JP2015125911A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine increase in a hydrogen cross leak amount.SOLUTION: A fuel cell system controls, on the basis of a load of a fuel cell, a pressure of a cathode gas supplied to the fuel cell and makes a pressure of an anode gas supplied to the fuel cell pulsate so that the pressure of the anode gas is higher than that of the cathode gas during pulsation boosting. The fuel cell system detects pressure variation of the anode gas and detects voltage variation of the fuel cell. The fuel cell system changes a cathode pressure and/or an anode pressure so that difference between a pulsation lower limit pressure of the anode gas and the pressure of cathode gas becomes larger, when a phase of the pressure variation and that of the voltage variation are reverse to each other; and determines whether or not a cross leak amount of the anode gas is increasing, on the basis of the phase of the pressure variation and that of the voltage variation after the pressure change.

Description

  The present invention relates to a fuel cell system.

  As a conventional fuel cell system, when the output voltage of the activation overvoltage region measured in a state where the pressure of the anode gas supplied to the fuel cell is maintained higher than the pressure of the cathode gas is below a predetermined voltage value, Some determine that the flow rate of the anode gas that leaks from the anode gas channel to the cathode gas channel through the electrolyte membrane (hereinafter referred to as “hydrogen cross leak amount”) is increasing (see Patent Document 1). . Thus, in this conventional fuel cell system, when the pressure of the anode gas supplied to the fuel cell is made higher than the pressure of the cathode gas, it is determined that the amount of hydrogen cross leak increases if the output voltage decreases. To do.

JP 2003-45466 A

  However, when the pressure of the anode gas supplied to the fuel cell is made higher than the pressure of the cathode gas, the cross-sectional area on the cathode side in the fuel cell decreases due to the pressure difference, the cathode gas flow rate decreases, and the hydrogen cross It has been found that the output voltage may decrease even if the amount of leakage does not increase. Therefore, in the above-described conventional fuel cell system, there is a risk that it is determined that the hydrogen cross leak amount is increasing although the hydrogen cross leak amount is not actually increasing.

  The present invention has been made paying attention to such problems, and an object thereof is to accurately determine an increase in the amount of hydrogen cross leak.

  According to an aspect of the present invention, a fuel cell system is provided in which anode gas and cathode gas are supplied to a fuel cell to generate power. This fuel cell system controls the pressure of the cathode gas supplied to the fuel cell based on the load of the fuel cell, and supplies the fuel cell so that the pressure of the anode gas at the time of pulsation increase is higher than the pressure of the cathode gas. The pressure of the anode gas to pulsate is pulsated. Moreover, the pressure change of anode gas is detected and the voltage change of a fuel cell is detected. Then, when the pressure change phase and the voltage change phase are opposite to each other, the cathode pressure and / or the anode pressure are set so that the differential pressure between the anode gas pulsation lower limit pressure and the cathode gas pressure is increased. Then, based on the pressure change phase and the voltage change phase after the pressure change, it is determined whether or not the cross leak amount of the anode gas is increased.

  According to this aspect, if the cause of the reverse phase is due to an increase in the amount of hydrogen cross leak, the pressure is increased so that the differential pressure increases, that is, the cathode pressure decreases as viewed from the anode side. Even if is changed, the state in which the phase of the pressure fluctuation of the anode pressure and the phase of the cell voltage fluctuation are opposite to each other is maintained. On the other hand, if the cause of the reverse phase is due to a decrease in the flow rate of the cathode gas due to a decrease in the cross-sectional area of the flow path, if the pressure is changed so that the differential pressure increases, The phase of the cell voltage fluctuation is the same phase.

  Therefore, by determining whether or not the hydrogen cross leak amount has increased based on the phase of the pressure fluctuation of the anode pressure after the pressure change and the phase of the cell voltage fluctuation, the pressure fluctuation of the anode pressure before the pressure change is determined. It can be accurately determined whether the cause of the phase and the phase of cell voltage fluctuation being opposite is due to an increase in the amount of hydrogen cross leak.

1 is a schematic perspective view of a fuel cell according to an embodiment of the present invention. It is II-II sectional drawing of the fuel cell of FIG. 1 is a schematic configuration diagram of an anode gas non-circulating fuel cell system according to an embodiment of the present invention. It is a flowchart explaining the pulsation operation control by one Embodiment of this invention. It is a map which calculates a pulsation width based on a target output current and HFR. It is a figure which compares and demonstrates the change of each cell voltage of a normal cell and a leak increase cell during a pulsation driving | operation. It is sectional drawing which shows the mode before the pulsation pressure | voltage rise of a normal cell in which the phase of the pressure fluctuation of an anode pressure and the phase of a cell voltage fluctuation are antiphase. It is sectional drawing which shows the mode after the pulsation pressure | voltage rise of the normal cell in which the phase of the pressure fluctuation of an anode pressure and the phase of a cell voltage fluctuation are antiphase. It is the figure which showed each cell voltage fluctuation | variation of the normal cell during a pulsation driving | operation, and before and after reducing a cathode pressure, and comparing it. It is the figure which showed each cell voltage fluctuation | variation of the normal cell in a pulsation driving | operation, and a flow rate fall cell before and after reducing a cathode pressure. It is a flowchart explaining the hydrogen cross leak determination control by one Embodiment of this invention.

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

  In a fuel cell, an electrolyte membrane is sandwiched between an anode electrode (fuel electrode) and a cathode electrode (oxidant electrode), an anode gas containing hydrogen in the anode electrode (fuel gas), and a cathode gas containing oxygen in the cathode electrode (oxidant) Electricity is generated by supplying gas. The electrode reaction that proceeds in both the anode electrode and the cathode electrode is as follows.

Anode electrode: 2H ₂ → 4H ⁺ + 4e ⁻ (1)
Cathode electrode: 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2)

  The fuel cell generates an electromotive force of about 1 volt by the electrode reactions (1) and (2).

  1 and 2 are diagrams illustrating the configuration of a fuel cell 10 according to an embodiment of the present invention. FIG. 1 is a schematic perspective view of the fuel cell 10. FIG. 2 is a II-II cross-sectional view of the fuel cell 10 of FIG.

  The fuel cell 10 is configured by arranging an anode separator 12 and a cathode separator 13 on both front and back surfaces of the MEA 11.

  The MEA 11 includes an electrolyte membrane 111, an anode electrode 112, and a cathode electrode 113. The MEA 11 has an anode electrode 112 on one surface of the electrolyte membrane 111 and a cathode electrode 113 on the other surface.

  The electrolyte membrane 111 is a proton-conductive ion exchange membrane formed of a fluorine-based resin. The electrolyte membrane 111 exhibits good electrical conductivity in a wet state.

  The anode electrode 112 includes a catalyst layer 112a and a gas diffusion layer 112b. The catalyst layer 112a is in contact with the electrolyte membrane 111. The catalyst layer 112a is formed of carbon black particles carrying platinum or platinum. The gas diffusion layer 112b is provided outside the catalyst layer 112a (on the opposite side of the electrolyte membrane 111) and is in contact with the anode separator 12. The gas diffusion layer 112b is formed of a member having sufficient gas diffusibility and conductivity, and is formed of, for example, a carbon cloth woven with yarns made of carbon fibers.

  Similarly to the anode electrode 112, the cathode electrode 113 includes a catalyst layer 113a and a gas diffusion layer 113b.

  The anode separator 12 is in contact with the gas diffusion layer 112b. The anode separator 12 has a plurality of groove-shaped anode gas flow passages 121 for supplying anode gas to the anode electrode 112.

  The cathode separator 13 is in contact with the gas diffusion layer 113b. The cathode separator 13 has a plurality of groove-like cathode gas flow paths 131 for supplying cathode gas to the cathode electrode 113.

  The anode gas flowing through the anode gas flow path 121 and the cathode gas flowing through the cathode gas flow path 131 flow in opposite directions in parallel to each other. You may make it flow in the same direction in parallel with each other.

  When such a fuel cell 10 is used as a power source for automobiles, a large amount of electric power is required. Therefore, the fuel cell 10 is used as a fuel cell stack 1 in which several hundred fuel cells are stacked. Then, the fuel cell system 100 that supplies the anode gas and the cathode gas to the fuel cell stack 1 is configured, and electric power for driving the vehicle is taken out.

  FIG. 3 is a schematic diagram of the fuel cell system 100 according to the first embodiment of the present invention.

  The fuel cell system 100 includes a fuel cell stack 1, a cathode gas supply / discharge device 2, an anode gas supply / discharge device 3, a stack cooling device 4, a power system 5, and a controller 6.

  The fuel cell stack 1 is formed by stacking a plurality of fuel cells 10 and receives power supplied from an anode gas and a cathode gas to generate electric power necessary for driving the vehicle. The fuel cell stack 1 includes an anode electrode side output terminal 1a and a cathode electrode side output terminal 1b as terminals for taking out electric power.

  The cathode gas supply / discharge device 2 includes a cathode gas supply passage 21, a cathode gas discharge passage 22, a filter 23, an airflow sensor 24, a cathode compressor 25, a cathode pressure sensor 26, and a water recovery device (Water Recovery Device; (Hereinafter referred to as “WRD”) 27 and a cathode pressure regulating valve 28. The cathode gas supply / discharge device 2 supplies the cathode gas to the fuel cell stack 1 and discharges the cathode off-gas discharged from the fuel cell stack 1 to the outside air.

  The cathode gas supply passage 21 is a passage through which the cathode gas supplied to the fuel cell stack 1 flows. The cathode gas supply passage 21 has one end connected to the filter 23 and the other end connected to the cathode gas inlet hole of the fuel cell stack 1.

  The cathode gas discharge passage 22 is a passage through which the cathode off gas discharged from the fuel cell stack 1 flows. One end of the cathode gas discharge passage 22 is connected to the cathode gas outlet hole of the fuel cell stack 1, and the other end is an open end. The cathode off gas is a mixed gas of the cathode gas and water vapor generated by the electrode reaction.

  The filter 23 removes foreign matters in the cathode gas taken into the cathode gas supply passage 21.

  The air flow sensor 24 is provided in the cathode gas supply passage 21 upstream of the cathode compressor 25. The air flow sensor 24 detects the flow rate of the cathode gas supplied to the cathode compressor 25 and finally supplied to the fuel cell stack 1.

  The cathode compressor 25 is provided in the cathode gas supply passage 21. The cathode compressor 25 takes air (outside air) as cathode gas through the filter 23 into the cathode gas supply passage 21 and supplies it to the fuel cell stack 1.

  The cathode pressure sensor 26 is provided in the cathode gas supply passage 21 between the cathode compressor 25 and the WRD 27. The cathode pressure sensor 26 detects the pressure of the cathode gas supplied to the fuel cell stack 1 (hereinafter referred to as “cathode pressure”).

  The WRD 27 is connected to each of the cathode gas supply passage 21 and the cathode gas discharge passage 22, collects moisture in the cathode off-gas flowing through the cathode gas discharge passage 22, and cathode that flows through the cathode gas supply passage 21 with the collected moisture. Humidify the gas.

  The cathode pressure regulating valve 28 is provided in the cathode gas discharge passage 22 downstream of the WRD 27. The cathode pressure regulating valve 28 is controlled to be opened and closed by the controller 6 and adjusts the pressure of the cathode gas supplied to the fuel cell stack 1 to a desired pressure. It should be noted that a restriction such as an orifice may be provided without providing the cathode pressure regulating valve 28.

  The anode gas supply / discharge device 3 supplies anode gas to the fuel cell stack 1 and discharges anode off-gas discharged from the fuel cell stack 1 to the cathode gas discharge passage 22. The anode gas supply / discharge device 3 includes a high pressure tank 31, an anode gas supply passage 32, an anode pressure regulating valve 33, an anode pressure sensor 34, an anode gas discharge passage 35, a buffer tank 36, a purge passage 37, and a purge. And a valve 38.

  The high pressure tank 31 stores the anode gas (hydrogen) supplied to the fuel cell stack 1 while maintaining the high pressure state.

  The anode gas supply passage 32 is a passage for supplying the anode gas discharged from the high-pressure tank 31 to the fuel cell stack 1. The anode gas supply passage 32 has one end connected to the high pressure tank 31 and the other end connected to the anode gas inlet hole of the fuel cell stack 1.

  The anode pressure regulating valve 33 is provided in the anode gas supply passage 32. The anode pressure regulating valve 33 is controlled to be opened and closed by the controller 6 and adjusts the pressure of the anode gas supplied to the fuel cell stack 1 to a desired pressure.

  The anode pressure sensor 34 is provided in the anode gas supply passage 32 downstream from the anode pressure regulating valve 33 and detects the pressure of the anode gas supplied to the fuel cell stack 1 (hereinafter referred to as “anode pressure”). In this embodiment, this anode pressure is used as the pressure in the anode system from the fuel cell stack 1 to the buffer tank 36.

  The anode gas discharge passage 35 has one end connected to the anode gas outlet hole of the fuel cell stack 1 and the other end connected to the buffer tank 36. The anode gas discharge passage 35 contains excess anode gas that has not been used in the electrode reaction and nitrogen or moisture (product water or water vapor) that has permeated from the cathode gas passage 131 to the anode gas passage 121. A mixed gas of the active gas (hereinafter referred to as “anode off gas”) is discharged.

  The buffer tank 36 temporarily stores the anode off gas that has flowed through the anode gas discharge passage 35. The anode off gas stored in the buffer tank 36 is discharged to the cathode gas discharge passage 22 through the purge passage 37 when the purge valve 38 is opened.

  The purge passage 37 has one end connected to the anode gas discharge passage 35 and the other end connected to the cathode gas discharge passage 22.

  The purge valve 38 is provided in the purge passage 37. The purge valve 38 is controlled to be opened and closed by the controller 6 and controls the flow rate of anode off-gas discharged from the anode gas discharge passage 35 to the cathode gas discharge passage 22 (hereinafter referred to as “bypass flow rate”). In the following description, opening the purge valve 38 and discharging the anode off gas to the cathode gas discharge passage 22 is referred to as “purge” as necessary.

  The anode off gas discharged to the cathode gas discharge passage 22 via the anode gas discharge passage 35 is mixed with the cathode off gas in the cathode gas discharge passage 22 and discharged to the outside of the fuel cell system 100. Since the anode off gas contains surplus hydrogen that has not been used for the electrode reaction, the hydrogen concentration in the exhaust gas is determined in advance by mixing with the cathode off gas and discharging it to the outside of the fuel cell system 100. It is made to become below the predetermined concentration.

  The stack cooling device 4 is a device that cools the fuel cell stack 1 and maintains the fuel cell stack 1 at a temperature suitable for power generation. The stack cooling device 4 includes a cooling water circulation passage 41, a radiator 42, a bypass passage 43, a three-way valve 44, a circulation pump 45, a PTC heater 46, an inlet water temperature sensor 47, and an outlet water temperature sensor 48. .

  The cooling water circulation passage 41 is a passage through which cooling water for cooling the fuel cell stack 1 circulates, and one end is connected to the cooling water inlet hole of the fuel cell stack 1 and the other end is the cooling water of the fuel cell stack 1. Connected to the outlet hole.

  The radiator 42 is provided in the cooling water circulation passage 41. The radiator 42 cools the cooling water discharged from the fuel cell stack 1.

  The bypass passage 43 has one end connected to the coolant circulation passage 41 and the other end connected to the three-way valve 44 so that the coolant can be circulated by bypassing the radiator 42.

  The three-way valve 44 is provided in the cooling water circulation passage 41 on the downstream side of the radiator 42. The three-way valve 44 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 predetermined temperature, the cooling water is circulated so that the cooling water discharged from the fuel cell stack 1 is supplied again to the fuel cell stack 1 via the radiator 42. Switch routes. On the other hand, when the temperature of the cooling water is lower than the predetermined temperature, the cooling water discharged from the cooling water discharged from the fuel cell stack 1 flows through the bypass passage 43 without passing through the radiator 42 and is again fuel cell stack. The circulation path of the cooling water is switched so as to be supplied to 1.

  The circulation pump 45 is provided in the cooling water circulation passage 41 on the downstream side of the three-way valve 44 and circulates the cooling water.

  The PTC heater 46 is provided in the bypass passage 43. The PTC heater 46 is energized when the fuel cell stack 1 is warmed up to raise the temperature of the cooling water.

  The inlet water temperature sensor 47 is provided in the cooling water circulation passage near the cooling water inlet hole of the fuel cell stack 1. The inlet water temperature sensor 47 detects the temperature of cooling water flowing into the fuel cell stack 1 (hereinafter referred to as “inlet water temperature”).

  The outlet water temperature sensor 48 is provided in the cooling water circulation passage in the vicinity of the cooling water outlet hole of the fuel cell stack 1. The outlet water temperature sensor 48 detects the temperature of the cooling water discharged from the fuel cell stack 1 (hereinafter referred to as “outlet water temperature”).

  In the present embodiment, the average water temperature of the inlet water temperature and the outlet water temperature is used as the temperature in the fuel cell stack 1 (hereinafter referred to as “stack temperature”).

  The power system 5 includes a current sensor 51, a voltage sensor 52, a traveling motor 53, an inverter 54, a battery 55, and a DC / DC converter 56.

  The current sensor 51 detects a current taken out from the fuel cell stack 1 (hereinafter referred to as “output current”).

  The voltage sensor 52 detects an inter-terminal voltage (hereinafter referred to as “output voltage”) between the anode electrode side output terminal 1a and the cathode electrode side output terminal 1b. The voltage sensor 52 detects the voltage (hereinafter referred to as “cell voltage”) of each of the fuel cells 10 constituting the fuel cell stack 1 and detects the total voltage of the fuel cell 10 as an output voltage. In addition, you may make it detect the voltage (cell group voltage) for every several sheets of the fuel cell 10. FIG.

  The travel motor 53 is a three-phase AC synchronous motor in which a permanent magnet is embedded in a rotor and a stator coil is wound around a stator. The travel motor 53 functions as an electric motor that is driven to rotate by receiving electric power supplied from the fuel cell stack 1 and the battery 55, and power generation that generates electromotive force at both ends of the stator coil during deceleration of the vehicle in which the rotor is rotated by external force. Function as a machine.

  The inverter 54 includes a plurality of semiconductor switches such as IGBTs (Insulated Gate Bipolar Transistors). The semiconductor switch of the inverter 54 is controlled to be opened / closed by the controller 6, whereby DC power is converted into AC power or AC power is converted into DC power. When the drive motor 53 functions as an electric motor, the inverter 54 converts the combined DC power of the power generated by the fuel cell stack 1 and the output power of the battery 55 into three-phase AC power and supplies the three-phase AC power to the drive motor 53. On the other hand, when the traveling motor 53 functions as a generator, the regenerative power (three-phase alternating current power) of the traveling motor 53 is converted into direct current power and supplied to the battery 55.

  The battery 55 charges the surplus power generated by the fuel cell stack 1 (output current × output voltage) and the regenerative power of the traveling motor 53. The electric power charged in the battery 55 is supplied to auxiliary equipment such as the cathode compressor 25 and the traveling motor 53 as necessary.

  The DC / DC converter 56 is a bidirectional voltage converter that raises and lowers the output voltage of the fuel cell stack 1. By controlling the output voltage of the fuel cell stack 1 by the DC / DC converter 56, the output current of the fuel cell stack 1, and thus the generated power, is controlled.

  The controller 6 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface).

  The controller 6 detects the operating state of the fuel cell system 100 such as an accelerator stroke sensor 61 that detects the amount of depression of the accelerator pedal (hereinafter referred to as “accelerator operation amount”) in addition to the airflow sensor 24 and the like described above. Signals from various sensors are input.

  The controller 6 calculates the target generated power of the fuel cell stack 1 based on the operating state of the fuel cell system 100. Specifically, the target generated power is calculated based on the required power of the traveling motor 53, the required power of auxiliary equipment such as the cathode compressor 25, the charge / discharge request of the battery 55, and the like. Based on the target generated power, the controller 6 calculates a target output current of the fuel cell stack 1 with reference to, for example, a predetermined IV characteristic (current-voltage characteristic) of the fuel cell stack 1.

  Then, the controller 6 controls the output voltage of the fuel cell stack 1 by the DC / DC converter 56 so that the output current of the fuel cell stack 1 becomes the target output current, and supplies the electric power necessary for the traveling motor 53 and the auxiliary machinery. Supply.

  Further, the controller 6 controls the cathode compressor 25, the circulation pump 45, and the like so that the wetness (water content) of the electrolyte membrane 111 becomes a wetness suitable for power generation. Specifically, the internal impedance (High Frequency Resistance; hereinafter referred to as “HFR”) of the fuel cell stack 1 correlated with the wetness of the electrolyte membrane 111 is calculated by, for example, an AC impedance method. Then, the cathode compressor 25 and the circulation pump 45 are controlled so that the HFR becomes the target HFR. The smaller the HFR, the higher the wetness of the electrolyte membrane 111. In the present embodiment, the target HFR is set to a predetermined value suitable for power generation determined in advance through experiments or the like.

  Further, the controller 6 determines the target value of the cathode pressure (hereinafter referred to as “target cathode pressure”) and the target value of the cathode flow rate (hereinafter referred to as “target cathode flow rate”) based on the load of the fuel cell stack 1, that is, the target output current. Is calculated). The target cathode pressure and the target cathode flow rate are set to values higher than the oxygen partial pressure necessary for the electrode reaction at least at the cathode electrode 113 of each fuel cell 10 when the target output current is extracted from the fuel cell stack 1. Is done. The controller 6 controls the cathode compressor 25, the cathode pressure regulating valve 28, and the like so that the cathode pressure and the cathode flow rate become the target cathode pressure and the target cathode flow rate, respectively.

  Further, the controller 6 performs a pulsating operation that periodically increases or decreases the anode pressure based on the operating state of the fuel cell system 100. In the pulsation operation, the anode pressure is periodically raised and lowered within the range of the pulsation upper limit pressure and the pulsation lower limit pressure set according to the target output current of the fuel cell stack 1 to pulsate the anode pressure. By performing such pulsation operation, the liquid water in the anode gas passage 121 is discharged to the anode gas discharge passage 35 when the anode pressure is increased (when the pulsation is increased), and drainage in the anode gas passage 121 is ensured. ing.

  The controller 6 controls the opening and closing of the purge valve 38 based on the operating state of the fuel cell system 100. Thus, the amount of anode off gas (bypass flow rate) discharged from the buffer tank 36 through the purge passage 37 to the outside of the anode system is adjusted, and the anode gas concentration in the anode system is adjusted to a predetermined concentration.

  FIG. 4 is a flowchart illustrating pulsation operation control according to the present embodiment.

  In step S1, the controller 6 refers to the map of FIG. 5 and calculates the pulsation width based on the target output current and the HFR. As shown in the map of FIG. 5, the pulsation width increases as the target output current increases and as the HFR decreases. That is, the pulsation width increases as the amount of water in the fuel cell stack 1 increases.

  In step S2, the controller 6 sets a pressure value equal to or higher than the target cathode pressure calculated based on the target output current as the pulsation lower limit pressure. In this embodiment, a pressure value slightly higher than the target cathode pressure is set as the pulsation lower limit pressure.

  Thus, in this embodiment, the pressure on the anode side in the fuel cell stack 1 is always equal to or higher than the pressure on the cathode side. This is because, for example, if the pulsation lower limit pressure is set to a value lower than the target cathode pressure, the anode side pressure becomes higher than the cathode side pressure in the fuel cell stack 1 by performing the pulsation operation. The state that becomes lower will come periodically. This is because there is a possibility that the MEA 11 is deteriorated due to the cyclic undulation of the MEA 11 due to a pressure difference between the anode side and the cathode side.

  This is merely an example of pressure setting for pulsation operation, and if the pulsation upper limit pressure is higher than the target cathode pressure, the pulsation lower limit pressure may be set to a value lower than the target cathode pressure. In other words, it is sufficient if the anode pressure is pulsated so that the anode pressure becomes higher than the cathode pressure at least when the anode pressure is increased (when pulsation is increased).

  In Step S3, the controller 6 sets a pressure value obtained by adding the pulsation width to the pulsation lower limit pressure as the pulsation upper limit pressure.

  In step S4, the controller 6 determines whether or not the anode pressure is equal to or higher than the pulsation upper limit pressure. If the anode pressure is equal to or higher than the pulsation upper limit pressure, the controller 6 performs the process of step S5 to reduce the anode pressure. On the other hand, if the anode pressure is less than the pulsation upper limit pressure, the process of step S6 is performed.

  In step S5, the controller 6 sets the target anode pressure to the pulsation lower limit pressure.

  In step S6, the controller 6 determines whether or not the anode pressure is equal to or lower than the pulsation lower limit pressure. If the anode pressure is equal to or lower than the pulsation lower limit pressure, the controller 6 performs the process of step S7 to increase the anode pressure. On the other hand, if the anode pressure is higher than the pulsation lower limit pressure, the process of step S8 is performed.

  In step S7, the controller 6 sets the target anode pressure to the pulsation upper limit pressure.

  In step S8, the controller 6 sets the target anode pressure to the same target anode pressure as the previous time.

  In step S9, when the pulsation lower limit pressure is set as the target anode pressure, the controller 6 feedback-controls the anode pressure regulating valve 33 so that the anode pressure becomes the pulsation lower limit pressure. As a result of this feedback control, the opening of the anode pressure regulating valve 33 is normally fully closed, and the supply of anode gas from the high-pressure tank 31 to the fuel cell stack 1 is stopped. Then, the anode gas left in the anode gas flow path 121 is consumed over time due to the electrode reaction of (1) described above, and the anode pressure decreases.

  Further, when the anode gas left in the anode gas channel 121 is consumed, the pressure in the buffer tank 36 temporarily becomes higher than the pressure in the anode gas channel 121 (in the fuel cell stack 1). The anode off gas flows backward from the buffer tank 36 toward the fuel cell stack 1 side.

  At this time, if the purge valve 38 is closed, the anode off-gas that has flowed back from the buffer tank 36 flows into the anode gas channel 121, and the remaining anode gas in the anode gas channel 121 and the anode in the back-flowed anode off-gas. Gas is consumed over time, and the anode pressure further decreases. On the other hand, if the purge valve 38 is opened, the anode off gas flowing backward from the buffer tank 36 is purged from the anode system via the purge passage 37.

  In step S9, when the pulsation upper limit pressure is set as the target anode pressure, the controller 6 feedback-controls the anode pressure regulating valve 33 so that the anode pressure increases to the pulsation upper limit pressure at a predetermined rate of increase in pressure. To do. As a result of this feedback control, the anode pressure regulating valve 33 is opened to a desired opening, anode gas is supplied from the high-pressure tank 31 to the fuel cell stack 1, and the anode pressure increases.

  Here, for example, when a hole is partially generated in the electrolyte membrane 111 due to damage or deterioration with time of the MEA 11, the amount of anode gas (hydrogen crossing) leaking from the anode gas channel 121 to the cathode gas channel 131 through the hole. Leakage) increases. When the amount of hydrogen cross leak increases, the hydrogen concentration in the cathode off-gas discharged from the cathode gas passage 131 to the cathode gas discharge passage 22 increases, and the hydrogen concentration in the exhaust gas finally discharged into the atmosphere becomes combustible. Concentration may be exceeded. In such a state, it is necessary to stop power generation in the fuel cell stack 1. Therefore, when the amount of hydrogen cross leak is increasing, it is required to detect it with high accuracy and not to stop power generation in the fuel cell stack 1 unnecessarily.

  The anode gas leaked from the anode gas channel 121 to the cathode gas channel 131 (hereinafter referred to as “leak hydrogen”) is consumed by reacting with oxygen in the cathode gas at the cathode electrode 113. Therefore, the oxygen concentration in the cathode gas channel 131 decreases as the hydrogen cross leak amount increases. Therefore, the fuel cell 10 (hereinafter referred to as “leak increase cell”) in which the amount of hydrogen cross leak is increased as compared with the cell voltage of a normal fuel cell 10 (hereinafter referred to as “normal cell”) in which no hydrogen cross leak has occurred. Cell voltage) decreases by the decrease in oxygen concentration.

  FIG. 6 is a diagram illustrating how the cell voltages of the normal cell and the leakage increasing cell change during pulsation operation.

  As shown in FIG. 6, during the pulsation operation, the cell voltage of the normal cell fluctuates slightly according to the pulsation of the anode pressure. Specifically, the cell voltage of a normal cell increases with an increase in the anode pressure when the anode pressure is increased toward the pulsation upper limit pressure (hereinafter referred to as “at the time of pulsation boosting”). When the anode pressure is decreased toward the pulsation lower limit pressure (hereinafter referred to as “at the time of pulsation pressure reduction”), the anode pressure decreases in accordance with the decrease in the anode pressure. That is, in the case of a normal cell, the phase of the pressure fluctuation of the anode pressure during the pulsation operation and the phase of the cell voltage fluctuation are the same phase.

  On the other hand, the cell voltage of the leak increasing cell decreases as the anode pressure increases when the pulsation is increased, and increases as the anode pressure decreases when the pulsation is decreased. That is, in the case of the leak increasing cell, the phase of the anode pressure fluctuation during the pulsation operation is opposite to the phase of the cell voltage fluctuation.

  When the pulsation operation is performed, the differential pressure between the anode pressure and the cathode pressure increases during the pulsation pressure increase. That is, the differential pressure (hereinafter referred to as “transmembrane differential pressure”) between the pressure in the anode gas channel 121 and the pressure in the cathode channel 131 sandwiching the electrolyte membrane 111 increases. Therefore, in the leak increasing cell, the amount of hydrogen cross leak increases when the pulsation is increased. As a result, the amount of decrease in the cell voltage due to the consumption of oxygen by reacting with leaked hydrogen is greater than the amount of increase in cell voltage due to the increase in anode pressure. It is considered that the phase and the phase of the cell voltage fluctuation are opposite to each other.

  Therefore, if there is a fuel cell 10 in which the phase of the cell voltage fluctuation is opposite to the phase of the pressure fluctuation of the anode pressure during pulsation operation, the fuel cell 10 may have an increased hydrogen cross leak amount. Conceivable.

  However, it has been found that even when the amount of hydrogen cross leak does not increase, the cell voltage may decrease or may not change during pulsation boosting. That is, it has been found that the phase of the anode pressure fluctuation and the phase of the cell voltage fluctuation may be in opposite phases during pulsating operation even in a normal cell. The reason for this will be described with reference to FIGS.

  FIG. 7 is a cross-sectional view showing a state before pulsation boosting of a normal cell in which the phase of pressure fluctuation of the anode pressure and the phase of cell voltage fluctuation are in opposite phases. FIG. 8 is a cross-sectional view showing a state after pulsation boosting of a normal cell in which the phase of the pressure fluctuation of the anode pressure and the phase of the cell voltage fluctuation are in opposite phases.

  As described above, when the pulsation operation is performed, the transmembrane pressure difference increases during the pulsation pressure increase. Therefore, as shown in FIG. 8, the MEA 11 is pressed to the cathode side during pulsation pressure increase, and the cross-sectional area of the cathode gas flow path 131 decreases, and the cathode gas flow rate may decrease compared to before pulsation pressure increase shown in FIG. is there. As a result, the oxygen concentration in the cathode gas flow channel 131 decreases at the time of pulsation boosting, and the cell due to the decrease in oxygen concentration is higher than the increase in cell voltage due to the increase in anode pressure, as in the case where the amount of cross leak increases. The amount of voltage decrease is larger, and the phase of the anode pressure variation and the phase of the cell voltage variation are opposite to each other even in a normal cell.

  Therefore, in order to accurately detect whether or not the hydrogen cross leak amount is increasing, the cause of the reverse phase of the anode pressure pressure fluctuation phase and the cell voltage fluctuation phase is the hydrogen cross leak amount. It is necessary to determine whether it is due to an increase or due to a decrease in the cathode gas flow rate due to a decrease in the flow path cross-sectional area.

  Therefore, in this embodiment, first, the pressure fluctuation of the anode pressure and the cell voltage fluctuation are detected, and whether or not there is the fuel cell 10 in which the phase of the cell voltage fluctuation is opposite to the phase of the pressure fluctuation of the anode pressure. Determine whether.

  Next, when there is such a fuel cell 10, one or both of the cathode pressure and the anode pressure are changed so that the pressure difference value obtained by subtracting the cathode pressure from the pulsation lower limit pressure increases in the positive direction.

  That is, when the pulsation lower limit pressure is controlled to be equal to or higher than the cathode pressure as in this embodiment, the cathode pressure is decreased or the pulsation lower limit pressure is increased so that the transmembrane pressure difference is increased. Or lower the cathode pressure and raise the pulsation lower limit pressure. On the other hand, if the cathode pressure is controlled to be higher than the pulsation lower limit pressure, for example, the transmembrane pressure difference is reduced until the cathode pressure becomes lower than the pulsation lower limit pressure, and the cathode pressure is reduced. After the pressure becomes equal to or lower than the pulsation lower limit pressure, the cathode pressure is decreased, or the pulsation lower limit pressure is increased, or the cathode pressure is decreased and the pulsation lower limit pressure is increased so that the transmembrane pressure increases. As described above, the differential pressure between the pulsation lower limit pressure and the cathode pressure is increased so that the pressure on the cathode side as viewed from the anode side decreases.

  Finally, it is determined whether or not the hydrogen cross leak amount is increased based on the pressure fluctuation phase of the anode pressure and the phase of the cell voltage fluctuation after changing one or both of the cathode pressure and the anode pressure. .

  The reason why it is possible to determine whether or not the hydrogen cross leak amount has increased based on the phase of the pressure fluctuation of the anode pressure after the pressure change and the phase of the cell voltage fluctuation is described with reference to FIGS. 9 and 10. I will explain.

  FIG. 9 is a diagram showing cell voltage fluctuations of the normal cell and the leak increasing cell during the pulsation operation before and after the cathode pressure is lowered. FIG. 10 shows that two normal cells during pulsation operation (one of which has a cathode gas flow rate decreased due to a decrease in the flow path cross-sectional area, and the anode pressure pressure fluctuation phase and the cell voltage fluctuation phase are opposite phases). It is the figure which showed each cell voltage fluctuation | variation of the normal cell (flow rate fall cell) which has become compared before and after lowering | hanging a cathode pressure.

  As shown in FIG. 9, if the reason why the phase of the anode pressure fluctuation and the phase of the cell voltage fluctuation are opposite is due to an increase in the amount of hydrogen cross leak, for example, the cathode pressure is lowered. Even if the pressure is changed so as to increase the transmembrane pressure difference, the phase of the pressure fluctuation of the anode pressure and the phase of the cell voltage fluctuation remain opposite to each other.

  This is because if the cause of the reverse phase is due to an increase in the amount of hydrogen cross leak, even if the transmembrane pressure difference is increased, the amount of hydrogen cross leak will increase and react with the leaked hydrogen. Only the amount of oxygen in the cathode gas channel 131 increases. For this reason, there is no change in the state where the amount of decrease in cell voltage due to consumption of oxygen by reacting with leaked hydrogen is greater than the amount of increase in cell voltage due to increase in anode pressure.

  On the other hand, as shown in FIG. 10, if the cause of the reverse phase is due to a decrease in the cathode gas flow rate due to a decrease in the cross-sectional area of the flow path during pulsation boosting, for example, the cathode pressure is decreased to When the pressure is changed so as to increase the differential pressure, the phase of the pressure fluctuation of the anode pressure and the phase of the cell voltage fluctuation become the same phase.

  This is because if the cause of the reverse phase is due to a decrease in the cross-sectional area of the flow path at the time of pulsation boosting, the MEA 11 is operated not only after the pulsation boosting but also before the pulsation boosting by increasing the transmembrane pressure difference. As a result, the cathode gas flow path 131 is reduced in cross-sectional area. That is, the cathode gas flow passage 131 is not in a state where the cross sectional area of the cathode gas flow passage 131 is reduced and the cathode gas flow rate is reduced only at the time of pulsation boosting, but is always in a state where the cross sectional area of the cathode gas flow passage 131 is reduced. It becomes.

  Therefore, although the cathode flow rate always decreases and the cell voltage decreases as a whole, the cell voltage increases as the anode pressure increases during pulsation pressure increase and decreases as the anode pressure decreases during pulsation pressure reduction. To come. That is, the phase of the anode pressure fluctuation and the phase of the cell voltage fluctuation are the same.

  Hereinafter, the hydrogen cross leak determination control according to the present embodiment will be described.

  FIG. 11 is a flowchart illustrating the hydrogen cross leak determination control performed by the controller 6.

  In step S11, the controller 6 detects the pressure fluctuation of the anode pressure and the cell voltage fluctuation.

  In step S12, the controller 6 determines whether or not the phase of the anode pressure pressure fluctuation and the phase of the cell voltage fluctuation are opposite to each other. The controller 6 performs the process of step S13 if the phase of the pressure fluctuation of the anode pressure is opposite to the phase of the cell voltage fluctuation, and otherwise ends the current process.

  In step S13, the controller 6 decreases the cathode pressure from the normal time. Specifically, correction for reducing the target cathode pressure calculated based on the target output current is performed. Then, the cathode compressor 25 and the cathode pressure regulating valve 28 are controlled so that the cathode pressure becomes the target cathode pressure corrected to decrease.

  In step S13, the pulsation lower limit pressure may be made higher than normal. Specifically, correction is performed to increase the pulsation lower limit pressure set according to the target cathode pressure. Further, in step S13, the cathode pressure may be lowered than usual and the pulsation lower limit pressure may be made higher than usual.

  In step S14, the controller 6 detects the pressure fluctuation of the anode pressure and the cell voltage fluctuation after the cathode pressure is lowered.

  In step S15, the controller determines whether the phase of the pressure fluctuation of the anode pressure after decreasing the cathode pressure is the same as the phase of the cell voltage fluctuation. If the phase of the pressure fluctuation of the anode pressure and the phase of the cell voltage fluctuation remain unchanged, the controller 6 performs the process of step S16. On the other hand, if the pressure fluctuation phase of the anode pressure and the phase of the cell voltage fluctuation have changed to the same phase, the process of step S17 is performed.

  In step S16, the controller 6 determines that the hydrogen cross leak amount has increased. In this case, power generation in the fuel cell stack 1 is stopped.

  In step S17, the controller 6 determines that the cross-sectional area of the cathode gas flow path 131 is smaller than normal and the cathode flow rate supplied into the fuel cell stack 1 is smaller than the target cathode flow rate, and the fuel The power generation amount of the battery stack 1 is limited. That is, the target output current is reduced to a predetermined upper limit value. Thereby, the pulsation width is reduced and the transmembrane pressure is also reduced. Therefore, a reduction in the cross-sectional area of the cathode gas channel 131 due to the MEA 11 being pressed toward the cathode during pulsation pressure increase is suppressed. As a result, a decrease in the cathode gas flow rate can be suppressed. The operation of the fuel cell system 100 may be continued with the target cathode pressure lowered without limiting the power generation amount of the fuel cell stack 1.

  The fuel cell system 100 according to the present embodiment described above controls the cathode pressure based on the load (target output current) of the fuel cell stack 1, and the anode pressure is set so that the anode pressure at the time of pulsation increase is higher than the cathode pressure. Pulsates. Further, the pressure fluctuation of the anode pressure is detected, and the cell voltage fluctuation is detected.

  When the anode pressure fluctuation phase and the cell voltage fluctuation phase are opposite, the cathode pressure difference value (pressure difference value) between the anode gas pulsation lower limit pressure and the cathode pressure is increased. One or both of the pressure and the anode pressure are changed, and it is determined whether or not the hydrogen cross leak amount is increased based on the phase of the pressure fluctuation of the anode pressure after the pressure change and the phase of the cell voltage fluctuation.

  If the cause of the reverse phase is due to an increase in the amount of hydrogen cross leak, the cathode pressure and anode pressure are set so that the pressure differential value increases, that is, the cathode side pressure decreases as viewed from the anode side. Even if one or both of these are changed, only the amount of oxygen in the cathode gas channel 131 consumed by reacting with leaked hydrogen increases. Therefore, there is no change in the state that the amount of decrease in cell voltage due to consumption of oxygen by reacting with leaked hydrogen is greater than the amount of increase in cell voltage due to increase in anode pressure. Therefore, even after the pressure is changed, the state in which the phase of the pressure fluctuation of the anode pressure is opposite to the phase of the cell voltage fluctuation is maintained.

  On the other hand, if the cause of the reverse phase is due to a decrease in the cathode gas flow rate due to a decrease in the flow path cross-sectional area during pulsation pressure increase, either the cathode pressure or the anode pressure or If both are changed, the MEA 11 is pressed to the cathode side not only after the pulsation boosting but also before the pulsation boosting, and the cross-sectional area of the cathode gas flow path 131 is reduced. That is, the cathode gas flow passage 131 is not in a state where the cross sectional area of the cathode gas flow passage 131 is reduced and the cathode gas flow rate is reduced only at the time of pulsation boosting, but is always in a state where the cross sectional area of the cathode gas flow passage 131 is reduced. It becomes.

  Therefore, although the cathode flow rate always decreases and the cell voltage decreases as a whole, the cell voltage increases as the anode pressure increases during pulsation pressure increase and decreases as the anode pressure decreases during pulsation pressure reduction. To come. That is, the phase of the anode pressure fluctuation and the phase of the cell voltage fluctuation are the same.

  Therefore, as in the fuel cell system 100 according to the present embodiment, it is determined whether or not the hydrogen cross leak amount has increased based on the phase of the pressure fluctuation of the anode pressure after the pressure change and the phase of the cell voltage fluctuation. Thus, it is possible to accurately determine whether the cause of the negative phase change of the anode pressure and the phase of the cell voltage change due to an increase in the hydrogen cross leak amount before the pressure change.

  Further, in the fuel cell system 100 according to the present embodiment, when the phase of the pressure fluctuation of the anode pressure and the phase of the cell voltage fluctuation are opposite, the cathode pressure is set to the load (target output current) of the fuel cell stack 1. ), The supply flow rate of the cathode compressor 25 can be reduced. Therefore, the power consumption of the cathode compressor 25 can be suppressed.

  On the other hand, for example, the target cathode pressure may be set to be equivalent to atmospheric pressure, and the cathode pressure may not be lowered any further. Therefore, in the fuel cell system 100 according to the present embodiment, if the pulsation lower limit pressure is increased when the phase of the pressure fluctuation of the anode pressure is opposite to the phase of the cell voltage fluctuation, the cathode pressure is reduced. Even when the operation state cannot be lowered, the hydrogen cross leak determination can be performed.

  Further, in the fuel cell system 100 according to the present embodiment, when changing the pressure, the cathode pressure is made lower than the pulsation lower limit pressure. As the cathode pressure becomes lower than the pulsation lower limit pressure, the MEA 11 is pressed toward the cathode side even before the pulsation pressure increase, and the cross-sectional area of the cathode gas channel 131 tends to decrease.

  Therefore, by reducing the cathode pressure below the pulsation lower limit pressure, the state where the MEA 11 is pressed to the cathode side and the cross-sectional area of the cathode gas flow channel 131 is reduced after the pressure change can be reliably maintained. Therefore, since the change from the reverse phase to the same phase after the pressure change can be reliably generated, the accuracy of the hydrogen cross leak determination can be improved.

  In addition, the fuel cell system 100 according to the present embodiment determines that the hydrogen cross leak amount has increased if the phase of the pressure fluctuation of the anode pressure after the pressure change and the phase of the cell voltage fluctuation remain in opposite phases. If the phase changes to the same phase, it is determined that the channel cross-sectional area of the cathode gas channel 131 is smaller than normal.

  As a result, the reason why the phase of the anode pressure fluctuation and the phase of the cell voltage fluctuation are opposite is due to an increase in the amount of hydrogen cross leak, or due to a decrease in the channel cross-sectional area during pulsation boosting. Whether the cathode gas flow rate is reduced can be identified.

  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 embodiment, as an example of the fuel cell system, a so-called dead end type system in which the anode off gas is not returned to the anode gas supply passage 32 by a pump or the like has been described. However, a so-called circulation system that returns the anode off gas to the anode gas supply passage 32 by a pump or the like may be used. In this case, the anode gas concentration may be controlled by adjusting the circulation amount of the anode off gas.

  Further, in the above embodiment, the buffer tank 36 is intentionally provided downstream of the fuel cell stack 1, but such a component is not necessarily required, and normal piping or the inside of the fuel cell stack 2 are not necessarily required. The manifold may be regarded as a buffer tank.

  In the above embodiment, the anode pressure is controlled not to be equal to or lower than the cathode pressure in order to suppress the deterioration of the MEA 11. Just do it.

  Further, in the above embodiment, the target cathode pressure is calculated based on the load of the fuel cell stack 1, but other than the load of the fuel cell stack 1, it is necessary for optimal operation of the fuel cell system 100. The target cathode pressure may be set in consideration of various conditions (for example, pressure resistance of parts, heat-resistant protection, etc.). In this case, the cathode pressure may be made lower than the target cathode pressure calculated in consideration of other than the load of the fuel cell stack 1.

6 Controller (cathode pressure control means, anode pressure control means, pressure fluctuation detection means, voltage fluctuation detection means, pressure change means, cross leak judgment means)
100 Fuel cell system

Claims (5)

A fuel cell system for generating power by supplying anode gas and cathode gas to a fuel cell,
Cathode pressure control means for controlling the pressure of the cathode gas supplied to the fuel cell based on the load of the fuel cell;
Anode pressure control means for pulsating the pressure of the anode gas supplied to the fuel cell so that the pressure of the anode gas at the time of pulsation increase is higher than the pressure of the cathode gas;
Pressure fluctuation detecting means for detecting the pressure fluctuation of the anode gas;
Voltage fluctuation detecting means for detecting voltage fluctuation of the fuel cell;
When the phase of the pressure fluctuation and the phase of the voltage fluctuation are opposite to each other, the cathode gas and / or the anode gas is controlled so that the differential pressure between the anode gas pulsation lower limit pressure and the cathode gas pressure increases. Pressure changing means for changing the pressure;
Cross-leak determination means for determining whether or not the amount of cross-leakage of the anode gas is increased based on the phase of the pressure fluctuation after the pressure change and the phase of the voltage fluctuation;
A fuel cell system comprising: The pressure changing means is
Lowering the cathode gas pressure from the cathode gas target pressure calculated by the cathode pressure control means based on the load of the fuel cell;
The fuel cell system according to claim 1. The pressure changing means is
Reducing the pressure of the cathode gas below the pulsation lower limit pressure of the anode gas,
The fuel cell system according to claim 1 or 2, characterized by the above. The pressure changing means is
Making the pulsation lower limit pressure of the anode gas higher than the pulsation lower limit pressure set by the anode pressure control means,
The fuel cell system according to any one of claims 1 to 3, characterized in that: The cross leak judging means
If the phase of the pressure fluctuation after the pressure change and the phase of the voltage fluctuation remain in opposite phases, it is determined that the cross leak amount of the anode gas has increased, and if the phase changes to the same phase, the cathode in the fuel cell Judging that the cross-sectional area of the gas flow path is smaller than normal,
The fuel cell system according to any one of claims 1 to 4, wherein the fuel cell system is provided.

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