FUEL CELL SYSTEM AND CONTROL METHODS OF THE FUEL CELL SYSTEM

Abstract

Fuel cell system (30) with: a fuel cell (100); a gas supply unit (120, 140) configured to supply gas to the fuel cell (100); an electrical power storage device (172) capable of storing at least electrical power generated by the fuel cell (100); a residual capacity monitor (173) configured to detect a residual capacity in the electrical power storage device (172); and a control unit (200) configured to perform a purging operation for purging an interior of the fuel cell (100) with the gas by controlling the gas supply unit (120, 140) and a charging operation for charging the remaining capacity of the electric power storage device (172) with the power generated by the fuel cell (100), wherein the control unit (200) determines, upon input of a stop instruction of the fuel cell system (30), whether the temperature conditions are met, wherein the low temperature conditions include that a temperature relating to a state of the fuel cell (100) is less than or equal to a predetermined set threshold value, the control unit (200), when determining that the low-temperature conditions are met, performs the purging operation such that more moisture stored in the fuel cell (100) is discharged to an outside of the fuel cell (100) compared to when determining that the low-temperature conditions are not met, and the control unit (200) performs the charging operation with a target remaining capacity of the electric power storage device (172) set to a smaller value compared to when determining that the low-temperature conditions are not met.

Description

Background area

[0001] The present disclosure relates to a fuel cell system and a control method of the fuel cell system. State of the art

[0002] For example, regarding a fuel cell system including a fuel cell and an electric power storage device, JP 2007-042313 A discloses a configuration in which purging and restarting of the system are reliably performed by charging the electric power storage device to a larger amount of charge when stopping the system at low temperature compared to the case of stopping the system at normal temperature.

[0003] However, in some cases, at low temperatures, the allowable charging power is restricted, which corresponds to the upper limit when controlling the power for charging an electric power storage device. In such cases, it may take a long time to increase the amount of charge in the electric power storage device, and thus the time required to complete the system shutdown may be extended. Brief description

[0004] (1) One embodiment of the present disclosure provides a fuel cell system. The fuel cell system includes a fuel cell, a gas supply unit configured to supply gas to the fuel cell, an electric power storage device capable of storing at least electric power generated by the fuel cell, a remaining capacity monitor configured to detect a remaining capacity in the electric power storage device, and a control unit configured to perform a purging operation for purging an interior of the fuel cell with the gas by driving the gas supply unit and a charging operation for charging the remaining capacity of the electric power storage device with the power generated by the fuel cell. The control unit determines whether the temperature conditions are met upon input of a stop instruction of the fuel cell system.wherein the low-temperature conditions include that a temperature related to a state of the fuel cell is less than or equal to a predetermined set threshold; the control unit, when determining that the low-temperature conditions are met, performs the purging process such that more moisture stored in the fuel cell is discharged to an outside of the fuel cell compared to when determining that the low-temperature conditions are not met; and the control unit performs the charging process with a target remaining capacity of the electric power storage device set to a smaller value compared to when determining that the low-temperature conditions are not met.

[0005] In the fuel cell system according to this embodiment, when it takes a relatively long time to charge the electric power storage device when it is determined that the low-temperature conditions are established upon input of the fuel cell system stop instruction, the charging operation is performed with the target remaining capacity set to a smaller value than when it is determined that the low-temperature conditions are not established. Consequently, it is possible to shorten the time for the charging operation, thereby shortening the time required to complete the stop. Furthermore, when it is determined that the low-temperature conditions are established, the control unit performs the purging operation upon system stop so that more of the moisture stored in the fuel cell is discharged to the outside of the fuel cell.Consequently, even in the case where the ambient temperature drops after the system is stopped, it is possible to suppress the freezing of liquid in the fuel cell.

[0006] (2) The fuel cell system according to the above-described configuration may further include a first temperature sensor configured to detect a temperature of the electric power storage device, wherein the control unit may determine that the low-temperature conditions are satisfied when the temperature of the electric power storage device is less than or equal to a predetermined first reference temperature and the remaining capacity of the electric storage device is less than or equal to a predetermined reference value.In the fuel cell system according to this configuration, when the system is stopped, as long as the temperature of the electric power storage device is equal to or less than the first reference temperature, the control unit performs the purging operation so that more moisture is discharged to the outside of the fuel cell even when the remaining capacity of the electric power storage device is equal to or less than the reference value, with the target remaining capacity for charging the electric power storage device set to a small value. Therefore, even when the remaining capacity value is small, it is possible to suppress freezing of the fuel cell while suppressing an extension of the time required to complete the system stop due to charging the electric power storage device.As long as the remaining capacity value of the electric power storage device is above the reference value, the control unit performs the purging operation so that less moisture is released to the outside of the fuel cell even when the temperature of the electric power storage device is less than or equal to the first reference temperature. Consequently, it is possible to suppress energy consumption by performing the purging operation when the system is stopped. As described above, when the remaining capacity value is large when the system is stopped, the amount of charge is small even if the target remaining capacity for charging when the system is stopped is set to a large value, thus suppressing an increase in the time required to complete the system stop due to charging the electric power storage device.In addition, the value of the residual capacity when the system is stopped is large and thus, if necessary, an anti-freeze measure can be taken during the system stoppage.

[0007] (3) The fuel cell system according to the above-described configuration may further include a second temperature sensor configured to detect an ambient temperature of the fuel cell system, wherein the control unit may determine that the low-temperature conditions are satisfied when the ambient temperature is less than or equal to a predetermined second reference temperature.

[0008] In the fuel cell system according to this embodiment, when the ambient temperature is equal to or lower than the second reference temperature, the control unit determines that the low-temperature conditions are established regardless of the temperature and remaining capacity of the electric power storage device. In the case where the fuel cell is likely to freeze during the system downtime, the purge process is performed in advance when the system is stopped. Consequently, the need for the anti-freeze measure for the fuel cell during the system downtime is eliminated. This makes it possible to increase the energy efficiency of the fuel cell system while suppressing fuel cell freezing.

[0009] (4) In the fuel cell system according to the above-described configuration, when freezing conditions are satisfied during a stoppage of the fuel cell system and the control unit has determined that the low-temperature conditions are satisfied at a previous stop of the fuel cell system, the control unit may perform a purge operation during the stoppage such that less of the moisture stored in the fuel cell is released to the outside of the fuel cell compared to when it determines that the low-temperature conditions are not satisfied, wherein the freezing conditions are set in advance as conditions under which freezing is most likely to occur in the fuel cell.

[0010] In the fuel cell system according to this embodiment, if the control unit has determined that the low-temperature conditions have not been established during the previous stop of the fuel cell system, after the freezing conditions have been established, the control unit executes the purging process during the stoppage period. Consequently, it is possible to suppress freezing of the fuel cell. If the control unit has determined that the low-temperature conditions have not been established during the previous stop of the fuel cell system, the control unit executes the purging process during the stoppage period so that more of the moisture stored in the fuel cell is released to the outside of the fuel cell. Thus, it is possible to suppress freezing of the fuel cell.

[0011] (5) The fuel cell system according to the above-described aspect may further include a third temperature sensor configured to detect a temperature of the fuel cell, wherein the control unit can determine that the freezing conditions are met when the temperature of the fuel cell is less than or equal to a predetermined third reference temperature. In the fuel cell system according to this aspect, the control unit is capable of determining that freezing is most likely to occur in the fuel cell by using the temperature of the fuel cell.

[0012] The present disclosure may be embodied in various configurations, for example, as claimed, as a control method of the fuel cell system, as a computer program for implementing the control method, and as a non-volatile recording medium configured to store the computer program. Short description of the drawings Fig. 1 is a block diagram showing a schematic configuration of a fuel cell vehicle. Fig. 2 shows an explanatory diagram schematically illustrating the process that can be carried out in the fuel cell vehicle. Fig. Figure 3 shows a flowchart illustrating a stopping routine. Fig. 4 is an explanatory diagram showing the relationship between temperature and an allowable charging power Win of an electric power storage device. Fig. Figure 5 shows a flowchart illustrating a flushing routine during a downtime. Fig. Figure 6 shows a flowchart illustrating a stopping routine. Detailed DescriptionA. First Embodiment:A-1. Overall Configuration of Fuel Cell System:

[0013] Fig. 1 shows the block diagram illustrating the schematic configuration of a fuel cell vehicle 20 equipped with a fuel cell system 30 serving as the first embodiment according to this disclosure. The fuel cell vehicle 20 is equipped, on a vehicle body 22, with the fuel cell system 30 including a fuel cell 100, a drive motor 170 configured to generate driving force for the vehicle, an electric power storage device 172 capable of supplying power for driving the fuel cell vehicle 20, and a control unit 200. In the fuel cell vehicle 20, the fuel cell 100 and the electric power storage device 172 are each capable of independently or simultaneously supplying power to loads including the drive motor 170.The fuel cell 100 is connected to a load, including the drive motor 170, via a DC-DC converter 104 and wiring 178. The electrical power storage device 172 is connected to a load, including the drive motor 170, via a DC-DC converter 174 and wiring 178. The DC-DC converter 104 and the DC-DC converter 174 are connected in parallel to the wiring 178.

[0014] The fuel cell system 30 includes the fuel cell 100 and also a hydrogen gas supply system 120 including a hydrogen tank 110 and an air supply system 140 including a compressor 130. The fuel cell system 30 also includes a coolant circulation system (not shown) configured to circulate a coolant within the fuel cell 100 to maintain the temperature of the fuel cell 100 within a predetermined range. The hydrogen gas supply system 120 and the air supply system 140 are also referred to as a "gas supply unit." The components included in the hydrogen gas supply system 120, the air supply system 140, and the coolant circulation system are driven when the fuel cell 100 generates power, and these components are also referred to as fuel cell auxiliaries.

[0015] The fuel cell 100 is formed in a stacked structure in which a plurality of unit cells are stacked one upon another. The fuel cell 100 is a solid polymer fuel cell in this embodiment, or it may alternatively be another type of fuel cell. Each of the unit cells included in the fuel cell 100 has, in an anode side, a flow path (hereinafter also referred to as an anode-side flow path) through which hydrogen, which is the fuel gas, flows, and, in a cathode side, a flow path (hereinafter also referred to as a cathode-side flow path) through which air, which is an oxidizing gas, flows, with an electrolyte membrane interposed between them.

[0016] The fuel cell 100 includes a fuel cell temperature sensor 105 capable of measuring the temperature of the fuel cell 100. For example, the fuel cell temperature sensor 105 may be disposed in at least one of the coolant flow paths described above and may be a temperature sensor that detects the temperature of the corresponding coolant circulating within the fuel cell 100 and discharged from the fuel cell 100. Alternatively, the fuel cell temperature sensor 105 may be a sensor that directly detects the temperature within the fuel cell 100. The fuel cell temperature sensor 105 is referred to as a "third temperature sensor."

[0017] The hydrogen tank 110 included in the hydrogen gas supply system 120 is a device for storing hydrogen-containing fuel gas. Specifically, the hydrogen tank 110 may be a tank that stores high-pressure hydrogen gas, or a tank that contains a hydrogen storage alloy inside and stores hydrogen by causing the hydrogen storage alloy to occlude hydrogen. The hydrogen gas supply system 120 includes a hydrogen supply flow path 121 extending from the hydrogen tank 110 to the fuel cell 100, a circulation flow path 122 for circulating anode off-gas containing unconsumed hydrogen gas to the hydrogen supply flow path 121, and a hydrogen discharge flow path 123 for discharging the anode off-gas to the atmosphere.In the hydrogen gas supply system 120, the hydrogen gas stored in the hydrogen tank 110 is forced to flow through the hydrogen supply flow path 121 by opening and closing an on-off valve 124 of the hydrogen supply flow path 121 and decompressed by a pressure reducing valve 125. The hydrogen gas is then supplied to the anode-side flow path of the fuel cell 100 from an injector 126 located downstream of the pressure reducing valve 125. The pressure of the hydrogen circulating in the circulation flow path 122 is adjusted by a circulation pump 127. The drive amounts of the injector 126 and the circulation pump 127 are adjusted by the control unit 200 based on a target current to be output from the fuel cell 100.

[0018] Note that the hydrogen gas flowing through the circulation flow path 122 partially passes through an on-off valve 129, which is provided in the hydrogen discharge flow path 123 branching from the circulation flow path 122 and is controlled in its opening / closing states, and is then discharged to the atmosphere. Consequently, it is possible to discharge impurities (such as water vapor and nitrogen) other than the hydrogen contained in the hydrogen gas circulating in the circulation flow path 122 to the outside of the flow path and suppress the increase of an impurity concentration in the hydrogen gas to be supplied to the fuel cell 100. The opening / closing timing of the above-described on-off valve 129 is controlled by the control unit 200.

[0019] The air supply system 140 supplies the fuel cell 100 with oxidizing gas (air in this embodiment) containing oxygen. The air supply system 140 includes the compressor 130 and also includes a first air flow path 141, a second air flow path 145, a third air flow path 146, a flow dividing valve 144, an air discharge flow path 142, and a pressure regulating valve 143. The first air flow path 141 and the second air flow path 145 supply the air sucked in by the air compressor 130 to the fuel cell 100. The second air flow path 145 is partially formed in the fuel cell 100 as the cathode-side flow path. The third air flow path 146 is a bypass flow path connected to the first air flow path 141 so as not to allow the air to pass through the fuel cell 100.The flow dividing valve 144 is arranged at a location where the first air flow path 141 branches off to the second air flow path 145 and the third air flow path 146, and is configured to change the distribution ratio of the air flowing into the second air flow path 145 and the third air flow path 146. The air passing through either the second air flow path 145 or the third air flow path 146 is discharged to the atmosphere through the air discharge flow path 142. The above-described hydrogen discharge flow path 123 is connected to the air discharge flow path 142, and the hydrogen discharged through the hydrogen discharge flow path 123 is diluted by the air flowing through the air discharge flow path 142 before being discharged to the atmosphere.The pressure regulating valve 143 is arranged in the second air flow path 145 on the downstream side of the cathode-side flow path and is capable of changing the back pressure of the cathode-side flow path in the fuel cell 100 by adjusting the opening of the pressure regulating valve 143. The control unit 200 adjusts the drive amount of the compressor 130, the opening of the pressure regulating valve 143, and the opening states of the flow dividing valve 144.

[0020] The electric power storage device 172 is of a chargeable and dischargeable type and is charged at least with the power generated by the fuel cell 100. An allowable charging power Win in the electric power storage device 172 is set as a charging power upper limit. Thus, the allowable charging power Win is used as the upper limit of the charging power when controlling the charging of the electric power storage device 172, for example, to suppress deterioration of the electric power storage device 172. In the electric power storage device 172 of this embodiment, the allowable charging power Win has a temperature dependency. The lower the temperature, the lower the allowable charging power Win. The electric power storage device 172 may be, for example, a lithium-ion battery or a nickel-hydrogen battery.The electric power storage device 172 is not limited to the secondary battery as described above.

[0021] The electrical power storage device 172 includes a remaining capacity monitor 173 and a temperature sensor 175. The remaining capacity monitor 173 detects an operating state, such as a remaining capacity of the electrical power storage device 172. The remaining capacity of the electrical power storage device 172 is an indicator indicating the amount of charge in the electrical power storage device 172. The remaining capacity is also referred to as a "state of charge." The remaining capacity monitor 173 may be configured to estimate the remaining capacity by, for example, integrating a current value and a charging and discharging time in the electrical power storage device 172. Alternatively, the remaining capacity monitor 173 may be configured to derive the remaining capacity using a voltage of the electrical power storage device 172. The remaining capacity monitor 173 outputs a signal indicating the remaining capacity to the control unit 200.The temperature sensor 175 detects the temperature of the electric power storage device 172 and outputs a detection signal to the control unit 200. Note that the temperature sensor 175 may be configured to directly detect the temperature of the electric power storage device 172 or to estimate it using, for example, the outside temperature and a heating value based on a charge / discharge amount of the electric power storage device 172. The temperature sensor 175 is also referred to as a "first temperature sensor."

[0022] The DC-DC converter 104 functions to change the output conditions of the fuel cell 100 upon receiving a control signal from the control unit 200. Specifically, the DC-DC converter 104 derives current and voltage from the fuel cell 100 for the loads described above and controls the current and voltage to be supplied from the fuel cell 100 by performing switching control. When the DC-DC converter 104 supplies a load such as the drive motor 170 with the current generated by the fuel cell 100, it raises the voltage output from the fuel cell 100 to the voltage available from the load described above.

[0023] The DC-DC converter 174 has a charge / discharge control function for controlling the charging and discharging of the electric power storage device 172, and is configured to control the charging and discharging of the electric power storage device 172 upon receiving the control signal from the control unit 200. Furthermore, the DC-DC converter 174 draws storage power from the electric power storage device 172 by adjusting the target voltage of its output side under the control of the control unit 200 and applies the voltage to the drive motor 170, thereby variably controlling the power draw conditions and the voltage level to be applied to the drive motor 170. Note that the DC-DC converter 174 is disconnected from the electric power storage device 172 and the wiring 178 when no charging or discharging is required in the electric power storage device 172.

[0024] The control unit 200 is configured with a so-called microcomputer, which has a CPU configured to perform logical operations, a ROM, a RAM, and the like. The control unit 200 obtains detection signals from various sensors, not only the above-described sensors included in the hydrogen gas supply system 120 and the air supply system 140, but also from an accelerator pedal opening sensor 180, an outside air temperature sensor 185, a shift position sensor, a vehicle speed sensor, and the like, and performs various types of control relating to the fuel cell vehicle 20. It should be noted that the Fig. 1 represent some of the functions to be performed by the control unit 200. In detail, the control unit 200 includes at least a purge controller 210 and a residual capacity controller 220 as functional blocks. The operation of these functional blocks will be described in more detail later.

[0025] The control unit 200 is configured to control the entire fuel cell vehicle 20 in Fig. 1, or alternatively, it may have a different configuration. For example, the control unit 200 may include a plurality of controllers, such as a controller configured to perform control relevant to the operation of the fuel cell system 30, a controller configured to perform control relevant to the travel of the fuel cell vehicle 20, and a controller configured to perform control for vehicle auxiliary machines not relevant to travel, and it also exchanges necessary information among the plurality of controllers. A-2. Processing to be carried out in the fuel cell vehicle:

[0026] Fig. Fig. 2 is an explanatory view schematically illustrating the processing that can be performed in the fuel cell vehicle 20. The fuel cell vehicle 20 includes a start switch (not shown) that allows a user to give an instruction to start and stop the fuel cell system 30. Fig. 2, "ON" indicates the time when a start instruction is input using the start switch to start the fuel cell system 30, and "OFF" indicates the time when a stop instruction is input to stop the fuel cell system 30. The following sequential descriptions are based on Fig. 2 with respect to various types of processing that can be carried out in the fuel cell vehicle 20.

[0027] In response to the input of the start instruction via the start switch, the control unit 200 of the fuel cell system 30 executes a "start processing". Fig. 2 (a) indicates the time period during which the "start-up processing" is executed. The "start-up processing" is executed during the period from the input of the start-up instruction to the start of power generation in the fuel cell 100. The "start-up processing" may include, for example, processing for starting the supply of hydrogen to the anode-side flow path and the supply of air to the cathode-side flow path, and processing for connecting the fuel cell 100 and a load such as the drive motor 170. This allows the fuel cell 100 to supply power to a load such as the drive motor 170.

[0028] When the “start processing” is completed and the fuel cell 100 starts generating electricity in the fuel cell system 30, the fuel cell vehicle 20 is in a drivable state. Fig. 2 (b) indicates the traveling period during which the fuel cell vehicle 20 is capable of traveling. During the traveling period, the fuel cell vehicle 20 travels as described above by using at least one of the fuel cell 100 and the electric power storage device 172 as a driving power source. At this time, the control unit 200 of the fuel cell vehicle 20 controls the driving conditions of the fuel cell system 30 and the drive motor 170 so that the remaining capacity of the electric power storage device 172 is greater than or equal to a preset lower limit value.

[0029] Thereafter, when the stop instruction is input using the start switch to stop the fuel cell system 30, the control unit 200 of the fuel cell system 30 executes "final processing". Fig. 2 (c) indicates the time period during which the "end processing" is executed. The "end processing" may include a "charging process," a "flushing process at stop," and a "system stop processing." As described later, the control unit 200 may execute "normal mode end processing" or "winter mode end processing" as the "end processing." The "normal mode end processing" and the "winter mode end processing" differ from each other in the contents of the "charging process" and the "flushing process at stop." The "normal mode end processing" and the "winter mode end processing" will be described in detail later.

[0030] The "charging process," which serves as the processing for increasing the remaining capacity of the electric power storage device 172 with the power generated by the fuel cell 100, is performed to charge the electric power storage device 172 by the fuel cell 100. Executing the "charging process" allows the electric power storage device 172 to secure the power to perform various types of processing in the fuel cell system 30 after the stop instruction is input, in the period from the stop instruction input to the restart of power generation by the fuel cell 100 in response to the next start instruction input.Therefore, in the case where, at the time of inputting the above-described stop instruction, the remaining capacity of the electric power storage device 172 is sufficient for the above-described current required by the electric power storage device 172, no substantial charging work needs to be performed in the above-described "charging process." The "charging process" is controlled by the remaining capacity controller 220 of the control unit 200 (see FIG. Fig. 1). The specific operation relevant to the "charging process" will be described in detail later.

[0031] The "purge at stop" is performed to purge the anode-side flow path and the cathode-side flow path with respective types of reaction gas (fuel gas and oxidizing gas) when power generation in the fuel cell 100 is stopped, thereby removing moisture from the flow paths. The "purge at stop" is controlled by the purge controller 210 of the control unit 200 (see Fig. 1). Regarding the anode-side flow path, in the "purge at stop" operation, the control unit 200 opens the on-off valve 124 and the injector 126 and drives the circulation pump 127, and also opens the on-off valve 129 at a predetermined timing. Regarding the cathode-side flow path, the control unit 200 drives the compressor 130 while maintaining the switching states of the flow dividing valve 144 so that air is supplied to the cathode-side flow path. Consequently, it is possible to purge the anode-side flow path with hydrogen serving as the fuel gas and the cathode-side flow path with air serving as the oxidizing gas, thereby removing moisture from the fuel gas flow path and the oxidizing gas flow path.By removing moisture from the reaction gas flow paths, it is possible to suppress the retention of liquid water in the reaction gas flow paths and to suppress the freezing of the remaining liquid water during the downtime of the fuel cell system 30, that is, the period before the fuel cell system 30 restarts after the fuel cell system 30 stops. In the "stop purge process," hydrogen is supplied to the anode-side flow path and air is supplied to the cathode-side flow path, thus enabling the fuel cell 100 to generate electricity. Note that if the fuel cell auxiliary devices and the like consume more electricity than the electricity generated in the "stop purge process," the electricity stored in the electric power storage device 172 is consumed in the "stop purge process."

[0032] In the "finishing process," either the "charging process" or the "stopping purge process" may be performed first. Note that if the "charging process" is performed before the "stopping purge process," the power required in the "stopping purge process" can be easily secured in the electric power storage device 172 by charging the electric power storage device 172 before the "purge process."

[0033] The "system stop processing" is executed to stop the fuel cell system 30. The "system stop processing" is executed after the "charging process" and the "purging process at stop" are completed. During the "system stop processing," the control unit 200 closes the on-off valve 124 of the hydrogen supply flow path 121, the on-off valve included in the injector 126, and the on-off valve 129 of the hydrogen discharge flow path 123. This processing seals the flow path, including the anode-side flow path from the injector 126 to the on-off valve 129 (hereinafter, this flow path is also referred to collectively as the anode-side flow path), so that the hydrogen gas is confined therein. The control unit 200 stops the compressor 130 and closes the pressure regulating valve 143.This processing seals the flow path, which includes the cathode-side flow path from the compressor 130 to the pressure regulating valve 143 (hereinafter, this flow path is also referred to collectively as the cathode-side flow path), so that air is trapped therein. When the flow paths are sealed as described above, the fuel cell 100 generates electricity using the hydrogen trapped in the anode-side flow path and the oxygen in the air trapped in the cathode-side flow path. The amount of hydrogen trapped in the anode-side flow path is excessive relative to the amount of oxygen in the air trapped in the cathode-side flow path, and therefore, power generation of the fuel cell 100 stops when the oxygen in the cathode-side flow path is consumed. As a result, the gas trapped in the cathode-side flow path is mostly nitrogen.When the stop of power generation in the fuel cell 100 is detected based on, for example, the voltage drop of the fuel cell 100, the control unit 200 disconnects the fuel cell 100 from loads such as the electric power storage device 172 and the fuel cell auxiliaries and stops the fuel cell system 30.

[0034] When the fuel cell 100 stops power generation at the time of stopping the fuel cell system 30, cross-gas leakage occurs in the fuel cell 100 through an electrolyte membrane between the anode-side flow path and the cathode-side flow path. This gradually equalizes the compositions of the gas in the anode-side flow path and the gas in the cathode-side flow path, and therefore the hydrogen concentration in the anode-side flow path gradually decreases.

[0035] During the downtime of the fuel cell system 30, the control unit 200 may in some cases perform a "purge during downtime". Fig. 2 (d) indicates the period during which the "downtime flushing operation" is executed. The specific control relevant to the "downtime flushing operation" will be described in detail later.

[0036] After the start instruction is input by the start switch, the above-described “start processing” is then executed again in the fuel cell system 30. A-3. Operation after system shutdown:

[0037] The following describes in more detail the operation when entering the stop command via the start switch.

[0038] Fig. 3 shows the flowchart illustrating the stoppage routine to be executed by the control unit 200 of this embodiment. This routine is executed by the control unit 200 during operation of the fuel cell system 30. When the routine is started, the CPU of the control unit 200 determines whether the stop command has been input via the start switch (step S100). The control unit 200 repeats the determination in step S100 until the stop command is input via the start switch.

[0039] If it is determined that the stop instruction has been input (step S100: YES), the CPU of the control unit 200 acquires the temperature of the electric power storage device 172 from the temperature sensor 175 corresponding to the first temperature sensor, and the remaining capacity of the electric power storage device 172 from the remaining capacity monitor 173 (step S110). The control unit 200 then determines whether preset low-temperature conditions are established or not using the acquired temperature and the acquired remaining capacity of the electric power storage device 172 (step S120).

[0040] The low-temperature conditions are set in advance as the conditions for determining that the fuel cell 100 is most likely to freeze. In this embodiment, the set low-temperature conditions include that the temperature related to the fuel cell 100 is less than or equal to the preset threshold. Specifically, in this embodiment, the low-temperature conditions are deemed to be established in the case where the temperature of the electric power storage device 172 is less than or equal to a preset first reference temperature and the remaining capacity of the electric power storage device 172 is less than or equal to a preset reference value.In this embodiment, the above-described first reference temperature relates to the state of the fuel cell and is set to indirectly determine that the fuel cell 100 is most likely to freeze, and also to determine that the temperature of the electric power storage device 172 decreases to such an extent that it takes a relatively long time to charge the electric power storage device 172. The first reference temperature can be set, for example, in the range of -20°C to -5°C.

[0041] The above-described reference value of the remaining capacity is set as the value to be used in determining whether the electric power storage device 172 is capable of supplying the current required by the fuel cell system 30 in the period after the fuel cell system 30 is stopped until the next restart of the fuel cell system 30 and until the fuel cell 100 starts generating power. The above-described current required by the fuel cell system 30 in the period until the fuel cell system 30 is next restarted and the fuel cell 100 starts generating power may include the current required in the "purge process during downtime" to be described later. The above-described reference value of the remaining capacity may be set in the range of 40% to 50%, for example.

[0042] Fig. Fig. 4 shows the explanatory diagram showing the relationship between the temperature of the electric power storage device 172 and the allowable charging power Win in the electric power storage device 172. The first reference temperature described above is further determined by Fig. 4. The allowable charging power Win, which is defined as the upper limit of the charging power in the electric power storage device 172, indicates the charging capacity of the electric power storage device 172. The larger the allowable charging power Win, the higher the charging capacity, that is, the faster the charging execution. As shown in Fig. 4, the allowable charging power Win is strongly influenced by the temperature of the electrical power storage device 172. In Fig. 4 is a temperature t1 as the temperature of the boundary between the temperature range (a Fig. 4), in which the allowable charging power Win increases relatively smoothly as the temperature of the electric power storage device 172 increases, and in which the allowable charging power Win is relatively small, and the temperature range (a range shown in Fig. 4), in which the allowable charging power Win increases relatively rapidly as the temperature of the electric power storage device 172 increases. In addition, in Fig. 4 a temperature t2 as the temperature of the boundary between the temperature range (the one in Fig. 4), in which the allowable charging power Win increases relatively rapidly as the temperature of the electric power storage device 172 increases, and the temperature range (a range shown in Fig. 4), in which the permissible charging power Win is stable at a relatively high level. The first reference temperature described above can be set, for example, to temperature t1 or higher, and it can be set in the range between temperature t1 and temperature t2 inclusive. Fig. The curve shown in Figure 4 is merely an example. Specifically, in the case where the electric power storage device 172 is a lithium-ion battery, the allowable charging power Win is greatly influenced by the temperature of the electric power storage device 172. Note that even in the case where the electric power storage device 172 is another type of electric power storage device, such as a nickel-hydrogen battery, the first reference temperature can be set in the same manner as long as the electric power storage device exhibits a similar tendency in the allowable charging power Win.

[0043] If it is determined in step S120 that the low-temperature conditions are established (step S120: YES), the CPU of the control unit 200 executes the "winter mode end processing" (step S140) and terminates this routine. If it is determined in step S120 that the low-temperature conditions are not established (step S120: NO), the CPU of the control unit 200 executes the "normal mode end processing" (step S130) and terminates this routine.

[0044] As described above, "end processing" can include "charging," "stop flushing," and "system end processing." The "normal mode end processing" and "winter mode end processing" differ in the contents of "charging" and "stop flushing."

[0045] In this embodiment, in the "winter mode end processing" executed when the low-temperature conditions are established, the "purge at stop" is executed so that more of the moisture stored in the fuel cell 100 is discharged to the outside of the fuel cell 100 compared to the "normal mode end processing" executed when the low-temperature conditions are not established. For example, in order to discharge more moisture to the outside of the fuel cell 100, the purge at stop in the "winter mode end processing" may be executed for a longer period of time compared to the case of the purge at stop in the "normal mode end processing."Alternatively, in the purging process when stopping in the "winter mode end processing," at least one type of the reactant gas to be supplied to the fuel cell 100 may be increased compared to the case of the purging process when stopping in the "normal mode end processing." For example, the amount of increase in the moisture to be discharged during the "winter mode end processing" compared to the "normal mode end processing" may be appropriately adjusted so that, even in the case where, as described later, an ambient temperature drops after the execution of the "winter mode end processing" during the downtime of the fuel cell system 30, as described later, the purging controller 210 of the control unit 200 executes the control relevant to the purging process included in the end processing described above (see FIG. Fig. 1).

[0046] In this embodiment, in the "winter mode end processing" executed when the low-temperature conditions are established, the charging operation is performed with the target remaining capacity of the electric power storage device 172 set to a smaller value compared to the "normal mode end processing" executed when the low-temperature conditions are not established. For example, the amount of increase in the charge amount in the "normal mode end processing" compared to the case of the "winter mode end processing" may be appropriately set so that, as described later, in the event that the ambient temperature drops after the execution of the "normal mode end processing" during the downtime of the fuel cell system 30, the purge operation can be performed during the downtime using the power supplied from the electric power storage device 172.The residual capacity controller 220 of the control unit 200 performs the control relevant to the charging process included in the final processing described above (see . Fig. 1).

[0047] In this embodiment, the case of executing the “winter mode end processing” when stopping the fuel cell system 30 differs from the case of executing the “normal mode end processing” in terms of the control required for the “purging process during the downtime” (refer to Fig. 2) is relevant, which is performed during the system stoppage. The "purging operation during the stoppage" will be described further below. The "purging operation during the stoppage" is performed to suppress freezing of liquid water in the reactant gas flow paths in the fuel cell 100 when the fuel cell system 30 is stopped and when the freezing conditions set in advance are established as the conditions under which the fuel cell 100 is most likely to freeze. In the fuel cell system 30 of this embodiment, when the system is stopped, not all of its functions are completely stopped, and some functions and the like of the control unit 200 are kept operating so as to monitor the temperature of the fuel cell 100 and, when necessary, purge the reactant gas flow paths as the "purging operation during the stoppage."The flushing control 210 of the control unit 200 carries out this control relevant to the flushing process (see . Fig. 1).

[0048] Fig. 5 shows the flowchart illustrating the downtime purge routine to be executed by the control unit 200 of this embodiment. This routine is executed by the control unit 200 when the fuel cell system 30 is stopped after the "final processing" is completed and the fuel cell system 30 is stopped.

[0049] When this routine is started, the CPU of the control unit 200 acquires the temperature of the fuel cell 100 from the FC temperature sensor 105 (step S200). The control unit 200 then determines whether the acquired temperature of the fuel cell 100 is less than or equal to the fuel cell temperature corresponding to a preset reference temperature (hereinafter referred to as a third reference temperature) (step S210). If the temperature of the fuel cell 100 is less than or equal to the third reference temperature, the control unit 200 determines that the preset freezing conditions have been established as the conditions under which the fuel cell 100 is most likely to freeze. The third reference temperature is set in advance as a low temperature close to, but higher than, the freezing point. The third reference temperature can be set to, for example, 5°C to 10°C.The control unit 200 repeats the execution of the steps of step S200 and step S210 until it is determined that the temperature of the fuel cell 100 is less than or equal to the third reference temperature.

[0050] If it is determined that the temperature of the fuel cell 100 is less than or equal to the third reference temperature (step S210: YES), the CPU of the control unit 200 determines whether or not the low-temperature conditions were established at the previous stop of the fuel cell system 30, that is, whether or not the winter mode end processing was executed at the previous stop (step S220). If the winter mode end processing was not executed at the previous stop, that is, if the normal mode end processing was executed (step S220: NO), the CPU of the control unit 200 executes the downtime purge process (step S230) and terminates this routine. If the winter mode end processing was executed at the previous stop (step S220: YES), the CPU of the control unit 200 terminates this routine without executing the downtime purge process.

[0051] The "purging operation during downtime" will be further described below. In the "purging operation during downtime," the control unit 200 temporarily starts the fuel cell system 30 to purge the anode-side flow path using the hydrogen stored in the hydrogen tank 110. Specifically, the control unit 200 opens the on-off valve 124 and the injector 126 and drives the circulation pump 127. It also opens the on-off valve 129 at a predetermined timing to purge the anode-side flow path using the hydrogen stored in the hydrogen tank 110. At this time, the control unit 200 drives the compressor 130 and switches the flow dividing valve 144 so that all the air flowing through the first air flow path 141 flows to the third air flow path 146. Consequently, the hydrogen discharged by the fuel cell system 30 via the hydrogen discharge flow path 123 is diluted.

[0052] When the temperature of the fuel cell 100 drops after the fuel cell system 30 stops, in some cases, the water vapor contained in the gas sealed in the flow path in the fuel cell 100 condenses and becomes liquid water. Even if liquid water is generated in the anode-side flow path, by performing the "purge during shutdown," it is possible to remove the liquid water from the anode-side flow path before the temperature of the liquid water drops to the temperature at which the liquid water freezes, thus suppressing freezing in the anode-side flow path. In this embodiment, only the anode-side flow path is purged as the "purge during shutdown."Alternatively, using the compressor 130, only the cathode-side flow path may be purged, or both the anode-side flow path and the cathode-side flow path may be purged.

[0053] In the fuel cell system 30 having the above-described configuration in this embodiment, when the stop instruction is input to the fuel cell system 30, in the case where the preset low-temperature conditions are established, the purge operation (the purge operation upon stop) is performed so that more of the moisture stored in the fuel cell 100 is discharged to the outside of the fuel cell 100 compared to the case where the preset low-temperature conditions are not established. Moreover, in the case where the above-described low-temperature conditions are established, the charging operation is performed with the target remaining capacity of the electric power storage device 172 set to a smaller value compared to the case where the low-temperature conditions are not established.As described above, when the low-temperature conditions are established and it takes a relatively long time to charge the electric power storage device 172, the charging operation is performed with the target remaining capacity set to a smaller value compared to the case where the low-temperature conditions are not established. Consequently, it is possible to shorten the time for the charging operation and the time required to complete the system stoppage. When the low-temperature conditions are established, the purging operation is performed so that more of the moisture stored in the fuel cell 100 is discharged to the outside of the fuel cell 100. Thus, even when the ambient temperature drops during the system stoppage, it is possible to suppress freezing of the liquid water in the fuel cell 100.

[0054] In this embodiment, in the case where the low-temperature conditions are not established, charging is performed with the target remaining capacity set to a larger value compared to the case where the low-temperature conditions are established. In the case where the low-temperature conditions are not established, the temperature of the electric power storage device 172 is high, and thus it takes a relatively short time to charge the electric power storage device 172. Accordingly, even if charging is performed with the target remaining capacity set to a larger value, it does not take an excessive amount of time to complete the system stop.Furthermore, even when low-temperature conditions are not established, a large amount of charge in the electric power storage device 172 is also ensured by the fact that relatively little moisture is released to the outside of the fuel cell 100 by the purging process during shutdown, so that the purging process during shutdown can be performed as needed without any problem during the system shutdown. Thus, by performing the purging process during shutdown as described above, it is possible to suppress the freezing of liquid water in the fuel cell 100 even when the ambient temperature drops during the system shutdown.In addition, it is considered that in the case where the low temperature conditions are not established, the ambient temperature is less likely to drop to the temperature at which freezing occurs during the system stoppage, so that the purging operation is carried out at the stoppage with the target residual capacity set to a small value so as to suppress the excessive execution of the purging operation.

[0055] As described above, regardless of whether the low-temperature conditions are established or not, this embodiment succeeds in reducing the time required to complete the stoppage of the system and also suppressing freezing of the fuel cell 100 in the period after the system stoppage until the next system restart and until the start of power generation of the fuel cell 100.

[0056] It should be noted that the amount of energy required for the purging operation during downtime is generally greater than the increased amount of energy corresponding to the energy consumed by performing the purging operation at the time when the low-temperature conditions are established. In an electric power storage device such as a lithium-ion battery, which has temperature dependence on its allowable charging power Win, low-temperature charging is more strictly restricted than low-temperature discharging from the viewpoint of preventing battery deterioration.Therefore, when the temperature of the electric power storage device 172 is low and the low-temperature conditions are established, the amount of extension of the system stop time in the case of employing the normal mode end processing due to the extended time in the charging process is greater than the amount of extension of the system stop time in the case of employing the winter mode end processing due to the extended time in the purge process at the stop. Accordingly, the adoption of the configuration of this embodiment succeeds in shortening the time required to stop the system as a whole.

[0057] In this embodiment, as long as the temperature of the electric power storage device 172 is equal to or less than the first reference temperature, the purge operation at stop is performed even when the remaining capacity of the electric power storage device 172 is equal to or less than the reference value by using the winter mode end processing to stop the system, so as to set the target remaining capacity to a small value and release more moisture to the outside of the fuel cell 100. Therefore, even if the value of the remaining capacity of the electric power storage device 172 is small at the time of system stop, it is possible to suppress an extension of the time required to complete the system stop due to charging of the electric power storage device 172 during the winter mode end processing and to suppress freezing of the fuel cell 100 by the purge operation at stop.As long as the remaining capacity of the electric power storage device 172 is above the reference value, even if the temperature of the electric power storage device 172 is less than or equal to the first reference temperature, the normal mode end processing is used when the system is stopped, thereby reducing the release of moisture to the outside of the fuel cell. Therefore, when the system is stopped, it is possible to suppress energy consumption by executing the purge process at the stop.As described above, when the value of the remaining capacity of the electric power storage device 172 is large when the system is stopped, the amount of charging of the electric power storage device 172 is small, and thus, even if the normal mode end processing is used for the charging operation to be performed when the system is stopped with the target remaining capacity set to a large value, an increase in the time required to complete the system stop due to the charging of the electric power storage device 172 is suppressed. Moreover, when the system is stopped, the value of the remaining capacity of the electric power storage device 172 is large, and thus, a freeze prevention measure can be performed on the fuel cell 100 as needed.

[0058] In this embodiment, when the freezing conditions are established during the downtime of the fuel cell system 30, if it was determined that the low-temperature conditions are not established at the previous stop of the fuel cell system 30, the purging process is performed during the downtime, while if it was determined that the low-temperature conditions are established at the previous stop of the fuel cell system 30, the purging process is not performed during the downtime. Therefore, if it was determined that the low-temperature conditions are not established at the previous stop of the fuel cell system 30, the purging process is performed during the downtime after the freezing conditions are established to suppress fuel cell freezing.In the case where it has been determined that the low-temperature conditions are established at the previous stop of the fuel cell system 30, freezing of the fuel cell can be suppressed at the time of stopping the system by the purging process at the time of stopping that has been executed as the winter mode end processing.

[0059] It should be noted that in the case where it has been determined that the low-temperature conditions are established at the previous stop of the fuel cell system 30 (step S220: YES), an operation other than that in the above-described embodiment can be performed as long as the purging operation during the stop time is performed so that less of the moisture stored in the fuel cell 100 is released to the outside of the fuel cell 100 compared to the case where it has been determined that the low-temperature conditions are not established (step S220: NO).For example, in the case where it is determined that the low-temperature conditions are established (step S220: YES), the purging operation during the standby period may be performed with a shorter purging time, or the purging operation during the standby period may be performed with a smaller amount of gas to be supplied to the fuel cell 100 compared to the case where it is determined that the low-temperature conditions are not established (step S220: NO). Note that the configuration that "the purging operation during the standby period is performed so that less of the moisture stored in the fuel cell 100 is released to the outside of the fuel cell 100" includes the configuration in which the purging operation during the standby period is not performed as in the above-described embodiment.

[0060] To suppress freezing of the fuel cell 100 when the low-temperature conditions are not established, the value of the target remaining capacity for use in the charging process during the normal mode final processing may be set so that more current is drawn from the electric power storage device 172 than the sum of the current required during the final processing after the charging process, the current required during the purging process during the idle time, and the current required during the startup processing. The above-described total current can be predicted in advance based on the conditions of the respective types of processing described above, and thus the value of the target remaining capacity can be calculated in advance and stored in the control unit 200. B. Second embodiment:

[0061] Fig. 6 shows the flowchart illustrating the stopping routine to be executed in the control unit 200 of the fuel cell system 30 according to the second embodiment of this disclosure. The fuel cell system 30 of the second embodiment has the same configuration as the fuel cell system 30 of the first embodiment. Therefore, the same reference numerals are assigned to the same parts as in the first embodiment, and the detailed description thereof is omitted. The fuel cell system 30 of the second embodiment executes the stopping routine as in the Fig. 2, the fuel cell system 30 of the second embodiment performs the start-up processing, the end-up processing, and the purge process during the downtime. The fuel cell system 30 of the second embodiment differs from that of the first embodiment in the operation of determining whether or not the low-temperature conditions are established.

[0062] Instead of the Fig. 3, when stopping the first embodiment, the routine shown in Fig. 6 is executed when stopping. In Fig. 6 will follow the same steps as those in Fig. 3 are assigned the same number of steps. The points different from the first embodiment are described below.

[0063] If it is determined that the stop instruction is input via the start switch (step S100: YES), the CPU of the control unit 200 of the second embodiment acquires the temperature of the electric power storage device 172 from the temperature sensor 175 serving as the first temperature sensor, the remaining capacity of the electric power storage device 172 from the remaining capacity monitor 173, and also the outside air temperature corresponding to the ambient temperature of the fuel cell system 30 from the outside air temperature sensor 185 (step S115). The outside air temperature sensor 185 is also referred to as a "second temperature sensor." The CPU of the control unit 200 determines whether the preset low temperature conditions are established by using the acquired temperature and remaining capacity of the electric power storage device 172 and the acquired outside temperature (step S125).

[0064] In the second embodiment, in the case where either the preset first low-temperature conditions or the preset second low-temperature conditions are established in step S125, it is determined that the low-temperature conditions are established. The first low-temperature conditions are the same as the low-temperature conditions of the first embodiment, and in the case where the temperature of the electric power storage device 172 is less than or equal to the preset first reference temperature and the remaining capacity of the electric power storage device 172 is less than or equal to the preset reference value, it is determined that the first low-temperature conditions are established. The second low-temperature conditions are based only on the outside temperature, which is the ambient temperature.If the outside temperature is less than or equal to a preset second reference temperature, it is determined that the second low-temperature conditions are established. In the second low-temperature conditions, the outside temperature is used as the temperature related to the state of the fuel cell 100.

[0065] The second reference temperature described above is set as the temperature for use in determining that the downtime purge operation is most likely required during the downtime of the fuel cell system 30. The second reference temperature may, for example, be set as the temperature at which the fuel cell 100 is most likely to freeze during the downtime of the system, and it may be set in the Fig.5, the purging process routine during the downtime can be set to be less than or equal to the third reference temperature. This is because if the ambient temperature is less than or equal to the third reference temperature, it is considered that the temperature of the fuel cell 100 will most likely drop to the third reference temperature or lower during the system downtime. Note that the second reference temperature can be set higher than the third reference temperature. The second reference temperature can be set to a temperature of 0°C or lower at which the fuel cell 100 is most likely to freeze during the system downtime.

[0066] The fuel cell system 30 of the second embodiment achieves the same effects as the first embodiment. In the second embodiment, when the ambient temperature is equal to or lower than the second reference temperature, it is determined that the low-temperature conditions are established regardless of the temperature and remaining capacity of the electric power storage device 172. Therefore, in the case where the downtime purge operation is most likely required during the system downtime, the downtime purge operation is performed in advance, so that the downtime purge operation is no longer required.As described above, the energy required for the purging operation during downtime is generally greater than the additional energy consumption by performing the purging operation during stoppage at the time when the low-temperature conditions are established. Thus, according to the second embodiment, the energy efficiency of the fuel cell system 30 is increased while freezing of the fuel cell 100 is suppressed. C. Further examples:

[0067] C1. In the first embodiment, it is determined that the low-temperature conditions are established when the first low-temperature conditions are established. In the second embodiment, it is determined that the low-temperature conditions are established when either the first low-temperature conditions or the second low-temperature conditions are established. Alternatively, the establishment of the low-temperature conditions may be determined based on a different standard. For example, in determining the low-temperature conditions, only the second low-temperature conditions may be used without using the value of the remaining capacity of the electric power storage device 172.Note that in the case where the remaining capacity value of the electric power storage device 172 is not used to determine the low-temperature conditions, and the fuel cell vehicle 20 is parked in a covered parking lot, for example, in winter, in some cases, a relatively high outside temperature may be detected even if the temperature of the electric power storage device 172 is relatively low. In this case, if normal mode final processing is selected based on the outside temperature, it may take a relatively long time to charge the electric power storage device 172.In order to achieve the effect of reducing the time required to complete the stop of the system while suppressing freezing of the fuel cell 100 regardless of, for example, a parking location of the fuel cell vehicle 20, the value of the remaining capacity of the electric power storage device 172 may preferably be used in determining the low-temperature conditions.

[0068] C2. In the second embodiment described above, it is determined that the second low-temperature conditions are satisfied when the ambient temperature detected by the outside air temperature sensor 185 is less than or equal to the second reference temperature. Alternatively, another configuration may be used. For example, data indicating, for example, an average temperature of the past few days, an average minimum temperature of the past few days, or an average temperature of the days with the same date of the past few years is acquired through communication or the like, and it can be determined that the low-temperature conditions are established when this temperature is less than or equal to a preset value.

[0069] C3. In each of the embodiments described above, it is determined that the freezing conditions are established when the temperature of the fuel cell detected by the FC temperature sensor 105 serving as the third temperature sensor is less than or equal to the third reference temperature during the system idle time. Alternatively, another configuration may be used. For example, it may be determined that the freezing conditions are established when the outside temperature, which corresponds to the ambient temperature, drops to a predetermined determination temperature or lower. Alternatively, it may be determined that the freezing conditions are established when the outside temperature drops to the determination temperature or lower, and further, when the time elapsed after the outside temperature drops to the determination temperature or lower exceeds a predetermined reference time.

[0070] C4. In each of the above-described embodiments, when the freezing conditions are established during the system downtime after the system is stopped by the normal mode end processing, the fuel cell 100 undergoes the downtime purge operation as the anti-freeze measure. Alternatively, another configuration may be adopted. For example, a heating device such as a heater configured to heat the fuel cell 100 may be disposed, and the fuel cell 100 may be heated using the above-described heating device when the freezing conditions are established during the system downtime. In the case where the normal mode end processing is executed when the system is stopped, charging is performed with the target remaining capacity of the electric power storage device set to a large value.Consequently, it is possible to secure the energy for the heating described above and to achieve the same effects as in the above embodiments.

[0071] C5. The fuel cell system 30 is used as a power source for driving a vehicle, or it can be used as a power source for driving a moving body other than a vehicle. Alternatively, the fuel cell system 30 can be used as a stationary power generator.

[0072] The present disclosure is not limited to the embodiments described above and may be embodied in various configurations within the scope of the claims.

Claims

[1] Fuel cell system (30) with: a fuel cell (100); a gas supply unit (120, 140) configured to supply gas to the fuel cell (100); an electrical power storage device (172) capable of storing at least electrical power generated by the fuel cell (100); a residual capacity monitor (173) configured to detect a residual capacity in the electrical power storage device (172); and a control unit (200) configured to perform a purging operation for purging an interior of the fuel cell (100) with the gas by controlling the gas supply unit (120, 140) and a charging operation for charging the remaining capacity of the electric power storage device (172) with the power generated by the fuel cell (100), wherein the control unit (200) determines, upon input of a stop instruction of the fuel cell system (30), whether the temperature conditions are met, wherein the low temperature conditions include that a temperature relating to a state of the fuel cell (100) is less than or equal to a predetermined set threshold value, the control unit (200), when determining that the low-temperature conditions are met, performs the purging operation such that more moisture stored in the fuel cell (100) is discharged to an outside of the fuel cell (100) compared to when determining that the low-temperature conditions are not met, and the control unit (200) performs the charging operation with a target remaining capacity of the electric power storage device (172) set to a smaller value compared to when determining that the low-temperature conditions are not met. [2] The fuel cell system (30) of claim 1, wherein the fuel cell system (30) further comprises: a first temperature sensor configured to detect a temperature of the electrical power storage device (172), wherein the control unit (200) determines that the low temperature conditions are met when the temperature of the electrical power storage device (172) is less than or equal to a predetermined first reference temperature and the remaining capacity of the electrical power storage device (172) is less than or equal to a predetermined reference value. [3] Fuel cell system (30) according to claim 1 or 2, wherein the fuel cell system (30) further comprises: a second temperature sensor configured to detect an ambient temperature of the fuel cell system (30), wherein the control unit (200) determines that the low temperature conditions are met when the ambient temperature is less than or equal to a predetermined second reference temperature. [4] The fuel cell system (30) according to any one of claims 1 to 3, wherein the control unit (200), when freezing conditions are satisfied during a stoppage of the fuel cell system (30), and when the control unit (200) has determined that the low-temperature conditions are satisfied at a previous stop of the fuel cell system (30), performs a purging operation during the stoppage such that less of the moisture stored in the fuel cell (100) is released to the outside of the fuel cell (100) as compared to when it determines that the low-temperature conditions are not satisfied, the freezing conditions being set in advance as conditions under which freezing is most likely to occur in the fuel cell (100). [5] The fuel cell system (30) according to claim 4, wherein the fuel cell system (30) further comprises: a third temperature sensor configured to detect a temperature of the fuel cell (100), wherein the control unit (200) determines that the freezing conditions are met when the temperature of the fuel cell (100) is less than or equal to a predetermined third reference temperature. [6] A control method of a fuel cell system (30), the fuel cell system (30) comprising: a fuel cell (100); a gas supply unit (120, 140) configured to supply gas to the fuel cell (100); an electrical power storage device (172) capable of storing at least electrical power generated by the fuel cell (100); and a residual capacity monitor (173) configured to detect a residual capacity in the electrical power storage device (172), the control procedure comprising the following steps: when a stop instruction is input to the fuel cell system (30), determining whether the temperature conditions are met, wherein the low temperature conditions include a temperature relating to a state of the fuel cell (100) being less than or equal to a predetermined set threshold; when it is determined that the low-temperature conditions are met, performing a purging operation such that more moisture stored in the fuel cell (100) is released to an outside of the fuel cell (100) as compared to when it is determined that the low-temperature conditions are not met, wherein the purging operation is performed to release the moisture stored in the fuel cell (100) to the outside of the fuel cell (100) by controlling the gas supply unit (120, 140); and performing a charging operation with a target remaining capacity of the electric power storage device (172) set to a smaller value as compared to when it is determined that the low-temperature conditions are not met, wherein the charging operation is performed to charge the remaining capacity of the electric power storage device (172) with the power generated by the fuel cell (100).

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