JP2008066114A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate the wet state of a fuel cell with favoble precision by detecting an emission amount of a carbon dioxide since a discharged amount of the carbon dioxide has a correlation with a water amount in the fuel cell. <P>SOLUTION: At starting a system, the discharged amount of the carbon dioxide discharged from an oxidizer electrode of the fuel cell is detected, and based on this detected discharged amount, the wet state of the fuel cell is estimated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to a method for determining a wet state of a fuel cell.

  Conventionally, a fuel gas (for example, hydrogen) is supplied to the fuel electrode, and an oxidant gas (for example, air) is supplied to the oxidant electrode, whereby these gases are reacted electrochemically to generate power. A fuel cell system including a battery is known. This type of fuel cell is configured by sandwiching a fuel cell structure (MEA: membrane-electrode assembly) in which an oxidant electrode and a fuel electrode are opposed to each other with an electrolyte and an electrode catalyst composite in between. As an electrolyte, a solid polymer electrolyte is often used in consideration of high energy density, low cost, light weight, and the like. The solid polymer electrolyte is composed of, for example, an ion conductive polymer membrane such as a fluororesin ion exchange membrane, and functions as an ion conductive electrolyte when saturated with water. Therefore, in such a fuel cell, since the wet state of the electrolyte membrane affects the power generation performance, it is important to determine the wet state.

For example, Patent Document 1 determines whether a wet state of a fuel cell is an excessive moisture state or a dry state by comparing an open circuit voltage (OCV) of the fuel cell with a threshold value. A technique is disclosed.
JP 2005-32587 A

  However, according to the method disclosed in Patent Document 1, it takes time for the voltage to stabilize, and the open circuit voltage changes depending on the temperature and pressure conditions, so that the wet state is accurately determined. There is a problem that it becomes difficult.

  The present invention has been made in view of such circumstances, and an object thereof is to accurately estimate the wet state of the fuel cell.

  In order to solve such a problem, the present invention provides a fuel cell system including a fuel cell, an emission amount detection unit, and an estimation unit. Here, in the fuel cell, fuel gas is supplied to the fuel electrode, and oxidant gas is supplied to the oxidant electrode, whereby the fuel gas and the oxidant gas are reacted electrochemically to generate electric power. To do. The emission amount detection means detects the emission amount of carbon dioxide emitted from the oxidizer electrode. The estimation means estimates the wet state of the fuel cell based on the carbon dioxide emission detected by the emission detection means when the system is activated.

  According to the present invention, since the amount of carbon dioxide emission has a correlation with the amount of water in the fuel cell, the wet state of the fuel cell can be accurately estimated by detecting the amount of carbon dioxide emission. .

  FIG. 1 is a configuration diagram schematically showing a fuel cell system according to an embodiment of the present invention. The fuel cell system includes a fuel cell stack 1 configured by stacking a plurality of fuel cells each sandwiched by a separator with a fuel cell structure in which an oxidant electrode and a fuel electrode are opposed to each other with a solid polymer electrolyte membrane interposed therebetween. . The fuel cell stack 1 is configured such that in each fuel cell, fuel gas is supplied to the fuel electrode and oxidant gas is supplied to the oxidant electrode to cause these gases to react electrochemically. Generate electricity. In this embodiment, a case will be described in which hydrogen is used as the fuel gas and oxygen (specifically, air containing oxygen) is used as the oxidant gas.

Fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ (1)
Oxidant electrode: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
Specifically, in each power generation cell, as shown in (1) and (2), a reaction occurs in which hydrogen supplied to the fuel electrode is separated into hydrogen ions and electrons. Hydrogen ions pass through the electrolyte and electrons move through the external circuit to the oxidant electrode side. At the oxidizer electrode, the oxygen in the supplied air reacts with the hydrogen ions and electrons that have moved through the electrolyte to produce water.

  This fuel cell system is mounted on a vehicle (fuel cell vehicle) as a power source for a vehicle drive motor or the like that drives the vehicle, for example.

  The fuel cell system includes a hydrogen system 10 for supplying hydrogen to the fuel cell stack 1 and an air system 20 for supplying air to the fuel cell stack 1.

  In the hydrogen system 10, hydrogen, which is a fuel gas, is supplied from the hydrogen supply unit 11 to the fuel electrode of the fuel cell stack 1 through the hydrogen supply channel 10 a. A hydrogen flow rate control valve 12 is provided in the hydrogen supply channel 10a. The opening degree of the hydrogen flow rate control valve 12 is controlled by the control unit 30 described later so that the hydrogen flow rate supplied to the fuel cell stack 1 becomes a desired value. On the other hand, gas discharged from the fuel electrode side of the fuel cell stack 1 (exhaust gas containing unused hydrogen) is discharged to the hydrogen discharge passage 10b.

  In the air system 20, for example, air that is an oxidant gas is supplied from the air supply unit 21 to the oxidant electrode of the fuel cell stack 1 via the air supply channel 20a. A hydrogen flow rate control valve 22 is provided in the air supply channel 20a. The opening degree of the air flow rate control valve 22 is controlled by the control unit 30 so that the air flow rate supplied to the fuel cell stack 1 becomes a desired value. On the other hand, the gas discharged from the oxidant electrode side of the fuel cell stack 1 (exhaust gas in which a part of oxygen is consumed) is discharged to the air discharge passage 20b.

  In the fuel cell system, an output extraction unit 2 is connected to the fuel cell stack 1. The output take-out unit 2 is controlled by the control unit 30 and takes out a necessary output (for example, electric power) from the fuel cell stack 1 in accordance with the required output, and uses the taken out output as a vehicle drive motor (not shown). , A secondary battery (not shown), or various auxiliary machines for operating the fuel cell system.

  The control unit 30 controls the power generation operation of the fuel cell stack 1 by controlling each part of the system based on the operating state of the fuel cell stack 1. As the control unit 30, for example, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an input / output interface can be used. In the present embodiment, the control unit 30 estimates the wet state of the fuel cell stack, specifically, the solid polymer electrolyte membrane, as a process at the time of system startup (startup process). And according to this estimation result, recovery control is performed so as to suppress the excessive water state or suppress the dry state.

Fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ (3)
: 4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (4)
Oxidant electrode: C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ (5)
: 4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (6)
Here, when the system is started in a state where the fuel cell stack 1 is stopped and air is present in the hydrogen supply flow path, the reactions shown in (3) and (4) occur at the fuel electrode, and the oxidant The reactions shown in (5) and (6) occur at the pole. This is because the supported carbon contained in the catalyst layer of the solid polymer electrolyte membrane reacts with water at the oxidant electrode, whereby carbon dioxide is discharged from the oxidant electrode side. In this case, since the amount of carbon dioxide emission increases as the amount of water increases, the wet state of the fuel cell stack 1 can be estimated by detecting the amount of carbon dioxide emission.

In order to detect the operating state of the fuel cell stack 1, detection signals from various detection units 31 to 37 are input to the control unit 30. The outlet gas analysis unit 31 is provided in the air discharge channel 20b and measures the amount of carbon dioxide (CO ₂ amount) discharged from the oxidant electrode. The fuel electrode inlet side voltmeter 32 indicates the generated voltage (hereinafter referred to as “inlet side voltage”) of the fuel cell existing on the hydrogen inlet side (supply side) in each fuel cell constituting the fuel cell stack 1. To detect. The fuel electrode outlet side voltmeter 33 indicates the power generation voltage (hereinafter referred to as “exit side voltage”) of the fuel cell existing on the hydrogen outlet side (discharge side) in each fuel cell constituting the fuel cell stack 1. To detect. The hydrogen supply flow rate detection unit 34 is provided in the hydrogen supply flow path 10 a and detects the flow rate of hydrogen supplied to the fuel electrode of the fuel cell stack 1. The stack temperature detection unit 35 detects the temperature of the fuel cell stack 1. The air discharge flow rate detection unit 36 is provided in the air discharge flow path 20 b and detects the flow rate of the gas discharged from the oxidant electrode of the fuel cell stack 1. The exhaust gas temperature detection unit 37 is provided in the air discharge flow path 20 b and detects the temperature of the gas discharged from the oxidant electrode of the fuel cell stack 1.

  FIG. 2 is a block diagram illustrating a configuration of the control unit 30. When the control unit 30 grasps this functionally, the discharge amount detection unit 30a, the discharge amount calculation unit 30b, the operation time storage unit 30c, the correction unit 30d, the estimation unit 30e, and the system control unit 30f Have

Emission detector 30a, based on the measured value of the CO ₂ amount measured by the exit gas analysis unit 31, detects the emissions of CO ₂ actually discharged from the oxidant electrode fuel cell stack 1. The emission amount calculation unit 30 b refers to the operation time stored in the operation time storage unit 30 c and calculates the emission amount of CO ₂ discharged from the oxidant electrode of the fuel cell stack 1. The operation time storage unit 30 c stores an operation time that is a past operation history of the fuel cell stack 1. The correction unit 30d corrects the calculated value of the CO ₂ emission amount calculated by the emission amount calculation unit 30b based on the temperature of the fuel cell stack 1, the hydrogen supply flow rate, and the oxygen concentration (O ₂ concentration) of the fuel electrode. Estimating unit 30e includes a detection value of the detected CO ₂ emissions by the discharge amount detector 30a, by comparing the calculated value of the CO ₂ emissions, excessive water state or a dry state such as the fuel cell stack 1 wet Estimate the state. The system control unit 30f performs recovery control for recovering the wet state by controlling the output extraction unit 2 or the air supply flow rate adjustment valve 22 as necessary based on the estimation result of the estimation unit 30e.

  FIG. 3 is a flowchart showing the procedure of the activation process according to the present embodiment. The processing shown in this flowchart is executed by the control unit 30 when the system is started, for example, in the case of a fuel cell vehicle, triggered by an ignition switch ON signal.

First, in step 1 (S1), the CO ₂ emission amount is calculated. In Step 1, the CO ₂ emission amount is calculated based on the operation time. Since the CO ₂ emission amount depends on the degree of deterioration of the carbon supported on the catalyst layer, that is, the electrolyte membrane, the total operation time, idle operation time, load operation time, load response frequency, start / stop frequency of the fuel cell stack 1, There is a correlation with the operation time with parameters such as the number of freezing. This operation time becomes larger as the value of each parameter becomes longer or larger.

FIG. 4 is an explanatory diagram showing a correspondence relationship between the operation time and the CO ₂ emission amount. As can be seen from the figure, the CO ₂ emission amount tends to decrease as the operation time increases. Therefore, a correspondence relationship between the operation time and the CO ₂ emission amount is acquired through experiments and simulations, and for example, the correspondence relationship between the two is stored in the control unit 30 as a calculation formula (see Formula 1).

(Formula 1)
X = f (Ta)
Here, X is the CO ₂ emission amount, Ta is the operation time until the current start-up, and f is a function that defines the correspondence between the operation time Ta and the CO ₂ emission amount X. The operating time storage unit 30c stores each parameter that is an element of the operating time every time the system is operated. Therefore, the CO ₂ emission amount X is uniquely calculated by referring to the operation time storage unit 30c and specifying the handling time Ta.

In step 2 (S2), the CO ₂ emission amount X is corrected. In step 1, the CO ₂ emission amount is calculated from the operation time. This value is affected by the temperature of the fuel cell stack 1 and the oxygen concentration (O ₂ concentration) of the fuel electrode of the fuel cell stack 1. The correction is performed in consideration of these values.

(1) Temperature of Fuel Cell Stack 1 FIG. 5 is an explanatory diagram showing the correspondence between the temperature of the fuel cell stack 1 and the correction coefficient. The CO ₂ emission amount tends to increase as the temperature of the fuel cell stack 1 increases. Therefore, through an experiment or simulation, a correction coefficient for correcting the CO ₂ emission amount (calculated value) is obtained in association with a temperature difference from a certain reference temperature. For example, a calculation formula that defines the correspondence between the temperature difference from the reference temperature and the correction coefficient is stored in the control unit 30 (see Formula 2).

(Formula 2)
A = g (Tb) = g (Ta−Tp)
Here, A is a temperature correction coefficient, and Tb is a temperature difference from the reference temperature. Further, Ta is the temperature of the fuel cell stack 1, and Tp is a reference temperature. G is a function that defines the correspondence between the temperature difference Tb from the reference temperature Tp and the temperature correction coefficient A. Therefore, the temperature correction coefficient A can be uniquely calculated from the temperature Ta of the fuel cell stack 1 detected by the stack temperature detection unit 35. For “Ta”, not only the detection value by the stack temperature detection unit 35 but also the detection value by the exhaust gas temperature detection unit 37 may be used.

(Formula 3)
X1 = A * X = f (Ta) * g (Tb)
That is, the CO ₂ emission amount X1 subjected to temperature correction can be expressed by Equation 3.

(2) Hydrogen Supply Flow Rate FIG. 6 is an explanatory diagram showing the correspondence between the hydrogen supply flow rate and the correction coefficient. The CO ₂ emission amount depends on the magnitude of the hydrogen supply flow rate at startup. Therefore, through experiments and simulations, correction coefficients for correcting the CO ₂ emission amount (calculated value) are obtained in association with various hydrogen supply flow rates. For example, a calculation formula that defines the correspondence between the hydrogen supply flow rate and the correction coefficient is stored in the control unit 30 (see Formula 4).

(Formula 4)
B = h (Fr)
Here, B is a flow rate correction coefficient, and Fr is a hydrogen supply flow rate. H is a function that defines the correspondence between the hydrogen supply flow rate Fr and the flow rate correction coefficient B. Therefore, the flow rate correction coefficient B can be uniquely calculated from the hydrogen supply flow rate Fr detected by the hydrogen supply flow rate detection unit 34.

(Formula 5)
X2 = B * A * X = h (Fr) * f (Ta) * g (Tb)
That is, the CO ₂ emission amount X2 for which the flow rate correction is performed in addition to the temperature correction can be expressed by Equation 5.

(3) O ₂ Concentration at Fuel Electrode FIG. 7 is an explanatory diagram showing the correspondence between the elapsed time until startup and the O ₂ concentration. Since the oxygen from the oxidant electrode permeates, the O ₂ concentration in the fuel electrode tends to increase as the elapsed time from the previous stop to the current start increases. Therefore, the transition of the O ₂ concentration according to the elapsed time is acquired through experiments and simulations. For example, a calculation formula that defines the correspondence between the elapsed time and the O ₂ concentration is stored in the control unit 30 (see Formula 6).

(Formula 6)
C = i (Tc)
Here, C is the O ₂ concentration, and Tc is the elapsed time. I is a function that defines the correspondence between the elapsed time Tc and the O ₂ concentration C. The previous stop time is further stored in the operation time storage unit 30c. Therefore, the O ₂ concentration C can be uniquely calculated by referring to the operation time storage unit 30c and specifying the elapsed time T.

FIG. 8 is an explanatory diagram showing the correspondence between the O ₂ concentration and the correction coefficient. The CO ₂ emission amount depends on the O ₂ concentration of the fuel electrode. Accordingly, through experiments and simulations, correction coefficients for correcting the CO ₂ emission amount (calculated value) are obtained in association with various O ₂ concentrations. Then, for example, a calculation formula that defines the correspondence between the O ₂ concentration and the correction coefficient is stored in the control unit 30 (see Formula 7).

(Formula 7)
D = j (C)
Here, D is an O ₂ concentration correction coefficient, and j is a function that defines the correspondence between the O ₂ concentration and the O ₂ concentration correction coefficient D. Therefore, the O ₂ concentration correction coefficient D can be uniquely calculated from the previously calculated O ₂ concentration C.

(Formula 8)
X3 = D * B * A * X = j (C) * h (Fr) * f (Ta) * g (Tb)
That is, the CO ₂ emission amount X3 subjected to the O ₂ concentration correction in addition to the temperature correction and the flow rate correction can be expressed by Equation 8.

In step 3 (S3), hydrogen and oxygen are supplied. In step 4 (S4), the CO ₂ amount (CO ₂ measurement value) measured by the outlet gas analyzer 31 is read.

In step 5 (S5), it is determined whether or not to end the CO ₂ measurement. FIG. 9 is an explanatory diagram showing the transition of the voltage of the fuel battery cell. When hydrogen is supplied to the fuel electrode at the time of startup and hydrogen reaches the inlet side of the fuel electrode, the inlet side voltage detected by the fuel electrode inlet side voltmeter 32 (that is, the power generation voltage of the fuel cell existing on the inlet side). Indicates a tendency to increase with time and converge to an open circuit voltage (OCV). However, in this case, since hydrogen has not reached on the outlet side of the fuel electrode, the outlet side voltage detected by the fuel electrode outlet side voltmeter 33 (that is, the power generation voltage of the fuel cell existing on the outlet side) is detected. There is no change. When hydrogen reaches the outlet side of the fuel electrode, the outlet side voltage of the fuel electrode outlet side voltmeter 33 also increases with time and tends to converge to the open end voltage. Here, the time required until the inlet side voltage corresponds to the outlet side voltage is “t”.

FIG. 10 is an explanatory diagram showing the relationship between the elapsed time from the start of gas supply and the measured CO ₂ value. As can be seen from the figure, the measured value of CO ₂ tends to reach a peak as the elapsed time increases and then decrease. Such a tendency is that when hydrogen is supplied to the fuel cell stack 1, the hydrogen reaches the fuel cell on the inlet side of the fuel electrode, and is then supplied to the individual fuel cells. This is caused by reaching the fuel cell on the outlet side of the fuel electrode. Therefore, the CO ₂ measurement is terminated on the condition that the time t required for the inlet side voltage and the outlet side voltage to have corresponded has reached from the timing when the CO ₂ was measured by the outlet gas analyzer 31. To do.

If a negative determination is made in step 5, that is, if the CO ₂ measurement is not terminated, the process returns to step 4 and the CO ₂ measurement value is read again. On the other hand, if an affirmative determination is made in step 5, that is, if the CO ₂ measurement is to be terminated, the process proceeds to step 6 (S6).

In step 6, based on CO ₂ measurements, CO ₂ emissions are identified (detected). Specifically, by calculating the sum of the time series in the loaded CO ₂ measurements in step 4, actually CO ₂ emissions of the detected CO ₂ measurements base is calculated.

In step 7 (S7), the wet state is determined. In this wetness determination, the theoretically calculated CO ₂ emission amount (specifically, the CO ₂ emission amount X3 corrected in step 2) and the CO ₂ measurement value-based CO ₂ emission amount (detected in step 6). The CO ₂ emission amount), the wet state is estimated. Since the theoretically calculated CO ₂ emission amount X3 is a value calculated in consideration that the wet state of the fuel cell stack 1 is a normal state, the actual CO ₂ emission amount is based on this value. The wet state of the fuel cell stack 1 can be estimated by determining whether it is more or less than that. Therefore, in this step 7, when the CO ₂ emission amount based on the CO ₂ measurement value is larger than the theoretically calculated CO ₂ emission amount by a predetermined threshold or more, the wet state of the fuel cell stack 1 is excessive. It is estimated that. On the other hand, when the CO ₂ emission amount based on the CO ₂ measurement value is smaller than the theoretically calculated CO ₂ emission by a predetermined threshold or more, it is estimated that the wet state of the fuel cell stack 1 is the dry state. .

  In step 8 (S8), the fuel cell system is controlled based on the wet state estimated in step 7. Specifically, when the wet state of the fuel cell stack 1 is estimated to be an excessive moisture state, the output extraction unit 2 starts to extract output from the fuel cell stack 1. Thereby, the heat generation of the fuel cell stack 1 is promoted, and the excessive water state tends to be suppressed. On the other hand, when the wet state of the fuel cell stack 1 is estimated to be a dry state, the output extraction unit 2 is in a state where the flow rate of the air supplied to the oxidant electrode side is smaller than that during normal control. After the upper limit output is determined from the fuel cell stack 1, the output extraction is started. Thereby, in the fuel cell stack 1, since the production | generation of the water accompanying a power generation reaction is accelerated | stimulated, it will become the tendency for a dry state to be suppressed. The system control according to the wet state continues, for example, for a predetermined time set in advance, or to the extent that the fuel cell is recognized to have returned from a state of excessive moisture (or a dry state) to a normal wet state. This is continued until the generated voltage of the stack 1 is restored. When the wet state of the fuel cell stack is in a normal state, that is, when it is neither an excessive moisture state nor a dry state, the control proceeds to normal control, and an output corresponding to the required output is taken out from the fuel cell stack 1.

  As described above, in the present embodiment, the fuel cell system includes the fuel cell, the discharge amount detection unit, and the estimation unit. Here, in the fuel cell, fuel gas is supplied to the fuel electrode, and oxidant gas is supplied to the oxidant electrode, whereby the fuel gas and the oxidant gas are reacted electrochemically to generate electric power. The fuel cell stack 1 corresponds to this. The discharge amount detection means has a function of detecting the discharge amount of carbon dioxide discharged from the oxidizer electrode, and the outlet gas analysis unit 31 and the discharge amount detection unit 30a correspond to this function. The estimation means has a function of estimating the wet state of the fuel cell based on the carbon dioxide emission detected by the emission detection means when the system is activated, and the estimation unit 30e corresponds to this.

  According to such a configuration, since the supported carbon contained in the catalyst layer of the solid polymer electrolyte membrane and water react at the oxidant electrode, carbon dioxide is discharged from the oxidant electrode side. In this case, since the amount of carbon dioxide emission has a correlation with the amount of water in the fuel cell, the wet state of the fuel cell can be accurately estimated by detecting the amount of carbon dioxide emission.

  In the present embodiment, the fuel cell system further includes an emission amount calculating means. Here, the emission amount calculation means has a function of calculating the emission amount of carbon dioxide emitted from the oxidizer electrode when the system is started based on the operation history of the system, and the emission amount calculation unit 30b performs this function. Applicable. In this case, the estimation means compares the carbon dioxide emission detected by the emission detection means with the carbon dioxide emission calculated by the emission calculation means, and based on the comparison result, the fuel cell Estimate the wet state. Here, the estimation means is configured such that when the carbon dioxide emission detected by the emission detection means is greater than the carbon dioxide emission calculated by the emission calculation means by a predetermined threshold or more, the fuel cell When it is estimated that there is an excessive state, and the carbon dioxide emission detected by the emission detection means is smaller than the carbon dioxide emission calculated by the emission calculation means by a predetermined threshold or more, the fuel cell Presumed to be dry.

  According to such a configuration, the carbon dioxide emission calculated by the theoretically calculated emission calculating means is a value calculated in consideration of the wet state of the fuel cell being in a normal state. The wet state of the fuel cell can be estimated by determining whether the emission amount of carbon dioxide detected by the emission amount detection means is greater or less than the reference value.

  In the present embodiment, the fuel cell system further includes a temperature detection unit and a correction unit. Here, the temperature detection unit has a function of detecting the temperature at the oxidant electrode of the fuel cell, and the stack temperature detection unit 35 and the exhaust gas temperature detection unit 37 correspond to this. The correcting unit has a function of correcting the carbon dioxide emission calculated by the emission calculating unit based on the temperature detected by the temperature detecting unit, and the correcting unit 30d corresponds to this function. Since the amount of carbon dioxide emitted from the oxidant electrode side has a correlation with the temperature at the oxidant electrode of the fuel cell, the amount of carbon dioxide emitted can be accurately calculated by performing correction using this. . Thereby, the determination of a wet state can be performed accurately.

  In the present embodiment, the fuel cell system further includes a flow rate detecting means. Here, the flow rate detection unit has a function of detecting the flow rate of the fuel gas supplied to the fuel electrode of the fuel cell, and the hydrogen supply flow rate detection unit 34 corresponds to this function. In this case, the correction means corrects the carbon dioxide emission amount calculated by the emission amount calculation means based on the flow rate of the fuel gas detected by the flow rate detection means. The amount of carbon dioxide emitted from the oxidizer electrode is correlated with the flow rate of the fuel gas supplied to the fuel electrode. Can do. Thereby, the determination of a wet state can be performed accurately. The correction means may perform correction using only the flow rate of the fuel gas, or may perform correction using both the temperature at the oxidizer electrode and the flow rate of the fuel gas.

  In the present embodiment, the correcting means may correct the carbon dioxide emission calculated by the emission calculating means based on the oxygen concentration in the oxidant electrode of the fuel cell. Since the discharge amount of carbon dioxide from the oxidant electrode side has a correlation with the oxygen concentration in the oxidant electrode, the discharge amount of carbon dioxide can be accurately calculated by performing correction using this. Thereby, the determination of a wet state can be performed accurately. The correction may be performed using only the oxygen concentration, or may be performed by combining two or more of the temperature at the oxidizer electrode, the flow rate of the fuel gas, and the oxygen concentration.

  Further, in the present embodiment, the fuel cell system may further include an output extraction unit and a control unit. Here, the output extraction means has a function of extracting the output from the fuel cell, and the output extraction unit 2 corresponds to this. The control unit has a function of controlling the output extraction unit based on the wet state of the fuel cell estimated by the estimation unit, and the system control unit 30f corresponds to this function. According to such a configuration, it is possible to recover the state of excessive moisture or dryness by taking out the output from the fuel cell based on the wet state.

  In the present embodiment, the control means may control the supply amount of the oxidant gas and the fuel gas to the fuel cell based on the wet state of the fuel cell estimated by the estimation means. According to such a configuration, it is possible to recover a state of excessive moisture or dryness by controlling the gas supply amount based on the wet state.

  For example, when the estimation unit estimates that the fuel cell is in an excessive water state, the control unit extracts the output from the fuel cell by the output extraction unit. Further, when the estimation unit estimates that the fuel cell is in a dry state, the control unit extracts the output from the fuel cell with an upper limit by the output extraction unit. In addition, when the estimation unit estimates that the fuel cell is in a dry state, the control unit decreases the supply amount of the oxidant gas supplied to the oxidant electrode of the fuel cell. According to such a configuration, it is possible to recover a state of excessive moisture or drying.

Configuration diagram schematically showing the fuel cell system The block diagram which shows the structure of the control part 30 Flow chart showing the procedure of startup processing Explanatory diagram showing the correspondence between operating time and CO ₂ emissions Explanatory drawing showing the correspondence between the temperature of the fuel cell stack 1 and the correction coefficient Explanatory diagram showing the correspondence between hydrogen supply flow rate and correction coefficient Explanatory diagram showing the correspondence between the elapsed time until startup and the O ₂ concentration Explanatory view showing a correspondence relationship between the O ₂ concentration and the correction factor Explanatory diagram showing the transition of the voltage of the fuel cell Explanatory view showing a relationship between an elapsed time and CO ₂ measurements from a gas supply is started

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Output extraction part 10 Hydrogen system 10a Hydrogen supply flow path 10b Hydrogen discharge flow path 11 Hydrogen supply part 12 Hydrogen flow control valve 20 Air system 20a Air supply flow path 20b Air discharge flow path 21 Air supply part 22 Hydrogen flow rate Control valve 22 Air supply flow rate adjustment valve 22 Air flow rate control valve 30 Control unit 30a Emission amount detection unit 30b Emission amount calculation unit 30c Operation time storage unit 30d Correction unit 30e Estimation unit 30f System control unit 31 Outlet gas analysis unit 32 Fuel electrode inlet Side voltmeter 33 Fuel electrode outlet side voltmeter 34 Hydrogen supply flow rate detection unit 35 Stack temperature detection unit 36 Air discharge flow rate detection unit 37 Exhaust gas temperature detection unit

Claims (12)

In the fuel cell system,
A fuel cell that generates electric power by electrochemically reacting the fuel gas and the oxidant gas by supplying a fuel gas to the fuel electrode and supplying an oxidant gas to the oxidant electrode;
An emission amount detecting means for detecting an emission amount of carbon dioxide discharged from the oxidant electrode;
A fuel cell system comprising: estimation means for estimating a wet state of the fuel cell based on a carbon dioxide emission detected by the emission detection means when the system is activated. Based on the operating history of the system, the system further includes an emission amount calculating means for calculating the amount of carbon dioxide emitted from the oxidant electrode at the time of starting the system,
The estimation means compares the carbon dioxide emission detected by the emission detection means with the carbon dioxide emission calculated by the emission calculation means, and based on the comparison result, the fuel cell The fuel cell system according to claim 1, wherein the wet state is estimated.   When the carbon dioxide emission detected by the emission detection means is greater than the carbon dioxide emission calculated by the emission calculation means by a predetermined threshold or more, the estimation means When the amount of carbon dioxide detected by the emission amount detection unit is estimated to be in an excessive water state, and the amount of carbon dioxide emission calculated by the emission amount calculation unit is less than a predetermined threshold, The fuel cell system according to claim 2, wherein the fuel cell is estimated to be in a dry state. Temperature detecting means for detecting the temperature at the oxidant electrode of the fuel cell;
4. The correction unit according to claim 2, further comprising a correction unit that corrects the carbon dioxide emission amount calculated by the emission amount calculation unit based on the temperature detected by the temperature detection unit. Fuel cell system. Flow rate detection means for detecting the flow rate of the fuel gas supplied to the fuel electrode of the fuel cell;
4. The apparatus according to claim 2, further comprising a correction unit that corrects a carbon dioxide emission amount calculated by the emission amount calculation unit based on a flow rate of the fuel gas detected by the flow rate detection unit. The described fuel cell system. 4. The correction device according to claim 2, further comprising a correction unit that corrects the carbon dioxide emission amount calculated by the emission amount calculation unit based on an oxygen concentration in the oxidant electrode of the fuel cell. 5. Fuel cell system. Temperature detecting means for detecting the temperature at the oxidant electrode of the fuel cell;
Flow rate detection means for detecting the flow rate of the fuel gas supplied to the fuel electrode of the fuel cell;
Based on any two or more of the temperature detected by the temperature detection means, the flow rate of the fuel gas detected by the flow rate detection means, and the oxygen concentration in the oxidant electrode of the fuel cell, the emission amount calculation means The fuel cell system according to claim 2, further comprising a correcting unit that corrects the carbon dioxide emission calculated by the formula (1). Output extraction means for extracting output from the fuel cell;
The fuel according to any one of claims 1 to 7, further comprising a control unit that controls the output extraction unit based on a wet state of the fuel cell estimated by the estimation unit. Battery system.   9. The control unit according to claim 8, wherein the control unit controls the supply amount of the oxidant gas and the fuel gas to the fuel cell based on the wet state of the fuel cell estimated by the estimation unit. Fuel cell system.   10. The control unit according to claim 8, wherein when the estimation unit estimates that the fuel cell is in an excessive water state, the control unit extracts an output from the fuel cell by the output extraction unit. Fuel cell system.   9. The control device according to claim 8, wherein when the estimation unit estimates that the fuel cell is in a dry state, the output extraction unit extracts an output from the fuel cell with an upper limit. Or 9. The fuel cell system according to 9.   The control means reduces the supply amount of oxidant gas supplied to the oxidant electrode of the fuel cell when the estimation means estimates that the fuel cell is in a dry state. The fuel cell system according to claim 9.

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