JP2019003885A - Fuel cell system - Google Patents

Abstract

To allow for avoidance control of partial deficiency state by detecting partial deficiency state of fuel gas occurring in a fuel cell, when supplying fuel gas to the fuel cell intermittently.SOLUTION: In a fuel cell system, oxidation gas is supplied, and in a state where the fuel gas is supplied intermittently, low frequency impedance is measured sequentially, and moving average value of low frequency impedance is found, with a predetermined section as the calculation unit of moving average, and the maximum value of the low frequency impedances, included in the section where moving average values are found, is found. When the difference of the maximum value and the moving average value goes above a preset threshold level, a fuel gas supply section is controlled to increase fuel gas supply amount, and when the difference is less than the threshold level, the fuel gas supply section is controlled to maintain the fuel gas supply amount.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fuel cell system.

  Patent Document 1 discloses an AC impedance of a fuel cell at a frequency in a low frequency region (hereinafter also referred to as “low frequency impedance”) and an AC impedance of a fuel cell at a frequency in a high frequency region (hereinafter also referred to as “high frequency impedance”). ), The fuel cell system for judging the operating state of the fuel cell is described. In this fuel cell system, when the measured value of the low frequency impedance exceeds the threshold value, it is determined that the supply state of the fuel gas (hydrogen gas) to the electrolyte membrane of the fuel cell is defective.

JP 2007-12419 A JP 2012-252986 A

Here, when a partial hydrogen deficient state in which hydrogen as a fuel is partially deficient occurs in the plane of the anode of the cell constituting the fuel cell, protons (H ⁺ ) are produced at the cathode to compensate for the deficient hydrogen. Is generated and travels through the electrolyte to the anode. The generation of protons at the cathode is due to the electrolysis of water by the carbon carrying the catalyst of the cathode, so that there is a problem that the carbon of the cathode deteriorates. For this reason, it is desirable to detect partial hydrogen deficiency and avoid partial hydrogen deficiency. The detection of partial hydrogen deficiency is considered to be basically detectable by determining whether or not the measured value of the low frequency impedance exceeds a threshold value.

  However, the fuel cell system configured to intermittently supply the fuel gas to the fuel cell (hereinafter also referred to as “intermittent supply”) by repeatedly opening and closing the fuel supply valve such as an injector has the following problems. That is, the low frequency impedance tends to increase during the period when the fuel supply valve is closed and the supply of fuel gas from the fuel supply valve is stopped. For this reason, if the low frequency impedance exceeds the threshold value, it is determined that there is partial hydrogen deficiency, and control is performed to avoid partial hydrogen deficiency. There is a possibility of performing control to avoid partial hydrogen deficiency. In addition, when the fuel gas manifold is closed, a state of hydrogen deficiency occurs in the entire cell, and complete hydrogen deficiency that causes deterioration of the catalyst layer of the anode of the cell can be detected by monitoring the cell voltage. However, partial hydrogen deficiency cannot be detected by monitoring the cell voltage.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, a fuel cell system is provided. The fuel cell system includes: a fuel cell; a fuel gas supply unit for intermittently supplying fuel gas to the fuel cell; an oxidizing gas supply unit for supplying oxidizing gas to the fuel cell; An impedance measurement unit that measures frequency impedance; and a control unit that controls the power generation operation of the fuel cell. The impedance measuring unit sequentially measures the low frequency impedance in a state where the oxidizing gas is supplied and the fuel gas is intermittently supplied, and a predetermined interval is a unit for calculating a moving average. As described above, the moving average value of the low frequency impedance is obtained, and the maximum value of the low frequency impedances included in the section in which the moving average value is obtained is obtained. The control unit performs control to increase the supply amount of the fuel gas by the fuel gas supply unit when the difference between the maximum value and the moving average value is larger than a preset threshold value, When the difference is less than the threshold, the supply amount of the fuel gas supplied by the fuel gas supply unit is maintained.
According to the fuel cell system of this embodiment, even if the low frequency impedance fluctuates in the period when the supply of the fuel gas is stopped by comparing the maximum value of the low frequency impedance and the moving average value, the fuel gas Thus, it is possible to determine whether or not the partial depletion state of the fuel gas is generated, and it is possible to avoid unnecessary control for avoiding the partial depletion state of the fuel gas.

  The present invention can be realized in various forms other than the fuel cell system described above. For example, it can be realized in the form of a control method for a fuel cell system, a method for detecting a partial depletion state of fuel gas, or the like.

It is explanatory drawing which shows schematic structure of the fuel cell system as 1st Embodiment of this invention. It is explanatory drawing which shows the procedure of the hydrogen shortage determination process by the hydrogen shortage determination part of a control part. It is explanatory drawing which shows typically the mode of the low frequency impedance measured. It is explanatory drawing which shows an example of the measured value of a low frequency impedance, a maximum value, and a moving average value. It is explanatory drawing which shows the lack of hydrogen determination result based on the measured value of the low frequency impedance shown in FIG. It is explanatory drawing which shows the equivalent circuit of a fuel cell at the time of supply of fuel gas, and a stop. It is explanatory drawing which shows the procedure of the hydrogen deficiency determination process of 2nd Embodiment.

A. First embodiment:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system 10 as a first embodiment of the present invention. The fuel cell system 10 is mounted on a vehicle, for example, and outputs electric power serving as a power source for the vehicle in response to a request from the driver. The fuel cell system 10 includes a fuel cell 20, a hydrogen supply / discharge mechanism 50, an air supply / discharge mechanism 30, a cooling water circulation mechanism 70, a control unit 80, a DC / DC converter 90, and an impedance measurement unit 95. Prepare. The fuel cell system 10 is started by an ON operation of a power switch (not shown) and stopped by an OFF operation.

  The fuel cell 20 has a stack in which an end plate 21, an insulating plate 22, a current collecting plate 23, a plurality of cells 24, a current collecting plate 23, an insulating plate 22, and an end plate 21 are stacked in this order. It has a structure.

  The hydrogen supply / discharge mechanism 50 supplies and discharges hydrogen gas as fuel gas to and from the anode of the fuel cell 20 under the control of the control unit 80. The hydrogen supply / discharge mechanism 50 includes a hydrogen tank 40, a shut valve 41, a hydrogen supply channel 51, a regulator 53, an injector 54, a circulation channel 55, a gas-liquid separator 56, a hydrogen pump 57, A drainage shut-off valve 58 and a discharge channel 59 are provided.

  The hydrogen tank 40 stores hydrogen. The hydrogen tank 40 stores hydrogen gas as high-pressure fuel gas having several tens of MPa. The hydrogen supply channel 51 is a pipe that connects the hydrogen tank 40 and the fuel cell 20. The shut valve 41 is a valve that shuts off the supply of hydrogen gas from the hydrogen tank 40 to the hydrogen supply passage 51 and is also called a main stop valve. Opening and closing of the shut valve 41 is controlled by the control unit 80. When the shut valve 41 is opened under the control of the control unit 80, hydrogen gas is supplied from the hydrogen tank 40 to the anode of the fuel cell 20 through the hydrogen supply passage 51, and when the shut valve 41 is closed, the supply of hydrogen gas is shut off. Is done.

  The regulator 53 adjusts the pressure of the hydrogen gas supplied from the hydrogen tank 40 under the control of the control unit 80. The injector 54 intermittently injects (supplies) the hydrogen gas, the pressure of which has been adjusted by the regulator 53, toward the anode under the control of the control unit 80.

  The gas-liquid separator 56 separates the gas and liquid discharged from the anode. The hydrogen pump 57 supplies the gas separated by the gas-liquid separator 56 to the fuel cell 20 again. The gas separated by the gas-liquid separator 56 is mainly composed of hydrogen discharged without being consumed, nitrogen permeated from the cathode side through the membrane electrode assembly provided in the fuel cell, and saturated water (water vapor). is there. The discharge channel 59 is a pipe that connects the gas-liquid separator 56 and an air discharge channel 39 (described later) provided in the air supply / discharge mechanism 30. The drain shut valve 58 is provided on the discharge channel 59. The drainage shut valve 58 is opened to discharge the liquid and nitrogen separated by the gas-liquid separator 56. The amount of hydrogen gas supplied to the fuel cell 20 is adjusted by control by the control unit 80 of the injector 54 and the drainage shut valve 58. The hydrogen supply / discharge mechanism 50 corresponds to a “fuel gas supply unit”, and the injector 54 corresponds to a “fuel supply valve”.

  The air supply / discharge mechanism 30 supplies and discharges air containing oxygen as an oxidizing gas to the cathode of the fuel cell 20 under the control of the control unit 80. The air supply / discharge mechanism 30 includes a compressor 31, an air supply flow path 32, a flow dividing valve 33, a pressure regulating valve 36, a bypass flow path 38, and an air discharge flow path 39.

  The air supply channel 32 is a pipe that connects the fuel cell 20 and the atmosphere opening port of the air supply channel 32. The air discharge channel 39 is a pipe that connects the fuel cell 20 and the air opening of the air discharge channel 39. The bypass flow path 38 is a pipe that branches from the upstream side of the fuel cell 20 in the air supply flow path 32 and is connected to the air discharge flow path 39. The compressor 31 is provided in the middle of the air supply flow path 32, and sucks air from the air release port side of the air supply flow path 32 to compress it. The position where the compressor 31 is provided is a position closer to the atmosphere opening than the connection portion between the air supply flow path 32 and the bypass flow path 38.

  The diversion valve 33 is provided on the downstream side of the compressor 31 in the air supply channel 32, that is, between the compressor 31 and the fuel cell 20, and at a connection site between the air supply channel 32 and the bypass channel 38. The diversion valve 33 switches the flow direction of the air flowing from the compressor 31 to either the fuel cell 20 side or the bypass flow path 38 side. Such a diversion valve 33 is also called a three-way valve. The bypass flow path 38 is a pipe that connects the diversion valve 33 and the air discharge flow path 39. The pressure regulating valve 36 is provided in the air discharge channel 39 closer to the fuel cell 20 than the connection portion between the air discharge channel 39 and the bypass channel 38. The pressure regulating valve 36 adjusts the cross-sectional area of the air discharge flow path 39 according to the opening degree. The air that has passed through the pressure regulating valve 36 passes through the connection portion with the bypass flow path 38 and is then discharged to the atmosphere from the atmosphere opening port. The operations of the compressor 31, the flow dividing valve 33, and the pressure regulating valve 36 are adjusted according to control from the control unit 80. The air supply / discharge mechanism 30 corresponds to an “oxidizing gas supply unit”.

  The coolant circulation mechanism 70 cools the fuel cell 20 according to the control of the control unit 80. The cooling water circulation mechanism 70 includes a radiator 71, a cooling water pump 72, a cooling water discharge channel 73, and a cooling water supply channel 74.

  The cooling water supply channel 74 is a channel that connects between the radiator 71 and the fuel cell 20, and is a pipe for supplying cooling water to the fuel cell 20. The cooling water discharge channel 73 is a channel for connecting the fuel cell 20 and the radiator 71 and is a pipe for discharging the cooling water from the fuel cell 20. The cooling water pump 72 is provided in the cooling water supply flow path 74 between the radiator 71 and the fuel cell 20, and the cooling water is circulated by the cooling water pump 72. The operations of the radiator 71 and the cooling water pump 72 are adjusted according to the control from the control unit 80.

  The control unit 80 is configured as a computer including a CPU, a RAM, and a ROM, and is specifically an ECU (Electronic Control Unit). The control unit 80 outputs a signal for controlling the operation of the fuel cell system 10. In response to the power generation request, the control unit 80 controls the respective units 30, 50, and 70 of the fuel cell system 10 to cause the fuel cell 20 to generate power. In addition, the control unit 80 functions as a lack of hydrogen determination unit 82 and executes a lack of hydrogen determination described later.

  The DC / DC converter 90 is a power control circuit that converts electric power output from the fuel cell 20 into electric power (voltage and current) that can be supplied to a load in accordance with control from the control unit 80 and outputs the electric power. For example, the power generation operation is controlled by controlling the sweep current from the fuel cell 20 to control the output voltage of the fuel cell 20, and the voltage and current output to the load are controlled.

  The impedance measurement unit 95 includes an AC signal application unit 96 and a measurement execution unit 97. The AC signal application unit 96 and the measurement execution unit 97 operate as described below in accordance with an instruction from the hydrogen deficiency determination unit 82 of the control unit 80. The AC signal applying unit 96 applies a predetermined low-frequency AC signal (AC voltage or AC current) to the positive and negative electrodes of the fuel cell 20. In this example, an AC voltage is applied. The measurement execution unit 97 uses the alternating voltage between the positive and negative bipolar terminals measured by the voltmeter 98 and the alternating current flowing between the positive and negative bipolar terminals measured by the ammeter 99 between the positive and negative bipolar terminals at the frequency of the applied AC signal. AC impedance (hereinafter also referred to as “low frequency impedance”) is sequentially measured to calculate the moving average value of the low frequency impedance, and the maximum value of the low frequency impedances included in the section in which the moving average value is obtained. . The obtained moving average value and maximum value of the low-frequency impedance are sent to the lack-of-hydrogen determination unit 82 of the control unit 80 and used for the determination of lack of hydrogen.

  FIG. 2 is an explanatory diagram showing the procedure of the lack of hydrogen determination process by the lack of hydrogen determination unit 82 of the control unit 80. The lack of hydrogen determination unit 82 continues the lack of hydrogen determination process from the start of power generation of the fuel cell 20 until the end of power generation. When the lack of hydrogen determination unit 82 starts the lack of hydrogen determination process, the impedance measurement unit 95 starts impedance measurement (step S101). At this time, as described above, the AC signal applying unit 96 of the impedance measuring unit 95 has a predetermined low frequency fz (hereinafter also referred to as “low frequency fz”) between the positive and negative electrodes of the fuel cell 20. An AC signal (for example, AC voltage) is applied. The low frequency fz changes according to the occurrence of a hydrogen deficient state in a low frequency region (region having a frequency of about 0.1 to 200 Hz) in which reaction resistance of the anode (hydrogen electrode) and the cathode (oxygen electrode) is detected. It is preferable to set the frequency so that the reaction resistance of the anode (hydrogen electrode) can be effectively detected. In this example, fz = 20 Hz.

  And the measurement execution part 97 of the impedance measurement part 95 measures the alternating current impedance (low frequency impedance) in the low frequency fz (step S102), calculates the moving average value (Zavg) of the measured low frequency impedance, and moves The maximum value (Zmax) of the low frequency impedances included in the section Tm as a unit for calculating the average value is obtained (step S103). The obtained moving average value (Zavg) and maximum value (Zmax) are sent to the hydrogen deficiency determination unit 82. The section Tm as a unit for obtaining the moving average is set to a length that allows the moving average value to be calculated, that is, a length that is at least one cycle of opening and closing of the injector 54. In this example, the opening / closing cycle of the injector 54 is 200 ms (the opening period is 100 ms, and the closing period is 100 ms), and the section Tm is set to 200 ms or more. For example, when the section Tm = 200 ms, at least four low-frequency impedances of fz = 20 Hz are measured in one section Tm (= 200 ms), so an average value is calculated from the four measured values.

  The lack-of-hydrogen determination unit 82 calculates a difference (Zdif = [Zmax−Zavg]) between the maximum value (Zmax) and the moving average value (Zavg) of low-frequency impedances sent in order (step S104), and the difference (Zdif) Is compared with a predetermined threshold value (Zth) (step S105) The threshold value (Zth) is determined in advance from the relationship between the amount of deterioration of the cell 24 of the fuel cell 20 and the difference when not in a hydrogen deficient state. The threshold value (Zth) will be described later. The threshold value (Zth) will be described later.

  When the difference (Zdif) ≦ the threshold value (Zth), the hydrogen deficiency determination unit 82 repeats the processing from the impedance measurement (step S102) because the hydrogen deficiency state does not occur inside the fuel cell 20. On the other hand, when the difference (Zdif)> the threshold value (Zth), it is determined that a partial hydrogen deficient state has occurred inside the fuel cell 20 (hydrogen deficient determination) (step S106), and the control unit A control unit (not shown) of the 80 hydrogen supply / discharge mechanism 50 is requested to increase the supply amount of fuel gas (hereinafter also referred to as “fuel supply amount”) (step S107). As a result, the fuel supply amount is increased by the hydrogen supply / discharge mechanism 50, and control is performed so as to avoid the state of partial hydrogen shortage. Then, the lack of hydrogen determination unit 82 repeats the processing from the impedance measurement (step S102) until the end of the processing is instructed (step S108: YES).

  FIG. 3 is an explanatory diagram schematically showing the state of the measured low frequency impedance. The upper stage shows the state of the injector 54 (fuel supply valve) that is opened intermittently, the middle stage shows the state of the supply amount (fuel supply amount) of the fuel gas (hydrogen gas) supplied to the fuel cell 20, and the lower stage shows fz. = Shows a state of low frequency impedance of 20 Hz.

  The fuel supply amount increases or decreases in accordance with the opening / closing cycle of the injector 54. For this reason, when the injector 54 is open, the fuel cell 20 is in a fuel-rich state, and when the injector 54 is closed, the fuel cell 20 is in a fuel-lean state due to consumption of fuel gas. At this time, the low frequency impedance including the hydrogen electrode reaction resistance increases when the fuel supply amount decreases, that is, when the injector 54 is closed, and when the fuel supply amount increases, that is, when the injector 54 opens. Decrease when you are. When the injector 54 is closed and the fuel supply amount is reduced, when a fuel gas partial deficiency state, that is, a partial hydrogen deficiency state occurs, the low frequency impedance is the fuel supply amount. In addition to the increase due to the decrease in quantity, it increases according to the degree of hydrogen deficiency. Therefore, if a change in the maximum value (Zmax) of the low frequency impedance that periodically changes according to the opening / closing cycle of the injector 54 is detected, the state of partial hydrogen deficiency that occurs when the injector 54 is closed can be determined. It seems possible. Specifically, when the maximum value (Zmax) of the low frequency impedance exceeds the added value (Zavg + Zth) of the moving average value (Zavg) of the low frequency impedance and the threshold value (Zth), a partial hydrogen deficient state occurs. It is thought that this can be determined. That is, when the difference (Zmax−Zavg) between the maximum value (Zmax) of the low frequency impedance and the moving average value (Zavg) exceeds the threshold value (Zth), it is considered possible to determine the occurrence of the partial hydrogen deficiency state. .

  Here, the offset of the fuel supply amount shown in FIG. 3 indicates the amount of hydrogen gas circulated and supplied by the hydrogen pump 57 (FIG. 1). During normal power generation, moisture and nitrogen separated by the gas-liquid separation unit 56 are appropriately discharged through the drain shut valve 58, and the amount of hydrogen gas supplied from the injector 54 is adjusted according to this discharge. Therefore, the offset is maintained. However, there is a case where power generation is performed in a state where the water and nitrogen separated by the gas-liquid separation unit 56 are not discharged through the drain shut valve 58. In this case, although illustration is omitted, the hydrogen gas component circulated is gradually consumed by the power generation, and finally there is no offset, and the supply amount of hydrogen gas to the fuel cell 20 is from the injector 54. Reduced to supply only. Therefore, the power generation of the fuel cell 20 in this case is power generation in a low hydrogen concentration state where the hydrogen concentration is low. The rate of fluctuation of the supply amount of hydrogen gas in such a low hydrogen concentration power generation state is larger than that during normal power generation having an offset. For this reason, the change of the low frequency impedance according to increase / decrease of the supply amount of hydrogen gas by opening and closing of the injector 54 becomes larger than the change at the time of normal power generation.

  FIG. 4 is an explanatory diagram illustrating an example of a measured value, a maximum value, and a moving average value of low frequency impedance. Time “0 sec” indicates the start of power generation at a low hydrogen concentration. As shown in FIG. 4, immediately after the start of low hydrogen concentration power generation, the state of low frequency impedance is the same as that during normal power generation, but the fluctuation of the low frequency impedance increases as the hydrogen concentration decreases, and the low frequency impedance The maximum value (Zmax) increases. However, the amount of increase in the moving average value (Zavg) of the low frequency impedance is very small compared to the amount of increase in the maximum value (Zmax), and if the moving average value (Zavg) is compared with the maximum value (Zmax), the fuel It can be seen that it is possible to determine the occurrence of a partial hydrogen deficient state even during normal power generation with a large supply amount and at a low hydrogen concentration with a small fuel supply amount.

  Therefore, as described above, the occurrence of a partial hydrogen deficient state depends on whether or not the difference (Zmax−Zavg) between the maximum value (Zmax) of the low frequency impedance (Zmax) and the moving average value (Zavg) exceeds the threshold (Zth). It can be said that determination (hydrogen deficiency determination) is possible.

  FIG. 5 is an explanatory view showing the result of the lack of hydrogen determination based on the measured value of the low frequency impedance shown in FIG. As described above, when the difference (Zdif) between the maximum value (Zmax) of the low frequency impedance and the moving average value (Zavg) and the threshold (Zth) are compared, as shown in FIG. It can be seen that it is possible to determine that a hydrogen deficiency (partial hydrogen deficiency) state has occurred at the portion. Although not shown and described, the same applies to normal power generation. Therefore, if the difference (Zdif) between the maximum value (Zmax) and moving average value (Zavg) of the low frequency impedance and the threshold (Zth) are compared, the low hydrogen concentration during normal power generation with a large amount of fuel supply or with a small amount of fuel supply Regardless of the time, it can be determined that a state of hydrogen deficiency (partial hydrogen deficiency) has occurred at some locations in the fuel cell 20.

  FIG. 6 is an explanatory diagram showing an equivalent circuit of the fuel cell at the time of supplying and stopping the fuel gas. The AC impedance (low frequency impedance) at a frequency in the low frequency region includes the oxygen electrode reaction resistance (Zo) and the capacitance component (Co) constituting the electric double layer on the oxygen electrode (cathode) side, and the membrane resistance (Rohm) of the electrolyte membrane. ), And a hydrogen electrode reaction resistance (Zh) and a capacity component (Ch) constituting the electric double layer on the hydrogen electrode (anode) side. For this reason, the low frequency impedance basically depends on not only the supply state of the fuel gas (hydrogen gas) to the fuel cell but also the supply state of the oxidizing gas (air containing oxygen gas) and the wet state of the electrolyte membrane. Also fluctuate.

  When the fuel gas (hydrogen gas) is intermittently supplied by opening and closing the injector 54, the hydrogen electrode reaction resistance is assumed that the air supply amount and the wet state of the electrolyte membrane are constant during the supply and stop of the fuel gas. Only fluctuates. In contrast to the hydrogen electrode reaction resistance Zh when the fuel gas is supplied, the hydrogen electrode reaction resistance when the fuel gas is stopped increases by a variation (Zα) according to the amount of decrease in the fuel gas. Therefore, by taking the difference between the average value (Zonavg) of the low-frequency impedance at the time of fuel gas supply and the maximum value (Zmax = Zh + Zα) of the low-frequency impedance at the time of stoppage, the hydrogen electrode reaction resistance due to the intermittent supply of fuel gas Only the fluctuation amount Zα can be extracted. The low frequency impedance at the time of fuel gas supply varies depending on the response characteristics and noise caused by the capacitive component Co on the oxygen electrode side and the capacitive component Co on the hydrogen electrode side. The average value (Zonavg) was used as the representative value.

  The fluctuation amount Zα further increases according to the degree of occurrence of the hydrogen deficient state in the fuel cell 20. Therefore, for example, a threshold value (Zth) in which a margin is included in the fluctuation amount Zα so that the fluctuation amount Zα in a state of hydrogen deficiency (partial hydrogen deficiency) generated in a part of the fuel cell 20 can be detected. Set. Then, the difference (Zdif) between the maximum value (Zmax) of the low frequency impedance and the average value (Zonavg) of the low frequency impedance at the time of supplying the fuel gas is compared with the threshold value (Zth). It is possible to determine whether or not a partial hydrogen deficiency state has occurred. Actually, as described above (see FIGS. 2 and 3), since it is difficult to calculate the average value (Zonavg) of the low frequency impedance when supplying the fuel gas, it is longer than the intermittent supply cycle. The moving average value (Zavg) for each set section Tm is used. Since the moving average value (Zavg) is a value obtained by smoothing the period fluctuation corresponding to the opening / closing period of the injector, the influence of the fluctuation of the low frequency impedance is small as shown in FIG. It is also possible to remove noise from the impedance measurement value. Therefore, the moving average value (Zavg) of the low frequency impedance may be replaced with the average value (Zonavg) of the low frequency impedance when the fuel gas is supplied.

  As described above, in the present embodiment, when the fuel gas is intermittently supplied to the fuel cell 20, the maximum value (Zmax) of the low frequency (fz = 20 Hz) AC impedance (low frequency impedance) and the moving average value are obtained. By comparing the difference (Zdif) with respect to (Zavg) with the threshold value (Zth), it is determined whether or not a partial hydrogen deficient state (partial hydrogen deficient state) occurs in the fuel cell 20. Can do. When a partial hydrogen deficiency state occurs, control can be performed to avoid the partial hydrogen deficiency state by increasing the amount of fuel gas supplied from the injector 54.

B. Second embodiment:
FIG. 7 is an explanatory diagram illustrating the procedure of the lack of hydrogen determination process according to the second embodiment. This lack-of-hydrogen determination process is executed in the lack-of-hydrogen determination unit 82 (FIG. 1) of the control unit 80 in the fuel cell system 10 (FIG. 1), as in the first embodiment.

  In the hydrogen deficiency determination process (FIG. 2) of the first embodiment, the moving average value (Zavg) is used as a value corresponding to the low-frequency impedance value (Zon) at the time of fuel gas supply described with reference to FIG. However, the minimum value (Zmin) in the same section Tm may be used instead of the moving average value (Zavg). Therefore, in the lack of hydrogen determination process of FIG. 7, steps S103 and S104 of the lack of hydrogen determination process (FIG. 2) of the first embodiment are replaced with steps S103B and S104B.

  In step S103B, the maximum value (Zmax) of the AC impedance (low frequency impedance) of the low frequency (fz = 20 Hz) is obtained and the minimum value (Zmin) is obtained for each section Tm similar to step S103 (FIG. 2). . In step S104B, a difference (Zdif = [Zmax−Zmin]) between the obtained maximum value (Zmax) and minimum value (Zmin) is calculated. Then, by comparing the difference (Zdif) with the threshold value (Zth) (step S105), a partial hydrogen deficient state (partial hydrogen deficient state) is formed inside the fuel cell 20 as in the first embodiment. It can be determined whether or not it has occurred. When a partial hydrogen deficiency state occurs, control can be performed to avoid the partial hydrogen deficiency state by increasing the amount of fuel gas supplied from the injector 54.

C. Other embodiments:
(1) In the above embodiment, the case where an AC voltage is applied between the positive and negative electrodes of the fuel cell 20 from the AC signal application unit 96 has been described as an example, but an AC current may be applied.

(2) In the above embodiment, the configuration in which the AC signal applying unit 96 of the impedance measuring unit 95 applies an AC signal between the positive and negative bipolar terminals of the fuel cell 20 has been described as an example, but the control unit 80 functions as an impedance measuring unit. You may let them. In this case, the control unit 80 as an impedance measuring unit controls the DC / DC converter 90 to change the current or voltage between the positive and negative terminals of the fuel cell 20 at a predetermined low frequency, and the voltmeter 98 and the current The low frequency impedance between the positive and negative terminals may be measured from the AC voltage and AC current measured by the meter 99.

  The present invention is not limited to the above-described embodiment, other embodiments, and modifications, and can be realized with various configurations without departing from the spirit of the invention. For example, the technical features in the embodiments and modifications corresponding to the technical features in each embodiment described in the summary section of the invention are intended to solve part or all of the above-described problems, or In order to achieve part or all of the effects, replacement or combination can be appropriately performed. Moreover, elements other than the elements described in the independent claims among the constituent elements in the embodiment and each modification described above are additional elements and can be omitted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Fuel cell 21 ... End plate 22 ... Insulating plate 23 ... Current collecting plate 24 ... Cell 30 ... Air supply discharge mechanism 31 ... Compressor 32 ... Air supply flow path 33 ... Diverging valve 36 ... Pressure regulating valve 38 ... Bypass flow path 39 ... Air discharge flow path 40 ... Hydrogen tank 41 ... Shut valve 50 ... Hydrogen supply / discharge mechanism 51 ... Hydrogen supply flow path 53 ... Regulator 54 ... Injector 55 ... Circulation flow path 56 ... Gas-liquid separation part 57 ... Hydrogen pump 58 ... Drain shut valve 59 ... Discharge flow path 70 ... Cooling water circulation mechanism 71 ... Radiator 72 ... Cooling water pump 73 ... Cooling water discharge flow path 74 ... Cooling water supply flow path 80 ... Control part 82 ... Hydrocarbon determination part 90 ... DC / DC converter 95 ... impedance measuring unit 96 ... AC signal applying unit 97 ... measurement executing unit 98 ... voltmeter 99 ... ammeter

Claims (1)

A fuel cell system,
A fuel cell;
A fuel gas supply unit for intermittently supplying fuel gas to the fuel cell;
An oxidizing gas supply unit for supplying an oxidizing gas to the fuel cell;
An impedance measuring unit for measuring the low-frequency impedance of the fuel cell;
A control unit for controlling the power generation operation of the fuel cell;
With
The impedance measuring unit is
In a state where the oxidizing gas is supplied and the fuel gas is intermittently supplied, the low frequency impedance is sequentially measured, and a predetermined interval is used as a unit for calculating the moving average. While obtaining a moving average value, obtain the maximum value of the low-frequency impedance included in the section obtained the moving average value,
The controller is
When the difference between the maximum value and the moving average value is greater than a preset threshold value, control is performed to increase the supply amount of the fuel gas by the fuel gas supply unit, and the difference is the threshold value. If less, the supply amount of the fuel gas supplied by the fuel gas supply unit is maintained,
Fuel cell system.

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