JP7346972B2 - fuel cell system - Google Patents

Description

The present invention relates to a fuel cell system.

2. Description of the Related Art Conventionally, a fuel cell system is known that is mounted on a vehicle and supplies electric power generated by a fuel cell to a rotating electric machine (for example, Patent Document 1). In the fuel cell system disclosed in Patent Document 1, electric power generated by a fuel cell is directly supplied to a rotating electric machine to run a vehicle. In the fuel cell system disclosed in Patent Document 2, electric power generated by the fuel cell is once supplied to a secondary battery, and the secondary battery supplies electric power to a rotating electric machine to run a vehicle.

Japanese Patent Application Publication No. 2016-35873 JP 2017-117599 Publication

In the fuel cell system of Patent Document 1, when receiving an instruction to stop the fuel cell, the fuel cell is placed in a dry mode. The electric power generated during the drying mode is supplied to and used by the air conditioner. That is, the electric power generated by the fuel cell is used for purposes other than energy for driving the vehicle. Therefore, for example, if air conditioning is not required, the power generated by the fuel cell is discarded. As a result, energy loss occurs in the vehicle.

On the other hand, the fuel cell system disclosed in Patent Document 2 causes the fuel cell to generate electricity according to the state of the secondary battery. For this reason, the fuel cell may continue to generate electricity for a long time. If a fuel cell continues to generate electricity for a long period of time, deterioration of the fuel cell will be accelerated.

An object of the present invention is to provide a fuel cell system that can suppress deterioration of a fuel cell while suppressing energy loss in a vehicle.

The fuel cell system according to the present invention is mounted on a vehicle. The fuel cell system includes a rotating electric machine, a secondary battery, a fuel cell, an internal resistance adjustment means, and a control unit. The rotating electric machine drives the drive wheels of the vehicle. The secondary battery supplies power to the rotating electric machine. A fuel cell is supplied with fuel gas and oxidant gas to generate electricity, and supplies power to a secondary battery. The internal resistance adjusting means adjusts the internal resistance of the fuel cell. The control unit controls the fuel cell system. Before stopping the fuel cell, the control section increases the temperature of the fuel cell using the internal resistance adjusting means to increase the internal resistance of the fuel cell.

According to this configuration, the internal resistance of the fuel cell can be increased before the fuel cell is stopped. In a fuel cell, when the internal resistance increases, deterioration of the catalyst used in the fuel cell is suppressed. Furthermore, the power generated until the fuel cell is stopped is supplied to the secondary battery. The electric power supplied to the secondary battery is supplied to the rotating electrical machine and used to drive the drive wheels when the vehicle is running. That is, it is used as energy when the vehicle runs. As a result, it is possible to provide a fuel cell system that can suppress deterioration of the fuel cell while suppressing energy loss in the vehicle.

The internal resistance adjusting means may be a cooling unit that cools the fuel cell. The control unit may perform first control to increase the internal resistance of the fuel cell by stopping the cooling unit and increasing the temperature of the fuel cell.

According to this configuration, since the cooling unit that cools the fuel cell stops, the internal temperature of the fuel cell increases. When the internal temperature of the fuel cell increases, the humidity inside the fuel cell decreases. This increases the internal resistance of the fuel cell. As a result, deterioration of the fuel cell can be suppressed.

The internal resistance adjusting means may be a humidifier that humidifies the oxidant gas. The control unit may perform second control to increase the internal resistance of the fuel cell by stopping the humidifying unit.

According to this configuration, the humidifying section that humidifies the oxidizing gas stops, so the oxidizing gas is in a non-humidified state. When the oxidant gas is not humidified, the internal resistance of the fuel cell increases. Thereby, deterioration of the fuel cell can be suppressed.

The control unit may prepare to stop the fuel cell. The control unit may perform either or both of the first control and the second control depending on the charging rate at the time of starting preparation. The control unit may stop the fuel cell when the internal resistance value of the fuel cell reaches a predetermined resistance value.

According to this configuration, the control unit increases the internal resistance of the fuel cell by performing either or both of the first control and the second control depending on the charging rate at the time of starting preparation. Thereby, the time for increasing the internal resistance can be shortened depending on the charging rate. That is, performing both the first control and the second control can increase the internal resistance in a shorter time than performing only the first control. Therefore, for example, it is possible to selectively perform the first control and the second control depending on the charging rate, and adjust the time for increasing the internal resistance.

The control unit may perform the first control and the second control when the charging rate at the time of starting preparation is smaller than the predetermined charging rate.

According to this configuration, the control unit can quickly increase the internal resistance when the charging rate is equal to or lower than the predetermined charging rate. That is, when the charging rate is below the predetermined charging rate, there are many chances that the secondary battery will run out of power. When there are many opportunities for the secondary battery to run out of power, the time from when the control unit stops the fuel cell to when it next starts the fuel cell may be short. Therefore, the control section performs both the first control and the second control to increase the internal resistance at an early stage. Thereby, even if the charging rate is below the predetermined charging rate, deterioration of the fuel cell can be suppressed.

In a fuel cell, fuel gas is supplied to an anode, and oxidant gas is supplied to a cathode, and the cathode may include an electrode catalyst in which a catalyst made of a platinum-based material is supported on a carrier made of a ceramic-based material.

According to this configuration, a catalyst made of a platinum-based material is supported on a ceramic carrier in the cathode, so that when the interior of the fuel cell or the oxidant gas is in a low humidified state, coarsening/elution of the platinum-based material is prevented. suppressed. This suppresses deterioration of the fuel cell.

According to the present invention, it is possible to provide a fuel cell system that can suppress deterioration of a fuel cell while suppressing energy loss in a vehicle.

1 is a system diagram showing a schematic configuration of a fuel cell system according to an embodiment of the present invention. FIG. 1 is a diagram showing a schematic internal configuration of a fuel cell according to an embodiment of the present invention. FIG. 3 is a diagram showing a control flow of a control unit according to an embodiment of the present invention. 1 is a timing chart showing a control state of a fuel cell system according to an embodiment of the present invention.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, a fuel cell system 1 includes a motor generator (an example of a rotating electrical machine) 2, a driving battery (an example of a secondary battery) 4, a fuel cell (hereinafter referred to as FC) 6, and a humidifier. (an example of internal resistance adjusting means) 8, a cooling section (an example of internal resistance adjusting means) 10, a control section 12, a hydrogen circulation pump 14, a hydrogen tank 16, and a DC-DC converter 18. In this embodiment, the fuel cell system 1 is mounted on a vehicle C such as a range extender type plug-in fuel cell vehicle (PFCV). The fuel cell system 1 is activated mainly when it is necessary to charge the driving battery 4, and converts the voltage of the electric power generated by the FC 6 using the DC-DC converter 18, and then supplies it to the driving battery 4. Further, when the output from the drive battery 4 to the motor generator 2 is insufficient, power is temporarily supplied to the motor generator 2.

Motor generator 2 drives drive wheels 2b via a reduction gear (not shown) and drive shaft 2a. Motor generator 2 is connected to drive battery 4 via inverter 2c. Further, the inverter 2c is electrically connected to the control section 12. In this embodiment, the motor generator 2 is a three-phase AC motor, and is controlled to perform power running and regeneration via the inverter 2c based on instructions from the control unit 12. When instructed by the control unit 12 to perform power running, the inverter 2c receives power from the drive battery 4, supplies power to the motor generator 2, and causes the motor generator 2 to perform power running. On the other hand, when inverter 2 c is instructed to perform regeneration by control unit 12 , inverter 2 c receives electric power generated by motor generator 2 and supplies electric power to drive battery 4 .

Drive battery 4 supplies power to motor generator 2 . In the present embodiment, the driving battery 4 is composed of a secondary battery such as a lithium ion battery, and has a battery module (not shown) that is composed of a plurality of battery cells. Drive battery 4 functions as a power source for motor generator 2 . Further, the driving battery 4 is connected to a battery control unit 4a that calculates a state of charge (hereinafter referred to as SOC) from the voltage of the battery module and the like. The driving battery 4 is electrically connected to the control section 12 via the battery control section 4a.

The FC 6 supplies power to the driving battery 4. Fuel gas and oxidizing gas are supplied to the FC 6, and the FC 6 generates electricity using the supplied fuel gas and oxidizing gas. In this embodiment, the fuel gas is hydrogen (H ₂ ), and the oxidant gas is air. The FC 6 is connected via a communication path 16c to a hydrogen tank 16 that stores compressed high-pressure hydrogen. A main valve 16a that opens and closes the communication path 16c and a pressure reducing valve 16b that reduces the pressure of high-pressure hydrogen in the hydrogen tank 16 are provided on the communication path 16c. The reduced pressure hydrogen is supplied to an anode 32, which will be described later. Hydrogen that has not been decomposed by the anode 32 is exhausted through the anode side exhaust passage 16d. However, a portion of the exhausted hydrogen is supplied back to the anode 32 via the hydrogen circulation pump 14. The main valve 16a, the pressure reducing valve 16b, and the hydrogen circulation pump 14 are electrically connected to the control unit 12.

Further, the FC 6 is connected to an air compressor 8b that takes in and compresses air outside the vehicle C, and a humidifier 8 that humidifies the compressed air, via an air communication path 8a. Air is supplied to the cathode 33, which will be described later. Air that has not reacted at the cathode 33 is exhausted through the cathode side exhaust passage 8c.

The FC6 includes a fuel cell output sensor (an example of a fuel cell output detection section) 20, an internal resistance measurement sensor (an example of an internal resistance detection section) 22, a temperature sensor (an example of a temperature detection section) 24, and a cell stack. 26. Fuel cell output sensor 20 detects the output of FC6. Internal resistance value measurement sensor 22 detects the internal resistance value of FC6. The temperature sensor 24 detects the temperature of the cell stack 26 of the FC 6. The cell stack 26 is configured by arranging a plurality of single cells 30, which will be described later. The fuel cell output sensor 20, internal resistance value measurement sensor 22, and temperature sensor 24 are electrically connected to the control unit 12.

As shown in FIG. 2, the single cell 30 includes an electrolyte membrane 31, an anode (fuel electrode or negative electrode) 32, a cathode (air electrode or positive electrode) 33, an anode separator 34, a cathode separator 35, and an external A circuit 36 is provided. In this embodiment, the FC 6 is a solid polymer fuel cell that uses a solid polymer membrane as the electrolyte membrane 31. The external circuit 36 is a circuit for extracting the electric power generated by each single cell 30 and supplying the electric power to the driving battery 4 or the motor generator 2. The external circuit 36 electrically connects the anode 32 and the cathode 33 across a load section 36b for extracting power.

The anode 32 includes an anode-side electrode catalyst layer 32a and an anode-side diffusion layer 32b. The anode side electrode catalyst layer 32a is provided in contact with the electrolyte membrane 31. In this embodiment, the anode side electrode catalyst layer 32a has a catalyst made of a platinum (Pt)-based material supported on a carrier made of a carbon-based material or a ceramic material such as tin oxide (SnO ₂ ). Consists of an electrocatalyst. Hydrogen is supplied to the anode 32 from the hydrogen tank 16 via the main valve 16a, the pressure reducing valve 16b, and a groove (not shown) provided in the anode side separator 34. Hydrogen supplied to the anode 32 is diffused by the anode-side diffusion layer 32b, and then decomposed into hydrogen ions and electrons by the electrode catalyst of the anode-side electrode catalyst layer 32a. The hydrogen ions pass through the electrolyte membrane 31 and move to the cathode electrode catalyst layer 33a. The electrons become a current and move to the cathode 33 via the external circuit 36.

The cathode 33 is provided on the opposite side of the anode 32 with the electrolyte membrane 31 in between. The cathode 33 includes a cathode electrode catalyst layer 33a and a cathode diffusion layer 33b. The cathode side electrode catalyst layer 33a is provided in contact with the electrolyte membrane 31. In this embodiment, the cathode side electrode catalyst layer 33a is composed of an electrode catalyst in which a catalyst made of a platinum (Pt)-based material is supported on a carrier made of a ceramic-based material such as tin oxide (SnO ₂ ). The cathode 33 is supplied with air that has passed through the air compressor 8b, the humidifier 8, and a groove (not shown) in the cathode separator 35. Oxygen (O ₂ ) in the air supplied to the cathode 33 is diffused by the cathode side diffusion layer 33b, and then is converted into hydrogen ions and the external circuit via the electrolyte membrane 31 by the electrode catalyst of the cathode side electrode catalyst layer 33a. It reacts with the electrons passed through 36 to produce water (H ₂ O).

In such an electrode catalyst, when power is generated for a long time, the platinum-based material is eluted or coarsened, and the FC6 deteriorates. In order to suppress this, when stopping the FC6, it is preferable to increase the internal resistance of the FC6. However, when the cathode-side electrode catalyst layer 33a is constructed of an electrode catalyst in which a catalyst made of a platinum (Pt)-based material is supported on a carrier made of a ceramic-based material, a large amount of generated water is generated during long-term power generation. Therefore, it becomes difficult for the internal resistance to rise when the FC6 is stopped. This is because the ceramic material is a hydrophilic carrier material that has the property of adsorbing water vapor in the atmosphere around the carrier.

Further, when the cathode side electrode catalyst layer 33a is a carrier made of a ceramic material, the internal resistance of the FC6 tends to increase as the humidity inside the FC6 decreases. This is because the lower the humidity inside the FC6, the higher the oxygen partial pressure in the atmosphere around the carrier, and the easier it is for oxygen to be adsorbed onto the carrier surface. Ceramic materials are carrier materials that have a characteristic that internal resistance increases when oxygen is adsorbed. This tendency is remarkable for tin oxide among ceramic materials.

As shown in FIG. 1, the cooling unit 10 cools the FC 6. The cooling unit 10 includes a radiator 10a, a cooling passage 10b, and a cooling pump (not shown). The radiator 10a is provided on the cooling passage 10b. The cooling passage 10b extends around each unit cell 30 of the FC6. A refrigerant passes through the inside of the cooling passage 10b, and absorbs the heat generated by each unit cell 30 of the FC6. The refrigerant that has absorbed heat is cooled by heat exchange with the radiator 10a. The cooling pump is electrically connected to the control unit 12, and when the cooling pump stops, the cooling unit 10 stops.

The control unit 12 is a functional configuration realized by software stored in an ECU (Electronic Control Unit) 13. The ECU 13 is actually constituted by a microcomputer including an arithmetic unit, a memory, an input/output buffer, and the like. Based on signals from each sensor and various devices, as well as maps and programs stored in memory, the ECU 13 controls at least the main valve 16a, the pressure reducing valve 16b, and the air compressor so that the fuel cell system 1 is in a desired operating state. The humidifying section 8b, the humidifying section 8, the load section 36b, and the cooling section 10 are controlled. Further, the control unit 12 acquires the charging rate of the driving battery 4, and calculates a target charging rate Bt according to the driving state of the vehicle C and the like. The control unit 12 starts the FC 6 to generate electricity, controls the DC-DC converter 18, and charges the drive battery 4 to the target charging rate Bt. Further, the control unit 12 calculates the output required of the vehicle C and controls the motor generator 2 via the inverter 2c. Note that various controls are not limited to processing by software, and may also be processed by dedicated hardware (electronic circuits). Further, various devices are electrically connected to the ECU 13.

Next, the control procedure of the control unit 12 of this embodiment will be explained using the flowchart of FIG. 3 and the timing chart of FIG. 4. In addition, the timing chart of FIG. 4 is a timing chart when both the 1st control which stops the cooling part 10 and the 2nd control which stops the humidification part 8 are performed.

The control unit 12 acquires the SOC from the battery control unit 4a, and determines whether the SOC has reached the target charging rate Bt, which is the charging rate at which preparations for stopping the FC 6 are started (S1). When the SOC reaches the target charging rate Bt (S1 Yes), the control unit 12 starts preparations to stop the FC 6 (S2 see time t1 in FIG. 4). Here, the control unit 12 determines whether the target charging rate Bt is equal to or higher than the predetermined charging rate Bp (S3). When the target charging rate Bt is equal to or higher than the predetermined charging rate Bp (S3 Yes), the control unit 12 performs first control to stop the cooling unit 10. On the other hand, if the target charging rate Bt is smaller than the predetermined charging rate Bp (S3 No), the control unit 12 performs a second control to stop the humidifying unit 8 in addition to the first control (S8). That is, the control unit 12 increases the internal resistance value Rf of the FC before stopping the FC 6. The control unit 12 causes the FC 6 to continue generating power until the SOC reaches the target charging rate Bt (S1 No).

As shown in the timing chart of FIG. 4 from time t1 to time t3, when the cooling unit 10 is stopped, the FC temperature Tf increases. When the FC temperature Tf increases, the humidity inside the FC decreases. When the humidity inside the FC 6 decreases, the internal resistance value Rf increases and the FC output Pf decreases. In addition to the first control, when the second control of stopping the humidifying section 8 is performed, the humidity of the air supplied to the cathode 33 is set to a low humidifying state where the humidity is lower than the state where the humidifying section 8 is operating. Become. As a result, the internal resistance value Rf increases earlier than when only the first control is performed.

On the other hand, if the FC temperature Tf rises too much, an abnormality may occur in the FC. Therefore, as shown in the flowchart of FIG. 3, the control unit 12 determines whether the FC temperature Tf is equal to or higher than the FC forced stop temperature Tmax (S5). The control unit 12 forcibly stops the FC when the FC temperature Tf becomes equal to or higher than the FC forced stop temperature Tmax (S5 Yes). If the FC temperature Tf is lower than the FC forced stop temperature Tmax (S5 No), the control unit 12 performs either or both of the first control and the second control depending on the SOC.

When the internal resistance value Rf becomes equal to or higher than the predetermined resistance value Rt (S6 Yes), the control unit 12 stops the air compressor 8b, closes the main valve 16a (see time t3 in FIG. 4), and turns on the FC. It is stopped (S7). After stopping the FC 6, the control unit 12 returns the process to the start. On the other hand, if the internal resistance value Rf is smaller than the predetermined resistance value Rt (S6 No), the control unit 12 returns the process to before S5 and performs either the first control or the second control depending on the SOC. Alternatively, both may be continued to increase the internal resistance value Rf.

As shown from time t1 to time t3 in the timing chart of FIG. 4, the power generated by the control unit 12 before stopping the FC 6 is supplied to the drive battery 4. The electric power supplied to the drive battery 4 is supplied to the motor generator 2 and used to drive the drive wheels 2b when the vehicle C runs. That is, it is used as energy when the vehicle C travels.

Further, as shown after time t3, the control unit 12 performs either or both of the first control and the second control according to the SOC in this way, not only when the FC 6 is preparing to stop. Even after stopping, the internal resistance value Rf can be increased. This is due to the fact that ceramic materials have a basic characteristic that their internal resistance increases as the FC voltage (not shown) increases. This characteristic is remarkable in tin oxide among ceramic materials. When the internal resistance increases, deterioration of FC6 is suppressed. More specifically, in the case of a ceramic material, the internal resistance increases while the FC6 is stopped, and the electron density on the carrier surface decreases, making it possible to suppress electron transfer of the platinum material, which leads to deterioration. In particular, when the carrier material is tin oxide, it is easy to suppress electron transfer of the platinum-based material, which leads to deterioration. That is, when a catalyst made of a platinum-based material is supported on a ceramic carrier in the cathode 33, if the air supplied to the inside of the FC 6 or the cathode 33 is in a low humidified state, the progress of coarsening/elution of the platinum-based material is suppressed. Ru. In particular, when tin oxide is used for the cathode 33, the progress of coarsening/elution of the platinum-based material is significantly suppressed. This suppresses deterioration of FC6.

Moreover, when the target charging rate Bt is smaller than the predetermined charging rate Bp, the control unit 12 quickly increases the internal resistance value Rf by performing the first control and the second control. That is, when the target charging rate Bt is smaller than the predetermined charging rate Bp, there are many chances that the power of the driving battery 4 supplied to the motor generator 2 will be insufficient. This increases the frequency with which the FC 6 needs to be restarted within a short period of time after being stopped. Therefore, the control unit 12 performs both the first control and the second control to increase the internal resistance at an early stage.

As explained above, according to the present invention, it is possible to provide the fuel cell system 1 that can suppress the deterioration of the FC 6 while suppressing the energy loss of the vehicle C.

<Other embodiments>
Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various changes can be made without departing from the gist of the invention. In particular, the plurality of modifications described in this specification can be arbitrarily combined as necessary.

(a) In the above embodiment, tin oxide, which is a ceramic material, is used as the carrier for the electrode catalyst of the cathode 33, but the present invention is not limited to this. Any known electrode material can be used as long as it is a ceramic material. Further, as the ceramic material used for the carrier, it is preferable to use a hydrophilic ceramic material because it can adsorb water vapor in the atmosphere. Such ceramics include titanium oxide, silicon oxide, aluminum oxide, niobium oxide, ruthenium oxide, tantalum oxide, zinc oxide, and zirconium oxide.

(b) In the above embodiment, as the electrode catalyst of the anode 32, a catalyst made of a platinum (Pt)-based material is placed on a carrier made of a carbon-based material or a carrier made of a ceramic-based material such as tin oxide (SnO ₂ ). Although a supported electrocatalyst was used, the present invention is not limited thereto. As the electrode catalyst of the anode 32, a known electrode material can be used.

(c) In the above embodiment, the first control and the second control are performed when the target charging rate Bt is lower than the predetermined charging rate Bp, and the first control is performed when the target charging rate Bt is equal to or higher than the predetermined charging rate Bp. Although the present invention has been described using an example in which the present invention is carried out, the present invention is not limited thereto. The control unit 12 may selectively combine the first control and the second control depending on the SOC at the time of starting preparations for stopping the FC 6.

1: Fuel cell system, 2: Motor generator (rotating electric machine)
2b: Drive wheel, 4: Drive battery (secondary battery)
6: FC, 8: Humidifying section, 10: Cooling section, 12: Control section 32: Anode, 33: Cathode Bp: Predetermined charging rate, Bt: Target charging rate C: Vehicle, Rf: Internal resistance value, Rt: Predetermined resistance Value Tf: FC temperature

Claims (4)

A fuel cell system installed in a vehicle,
a rotating electric machine that drives drive wheels of the vehicle;
a secondary battery that supplies power to the rotating electrical machine;
a fuel cell supplied with fuel gas and oxidant gas to generate electricity and supply power to the secondary battery;
internal resistance adjustment means for adjusting the internal resistance of the fuel cell;
a control unit that controls the fuel cell system;
Equipped with
The fuel cell supplies the fuel gas to an anode, the oxidant gas to a cathode, and the cathode includes an electrode catalyst in which a catalyst made of a platinum-based material is supported on a carrier made of a ceramic-based material,
The internal resistance adjusting means is a cooling unit that cools the fuel cell,
The control unit performs first control to stop the cooling unit and increase the temperature of the fuel cell to increase the internal resistance of the fuel cell,
before stopping the fuel cell, increasing the internal resistance of the fuel cell;
fuel cell system. A fuel cell system installed in a vehicle,
a rotating electric machine that drives drive wheels of the vehicle;
a secondary battery that supplies power to the rotating electrical machine;
a fuel cell supplied with fuel gas and oxidant gas to generate electricity and supply power to the secondary battery;
internal resistance adjustment means for adjusting the internal resistance of the fuel cell;
a control unit that controls the fuel cell system;
Equipped with
The fuel cell supplies the fuel gas to an anode, the oxidant gas to a cathode, and the cathode includes an electrode catalyst in which a catalyst made of a platinum-based material is supported on a carrier made of a ceramic-based material,
The internal resistance adjusting means is a humidifier that humidifies the oxidant gas,
The control unit performs second control to stop the humidification unit and increase internal resistance of the fuel cell,
before stopping the fuel cell, increasing the internal resistance of the fuel cell;
fuel cell system. The internal resistance adjusting means is a humidifier that humidifies the oxidant gas,
The control unit performs second control to stop the humidification unit and increase internal resistance of the fuel cell,
preparing to stop the fuel cell;
Performing one or both of the first control and the second control depending on the charging rate when starting the preparation,
stopping the fuel cell when the internal resistance value of the fuel cell reaches a predetermined resistance value;
The fuel cell system according to claim 1 . The control unit performs the first control and the second control when the charging rate at the time of starting the preparation is smaller than a predetermined charging rate.
The fuel cell system according to claim 3 .