Fuel cell system

Abstract

The present invention provides a fuel cell system capable of detecting cathode gas leaks during normal operation and identifying the location of the leak. [Solution] The fuel cell system of the present invention comprises a fuel cell that generates electricity by the reaction of anode gas and cathode gas, a cathode gas supply passage, a cathode gas discharge passage, a compressor that pressurizes and pumps cathode gas, a back pressure valve that opens and closes the cathode gas discharge passage, a pressure detection means for detecting the actual cathode pressure, a rotation speed detection means for detecting the rotation speed of the compressor, an opening degree detection means for detecting the opening degree of the back pressure valve, a power generation state detection means for detecting the power generation state of the fuel cell, and a control unit for detecting cathode gas leakage. The control unit obtains an estimated cathode pressure based on at least one of the rotation speed of the compressor and the opening degree of the back pressure valve, and identifies the cathode gas leakage location based on the difference between the actual cathode pressure and the estimated cathode pressure and the power generation state.

Description

Technical Field

[0001] The present invention relates to a fuel cell system capable of efficiently identifying a leakage site when leakage of cathode gas occurs.

Background Art

[0002] In recent years, research and development on fuel cells that contribute to energy efficiency have been conducted to enable more people to access affordable, reliable, sustainable, and advanced energy.

[0003] In a general fuel cell system, air containing oxygen is often used as the cathode gas supplied to the cathode, and compressed air using a compressor such as an air pump is supplied to the cathode to improve power generation efficiency. Here, in the air supply path and the exhaust path, if air leakage occurs due to pipe breakage or disconnection, etc., it may become difficult to continue power generation or appropriate dilution of the exhaust gas may not be possible.

[0004] As a countermeasure against such problems, for example, in Patent Document 1, when an abnormality is detected in power generation by a fuel cell system, the operating state of the fuel cell system is switched from normal operation to intermittent operation in which the air supply amount is minimized and the power generation amount is set to a constant value. When the power generation amount in this state is smaller than a threshold value and the air pressure is smaller than a threshold value, a technique for determining pipe disconnection in the supply path or the bypass path or sticking of the bypass valve is disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the technology described in Patent Document 1 above, it is necessary to switch the operating state of the fuel cell system from normal operation to intermittent operation in order to determine whether there is a leak of air, which is the cathode gas. Therefore, it is not possible to determine whether there is an air leak in the normal operating state. Consequently, it has been difficult to quickly detect an air leak and take appropriate action according to the situation.

[0007] Furthermore, in the technology described in Patent Document 1, since the abnormality identification process is initiated only when an abnormality in the power generation amount is detected, air leakage cannot be detected unless an abnormality occurs in the power generation amount. However, for example, if leakage occurs in the air discharge path after the air has passed through the fuel cell stack, air will be supplied to the fuel cell stack as usual, so it is conceivable that no abnormality will occur in the power generation amount. Therefore, the technology described in Patent Document 1 has the problem that it cannot detect air leakage in piping or the like on the downstream side of the fuel cell stack.

[0008] This invention was made to solve these problems and aims to provide a fuel cell system that can detect cathode gas leakage during normal operation of the fuel cell system and can identify whether the leakage is occurring upstream or downstream of the fuel cell. Ultimately, this contributes to energy efficiency. [Means for solving the problem]

[0009] To achieve this objective, a fuel cell system according to a first aspect of the present invention comprises a fuel cell that generates electricity by the reaction of anode gas supplied to the anode as a fuel gas and cathode gas supplied to the cathode as an oxidizer gas; a cathode gas supply passage through which cathode gas supplied to the fuel cell flows; a cathode gas discharge passage through which off-gas of cathode gas that has passed through the fuel cell flows; a compressor that pressurizes cathode gas to the fuel cell via the cathode gas supply passage; a back pressure valve provided in the cathode gas discharge passage which opens and closes the cathode gas discharge passage according to its opening degree; a pressure detection means for detecting the actual cathode pressure, which is the pressure of the cathode gas supplied to the fuel cell; a rotation speed detection means for detecting the rotation speed of the compressor; an opening degree detection means for detecting the opening degree of the back pressure valve; a power generation state detection means for detecting parameters indicating the power generation state of the fuel cell; and a control unit for detecting cathode gas leakage. The control unit obtains the estimated cathode gas pressure, which is estimated based on at least one of the compressor rotation speed and the opening degree of the back pressure valve, as the estimated cathode pressure, and identifies the cathode gas leakage site based on the difference between the actual cathode pressure and the estimated cathode pressure, and parameters indicating the power generation state.

[0010] In this fuel cell system, the control unit acquires the estimated cathode gas pressure, which is estimated based on at least one of the compressor rotation speed and the opening degree of the back pressure valve. Then, based on the difference between the actual cathode pressure detected by the pressure detection means and the estimated cathode pressure, and parameters indicating the power generation state of the fuel cell detected by the power generation state detection means, the location of the cathode gas leak can be identified.

[0011] The estimated cathode pressure, calculated based on at least one of the compressor rotation speed and the back pressure valve opening, is the cathode gas pressure expected when the cathode gas is flowing normally. Therefore, in normal operation of a fuel cell, if the actual cathode pressure is lower than the estimated cathode pressure, it is considered that a leak is occurring somewhere in the cathode gas flow path. If a cathode gas leak is occurring, it is possible to determine whether the leak is occurring upstream or downstream of the fuel cell, depending on the parameters indicating the fuel cell's power generation state.

[0012] In other words, if the parameters indicating the power generation state of the fuel cell are worse than those expected under normal conditions, it can be assumed that the cathode gas supplied to the fuel cell is decreasing, making normal power generation impossible. Therefore, it can be inferred that a cathode gas leak is occurring upstream of the fuel cell. Furthermore, if the parameters indicating the power generation status of the fuel cell are at the same level as those expected under normal conditions, it can be assumed that there is no abnormality in the amount of cathode gas supplied to the fuel cell, and therefore the leak can be estimated to be occurring downstream of the fuel cell.

[0013] In this way, this configuration makes it possible to detect cathode gas leakage during normal operation of the fuel cell and to identify whether the leakage is occurring on the upstream or downstream side of the fuel cell.

[0014] A fuel cell system according to a second aspect of the present invention is characterized in that, in the fuel cell system according to the first aspect, the power generation state detection means detects the actual voltage of the fuel cell as a parameter indicating the power generation state, and the control unit determines that a cathode gas leak is occurring in the cathode gas supply path when the actual cathode pressure is lower than the estimated cathode pressure by a predetermined amount and the actual voltage is lower than the estimated voltage estimated from the target current of the fuel cell by a predetermined amount.

[0015] In this configuration, the actual voltage of the fuel cell is detected as a parameter indicating the power generation state of the fuel cell. If the actual cathode pressure is lower than the estimated cathode pressure by a predetermined amount or more, this actual voltage is compared with the estimated voltage estimated from the fuel cell's target current. If the actual voltage is lower than the estimated voltage by a predetermined amount or more, it is determined that the reaction between the cathode gas and anode gas is not occurring sufficiently due to insufficient supply of cathode gas to the fuel cell. Based on this, it is determined that a cathode gas leak is occurring upstream of the fuel cell, i.e., in the cathode gas supply path. In this way, based on the difference between the actual cathode pressure and the estimated cathode pressure during normal operation of the fuel cell, and the difference between the actual voltage and the estimated voltage, cathode gas leakage in the cathode gas supply path can be identified quickly and accurately.

[0016] A third aspect of the present invention is a fuel cell system according to the second aspect, characterized in that, when the control unit determines that a cathode gas leak is occurring in the cathode gas supply path, it performs control to increase the rotational speed of the compressor.

[0017] In this configuration, if a cathode gas leak is detected in the cathode gas supply path, control is executed to increase the compressor's rotational speed. Therefore, the amount of cathode gas leaked can be compensated for by increasing the amount of cathode gas supplied due to the increased compressor rotational speed. As a result, even if a leak occurs in the cathode gas supply path, it becomes possible to supply sufficient cathode gas to the fuel cell and continue power generation.

[0018] A fourth aspect of the present invention is a fuel cell system according to the first aspect, characterized in that the power generation state detection means detects the actual voltage of the fuel cell as a parameter indicating the power generation state, and the control unit determines that cathode gas leakage is occurring in the cathode gas discharge path when the actual cathode pressure is lower than the estimated cathode pressure by a predetermined amount and the actual voltage is not lower than the estimated voltage estimated from the target current of the fuel cell by a predetermined amount.

[0019] In this configuration, the actual voltage of the fuel cell is detected as a parameter indicating the power generation state of the fuel cell. If the actual cathode pressure is lower than the estimated cathode pressure by a predetermined amount or more, this actual voltage is compared with the estimated voltage estimated from the fuel cell's target current. If the actual voltage is not lower than the estimated voltage by a predetermined amount or more, it is determined that the reaction between the cathode gas and anode gas is proceeding normally, as the supply of cathode gas to the fuel cell is normal. Based on this, it is determined that a cathode gas leak is occurring downstream of the fuel cell, i.e., in the cathode gas discharge path, rather than upstream. In this way, based on the difference between the actual cathode pressure and the estimated cathode pressure, and the difference between the actual voltage and the estimated voltage during normal operation of the fuel cell, cathode gas leakage in the cathode gas discharge path can be identified quickly and accurately.

[0020] A fifth aspect of the present invention is a fuel cell system according to the fourth aspect, further comprising: a bypass channel that branches off from a cathode gas supply channel, bypasses the fuel cell, and communicates with a cathode gas discharge channel; and a bypass valve provided in the bypass channel, which can adjust the flow rate of cathode gas flowing through the bypass channel according to its opening degree, wherein the control unit, when it determines that a cathode gas leak is occurring in the cathode gas discharge channel, controls the opening degree of the bypass valve to the open side and performs control to increase the rotational speed of the compressor.

[0021] In fuel cell systems, a common configuration involves merging the off-gas discharge channel of the anode gas supplied to the anode with the cathode gas discharge channel, mixing the anode gas off-gas with the cathode gas off-gas to dilute it, reduce its concentration, and then release it into the atmosphere. In such a configuration, if cathode gas leakage occurs in the cathode gas discharge channel, a problem arises where the dilution of the anode gas becomes insufficient.

[0022] To address such problems, in the configuration of the above aspect, when it is determined that cathode gas leakage has occurred in the cathode gas discharge path, the opening degree of the bypass valve is controlled to the open side, and control is executed to increase the rotational speed of the compressor. As a result, the flow rate of the cathode gas flowing from the cathode gas supply path through the bypass flow path to the cathode gas discharge path can be increased, so the amount of cathode gas leakage can be compensated by the increase in the flow rate of the cathode gas passing through the bypass flow path. Thereby, even in a situation where leakage is occurring in the cathode gas discharge path, the off-gas of the anode gas introduced into the cathode gas discharge path can be sufficiently diluted.

[0023] The fuel cell system according to the sixth aspect of the present invention is the fuel cell system according to the first to fifth aspects, wherein the control unit estimates and acquires the estimated cathode pressure at each predetermined cycle or in real time during the normal operation of the fuel cell.

[0024] According to this configuration, since the estimated cathode pressure is acquired at each predetermined cycle or in real time during the normal operation of the fuel cell, it is possible to detect the leakage of the cathode gas and identify the leakage location using the estimated cathode pressure during the normal operation of the fuel cell.

Effects of the Invention

[0025] According to the present invention, it is possible to provide a fuel cell system capable of detecting the leakage of the cathode gas during the normal operation of the fuel cell system and identifying whether the leakage occurs on the upstream side or the downstream side of the fuel cell.

Brief Description of the Drawings

[0026] [Figure 1] It is a schematic configuration diagram of a fuel cell vehicle equipped with a fuel cell system (FC system) according to an embodiment of the present invention. [Figure 2] It is a configuration diagram showing the configuration of the control system of the fuel cell system according to an embodiment. [Figure 3]This is a flowchart showing the leak detection and control process in a fuel cell system according to one embodiment. [Figure 4] This is a flowchart showing the supply air compensation control process. [Figure 5] This timing chart illustrates the changes in cathode pressure, stack voltage, and cathode gas supply rate when performing supply air compensation control. [Figure 6] This is a flowchart showing the bypass air compensation control process. [Figure 7] This timing chart illustrates the changes in cathode pressure, stack voltage, cathode gas supply rate, and bypass air flow rate when performing bypass air compensation control. [Modes for carrying out the invention]

[0027] Preferred embodiments of the fuel cell system of the present invention will be described in detail below with reference to the drawings. The fuel cell system according to the exemplary embodiment is mounted on a fuel cell vehicle and functions as one of the power sources of the fuel cell vehicle. The fuel cell vehicle may be a two-wheeled, three-wheeled, or four-wheeled automobile. The configuration described below is illustrative of the present invention and is not limited thereto. For example, the fuel cell system of the present invention may be mounted on mobile bodies other than vehicles, such as ships and airplanes, or it may be used in stationary facilities such as houses and buildings.

[0028] Figure 1 is a schematic diagram of a fuel cell vehicle 100 equipped with a fuel cell (FC) system 1 according to one embodiment. The fuel cell vehicle 100 is, for example, a fuel cell electric vehicle and, as shown in the figure, includes the FC system 1, a motor 200, a battery 300, and the like. Other components of the fuel cell vehicle 100 are not shown.

[0029] The motor 200 is, for example, a three-phase AC motor, and is driven using the electric power supplied from the FC system 1 or the battery 300 as a power source. The rotor of the motor 200 is connected to a drive wheel (not shown), and the motor 200 outputs a driving force used for the running of the fuel cell vehicle 100 to the drive wheel under the control of an upper controller (not shown) mounted on the fuel cell vehicle 100. Further, the motor 200 performs regenerative power generation using the kinetic energy of the vehicle when the vehicle decelerates.

[0030] The battery 300 is a secondary battery such as a lithium ion battery, for example. The battery 300 stores the electric power generated in the FC system 1 or the motor 200, and supplies the electric power for the running of the fuel cell vehicle 100 to the motor 200 under the control of an upper controller. Sensors such as a current sensor, a voltage sensor, and a temperature sensor (not shown) are provided in the battery 300, and the current value, voltage value, temperature, etc. detected by these sensors are output to an upper controller.

[0031] <FC system 1 configuration> The specific configuration of the FC system 1 will be described below. Note that the configuration described below is merely an example, and any configuration may be used as long as it is a system configuration that generates power using an anode and a cathode. The FC system 1 includes an FC (fuel cell) stack 2, a cathode gas supply device 3, an anode gas supply device 4, a control device 5, a VCU (Voltage Control Unit) 6, and a cooling system 7.

[0032] The FC stack 2 is a structure in which a plurality of power generation cells 21 are stacked. The FC stack 2 is provided with a cathode gas inlet 2a, a cathode gas outlet 2b, an anode gas inlet 2c, an anode gas outlet 2d, and an electrode 2e, respectively.

[0033] Each power generation cell 21 is a battery that generates electricity through an electrochemical reaction between an anode gas supplied to the anode as a fuel gas and a cathode gas supplied to the cathode as an oxidizing gas. In this embodiment, hydrogen gas is used as the anode gas and air containing oxygen is used as the cathode gas. Each power generation cell 21 has a configuration in which a solid polymer electrolyte membrane (hereinafter also simply referred to as an electrolyte membrane) 22, which is made of a cation exchange membrane such as a thin film of perfluorosulfonic acid containing water, is sandwiched between an anode electrode 23 and a cathode electrode 24. In addition to fluorine-based electrolytes, hydrocarbon-based electrolytes and the like can be used as the electrolyte membrane 22.

[0034] Hydrogen gas, known as anode gas, is supplied to the anode electrode 23 from the anode gas supply device 4. Oxygen-containing air, known as cathode gas, is supplied to the cathode electrode 24 from the cathode gas supply device 3. The hydrogen in the anode gas supplied to the anode electrode 23 is ionized by a catalytic reaction on an anode catalyst (not shown), and the generated hydrogen ions permeate the electrolyte membrane 22 and move to the cathode electrode 24. The electrons released as a result of hydrogen ionization move to an external circuit via electrode 2e, generating an electric current, thereby producing electricity. The hydrogen ions that have moved from the anode electrode 23 to the cathode electrode 24 react with the oxygen in the cathode gas supplied to the cathode electrode 24 to produce water.

[0035] The cathode gas supply device 3 includes an air pump 31 that compresses air from the atmosphere and supplies it to the FC stack 2. The air pump 31 is located in the cathode gas supply path 32. The air pump 31 is driven by an actuator (not shown). The rotational speed of the air pump 31 is controlled by a rotational speed control unit 52 of the control device 5, which will be described later. The rotational speed of the air pump 31 is detected by a rotational speed sensor 31A, and the detection signal is transmitted sequentially to the control device 5.

[0036] A humidifier 33 is provided downstream of the air pump 31 in the cathode gas supply path 32. The cathode gas supply path 32 also communicates with the cathode gas inlet 2a of the FC stack 2 downstream of the humidifier 33. Furthermore, a flow sensor 31B for detecting the air flow rate into the air pump 31 is installed upstream of the air pump 31 in the cathode gas supply passage 32. The detection signal from the flow sensor 31B is transmitted sequentially to the control device 5. Furthermore, a pressure sensor 38 for detecting the pressure of the cathode gas supplied to the FC stack 2 is installed downstream of the air pump 31 in the cathode gas supply path 32. The detection signal from the pressure sensor 38 is transmitted sequentially to the control device 5.

[0037] Furthermore, a bypass channel 35 is connected to the cathode gas supply channel 32, branching off from the cathode gas supply channel 32 and bypassing the FC stack 2 to communicate with the cathode gas discharge channel 34, which will be described later. A bypass valve 36 is provided in the bypass channel 35. The bypass valve 36 is configured to adjust the flow rate of cathode gas flowing through the bypass channel 35 according to its opening degree. The opening degree of the bypass valve 36 is controlled by the opening degree control unit 53 of the control device 5, which will be described later.

[0038] The cathode gas outlet 2b is connected to the cathode gas discharge passage 34. The cathode gas discharge passage 34, after passing through the humidifier 33, communicates with the outside of the FC system 1 and releases the off-gas (cathode off-gas) of the cathode gas that has passed through the FC stack 2 to the outside. The cathode gas discharge passage 34 may be configured to communicate with the outside of, for example, the fuel cell vehicle 100 and release the cathode off-gas into the atmosphere.

[0039] The humidifier 33 recovers moisture from the cathode off-gas discharged from the cathode gas outlet 2b and passing through the cathode gas discharge passage 34, and uses this moisture to humidify the cathode gas passing through the cathode gas supply passage 32. This allows the electrolyte membrane 22 in each power generation cell 21 of the FC stack 2 to be maintained at a humidity level suitable for power generation.

[0040] A back pressure valve 37 is provided downstream of the humidifier 33 in the cathode gas discharge passage 34. The back pressure valve 37 opens and closes the cathode gas discharge passage 34 according to the opening degree of a diaphragm that is pressed to close the orifice inside the valve body at an arbitrarily set pressure. With this configuration, the back pressure valve 37 functions to maintain a constant pressure of cathode gas in the FC stack 2. The back pressure valve 37 is equipped with an opening degree sensor 37A that detects its opening degree, and the detection signal is transmitted sequentially to the control device 5.

[0041] The anode gas supply device 4 has a hydrogen tank 41 for storing high-pressure hydrogen gas. The hydrogen tank 41 communicates with the anode gas inlet 2c of the FC stack 2 via an anode gas supply passage 42. An injector 43 and an ejector 44 are provided in series in the anode gas supply passage 42. The injector 43's opening is controlled by the control device 5, which defines the flow rate and timing of the anode gas supplied to the FC stack 2. The ejector 43, by creating negative pressure inside, sucks in a portion of the off-gas (anode off-gas) of the anode gas discharged from the anode gas outlet 2d to the anode gas discharge passage 45 and recirculates it to the anode gas supply passage 42.

[0042] An anode gas discharge passage 45 is connected to the anode gas outlet 2d of the FC stack 2, and a gas-liquid separator 46 is connected to the anode gas discharge passage 45. The gas-liquid separator 46 separates the anode off-gas discharged from the anode gas outlet 2d of the FC stack 2 into a gaseous component and a liquid component. The liquid component separated from the anode off-gas is discharged into the purge channel 49 via a drain valve 47, which is controlled to open and close by the control device 5. The gaseous component separated from the off-gas is partially recirculated via an ejector 44, and the remaining portion is discharged into the purge channel 49 via a purge valve 48, which is also controlled to open and close by the control device 5.

[0043] The purge channel 49 is a channel for discharging anode off-gas to the outside, and it merges with the cathode gas discharge channel 34 at its downstream end. The anode off-gas flowing through the purge channel 49 is diluted by mixing with the cathode off-gas flowing through the cathode gas discharge channel 34, and is discharged to the outside with a reduced hydrogen concentration. Furthermore, a diluent may be provided separately downstream of the confluence of the cathode gas discharge channel 34 with the purge channel 49 to ensure more reliable dilution of the anode off-gas.

[0044] VCU6 is, for example, a boost DC-DC converter. VCU6 is positioned between the anode electrode 23 and cathode electrode 24 of the FC stack 2 and an external electrical load of the FC system 1. The VCU6 has the function of boosting the output voltage to a desired voltage when supplying power generated by the FC stack 2 to loads such as the motor 200, battery 300, air pump 31, and other various auxiliary equipment. A voltage sensor 25 is installed between the VCU 6 and the FC stack 2 to detect the generated voltage of the FC stack 2. The detection signal from the voltage sensor 25 is sequentially transmitted to the control device 5.

[0045] The cooling system 7 cools the FC stack 2 in accordance with the control of the control device 5. For example, the cooling system 7 includes a radiator and a water pump (not shown) and cools the FC stack 2 by circulating a refrigerant such as pure water or ethylene glycol through a refrigerant flow path (not shown) provided within the FC stack 2.

[0046] The control unit 5 is an ECU composed of a microcomputer consisting of a CPU, RAM, ROM, and I / O interfaces (none of which are shown). The control device 5 is configured to acquire information regarding the power generation status of the FC system 1 based on the detection values ​​of various sensors. The acquired power generation status of the FC system includes, for example, the current voltage of the FC stack 2 and the power generated.

[0047] In addition, the control device 5 performs control such as opening / closing control of various valves in the FC system 1, driving control of various auxiliary machines (such as the air pump 31), and power generation amount control of the FC stack 2 via the VCU 6. Further, the control device 5 controls the opening degree of the injector 43 while referring to the value of a pressure sensor (not shown) provided in, for example, the anode gas supply passage 42 and detecting the pressure of the anode gas, thereby controlling the supply amount and supply timing of the anode gas supplied to the FC stack 2. Furthermore, the control device 5 operates the cooling system 7 to perform control related to temperature adjustment of the FC stack 2. Also, the control device 5 may perform charge / discharge control of the battery 300 and power running / regenerative drive control of the motor 300.

[0048] Also, as described above, the detection signals of the pressure sensor 38, the rotation speed sensor 31A, the opening degree sensor 37A, and the voltage sensor 25 are sequentially input to the control device 5. Based on the inputs from these sensors, the control device 5 reads and executes a program stored in the ROM or RAM, thereby realizing the functions of the leakage detection unit 51, the rotation speed control unit 52, and the opening degree control unit 53, which will be described later.

[0049] <Power generation operation of the FC system 1> The power generation operation of the FC system 1 configured as described above (power generation operation in the FC stack 2) will be described below.

[0050] The cathode gas supply device 3 supplies air as the cathode gas to the cathode gas supply passage 32 via the air pump 31. The cathode gas is humidified when passing through the humidifier 33 and then supplied to the FC stack 2 from the cathode gas inlet 2a.

[0051] On the other hand, the anode gas supply device 4 supplies hydrogen gas as the anode gas from the hydrogen tank 41 to the anode gas supply passage 42 based on the opening degree control of the injector 42 by the control device 5. The anode gas is supplied to the FC stack 2 from the anode gas inlet 2c after passing through the ejector 43. [[ID=2I]]

[0052] The cathode gas supplied to the FC stack 2 from the cathode gas inlet 2a is supplied to the cathode electrode 24 of each power generation cell 21. Meanwhile, the anode gas supplied to the FC stack 2 from the anode gas inlet 2c is supplied to the anode electrode 23 of each power generation cell 21. As a result, in each power generation cell 21, hydrogen in the anode gas and oxygen in the cathode gas are consumed by an electrochemical reaction, generating electricity. The electricity generated by the generator is supplied to the motor 200, battery 300, and other various auxiliary equipment via the VCU 7, based on the control of the control device 5.

[0053] The cathode-off gas at the cathode electrode 24 of each power generation cell 21 is discharged from the cathode gas outlet 2b to the cathode gas discharge passage 34. The discharged cathode-off gas has its moisture recovered when it passes through the humidifier 33 and is then discharged to the outside. As described above, the moisture recovered by the humidifier 33 is used to humidify the cathode gas passing through the cathode gas supply passage 32, thereby adjusting the humidity of the electrolyte membrane 22 in each power generation cell 21 of the FC stack 2.

[0054] Furthermore, the anode off-gas at the anode electrode 23 of each power generation cell 21 is discharged from the anode gas outlet 2d to the anode gas discharge channel 45. The discharged anode off-gas is then introduced from the anode gas discharge channel 45 to a gas-liquid separator 46 where the liquid water is separated. Subsequently, the gaseous component of the anode off-gas is either recirculated via the ejector 44 or flows through the purge channel 49 to the cathode gas discharge channel 34, where it is mixed with the cathode off-gas, diluted, and then discharged to the outside.

[0055] Furthermore, during the execution of the series of power generation operations described above, the cooling system 7 operates according to the temperature of the FC stack 2 based on the control of the control device 5 to cool the FC stack 2.

[0056] <Configuration of control device 5> Next, the configuration of the control device 5 will be described. As shown in Figure 2, in this embodiment, the control device 5 includes a leak detection unit 51, a rotation speed control unit 52, and an opening degree control unit 53. Each of these functional units is realized, for example, by a hardware processor such as the CPU of the control device 5 reading and executing a program (software). Such a program may be stored in the ROM or RAM of the control device 5, or it may be stored in an external storage device (a storage device equipped with a non-transient storage medium such as an HDD or flash memory).

[0057] The leak detection unit 51 detects cathode gas leaks in the FC system 1 and, if a leak is detected, identifies the location of the leak. Specifically, in the leak detection control of the FC system 1 described later, the leak detection unit 51 estimates the pressure of the cathode gas in the FC stack 2 based on at least one of the rotational speed of the air pump 31 obtained based on the detection signal of the rotational speed sensor 31A and the opening degree of the back pressure valve 37 obtained based on the detection signal of the opening degree sensor 37A, and obtains it as the estimated cathode pressure PE. Furthermore, the leak detection unit 51 determines whether or not there is a cathode gas leak in the FC system 1 by comparing the acquired estimated cathode pressure with the actual cathode pressure PA, which is the actual pressure of the cathode gas acquired based on the detection signal of the pressure sensor 38.

[0058] In this embodiment, for example, a map or model representing the relationship between the rotational speed of the air pump 31 and the cathode gas pressure, and the relationship between the opening degree of the back pressure valve 37 and the cathode gas pressure is created in advance through experiments or simulations, and stored in the storage unit such as the ROM of the control device 5. Then, the leak detection unit 51 uses this map or model to obtain an estimated cathode pressure PE from the rotational speed of the air pump 31 and the opening degree of the back pressure valve 37 that have been actually obtained.

[0059] In this embodiment, the pressure sensor 38 is located upstream of the FC stack 2. However, if a cathode gas leak occurs, regardless of whether the leak is located upstream or downstream of the FC stack 2, the actual cathode pressure detected by the pressure sensor 38 located upstream will be smaller than the value when there is no leak. Therefore, regardless of whether the leak is located upstream or downstream of the FC stack 2, it is possible to detect a cathode gas leak by comparing the estimated cathode pressure PE with the actual cathode pressure PA.

[0060] Furthermore, if the leak detection unit 51 determines that a cathode gas leak has occurred, it identifies whether the cathode gas leak is occurring on the upstream or downstream side of the FC stack 2, based on the information regarding the power generation status of the FC system 1 acquired by the control device 5.

[0061] In other words, if the power generation state in FC stack 2 is worse than what would be expected under normal conditions, it is determined that the flow rate of cathode gas supplied to FC stack 2 has decreased, and therefore the leak is located upstream of FC stack 2. Furthermore, if the power generation status in FC stack 2 is at the same level as what would be expected under normal circumstances, it is determined that there is no abnormality in the flow rate of cathode gas supplied to FC stack 2, and that the leak is occurring on the downstream side of FC stack 2.

[0062] In this embodiment, the leakage detection unit 51 uses the actual stack voltage VA of the FC stack 2, obtained based on the detection signal of the voltage sensor 25, as the power generation state of the FC stack 2 used for the above determination. Furthermore, based on a data table or map of the IV characteristics of the FC stack 2, which has been acquired in advance through experiments and stored in the memory unit such as the ROM of the control device 5, the estimated stack voltage VE of the FC stack 2, which is estimated from the current target current of the FC stack 2, is obtained. Then, by comparing the actual stack voltage VA with the estimated stack voltage VE, it is determined whether or not there is an abnormality in the power generation state of FC stack 2.

[0063] Note that, as the power generation state of the FC stack 2 used for the above determination, it is also possible to use the value of the power generation power of the FC stack 2 instead of the actual stack voltage VA of the FC stack 2. In that case, the leakage detection unit 51 acquires the estimated power instead of the estimated stack voltage VE and performs the abnormality determination of the power generation state.

[0064] The rotation speed control unit 52 controls the rotation speed of the air pump 31. In the leakage detection control process of the FC system 1 described later, when it is determined that a cathode gas leakage has occurred upstream of the FC stack 2, the rotation speed control unit 52 controls to increase the rotation speed of the air pump 31. Thereby, the supply amount of the cathode gas supplied to the FC stack 2 is increased, and power generation can be continued even in a situation where a cathode gas leakage has occurred upstream of the FC stack 2.

[0065] The opening degree control unit 53 controls the opening degree of the bypass valve 36. In the leakage detection control process of the FC system 1 described later, when it is determined that a cathode gas leakage has occurred downstream of the FC stack 2, the opening degree control unit 53 controls to change the opening degree of the bypass valve to the open side. Also, in conjunction with this, the above-described rotation speed control unit 52 controls to increase the rotation speed of the air pump 31. Thereby, by increasing the flow rate of the cathode gas flowing through the bypass flow path 35, the flow rate of the cathode gas flowing through the cathode gas discharge path 34 can be increased. Therefore, even in a situation where a leakage has occurred downstream of the FC stack 2, it is possible to sufficiently dilute the anode off-gas that merges into the cathode gas discharge path 34 via the purge flow path 49.

[0066] <Leakage Detection Control of FC System 1> Subsequently, the leakage detection control in the FC system 1 of the present embodiment, and the supply air compensation control and bypass air compensation control which are its subroutines, will be described with reference to FIGS. 3 to 7. Figure 3 is a flowchart showing the control process for leak detection control of FC system 1. This process is executed repeatedly at predetermined timings or periods during normal operation of FC system 1.

[0067] In this control process, first, in step 301 (illustrated as "S301"; the same applies hereafter), an estimated cathode pressure PE is obtained based on the rotational speed of the air pump 31 and the opening degree of the back pressure valve 37 using a map or model stored in the memory unit such as the ROM of the control device 5. Next, in step 302, the actual cathode pressure PA is obtained based on the detection signal of the pressure sensor 18.

[0068] After obtaining the estimated cathode pressure PE and the actual cathode pressure PA, step 303 determines whether the value of the actual cathode pressure PA is less than or equal to a predetermined value than the value of the estimated cathode pressure PE. Here, "smaller than or equal to the specified value" includes both the meaning of "smaller than or equal to the specified value" and the meaning of "smaller than or equal to the specified percentage." This makes it possible to set an appropriate value or percentage that can reliably detect pressure loss due to cathode gas leakage while eliminating false detection of pressure fluctuations within the normal error range during normal operation of the FC system 1.

[0069] If, as a result of the determination in step 303, the actual cathode pressure PA is not less than or equal to the estimated cathode pressure PE (step 303: NO), it is determined that no cathode gas leakage has occurred, and the process returns to step 301 and repeats from the beginning.

[0070] Furthermore, when repeating the process in step 301, the acquisition of the estimated cathode pressure PE may be set to be performed at predetermined intervals. Alternatively, by shortening the predetermined interval to the absolute minimum, the system may be set to continuously acquire the estimated cathode pressure PE in virtually real time. Furthermore, if no cathode gas leak is detected, the control process may be terminated after repeating the loop of steps 301 to 303 a predetermined number of times or for a predetermined period of time, and then executed again after a predetermined period of time has elapsed.

[0071] On the other hand, if the result of the determination in step 303 is that the actual cathode pressure PA is less than or equal to a predetermined value than the estimated cathode pressure PE (step 303: YES), it is determined that a cathode gas leak is occurring at some point downstream of the pressure sensor 38, and the process proceeds to the next step 304.

[0072] In step 304, the estimated stack voltage VE is obtained based on the target current of the FC stack 2, using a data table or map showing the IV characteristics of the FC stack 2 stored in the memory unit of the control device 5, such as the ROM. The target current of the FC stack 2 is a current value set to generate the necessary power for the FC system 1, depending on, for example, the operating state of the fuel cell vehicle 100 or the charge state of the battery 300. The target current of the FC stack 2 may be set by a higher-level controller of the fuel cell vehicle 100, or it may be set by the control device 5.

[0073] Next, in step 305, the actual stack voltage VA of the FC stack 2 is obtained based on the detection signal from the voltage sensor 25.

[0074] After obtaining the estimated stack voltage VE and the actual stack voltage VA, step 306 determines whether the value of the actual stack voltage VA is less than or equal to a predetermined value than the value of the estimated stack voltage VE. Similar to step 303, the term "smaller than or equal to a predetermined value" here includes both the meaning of "smaller than or equal to a predetermined value" and the meaning of "smaller than or equal to a predetermined percentage." This makes it possible to set an appropriate value or percentage that can reliably detect a voltage drop due to a decrease in the flow rate of cathode gas supplied to the FC stack 2, while eliminating false detections of voltage fluctuations within the normal error range during normal operation of the FC system 1.

[0075] If, as a result of the determination in step 306, the value of the actual stack voltage VA is less than or equal to the value of the estimated stack voltage VE (step 306: YES), it is determined that the reaction between the cathode gas and anode gas is not occurring sufficiently due to insufficient supply of cathode gas to the FC stack 2. Based on this, it is determined that the cathode gas leak is occurring on the upstream side of the FC stack 2, i.e., in the cathode gas supply path 32. In this case, in order to continue power generation in FC system 1 for as long as possible, the process is terminated after supply air compensation control is performed in the following step 307. Details of the supply air compensation control will be described later.

[0076] On the other hand, if the result of the determination in step 306 is that the actual stack voltage VA is not less than a predetermined amount less than the estimated stack voltage VE (step 306: NO), then it is determined that the reaction between the cathode gas and anode gas is proceeding normally because the supply amount of cathode gas to the FC stack 2 is normal. Based on this, it is determined that the cathode gas leak is occurring downstream of the FC stack 2, i.e., in the cathode gas discharge path 34. In this case, in order to continue sufficient dilution of the anode off-gas flowing into the cathode gas discharge passage 34, the process is terminated after bypass air compensation control is performed in the subsequent step 308. Details of the bypass air compensation control will be described later.

[0077] Next, we will explain the supply air compensation control in step 307. Figure 4 is a flowchart of the control process for supply air compensation control. In this control process, first, in step 401, the amount of insufficient air PS, which is the amount of cathode gas that would have been supplied to the FC stack 2 under normal circumstances, is estimated based on the pressure difference ΔP between the estimated cathode pressure PE and the actual cathode pressure PA. In other words, the amount of insufficient air PS approximates the amount of cathode gas leaking in the cathode gas supply path 32.

[0078] Next, in step 402, the supply air volume target value is added to the deficit air volume PS. The supply air volume target value is a value that indicates the flow rate of cathode gas to be supplied to the FC stack 2, and is stored in the ROM or other storage unit of the control device 5 as a data table or map that serves as a reference when the control device 5 (rotation speed control unit 52) ​​determines the rotation speed of the air pump 31. By adding the deficit air volume PS to this supply air volume target value, a new supply air volume target value is set that compensates for the leakage of cathode gas in the cathode gas supply path 32.

[0079] Next, in step 403, the rotation speed of the air pump 31 is controlled based on the set target value of the supplied air volume, and this process is terminated. That is, the air pump 31 is controlled to increase its rotation speed based on the increased target value of the supplied air volume.

[0080] In this way, in the supply air compensation control, the amount of cathode gas leaking in the cathode gas supply path 32 is estimated as the amount of insufficient air PS, and the amount of insufficient air PS is added to the supply air target value to increase the rotation speed of the air pump 31, thereby increasing the amount of cathode gas supplied to the FC stack 2. This makes it possible to continue power generation by the FC stack 2 even when cathode gas leakage occurs on the upstream side of the FC stack 2.

[0081] Figure 5 is a timing chart showing an example of changes in cathode pressure, stack voltage, and cathode gas supply rate when supply air compensation control is performed. In this figure, an example is shown in which the estimated cathode pressure PE is estimated mainly based on the opening degree of the back pressure valve 37.

[0082] At time t1, if a cathode gas leak occurs in the cathode gas supply passage 32, a pressure loss occurs at the leak site. However, as a result, the opening of the back pressure valve 37 changes to the closed position, and the actual cathode pressure PA is maintained at a nearly constant value. On the other hand, the leak detection unit 51 estimates the estimated cathode pressure PE mainly based on the opening of the back pressure valve 37. Therefore, based on the opening of the back pressure valve 37 which has changed to the closed position, the value of the estimated cathode pressure PE gradually increases.

[0083] Furthermore, observing the stack voltage, we see that due to the leakage of cathode gas at time t1, the amount of cathode gas supplied to FC stack 2 gradually decreases, and therefore the actual stack voltage VA also gradually decreases.

[0084] Subsequently, at time t2, it is confirmed that the difference between the estimated cathode pressure PE and the actual cathode pressure PA is greater than or equal to a predetermined value, and the difference between the estimated stack voltage VE and the actual stack voltage VA is greater than or equal to a predetermined value. As a result, leakage on the upstream side of FC stack 2 is detected, and supply air compensation control is initiated. As a result, the cathode gas supply will increase compared to when supply air compensation control is not performed. In this case, to avoid abrupt changes in the cathode gas supply, the system will be controlled to increase the cathode gas supply at a predetermined rate. Furthermore, the increased cathode gas supply causes the reaction between the cathode gas and anode gas in FC stack 2 to return to normal, which increases the actual stack voltage VA and brings it closer to the estimated stack voltage VE. In this way, by implementing supply air compensation control, it becomes possible to continue generating power in FC stack 2.

[0085] Furthermore, if the estimated air deficit PS is large and adding the air deficit PS to the target supply air volume makes it difficult to match the rotation speed of the air pump 31 to the target supply air volume, control may be implemented to temporarily limit the power generation of the FC stack 2 or to stop power generation.

[0086] Next, we will explain the bypass air compensation control in step 308. Figure 6 is a flowchart showing the control process for bypass air compensation control. In this control process, first, in step 601, the amount of insufficient air PS, which is the amount of cathode gas that would have otherwise flowed into the cathode gas discharge passage 34, is estimated based on the pressure difference ΔP between the estimated cathode pressure PE and the actual cathode pressure PA. In other words, the amount of insufficient air PS approximates the amount of cathode gas leaking in the cathode gas discharge passage 34.

[0087] Next, in step 602, the bypass air volume target value is added to the insufficient air volume PS. The bypass air volume target value is a value that indicates the flow rate of cathode gas that should flow through the bypass passage 35, and is stored in the ROM or other storage unit of the control device 5 as a data table or map that serves as a reference when the control device 5 (rotation speed control unit 52 and opening degree control unit 53) determines the opening degree of the bypass valve 36 and the rotation speed of the air pump 31. By adding the insufficient air volume PS to this bypass air volume target value, a new bypass air volume target value is set that compensates for the leakage of cathode gas in the cathode gas discharge passage 34.

[0088] Next, in step 603, the opening degree of the bypass valve 36 and the rotation speed of the air pump 31 are controlled based on the set bypass air volume target value, and this process is terminated. Specifically, the opening degree of the bypass valve 36 is controlled to the open side based on the increased bypass air volume target value. In addition, the rotation speed of the air pump 31 is controlled to increase based on the increased bypass air volume target value.

[0089] In this bypass air compensation control, the amount of cathode gas leaking in the cathode gas discharge passage 34 is estimated as the amount of insufficient air PS. This amount of insufficient air PS is added to the bypass air target value, and the opening of the bypass valve 36 is controlled to the open side, while the rotational speed of the air pump 31 is increased. This increases the flow rate of cathode gas flowing to the cathode gas discharge passage 34 via the bypass passage 35. Therefore, even when cathode gas leakage occurs downstream of the FC stack 2, the anode off gas introduced into the cathode gas discharge passage 34 can be sufficiently diluted.

[0090] Figure 7 is a timing chart showing an example of changes in cathode pressure, stack voltage, cathode gas supply rate, and bypass air flow rate when bypass air compensation control is performed. In this figure, as explained in Figure 5, an example is shown in which the estimated cathode pressure PE is estimated mainly based on the opening degree of the back pressure valve 37.

[0091] At time t1, if cathode gas leakage occurs in the cathode gas discharge passage 34, a pressure loss occurs at the leakage site. As a result, the opening of the back pressure valve 37 changes to the closed position, and the actual cathode pressure PA is maintained at a nearly constant value. On the other hand, the leakage detection unit 51 estimates the estimated cathode pressure PE mainly based on the opening of the back pressure valve 37. Therefore, based on the opening of the back pressure valve 37 which has changed to the closed position, the value of the estimated cathode pressure PE gradually increases.

[0092] Furthermore, examining the stack voltage and cathode gas supply, the cathode gas leakage that occurred at time t1 occurred downstream of FC stack 2, so the flow rate of cathode gas supplied to FC stack 2 remains unchanged after time t1. Also, since FC stack 2 is supplied with sufficient cathode gas for the reaction, the actual stack voltage VA also remains unchanged after time t1.

[0093] Subsequently, at time t2, it was confirmed that the difference between the estimated cathode pressure PE and the actual cathode pressure PA was greater than a predetermined value, and the difference between the estimated stack voltage VE and the actual stack voltage VA was not greater than a predetermined value. As a result, leakage downstream of FC stack 2 was detected, and bypass air compensation control was initiated. Consequently, the bypass air flow rate increased compared to when bypass air compensation control was not performed. In this way, by implementing bypass air compensation control, it becomes possible to sufficiently dilute the off-gas of the anode gas introduced into the cathode gas discharge path.

[0094] <Effects of this embodiment> The effects of this embodiment will be described below. In the fuel cell system 1 of this embodiment, the control device 5 obtains the estimated cathode pressure PE based on at least one of the rotational speed of the air pump 31 and the opening degree of the back pressure valve 37. Then, based on the difference between the actual cathode pressure PA detected by the pressure sensor 38 and the estimated cathode pressure PE, and parameters indicating the power generation state of the FC stack 2, the location of the cathode gas leak can be identified.

[0095] In other words, during normal operation of FC stack 2, if the actual cathode pressure PA is lower than the estimated cathode pressure PE by a predetermined amount or more, a cathode gas leak can be detected, and it is possible to identify whether the leak is occurring on the upstream or downstream side of the fuel cell, according to parameters indicating the power generation state of FC stack 2. Specifically, if the parameters indicating the power generation status of FC stack 2 are worse than those expected under normal conditions, it is presumed that a cathode gas leak is occurring upstream of the fuel cell. Conversely, if the parameters indicating the power generation status of FC stack 2 are at the same level as those expected under normal conditions, it is presumed that the leak is occurring downstream of the fuel cell. Therefore, according to this embodiment, it is possible to detect cathode gas leakage during normal operation of the FC stack 2, and to identify whether the leakage is occurring on the upstream or downstream side of the FC stack 2.

[0096] Furthermore, as a parameter indicating the power generation status of FC stack 2, the actual stack voltage VA of FC stack 2 is detected, and if the actual cathode pressure PA is lower than the estimated cathode pressure PE by a predetermined amount or more, the actual stack voltage VA is compared with the estimated stack voltage VE. If the actual stack voltage VA is lower than the estimated stack voltage VE by a predetermined amount or more, it is determined that cathode gas leakage is occurring on the upstream side of FC stack 2, i.e., in the cathode gas supply path 32. Therefore, based on the difference between the actual cathode pressure PA and the estimated cathode pressure PE during normal operation of the FC stack 2, and the difference between the actual stack voltage VA and the estimated stack voltage VE, cathode gas leakage in the cathode gas supply path 32 can be quickly and accurately identified.

[0097] Furthermore, if it is determined that a cathode gas leak is occurring in the cathode gas supply path 32, control is executed to increase the rotation speed of the air pump 31. This allows the leakage of cathode gas to be compensated for by increasing the amount of cathode gas supplied due to the increased rotation speed of the air pump 31. Therefore, even if a leak occurs in the cathode gas supply path 32, it becomes possible to supply sufficient cathode gas to the FC stack 2 and continue power generation.

[0098] Furthermore, if the actual cathode pressure PA is lower than the estimated cathode pressure PE by a predetermined amount or more, the actual stack voltage VA is compared with the estimated stack voltage VE. If the actual stack voltage VA is not lower than the estimated stack voltage VE by a predetermined amount or more, it is determined that cathode gas leakage is occurring downstream of the FC stack 2, i.e., in the cathode gas discharge passage 34. Therefore, based on the difference between the actual cathode pressure PA and the estimated cathode pressure PE during normal operation of the FC stack 2, and the difference between the actual stack voltage VA and the estimated stack voltage VE, cathode gas leakage in the cathode gas discharge passage 34 can be identified quickly and accurately.

[0099] Furthermore, if it is determined that cathode gas is leaking in the cathode gas discharge channel 34, the opening of the bypass valve 36 is controlled to the open side, and the rotational speed of the air pump 31 is increased. This allows the leakage of cathode gas to be compensated for by increasing the flow rate of cathode gas passing through the bypass channel 35. Therefore, even if leakage occurs in the cathode gas discharge channel 34, it is possible to continue sufficient dilution of the anode off gas introduced into the cathode gas discharge channel 34.

[0100] Furthermore, since the estimated cathode pressure PE is acquired at predetermined intervals or in real time during normal operation of FC stack 2, cathode gas leakage can be detected using the estimated cathode pressure PE during normal operation of FC stack 2, and the location of the leakage can be identified.

[0101] Furthermore, the present invention is not limited to the embodiments described and can be implemented in various forms. In addition, the details of the configuration can be modified as appropriate within the scope of the spirit of the present invention. [Explanation of symbols]

[0102] 1…FC system (fuel cell system) 2…FC stack (fuel cell) 3… Cathode gas supply device 4…Anode gas supply device 5…Control device (control unit) 25…Voltage sensor (means for detecting power generation status) 31... Air pump (compressor) 31A... Rotation speed sensor (rotation speed detection means) 32… Cathode gas supply line 34… Cathode gas discharge channel 35…Bypass channel 36... Bypass valve 37... Back pressure valve 37A...Opening degree sensor 38…Pressure sensor (pressure detection means)

Claims

1. A fuel cell generates electricity through the reaction of anode gas supplied to the anode as fuel gas and cathode gas supplied to the cathode as oxidizer gas, A cathode gas supply path through which the cathode gas supplied to the fuel cell flows, A cathode gas discharge path through which the off-gas of the cathode gas that has passed through the fuel cell flows, A compressor that pumps the cathode gas to the fuel cell via the cathode gas supply path, A back pressure valve is provided in the cathode gas discharge passage and opens and closes the cathode gas discharge passage according to its opening degree, A pressure detection means for detecting the actual cathode pressure, which is the pressure of the cathode gas supplied to the fuel cell, A rotation speed detection means for detecting the rotation speed of the compressor, An opening degree detection means for detecting the opening degree of the back pressure valve, A power generation state detection means for detecting parameters indicating the power generation state of the fuel cell, The system includes a control unit for detecting the leakage of the cathode gas, A fuel cell system comprising: a control unit that obtains the pressure of the cathode gas estimated based on at least one of the rotational speed of the compressor and the opening degree of the back pressure valve as the estimated cathode pressure, and identifies the location of the cathode gas leak based on the difference between the actual cathode pressure and the estimated cathode pressure, and a parameter indicating the power generation state.

2. The power generation state detection means detects the actual voltage of the fuel cell as a parameter indicating the power generation state, The fuel cell system according to claim 1, characterized in that the control unit determines that a cathode gas leak is occurring in the cathode gas supply path when the actual cathode pressure is lower than the estimated cathode pressure by a predetermined amount and the actual voltage is lower than the estimated voltage estimated from the target current of the fuel cell by a predetermined amount.

3. The fuel cell system according to claim 2, characterized in that the control unit performs control to increase the rotational speed of the compressor when it determines that a leak of cathode gas is occurring in the cathode gas supply path.

4. The power generation state detection means detects the actual voltage of the fuel cell as a parameter indicating the power generation state, The fuel cell system according to claim 1, characterized in that the control unit determines that a cathode gas leak is occurring in the cathode gas discharge path when the actual cathode pressure is lower than the estimated cathode pressure by a predetermined amount and the actual voltage is not lower than the estimated voltage estimated from the target current of the fuel cell by a predetermined amount.

5. A bypass channel that branches off from the cathode gas supply channel, bypasses the fuel cell, and communicates with the cathode gas discharge channel, The bypass passage is further provided with a bypass valve capable of adjusting the flow rate of the cathode gas flowing through the bypass passage according to its opening degree, The fuel cell system according to claim 4, characterized in that when the control unit determines that a cathode gas leak is occurring in the cathode gas discharge passage, it controls the opening of the bypass valve to the open side and increases the rotational speed of the compressor.

6. The fuel cell system according to any one of claims 1 to 5, characterized in that the control unit estimates and acquires the estimated cathode pressure at predetermined intervals or in real time during normal operation of the fuel cell.

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