JP2016134258A - Control device for fuel battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for a fuel battery system that can enhance the determination precision of flooding.SOLUTION: A control device 200 for a fuel battery system 100 is configured to estimate a proper IV characteristic corresponding to deterioration degree of catalyst of a single cell 1 based on an operation history of the fuel battery system 100, calculate a proper temperature of single cells 1 corresponding to the load of a fuel battery stack 10 based on the proper IV characteristic, acquire the temperature of at least two single cells 1 of a representative cell selected from the single cells 1 and a flooding determination cell in which flooding is more liable to occur than the representative cell, and determines that flooding occurs in at least the flooding determination cell when the temperature of the flooding determination cell is equal to a proper temperature or more, and the temperature difference between the flooding determination cell and the representative cell is equal to a predetermined value or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for a fuel cell system.

  As a control device of a conventional fuel cell system, it is determined whether or not there is a fuel cell single cell (hereinafter referred to as “single cell”) whose voltage is lower than a predetermined threshold, and a single cell whose voltage is lower than the predetermined threshold. If there is, further determine whether the cause of the voltage drop is due to excessive humidification (flooding) or excessive drying of the electrolyte membrane, and depending on the determination result, water discharge operation (flooding elimination operation) or There is one configured to perform either one of the drying suppression operations (see Patent Document 1).

JP 2011-113647 A

  However, the voltage drop of the single cell is not limited to the temporary deterioration of the IV characteristics due to the change in the wet and dry state of the electrolyte membrane as described above, but also due to the permanent deterioration of the IV characteristics due to the deterioration of the catalyst over time. There is a case.

  Therefore, as in the conventional fuel cell system control device described above, when there is a single cell that is lower than the predetermined threshold, it is always configured to perform either the water discharge operation or the drying suppression operation. If the cause of the voltage drop of the cell is due to the deterioration of IV characteristics due to the deterioration of the catalyst over time, the water discharge operation or the drying suppression operation is surely performed even though the dry and wet state of the electrolyte membrane is in an appropriate state. Either of these will be implemented. Therefore, there is a risk of further voltage drop.

  That is, the above-described conventional fuel cell system control device does not consider the deterioration of the IV characteristics due to the deterioration of the catalyst over time when determining whether or not the flooding has occurred. there were.

  The present invention has been made paying attention to such a problem, and an object thereof is to perform flooding determination with high accuracy in consideration of deterioration of IV characteristics due to deterioration of a catalyst over time.

  In order to solve the above problems, according to one aspect of the present invention, there is provided a fuel cell stack configured by stacking a plurality of fuel cell single cells that generate electric power by an electrochemical reaction between a fuel gas and an oxidant gas. A control device that controls the fuel cell system estimates an appropriate IV characteristic according to the degree of deterioration of the catalyst of the single fuel cell based on the operation history of the fuel cell system, and loads the load on the fuel cell stack based on the appropriate IV characteristic. The appropriate temperature of the corresponding single fuel cell is calculated, and at least two fuel cell single cells of the representative cell selected from the single fuel cell and a flood determination cell that is more likely to cause flooding than the representative cell are obtained. When the temperature of the flood determination cell is equal to or higher than the appropriate temperature and the temperature difference between the flood determination cell and the representative cell is equal to or higher than the specified value. It is configured to determine that flooding occurs at least flooding judgment cells.

  According to this aspect, in determining whether flooding has occurred, since it is determined whether the temperature of the flooding determination cell is higher than the appropriate temperature of the single cell according to the degree of deterioration with time of the catalyst, Whether the temperature of the flooding determination cell is increased due to temporary deterioration of IV characteristics due to flooding, or whether the temperature of the flooding determination cell is increased due to permanent deterioration of IV characteristics due to deterioration of the catalyst over time. Can be determined. In addition, since it is determined whether or not the temperature difference between the flooding determination cell and the representative cell is equal to or greater than a predetermined value, the amount of heat released from the flooding determination cell is small, so the temperature of the flooding determination cell is high. Or whether the temperature of the flooding determination cell is high due to temporary deterioration of IV characteristics due to flooding. Therefore, it is possible to perform the flooding determination with high accuracy in consideration of the deterioration of the catalyst with time.

FIG. 1 is a schematic configuration diagram of a fuel cell system and an electronic control unit that controls the fuel cell system according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the relationship between the IV characteristics of a single cell and the calorific value of the single cell during power generation. FIG. 3 is a diagram illustrating flooding determination control according to an embodiment of the present invention. FIG. 4 is a flowchart illustrating flooding determination control according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals are assigned to similar components.

  FIG. 1 is a schematic configuration diagram of a fuel cell system 100 and an electronic control unit 200 that controls the fuel cell system 100 according to an embodiment of the present invention.

  The fuel cell system 100 includes a fuel cell stack 10, a fuel gas supply / discharge device 20 for supplying / discharging fuel gas to / from the fuel cell stack 10, and supplying / discharging oxidant gas to / from the fuel cell stack 10. An oxidant gas supply / discharge device 30 for carrying out, a cooling water circulation device 40 for circulating cooling water for cooling the fuel cell stack 10, and an electric load unit 50 electrically connected to an output terminal of the fuel cell stack 10 And comprising.

  The fuel cell stack 10 is formed by stacking a plurality of fuel cell single cells (hereinafter referred to as “single cells”) 1 along the stacking direction and electrically connecting the single cells 1 in series. Each single cell 1 includes a membrane electrode assembly 1a. The membrane electrode assembly 1a includes an electrolyte membrane, an anode electrode formed on one side of the electrolyte membrane, and a cathode electrode formed on the other side of the electrolyte membrane.

When power generation is performed in the fuel cell stack 10, the following electrochemical reactions occur at the anode and cathode electrodes.
Anode electrode: 2H ₂ → 4H ⁺ + 4e ⁻
Cathode electrode: 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O

  In each single cell 1, a hydrogen flow passage 2a for supplying hydrogen as fuel gas to the anode electrode and an air flow passage 3a for supplying air as oxidant gas to the cathode electrode are formed. The Further, a cooling water flow passage 4a for supplying cooling water is formed between two adjacent single cells 1.

  The hydrogen flow passage 2a, the air flow passage 3a, and the cooling water flow passage 4a of each unit cell 1 are connected in parallel in the fuel cell stack 10, respectively, so that the hydrogen passage 2 and the air passage are provided in the fuel cell stack 10. 3 and the cooling water passage 4 are formed. The inlets and outlets of the hydrogen passage 2, the air passage 3, and the cooling water passage 4 are respectively provided on one end side in the stacking direction of the fuel cell stack 10. In the present embodiment, hydrogen and air are respectively supplied to the hydrogen passage 2 and the air passage 3 so that the flow directions of hydrogen and air in the fuel cell stack 10 are opposite to each other. Hydrogen and air may be supplied. In this embodiment, the direction in which the cooling water flows is the same as the direction in which hydrogen flows, but it may be reversed.

  The fuel gas supply / discharge device 20 includes a hydrogen supply pipe 21, a high-pressure hydrogen tank 22 as a hydrogen source, a hydrogen supply control valve 23, a buffer unit 24, a purge pipe 25, and a purge control valve 26.

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

  The high-pressure hydrogen tank 22 stores hydrogen to be supplied to the hydrogen passage 2 through the hydrogen supply pipe 21.

  The hydrogen supply control valve 23 includes a shutoff valve 231, a regulator 232, and an injector 233.

  The shut-off valve 231 is an electromagnetic valve that is opened and closed by the electronic control unit 200 and is provided in the hydrogen supply pipe 21. When the shut-off valve 231 is opened, hydrogen flows out from the high-pressure hydrogen tank 22 to the hydrogen supply pipe 21. When the shut-off valve 231 is closed, hydrogen does not flow out from the high-pressure hydrogen tank 22 to the hydrogen supply pipe 21.

  The regulator 232 is provided in the hydrogen supply pipe 21 downstream from the shutoff valve 231. The regulator 232 is a pressure control valve capable of adjusting the opening degree continuously or stepwise, and 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 from the injector 233 is controlled.

  The injector 233 is provided in the hydrogen supply pipe 21 downstream from the regulator 232. The injector 233 is a needle valve, for example, and is controlled to be opened and closed by the electronic control unit 200. By controlling the valve opening period of the injector 233, the flow rate of hydrogen injected from the injector 233 is controlled.

  Thus, the hydrogen supply control valve 23 controls the supply of hydrogen from the high-pressure hydrogen tank 22 to the hydrogen passage 2. That is, hydrogen controlled to a desired pressure and flow rate by the hydrogen supply control valve 23 is intermittently supplied to the hydrogen passage 2.

  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 representative of the pressure of hydrogen in the hydrogen passage 2 (hereinafter referred to as “anode pressure”).

  The buffer unit 24 is, for example, a tank that communicates with the outlet of the hydrogen passage 2, and temporarily stores the anode off gas that has flowed out of the hydrogen passage 2. The anode off-gas is composed of surplus hydrogen that has not been used for the electrochemical reaction in each single cell 1 and inert gas such as nitrogen or water vapor leaking from the air passage 3 to the hydrogen passage 2 through the membrane electrode assembly 1a. And mixed gas. The buffer unit 24 only needs to have a function of temporarily storing the anode off gas. For example, a space is formed on the downstream side (near the outlet) of the hydrogen passage 2 to the extent that the anode off gas can be temporarily stored. The space may be used as the buffer unit 24. That is, the hydrogen passage 2 may be formed so that the downstream side of the hydrogen passage 2 functions as the buffer portion 24.

  The purge pipe 25 has one end connected to the buffer unit 24 and the other end connected to a diluter 39 provided in a cathode offgas pipe 37 described later.

  The purge control valve 26 is an electromagnetic valve that is opened and closed by the electronic control unit 200 and is provided in the purge pipe 25. The purge control valve 26 is normally closed and is periodically opened over a short time. When the purge control valve 26 is opened, the anode off gas in the buffer unit 24 flows into the diluter 39 through the purge pipe 25.

  The oxidant gas supply / discharge device 30 includes an air supply pipe 31, an air cleaner 32, a compressor 33, an intercooler 34, a bypass control valve 35, a bypass pipe 36, a cathode offgas pipe 37, and a cathode pressure control valve 38. And a diluter 39.

  The air supply pipe 31 is a pipe through which air supplied to the air passage 3 flows. One end of the air supply pipe 31 is connected to the air cleaner 32 and the other end is connected to the inlet of the air passage 3.

  The air cleaner 32 removes foreign matter in the air sucked into the air supply pipe 31. The air cleaner 32 is disposed in the atmosphere serving as the oxygen source 32a. That is, the oxygen source 32a communicates with the air supply pipe 31 via the air cleaner.

  The compressor 33 is, for example, a centrifugal or axial flow turbo compressor, and is provided in the air supply pipe 31. The compressor 33 compresses and discharges the air sucked into the air supply pipe 31 via the air cleaner 32.

  The intercooler 34 is provided in the air supply pipe 31 downstream of the compressor 33, and cools the air discharged from the compressor 33 with, for example, traveling wind or cooling water.

  A first flow rate sensor 212 is provided in the air supply pipe 31 between the compressor 33 and the intercooler 34. The first flow rate sensor 212 detects the flow rate of air discharged from the compressor 33 (hereinafter referred to as “discharged air flow rate”). Note that the first flow rate sensor 212 may be provided in the air supply pipe 31 upstream of the compressor 33, and the first flow rate sensor 212 may detect the flow rate of the air sucked by the compressor 33.

  The bypass pipe 36 is a pipe for allowing a part or all of the air discharged from the compressor 33 to flow directly into the cathode offgas pipe 37 without passing through the fuel cell stack 10 as necessary. One end of the bypass pipe 36 is connected to the second outlet port 35 c of the bypass control valve 35, and is connected to a cathode offgas pipe 37 between the cathode pressure control valve 38 and the diluter 39.

  The bypass pipe 36 is provided with a second flow rate sensor 213. The second flow rate sensor 213 detects the flow rate of air (hereinafter referred to as “bypass air”) that has flowed into the bypass pipe 36 via the bypass control valve 35.

  The bypass control valve 35 is an electric three-way valve whose opening degree can be adjusted continuously or stepwise, and includes an inlet port 35a, a first outlet port 35b, and a second outlet port 35c. The opening degree of the bypass control valve 35 is controlled by the electronic control unit 200. The inlet port 35a is connected to the air supply pipe 31 on the intercooler 34 side. The first outlet port 35b is connected to the air supply pipe 31 on the fuel cell stack 10 side. The second outlet port 35 c is connected to the bypass pipe 36. By adjusting the opening degree of the bypass control valve 35, the communication state between the inlet port 35a, the first outlet port 35b, and the second outlet port 35c is adjusted.

  Specifically, when the bypass control valve 35 is fully closed, the inlet port 35a and the first outlet port 35b are in communication with each other, and the inlet port 35a and the second outlet port 35c are in communication with each other. As a result, the air discharged from the compressor 33 does not flow into the bypass pipe 36 but flows entirely into the air passage 3 from the air supply pipe 31 via the bypass control valve 35.

  On the other hand, when the bypass control valve 35 is fully opened, the inlet port 35a and the first outlet port 35b are not communicated, and the inlet port 35a and the second outlet port 35c are communicated. As a result, all the air discharged from the compressor 33 flows into the bypass pipe 36 via the bypass control valve 35 and does not flow into the air passage 3.

  When the bypass valve control valve is opened to any opening other than fully closed and fully open (arbitrary intermediate opening), the inlet port 35a communicates with the first outlet port 35b and the second outlet port 35c, respectively. Become. As a result, a part of the air discharged from the compressor 33 according to the opening degree of the bypass control valve 35 flows into the bypass pipe 36 via the bypass control valve 35, and the rest flows through the bypass control valve 35. 31 flows into the air passage 3. The larger the opening degree of the bypass control valve 35, the higher the ratio of the air flowing into the bypass pipe 36 out of the air discharged from the compressor 33.

  Thus, the bypass control valve 35 controls the amount of air supplied to the air passage 3 and the amount of air flowing into the bypass pipe 36 out of the air discharged from the compressor 33.

  The cathode offgas pipe 37 is a pipe through which the cathode offgas flowing out from the outlet of the air passage 3 flows. One end of the cathode offgas pipe 37 is connected to the outlet of the air passage 3 and the other end opens to the atmosphere. The cathode off gas is a mixed gas of excess oxygen that has not been used for the electrochemical reaction in each single cell 1, an inert gas such as nitrogen, and water vapor generated by the electrochemical reaction.

  The cathode pressure control valve 38 is provided in the cathode offgas pipe 37. The cathode pressure control valve 38 is an electromagnetic valve whose opening degree can be adjusted continuously or stepwise, and the opening degree is controlled by the electronic control unit 200. By controlling the opening of the cathode pressure control valve 38, the cathode pressure, which is the pressure in the air passage 3, is controlled.

  A cathode pressure sensor 214 is provided in the cathode offgas pipe 37 upstream of the cathode pressure control valve 38. The cathode pressure sensor 214 detects the pressure in the cathode offgas pipe 37 upstream of the cathode pressure control valve 38 as a value representing the pressure in the air passage 3 (cathode pressure).

  The diluter 39 is provided in the cathode offgas pipe 37 downstream of the cathode pressure control valve 38. As described above, the purge pipe 25 is connected to the diluter 39, and cathode off gas and bypass air flow in through the cathode off gas pipe 37, and anode off gas flows in through the purge pipe 25. As a result, the cathode off gas, the bypass air, and the anode off gas are mixed inside the diluter 39, and these mixed gases are discharged as exhaust gas from the cathode off gas pipe 37 downstream of the diluter 39 to the atmosphere. In this way, by mixing the cathode offgas, the bypass air, and the anode offgas inside the diluter 39, the hydrogen in the anode offgas is diluted with the cathode offgas and the bypass air, and the hydrogen concentration of the exhaust gas discharged to the atmosphere is reduced. The concentration is less than the reference concentration (for example, 4%).

  As described above, in this embodiment, the anode off-gas flowing out from the hydrogen passage 2 to the purge pipe 25 is discharged to the atmosphere from the cathode off-gas pipe 37 without returning to the hydrogen supply pipe 21. That is, the fuel cell system 100 according to the present embodiment is a hydrogen non-circulation type.

  In the case of the hydrogen non-circulation type fuel cell system 100, a circulation pump or the like for returning the anode off gas to the hydrogen supply pipe 21 and circulating it is compared with a hydrogen circulation type system for returning the anode off gas to the hydrogen supply pipe 21 and circulating it. It becomes unnecessary. Therefore, the hydrogen non-circulation type fuel cell system 100 does not require electric power for driving the circulation pump as compared with the hydrogen circulation type system, and can improve fuel efficiency and simplify the configuration. Cost can be reduced.

  The cooling water circulation device 40 includes 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.

  The cooling water circulation pipe 41 is a pipe that circulates cooling water for cooling the fuel cell stack 10, and has one end connected to the inlet of the cooling water passage 4 and the other end 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, and the inlet side of the cooling water passage 4 is defined as downstream of the cooling water circulation pipe 41.

  The cooling water pump 42 is provided on the downstream side of the cooling water circulation pipe 41 and circulates the cooling water.

  The radiator 43 is provided in the cooling water circulation pipe 41 upstream of the cooling water pump 42, and cools the cooling water flowing out from the outlet of the cooling water passage 4 by, for example, running air or air sucked by the radiator fan 46.

  The radiator bypass pipe 44 is a pipe provided so that cooling water can be circulated without passing through the radiator 43, and one end is connected to the radiator bypass control valve 45 and the other end is connected to the radiator 43 and the cooling water. It is connected to a cooling water circulation pipe 41 between the pump 42.

  The radiator bypass control valve 45 is, for example, a thermostat, and is provided in the cooling water circulation pipe 41 upstream of the radiator 43. The radiator bypass control valve 45 switches the cooling water circulation path according to the temperature of the cooling water. Specifically, when the temperature of the cooling water is higher than a preset reference temperature, the cooling water that has flowed out of the cooling water passage 4 into the cooling water circulation pipe 41 flows again into the cooling water passage 4 via the radiator 43. Switch the cooling water circulation path so that it flows. On the contrary, when the temperature of the cooling water is lower than the reference temperature, the cooling water flowing out from the cooling water passage 4 to the cooling water circulation pipe 41 flows through the radiator bypass pipe 44 without passing through the radiator 43 and directly enters the cooling water passage 4. The cooling water circulation path is switched so as to flow into the.

  A coolant temperature sensor 215 is provided in the coolant circulation pipe 41 upstream of the radiator bypass control valve 45. The water temperature sensor 215 detects the temperature of the cooling water flowing out from the cooling water passage 4 to the cooling water circulation pipe 41. The cooling water pump 42 is controlled based on a control signal from the electronic control unit 200 so that the temperature of the cooling water detected by the water temperature sensor 215 becomes a predetermined target temperature (for example, 60 ° C.).

  The electrical load unit 50 includes a first converter 51, a circuit breaker 52, a battery 53, a second converter 54, a motor generator 55, and an inverter 56.

  A connection line 57 between the electric load unit 50 and the output terminal of the fuel cell stack 10 includes a current sensor 216 for detecting a current taken out from the fuel cell stack 10 (hereinafter referred to as “stack current”), and a fuel cell stack. And a voltage sensor 217 for detecting an inter-terminal voltage (hereinafter referred to as “stack voltage”) of the ten output terminals. The stack current detected by the current sensor 216 corresponds to the load of the fuel cell stack 10 (or single cell 1).

  The first converter 51 is a bidirectional DC / DC converter provided with an electric circuit capable of increasing / decreasing the voltage between terminals of the primary side terminal, and the primary side terminal is a fuel cell via the circuit breaker 52. Connected to the output terminal of the stack 10, the secondary side terminal is connected to the DC side terminal of the inverter 56. The first converter 51 raises or lowers the stack voltage, which is the primary terminal voltage, based on a control signal from the electronic control unit 200, and sets the stack voltage according to the operating state of the fuel cell system 100. Control to voltage.

  The circuit breaker 52 is opened and closed by the electronic control unit 200 and electrically connects or disconnects the fuel cell stack 10 and the electric load unit 50. The circuit breaker 52 is not necessarily provided.

  The battery 53 is a rechargeable secondary battery such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium ion battery. The battery 53 is charged with surplus power from the fuel cell stack 10 and regenerative power from the motor generator 55. The electric power charged in the battery 53 is used to drive each control component provided in the fuel cell system 100 such as the motor generator 55 and the compressor 33 as necessary.

  The second converter 54 is a bidirectional DC / DC converter provided with an electric circuit capable of increasing / decreasing the voltage between terminals of the secondary side terminal, for example, and the primary side terminal is connected to the output terminal of the battery 53. The secondary side terminal is connected to the DC side terminal of the inverter 56. The second converter 54 raises or lowers the input voltage of the inverter 56 that is the secondary terminal voltage based on the control signal from the electronic control unit 200, and sets the input voltage according to the operating state of the fuel cell system 100. The target input voltage is controlled.

  The motor generator 55 is, for example, a three-phase permanent magnet type synchronous motor, and has a function as a motor that generates power of a vehicle on which the fuel cell system 100 is mounted, and a function as a generator that generates power when the vehicle is decelerated. Prepare. Motor generator 55 is connected to the AC side terminal of inverter 56, and is driven by the generated power of fuel cell stack 10 and the power of battery 53.

  The inverter 56 converts a DC current input from the DC side terminal into an AC current based on a control signal from the electronic control unit 200 and outputs the AC current from the AC side terminal, and conversely based on a control signal from the electronic control unit 200. And an electric circuit capable of converting an alternating current input from the alternating current side terminal into a direct current and outputting the direct current from the direct current side terminal. The DC side terminal of inverter 56 is connected to the secondary side terminals of first converter 51 and second converter 54, and the AC side terminal of inverter 56 is connected to the input / output terminal of motor generator 55. When the motor generator 55 functions as a motor, the inverter 56 converts the combined direct current of the stack current of the fuel cell stack 10 and the stack current of the battery 53 into an alternating current (three-phase alternating current in the present embodiment) and converts the motor into a motor. This is supplied to the generator 55. On the other hand, when the motor generator 55 functions as a generator, the inverter 56 converts the alternating current from the motor generator 55 into a direct current and supplies it to the battery 53 and the like.

  The electronic control unit 200 is composed of a digital computer and is connected to each other by a bi-directional bus 201. A ROM (read only memory) 202, a RAM (random access memory) 203, a CPU (microprocessor) 204, an input port 205, and an output port 206.

  In addition to the anode pressure sensor 211, the first flow sensor 212, the second flow sensor 213, the cathode pressure sensor 214, the water temperature sensor 215, the current sensor 216, and the voltage sensor 217, the input port 205 includes the first single cell. Output signals such as the temperature sensor 218, the second single cell temperature sensor 219, and an impedance sensor (not shown) for detecting the impedance of the fuel cell stack 10 are input via the corresponding AD converters 207. In addition, an output signal from the start switch 220 for determining whether the fuel cell system 100 is started or stopped is input to the input port 205.

The first single cell temperature sensor 218 is a sensor for detecting the temperature T ₁ of _one single cell selected from the single cells 1 (hereinafter referred to as “representative cell”), for example, a thermocouple. Can be used. In the present embodiment, a single cell that is located at the center in the stacking direction of the fuel cell stack 10 and exhibits an average voltage behavior among the single cells 1 is used as a representative cell.

The second unit cell temperature sensor 219 is a sensor for detecting a temperature T ₂ of the selected flooded judgment cells as single cells flooding is likely to occur than the representative cells from each unit cell 1, for example, a thermoelectric Pairs can be used. In this embodiment, an end cell that is located on the other end side in the stacking direction of the fuel cell stack 10 (the side opposite to the side where the air passage inlet is formed) and that is most likely to be flooded among the single cells 1 is determined as flooding. Cell.

  The output port 206 is connected to the hydrogen supply control valve 23 (shutoff valve 231, regulator 232 and injector 233), purge control valve 26, compressor 33, bypass control valve 35, cathode pressure control valve 38, via a corresponding drive circuit 208. Control components such as the cooling water pump 42, the first converter 51, the circuit breaker 52, the second converter 54, the motor generator 55, and the inverter 56 are electrically connected.

  As described above, the output signals of various sensors necessary for controlling the fuel cell system 100 are input to the input port 205, and the electronic control unit 200 receives the output signals of the various sensors input to the input port 205. Based on this, a control signal for controlling each control component is output from the output port 206.

  Here, when power generation is performed in the fuel cell stack 10, water is generated in the catalyst layer in the cathode electrode of the single cell 1 by the electrochemical reaction described above. When this generated water is excessively accumulated in the gas diffusion layer in the cathode electrode, a phenomenon called flooding occurs in which the supply of air to the catalyst layer is hindered by the generated water accumulated in the gas diffusion layer. In the single cell 1 in which flooding occurs, the supply of air to the catalyst layer is hindered by the generated water accumulated in the gas diffusion layer. Therefore, in the single cell 1 in which flooding occurs, the IV characteristics temporarily deteriorate compared to other normal single cells 1 (single cell 1 in which no flooding occurs), and the voltage of the single cell 1 also decreases. become.

  As described above, the IV characteristics of the single cell 1 are temporarily deteriorated when the electrolyte membrane of the single cell 1 is excessively humidified. However, even if the electrolyte membrane is excessively dried, the IV characteristic is temporarily reduced. Worse. That is, the voltage of the single cell 1 temporarily decreases when the electrolyte membrane of the single cell 1 is excessively humidified, and similarly decreases temporarily even when the electrolyte membrane is excessively dried.

  Therefore, in the control device of the conventional fuel cell system described above, it is determined whether there is a single cell whose voltage is lower than a predetermined threshold, and when there is a single cell whose voltage is lower than a predetermined threshold, Furthermore, it is determined whether the voltage drop is caused by excessive humidification (flooding) or excessive drying of the electrolyte membrane, and either water discharge operation (flooding elimination operation) or drying suppression operation is performed depending on the determination result. Had to do.

  However, the deterioration of the IV characteristics of the unit cell 1 is not limited to the temporary deterioration due to the change in the wet and dry state of the electrolyte membrane as described above, but may be permanent due to the deterioration of the catalyst over time. Hereinafter, permanent deterioration of IV characteristics due to deterioration of the catalyst with time will be described.

  The catalyst (for example, platinum) contained in the catalyst layers in both electrodes of the single cell 1 becomes an ionic state and elutes into the electrolyte membrane when the electrode potential becomes a predetermined potential (for example, 0.8 V) or more, and the predetermined potential is released. When it becomes less than, it re-deposits in the electrolyte membrane. In other words, when the stack voltage becomes equal to or higher than the predetermined catalyst deterioration voltage (stack voltage at which the electrode potential is equal to or higher than the predetermined potential), platinum contained in the catalyst layer starts to elute, and when the stack voltage is lower than the catalyst deterioration voltage, the eluted platinum is deposited. start.

  During the operation of the fuel cell system 100, the stack voltage repeatedly moves up and down across the catalyst deterioration voltage according to the load fluctuation (change in the stack current) of the fuel cell stack 10, and in particular, the potential of the anode electrode. Repeatedly moves up and down across a predetermined potential. As a result, elution and deposition of the catalyst contained in the catalyst layer in the anode electrode are repeated, the surface area of the catalyst gradually decreases, and the catalyst deteriorates with time. When the catalyst deteriorates with time and the surface area of the catalyst decreases, the electrochemical reaction is less likely to occur, and the IV characteristics of the single cell 1 are permanently deteriorated.

  Accordingly, when there is a single cell whose voltage is lower than a predetermined threshold as in the conventional control device of the fuel cell system described above, if one of the water discharge operation or the drying suppression operation is always performed, If the cause of the voltage drop is due to the deterioration of the IV characteristics due to the deterioration of the catalyst over time, either the water discharge operation or the drying suppression operation must be performed regardless of whether the electrolyte membrane is in an appropriate state. Will be implemented. For this reason, there is a risk of further voltage drop of the single cell.

  In other words, the above-described conventional control device for a fuel cell system does not consider the deterioration of the IV characteristics due to the deterioration of the catalyst over time, so there is a problem in the determination accuracy of whether or not flooding has occurred.

  Below, with reference to FIG. 2, the relationship between the IV characteristic of the single cell 1 and the emitted-heat amount of the single cell 1 at the time of electric power generation is demonstrated first. In FIG. 2, the solid line is the IV characteristic (hereinafter referred to as “initial IV characteristic”) of a single cell in which deterioration of the catalyst with time does not occur and temporary deterioration of IV characteristics does not occur. On the other hand, the broken line is the IV characteristic of a single cell whose IV characteristic has deteriorated from the initial IV characteristic for some reason.

  As shown in FIG. 2, when all the chemical energy possessed by hydrogen as the fuel gas can be converted into electric energy, the single cell voltage becomes the theoretical voltage (1.23 V).

  However, during power generation, various losses such as resistance polarization, activation polarization, and diffusion polarization occur inside the single cell 1, so that it is not possible to convert all chemical energy into electrical energy, and part of the chemical energy is lost. As thermal energy. The loss generated during power generation is the amount of heat generated by the single cell 1 during power generation.

  As shown by the broken line in FIG. 2, when the IV characteristics of the single cell 1 deteriorate due to some factor, even if the power is generated with the same load, the loss increases by the amount of the deteriorated IV characteristics. The calorific value of the single cell 1 at the time increases. That is, the temperature of the single cell 1 in which the IV characteristics are deteriorated tends to be higher than the temperature of other normal single cells 1.

  Therefore, in this embodiment, the calorific value of the single cell 1 during power generation changes according to the IV characteristics of the single cell 1, and as a result, the temperature of the single cell 1 whose IV characteristics are deteriorated is another normal single cell 1. Focusing on the fact that the temperature becomes higher than the above temperature, a highly accurate flood determination is performed in consideration of the deterioration of the IV characteristics of the single cell 1 due to the deterioration of the catalyst over time. Hereinafter, flooding determination control according to the present embodiment will be described with reference to FIGS. 3 and 4.

  As shown by a broken line in FIG. 3, when the fuel cell system 100 is operated, the catalyst deteriorates with time according to the operation history, and the IV characteristics of the single cell 1 gradually deteriorate from the initial IV characteristics. The deterioration of the IV characteristics of the single cell 1 due to the deterioration of the catalyst over time is permanent.

  Therefore, the current IV characteristics of the single cell 1 during the operation of the fuel cell system 100 are the IV characteristics that are deteriorated due to deterioration of the catalyst over time if the dry and wet state of the electrolyte membrane is appropriate. That is, the IV characteristics deteriorated by the deterioration of the catalyst with time are appropriate IV characteristics of the single cell 1.

  Here, the temperature of the single cell 1 during power generation changes according to the amount of heat generated by the single cell 1 during power generation, and the amount of heat generated by the single cell 1 during power generation depends on the IV characteristics of the single cell 1 as described above. Will change accordingly. That is, the temperature of the single cell 1 during power generation changes according to the IV characteristics of the single cell 1. Therefore, if the IV characteristics of the single cell 1 are known, the temperature of the single cell 1 during power generation can be estimated.

  Therefore, in the present embodiment, the appropriate IV characteristic of the single cell 1 is estimated based on the degree of deterioration of the catalyst with time based on the operating history of the fuel cell system 100, and the degree of deterioration with time of the catalyst is considered based on the appropriate IV characteristic. The appropriate temperature of the single cell 1 is calculated according to the load of the fuel cell stack 10. In other words, the appropriate temperature of the single cell 1 in consideration of the degree of deterioration with time of the catalyst is, in other words, the amount of heat generated (loss) of the single cell 1 when power generation is performed with the IV characteristic of the single cell 1 being in the proper IV characteristic. ) Is the temperature of the single cell 1 expected from FIG.

  As shown by the one-dot chain line in FIG. 3, the IV characteristics of the single cell 1 in which flooding occurs are further deteriorated from the appropriate IV characteristics. Therefore, the temperature of the single cell 1 in which flooding occurs is Therefore, it becomes higher than the appropriate temperature.

  On the other hand, the temperature of the single cell 1 during power generation is not limited to the calorific value of the single cell 1 during power generation, but the amount of heat taken away from the single cell 1 by heat exchange with cooling water or outside air during power generation (hereinafter “single cell 1”). It also depends on the amount of "heat dissipation from". Therefore, for example, if the amount of heat released from the single cell 1 is smaller than expected, the temperature of the single cell 1 may be higher than the appropriate temperature even if no flooding occurs. In addition, since the temperature of the cooling water or outside air which each single cell 1 contacts is basically the same, the heat radiation amount from each single cell 1 is also basically the same.

  Therefore, in the present embodiment, whether or not flooding may occur is determined based on whether or not the temperature of the single cell 1 is higher than the appropriate temperature, and the influence of the heat dissipation from the single cell 1 is eliminated. In order to do this, the temperature difference between at least two single cells 1 of the single cell 1 whose temperature is higher than the appropriate temperature and the single cell 1 different from the single cell 1 is compared, and the comparison result Based on this, it is finally determined whether flooding has occurred.

  FIG. 4 is a flowchart for explaining flooding determination control according to this embodiment performed by the electronic control unit 200.

In step S1, the electronic control unit 200 calculates the amount of liquid water on the cathode electrode based on the following equation (1).
Amount of liquid water on the cathode pole = amount of produced water + amount of water transferred between the electrodes-amount of liquid water discharged-amount of steam discharged ...

  The amount of generated water is the amount of liquid water generated on the cathode electrode by an electrochemical reaction during power generation. The amount of generated water can be calculated by referring to a table stored in advance in the ROM 202 based on, for example, the stack current (load).

  The interelectrode water transfer amount is the balance of water that moves between the electrodes through the electrolyte membrane, and from the amount of water transfer by electroosmosis that moves from the anode electrode to the cathode electrode as protons move during power generation, It is a value obtained by subtracting the amount of water movement due to diffusion that moves from the cathode electrode to the anode electrode due to the gradient of the moisture content in the thickness direction of the electrolyte membrane. The amount of interpolar water transfer can be calculated by various known methods. The amount of water movement due to electroosmosis can be calculated by referring to a table stored in advance in the ROM 202 based on, for example, the stack current (load). The amount of water movement due to diffusion is calculated based on, for example, the moisture content of the electrolyte membrane, the water diffusion coefficient in the electrolyte membrane, the differential pressure between the cathode pressure and the anode pressure, and the like, refer to a map stored in the ROM 202 in advance. Can be calculated. The moisture content of the electrolyte membrane can be calculated from, for example, the impedance of the fuel cell stack 10. The water diffusion coefficient in the electrolyte membrane is a physical property value determined according to the thickness or material of the electrolyte membrane.

  The liquid water discharge amount is the amount of liquid water discharged from the air passage 3. For the liquid water discharge amount, refer to a map or the like stored in advance in the ROM 202 based on, for example, the stack current (load) and the flow rate of air flowing into the air passage 3 (= discharge air flow rate−bypass air flow rate). It can be calculated by

  The steam discharge amount is the amount of water vapor discharged from the air passage 3. The steam discharge amount can be calculated by referring to a map or the like stored in advance in the ROM 202 based on, for example, the temperature of the cooling water and the flow rate of the air flowing into the air passage 3.

  In step S2, the electronic control unit 200 estimates an appropriate IV characteristic of the single cell 1 according to the degree of deterioration with time of the catalyst based on the operation history of the fuel cell system 100.

  As described above, the deterioration of the catalyst with time is caused by repeated elution and reprecipitation of the catalyst as the stack voltage repeatedly moves up and down across the catalyst deterioration voltage. Therefore, the degree of deterioration with time of the catalyst can be determined from the operation history of the fuel cell system 100, for example, the total operation time of the fuel cell system 100 and the time when the stack voltage is equal to or higher than the catalyst deterioration voltage.

  Therefore, in the present embodiment, a map in which the operation history of the fuel cell system 100 and the degree of deterioration with time of the catalyst are associated with each other is created in advance through experiments and stored in the ROM 202 in advance. Based on the operation history of the fuel cell system 100, the degree of deterioration with time of the catalyst is calculated with reference to the map described above, and the initial IV characteristics are corrected based on the degree of deterioration with time of the catalyst. The appropriate IV characteristic of the single cell 1 corresponding to the degree is estimated.

  In addition, since elution of the catalyst is more likely to occur in a high temperature and high humidity state, parameters that correlate with the temperature of the cooling water when the stack voltage is equal to or higher than the catalyst deterioration voltage and the dry and wet state of the electrolyte membrane (for example, the cathode) Even if the degree of deterioration with time of the catalyst is corrected based on one or both of the highest amount of liquid water and the impedance of the fuel cell stack 10), the appropriate IV characteristic of the single cell 1 corresponding to the degree of deterioration with time of the catalyst is estimated. good.

  Further, the appropriate IV characteristics may be sequentially corrected based on the actual IV characteristics based on the stack current detected by the current sensor 216 and the stack voltage detected by the voltage sensor 217.

  In step S3, the electronic control unit 200 determines whether or not it is in an operation state in which flooding is likely to occur. If the amount of liquid water on the cathode electrode is less than the predetermined amount, the electronic control unit 200 determines that the operation state is not likely to cause flooding, and proceeds to the process of step S4. On the other hand, if the amount of liquid water on the cathode electrode is equal to or greater than a predetermined amount, the electronic control unit 200 determines that the operation state is likely to cause flooding, and proceeds to the process of step S5.

  In step S4, the electronic control unit 200 operates the fuel cell system 100 normally. Specifically, the electronic control unit 200 controls the compressor and the cathode pressure control valve so that the discharge air flow rate and the cathode pressure become the target discharge air flow rate and the target cathode pressure corresponding to the stack current (load). Further, the cooling water pump is controlled so that the temperature of the cooling water becomes a predetermined target temperature.

In step S5, the electronic control unit 200, a stack current sensed by the current sensor 216, the temperature T ₁ of the detected representative cells by the first unit cell temperature sensor 218, detected by the second unit cell temperature sensor 219 and the temperature T ₂ of the flooding judgment cells were acquires.

  In step S6, the electronic control unit 200 calculates an appropriate temperature of the single cell 1 according to the load of the fuel cell stack 10 based on the appropriate IV characteristic estimated in step S2. Specifically, the electronic control unit 200 refers to an optimal map selected from a plurality of maps stored in advance in the ROM 202 based on the appropriate IV characteristics and the stack current as the load of the fuel cell stack 10. Thus, the appropriate temperature of the single cell 1 is calculated.

  Each map stored in the ROM 202 stores the appropriate temperature of the single cell 1 corresponding to the stack current for each IV characteristic corresponding to the degree of deterioration of the catalyst with time. The electronic control unit 200 selects an IV characteristic that matches the appropriate IV characteristic or an IV characteristic close to the appropriate IV characteristic from among the IV characteristics corresponding to the degree of deterioration with time of the catalyst, and a map corresponding to the selected IV characteristic. Referring to FIG. 5, the appropriate temperature of the single cell 1 is calculated according to the stack current acquired in step S3.

  As described above, the appropriate temperature is the temperature of the single cell 1 that is expected from the amount of heat generated (loss) of the single cell 1 when power generation is performed with the IV characteristic of the single cell 1 being the proper IV characteristic. It is. Therefore, if the initial temperature of the single cell 1 is different, the appropriate temperature may also change. Therefore, the appropriate temperature calculated based on the appropriate IV characteristic may be corrected based on the initial temperature of the single cell 1, for example, the outside air temperature, the temperature of the cooling water immediately after system startup, or the like.

  In step S6, the appropriate temperature is calculated directly from the appropriate IV characteristic. However, the appropriate temperature may be calculated indirectly from the appropriate IV characteristic. For example, the fuel cell stack 10 of the fuel cell stack 10 may be calculated based on the appropriate IV characteristic. The heat generation amount of the single cell 1 according to the load may be calculated, and the appropriate temperature may be calculated based on the heat generation amount of the single cell 1. Thus, the method for calculating the appropriate temperature based on the appropriate IV characteristics is not particularly limited.

  In step S6, since the stack current as the load of the fuel cell stack 10 can be regarded as the load of the single cell 1, the appropriate temperature of the single cell 1 is calculated from the stack current. The appropriate temperature of the single cell 1 may be calculated from the single cell current as the load of the divided single cell 1.

In step S7, the electronic control unit 200 determines whether the high or not than temperature T ₂ is the proper temperature of the flooding decision cell. Such a determination is made because if the temperature of the flooding determination cell is higher than the appropriate temperature, the IV characteristic is temporarily deteriorated from the appropriate IV characteristic, and as a result, the amount of generated heat is increased and the flooding determination cell temperature T ₂ is because it is considered that there is a possibility that is higher than the proper temperature. That is, higher than the temperature T ₂ is the proper temperature of the flooding decision cell, because the flooding in the flooding decision cell is considered may be occurring.

Thus the electronic control unit 200 is higher than the temperature T ₂ is the proper temperature of the flooding determining cell, the process proceeds to determine the flooding is likely to have occurred in the process of step S8 in the flooding decision cell. On the other hand, if less temperature T ₂ is the proper temperature of the flooding decision cell, it is determined that there is no possibility of flooding occurs in flooding determining cell process proceeds to step S4.

  In step S8, the electronic control unit 200 determines whether the temperature difference between the flooding determination cell and the representative cell is equal to or greater than a predetermined value. Such a determination is made for the following reason.

As described above, the temperature of the single cell 1 during power generation varies depending on the amount of heat released from the single cell 1 during power generation in addition to the amount of heat generated by the single cell 1 during power generation. Therefore, even if no flooding occurs in flooding determination cell, if the heat radiation amount from the flooding decision cell is less than expected, it is the temperature T ₂ of the flooding decision cell is higher than a proper temperature. When the heat radiation amount from the flooding decision cell is less than expected, because running low as well heat radiation amount from the representative cell becomes higher temperature T ₁ of the representative cell with a decrease in heat dissipation. Therefore, there is almost no difference in the temperature difference between the two cells.

  On the other hand, if flooding has occurred in the flood determination cell and the flooding has not yet occurred in the representative cell, only the IV characteristics of the flood determination cell will be temporarily deteriorated, resulting in an increase in heat generation. A temperature difference occurs between the two.

Therefore, it can be considered that the temperature difference is less than the predetermined value, in order to simply the heat radiation amount is less temperature T ₂ of the flooding decision cell is higher than a proper temperature. That can be considered by a factor other than a temporary deterioration of IV characteristics, and the temperature T ₂ of the flooding decision cell is higher than a proper temperature. Then, it can be considered the temperature difference is equal to or greater than a predetermined value, and by the amount of heat generation is increased by a temporary deterioration of the IV characteristic due to flooding temperature T ₂ of the flooding decision cell is higher than the appropriate temperature .

Thus the electronic control unit 200, if the temperature difference is greater than a predetermined value, it is determined that the temperature T ₂ of the flooding judgment cells for flooding occurs in flooding determining cell is higher than the proper temperature, The process proceeds to step S9. On the other hand an electronic control unit 200, the determined temperature difference is less than the predetermined value, only the temperature T ₂ of the flooding decision for a cell to the heat radiation amount from the flooding decision cell is small is higher than an appropriate temperature Then, the process proceeds to step S4.

  In step S9, the electronic control unit 200 performs a flooding elimination operation. Specifically, the electronic control unit 200 performs control to increase the discharge air flow rate from the target discharge air flow rate according to the stack current (load), and lowers the cathode pressure from the target cathode pressure according to the stack current (load). And at least one of control for increasing the temperature of the cooling water above a predetermined target temperature.

According to this embodiment described above, a fuel including a fuel cell stack 10 configured by stacking a plurality of single cells 1 that generate electric power by an electrochemical reaction between hydrogen as a fuel gas and air as an oxidant gas. An electronic control unit (control device) 200 that controls the battery system 100 estimates an appropriate IV characteristic according to the degree of deterioration of the catalyst of the single cell 1 based on the operation history of the fuel cell system 100, and based on the appropriate IV characteristic. The appropriate temperature of the single cell 1 is calculated according to the load of the fuel cell stack 10, and at least two of the representative cell selected from the single cell 1 and the flood determination cell that is more likely to cause flooding than the representative cell get the temperature of the single cell 1, there is flooding determining cell temperature T ₂ is the proper temperature or more, the flooding decision cell temperature of a representative cell When the degree difference is equal to or greater than a predetermined value, it is determined that flooding has occurred at least in the flooding determination cell.

  As described above, according to this embodiment, the appropriate IV characteristic corresponding to the degree of deterioration of the catalyst with time is estimated from the operation history of the fuel cell system 100, and the single cell corresponding to the degree of deterioration of the catalyst with time is estimated from the estimated appropriate IV characteristic. Calculate an appropriate temperature of 1.

  In determining whether flooding has occurred, it is determined whether the temperature of the flooding determination cell is higher than an appropriate temperature. Therefore, the temperature of the flooding determination cell is temporarily deteriorated due to temporary deterioration of IV characteristics due to flooding. It is possible to determine whether or not the temperature of the flooding determination cell is high due to permanent deterioration of IV characteristics due to aging deterioration of the catalyst.

  In addition, since it is determined whether or not the temperature difference between the flooding determination cell and the representative cell is equal to or greater than a predetermined value, the amount of heat released from the flooding determination cell is small, so the temperature of the flooding determination cell is high. Or whether the temperature of the flooding determination cell is high due to temporary deterioration of IV characteristics due to flooding.

  Therefore, it is possible to perform flooding determination with high accuracy in consideration of the degree of deterioration with time of the catalyst. That is, it is possible to carry out a highly accurate flood determination in consideration of a change in the heat generation amount of the single cell 1 during power generation according to the degree of deterioration of the catalyst with time and a change in the heat release amount from the single cell 1 during power generation. it can.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  For example, in the above-described embodiment, whether the liquid water amount on the cathode electrode is calculated in step S1 of the flowchart of FIG. 4 and whether the liquid water amount on the cathode electrode is compared with a predetermined amount in step S3 is an operation state in which flooding is likely to occur. However, since there is a correlation between the dry / wet state (moisture content) of the electrolyte membrane and the impedance of the fuel cell stack 10, the impedance of the fuel cell stack 10 is calculated in step S1, for example. In S3, the impedance of the fuel cell stack 10 may be compared with a predetermined value to determine whether or not the operation state is likely to cause flooding.

  In the above embodiment, as the operation history of the fuel cell system 100 for determining the degree of deterioration of the catalyst with time, the total operation time of the fuel cell system 100, the time when the stack voltage is equal to or higher than the catalyst deterioration voltage, However, the present invention is not limited to this, and the fluctuation range of the stack voltage or the number of times the stack voltage has crossed the catalyst deterioration voltage may be used as the operation history.

  In the above embodiment, the hydrogen non-circulation type fuel cell system 100 has been described as an example. However, a hydrogen circulation type fuel cell system may be used.

DESCRIPTION OF SYMBOLS 1 Fuel cell single cell 10 Fuel cell stack 100 Fuel cell system 200 Electronic control unit (control apparatus)

Claims (1)

A control device for a fuel cell system including a fuel cell stack configured by stacking a plurality of fuel cell single cells that generate electric power by an electrochemical reaction between a fuel gas and an oxidant gas,
Based on the operating history of the fuel cell system, the appropriate IV characteristic according to the degree of deterioration of the catalyst of the fuel cell single cell is estimated,
Based on the appropriate IV characteristics, calculate the appropriate temperature of the single fuel cell according to the load of the fuel cell stack,
The temperature of at least two of the fuel cell single cells of the representative cell selected from the single fuel cell and a flood determination cell that is more likely to be flooded than the representative cell is obtained, and the flood determination cell When the temperature of the flood determination cell is equal to or higher than the appropriate temperature and the temperature difference between the flood determination cell and the representative cell is equal to or greater than a predetermined value, it is determined that at least flooding has occurred in the flood determination cell. Was
A control apparatus for a fuel cell system.

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