Fuel cell system

Abstract

To stabilize power generation of a fuel battery stack under an environment in which the concentration of oxygen in the fuel battery system easily drops.SOLUTION: A fuel battery system 1 includes: a fuel battery stack FCS formed by depositing a plurality of fuel battery cells C; a cell voltage detection unit VD for detecting the respective voltages V1 to Vn of the fuel battery cells C1 To Cn; and a control unit 3 for controlling operations of a fan F according to the temperature Tfcs of the fuel battery stack FCS in a normal mode and driving the fan F in a ventilation mode. The control unit 3 shifts the normal mode to the ventilation mode when the voltage V of the fuel battery stack FCS becomes a threshold value Vth1 or smaller.SELECTED DRAWING: Figure 1

Description

Technical Field

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

[0002] Some fuel cell systems are installed in vehicles and generators.

[0003] However, when the fuel cell system is installed in a vehicle where an air supply inlet is not provided at the front of the vehicle and it is difficult to intake traveling wind, or when the fuel cell system is installed in a stationary generator, external air cannot be actively drawn into the fuel cell system, which may cause a decrease in oxygen concentration inside the fuel cell system and a voltage drop of the fuel cell stack in the fuel cell system.

[0004] In addition, when air with reduced oxygen concentration generated by power generation is discharged from the fuel cell stack into the fuel cell system, the discharged air is supplied from the air compressor to the fuel cell stack, which may cause a voltage drop of the fuel cell stack.

[0005] Therefore, it has been considered that the fuel cell system is provided with a ventilation member such as a fan for actively drawing external air into the fuel cell system and discharging air discharged from the fuel cell stack out of the fuel cell system. A related technique is disclosed in Patent Document 1.

[0006] However, when the ventilation member is continuously driven to maintain the oxygen concentration inside the fuel cell system, the airflow generated by the ventilation member excessively cools the fuel cell stack and auxiliary devices, so that the temperatures of the fuel cell stack and the auxiliary devices deviate from the rated temperature range, which may lead to unstable power generation of the fuel cell stack. Prior Art Literature Patent Literature

[0007] Patent Document 1 Japanese Patent Publication No. 2010-257580 [Overview of the project] [Problems that the invention aims to solve]

[0008] One aspect of the present invention is to stabilize the power generation of a fuel cell stack in an environment where the oxygen concentration in the fuel cell system tends to decrease. [Means for solving the problem]

[0009] One embodiment of the present invention is a fuel cell system comprising a fuel cell stack formed by stacking a plurality of fuel cell cells and an auxiliary device for generating power from the fuel cell stack, the system comprising a voltage detection unit for detecting a voltage related to the fuel cell stack, a ventilation unit for ventilating the inside of the fuel cell system, and a control unit that controls the operation of the ventilation unit according to the temperature of the fuel cell stack or the auxiliary device in normal mode and drives the ventilation unit in ventilation mode, wherein the control unit transitions from normal mode to ventilation mode when the voltage related to the fuel cell stack falls below a first threshold.

[0010] This allows the ventilation unit to be activated when the oxygen concentration in the fuel cell system decreases and the voltage of the fuel cell stack falls below the first threshold, thereby ventilating the fuel cell system. This allows outside air to be drawn into the fuel cell system and the air discharged from the fuel cell stack to be expelled outside the fuel cell system, thereby suppressing the decrease in oxygen concentration within the fuel cell system. Furthermore, when the voltage of the fuel cell stack is not below the first threshold, the operation of the ventilation unit can be controlled according to the temperature of the fuel cell stack or auxiliary equipment in normal mode, thereby adjusting the temperature of the fuel cell stack or auxiliary equipment within the rated temperature range and stabilizing the power generation of the fuel cell stack.

[0011] Furthermore, the control unit may be configured to drive the ventilation unit from the normal mode to the ventilation mode until a predetermined driving time has elapsed, and then, when the voltage related to the fuel cell stack becomes greater than or equal to a second threshold greater than the first threshold, it may transition from the ventilation mode to the normal mode.

[0012] As a result, when the voltage of the fuel cell stack exceeds the first threshold after transitioning from normal mode to ventilation mode, the frequent switching between normal mode and ventilation mode can be suppressed compared to the case where the transition is made from ventilation mode to normal mode, thereby further stabilizing the power generation of the fuel cell stack.

[0013] Furthermore, the voltage detection unit may be configured to detect the voltage of each of the plurality of fuel cell cells, and the control unit may be configured to use the average value of the voltages detected by the voltage detection unit as the voltage for the fuel cell stack.

[0014] This reduces unnecessary ventilation within the fuel cell system, thereby further stabilizing power generation from the fuel cell stack.

[0015] Furthermore, the ventilation unit is a fan that increases the amount of heat dissipated by the radiator, which exchanges heat between the refrigerant heated by the heat generated by the fuel cell stack and the air. The exhaust port from which air is discharged from the fuel cell stack may be positioned downwind of the airflow created by the ventilation unit relative to the intake port of the fuel cell stack.

[0016] This suppresses the supply of air discharged from the exhaust port to the fuel cell stack, thereby suppressing the decrease in oxygen concentration in the air supplied to the fuel cell stack, and further suppressing the decrease in oxygen concentration within the fuel cell system. [Effects of the Invention]

[0017] According to the present invention, power generation of a fuel cell stack can be stabilized in an environment with a relatively low oxygen concentration within a fuel cell system. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0018] [Figure 1] FIG. 1 is a diagram showing an application example of the fuel cell system according to the embodiment. [Figure 2] FIG. 2 is a diagram showing another application example of the fuel cell system according to the embodiment. [Figure 3] FIG. 3 is a flowchart showing an example of the operation of a control unit during mode switching. [Figure 4] FIG. 4 is a diagram showing an arrangement example of exhaust ports or fans of a fuel cell stack. [MODE FOR CARRYING OUT THE INVENTION]

[0019] Embodiments will be described in detail below with reference to the drawings.

[0020] FIG. 1 is a diagram showing an application example of the fuel cell system according to the embodiment.

[0021] In the application example of the fuel cell system shown in FIG. 1, a fuel cell system 1 is mounted on a vehicle Ve. For example, the vehicle Ve is an industrial vehicle such as a forklift. Further, it is assumed that the vehicle Ve is mounted with a load Lo such as an inverter that drives a traveling motor, and electric power is supplied from the fuel cell system 1 to the load Lo. Furthermore, it is assumed that since an air supply port (not shown) is provided on a side surface of the vehicle Ve relative to the forward direction of the vehicle Ve, or the traveling speed of the vehicle Ve is relatively low, it is difficult to introduce traveling wind into the vehicle Ve, and it is difficult to ventilate the inside of the fuel cell system 1 by the traveling wind.

[0022] Further, FIG. 2 is a diagram showing another application example of the fuel cell system according to the embodiment. Note that the fuel cell system 1 shown in FIG. 2 is the same as the fuel cell system 1 shown in FIG. 1.

[0023] In the application example of the fuel cell system 1 shown in Figure 2, the fuel cell system 1 is installed on a stationary generator Sg. For example, the stationary generator Sg is a generator that supplies power to load Lo in cooperation with commercial power sources or solar power generators, and power is supplied to load Lo from the fuel cell system 1. Furthermore, since the stationary generator Sg is fixed in a predetermined location and does not move, it is difficult to ventilate the inside of the fuel cell system 1 using airflow from driving. In other words, the fuel cell system 1 shown in Figure 1 or Figure 2 is assumed to be in an environment where the oxygen concentration inside the fuel cell system 1 is relatively low.

[0024] Furthermore, the fuel cell system 1 shown in Figure 1 or Figure 2 comprises a fuel cell stack FCS, a cell voltage detection unit VD (voltage detection unit), a fuel tank Tk, a main shut-off valve SV, an injector INJ, a gas-liquid separator GLS, a circulation pump HP, an exhaust and drain valve EDV, a diluent DIL, an air compressor ACP, an air pressure regulating valve ARV, and an air shut-off valve ASV.

[0025] Furthermore, the fuel cell system 1 shown in Figure 1 or Figure 2 includes a radiator R, a fan F (ventilation unit), a water pump WP, an intercooler IC, a DC-DC converter CNV, an energy storage device B, a voltage sensor Sv, a current sensor Si, a temperature sensor St, a memory unit 2, and a control unit 3.

[0026] A fuel cell stack (FCS) is a fuel cell composed of multiple fuel cell cells C (fuel cell cells C1 to Cn) stacked together, and generates electricity through an electrochemical reaction between hydrogen contained in hydrogen gas and oxygen contained in air. Generally, the voltage of a fuel cell C is the voltage obtained by subtracting three types of overvoltages—resistive overvoltage, activation overvoltage, and concentration overvoltage—from the theoretical electromotive force. Resistive overvoltage is a voltage that arises from the difficulty of electrons and platons moving within the fuel cell C. Activation overvoltage is a voltage that arises from the difficulty of hydrogen oxidation reactions at the anode of the fuel cell C and oxygen reduction reactions at the cathode of the fuel cell C. Concentration overvoltage is a voltage that arises from the difficulty of hydrogen gas and air diffusion within the fuel cell C. Therefore, if at least one of the overvoltages—resistive overvoltage, activation overvoltage, and concentration overvoltage—increases, the voltage of the fuel cell stack (FCS) will decrease.

[0027] The cell voltage detection unit VD detects the voltages V1 to Vn of each fuel cell cell C1 to Cn and sends the detected voltages V1 to Vn to the control unit 3.

[0028] The fuel tank Tk is a storage container for hydrogen gas. The hydrogen gas stored in the fuel tank Tk is supplied to the fuel cell stack FCS via the main shut-off valve SV and the injector INJ.

[0029] The main shut-off valve SV is composed of a solenoid valve or the like and supplies hydrogen gas to the injector INJ. The main shut-off valve SV also shuts off the supply of hydrogen gas to the injector INJ through the operation control of the control unit 3. When the fuel cell system 1 is installed in a vehicle Ve, the fuel tank Tk and the main shut-off valve SV are installed inside the vehicle Ve. When the fuel cell system 1 is installed in a stationary generator Sg, the fuel tank Tk and the main shut-off valve SV are installed outside the stationary generator.

[0030] The injector (INJ) adjusts the flow rate of hydrogen gas supplied to the fuel cell stack (FCS) so that the pressure of the hydrogen gas remains constant.

[0031] The gas-liquid separator (GLS) separates hydrogen gas and liquid water discharged from the fuel cell stack (FCS).

[0032] The circulation pump HP resupplies the hydrogen gas separated by the gas-liquid separator GLS back to the fuel cell stack FCS.

[0033] The exhaust and drain valve EDV sends the liquid water separated by the gas-liquid separator GLS to the diluent DIL. The liquid water sent to the diluent DIL is stored in a tank within the diluent DIL. In addition, the air discharged from the fuel cell stack FCS via the air pressure regulating valve ARV merges with the hydrogen gas discharged from the exhaust and drain valve EDV in the diluent DIL, and this air is discharged into the fuel cell system 1 from the exhaust port of the diluent DIL. Thus, the air discharged from the exhaust port of the diluent DIL, i.e., the exhaust port of the fuel cell stack FCS, has a lower oxygen concentration than the air outside the fuel cell system 1 because oxygen is consumed within the fuel cell stack FCS during power generation.

[0034] The air compressor ACP takes in air from the intake port within the fuel cell system 1, compresses the taken-in air, and supplies the compressed air to the fuel cell stack FCS via the intercooler IC and air shut-off valve ASV. The compression ratio of the air compressor ACP is controlled by adjusting the opening degree of the air pressure regulating valve ARV located downstream of the fuel cell stack FCS.

[0035] The intercooler IC exchanges heat between compressed, high-temperature air and a refrigerant such as cooling water flowing through it.

[0036] The air shut-off valve (ASV) shuts off the supply of air to the fuel cell stack (FCS) through the operation control of the control unit (3).

[0037] The air pressure regulating valve (ARV) adjusts the pressure and flow rate of the air supplied to the fuel cell stack (FCS).

[0038] The radiator R exchanges heat between the refrigerant, which has been heated by the heat generated by the fuel cell stack (FCS), and the air inside the fuel cell system (1).

[0039] Fan F increases the heat dissipation rate of the radiator R. In other words, the airflow generated by the operation of fan F hits the radiator R, lowering its temperature. Note that the fan used as a ventilation unit for ventilating the inside of the fuel cell system 1 may be a fan F' (not shown) used to cool auxiliary equipment such as the energy storage device B, and is not limited to fan F.

[0040] The water pump (WP) supplies the refrigerant cooled by the radiator (R) to the fuel cell stack (FCS) via the intercooler (IC).

[0041] The DC-DC converter (CNV) is connected downstream of the fuel cell stack (FCS) and converts the voltage output from the FCS to a predetermined voltage. The power output from the DC-DC converter (CNV) is supplied to auxiliary equipment such as the load (Lo), circulation pump (HP), air compressor (ACP), and water pump (WP).

[0042] Energy storage device B consists of lithium-ion capacitors and other components and is connected between the DC-DC converter CNV and the load Lo.

[0043] If the supplied power, which is the difference between the power output from the DC-DC converter CNV and the total power supplied to the auxiliary equipment, is greater than the required power requested by the load Lo, then the power equivalent to the required power is supplied to the load Lo, and the remaining power is supplied to the energy storage device B. When power is supplied from the DC-DC converter CNV to the energy storage device B, the energy storage device B is charged, and the charge amount Ch of the energy storage device B increases. Also, if the supplied power, which is the difference between the power output from the DC-DC converter CNV and the total power supplied to the auxiliary equipment, is less than the required power requested by the load Lo, then the supplied power is supplied to the load Lo, and the remaining power is supplied to the load Lo from the energy storage device B. When power is supplied from the energy storage device B to the load Lo, the energy storage device B is discharged, and the charge amount Ch of the energy storage device B decreases. Note that the charge amount Ch is defined as the charge rate [%] of the energy storage device B (the ratio of the remaining capacity to the full charge capacity of the energy storage device B), or the open-circuit voltage [V] of the energy storage device B when no current is flowing through it, or the closed-circuit voltage [V] of the energy storage device B when current is flowing through it, or the integrated value [Ah] of the current flowing through the energy storage device B.

[0044] The voltage sensor Sv is composed of multiple voltage divider resistors and other components, and detects the total voltage Vfcs of the fuel cell stack FCS, sending the detected voltage Vfcs to the control unit 3.

[0045] The current sensor Si is composed of a shunt resistor, a Hall element, etc., and detects the current Ifcs flowing from the fuel cell stack FCS to the DC-DC converter CNV, and sends the detected current Ifcs to the control unit 3.

[0046] The temperature sensor St is composed of a thermistor or the like and detects the temperature T of the refrigerant flowing from the fuel cell stack FCS to the radiator R, and sends the detected temperature T to the control unit 3. The control unit 3 estimates the temperature Tfcs of the fuel cell stack FCS based on the temperature T. Alternatively, the temperature sensor St may be configured to directly detect the temperature Tfcs of the fuel cell stack FCS and send the detected temperature Tfcs to the control unit 3.

[0047] Memory unit 2 is composed of RAM (Random Access Memory) and ROM (Read Only Memory), among other components. Memory unit 2 also stores threshold values ​​Vth1 and Vth2, which will be described later.

[0048] The control unit 3 is composed of a microcomputer and the like.

[0049] Furthermore, when the fuel cell stack FCS is generating power, the control unit 3 changes the target power generation Pt in steps according to the charge amount Ch of the energy storage device B.

[0050] Furthermore, when the fuel cell stack FCS is generating power, the control unit 3 controls the operation of auxiliary equipment so that the power generated by the fuel cell stack FCS (the product of current Ifcs and voltage Vfcs) follows the target power generated Pt. For example, when the fuel cell stack FCS is generating power, the control unit 3 uses PI (Proportional-Integral) control to control the operation of auxiliary equipment so that the difference between the power generated by the fuel cell stack FCS and the target power generated Pt becomes zero.

[0051] Furthermore, when the fuel cell stack FCS is generating power, the control unit 3 changes the operation control of the fan F according to the type of mode (normal mode or ventilation mode).

[0052] In other words, in normal mode, the control unit 3 drives the fan F when the temperature Tfcs of the fuel cell stack FCS becomes equal to or greater than the temperature threshold Tth1, and stops the fan F when the temperature Tfcs becomes equal to or less than the temperature threshold Tth2. The temperature threshold Tth1 is, for example, a value determined by the upper limit of the rated temperature of the fuel cell cell C. The temperature threshold Tth2 is a value smaller than the temperature threshold Tth1, for example, a value obtained by subtracting the detection error of the temperature sensor St from the temperature threshold Tth1.

[0053] Furthermore, if a fan F' (not shown) is used as a ventilation unit to cool the auxiliary equipment, the control unit 3 may be configured in normal mode to drive the fan F' when the temperature of the auxiliary equipment exceeds the temperature threshold Tth1', and to stop the fan F' when the temperature of the auxiliary equipment falls below the temperature threshold Tth2'. The temperature threshold Tth1' is, for example, a value determined by the upper limit of the rated temperature of the auxiliary equipment. The temperature threshold Tth2' is a value smaller than the temperature threshold Tth1', for example, a value obtained by subtracting the detection error of the temperature sensor (not shown) that detects the temperature of the auxiliary equipment from the temperature threshold Tth1'.

[0054] Furthermore, in ventilation mode, the control unit 3 actively drives the fan F. For example, in ventilation mode, the control unit 3 forcibly drives the fan F to satisfy the following equation 1. The wind (airflow) created by the fan F is discharged outside the fuel cell system 1 through an opening provided in the housing surrounding the fuel cell system 1 (dashed line frame shown in Figure 1).

[0055] The predetermined drive amount = Fan F wind speed [m / sec] × Area of ​​the opening provided in the housing surrounding the fuel cell system 1 [m²] 2 ] × Fan F operating time t [sec] > Volume of the enclosure surrounding the fuel cell system 1 [m 3 ]...expression 1

[0056] In addition, in ventilation mode, the control unit 3 may compare the rotational speed of fan F when the above equation 1 is satisfied with the rotational speed of fan F when the temperature Tfcs is equal to or greater than the temperature threshold Tth1, and drive fan F at the larger rotational speed.

[0057] Furthermore, in ventilation mode, the control unit 3 may change the rotation speed of the fan F according to the voltage V related to the fuel cell stack FCS. In this case, it is preferable to increase the rotation speed of the fan F as the voltage V related to the fuel cell stack FCS decreases.

[0058] Furthermore, the control unit 3 switches between normal mode and ventilation mode depending on the voltage related to the fuel cell stack (FCS).

[0059] Figure 3 is a flowchart showing an example of the operation of the control unit 3 during mode switching.

[0060] First, the control unit 3 calculates the voltage V related to the fuel cell stack FCS (step S1). For example, the control unit 3 uses the average value of the voltages V1 to Vn detected by the cell voltage detection unit VD as the voltage V related to the fuel cell stack FCS. Alternatively, the control unit 3 uses the voltage Vfcs detected by the voltage sensor Sv as the voltage V related to the fuel cell stack FCS.

[0061] Next, if the voltage V calculated in step S1 is greater than the threshold Vth1 (first threshold) (step S2: No), the control unit 3 repeats the processes of steps S1 and S2. If the voltage V calculated in step S1 becomes less than or equal to the threshold Vth1 (step S2: Yes), it transitions from normal mode to ventilation mode (step S3). Thus, when the voltage V calculated in step S1 becomes less than or equal to the threshold Vth1, it can be inferred that the oxygen concentration inside the fuel cell system 1 is relatively low, and it is necessary to actively drive the fan F to ventilate the fuel cell system 1 and increase the oxygen concentration inside the fuel cell system 1.

[0062] Next, the control unit 3 transitions from normal mode to ventilation mode and maintains the ventilation mode (the state in which the fan F is continuously driven) until a predetermined driving time (for example, the above driving time t) has elapsed. Once the predetermined driving time has elapsed (step S4: Yes), it calculates the voltage V related to the fuel cell stack FCS (step S5).

[0063] Then, if the voltage V calculated in step S5 is less than the threshold Vth2 (second threshold) (step S6: No), the control unit 3 repeats the processing in steps S4 to S6. If the voltage V calculated in step 5 is equal to or greater than the threshold Vth2 (step S6: Yes), it transitions from ventilation mode to normal mode (step S7). In this way, when the voltage V calculated in step S5 is equal to or greater than the threshold Vth2, it can be inferred that the oxygen concentration in the fuel cell system 1 has returned to a normal oxygen concentration, and it is not necessary to actively drive the fan F for ventilation in the fuel cell system 1.

[0064] The threshold Vth2 is the voltage V calculated when the oxygen concentration in the fuel cell system 1 is at a normal oxygen concentration. The threshold Vth1 is set to a value smaller than the threshold Vth2, for example, by subtracting the detection error of the cell voltage detection unit VD or the voltage sensor Sv from the threshold Vth2. By setting thresholds Vth1 and Vth2 to different values ​​in this way, when the voltage V becomes greater than the threshold Vth1 after transitioning from normal mode to ventilation mode, the frequent switching between normal mode and ventilation mode can be suppressed compared to when transitioning from ventilation mode to normal mode, thereby stabilizing the power generation of the fuel cell stack FCS.

[0065] Incidentally, the oxygen concentration in the atmosphere (oxygen concentration of the air outside the fuel cell system 1) is generally about 21%, but the oxygen concentration of the air discharged from the fuel cell stack (FCS) due to oxygen consumption during power generation is lower than that of the atmosphere. Therefore, when the air compressor (ACP) draws in the air discharged from the fuel cell stack (FCS), the oxygen concentration of the air supplied from the air compressor (ACP) to the fuel cell stack (FCS) becomes relatively low, causing the concentration overvoltage to increase and the voltage V related to the fuel cell stack (FCS) to decrease.

[0066] Furthermore, if the fuel cell system 1 is installed in a vehicle Ve with an air intake on the side, or in a vehicle Ve with a relatively slow travel speed, or if the fuel cell system 1 is installed in a stationary generator Sg, outside air cannot be actively taken into the fuel cell system 1, and the oxygen concentration of the air supplied from the air compressor ACP to the fuel cell stack FCS becomes relatively low, causing the concentration overvoltage to increase and the voltage V related to the fuel cell stack FCS to decrease.

[0067] Therefore, in the fuel cell system 1 of this embodiment, when the voltage V related to the fuel cell stack FCS falls below the threshold Vth1, the fan F is actively driven to ventilate the inside of the fuel cell system 1. This allows outside air to be taken into the fuel cell system 1 and the air discharged from the fuel cell stack FCS to be discharged outside the fuel cell system 1, thereby suppressing a decrease in oxygen concentration inside the fuel cell system 1 and suppressing a decrease in oxygen concentration in the air supplied to the fuel cell stack FCS. Furthermore, when the voltage V related to the fuel cell stack FCS is not below the threshold Vth1, the operation of the fan F can be controlled according to the temperature Tfcs of the fuel cell stack FCS in normal mode, or the operation of the fan F' can be controlled according to the temperature of the auxiliary equipment in normal mode, thereby adjusting the temperature Tfcs of the fuel cell stack FCS or the temperature of the auxiliary equipment within the rated temperature range, and stabilizing the power generation of the fuel cell stack FCS.

[0068] Furthermore, generally, when the oxygen concentration in the fuel cell system 1 decreases, the voltages V1 to Vn of each fuel cell C also decrease. Therefore, as in the fuel cell system 1 of the embodiment, by setting the average value of the voltages V1 to Vn of each fuel cell C as the voltage V related to the fuel cell stack FCS, it is possible to prevent active ventilation within the fuel cell system 1 when the voltage V is greater than the threshold Vth1, that is, when the voltages V1 to Vn of each fuel cell C are not relatively low. This makes it possible to suppress ventilation within the fuel cell system 1 when the voltage of the fuel cell stack FCS decreases due to factors other than a decrease in the oxygen concentration in the fuel cell system 1. In other words, unnecessary ventilation within the fuel cell system 1 is suppressed, which further stabilizes the power generation of the fuel cell stack FCS.

[0069] Furthermore, if the average of the voltages V1 to Vn of each fuel cell C is used as the voltage V for the fuel cell stack FCS, then even if the number of fuel cell Cs changes and the overall voltage Vfcs of the fuel cell stack FCS changes, there is no need to significantly change the thresholds Vth1 and Vth2. Therefore, it is possible to flexibly respond to changes such as increasing or decreasing the number of cells that make up the fuel cell stack FCS. In this way, the versatility of the fuel cell system 1 can be improved.

[0070] <Examples of exhaust port or fan F placement for fuel cell stack (FCS)> Here, Figure 4 shows an example of the arrangement of the exhaust port or fan F of the fuel cell stack FCS. Figures 4(a) to 4(d) show examples of the arrangement of the intake port of the air compressor ACP, the exhaust port of the fuel cell stack FCS, the fan F, and the openings provided in the housing of the fuel cell system 1. The dashed lines in Figures 4(a) to 4(d) indicate the airflow drawn into the fan F, and the dashed lines in Figures 4(a) to 4(d) indicate the airflow pushed out from the fan F. The airflow drawn into the fan F is assumed to have relatively low directionality, while the airflow pushed out from the fan F is assumed to have relatively high directionality.

[0071] In the arrangement shown in Figure 4(a), the air intake of the air compressor ACP, the exhaust port of the fuel cell stack FCS, the fan F, and the opening provided in the housing of the fuel cell system 1 are arranged in that order. In this case, the air discharged from the exhaust port is carried by the airflow drawn into the fan F and sent out from the fan F, and discharged outside the fuel cell system 1 through the opening. In addition, in the arrangement shown in Figure 4(a), the exhaust port is positioned downwind of the airflow created by the fan F relative to the air intake port, so that the air discharged from the exhaust port is not drawn into the air intake port.

[0072] In the arrangement shown in Figure 4(b), the air intake of the air compressor ACP, the fan F, the exhaust port of the fuel cell stack FCS, and the opening provided in the housing of the fuel cell system 1 are arranged in that order. In this case, the air discharged from the exhaust port is carried by the air pushed out by the fan F and discharged outside the fuel cell system 1 through the opening. Also, in the arrangement shown in Figure 4(b), since the exhaust port is located downwind of the airflow created by the fan F relative to the air intake port, it is possible to suppress the air discharged from the exhaust port from being drawn into the air intake port.

[0073] In the arrangement shown in Figure 4(c), the air intake of the air compressor ACP, the fan F, the opening provided in the housing of the fuel cell system 1, and the exhaust port of the fuel cell stack FCS are arranged in that order. In this case, the air discharged from the exhaust port is discharged outside the fuel cell system 1, and then carried away from the fuel cell system 1 by the air pushed out from the fan F through the opening. Furthermore, in the arrangement shown in Figure 4(c), since the exhaust port is located downwind of the airflow created by the fan F relative to the air intake, it is possible to suppress the air discharged from the exhaust port from being drawn into the air intake.

[0074] In the arrangement shown in Figure 4(d), the air intake of the air compressor ACP, the exhaust port of the fuel cell stack FCS, an opening in the housing of the fuel cell system 1, and the fan F are arranged in that order. In this case, the air discharged from the exhaust port is carried by the air drawn into the fan F and discharged outside the fuel cell system 1 through the opening. Also, in the arrangement shown in Figure 4(d), since the exhaust port is located downwind of the airflow created by the fan F relative to the air intake port, it is possible to suppress the air discharged from the exhaust port from being drawn into the air intake port.

[0075] According to the arrangement examples shown in Figures 4(a) to 4(d), the exhaust port is positioned downwind of the airflow created by the fan F relative to the intake port. This suppresses the supply of air discharged from the exhaust port to the fuel cell stack FCS via the intake port of the air compressor ACP, thereby suppressing the decrease in oxygen concentration of the air supplied to the fuel cell stack FCS and further suppressing the decrease in oxygen concentration within the fuel cell system 1.

[0076] Furthermore, when the air discharged from the exhaust port is carried by the air drawn into the fan F and discharged outside the fuel cell system 1, the airflow drawn into the fan F has relatively low directionality. Therefore, if there are no constraints on the layout within the fuel cell system 1, it is desirable to place the exhaust port as close to the fan F as possible. This allows the air discharged from the exhaust port to be efficiently discharged outside the fuel cell system 1.

[0077] It should be noted that the present invention is not limited to the embodiments described above, and various improvements and modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0078] 1. Fuel cell system 2 Storage section 3. Control Unit Vehicle Lo load Sg Stationary Generator FCS Fuel Cell Stack Tk fuel tank SV Main stop valve INJ Injector GLS gas-liquid separator HP Circulation Pump EDV Exhaust Drain Valve DIL Diluent ACP Air Compressor ARV Air Pressure Regulating Valve ASV Air Shut-Off Valve R Radiator F Fan WP Water Pump IC Intercooler CNV DC-DC converter B Energy storage device Sv voltage sensor Si current sensor St temperature sensor

Claims

1. A fuel cell system comprising a fuel cell stack formed by stacking multiple fuel cell cells and an auxiliary device for generating power from the fuel cell stack, A voltage detection unit for detecting the voltage related to the fuel cell stack, A ventilation unit for ventilating the inside of the fuel cell system, A control unit that controls the operation of the ventilation unit in normal mode according to the temperature of the fuel cell stack or the auxiliary equipment, and keeps the ventilation unit running in ventilation mode, Equipped with, The control unit transitions from the normal mode to the ventilation mode when the voltage related to the fuel cell stack falls below a first threshold. A fuel cell system characterized by the following features.

2. A fuel cell system according to claim 1, The fuel cell system is characterized in that the control unit drives the ventilation unit for a predetermined period of time after transitioning from the normal mode to the ventilation mode, and then, when the voltage related to the fuel cell stack becomes greater than or equal to a second threshold greater than the first threshold, it transitions from the ventilation mode to the normal mode.

3. A fuel cell system according to claim 1, The voltage detection unit detects the voltage of each of the plurality of fuel cell cells, The control unit sets the average value of each voltage detected by the voltage detection unit as the voltage related to the fuel cell stack. A fuel cell system characterized by the following features.

4. A fuel cell system according to claim 1, The ventilation unit is a fan that increases the amount of heat dissipated by the radiator, which exchanges heat between the refrigerant heated by the heat generated by the fuel cell stack and the air. The exhaust port from which air is discharged from the fuel cell stack is positioned downwind of the airflow created by the ventilation unit relative to the intake port of the fuel cell stack. A fuel cell system characterized by the following features.

5. A fuel cell system according to claim 1, When the voltage related to the fuel cell stack falls below a first threshold, the control unit estimates that the oxygen concentration in the fuel cell system is decreasing and transitions from the normal mode to the ventilation mode. A fuel cell system characterized by the following features.

6. A fuel cell system according to claim 1, The control unit drives the ventilation unit in the ventilation mode such that a predetermined amount of drive by the ventilation unit is greater than the volume of the housing surrounding the fuel cell system. A fuel cell system characterized by the following features.

7. A fuel cell system according to claim 1, In the ventilation mode, the control unit compares the rotational speed of the ventilation unit with the rotational speed determined based on the temperature of the fuel cell stack or the auxiliary equipment, and drives the ventilation unit at the larger rotational speed. A fuel cell system characterized by the following features.

8. A fuel cell system according to claim 1, The control unit increases the rotation speed of the ventilation unit as the voltage to the fuel cell stack decreases in the ventilation mode. A fuel cell system characterized by the following features.

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