JP4085805B2 - Fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system that generates power using a fuel cell body composed of a plurality of power generation cells, and more particularly to a technique for suppressing variations in cell voltage.
[0002]
[Prior art]
The fuel cell system supplies hydrogen gas to the anode electrode of the fuel cell main body and air to the cathode electrode, respectively, and causes hydrogen and oxygen to react electrochemically at each electrode to obtain generated power. Such a fuel cell system is highly expected to be put into practical use, for example, as a power source for automobiles. Currently, research and development for practical use is actively performed.
[0003]
As a fuel cell main body used in a fuel cell system, a solid polymer type fuel cell main body is known as one particularly suitable for mounting in an automobile. This solid polymer type fuel cell body has a membrane-like solid polymer provided between an anode (hydrogen electrode) and a cathode (air electrode), and this solid polymer membrane is a hydrogen ion conductor. It is supposed to function as. In a solid polymer type fuel cell body, a reaction in which hydrogen gas is separated into hydrogen ions and electrons occurs at the anode, and a reaction in which water is generated from oxygen gas, hydrogen ions and electrons at the cathode. At this time, the solid polymer film functions as an ion conductor, and hydrogen ions move through the solid polymer film toward the cathode.
[0004]
By the way, in order for the solid polymer film to function as an ion conductor, it is necessary to include a certain amount of moisture in the solid polymer film. For this reason, in a fuel cell system using such a solid polymer type fuel cell main body, the solid polymer membrane of the fuel cell main body is supplied by supplying hydrogen gas to the fuel cell main body while being humidified by a humidifier. It is generally performed to humidify.
[0005]
Further, as an effective method for humidifying the solid polymer membrane, a hydrogen circulation type fuel cell system is known in which unused hydrogen gas in the fuel cell body is circulated again to the fuel cell body for reuse. Yes. In this hydrogen circulation type fuel cell system, hydrogen gas is supplied to the anode of the fuel cell body somewhat more than the amount of hydrogen required for power consumed by a load connected to the outside of the fuel cell body (hereinafter referred to as an external load). Then, unused hydrogen gas is discharged from the anode outlet, and this discharged hydrogen (hereinafter referred to as circulating hydrogen) is returned to the anode inlet of the fuel cell main body and reused. Since the circulating hydrogen discharged from the anode outlet contains a lot of water vapor, the circulating hydrogen containing a lot of water vapor is mixed with the dry hydrogen from the hydrogen tank and supplied to the anode of the fuel cell body. The solid polymer membrane of the fuel cell main body is humidified.
[0006]
In the hydrogen circulation type fuel cell system described above, a slightly larger amount of hydrogen gas than the amount of hydrogen required for the electric power consumed by the external load is supplied to the anode electrode of the fuel cell main body. Therefore, the flow rate of hydrogen supplied to the anode electrode is larger than the amount of hydrogen necessary for power generation. At this time, if only the amount of hydrogen necessary for power generation is supplied to the anode electrode, hydrogen will not reach the cells near the anode outlet efficiently and power generation efficiency will be reduced. By supplying more hydrogen gas to the anode electrode, power generation in all the cells of the fuel cell system can be performed with high efficiency. In the fuel cell system, the same can be said for the cathode electrode. Therefore, not only the amount of oxygen (air) necessary for power generation is supplied, but a little extra oxygen is supplied to the cathode electrode. The ratio of the amount of hydrogen (air) actually supplied to the amount of hydrogen (air) required for power generation is usually called the raw material gas stoichiometric ratio, but this raw material gas stoichiometric ratio is set to an optimum value of 1 or more for the above reason. Has been.
[0007]
In this way, the raw material gas stoichiometry is set so as to efficiently generate power in the fuel cell main body. However, since the state of the fuel cell body changes depending on the operating state, even when the stoichiometric ratio is set to the optimum value, the power generation efficiency is deteriorated due to the influence of the operating load or aging, and as a result, the variation in cell voltage increases. There is a problem. If the cell voltage variation exceeds the allowable range and falls below the lower voltage limit, the polymer film constituting the fuel cell body may be damaged, and the cell voltage variation It is necessary to change the stoichiometric ratio so that the total voltage does not decrease so as not to occur.
[0008]
As an operation method for suppressing the cell voltage variation of the fuel cell main body, for example, when the cell voltage varies, the flow rate of the raw material gas supplied to the fuel cell main body is increased by a predetermined amount. A method for increasing the ratio has been proposed (see, for example, Patent Document 1).
[0009]
[Patent Document 1]
JP 2002-164068 A
[0010]
[Problems to be solved by the invention]
However, as described in Patent Document 1, if the stoichiometric ratio is always increased when the cell voltage varies or the total voltage decreases, waste of raw materials or waste of raw material supply power is caused. May be used.
[0011]
For example, the causes of variations in cell voltage are due to deterioration in performance of the power generation cell, and when the cell voltage is relatively low in the operation state at that time due to the distribution of the raw material gas in the fuel cell body. There is.
[0012]
In the former case, if the load is increased as it is, the performance deterioration of the power generation cell proceeds and the performance of the entire fuel cell main body is reduced. Further, if the stoichiometric ratio is set low, uneven supply of the raw material gas to each power generation cell occurs, and the variation in cell voltage is increased. Therefore, in this case, it is effective to set the stoichiometric ratio to increase as in the technique described in Patent Document 1.
[0013]
On the other hand, in the latter case, if the load is increased as it is, the distribution of the raw material gas in the fuel cell body changes and the cell voltage of the power generation cell having a low voltage is restored. If the stoichiometric ratio is set so as to rescue the cell, the raw material or the raw material supply power is wasted.
[0014]
For example, if the hydrogen source stoichiometry is set high, the amount of hydrogen to be circulated increases. This causes an increase in raw material supply power. In addition, by increasing the hydrogen stoichiometry, moisture circulating in the hydrogen circulation system is increased, and the frequency of releasing hydrogen in the atmosphere for purging is increased, which may lead to waste of raw materials. On the other hand, if the stoichiometry of the air raw material is set high, the air that has not been used for power generation is discarded as it is, which causes wasteful use of the air raw material supply power.
[0015]
Therefore, if the raw material gas stoichiometric ratio is always set high as in the technique described in Patent Document 1, the raw material gas stoichiometric ratio is also set high in the latter case, and the amount of raw material that is wasted is increased, and the power for supplying the raw material is increased. It becomes a wasteful use.
[0016]
The present invention has been proposed in view of the above-mentioned problems of the prior art, and supplies a raw material gas at an optimal flow rate to the fuel cell body, while eliminating waste of the raw material gas and the raw material supply power. It is an object of the present invention to provide a fuel cell system that can suppress variations in cell voltages of the battery body and can always make the cell voltage equal to or higher than the lower limit value.
[0017]
[Means for Solving the Problems]
The fuel cell system of the present invention includes a fuel cell main body that includes a plurality of power generation cells and that generates electric power by electrochemically reacting hydrogen and oxygen, which are raw material gases, and a gas containing hydrogen at the anode electrode of the fuel cell main body. And a hydrogen-containing gas supply device for supplying oxygen-containing gas to the cathode electrode of the fuel cell main body. Then, when variation occurs in the voltage of the power generation cells constituting the fuel cell main body, it is determined whether the cause is due to the distribution of the raw material gas within the fuel cell main body or due to cell deterioration, The raw material gas stoichiometric ratio is set according to the result.
[0018]
When the cell voltage varies, the voltage of a specific power generation cell may become relatively low due to the deterioration of the power generation cell and the poor performance due to the fuel gas distribution in the fuel cell body. There is a case. In the latter case, if the load is increased as it is, the source gas distribution in the fuel cell body will change and the voltage of the low voltage cell will recover, but in the former case, the power generation cell will be weakened further and the fuel cell body will May cause damage.
[0019]
Therefore, if the stoichiometric ratio is set so that the power generation cell having a low voltage is always relieved when the cell voltage varies, in the latter case, the raw material or the raw material supply power is wasted. On the other hand, if the stoichiometric ratio is set low in order to save the raw material, the raw material supply unevenness to each cell may occur, the cell voltage may vary, and the fuel cell main body may be damaged.
[0020]
In the present invention, when variation occurs in the voltage of the power generation cells constituting the fuel cell main body, it is determined whether the cause is due to the distribution of the raw material gas inside the fuel cell main body or due to cell deterioration, Since the raw material gas stoichiometric ratio is set according to the determination result, operation at an appropriate raw material gas stoichiometric ratio is always realized.
[0021]
【The invention's effect】
According to the fuel cell system of the present invention, the raw material gas is supplied to the fuel cell main body at an optimum flow rate, and the operation is always performed at an appropriate raw material gas stoichiometric ratio. While suppressing, variation in each cell voltage of the fuel cell main body can be suppressed. It is also possible to prevent damage to the fuel cell body due to excessive cell voltage variations.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0023]
An overall configuration of a fuel cell system to which the present invention is applied is shown in FIG. A fuel cell system 1 shown in FIG. 1 includes a solid polymer type fuel cell main body 2 having a solid polymer film as an electrolyte. The fuel cell main body 2 has a stack structure in which a plurality of power generation cells are stacked. In each power generation cell, oxygen in the air supplied to the cathode electrode as raw material gas and hydrogen supplied to the anode electrode are electrochemically generated. To generate electricity.
[0024]
In the fuel cell main body 2, an air supply device 4 such as a compressor or a blower is connected to a cathode electrode inlet via an air supply pipe 3. The air supply device 4 corresponds to an oxygen-containing gas supply device that supplies oxygen-containing gas to the cathode electrode of the fuel cell main body 2, and air (oxygen) whose flow rate and pressure are adjusted by the air supply device 4. Gas) is supplied to the cathode inlet of the fuel cell body 2 through the air supply pipe 3.
[0025]
In the fuel cell system 1, not all the air supplied from the cathode electrode inlet is consumed, but oxygen remaining without being consumed and other components in the air are discharged as exhaust air from the exhaust air pipe 5. . The exhaust air pipe 5 is open to the atmosphere, and the exhaust air is released into the atmosphere.
[0026]
Further, the fuel cell main body 2 is connected to the anode inlet via a hydrogen supply pipe 6 through a hydrogen supply device 7 composed of, for example, a hydrogen tank. This hydrogen supply device 7 corresponds to a hydrogen-containing gas supply device that supplies a gas containing hydrogen to the anode electrode of the fuel cell main body 2. A hydrogen supply valve 8 is disposed in the middle of the hydrogen supply pipe 6, and hydrogen gas having a target flow rate (hereinafter referred to as raw material hydrogen) is supplied from the hydrogen supply device 7 to the anode electrode inlet of the fuel cell main body 2. It can be supplied to the side.
[0027]
The fuel cell system 1 is configured as a hydrogen circulation type, and is a circulating hydrogen pipe that serves as a path for exhaust hydrogen (circulated hydrogen) discharged from the fuel cell main body 2 without being used for power generation in the fuel cell main body 2. 9 is provided. A circulating hydrogen pump 10 is disposed in the middle of the circulating hydrogen pipe 9, and circulating hydrogen containing a large amount of water vapor discharged from the fuel cell main body 2 is supplied to the circulating hydrogen pump 10 by driving the circulating hydrogen pump 10. It is circulated to the anode electrode inlet side of the fuel cell main body 2 through the pipe 9 and joins with the raw material hydrogen supplied from the hydrogen supply device 7. Therefore, in the fuel cell system 1, mixed hydrogen of raw hydrogen supplied from the hydrogen supply device 7 and circulating hydrogen containing a large amount of water vapor is supplied to the anode electrode of the fuel cell main body 2.
[0028]
As described above, in the fuel cell system 1 of the present embodiment, the circulating hydrogen containing a large amount of water vapor is mixed with the raw material hydrogen and supplied to the anode electrode of the fuel cell main body 2, whereby the solid polymer membrane of the fuel cell main body 2 is formed. I try to humidify it. In addition, in order to further improve the humidification effect, a humidifier may be separately installed at the subsequent stage of the hydrogen supply device 7. By installing such a humidifier, the anode of the fuel cell body 2 is supplied with a mixed hydrogen of raw hydrogen and circulating hydrogen humidified by passing through the humidifier. The solid polymer film 2 can be sufficiently humidified.
[0029]
In the fuel cell system 1, an exhaust hydrogen pipe 12 provided with a purge valve 11 for releasing surplus hydrogen gas and water vapor in the circulating hydrogen pipe 9 into the atmosphere is provided as a circulating hydrogen pipe 8. It is provided by branching.
[0030]
And the external load 13 which consumes the electric power generated with the said fuel cell main body 2 is connected to the fuel cell main body 2 of this embodiment. Specifically, for example, an inverter is connected to the fuel cell main body 2 as the external load 13, and power generated by the fuel cell main body 2 is converted into energy by the inverter and supplied to a drive motor or the like. This drive motor is used as power for driving the vehicle when the fuel cell system 1 is applied to a vehicle.
[0031]
A voltage sensor 14 and a load current sensor 15 are arranged between the fuel cell main body 2 and the external load 13, and the generated voltage in the fuel cell main body 2 is detected by the voltage sensor 14, and the load current sensor 15 A load current supplied from the fuel cell main body 2 to the external load 13 is detected.
[0032]
The fuel cell main body 2 is provided with a temperature sensor 16 that detects the operating temperature of the fuel cell main body 2. In the fuel cell system 1, heat is generated during the reaction in the fuel cell main body 2, but it is cooled by a cooling mechanism (not shown) and the operating temperature of the fuel cell main body 2 is monitored by the temperature sensor 16. Operation at an optimum temperature is possible.
[0033]
Further, the fuel cell main body 2 is provided with a cell voltage measuring device 17 corresponding to cell voltage detecting means for detecting the voltage of each power generation cell constituting the fuel cell main body 2. In the fuel cell system 1 of the present embodiment, based on the measurement result by the cell voltage measurement device 17, the power generation cell in which the cell voltage has decreased is identified and the cause is determined.
[0034]
The fuel cell system 1 includes a controller 18 for performing the control of the present invention. The controller 18 includes a CPU, a ROM, a RAM, a CPU peripheral circuit, and the like, and has a microprocessor configuration in which these are connected via a bus. The controller 18 receives measurement results from the cell voltage measurement device 17 and information from the circulating hydrogen pump 10, and the CPU executes a control program stored in the ROM using the RAM as a work area. When variation occurs in the voltage of the power generation cells constituting the fuel cell main body 2, it is determined whether the cause is due to the distribution of the raw material gas in the fuel cell main body 2 or due to cell deterioration. Then, an instruction is sent to the air supply device 4 and the hydrogen supply device 7 in accordance with the determination result, and the raw material gas stoichiometric ratio is set.
[0035]
The internal configuration of the controller 18 is shown in FIG. As shown in FIG. 2, the controller 18 basically includes a source gas distribution changing unit 19, a cell deterioration determining unit 20, and a source gas stoichiometric ratio changing unit 21.
[0036]
The raw material gas distribution changing means 19 changes the raw material gas distribution by changing the raw material gas flow rate to increase transiently in a steady state where there is no load transient change. For example, it has a cathode pressure regulating valve and an anode pressure regulating valve, and changes the distribution of the raw material gas by transiently increasing the cathode pressure or anode pressure of the fuel cell body or both in a steady state when there is no load transient change. To do. The source gas distribution changing means 19 can, for example, increase the source gas flow rate transiently, and examine the state of the cell voltage change at that time, thereby determining the cause of cell deterioration.
[0037]
The cell deterioration judging means 20 judges the cause of the cell voltage drop based on the change of the cell voltage when the raw material gas distribution changing means 19 changes the raw gas distribution, and the cell voltage measuring device 17 performs the measurement. Cell voltage determination means 22 is provided for determining whether each cell voltage has a desired voltage value based on the result. When the source gas distribution changing means 19 changes the source gas distribution inside the fuel cell main body 2, the cell deterioration determining means 20 increases the cell voltage of the power generation cell determined by the cell voltage determining means 22 to be low. In this case, it is determined that the cause is due to the distribution of the raw material gas inside the fuel cell main body 2, and when the cell voltage of the power generation cell determined by the cell voltage determination means 22 to be low is not increased, It is determined that the cause is due to cell deterioration.
[0038]
The cell voltage determination means 22 is a cell voltage calculation means (shown) for calculating a desired cell voltage in each power generation cell by referring to, for example, a fuel cell current voltage performance function that receives the load current and the operating temperature of the fuel cell body. And a first voltage drop cell discriminating means 23 for discriminating a power generation cell having a voltage lower than the output from the cell voltage calculating means, and a relative voltage comparing means for comparing each cell voltage with another cell voltage. (Not shown) and second voltage drop cell discriminating means 24 for discriminating a power generation cell having a relatively low voltage based on information from the relative voltage comparing means. Then, the power generation cell which has been determined that the voltage is relatively low by the second voltage drop cell discriminating means 24 and which has been judged to be lower than the desired voltage value by the first voltage drop cell discrimination means 23 Is determined that the cell voltage is low.
[0039]
The raw material gas stoichiometric ratio changing unit 21 sets the raw material gas stoichiometric ratio so that the cell voltage of the deteriorated power generation cell becomes equal to or higher than a lower limit value when the cell deterioration determining unit 20 determines that the cause is due to cell deterioration. When the cell deterioration determining means 20 determines that the cause is due to the distribution of the raw material gas in the fuel cell main body 2, the raw material gas stoichiometric ratio is set to a predetermined lower limit value. The raw material gas stoichiometric ratio changing means 21 has an average voltage calculating means for calculating a weighted average voltage by relatively increasing the weighting for the power generation cell having a low voltage, and based on the output from the average voltage calculating means. Calculate the raw material gas stoichiometric ratio.
[0040]
The configuration of the controller 18 has been described above. Next, an example of processing by the controller 18 will be specifically described with reference to the flowchart of FIG.
[0041]
The controller 18 first calculates a desired cell voltage in the cell voltage calculation means incorporated in the cell voltage determination means 22 (step S10). This desired cell voltage is calculated by referring to the current-voltage characteristic function (IV characteristic) of the fuel cell main body 2. An example of the current-voltage characteristic function of the fuel cell main body 2 is shown in FIG. The cell voltage calculation means inputs the current load current to the current voltage characteristic function and calculates a desired cell voltage at the load current. If a plurality of current-voltage characteristic functions are prepared according to the fuel cell operating temperature, a desired cell voltage can be calculated according to the operating temperature.
[0042]
Next, the cell voltage variation is measured by the cell voltage measuring device 17 (step S20). The cell voltage variation is measured by relatively comparing each cell voltage with another cell voltage in a relative voltage comparison unit incorporated in the cell voltage determination unit 22. In this embodiment, the difference from the cell voltage average value is measured. A cell voltage histogram may be created.
[0043]
In step S30, it is determined whether there is a power generation cell having a low voltage. In the present embodiment, the first voltage drop cell discriminating unit 23 discriminates a power generation cell having a voltage lower than a desired voltage in the previous step S10, and in step S20, the second voltage drop cell discriminating unit 24 relatively determines the voltage. If there is a power generation cell that is determined as a low cell (a cell having a difference from the cell voltage average value equal to or greater than a predetermined value), it is determined that the power generation cell has a low voltage. In the next step S40, the cell number of the power generation cell having the low voltage is stored.
[0044]
On the other hand, if it is determined in step S30 that there is no cell having a low voltage, 0 is substituted for the identification variable “FLAG_Cell_V” (initialization) in step S35, and the process jumps to return and ends. The identification variable “FLAG_Cell_V” is a variable for determining whether the cell voltage drop is caused by the gas distribution inside the fuel cell main body 2 or by the deterioration of the power generation cell itself.
[0045]
Next, the raw material gas distribution changing means 19 changes the raw material flow rate by a predetermined amount to change the raw material gas distribution inside the fuel cell main body 2 (step S50). In the present embodiment, only the air flow rate is changed, but both air and hydrogen may be changed, or hydrogen may be changed instead of air. However, when the hydrogen is increased and changed, it is necessary to discharge the excess hydrogen to the atmosphere and discard it, and the fuel is wasted. In this embodiment, only the air flow rate is changed. In addition, when hydrogen or air is reduced and changed, there is a possibility that the voltage will be further reduced due to a shortage of raw materials. Therefore, in this embodiment, the air flow rate is increased and changed transiently by ΔF for Δt seconds. In the case where there are pressure control valves for the anode and cathode of the fuel cell main body 2, the pressure may be changed by adjusting the valve opening degree.
[0046]
In step S60, it is checked whether or not the voltage of the low voltage cell stored in step S40 has changed. In step S62, when the voltage of the low voltage cell stored in step S40 increases, it is determined that the decrease in the cell voltage is caused by the distribution of the raw material gas in the fuel cell main body 2, and the identification variable “FLAG_Cell_V” is set to 1. Is substituted (initial value is 0). If the cell voltage does not increase, it is determined that the cell voltage decrease is caused by the deterioration of the cell itself, and 2 is assigned to the identification variable “FLAG_Cell_V” in step S64.
[0047]
In step S70, a weighted average voltage of the cell voltage is calculated. In the case of “FLAG_Cell_V” = 2, that is, when there is a cell in which the cell voltage is reduced due to deterioration, the voltage of the cell is weighted most. In this embodiment, the weight is given as a real number from 0 to 1, and a relatively large weight, for example, 1 is given to the deteriorated cell voltage. For example, 0.3 is given to other cells to calculate the weighted average. By doing so, the deteriorated cell voltage is reflected more strongly in the average voltage.
[0048]
On the other hand, when “FLAG_Cell_V” = 1, that is, when it is determined that the cell voltage drop is caused by the distribution of the raw material gas in the fuel cell body 2, for example, 0.6 is given to the low voltage cell, Is given 0.5. By doing so, the influence of the cell having a low cell voltage is not reflected in the average voltage. The weighting uses a membership function often used in fuzzy theory, so that automatic processing by a computer is facilitated. In this embodiment, this method is used.
[0049]
In step S80, the difference between the weighted average voltage of the cell voltage calculated in step S70 and the voltage obtained by averaging the desired cell voltage calculated in step S10 is calculated.
[0050]
In step S90, it is checked whether or not the absolute value of the voltage difference calculated in step S80 is greater than or equal to a predetermined value. If it is equal to or smaller than the predetermined value, the process proceeds to step S100, and the stoichiometric ratio changing means 21 sets the stoichiometric ratio to a predetermined minimum value. In this case, even if the cell voltage is lowered, it depends on the raw material gas distribution in the fuel cell main body 2, so that the stoichiometric ratio is set to the lowest value to save the raw material / raw material supply power.
[0051]
If the absolute value of the voltage difference calculated in step S80 is greater than or equal to a predetermined value, the process proceeds to step S110.
[0052]
In this embodiment, the weighted average voltage of the cell voltage is calculated, and the stoichiometric ratio is changed according to the difference between the weighted average voltage and the voltage obtained by averaging the desired cell voltage calculated in step S10.
[0053]
In the present embodiment, a function that relates the difference between the weighted average voltage and the voltage obtained by averaging the desired cell voltage calculated in step S10 and the stoichiometric change amount is stored in the computer in advance, and this function is referred to. Thus, the stoichiometric ratio change amount is calculated. Further, the stoichiometric change amount increases as the differential voltage increases. In this way, the stoichiometric ratio is increased so as to maintain the cell voltage that has deteriorated and the voltage has decreased to the upper limit value or more. FIG. 5 shows an example of the function.
[0054]
In the fuel cell system 1 of the present embodiment having the above configuration, it is determined whether the cell voltage variation depends on the distribution of the raw material gas in the fuel cell main body 2 or on the deterioration of the power generation cell itself. Since the raw material gas stoichiometric ratio is set, waste of raw material and raw material power can be saved, and damage to the fuel cell main body 2 due to excessive variation in cell voltage can be prevented.
[0055]
Further, in the fuel cell system 1 of the present embodiment, when the source gas distribution in the fuel cell main body 2 is changed, it is checked whether the cell voltage determined to be low has risen, and when the voltage has risen. Determines that the cell voltage drop is caused by the distribution of the raw material gas in the fuel cell main body 2 in the operating state at that time, and if the voltage of the cell determined to be low does not rise, the cell voltage drop is It is possible to determine that it was caused by the deterioration of the battery, and an accurate determination is possible. The change in the distribution of the raw material gas in the fuel cell main body 2 can be easily performed by, for example, transiently increasing the pressure difference between the raw material supply side and the outlet of the fuel cell in a steady state where there is no load transient change.
[0056]
Furthermore, in the present embodiment, it is possible to determine a cell having a low voltage compared to a desired cell voltage value of each cell voltage. For example, if the desired cell voltage value is calculated from the voltage-current performance characteristics of the fuel cell, the desired cell voltage value corresponding to the load current value can be calculated to determine a cell having a low voltage. In addition, if a plurality of voltage current performance characteristics are prepared using temperature as a parameter and referred to according to the operating temperature of the fuel cell, a desired cell voltage value corresponding to the operating temperature of the fuel cell is calculated and the voltage is calculated. Cell having a low value can be determined. Also, each cell voltage can be compared with other cell voltages to determine a cell having a relatively low voltage, and a cell having a specific low voltage can be determined. The cell voltage drop can be determined by comparing it with the desired voltage value, but the relative comparison can clarify the variation in the cell voltage, and it is possible to determine a cell with a low voltage that requires special attention. it can.
[0057]
Further, in this embodiment, when it is determined that the cell voltage drop is caused by the deterioration, the raw material stoichiometric ratio is calculated so that the voltage of the low voltage cell is deteriorated and becomes the lower limit value or more. Thus, it is possible to prevent further weakening of the deteriorated cells, and damage to the fuel cell main body 2 can be prevented. When it is determined that the cell voltage drop is caused by the gas distribution inside the fuel cell, the stoichiometric ratio can be set to a predetermined lower limit value, which can save the waste of the raw material and the power required for the raw material supply. .
[0058]
Furthermore, in the fuel cell system 1 of the present embodiment, the average voltage of all the cells can be calculated by relatively weighting the voltage of the low voltage cell, and the raw material gas stoichiometric ratio can be calculated. If there is a low voltage cell, the weight of the deteriorated cell voltage is set to a relatively extreme value (by increasing the weight difference with other cells), and the voltage of the deteriorated cell becomes the lower limit. It can be set to calculate the raw material stoichiometric ratio as described above, can prevent further weakening of the deteriorated and weak cells, and prevent damage to the fuel cell main body 2 Can do. If it is determined that the cell voltage drop is caused by the distribution of the raw material gas in the fuel cell main body 2, the weight of the cell voltage having a low voltage is relatively increased, and the weight difference with other cells is increased. By calculating the weighted average of the cell voltage so as to decrease the value and setting the stoichiometric ratio to a predetermined lower limit, it is possible to save waste of the raw material and the power necessary for supplying the raw material.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a fuel cell system according to an embodiment.
FIG. 2 is a diagram for explaining functions realized by a controller of the fuel cell system.
FIG. 3 is a flowchart for explaining an example of processing by a controller;
FIG. 4 is a characteristic diagram showing an example of a current-voltage characteristic function of the fuel cell main body.
FIG. 5 is a characteristic diagram showing an example of a function for setting a stoichiometric ratio.
[Explanation of symbols]
1 Fuel cell system
2 Fuel cell body
4 Air supply device
7 Hydrogen supply equipment
10 Circulating hydrogen pump
17 Cell voltage measuring device
18 Controller
19 Raw material gas distribution change means
20 Cell deterioration judgment means
21 Raw material gas stoichiometric ratio change means
22 Cell voltage judgment means
23 First voltage drop cell discrimination means
24 Second voltage drop cell discrimination means

Claims (9)

A fuel cell body that includes a plurality of power generation cells and that generates electricity by electrochemically reacting hydrogen and oxygen as raw material gases;
A hydrogen-containing gas supply device for supplying a gas containing hydrogen to the anode electrode of the fuel cell body;
An oxygen-containing gas supply device for supplying a gas containing oxygen to the cathode electrode of the fuel cell main body,
When variation occurs in the voltage of the power generation cells constituting the fuel cell body, it is determined whether the cause is due to the distribution of the raw material gas inside the fuel cell body or due to cell deterioration, and the determination A fuel cell system, wherein a raw material gas stoichiometric ratio is set according to a result. Cell voltage detection means for detecting the voltage of each power generation cell constituting the fuel cell main body;
Source gas distribution changing means for changing the distribution of the source gas inside the fuel cell;
Cell deterioration determining means for determining the cause based on a change in cell voltage when the source gas distribution is changed by the source gas distribution changing means;
A raw material gas stoichiometric ratio is calculated based on an output from the cell deterioration determining means, and a raw material gas stoichiometric ratio changing means for controlling the supply of the raw material gas to the fuel cell main body so as to be the raw material gas stoichiometric ratio. The fuel cell system according to claim 1. The cell deterioration determining means includes cell voltage determining means for determining whether or not each cell voltage has a desired voltage value.
When the source gas distribution inside the fuel cell main body is changed by the source gas distribution changing means, and the cell voltage of the power generation cell determined by the cell voltage determining means is low, the cause is If the cell voltage of the power generation cell is determined to be due to the distribution of the raw material gas inside the fuel cell body and the voltage is determined to be low by the cell voltage determination means, the cause is determined to be due to cell deterioration. The fuel cell system according to claim 2. The cell voltage determination means includes
Cell voltage calculation means for calculating a desired cell voltage in each power generation cell by referring to a fuel cell current voltage performance function that receives the load current and the operating temperature of the fuel cell body;
First voltage drop cell determining means for determining a power generation cell having a voltage lower than the output from the cell voltage calculating means;
Relative voltage comparison means for comparing each cell voltage with other cell voltages;
4. The fuel cell system according to claim 3, further comprising: a second voltage drop cell determining unit configured to determine a power generation cell having a relatively low voltage based on information from the relative voltage comparing unit. The cell voltage determination means determines that the voltage is relatively low by the second voltage drop cell determination means, and determines that the voltage is lower than a desired voltage value by the first voltage drop cell determination means. The fuel cell system according to claim 4, wherein the power generation cell is determined to have a low voltage. The raw material gas stoichiometric ratio changing means is:
When it is determined by the cell deterioration determination means that the cause is due to cell deterioration, the raw material gas stoichiometric ratio is calculated so that the cell voltage of the deteriorated power generation cell is equal to or higher than the lower limit value,
The raw material gas stoichiometric ratio is set to a predetermined lower limit value when the cause is judged by the cell deterioration judging means to be a raw material gas distribution inside the fuel cell main body. Fuel cell system. The raw material gas stoichiometric ratio changing means has an average voltage calculating means for calculating a weighted average voltage by relatively increasing the weighting for the power generation cell having a low voltage, and based on the output from the average voltage calculating means, the raw material gas stoichiometric ratio The fuel cell system according to claim 2, wherein the fuel cell system is calculated. 3. The fuel cell system according to claim 2, wherein the raw material gas distribution changing unit changes the raw material gas distribution by changing the raw material gas flow rate in a transient manner when there is no load transient change. 4. The raw material gas distribution changing means has a cathode pressure adjusting valve and an anode pressure adjusting valve, and changes the cathode pressure and / or anode pressure of the fuel cell main body in a transient manner when there is no load transient change. The fuel cell system according to claim 2, wherein the distribution of the raw material gas is changed by the above.

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