Fuel cell system and its control method

Abstract

The present invention provides a fuel cell system capable of stabilizing the in-plane state of the cathode of a fuel cell stack at low temperatures. [Solution] The fuel cell system can stabilize the in-plane state of the fuel cell stack by making the amount of cathode gas increased in the cell voltage recovery control from low-temperature startup until the fuel cell stack reaches a predetermined dry state smaller than the amount of cathode gas increased in the cell voltage recovery control after normal startup.

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system that generates electricity through an electrochemical reaction of cathode gas and anode gas, and a control method thereof.

Background Art

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

[0003] For example, Japanese Patent Application Laid-Open No. 2010-123430 discloses a technique for increasing the flow rate of air (cathode gas) to recover the voltage when flooding occurs in a fuel cell stack and the voltage of the fuel cell stack decreases (see, for example,

[0037] of the same publication).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when the fuel cell stack is started at low temperature, the activity of the electrode catalyst is in an unstable state. Therefore, when the stack voltage decreases under an unstable state, if the increased amount of cathode gas is not appropriate, the fuel cell stack may become more unstable.

[0006] The present disclosure aims to solve the above-described problems.

Means for Solving the Problems

[0007] One aspect of the present disclosure is a fuel cell system that performs low-temperature startup control when the temperature of a fuel cell stack that generates electricity by the reaction of anode gas and cathode gas is below a low-temperature threshold, and performs normal startup control when the temperature of the fuel cell stack is above the low-temperature threshold, and increases the amount of cathode gas to perform voltage recovery control of the fuel cell stack when the voltage of the fuel cell stack decreases after low-temperature startup by the low-temperature startup control or after normal startup by the normal startup control, wherein the amount of cathode gas increased in the voltage recovery control from after low-temperature startup until the fuel cell stack reaches a predetermined dry state is smaller than the amount of cathode gas increased in the voltage recovery control after normal startup.

[0008] Another aspect of the present disclosure is a control method for a fuel cell system comprising: performing low-temperature startup control when the temperature of a fuel cell stack that generates electricity by the reaction of anode gas and cathode gas is below a low-temperature threshold; performing normal startup control when the temperature is above the low-temperature threshold; a voltage drop determination step for determining whether the voltage of the fuel cell stack has decreased after the low-temperature startup by the low-temperature startup control or after the normal startup by the normal startup control; and a voltage recovery control step for performing voltage recovery control by increasing the amount of cathode gas when the voltage of the fuel cell stack has decreased, wherein the amount of cathode gas increased in the voltage recovery control step from after the low-temperature startup until the fuel cell stack reaches a predetermined dry state is smaller than the amount of cathode gas increased in the voltage recovery control step after the normal startup. [Effects of the Invention]

[0009] According to this disclosure, the cathode gas increase amount for voltage recovery control is set according to the state of the fuel cell stack at startup, i.e., whether it is a low-temperature startup or a normal startup, so that the voltage recovery control of the fuel cell stack can be performed appropriately. In particular, the cathode gas increase amount for voltage recovery control from low-temperature startup until the fuel cell stack reaches a predetermined dry state is set to be smaller than the cathode gas increase amount for voltage recovery control after normal startup, so that the in-plane state of the fuel cell stack at low temperatures can be stabilized. This, in turn, contributes to energy efficiency. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of a fuel cell vehicle incorporating a fuel cell system according to the embodiment. [Figure 2] Figure 2 is a flowchart illustrating the operation of the embodiment. [Figure 3] Figure 3A is a detailed flowchart of the process in step S13 in Figure 2. Figure 3B is a detailed flowchart of the other processes in step S13 in Figure 2. [Figure 4] Figure 4 is a timing chart used to explain the operation during startup at room temperature. [Figure 5] Figure 5 is a timing chart used to explain the operation during low-temperature startup. [Figure 6] Figure 6 is a flowchart used to explain the operation of other embodiments. [Modes for carrying out the invention]

[0011] [Embodiment] [composition] Figure 1 is a schematic diagram of a fuel cell vehicle 12 incorporating the fuel cell system 10 according to this embodiment.

[0012] The fuel cell system 10 can be incorporated into other mobile devices such as ships, aircraft, and robots, in addition to the fuel cell vehicle 12, and can also be installed in fixed structures such as houses.

[0013] The fuel cell vehicle 12 consists of a control device 15 that controls the entire fuel cell vehicle 12, the fuel cell system 10, and an output unit 16 that is electrically connected to the fuel cell system 10.

[0014] The control device 15 may not be a single unit, but rather divided into two or more control devices, for example, one for the fuel cell system 10 and one for the output unit 16.

[0015] The fuel cell system 10 is composed of a fuel cell stack 18, a hydrogen tank 20, an oxidant gas supply device 22, a fuel gas supply device 24, and a medium supply device (heat exchange medium supply device) 26.

[0016] The oxidant gas supply device 22 includes a compressor (CP) 28, an intercooler (IC) 128, and a humidifier (HUM) 30.

[0017] The fuel gas supply device 24 includes a shut-off valve 21, an injector (INJ) 32, an ejector 34, and a gas-liquid separator 36. The injector 32 may be substituted for a pressure reducing valve. The medium supply device 26 includes a medium pump (WP) 38 and a radiator 40.

[0018] The output unit 16 includes a drive unit 42, a high-voltage power storage device (battery) 44, and a motor (electric motor) 46. The load of the drive unit 42 includes, in addition to the motor 46 which is the main machine, auxiliary machines such as the compressor 28, the medium pump 38, and an air conditioner (not shown). The fuel cell vehicle 12 travels by the driving force generated by the motor 46.

[0019] For the auxiliary machines, a DC voltage of the high voltage of the power storage device 44 or a DC voltage of a low-voltage power storage device (not shown) is applied. The low-voltage power storage device is charged by the low-voltage power obtained by stepping down the high voltage of the power storage device 44 by a step-down converter (not shown).

[0020] The remaining capacity SOC of the power storage device 44 is acquired by an SOC sensor 45. The battery temperature Tbat of the power storage device 44 is acquired by a temperature sensor 43.

[0021] In the fuel cell stack 18, a plurality of fuel cells (also referred to as power generation cells or fuel cells) 50 are stacked. The fuel cell 50 includes an electrolyte membrane - electrode structure (membrane electrode structure) 52, and separators 53, 54 sandwiching the electrolyte membrane - electrode structure 52.

[0022] The electrolyte membrane / electrode structure 52 comprises, for example, a solid polymer electrolyte membrane 55 which is a thin film of perfluorosulfonic acid containing water, and a cathode electrode 56 and an anode electrode 57 that sandwich the solid polymer electrolyte membrane 55.

[0023] On one side of the separator 53, a cathode channel (oxidant gas channel) 58 is formed on the surface facing the electrolyte membrane / electrode structure 52, connecting the oxidant gas inlet port 101 and the oxidant gas outlet port 102.

[0024] On the other side of the separator 54 facing the electrolyte membrane / electrode structure 52, an anode channel (fuel gas channel) 59 is formed that connects the fuel gas inlet port 103 and the fuel gas outlet port 104.

[0025] Fuel gas (also called anode gas) (H2) flows through the anode channel 59, which is formed by the anode electrode 57 and the separator 54 stacked on the anode electrode 57.

[0026] An oxidizing agent gas (also called cathode gas) (air) flows through the cathode channel 58, which is formed by the cathode electrode 56 and the separator 53 stacked on the cathode electrode 56.

[0027] At the anode electrode 57, when fuel gas is supplied, hydrogen ions are generated from hydrogen molecules by an electrode reaction in the electrode catalyst layer. These hydrogen ions then permeate the solid polymer electrolyte membrane 55 and move to the cathode electrode 56, while electrons are released from the hydrogen molecules.

[0028] Electrons released from hydrogen molecules move from the negative electrode terminal 106 (Figure 1) through the drive unit 42 and the motor 46, and then through the positive electrode terminal 108 to the cathode electrode 56.

[0029] At the cathode electrode 56, the hydrogen ions and electrons react with the oxygen contained in the supplied oxidizing gas due to the action of the electrode catalyst layer to produce water.

[0030] Each fuel cell 50 constituting the fuel cell stack 18 is provided with a cell voltage sensor 51 that measures the cell voltage Vcell, which is the voltage between the terminals of each fuel cell 50.

[0031] The generated power (generated voltage Vfc × generated current Ifc) between the positive terminal 108 and the negative terminal 106 is supplied via the drive unit 42 to the main motor 46 and auxiliary equipment such as the compressor 28. The generated voltage (stack voltage) Vfc is equal to the integrated value of the cell voltage Vcell.

[0032] The compressor 28 is a mechanical supercharger, etc., driven by a compressor motor (not shown) to which power from the energy storage device 44 is supplied via the drive unit 42. The compressor 28 has functions such as drawing in outside air (atmosphere, air) from the outside air intake 113, pressurizing it, and supplying it to the fuel cell stack 18 via the humidifier 30.

[0033] The intercooler 128 is located downstream of the compressor 28 in the oxidant gas supply channel 61. The intercooler 128 regulates the temperature of the oxidant gas (compressed oxidant gas, supercharger gas) supplied from the compressor 28. The intercooler 128 cools the oxidant gas supplied from the compressor 28. The cooling medium used to cool the fuel cell stack 18 flows through the intercooler 128.

[0034] When the ambient temperature outside the fuel cell system 10 is below freezing, the temperature of the cooling medium led to the intercooler 128 becomes higher than the temperature of the oxidizer gas supplied from the compressor 28 by circulating through the fuel cell stack 18. Therefore, the intercooler 128 can raise the temperature of the oxidizer gas supplied from the compressor 28 when the ambient temperature is below freezing. A temperature sensor 130 is provided at the outlet of the intercooler 128 to measure the outlet temperature Tic of the oxidizer gas.

[0035] The humidifier 30 has two passages, 31A and 31B. Compressed and heated to a high temperature by the compressor 28, and dried air (oxidizer gas) flows through passage 31A. Exhaust gas discharged from the oxidizer gas outlet communication port 102 of the fuel cell stack 18 flows through passage 31B. The humidifier 30 has the function of humidifying the oxidizer gas supplied from the compressor 28. That is, the humidifier 30 humidifies the supply gas (oxidizer gas) flowing from the flow path 31B through the porous membrane inside to the flow path 31A by transferring moisture contained in the exhaust gas (off-gas). The humidifier 30 supplies the humidified oxidizer gas to the fuel cell stack 18 through the oxidizer gas inlet 91.

[0036] The oxidizer gas supply channel 61, from the outside air intake 113 to the oxidizer gas inlet 91, is equipped with, in order from the outside air intake 113, a shut-off valve 114, an airflow sensor (AFS: flow sensor) 116, a compressor 28, an intercooler 128, an input-side sealing valve 118, and a humidifier 30. Note that the flow channels such as the oxidizer gas supply channel 61, which are drawn with double lines, are formed by piping (the same applies hereafter).

[0037] The shut-off valve 114 is opened and closed to open or close the intake of air into the oxidizer gas supply passage 61. The airflow sensor 116 measures the mass flow rate of the oxidizer gas supplied to the fuel cell stack 18 through the compressor 28. The input-side sealing valve 118 opens and closes the oxidizer gas supply channel 61.

[0038] When the bypass valve 122 is open, it supplies heated compressed air (cathode gas) from the compressor 28 to the cathode flow path 58 of the fuel cell stack 18, bypassing the humidifier 30.

[0039] The oxidant off-gas flow path 62, which communicates with the oxidant gas outlet communication port 102 through the oxidant off-gas outlet 92, is equipped with a humidifier 30 and an exhaust-side sealing valve 120, which also functions as a back pressure valve, in that order from the oxidant off-gas outlet 92.

[0040] Between the intake port of the input-side sealing valve 118 and the discharge port of the discharge-side sealing valve 120, a bypass passage 64 is provided that bypasses the fuel cell stack 18 and connects the oxidizer gas supply passage 61 and the oxidizer off-gas passage 62. The bypass passage 64 is equipped with a bypass valve 122 that opens and closes the bypass passage 64. The bypass valve 122 adjusts the flow rate of the oxidizer gas that bypasses the fuel cell stack 18. The combined passage of the bypass passage 64 and the oxidizer off-gas passage 62 is connected to the discharge passage 62A.

[0041] The hydrogen tank 20 is a container equipped with an electromagnetically operated shut-off valve 21 and is used to store high-purity hydrogen compressed at high pressure.

[0042] The fuel gas discharged from the hydrogen tank 20 is supplied to the inlet of the anode passage 59 via the fuel gas inlet 93 and fuel gas inlet communication port 103 of the fuel cell stack 18, through the shut-off valve 21 and injectors 32 and ejectors 34 provided in the fuel gas supply passage 72. A pressure sensor 83 is provided in the fuel gas supply passage 72 near the fuel gas inlet 93 to detect (measure and acquire) the inlet pressure of the anode passage 59 as the anode inlet pressure Pin.

[0043] The outlet of the anode passage 59 is connected to the inlet 151 of the gas-liquid separator 36 through the fuel gas outlet communication port 104, the fuel off-gas outlet 94, and the fuel off-gas passage 74, and the fuel off-gas, which is a hydrogen-containing gas, is supplied to the gas-liquid separator 36 from the anode passage 59.

[0044] The gas-liquid separator 36 separates the fuel off-gas into a gaseous component and a liquid component (liquid water). The gaseous component of the fuel off-gas (fuel exhaust gas) is discharged from the gas outlet 152 of the gas-liquid separator 36 and, while the purge valve 70 is closed, is supplied to the suction port of the ejector 34 through the circulation passage 77.

[0045] On the other hand, when the purge valve 70 is opened, the fuel off-gas is mixed with the exhaust gas discharged from the exhaust passage 62A via the purge passage 78 and discharged to the outside (atmosphere) through the exhaust passage 99 and exhaust gas outlet 168.

[0046] The liquid component of the fuel off-gas is mixed with the exhaust gas discharged from the discharge channel 62A through the drain channel 162, which is equipped with a drain valve 164, from the liquid outlet 160 of the gas-liquid separator 36, and then discharged to the outside (atmosphere) through the discharge channel 99 and the exhaust gas outlet 168.

[0047] To reiterate, in the discharge channel 99, the oxidizer off-gas from the discharge channel 62A dilutes the liquid water discharged from the drain channel 162 or the purge channel 78 with the fuel gas in the fuel off-gas, and this is then discharged to the outside (atmosphere) of the fuel cell vehicle 12 through the exhaust gas outlet 168.

[0048] The medium supply device 26 of the fuel cell system 10 has a medium supply channel 140 for circulating the heat exchange medium and a medium discharge channel 142.

[0049] The medium supply channel 140 supplies heat exchange medium to the medium channel 60 inside the fuel cell stack 18, and the heat exchange medium that has flowed through the medium channel 60 of the fuel cell stack 18 is discharged into the medium discharge channel 142.

[0050] The medium discharge channel 142 communicates with the radiator 40 and the first input valve of the three-way valve 148 through a channel in the heater 146, and also communicates with the second input valve of the three-way valve 148 through the radiator 40. The radiator 40 cools the heat exchange medium.

[0051] The output valve of the three-way valve 148 communicates with the medium supply channel 140. A medium pump 38 is provided in the medium supply channel 140. The medium pump 38 circulates the heat exchange medium within the heat exchange medium circulation circuit.

[0052] The media supply channel 140 communicates with the refrigerant supply port of the intercooler 128 through the intercooler valve 126. The refrigerant discharge port of the intercooler 128 communicates with the media discharge channel 142 through a channel in the heater 146.

[0053] Temperature sensors (temperature acquisition units) 85 and 86 are provided in the medium supply channel 140 and the medium discharge channel 142, respectively. The temperature of the heat exchange medium (refrigerant temperature, medium outlet temperature) Tco detected by the temperature sensor 86 is estimated to be the (internal) temperature of the fuel cell stack 18.

[0054] [Description of control device 15] All components of the fuel cell system 10, including actuators such as the compressor 28, injector 32, and electric pump (medium pump) 38, are centrally controlled by the control device 15.

[0055] Excluding the shut-off valves 21 and 114, which are shut-off valves whose opening and closing are controlled by the control device 15, the input-side sealing valve 118, discharge-side sealing valve 120, purge valve 70, drain valve 164, and bypass valve 122 are flow control valves whose opening degree is controlled by the control device 15, but duty cycle control may also be used with shut-off valves.

[0056] The control device 15 is an electronic device (computer) provided in the fuel cell system 10. The control device 15 includes an arithmetic unit (processing unit) 200, a storage unit 202, a display unit, and an operation unit.

[0057] The arithmetic unit 200 may be composed of a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). In other words, the arithmetic unit may be composed of processing circuitry.

[0058] The arithmetic unit 200 includes a determination unit and a control unit. The determination unit and the control unit can be realized by the arithmetic unit 200 executing a program stored in the storage unit 202.

[0059] Furthermore, at least a portion of the determination unit and control unit may be implemented using integrated circuits such as ASICs (Application Specific Integrated Circuits) and FPGAs (Field-Programmable Gate Arrays). Alternatively, at least a portion of the determination unit and control unit may be composed of electronic circuits including discrete devices.

[0060] The storage unit 202 may consist of a volatile memory (not shown) and a non-volatile memory (not shown). Examples of volatile memory include RAM (Random Access Memory). This volatile memory is used as the processor's working memory and temporarily stores data necessary for processing or calculations. Examples of non-volatile memory include ROM (Read Only Memory) and flash memory. This non-volatile memory is used as storage memory and stores programs, tables, maps, etc. At least a portion of the storage unit 202 may be provided in the processor, integrated circuit, etc., as described above.

[0061] The calculation unit 200 of the control device 15 performs calculations according to the program, thereby controlling the operation of the fuel cell vehicle 12 and the fuel cell system 10.

[0062] [Operation] Next, the operation of the above embodiment, which is basically configured as described above, will be explained in detail based on the flowchart shown in Figure 2.

[0063] Furthermore, this disclosure clarifies how to set the amount of increase in the cathode gas (air) flow rate (referred to as the air amount) when performing cell voltage recovery control during startup. Therefore, the following explanation will focus on the air amount.

[0064] In step S1, if the arithmetic unit 200 of the control device 15 determines that the power switch 71 has been switched from the off state to the on state and that startup has begun (S1: YES), the process proceeds to step S2. In the following description, the arithmetic unit 200 of the control device 15 will be described as the control device 15.

[0065] In step S2, the control device 15 determines whether the current startup is a startup at a low temperature (low-temperature startup) or not (a startup at room temperature).

[0066] In this case, if the temperature Tco of the heat exchange medium detected by the temperature sensor 86 is below the low temperature threshold (low temperature judgment threshold) Tth0 (S2:YES), the control device 15 determines that it is a low-temperature startup and proceeds to step S4. If the temperature is above the low temperature threshold Tth0 (S2:NO), it determines that it is a normal startup (room temperature startup) and proceeds to step S3.

[0067] The low-temperature threshold Tth0 can be any temperature within the temperature range of the fuel cell stack 18 during power generation (e.g., 0°C to 120°C) that can be judged as low temperature. For example, it can be below freezing or 0°C, but it is not limited to this and can be set to a temperature suitable for the fuel cell system 10 and the fuel cell vehicle 12.

[0068] In this embodiment, starting at a temperature below the low-temperature threshold Tth0 is referred to as low-temperature startup (low-temperature startup control), and starting at a temperature above the low-temperature threshold Tth0 is referred to as normal startup (normal startup control).

[0069] If it is a normal startup (S2:NO), in step S3, the control device 15 starts the compressor 28, sets the air volume to the initial air volume Sp1, starts power generation in a normal startup state, and proceeds to step S8.

[0070] On the other hand, in the case of low-temperature startup, the control device 15 sets the air volume to the initial air volume Sp1 and operates the fuel cell stack 18 for a predetermined time (start power generation), and proceeds to step S5.

[0071] In step S5, the control device 15 operates the fuel cell stack 18 in either a first warm-up mode, which operates it at a first output [kW], or a second warm-up mode, which operates it at a second output [kW] greater than the first output (first output < second output), according to the battery temperature Tbat [°C] of the energy storage device 44 acquired by the temperature sensor 43 and the SOC [%] of the energy storage device 44 acquired by the SOC sensor 45 (first output < second output), and proceeds to step S6. Note that in step S5, in the first and second warm-up modes (warm-up power generation, warm-up control), the amount of air is set to a warm-up air amount Sp3 that is smaller than the initial air amount Sp1 (Sp3 <Sp1)。

[0072] Note that, due to the low temperature, the battery capacity [kWh] will be smaller compared to room temperature. However, in this state, if the SOC is relatively small, there will be more margin for charge (rechargeable amount), so the system will operate in the second warm-up mode. If the SOC is relatively large, there will be less margin for charge, so the system will operate in the first warm-up mode.

[0073] In step S6, the control device 15 determines whether the medium outlet temperature Tco of the heat exchange medium detected by the temperature sensor 86 has risen to a temperature exceeding the first temperature threshold Tth1 for determining the completion of warm-up. The process in steps S5 and S6 is repeated until a positive determination is made. If a positive determination is made (S6: YES), the process proceeds to step S7.

[0074] Within the temperature range (e.g., 0°C to 120°C) during power generation of the fuel cell stack 18, the first temperature threshold Tth1 for determining warm-up completion should be a predetermined value greater than the low-temperature threshold Tth0.

[0075] In step S7, the control device 15 starts humidity-controlled power generation, and after the humidity-controlled power generation is completed, proceeds to step S8. Here, humidity-controlled power generation is a process to dry the fuel cell stack 18, which has become wet due to the first and second warm-up modes during low-temperature startup.

[0076] Specifically, the input-side sealing valve 118 is opened, and power generation is continued for a predetermined time (humidification time) with the fuel cell stack 18 supplied with an air volume Sp2 which is the initial air volume Sp1 plus a predetermined air increase amount ΔSpa. Note that the air volume Sp2 is greater than the warm-up air volume Sp3. Here, the predetermined time (humidification time) is set to be longer the lower the medium outlet temperature Tco at startup. This humidity-controlled power generation can eliminate the over-humidified state inside the power generation cell 50. In addition to the elapsed time, the completion of humidity-controlled power generation may also be determined when the temperature of the fuel cell system 10 exceeds the warm-up completion temperature threshold or a predetermined humidity-controlled completion temperature threshold set separately from the warm-up completion temperature threshold.

[0077] In step S8, the control device 15 determines whether or not the cell voltage Vcell has decreased during startup (voltage drop determination step).

[0078] The control device 15 determines whether the cell voltage Vcell has decreased based on whether the difference ΔV (ΔV = Vcellmean - Vcellmin), obtained by subtracting the minimum cell voltage Vcellmin from the average cell voltage Vcellmean, exceeds the execution determination threshold ΔVtha (ΔV > Vtha).

[0079] If the cell voltage Vcell is not decreasing (S8: NO, ΔV≦Vtha), the humidity-controlled power generation is stopped and the startup process is terminated, and thereafter, power generation (normal power generation) operation according to the requested output of the fuel cell vehicle 12 is performed.

[0080] On the other hand, if the cell voltage Vcell is found to be low (S8: YES, ΔV > ΔVtha), the startup process (cell voltage recovery control process) is continued, and the process proceeds to step S9.

[0081] In step S9, the control device 15 determines whether the decrease in cell voltage Vcell occurred after a low-temperature startup (normal startup).

[0082] The control device 15 proceeds to step S10 if it is not after a low-temperature startup (S9: NO), and proceeds to step S12 if it is after a low-temperature startup (S9: YES).

[0083] In step S10, the control device 15 performs normal cell voltage recovery control. That is, the control device 15 sets the air volume to an air volume Sp2 (Sp2 = Sp1 + ΔSpa) which is the initial air volume Sp1 plus a predetermined air increase amount ΔSpa, increases the rotation speed of the compressor 28, and proceeds to step S11.

[0084] In step S11, the control device 15 determines whether the drop in cell voltage Vcell has been resolved and whether the cell voltage Vcell has recovered. If it has not recovered (S11: NO), the control device continues the cell voltage recovery control with the normal amount of air as in step S10.

[0085] In the recovery determination in step S11, the control device 15 determines whether the cell voltage Vcell has recovered based on whether the difference ΔV (ΔV = Vcellmean - Vcellmin), obtained by subtracting the minimum cell voltage Vcellmin from the average cell voltage Vcellmean, falls below the release determination threshold ΔVthb (ΔV < ΔVthb).

[0086] Here, the release threshold ΔVthb is made smaller than the execution threshold ΔVtha (ΔVthb < ΔVtha) to introduce hysteresis. This suppresses the occurrence of control hunting.

[0087] After the cell voltage Vcell recovers (S11:YES), the control device 15 terminates the startup process and thereafter performs power generation operation according to the requested output of the fuel cell vehicle 12.

[0088] On the other hand, in the determination in step S9 described above, if the control device 15 determines that it has been started at a low temperature (S9: YES), it proceeds to step S12.

[0089] In step S12, the control device 15 performs cell voltage recovery control for low-temperature startup. In this low-temperature startup cell voltage recovery control, the air volume is set to an air volume Sp2' (Sp2' = Sp1 + ΔSpb) which is the initial air volume Sp1 plus a predetermined air increase amount ΔSpb, and the rotation speed of the compressor 28 is increased, and the process proceeds to step S13.

[0090] Here, the air increase ΔSpb in the cell voltage recovery control during low-temperature startup is set to a smaller value than the air increase ΔSpa in the cell voltage recovery control during normal-temperature startup (ΔSpb < ΔSpa). In this way, the air increase for cell voltage recovery control is set according to the state of the fuel cell stack 18 at startup, i.e., whether it is a low-temperature startup or a normal startup (air increase ΔSpb for low-temperature startup < air increase ΔSpa for normal-temperature startup), so that the cell voltage recovery control of the fuel cell stack 18 can be executed appropriately. The cell voltage recovery control after low-temperature startup in step S12 will be explained in more detail, including its background.

[0091] Whether starting at room temperature or low temperature, if the cell voltage Vcell of the fuel cell stack 18 decreases, the amount of air (cathode gas) supplied to the fuel cell stack 18 is increased to promote drainage in the cathode channel 58 and restore the cell voltage Vcell.

[0092] However, especially after low-temperature startup, power generation may continue even with a reduced cell voltage (Vcell). In such cases, the cell voltage recovery control described above is performed, but if the air volume is changed after the cell voltage (Vcell) has decreased following low-temperature startup, it may have a counterproductive effect due to the unstable in-plane state of the fuel cell stack 18, causing the cell voltage (Vcell) to decrease further.

[0093] Therefore, in this embodiment, if it is after a low-temperature startup (S9:YES), the air increase amount ΔSpb for low-temperature startup (a predetermined cathode gas increase recovery amount) is set to be smaller than the air increase amount ΔSpa for normal temperature startup (S12), so that the recovery control of the cell voltage Vcell can be performed appropriately. After a low-temperature startup, the air amount may be set to a small amount from the beginning until it returns to a normal state.

[0094] Furthermore, the cause of the decrease in cell voltage Vcell can be found not only on the cathode electrode 56 side but also on the anode electrode 57 side. For example, if the hydrogen concentration on the anode channel 59 side is reduced due to excess nitrogen as measured by a hydrogen concentration meter (not shown), the amount of anode gas may be increased and a nitrogen purge may be performed.

[0095] Returning to the flowchart, the subroutine in step S13 defines the process of determining whether the medium outlet temperature Tco has recovered to room temperature.

[0096] In step S13, the control device 15 determines whether the medium outlet temperature Tco of the fuel cell stack 18 has recovered to room temperature. If it has not recovered (S13: NO), it continues the cell voltage recovery control for low-temperature startup in step S12 until it recovers. If it has recovered (S13: YES), it proceeds to step S10.

[0097] Figures 3A and 3B are flowcharts detailing the process of determining whether or not the temperature has recovered to room temperature in step S13, respectively.

[0098] Regarding the process shown in Figure 3A, in step S13a of Figure 3A, the control device 15 determines whether the medium outlet temperature Tco has risen to a temperature above the second temperature threshold Tth2 for determining warm-up completion. If it has not risen (S13a: NO), the control device 15 continues the cell voltage recovery control for low-temperature startup in step S12. If it has risen (S13a: YES), the process proceeds to step S13b. The second temperature threshold Tth2 for determining warm-up completion is set to a temperature higher than or equal to the first temperature threshold Tth1 for determining warm-up completion (Tth2 ≥ Tth1).

[0099] In step S13b, the control device 15 determines whether the outlet temperature Tic of the intercooler 128 has exceeded the threshold temperature Ticth [°C]. If it has not exceeded the threshold temperature (S13b: NO), it continues the cell voltage recovery control for low-temperature startup in step S12. If it has exceeded the threshold temperature (S13b: YES), it proceeds to step S13c.

[0100] In step S13c, the control device 15 determines whether a predetermined time tmth has elapsed since the completion of humidity-controlled power generation. If the time has not elapsed (S13c: NO), it continues the cell voltage recovery control for low-temperature startup in step S12. If the time has elapsed (S13c: YES), it determines that the medium outlet temperature Tco has recovered to the equivalent of room temperature, and proceeds to the normal cell voltage recovery control in step S10. The timing for starting the count to determine whether a predetermined time tmth has elapsed may be any of the following: when the fuel cell temperature reaches the first temperature threshold Tth1 for determining warm-up completion, when the fuel cell temperature reaches the second temperature threshold Tth2 for determining warm-up completion, or when humidity-controlled power generation is completed.

[0101] Regarding the process shown in Figure 3B, in step S13d of Figure 3B, the control device 15 determines whether the medium outlet temperature Tco has risen to a temperature that exceeds the third temperature threshold Tth3 for determining warm-up completion, which is higher than the second temperature threshold Tth2 for determining warm-up completion. If it has not risen to a temperature that exceeds the threshold (S13d: NO), the control device 15 continues the cell voltage recovery control for low-temperature startup in step S12. If it has risen to a temperature that exceeds the threshold (S13d: YES), the control device 15 determines that the medium outlet temperature Tco has recovered to a temperature equivalent to room temperature and proceeds to the normal cell voltage recovery control in step S10.

[0102] The judgments in steps S13a to S13c may be logical AND but logical OR judgments, and if any one of them is a positive judgment, the process may proceed to step S10. In this case, at least one of the second temperature threshold Tth2 for determining warm-up completion, the predetermined time tmth, or the third temperature threshold Tth3 for determining warm-up completion may have values ​​corresponding to the first warm-up mode and the second warm-up mode, respectively. In this case, the value of at least one of the second temperature threshold Tth2, the predetermined time tmth, or the third temperature threshold Tth3 for determining warm-up completion may be greater in the second warm-up mode than in the first warm-up mode, and conversely, the value in the first warm-up mode may be greater than the value in the second warm-up mode.

[0103] To reiterate, in step S10, the control device 15 performs normal cell voltage recovery control. That is, the control device 15 sets the air volume to the initial air volume Sp1 plus a predetermined air increase amount ΔSpa to get air volume Sp2 (Sp2 = Sp1 + ΔSpa), increases the rotation speed of the compressor 28, and proceeds to step S11.

[0104] In step S11, the control device 15 determines whether the drop in cell voltage Vcell has been resolved and whether the cell voltage Vcell has recovered. If it has not recovered (S11: NO), the control device continues the cell voltage recovery control with the normal amount of air as in step S10.

[0105] In step S11, the control device 15 determines whether the cell voltage Vcell has recovered based on whether the difference ΔV (ΔV = Vcellmean - Vcellmin), obtained by subtracting the minimum cell voltage Vcellmin from the average cell voltage Vcellmean, falls below the release determination threshold ΔVthb (ΔV < ΔVthb).

[0106] Here, the release threshold ΔVthb is made smaller than the execution threshold ΔVtha (ΔVthb < ΔVtha) to introduce hysteresis. This suppresses the occurrence of control hunting.

[0107] After the cell voltage Vcell recovers (S11:YES), the startup process is terminated, and thereafter, power generation processing is performed according to the requested output of the fuel cell vehicle 12.

[0108] [Explanation using a timing chart] An example of the operation described in the flowchart of Figure 2 will be explained with reference to the timing charts in Figures 4 and 5. For ease of understanding, some of the step numbers from the flowchart in Figure 2 will be inserted in the following explanation.

[0109] Figure 4 shows the timing chart for startup at room temperature, and Figure 5 shows the timing chart for startup at low temperature.

[0110] <Starts at room temperature> At time t0 in Figure 4, when the power switch 71 is switched from the off state to the on state, the start-up process (start-up power generation) of the fuel cell system 10 with the initial air amount Sp1 is initiated after the determination in step S2 (S2: NO) (S3).

[0111] During this room-temperature startup, when the difference ΔV obtained by subtracting the minimum cell voltage Vcellmin from the average cell voltage Vcellmean detected by the cell voltage sensor 51 exceeds the threshold voltage, which is the execution determination threshold ΔVtha (S8:YES), the cell voltage recovery request flag is set to 1 (Yes). Note that the larger the difference ΔV, the lower the minimum cell voltage Vcellmin will be.

[0112] From time t1 onward, the air volume is increased by the amount of increased air volume ΔSpa to an air volume Sp2 (Sp2 = Sp1 + ΔSpa), and the cell voltage recovery power generation process (S10, S11) is performed with this increased air volume.

[0113] If, at time t2, the difference ΔV falls below ΔVthb (ΔVthb < ΔVtha) (S11: YES), the cell voltage recovery request flag is set to 0 (none), the normal startup control related to cell voltage recovery power generation is terminated, and normal power generation is performed.

[0114] <Low-temperature startup> At time t0 in Figure 5, when the power switch 71 is switched from the off state to the on state, the start-up process (start-up power generation) of the fuel cell system 10 with the initial air amount Sp1 is initiated after the determination in step S2 (S2: YES) (S4).

[0115] In the case of low-temperature startup, at time t3, the air volume is reduced from the initial air volume Sp1 to the warm-up air volume Sp3, and warm-up power generation is performed in either the first or second warm-up mode (S5). This warm-up power generation reduces the average voltage Vcellmean, and this performance reduction can be used as additional heat generation to accelerate the heating rate.

[0116] When the medium outlet temperature Tco exceeds the first temperature threshold Tth1 used to determine when warming is complete (time t5, S6: YES), humidity-controlled power generation (S7) is initiated, which involves supplying dry cathode gas to the fuel cell stack 18, bypassing the humidifier 30.

[0117] At time t5, it is determined whether the cell voltage Vcell has decreased. In this case, since it was determined at time t4 that the cell voltage Vcell has decreased, the air volume is increased from the warm-up air volume Sp3 to the air volume Sp2'.

[0118] The air volume Sp2' is set to an air increase of ΔSpb that is less than the air increase ΔSpa when starting at room temperature (Sp2' = Sp1 + ΔSpb).

[0119] When the time elapsed from the end of humidity control power generation (t6) reaches a predetermined time (tmth), at time t7, it is determined that the warm-up process is complete.

[0120] From time t7 onward, the air volume is increased to air volume Sp2 (an increase of ΔSpc from the initial air volume Sp1), and cell voltage recovery control is continued. At time t8, if the difference ΔV falls below the release judgment threshold ΔVthb (S11: YES), the cell voltage recovery request flag is set to 0, cell voltage recovery power generation is terminated, and normal power generation is performed. Note that the air increase amount ΔSpc is set to approximately the same amount as the air increase amount ΔSpa (see Figure 4).

[0121] The above embodiment can also be modified as follows.

[0122] <Variation> Figure 6 shows a flowchart relating to a modified example. Note that the same steps as in the flowchart in Figure 2 are given the same step numbers, and only the differences are explained.

[0123] In the flowchart of Figure 6, if a decrease in the cell voltage Vcell is detected in step S8 (S8: YES), the system uniformly performs cell voltage recovery control for low-temperature startup without determining whether or not a low-temperature startup has occurred (S9 in Figure 2). This control allows for proper execution of cell voltage recovery control of the fuel cell stack, ultimately contributing to energy efficiency.

[0124] [Note] In addition to the disclosures mentioned above, the following further notes are made:

[0125] (Note 1) The fuel cell system (10) performs low-temperature startup control when the temperature (Tco) of the fuel cell stack (18), which generates electricity through the reaction of anode gas and cathode gas, is below a low-temperature threshold (Tth0), and performs normal startup control when it is above the low-temperature threshold. If the voltage of the fuel cell stack drops after low-temperature startup by the low-temperature startup control or after normal startup by the normal startup control, the system increases the amount of cathode gas to restore the voltage of the fuel cell stack, wherein the amount of cathode gas increase (ΔSpb) for the voltage restoration control from after low-temperature startup until the fuel cell stack reaches a predetermined dry state is smaller than the amount of cathode gas increase (ΔSpa) for the voltage restoration control after normal startup.

[0126] In this way, the cathode gas increase for voltage recovery control is set according to the state of the fuel cell stack at startup, i.e., whether it is a low-temperature startup or a normal startup, so that the voltage recovery control of the fuel cell stack can be performed appropriately.

[0127] In particular, the amount of cathode gas increase in the voltage recovery control from low-temperature startup until the fuel cell stack reaches a predetermined dry state is smaller than the amount of cathode gas increase in the voltage recovery control after normal startup, thereby stabilizing the in-plane state of the fuel cell stack at low temperatures.

[0128] (Note 2) The fuel cell system performs low-temperature startup control when the temperature of the fuel cell stack, which generates electricity through the reaction of anode gas and cathode gas, is below a low-temperature threshold, and performs normal startup control when the temperature is above the low-temperature threshold. If the voltage of the fuel cell stack decreases after low-temperature startup by the low-temperature startup control or after normal startup by the normal startup control, the system increases the amount of cathode gas to restore the voltage of the fuel cell stack, wherein the amount of cathode gas increase (ΔSpb) for the voltage restoration control from after low-temperature startup until the fuel cell stack reaches a predetermined dry state is smaller than the amount of cathode gas increase (ΔSpc) for the voltage restoration control from after low-temperature startup until the fuel cell stack reaches a predetermined dry state.

[0129] This allows for appropriate voltage recovery control of the fuel cell stack based on the state of the fuel cell stack after low-temperature startup.

[0130] (Note 3) In the fuel cell system described in Appendix 1 or 2, after the low-temperature startup, warm-up control of the fuel cell stack (S5, time points t3 to t5) is performed, and it may be determined that the fuel cell stack has reached a predetermined dry state when the elapsed time from the time (t6) when the fuel cell temperature after the low-temperature startup reaches or exceeds the warm-up completion determination temperature threshold (Tth2), or when the fuel cell temperature after the low-temperature startup reaches a room temperature determination threshold (Tth3) that exceeds the warm-up completion determination temperature threshold.

[0131] According to this, voltage recovery control of the fuel cell stack can be appropriately performed based on whether or not the fuel cell stack has reached a predetermined dry state after low-temperature startup.

[0132] (Note 4) In the fuel cell system described in Appendix 1 or 2, after the low-temperature startup, warm-up control of the fuel cell stack is performed, and after the warm-up control is performed, humidity-controlled power generation is performed by increasing the amount of cathode gas supplied to the fuel cell stack compared to the time of the warm-up control, and when the elapsed time from the completion of the humidity-controlled power generation is a predetermined time or longer, it may be determined that the fuel cell stack has reached a predetermined dry state.

[0133] (Note 5) In the fuel cell system described in Appendix 3, the warm-up control includes a first warm-up mode in which the fuel cell stack is operated at a first output, and a second warm-up mode in which it is operated at a second output higher than the first output, and at least one of the warm-up completion determination temperature threshold (Tth2), the predetermined time (tmth), and the room temperature determination threshold (Tth3) may have values ​​corresponding to the first warm-up mode and the second warm-up mode, respectively.

[0134] This allows for proper voltage recovery control of the fuel cell stack based on the output of the fuel cell stack during warm-up control.

[0135] (Note 6) In the fuel cell system described in Appendix 5, the value in the second warm-up mode may be greater than the value in the first warm-up mode.

[0136] This allows for proper voltage recovery control of the fuel cell stack based on the output of the fuel cell stack during warm-up control.

[0137] (Note 7) In the fuel cell system described in Appendix 5, there is an energy storage device (44) that charges the output of the fuel cell stack, the first output and the second output are the target output of the fuel cell stack, and the first warm-up mode and the second warm-up mode may be switched based on the remaining capacity (SOC) of the energy storage device.

[0138] According to this, the voltage recovery control of the fuel cell stack can be appropriately performed based on the output of the fuel cell stack during warm-up control.

[0139] (Note 8) A control method for a fuel cell system comprises: performing low-temperature startup control when the temperature of a fuel cell stack that generates electricity through the reaction of anode gas and cathode gas is below a low-temperature threshold; performing normal startup control when the temperature is above the low-temperature threshold; a voltage drop determination step for determining whether the voltage of the fuel cell stack has decreased after low-temperature startup by the low-temperature startup control or after normal startup by the normal startup control; and a voltage recovery control step for performing voltage recovery control by increasing the amount of cathode gas when the voltage of the fuel cell stack has decreased, wherein the amount of cathode gas increased in the voltage recovery control step from after low-temperature startup until the fuel cell stack reaches a predetermined dry state is smaller than the amount of cathode gas increased in the voltage recovery control step after normal startup.

[0140] According to this, the amount of cathode gas increase for voltage recovery control is set according to the state of the fuel cell stack at startup, i.e., whether it is a low-temperature startup or a normal startup, so that voltage recovery control of the fuel cell stack can be properly performed at low temperatures.

[0141] This disclosure is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the gist of this disclosure or from the spirit of this disclosure derived from the claims and their equivalents. These embodiments can also be implemented in combination. For example, the order of operations and processes in the embodiments described above are given as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above. [Explanation of Symbols]

[0142] 10…Fuel cell system 12…Fuel cell vehicle 15…Control device 18…Fuel cell stack 44... Energy storage device 50... Fuel cell 56... Cathode electrode 57... Anode electrode 58... Cathode channel 59... Anode channel 64... Bypass channel 86... (Media outlet) Temperature sensor 122... Bypass valve 128... Intercooler

Claims

1. A fuel cell system that performs low-temperature startup control when the temperature of a fuel cell stack that generates electricity through the reaction of anode gas and cathode gas is below a low-temperature threshold, and normal startup control when the temperature of the fuel cell stack is above the low-temperature threshold, and increases the amount of cathode gas to perform voltage recovery control of the fuel cell stack when the voltage of the fuel cell stack drops after low-temperature startup by the low-temperature startup control or after normal startup by the normal startup control, The amount of cathode gas increase in the voltage recovery control from the low-temperature startup until the fuel cell stack reaches a predetermined dry state is made smaller than the amount of cathode gas increase in the voltage recovery control after normal startup. Fuel cell system.

2. A fuel cell system that performs low-temperature startup control when the temperature of a fuel cell stack that generates electricity through the reaction of anode gas and cathode gas is below a low-temperature threshold, and normal startup control when the temperature of the fuel cell stack is above the low-temperature threshold, and increases the amount of cathode gas to perform voltage recovery control of the fuel cell stack when the voltage of the fuel cell stack drops after low-temperature startup by the low-temperature startup control or after normal startup by the normal startup control, The amount of cathode gas increase in the voltage recovery control from the time of low-temperature startup until the fuel cell stack reaches a predetermined dry state is made smaller than the amount of cathode gas increase in the voltage recovery control when the fuel cell stack reaches a predetermined dry state after low-temperature startup. Fuel cell system.

3. In the fuel cell system according to claim 1 or 2, After the low-temperature startup, the warm-up control of the fuel cell stack is performed. If the time elapsed since the fuel cell temperature after the low-temperature startup reached the warm-up completion threshold has exceeded a predetermined time, Or, if the fuel cell temperature after the low-temperature startup becomes a room temperature threshold that exceeds the warm-up completion determination temperature threshold, The fuel cell stack is determined to have reached a predetermined dry state. Fuel cell system.

4. In the fuel cell system according to claim 1 or 2, After the low-temperature startup, warm-up control of the fuel cell stack is performed, and after the warm-up control is performed, humidity-controlled power generation is performed by increasing the amount of cathode gas supplied to the fuel cell stack compared to the amount supplied during the warm-up control. A fuel cell system that determines that the fuel cell stack has reached a predetermined dry state when the elapsed time since the completion of the humidity-controlled power generation exceeds a predetermined time.

5. In the fuel cell system according to claim 3, The warm-up control includes a first warm-up mode in which the fuel cell stack is operated at a first output, and a second warm-up mode in which it is operated at a second output higher than the first output. At least one of the warm-up completion determination temperature threshold, the predetermined time, and the room temperature determination threshold has a value corresponding to the first warm-up mode and the second warm-up mode, Fuel cell system.

6. In the fuel cell system according to claim 5, At least one of the warm-up completion temperature threshold, the predetermined time, and the ambient temperature threshold is greater in the second warm-up mode than in the first warm-up mode. Fuel cell system.

7. In the fuel cell system according to claim 5, The device includes an energy storage device that charges the output of the fuel cell stack, The first output and the second output are the target outputs of the fuel cell stack, The first warm-up mode and the second warm-up mode are switched based on the remaining capacity of the energy storage device. Fuel cell system.

8. A control method for a fuel cell system comprising: performing low-temperature startup control when the temperature of the fuel cell stack, which generates electricity by the reaction of anode gas and cathode gas, is below a low-temperature threshold; performing normal startup control when the temperature is above the low-temperature threshold; a voltage drop determination step for determining whether the voltage of the fuel cell stack has decreased after the low-temperature startup by the low-temperature startup control or after the normal startup by the normal startup control; and a voltage recovery control step for performing voltage recovery control by increasing the amount of cathode gas when the voltage of the fuel cell stack has decreased, wherein The amount of cathode gas increased during the voltage recovery control process from the low-temperature startup until the fuel cell stack reaches a predetermined dry state is made smaller than the amount of cathode gas increased during the voltage recovery control process after normal startup. A method for controlling a fuel cell system.

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