CONTROL DEVICE FOR A FUEL CELL SYSTEM

Abstract

Control device for a fuel cell system for controlling the fuel cell system, the fuel cell system includes: a fuel cell with an anode electrode that includes a water electrolysis catalyst; an electrical load component that is electrically connected to the fuel cell; and a circuit interrupting device configured to physically interrupt an electrical connection between the fuel cell and the electrical load part, wherein The control device for a fuel cell system includes: a hydrogen shortage assessment component configured to assess whether a hydrogen shortage has occurred, which is a condition in which the amount of hydrogen supplied to the fuel cell is insufficient compared to the amount of hydrogen required to generate power; a hydrogen deficiency elimination assessment part that is configured to assess whether the hydrogen deficiency has been eliminated after the hydrogen deficiency assessment part has assessed that the hydrogen deficiency has occurred; and an interrupt control section configured to cause the circuit interrupt device to temporarily interrupt an electrical connection between the fuel cell and the electrical load section when the hydrogen shortage elimination assessment section judges that the hydrogen shortage has been eliminated.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a control device for a fuel cell system. BACKGROUND

[0002] Japanese patent publication JP 2003-508877A discloses a fuel cell having an anode electrode in which, for example, platinum or another catalyst for promoting a hydrogen oxidation reaction and also a catalyst for promoting the electrolysis of water (water electrolysis catalyst) are included. SUMMARY

[0003] By incorporating a water electrolysis catalyst into the anode electrode of a fuel cell, the carbon within the anode electrode can be prevented from being corroded by oxidation when the amount of hydrogen supplied to the fuel cell becomes insufficient compared to the amount of hydrogen required for power generation, that is, when a hydrogen deficiency occurs. However, even if a water electrolysis catalyst is incorporated into the anode electrode of a fuel cell, when a hydrogen deficiency occurs, the fuel cell voltage will drop, resulting in a negative voltage. As a result, a film-like oxide layer will form on the surface of the platinum catalyst in the anode electrode.Even after the hydrogen deficiency is eliminated, there is the problem that time is needed for the voltage of the fuel cell to return to a normal voltage value.

[0004] The present disclosure has been made in recognition of such a problem, and an object thereof is to quickly return the voltage of the fuel cell to a normal voltage value after a hydrogen shortage is eliminated when a hydrogen shortage occurs and the voltage of the fuel cell drops.

[0005] To solve this problem, according to one aspect of the present disclosure, a control device for a fuel cell system is provided for controlling the fuel cell system. The fuel cell system includes a fuel cell having an anode electrode including a water electrolysis catalyst, an electrical load part electrically connected to the fuel cell, and a circuit breaker that physically breaks an electrical connection between the fuel cell and the electrical load part.The control device for the fuel cell system includes a hydrogen shortage judgment part configured to judge whether hydrogen shortage, which is a state in which an amount of hydrogen supplied to the fuel cell is insufficient compared to an amount of hydrogen required for power generation, has occurred, a hydrogen shortage removal judgment part configured to judge whether the hydrogen shortage has been removed after the hydrogen shortage judgment part judges that the hydrogen shortage has occurred, and an interruption control part configured to temporarily cause the circuit interruption device to interrupt electrical connection of the fuel cell and the electrical load part when the hydrogen shortage removal judgment part judges that the hydrogen shortage has been removed.

[0006] According to this aspect of the present disclosure, when a hydrogen shortage occurs and the voltage of the fuel cell drops after the hydrogen shortage is eliminated, the voltage of the fuel cell can be quickly returned to a normal voltage value. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing the configuration of a fuel cell system and an electronic control unit that controls the fuel cell system according to a first embodiment of the present disclosure. Fig. 2 shows a flowchart for explaining a voltage recovery control according to the first embodiment of the present disclosure. Fig. 3 is a timing chart for explaining the operation of a voltage recovery controller according to the first embodiment of the present disclosure. Fig. 4 shows a flowchart for explaining a voltage recovery control according to a second embodiment of the present disclosure. Fig. 5 shows a table for calculating a freezing removal evaluation time based on an initial water temperature. Fig. 6 is a timing chart for explaining the operation of a voltage recovery controller according to the second embodiment of the present disclosure. Fig. 7 is a flowchart for explaining voltage recovery control according to a third embodiment of the present disclosure. Fig. 8 is a timing chart for explaining the operation of a voltage recovery controller according to the third embodiment of the present disclosure. Fig. 9 is a flowchart for explaining voltage recovery control according to a fourth embodiment of the present disclosure. Fig. 10 is a timing chart for explaining the operation of a voltage recovery controller according to the fourth embodiment of the present disclosure. DESCRIPTION OF THE EMBODIMENTS

[0007] Embodiments of the present disclosure will be explained in detail below with reference to the drawings. Note that similar components are denoted by the same reference numerals in the following explanation. First embodiment

[0008] Fig. 1 shows a schematic diagram of the configuration of a fuel cell system 100 and an electronic control unit 200 that controls the fuel cell system 100 according to a first embodiment of the present disclosure.

[0009] The fuel cell system 100 includes a fuel cell stack 10, a hydrogen supply / discharge device 20 for supplying and discharging hydrogen as an anode gas (fuel gas) to and from the fuel cell stack 10, an air supply / discharge device 30 for supplying and discharging air as a cathode gas (oxidizer gas) to and from the fuel cell stack 10, a cooling water circulation device 40 for causing the cooling water that cools the fuel cell stack 10 to circulate, and an electrical load part 50 electrically connected to an output terminal of the fuel cell stack 10.

[0010] The fuel cell stack 10 is obtained by stacking a plurality of fuel cell unit cells (hereinafter referred to as the "unit cells") 1 together along the stacking direction and electrically connecting the unit cells 1 in series. Each of the unit cells 1 is provided with an MEA (membrane electrode assembly) 1a.

[0011] An MEA 1a comprises a proton-conductive ion exchange membrane formed by a solid-state polymer material (hereinafter referred to as an "electrolyte membrane"), with an anode electrode formed on one surface and a cathode electrode formed on the other surface, all of which are integrally connected. When the fuel cell stack 10 generates power, the following electrochemical reactions occur at each anode electrode and cathode electrode: Anode electrode: 2H2→4H + +4e -(1) Cathode electrode: 4H + +4e - +O2→2H2O (2)

[0012] An anode electrode and a cathode electrode are each provided with a catalyst layer comprising a porous carbon material on which a catalyst is supported. Each catalyst layer includes platinum as a catalyst to promote an electrochemical reaction between hydrogen and oxygen (hydrogen oxidation reaction according to equation (1) and hydrogen reduction reaction according to equation (2)). Note that the two outer surfaces of an MEA 1a may also be further provided with an anode gas diffusion layer and a cathode gas diffusion layer.

[0013] Furthermore, in the present embodiment, the catalyst layer of an anode electrode further includes a catalyst for promoting a water electrolysis reaction when the supply amount of hydrogen to the unit cell 1 is insufficient (hereinafter referred to as a "water electrolysis catalyst"). For example, ruthenium oxide, iridium oxide, etc., can be cited as the water electrolysis catalyst. In the present embodiment, the reason for causing the catalyst layer of an anode electrode to include a water electrolysis catalyst will be explained below.

[0014] In each unit cell 1, a hydrogen channel 2a for supplying hydrogen to the anode electrode and an air channel 3a for supplying air to the cathode electrode are formed. Furthermore, a cooling water channel 4a for supplying cooling water is formed between two adjacent unit cells.

[0015] The hydrogen channels 2a, the air channels 3a, and the cooling water channels 4a of the unit cells 1 are each connected in parallel within the fuel cell stack 10. Therefore, a hydrogen passage 2, an air passage 3, and a cooling water passage 4 are formed within the fuel cell stack 10.

[0016] In the present embodiment, an inlet and an outlet of the hydrogen passage 2 are provided at one end side of the fuel cell stack 10 in the stacking direction (right side in the figure), while inlets and outlets of the air passage 3 and the cooling water passage 4 are provided at the other end side of the fuel cell stack 10 in the stacking direction (left side in the figure), but the disclosure is not limited to this. Furthermore, in the present embodiment, the hydrogen passage 2 and the air passage 3 are each supplied with hydrogen and air so that the flow directions of hydrogen and air within a unit cell 1 become opposite to each other, but they may also be supplied with hydrogen and air so that the directions become the same.Further, in the present embodiment, the flow direction of the cooling water within a unit cell 1 is made the same direction as the flow direction of the hydrogen, but it may also be made an opposite direction.

[0017] The hydrogen supply / discharge device 20 is provided with a hydrogen supply pipe 21, a high-pressure hydrogen tank 22 as a hydrogen source, a hydrogen supply control part 23, an anode exhaust pipe 24, a gas-liquid separator 25, a hydrogen return pipe 26, a hydrogen circulation pump 27, a purge pipe 28, and a purge control valve 29.

[0018] The hydrogen supply pipe 21 is a pipe through which the hydrogen supplied to the hydrogen passage 2 flows. One end is connected to the high-pressure hydrogen tank 22, while the other end is connected to the inlet of the hydrogen passage 21.

[0019] The high-pressure hydrogen tank 22 stores hydrogen for supply to the hydrogen passage 2 through the hydrogen supply pipe 21.

[0020] The hydrogen supply control part 23 is provided with a main shut-off valve 231, a regulating device 232 and an injector 233.

[0021] The main shutoff valve 231 is a solenoid valve that is opened and closed by the electronic control unit 200 and is provided at the hydrogen supply pipe 21. When the main shutoff valve 231 is opened, hydrogen flows from the high-pressure hydrogen tank 22 to the hydrogen supply pipe 21. When the main shutoff valve 231 is closed, the outflow of hydrogen from the high-pressure hydrogen tank 22 is stopped.

[0022] The regulator 232 is provided on the hydrogen supply pipe 21 downstream of the main shutoff valve 231. The regulator 232 is a pressure control valve capable of continuously or stepwise adjusting its opening degree. The opening degree is controlled by the electronic control unit 200. By controlling the opening degree of the regulator 232, the pressure of hydrogen downstream of the regulator 232, that is, the pressure of hydrogen injected by the injector 233, is controlled.

[0023] The injector 233 is provided on the hydrogen supply pipe 21 downstream of the regulator 232. The injector 233 is, for example, a needle valve and is controlled for opening and closing by the electronic control unit 200. By controlling the opening time of the injector 233, the flow rate of hydrogen injected by the injector 233 is controlled.

[0024] In this way, the supply of hydrogen from the high-pressure hydrogen tank 22 to the hydrogen passage 2 is controlled by the hydrogen supply control part 23. That is, due to the hydrogen supply control part 23, hydrogen controlled to the desired pressure and flow rate is supplied to the hydrogen passage 2.

[0025] An anode pressure sensor 211 is provided in the hydrogen supply pipe 21 downstream of the injector 233. The anode pressure sensor 211 detects the pressure of hydrogen in the hydrogen supply pipe 21 downstream of the injector 233 as a value representing the pressure of hydrogen within the hydrogen passage 2 (hereinafter referred to as the "anode pressure").

[0026] The anode exhaust pipe 24 is a pipe through which the anode exhaust gas flowing out of the hydrogen passage 2 flows. One end is connected to the outlet of the hydrogen passage 2, while the other end is connected to the gas inlet port 25a of the gas-liquid separator 25. The anode exhaust gas is a gas that includes the excess hydrogen that has not been used in the electrochemical reactions in the unit cells 1, and the nitrogen or other inert gas, as well as moisture (liquid water and vapor) that have flowed out from the air passage 3a through the MEA 1a and passed through the hydrogen channel 2a.

[0027] The gas-liquid separator 25 is provided with a gas inflow port 25a, a gas outflow port 25b, and a liquid water outflow port 25c. The gas-liquid separator 25 separates the water from the anode off-gas that has flowed into an associated interior from the gas inflow port 25a. Furthermore, the gas-liquid separator 25 discharges the separated water from the liquid water outflow port 25c to the purge pipe 28 and discharges the anode off-gas containing the hydrogen from which the water has been separated from the gas outflow port 25b to the hydrogen return pipe 26.

[0028] The hydrogen recirculation pipe 26 is a pipe with one end connected to the gas discharge port 25b of the gas-liquid separator 25 and the other end connected to the hydrogen supply pipe 21 downstream of the hydrogen supply control part 23. An anode exhaust gas discharged from the gas discharge port 25b of the gas-liquid separator 25 flows therethrough.

[0029] The hydrogen circulation pump 27 is provided at the hydrogen return pipe 26. The hydrogen circulation pump 27 is a pump for returning the hydrogen contained in the anode exhaust gas, i.e., the excess hydrogen that has not been used for the electrochemical reactions within the unit cells 1, to the hydrogen supply pipe 21 for recirculation. The hydrogen circulation pump 27 pressurizes the anode exhaust gas discharged from the gas discharge port 25b of the gas-liquid separator 25 and pumps it to the hydrogen supply pipe 21.

[0030] The purge pipe 28 is a pipe having one end connected to a liquid water discharge port 25c of the gas-liquid separator 25 and the other end open to the atmosphere.

[0031] The purge control valve 29 is a solenoid valve that is opened and closed by the electronic control unit 200 and is provided at the purge pipe 28. The purge control valve 29 is normally closed and periodically opened for short periods. When the purge control valve 29 is open, the water separated within the gas-liquid separator 25 is expelled to the outside of the fuel cell system 100 through the purge pipe 28.

[0032] In this way, the fuel cell system 100 according to the present embodiment is a hydrogen circulation type fuel cell system that returns the anode off-gas flowing out of the hydrogen passage 2 to the hydrogen supply pipe 21 for recirculation, but it may also be a non-circulating hydrogen type fuel cell system in which an anode off-gas flowing out of the hydrogen passage 2 is not returned to the hydrogen supply pipe 21.

[0033] The air supply / exhaust device 30 is provided with an air supply pipe 31, an air cleaner 32, a compressor 33, an intercooler 34, a cathode exhaust pipe 35, a humidifier 36, and a cathode pressure control valve 37.

[0034] The air supply pipe 31 is a pipe through which air flows, supplied to the air passage 3. One end is connected to the air cleaning device 32, while the other end is connected to the inlet of the air passage 3.

[0035] The air purifier 32 removes foreign matter from the air drawn into the air supply pipe 31. The air purifier 32 is disposed in the atmosphere that forms the oxygen source 32a. That is, the oxygen source 32 is connected to the air supply pipe 31 through the air purifier.

[0036] The compressor 33 is, for example, a centrifugal-type or axial-flow turbocompressor and is provided with the air supply pipe 31. The compressor 33 compresses and discharges the air drawn into the air supply pipe 31 via the air cleaner 32.

[0037] The intercooler 34 is provided at the air supply pipe 31 downstream of the compressor 33 and cools the air discharged from the compressor 33, for example, by the air flow, a cooling water, etc.

[0038] The cathode exhaust pipe 35 is a pipe through which the cathode exhaust gas flows, flowing from the outlet of the air passage 3. One end is connected to the outlet of the air passage 3, while the other end is open to the atmosphere. The cathode exhaust gas is a gas that includes excess oxygen not used for the electrochemical reactions in the unit cells 1, nitrogen or another inert gas, and moisture produced due to the electrochemical reactions (liquid water or steam).

[0039] The humidifier 36 is connected to the air supply pipe 31 and the cathode exhaust pipe 35, recovers the moisture in the cathode exhaust gas flowing through the cathode exhaust pipe 35, and uses the recovered moisture to humidify the air flowing through the air supply pipe 31.

[0040] The cathode pressure control valve 37 is provided at the cathode exhaust pipe 35 downstream of the humidifier 36. The cathode pressure control valve 37 is a solenoid valve capable of continuously or stepwise adjustment of its opening degree. The corresponding opening degree is controlled by the electronic control unit 200. By controlling the opening degree of the cathode pressure control valve 37, the cathode pressure within the air passage 3 is controlled.

[0041] A cathode pressure sensor 212 is provided in the cathode exhaust pipe 35 upstream of the humidifier 36. The cathode pressure sensor 212 detects the pressure within the cathode exhaust pipe 35 downstream of the cathode pressure control valve 37 as a value representing the pressure within the air passage 3 (cathode pressure).

[0042] The cooling water circulation device 40 is provided with a cooling water circulation pipe 41, a cooling water pump 42, a radiator 43, a radiator bypass pipe 44 and a radiator bypass control valve 45.

[0043] The cooling water circulation pipe 41 is a pipe through which cooling water is circulated for cooling the fuel cell stack 10. One end is connected to the inlet of the cooling water passage 4, while the other end is connected to the outlet of the cooling water passage 4. Hereinafter, the outlet side of the cooling water passage 4 is defined as "upstream of the cooling water circulation pipe 41," while the inlet side of the cooling water passage 4 is defined as "downstream of the cooling water circulation pipe 41" in the description.

[0044] The cooling water pump 42 is provided at the upstream side of the cooling water circulation pipe 41 and causes the cooling water to circulate.

[0045] A water temperature sensor 213 is provided in the cooling water circulation pipe 41 upstream of the cooling water pump 42, that is, the cooling water circulation pipe 41 near the outlet of the cooling water passage 4. The water temperature sensor 213 detects the temperature of the cooling water flowing from the cooling water passage 4 to the cooling water circulation pipe 41 as a value representing the temperature of the fuel cell stack 10. The cooling water pump 42 is controlled based on a control signal from the electronic control unit 200 such that the temperature of the cooling water detected by this water temperature sensor 213 becomes a predetermined target temperature (for example, 60°C).

[0046] The radiator 43 is provided at the cooling water circulation pipe 41 downstream of the cooling water pump 42. The cooling water flowing out of the outlet of the cooling water passage 4 is cooled, for example, by the wind flow or air sucked in by a cooling fan 46.

[0047] The radiator bypass pipe 44 is a pipe provided to allow the cooling water to circulate without passing through the radiator 43. One end is connected to the cooling water circulation pipe 41 between the cooling water pump 42 and the radiator 43, while the other end is connected to the radiator bypass control valve 45.

[0048] The radiator bypass control valve 45 is, for example, a three-way valve of an electronic control type and is provided at the cooling water circulation pipe 41 downstream of the radiator 43. The radiator bypass control valve 45 switches the circulation path of the cooling water according to the temperature of the cooling water. Specifically, when the temperature of the cooling water is higher than a predetermined reference temperature, the circulation path of the cooling water is switched so that the cooling water flowing from the cooling water passage 4 to the cooling water circulation pipe 41 passes through the radiator 43 to flow back into the cooling water passage 4.Conversely, when the temperature of the cooling water is the reference temperature or less, the circulation path of the cooling water is switched so that the cooling water flowing out from the cooling water passage 4 to the cooling water circulation pipe 41 is caused to flow through the radiator bypass pipe 44 to flow directly into the cooling water passage 41 without passing through the radiator 43.

[0049] The electrical load part 50 is provided with a first converter 51, a circuit breaker 52, a battery 53, a second converter 54, a motor generator 55 and an inverter 56.

[0050] A current sensor 214 for detecting the current drawn from the fuel cell stack 10 (hereinafter referred to as the "stack current") and a voltage sensor 215 for detecting the terminal voltage of the output terminal of the fuel cell stack 10 (hereinafter referred to as the "stack voltage") are provided on the connecting line 57 between the electrical load part 50 and the output terminal of the fuel cell stack 10. The stack current detected by this current sensor 214 corresponds to the load of the fuel cell stack 10.

[0051] The first converter 51 is a bidirectional DC / DC converter equipped with an electrical circuit capable of causing the terminal voltage of the primary side terminal to rise and fall. The primary side terminal is connected to the output terminal of the fuel cell stack 10 through the circuit breaker 52, while the secondary side terminal is connected to the DC side terminal of the inverter 56. The first converter 51 causes the stack voltage, which becomes the primary side terminal voltage, to rise and fall and controls the stack voltage to a target stack voltage set according to the operating state of the fuel cell system 100, based on a control signal from the electronic control unit 200.

[0052] The circuit breaker 52 is opened and closed by the electronic control unit 200 and electrically and physically connects or breaks the connection of the fuel cell stack 10 and the electrical load part 50.

[0053] The battery 53 is, for example, a nickel-cadmium storage battery or a nickel-hydrogen storage battery, a lithium-ion battery, or another rechargeable secondary battery. The battery 53 is charged by the surplus power of the fuel cell stack 10 and the power generated by the motor generator 55. The power charged at the battery 53 is used as needed to drive the motor generator 55, the compressor 33, or other controlled parts provided in the fuel cell system 100.

[0054] The second converter 54 is, for example, a bidirectional DC / DC converter (DC / DC converter) equipped with an electrical circuit capable of causing the terminal voltage of the secondary side terminal to rise and fall. The primary side terminal is connected to the output terminal of the battery 53, while the secondary side terminal is connected to the DC side terminal of the inverter 56. The second converter 54 causes the input voltage of the inverter 56, which becomes the secondary side terminal voltage, to rise and fall and controls the input voltage to a target input voltage set according to the operating state of the fuel cell system 100, based on a control signal from the electronic control unit 200.

[0055] The motor generator 55 is, for example, a three-phase permanent magnet type synchronous motor and functions as a motor that generates power of the vehicle in which the fuel cell system 100 is mounted and as a generator that generates power when the vehicle decelerates. The motor generator 55 is connected to the AC side terminal of the inverter 56 and is driven by the power generated by the fuel cell stack 10 and the power of the battery 53.

[0056] The inverter 56 is provided with an electrical circuit that enables it to convert the DC power input from the DC-side terminal into an AC power and output it from the AC-side terminal based on a control signal from the electronic control unit 200, while conversely enabling it to convert the AC power input from the AC-side terminal into a DC power and output it from the DC-side terminal based on a control signal from the electronic control unit 200. The DC-side terminal of the inverter 56 is connected to the secondary-side terminals of the first converter 51 and the second converter 54, while the AC-side terminal of the inverter 56 is connected to the input / output terminal of the motor generator 55.When the motor generator 55 is caused to function as a motor, the inverter 56 converts the combined DC power of the fuel cell power of the fuel cell stack 10 and the battery power of the battery 53 into an AC power (in the present embodiment, a three-phase AC power), which it then supplies to the motor generator 55. In contrast, when the motor generator 55 is caused to function as a generator, the inverter 56 converts the AC power from the motor generator 55 into a DC power, which it then supplies to the battery 53, and so on.

[0057] The electronic control unit 200 comprises a digital computer provided with components connected to each other by a bidirectional bus 201, such as a ROM (Read Only Memory) 202, a RAM (Random Access Memory) 203, a CPU (microprocessor) 204, an input terminal 205, and an output terminal 206.

[0058] At the input terminal 205, output signals from the aforementioned anode pressure sensor 211 and cathode pressure sensor 212, the water temperature sensor 213, the current sensor 214, the voltage sensor 215, etc., are input via the corresponding AD converters 207. Furthermore, at the input terminal 205, an output signal from the starter switch 220 for judging the starting or shutdown of the fuel cell system 100 is input.

[0059] At the output port 206, hydrogen supply control parts 23 (main shutoff valve 231, regulator 232, and injector 233) and control parts of the purge control valve 29 of the compressor 33, the cathode pressure control valve 37, the cooling water pump 42, the radiator bypass control valve 45 of the first converter 51, the circuit breaker 52, the second converter 54, the motor generator 55, the inverter 56, etc. are electrically connected via the corresponding drive circuits 208.

[0060] In this way, output signals from the various sensors required for controlling the fuel cell system 100 are input to the input terminal 205. The electronic control unit 200 outputs control signals for controlling the various control parts from the output terminal 206 based on the output signals from the various sensors input to the input terminal 205.

[0061] Here, when the fuel cell system 100 is mounted in a vehicle, the fuel cell system 100 is sometimes started in a low temperature, such as when the outside air temperature becomes lower than 0°C. During operation of the fuel cell system 100, water generated at the cathode electrode side is generated by the oxygen reduction reaction according to the above-mentioned equation (2), so sometimes parts of this generated water pass from the cathode electrode side to the anode electrode side during operation of the fuel cell system 100 and remain in the anode electrode-side hydrogen channel 2a even after the fuel cell system 100 is shut down.

[0062] Furthermore, in the case of the hydrogen circulation-type fuel cell system 100 such as the present embodiment, while the gas-liquid separator 25 separates the moisture in the anode exhaust gas, complete separation of the moisture is sometimes not possible. For this reason, the hydrogen supplied to the hydrogen passage 2 and in turn to the hydrogen channels 2a sometimes contains moisture. The moisture contained in the hydrogen sometimes remains in the hydrogen channels 2a. Furthermore, water may also intrude into the hydrogen channels 2a for some reason, and the intruded water remains in the hydrogen channels 2a even after the fuel cell system 100 is shut down.

[0063] For this reason, in a low-temperature environment, water remaining in the hydrogen channels 2a (hereinafter referred to as the "residual water") tends to freeze while the fuel cell system 100 is shut down. At the time of starting up the fuel cell system 100, when such freezing of the residual water occurs, for example, in the combtooth parts (parts for distributing hydrogen to the anode electrodes of the unit cells 1 from the hydrogen distributor (hydrogen passage 2) formed when the unit cells 1 are stacked) and the rest of the hydrogen channels 2a, supply of hydrogen to a unit cell 1 where freezing has occurred is hindered.

[0064] In this way, when the fuel cell system 100 is operated in the state where the supply of hydrogen to at least a part of the unit cells 1 is hindered, a unit cell 1 to which the supply of hydrogen is hindered enters a hydrogen deficiency state in which the amount of hydrogen required for power generation becomes insufficient, that is, a state in which the amount of hydrogen supplied becomes insufficient compared with the amount of hydrogen required for power generation set according to the load of the fuel cell stack 10.

[0065] In the anode electrode of a unit cell 1 suffering from a hydrogen deficiency, it is no longer possible to generate hydrogen ions (protons) through the hydrogen oxidation reaction according to the above-mentioned equation (1). Therefore, at the anode electrode of a unit cell 1 suffering from a hydrogen deficiency, using the carbon contained in the anode electrode, a carbon oxidation reaction shown in the following equation (3) prevails, hydrogen ions are generated, and the following electrochemical reactions take place at the electrodes. Anode electrode: C+2H2O→CO2+4H + +4e - (3) Cathode electrode: 4H + +4e - +O2→2H2O (2)

[0066] In this way, when a carbon oxidation reaction occurs in an anode electrode, the carbon in the anode electrode is corroded by oxidation, so that the performance of the unit cell suffering from hydrogen deficiency is reduced.

[0067] Therefore, in the present embodiment, in order to suppress a carbon oxidation reaction at an anode electrode of a unit cell 1 suffering from a hydrogen deficiency, the anode electrode is made to include a water electrolysis catalyst. When an anode electrode includes a water electrolysis catalyst, when the cell suffers from a hydrogen deficiency, the water in the electrolyte membrane is utilized so that, instead of a carbon oxidation reaction, the water electrolysis reaction shown by the following equation (4) becomes predominant, generating hydrogen ions, and the following electrochemical reactions take place at the electrodes. Anode electrode: 2H2O→O2+4H + +4e - (4) Cathode electrode: 4H + +4e - +O2→2H2O (2)

[0068] For this reason, by ensuring that the anode electrode contains a water electrolysis catalyst, even if the cell suffers from a hydrogen deficiency, the carbon can be prevented from being corroded by oxidation.

[0069] In this regard, the potential of an anode electrode (standard electrode potential) when a hydrogen oxidation reaction shown in equation (1) occurs at the anode electrode is generally 0 V or becomes lower than the potential of the cathode electrode (generally 0.6 V to 0.8 V or so) when an oxygen reduction reaction shown in equation (2) occurs at the cathode electrode.

[0070] However, when a carbon oxidation reaction shown in equation (3) or a water electrolysis reaction shown in equation (4) occurs at an anode electrode, the potential of the anode electrode tends to become higher than the potential of the aforementioned cathode electrode. That is, the cell voltage of a unit cell 1 suffering from hydrogen deficiency (potential of the cathode electrode - potential of the anode electrode) tends to become a negative voltage, regardless of the presence of a water electrolysis catalyst.

[0071] When a platinum catalyst in the anode electrode is exposed to a certain potential (generally 0.6 V or higher) or higher, it oxidizes, forming a film-like oxide layer on the surface. The coverage rate increases the higher the potential.

[0072] Consequently, when the fuel cell system 100 is operated in the state where there is a unit cell 1 suffering from hydrogen deficiency, the cell voltage of this unit cell 1 becomes a negative voltage. Regardless of the presence of a water electrolysis catalyst, a film-like oxide layer is formed on the surface of the platinum catalyst in the anode electrode. It should be noted that the potential of an anode electrode when a water electrolysis reaction is taking place becomes lower than the potential of an anode electrode when a carbon oxidation reaction is taking place, so by causing an anode electrode to include a water electrolysis catalyst, the coverage rate of the film-like oxide layer formed on the surface of the platinum catalyst itself can be reduced.

[0073] The film-like oxide layer formed on the surface of the platinum catalyst in an anode electrode is removed by reduction by hydrogen when the hydrogen deficiency is eliminated and hydrogen is supplied to the hydrogen channel 2a, that is, when it is placed in a hydrogen atmosphere (reducing atmosphere).

[0074] However, once the platinum catalyst is covered by a film-like oxide layer, the platinum catalyst loses its activity, making it difficult for a hydrogen oxidation reaction to occur at the anode electrode even after the hydrogen deficiency has been eliminated. Sufficient hydrogen ions can no longer be generated solely through a hydrogen oxidation reaction. Therefore, if the anode electrode does not contain a water electrolysis catalyst, a carbon oxidation reaction will occur to compensate for the insufficient hydrogen ions, even after the hydrogen deficiency has been eliminated. If a water electrolysis catalyst is included, a water electrolysis reaction will generally occur.

[0075] Consequently, even after a hydrogen deficiency is eliminated, a state in which the anode electrode has a high potential continues, and a film-like oxide layer is easily formed, so time is required for the reduction of the film-like oxide layer by hydrogen. Furthermore, a hydrogen oxidation reaction also occurs, and the hydrogen required for the reduction of the film-like oxide layer is consumed by the hydrogen oxidation reaction, so time is required for the reduction of the film-like oxide layer by hydrogen for this reason as well.

[0076] Even if an anode electrode is caused to include a water electrolysis catalyst in this way, when the fuel cell system 100 is operated in a state where there is a unit cell 1 suffering from a hydrogen deficiency, the cell voltage of this unit cell 1 becomes a negative voltage, and a film-like oxide layer is formed on the surface of the platinum catalyst in the anode electrode. Furthermore, when the cell voltage becomes a negative voltage and the platinum catalyst is covered by a film-like oxide layer, even after the hydrogen deficiency is eliminated, the state in which the cell voltage is a negative voltage continues for a while, and it takes time for the cell voltage to return from the negative voltage to a normal voltage value.

[0077] Therefore, when the cell voltage becomes a negative voltage, it may also be considered to limit the output to temporarily make the target generation power zero and stop power generation by the fuel cell stack 10. By limiting the output in this way, power is no longer generated in the unit cell 1, and a hydrogen oxidation reaction and a water electrolysis reaction no longer occur at an anode electrode, so that it may be possible to rapidly reduce the film-like oxide layer by hydrogen in a hydrogen atmosphere.

[0078] However, even if the output is limited in this manner, if the electrical connection between the fuel cell stack 10 and the electrical load part 50 is not physically interrupted by the circuit breaker 52, a slight dark current will sometimes flow through the connection line 57 from the fuel cell stack 10 to the electrical load part 50. That is, even if the output is limited, a state arises in which a hydrogen oxidation reaction eventually occurs within a unit cell 1, and the hydrogen required for reducing the oxide film is ultimately consumed by the hydrogen oxidation reaction. As a result, the reduction of the oxide film by hydrogen does not progress rapidly. It is likely that time will be required for the cell voltage to return from a negative voltage to a normal voltage value.

[0079] Accordingly, in the present embodiment, it is decided to judge whether a hydrogen shortage has occurred, judge whether this hydrogen shortage has been eliminated, and, when it is judged that the hydrogen shortage has been eliminated, temporarily physically interrupt the electrical connection of the fuel cell stack 10 and an electrical load part 50 by the circuit interrupting means 52.

[0080] By physically interrupting the electrical connection between the fuel cell stack 10 and the electrical load part 50 by the circuit interrupter 52 in this way, power is no longer generated within the unit cell 1, and a dark current no longer flows through the connection line 57, making it possible to rapidly reduce the oxide film by hydrogen in a hydrogen atmosphere. Therefore, it is possible to shorten the time until the cell voltage returns from a negative voltage to a normal voltage value. The voltage recovery control according to the present embodiment will be explained below.

[0081] Fig. Figure 2 shows a flowchart for explaining the voltage recovery control according to the present embodiment. The electronic control unit 200 repeatedly executes the present routine during operation of the fuel cell system 100 for a predetermined processing time period Δt (ms).

[0082] In step S1, the electronic control unit 200 reads a cooling water temperature Tw detected by the water temperature sensor 213.

[0083] In step S2, the electronic control unit 200 judges whether a flag F1 has been set to "0." The flag F1 is a flag that is set to "1" when it is judged in step S3, explained below, that a hydrogen shortage has occurred, and is reset to "0" when the hydrogen shortage is resolved in step S6, explained below. The initial value is set to "0."

[0084] In step S3, the electronic control unit 200 judges whether there is a unit cell 1 suffering from a hydrogen shortage. In the present embodiment, when the cooling water temperature Tw is lower than a predetermined freezing judgment water temperature Tw1 (for example, 0°C), the electronic control unit 200 judges that there is a cell 1 suffering from a hydrogen shortage and proceeds to the processing of step S4. This is because when the cooling water temperature Tw is lower than the freezing judgment water temperature Tw1, it can be judged that water freezing causes the supply of hydrogen to at least part of the unit cells 1 to be hindered.On the other hand, the electronic control unit 200 judges that there is no unit cell 1 suffering from hydrogen shortage due to freezing of the residual water, and ends the current processing when the cooling water temperature Tw is the freezing judgment water temperature Tw1 or more.

[0085] In step S4, the electronic control unit 200 sets the flag F1 to “1”.

[0086] In step S5, the electronic control unit 200 performs a rapid warm-up operation to assist warm-up of the fuel cell stack 10. In the present embodiment, the electronic control unit 200 controls a cathode compressor 33 such that the flow rate of air supplied to the air passage 3 becomes exactly a predetermined amount smaller than the target air flow rate set according to the load of the fuel cell stack 10. Due to this, the IV characteristic of the fuel cell stack 10 deteriorates, and heat loss increases by the amount of deterioration of the IV characteristic, so that warm-up of the fuel cell stack 10 can be assisted.

[0087] In step S6, the electronic control unit 200 judges whether the hydrogen shortage has been eliminated. In the present embodiment, the electronic control unit 200 judges that the hydrogen shortage has been eliminated when the cooling water temperature Tw is a predetermined freezing elimination water temperature Tw2 (for example, 10°C) higher than the freezing judgment water temperature Tw1, or more. This is because when the cooling water temperature Tw is the freezing elimination water temperature Tw2 or more, it can be judged that the freezing of the residual water is eliminated and that hydrogen is normally supplied to a unit cell 1. The electronic control unit 200 proceeds to the processing of step S7 when the cooling water temperature Tw is the freezing elimination water temperature Tw2 or more.On the other hand, the electronic control unit 200 ends the current processing when the cooling water temperature Tw is lower than the antifreeze water temperature Tw2.

[0088] In step S7, the electronic control unit 200 resets the flag F1 to “0”.

[0089] In step S8, the electronic control unit 200 opens the circuit interruption device 52 for exactly a predetermined interruption time ts and physically temporarily interrupts the electrical connection between the fuel cell stack 10 and the electrical load part 50 through the circuit interruption device 52.

[0090] In this way, by using the circuit breaker 52 to physically interrupt the electrical connection between the fuel cell stack 10 and the electrical load part 50 after the hydrogen shortage is eliminated, it is possible to completely stop the hydrogen oxidation reaction at the anode electrode while placing the anode electrode in a hydrogen atmosphere. Therefore, it is possible to rapidly reduce the film-like oxide layer formed on the surface of the platinum catalyst with hydrogen while physically interrupting the electrical connection between the fuel cell stack 10 and the electrical load part 50.

[0091] According to the results of experiments by the inventors, when attempting to restore the voltage of a unit cell 1 in which the output had been limited without physically interrupting the electrical connection, it took 100 seconds or so, resulting in a negative voltage. In contrast, it has been confirmed that when the voltage recovery control according to the present embodiment is performed, it is possible to restore the cell voltage of the unit cell 1 to a normal voltage value (about 0.8 V) during the interruption time ts.

[0092] Note that the lower limit of the disconnection time ts is generally 1 msec or so. In the present embodiment, the disconnection time ts is set to 1 sec. On the other hand, the upper limit of the disconnection time ts is not specifically set, but while the connection is disconnected, power can no longer be supplied by the fuel cell stack 10, so the time is preferably within the time range in which the battery 53 can supply power, for example, within 30 minutes, preferably within one minute, more preferably within three seconds.

[0093] Fig. 3 is a timing chart for explaining the operation of a voltage recovery controller according to the present embodiment.

[0094] At time t1, the fuel cell system 100 is started, and the fuel cell system 100 begins operation. At this time, in the example shown in Fig. 3, the cooling water temperature Tw is lower than the freezing judgment water temperature Tw1, and a portion of the unit cells 1 are conducting hydrogen deficiency. As a result, during operation of the fuel cell system 100, from time t1 onward, the cell voltage becomes a negative voltage, and a film-like oxide layer is formed on the surface of the platinum catalyst in the anode electrode of a unit cell 1 suffering from hydrogen deficiency.

[0095] When, at time t2, the cooling water temperature Tw becomes the antifreeze water temperature Tw2 or higher, it is judged that the hydrogen deficiency has been eliminated, the circuit breaker 52 is opened for exactly a predetermined break time ts, and the electrical connection of the fuel cell stack 10 and the electrical load part 50 is physically interrupted. Due to this, the film-like oxide layer formed on the surface of the platinum catalyst while the cell voltage was a negative voltage can be rapidly reduced by hydrogen, making it possible to quickly restore the cell voltage to a normal voltage value.

[0096] According to the present embodiment explained above, an electronic control unit 200 (control device) is provided for controlling a fuel cell system 100. The fuel cell system 100 includes a fuel cell (unit cell 1 or fuel cell stack 10) having an anode electrode including a water electrolysis catalyst, an electrical load part 50 electrically connected to the fuel cell, and a circuit breaker 52 that physically breaks the electrical connection between the fuel cell and the electrical load part 50.The electronic control unit 200 is configured to be provided with a hydrogen shortage judgment part that judges whether hydrogen shortage, which is a state in which an amount of hydrogen supplied to the fuel cell is insufficient compared to an amount of hydrogen required for power generation, has occurred, a hydrogen shortage removal judgment part that judges whether the hydrogen shortage has been removed after the hydrogen shortage judgment part judges that the hydrogen shortage has occurred, and an interruption control part that causes the circuit interruption device 52 to temporarily interrupt an electrical connection of the fuel cell stack 10 and the wet electrical part 50 when the hydrogen shortage removal judgment part judges that the hydrogen shortage has been removed.

[0097] In this way, by using the circuit breaker 52 to physically interrupt the electrical connection between a fuel cell and the electrical load part 50 after the hydrogen shortage has been eliminated, it is possible to completely stop the hydrogen oxidation reaction at the anode electrode of the fuel cell while the anode electrode is placed in a hydrogen atmosphere. For this reason, it is possible to quickly reduce the film-like oxide layer formed on the surface of the platinum catalyst with hydrogen while the electrical connection between the fuel cell and the electrical load part 50 is physically interrupted. Consequently, it is possible to quickly return the voltage of the fuel cell to a normal voltage value after the hydrogen shortage has been eliminated.

[0098] Furthermore, according to the present embodiment, the hydrogen deficiency judgment part is configured to judge that a hydrogen deficiency has occurred when the cooling water temperature Tw, which represents the temperature of the fuel cell (representative temperature), is lower than a predetermined freezing judgment temperature Tw1 at which water inside the fuel cell is likely to freeze. Furthermore, the hydrogen deficiency elimination judgment part is configured to determine that the hydrogen deficiency has been eliminated when the cooling water temperature Tw (representative temperature) has become or has become a predetermined freezing elimination judgment temperature Tw2, which is higher than the freezing judgment temperature Tw1.

[0099] This makes it possible to precisely assess the occurrence and elimination of hydrogen deficiency due to freezing of residual water. Second embodiment

[0100] Next, a second embodiment of the present disclosure will be explained. The present embodiment differs from the first embodiment in the point of judging whether the hydrogen shortage has been eliminated based on the elapsed time te from the time when it was judged that the hydrogen shortage had occurred. The following description will focus on this point of difference.

[0101] Fig. Figure 4 shows a flowchart explaining the voltage recovery control according to the present embodiment. The electronic control unit 200 repeatedly executes this routine during operation of the fuel cell system 100 with a predetermined processing time period Δt (ms). Fig. 4, steps S1 to S5 and S8 perform processing similar to the first embodiment, so explanations are omitted here.

[0102] In step S21, the electronic control unit 200 calculates the elapsed time te from the point in time when it is judged that hydrogen shortage has occurred. In the present embodiment, the electronic control unit 200 adds the processing time Δt of the present routine to the previous value of the elapsed time te to calculate the elapsed time te. The initial value of the elapsed time te is zero.

[0103] It should be noted that in the present embodiment, in this way, the time from a point of time when it is judged that the hydrogen shortage has occurred is made the elapsed time te, but instead, it is also possible to make the time from a point of time when the fuel cell system 100 is started or the time from a point of time when the fuel cell stack 100 starts generating power after starting the fuel cell system 100 the elapsed time te.

[0104] In step S22, the electronic control unit 200 stores the cooling water temperature Tw when it is judged in step S3 that the hydrogen shortage has occurred as the initial water temperature Tw0.

[0105] In step S23, the electronic control unit 200 refers to a diagram according to Fig. 5, which is prepared in advance through experiments, etc., calculating the time until the hydrogen deficiency is eliminated, that is, the time until the freezing of the residual water is eliminated (hereinafter referred to as the "freezing elimination evaluation time"), te1, based on the initial water temperature Tw0. The diagram according to Fig. 5 is basically set such that the freezing elimination judgment time te1 becomes longer when the initial water temperature Tw0 is low compared to a case where it is high. In the present embodiment, it is set such that the lower the initial water temperature Tw0, the longer the freezing elimination judgment time te1.

[0106] In step S24, the electronic control unit 200 judges whether the hydrogen deficiency has been eliminated. In the present embodiment, the electronic control unit 200 judges that the hydrogen deficiency has been eliminated when the elapsed time te is the freezing elimination judgment time te1 or more. The electronic control unit 200 proceeds to the processing of step S7 when the elapsed time te is the freezing elimination judgment time te1 or more. On the other hand, the electronic control unit 200 ends the current processing when the elapsed time te is less than the freezing elimination judgment time te1.

[0107] In step S25, the electronic control unit 200 resets the flag F1 to “0” and resets the elapsed time te to the initial value of “0”.

[0108] Fig. 6 is a timing chart for explaining the operation of the voltage recovery control according to the present embodiment.

[0109] At time t1, the fuel cell system 100 is started, and the fuel cell system 100 begins to operate. At this time, in the example shown in Fig. 6, the cooling water temperature Tw becomes lower than the freezing judgment water temperature Tw1. A part of the unit cells 1 suffers from hydrogen deficiency. As a result, from time t1 during operation of the fuel cell system 100, the cell voltage becomes a negative voltage, and a film-like oxide layer is formed on the surface of the platinum catalyst in the anode electrode of a unit cell 1 suffering from hydrogen deficiency. Further, in the present embodiment, at time t1, the cooling water temperature Tw becomes lower than the freezing judgment water temperature Tw1, so the cooling water temperature Tw at time t1 is stored as the initial water temperature Tw0, and the freezing elimination judgment time te1 is set based on the initial water temperature Tw0.

[0110] At time t2, when the elapsed time te becomes the freezing elimination judgment time te1 or more, it is judged that the hydrogen deficiency has been eliminated, the circuit interruption device 52 is opened for exactly a predetermined interruption time ts, and the electrical connection between the fuel cell stack 100 and the electrical load part 50 is physically interrupted. Due to this, while the cell voltage is a negative voltage, the film-like oxide layer formed on the surface of the platinum catalyst can be rapidly reduced by the hydrogen, so that the cell voltage can be quickly restored to the normal voltage value.

[0111] According to the present embodiment explained above, the freeze-removal judging part of the electronic control unit 200 is configured to judge that the hydrogen deficiency has been eliminated when the elapsed time te from a time point when the hydrogen deficiency was judged becomes a freeze-removal judging time te1 or more, which is set based on the cooling water temperature when the hydrogen deficiency was judged (i.e., the initial water temperature Tw0). Further, the freeze-removal judging part is configured to lengthen the freeze-removal judging time te1 when the cooling water temperature when the hydrogen deficiency was judged (i.e., the initial water temperature Tw0) is low compared to a case where it is high.

[0112] As a result, advantageous effects similar to the first embodiment are obtained. Likewise, the elimination of hydrogen deficiency due to freezing of the residual water can be precisely assessed based on the initial water temperature Tw0. Third embodiment

[0113] Next, a third embodiment of the present disclosure will be explained. The present embodiment differs from the first embodiment in the point of judging whether the hydrogen shortage has been eliminated based on the internal impedance Z of the fuel cell stack 10 (HFR: High Frequency Resistance). The following description will focus on this point of difference.

[0114] Fig. Figure 7 shows a flowchart for explaining voltage recovery control according to the present embodiment. The electronic control unit 200 repeatedly executes the present routine during operation of the fuel cell system 100 at a predetermined processing time period Δt (ms). Fig. 5, steps S1 to S5 and steps S7 to S8 perform processing similar to the first embodiment, so explanations are omitted here.

[0115] In step S31, the electronic control unit 200 reads the internal impedance Z of the fuel cell stack 10, which is calculated at any time during operation of the fuel cell system 100 separately from the present routine. It is known that the internal impedance Z correlates with the humidity level of the electrolyte membrane. When the humidity level of the electrolyte membrane becomes a constant level or less (that is, the amount of moisture in the electrolyte membrane becomes a constant level or less), the internal impedance Z tends to increase.

[0116] Note that the method of calculating the internal impedance Z is not specifically limited. Various known methods (for example, the AC impedance method) can be used to calculate it. Furthermore, it is also possible to separately provide a device for measuring the internal impedance Z and actually measure the internal impedance Z. Note that the internal impedance Z is not limited to one calculated for the fuel cell stack 10 as a whole. It is also possible to configure the disclosure to calculate the internal impedances of the unit cells 1 in the fuel cell stack 10 and obtain the humidity level of the electrolyte membrane based on at least one of the internal impedances of the unit cells 1.For example, if the position in a unit cell 1 of the fuel cell in which freezing is likely to occur is known in advance, it is possible to calculate the internal impedance of the easily freezing unit cell 1 and obtain the humidity degree of the electrolyte membrane based thereon.

[0117] In step S32, the electronic control unit 200 judges whether the hydrogen deficiency has been eliminated. In the present embodiment, the electronic control unit 200 judges that the hydrogen deficiency has been eliminated when a differential value (dZ / dt) of the internal impedance Z is a predetermined value X or more. That is, the electronic control unit 200 judges that the hydrogen deficiency has been eliminated when the humidity level of the electrolyte membrane becomes a constant level or less and the internal impedance Z starts to increase by a gradient of a certain constant gradient or more.

[0118] The following explains the reason why it can be judged that the hydrogen deficiency has been eliminated when a differential value of the internal impedance (dZ / dt) is a predetermined value X or more.

[0119] As explained above, when the fuel cell system 100 is operated in a hydrogen-deficient unit cell 1, if a water electrolysis catalyst is included in the anode electrode, the anode electrode of the unit cell 1 utilizes the water within the electrolyte membrane, the water electrolysis reaction shown in equation (4) becomes predominant, and hydrogen ions are generated. As a result, the cell voltage becomes a negative voltage, and a film-like oxide layer is formed on the surface of the platinum catalyst in the anode electrode.

[0120] Once the platinum catalyst is covered by a film-like oxide layer, the platinum catalyst loses activity, so that even after the hydrogen deficiency is eliminated, the hydrogen oxidation reaction shown in equation (1) hardly occurs at the anode electrode, and hydrogen ions can no longer be generated sufficiently with only a hydrogen oxidation reaction. Therefore, if the anode electrode is arranged to include a water electrolysis catalyst, a water electrolysis reaction will occur to compensate for the insufficient hydrogen ions even after the hydrogen deficiency is eliminated.

[0121] That is, when the fuel cell system 100 is operated with a hydrogen deficiency and a film-like oxide layer is formed on the surface of the platinum catalyst of the anode electrode, a water electrolysis reaction continues to occur at the anode electrode even after the hydrogen deficiency is eliminated. The water in the electrolyte membrane is used in the water electrolysis reaction, so as the water electrolysis reaction continues, the electrolyte membrane gradually dries. When the humidity level of the electrolyte membrane becomes a constant level or less, the internal impedance Z, which has been maintained at a generally constant value, begins to increase by a gradient of a certain constant gradient or more.

[0122] At this time, for example, when freezing is caused by hydrogen deficiency, the time until the hydrogen deficiency is eliminated, that is, until the freezing is eliminated, is sufficiently shorter than the time until the humidity level of the electrolyte membrane becomes a constant level or less due to the water electrolysis reaction that continues to be carried out after hydrogen deficiency occurs, that is, than the time until the internal impedance Z turns to increase by a gradient of a certain constant gradient or more.

[0123] For this reason, when the differential value (dZ / dt) of the internal impedance Z becomes a predetermined value X or more after judging that hydrogen deficiency has occurred, it can be judged that the hydrogen deficiency has been eliminated.

[0124] Fig. 8 is a timing chart for explaining the operation of a voltage recovery controller according to the present embodiment.

[0125] At time t1, the fuel cell system 10 is started, and the fuel cell system 10 begins to operate. At this time, in the example shown in Fig. As shown in FIG. 8, the cooling water temperature Tw is lower than the freezing judgment water temperature Tw1, and a portion of the unit cells 1 suffers from hydrogen deficiency. As a result, during operation of the fuel cell system 100, from time t1 onward, the cell voltage becomes a negative value, and a film-like oxide layer is formed on the surface of the platinum catalyst in the anode electrode of a unit cell 1 suffering from hydrogen deficiency.

[0126] At time t2, when the hydrogen deficiency is eliminated along with the rise in the cooling water temperature Tw, the anode electrode is placed in a hydrogen atmosphere. However, because a film-like oxide layer is formed on the surface of the platinum catalyst in the anode electrode, as explained above, a water electrolysis reaction occurs at the anode electrode. For this reason, even at time t2, the cell voltage remains a negative voltage.

[0127] The water electrolysis reaction at the anode electrode continues to occur even after the hydrogen deficiency is eliminated at time t2, whereby the electrolyte membrane gradually dries out from time t2 onward. As a result, when the humidity level of the electrolyte membrane becomes a certain level or less at time t3, the internal impedance Z increases by a gradient of a certain constant gradient or more. In the present embodiment, it is judged that the hydrogen deficiency has been eliminated at this time, the circuit breaker 52 is opened for exactly a predetermined break time ts, and the electrical connection of the fuel cell stack 10 and the electrical load part 50 is physically interrupted.Due to this, while the cell voltage is a negative voltage, it is possible to quickly reduce the film-like oxide layer formed on the surface of the platinum catalyst by hydrogen, so that it is possible to quickly restore the cell voltage to the normal voltage value.

[0128] According to the present embodiment explained above, the freezing elimination judging part of the electronic control unit 200 is configured to judge that the hydrogen deficiency has been eliminated when the humidity level of the electrolyte membrane of the fuel cell stack 10 has become a predetermined humidity level or less. Specifically, the freezing elimination judging part is configured to judge that the humidity level of the electrolyte membrane of the fuel cell stack 10 has become a predetermined humidity level or less when the differential value of the internal impedance Z of the fuel cell stack 10 has become a predetermined value X or more.

[0129] Due to this, an advantageous effect similar to the first embodiment is obtained, wherein elimination of the hydrogen shortage that occurred due to the freezing of the residual water can be judged based on the internal impedance Z of the fuel cell stack 10. Note that the disclosure is not limited to the case of judging the humidity level of the electrolyte membrane of the fuel cell stack 10 based on the differential value of the internal impedance Z as explained above. For example, it may also be configured to judge that the humidity level of the electrolyte membrane of the fuel cell stack 10 has become a predetermined humidity level or less when the value of the internal impedance Z has become a predetermined value X2 or more. Fourth embodiment

[0130] Next, a fourth embodiment of the present disclosure will be explained. The present embodiment differs from the above-described embodiments in the point of further judging whether the unit cell 1 is suffering from a hydrogen shortage due to the risk or likelihood of flooding. The following description will focus on this point of difference.

[0131] In the above-described first embodiment to third embodiment, when the cooling water temperature Tw is lower than the freezing judgment water temperature Tw1, it is judged that a unit cell suffers from hydrogen deficiency due to the risk or likelihood of freezing of the residual water.

[0132] In some cases, however, the supply of hydrogen to a unit cell is blocked by factors other than such freezing of the residual water.

[0133] In the above-mentioned manner, the electronic control unit 200 controls the cooling water pump 42 such that the cooling water temperature Tw becomes a predetermined target temperature (for example, 60°C). However, when power is continuously generated by a relatively low load after the fuel cell system 10 is started, etc., it sometimes takes time for the cooling water temperature Tw to reach the target temperature. When power is generated in this way in a state where the cooling water Tw is lower than the target temperature, during power generation, the raw water passing from the cathode electrode side to an anode electrode side will not evaporate but will remain in a hydrogen channel 2a, resulting in flooding in the hydrogen channel 2a in some cases. As a result, the supply of hydrogen to a unit cell 1 is sometimes hindered.

[0134] Therefore, in the present embodiment, when there has been a unit cell 1 suffering from a hydrogen shortage due to flooding, after the flooding has been removed, the circuit interruption device 52 is used to physically temporarily interrupt the electrical connection of the fuel cell stack 10 and the electrical load part 50. This voltage recovery control according to the present embodiment will be explained below.

[0135] Fig. Figure 9 shows a flowchart explaining voltage recovery control according to the present embodiment. The electronic control unit 200 repeatedly executes this routine during operation of the fuel cell system 100 at a predetermined processing time period Δt (ms). Fig. 9, steps S1 to S8 perform processing similar to the first embodiment, so explanations are omitted here.

[0136] In step S41, the electronic control unit 200 judges whether there is a danger or likelihood of a unit cell 1 having suffered from hydrogen deficiency due to flooding. In the present embodiment, when the cooling water temperature Tw is less than a predetermined flooding judgment water temperature Tw3 (for example, 50°C), the electronic control unit 200 judges that there is a danger or likelihood of a unit cell 1 having suffered from hydrogen deficiency due to flooding, and proceeds to the processing of step S42. On the other hand, when the cooling water temperature Tw is the flooding judgment water temperature Tw3 or more, the electronic control unit 200 ends the current processing.

[0137] In step S42, the electronic control unit 200 reads the internal impedance Z of the fuel cell stack 10, which is calculated at any time during operation of the fuel cell system 100 separately from the present routine.

[0138] In step S43, the electronic control unit 200 judges whether the differential value (dZ / dt) of the internal impedance Z is a predetermined value X or more. The reason why it is judged whether the differential value (dZ / dt) of the internal impedance Z has become a predetermined value X or more in a situation where the cooling water temperature Tw is the freezing judgment water temperature Tw1 or more and is lower than the flood judgment water temperature Tw3 is as follows.

[0139] When the cooling water temperature Tw is lower than the flooding judgment water temperature Tw3, the fuel cell stack 10 reaches a lower temperature than usual, so the moisture content of the electrolyte membrane generally becomes higher (that is, the membrane is not dry). Therefore, when the differential value (dZ / dt) of the internal impedance Z is the predetermined value X or more in a situation where the cooling water temperature Tw is the freezing judgment water temperature Tw1 or more and is lower than the flooding judgment water temperature Tw3, flooding causes at least a portion of the unit cells 1 to suffer from hydrogen deficiency. A water electrolysis reaction continuously occurs in the anode electrodes of these unit cells 1, resulting in the drying of the electrolyte membranes, and it can be judged that the internal impedance Z has begun to increase.

[0140] Therefore, when the differential value (dZ / dt) of the internal impedance Z is a predetermined value X or more in step S43, the electronic control unit 200 proceeds to the processing of steps S44 and S45, in which it performs a flooding elimination operation for exactly a predetermined time to cause the hydrogen flow rate to temporarily increase to eliminate the flooding, and then proceeds to the processing of step S8, in which it opens the circuit breaker 52 for exactly a predetermined interruption time ts and physically temporarily interrupts the electrical connection of the fuel cell stack 10 and the electrical load part 50 through the circuit breaker 52.

[0141] On the other hand, if the differential value (dZ / dt) of the internal impedance Z is less than the predetermined value X in step S43, the electronic control unit 200 terminates the current processing. Note that when the cooling water temperature Tw is the freezing judgment water temperature Tw1 or more and less than the flood judgment water temperature Tw3, flooding does not necessarily occur, so in principle, if there is no unit cell 1 suffering from hydrogen deficiency due to flooding, the differential value (dZ / dt) of the internal impedance Z will not become a predetermined value X or more. Therefore, in such a case, the routine proceeds to NO at step S43.

[0142] In step S44, the electronic control unit 200 performs a flooding elimination operation that eliminates flooding by temporarily causing the hydrogen flow rate to increase.

[0143] In step S45, the electronic control unit 200 judges whether the flooding elimination operation has been performed for a predetermined time. That is, it judges whether the hydrogen deficiency due to flooding has been eliminated. The electronic control unit 200 proceeds to the processing of step S8 if the flooding elimination operation has been performed for a predetermined time. Conversely, if the flooding elimination operation has not been performed for a predetermined time, the electronic control unit 200 continues the flooding elimination operation.

[0144] Fig. 10 is a timing chart explaining the operation of a voltage recovery controller according to the present embodiment.

[0145] At time t1, when flooding causes a hydrogen shortage during operation of the fuel cell system 100, the cell voltage of the unit cell 1 in the hydrogen shortage becomes a negative voltage. In the example shown in Fig. 10, from time t1 onward, the cooling water temperature Tw becomes smaller than the flooding judgment water temperature Tw3, so that it is continuously judged whether the differential value (dZ / dt) of the internal impedance Z has become a predetermined value X or more.

[0146] From time t1 to time t2, a water electrolysis reaction occurs at an anode electrode of a unit cell 1 suffering from hydrogen deficiency due to flooding, and the electrolyte membrane dries out. As a result, from time t1 onward, the electrolyte membrane gradually dries out. When the humidity level of the electrolyte membrane becomes a constant level or less at time t2, the internal impedance Z increases by a gradient of a certain constant gradient or more. Due to this, at time t2, power has been continuously generated in a state where the cooling water temperature Tw has been lower than the target temperature, so it is judged that flooding has caused a unit cell 1 to suffer from hydrogen deficiency, and the flooding elimination operation is performed for exactly a predetermined time to eliminate the flooding.

[0147] Furthermore, at time t3, after the flood removal operation has been performed for exactly a predetermined time, the circuit breaker 52 is opened for exactly a predetermined break time ts, physically interrupting the electrical connection between the fuel cell stack 10 and the electrical load part 50. Due to this, while the cell voltage is a negative voltage, the film-like oxide layer formed on the surface of the platinum catalyst can be rapidly reduced by the hydrogen, so that the cell voltage can be quickly restored to a normal voltage value.

[0148] According to the present embodiment explained above, the hydrogen deficiency judging part of the electronic control unit 200 is configured to be provided with a first judging part that judges that freezing of water has caused hydrogen deficiency when a cooling water temperature Tw, which represents the temperature of the fuel cell (representative temperature), is lower than a predetermined freezing judging temperature Tw1 at which freezing of water within the fuel cell is likely to occur, and a second judging part that judges that flooding of water has caused hydrogen deficiency when the differential value of the internal impedance Z of a fuel cell has become a predetermined value X or more in the casewhere the cooling water temperature Tw is the freezing judgment temperature Tw1 or higher and is lower than a predetermined flooding judgment temperature Tw3 at which flooding is likely to occur in the hydrogen channel 2a in the fuel cell. Furthermore, the freezing elimination judgment part is configured to judge that the hydrogen shortage has been eliminated when a flooding elimination operation is performed for a predetermined time, temporarily increasing the amount of hydrogen supplied to the fuel cell to eliminate the flooding when it is judged that flooding has caused a hydrogen shortage.

[0149] Due to this, an effect similar to the first embodiment occurs. Likewise, in addition to the hydrogen deficiency caused by the freezing of residual water, it is possible to judge the occurrence and elimination of a hydrogen deficiency caused by flooding. Therefore, even if flooding causes a hydrogen deficiency and the voltage drops, it is possible to quickly restore the voltage of a unit cell 1 that has suffered from a hydrogen deficiency to a normal voltage value after eliminating the hydrogen deficiency caused by flooding.

[0150] Embodiments of the present disclosure have been explained above, but the embodiments only show parts of the examples of application of the present disclosure and are not intended to limit the technical scope of the present disclosure to the specific compositions of the embodiments.

[0151] A control device 200 for a fuel cell system 100 includes a hydrogen shortage judgment part configured to judge whether hydrogen shortage, which is a state in which an amount of hydrogen supplied to the fuel cell 1 is insufficient compared to an amount of hydrogen required for power generation, has occurred, a hydrogen shortage removal judgment part configured to judge whether the hydrogen shortage has been removed after the hydrogen shortage judgment part judges that the hydrogen shortage has occurred, and an interruption control part configured to cause the circuit interruption device 52 to temporarily interrupt an electrical connection of the fuel cell 1 and the electrical load part 50 when the hydrogen shortage removal judgment part judges that the hydrogen shortage has been removed.

Claims

[1] Control device for a fuel cell system for controlling the fuel cell system, wherein the fuel cell system comprises: a fuel cell having an anode electrode containing a water electrolysis catalyst; an electrical load part electrically connected to the fuel cell; and a circuit interruption device configured to physically interrupt an electrical connection of the fuel cell and the electrical load part, wherein the control device for a fuel cell system comprises: a hydrogen shortage judging part configured to judge whether hydrogen shortage, which is a state in which an amount of hydrogen supplied to the fuel cell is insufficient compared to an amount of hydrogen required for power generation, has occurred; a hydrogen deficiency elimination judgment part configured to judge whether the hydrogen deficiency has been eliminated after the hydrogen deficiency judgment part judges that the hydrogen deficiency has occurred; and an interruption control part configured to cause the circuit interruption device to temporarily interrupt an electrical connection of the fuel cell and the electrical load part when the hydrogen deficiency elimination judging part judges that the hydrogen deficiency has been eliminated. [2] A control device for a fuel cell system according to claim 1, wherein the hydrogen deficiency judgment part is configured to judge that a hydrogen deficiency has occurred when a representative temperature representing the temperature of the fuel cell is lower than a predetermined freezing judgment temperature at which there is a risk of water freezing inside the fuel cell. [3] The control device for a fuel cell system according to claim 2, wherein the hydrogen deficiency elimination judging part is configured to judge that the hydrogen deficiency has been eliminated when the representative temperature has become a predetermined freezing elimination judgment temperature higher than the freezing judgment temperature or more. [4] The control device for a fuel cell system according to claim 2, wherein the hydrogen deficiency elimination judging part is configured to judge that the hydrogen deficiency has been eliminated when an elapsed time from a time point when the hydrogen deficiency was judged has become a freezing elimination judging time or more, which is set based on the representative temperature when the hydrogen deficiency was judged. [5] The control device for a fuel cell system according to claim 4, wherein the hydrogen deficiency elimination judging part is configured to lengthen the freezing elimination judging time when the representative temperature when the hydrogen deficiency has been judged is low compared to when it is high. [6] The control device for a fuel cell system according to claim 2, wherein the hydrogen deficiency elimination judging part is configured to judge that the hydrogen deficiency has been eliminated when a humidity level of an electrolyte membrane of the fuel cell has become a predetermined humidity level or less. [7] The control device for a fuel cell system according to claim 6, wherein the hydrogen deficiency elimination judging part is configured to judge that the humidity level of the electrolyte membrane of the fuel cell has become a predetermined humidity level or less when a differential value of an internal impedance of the fuel cell has become a predetermined value or more. [8] A control device for a fuel cell system according to claim 1, wherein the hydrogen deficiency judging part comprises: a first judgment part configured to judge that the hydrogen shortage has occurred due to water freezing when a representative temperature representing the temperature of the fuel cell is lower than a predetermined freezing judgment temperature at which there is a risk of water freezing occurring within the fuel cell; and a second judgment part configured to judge that the hydrogen shortage has occurred due to flooding of water when a differential value of an internal impedance of the fuel cell becomes a predetermined value or more in a case where the representative temperature is the freezing judgment temperature or more and the representative temperature is less than a predetermined flooding judgment temperature at which there is a risk of flooding occurring in a hydrogen channel in the fuel cell, and a hydrogen shortage elimination judging part configured to judge that the hydrogen shortage has been eliminated when a flooding elimination operation is performed for a predetermined time to temporarily increase the amount of hydrogen supplied to the fuel cell to eliminate flooding when it is judged that the hydrogen shortage has occurred due to flooding. [9] A control device for a fuel cell system according to any one of claims 1 to 8, wherein an interruption time during which the circuit interruption means temporarily interrupts the electrical connection of the fuel cell and the electrical load part is 1 millisecond to 30 minutes. [10] A control device for a fuel cell system according to claim 9, wherein the interruption time is 1 millisecond to 1 minute. [11] A control device for a fuel cell system according to claim 10, wherein the interruption time is 1 millisecond to 3 seconds.

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