the like.

[0060] In this embodiment, the sensor 170 is provided in the portion 111U. In this case, water is likely to affect the detection results of the sensor 170. This is because the portion 111U is likely to be in a high humidity state due to water 106 produced by a chemical reaction during power generation in the fuel cell 120. In this case, it is possible to obtain a significant benefit in that it is possible to avoid a situation in which control for discharging the anode off-gas 105 cannot be executed in the presence of water that may affect the detection results. Specifically, the sensor 170 is provided in the portion 111q.

[0061] In the embodiment, the controller 190 is configured to execute abnormality response control when water is present on the propagation path of the ultrasonic waves SGx. The ultrasonic waves SGx are the ultrasonic waves SG1 or SG2. This configuration makes it possible to avoid a situation in which control to discharge the anode off-gas 105 cannot be executed in the presence of water that may affect the detection results of the sensor 170 based on the ultrasonic waves SGx. In the embodiment, the propagation path of the ultrasonic waves SGx includes an area on the ultrasonic wave transmission / reception surface of the ultrasonic transducer 171, an area on the ultrasonic wave transmission / reception surface of the ultrasonic transducer 172, and an area where the ultrasonic waves propagate between the transmission / reception surface of the ultrasonic transducer 171 and the transmission / reception surface of the ultrasonic transducer 172.

[0062] In this embodiment, during abnormality response control triggered by the occurrence of an abnormality in the detection result of the sensor 170, if the estimated value m is lower than the threshold value, the controller 190 increases the discharge pressure of the pump 150. This configuration makes it easier to avoid a shortage of hydrogen in the fuel cell 120. The threshold value is, for example, 1.2 to 10 times the target value R.

[0063] In one example, the condition for terminating the second mode is that a predetermined time has elapsed since switching from the first mode to the second mode. Therefore, the controller 190 terminates the abnormality response control triggered by the occurrence of an abnormality in the detection result of the sensor 170 at the predetermined time. This condition may be based on the assumption that the abnormality in the detection result of the sensor 170 will be resolved within the predetermined time. The predetermined time is, for example, between 3 minutes and 300 minutes.

[0064] For example, consider a case where an abnormality in the detection result of sensor 170 is caused by the influence of water. In this embodiment, gas-liquid separators 161 and 162 are provided. Sensor 170 also has a drainage function due to holes in its housing 175. Therefore, the abnormality in the detection result of sensor 170 can be resolved over time.

[0065] In one example, the controller 190 terminates the abnormality response control that was triggered when an abnormality occurred in the detection result of the sensor 170 when the abnormality has been resolved.

[0066] In the embodiment, the abnormality in the detection result of sensor 170 is an abnormality that is stored in advance in controller 190. Controller 190 is configured to be able to determine an abnormality in the detection result of sensor 170. A start condition for the second mode is a condition that controller 190 has determined an abnormality in the detection result of sensor 170. A termination condition for the second mode is a condition that controller 190 has determined that the abnormality in the detection result of sensor 170 has been resolved.

[0067] In the first example, the abnormality in the detection result of the sensor 170 is an abnormality in the estimated value m. The start condition for the second mode is set so that the control mode switches from the first mode to the second mode when a first predetermined condition is satisfied. In the second mode, the controller 190 continues the abnormality response control triggered by the satisfaction of the first predetermined condition. Therefore, the controller 190 starts the abnormality response control when the first predetermined condition is satisfied. The first predetermined condition is a condition that the estimated value m is smaller than the target value R by a predetermined value or more. The predetermined value is a value greater than zero. As can be understood from the above description, in this embodiment, the estimated value m gradually decreases due to nitrogen cross leak. In one specific example of the first example, the predetermined value is set so that the first predetermined condition is not satisfied solely due to nitrogen cross leak, and the effect of water on the detection value of the sensor 170 satisfies the first predetermined condition. Therefore, if the mass flow rate of hydrogen in the hydrogen circulation system 116 decreases due to nitrogen cross-leakage, the discharge process in the first mode may be initiated, whereas if water is affecting the detection value of the sensor 170, the discharge process in the second mode may be initiated.

[0068] Specifically, in a first example, the condition for starting the second mode is that a first predetermined condition continues to be met for a first predetermined time. Therefore, the controller 190 starts abnormality response control when the first predetermined condition continues to be met for the first predetermined time. The first predetermined time is, for example, longer than 0 minutes and equal to or shorter than 30 minutes. Specifically, the first predetermined time may be, for example, greater than 1 minute and equal to or shorter than 30 minutes.

[0069] In the first example, the termination condition for the second mode is set so that the control mode switches from the second mode to the first mode when a second predetermined condition is satisfied. Therefore, the controller 190 terminates the abnormality response control triggered by the satisfaction of the first predetermined condition when the second predetermined condition is satisfied. The second predetermined condition is a condition in which the estimated value m is equal to or greater than the target value R.

[0070] Specifically, in the first example, the condition for terminating the second mode is that the second predetermined condition continues to be satisfied for a second predetermined time. Therefore, the controller 190 terminates the abnormality response control triggered by the satisfaction of the first predetermined condition when the second predetermined condition continues to be satisfied for the second predetermined time. The second predetermined time is, for example, from 3 minutes to 300 minutes.

[0071] As can be understood from the above explanation, in the first example, the abnormality response control triggered by the occurrence of an abnormality in the detection result of sensor 170 is abnormality response control triggered by the occurrence of an abnormality in the estimated value m, specifically, abnormality response control triggered by the satisfaction of a first predetermined condition, and more specifically, abnormality response control that is initiated when the satisfaction of the first predetermined condition continues for a first predetermined time.

[0072] In a second example, the abnormality detected by the sensor 170 is an abnormality in the voltage value Vx. The voltage value Vx is the voltage value V1 or the voltage value V2. The start condition for the second mode is set so that the control mode switches from the first mode to the second mode when a first specific condition is met. In the second mode, the controller 190 continues the abnormality response control triggered by the first specific condition being met. Therefore, the controller 190 starts the abnormality response control when the first specific condition is met. The first specific condition is a condition in which the voltage value Vx is smaller than a specific value. Typically, the specific value is a value smaller than the rated value of the voltage value Vx. For example, the specific value is a voltage value that is equal to or smaller than 1 / 5 of the rated value of the voltage value Vx.

[0073] Specifically, in the second example, the condition for starting the second mode is that the first specific condition has been met for a first specific time. Therefore, the controller 190 starts abnormality response control when the first specific condition has been met for the first specific time. The first specific time is, for example, longer than 0 minutes and less than or equal to 30 minutes. Specifically, the first specific time may be, for example, 1 second or longer and less than or equal to 30 minutes, or 5 seconds or longer and less than or equal to 30 minutes.

[0074] In the second example, the termination condition for the second mode is set so that the control mode switches from the second mode to the first mode when a second specific condition is satisfied. Therefore, the controller 190 terminates the abnormality response control triggered by the satisfaction of the first specific condition when the second specific condition is satisfied. The second specific condition is a condition in which the voltage value Vx is equal to or greater than a specific value.

[0075] Specifically, in the second example, the condition for terminating the second mode is that the second specific condition has been met for a second specific time. Therefore, the controller 190 terminates the abnormality response control triggered by the first specific condition being met when the second specific condition has been met for a second specific time. The second specific time is, for example, 3 minutes or more and 300 minutes or less.

[0076] As can be understood from the above explanation, in the second example, the abnormality response control triggered by the occurrence of an abnormality in the detection result of sensor 170 is abnormality response control triggered by the occurrence of an abnormality in the voltage value Vx, specifically, abnormality response control triggered by the satisfaction of a first specific condition, and more specifically, abnormality response control that is initiated when the satisfaction of the first specific condition continues for a first specific time.

[0077] In the embodiment, in the first mode, the controller 190 controls the discharge pressure of the pump 150 based on the detection result of the sensor 170, and executes a discharge process when the estimated value m drops below the target value R. When an abnormality occurs in the detection result of the sensor 170, the controller 190 switches the control mode from the first mode to the second mode. In the second mode, the controller 190 does not reflect the detection result in the control of the discharge pressure of the pump 150, and continues the abnormality response control triggered by the occurrence of an abnormality in the detection result of the sensor 170.

[0078] According to the above configuration, in the first mode, the pump 150 can adjust the amount of gas circulated through the circulation path 111 and perform timely discharge processing based on information about the circulation path 111 from the sensor 170. This allows the supply of hydrogen to the fuel cell 120 to be appropriately controlled, and hydrogen consumption in the fuel cell 120 to be adjusted within a target range. This makes it possible to suppress deterioration of the fuel cell 120 and ensure the power generation efficiency of the fuel cell 120. Furthermore, according to the above configuration, in the second mode, problems caused by inaccurate detection results from the sensor 170 can be avoided. For example, a problem could occur where the controller 190 is unable to obtain an accurate estimate of m and therefore is unable to discharge the anode off-gas 105. Another example could occur where the controller 190 generates an inappropriate control command based on the inaccurate detection result and sends the control command to the pump 150, resulting in an insufficient supply of hydrogen to the fuel cell 120.

[0079] In this embodiment, in the second mode, the controller 190 controls the discharge pressure of the pump 150 to a constant value that corresponds to the power generated by the fuel cell 120. This configuration allows the fuel cell 120 to continue generating power, while avoiding a situation in which the fuel cell 120 is degraded due to an insufficient supply of hydrogen to the fuel cell 120 caused by an inaccurate detection result from the sensor 170.

[0080] (Technologies Applicable to the Embodiments) Various technologies can be applied to the embodiments. Unless there is a particular contradiction, a combination of the technologies described below may be applied to the embodiments.

[0081] The first and second examples may be combined. In one example, the start condition for the second mode is set so that the control mode switches from the first mode to the second mode when at least one of a first predetermined condition and a first specific condition is satisfied. Specifically, the start condition for the second mode is at least one of the following conditions: that the first predetermined condition continues to be satisfied for a first predetermined time; and that the first specific condition continues to be satisfied for a first specific time. When the second mode is started upon satisfaction of the first predetermined condition, the control related to the second mode described in the first example of the embodiment may be performed, such as continuing the abnormality response control triggered by the satisfaction of the first predetermined condition in the second mode. When the second mode is started upon satisfaction of the first specific condition, the control related to the second mode described in the second example of the embodiment may be performed, such as continuing the abnormality response control triggered by the satisfaction of the first specific condition in the second mode.

[0082] It is not essential that the control modes of the controller 190 have the first mode and the second mode. The number of control modes of the controller 190 may be one.

[0083] The discharge valve 180 may be an on-off valve or a flow rate adjusting valve. Here, the on-off valve is a valve whose opening degree is set to one of two values, 0% (fully closed) and 100% (fully open). The flow rate adjusting valve is a valve that can have an opening degree not only of 0% or 100%, but also greater than 0% and less than 100%.

[0084] The configuration of the sensor is not limited to the configuration of the sensor 170 shown in Figures 2 to 4. Figures 8 and 9 are explanatory diagrams of a sensor 270 according to a modified example. The sensor 270 is an ultrasonic sensor. The sensor 270 includes an ultrasonic vibrator 271, an ultrasonic vibrator 272, and a reflection position 273. The reflection position 273 may be part of the inner wall of a structure (e.g., a pipe) that constitutes the circulation path 111. In the circulation path 111, the ultrasonic vibrator 271 is provided upstream of the reflection position 273, and the reflection position 273 is provided upstream of the ultrasonic vibrator 272.

[0085] The direction in which the ultrasonic vibrator 271 and the reflection position 273 face each other deviates from the flow direction D3 of the anode off-gas 105 at a position 218 therebetween. The direction in which the reflection position 273 and the ultrasonic vibrator 272 face each other deviates from the flow direction D4 of the anode off-gas 105 at a position 219 therebetween.

[0086] 8, an ultrasonic wave SG1 is transmitted by an ultrasonic transducer 271, reflected at a reflection position 273, and received by an ultrasonic transducer 272. The sensor 270 measures the propagation time t1 of the ultrasonic wave SG1 from transmission to reception.

[0087] 9, an ultrasonic wave SG2 is transmitted by an ultrasonic transducer 272, reflected at a reflection position 273, and received by an ultrasonic transducer 271. The sensor 270 measures a propagation time t2 of the ultrasonic wave SG2 from transmission to reception.

[0088] In the embodiment, the sensor 170 estimates the mass flow rate of hydrogen in the circulation path 111 based on the propagation time t1 and the propagation time t2. As a result, the sensor 170 obtains an estimated value m of the mass flow rate of hydrogen in the circulation path 111. Such estimation of the mass flow rate can be performed, for example, as follows. That is, the sensor 170 calculates the volumetric flow rate of the gas in the circulation path 111 and the hydrogen concentration of the gas based on the propagation time t1 and the propagation time t2. The sensor 170 calculates the estimated value m by multiplying the calculated value of the volumetric flow rate by the calculated value of the hydrogen concentration. This example belongs to the first acquisition mode. As described above, in the first acquisition mode, the detection result of the sensor 170 includes the estimated value m. The controller 190 receives the estimated value m from the sensor 170. As a result, the controller 190 obtains the estimated value m.

[0089] As described above, the second acquisition mode can also be employed. In one example of the second acquisition mode, the sensor 170 calculates the volumetric flow rate of the gas in the circulation path 111 and the hydrogen concentration of the gas based on the propagation time t1 and the propagation time t2. The detection results of the sensor 170 include a calculated value of the volumetric flow rate and a calculated value of the hydrogen concentration. The controller 190 receives the calculated value of the volumetric flow rate and the calculated value of the hydrogen concentration from the sensor 170. The controller 190 calculates the estimated value m by multiplying the calculated value of the volumetric flow rate by the calculated value of the hydrogen concentration. In this way, the controller 190 obtains the estimated value m.

[0090] The mass flow rate of hydrogen may be calculated by subtracting the mass flows of components other than hydrogen from the mass flow rates of the components in the gas in the circulation path 111. In this way, an estimated value m can also be obtained.

[0091] The sensor 170 in the examples of Figures 2 to 4 and 8 and 9 is a transit time type ultrasonic sensor. However, a Doppler type ultrasonic sensor or a sensor other than an ultrasonic sensor may also be used. An example of a sensor other than an ultrasonic sensor is a thermal sensor. An example of a thermal sensor is a MEMS (Micro Electro Mechanical Systems) sensor.

[0092] In one example using a MEMS sensor, the MEMS sensor includes a heater and multiple thermometers. The multiple thermometers include a first pair of thermometers and a second pair of thermometers. The first pair of thermometers are arranged on either side of the heater in the gas flow direction in the circulation path 111. The second pair of thermometers are arranged on either side of the heater in a direction that allows the same temperature to be obtained regardless of the gas flow. The MEMS sensor detects a temperature distribution between the first pair of thermometers (hereinafter referred to as the first temperature distribution), a temperature distribution between the second pair of thermometers (hereinafter referred to as the second temperature distribution), and an absolute value of the gas temperature. The MEMS sensor calculates the volumetric flow rate of the gas in the circulation path 111 and the hydrogen concentration of the gas based on the detected values ​​of the first temperature distribution, the detected values ​​of the second temperature distribution, and the detected values ​​of the absolute value of the temperature. The MEMS sensor calculates an estimated value m by multiplying the calculated volumetric flow rate by the calculated hydrogen concentration. As a result, the MEMS sensor obtains an estimated value m of the mass flow rate of hydrogen in the circulation path 111. The detection result of the MEMS sensor includes the estimated value m. The controller 190 receives the estimated value m from the MEMS sensor. As a result, the controller 190 obtains the estimated value m. This example belongs to the first obtaining mode.

[0093] In another example using a MEMS sensor, the MEMS sensor includes a heater and multiple thermometers. The multiple thermometers include a first pair of thermometers and a second pair of thermometers. The first pair of thermometers are arranged on either side of the heater in the gas flow direction in the circulation path 111. The second pair of thermometers are arranged on either side of the heater in a direction that allows the same temperature to be obtained regardless of the gas flow. The MEMS sensor detects a temperature distribution between the first pair of thermometers (hereinafter referred to as the first temperature distribution), a temperature distribution between the second pair of thermometers (hereinafter referred to as the second temperature distribution), and an absolute value of the gas temperature. The detection results of the MEMS sensor include a detected value of the first temperature distribution, a detected value of the second temperature distribution, and a detected value of the absolute value of the temperature. The controller 190 receives the detected values ​​of the first temperature distribution, the detected value of the second temperature distribution, and the detected value of the absolute value of the temperature from the MEMS sensor. The controller 190 calculates the volumetric flow rate of the gas and the hydrogen concentration of the gas in the circulation path 111 based on the detected value of the first temperature distribution, the detected value of the second temperature distribution, and the detected value of the absolute value of the temperature. The controller 190 calculates an estimated value m by multiplying the calculated value of the volumetric flow rate by the calculated value of the hydrogen concentration. In this way, the controller 190 obtains the estimated value m of the mass flow rate of hydrogen in the circulation path 111. This example belongs to the second obtaining mode.

[0094] Other examples of sensors besides ultrasonic sensors include thermal conduction sensors and calorimeters. Thermal conduction sensors measure gas concentration by utilizing differences in the way heat is transmitted inherently through gases. Calorimeters convert incident high-frequency waves into heat by absorbing them in a load, and measure the high-frequency power by referencing the DC power that generates an equivalent amount of heat.

[0095] The location where the sensor 170 is provided is not limited to the portion 111q of the circulation path 111. The estimated value m is not limited to the estimated value of the mass flow rate of hydrogen in the portion 111q.

[0096] 10 is a configuration diagram of a fuel cell system 300 according to a modified example. In this modified example, the sensor 170 is provided in a portion 111p of the circulation path 111 that is downstream of the anode off-gas discharge port 133 and upstream of the discharge position 117. The estimated value m is an estimate of the mass flow rate of hydrogen in the portion 111p.

[0097] 11 is a configuration diagram of a fuel cell system 400 according to another modification. In this modification, the sensor 170 is provided in a portion 111D of the circulation path 111 that is downstream of the supply position 118 and upstream of the hydrogen supply port 131. The estimated value m is an estimated value of the mass flow rate of hydrogen in the portion 111D. This modification can be explained by appropriately changing the terms used in the description of the embodiment. Such changes include, for example, changing "anode off-gas 105" to "mixed gas 103."

[0098] In the abnormality response control of the embodiment, the discharge process is executed continuously. In other words, in the abnormality response control of the embodiment, the discharge time T1, which will be described later, appears continuously. However, in the abnormality response control, the discharge process may be executed intermittently. FIG. 12 is an explanatory diagram of the intermittent discharge process. In FIG. 12, the horizontal axis represents time, and the vertical axis represents the opening degree of the discharge valve 180.

[0099] 12 , in the intermittent discharge process, discharge time T1 and pause time T2 alternate. Discharge time T1 is the time during which the discharge process is performed. Pause time T2 is the time during which the discharge process is paused. Specifically, during discharge time T1, the discharge valve 180 is maintained in an open state. During pause time T2, the discharge valve 180 is maintained in a closed state.

[0100] Specifically, in the example of FIG. 12, in the intermittent discharge process in the abnormality response control, the controller 190 sets at least one selected from the group consisting of: (a) the length of the discharge time T1; (b) the length of the pause time T2; and (c) the ratio of the length of the discharge time T1 to the sum of the length of the discharge time T1 and the length of the pause time T2, in accordance with the power generation power of the fuel cell 120.

[0101] Unless there is a particular contradiction, in the above description, "when an abnormality occurs in the detected value of the sensor" may be read as "when water is present on the propagation path of the ultrasonic waves." For example, this may be done in the description of the intermittent discharge process.

[0102] As can be understood from the above description, the present disclosure discloses a control method for a fuel cell system. From a first viewpoint, the control method includes a step of executing an abnormality response control when an abnormality occurs in the detection result of a sensor. Also, from a second viewpoint, the control method includes a step of executing an abnormality response control when water is present on a propagation path of ultrasonic waves.

[0103] A computer program may be configured with instructions that, when executed by a processor, cause the processor to perform the control method, such as a central processing unit (CPU), an application specific integrated circuit (ASIC), or a field programmable gate array (FPGA).

[0104] The computer program can be recorded on a non-transitory computer-readable recording medium. Examples of the recording medium include semiconductor recording media, magnetic recording media, magneto-optical recording media, and optical recording media. Examples of the semiconductor recording media include secure digital (SD) cards, universal serial bus (USB) memories, and solid state drives (SSDs). Examples of the magnetic recording media include hard disk drives (HDDs) and flexible disks. Examples of the magneto-optical recording media include magneto-optical disks (MOs). Examples of the optical recording media include compact discs (CDs) and digital versatile discs (DVDs).

[0105] (Additional Note) The present disclosure discloses the following techniques.

[0106] (Technology 1) A fuel cell system comprising: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; a sensor provided in the circulation path; and a controller that executes abnormality response control when an abnormality occurs in the detection result of the sensor, wherein the abnormality response control executes a discharge process in which the discharge valve is set to an open state to discharge anode off-gas from the anode off-gas discharge port via the discharge path.

[0107] (Technology 2) The fuel cell system according to Technology 1, wherein the abnormality is an abnormality caused by the influence of water.

[0108] (Technology 3) The fuel cell system according to Technology 1 or 2, wherein the controller terminates the abnormality response control after a given time.

[0109] (Technology 4) The fuel cell system according to any one of Technologies 1 to 3, wherein the controller terminates the abnormality response control when the abnormality detected as a result of the detection is resolved.

[0110] (Technology 5) The fuel cell system according to any one of Technologies 1 to 4, wherein the controller obtains an estimate of a mass flow rate of hydrogen in the circulation path based on the detection result, and the controller starts the abnormality response control when a first predetermined condition is met that the estimate is smaller than a target value by a predetermined value or more.

[0111] (Technology 6) The fuel cell system according to Technology 5, wherein the controller starts the abnormality response control when the first predetermined condition continues to be satisfied for a first predetermined time.

[0112] (Technology 7) A fuel cell system according to Technology 5 or 6, wherein the control modes of the controller include a first mode and a second mode, and the controller executes the discharge process in the first mode when the estimated value falls below the target value, switches the control mode from the first mode to the second mode when the first predetermined condition is met, and continues the abnormality response control in the second mode.

[0113] (Technology 8) The fuel cell system according to any one of Techniques 5 to 7, wherein the controller terminates the abnormality response control when a second predetermined condition is satisfied, that is, the estimated value is equal to or greater than a target value.

[0114] (Technology 9) The fuel cell system according to Technology 8, wherein the controller terminates the abnormality response control when the second predetermined condition continues to be satisfied for a second predetermined time.

[0115] (Technology 10) A fuel cell system according to any one of technologies 1 to 9, wherein the sensor receives ultrasonic waves transmitted from the sensor and acted upon by the gas flowing through the circulation path, the detection result includes a voltage value generated in the sensor by the reception, and the controller starts the abnormality response control when a first specific condition is met that the voltage value is smaller than a specific value.

[0116] (Technology 11) The fuel cell system according to Technology 10, wherein the controller starts the abnormality response control when the first specific condition continues to be satisfied for a first specific time.

[0117] (Technology 12) The fuel cell system according to Technology 10 or 11, wherein the controller terminates the abnormality response control when a second specific condition is met, that is, the voltage value is equal to or greater than a specific value.

[0118] (Technology 13) The fuel cell system according to Technology 12, wherein the controller terminates the abnormality response control when the second specific condition continues to be satisfied for a second specific time.

[0119] (Technology 14) The fuel cell system according to any one of technologies 1 to 13, further comprising a pump provided in the circulation path, wherein the controller obtains an estimate of the mass flow rate of hydrogen in the circulation path based on the detection result, and increases the discharge pressure of the pump if the estimate is lower than a threshold during the abnormality response control.

[0120] (Technology 15) The fuel cell system according to any one of Technologies 1 to 14, wherein the circulation path includes a portion downstream of the anode off-gas discharge port and upstream of the supply position, and the sensor is provided in the portion.

[0121] (Technology 16) The fuel cell system according to any one of technologies 1 to 15, further comprising: a pump provided in the circulation path; wherein the control modes of the controller include a first mode and a second mode; wherein the controller: obtains an estimate of the mass flow rate of hydrogen in the circulation path based on the detection result; in the first mode, controls the discharge pressure of the pump based on the detection result, and executes the discharge process when the estimate drops below a target value; when the abnormality occurs, switches the control mode from the first mode to the second mode; and in the second mode, continues the abnormality response control without reflecting the detection result in the control of the discharge pressure of the pump.

[0122] (Technology 17) The fuel cell system according to Technology 16, wherein the controller controls the discharge pressure of the pump to a constant value according to the power generated by the fuel cell in the second mode.

[0123] (Technology 18) The fuel cell system according to any one of Technologies 1 to 17, wherein the hydrogen-containing gas is pure hydrogen gas.

[0124] (Technology 19) The fuel cell system according to any one of Technologies 1 to 18, wherein the discharge process is continuously executed in the abnormality response control.

[0125] (Technology 20) The fuel cell system according to any one of Technologies 1 to 18, wherein in the abnormality response control, the discharge process is intermittently executed in a manner that discharge periods during which the discharge process is executed and pause periods during which the discharge process is paused alternate.

[0126] (Technology 21) The fuel cell system according to Technology 20, wherein the controller, in the abnormality response control, sets at least one selected from the group consisting of: (a) the length of the discharge time; (b) the length of the pause time; and (c) the ratio of the length of the discharge time to the sum of the length of the discharge time and the length of the pause time, in accordance with the power generated by the fuel cell.

[0127] (Technology 22) A fuel cell system comprising: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; a sensor provided in the circulation path; and a controller, wherein the sensor receives ultrasonic waves transmitted from the sensor and affected by gas flowing through the circulation path; and the controller performs abnormality response control when water is present on the propagation path of the ultrasonic waves, and the abnormality response control performs a discharge process in which the discharge valve is set to an open state to discharge anode off-gas from the anode off-gas discharge port via the discharge path.

[0128] (Technology 23) The fuel cell system according to Technology 22, wherein the discharge process is continuously executed in the abnormality response control.

[0129] (Technology 24) The fuel cell system according to Technology 22, wherein in the abnormality response control, the discharge process is intermittently executed in a manner in which discharge periods during which the discharge process is executed and pause periods during which the discharge process is paused alternate.

[0130] (Technology 25) The fuel cell system according to Technology 24, wherein the controller, in the abnormality response control, sets at least one selected from the group consisting of: (a) the length of the discharge time; (b) the length of the pause time; and (c) the ratio of the length of the discharge time to the sum of the length of the discharge time and the length of the pause time, in accordance with the power generated by the fuel cell.

[0131] (Technology 26) A control method for a fuel cell system including: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; and a sensor provided in the circulation path, the control method including performing abnormality response control when an abnormality occurs in the detection result of the sensor, wherein the abnormality response control performs a discharge process of discharging anode off-gas from the anode off-gas discharge port via the discharge path by setting the discharge valve to an open state.

[0132] (Technology 27) A control method for a fuel cell system comprising: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; and a sensor provided in the circulation path, wherein the sensor receives ultrasonic waves transmitted from the sensor and affected by gas flowing through the circulation path, the control method including performing an abnormality response control when water is present on a propagation path of the ultrasonic waves, the abnormality response control including performing a discharge process of discharging anode off-gas from the anode off-gas discharge port via the discharge path by setting the discharge valve to an open state.

[0133] (Technique 28) A computer program comprising instructions that, when executed by a processor, cause the processor to perform the control method according to Technique 26 or 27.

[0134] (Technology 29) A computer-readable non-transitory recording medium on which the computer program according to Technology 28 is recorded.

[0135] For example, in one example of the present disclosure, there is a temporary period in which the sensor detection results are inaccurate due to the influence of water. According to the technology of the present disclosure, even during this period, it is possible to avoid situations that impede control. The situation that impedes control includes a situation in which control to discharge anode off-gas cannot be executed. Furthermore, from the perspective of the controlled object, the situation that impedes control includes a situation in which the controller issues an inappropriate control command to the discharge valve and / or pump, causing the discharge valve and / or pump to operate inappropriately. According to the technology of the present disclosure, even during the above-mentioned period, the controller can set the discharge valve to an open state to discharge anode off-gas, and the pump can continue to operate, thereby allowing the fuel cell to continue generating electricity.

Claims

1. A fuel cell system comprising: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; a sensor provided in the circulation path; and a controller that executes abnormality response control when an abnormality occurs in the detection result of the sensor, wherein the abnormality response control executes a discharge process in which the discharge valve is set to an open state to discharge anode off-gas from the anode off-gas discharge port via the discharge path.

2. The fuel cell system according to claim 1, wherein the abnormality is an abnormality caused by the influence of water.

3. The fuel cell system according to claim 1, wherein the controller terminates the abnormality response control after a given time.

4. The fuel cell system according to claim 1, wherein the controller terminates the abnormality response control when the abnormality detected by the detection result has been resolved.

5. The fuel cell system of claim 1, wherein the controller obtains an estimate of the mass flow rate of hydrogen in the circulation path based on the detection result, and the controller initiates the abnormality response control when a first predetermined condition is met that the estimate is smaller than a target value by a predetermined value or more.

6. The fuel cell system according to claim 5, wherein the controller starts the abnormality response control when the first predetermined condition continues to be satisfied for a first predetermined time.

7. A fuel cell system as described in claim 5, wherein the control modes of the controller include a first mode and a second mode, and the controller executes the discharge process in the first mode when the estimated value falls below the target value, switches the control mode from the first mode to the second mode when the first predetermined condition is met, and continues the abnormality response control in the second mode.

8. The fuel cell system according to claim 5, wherein the controller terminates the abnormality response control when a second predetermined condition is met, that is, the estimated value is equal to or greater than a target value.

9. The fuel cell system according to claim 8, wherein the controller terminates the abnormality response control when the second predetermined condition continues to be satisfied for a second predetermined time.

10. The fuel cell system described in claim 1, wherein the sensor receives ultrasonic waves transmitted from the sensor and acted upon by the gas flowing through the circulation path, the detection result includes a voltage value generated in the sensor by the reception, and the controller initiates the abnormality response control when a first specific condition is met in which the voltage value is smaller than a specific value.

11. The fuel cell system according to claim 10, wherein the controller starts the abnormality response control when the first specific condition continues to be met for a first specific time.

12. The fuel cell system according to claim 10, wherein the controller terminates the abnormality response control when a second specific condition is met, that is, the voltage value is equal to or greater than a specific value.

13. The fuel cell system according to claim 12, wherein the controller terminates the abnormality response control when the second specific condition continues to be satisfied for a second specific time.

14. The fuel cell system of claim 1, further comprising a pump provided in the circulation path, and the controller obtains an estimate of the mass flow rate of hydrogen in the circulation path based on the detection result, and increases the discharge pressure of the pump if the estimate is lower than a threshold value during the abnormality response control.

15. The fuel cell system according to claim 1, wherein the circulation path includes a portion downstream of the anode off-gas discharge port and upstream of the supply position, and the sensor is provided in the portion.

16. The fuel cell system according to claim 1, wherein the fuel cell system comprises a pump provided in the circulation path, the control modes of the controller have a first mode and a second mode, the controller: obtains an estimate of the mass flow rate of hydrogen in the circulation path based on the detection result, controls the discharge pressure of the pump based on the detection result in the first mode, and executes the discharge process when the estimated value drops below a target value, when the abnormality occurs, switches the control mode from the first mode to the second mode, and continues the abnormality response control in the second mode without reflecting the detection result in the control of the discharge pressure of the pump.

17. The fuel cell system according to claim 16, wherein in the second mode, the controller controls the discharge pressure of the pump to a constant value according to the power generated by the fuel cell.

18. The fuel cell system according to claim 1, wherein the hydrogen-containing gas is pure hydrogen gas.

19. The fuel cell system according to claim 1, wherein the discharge process is continuously performed during the abnormality response control.

20. The fuel cell system according to claim 1, wherein in the abnormality response control, the discharge process is performed intermittently in a manner that discharge periods during which the discharge process is performed and pause periods during which the discharge process is paused alternate with each other.

21. The fuel cell system of claim 20, wherein the controller, in the abnormality response control, sets at least one selected from the group consisting of: (a) the length of the discharge time; (b) the length of the pause time; and (c) the ratio of the length of the discharge time to the sum of the length of the discharge time and the length of the pause time, in accordance with the power generated by the fuel cell.

22. A fuel cell system comprising: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; a sensor provided in the circulation path; and a controller, wherein the sensor receives ultrasonic waves transmitted from the sensor and affected by gas flowing through the circulation path; and the controller performs abnormality response control when water is present on the propagation path of the ultrasonic waves, and the abnormality response control performs a discharge process in which the discharge valve is set to an open state to discharge anode off-gas from the anode off-gas discharge port via the discharge path.

23. The fuel cell system according to claim 22, wherein the discharge process is continuously performed during the abnormality response control.

24. The fuel cell system according to claim 22, wherein in the abnormality response control, the discharge process is performed intermittently in a manner that discharge periods during which the discharge process is performed and pause periods during which the discharge process is paused alternate with each other.

25. The fuel cell system of claim 24, wherein the controller, in the abnormality response control, sets at least one selected from the group consisting of: (a) the length of the discharge time; (b) the length of the pause time; and (c) the ratio of the length of the discharge time to the sum of the length of the discharge time and the length of the pause time, in accordance with the power generated by the fuel cell.

26. A control method for a fuel cell system including: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; and a sensor provided in the circulation path, the control method including executing abnormality response control when an abnormality occurs in the detection result of the sensor, wherein the abnormality response control executes a discharge process in which the discharge valve is set to an open state to discharge anode off-gas from the anode off-gas discharge port via the discharge path.

27. A control method for a fuel cell system comprising: a fuel cell having a hydrogen supply port and an anode off-gas discharge port; a circulation path in which the anode off-gas discharge port, a discharge position, a supply position, and the hydrogen supply port appear in this order; a supply path connected to the circulation path at the supply position and supplying a hydrogen-containing gas to the circulation path; a discharge path connected to the circulation path at the discharge position; a discharge valve provided in the discharge path; and a sensor provided in the circulation path, wherein the sensor receives ultrasonic waves transmitted from the sensor and affected by gas flowing through the circulation path, the control method including executing abnormality response control when water is present on the propagation path of the ultrasonic waves, the abnormality response control including setting the discharge valve to an open state and performing a discharge process to discharge anode off-gas from the anode off-gas discharge port via the discharge path.

28. A computer program comprising instructions which, when executed by a processor, cause the processor to carry out a control method according to claim 26 or 27.

29. A computer-readable non-transitory recording medium on which the computer program according to claim 28 is recorded.

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