JP6149475B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  Patent Document 1 discloses a system that detects an increase in contact resistance of a fuel cell stack due to deterioration over time. Specifically, the inside of the fuel cell stack is controlled to be in a wet state. Then, an increase in the contact resistance of the fuel cell stack is detected based on the difference between the impedance when sufficiently wetted and the reference impedance. Whether or not the wet state is sufficient is determined by the fact that the change in impedance is small even if the wet state is changed.

JP 2008-282682 A

  However, in the determination that the change in impedance is small, it is difficult to set the determination reference value. Depending on the criterion value, there is a possibility that contact resistance cannot be detected accurately due to insufficient wetting. Also, there is a possibility of flooding due to too much water to ensure wetting.

  The present invention has been made paying attention to such conventional problems. It is an object of the present invention to provide a fuel cell system having a deterioration detection technique that can determine that the wet state is optimal for deterioration detection and suppress the above-described inconvenience.

  The present invention solves the above problems by the following means.

One aspect of the fuel cell system according to the present invention includes a fuel cell stack that generates electric power by an electrochemical reaction between a fuel gas supplied to the anode side and an oxidant gas supplied to the cathode side via the electrolyte membrane, a first application unit for applying an AC signal of a first frequency to the fuel cell stack, and an impedance detector for detecting the impedance of the electrolyte membrane based on the output signal of the AC signal and the fuel cell stack of the first frequency, detecting A deterioration detecting unit that detects the degree of deterioration based on the impedance and the reference impedance. Further, a second application unit that applies an AC signal having a second frequency lower than the first frequency to the fuel cell stack, and a phase angle based on the AC signal having the second frequency and the output signal of the fuel cell stack. And a phase angle detector for detecting. And the said deterioration detection part starts the detection of the said deterioration degree based on the phase angle detected by the said phase angle detection part.

  The phase angle at the second frequency increases as it gets wet. In this aspect, the wet state is determined based on this phase angle, and an increase in contact resistance is detected from the impedance when it is determined that the liquid is sufficiently wet and the reference impedance. In addition, flooding due to overwetting can be prevented, and contact resistance (degradation degree) can be accurately detected.

  Embodiments of the present invention and advantages of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram of an anode gas pulsation supply system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a fuel cell stack. FIG. 3 is a perspective view showing an example of a fuel cell stack. FIG. 4 is a schematic diagram for explaining the reaction of the electrolyte membrane in the fuel cell stack. FIG. 5 is a diagram showing a change in impedance when the inside of the fuel cell stack is wetted. FIG. 6 is a diagram showing an equivalent circuit of the fuel cell stack. FIG. 7 is a diagram showing a voltage drop margin with respect to the current of the fuel cell. FIG. 8 is a flowchart showing a contact resistance change (deterioration) detection routine. FIG. 9 is a flowchart showing a reference phase angle setting routine. FIG. 10 is a flowchart showing a wetting control routine after the contact resistance is changed. FIG. 11 is a diagram showing the power generation characteristics (IV characteristics) of the fuel cell stack. FIG. 12 is a flowchart illustrating a reference phase angle setting routine according to the second embodiment. FIG. 13 is a flowchart illustrating a reference phase angle setting routine according to the third embodiment.

(First embodiment)
First, in order to facilitate understanding of the embodiment, an anode gas pulsation supply system using a fuel cell system according to the present invention will be described.

  FIG. 1 is a schematic configuration diagram of an anode gas pulsation supply system according to an embodiment of the present invention.

  The anode gas pulsation supply system 1 includes a fuel cell stack 100, a cathode gas supply / discharge device 3, an anode gas supply / discharge device 4, a stack cooling device 6, and a controller 7.

  A plurality of power generation cells 10 are stacked on the fuel cell stack 100. The fuel cell stack 100 is supplied with the anode gas and the cathode gas, and generates electric power necessary for driving the vehicle (for example, electric power necessary for driving the motor).

  The cathode gas supply / discharge device 3 includes a cathode gas supply channel 31, a filter 32, a cathode compressor 33, a cathode gas discharge passage 35, and a cathode pressure regulating valve 36.

  The cathode gas supply passage 31 is a passage through which the cathode gas supplied to the fuel cell stack 100 flows.

  The filter 32 removes foreign matter from the air (outside air) as the cathode gas. The cathode gas that has passed through the filter 32 flows through the cathode gas supply passage 31.

  A cathode compressor 33 is arranged in the middle of the cathode gas supply passage 31.

  The cathode gas discharge passage 35 is a passage through which the cathode off gas discharged from the fuel cell stack 100 flows. The cathode gas discharge passage 35 is connected to the cathode discharge port 22b of the fuel cell stack 100, and the downstream end is opened to the atmosphere.

  The cathode pressure regulating valve 36 is disposed in the cathode gas discharge passage 35. The cathode pressure regulating valve 36 adjusts the cathode gas supplied from the cathode compressor 33 to a desired pressure. Since the structure of the cathode pressure regulating valve 36 is known, a detailed description is omitted, but a butterfly type valve element built in the housing is driven by a motor. The opening degree of the cathode pressure regulating valve 36 is controlled by the controller 7.

  The anode gas supply / discharge device 4 includes a high pressure tank 41, an anode gas supply passage 42, an anode pressure regulating valve 43, an anode gas discharge passage 45, a purge passage 46, a purge valve 47, and a buffer tank 400. .

  The high pressure tank 41 stores the anode gas supplied to the fuel cell stack 100 in a high pressure state.

  The anode gas supply passage 42 is a passage for supplying the anode gas of the high-pressure tank 41 to the fuel cell stack 100. The anode gas supply passage 42 is connected to the high-pressure tank 41 and the anode supply port 21 a of the fuel cell stack 100.

  The anode pressure regulating valve 43 is provided in the anode gas supply passage 42. The anode pressure regulating valve 43 adjusts the anode gas discharged from the high pressure tank 41 to a desired pressure. The anode pressure regulating valve 43 is an electromagnetic valve whose opening degree is adjusted continuously or stepwise. The opening degree of the anode pressure regulating valve 43 is controlled by the controller 7.

  The anode gas discharge passage 45 is connected to the anode discharge port 21 b of the fuel cell stack 100 and the buffer tank 400. In the anode gas discharge passage 45, a mixed gas (hereinafter referred to as “anode off gas”) of excess anode gas that has not been used for the electrode reaction and an inert gas such as nitrogen or water vapor that has permeated from the cathode side to the anode side. ) Flows.

  The buffer tank 400 temporarily stores the anode off gas that has flowed through the anode gas discharge passage 45. When the anode pressure inside the fuel cell stack 100 decreases, the anode gas in the buffer tank 400 flows backward and is supplied to the fuel cell stack 100.

  The purge passage 46 is connected to the anode gas discharge passage 45 and the cathode gas discharge passage 35.

  The purge valve 47 is provided in the purge passage 46. The purge valve 47 is an electromagnetic valve that is adjusted to be fully open or fully closed. The purge valve 47 is controlled by the controller 7. When the purge valve 47 is opened, the anode off gas in the buffer tank 400 flows through the purge passage 46, mixes with the cathode off gas in the cathode gas discharge passage 35, and is discharged to the outside air. In this way, the anode off gas is mixed with the cathode off gas and discharged to the outside air, so that the anode gas concentration in the outside air exhaust gas is lower than the flammable concentration.

  Moreover, the anode gas concentration in the buffer tank 400 is adjusted by discharging the anode off-gas from the buffer tank 400 to the outside air. If the anode gas concentration (hydrogen concentration) in the buffer tank 400 is too low, the anode gas used for the electrode reaction is insufficient in the operation of supplying the anode gas in a pulsating manner. If it does in this way, while generating efficiency falls, there exists a possibility that a fuel cell may deteriorate. On the other hand, if the anode gas concentration (hydrogen concentration) in the buffer tank 400 is too high, the amount of the anode gas discharged to the outside air together with the inert gas in the anode off-gas through the purge passage 46 increases. Getting worse. Therefore, the purge valve 47 is opened and closed so that the anode gas concentration in the buffer tank 400 becomes an appropriate value in consideration of power generation efficiency and fuel consumption.

  The stack cooling device 6 is a device that cools the fuel cell stack 100 and maintains the fuel cell stack 100 at a temperature suitable for power generation. The stack cooling device 6 includes a cooling water circulation passage 61, a radiator 62, a bypass passage 63, a three-way valve 64, a cooling water pump 65, and a PTC (Positive Temperature Coefficient) heater 66.

  The cooling water circulation passage 61 is a passage through which cooling water for cooling the fuel cell stack 100 circulates. The cooling water circulation passage 61 is connected to the cooling water supply port 23 a and the cooling water discharge port 23 b of the fuel cell stack 100. Below, the cooling water discharge passage 23b side in the cooling water circulation passage 61 will be described as the upstream side, and the cooling water supply port 23a side will be described as the downstream side.

  The radiator 62 is provided in the cooling water circulation passage 61. The radiator 62 cools the cooling water discharged from the fuel cell stack 100.

  The bypass passage 63 allows the cooling water to bypass the radiator 62. The bypass passage 63 is connected to the cooling water circulation passage 61 and the three-way valve 64.

  The three-way valve 64 is provided in the cooling water circulation passage 61 on the downstream side of the radiator 62. The three-way valve 64 switches the cooling water circulation path according to the temperature of the cooling water. Specifically, if the temperature of the cooling water is high, the three-way valve 64 switches so that the cooling water flows through the radiator 62. If the temperature of the cooling water is low, the three-way valve 64 switches so that the cooling water flows through the bypass passage 63.

  The cooling water pump 65 is provided in the cooling water circulation passage 61 on the downstream side of the three-way valve 64. The cooling water pump 65 circulates cooling water.

  The PTC heater 66 is provided in the bypass passage 63. The PTC heater 66 is energized when the fuel cell stack 100 is warmed up to raise the temperature of the cooling water.

  The controller 7 periodically opens and closes the anode pressure regulating valve 43 to periodically increase and decrease the anode pressure. When the anode pressure regulating valve 43 is opened and anode gas is supplied, the anode pressure increases. When the anode pressure regulating valve 43 is closed, the anode gas is consumed by the power generation reaction, and the anode pressure decreases. Such an operation that varies the pressure is called a pulsation supply operation. Further, the controller 7 adjusts the flow rate of the anode off gas discharged from the buffer tank 400 by adjusting the opening of the purge valve 38 so as to keep the anode gas concentration in the buffer tank 400 at a desired concentration.

  By performing the pulsation supply operation, an impurity gas such as nitrogen that has permeated from the cathode side to the anode side through the electrolyte membrane 111 can be pushed into the buffer tank 400. As a result, it is possible to suppress the impure gas from accumulating in the anode channel and hindering the electrode reaction, and stable power generation can be performed.

  2A and 2B are diagrams illustrating a fuel cell stack, FIG. 2A is an external perspective view, and FIG. 2B is an exploded view showing the structure of a power generation cell.

  As shown in FIG. 2A, the fuel cell stack includes a plurality of stacked power generation cells 10 and a current collecting plate 20. The fuel cell stack is a rectangular parallelepiped.

  The power generation cell 10 is a unit cell of a fuel cell. Each power generation cell 10 generates an electromotive voltage of about 1 volt (V). Details of the configuration of each power generation cell 10 will be described later.

  The current collecting plates 20 are a pair and are respectively arranged outside the plurality of stacked power generation cells 10. The current collecting plate 20 is formed of a gas impermeable conductive member such as dense carbon or a metal material.

  One current collecting plate 20 (the current collecting plate 20 on the left front side in FIG. 2A) has an anode supply port 21a, an anode discharge port 21b, a cathode supply port 22a, a cathode along the short side. A discharge port 22b, a cooling water supply port 23a, and a cooling water discharge port 23b are provided. In the present embodiment, the anode supply port 21a, the cooling water supply port 23a, and the cathode discharge port 22b are provided on the right side in the drawing. The cathode supply port 22a, the cooling water discharge port 23b, and the anode discharge port 21b are provided on the left side in the drawing.

  As a method of supplying hydrogen as anode gas to the anode supply port 21a, for example, a method of supplying hydrogen gas directly from a hydrogen storage device or a hydrogen-containing gas reformed by reforming a fuel containing hydrogen is supplied. There are methods. Examples of the hydrogen storage device include a high-pressure gas tank, a liquefied hydrogen tank, and a hydrogen storage alloy tank. Examples of the fuel containing hydrogen include natural gas, methanol, and gasoline. Air is generally used as the cathode gas supplied to the cathode supply port 22a.

  As shown in FIG. 2B, the power generation cell 10 includes an anode separator (anode bipolar plate) 12a and a cathode separator (cathode bipolar plate) on both surfaces of a membrane electrode assembly (MEA) 11. 12b is arranged.

  In the MEA 11, electrode catalyst layers 112 are formed on both surfaces of an electrolyte membrane 111 made of an ion exchange membrane. A gas diffusion layer (GDL) 113 is formed on the electrode catalyst layer 112.

  The electrode catalyst layer 112 is formed of carbon black particles on which platinum is supported, for example.

  The GDL 113 is formed of a member having sufficient gas diffusibility and conductivity, such as carbon fiber.

  The anode gas supplied from the anode supply port 21a flows through this GDL 113a, reacts with the anode electrode catalyst layer 112 (112a), and is discharged from the anode discharge port 21b.

  The cathode gas supplied from the cathode supply port 22a flows through this GDL 113b, reacts with the cathode electrode catalyst layer 112 (112b), and is discharged from the cathode discharge port 22b.

  The anode separator 12a is overlaid on one side of the MEA 11 (back side in FIG. 2B) via the GDL 113a and the seal 14a. The cathode separator 12b is stacked on one side of the MEA 11 (the surface in FIG. 2B) via the GDL 113b and the seal 14b. The seal 14 (14a, 14b) is a rubber-like elastic material such as silicone rubber, ethylene propylene diene monomer (EPDM), or fluorine rubber. The anode separator 12a and the cathode separator 12b are formed by press-molding a separator base made of metal such as stainless steel so that a reaction gas channel is formed on one surface and alternately arranged with a reaction gas channel on the opposite surface. A cooling water flow path is formed. As shown in FIG. 2B, the anode separator 12a and the cathode separator 12b are overlapped to form a cooling water flow path.

  The MEA 11, the anode separator 12a, and the cathode separator 12b are respectively formed with holes 21a, 21b, 22a, 22b, 23a, and 23b, which are overlapped to form an anode supply port (anode supply manifold) 21a and an anode discharge port. (Anode discharge manifold) 21b, cathode supply port (cathode supply manifold) 22a, cathode discharge port (cathode discharge manifold) 22b, cooling water supply port (cooling water supply manifold) 23a and cooling water discharge port (cooling water discharge manifold) 23b Is formed.

  In FIG. 2, the current collector plate 20 on the front side is provided with an anode supply port 21 a, an anode discharge port 21 b, a cathode supply port 22 a, a cathode discharge port 22 b, a cooling water supply port 23 a, and a cooling water discharge port 23 b. However, the present invention is not limited to this. For example, the anode outlet 21b, the cathode outlet 22b, and the cooling water outlet 23b may be provided on the current collecting plate 20 on the back side. Such a type is used in the anode gas pulsation supply system of FIG.

  FIG. 3 is a perspective view showing an example of a fuel cell stack, FIG. 3 (A) shows an exploded state, and FIG. 3 (B) shows an assembled state.

  The fuel cell stack 100 has a structure in which the periphery of a predetermined number of power generation cells 10 is sandwiched between a fastening plate 122 and a reinforcing plate 123.

  The power generation cell 10 has a structure in which separators 12 (an anode separator 12 a and a cathode separator 12 b) are disposed on both front and back surfaces of the MEA module 11.

  A pair of current collecting plates 21 are disposed at both ends of the power generation cell 10 in the stacking direction (pressing direction). A spacer 21 is arranged on one current collecting plate 21 (the current collecting plate 21 in FIG. 2A). Further, end plates 121 are arranged on both outer sides. The end plate 121 is made of metal or resin. A thin fastening plate 122 and a reinforcing plate 123 are disposed around the power generation cell 10.

  Then, the end plate 121, the fastening plate 122, and the reinforcing plate 123 are fastened with bolts 124.

  In this way, the fuel cell stack 100 as shown in FIG. The number of bolts 124 and the positions of the bolt holes are examples.

  FIG. 4 is a schematic diagram for explaining the reaction of the electrolyte membrane in the fuel cell stack.

The fuel cell stack 100 is supplied with reaction gas (cathode gas O ₂ , anode gas H ₂ ) to generate power. The fuel cell stack 100 is configured by stacking hundreds of membrane electrode assemblies (MEA) in which a cathode electrode catalyst layer and an anode electrode catalyst layer are formed on both surfaces of an electrolyte membrane. One of the MEAs is shown in FIG. Here, the cathode gas is supplied to the MEA (cathode in) and discharged from the diagonal side (cathode out), while the anode gas is supplied (anode in) and discharged from the diagonal side (anode out). An example is shown.

  In each membrane electrode assembly (MEA), the following reaction proceeds in the anode electrode catalyst layer and the cathode electrode catalyst layer according to the load to generate power.

As shown in FIG. 4B, as the reaction gas (cathode gas O ₂ ) flows through the cathode flow path, the reaction of the above formula (1-2) proceeds and water vapor is generated. Then, the relative humidity increases on the downstream side of the cathode channel. As a result, the relative humidity difference between the cathode side and the anode side increases. With this relative humidity difference as the driving force, water is back-diffused and the anode upstream side is humidified. This moisture further evaporates from the MEA to the anode channel, and humidifies the reaction gas (anode gas H ₂ ) flowing through the anode channel. Then, it is transported downstream of the anode and humidifies the MEA downstream of the anode.

  In order to generate electric power efficiently by the above reaction, the electrolyte membrane needs to be in an appropriate wet state. If there is little water in the electrolyte membrane and the wetness of the electrolyte membrane is too small, the above reaction will not be promoted. On the other hand, if there is too much water in the electrolyte membrane, excess water overflows into the reaction gas flow path and the gas flow is hindered. In such a case, the reaction is not promoted. Therefore, power is efficiently generated when the electrolyte membrane is in a moderately wet state.

  The wet state of the electrolyte membrane is detected based on, for example, HFR (High Frequency Resistance) obtained using a known AC impedance method. The voltage value of the fuel cell stack 100 when a high-frequency alternating current is superimposed on the output current of the fuel cell stack 100 is detected by a voltage sensor, the voltage amplitude of the superimposed alternating current is calculated based on the voltage value, and the voltage The impedance (HFR) is calculated by dividing the amplitude by the current amplitude of the alternating current superimposed. The larger the impedance (HFR), the dry the electrolyte membrane. The method for calculating impedance (HFR) is not limited to the above method, and for example, a method described in Japanese Patent Application Laid-Open No. 2012-054153 filed by the present applicant may be used.

  By the way, the inventors have found that the internal resistance of the fuel cell stack increases as it deteriorates. If this change in internal resistance is not taken into account, accurate HFR cannot be detected. The inventors considered the cause of the change in internal resistance as follows. That is, a high-pressure anode gas is pulsated and supplied to the fuel cell stack, and the pressure inside the stack fluctuates. Then, over time, the MEA (electrolyte membrane 111, electrode catalyst layer 112, GDL 113) sags and the internal contact resistance increases.

  In Japanese Patent Application Laid-Open No. 2008-282682, the inside of the fuel cell stack is wetted until the impedance hardly changes. That is, as shown in FIG. 5, the impedance changes according to the wet state, but saturates when the wetness increases. An increase in the contact resistance of the fuel cell stack is detected based on the difference between the impedance in this state and the reference impedance.

  However, with such a method, it is difficult to set a determination reference value for determining whether or not the impedance hardly changes. Depending on the criterion value, there is a possibility that the wet state is not sufficient. On the other hand, there is a possibility of flooding due to excessive water in order to ensure wetting.

  Therefore, the present embodiment provides a technique that can detect the increase in the contact resistance of the fuel cell stack at an appropriate timing. First, in order to facilitate understanding of the present embodiment, a basic concept will be described.

  First, the inventor set up an equivalent circuit of the fuel cell stack as shown in FIG.

  That is, the electrolyte membrane resistance is connected in series with the voltage, the reaction resistance and the electric double layer capacitance are further connected in parallel, and the contact resistance is further connected.

  In such a circuit, the electric double layer capacitance becomes conductive by applying a high-frequency (for example, 1000 Hz) AC signal (AC current). Then, there is almost no conduction in the reaction resistance, and the impedance of the portion where the membrane resistance and the contact resistance are connected in series is detected. As the frequency of the alternating signal (alternating current) is lowered, the alternating current hardly flows to the electric double layer capacity side, and the reaction resistance also becomes conductive. For this reason, the phase delay of the output signal with respect to the input signal increases. FIG. 7 shows such a relationship in the Bode diagram. In a normal wet state, the reaction resistance is small (for example, about 0.1Ω), and the characteristic at this time is as shown by a broken line. On the other hand, in an excessively wet state, the reaction resistance is large (for example, about 0.5Ω), and the characteristic at this time is as shown by a solid line. In an excessively wet state, the reaction resistance increases because there is a lot of water and oxygen hardly reaches the electrolyte membrane and becomes difficult to react.

  As is clear from this Bode diagram, the phase lag changes significantly at a second frequency lower than the first frequency (for example, 1000 Hz) when the impedance (HFR) is detected.

  Therefore, in this embodiment, the wet state is determined based on the phase delay when the AC signal of the second frequency is applied, and the contact resistance of the fuel cell stack is increased based on the difference between the impedance at that time and the reference impedance. It was made to detect.

  FIG. 8 is a flowchart showing a contact resistance change (deterioration) detection routine.

  In step S101, the controller determines whether or not the water temperature is higher than a predetermined water temperature. If the water temperature is low, the reaction resistance is greatly changed by the temperature change, so the measurement reliability is poor. Therefore, it is determined whether or not the temperature is a stable region. If the determination result is affirmative, the controller proceeds to step S102, and if the determination result is negative, the controller exits the process.

  In step S102, the controller determines whether or not it is time to detect contact resistance. Since the change in contact resistance occurs gradually, it may not be frequently detected. For example, the detection may be about 1 or 2 times per month. Therefore, the determination may be made after a certain period of time. The determination may be made based on the accumulated power generation time of the fuel cell stack. If the determination result is positive, the controller proceeds to step S103, and if the determination result is negative, the controller exits the process.

  In step S103, the controller starts the wet operation so that the state of the electrolyte membrane of the fuel cell becomes a wet state. Specifically, control is performed so that the amount of drainage from the fuel cell stack is reduced. For this purpose, for example, the cooling water pump 65 may be rotated to increase the flow rate of the cooling water to lower the temperature of the fuel cell stack. The cathode gas flow rate may be reduced by lowering the rotation of the cathode compressor 33. Further, the cathode gas pressure may be increased by reducing the opening of the cathode pressure regulating valve 36. You may combine these suitably. In this way, the wet operation is performed.

  In step S104, the controller increases the concentration of the anode gas supplied to the fuel cell stack. By doing so, hydrogen starvation is prevented. In order to increase the concentration of the anode gas, the operation may be performed so that the hydrogen partial pressure increases. In addition, if the system is not a system that pulsates the anode gas but a system that circulates the anode gas, the circulation amount may be increased.

  In step S105, the controller applies an AC signal (AC current or AC voltage) having the first frequency and the second frequency to the fuel cell. Here, the first frequency is a frequency at which impedance (HFR) can be detected, and is, for example, 1000 Hz. The second frequency is a frequency lower than the first frequency, and the phase angle changes in accordance with the change in wetness. For example, the frequency is about 100 to 300 Hz. These frequencies can be superimposed and applied to the fuel cell.

  In step S106, the controller detects the impedance based on the first frequency and detects the phase angle of the second frequency.

  In step S107, the controller sets a reference phase angle. Specific contents will be described later.

  In step S108, the controller determines whether or not the difference between the detected phase angle value and the reference phase angle is greater than a predetermined value. Thus, it is determined whether or not the contact resistance change (deterioration) of the fuel cell stack can be detected. If the determination result is positive, the controller proceeds to step S109. If the determination result is negative, the controller exits the process.

  In step S109, the controller sets the difference between the detected impedance value and the initial impedance value (reference impedance) as the contact resistance change amount.

  In step S110, the controller stores the contact resistance change amount in an EEPROM (Electrically Erasable Programmable Read Only Memory).

  In step S111, the controller ends the wet operation.

  FIG. 9 is a flowchart showing a reference phase angle setting routine.

  In step S1071, the controller sets the first phase angle as the reference phase angle. This first phase angle may be a phase angle detected by processing step S106 for the first time, or may be a preset initial value. Further, it may be a phase angle in normal operation.

  FIG. 10 is a flowchart showing a wetting control routine after the contact resistance changes, that is, after deterioration.

  In step S201, the controller obtains an initial target impedance at the first frequency. Specifically, a fixed value set in advance may be used. Alternatively, the current value may be input to a preset table to pick up the value.

  In step S202, the controller sets the target impedance by adding the contact resistance change amount to the initial target impedance.

  In step S203, the controller detects the impedance based on the first frequency.

  In step S204, the controller determines whether or not the detected impedance value is equal to the target impedance. If the determination result is negative, the controller proceeds to step S205, and if the determination result is positive, the controller proceeds to step S208.

  In step S205, the controller determines whether or not the detected impedance value is smaller than the target impedance. If the determination result is negative, the controller proceeds to step S206, and if the determination result is positive, the controller proceeds to step S207.

  In step S206, the controller performs a wet operation. Specifically, control is performed so that the amount of drainage from the fuel cell stack is smaller than in normal operation. For this purpose, for example, the cooling water pump 65 may be rotated to increase the flow rate of the cooling water to lower the temperature of the fuel cell stack. The cathode gas flow rate may be reduced by lowering the rotation of the cathode compressor 33. Further, the cathode gas pressure may be increased by reducing the opening of the cathode pressure regulating valve 36. You may combine these suitably. In this way, the wet operation is performed.

  In step S207, the controller performs a dry operation. Specifically, control is performed so that the amount of drainage from the fuel cell stack is greater than in normal operation. For this purpose, for example, the temperature of the fuel cell stack may be raised by lowering the rotation of the cooling water pump 65 to reduce the flow rate of the cooling water. Further, the cathode compressor 33 may be rotated to increase the cathode gas flow rate. The cathode gas pressure may be lowered by increasing the opening of the cathode pressure regulating valve 36. You may combine these suitably. In this way, the dry operation is executed.

  In step S208, the controller executes normal operation.

  As described above, after the contact resistance is changed, that is, after deterioration, the target impedance is corrected and the wetting control is executed.

  As described above, in this embodiment, an AC signal having a second frequency lower than the first frequency for detecting impedance is applied. Then, the phase angle at the second frequency is detected. This phase angle increases as it gets wet. Then, the wet state is determined based on this phase angle, and the contact resistance is increased from the impedance when the wet state is determined to be sufficiently wet (that is, the impedance when the wetness is saturated) and the reference impedance. Is detected. As a result, erroneous detection due to insufficient wetting and flooding due to overwetting can be prevented, and contact resistance (degradation degree) can be detected with high accuracy.

  In the present embodiment, the detection of deterioration is started based on the deviation between the phase angle after the wet change and the reference phase angle. If an attempt is made to determine the wet saturation state by the phase angle alone, there is a possibility that the saturation state cannot be accurately determined when the reaction resistance or the electric double layer capacity changes due to deterioration. By using the phase angle difference between the dry side and the wet side, changes in reaction resistance and electric double layer capacitance due to deterioration can be canceled, so that deterioration (increase in contact resistance) can be detected more accurately.

  Further, when the contact resistance is increased, the impedance detection value of the first frequency is increased by the increase of the contact resistance in the same wet state. Therefore, it is possible to control in a constant wet state by correcting the target impedance of the first frequency to the increasing side based on the increase in contact resistance.

  It is more preferable to detect the phase angle at a current higher than a predetermined current. This will be described with reference to FIG. That is, the power generation characteristics (IV characteristics) of the fuel cell stack are as shown in FIG. 11, and the voltage tends to decrease as the current increases. However, in a region where the current is very small, the voltage becomes very high. Such a region is called an activated overvoltage region. Since the reaction resistance is very high in the extremely low current region where the activation overvoltage is dominant as the cause of the overvoltage change with respect to the current change, the phase angle increases even in a non-wet state, making it difficult to judge the wet state This increases the risk of misjudgment. Therefore, the deterioration (increase in contact resistance) can be detected more accurately by carrying out in a current region larger than the activation overvoltage region, not in such a current region.

(Second Embodiment)
FIG. 12 is a flowchart illustrating a reference phase angle setting routine according to the second embodiment.

  In step S10721, the controller determines whether or not the detected impedance value is smaller than the reference value. Here, the reference value is a value with which it can be determined that the overdried state is not achieved. Even in the overdried state, the impedance may decrease, and therefore, determination is made in step S10721 in order to eliminate such an irregular state. If the determination result is positive, the process proceeds to step S10722, and if the determination result is negative, the process is exited.

  In step S10722, the controller sets the phase angle detection value as the reference phase angle.

  According to this embodiment, it is possible to eliminate an irregular state in which the impedance is lowered in an overdried state. That is, even when the fuel cell stack becomes dry more than expected, the phase angle at the second frequency increases. Therefore, there is a possibility that the wet operation is performed more than necessary when the wet state is determined by the phase angle deviation. On the other hand, in the present embodiment, deterioration (contact) is achieved in a short time by determining the deviation from the phase angle in a state where it can be determined that the dry state is not unexpected by looking at the impedance detected at the first frequency. It is possible to detect an increase in resistance).

(Third embodiment)
FIG. 13 is a flowchart illustrating a reference phase angle setting routine according to the third embodiment.

  In step S10731, the controller determines whether or not the phase angle detection value is smaller than the reference phase angle. If the determination result is affirmative, the process proceeds to step S10732. If the determination result is negative, the process ends.

  In step S10732, the controller sets the phase angle detection value as the reference phase angle.

  The phase angle is changed by changing the wet state of the electrolyte membrane, but the minimum phase angle can be set as the reference phase angle by repeating the above process at a minute interval.

  According to this embodiment, even when the fuel cell stack is in a dry state more than expected, the phase angle at the second frequency is increased. Therefore, there is a possibility that the wet operation is performed more than necessary when the wet state is determined by the phase angle deviation. On the other hand, in the present embodiment, the deterioration (increase in contact resistance) can be detected in a short time by updating the reference phase angle to the minimum value.

  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, FIG. 1 illustrates a system for supplying pulsating anode gas, but the present invention can also be applied to a system in which anode gas circulates.

  In step S108, the deterioration detection is started in accordance with the difference between the phase angle detection value and the reference phase angle. For simplicity, the deterioration is determined depending on whether or not the phase angle detection value exceeds the reference value. The detection may be started.

  In addition, the said embodiment can be combined suitably.

DESCRIPTION OF SYMBOLS 100 Fuel cell stack S105 1st application part, 2nd application part S106 Impedance detection part S108 Phase angle detection part S109 Deterioration detection part

Claims (7)

A fuel cell stack that generates electric power by an electrochemical reaction between a fuel gas supplied to the anode side and an oxidant gas supplied to the cathode side via the electrolyte membrane;
A first application unit for applying an alternating current signal having a first frequency to the fuel cell stack;
An impedance detector for detecting an impedance of the electrolyte membrane based on the alternating current signal of the first frequency and the output signal of the fuel cell stack;
A deterioration detector that detects the degree of deterioration based on the detected impedance and the reference impedance;
In a fuel cell system comprising:
A second application unit that applies an AC signal having a second frequency lower than the first frequency to the fuel cell stack ;
A phase angle detector for detecting a phase angle based on the alternating signal of the second frequency and the output signal of the fuel cell stack;
With
The deterioration detector starts detecting the degree of deterioration based on the phase angle detected by the phase angle detector ;
Fuel cell system. The fuel cell system according to claim 1, wherein
The second frequency is a frequency at which the phase angle changes in response to a change in wetness.
Fuel cell system. The fuel cell system according to claim 1 or 2,
A wet operation unit for changing the wet state of the fuel cell stack to wet;
A reference phase angle setting unit for setting the first phase angle as a reference phase angle;
With
The deterioration detection unit starts detection of the deterioration degree based on a deviation between the phase angle after the wet change and the reference phase angle.
Fuel cell system. The fuel cell system according to claim 1 or 2,
A wet operation unit for changing the wet state of the fuel cell stack to wet;
A reference phase angle setting unit that sets the phase angle when the impedance detection value of the first frequency is smaller than a predetermined value as a reference phase angle when the wet operation is performed;
With
The deterioration detection unit starts detection of the deterioration degree based on a deviation between the phase angle after the wet change and the reference phase angle.
Fuel cell system. The fuel cell system according to claim 1 or 2,
A wet operation unit for changing the wet state of the fuel cell stack to wet;
A reference phase angle setting unit that sets a minimum value of the detected value of the phase angle during wet operation as a reference phase angle;
With
The deterioration detection unit starts detection of the deterioration degree based on a deviation between the phase angle after the wet change and the reference phase angle.
Fuel cell system. In the fuel cell system according to any one of claims 1 to 5,
The phase angle detector detects the phase angle when the output current of the fuel cell is larger than a predetermined value.
Fuel cell system. The fuel cell system according to any one of claims 1 to 6, wherein
An operation unit for operating the fuel cell stack so that the impedance detected by the impedance detection unit becomes a target value;
The target value is set to be larger as the degree of deterioration detected by the deterioration detection unit increases.
Fuel cell system.