JP2004281132A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent erroneous diagnosis of fuel gas leakage even in the case a difference between a fuel gas consumption amount and a fuel gas supply amount becomes temporarily large at the time of a rapid load fluctuation by precisely carrying out leakage judgment of the fuel gas. <P>SOLUTION: A hydrogen consumption amount is calculated based on an output current value from a fuel cell stack, and a hydrogen permeation amount of hydrogen supplied to an anode electrode of the fuel cell stack and flowing to a cathode electrode side through a solid polyelectrolyte film is estimated. Then, the hydrogen leakage is judged based on these calculated hydrogen consumption amount value, estimated hydrogen permeation value, a purge-time hydrogen discharge amount to be discharged from the fuel cell stack by the purge, and a detected hydrogen supply amount value detected by a flow sensor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell system, and more particularly to a fuel cell system capable of accurately determining leakage of fuel gas.
[0002]
[Prior art]
In a fuel cell system, a fuel gas containing hydrogen is supplied to an anode of a fuel cell stack, and an oxidizing gas (air) containing oxygen is supplied to a cathode, and hydrogen and oxidizing gas in these fuel gases are oxidized through an electrolyte membrane. This is to obtain generated power by electrochemically reacting oxygen in the agent gas. Such fuel cell systems are expected to be put to practical use, for example, as power sources for automobiles, and research and development for practical use are being actively conducted.
[0003]
As a fuel cell stack used in a fuel cell system, a solid polymer type fuel cell stack is known as a fuel cell stack particularly suitable for mounting on an automobile. In this solid polymer type fuel cell stack, a film-like solid polymer is provided as an electrolyte between an anode and a cathode. In the polymer electrolyte fuel cell stack, a reaction occurs in which hydrogen is separated into hydrogen ions and electrons at the anode, and a reaction occurs to generate water from oxygen, hydrogen ions, and electrons at the cathode. At this time, the solid polymer membrane functions as an ion conductor, and hydrogen ions move to the cathode through the solid polymer membrane.
[0004]
By the way, in the fuel cell system which obtains the generated power by the reaction between hydrogen and oxygen as described above, it is difficult to seal completely because the molecular weight of hydrogen is small. It is assumed that fuel gas leaks from gaps or the like in the stacks constituting each power generation cell of the battery stack. For example, in the case of an in-vehicle fuel cell system, a change in the operating temperature of the fuel cell stack, or vibration or impact applied to the fuel cell stack or the fuel supply system causes fuel containing hydrogen from a joint or a slight gap in the piping. It is assumed that gas leaks.
[0005]
Therefore, in such a fuel cell system, it is extremely important to quickly and accurately determine when a fuel gas leak has occurred and to take necessary countermeasures. Various methods for judging the leakage have been studied (for example, see Patent Document 1).
[0006]
According to the technology described in Patent Document 1, the fuel gas consumption in the fuel cell stack is calculated based on the output current value of the fuel cell stack, and the fuel gas pressure in the fuel gas cylinder is calculated from the fuel gas consumption. Leakage of fuel gas is determined by comparing the calculated gas pressure with the actual gas pressure detected by the pressure sensor in the fuel gas cylinder.
[0007]
[Patent Document 1]
JP-A-11-224681
[0008]
[Problems to be solved by the invention]
By the way, in a fuel cell system using a solid polymer type fuel cell stack, it is known that the larger the gas partial pressure difference between both ends of the solid polymer membrane, the larger the flow rate of gas permeating the solid polymer membrane. I have. Therefore, when the gas partial pressure difference between both ends of the solid polymer membrane is large, the amount of permeated fuel gas permeating through the solid polymer membrane and flowing from the anode side to the cathode side also increases, and it is determined that fuel gas is leaking. In this case, it is assumed that the fuel gas permeation amount becomes a level that cannot be ignored.
[0009]
However, in the technique disclosed in Patent Document 1, such a fuel gas permeation amount is not considered at all, so that it is necessary to set a large threshold value for use in fuel gas leak determination, and the accuracy of fuel gas leak determination is high. May be lowered. If the accuracy of fuel gas leak determination is low, erroneous determination may be made in some cases, which may cause unnecessary shutdown of the fuel cell system or excessive fuel gas leakage, which significantly impairs the reliability of the fuel cell system. Results.
[0010]
Further, in the technique disclosed in Patent Literature 1, at the time of a rapid load change, the difference between the fuel gas consumption and the fuel gas supply becomes large due to a temporary delay in fuel gas supply with respect to fuel gas consumption. It can also cause misdiagnosis of a leak.
[0011]
The present invention has been proposed in order to solve the problems of the conventional technology as described above, and a fuel cell system capable of accurately determining fuel gas leakage to obtain high reliability. It is intended to provide.
[0012]
[Means for Solving the Problems]
The fuel cell system of the present invention has a solid polymer membrane as an electrolyte, and receives a supply of a fuel gas containing hydrogen and an oxidant gas containing oxygen to generate power, and a fuel cell stack. A fuel gas supply amount detecting means for detecting a supply amount of the fuel gas, an output current detecting means for detecting an output current of the fuel cell stack, and a fuel gas leak determining means for determining fuel gas leakage. Then, the fuel gas leak determining means calculates the fuel gas consumption in the fuel cell stack based on the output current detected from the output current detecting means, and determines whether the fuel gas supplied to the anode side of the fuel cell stack is high in solid state. The fuel gas permeation amount flowing out to the cathode side through the molecular membrane is estimated, and the fuel gas consumption amount calculation value and the fuel gas permeation amount estimation value, and the fuel gas discharge amount calculation value discharged from the fuel cell stack by purging, and Leakage of fuel gas is determined from a fuel gas supply amount detection value detected by the fuel gas supply amount detection means.
[0013]
As described above, in the fuel cell system of the present invention, the fuel gas leak determination means estimates the amount of permeated fuel gas flowing from the anode side of the fuel cell stack to the cathode side through the solid polymer membrane, and The leakage of the fuel gas is determined in consideration of the fuel gas permeation amount in addition to the consumption amount, the fuel gas discharge amount due to the purge, and the fuel gas supply amount. Therefore, accurate fuel gas leak determination is realized.
[0014]
Further, in the fuel cell system of the present invention, the fuel gas leak determining means may add a correction corresponding to the response characteristic from the fuel gas supply amount detecting means to the fuel cell stack when calculating the fuel gas consumption, or The fuel gas leak diagnosis may be stopped when the load changes abruptly when the gradient of the change in the amount of power generation of the fuel cell stack exceeds a predetermined value. This can also prevent erroneous diagnosis of fuel gas leakage caused by a temporary difference between the fuel gas consumption and the fuel gas supply during a sudden load change.
[0015]
【The invention's effect】
According to the fuel cell system of the present invention, the permeation amount of the fuel gas flowing from the anode side of the fuel cell stack to the cathode side through the solid polymer membrane is estimated, and the estimated permeation amount of the fuel gas is also taken into consideration. Thus, the leakage of the fuel gas is determined, so that the determination of the leakage of the fuel gas can be accurately performed. Further, when calculating the fuel gas consumption, a correction corresponding to the response characteristic from the fuel gas supply amount detecting means to the fuel cell stack is added, or the inclination of the change in the power generation amount of the fuel cell stack with respect to a predetermined time becomes equal to or more than a predetermined value. Stopping the fuel gas leak diagnosis at the time of a sudden load change causes an error in the fuel gas leakage due to the temporary difference between the fuel gas consumption and the fuel gas supply at the time of the sudden load change. Diagnosis can also be prevented.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 schematically shows a main configuration of a fuel cell system to which the present invention is applied. This fuel cell system includes a fuel cell stack 1 that generates power by a reaction between hydrogen as a fuel gas and oxygen in the air as an oxidant gas. Here, a case where the present invention is applied to a so-called direct hydrogen type fuel cell system that uses hydrogen gas as a fuel gas supplied to the fuel cell stack 1 will be described as an example. The present invention is not limited thereto, and can be effectively applied to other types of fuel cell systems, such as a system using a hydrogen-rich reformed gas as a fuel gas.
[0018]
The fuel cell stack 1 is configured such that an anode electrode 1a to which hydrogen as a fuel gas is supplied and a cathode electrode 1b to which air as an oxidant gas is supplied are overlapped with an electrolyte therebetween to form a power generation cell. Has a stack structure in which a plurality of power generation cells are stacked, and converts chemical energy into electric energy by an electrochemical reaction based on hydrogen and oxygen in air. In each power generation cell of the fuel cell stack 1, a reaction occurs in which hydrogen supplied to the anode 1a is separated into hydrogen ions and electrons, the hydrogen ions pass through the electrolyte, and the electrons pass through an external circuit to generate power. To move to the cathode 1b. At the cathode 1b, oxygen in the supplied air reacts with hydrogen ions and electrons that have moved through the electrolyte to produce water, which is discharged to the outside.
[0019]
As the electrolyte of the fuel cell stack 1, a solid polymer electrolyte membrane is used in consideration of high energy density, low cost, light weight, and the like. The solid polymer electrolyte membrane is formed of an ion (proton) conductive polymer membrane such as a fluororesin-based ion exchange membrane, and functions as an ion conductive electrolyte when saturated with water.
[0020]
In order to generate power in the fuel cell stack 1, it is necessary to supply hydrogen as a fuel gas and air as an oxidizing gas to the anode 1a and the cathode 1b of each power generation cell. As a fuel supply system and an air supply system.
[0021]
The fuel supply system includes, for example, a hydrogen tank 2, which is a hydrogen supply source, a hydrogen gas supply valve 3, a hydrogen supply flow path 4, an ejector 5, a hydrogen circulation flow path 6, an anode exhaust gas discharge flow path 7, a hydrogen purge valve 8, and the like. The hydrogen supplied from the hydrogen tank 2 is decompressed by the hydrogen gas supply valve 3, passes through the hydrogen supply path 4 and the ejector 5, and is supplied by a necessary amount according to the amount of power generated by the fuel cell stack 1. The stack 1 is fed to the anode 1a. The surplus hydrogen that has not contributed to the power generation in the fuel cell stack 1 is circulated by the ejector 5 through the hydrogen circulation channel 6, mixed with the hydrogen newly supplied from the hydrogen tank 2, and again. The fuel is supplied to the anode 1 a of the fuel cell stack 1.
[0022]
Further, in this fuel supply system, impurities such as nitrogen may be accumulated in the fuel cell stack 1 and the hydrogen circulation flow path 6 by circulating hydrogen, and if the impurities are excessively accumulated, the fuel supply system may accumulate impurities. Since the hydrogen partial pressure drops and leads to a decrease in the efficiency of the fuel cell stack 1, in such a case, the hydrogen purge valve 8 provided in the anode exhaust gas exhaust flow path 7 is opened to purge the hydrogen, thereby removing impurities. The quality is discharged out of the system together with hydrogen.
[0023]
On the other hand, the air supply system includes, for example, a compressor and an air supply channel for sending air to the cathode 1b of the fuel cell 1, a cathode exhaust gas exhaust channel and an exhaust valve for discharging exhaust gas from the cathode 1b. Is done. Since this air supply system has little to do with the features of the present invention, illustration and detailed description are omitted.
[0024]
In the fuel cell system to which the present invention is applied, the hydrogen tank 2 is provided with an in-tank pressure sensor 9, and the hydrogen supply flow path 4 is provided with a flow rate sensor 10. Further, a pressure sensor 11 and a temperature sensor 12 are provided in the fuel cell stack 1, respectively, and an ammeter 14 is provided in an output current path 13 for extracting a current from the fuel cell stack 1. Necessary information is detected by each of the above-described detection means, and the detected information is supplied to a control unit (not shown) that controls the entire fuel cell system.
[0025]
In the fuel cell system configured as described above, under the control of the control unit, the required hydrogen gas is taken out of the hydrogen tank 2 in accordance with the amount of power generated by the fuel cell stack 1 and decompressed by the hydrogen gas supply valve 3. Then, it is supplied to the anode 1 a of the fuel cell stack 1 through the hydrogen supply flow path 3. Here, the flow rate of the hydrogen gas supplied to the anode 1a of the fuel cell stack 1 is the hydrogen supply amount shown in FIG.
[0026]
The hydrogen gas supplied to the anode 1a of the fuel cell stack 1 is decomposed into hydrogen ions and electrons at the anode 1a and is consumed as electric power. The amount of hydrogen consumed as the electric power is a value corresponding to the output current from the fuel cell stack 1 and is the amount of hydrogen consumption shown in FIG. At this time, part of the hydrogen gas supplied to the anode electrode 1a of the fuel cell stack 1 remains as hydrogen gas due to the gas partial pressure difference between the anode electrode 1a and the cathode electrode 1b separated by the solid polymer electrolyte membrane. After passing through the solid polymer electrolyte membrane, it flows from the anode 1a to the cathode 1b. The amount of hydrogen permeating the solid polymer electrolyte membrane as it is as the hydrogen gas is the hydrogen permeation amount shown in FIG.
[0027]
When the hydrogen purge valve 8 is opened, the hydrogen gas is discharged to the outside together with impurities such as nitrogen from the anode exhaust gas exhaust passage 7, and the amount of hydrogen discharged to the outside by opening the hydrogen purge valve 8 is reduced. 1 shows the amount of hydrogen discharged during purging shown in FIG.
[0028]
In the fuel cell system as described above, a change in the operating temperature of the fuel cell stack 1 or vibration or impact applied to the fuel cell stack 1 or the fuel supply system causes hydrogen having a small molecular weight from a seam or a slight gap of the pipe. It is also assumed that (fuel gas) leaks. Therefore, in the fuel cell system to which the present invention is applied, the control unit has a function of determining hydrogen leakage, and when hydrogen leakage occurs, the hydrogen supply valve 3 is closed to stop the supply of hydrogen gas. It has become.
[0029]
Here, in the fuel cell system having the above-described configuration, the hydrogen leakage amount can be represented as follows from the hydrogen supply amount, the hydrogen consumption amount, the hydrogen permeation amount, and the purge hydrogen discharge amount shown in FIG. .
[0030]
Hydrogen leak amount = hydrogen supply amount− (hydrogen consumption amount + hydrogen permeation amount + purging hydrogen discharge amount) Then, the hydrogen consumption amount is detected by the fuel cell stack 1 detected by the ammeter 14 installed in the output current path 13. Is calculated based on the output current value of. In addition, it is generally known that the permeability of a gas permeating a solid polymer electrolyte membrane depends on the partial pressure difference of the gas at both ends and the temperature of the gas. The hydrogen permeation amount is determined by a pressure sensor inside the fuel cell stack 1. Estimated from the detected value by the temperature sensor 11 and the detected value by the temperature sensor 12. Further, the amount of hydrogen discharged at the time of purging can be derived from experimental results such as the relationship between the value detected by the pressure sensor 11 inside the fuel cell stack 1 and the amount of hydrogen discharged. Further, the hydrogen supply amount can be known from the detection value obtained by the flow rate sensor 10 provided in the hydrogen supply flow path 4.
[0031]
Therefore, the control unit compares the calculated value of the hydrogen consumption, the estimated value of the hydrogen permeation amount, and the calculated value of the hydrogen emission with the hydrogen supply amount to determine whether or not there is a hydrogen leak. In the fuel cell system to which the present invention is applied, the control unit constantly determines the presence / absence of high-precision hydrogen leakage using the above-described method. Closes the hydrogen supply valve 3 to stop the supply of hydrogen gas.
[0032]
FIG. 2 shows the relationship between the amount of hydrogen supplied and the amount of hydrogen consumed when the load of the fuel cell stack 1 changes suddenly. As can be seen from FIG. 2, during a rapid load change, the supply response is delayed by ΔT (dead time) with respect to the hydrogen consumption response after the current extraction command. This is due to the effects of the responsiveness of the hydrogen gas supply valve 3, the responsiveness of the flow rate sensor 10, the length of the piping of the hydrogen supply flow path 4, and the like. As a result, during a rapid load change, a large difference is temporarily generated between the hydrogen supply amount and the hydrogen consumption amount, and the hydrogen supply amount-hydrogen consumption exceeds the threshold value of the hydrogen leakage determination, and there is no hydrogen leakage. Even in a normal operation state, there is a possibility that an erroneous diagnosis is made that hydrogen leakage has occurred.
[0033]
Therefore, in the fuel cell system to which the present invention is applied, the control unit performs a calculation corresponding to the response characteristics from the flow sensor 10 to the fuel cell stack 1 when calculating the hydrogen consumption, thereby obtaining the flow sensor 10. The effect of the delay in the supply of hydrogen due to the response characteristics from the fuel cell stack 1 to the fuel cell stack 1 is reduced, and the detection accuracy of hydrogen leakage is increased. More specifically, the control unit considers the temporary delay and the dead time, and calculates the hydrogen consumption amount as HC, the time constant of the first-order lag as T, the proportional gain as K, and the dead time as ΔT. The consumption correction value is calculated by the following equation.
[0034]
HC × K / (Ts + 1) × e−ΔT · s
By performing the necessary correction when calculating the hydrogen consumption in this way, as shown in FIG. 3, the supply response is delayed by ΔT (dead time) much more than the hydrogen consumption response at the time of a sudden load change. Even in this case, the hydrogen supply amount-hydrogen consumption amount does not exceed the threshold value of the hydrogen leak determination due to this, and erroneous diagnosis of the hydrogen leak can be effectively prevented.
[0035]
At this time, if the time constant T of the first-order lag, the proportional gain K, and the dead time ΔT are changed depending on the operating state of the fuel cell stack 1 and the layout of the fuel cell system, the magnitude of the load fluctuation may vary. This can also reduce the influence of the delay in supplying hydrogen. Thereby, even if the hydrogen gas pipe becomes long and the response delay of the hydrogen supply becomes large, it is possible to accurately determine the hydrogen leakage over a wide range of the hydrogen gas path.
[0036]
FIGS. 4 to 6 conceptually show a method of determining hydrogen leakage by a control unit in a fuel cell system to which the present invention is applied. Here, when estimating the hydrogen permeation amount, the control unit changes the estimated value of the hydrogen gas permeation amount according to the fuel gas pressure inside the fuel cell stack 1, or changes the hydrogen permeation amount according to the temperature inside the fuel cell stack 1. The gas permeation amount estimation value is changed, or the hydrogen gas permeation amount estimation value is changed according to both of them.
[0037]
FIG. 4 estimates the hydrogen permeation amount based on the detection value from the pressure sensor 11 indicating the fuel gas pressure inside the fuel cell stack 1 when it can be assumed that the temperature inside the fuel cell stack 1 is constant. An example in which hydrogen leakage is determined is shown. In this example, first, the hydrogen supply amount is obtained from the detection value of the flow rate sensor 10, and this is counted as a positive value. Next, the amount of hydrogen consumption is calculated based on the output current value of the fuel cell stack 1 detected by the ammeter 14, and is counted as a negative value after adding the above-described correction. Further, the purged hydrogen discharge amount is calculated based on the detected value of the pressure sensor 11 inside the fuel cell stack 1 and counted as a negative value, and the hydrogen permeation amount is estimated based on the detected value of the pressure sensor 11 to obtain a negative value. Count as the value of Then, the presence or absence of hydrogen leakage is determined based on whether or not those subtracted values exceed a threshold value.
[0038]
FIG. 5 illustrates a case where it can be assumed that the pressure of the fuel cell stack 1 is constant, a hydrogen permeation amount is calculated based on a detection value from a temperature sensor 12 indicating a temperature inside the fuel cell stack 1, and the leakage of hydrogen is calculated. Is shown. Also in this example, similarly to the example shown in FIG. 4, the presence / absence of hydrogen leakage is determined based on whether or not the subtracted values of the hydrogen supply amount, the hydrogen consumption amount, the purged hydrogen discharge amount, and the hydrogen permeation amount exceed threshold values. However, in this example, the hydrogen permeation amount is estimated based on the detection value of the temperature sensor 12.
[0039]
FIG. 6 shows the hydrogen permeation amount based on both the detection value from the pressure sensor 11 indicating the fuel gas pressure inside the fuel cell stack 1 and the detection value from the temperature sensor 12 indicating the temperature inside the fuel cell stack 1. An example is shown in which calculation is made to determine the leakage of hydrogen. Also in this example, as in the examples shown in FIGS. 4 and 5, whether or not hydrogen is leaked depends on whether or not the subtracted values of the hydrogen supply amount, the hydrogen consumption amount, the purge hydrogen discharge amount, and the hydrogen permeation amount exceed the threshold values. In this example, the hydrogen permeation amount is estimated based on both the detected value of the pressure sensor 11 and the detected value of the temperature sensor 12.
[0040]
Here, in the fuel cell system to which the present invention is applied, a flow of a series of processes of the hydrogen leak determination executed by the control unit will be described with reference to a flowchart of FIG.
[0041]
When the operation of the fuel cell stack 1 is started and the hydrogen gas supply valve 3 is opened (Step S1), the hydrogen gas from the hydrogen tank 2 is supplied to the anode 1a of the fuel cell stack 1. Then, when it is confirmed that the hydrogen gas supply valve 3 is open, the control unit starts determination of hydrogen leakage.
[0042]
In determining the hydrogen leakage, first, the output current of the fuel cell stack 1 is detected by the ammeter 14 (Step S2), and the hydrogen consumption corrected by the above-described hydrogen supply response delay is calculated (Step S3). Further, the pressure (and / or temperature) in the fuel cell stack 1 is detected by the pressure sensor 11 (and / or the temperature sensor 12) (Step S4), and the permeation amount of the hydrogen gas to the cathode 1a side is estimated. (Step S5).
[0043]
Here, it is confirmed whether or not the hydrogen purge valve 8 is in a closed state (step S6). If the hydrogen purge valve 8 is open, a map is obtained from data obtained through experiments and the like based on the detection value from the pressure sensor 11. Utilizing the above, the purged hydrogen discharge amount is calculated (step S7). Further, the hydrogen supply amount is calculated by the flow rate sensor 10 (Step S8), and the total of the hydrogen consumption amount, the hydrogen permeation amount, and the hydrogen discharge amount at the time of the purge determined as described above is compared with the hydrogen supply amount. The hydrogen leakage amount is calculated (Step S9).
[0044]
Then, it is determined whether the calculated amount of hydrogen leakage is equal to or smaller than a predetermined threshold (step S10). If the calculated amount of hydrogen leakage is equal to or smaller than the threshold, it is determined that there is no hydrogen leakage and step S1 is performed. Return to On the other hand, if the calculated hydrogen leakage amount exceeds the threshold, it is determined that hydrogen leakage has occurred, the hydrogen gas supply valve 3 is closed (step S11), and the operation of the fuel cell stack 1 is started. The operation is stopped and the hydrogen leak determination ends.
[0045]
As described above, in the fuel cell system to which the present invention is applied, the control unit controls the amount of hydrogen permeated from the anode 1a of the fuel cell stack 1 through the solid polymer electrolyte membrane to the cathode 1b. The hydrogen leakage is determined by considering the hydrogen permeation amount in addition to the hydrogen consumption amount, the hydrogen discharge amount during purge, and the hydrogen supply amount. Can be performed with high accuracy.
[0046]
The amount of hydrogen permeation can be estimated based on the value detected by the pressure sensor 11 and the value detected by the temperature sensor 12 provided in the fuel cell stack 1, or the value detected from both of them. , Can be calculated based on the output current value of the fuel cell stack 1 detected by the ammeter 14, and the amount of hydrogen discharged at the time of purging can be calculated based on the relationship between the detected value of the pressure sensor 11 and the amount of hydrogen discharged. Since it can be derived from the experimental results, and the hydrogen supply amount can be obtained from the value detected by the flow rate sensor 10, it is possible to realize accurate hydrogen leakage judgment without changing the configuration of the fuel cell system. Can be.
[0047]
Further, in the fuel cell system to which the present invention is applied, if the estimated value of the amount of hydrogen permeated to the cathode 1b is changed according to the pressure inside the fuel cell stack 1, the pressure of the fuel cell stack 1 can be changed. And the amount of hydrogen permeation is high, the determination of the presence or absence of hydrogen leakage can be made accurately. Further, if the estimated value of the amount of permeated hydrogen to the cathode 1b is changed in accordance with the temperature inside the fuel cell stack 1, even if the temperature of the fuel cell stack 1 is high and the amount of permeated hydrogen is large, hydrogen It is possible to accurately determine the presence or absence of leakage.
[0048]
Furthermore, in the fuel cell system to which the present invention is applied, when calculating the fuel gas consumption, a correction corresponding to the response characteristics from the flow sensor 10 to the fuel cell stack 1 is added, so that a sudden load It is possible to effectively prevent inconvenience such as erroneous diagnosis of hydrogen leakage due to a temporary difference between the hydrogen consumption amount and the hydrogen supply amount during the fluctuation. At this time, if the correction value corresponding to the response characteristic is changed in accordance with the operating condition of the fuel cell stack 1, even if the magnitude of the load change differs depending on the operating condition of the fuel cell stack 1, the hydrogen supply delay Can be reduced.
[0049]
In the above, a specific example of the method of performing the hydrogen leak determination in the control unit in the fuel cell system to which the present invention is applied has been described. However, the hydrogen leak determination performed by the control unit is not limited to the above example. Instead, various modifications are possible. For example, in the above example, when a large difference is temporarily generated between the hydrogen supply amount and the hydrogen consumption amount at the time of a sudden load change, when calculating the fuel gas consumption amount, the fuel cell stack 1 is detected by the flow sensor 10. Although the correction corresponding to the response characteristics up to the above is made, it is also possible not to make the hydrogen leak determination in such a situation.
[0050]
In this case, the control unit detects a gradient of a change in the amount of power generation of the fuel cell stack 1 with respect to a predetermined time, and when the gradient of the change in the amount of power generation becomes equal to or more than a predetermined value, a sudden load change occurs. It is only necessary to determine that there is a hydrogen leak and stop the hydrogen leak determination. As described above, even when the hydrogen leak determination is not performed at the time of a sudden load change, the erroneous diagnosis of the hydrogen leak is caused due to a temporary difference between the fuel gas consumption and the fuel gas supply. Can be effectively prevented.
[0051]
In the above example, the supply amount of hydrogen gas is calculated based on the detection value of the flow rate sensor 10. However, the supply amount of hydrogen gas is calculated based on the hydrogen tank 2 detected by the tank pressure sensor 9. The change in the remaining pressure may be corrected by the temperature difference between the fuel cell stack 1 and the hydrogen tank 2. Also in this case, the control unit can accurately grasp the hydrogen supply amount, and can accurately determine the leakage of hydrogen.
[0052]
Further, in the above example, based on the detection value from the pressure sensor 11 provided in the fuel cell stack 1, the purged hydrogen discharge amount is calculated by utilizing a map or the like from data obtained by an experiment or the like. However, the amount of hydrogen discharged at the time of purging is calculated from the differential pressure of the hydrogen purge valve 8 and the opening area of the hydrogen purge valve 8 using the detection values from the pressure sensor 11 and the temperature sensor 12 provided in the fuel cell stack 1. May be used to calculate. Also in this case, the control unit can accurately grasp the amount of hydrogen discharged at the time of purging, and can accurately determine the leakage of hydrogen.
[Brief description of the drawings]
FIG. 1 is a diagram showing a main configuration of a fuel cell system to which the present invention is applied.
FIG. 2 is a diagram showing a state of a delay in hydrogen supply when a sudden change in load occurs.
FIG. 3 is a diagram illustrating a state of a change in a hydrogen supply amount-hydrogen consumption amount when a hydrogen consumption amount is corrected in consideration of a hydrogen supply delay.
FIG. 4 is a view conceptually showing a method of determining hydrogen leakage by a control unit, and shows an example in which it can be assumed that the temperature of the fuel cell stack is constant.
FIG. 5 is a diagram conceptually showing a method of determining hydrogen leakage by a control unit, and shows an example in which it can be assumed that the pressure of the fuel cell stack is constant.
FIG. 6 is a view conceptually showing a method of determining hydrogen leakage by a control unit, and shows an example of estimating a hydrogen permeation amount based on both detected values of gas pressure and temperature inside a fuel cell stack. is there.
FIG. 7 is a flowchart showing a flow of a series of processes for determining hydrogen leakage executed by the control unit.
[Explanation of symbols]
1 Fuel cell stack
2 Hydrogen tank
3 Hydrogen gas supply valve
4 Hydrogen supply channel
8 Hydrogen purge valve
10 Flow sensor
11 Pressure sensor
12 Temperature sensor
14 Ammeter

Claims (10)

A fuel cell stack having a solid polymer membrane as an electrolyte, receiving power from a fuel gas containing hydrogen and an oxidizing gas containing oxygen, and generating electricity, and a supply amount of the fuel gas to the fuel cell stack Fuel gas supply amount detecting means for detecting
Output current detection means for detecting an output current of the fuel cell stack;
Fuel gas leak determination means for determining the leakage of the fuel gas,
The fuel gas leak determination means calculates a fuel gas consumption amount in the fuel cell stack based on the output current detected from the output current detection means, and the fuel gas supplied to the anode side of the fuel cell stack is Estimating the fuel gas permeation amount flowing out to the cathode side through the solid polymer membrane, the fuel gas consumption amount calculation value and the fuel gas permeation amount estimation value, and the fuel gas discharge amount discharged from the fuel cell stack by purging A fuel cell system comprising: determining a fuel gas leak from a calculated value and a fuel gas supply amount detection value detected by the fuel gas supply amount detection means. 2. The fuel gas leak determining means, when estimating the fuel gas permeation amount, changes the fuel gas permeation amount estimated value at least according to a fuel gas pressure inside the fuel cell stack. The fuel cell system according to item 1. 2. The fuel gas leakage determination unit according to claim 1, wherein when estimating the fuel gas permeation amount, the fuel gas leakage determination unit changes the fuel gas permeation amount estimation value at least according to a temperature inside the fuel cell stack. 3. Fuel cell system. 2. The fuel gas leak determination unit according to claim 1, wherein, when calculating the fuel gas consumption, a correction corresponding to a response characteristic from the fuel gas supply amount detection unit to the fuel cell stack is performed. A fuel cell system as described. 5. The fuel cell system according to claim 4, wherein the fuel gas leak determination unit corrects the calculated fuel gas consumption value by adding a first-order lag and a dead time. The fuel gas leak determination means calculates the fuel gas consumption correction value by the following equation when the calculated fuel gas consumption value is HC, the time constant of the first-order lag is T, the proportional gain is K, and the dead time is ΔT. The fuel cell system according to claim 5, wherein the calculation is performed.
HC × K / (Ts + 1) × e−ΔT · s 7. The fuel gas leak determination unit according to claim 6, wherein the first-order lag time constant T, the proportional gain K, and the dead time ΔT are changed according to the operating state of the fuel cell stack and the layout of the fuel cell system. Fuel cell system. The fuel gas leak judging means stops the fuel gas leak diagnosis when the load changes abruptly when the gradient of the power generation amount change of the fuel cell stack with respect to a predetermined time is equal to or more than a predetermined value. 2. The fuel cell system according to 1. The fuel gas supply amount detecting means calculates a supply amount of the fuel gas to the fuel cell stack by adding a correction based on a temperature difference between the fuel cell stack and the fuel gas tank to a change in the residual pressure of the fuel gas tank. The fuel cell system according to claim 1, wherein: The amount of fuel gas discharged from the fuel cell stack by the purge is determined by using the detection values of the pressure sensor and the temperature sensor provided in the fuel cell stack, and calculating the orifice equation from the purge valve vertical differential pressure and the purge valve opening area. The fuel cell system according to claim 1, wherein the fuel cell system is used to calculate.

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