JP5509728B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  A conventional fuel cell system includes a relationship between a generated current and a reactive gas flow rate as a map, and adjusts the reactive gas flow rate based on the map to prevent flooding (see Patent Document 1).

JP 2005-190843 A

  However, the above-described conventional fuel cell system adjusts the reaction gas flow rate according to a uniquely defined map. For this reason, there is a problem in that the occurrence of flooding cannot be suppressed if the conditions for occurrence of flooding change due to changes in the fuel cell over time. Further, in order to cope with such problems, it is necessary to set the reaction gas flow rate excessively in advance, and there is a problem that fuel consumption deteriorates.

  The present invention has been made paying attention to such a conventional problem, and an object of the present invention is to suppress deterioration of fuel consumption while suppressing generation of flooding and performing stable power generation.

The present invention solves the above problems by the following means. The present invention relates to a fuel cell system that generates power by supplying a reaction gas to a fuel cell, and the target reaction gas flow rate that can suppress flooding with respect to the power generation current of the fuel cell is increased to increase the degree of change with time of the fuel cell. Decrease accordingly.

  According to the present invention, it is possible to supply the fuel cell stack with an optimal target reaction gas flow rate that can suppress flooding in accordance with changes in the fuel cell over time. Therefore, it is possible to suppress deterioration of fuel consumption because an excessive amount of reaction gas is not supplied while suppressing generation of flooding and performing stable power generation.

It is a schematic block diagram of a fuel cell system. It is a figure which shows a part of cross section of a single cell. It is the figure which showed the relationship between electric power generation time and the limit SR. It is the figure which showed the relationship between the electric power generation time by 1st Embodiment, the limit SR, and target SR. It is a flowchart explaining the calculation method of the target cathode gas flow volume by 1st Embodiment. It is the figure which showed the relationship between electric power generation amount, limit SR, and target SR. It is the figure which showed the relationship between the frequency | count of power generation, limit SR, and target SR. It is the figure which showed the relationship between the electric power generation time by 4th Embodiment, the limit SR, and target SR. It is the figure which showed the relationship between the electric power generation time by 5th Embodiment, the limit SR, and target SR. It is the figure which showed the relationship between the electric power generation time by 6th Embodiment, the limit SR, and target SR.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
A fuel cell has an electrolyte membrane sandwiched between an anode electrode (fuel electrode) and a cathode electrode (oxidant electrode), an anode gas containing hydrogen in the anode electrode (fuel gas), and a cathode gas containing oxygen in the cathode electrode (oxidant) Electricity is generated by supplying gas. The electrode reaction that proceeds in both the anode electrode and the cathode electrode is as follows.

Anode electrode: 2H ₂ → 4H ⁺ + 4e ⁻ (1)
Cathode electrode: 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2)
The fuel cell generates an electromotive force of about 1 volt by the electrode reactions (1) and (2).

  When such a fuel cell is used as a power source for automobiles, a large amount of electric power is required, so that it is used as a fuel cell stack in which several hundred fuel cells are stacked. Then, a fuel cell system that supplies anode gas and cathode gas to the fuel cell stack is configured, and electric power for driving the vehicle is taken out.

  FIG. 1 is a schematic configuration diagram of a fuel cell system 1 according to a first embodiment of the present invention.

  The fuel cell system 1 includes a fuel cell stack 10, an anode gas passage 20, a cathode gas passage 30, and a controller 40.

  The fuel cell stack 10 is configured by stacking a plurality of single cells in which separators are arranged on both surfaces of a membrane electrode assembly (hereinafter referred to as “MEA”) including an anode electrode and a cathode electrode. Details of the single cell will be described later with reference to FIG.

  The anode gas passage 20 is connected to the anode gas inlet hole 10 a and the anode gas outlet hole 10 b of the fuel cell stack 10. The anode gas passage 20 includes a fuel tank 21 and a pressure regulating valve 22 on the upstream side of the fuel cell stack 10, and a circulation pump 23 and a purge valve 24 on the downstream side of the fuel cell stack 10.

  The fuel tank 21 stores the anode gas (hydrogen) supplied to the fuel cell stack 10 in a high pressure state.

  The pressure regulating valve 22 reduces the pressure of the fuel tank 11 to an appropriate pressure.

  The circulation pump 23 circulates the anode gas. A circulation channel 25 is provided downstream of the circulation pump 23 to supply unreacted reaction gas discharged from the fuel cell stack 10 to the fuel cell stack 10 again.

  The purge valve 24 purges impurity gases such as nitrogen and liquid water existing in the anode gas passage 20 out of the system.

  The cathode gas passage 30 is connected to the cathode gas inlet hole 10 c and the cathode gas outlet hole 10 d of the fuel cell stack 10. The cathode gas passage 30 includes a compressor 31 on the upstream side of the fuel cell stack 10 and a pressure adjustment valve 32 on the downstream side of the fuel cell stack 10.

  The compressor 31 pumps and supplies the cathode gas (air) to the fuel cell stack 10.

  The pressure adjustment valve 32 adjusts the supply pressure of the cathode gas supplied to the fuel cell stack 10.

  The controller 40 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). Signals from various sensors that detect the operating state of the fuel cell stack 10 are input to the controller 40. For example, a signal from a voltage sensor 41 that detects the voltages of all the single cells 11 constituting the fuel cell stack 10 is input. The controller 40 controls the compressor 31 and the like based on these input signals, and controls the flow rates of the reaction gas supplied to the fuel cell stack 10, that is, the cathode gas and the anode gas.

  Below, with reference to FIG. 2, the single cell 11 which comprises the fuel cell stack 10 is demonstrated in detail.

  FIG. 2 is a diagram showing a part of a cross section of the single cell 11.

  The single cell 11 is configured by arranging separators 100 on both front and back surfaces of a membrane electrode assembly (hereinafter referred to as “MEA”) 12.

  The MEA 12 includes a solid polymer electrolyte membrane 13, an anode electrode 14, and a cathode electrode 15. The MEA 12 has an anode electrode 14 on one surface of the solid polymer electrolyte membrane 13 and a cathode electrode 15 on the other surface.

  The solid polymer electrolyte membrane 13 is a proton-conductive ion exchange membrane formed of a fluorine-based resin. The solid polymer electrolyte membrane 13 exhibits good electrical conductivity in a wet state.

  The anode electrode 14 includes a catalyst layer 16 and a gas diffusion layer 17.

  The catalyst layer 16 is in contact with the solid polymer electrolyte membrane 13. The catalyst layer 16 is formed from carbon black particles on which platinum or platinum is supported.

  The gas diffusion layer 17 is provided on the outer side of the catalyst layer 16 (opposite side of the electrolyte membrane 13) and is in contact with the separator 100. The gas diffusion layer 17 is formed of a member having sufficient gas diffusibility and conductivity, and is formed of, for example, a carbon cloth woven with yarns made of carbon fibers. Hereinafter, in particular, the gas diffusion layer 17 that is in direct contact with the ribs (partitions) 112 of the separator 100 is referred to as “under-rib gas diffusion layer 17a”. On the other hand, the gas diffusion layer 17 in contact with the gas flow path 111 of the separator 100 is referred to as “under-flow path gas diffusion layer 17b”.

  Similarly to the anode electrode 14, the cathode electrode 15 includes a catalyst layer 16 and a gas diffusion layer 17.

  The separator 100 is in contact with the gas diffusion layer 17. The separator 100 has a plurality of gas flow paths 111 for supplying reaction gas to the anode electrode 14 and the cathode electrode 15 on the side in contact with the gas diffusion layer 17. The gas flow path 111 is a flow path formed between the ribs 112 that are in direct contact with the gas diffusion layer 17.

  Next, the operation of the fuel cell stack 10 according to the present embodiment will be described with reference to FIGS. 1 and 2.

  As shown in FIGS. 1 and 2, the anode gas flows from the anode gas inlet hole 10a into the gas flow path 111 formed in the anode electrode side separator 100 (the separator on the left side in FIG. 2). The anode gas contacts the catalyst layer 16 through the gas diffusion layer 17 while flowing through the gas flow path 111. Thereby, in the anode electrode 14, reaction of Formula (1) mentioned above arises. Excess anode gas that has flowed through the gas flow path 111 and was not used for the reaction is discharged to the outside from the anode gas outlet hole 10b.

On the other hand, the cathode gas flows from the cathode gas inlet hole 10c into the gas flow path 111 formed in the cathode electrode side separator 100 (the separator on the right side in FIG. 2). The cathode gas contacts the catalyst layer 16 through the gas diffusion layer 17 while flowing through the gas flow path 111. Thereby, in the cathode electrode 15, reaction of Formula (2) arises from cathode gas, the proton H ^<+> produced by reaction of Formula (1), and electron e ^{< - >} .

  The water generated by the cathode reaction flows through the gas flow path 111 together with the excess cathode gas not used for the reaction, and is discharged to the outside from the cathode gas outlet hole 10d. Therefore, the moisture concentration in the cathode gas increases in the latter half of the gas flow path. In addition, the moisture concentration in the gas diffusion layer also increases.

  Then, depending on the operating conditions and the like, the condensed generated water may block the gas flow path 111 in the vicinity of the cathode gas outlet hole 10d, and water clogging may occur. Thereby, the flow of the cathode gas flowing through the gas flow path 111 is hindered, and the supply amount of the cathode gas to the cathode electrode 15 becomes insufficient. As a result, a phenomenon called flooding in which the concentration overvoltage increases due to a decrease in gas diffusibility occurs, resulting in a decrease in power generation efficiency.

  Further, water generated by the cathode reaction diffuses through the MEA 12 to the gas flow path 111 formed in the separator 100 on the anode electrode side, so that flooding may occur on the anode side and power generation efficiency may be reduced. .

  Therefore, in order to improve the power generation efficiency of the single cell 1, the flow rate of one or both of the cathode gas and the anode gas is controlled so that no flooding occurs, and the water generated by the power generation reaction of the single cell 1 is promptly fueled. It is necessary to discharge the battery stack 10 to the outside.

  For this reason, in the conventional example, the reactive gas flow rate is controlled according to a map showing the relationship between a predetermined power generation current and the reactive gas flow rate so that no flooding occurs. However, the inventors' diligent research has revealed that the generation condition of flooding changes according to the change with time of the fuel cell stack 10.

  Therefore, in the present embodiment, the generation of flooding is suppressed by controlling the reaction gas flow rate as follows. In the following description, the cathode gas will be described as an example of the reaction gas, but of course, the anode gas may be used, or both may be used.

  FIG. 3 is a diagram showing the relationship between the power generation time and the limit stoichiometric ratio (hereinafter referred to as “limit SR”).

  Here, the power generation time refers to the total power generation time from the initial state to the present, and the initial state refers to a so-called new state (when shipped, mounted on the vehicle, when the fuel cell stack 10 is assembled).

  The limit SR is the cathode gas flow rate theoretically required for the reaction (hereinafter referred to as “basic cathode gas flow rate”) determined according to the operating state such as the accelerator pedal depression amount and auxiliary machine operation status, and the occurrence of flooding. It is a ratio of the minimum required cathode gas flow rate to suppress the above. The larger the limit SR, the higher the minimum cathode gas flow rate necessary for suppressing the occurrence of flooding with respect to the basic cathode gas flow rate.

  As shown in FIG. 3, the limit SR is greater than 1 until the power generation time reaches a predetermined time, and decreases as the power generation time increases. And after power generation time reaches predetermined time, it becomes fixed. In the present embodiment and each of the following embodiments, the value when the limit SR becomes constant is 1. However, this is an example in an ideal state, and is actually constant at a value slightly larger than 1. It becomes.

  As described above, the minimum necessary cathode gas flow rate for suppressing flooding decreases as the power generation time increases. This is because the contact state between the rib 112 of the separator 100 and the gas diffusion layer 17 is not optimal from the viewpoint of drainage at the initial assembly of the fuel cell stack 10, and the contact state is improved as the number of power generations increases. This is probably because of this.

  In other words, among the generated water condensed inside the gas diffusion layer 17, the generated water in the gas diffusion layer 17 b under the flow path is taken out to the gas flow path 111 by the reaction gas passing through the gas flow path 111. On the other hand, the generated water of the under-rib gas diffusion layer 17a is taken out to the gas flow path 111 by the surface tension with the rib 112 of the separator 100 or the like. In the initial assembly of the fuel cell stack 10, since the contact state between the separator 100 and the gas diffusion layer 17 is not optimal from the viewpoint of drainage, the generated water is taken out from the gas diffusion layer 17a under the ribs. Easy to be disturbed. For this reason, flooding is likely to occur, and the limit SR is considered to increase.

  Therefore, in the present embodiment, the target stoichiometric ratio (hereinafter referred to as “target SR”) is decreased as the limit SR decreases with the power generation time. Here, the target SR is a ratio between the basic cathode gas flow rate and the cathode gas flow rate actually supplied to the fuel cell stack 10 (hereinafter referred to as “target cathode gas flow rate”). The larger the target SR, the greater the target cathode gas flow rate with respect to the basic cathode gas flow rate.

  FIG. 4 is a diagram showing the relationship between the power generation time, the limit SR, and the target SR.

  As shown in FIG. 4, the target SR is set to take a value slightly larger than the limit SR. Thereby, generation | occurrence | production of flooding can be suppressed reliably and the stable electric power generation can be implemented. Further, since the cathode gas is not supplied more than necessary, the power consumption of the compressor can be suppressed, so that the fuel consumption can be improved.

  FIG. 5 is a flowchart illustrating a method for calculating the target cathode gas flow rate according to the present embodiment. The controller 40 executes this routine at a predetermined calculation cycle (for example, 10 ms) during operation of the fuel cell stack 10.

  In step S1, the controller 40 calculates a target generated current according to the operating state with reference to a map determined in advance by experiments or the like. The target generated current increases as the load of the fuel cell stack 10 increases.

  In step S <b> 2, the controller 40 calculates a basic cathode gas flow rate based on the target generated current with reference to a table previously determined by experiments or the like. The basic cathode gas flow rate increases as the target generated current increases.

  In step S3, the controller 40 calculates the target SR based on the change with time of the fuel cell with reference to the table of FIG. Specifically, the target SR is calculated based on the power generation time.

  In step S4, the controller 40 calculates the target cathode gas flow rate by multiplying the basic cathode gas flow rate by the target SR.

  According to the present embodiment described above, the target SR is changed as the limit SR decreases as the fuel cell stack 10 changes with time, that is, the power generation time increases, and the target SR becomes the limit SR. I tried to take a slightly larger value. Then, the basic cathode gas flow rate is calculated according to the operating state, and the target cathode gas flow rate is calculated by multiplying the basic cathode gas flow rate by the target SR.

  As a result, the cathode gas flow rate (target cathode gas flow rate) actually supplied to the fuel cell stack 10 is always determined according to the operating state, and the theoretically necessary cathode gas flow rate (basic cathode gas flow rate) and generation of flooding. It becomes larger than the minimum cathode gas flow rate required for suppressing the above.

  For this reason, the generation of flooding can be reliably suppressed and stable power generation can be performed. Further, since the cathode gas is not supplied more than necessary, the power consumption of the compressor can be suppressed, so that the fuel consumption can be improved.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The second embodiment of the present invention is different from the first embodiment in that the target SR is changed according to the power generation amount. Hereinafter, the difference will be described. In each embodiment described below, the same reference numerals are used for portions that perform the same functions as those of the above-described embodiments, and repeated description is appropriately omitted.

  FIG. 6 is a diagram showing the relationship between the power generation amount, the limit SR, and the target SR. In addition, the power generation amount here means the total power generation amount from the initial state to now.

  As shown in FIG. 6, the limit SR is larger than 1 until the power generation amount reaches a predetermined amount, and decreases as the power generation amount increases. Then, it becomes constant after the power generation amount reaches a predetermined amount.

  Therefore, in the present embodiment, the target SR is decreased as the limit SR decreases with the power generation amount. Then, the target SR is set to take a value slightly larger than the limit SR. Thereby, the effect similar to 1st Embodiment can be acquired.

(Third embodiment)
Next, a third embodiment of the present invention will be described. The third embodiment of the present invention is different from the first embodiment in that the target SR is changed according to the number of times of power generation. Hereinafter, the difference will be described.

  FIG. 7 is a diagram showing the relationship between the number of power generations, the limit SR, and the target SR. Here, the number of power generations refers to the total number of power generations from the initial state until now.

  As shown in FIG. 7, the limit SR is greater than 1 until the number of power generations reaches a predetermined number, and decreases as the number of power generations increases. And it becomes constant after the frequency | count of electric power generation reaches predetermined number of times.

  Therefore, in the present embodiment, the target SR is decreased as the limit SR decreases with the number of power generations. Then, the target SR is set to take a value slightly larger than the limit SR. Thereby, the effect similar to 1st Embodiment can be acquired.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. In the fourth embodiment of the present invention, the target SR is uniformly set to a high SR until the power generation time (which may be the amount of power generation or the number of power generations) reaches a predetermined time, and is uniformly set to a low SR after the predetermined time is reached. It differs from the first embodiment in that it is set. Hereinafter, the difference will be described.

  FIG. 8 is a diagram showing the relationship between the power generation time, the limit SR, and the target SR according to this embodiment.

  As shown in FIG. 8, in this embodiment, the target SR is uniformly set to high SR until the power generation time reaches a predetermined time, and after reaching the predetermined time, it is uniformly set to low SR.

  According to this embodiment, the same effect as the first embodiment can be obtained, and the target SR is only switched in two steps step by step, so that the target SR is continuously changed according to the power generation time. The cathode gas flow rate can be easily controlled.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described. The fifth embodiment of the present invention is different from the first embodiment in that the target SR is increased when flooding is detected. Hereinafter, the difference will be described.

  FIG. 9 is a diagram showing the relationship between the power generation time, the limit SR, and the target SR according to this embodiment.

  In the present embodiment, similarly to the first embodiment, the target SR is continuously reduced according to the limit SR according to the power generation time. At this time, while there is an individual difference in the fuel cell stack 10, the limit SR is uniformly determined in advance by experiments or the like. Therefore, depending on the solid, there is a deviation between the predetermined limit SR and the actual limit SR. May occur. Therefore, the actual limit SR may take a value larger than the predetermined limit SR, and the target SR may fall below the limit SR.

  Thus, in the present embodiment, as shown in FIG. 9, when it can be determined that the target SR has fallen below the actual limit SR, that is, when it is determined that flooding has occurred, the target SR is increased by a predetermined value. Then, after the increase, the target SR is decreased again according to the power generation time in accordance with the inclination of the limit SR determined in advance with the increased target SR as a reference.

  Whether flooding has occurred can be determined as follows. That is, it can be determined that flooding has occurred if the voltage of another single cell 11 in the vicinity of the single cell 11 that is equal to or lower than the predetermined voltage is greater than the humidification excess determination voltage greater than the predetermined voltage.

  According to the present embodiment described above, the same effect as that of the first embodiment can be obtained, and when the flooding occurs, the set value of the target SR can be corrected, so that the occurrence of flooding can be more reliably suppressed. it can.

(Sixth embodiment)
Next, a sixth embodiment of the present invention will be described. In the sixth embodiment of the present invention, when flooding occurs at the same target SR a plurality of times after a predetermined time has elapsed, the target SR or a value obtained by increasing the target SR by a predetermined value is set as the final target. It differs from the first embodiment in that it is set as SR. Hereinafter, the difference will be described.

  FIG. 10 is a diagram showing the relationship between the power generation time, the limit SR, and the target SR according to the present embodiment.

  In the present embodiment, similarly to the first embodiment, the target SR is continuously reduced according to the limit SR according to the power generation time. When it is determined that flooding has occurred, the target SR is increased by a predetermined value. At this time, when flooding occurs in the same target SR a plurality of times after a predetermined time has elapsed, the target SR or a value obtained by increasing the target SR by a predetermined value is set as the final target SR.

  As a result, the same effects as those of the first embodiment can be obtained, the limit SR can be grasped for each solid, and the limit SR can be set as the target SR. Therefore, since the minimum necessary cathode gas that can suppress the occurrence of flooding can be supplied, the fuel consumption can be further improved.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  For example, in each of the above-described embodiments, the power generation time, the power generation amount, and the number of power generations are used as an index representing the change with time of the fuel cell stack 10. Instead, the number of times of starting and stopping the fuel cell system 1, the number of times of lubrication accompanying power generation, the number of times of shrinkage due to drying, and the like may be used as an index representing the change with time of the fuel cell stack 10.

  Further, in each of the above embodiments, the generation of flooding is suppressed by controlling the flow rate of the cathode gas in accordance with the change with time of the fuel cell stack 10. However, the generation of flooding may be suppressed by controlling the flow rate of the anode gas, or the generation of flooding may be suppressed by controlling the flow rates of both the cathode gas and the anode gas. At this time, the decrease width of the anode gas flow rate (the magnitude of the inclination of the target SR) may be the same as or different from the cathode gas flow rate.

  In the first to third embodiments, the target SR is set to be slightly larger than the limit SR. However, the target SR and the limit SR may be the same.

  Further, the change with time of the fuel cell stack 10 may be obtained with high accuracy in consideration of all of the power generation time, the power generation amount, and the number of power generations.

1 Fuel Cell System 10 Fuel Cell Stack (Fuel Cell)
S1 target generation current calculation means S2 basic reaction gas flow rate calculation means S1 to S4 target reaction gas flow rate calculation means

Claims (9)

A fuel cell system for generating power by supplying a reaction gas to a fuel cell,
A fuel cell system comprising target reaction gas flow rate calculation means for reducing a target reaction gas flow rate capable of suppressing flooding with respect to the generated current of the fuel cell in accordance with an increase in the degree of change with time of the fuel cell. The target reaction gas flow rate calculating means includes:
Target generated current calculation means for calculating a target generated current according to the operating state;
A basic reaction gas flow rate calculating means for calculating a basic reaction gas flow rate according to the target generated current,
The pre-Symbol basic reaction gas flow rate and increasing correction, and calculates a target flow rate of the reaction gas supplied to the fuel cell,
The fuel cell system according to claim 1, wherein the correction amount of the basic reaction gas flow rate is decreased as the degree of change with time of the fuel cell increases . The fuel cell system according to claim 2, wherein the correction amount of the basic reaction gas flow rate is changed stepwise. The target reaction gas flow rate calculating means includes:
When flooding is detected, the correction amount of the basic reaction gas flow rate is increased, and after the increase, the increased correction amount is decreased again according to the increase in the degree of change with time of the fuel cell. The fuel cell system according to claim 2 or 3. 5. The fuel cell system according to claim 4, wherein when a correction amount of the basic reaction gas flow rate when the flooding is detected is the same value a plurality of times, the subsequent correction amount is fixed to the same value. . The target reaction gas flow rate calculating means includes:
Includes a target stoichiometric ratio calculating means for calculating a target stoichiometric ratio taking one or more values in response to aging degree physician of the fuel cell,
The fuel cell system according to any one of claims 2, wherein up to 5 to calculate the reaction gas flow rate by multiplying the target stoichiometric ratio to the basic reaction gas flow rate. The target reaction gas flow rate calculation means determines an increase in the degree of change with time of the fuel cell based on the total number of power generations of the fuel cell, according to any one of claims 1 to 6 . Fuel cell system. The target reaction gas flow rate calculating means determines an increase in the degree of change with time of the fuel cell based on the total power generation amount of the fuel cell, according to any one of claims 1 to 6 . Fuel cell system. The target reaction gas flow rate calculation means determines an increase in the degree of change with time of the fuel cell based on the total power generation time of the fuel cell, according to any one of claims 1 to 6 . Fuel cell system.

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