JP6186956B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system that supplies anode gas and cathode gas to a fuel cell.

  As a conventional fuel cell system, there is one that raises or lowers the pressure of anode gas supplied to the fuel cell (see Patent Document 1).

JP 2005-243476 A

  In the fuel cell system currently under development, the cathode gas pressure and the anode gas pressure are mutually controlled in order to avoid the deterioration of the electrolyte membrane due to the differential pressure between the cathode gas pressure and the anode gas pressure in the fuel cell.

  In this fuel cell system, in order to maintain the wetness in the fuel cell, water vapor generated by the fuel cell is generated between the cathode off-gas discharged from the fuel cell and the cathode gas supplied to the fuel cell. A humidifier to be replaced is provided.

  A sensor for detecting the cathode gas pressure is provided in the vicinity of the inlet of the humidifier. The maximum value of the pressure loss generated in the humidifier is subtracted from the pressure value detected by the sensor to obtain the cathode gas pressure at the fuel cell inlet. Is estimated. Although the pressure loss of the humidifier used for pressure estimation can be obtained from the flow rate of the cathode gas flowing into the humidifier, it can be operated in consideration of the risk of malfunction due to failure of the cathode gas flow sensor. The maximum pressure loss that can be taken inside is used.

  However, in practice, the smaller the flow rate of the cathode gas flowing into the humidifier, the smaller the actual pressure loss in the humidifier, so the error between the actual value and the maximum value of pressure loss increases. Therefore, there is a case where the estimated value of the cathode gas pressure at the fuel cell inlet is lower than the atmospheric pressure, resulting in a practically impossible result.

  Even in such a case, it is diagnosed whether the estimated differential pressure between the cathode gas pressure and the anode gas pressure estimated to be lower than necessary exceeds the allowable pressure of the electrolyte membrane, and the estimated differential pressure does not exceed the allowable pressure. If it is determined that the pressure exceeds the allowable pressure difference, for example, the anode gas pressure is limited to be low. For this reason, the anode gas pressure is lowered below the pressure value set by the required power, and the generated power of the fuel cell is lowered.

  In this way, the cathode gas pressure may be estimated to be lower than necessary by considering the pressure loss of the humidifier. In this case, the differential pressure between the cathode gas pressure and the anode gas pressure in the fuel cell is more than necessary. Will be greatly estimated. For this reason, there is a concern that the operation of the fuel cell may be restricted more than necessary depending on the result of the differential pressure diagnosis.

  The present invention has been made paying attention to such a problem, and an object of the present invention is to provide a fuel cell system that eliminates the fuel cell operation limitation caused by the estimation error of the cathode gas pressure.

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

  One aspect of the fuel cell system according to the present invention is a fuel cell system that supplies anode gas and cathode gas to the fuel cell and generates electric power in accordance with a load. The fuel cell system includes a humidifier that is provided in the cathode gas supply passage and humidifies the cathode gas, a gas pressure detector that is provided upstream of the humidifier and detects the pressure of the cathode gas, and the gas pressure detector. An estimation unit that estimates a value obtained by subtracting the pressure loss of the humidifier from the pressure detected in step 1 as the pressure of the cathode gas in the fuel cell, and the pressure difference between the pressure of the cathode gas and the pressure of the anode gas in the fuel cell And a diagnostic unit that determines whether or not the fuel cell protection exceeds an allowable threshold, and when the diagnostic unit determines that the value estimated by the estimation unit is lower than atmospheric pressure, The cathode gas pressure in the fuel cell is set to the atmospheric pressure.

  According to this aspect, the diagnostic unit changes the cathode gas pressure from the estimated value to the detected value of the atmospheric pressure when the estimated value of the cathode gas pressure considering the pressure loss of the humidifier is lower than the atmospheric pressure. . Then, the diagnosis unit executes a differential pressure diagnosis as to whether or not the differential pressure between the changed cathode gas pressure and the anode gas pressure exceeds an allowable threshold value.

  As a result, it is possible to avoid performing a differential pressure diagnosis based on an estimated value of the cathode gas pressure that cannot actually occur. As a result of the differential pressure diagnosis, the pressure of the cathode gas or the anode gas is limited more than necessary. This can be prevented.

  Therefore, it is possible to eliminate the operation limitation caused by the estimation error of the cathode gas pressure.

  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 diagram showing a configuration of a fuel cell system according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a monitoring unit of the fuel cell system. FIG. 3 is a diagram showing an estimation method of the inter-electrode differential pressure. FIG. 4 is a flowchart showing a method for diagnosing the differential pressure between the electrodes. FIG. 5 is a block diagram showing the configuration of the anode gas control unit. FIG. 6 is a block diagram showing a configuration of the anode gas differential pressure control unit.

  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 (oxidation electrode). Power is generated by supplying the agent 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).

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

(First embodiment)
FIG. 1 is a schematic diagram of a fuel cell system 100 according to a 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, and a controller 4.

  The fuel cell stack 1 is formed by stacking several hundred fuel cells, and receives the supply of anode gas and cathode gas to generate electric power necessary for driving the vehicle.

  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 / discharge device 2 includes a cathode gas supply passage 21, a cathode gas discharge passage 22, a filter 23, a cathode compressor 24, an intercooler 25, and a water recovery device (hereinafter referred to as "WRD"). ) 26, a cathode pressure regulating valve 27, an air flow sensor 41, a temperature sensor 42, and a cathode pressure sensor 43.

  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. Cathode off-gas is a mixed gas of water vapor generated by cathode gas and electrode reaction.

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

  The cathode compressor 24 is provided in the cathode gas supply passage 21. The cathode compressor 24 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 intercooler 25 is provided in the cathode gas supply passage 21 downstream of the cathode compressor 24. The intercooler 25 cools the cathode gas discharged from the cathode compressor 24.

  The WRD 26 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 27 is provided in the cathode gas discharge passage 22 downstream of the WRD 26. The cathode pressure regulating valve 27 is controlled to be opened and closed by the controller 4 and adjusts the pressure of the cathode gas supplied to the fuel cell stack 1 to a desired pressure.

  The air flow sensor 41 is provided in the cathode gas supply passage 21 upstream of the cathode compressor 24. The air flow sensor 41 detects the flow rate of the cathode gas supplied to the cathode compressor 24 and finally supplied to the fuel cell stack 1 (hereinafter referred to as “stack supply flow rate”).

  The temperature sensor 42 is provided in the cathode gas supply passage 21 between the intercooler 25 and the WRD 26. The temperature sensor 42 detects the temperature on the cathode gas inlet side of the WRD 26 (hereinafter referred to as “WRD inlet temperature”).

  The cathode pressure sensor 43 is provided in the cathode gas supply passage 21 upstream of the WRD 26. Specifically, the cathode pressure sensor 43 is provided in the cathode gas supply passage 21 between the intercooler 25 and the WRD 26. The cathode pressure sensor 43 detects the pressure on the cathode gas inlet side of the WRD 26 (hereinafter referred to as “WRD inlet cathode pressure”).

  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 gas discharge passage 34, a purge valve 35, and an anode pressure sensor 44.

  The high pressure tank 31 stores the anode gas supplied to the fuel cell stack 1 in a 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 4 and adjusts the pressure of the anode gas supplied to the fuel cell stack 1 to a desired pressure.

  The anode pressure sensor 44 is provided in the cathode gas supply passage 21 between the anode pressure regulating valve 33 and the anode gas inlet hole of the fuel cell stack 1. The anode pressure sensor 44 detects the pressure at the anode gas inlet hole of the fuel cell stack 1 (hereinafter referred to as “stack inlet anode pressure”).

  The anode gas discharge passage 34 is a passage through which the anode off gas discharged from the fuel cell stack 1 flows. The anode gas discharge passage 34 has one end connected to the anode gas outlet hole of the fuel cell stack 1 and the other end connected to the cathode gas discharge passage 22. The anode off gas is a mixed gas of excess anode gas that has not been used in the electrode reaction, an inert gas such as nitrogen leaking from the cathode side, and water vapor.

  The anode off gas discharged to the cathode gas discharge passage 22 through the anode gas discharge passage 34 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.

  Further, since the anode off gas contains excess anode gas (hydrogen) that has not been used for the electrode reaction, it is mixed with the cathode off gas and discharged outside the fuel cell system 100. Thereby, the hydrogen concentration in the exhaust gas is set to be equal to or lower than a predetermined concentration.

  The purge valve 35 is provided in the anode gas discharge passage 34. The purge valve 35 is controlled to be opened and closed by the controller 4 and controls the flow rate of the anode off gas discharged from the anode gas discharge passage 34 to the cathode gas discharge passage 22.

  The controller 4 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).

  In addition to the airflow sensor 41, the temperature sensor 42, the cathode pressure sensor 43, and the anode pressure sensor 44, signals from various sensors such as an atmospheric pressure sensor 45 that detects atmospheric pressure are input to the controller 4. The atmospheric pressure sensor 45 is provided, for example, in the passenger compartment. Further, as various sensors, there is an accelerator stroke sensor that detects the amount of depression of an accelerator pedal (hereinafter referred to as “accelerator operation amount”).

  The controller 4 controls the cathode compressor 24, the cathode pressure regulating valve 27, the anode pressure regulating valve 33, the purge valve 35, and the like based on detection signals of these various sensors and operating states of various electric components.

  FIG. 2 is a block diagram illustrating a functional configuration of the controller 4.

  The controller 4 includes a monitoring unit 200 and a system control unit 300.

  The monitoring unit 200 monitors the state of the fuel cell system 100, for example, the pressure state of the anode gas and the cathode gas, the voltage state of the fuel cell stack 1, and the like.

  The monitoring unit 200 causes a difference between the cathode gas pressure and the anode gas pressure in the fuel cell stack 1 because an excessive stress is applied to the electrolyte membrane of the fuel cell stack 1 to deteriorate the power generation performance. The pressure (hereinafter referred to as “differential pressure between electrodes”) is monitored.

  The monitoring unit 200 includes a stack inlet pressure estimation unit 210, a WRD pressure loss holding unit 211, and an inter-electrode differential pressure diagnosis unit 220.

  The WRD pressure loss holding unit 211 holds a WRD pressure loss in advance. The WRD pressure loss is the maximum value of the pressure loss that occurs between the cathode gas inlet end and the cathode gas outlet end of the WRD 26. The WRD pressure loss can be obtained from the flow rate of the cathode gas flowing into the WRD 26. However, the pressure that can be taken during the operation of the fuel cell stack 1 in consideration of the risk of malfunction due to the failure of the flow sensor. The maximum loss is used.

  The stack inlet pressure estimation unit 210 uses the detected value of the cathode pressure sensor 43 and the WRD pressure loss of the WRD pressure loss holding unit 211 to pressure the cathode gas flowing through the inlet of the fuel cell stack 1 (hereinafter referred to as “stack inlet cathode pressure”). ).

  In the present embodiment, the stack inlet pressure estimation unit 210 obtains the WRD inlet cathode pressure from the cathode pressure sensor 43 and subtracts the WRD pressure loss from the WRD inlet cathode pressure as the estimated value of the stack inlet cathode pressure. Output to the differential pressure diagnosis unit 220.

  The inter-electrode differential pressure diagnosis unit 220 diagnoses whether or not the inter-electrode differential pressure between the anode gas pressure and the cathode gas pressure generated in the electrolyte membrane in the fuel cell stack 1 exceeds an allowable threshold value. The allowable threshold value is a threshold value for protecting the electrolyte membrane from an excessive interpolar pressure difference. The inter-electrode differential pressure diagnosis unit 220 makes a diagnosis based on the detection value of the anode pressure sensor 44 and the estimated value estimated by the stack inlet pressure estimation unit 210.

  The system control unit 300 controls the fuel cell system 100. For example, when it is diagnosed that the inter-electrode differential pressure between the anode gas pressure and the cathode gas pressure exceeds the allowable threshold, the system control unit 300 determines whether the anode control is based on the difference between the inter-electrode differential pressure and the allowable threshold. Control gas pressure or cathode gas pressure.

  In such a fuel cell system, the smaller the flow rate of the cathode gas flowing into the WRD 26, the smaller the pressure loss of the WRD 26. Therefore, the error between the actual pressure loss value and the maximum value of the WRD pressure loss holding unit 211 increases. As a result, as shown in FIG. 3, the stack inlet cathode pressure may be estimated to an unrealistic pressure value.

  FIG. 3 is a diagram showing the differential pressure between the electrodes when the flow rate of the cathode gas flowing to the WRD 26 is small.

  FIG. 3 shows the stack inlet anode pressure detected by the anode pressure sensor 44, the WRD inlet cathode pressure detected by the cathode pressure sensor 43, and the atmospheric pressure detected by the atmospheric pressure sensor 45.

  The estimated differential pressure between the anode gas pressure Pa_gs and the estimated value Pc_gs of the cathode gas pressure considering the sensor error is indicated by a broken line, and the actual differential pressure is indicated by a solid line.

  The anode gas pressure Pa_gs is a value obtained by adding the error Er3 of the anode pressure sensor 44 to the stack inlet anode pressure detected by the anode pressure sensor 44.

  The cathode gas pressure Pc_gs is a value obtained by subtracting the maximum value of the WRD pressure loss from the pressure value obtained by subtracting the error Er1 of the cathode pressure sensor 43 from the WRD inlet cathode pressure Pc_wrd detected by the cathode pressure sensor 43.

  In FIG. 3, since the flow rate of the cathode gas flowing into the WRD 26 is small and the pressure loss of the WRD 26 is small, and the error between the maximum value of the WRD pressure loss and the actual value is large, the estimated value Pc_gs of the cathode gas pressure is large. Estimated lower than atmospheric pressure. However, since the cathode gas supply passage 21 communicates with the outside air, it is practically impossible that the cathode gas pressure becomes lower than the atmospheric pressure.

  Even in such a case, it is diagnosed whether the estimated differential pressure between the estimated value Pc_gs of the cathode gas pressure and the anode gas pressure Pa_gs, which cannot actually occur, exceeds the allowable threshold value. When it is determined that the estimated differential pressure exceeds the allowable threshold, for example, the anode gas pressure is limited to be low so as not to exceed the allowable threshold.

  Therefore, in the present invention, when the estimated value of the stack inlet cathode pressure is lower than the atmospheric pressure using the atmospheric pressure sensor 45, the estimated value of the stack inlet cathode pressure is changed to the atmospheric pressure and then the differential pressure diagnosis is performed. Do.

  FIG. 4 is a follow chart showing a method for diagnosing the differential pressure between the electrodes in the first embodiment of the present invention.

  First, in step S <b> 901, the inter-electrode differential pressure diagnosis unit 220 acquires the stack inlet anode pressure Pag from the anode pressure sensor 44.

  In step S902, the stack inlet pressure estimation unit 210 acquires the WRD inlet cathode pressure Pcg_wrd from the cathode pressure sensor 43.

  In step S903, the stack inlet pressure estimation unit 210 acquires the WRD pressure loss from the WRD pressure loss holding unit 211, and estimates the value obtained by subtracting the WRD pressure loss from the WRD inlet cathode pressure Pcg_wrd as the stack inlet cathode pressure Pcg.

  In step S <b> 904, the inter-electrode differential pressure diagnosis unit 220 acquires the atmospheric pressure detection value Pair from the atmospheric pressure sensor 45.

  In step S905, the inter-electrode differential pressure diagnosis unit 220 determines whether the stack inlet cathode pressure Pcg is equal to or higher than the atmospheric pressure Pair. The inter-electrode differential pressure diagnosis unit 220 sets the stack inlet cathode pressure Pcg as the cathode gas pressure in the fuel cell stack 1 when the stack inlet cathode pressure Pcg is equal to or higher than the atmospheric pressure Pair.

  Thereafter, in step S906, the inter-electrode differential pressure diagnosis unit 220 sets a value obtained by subtracting the stack inlet cathode pressure Pcg from the stack inlet anode pressure Pag as the inter-electrode differential pressure Pd.

  In step S907, the inter-electrode differential pressure diagnosis unit 220 sets a value obtained by adding the error Er_cg of the cathode pressure sensor 43 to a predetermined allowable differential pressure as the allowable threshold Th. The allowable differential pressure is a value determined by the stress allowable in the electrolyte membrane. The value of the allowable differential pressure is determined based on experimental data, for example.

  On the other hand, when the stack inlet cathode pressure Pcg is lower than the atmospheric pressure Pair in step S905, the inter-electrode differential pressure diagnosis unit 220 sets the atmospheric pressure Pair as the cathode gas pressure in the fuel cell stack 1.

  Thereafter, in step S910, the inter-electrode differential pressure diagnosis unit 220 sets a value obtained by subtracting the atmospheric pressure Pair from the stack inlet anode pressure Pag as the inter-electrode differential pressure Pd.

  In step S911, the inter-electrode differential pressure diagnosis unit 220 sets a value obtained by adding the error Er_air of the atmospheric pressure sensor 45 to the allowable differential pressure as the allowable threshold Th. In the present embodiment, the error Er_air of the atmospheric pressure sensor 45 is smaller than the error Er_cg of the cathode pressure sensor 43. The atmospheric pressure sensor 45 is a detector having a narrower detectable range than the cathode pressure sensor 43. In general, the detection error is smaller as the detection range is narrower.

  In step S908, the inter-electrode differential pressure diagnosis unit 220 determines whether the inter-electrode differential pressure Pd exceeds the allowable threshold Th.

  In step S909, the inter-electrode differential pressure diagnosis unit 220 outputs an abnormality command to the system control unit 300 when the inter-electrode differential pressure Pd exceeds the allowable threshold Th. When receiving the abnormality command, the system control unit 300 reduces the anode gas pressure.

  On the other hand, in step S912, the inter-electrode differential pressure diagnosis unit 220 outputs a normal command to the system control unit 300 when the inter-electrode differential pressure Pd is less than the allowable threshold Th. After the processing of step S909 or step S912, the series of processing from step S901 to step S912 of the diagnostic method ends.

  According to the first embodiment of the present invention, the inter-electrode differential pressure diagnosis unit 220 estimates the stack inlet cathode pressure using the maximum value of the pressure loss of the WRD 26, and as a result, the estimated value becomes lower than the atmospheric pressure. In this case, the cathode gas pressure is changed from the estimated value to the detected value of the atmospheric pressure. Then, the inter-electrode differential pressure diagnosis unit 220 executes a differential pressure diagnosis as to whether or not the inter-electrode differential pressure between the changed cathode gas pressure and anode gas pressure exceeds an allowable threshold.

  Thereby, the inter-electrode differential pressure diagnosis unit 220 can avoid performing the differential pressure diagnosis based on the estimated value of the stack inlet cathode pressure lower than the atmospheric pressure. Therefore, as a result of differential pressure diagnosis, it is possible to prevent the pressure difference between the electrodes from being overestimated based on an estimated value that cannot actually occur, and preventing the cathode gas and anode gas pressure from being restricted more than necessary. Can do.

  Therefore, it is possible to eliminate the operation restriction caused by the estimation error of the cathode gas pressure in the fuel cell stack 1.

  Further, a detection error of the pressure sensor is added to the allowable threshold value used for the differential pressure diagnosis. As shown in FIG. 3, the detection error Er1 of the atmospheric pressure sensor 45 is smaller than the detection error Er2 of the cathode pressure sensor 43 used to estimate the stack inlet cathode pressure.

  Therefore, in this embodiment, when the estimated value of the stack inlet cathode pressure is changed to atmospheric pressure, the inter-electrode differential pressure diagnosis unit 220 increases the sensor error added to the allowable threshold from the error of the cathode pressure sensor 43. Switching to the error of the atmospheric pressure sensor 45.

  Since the detection error of the atmospheric pressure sensor 45 is smaller than the detection error of the cathode pressure sensor 43, by switching the sensor error to be added to the allowable threshold value to the detection error of the atmospheric pressure sensor 45, the diagnostic error of the differential pressure between the electrodes can be reduced. can do.

  Further, in the present embodiment, the inter-electrode differential pressure diagnosis unit 220 determines that the differential pressure between the atmospheric pressure and the stack inlet anode pressure has an allowable threshold when the estimated value estimated by the stack inlet pressure estimation unit 210 is lower than the atmospheric pressure. When it exceeds, an abnormal command is output. When the system control unit 300 receives the abnormality command, the system control unit 300 limits the pressure of the anode gas so as not to exceed the allowable threshold.

  In this way, changing the cathode gas pressure to atmospheric pressure reduces the estimated differential pressure and approaches the actual differential pressure. In this state, the pressure of the anode gas or cathode gas is limited, so the excess differential pressure limit is relaxed. can do.

  In the first embodiment, the example in which the estimated value of the stack inlet cathode pressure is changed to the atmospheric pressure when the estimated value is lower than the atmospheric pressure has been described. However, such an estimation error correction process constitutes the system control unit 300. This can also be applied to differential pressure control of the anode gas control unit. Thus, an application example of the anode gas control unit to the differential pressure control will be described in the second embodiment.

(Second Embodiment)
FIG. 5 is a diagram illustrating a configuration example of the anode gas control unit 310 according to the second embodiment of the present invention.

  The anode gas control unit 310 pulsates the pressure of the anode gas by controlling the anode pressure regulating valve 33 in order to push out impurities such as nitrogen and water vapor remaining in the fuel cell stack 1. In this embodiment, the pulsation lower limit pressure of the anode gas is set based on the pressure of the cathode gas for the purpose of reducing the inter-electrode differential pressure as much as possible.

  The anode gas control unit 310 includes an excessive pressure prevention upper limit value calculation unit 321, an anode gas differential pressure control unit 400, a target pulsation width calculation unit 323, a target upper limit pressure calculation unit 324, a pulsation upper limit pressure setting unit 325, And a pulsation waveform calculation unit 326.

  The excessive pressure prevention upper limit value calculation unit 321 calculates an excessive anode pressure prevention upper limit value for preventing an excessive pressure of the anode gas, and outputs the calculation result to the pulsation upper limit pressure setting unit 325. The excessive anode pressure prevention upper limit value is stored in advance in the excessive pressure prevention upper limit value calculation unit 321, for example, and is determined in consideration of the durability of the anode gas flow path in the fuel cell stack 1.

  The anode gas differential pressure control unit 400 controls the pressure of the anode gas so that the inter-electrode differential pressure does not exceed the allowable threshold value in order to prevent an excessive inter-electrode differential pressure on the electrolyte membrane. In the present embodiment, the anode gas differential pressure control unit 400 calculates the excessive differential pressure prevention upper limit value using the WRD inlet cathode pressure and the detected value of the atmospheric pressure. The anode gas differential pressure control unit 400 outputs the excessive differential pressure prevention upper limit value to the pulsation upper limit pressure setting unit 325. The detailed configuration of the anode gas differential pressure control unit 400 will be described later with reference to FIG.

  The target pulsation width calculation unit 323 calculates a target value of the pulsation width for ensuring impurity discharge based on a target value of power generation current taken out from the fuel cell stack 1 (hereinafter referred to as “target current”). The target pulsation width calculator 323 increases the target value of the pulsation width as the target current increases.

  The target current is set based on a load such as a drive motor connected to the fuel cell stack 1. For example, as the accelerator operation amount increases, the required power required for the drive motor increases, so the target current is set to a large value. The target current is also adjusted by detection signals of various sensors provided in the fuel cell system 100, operating states of various electric components, and the like.

  In the present embodiment, the target pulsation width calculation unit 323 stores in advance a pulsation width map in which the generated current and the pulsation width are associated with each other. When the target pulsation width calculation unit 323 receives the target current, the target pulsation width calculation unit 323 outputs a target value of the pulsation width associated with the target current to the target upper limit pressure calculation unit 324 with reference to the pulsation width map.

  The target upper limit pressure calculation unit 324 acquires the target value of the pulsation width from the target upper limit pressure calculation unit 324 and acquires the target cathode pressure from the pulsation lower limit pressure signal line 327. The target cathode pressure is a target value of the cathode gas pressure necessary for power generation of the fuel cell stack 1, and is set based on the target current.

  The target upper limit pressure calculation unit 324 adds the target value of the pulsation width to the target cathode pressure, and outputs the added value to the pulsation upper limit pressure setting unit 325 as the target upper limit pressure.

  The pulsation upper limit pressure setting unit 325 selects the smallest value among the excessive anode pressure prevention upper limit value, the excessive differential pressure prevention upper limit value, and the calculated value of the target upper limit pressure, and pulsates using the selected value as the pulsation upper limit pressure. The waveform calculation unit 326 is set.

  For example, in a situation where the excessive differential pressure prevention upper limit value is smaller than the excessive anode pressure prevention upper limit value, and the target upper limit pressure exceeds the excessive differential pressure prevention upper limit value as the target current increases, the pulsation upper limit pressure setting unit 325 The pulsation upper limit pressure is limited to an excessive differential pressure prevention upper limit value.

  Alternatively, the stack input cathode pressure increases as the target current increases, and the excessive differential pressure prevention upper limit value may become higher than the excessive anode pressure prevention upper limit value. In this case, when the target upper limit pressure exceeds the excessive differential pressure prevention upper limit value, the pulsation upper limit pressure setting unit 325 limits the pulsation upper limit pressure to the excessive anode pressure prevention upper limit value.

  The pulsation waveform calculation unit 326 receives the pulsation upper limit pressure from the pulsation upper limit pressure setting unit 325 and also receives the target cathode pressure as the pulsation lower limit pressure. Further, the pulsation waveform calculator 326 acquires the stack inlet anode pressure from the anode pressure sensor 44. The pulsation waveform calculation unit 326 calculates a target value of the anode gas pressure (hereinafter referred to as “target anode pressure”) based on the set values of the pulsation upper limit pressure and the pulsation lower limit pressure and the detected value of the stack inlet anode pressure. .

  For example, the pulsation waveform calculation unit 326 sets the target anode pressure to the pulsation upper limit pressure and switches the target anode gas pressure to the pulsation lower limit pressure when it is confirmed that the stack inlet anode pressure rises to the pulsation upper limit pressure. Then, after confirming that the stack inlet anode pressure has decreased to the pulsation lower limit pressure, the pulsation waveform calculation unit 326 sets the target anode gas pressure to the pulsation upper limit pressure again. In this way, the pulsation waveform calculation unit 326 pulsates the pressure of the anode gas supplied to the fuel cell stack 1.

  FIG. 6 is a block diagram showing a detailed configuration of the anode gas differential pressure control unit 400.

  The anode gas differential pressure control unit 400 includes a WRD pressure loss holding unit 411, a stack inlet pressure calculation unit 412, a cathode pressure switching unit 413, an excessive differential pressure prevention upper limit value calculation unit 414, and a threshold setting unit 420. . The WRD pressure loss holding unit 411 is the same as the WRD pressure loss holding unit 211 shown in FIG.

  The stack inlet pressure calculation unit 412 acquires the detected value of the WRD inlet cathode pressure from the cathode pressure sensor 43, and subtracts the maximum value of the pressure loss held in the WRD pressure loss holding unit 411 from the detected value. The stack inlet pressure calculation unit 412 outputs the subtracted value to the cathode pressure switching unit 413 as an estimated value of the stack inlet cathode pressure.

  The cathode pressure switching unit 413 acquires the estimated value of the stack inlet cathode pressure from the stack inlet pressure calculation unit 412 and acquires the detected value of atmospheric pressure from the atmospheric pressure sensor 45. The cathode pressure switching unit 413 selects the larger value of the estimated value of the stack inlet cathode pressure and the detected value of the atmospheric pressure, and uses the selected value as the cathode gas pressure in the fuel cell stack 1 to prevent excessive differential pressure. The data is output to the upper limit calculator 414.

  For example, when the estimated value of the stack inlet cathode pressure is smaller than the atmospheric pressure, the cathode pressure switching unit 413 outputs the selected larger atmospheric pressure as the cathode gas pressure.

  Further, when the selected value is an estimated value of the stack inlet cathode pressure, the cathode pressure switching unit 413 sets the sensor switching flag to “0”, and the selected value is the detection value of the atmospheric pressure sensor. In this case, the sensor switching flag is switched from “0” to “1”.

  The threshold value setting unit 420 sets an allowable threshold value for protecting the electrolyte membrane in the excessive differential pressure prevention upper limit value calculation unit 414.

  The threshold setting unit 420 includes an allowable differential pressure holding unit 421, a cathode pressure sensor error holding unit 422, an atmospheric pressure sensor error holding unit 423, a sensor error switching unit 424, and an allowable threshold value calculating unit 425.

  The permissible differential pressure holding unit 421 holds the withstand pressure upper limit value of the inter-electrode differential pressure that can be allowed by the electrolyte membrane as the permissible differential pressure between the cathode gas pressure and the anode gas pressure.

  The cathode pressure sensor error holding unit 422 holds an error value related to a detection error (sensor error) of the cathode pressure sensor 43.

  As the error value related to the cathode pressure sensor 43, for example, a square sum average value of the detection error of the anode pressure sensor 44 used in the pulsation control of the anode gas and the detection error of the cathode pressure sensor 43 is used. Note that the mean square value of the detection errors and control errors of the cathode pressure sensor 43 and the anode pressure sensor 44 may be used. Thereby, it can prevent more reliably that an excessive differential pressure | voltage arises in an electrolyte membrane by a detection error and a control error.

  The atmospheric pressure sensor error holding unit 423 holds an error value related to the detection error of the atmospheric pressure sensor 45.

  As the error value related to the detection error of the atmospheric pressure sensor 45, the square sum average value of the detection errors of the anode pressure sensor 44 and the atmospheric pressure sensor 45 may be used similarly to the error value related to the cathode pressure sensor 43. Or you may use the square sum average value of each detection error of the anode pressure sensor 44 and the atmospheric pressure sensor 45, and a control error. Also in this case, an excessive differential pressure with respect to the electrolyte membrane due to a detection error and a control error can be prevented more reliably.

  Based on the sensor switching flag, the sensor error switching unit 424 switches the sensor error amount that should be considered as the allowable threshold value from the error value of the cathode pressure sensor error holding unit 422 to the error value of the atmospheric pressure sensor error holding unit 423.

  For example, when the sensor switching flag indicates “0”, the sensor error switching unit 424 uses the estimated value of the stack inlet cathode pressure for calculating the excessive differential pressure prevention upper limit value. From 422, the error value is output to the allowable threshold value calculation unit 425.

  In addition, when the sensor switching flag indicates “1”, the sensor error switching unit 424 uses the atmospheric pressure to calculate the excessive differential pressure prevention upper limit value. Therefore, the sensor error switching unit 424 sets the error value from the atmospheric pressure sensor error holding unit 423. The result is output to the allowable threshold calculation unit 425.

  The allowable threshold calculation unit 425 subtracts the sensor error value from the allowable differential pressure held in the allowable differential pressure holding unit 421, and outputs the subtracted value to the excessive differential pressure prevention upper limit value calculation unit 414 as the allowable threshold.

  The excessive differential pressure prevention upper limit value calculation unit 414 adds the cathode gas pressure from the cathode pressure switching unit 413 to the allowable threshold value, and uses the added value as the anode gas excessive pressure difference prevention upper limit value to the pulsation upper limit pressure setting unit 325. Output.

  In this way, the anode gas differential pressure control unit 400 sets the value obtained by adding the allowable threshold to the cathode gas pressure (the excessive differential pressure prevention upper limit value) in the pulsation upper limit pressure setting unit 325, whereby the pulsation upper limit pressure of the anode gas is set. The target anode gas pressure is limited so as not to exceed an acceptable threshold.

  As for the cathode gas pressure, when the estimated value of the stack inlet cathode pressure is lower than the atmospheric pressure, the cathode pressure switching unit 413 determines that the cathode gas pressure does not become lower than the atmospheric pressure. Can be switched to. Thereby, it is possible to avoid setting the excessive differential pressure prevention upper limit value to be low due to the estimated value lower than the atmospheric pressure, so that it is possible to prevent the pulsation operation from being restricted by setting the pulsation upper limit pressure too low.

  As for the permissible threshold, the sensor error switching unit 424 changes the sensor error amount added to the permissible threshold from the error related to the cathode pressure sensor 43 to the error related to the atmospheric pressure sensor 45 when the cathode gas pressure is set to atmospheric pressure. Can be switched. As a result, when the cathode gas pressure is set to atmospheric pressure, the error of the atmospheric pressure sensor 45, which has a smaller detection error than the cathode pressure sensor 43, is appropriately reflected in the allowable threshold. The error can be reduced.

  In this embodiment, the pulsation upper limit pressure is limited by the anode gas differential pressure control. Therefore, as the sensor error increases, the upper limit value for preventing the excessive differential pressure, which is the limit value, must be lowered. Subtract the error.

  On the other hand, in a configuration in which the pulsation lower limit pressure is limited to be low by anode gas differential pressure control, the lower limit value of the pulsation lower limit pressure must be limited to be lower as the sensor error is larger. Therefore, when the cathode gas pressure is set to the atmospheric pressure by the cathode pressure switching unit 413, the sensor error of the atmospheric pressure sensor 45 is added to the allowable differential pressure, and the allowable threshold value is calculated.

  Thus, in the threshold setting unit 420, the sensor error is subtracted from the allowable threshold when the upper limit pressure is limited by differential pressure control, and the sensor error is added to the allowable threshold when the lower limit pressure is limited.

  According to the second embodiment of the present invention, when the estimated value of the stack inlet cathode pressure is lower than the atmospheric pressure, the anode gas differential pressure control unit 400 converts the atmospheric pressure into the cathode gas pressure by the cathode pressure switching unit 413. Is set. The pulsation upper limit pressure setting unit 325 sets the set value of the cathode gas pressure to the pulsation lower limit pressure, adds the target value of the pulsation width to the set value of the pulsation lower limit pressure, and outputs the target upper limit pressure.

  The pulsation upper limit pressure setting unit 325 determines that the differential pressure between the atmospheric pressure and the target upper limit pressure has exceeded the allowable threshold when the target upper limit pressure exceeds the excessive differential pressure prevention upper limit value of the anode gas differential pressure control unit 400. Then, the pulsation upper limit pressure is set to an excessive differential pressure prevention upper limit value. That is, the anode gas differential pressure control unit 400 limits the pulsation upper limit pressure by the excessive differential pressure prevention upper limit value when it is determined that the differential pressure between the atmospheric pressure and the target upper limit pressure exceeds the allowable threshold.

  As described above, the cathode gas pressure is changed from the estimated value to the atmospheric pressure, and the differential control of the pulsation upper limit pressure is executed based on the changed cathode gas pressure, thereby suppressing the limitation of the pulsation width of the anode gas. Can do. For this reason, it is possible to prevent the pulsation operation from being extremely limited by an unrealistic estimated value of the cathode gas pressure.

  In this embodiment, the example in which the pressure of the anode gas is controlled as the differential pressure control performed by the system control unit 300 has been described. However, the differential pressure between the set value of the pulsation upper limit pressure and the set value of the cathode gas pressure is acceptable. The cathode gas pressure may be controlled so as not to exceed the threshold value. In this way, the same effect can be obtained when the differential pressure control is executed by the cathode gas control unit.

  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 this embodiment, the detected value of the stack inlet anode pressure is used to estimate the inter-electrode differential pressure, but a set value of the target anode gas pressure may be used.

  In the present embodiment, the WRD 26 is used as a humidifier that humidifies the cathode gas. However, the humidifier may be any one that causes pressure loss during humidification.

  In addition, the said embodiment can be combined suitably.

100 Fuel cell system 1 Fuel cell stack 26 WRD (humidifier)
43 Cathode pressure sensor (gas pressure detector)
210 Stack inlet pressure estimation unit (estimation unit)
220 Interpolar differential pressure diagnosis unit (diagnosis unit)
300 System controller (differential pressure controller)
325 Pulsation upper limit pressure setting unit (Pulse calculation unit)
400 Anode gas differential pressure control unit (differential pressure control unit)

Claims (4)

A fuel cell system that supplies anode gas and cathode gas to a fuel cell and generates electric power according to a load,
A humidifier provided in the cathode gas supply passage to humidify the cathode gas;
A gas pressure detector that is provided upstream of the humidifier and detects the pressure of the cathode gas;
An estimation unit that estimates a value obtained by subtracting the pressure loss of the humidifier from the pressure detected by the gas pressure detector as the pressure of the cathode gas in the fuel cell;
A diagnostic unit for determining whether or not a differential pressure between the pressure of the cathode gas and the pressure of the anode gas in the fuel cell exceeds an allowable threshold for protecting the fuel cell,
When the diagnosis unit determines that the value estimated by the estimation unit is lower than the atmospheric pressure, the cathode gas pressure in the fuel cell is set to the atmospheric pressure.
Fuel cell system. The fuel cell system according to claim 1, wherein
The pressure of the cathode gas or the anode gas supplied to the fuel cell when the differential pressure between the atmospheric pressure and the anode gas pressure exceeds the allowable threshold when the value estimated by the estimation unit is lower than the atmospheric pressure. A fuel cell system further including a differential pressure control unit for limiting the pressure. The fuel cell system according to claim 1 or 2,
An atmospheric pressure detector provided outside the fuel cell for detecting the atmospheric pressure;
The diagnostic unit adds the error of the atmospheric pressure detector to an allowable threshold when the atmospheric pressure is set as the cathode gas pressure, and when the estimated value is set as the cathode gas pressure. Adding the gas pressure detector error to an acceptable threshold;
Fuel cell system. In the fuel cell system according to any one of claims 1 to 3,
A pulsation calculating unit that calculates the pulsation upper limit pressure of the anode gas based on the pressure of the anode gas based on the pressure of the cathode gas in the fuel cell and the pulsation width necessary for discharging impurities in the fuel cell;
A differential pressure control unit that reduces the pulsation upper limit pressure of the anode gas when the differential pressure between the pulsation upper limit pressure of the anode gas and the pressure of the cathode gas exceeds the allowable threshold;
Including fuel cell system.

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