JP6287010B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  Some conventional fuel cell systems include a humidifier that humidifies the cathode gas supplied to the fuel cell (see Patent Document 1).

JP 2005-038823 A

  In the fuel cell system currently under development, the pressure on the anode side in the fuel cell is set to be higher than the pressure on the cathode side. Therefore, unless the differential pressure between the membrane electrode assembly on the anode side and the cathode side in the fuel cell (hereinafter referred to as “transmembrane differential pressure”) is not properly managed, unexpected stress is applied to the membrane electrode assembly. It becomes a factor which degrades a fuel cell.

  In the fuel cell system currently under development, a pressure sensor for detecting the pressure of the cathode gas is disposed upstream of the cathode gas humidifier to prevent freezing. Therefore, it is considered that the pressure on the cathode side in the fuel cell is estimated based on the detection value of the pressure sensor in consideration of the pressure loss of the humidifier. The differential pressure (hereinafter referred to as “estimated differential pressure”) between the detected pressure value on the anode side in the fuel cell detected by a sensor or the like and the estimated pressure value on the cathode side in the fuel cell is a predetermined allowable membrane. When the differential pressure exceeds the differential pressure, control for preventing excessive differential pressure is performed to reduce the differential pressure by limiting the upper limit of the pressure of the anode gas.

  Here, if the pressure loss of the humidifier is set to the maximum possible value, the estimated pressure value on the cathode side in the fuel cell will be lower than the actual value, so the estimated differential pressure will be the actual transmembrane pressure difference. It won't get bigger. For this reason, if the estimated differential pressure exceeds the allowable transmembrane differential pressure, the actual transmembrane pressure does not exceed the allowable transmembrane pressure if it is restricted so that the differential pressure does not increase any more. Therefore, it can be said that it is safest to set the pressure loss of the humidifier to the maximum value and calculate the estimated pressure value on the cathode side from the viewpoint of suppressing the excessive transmembrane pressure difference.

  However, if the pressure loss of the humidifier is set to the maximum value, the estimated differential pressure becomes larger than the actual transmembrane pressure difference, so excessive pressure differential prevention control is performed unnecessarily, reducing output. There is a risk of inviting.

  Therefore, the pressure loss of the humidifier should be set to a predetermined value lower than the maximum value in consideration of the actual pressure loss as much as possible. Then, the supply flow rate of the compressor increases and the pressure loss at the humidifier increases. When this is done, the actual pressure loss may be larger than the set predetermined value. As a result, the estimated pressure value on the cathode side becomes higher than the actual value, and the estimated differential pressure may be smaller than the actual transmembrane pressure difference. Therefore, even though the actual transmembrane differential pressure exceeds the allowable transmembrane differential pressure, the excessive differential pressure prevention control may not be performed, and the fuel cell may be deteriorated.

  The present invention has been made paying attention to such a problem, and in the case where the differential pressure excess prevention control is performed based on the estimated differential pressure, the actual transmembrane pressure exceeds the allowable transmembrane pressure. It aims at suppressing it.

  A fuel cell system according to an aspect of the present invention includes a compressor that adjusts the flow rate of cathode gas supplied to a fuel cell, a humidifier that humidifies cathode gas discharged from the compressor, and a compressor provided upstream from the humidifier. Equipped with pressure detection means for detecting the pressure of the discharged cathode gas, the pressure loss of the humidifier is set to a predetermined value, and the estimated pressure value on the cathode side in the fuel cell is calculated according to the detected value of the pressure detection means and the predetermined value When the differential pressure between the detected pressure value on the anode side in the fuel cell and the estimated pressure value exceeds a predetermined allowable transmembrane pressure difference, the differential pressure is reduced. Then, the compressor supply flow rate is set according to the requirements of the fuel cell, the compressor supply flow rate at which the pressure loss of the humidifier becomes a predetermined value is set as the upper limit flow rate, and the compressor supply flow rate set according to the operating state The compressor is controlled based on the smaller of the upper limit flow rate and the upper limit flow rate.

  According to this aspect, the compressor supply flow rate at which the pressure loss of the humidifier becomes a predetermined value is set as the upper limit flow rate, and the compressor flow rate is controlled so as not to exceed the upper limit flow rate. Therefore, it can suppress that the pressure loss of a humidifier becomes more than predetermined value, and can suppress that an actual pressure loss becomes larger than the predetermined value which set.

  Therefore, since the estimated pressure value on the cathode side in the fuel cell can be suppressed from becoming higher than the actual value, the differential pressure between the detected pressure value on the anode side in the fuel cell and the estimated pressure value on the cathode side can be reduced. It can suppress becoming smaller than an actual transmembrane differential pressure. Therefore, when the differential pressure between the detected pressure value on the anode side in the fuel cell and the estimated pressure value on the cathode side exceeds the predetermined allowable transmembrane pressure, limit the differential pressure so that it does not increase any more. Therefore, it is possible to suppress the actual transmembrane pressure difference from exceeding the allowable transmembrane pressure.

1 is a schematic view of a fuel cell system according to a first embodiment of the present invention. It is a flowchart explaining the anode gas supply control by 1st Embodiment of this invention. It is a table which calculates the pulsation width | variety of the anode pressure at the time of implementing pulsation driving | operation based on target output current. It is a block diagram explaining cathode gas supply control by a 1st embodiment of the present invention. It is a block diagram explaining the cathode gas supply control by 2nd Embodiment of this invention. It is a flowchart explaining the upper limit flow volume calculation part by 2nd Embodiment of this invention.

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

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

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

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

  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.

  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 cathode gas (air) to the fuel cell stack 1 and discharges 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, a bypass passage 28, a bypass valve 29, a first air flow sensor 41, a second air flow sensor 42, a cathode pressure sensor 43, and a temperature sensor 44.

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

  The cathode gas discharge passage 22 is a passage through which the cathode off gas discharged from the fuel cell stack 1 flows. One end of the cathode gas discharge passage 22 is connected to the cathode gas outlet hole of the fuel cell stack 1, and the other end is an open end. The cathode off gas is a mixed gas such as oxygen not used in the electrode reaction, nitrogen contained in the cathode gas, and water vapor generated by the electrode reaction.

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

  The cathode compressor 24 is provided in the cathode gas supply passage 21. The cathode compressor 24 takes air as cathode gas into the cathode gas supply passage 21 through the filter 23 and supplies the air 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 bypass passage 28 is provided so that a part of the cathode gas discharged from the cathode compressor 24 can be directly discharged to the cathode gas discharge passage 22 without going through the fuel cell stack 1 as necessary. It is. One end of the bypass passage 28 is connected to the cathode gas supply passage 21 between the cathode compressor 24 and the intercooler 25, and the other end is connected to the cathode gas discharge passage 22 downstream of the cathode pressure regulating valve 27.

  The bypass valve 29 is provided in the bypass passage 28. The bypass valve 29 is controlled to be opened and closed by the controller 4 to adjust the flow rate of the cathode gas flowing through the bypass passage 28 (hereinafter referred to as “bypass flow rate”).

  The first air flow sensor 41 is provided in the cathode gas supply passage 21 upstream from the cathode compressor 24. The first air flow sensor 41 detects the flow rate of the cathode gas supplied to the cathode compressor 24 (hereinafter referred to as “compressor supply flow rate”). Hereinafter, the detection value of the first air flow sensor 41 is referred to as “detected compressor supply flow rate”.

  The second air flow sensor 42 is provided in the cathode gas supply passage downstream of the connection portion with the bypass passage 28. The second air flow sensor 42 detects the flow rate of the cathode gas supplied to the fuel cell stack 1 out of the cathode gas discharged from the cathode compressor 24 (hereinafter referred to as “stack supply flow rate”). The stack supply flow rate is a flow rate obtained by subtracting the bypass flow rate from the compressor supply flow rate. Hereinafter, the detection value of the second air flow sensor 42 is referred to as “detection stack supply flow rate”.

  The cathode pressure sensor 43 is provided in the cathode gas supply passage 21 near the cathode gas inlet side of the WRD 26. The cathode pressure sensor 43 detects the pressure of the cathode gas in the vicinity of the cathode gas inlet side of the WRD 26. Hereinafter, the detected value of the cathode pressure sensor 43 is referred to as “detected cathode pressure”.

  The temperature sensor 44 is provided in the cathode gas supply passage 21 between the intercooler 25 and the WRD 26. The temperature sensor 44 detects the temperature on the cathode gas inlet side of the WRD 26 (hereinafter referred to as “WRD inlet temperature”).

  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 45.

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

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

  The anode pressure regulating valve 33 is provided in the anode gas supply passage 32. The anode pressure regulating valve 33 is controlled to be opened and closed by the controller 4 and adjusts the pressure of the anode gas supplied to the fuel cell stack 1 to a desired 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 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. Since the anode off gas contains excess anode gas that was not used for the electrode reaction, the anode off gas is mixed with the cathode off gas and discharged to the outside of the fuel cell system 100, so that the hydrogen concentration in the exhaust gas is preliminarily set. It is set to be equal to or less 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 adjusts the flow rate of the anode off gas discharged from the anode gas discharge passage 34 to the cathode gas discharge passage 22.

  The anode pressure sensor 45 is provided in the anode gas supply passage 32 downstream of the anode pressure regulating valve 33 and detects the pressure of the anode gas supplied to the fuel cell stack 1 (hereinafter referred to as “anode pressure”). Hereinafter, the detected value of the anode pressure sensor 45 is referred to as “detected anode pressure”.

  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 first airflow sensor 41 and the like described above, the controller 4 includes a current sensor 46 that detects a current (output current) extracted from the fuel cell stack 1 and a voltage sensor that detects an output voltage of the fuel cell stack 1. 47. Signals from various sensors such as an accelerator stroke sensor 48 for detecting the amount of depression of the accelerator pedal (hereinafter referred to as “accelerator operation amount”) and an SOC sensor 49 for detecting the battery charge amount are input.

  The controller 4 detects the operating state of the fuel cell system 100 based on signals from these various sensors, and controls the flow rate and pressure of the anode gas and cathode gas supplied to the fuel cell stack 1.

  Specifically, the cathode compressor 24, the anode pressure regulating valve 33, and the like are controlled so that the pressure on the anode side in the fuel cell stack 1 becomes equal to or higher than the pressure on the cathode side. Therefore, unless the transmembrane pressure difference is properly managed so as not to exceed a predetermined allowable transmembrane pressure difference, an unexpected stress is applied to the membrane electrode assembly, which causes the fuel cell stack 1 to deteriorate. In particular, in this embodiment, in order to ensure drainage performance and the like on the anode side in the fuel cell stack 1, a pulsation operation in which the anode pressure is periodically raised and lowered is performed, so that the transmembrane pressure difference tends to be excessive at the time of pressure increase. More appropriate management of transmembrane pressure difference is needed.

  For this reason, when the transmembrane pressure difference exceeds a predetermined allowable transmembrane pressure difference, an excessive pressure difference is reduced by limiting the upper limit of the anode pressure in the fuel cell stack 1 to reduce the transmembrane pressure difference. I want to implement control.

  Here, the detected value (detected anode pressure) of the anode pressure sensor 45 provided in the anode gas supply passage near the anode gas inlet hole of the fuel cell stack 1 is used as the pressure on the anode side in the fuel cell stack 1. Can do.

  On the other hand, when the cathode pressure sensor 43 is provided in the cathode gas supply passage 21 near the cathode gas inlet hole of the fuel cell stack 1, the cathode pressure sensor 43 may be frozen by moisture in the cathode gas humidified by the WRD 26. Therefore, in this embodiment, the cathode pressure sensor 43 is provided in the cathode gas supply passage 21 upstream of the WRD 26. Therefore, it is desirable to estimate the pressure on the cathode side in the fuel cell stack 1 based on the detected value (detected cathode pressure) of the cathode pressure sensor 43 in consideration of the pressure loss of the WRD 26.

  In this embodiment, the pressure difference (hereinafter referred to as “estimated transmembrane pressure”) between the detected anode pressure and the estimated pressure value on the cathode side in the fuel cell stack 1 (hereinafter referred to as “estimated cathode pressure”). ) Is considered to carry out the control for preventing the excessive pressure difference when the pressure exceeds a predetermined allowable transmembrane pressure difference.

  Here, in addition to protecting the components of the cathode compressor 24 itself, the compressor supply flow rate is set to a value lower than the maximum rated flow rate of the cathode compressor 24 from the viewpoint of pressure resistance and heat resistance protection of the entire system. Therefore, in calculating the estimated cathode pressure, for example, if the pressure loss of the WRD 26 is set to the pressure loss value when the maximum rated flow rate of the cathode compressor 24 is passed through the WRD 26, the estimated cathode pressure is always the fuel cell stack 1 Lower than the actual pressure on the cathode side (hereinafter referred to as “in-stack cathode pressure”). Therefore, the estimated transmembrane pressure does not become larger than the actual transmembrane pressure. Therefore, if the estimated transmembrane pressure does not exceed the allowable transmembrane pressure, the actual transmembrane pressure will not exceed the allowable transmembrane pressure. . Therefore, it can be said that it is safest to calculate the estimated cathode pressure by setting the pressure loss of the WRD 26 to the maximum rated flow rate of the cathode compressor 24 from the viewpoint of suppressing an excessive transmembrane pressure difference.

  However, when the estimated cathode pressure is calculated by setting the pressure loss of the WRD 26 to the pressure loss value when the maximum rated flow rate of the cathode compressor 24 is passed through the WRD 26, the estimated transmembrane pressure is basically the actual transmembrane pressure. Over pressure. For this reason, particularly in a low load region where the pressure loss of the WRD 26 is small, an error between the estimated transmembrane pressure difference and the actual transmembrane pressure difference becomes large, and there is a possibility that the control for preventing excessive pressure differential will be performed unnecessarily. When the differential pressure excess prevention control is performed and, for example, the upper limit of the pressure on the anode side is limited, the drainage performance is lowered, and consequently the output is lowered.

  Therefore, the pressure loss of the WRD 26 is set to a predetermined pressure loss value within a range that can actually be taken during the operation of the fuel cell system 100. However, if this is done, the compressor supply flow rate increases in the high load region and the pressure loss of the WRD 26 When becomes larger, the actual pressure loss may become larger than the predetermined pressure loss value set. As a result, the estimated cathode pressure becomes higher than the in-stack cathode pressure, and the estimated transmembrane pressure may be smaller than the actual transmembrane pressure. As a result, even though the actual transmembrane pressure difference exceeds the allowable transmembrane pressure difference, the excessive pressure differential prevention control may not be performed, and the fuel cell stack 1 may be deteriorated.

  Therefore, in this embodiment, the compressor supply flow rate at which the pressure loss of the WRD 26 becomes a predetermined pressure loss value set in advance is set as the upper limit flow rate, and the cathode compressor 24 is controlled so as not to exceed this upper limit flow rate.

  Hereinafter, the anode gas supply control and the cathode gas supply control according to this embodiment will be described.

  FIG. 2 is a flowchart for explaining anode gas supply control. The controller 4 repeatedly executes this routine at a predetermined calculation cycle.

  In step S <b> 1, the controller 4 calculates the target output current of the fuel cell stack 1 based on the operating state of the fuel cell system 100. Specifically, the target output power of the fuel cell stack 1 is determined based on the required power of an auxiliary machine such as a drive motor (not shown) that generates the driving force of the vehicle and the cathode compressor 24, and the charge / discharge request of the battery. The target output current is calculated from the IV characteristics of the fuel cell stack 1 based on the target output power.

  In Step S2, the controller 4 refers to the table of FIG. 3 and calculates the pulsation width of the anode pressure when performing the pulsation operation based on the target output current. As shown in the table of FIG. 3, the pulsation width is greater when the target output current is higher than when the target output current is low. This is because, as the target output current increases, the amount of water that permeates from the cathode side to the anode side increases, so it is necessary to increase the anode pressure to ensure drainage performance.

  In step S3, the controller 4 sets a pulsation upper limit target pressure and a pulsation lower limit target pressure. Specifically, the detected cathode pressure is set as the pulsation lower limit target pressure, and the pressure obtained by adding the pulsation width to the pulsation lower limit target pressure is set as the pulsation upper limit target pressure.

  Thus, in this embodiment, the pressure on the anode side in the fuel cell stack 1 is always equal to or higher than the pressure on the cathode side. For example, if the pulsation lower limit target pressure is set to a value lower than the detected anode pressure, the pulsation upper limit target pressure may become higher than the detected anode pressure. Therefore, by performing the pulsation operation, a state in which the pressure on the anode side becomes higher than a pressure on the cathode side in the fuel cell stack 1 periodically appears. This is because the membrane / electrode assembly may be deteriorated due to the cyclic undulation of the membrane / electrode assembly due to a pressure difference between the anode side and the cathode side.

  In step S4, the controller 4 calculates an estimated cathode pressure. Specifically, the controller 4 calculates the estimated cathode pressure by subtracting a predetermined pressure loss value determined in advance from the detected cathode pressure. This predetermined pressure loss value is set to a value within a range that can actually be taken during operation of the fuel cell system 100. The specified pressure loss value should be increased from the viewpoint of safety so that the transmembrane pressure does not exceed the allowable transmembrane pressure, but the output is reduced so that the control for preventing excessive pressure differential is not performed unnecessarily. It is better to make it smaller from the viewpoint of prevention. Therefore, it may be set appropriately in consideration of these balances. In the present embodiment, the maximum value within the range that can actually be taken during operation of the fuel cell system 100 (<pressure loss at the maximum rated flow rate) is set.

  In step S5, the controller 4 calculates an estimated transmembrane pressure difference. Specifically, the controller 4 calculates the estimated transmembrane pressure difference obtained by subtracting the estimated cathode pressure from the detected anode pressure.

  In step S6, the controller 4 determines whether or not the estimated transmembrane pressure is greater than the allowable transmembrane pressure. If the estimated transmembrane pressure is less than or equal to the allowable transmembrane pressure, the controller 4 performs the process of step S8, and otherwise performs the process of step S7.

  In step S7, the controller 4 performs an excessive differential pressure prevention control for making the estimated transmembrane pressure equal to or lower than the allowable transmembrane pressure, and corrects to lower the pulsation upper limit target pressure set in step S3. Specifically, a value obtained by subtracting the difference between the estimated transmembrane pressure difference and the allowable transmembrane pressure difference from the pulsation upper limit target pressure set in step S3 is reset as the pulsation upper limit target pressure. In addition, the specific method of the excessive pressure difference prevention control is not limited to this, and the cathode pressure may be increased so that the estimated transmembrane pressure is equal to or lower than the allowable transmembrane pressure, or the anode pressure and the cathode pressure. Each of these may be controlled.

  In step S8, the controller 4 determines whether or not the anode pressure is higher than the pulsation upper limit target pressure. If the anode pressure is equal to or higher than the pulsation upper limit target pressure, the controller 4 performs the process of step S9 to reduce the anode pressure. On the other hand, if the anode pressure is less than the pulsation upper limit target pressure, the process of step S10 is performed.

  In step S9, the controller 4 sets the target anode pressure to the pulsation lower limit target pressure. Thereby, the opening degree of the anode pressure regulating valve 33 is feedback-controlled so that the anode pressure becomes the lower limit target pressure during pulsation. As a result of this feedback control, the opening of the anode pressure regulating valve 33 is normally fully closed, and the supply of anode gas from the high-pressure tank 31 to the fuel cell stack 1 is stopped. As a result, the anode pressure decreases due to the consumption of the anode gas in the fuel cell stack 1 by power generation.

  In Step S10, the controller 4 determines whether or not the anode pressure is equal to or lower than the pulsation lower limit target pressure. If the anode pressure is equal to or lower than the pulsation lower limit target pressure, the controller 4 performs the process of step S11 to increase the anode pressure. On the other hand, if the anode pressure is higher than the pulsation lower limit target pressure, the process of step S12 is performed.

  In step S11, the controller 4 sets the target anode pressure to the pulsation upper limit target pressure. Thereby, the opening degree of the anode pressure regulating valve 33 is feedback-controlled so that the anode pressure becomes the pulsation upper limit target pressure. As a result of this feedback control, the anode pressure regulating valve 33 is opened to a desired opening, anode gas is supplied from the high-pressure tank 31 to the fuel cell stack 1, and the anode pressure rises.

  In step S12, the controller 4 sets the target anode pressure to the same target anode pressure as the previous time.

  FIG. 4 is a block diagram illustrating the cathode gas supply control according to this embodiment.

  The target output current is input to the oxygen partial pressure securing request stack supply flow rate calculation unit 101. The oxygen partial pressure securing request stack supply flow rate calculation unit 101 calculates the oxygen partial pressure securing request stack supply flow rate based on the target output current. This oxygen partial pressure securing request stack supply flow rate is the stack supply necessary for securing the oxygen partial pressure necessary for the electrode reaction in the cathode electrode of each fuel cell when the target output current is taken out from the fuel cell stack 1. This is the target flow rate. The oxygen supply partial pressure securing request stack supply flow rate is larger when the target output current is large than when the target output current is small.

  The wetness control request stack supply flow rate calculation unit 102 receives, for example, the impedance of the fuel cell stack 1 calculated by the AC impedance method and a target impedance that is predetermined according to the target output current of the fuel cell stack 1. Is done. The wetness control request stack supply flow rate calculation unit 102 calculates the target value of the stack supply flow rate for setting the impedance to the target impedance as the wetness control request stack supply flow rate based on the deviation between the impedance and the target impedance. In other words, the stack supply flow rate required for controlling the wetness is the stack supply flow rate necessary for controlling the wetness (moisture content) of the electrolyte membrane to an optimum wetness according to the target output current of the fuel cell stack 1. It is.

  The maximum value selection unit 103 receives an oxygen partial pressure securing request stack supply flow rate and a wetness control request stack supply flow rate. The maximum value selection unit 103 selects and outputs the larger one of these two.

  The target stack supply flow rate calculation unit 104 receives the output value of the maximum value selection unit 103 and the upper limit flow rate. The target stack supply flow rate calculation unit 104 calculates the smaller one of these two input values as the target stack supply flow rate. The upper limit flow rate is a flow rate at which the pressure loss of the WRD 26 becomes a predetermined pressure loss value set in advance even under the worst environmental conditions such as the temperature of the cathode gas. Therefore, if the flow rate of the cathode gas supplied to the WRD 26, that is, the stack supply flow rate is less than or equal to the upper limit flow rate, the pressure loss of the WRD 26 is always less than or equal to the predetermined pressure loss value.

  Thus, by calculating the smaller of the output value and the upper limit flow rate of the maximum value selection unit 103 as the target stack supply flow rate, the target stack supply flow rate does not become larger than the upper limit flow rate. The loss can be suppressed to a predetermined pressure loss or less. Therefore, it is possible to suppress the estimated transmembrane pressure from becoming smaller than the actual transmembrane pressure.

  The detected stack supply flow rate and the target stack supply flow rate are input to the stack required compressor supply flow rate calculation unit 105. The stack required compressor supply flow rate calculation unit 105 calculates a target value of the compressor supply flow rate to make the detected stack supply flow rate the target stack supply flow rate based on the deviation between the detected stack supply flow rate and the target stack supply flow rate. Calculate as supply flow rate. Note that the stack demand compressor supply flow rate, such as the oxygen partial pressure securing request or the wetness control request, is output when the output value of the maximum value selection unit 103 is calculated as the target stack supply flow rate in the target stack supply flow rate calculation unit 104. This is the compressor supply flow rate necessary to satisfy the requirements of the fuel cell stack 1. Further, when the upper limit flow rate is calculated as the target stack supply flow rate in the target stack supply flow rate calculation unit 104, the upper limit value of the compressor supply flow rate required to make the pressure loss of the WRD 26 equal to or less than the predetermined pressure loss value.

  The target compressor supply flow rate calculation unit 106 receives the stack request compressor supply flow rate and the dilution request compressor supply flow rate determined according to the target output current of the fuel cell stack 1. For the target compressor supply flow rate, the larger one of these two input values is calculated as the target compressor supply flow rate. The dilution demand compressor supply flow rate is a compressor supply flow rate necessary for setting the hydrogen concentration of the exhaust gas discharged outside the fuel cell system 100 to a predetermined concentration or less. In the present embodiment, the dilution request compressor supply flow rate is increased when the target output current is large compared to when the target output current is small, but may be a constant value regardless of the target output current.

  The cathode compressor control unit 107 receives a compressor supply flow rate and a target compressor supply flow rate. The cathode compressor control unit 107 calculates a torque command value for the cathode compressor 24 based on the deviation between the compressor supply flow rate and the target compressor supply flow rate, and controls the cathode compressor 24 according to the torque command value.

  The target bypass valve opening degree calculation unit 108 receives the stack supply flow rate and the target stack supply flow rate. The target bypass valve opening degree calculation unit 108 determines the opening degree of the bypass valve 29 for changing the stack supply flow rate to the target stack supply flow rate based on the deviation between the stack supply flow rate and the target stack supply flow rate. Calculate as

  Note that the target bypass valve opening is zero when the target compressor supply flow rate calculation unit 106 calculates the stack required compressor supply flow rate as the target compressor supply flow rate. On the other hand, when the target compressor supply flow rate calculation unit 106 calculates the dilution request compressor supply flow rate as the target compressor supply flow rate, it is necessary to supply a cathode gas larger than the stack request compressor supply flow rate by the cathode compressor 24. Therefore, it is necessary to flow the flow rate unnecessary for the fuel cell stack 1 (= dilution request compressor supply flow rate−stack request compressor supply flow rate) to the bypass passage 28. Therefore, the target bypass valve opening is a value larger than zero.

  A target bypass opening is input to the bypass valve control unit 109. The bypass valve control unit 109 controls the opening degree of the bypass valve 29 to the target bypass valve opening degree.

  According to the present embodiment described above, the pressure loss of the WRD 26 is set to a predetermined pressure loss value within a range that can actually be taken during the operation of the fuel cell system 100, and the fuel cell stack 1 is set based on the detected cathode pressure. The estimated pressure value on the cathode side (estimated cathode pressure) is calculated. Then, when the differential pressure between the detected anode pressure and the estimated cathode pressure exceeds a predetermined allowable transmembrane pressure difference, the differential pressure excess prevention control is performed so that the differential pressure does not become larger than the allowable transmembrane pressure difference. .

  On the other hand, based on the smaller one of the compressor supply flow rate set according to the request of the fuel cell stack 1 and the upper limit flow rate of the compressor supply flow rate at which the pressure loss of the WRD 26 is equal to or less than the predetermined pressure loss value, the cathode compressor 24 To control. In other words, the target stack supply flow rate calculation unit 104 calculates the stack requested compressor supply flow rate when the output value of the maximum value selection unit 103 is calculated as the target stack supply flow rate, and the target stack supply flow rate calculation unit 104 sets the upper limit flow rate as the target. The cathode compressor 24 is controlled based on the smaller one of the stack required compressor supply flow rates calculated as the stack supply flow rate.

  As described above, the compressor supply flow rate at which the pressure loss of the WRD 26 is equal to or less than the predetermined pressure loss value is set as the upper limit flow rate, and the cathode compressor 24 is controlled so as not to exceed the upper limit flow rate. Therefore, it can suppress that the pressure loss of WRD26 becomes larger than a predetermined pressure loss value, and can suppress that an actual pressure loss becomes larger than the predetermined pressure loss value set.

  Therefore, since the estimated cathode pressure can be prevented from becoming higher than the cathode pressure in the stack, the differential pressure between the detected anode pressure and the estimated cathode pressure is prevented from becoming smaller than the actual transmembrane pressure difference. it can. Therefore, when the differential pressure between the detected anode pressure and the estimated cathode pressure exceeds the predetermined allowable transmembrane pressure, the actual transmembrane pressure is allowed by limiting so that the differential pressure does not increase any more. Exceeding the transmembrane pressure difference can be suppressed.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the second embodiment of the present invention, when the detected value of the second air flow sensor 42 is larger than the detected value of the first air flow sensor 41 when the bypass valve is fully closed, correction is performed to reduce the upper limit flow rate. This is different from the first embodiment. Hereinafter, the difference will be mainly described. In each embodiment described below, the same reference numerals are used for portions that perform the same functions as those of the above-described embodiments, and repeated description is appropriately omitted.

  FIG. 5 is a block diagram illustrating the cathode gas supply control according to this embodiment.

  As shown in FIG. 5, the cathode gas supply control according to the present embodiment includes an upper limit flow rate calculation unit 110. Details of the upper limit flow rate calculation unit 110 will be described with reference to the flowchart of FIG.

  As in the present embodiment, the fuel cell system 100 capable of bypassing the fuel cell stack 1 and discharging part of the cathode gas discharged from the cathode compressor 24 is a first air flow that detects the compressor supply flow rate. Two air flow sensors, that is, a sensor 41 and a second air flow sensor 42 that detects the stack supply flow rate, are provided.

  As shown in FIG. 5, the cathode compressor 24 is controlled based on the detected value (detected compressor supply flow rate) of one of the first airflow sensors 41 and the target compressor supply flow rate.

  Here, when the bypass valve is fully closed, the detection values of the first air flow sensor 41 and the second air flow sensor 42, that is, the detected compressor supply flow rate and the detection stack supply flow rate should be the same. May cause a difference between the detected compressor supply flow rate and the detected stack supply flow rate.

  When such a deviation occurs when the bypass valve is fully closed and the detected stack supply flow rate becomes larger than the detected compressor supply flow rate, the following problems will occur when the upper limit flow rate is selected as the target stack supply flow rate: Occurs.

  When the upper limit flow rate is selected as the target stack supply flow rate and the detected stack supply flow rate matches the upper limit flow rate, the target compressor supply flow rate also becomes the upper limit flow rate when the bypass valve is fully closed. At this time, if the detected stack supply flow rate is larger than the detected compressor supply flow rate, the detected compressor supply flow rate is lower than the upper limit flow rate.

  Then, in this embodiment, since the cathode compressor 24 is controlled based on the detected compressor supply flow rate and the target compressor supply flow rate, the compressor supply flow rate is increased. As a result, the stack supply flow rate becomes larger than the upper limit flow rate, and the pressure loss of the WRD 26 may become larger than the predetermined pressure loss value.

  Therefore, in this embodiment, when the detected stack supply flow rate is larger than the detected compressor supply flow rate when the bypass valve is fully closed, the upper limit flow rate is corrected to be small.

  Accordingly, the target compressor supply flow rate is calculated so that the detected stack supply flow rate becomes the corrected upper limit flow rate, and thus the target compressor supply flow rate can be lowered. Therefore, even if the detected stack supply flow rate is larger than the detected compressor supply flow rate, the cathode compressor 24 can be controlled based on the reduced target compressor supply flow rate and detected compressor supply flow rate. Increase in flow rate can be suppressed. Hereinafter, this upper limit flow rate correction method will be described with reference to FIG.

  FIG. 6 is a flowchart illustrating the details of the upper limit flow rate calculation unit 110.

  In step S21, the controller 4 determines whether or not the bypass valve 29 is fully closed. The controller 4 performs the process of step S22 if the bypass valve 29 is fully closed, and performs the process of step S23 if the bypass valve is open.

  In step S <b> 22, the controller 4 determines whether or not the detected value (detected stack supply flow rate) of the second air flow sensor 42 is larger than the detected value (detected compressor supply flow rate) of the first air flow sensor 41. If the detected stack supply flow rate is greater than the detected compressor supply flow rate, the controller 4 performs the process of step S24. On the other hand, if the detected stack supply flow rate is equal to or lower than the detected compressor supply flow rate, the controller 4 performs the process of step S23.

  In step S23, similarly to the first embodiment, the controller 4 sets the compressor supply flow rate at which the pressure loss of the WRD 26 becomes a predetermined pressure loss value as the upper limit flow rate. Hereinafter, this upper limit flow rate is referred to as “normal upper limit flow rate” for distinction.

  In step S24, the controller 4 sets a flow rate obtained by subtracting the difference between the detected stack supply flow rate and the detected compressor supply flow rate from the normal upper limit flow rate as the upper limit flow rate. Hereinafter, this upper limit flow rate is referred to as “correction upper limit flow rate”.

  According to the present embodiment described above, the detected value (detected stack supply flow rate) of the second air flow sensor 42 when the bypass valve is fully closed is larger than the detected value (detected compressor supply flow rate) of the first air flow sensor 41. When the compressor supply flow rate is limited to the upper limit flow rate, the corrected upper limit flow rate obtained by subtracting the difference between the detected stack supply flow rate and the detected compressor supply flow rate from the preset upper limit flow rate (normal upper limit flow rate), The cathode compressor 24 is controlled based on the detected value of the 1 air flow sensor 41.

  That is, the target compressor supply flow rate is set so that the detected stack supply flow rate becomes the correction upper limit flow rate, and the cathode compressor 24 is controlled based on the target compressor supply flow rate and the detected compressor supply flow rate.

  Thus, the first air flow sensor 41 for detecting the compressor supply flow rate and the second air flow sensor 42 for detecting the stack supply flow rate are provided, and the cathode compressor 24 is detected by the detected compressor supply flow rate and the target compressor supply flow rate. In the fuel cell system 100 controlled based on the above, even if the detected stack supply flow rate is larger than the detected compressor supply flow rate, it is possible to suppress the stack supply flow rate from exceeding the normal upper limit flow rate, and the pressure loss of the WRD 26 Can be prevented from becoming larger than the predetermined pressure loss value.

  In controlling the cathode compressor 24, when the detected stack supply flow rate is larger than the detected compressor supply flow rate, a measure such as switching the sensor used for control from the first air flow sensor 41 to the second air flow sensor 42 is used. However, from the viewpoint of control reliability, it is not desirable to take measures such as switching the sensor to be used as much as possible. Therefore, according to the present embodiment, it is possible to prevent the stack supply flow rate from becoming higher than the normal upper limit flow rate without taking such measures, and it is possible to ensure control reliability.

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

  For example, in the first embodiment, the target stack supply flow rate calculation unit 104 selects the smaller one of the output value of the maximum value selection unit 103 and the upper limit flow rate as the target stack supply flow rate. However, the present invention is not limited to this method. When the output value of the maximum value selection unit 103 is compared with the upper limit flow rate and the output value of the maximum value selection unit 103 is larger than the upper limit flow rate, the maximum value selection unit Correction may be made so that the output value 103 becomes the upper limit flow rate.

1 Fuel cell stack (fuel cell)
4 Controller (pressure estimation value calculation means, differential pressure excess prevention means, supply flow rate setting means, upper limit flow rate setting means, compressor control means)
24 Cathode compressor (compressor)
26 Humidifier (WRD)
29 Bypass valve 41 First air flow sensor (first flow sensor)
42 Second air flow sensor (second flow sensor)
43 Cathode pressure sensor (pressure detection means)
100 Fuel cell system

Claims (3)

A fuel cell system for generating electricity by supplying an anode gas and a cathode gas to a fuel cell,
A compressor for adjusting the flow rate of the cathode gas supplied to the fuel cell;
A humidifier for humidifying the cathode gas discharged from the compressor;
A pressure detecting means provided upstream of the humidifier and detecting the pressure of the cathode gas discharged from the compressor;
Pressure estimation value calculating means for calculating a pressure estimated value on the cathode side in the fuel cell based on the detected value of the pressure detecting means and the predetermined value, with the pressure loss of the humidifier as a predetermined value;
When the differential pressure between the detected pressure value on the anode side in the fuel cell and the estimated pressure value exceeds a predetermined allowable transmembrane differential pressure, a differential pressure excessive prevention means for reducing the differential pressure;
Supply flow rate setting means for setting the supply flow rate of the compressor according to the demand of the fuel cell;
Upper limit flow rate setting means for setting the supply flow rate of the compressor at which the pressure loss of the humidifier becomes the predetermined value as an upper limit flow rate;
Compressor control means for controlling the compressor based on the smaller one of the supply flow rate of the compressor set by the supply flow rate setting means and the upper limit flow rate set by the upper limit flow rate setting means;
A fuel cell system comprising: A cathode gas bypass type cathode gas supply system for discharging a part of the cathode gas discharged from the compressor provided in the cathode gas supply passage by bypassing the fuel cell through the bypass passage;
A first flow rate sensor that is provided in the cathode gas supply passage upstream of the bypass passage and detects the flow rate of the cathode gas supplied by the compressor;
A second flow sensor provided in the cathode gas supply passage after branching from the bypass passage and detecting the flow rate of the cathode gas supplied to the fuel cell;
A bypass valve provided in the bypass passage for adjusting a flow rate of the cathode gas flowing through the bypass passage;
With
The compressor control means includes
When the detected value of the second flow rate sensor when the bypass valve is fully closed is larger than the detected value of the first flow rate sensor, the upper limit flow rate is controlled when the compressor flow rate is controlled to the upper limit flow rate. The compressor is controlled based on the correction upper limit flow rate and the detection value of the first flow rate sensor.
The fuel cell system according to claim 1. The corrected upper limit flow rate is a flow rate obtained by subtracting the difference between the detection value of the second flow rate sensor and the detection value of the first flow rate sensor from the upper limit flow rate.
The fuel cell system according to claim 2.

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