Fuel cell system

Abstract

A low-cost configuration for detecting internal leaks in the humidifier of a fuel cell system. [Solution] The fuel cell system 100 includes a gas supply unit that supplies cathode gas to the fuel cell stack 1 via a supply channel, a humidifier 32 provided at the intersection of the supply channel and the discharge channel to humidify the cathode gas with moisture contained in the cathode exhaust gas, a pressure sensor 52 that detects the pressure of the cathode gas flowing through the dry channel 32a inside the humidifier 32, and a controller that calculates the pressure of the cathode exhaust gas flowing through the wet channel 32b inside the humidifier. The controller calculates the amount of cathode gas leakage from the dry channel 32a to the wet channel 32b based on the deviation between the cathode gas pressure and the cathode exhaust gas pressure.

Description

【Technical Field】 【0001】 The present invention relates to a fuel cell system including a humidifier. 【Background Art】 【0002】 In recent years, in order to enable more people to access affordable, reliable, sustainable and advanced energy, technical development related to fuel cells that contribute to energy efficiency has been carried out. This type of fuel cell generally includes a humidifier for humidifying the cathode gas supplied to the fuel cell stack. As a technology related to such a fuel cell, a technology for detecting an internal leak of the humidifier is known. 【0003】 For example, in the fuel cell system described in Patent Document 1, the oxygen concentration of the cathode exhaust gas flowing out from the fuel cell stack is detected by an oxygen sensor, and the cathode stoichiometry is obtained based on the detection value of the oxygen sensor. Then, by comparing this cathode stoichiometry with the amount of oxygen supplied to the fuel cell system, an internal leak of the cathode gas from the dry side to the wet side of the humidifier is detected. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 U.S. Patent Application Publication No. 2008 / 0014478 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 However, the fuel cell system described in Patent Document 1 above needs to include an oxygen sensor for detecting an internal leak, which is accompanied by an increase in cost. 【Means for Solving the Problems】 【0006】 A fuel cell system according to one aspect of the present invention comprises a fuel cell stack to which a cathode gas containing oxygen is supplied via a supply channel and cathode exhaust gas is discharged via an exhaust channel; a gas supply unit to supply cathode gas to the fuel cell stack via a supply channel; a humidifier provided in the supply channel and the exhaust channel to humidify the cathode gas with moisture contained in the cathode exhaust gas; a first pressure acquisition unit to acquire a first pressure of the cathode gas on the inlet side of the humidifier; a second pressure acquisition unit to acquire a second pressure of the cathode exhaust gas on the outlet side of the humidifier; and a leak calculation unit to calculate the amount of cathode gas leakage from the first channel through which the cathode gas flows to the second channel through which the cathode exhaust gas flows inside the humidifier based on the deviation between the first pressure and the second pressure. The second pressure acquisition unit determines the first pressure drop, which is the pressure loss of cathode gas from the gas inlet of the fuel cell stack to which the supply channel is connected, to the gas outlet of the fuel cell stack to which the discharge channel is connected, and the second pressure drop, which is the pressure loss of cathode exhaust gas from the gas outlet to the humidifier. Based on the first pressure, first pressure drop, and second pressure drop acquired by the first pressure acquisition unit, the second pressure is calculated. The fuel cell system further includes a first temperature detection unit that detects the temperature of the cooling medium flowing into the fuel cell stack, and a second temperature detection unit that detects the temperature of the cooling medium flowing out of the fuel cell stack. The second pressure acquisition unit calculates the first pressure drop based on the temperature of the cooling medium detected by the first temperature detection unit, and calculates the second pressure drop based on the temperature of the cooling medium detected by the second temperature detection unit. [Effects of the Invention] 【0007】 According to the present invention, internal leaks in a humidifier can be detected with an inexpensive configuration. [Brief explanation of the drawing] 【0008】 [Figure 1] A diagram showing a schematic configuration of a fuel cell system according to an embodiment of the present invention. [Figure 2] This diagram schematically shows the overall configuration of the fuel cell stack included in the fuel cell system shown in Figure 1. [Figure 3] This diagram schematically shows the configuration of the humidifier included in the fuel cell system shown in Figure 1. [Figure 4] Figure 3 illustrates the principle of internal leakage in the humidifier. [Figure 5] Figure 3 shows the results of the durability test for the humidifier. [Figure 6] A block diagram showing the control configuration of a leak detection device according to an embodiment of the present invention. [Figure 7] Figure 6 schematically shows the flow path through which pressure loss is calculated by the pressure calculation unit. [Figure 8] A flowchart showing an example of the process executed by the controller in Figure 6. [Modes for carrying out the invention] 【0009】 Embodiments of the present invention will be described below with reference to Figures 1 to 8. Figure 1 is a diagram showing a schematic configuration of a fuel cell system 100 according to an embodiment of the present invention. The fuel cell system 100 in Figure 1 is mounted on a vehicle (fuel cell vehicle), for example, and generates electricity to be supplied to the vehicle's drive motor. 【0010】 As shown in Figure 1, the fuel cell system 100 includes a fuel cell stack 1, a fuel gas supply system 2 that supplies fuel gas (anode gas) to the fuel cell stack, an oxidant gas supply system 3 that supplies oxidant gas (cathode gas) to the fuel cell stack 1, and a cooling medium supply system 4 that supplies a cooling medium to the fuel cell stack 1. The fuel gas is, for example, hydrogen. The oxidant gas is, for example, air containing oxygen. The cooling medium is, for example, water or a coolant liquid containing ethylene glycol or propylene glycol. 【0011】 Figure 2 is a schematic perspective view showing the overall configuration of the fuel cell stack 1. For convenience, the three mutually orthogonal axial directions shown in the figure will be defined as the X1-X2 direction, the Y1-Y2 direction, and the Z1-Z2 direction. As shown in Figure 2, the fuel cell stack 1 has a stacked body 1a formed by stacking multiple power generation cells 10 in the Y1-Y direction. For convenience, Figure 1 shows the configuration of a single power generation cell 10. 【0012】 The power generation cell 10 includes a substantially rectangular plate-shaped membrane electrode assembly 11 extending in the X1-X2 direction and the Z1-Z2 direction, and a pair of substantially rectangular plate-shaped separators, namely an anode separator 12 and a cathode separator 13, arranged on both sides of the membrane electrode assembly 11 in the Y1-Y2 direction. Through holes 10a to 10f are opened at the X1-X2 end of the power generation cell 10 (membrane electrode assembly 11, anode separator 12, cathode separator 13), penetrating the power generation cell 10 in the Y1-Y2 direction. More specifically, through holes 10a to 10c are arranged along the Z1-Z2 direction at the X1 end of the power generation cell 10, and through holes 10d to 10f are arranged along the Z1-Z2 direction at the X2 end. The through holes 10a to 10c are for fuel gas supply, cooling medium discharge, and oxidizer gas discharge, respectively. Through-holes 10d to 10f are for supplying oxidizer gas, cooling medium, and fuel gas, respectively. 【0013】 Approximately rectangular plate-shaped end units 14 and 15 are arranged on both sides of the laminate 1a in the Y1-Y2 direction. The end unit 15 is provided with through holes 15a to 15f that penetrate the end unit 15 in the Y1-Y2 direction and communicate with through holes 10a to 10f. More specifically, at the end of the end unit 15 on the X1 direction side, a through hole 15a for fuel gas supply, a through hole 15b for cooling medium discharge, and a through hole 15c for oxidizer gas discharge are arranged along the Z1-Z2 direction. At the end of the end unit 15 on the X2 direction side, a through hole 15d for oxidizer gas supply, a through hole 15e for cooling medium supply, and a through hole 15f for fuel gas discharge are arranged along the Z1-Z2 direction. 【0014】 Fuel gas is supplied to each power generation cell 10 of the fuel cell stack 1 through through holes 15a and 10a as shown by arrow PA1 (solid line), oxidizer gas is supplied through through holes 15d and 10d as shown by arrow PA4 (dotted line), and cooling medium is supplied through through holes 15e and 10e as shown by arrow PA5 (dotted line). Fuel gas is discharged from the fuel cell stack 1 through through holes 10f and 15f as shown by arrow PA6 (solid line), oxidizer gas is discharged through through holes 10c and 15c as shown by arrow PA3 (dotted line), and cooling medium is discharged through through holes 10b and 15b as shown by arrow PA2 (dotted line). 【0015】 Although not shown in the diagram, the membrane electrode assembly 11 has an electrolyte membrane and a pair of electrodes formed on both sides of the electrolyte membrane in the Y1-Y2 direction. The electrolyte membrane is, for example, a solid polymer electrolyte membrane. The electrode on the Y2 direction side is an anode electrode positioned opposite the anode separator 12, and an anode channel PAa (solid line) is formed between the anode electrode and the anode separator 12 so as to communicate with the through holes 10a and 10f. As a result, fuel gas flows along the anode channel PAa from the X1 direction to the X2 direction, as shown by the solid arrow. 【0016】 The electrode on the Y1 direction side is a cathode electrode positioned opposite the cathode separator 13, and a cathode channel PAc (dotted line) is formed between the cathode electrode and the cathode separator 13 so as to communicate with the through holes 10d and 10c. As a result, as shown by the dotted arrow, the oxidizing gas flows along the cathode channel PAc from the X2 direction to the X1 direction. The anode separator 12 and cathode separator 13 of adjacent power generation cells 10, 10 are positioned adjacent to each other in the Y1-Y2 direction, and a cooling medium channel is formed between the anode separator 12 and the cathode separator 13 so as to communicate with the through holes 10e and 10b. As a result, the cooling medium flows along the cooling medium channel from the X2 direction to the X1 direction. 【0017】 In the anode electrode of the membrane electrode assembly 11, the fuel gas (hydrogen) supplied through the anode separator 12 is ionized by the action of the catalyst, passes through the electrolyte membrane, and moves to the cathode electrode side. The electrons generated at this time pass through the external circuit and are taken out as electrical energy. In the cathode electrode of the membrane electrode assembly 11, the oxidant gas (oxygen) supplied through the cathode separator 13 reacts with the hydrogen ions guided from the anode electrode and the electrons transferred from the anode electrode, and water is generated. The generated water gives appropriate humidity to the electrolyte membrane, and the excess water is discharged to the outside. 【0018】 As shown in FIG. 1, the fuel gas supply system 2 includes a fuel gas tank 21 in which the fuel gas (anode gas) is stored, a fuel gas supply flow path PA21 that guides the fuel gas in the fuel gas tank to the fuel gas inlet 21a of the fuel cell stack 1, and a fuel gas discharge flow path PA22 through which the fuel gas (fuel exhaust gas) discharged from the fuel gas outlet 21b of the fuel cell stack 1 flows. The fuel gas inlet 21a communicates with the through hole 15a of the end unit 15 (FIG. 2), and the fuel gas outlet 21b communicates with the through hole 15f. An injector 22 and an ejector 23 are arranged in the fuel gas supply flow path PA21. A gas-liquid separator 24 is connected to the fuel gas discharge flow path PA22. 【0019】 The injector 22 is composed of a single or a plurality of electromagnetic injectors connected in parallel. By driving the injector 22, the fuel gas is injected toward the ejector 23. The ejector 23 has a nozzle portion, a suction portion, a confluence portion, and a diffuser portion. The fuel gas injected from the injector 22 passes through the small-diameter nozzle portion and then flows into the diffuser portion through the confluence portion. The fuel gas passing through the ejector 23 is supplied to the fuel cell stack 1 through the fuel gas inlet 21a. 【0020】 The fuel gas discharged from the fuel gas outlet 21b, i.e., fuel exhaust gas (anode-off gas), is separated into fuel gas and water in the gas-liquid separator 24. The water separated in the gas-liquid separator 24 is discharged to the outside via the electromagnetic drain valve 25 and the drain passage PA23. The fuel gas separated in the gas-liquid separator 24 is led to the circulation passage PA24. The gas-liquid separator 24 is connected to the ejector 23 via the circulation passage PA24. The fuel gas flowing through the circulation passage PA24 can be discharged to the outside via the drain passage PA25 and the electromagnetic drain valve 26. 【0021】 The fuel gas, separated into gas and liquid form by the gas-liquid separator 24 due to the flow of fuel gas injected from the injector 22, is drawn into the ejector 23 via the circulation channel PA24. The drawn-in fuel gas merges with the fuel gas that has passed through the nozzle section of the ejector 23 at the confluence section of the ejector 23, and is then made into a uniform flow in the diffuser section of the ejector 23 before being supplied to the fuel cell stack 1 via the fuel gas inlet 21a. 【0022】 The oxidant gas supply system 3 includes an electric air pump 31 that generates high-pressure oxidant gas (cathode gas), an oxidant gas supply channel PA31 that guides the oxidant gas generated by the air pump 31 to the oxidant gas inlet 31a of the fuel cell stack 1, and an oxidant gas discharge channel PA32 through which the oxidant gas (oxidant exhaust gas) discharged from the oxidant gas outlet 31b of the fuel cell stack 1 flows. The oxidant gas inlet 31a communicates with a through-hole 15d of the end unit 15 (Figure 2), and the oxidant gas outlet 31b communicates with a through-hole 15c. The air pump 31 functions as a gas supply unit that compresses air taken in from the atmosphere to generate high-pressure oxidant gas. The air pump 31 may also be configured as a compressor. Humidifiers 32 are arranged in the oxidant gas supply channel PA31 and the oxidant gas discharge channel PA32, intersecting these channels PA31 and PA32. 【0023】 The humidifier 32 has a dry channel 32a that communicates with the oxidant gas supply channel PA31 and a wet channel 32b that communicates with the oxidant gas discharge channel PA32. The oxidant exhaust gas (anode off gas) contains moisture generated in the fuel cell stack 1. Therefore, the humidity of the oxidant exhaust gas flowing through the wet channel 32b is higher than the humidity of the oxidant gas flowing through the dry channel 32a. In the humidifier 32, humidity exchange occurs between the oxidant gas and the oxidant exhaust gas, and the moisture (water vapor) contained in the oxidant exhaust gas in the wet channel 32b humidifies the oxidant gas in the dry channel 32a. 【0024】 The oxidizer gas supply system 3 further includes a bypass channel PA33. The bypass channel PA33 is connected to the oxidizer gas supply channel PA31 upstream of the humidifier 32 and the oxidizer gas discharge channel PA32 downstream of the humidifier 32. Through the bypass channel PA33, the oxidizer gas can be supplied while bypassing the humidifier 32 and the fuel cell stack 1. 【0025】 In the oxidizer gas supply channel PA31, an adjustable electromagnetic control valve 33 is provided between the bypass channel PA33 and the humidifier 32. In the oxidizer gas discharge channel PA32, an adjustable electromagnetic control valve 34 is provided between the bypass channel PA33 and the humidifier 32. An adjustable electromagnetic control valve 35 is provided in the bypass channel PA33. By controlling the air pump 31 and the control valves 33-35, the supply amount and pressure of the oxidizer gas supplied to the fuel cell stack 1 can be adjusted. Furthermore, by controlling the control valves 33-35, the amount of oxidizer gas bypassing the fuel cell stack 1 can be adjusted. 【0026】 The oxidant gas supply channel PA31 is not equipped with a pressure sensor, and the pressure of the oxidant gas supplied to the fuel cell stack 1 is determined by calculation, as will be described later. On the other hand, the oxidant gas discharge channel PA32 is not equipped with a pressure sensor, and the pressure of the oxidant exhaust gas discharged from the fuel cell stack 1 is determined by calculation, as will be described later. 【0027】 A diluent 36 is connected to the downstream end of the oxidizer gas discharge channel PA32. The ends of the drain channels PA23 and PA25 are also connected to the diluent 36. In the diluent 36, the fuel exhaust gas introduced via the drain channel PA25 is diluted with the oxidizer exhaust gas and discharged to the outside (into the atmosphere) via the drain channel PA34 together with the liquid water introduced via the drain channel PA23. 【0028】 The cooling medium supply system 4 includes a cooling device 41, a cooling medium supply channel PA41 connecting the cooling device 41 to the cooling medium inlet 41a of the fuel cell stack 1, and a cooling medium discharge channel PA42 connecting the cooling device 41 to the cooling medium outlet 41b of the fuel cell stack 1. The cooling medium inlet 41a communicates with the through hole 15e of the end unit 15 (Figure 2), and the cooling medium outlet 41b communicates with the through hole 15b. The cooling medium supply channel PA41 is provided with a temperature sensor 53 for detecting the temperature of the cooling medium (cooling medium inlet temperature). The cooling medium discharge channel PA42 is provided with a temperature sensor 54 for detecting the temperature of the cooling medium. Although not shown in the figures, the cooling device 41 includes a pump for pressurizing the cooling medium toward the fuel cell stack 1, a heat exchanger (radiator) for cooling the cooling medium that has been heated after passing through the fuel cell stack 1, and a cooling fan for blowing cooling air to the heat exchanger. 【0029】 Figure 3 is a schematic diagram showing the configuration of the humidifier 32. In Figure 3, three mutually orthogonal axial directions are shown as the α direction, β direction, and γ direction. When the humidifier 32 is mounted on a vehicle, the α direction or β direction coincides, for example, with the direction of gravity. As shown in Figure 3, the humidifier 32 has a case 320 that is roughly rectangular in shape and a plurality of water permeable membranes 321 stacked within the case 320. The water permeable membranes 321 extend in the α and β directions, forming roughly rectangular plates, and are stacked in the γ direction. 【0030】 More specifically, inside the humidifier, a wet channel 32b (Figure 1) through which the oxidizing agent exhaust gas flows and a dry channel 32a (Figure 1) through which the oxidizing agent gas flows are alternately formed via a water permeable membrane 321. The flow direction of the oxidizing agent gas is, for example, the α direction, and the flow direction of the oxidizing agent exhaust gas is, for example, the β direction. Note that both the flow direction of the oxidizing agent gas and the oxidizing agent exhaust gas may be either the α direction or the β direction. For example, the oxidizing agent gas may flow toward one side in the α direction, and the oxidizing agent exhaust gas may flow toward the other side in the α direction. 【0031】 An oxidant gas supply channel PA31 (Figure 1) is connected to one end and the other end of case 320 in the β direction, and the oxidant gas supply channel PA31 communicates with the dry channel 32a. An oxidant gas discharge channel PA32 (Figure 1) is connected to one end and the other end of case 320 in the α direction, and the oxidant gas discharge channel PA32 communicates with the wet channel 32b. 【0032】 In this way, a wet channel 32b and a dry channel 32a are alternately formed inside the humidifier 32 via a water permeable membrane 321. The water permeable membrane 321 is, for example, a hollow fiber membrane made of hollow fibers of a polymer resin. In such a water permeable membrane 321, moisture contained in the oxidizing agent exhaust gas is separated by the capillary action of the hollow fiber membrane, and the separated moisture permeates through the hollow fiber membrane and moves from the wet channel 32b to the dry channel 32a, humidifying the oxidizing agent gas. For this reason, the water permeable membrane 321 can only allow moisture (water vapor) contained in the oxidizing agent exhaust gas to pass through. 【0033】 When the fuel cell system 100 is operating, the pressure of the oxidizer gas flowing through the dry channel 32a is higher than the pressure of the oxidizer exhaust gas flowing through the wet channel 32b, creating a pressure difference between channels 32a and 32b. This pressure difference increases with increasing supply of oxidizer gas. As a result, internal leakage due to this pressure difference may occur in the humidifier 32, as shown in Figure 4. 【0034】 In other words, as shown by the dotted arrow in Figure 4, there is a risk that oxidizing gas may leak from the dry channel 32a to the wet channel 32b through the water permeable membrane 321. Alternatively, the water permeable membrane 321 may be severely damaged, such as by rupturing, which could lead to a significant increase in leakage. 【0035】 Figure 5 shows the results of a durability test of the humidifier 32 when a predetermined differential pressure is applied between the flow paths 32a and 32b. The horizontal axis of Figure 5 represents time T (number of times the differential pressure occurs), and the vertical axis represents the amount of internal leak L. As shown in Figure 5, the amount of internal leak L gradually increases over time, and becomes almost constant (L1) when a predetermined time Ta is reached. After that, the amount of internal leak L remains constant until a predetermined time Tb is reached, and beyond the predetermined time Tb, the amount of internal leak L increases rapidly. The reason for the rapid increase in the amount of internal leak L is, for example, that a hole has formed in the water permeable membrane 321. Based on the test results in Figure 5, the durability life of the humidifier 32 can be determined, for example, to a predetermined time Tb. 【0036】 If an internal leak occurs in the humidifier 32, the supply of oxidant gas to the fuel cell stack 1 will be insufficient, leading to unstable power generation. Therefore, it is preferable to detect the amount of internal leak in the humidifier 32 and increase the supply of oxidant gas flowing through the humidifier 32 by an amount equivalent to the amount of internal leak, thereby suppressing instability in power generation. In this embodiment, the amount of internal leak is detected using a leak detection device. The leak detection device is included in the fuel cell system 100 and is configured to detect the amount of internal leak with an inexpensive configuration. The configuration of the leak detection device will be described below. 【0037】 Figure 6 is a block diagram showing the control configuration of the leak detection device 200. As shown in Figure 6, the leak detection device 200 includes a controller 50, temperature sensors 53 and 54 that are respectively connected to the controller 50 in a communicative manner, and a gas supply unit 55. The gas supply unit 55 is a general term for elements that supply oxidant gas to the fuel cell stack 1 via the oxidant gas supply channel PA 31, such as an air pump 31 and control valves 33 to 35. 【0038】 The controller 50 reads signals indicating temperatures T1 and T2 detected by temperature sensors 53 and 54. Furthermore, the controller 50 communicates with other controllers (for example, a power generation control controller) and reads the target flow rate of oxidizer gas (oxidizer gas target value Ga) corresponding to the amount of power generation requested by the vehicle (requested power generation amount), which is output by the other controller. 【0039】 More specifically, the power generation control controller calculates the target drive torque of the drive motor based on a signal from an accelerator pedal position sensor that detects the opening degree of the accelerator pedal, and calculates the required amount of power generation necessary for the drive motor to generate the target drive torque. Alternatively, the power generation control controller calculates the required amount of power generation based on a signal from a battery sensor that detects the remaining battery capacity (SOC), so that the remaining battery capacity reaches a predetermined value. Then, it calculates the target value Ga of the oxidizer gas corresponding to the required amount of power generation and outputs it to the controller 50. 【0040】 The controller 50 is a computer comprising a processing unit having a CPU, ROM, RAM, and peripheral circuits. Functionally, the controller 50 has a pressure calculation unit 501, a leak amount calculation unit 502, a determination unit 503, an output unit 504, and a storage unit 505. The storage unit 505 stores in advance the shape (area, length, etc.) of each flow path through which the oxidizer gas flows, as well as the pressure loss coefficient. 【0041】 As shown in Figure 2, the through-hole 15d for supplying oxidant gas to the fuel cell stack 1 is located near the through-hole 15e for supplying the cooling medium. Therefore, the temperature of the oxidant gas at the stack inlet (gas inlet temperature T11) has a predetermined correlation with the temperature T1 of the cooling medium at the stack inlet detected by the temperature sensor 53, and the higher the temperature T1, the higher the gas inlet temperature T11. Also, the through-hole 15c for discharging oxidant gas to the fuel cell stack 1 is located near the through-hole 15b for discharging the cooling medium. Therefore, the temperature of the oxidant gas at the stack outlet (gas outlet temperature T12) has a predetermined correlation with the temperature T2 of the stack outlet detected by the temperature sensor 54, and the higher the temperature T2, the higher the gas outlet temperature T12. These correlations are also stored in the storage unit 505 in advance. 【0042】 The pressure calculation unit 501 calculates the pressure drop in the flow path from the dry flow path 32a to the wet flow path 32b of the humidifier 32 via the fuel cell stack 1. Figure 7 is a schematic diagram showing the flow path for which the pressure drop is calculated. As shown in Figure 7, the flow path from the dry flow path 32a to the wet flow path 32b of the humidifier 32 can be divided into the pre-stack flow path PA35 from the dry flow path 32a to the fuel cell stack 1, the in-stack flow path PA36 from the oxidizer gas inlet 31a to the oxidizer gas outlet 31b of the fuel cell stack 1, and the post-stack flow path PA37 from the fuel cell stack 1 to the humidifier 32. 【0043】 Of these flow paths PA35 to PA37, the pressure drop ΔP1 in the pre-stack flow path PA35 is small (almost zero), and this pressure drop ΔP1 can be ignored. Therefore, the pressure at the inlet of the oxidizer gas in the fuel cell stack 1 (inlet pressure) P11 is approximately equal to the pressure P1 (dry side pressure) in the dry flow path 32a of the humidifier 32, and the pressure calculation unit 501 considers the inlet pressure P11 to be pressure P1. 【0044】 The pressure calculation unit 501 calculates the inlet pressure P11 based on the oxidizer gas target value Ga and the temperature T1 detected by the temperature sensor 53. Specifically, the pressure calculation unit 501 first calculates the gas inlet temperature T11 based on the temperature T1 of the cooling medium stack inlet detected by the temperature sensor 53, using a predetermined correlation relationship stored in the storage unit 505. Next, the pressure calculation unit 501 calculates the inlet pressure P11 (pressure P1) based on the calculated gas inlet temperature T11 and the oxidizer gas target value Ga. 【0045】 The pressure calculation unit 501 further calculates the pressure loss ΔP2 in the stack channel PA36 and the pressure loss ΔP3 in the post-stack channel PA37. In this case, the pressure calculation unit 501 first calculates the gas inlet temperature T11 based on the temperature T1 of the cooling medium stack inlet detected by the temperature sensor 53, using a predetermined correlation relationship stored in the storage unit 505. Next, the pressure calculation unit 501 calculates the volumetric flow rate of the oxidizer gas at the stack inlet based on the calculated gas inlet temperature T11 and the inlet pressure P11 (pressure P1), and calculates the pressure loss ΔP2 of the oxidizer gas in the stack channel PA36 based on this volumetric flow rate and the pressure loss coefficient ζ1 of the stack channel PA36 stored in the storage unit 505. 【0046】 Next, the pressure calculation unit 501 calculates the gas outlet temperature T12 based on the temperature T2 of the cooling medium stack outlet detected by the temperature sensor 54, using a predetermined correlation relationship stored in the memory unit 505. Furthermore, the pressure calculation unit 501 subtracts the pressure drop ΔP2 from the inlet pressure P11 to calculate the pressure (outlet pressure) P12 at the outlet of the oxidizer gas of the fuel cell stack 1. Then, based on the calculated gas outlet temperature T12 and outlet pressure P12, it calculates the volumetric flow rate of the oxidizer gas at the stack outlet, and based on this volumetric flow rate and the pressure drop coefficient ζ2 of the post-stack flow path PA37 stored in the memory unit 505, it calculates the pressure drop ΔP3 of the oxidizer gas in the post-stack flow path PA37. 【0047】 Next, the pressure calculation unit 501 calculates the pressure P2 (wet side pressure) in the wet flow path 32b. Specifically, the wet side pressure P2 is calculated by subtracting the pressure loss ΔP2 in the in-stack flow path PA36 and the pressure loss ΔP3 in the post-stack flow path PA37 from the dry side pressure P1. Furthermore, the differential pressure ΔPa inside the humidifier 32 is calculated by subtracting the wet side pressure P2 from the dry side pressure P1. 【0048】 In the above, the pressure loss ΔP1 in the pre-stack flow path PA35 was ignored. However, when the pressure loss ΔP1 cannot be ignored, the pressure loss ΔP1 may be calculated using the temperature of the oxidizer gas at the outlet of the dry flow path 32a (for example, the temperature detected by a temperature sensor), the pressure P1, and the pressure loss coefficient of the pre-stack flow path PA35. In this case, the pressure calculation unit 501 should calculate the wet side pressure P2 by subtracting the pressure losses ΔP1, ΔP2, and ΔP3 from the dry side pressure P1. The pressure P1 may be detected by a pressure sensor rather than being determined by calculation. For example, a pressure sensor may be provided between the humidifier 32 and the control valve 33. 【0049】 The internal leak rate L of the humidifier 32 increases as the differential pressure ΔPa increases, and there is a predetermined correlation between the internal leak rate L and the differential pressure ΔPa. This correlation is stored in the memory unit 505 beforehand. The leak rate calculation unit 502 calculates the internal leak rate L of the humidifier 32 based on the differential pressure ΔPa calculated by the pressure calculation unit 501 and the predetermined correlation stored in the memory unit 505. 【0050】 The determination unit 503 determines whether the internal leak amount L calculated by the leak amount calculation unit 502 is less than or equal to a predetermined value La stored in the storage unit 505. The predetermined value La corresponds to the internal leak amount at which it becomes difficult to continue stable power generation. For example, the predetermined value L1 in Figure 5 is set to the predetermined value La. If the internal leak amount L exceeds the predetermined value La, the determination unit 503 determines that it is difficult to continue stable power generation. 【0051】 The output unit 504 outputs a control signal to the gas supply unit 55 (such as the air pump 31) to supply oxidant gas corresponding to the target value Ga of oxidant gas. More specifically, the output unit 504 controls the gas supply unit 55 to increase the amount of oxidant gas supplied by the amount of internal leak L calculated by the leak amount calculation unit 502. This is called leak addition control. As a result, fuel gas and oxidant gas are supplied to the fuel cell stack 1 in a predetermined ratio, enabling stable power generation. 【0052】 The output unit 504 controls the gas supply unit 55 to stop power generation when the determination unit 503 determines that the internal leak amount L exceeds a predetermined value La. This is called stop control. In stop control, the drive of the air pump 31 is stopped, or the control valves 33-35 are controlled to stop the supply of oxidizer gas to the fuel cell stack 1. 【0053】 Figure 8 is a flowchart showing an example of the process performed by the controller 50. The process shown in this flowchart starts, for example, when the power generation operation of the fuel cell system 100 begins. First, in step S1, the controller 50 reads a signal (oxidizer gas target value Ga) from the power generation control controller and also reads signals from the temperature sensors 53 and 54. 【0054】 Next, in step S2, the controller 50 calculates the inlet pressure P11 based on the oxidizer gas target value Ga and the temperature T1 detected by the temperature sensor 53. The inlet pressure P11 is considered to be the pressure P1 (dry side pressure) of the dry flow path 32a of the humidifier 32. Next, in step S3, the controller 50 calculates the pressure loss ΔP2 of the in-stack flow path PA36 based on the calculated inlet pressure, the temperature T1 detected by the temperature sensor 53, and the pressure loss coefficient ζ1 of the in-stack flow path PA36. Furthermore, the controller 50 calculates the pressure loss ΔP3 of the post-stack flow path PA37 based on the calculated pressure loss ΔP2, the temperature T2 detected by the temperature sensor 54, and the pressure loss coefficient ζ2 of the post-stack flow path PA37. 【0055】 Next, in step S4, the controller 50 calculates the wet side pressure P2 by subtracting the pressure losses ΔP2 and ΔP3 calculated in step S3 from the dry side pressure P1 calculated in step S2. Furthermore, the controller 50 calculates the internal leak amount L of the humidifier 32 based on the differential pressure ΔPa between the dry side pressure P1 and the wet side pressure P2. 【0056】 Next, in step S5, the controller 50 determines whether the internal leak amount L calculated in step S4 is greater than a predetermined value La. If the result in step S5 is positive, the process proceeds to step S6; otherwise, it proceeds to step S7. In step S6, a control signal is output to the gas supply unit 55 to perform leak addition control, increasing the supply amount of oxidizer gas by the amount of the internal leak amount L. Meanwhile, in step S7, a control signal is output to the gas supply unit 55 to perform stop control, stopping power generation. 【0057】 The operation of the leak detection device 200 can be summarized as follows: The dry-side pressure P1 of the oxidizer gas in the dry channel 32a of the humidifier 32 is calculated based on a signal indicating the target value Ga of the oxidizer gas transmitted from another controller and from the temperature sensor 53 (step S2). The wet-side pressure P2 of the oxidizer exhaust gas in the wet channel 32b is calculated using the dry-side pressure P1 and signals from the temperature sensors 53 and 54. Specifically, the pressure loss ΔP2 of the in-stack channel PA36 is calculated based on the dry-side pressure P1, the temperature T1 detected by the temperature sensor 53, and the pressure loss coefficient ζ1 of the in-stack channel PA36. Furthermore, the pressure loss ΔP3 of the post-stack channel PA37 is calculated based on the pressure loss ΔP2, the temperature T2 detected by the temperature sensor 54, and the pressure loss coefficient ζ2 of the post-stack channel PA37 (step S3). Then, the wet side pressure P2 is calculated by subtracting the pressure losses ΔP2 and ΔP3 from the dry side pressure P1. 【0058】 This eliminates the need to separately provide pressure sensors to detect the dry side pressure P1 and the wet side pressure P2, simplifying the configuration of the leak detection device 200. Furthermore, since the pressure drops ΔP2 and ΔP3 are calculated based on the temperatures T1 and T2 of the cooling medium, there is no need to provide sensors to detect the temperature of the oxidizer gas and oxidizer exhaust gas, saving on the number of sensors. Once the wet side pressure P2 is calculated, the internal leak amount L is calculated based on the differential pressure ΔPa between the oxidizer gas in the dry channel 32a and the oxidizer exhaust gas in the wet channel 32b (step S4). This allows the internal leak amount L to be determined with an inexpensive configuration. 【0059】 When the internal leak amount L is calculated, the amount of oxidant gas supplied to the humidifier 32 increases by an amount equivalent to the internal leak amount L (step S6). As a result, the fuel cell stack 1 is supplied with oxidant gas equivalent to the target value Ga, enabling stable power generation. On the other hand, if the internal leak amount L exceeds a predetermined value La, the supply of oxidant gas to the fuel cell stack 1 is stopped (step S7). This ensures high safety, as power generation in the fuel cell stack 1 can be stopped if the humidifier 32 is damaged. 【0060】 This embodiment can provide the following effects and advantages. (1) The fuel cell system 100 includes a fuel cell stack 1 to which an oxidant gas (cathode gas) containing oxygen is supplied via an oxidant gas supply channel PA31 and oxidant exhaust gas (cathode-off gas) is discharged via an oxidant gas discharge channel PA32; a gas supply unit 55 to supply oxidant gas to the fuel cell stack 1 via the oxidant gas supply channel PA31; and a humidifier 32 provided in the oxidant gas supply channel PA31 and the oxidant gas discharge channel PA32 to humidify the oxidant gas with moisture contained in the oxidant exhaust gas. The humidifier 32 includes a pressure calculation unit 501 that calculates the pressure of the oxidizing agent gas flowing through the dry channel 32a on the inlet side of the humidifier 32 (dry side pressure P1) and the pressure of the oxidizing agent exhaust gas flowing through the wet channel 32b on the outlet side of the humidifier 32 (wet side pressure P2), and a leak amount calculation unit 502 that calculates the amount of oxidizing agent gas leaking from the dry channel 32a to the wet channel 32b inside the humidifier 32 (internal leak amount L) based on the difference between the dry side pressure P1 and the wet side pressure P2, i.e., the differential pressure ΔPa (Figures 1 and 6). This eliminates the need for an oxygen sensor or the like to detect the oxygen concentration of the oxidizing agent exhaust gas, and allows for the detection of the internal leak amount L of the humidifier 32 with an inexpensive configuration. 【0061】 (2) The fuel cell system 100 (leak detection device 200) further includes an output unit 504 that controls the gas supply unit 55 based on the amount of oxidant gas leakage calculated by the leak amount calculation unit 502 (Figure 6). This makes it possible to increase the flow rate of oxidant gas flowing into the humidifier 32 by an amount equivalent to the internal leak amount L, enabling stable power generation in the fuel cell stack 1. 【0062】 (3) The pressure calculation unit 501 determines the pressure drop ΔP2 of the oxidant gas from the oxidant gas inlet 31a of the fuel cell stack 1 to which the oxidant gas supply channel PA31 is connected, to the oxidant gas outlet 31b of the fuel cell stack 1 to which the oxidant gas discharge channel PA32 is connected, and the pressure drop ΔP3 of the oxidant exhaust gas from the oxidant gas outlet 31b to the humidifier 32. Based on the calculated dry-side pressure P1 and pressure drops ΔP2 and ΔP3, it calculates the wet-side pressure P2 (Figure 7). This eliminates the need for pressure sensors or the like to detect the wet-side pressure P2, and allows the wet-side pressure P2 to be calculated with an inexpensive configuration. 【0063】 (4) The fuel cell system 100 further includes a temperature sensor 53 for detecting the temperature T1 of the cooling medium flowing into the fuel cell stack 1, and a temperature sensor 54 for detecting the temperature T2 of the cooling medium flowing out of the fuel cell stack 1 (Figure 1). The pressure calculation unit 501 calculates the pressure drop ΔP1 based on the temperature T1 of the cooling medium detected by the temperature sensor 53, and calculates the pressure drop ΔP2 based on the temperature T2 of the cooling medium detected by the temperature sensor 54. This eliminates the need for temperature sensors to detect the temperature of the oxidizer gas and oxidizer exhaust gas, and allows for the calculation of pressure drops ΔP1 and ΔP2 with an inexpensive configuration. 【0064】 (5) The output unit 504 controls the gas supply unit 55 so that the flow rate of oxidant gas supplied to the fuel cell stack 1 increases as the amount of oxidant gas leakage (internal leakage amount L) calculated by the leakage amount calculation unit 502 increases. Furthermore, the output unit 504 controls the power generation operation to stop power generation in the fuel cell stack 1 when the amount of oxidant gas leakage calculated by the leakage amount calculation unit 502 exceeds a predetermined value La (Figure 8). This allows stable power generation to continue in the fuel cell stack 1. 【0065】 (6) The humidifier 32 is constructed by stacking multiple water permeable membranes 321, with dry channels 32a and wet channels 32b alternately formed in the stacking direction of the water permeable membranes 321 (Figure 3). This allows for good humidity exchange between the oxidizing gas and the oxidizing exhaust gas. 【0066】 The above embodiment can be modified into various forms. Several modifications are described below. In the above embodiment, oxidant gas (cathode gas) is supplied to the fuel cell stack 1 via an oxidant gas supply channel (supply channel), and oxidant exhaust gas (cathode exhaust gas) is discharged from the fuel cell stack 1 via an oxidant gas discharge channel (discharge channel). However, the configuration of the supply channel and discharge channel is not limited to those described above. In the above embodiment, a humidifier 32 is constructed by stacking a plurality of water permeable membranes 321. However, the configuration of the humidifier can be any as long as it is provided in the supply channel and discharge channel and humidifies the cathode gas with moisture contained in the cathode exhaust gas. 【0067】 In the above embodiment, the pressure calculation unit 501 calculates the pressure of the cathode gas flowing through the dry channel 32a (first channel) inside the humidifier 32, i.e., the dry-side pressure P1 (first pressure). However, it may also be detected by a pressure sensor, and the configuration of the first pressure acquisition unit is not limited to that described above. In the above embodiment, the pressure calculation unit 501 calculates the pressure of the cathode exhaust gas (cathode-off gas) in the wet channel 32b (second channel) inside the humidifier 32, i.e., the wet-side pressure P2 (second pressure). Specifically, the wet-side pressure P2 is calculated based on the pressure drop ΔP2 (first pressure drop) of the cathode gas from the oxidizer gas inlet 31a (gas inlet) to the oxidizer gas outlet 31b (gas outlet) of the fuel cell stack 1, and the pressure drop ΔP3 (second pressure drop) of the cathode exhaust gas from the oxidizer gas outlet 31b to the humidifier 32. However, the configuration of the second pressure acquisition unit is not limited to that described above. 【0068】 In the above embodiment, the leak amount calculation unit 502 calculates the internal leak amount based on the differential pressure ΔPa (deviation) between the dry side pressure P1 and the wet side pressure P2, but the configuration of the leak calculation unit is not limited to that described above. In the above embodiment, the output unit 504 controls the gas supply unit 55 based on the internal leak amount L calculated by the leak amount calculation unit 502, but the configuration of the control unit is not limited to that described above. In the above embodiment, the temperature sensor 53 (first temperature detection unit) detects the temperature T1 of the cooling medium flowing into the fuel cell stack 1, and the temperature T2 of the cooling medium flowing out of the fuel cell stack 1 is detected by the temperature sensor 54 (second temperature detection unit), but the configurations of the first temperature detection unit and the second temperature detection unit are not limited to those described above. The temperature T11 of the cathode gas at the stack inlet and the temperature T12 of the cathode exhaust gas at the stack outlet may be detected or calculated without using the temperatures T1 and T2 of the cooling medium. 【0069】 The above describes an example of applying the fuel cell system 100 to a fuel cell vehicle, but the fuel cell system of the present invention can also be applied to vehicles other than fuel cell vehicles. 【0070】 The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other. [Explanation of Symbols] 【0071】 1 Fuel cell stack, 31 Air pump, 32 Humidifier, 32a Dry channel, 32b Wet channel, 33-35 Control valve, 50 Controller, 53, 54 Temperature sensor, 55 Gas supply unit, 501 Pressure calculation unit, 502 Leakage amount calculation unit, 503 Judgment unit, 504 Output unit, PA31 Oxidizer gas supply channel, PA32 Oxidizer gas discharge channel, P1 Dry side pressure, P2 Wet side pressure, ΔPa Differential pressure, ΔP2, ΔP3 Pressure loss

Claims

[Claim 1] A fuel cell stack in which a cathode gas containing oxygen is supplied via a supply channel and cathode exhaust gas is discharged via an exhaust channel, A gas supply unit that supplies cathode gas to the fuel cell stack via the supply channel, A humidifier is provided in the supply channel and the discharge channel, which humidifies the cathode gas with moisture contained in the cathode exhaust gas, A first pressure acquisition unit for acquiring the first pressure of the cathode gas on the inlet side of the humidifier, A second pressure acquisition unit for acquiring the second pressure of the cathode exhaust gas on the outlet side of the humidifier, The humidifier includes a leak calculation unit that calculates the amount of cathode gas leaking from a first channel through which cathode gas flows to a second channel through which cathode exhaust gas flows, based on the deviation between the first pressure and the second pressure, The second pressure acquisition unit is, The first pressure drop, which is the pressure loss of cathode gas from the gas inlet of the fuel cell stack to which the supply channel is connected, to the gas outlet of the fuel cell stack to which the discharge channel is connected, and the second pressure drop, which is the pressure loss of cathode exhaust gas from the gas outlet to the humidifier, are determined, and the second pressure is calculated based on the first pressure, the first pressure drop and the second pressure drop obtained by the first pressure acquisition unit. A first temperature detection unit for detecting the temperature of the cooling medium flowing into the fuel cell stack, The system further includes a second temperature detection unit for detecting the temperature of the cooling medium that has leaked out from the fuel cell stack, The fuel cell system is characterized in that the second pressure acquisition unit calculates the first pressure loss based on the temperature of the cooling medium detected by the first temperature detection unit, and calculates the second pressure loss based on the temperature of the cooling medium detected by the second temperature detection unit. [Claim 2] In the fuel cell system according to claim 1, A fuel cell system further comprising a control unit that controls the gas supply unit based on the amount of cathode gas leakage calculated by the leakage calculation unit. [Claim 3] In the fuel cell system according to Claim 2, The control unit controls the gas supply unit so that the flow rate of cathode gas supplied to the fuel cell stack increases in response to an increase in the amount of cathode gas leakage calculated by the leakage calculation unit. Furthermore, the fuel cell system is characterized in that the control unit controls the power generation operation to stop power generation in the fuel cell stack when the amount of cathode gas leakage calculated by the leakage calculation unit exceeds a predetermined amount. [Claim 4] In the fuel cell system according to any one of claims 1 to 3, The humidifier is characterized in that the first channel and the second channel are alternately stacked with a water permeable membrane in between.

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