JP5181709B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  Conventionally, there is a fuel cell system that detects voltages at a plurality of measurement points on a single cell and determines whether the power generation state is abnormal based on the detected voltages (see Patent Document 1).

Also, there is a fuel cell system that measures the voltage of cells at both ends of the fuel cell stack and controls the humidity of the supply gas based on the measurement result (see Patent Document 2), and the fuel gas outlet and the oxidant gas of the fuel cell There is a fuel cell system that detects clogging by detecting the voltage at the outlet (see Patent Document 3), and the output of the cell adjacent to the electrode plate of the module connected to the most downstream, and the other unit cell There is a fuel cell system that detects an output and determines the amount of water accumulated in a fuel gas flow path based on a detected value (see Patent Document 4).
JP 2005-209456 A Japanese Patent Laid-Open No. 2002-246048 JP 2006-244952 A JP 2006-338921 A

  In the fuel cell system, in order to perform efficient power generation, it is preferable that the water content in the fuel cell is an appropriate amount, and that the water is uniformly distributed in the fuel cell. In addition, when flooding occurs in which water overflows to the gas diffusion layer or flow path as the operation continues, power generation may not be possible, and water shortage may occur temporarily in the fuel cell during high temperature operation. Furthermore, in order to enable starting below freezing point, it is preferable that the amount of water in the fuel cell is less than that during normal operation and that it does not dry completely. For this reason, when operating the fuel cell, it is preferable that the water content in the fuel cell is appropriately controlled for the purpose of efficient power generation and the prevention of problems.

  However, in the fuel cell, the distribution of water in the stacking direction of the stack and in the plane of each cell depends on the gas flow direction, the amount of humidified gas, the water generated during power generation, the temperature difference in the fuel cell, etc. Non-uniformity, that is, uneven distribution of water in the fuel cell occurs. For this reason, in order to appropriately control the water content, it is preferable to know the distribution of water in the fuel cell.

  In view of the above problems, an object of the present invention is to provide a fuel cell system capable of estimating the inclination of water distribution in a fuel cell, that is, the uneven distribution of water in the fuel cell.

  In order to solve the above-described problems, the present invention includes the following means in a fuel cell system. That is, the present invention relates to a fuel cell that generates electric power by an electrochemical reaction between an oxidizing gas and a fuel gas, a measuring unit that measures a voltage at a plurality of measurement points in the fuel cell, and a voltage measured by the measuring unit. Estimating the uneven distribution of moisture between the plurality of measurement points of the fuel cell based on the difference in water content between the plurality of measurement points, which is estimated from the difference in voltage measured at different measurement points. And a fuel cell system.

The measuring means measures the voltage in at least two places where a difference in water content may occur in the fuel cell. The output voltage from the fuel cell depends on the water content at the measurement location. This is because a sufficiently wet location of the fuel cell has high power generation efficiency, and a dry location of the fuel cell has low power generation efficiency. For this reason, the estimation means can estimate the difference in moisture content between the measurement locations from the difference in voltage measured at different measurement locations, thereby estimating the uneven distribution of moisture in the fuel cell.

  Here, in estimating the uneven distribution of moisture, it is estimated whether or not the moisture is unevenly distributed in the fuel cell, and the degree of uneven distribution of moisture generated in the fuel cell (inclination of water content). ) Is included. Moreover, as a some measurement location, the different location in a single cell and the different cell in a stack are mentioned. By appropriately setting the measurement location according to the region and range where moisture distribution is to be estimated, the moisture distribution in various regions within the fuel cell, such as the uneven distribution of moisture in a single cell and the uneven distribution of moisture in the stacking direction of the stack, etc. Uneven distribution can be estimated.

  In addition, the estimation unit may estimate that moisture is unevenly distributed in the fuel cell when the voltage difference is equal to or greater than a predetermined threshold. That is, according to the present invention, when the voltage difference is greater than or equal to a predetermined threshold, a difference in moisture content greater than or equal to a predetermined value occurs between the measurement points, and the uneven distribution of moisture occurs in the fuel cell. It is possible to estimate.

  The threshold value used here is based on the relationship between the voltage difference measured in advance in the fuel cell and the difference in moisture content, so that the difference in moisture content is such that it can be determined that moisture is unevenly distributed. For example, a difference in voltage measured in the case of reaching the above may be adopted. However, it is preferable that the threshold value is determined using an optimum method as appropriate according to the embodiment, such as a method determined based on an actual measurement value or a method determined based on a theoretical value. In addition, the standard for determining that the uneven distribution of moisture has occurred at the time when the difference in moisture content occurs may vary depending on the embodiment, such as the purpose of the subsequent moisture content control processing.

  In addition, the fuel cell system according to the present invention further includes control means for controlling the uneven distribution of water or the amount of water in the fuel cell based on the uneven distribution of water in the fuel cell estimated by the estimating means. Also good. As a result, it is possible to improve power generation efficiency by eliminating the uneven distribution of moisture, improve below-freezing startability by minimizing the amount of moisture, and prevent cells from dropping due to relaxation of load fluctuations.

  Here, the control means adjusts at least one of the humidity of the gas supplied to the fuel cell, the flow rate of the gas, and the gas pressure, for example, so that the uneven distribution of moisture or the amount of moisture in the fuel cell Can be controlled. More specifically, by adjusting the gas humidity, the amount of moisture supplied to the fuel cell can be adjusted, and the water content of the fuel cell can be directly increased or decreased. Further, by adjusting the gas flow rate or gas pressure, it is possible to adjust the amount of moisture removed from the fuel cell or to promote the movement of moisture in the fuel cell, thereby controlling the uneven distribution of moisture in the fuel cell.

  Further, in the fuel cell system according to the present invention, when the estimation unit estimates that uneven distribution of moisture occurs in the fuel cell, any of the two poles in the fuel cell is the opposite pole. It may further comprise a determination means for determining which electrode is a dry electrode that is drier, and which electrode is a wet electrode that is wetter than the opposite electrode.

As a result, in addition to the uneven distribution of moisture on the surface of a single cell and the uneven distribution of moisture between cells in the stacking direction of the stack, any pole (anode or cathode) in the cell where the uneven distribution of moisture occurs. It is possible to determine whether is a dry electrode or a wet electrode. For this reason, according to the present invention, it becomes possible to estimate the uneven distribution of moisture in more detail, and based on the estimation result, the control means can control the uneven distribution of moisture with higher accuracy. It becomes possible.

  Here, the determination means determines, for example, which of the two electrodes is the dry electrode and the wet electrode based on the dew point of the off-gas discharged from each of the two electrodes. I can do it.

  In addition, the control unit may promote the movement of moisture from the wet electrode to the dry electrode by increasing the flow rate of the gas supplied to the electrode determined to be the dry electrode by the determination unit. In addition, by reducing the gas pressure of the electrode determined to be the dry electrode by the determination unit with respect to the gas pressure of the wet electrode, the movement of moisture from the wet electrode to the dry electrode is promoted. Also good.

  Membrane electrode from the opposite electrode (wet electrode) to the dry electrode by increasing the flow rate of the gas supplied to the dry electrode or the gas pressure of the dry electrode is lower than the gas pressure of the wet electrode Moisture permeation through the joined body is promoted. Thereby, the difference in the amount of water between the dry electrode and the wet electrode, that is, the uneven distribution of water can be alleviated.

  In addition, the fuel cell system according to the present invention includes a circulation unit that circulates the fuel off-gas discharged from the fuel cell and supplies the fuel off-gas again to the anode electrode, and the fuel off-gas circulated by the circulation unit externally at a predetermined timing. Purge means for purging the fuel cell, and supply means for supplying the fuel cell with a fuel gas that is dry compared to the fuel off-gas discharged from the fuel cell in accordance with the purge by the purge means. When the wet electrode is an electrode to which fuel gas is supplied, the humidity of the fuel gas supplied to the wet electrode is lowered by increasing the purge amount or purge frequency by the purge means, and the wet electrode The amount of water may be reduced.

  Here, the fuel gas supplied by the supply means is generally the fuel gas supplied from the fuel tank. The fuel off-gas discharged from the fuel cell is wet compared to the fuel gas supplied from the fuel tank or the like because it is humidified or contains moisture in the fuel cell. Therefore, in the present invention, in a fuel cell system that circulates fuel off-gas, the frequency or amount of purging wet fuel off-gas is increased, and the frequency or amount of supplying dry fuel gas compared to fuel off-gas is increased to increase moisture content. It was possible to reduce the moisture content of the wet pole due to the uneven distribution.

  The measuring means measures a voltage in the vicinity of the inlet of the supplied gas and a voltage in the vicinity of the outlet in the single cell, and the estimating means determines the single cell based on the difference between the measured voltages. You may estimate the uneven distribution state of the water | moisture content. And here, when the estimation means estimates that the vicinity of the gas inlet is dry compared to the vicinity of the outlet by the estimation means, the control means increases the flow rate of the gas to be supplied from the opposite pole. You may accelerate | stimulate the movement of the water | moisture content to the entrance vicinity.

  In a single cell, if there is an uneven distribution of moisture between the vicinity of the gas inlet and the vicinity of the outlet, and it is estimated that the vicinity of the gas inlet is dry compared to the vicinity of the outlet, By increasing the flow rate of the supplied gas, moisture permeation through the membrane electrode assembly from the opposite electrode to the dry portion (near the inlet) is promoted. As a result, the difference in the amount of water between the vicinity of the gas inlet and the vicinity of the outlet, that is, uneven distribution of water can be reduced.

In addition, the fuel cell is a fuel cell in which a plurality of cells are stacked, the measuring unit measures voltages in different cells, and the estimating unit is configured to measure the stack of cells based on the measured voltage difference. You may estimate the uneven distribution of the water | moisture content between the cells in which the voltage was measured in the direction. Here, the control unit varies the flow rate or gas pressure of the gas supplied to the fuel cell when the estimation unit estimates that the moisture is unevenly distributed in the stacking direction of the plurality of cells. In this case, the flow rate or the gas pressure may be gradually changed.

  If there is uneven distribution of moisture in the cell stacking direction, if the operation is continued, flooding occurs in the cell with a large amount of moisture, and there is a high possibility that so-called cell dropping will occur. Become. Therefore, in the present invention, when it is estimated that moisture is unevenly distributed in the stacking direction, the flow rate of the gas supplied to the fuel cell or the fluctuation speed of the gas pressure is reduced, that is, the load in the operation of the fuel cell. Reduce fluctuations. As a result, according to the present invention, gas penetrates into a cell having a large amount of water, and so-called cell dropping can be prevented.

  In addition, the estimation means may determine the moisture content in the fuel cell based on the voltage difference when the flow rate of the gas supplied to the fuel cell is an appropriate flow rate for the fuel cell to generate power. May be estimated.

  Only when the flow rate of the supplied gas is an appropriate flow rate for power generation, by estimating the uneven distribution of moisture, the flow rate of gas as a voltage fluctuation factor is excluded, and the moisture content based on the voltage difference It is possible to estimate the uneven distribution of moisture in a state suitable for estimating the difference.

  According to the present invention, it is possible to provide a fuel cell system capable of estimating the uneven distribution of water in a fuel cell.

  Embodiments of a fuel cell system according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an outline of the configuration of the fuel cell system in the present embodiment. The fuel cell system includes a fuel cell 1, a gas tank 21 for storing fuel gas, a fuel gas passage 22, a circulation passage 25, a fuel off-gas passage 30, an air blower 51, an oxidizing gas passage 52, and an oxidizing off-gas passage. 53, a measuring device 60, a humidifier 70, and an electronic control unit (hereinafter referred to as “ECU”) 90. The fuel cell system performs an electrochemical reaction in the fuel cell 1 by the fuel gas supplied from the gas tank 21 through the fuel gas passage 22 and the oxidizing gas supplied from the air blower 51 through the oxidizing gas passage 52. Electric power is generated by advancing.

  A pressure reducing valve 23 and a flow control valve 24 are provided in the fuel gas passage 22. The fuel gas supplied from the gas tank 21 to the fuel cell 1 is reduced to a predetermined pressure by the pressure reducing valve 23, the flow rate is adjusted by the flow rate control valve 24, and supplied to the fuel cell 1 through the fuel gas passage 22. . The fuel gas that has passed through the fuel cell 1 is discharged to the circulation passage 25.

  A circulation pump 26 is provided in the circulation passage 25. The circulation pump 26 can return the fuel gas discharged from the fuel cell 1 to the fuel gas passage 22 and increase the flow rate of hydrogen gas supplied to the fuel cell 1 per unit time.

  A purge valve 31 is provided in the fuel off-gas passage 30. Since the hydrogen gas concentration in the gas decreases due to the circulation of the fuel gas, the purge valve 31 is controlled to discharge the fuel off-gas having a low hydrogen gas concentration from the circulation passage 25 to the fuel off-gas passage 30 and the flow control valve 24. By controlling the above, fuel gas having a high hydrogen gas concentration is supplied from the gas tank 21.

  The measuring device 60 measures various states of the fuel cell 1 including the voltage of each cell 10 (see FIG. 2) of the fuel cell 1 and the voltage at a predetermined location on the cell surface described later. The voltage of each cell 10 measured by the measuring device 60 is sent to the ECU 90.

  In addition to the CPU, the ECU 90 includes a ROM, a RAM, and the like that store various programs and maps to be described later, and controls each element of the entire fuel cell system. The purge valve 31, the pressure reducing valve 23, and the flow rate control valve 24 are controlled to open and close by the ECU 90. The ECU 90 controls the purge valve 31, the pressure reducing valve 23, and the flow rate control valve 24 so that the power generation efficiency of the fuel cell is optimized based on the state of the fuel cell including the estimated water distribution in the fuel cell.

  The ECU 90 determines the uneven distribution of water in the stacking direction of the stack of the fuel cell 1 or the cell surface based on the voltage or the like of each cell 10 measured by the measuring device 60, and the moisture in the fuel cell is determined according to the determination result. Control the amount. That is, the ECU 90 corresponds to the estimation means, determination means, and control means of the present invention.

  FIG. 2 is a schematic cross-sectional view of the cell 10 constituting the fuel cell 1 in the present embodiment. The fuel cell 1 has a stack formed by stacking a plurality of cells 10, and each cell 10 has a cathode-side separator 11, a cathode-side gas diffusion layer 12, a membrane having an oxidizing gas channel 16 on the inner surface. An electrode assembly 13, an anode side gas diffusion layer 14, and an anode side separator 15 having a fuel gas flow path 17 on the inner surface are sequentially laminated. The fuel cell 1 causes the electrochemical reaction by the supplied reaction gas to proceed in the membrane electrode assembly 13 in which the cathode side catalyst layer 13c, the electrolyte membrane 13b, and the anode side catalyst layer 13a are laminated, thereby generating power. Do. The reaction gas is a fuel gas supplied from a fuel tank (not shown) and an oxidizing gas obtained from the outside air and supplied. The oxidizing gas is supplied to the cathode side gas diffusion layer 12, and the fuel gas is supplied to the anode side gas diffusion layer 14.

  FIG. 3 is a plan view of the cell 10 constituting the fuel cell 1 in the present embodiment. The oxidizing gas supplied to the cell 10 is diffused to the cathode side gas diffusion layer 12 through the oxidizing gas channel 16 formed so as to meander on the surface of the cell 10. Similarly, the fuel gas supplied to the cell 10 is diffused to the anode-side gas diffusion layer 14 through the fuel gas channel 17 formed so as to meander on the surface of the cell 10. The oxidizing gas channel 16 and the fuel gas channel 17 are arranged so that the oxidizing gas and the fuel gas flow in directions facing each other (so-called counter flow structure). Furthermore, voltmeters 61 and 62 and dew point meters 63 and 64 connected to the measuring device 60 are installed in the cell 10.

  Here, the oxidizing gas channel 16, the cathode side gas diffusion layer 12, the fuel gas channel 17, and the anode side gas diffusion layer 14 are uniformly diffused with respect to the membrane electrode assembly 13, because the oxidizing gas and the fuel gas are uniformly diffused. However, the water distribution is uneven and the generated voltage is not uniform. For example, on the cathode side where generated water is generated by power generation, gas flows in from the inlet side to move the water on the cathode side. Therefore, when the vicinity of the inlet of the oxidizing gas channel 16 is compared with the vicinity of the outlet, the vicinity of the outlet is usually wet. The vicinity of the entrance is relatively dry. In addition, the temperature near the outer extension of the cell 10 tends to be lower due to heat radiation than in the central portion, which causes a difference in moisture content between the outside and the inside of the cell 10.

The voltmeter 61 and the voltmeter 62 are provided at a position where the power generation voltage can be measured at a predetermined location on the cell surface. In the present embodiment, the voltmeter 61 is provided at a position where a voltage (hereinafter referred to as voltage 1) in the vicinity of the inlet of the oxidizing gas passage 16 (that is, in the vicinity of the outlet of the fuel gas passage 17) can be measured. Similarly, the voltmeter 62 is located near the outlet of the oxidizing gas channel 16 (
That is, it is provided at a position where a voltage (hereinafter referred to as voltage 2) in the vicinity of the inlet of the fuel gas channel 17 can be measured. The fuel cell system according to this embodiment determines the uneven distribution of water in the single cell based on the voltage difference between the voltage 1 and the voltage 2. In this embodiment, the voltmeter is provided in the vicinity of the gas inlet / outlet. However, the uneven distribution of moisture in the fuel cell 1 may occur regardless of the gas flow. For this reason, the installation location of the voltmeter is not limited to the vicinity of the entrance and exit of the gas flow path, but is preferably determined as appropriate according to the embodiment and the location where the uneven distribution of moisture is to be estimated.

  The dew point meters 63 and 64 are provided at positions where the dew point of off gas can be measured. The dew point meter 63 is provided at a position where the dew point of the fuel off gas in the vicinity of the outlet of the fuel gas channel 17 can be measured. The dew point meter 64 is provided at a position where the dew point of the oxidizing off gas in the vicinity of the outlet of the oxidizing gas channel 16 can be measured. The ECU 90 receives the measurement results from the dew point meters 63 and 64, and determines which of the anode side and cathode side electrodes is dry (whether it is a dry electrode) in the cell 10 provided with the dew point meters 63 and 64. To do. Specifically, the ECU 90 determines that the side where the off-gas dew point is lower than the saturation point is the dry electrode.

  FIG. 4 is a diagram illustrating the relationship between the voltage difference and the slope of the water distribution in the present embodiment. The vertical axis indicates the amount of water at a predetermined location on the cell surface, and two points on the horizontal axis indicate the measurement location by the voltmeter 61 and the measurement location by the voltmeter 62. That is, FIG. 4 shows a state in which the water distribution is inclined from the measurement point by the voltmeter 62 (near the outlet of the oxidizing gas channel 16) to the measurement point by the voltmeter 61 (near the inlet of the oxidizing gas channel 16). Show.

  The slope of the water distribution increases as the voltage difference between voltage 1 and voltage 2 increases, and decreases as the voltage difference decreases. This is because in a state where flooding or the like does not occur, the power generation efficiency generally increases as the electrolyte membrane 13b gets wet. Moreover, in the state where flooding or the like does not occur, the amount of water at the place where the voltmeter 62 is installed is substantially constant. In addition, in order to perform the water distribution estimation process in the present embodiment, it is preferable that the cell 10 is supplied with sufficient and appropriate amounts of fuel gas and oxidizing gas for power generation. This is because the air-fuel ratio can be excluded as a voltage fluctuation factor when sufficient and appropriate amounts of fuel gas and oxidizing gas for power generation are supplied. The change in the area of the trapezoid surrounded by the frame line in FIG. 4 and the line indicating the slope of the water distribution is a voltage 1 between the voltage difference and the cell water content that is the amount of moisture contained in the entire cell 10. It shows that there is a correlation that the cell water content is smaller as the voltage difference between the voltage and the voltage 2 is larger and the cell water content is larger as the voltage difference is smaller.

  FIG. 5 is a graph showing the relationship between the voltage difference in the cell 10 and the cell water content in the present embodiment. Usually, the vicinity of the outlet of the oxidizing gas flow path 16 is sufficiently wet. Therefore, when the voltage difference is extremely small, the vicinity of the inlet of the oxidizing gas flow path 16 is also sufficiently wet, and the cell water content is estimated to be large. On the other hand, when the voltage difference is large, it is considered that the vicinity of the inlet of the oxidizing gas channel 16 is dry, and the cell water content is estimated to be small.

  Therefore, the ECU 90 in this embodiment uses the relationship between the voltage difference (inclination of water distribution) and the cell moisture content shown in FIG. 5 in order to control the cell moisture content to the target state. That is, when it is desired to maximize the cell water content, the ECU 90 performs control while monitoring the voltage difference or the slope of the estimated water distribution, and controls so that the voltage difference or the slope of the water distribution is minimized. Cell water content can be maximized. On the other hand, when it is desired to minimize the cell water content, the voltage difference or the slope of the water distribution may be controlled to be maximized.

FIG. 6 is a flowchart showing a processing flow for maximizing the cell water content in the present embodiment. The processing shown in this flowchart is periodically executed when the fuel cell 1 is in an operating environment where it is preferable to maximize the power generation efficiency. Further, the processing shown in this flowchart is executed for every cell 10 provided in the fuel cell 1.

  In step S101, voltage 1 and voltage 2 are measured. The voltmeter 61 and the voltmeter 62 measure the voltage at the installation location and output it to the ECU 90. Thereafter, the process proceeds to step S102.

  In step S102, it is determined whether or not the fuel gas and the oxidizing gas are sufficiently and appropriately supplied in the cell 10 to be processed. The ECU 90 supplies the oxidizing gas supply amount measured by a measuring instrument (not shown) installed in the oxidizing gas passage 52, and the fuel gas measured by a measuring instrument (not shown) installed in the fuel gas passage 22. Based on the relationship between the supply amount and the stoichiometric air-fuel ratio, it is determined whether the fuel gas and the oxidizing gas are sufficiently and appropriately supplied.

  However, the state in which the fuel gas and the oxidizing gas are sufficiently and appropriately supplied is not limited to the state in which the ratio between the fuel gas supply amount and the oxidizing gas supply amount matches the stoichiometric air-fuel ratio. Actually, the ratio of the fuel gas to the oxidizing gas is adjusted according to the power generation efficiency in the fuel cell 1. If it is determined that the gas supply is sufficient and appropriate, the process proceeds to step S103. When it is determined that the gas supply is not sufficient and appropriate, the processing shown in this flowchart ends. This is because the air-fuel ratio cannot be excluded as a voltage fluctuation factor, and it is difficult to estimate the slope of the water distribution from the voltage difference. In the present embodiment, the process shown in step S102 is executed in order to exclude the air-fuel ratio as a voltage fluctuation factor. However, this process may be omitted.

  In step S103, the uneven distribution of water on the cell surface is estimated based on the voltage difference. Receiving the measurement result output in step S101, the ECU 90 calculates the voltage difference between the voltage 1 and the voltage 2, and compares the calculated voltage difference with a preset threshold value, so Estimate the uneven distribution of This threshold value is a threshold value for determining whether or not the cell water content is maximized. When the voltage difference is smaller than the threshold value, the cell water content is maximized, and it is estimated that the water on the cell surface is distributed substantially uniformly. In this case, since the control for maximizing the water content (making the water distribution uniform) is unnecessary, the processing shown in this flowchart is terminated. On the other hand, when the voltage difference is equal to or greater than the threshold value, the cell water content is not maximized, and it is estimated that uneven distribution of water (non-uniform water distribution) occurs on the cell surface. In this case, the process proceeds to step S104, and thereafter, control for maximizing the water content (making the water distribution uniform) is performed.

  In step S104 and step S105, control for maximizing the water content (homogenizing the water distribution) is performed. The ECU 90 controls the humidifier 70 to increase the amount of humidification to the gas supplied from the gas flow path inlet near the installation location of the voltmeters 61 and 62 on which the low voltage is detected. For example, when the voltage 1 near the inlet of the oxidizing gas channel 16 is lower than the voltage 2, the ECU 90 supplies the oxidizing gas to the oxidizing gas, which is a gas supplied from the gas channel inlet near the installation location of the voltmeter 61. Increase the amount of humidification.

  Further, the ECU 90 controls the air blower 51 or the flow rate control valve 24 to increase the flow rate of the gas supplied to the pole that the ECU 90 has determined to be the dry pole based on the measurement results from the dew point meters 63 and 64. . For example, when the ECU 90 determines that the cathode side is the dry electrode, the ECU 90 increases the flow rate of the oxidizing gas supplied to the cell 10.

FIG. 7 is a diagram showing a mechanism for promoting moisture movement from the opposite pole by increasing the gas flow rate in the present embodiment. As the flow rate of the humidified gas increases, the amount of moisture carried away at the drying electrode increases. Then, the movement of moisture through the electrolyte membrane 13b from the opposite electrode (that is, the anode side on the opposite side when the flow rate of the oxidizing gas is increased) is promoted, and as a result, the moisture content of the dry electrode increases. Then, the water distribution is made uniform. Thereafter, in the processing from step S101 to step S105, it is determined in step S102 that the gas supply is not sufficient and appropriate, or in step S103, it is determined that the voltage difference is smaller than the threshold (that is, the cell is included). It is repeated until the amount of water is maximized and the water on the cell surface is estimated to be distributed substantially uniformly).

  FIG. 8 is a schematic diagram showing a mechanism in which the amount of moisture moving from the opposite catalyst layer changes according to a change in gas flow rate in the present embodiment. FIG. 8 shows the relationship between the gas flow rate, the water content of the catalyst layer, and the amount of moisture transfer with respect to local moisture transfer when the size of the cell 10 is not taken into consideration. Of the equations shown in FIG. 8, Equation 1 is an equation showing the relationship between the amount of water carried away dQg / dt per unit time on the anode side and the gas vapor pressure Pwa at the anode side inlet, and Equation 2 is The equation shows the relationship between the gas vapor pressure at the anode side inlet, Pwa, and the fuel gas flow rate QH2. Equation 3 is an equation showing the relationship between the amount dQg / dt of water removal per unit time on the cathode side and the gas vapor pressure Pwc at the cathode side inlet, and Equation 4 is the gas vapor pressure at the cathode side inlet. And Pwc and the fuel gas flow rate Qair.

  In the equation shown in FIG. 8, s is the water content of the anode side catalyst layer 13a, u is the water content of the cathode side catalyst layer 13c, Pwa is the anode inlet gas vapor pressure, Pwc is the cathode inlet gas vapor pressure, k1 is a water transfer coefficient of the electrolyte membrane, k2 and k3 are gas removal coefficients, and V is an allowable water content in each layer. Formula 5 is a formula showing the amount of water movement Qm per unit time in the electrolyte membrane.

  For example, when it is estimated that the anode inlet voltage is low and the vicinity of the anode inlet is dry, increasing the fuel gas flow rate QH2 reduces Pwa (see Equation 2), and unit time accordingly. The amount of water taken away per hit Qg and the water content s of the anode catalyst layer are reduced (see Formula 1). As a result, the amount of water movement Qm per unit time in the electrolyte membrane increases (see Formula 5). The same applies to the case where the voltage at the cathode inlet is low. That is, according to the schematic diagram shown in FIG. 8, it is understood that the movement of moisture from the opposite electrode is promoted by increasing the gas flow rate.

  According to the present embodiment, it is possible to estimate the uneven distribution of water (water distribution) and make the water distribution uniform on the cell surface based on this result. By making the water distribution uniform based on the water distribution, the operation efficiency of the fuel cell can be optimized.

  In the flowchart shown in FIG. 6, the control for maximizing the performance of the fuel cell 1 by maximizing the cell water content based on the voltage difference is described. However, the water based on the voltage difference in the present invention is described. The estimation of uneven distribution may be used for control for minimizing the cell water content. The minimization of the water content of the cell is performed at the time of termination processing of the fuel cell for the purpose of improving the startability (particularly, the startability below freezing point).

  FIG. 9 is a flowchart showing the flow of processing for minimizing the cell water content in this embodiment. The process shown in this flowchart is executed when it is necessary to minimize the water content in the fuel cell 1 while the fuel cell 1 is in operation (for example, during the operation end process). Further, the processing shown in this flowchart is executed for every cell 10 provided in the fuel cell 1.

In Step S201 and Step S202, the voltage 1 and the voltage 2 are measured, and it is determined whether or not the fuel gas and the oxidizing gas are sufficiently and appropriately supplied in the cell 10 to be processed. Details of the processing are the same as steps S101 and S102 described in FIG. Thereafter, the process proceeds to step S203.

  In step S203, the uneven distribution of water on the cell surface is estimated based on the voltage difference. Receiving the measurement result output in step S201, the ECU 90 calculates the voltage difference between the voltage 1 and the voltage 2, and compares the calculated voltage difference with a preset threshold value, so Estimate the uneven distribution of This threshold value is a threshold value for determining whether or not the cell water content is minimized, and is a threshold value set to a value different from the threshold value used in step S103. If the voltage difference is greater than the threshold, it is estimated that the cell water content is minimized. In this case, since the control for minimizing the water content is unnecessary, the process shown in this flowchart ends. On the other hand, when the voltage difference is equal to or less than the threshold value, it is estimated that the cell water content is not minimized. In this case, the process proceeds to step S204, and thereafter, control for minimizing the water content is performed.

  In step S204 and step S205, control for minimizing the water content is performed. The ECU 90 controls the humidifier 70 to reduce the amount of humidification to the supplied gas. Further, the ECU 90 controls the air blower 51 or the flow rate control valve 24 to increase the flow rate of the supplied gas. Here, in general, since the amount of moisture removed from the cathode side outlet is larger than the amount of moisture removed from the anode side outlet, at least the humidification amount for the oxidizing gas can be reduced and the flow rate of the oxidizing gas can be increased. preferable.

  FIG. 10 is a diagram showing a mechanism for decreasing the cell water content by increasing the gas flow rate in the present embodiment. As the flow rate of the dried gas increases, the amount of moisture carried away near the flow channel inlet of the supplied gas increases. Then, the moisture content in the vicinity of the wet gas inlet decreases, and the cell moisture content decreases. Thereafter, in the processing from step S201 to step S205, it is determined in step S202 that the gas supply is not sufficient and appropriate, or in step S203, it is determined that the voltage difference is larger than the threshold (that is, the cell is included). Repeat until the water volume is estimated to be minimized).

  According to this embodiment, it is possible to estimate the uneven distribution of water (water distribution) and to minimize the cell water content based on this result. As a result, it is possible to improve the startability (particularly, below freezing point startability) of the fuel cell 1.

  Next, a method of estimating the water distribution gradient (water uneven distribution) in the stacking direction of the stack of the fuel cell 1 and controlling the water content in the fuel cell 1 based on this will be described.

  FIG. 11 is a schematic cross-sectional view of the stack of the fuel cell 1 in the present embodiment. As described above, the stack of the fuel cell 1 is formed by stacking a plurality of cells 10. The stack of the fuel cell 1 is sandwiched between end plates 18 and 19 provided at both ends. In the stack of the fuel cell 1, gas is supplied from one end (supply / discharge end) and distributed to all the cells 10 in the stack. The gas discharged from the cell 10 is discharged from the supply / discharge end.

Here, the gas flow is weaker at the end opposite to the supply / discharge end compared to the supply / discharge end having the supply / discharge port, and the cell near the end plate (hereinafter referred to as “end cell”) is the cell near the center of the stack. The uneven distribution of water in the stacking direction occurs due to the fact that the temperature is lower than that of the “central cell” (hereinafter referred to as “central cell”) and the water is liable to liquefy. FIG. 12 is a diagram showing how water moves from the cathode side to the anode side in the end cell near the end opposite to the supply / discharge end. The end cell is provided with a voltmeter 65 for measuring the output voltage from the end cell, and the center cell is provided with a voltmeter 66 for measuring the output voltage from the center cell.

  FIG. 13 is a diagram showing the relationship between the water content and the voltage that change with the operation of the fuel cell 1. Here, it is assumed that the end cell is sufficiently wet and the center cell is slightly dry at the start of operation of the fuel cell 1 (see the upper graph in FIG. 13). Thereafter, as the operation of the fuel cell 1 is continued, the water content of the central cell increases and the power generation efficiency increases. However, when the central cell becomes wet to some extent, moisture is gradually distributed to the end cells thereafter. Here, as the uneven distribution of water in the end cell increases, the voltage difference between the end cell and the center cell increases.

  In the present invention, the uneven distribution of water in the end cell is estimated when this voltage difference is equal to or greater than a preset threshold value. In addition, if the operation is continued without eliminating the uneven distribution of water after the uneven distribution of water occurs, flooding occurs in the end cell, making it difficult to continue power generation in the end cell (cell dropping occurs, The voltage at the end cell drops). For this reason, the fuel cell system according to the present embodiment estimates the uneven distribution of water in the stacking direction of the stack based on the voltage difference between the end cell and the center cell, and predicts the occurrence of flooding. And based on a voltage difference, the control which eliminates the uneven distribution of water and prevents the cell drop by generation | occurrence | production of flooding is performed.

  FIG. 14 is a flowchart showing the flow of processing for lowering the end cell water content in the present embodiment. The processing shown in this flowchart is periodically executed when the fuel cell 1 is in an operating environment where it is preferable to maximize the power generation efficiency.

  In step S301, the end cell voltage and the central cell voltage are measured. Voltmeters 65 and 66 measure the end cell voltage and the central cell voltage and output them to ECU 90. Thereafter, the process proceeds to step S302.

  In step S302, it is determined whether or not the fuel gas and the oxidizing gas are sufficiently and appropriately supplied in the fuel cell 1. Details of the processing are the same as step S102 described in FIG. Thereafter, the process proceeds to step S303.

  In step S303, the uneven distribution of water in the stack is estimated based on the voltage difference. The ECU 90 that has received the measurement result output in step S301 calculates a voltage difference between the end cell voltage and the center cell voltage, and compares the calculated voltage difference with a preset threshold value to thereby determine the stacking direction. Estimate the uneven distribution of water. This threshold is a threshold for determining uneven distribution of water in the stack, and is a threshold set to a value different from the threshold used in step S103 or step S203.

  This threshold is determined based on the voltage difference between the end cell and the central cell at the timing when the moisture content increases in the end cell with the operation of the fuel cell and the uneven distribution of moisture occurs (see FIG. 13). When the voltage difference is smaller than the threshold value, it is estimated that water is not unevenly distributed in the stack. In this case, since the control for reducing the water content in the end cell is not necessary, the processing shown in this flowchart ends. On the other hand, when the voltage difference is equal to or greater than the threshold value, it is estimated that water is unevenly distributed in the stack. In this case, the process proceeds to step S304, and thereafter, control for reducing the end cell water content is performed.

In step S304, control for reducing the water content of the end cell is performed. The ECU 90 controls the supply gas flow rate, purge frequency, supply gas pressure, and the like to reduce the end cell moisture content. For example, when water has accumulated on the anode side of the cell adjacent to the opposite end of the supply / discharge end, as a specific method of eliminating this uneven distribution of water, the flow control valve 24 is controlled to control the flow rate of the fuel gas. By increasing the amount of moisture removed from the anode side, the purge valve 31 is controlled, and the purge frequency of the fuel gas is increased to supply the dry fuel gas from the fuel tank 21 to the fuel cell. A method of increasing the amount, a method of increasing the amount of moisture removed from the stack by reducing the gas pressure of the fuel gas, a method of promoting the permeation of moisture from the anode side to the cathode side by reducing the gas pressure of the oxidizing gas, Etc. It is preferable that a specific method for eliminating the uneven distribution of water is executed by selecting one or a plurality of methods depending on the situation. Thereafter, the process proceeds to step S305.

  In step S305, control is performed to moderate load fluctuations in order to prevent end cell dropping. Specifically, the ECU 90 moderates the rate of fluctuation of the gas flow rate and gas pressure in the control of the gas flow rate and gas pressure. That is, when changing the gas flow rate or gas pressure, by slowing the rate of change, the gas can reach the end cells where flooding occurs, and the gas does not pass through the cells that are clogged with water. This prevents the occurrence of a phenomenon (cell loss) that prevents power generation.

  Thereafter, in the processing from step S301 to step S305, it is determined in step S302 that the gas supply is not sufficient and appropriate, or in step S303, it is determined that the voltage difference is smaller than the threshold (that is, in the stack). It is repeated until it is estimated that no water is unevenly distributed).

  According to the present embodiment, it is possible to estimate the uneven distribution of water (water distribution) and reduce the water content of the end cell based on this result. As a result, it is possible to optimize the operation efficiency of the fuel cell, and to prevent the end cell from dropping due to flooding.

It is the figure which showed the outline of the structure of the fuel cell system in embodiment. It is a schematic sectional drawing of the cell which comprises the fuel cell in embodiment. It is a top view of the cell which constitutes the fuel cell in an embodiment. It is a figure which shows the relationship between the voltage difference and the inclination of water distribution in embodiment. It is a graph which shows the relationship between the voltage difference in a cell and cell water content in embodiment. It is a flowchart which shows the flow of the process which maximizes cell water content in embodiment. It is a figure which shows the mechanism which accelerates | stimulates the water movement from an opposite pole by increasing the gas flow rate in embodiment. It is a schematic diagram which shows the mechanism in which the quantity of the water | moisture content which moves from the catalyst layer of the other side changes according to the change of the gas flow rate in embodiment. It is a flowchart which shows the flow of the process which minimizes cell water content in embodiment. It is a figure which shows the mechanism in which cell water content is decreased by increasing the gas flow rate in embodiment. It is a schematic sectional drawing of the stack of the fuel cell in an embodiment. It is a figure which shows a mode that the movement of the water from a cathode side to an anode side generate | occur | produces in the end cell of the other end near the supply discharge end. It is a figure which shows the relationship between the water content and voltage which change with the driving | operation of a fuel cell. It is a flowchart which shows the flow of the process which reduces an end cell moisture content in embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 10 Cell 12 Cathode side gas diffusion layer 13 Membrane electrode assembly 14 Anode side gas diffusion layer 16 Oxidation gas flow path 17 Fuel gas flow path 18, 19 End plate 24 Flow control valve 25 Circulation path 31 Purge valve 60 Measuring device 61, 62 Voltmeter 63, 64 Dew point meter 65, 66 Voltmeter 70 Humidifier 90 Electronic control unit (ECU)

Claims (12)

A fuel cell that generates electricity by an electrochemical reaction between an oxidizing gas and a fuel gas;
Measuring means for measuring voltage at a plurality of measurement points in the fuel cell;
The plurality of measurements of the fuel cell based on the difference in water content between the plurality of measurement points, which is estimated from the difference between the voltages measured at different measurement points among the voltages measured by the measurement unit. and estimating means for estimating the uneven distribution status of moisture between locations,
Control means for controlling the uneven distribution of water or the amount of water in the fuel cell based on the uneven distribution of water in the fuel cell estimated by the estimating means;
When it is estimated by the estimation means that uneven distribution of moisture occurs in the fuel cell, any one of the two poles in the fuel cell is a dry pole that is dried from the opposite pole, and Determination means for determining which pole is a wet pole wetter than the opposite pole,
Fuel cell system. The estimation means estimates that the uneven distribution of moisture occurs in the fuel cell when the voltage difference is equal to or greater than a predetermined threshold.
The fuel cell system according to claim 1. The control means controls the uneven distribution of moisture or the amount of moisture in the fuel cell by adjusting at least one of the humidity, gas flow rate and gas pressure of the gas supplied to the fuel cell.
The fuel cell system according to claim 1 or 2 . The determination means determines which of the two poles is the dry electrode and the wet electrode based on the dew point of the off gas discharged from each of the two electrodes.
The fuel cell system according to claim 1 . The control means promotes the movement of moisture from the wet electrode to the dry electrode by increasing the flow rate of the gas supplied to the electrode determined to be the dry electrode by the determining device.
The fuel cell system according to claim 1 or 4 . The control means reduces the gas pressure of the electrode determined to be the dry electrode by the determination device with respect to the gas pressure of the wet electrode, thereby moving moisture from the wet electrode to the dry electrode. Facilitate,
The fuel cell system according to any one of claims 1, 4, and 5 . Circulating means for circulating the fuel off-gas discharged from the fuel cell and supplying it again to the anode electrode;
Purge means for purging the fuel off-gas circulated by the circulation means to the outside at a predetermined timing;
Supply means for supplying the fuel cell with a fuel gas that is dry compared to the fuel off-gas discharged from the fuel cell in accordance with the purge by the purge means;
When the wet electrode is an electrode to which fuel gas is supplied, the control unit lowers the humidity of the fuel gas supplied to the wet electrode by increasing the purge amount or the purge frequency by the purge unit, Reduce the moisture content of the wet pole,
The fuel cell system according to any one of claims 1, 4, 5, and 6 . A fuel cell that generates electricity by an electrochemical reaction between an oxidizing gas and a fuel gas;
Measuring means for measuring voltage at a plurality of measurement points in the fuel cell;
The plurality of measurements of the fuel cell based on the difference in water content between the plurality of measurement points, which is estimated from the difference between the voltages measured at different measurement points among the voltages measured by the measurement unit. An estimation means for estimating the uneven distribution of moisture between locations;
With
The measuring means measures the voltage in the vicinity of the inlet of the supplied gas and the voltage in the vicinity of the outlet in a single cell,
The estimation means estimates the uneven distribution of moisture in a single cell based on the measured voltage difference.
Fuel cell system. When the estimation means estimates that the vicinity of the gas inlet is dry compared to the vicinity of the outlet, the control means increases the flow rate of the supplied gas to increase the flow rate of the supplied gas from the opposite pole to the vicinity of the inlet. Promote the movement of moisture,
The fuel cell system according to claim 8 . The fuel cell is a fuel cell in which a plurality of cells are stacked,
The measuring means measures voltages in different cells;
The estimation means estimates the uneven distribution of moisture between the cells in which the voltage is measured in the direction of the stack, based on the measured voltage difference.
The fuel cell system according to any one of claims 1 to 7 . When the control means estimates that the moisture is unevenly distributed in the stacking direction of the plurality of cells by the estimation means, when changing the flow rate or gas pressure of the gas supplied to the fuel cell, Slowly change the flow rate or gas pressure compared to the case where there is no uneven distribution of moisture ,
The fuel cell system according to claim 10 . When the flow rate of the gas supplied to the fuel cell is an appropriate flow rate for the power generation by the fuel cell, the estimation means is configured to distribute moisture in the fuel cell based on the voltage difference. Estimating the situation,
The fuel cell system according to any one of claims 1 to 11 .

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