JP7787003B2 - fuel cell system - Google Patents

Description

This disclosure relates to a fuel cell system.

The fuel cell system disclosed in Patent Document 1 includes a fuel cell stack. The fuel cell stack generates electricity through a chemical reaction between hydrogen and oxygen.

Japanese Patent Application Laid-Open No. 2022-22829

If a hydrogen deficiency occurs in a fuel cell stack, it can cause the fuel cell stack to deteriorate. For this reason, it is necessary to determine when a hydrogen deficiency has occurred in a fuel cell stack.

A fuel cell system that solves the above problem comprises a fuel cell stack having multiple fuel cell cells, a measurement unit that measures the impedance of the fuel cell stack, and a control device. The control device obtains the impedance measured by the measurement unit by applying an AC voltage to the fuel cell stack, calculates the charge transfer resistance from the real component of the impedance measured by the measurement unit and the imaginary component of the impedance measured by the measurement unit, and, based on the correlation between the charge transfer resistance and hydrogen deficiency in the fuel cell stack, determines that hydrogen deficiency has occurred if the charge transfer resistance is equal to or greater than a threshold value.

There is a correlation between charge transfer resistance and hydrogen deficiency in the fuel cell stack. When hydrogen deficiency occurs in the fuel cell stack, the charge transfer resistance increases. By setting a threshold value for charge transfer resistance, the control device can determine when hydrogen deficiency has occurred in the fuel cell stack.

The above fuel cell system may include a circulation path that circulates hydrogen through the fuel cell stack and an exhaust/drain valve that exhausts hydrogen from the circulation path, and the control device may perform at least one of control to increase the amount of hydrogen circulating through the circulation path and control to shorten the opening interval of the exhaust/drain valve when the charge transfer resistance is equal to or greater than a threshold value.

In the above fuel cell system, when the charge transfer resistance is equal to or greater than a threshold value and the voltage of the fuel cell with the lowest voltage among the plurality of fuel cell units is not a negative voltage, the control device may perform at least one of control to increase the amount of hydrogen circulating through the circulation path and control to shorten the opening interval of the exhaust drain valve.

The above fuel cell system may also include a DC/DC converter that transforms the output power of the fuel cell stack, the DC/DC converter superimposing an AC voltage on the output voltage of the fuel cell stack, and the measurement unit measuring the impedance from the output current of the fuel cell stack and the output voltage of the fuel cell stack.

The present invention makes it possible to determine when a hydrogen deficiency has occurred in a fuel cell stack.

FIG. 1 is a schematic diagram of a fuel cell system. FIG. 2 is a schematic diagram of a fuel cell; 10 is a flowchart showing hydrogen deficiency determination control. 1 is a Nyquist plot of a fuel cell stack. FIG. 10 is a diagram for explaining a method for calculating charge transfer resistance. FIG. 10 is a graph showing the relationship between charge transfer resistance and anode stoichiometric ratio.

An embodiment of a fuel cell system will now be described.
As shown in Fig. 1, the industrial vehicle 10 includes a vehicle load 11 and a fuel cell system 20. The vehicle load 11 is a device driven by electricity. For example, the vehicle load 11 is an electric motor driven by electricity. The industrial vehicle 10 travels by being driven by this electric motor.

<Fuel cell system>
The fuel cell system 20 includes a fuel cell stack 21 , a cathode system 40 , an anode system 60 , a diluter 71 , and a control device 110 .

The fuel cell stack 21 includes multiple fuel cell cells 22. The fuel cell cells 22 are polymer membrane fuel cell cells. The fuel cell cells 22 generate electricity through a chemical reaction between oxygen in the air and hydrogen.

As shown in FIG. 2, the fuel cell 22 includes an ion-permeable electrolyte membrane 23, an anode-side catalyst layer 24, an anode-side microporous layer 25, an anode-side diffusion layer 26, a cathode-side catalyst layer 27, a cathode-side microporous layer 28, and a cathode-side diffusion layer 29. The anode-side catalyst layer 24 and the cathode-side catalyst layer 27 sandwich the electrolyte membrane 23. The anode-side microporous layer 25 and the cathode-side microporous layer 28 sandwich the electrolyte membrane 23 and the catalyst layers 24 and 27. The anode-side diffusion layer 26 and the cathode-side diffusion layer 29 sandwich the electrolyte membrane 23, the catalyst layers 24 and 27, and the microporous layers 25 and 28.

Each catalyst layer 24, 27 promotes the reaction of hydrogen and oxygen using a catalyst. Each catalyst layer 24, 27 includes a catalyst, a carrier that supports the catalyst, and an ionomer that coats the catalyst and the carrier. Examples of catalysts that can be used include platinum and ruthenium. Examples of carriers that can be used include carbon. Examples of ionomers that can be used include an ion-conductive polymer electrolyte. For example, the same material as the electrolyte membrane 23 can be used as the ionomer.

Each microporous layer 25, 28 facilitates the discharge of water generated by chemical reactions during power generation to the outside, preventing it from remaining in each catalyst layer 24, 27. Each microporous layer 25, 28 is composed of, for example, a water-repellent resin and a conductive material such as carbon.

Each diffusion layer 26, 29 serves as a pathway for electrons, hydrogen, and oxygen. Each diffusion layer 26, 29 is made of a material that is gas permeable and electron conductive. Each diffusion layer 26, 29 is made of, for example, carbon.

As shown in FIG. 1, the fuel cell stack 21 includes a cathode flow path 30 and an anode flow path 33. Air flows through the cathode flow path 30. Hydrogen flows through the anode flow path 33. The cathode flow path 30 includes an inlet 31 and an outlet 32. Air flows into the cathode flow path 30 through the inlet 31 and flows out through the outlet 32. The anode flow path 33 includes an inlet 34 and an outlet 35. Hydrogen flows into the anode flow path 33 through the inlet 34 and flows out through the outlet 35.

The cathode system 40 includes an intake port 41, an electric compressor 42, an inverter 44, an intercooler 45, a cathode supply path 46, a cathode discharge path 49, a first valve 51, and a second valve 52.

The intake port 41 draws air into the fuel cell system 20. The intake port 41 may be open to the atmosphere or may be connected to a gas cylinder.
The electric compressor 42 includes an electric motor 43. The electric compressor 42 is driven by the electric motor 43. The electric compressor 42 supplies air to the fuel cell stack 21. Specifically, the electric compressor 42 compresses the air supplied from the intake port 41 and supplies the compressed air to the fuel cell stack 21. The air supplied from the electric compressor 42 to the fuel cell stack 21 flows through the cathode flow path 30.

The inverter 44 is connected to the electric motor 43. The inverter 44 converts DC power into AC power and supplies it to the electric motor 43. This drives the electric motor 43.

Air discharged from the electric compressor 42 is supplied to the intercooler 45. The intercooler 45 cools the air supplied from the electric compressor 42. The air supplied to the fuel cell stack 21 is air that has been cooled by the intercooler 45.

The cathode supply path 46 connects the electric compressor 42 and the cathode flow path 30. More specifically, the cathode supply path 46 connects the electric compressor 42 and the inlet 31 of the cathode flow path 30. The cathode supply path 46 includes a first supply path 47 and a second supply path 48. The first supply path 47 connects the electric compressor 42 and the intercooler 45. The second supply path 48 connects the intercooler 45 and the cathode flow path 30.

The cathode discharge channel 49 connects the cathode flow path 30 and the diluter 71. More specifically, the cathode discharge channel 49 connects the outlet 32 of the cathode flow path 30 and the diluter 71. The cathode discharge channel 49 is a passage through which the cathode exhaust gas flows. The cathode exhaust gas is air discharged from the fuel cell stack 21 and contains produced water. The produced water is water produced by the power generation in the fuel cell stack 21.

The first valve 51 is provided in the cathode supply path 46. In this embodiment, the first valve 51 is provided in the second supply path 48, i.e., between the intercooler 45 and the cathode flow path 30. The first valve 51 may also be provided in the first supply path 47, i.e., between the intercooler 45 and the electric compressor 42.

The second valve 52 is provided in the cathode discharge path 49. The second valve 52 has an adjustable opening. The compression ratio of the electric compressor 42 can be controlled by adjusting the opening of the second valve 52.

The anode system 60 includes a tank 61, a pressure reducing valve 62, a hydrogen supply unit 63, a supply line 64, a circulation line 65, a gas-liquid separator 66, a circulation pump 67, an inverter 69, and an exhaust/drain valve 70.

The tank 61 stores hydrogen.
Hydrogen is supplied to the pressure reducing valve 62 from the tank 61. The pressure reducing valve 62 reduces the pressure of the hydrogen supplied from the tank 61. The reduced pressure hydrogen is supplied to the hydrogen supply unit 63.

The hydrogen supply unit 63 is a component for adjusting the amount of hydrogen supplied to the fuel cell stack 21. The amount of hydrogen supplied to the fuel cell stack 21 can be adjusted by controlling the hydrogen supply unit 63. The hydrogen supply unit 63 can be, for example, a solenoid valve such as an injector.

The supply channel 64 connects the hydrogen supply unit 63 to the anode flow path 33. More specifically, the supply channel 64 connects the hydrogen supply unit 63 to the inlet 34 of the anode flow path 33. Hydrogen injected from the hydrogen supply unit 63 is supplied to the fuel cell stack 21 through the supply channel 64.

The circulation path 65 connects the anode flow path 33 and the supply path 64. More specifically, the circulation path 65 connects the outlet 35 of the anode flow path 33 and the supply path 64. Anode exhaust gas flows through the circulation path 65. The anode exhaust gas contains unreacted hydrogen and generated water. The circulation path 65 is a passage for returning the unreacted hydrogen contained in the anode exhaust gas to the supply path 64.

The gas-liquid separator 66 is provided in the circulation path 65. The gas-liquid separator 66 separates the anode exhaust gas into hydrogen and produced water. The produced water separated from the anode exhaust gas is stored in the gas-liquid separator 66.

The circulation pump 67 is provided in the circulation path 65. The circulation pump 67 includes an electric motor 68. The circulation pump 67 is driven by the electric motor 68. The circulation pump 67 supplies hydrogen separated from the anode exhaust gas by the gas-liquid separator 66 to the supply path 64. This circulates the hydrogen.

The inverter 69 is connected to the electric motor 68. The inverter 69 converts DC power into AC power and supplies it to the electric motor 68. This drives the electric motor 68.

The exhaust drain valve 70 is connected to the gas-liquid separator 66. The exhaust drain valve 70 can be switched between an open and closed state. When the exhaust drain valve 70 is open, the produced water is discharged from the gas-liquid separator 66. In addition, exhaust is performed through the circulation path 65. When the exhaust drain valve 70 is closed, the produced water cannot be discharged from the gas-liquid separator 66. In other words, when the exhaust drain valve 70 is closed, the produced water accumulates in the gas-liquid separator 66. The exhaust drain valve 70 is switched from a closed state to an open state at predetermined valve opening intervals.

The gas-liquid separator 66 is connected to a diluter 71. When the exhaust/drain valve 70 is opened, the produced water stored in the gas-liquid separator 66 and the anode exhaust gas are supplied to the diluter 71. The diluter 71 dilutes the anode exhaust gas with the cathode exhaust gas and discharges it into the atmosphere.

The cooling system 80 includes a refrigerant circulation path 81 , a heat exchanger 82 , a fan 83 , a refrigerant pump 84 , an inverter 86 , and a temperature measurement unit 87 .
The refrigerant circulation path 81 connects the fuel cell stack 21 and a heat exchanger 82. The heat exchanger 82 is, for example, a radiator. A refrigerant circulates through the refrigerant circulation path 81. The refrigerant may be, for example, water, antifreeze, or air.

The fan 83 blows air toward the heat exchanger 82. The air blown from the fan 83 cools the refrigerant inside the heat exchanger 82.
The refrigerant pump 84 circulates the refrigerant through the refrigerant circulation path 81. The refrigerant pump 84 includes an electric motor 85. The refrigerant pump 84 is driven by the electric motor 85. The refrigerant cooled in the heat exchanger 82 is supplied to the fuel cell stack 21 through the refrigerant circulation path 81, thereby cooling the fuel cell stack 21.

The inverter 86 is connected to the electric motor 85. The inverter 86 converts DC power into AC power and supplies it to the electric motor 85. This drives the electric motor 85.

The temperature measurement unit 87 measures the temperature of the refrigerant. The temperature measurement unit 87 may be configured to measure the temperature of the refrigerant before heat exchange with the fuel cell stack 21, or may be configured to measure the temperature of the refrigerant after heat exchange with the fuel cell stack 21.

The electrical system 90 includes a first DC/DC converter 91, a current sensor 93, a voltage sensor 94, a second DC/DC converter 95, a first power storage device 96, a charge state detection unit 98, and a second power storage device 99.

The first DC/DC converter 91 is connected to the fuel cell stack 21. The first DC/DC converter 91 is a DC/DC converter that transforms and outputs the output power of the fuel cell stack 21. The first DC/DC converter 91 transforms and outputs the output power of the fuel cell stack 21 to, for example, 48 V. The output power from the first DC/DC converter 91 is supplied to the vehicle load 11. The first DC/DC converter 91 is equipped with a switching element 92. The first DC/DC converter 91 performs the transformation by controlling the switching of the switching element 92.

The current sensor 93 measures the output current of the fuel cell stack 21 .
The voltage sensor 94 measures the output voltage of the fuel cell stack 21. The voltage sensor 94 used is one that can individually measure the voltages of the multiple fuel cell cells 22. For example, the voltage sensor 94 used is one that has multiple ports, with the positive and negative electrodes of the fuel cell cells 22 connected to each of the multiple ports. This allows the voltage sensor 94 to individually measure the voltages of the fuel cell cells 22.

The second DC/DC converter 95 is connected to the first DC/DC converter 91. The second DC/DC converter 95 transforms the output power of the first DC/DC converter 91 and outputs it. For example, the second DC/DC converter 95 transforms the output power of the first DC/DC converter 91 to 12 V and outputs it.

The first storage device 96 is connected to the first DC/DC converter 91. The first storage device 96 is connected in parallel with the 48V auxiliary equipment 97 relative to the first DC/DC converter 91. When the output power from the first DC/DC converter 91 exceeds the power consumption of the vehicle load 11 and the 48V auxiliary equipment 97, the first storage device 96 is charged with the surplus power. When the output power from the first DC/DC converter 91 is lower than the power consumption of the vehicle load 11 and the 48V auxiliary equipment 97, the first storage device 96 discharges. Any device capable of charging and discharging may be used as the first storage device 96. Examples of the first storage device 96 include a secondary battery and a capacitor. The 48V auxiliary equipment 97 includes the electric compressor 42, the circulation pump 67, and the refrigerant pump 84.

The charge state detection unit 98 detects the charge state of the first storage device 96. The charge state detection unit 98 is, for example, a battery management system. The charge state detection unit 98 includes a sensor and a derivation unit that derives the state of the first storage device 96 from the sensor detection results. The sensor is, for example, a current sensor and a voltage sensor. The derivation unit can derive the charge rate of the first storage device 96 from the sensor detection results. Methods for deriving the charge rate include, for example, a method using the open-circuit voltage of the first storage device 96, a current integration method, or a combination of these.

The second storage device 99 is connected to the second DC/DC converter 95. The second storage device 99 is connected in parallel with the 12V auxiliary device 100 relative to the second DC/DC converter 95. When the output power from the second DC/DC converter 95 exceeds the power consumption of the 12V auxiliary device 100, the second storage device 99 is charged with the surplus power. When the output power from the second DC/DC converter 95 is lower than the power consumption of the 12V auxiliary device 100, the second storage device 99 discharges. Any device that can be charged and discharged may be used as the second storage device 99. Examples of the second storage device 99 include a secondary battery and a capacitor. The 12V auxiliary device 100 includes a fan 83, a first valve 51, and a second valve 52.

The control device 110 includes a processor 111 and a memory unit 112. The memory unit 112 includes RAM (Random Access Memory) and ROM (Read Only Memory). The memory unit 112 stores program code or instructions configured to cause the processor 111 to execute processes. The memory unit 112, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control device 110 may be configured with hardware circuits such as ASICs and FPGAs. The control device 110, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as ASICs and FPGAs, or a combination thereof.

The control device 110 controls the fuel cell system 20 .
The control device 110 controls the power generation of the fuel cell stack 21. The control device 110 switches the fuel cell stack 21 between a power generation state and a power generation stop state depending on the charging rate of the first power storage device 96. The power generation states include a low power generation state, a medium power generation state, and a high power generation state. The power generated in the low power generation state is lower than the power generated in the medium power generation state. The power generated in the medium power generation state is lower than the power generated in the high power generation state. By transitioning the power generation state, the control device 110 can gradually change the power generation depending on the charging rate of the first power storage device 96. For example, the control device 110 controls the power generation of the fuel cell stack 21 so that the power generation decreases as the charging rate of the first power storage device 96 increases.

<Hydrogen deficiency determination control>
The control device 110 performs hydrogen deficiency determination control, which determines whether or not hydrogen deficiency has occurred in the fuel cell stack 21.

As shown in FIG. 3, in step S1, the control device 110 determines whether or not to permit measurement of the impedance of the fuel cell stack 21. If the fuel cell stack 21 is in a power generating state, the control device 110 permits measurement of the impedance of the fuel cell stack 21. If the determination result in step S1 is positive, the control device 110 performs processing in step S2. If the determination result in step S2 is negative, the control device 110 terminates the hydrogen deficiency determination control.

In step S2, the control device 110 measures the impedance of the fuel cell stack 21. As a result, the control device 110 obtains the impedance of the fuel cell stack 21. The impedance of the fuel cell stack 21 can be measured using impedance spectroscopy. The control device 110 applies an AC voltage to the fuel cell stack 21 by controlling the first DC/DC converter 91. As a result, the AC voltage is superimposed on the DC voltage of the fuel cell stack 21. The control device 110 superimposes the AC voltage on the DC voltage of the fuel cell stack 21 by controlling the switching element 92 of the first DC/DC converter 91. The control device 110 obtains detection results from the current sensor 93 and the voltage sensor 94. The control device 110 extracts AC components from the output current and output voltage of the fuel cell stack 21. The control device 110 measures the impedance of the fuel cell stack 21 using the AC impedance method. The frequency of the AC voltage applied to the fuel cell stack 21 by the control device 110 is set so that the charge transfer resistance can be measured. The control device 110 is a measurement unit. This is described in detail below.

Figure 4 is a Nyquist plot showing the impedance characteristics of the fuel cell stack 21. The Nyquist plot displays the impedance characteristics of the fuel cell stack 21 on a complex plane using impedance spectroscopy. The horizontal axis of Figure 4 represents the real component of the impedance. The vertical axis of Figure 4 represents the imaginary component of the impedance. The vertical axis of Figure 4 is inverted in sign, and the larger the value along the vertical axis, the smaller the imaginary component. The "large" and "small" on the vertical axis can also be said to represent "large" and "small" in the negative direction.

Two arcs C1 and C2 can be obtained from the Nyquist plot. The diameter of arc C1, which is the lower frequency of the two arcs C1 and C2, represents mass transfer resistance. Mass transfer resistance is a resistance value resulting from oxygen transfer in the diffusion layers 26 and 29. The diameter of arc C2, which is the higher frequency of the two arcs C1 and C2, represents charge transfer resistance. Charge transfer resistance is a resistance value resulting from electron transfer in the catalyst layers 24 and 27. The higher frequency side of arc C2 represents electrolyte membrane resistance. Electrolyte membrane resistance is a resistance value resulting from ion transfer in the electrolyte membrane 23. The diameter of arc C2 can be calculated by regarding arc C2 as a semicircle bisected by the horizontal axis and calculating the impedance at the intersection of arc C2 and the horizontal axis, as well as the impedance on arc C2. The inventors used impedance spectroscopy to determine the impedance characteristics of the fuel cell stack 21 and found that the impedance of the fuel cell stack 21 deviates from arc C2 at a frequency of 250 Hz. The impedance obtained by applying an AC voltage of 250 Hz or higher is considered to be the impedance at the point where arc C2 intersects with the horizontal axis. Furthermore, frequencies between 10 Hz and 25 Hz can be considered to be the impedance on arc C2, which indicates charge transfer resistance. Therefore, the control device 110 measures the impedance at one point among frequencies above 250 Hz and one point among frequencies between 10 Hz and 25 Hz. In this embodiment, the control device 110 measures the impedance by applying an AC voltage of 250 Hz to the fuel cell stack 21. The control device 110 measures the impedance by applying an AC voltage of 25 Hz to the fuel cell stack 21.

As shown in FIG. 3, next, in step S3, the control device 110 determines whether the minimum cell voltage is not a negative voltage and whether the charge transfer resistance is equal to or greater than the threshold value Imp1. The minimum cell voltage is the voltage of the fuel cell 22 with the lowest voltage among the multiple fuel cell cells 22. The control device 110 determines whether the minimum cell voltage is a negative voltage based on the detection result of the voltage sensor 94.

The control device 110 calculates the charge transfer resistance from the impedance measured in step S2. The control device 110 then determines whether the charge transfer resistance is greater than or equal to a threshold value Imp1. The charge transfer resistance can be calculated using the real and imaginary components of the impedance.

As shown in Figure 5, the real part of the impedance at 250 [Hz] is R _H and the imaginary part is C _H. The real part of the impedance at 25 [Hz] is R _L and the imaginary part is C _L. As mentioned above, the impedance at 250 [Hz] is considered to be the impedance at the intersection of arc C2 and the horizontal axis. In this case, the diameter R _act of arc C2 can be calculated using the following formula.

The control device 110 regards the diameter R _act of the arc C2 as the charge transfer resistance and determines whether the charge transfer resistance is equal to or greater than the threshold Imp1. If the determination result of step S3 is negative, the control device 110 returns to the processing of step S1. If the determination result of step S3 is positive, the control device 110 performs the processing of step S4.

As shown in FIG. 3, in step S4, the control device 110 starts a deficiency elimination process. If the determination result in step S3 is positive, the control device 110 determines that a hydrogen deficiency has occurred in the fuel cell stack 21. Then, in step S4, the control device 110 starts a deficiency elimination process to eliminate the hydrogen deficiency in the fuel cell stack 21.

The shortage elimination process is a process that executes at least one of the following: control to increase the amount of hydrogen circulating through the circulation path 65, and control to shorten the opening interval of the exhaust/drain valve 70. In this embodiment, the shortage elimination process executes both control to increase the amount of hydrogen circulating through the circulation path 65 and control to shorten the opening interval of the exhaust/drain valve 70. The expression "at least one" used in this embodiment means "one or more" of the desired options. As an example, the expression "at least one" used in this specification means "only one option" or "both of the two options" if there are two options.

The amount of hydrogen circulating through the circulation path 65 is increased by increasing the rotational speed of the circulation pump 67. This increases the amount of hydrogen supplied to the fuel cell stack 21, thereby resolving the hydrogen shortage. Nitrogen contained in the air moves to the circulation path 65 through the electrolyte membrane 23. By shortening the opening interval of the exhaust drain valve 70, it is possible to prevent the nitrogen concentration in the circulation path 65 from increasing. This eliminates the hydrogen shortage in the fuel cell stack 21.

Next, in step S5, the control device 110 determines whether the time elapsed since the start of the deficiency elimination process has exceeded the first predetermined time T1. The first predetermined time T1 is set to a time that is expected to be sufficient to eliminate the hydrogen deficiency in the fuel cell stack 21 through the deficiency elimination process. If the determination result in step S5 is negative, the control device 110 returns to the process of step S4. That is, the control device 110 continues to execute the deficiency elimination process until the first predetermined time T1 has elapsed. If the determination result in step S5 is positive, the control device 110 performs the process of step S6.

In step S6, the control device 110 determines whether the time elapsed since the start of the deficiency resolution process has exceeded the second predetermined time T2. The second predetermined time T2 is longer than the first predetermined time T1. If the opening interval of the exhaust drain valve 70 is shortened during the first predetermined time T1, there is a risk that the concentration of hydrogen discharged outside the fuel cell system 20 will become excessively high. For this reason, after the first predetermined time T1 has elapsed, the deficiency resolution process will not be performed until the second predetermined time T2 has elapsed. The control device 110 repeats the process of step S6 until the determination result of step S6 becomes positive. When the determination result of step S6 becomes positive, the control device 110 ends the hydrogen deficiency determination control.

[Operation of this embodiment]
FIG. 6 , with one vertical axis representing charge transfer resistance, the other vertical axis representing anode stoichiometric ratio, and the horizontal axis representing time, shows the charge transfer resistance as the anode stoichiometric ratio is decreased over time. Line L1 in FIG. 6 indicates an anode stoichiometric ratio of 1.0. The higher the anode stoichiometric ratio, the greater the amount of hydrogen supplied to the fuel cell stack 21. In FIG. 6 , the anode stoichiometric ratio is plotted at point P1, and the charge transfer resistance is plotted at point P2. As shown in FIG. 6 , the charge transfer resistance increases as the anode stoichiometric ratio is decreased. In particular, it can be seen that the charge transfer resistance increases rapidly when the anode stoichiometric ratio decreases to a value close to 1.0. FIG. 6 shows the relationship between charge transfer resistance and anode stoichiometric ratio when the output current of the fuel cell stack 21 is set to 100 A, 150 A, and 200 A. The above correlation exists regardless of the output current of the fuel cell stack 21. 6 shows that there is a correlation between the charge transfer resistance and hydrogen deficiency in the fuel cell stack 21. By setting the charge transfer resistance corresponding to the anode stoichiometric ratio when hydrogen deficiency occurs as the threshold value Imp1, the control device 110 can determine whether hydrogen deficiency has occurred from the charge transfer resistance.

[Effects of this embodiment]
(1) There is a correlation between the charge transfer resistance and hydrogen deficiency in the fuel cell stack 21. When hydrogen deficiency occurs in the fuel cell stack 21, the charge transfer resistance increases. By setting a threshold Imp1 for the charge transfer resistance, the control device 110 can determine that hydrogen deficiency has occurred in the fuel cell stack 21.

(2) When hydrogen deficiency occurs in the fuel cell stack 21, the control device 110 executes at least one of the following controls: increasing the amount of hydrogen circulating through the circulation path 65, and shortening the opening interval of the exhaust drain valve 70. This eliminates the hydrogen deficiency in the fuel cell stack 21.

(3) When the charge transfer resistance is equal to or greater than the threshold value Imp1 and the minimum cell voltage is not a negative voltage, the control device 110 performs deficiency elimination processing. When a fuel cell 22 with a negative voltage is present, the hydrogen deficiency is eliminated by limiting the output current of the fuel cell stack 21. When a fuel cell 22 with a negative voltage is present, the deficiency elimination processing is not performed, allowing priority to be given to limiting the output current of the fuel cell stack 21.

(4) The first DC/DC converter 91 measures the impedance by applying an AC voltage to the fuel cell stack 21. Because the impedance of the fuel cell stack 21 can be measured using the first DC/DC converter 91, the number of parts can be reduced compared to when a dedicated device for measuring impedance is provided.

[Example of change]
The embodiment can be modified as follows: The embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

The control device 110 is only required to determine that a hydrogen deficiency has occurred when the charge transfer resistance is equal to or greater than the threshold value Imp1, and any control that may be performed after determining that a hydrogen deficiency has occurred is optional. For example, the control device 110 may limit the output current of the fuel cell stack 21 or may notify the passengers of the industrial vehicle 10.

When the charge transfer resistance is equal to or greater than the threshold Imp1, the control device 110 may execute the starvation elimination process regardless of whether the lowest cell voltage is a negative voltage.
The fuel cell system 20 may be installed in a passenger vehicle, a ship, a train, or the like.

The fuel cell system 20 may be used as a stationary power generation device.
The measurement unit may be a control unit that controls the first DC/DC converter 91 .
The fuel cell system 20 may be provided with a dedicated device for measuring impedance.

20... fuel cell system, 21... fuel cell stack, 22... fuel cell cell, 65... circulation path, 70... exhaust and drain valve, 91... first DC/DC converter which is a DC/DC converter, 110... control device which is a measurement unit.

Claims (2)

a fuel cell stack including a plurality of fuel cell units;
a measurement unit for measuring the impedance of the fuel cell stack;
a circulation path for circulating hydrogen through the fuel cell stack;
an exhaust drain valve for exhausting air from the circulation path;
a control device;
The control device
Acquiring the impedance measured by the measuring unit by applying an AC voltage to the fuel cell stack;
calculating a charge transfer resistance from a real component of the impedance measured by the measurement unit and an imaginary component of the impedance measured by the measurement unit;
determining that hydrogen deficiency has occurred when the charge transfer resistance is equal to or greater than a threshold value based on a correlation between the charge transfer resistance and hydrogen deficiency in the fuel cell stack;
When the charge transfer resistance is equal to or greater than a threshold value and the voltage of the fuel cell having the lowest voltage among the plurality of fuel cell units is not a negative voltage, the fuel cell system executes at least one of control to increase the amount of hydrogen circulating through the circulation path and control to shorten the opening interval of the exhaust drain valve . a DC/DC converter that transforms the output power of the fuel cell stack;
the DC/DC converter superimposes an AC voltage on the output voltage of the fuel cell stack;
2. The fuel cell system according to claim 1 , wherein the measurement unit measures the impedance from an output current of the fuel cell stack and an output voltage of the fuel cell stack.