JP2005293928A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of restraining power loss at normal operation while promoting temperature increase at starting at low temperature. <P>SOLUTION: Current take-out plates 8, 9 arranged adjacent to a fuel cell part are constituted by separated current take-out plates 8a, 8b, 9a, 9b at least divided into two in a direction of face or insulated from each other, and a current take-out plate to be connected to a load can be selected from the separated current take-out plates 8a, 8b, 9a, 9b by the control of a control unit. While the temperature of the fuel cell is low at starting, the temperature increase is promoted by connecting only the separated current take-out plates 8a, 9a of small area to the load, and generating heat at the inside of the separators 6, 7 by supplying electric current. After the temperature of the fuel cell is increased, all separated current take-out plates 8a, 8b, 9a, 9b, or that having larger area are connected to the load, and the power loss due to the heat generation at the separators 6, 7 is restrained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system including a solid polymer electrolyte type fuel cell using a solid polymer membrane as an electrolyte, and particularly to a mobile body such as a vehicle, a ship and a portable generator. And an effective fuel cell system.

  The fuel cell system supplies a fuel gas such as hydrogen to the fuel electrode of the fuel cell and also supplies an oxidant gas such as air to the oxidant electrode. It generates a reaction by generating a reaction. The electrode reaction proceeding at both the fuel electrode and the oxidant electrode at this time is as follows.

Fuel electrode: 2H ₂ → 4H ⁺ + 4e ⁻ (1)
Oxidant electrode: 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2)
In the fuel cell, when a fuel gas containing hydrogen is supplied to the fuel electrode, the reaction (1) proceeds at the fuel electrode to generate hydrogen ions. When the generated hydrogen ions permeate (diffuse) the electrolyte in a hydrated state to reach the oxidant electrode, and an oxygen-containing gas such as air is supplied to the oxidant electrode, The reaction proceeds. When the electrode reactions (1) and (2) proceed at each electrode, the fuel cell generates an electromotive force.

  By the way, fuel cells are classified into various types depending on electrolytes and the like. As one of them, a solid polymer electrolyte type fuel cell using a solid polymer membrane as an electrolyte is known. A solid polymer electrolyte type fuel cell is easy to make compact at a low cost and has a high output density, so that it is expected to be used as a power source for moving bodies such as vehicles.

  Such a solid polymer electrolyte type fuel cell generally comprises a unit cell as a power generation unit by sandwiching a solid polymer electrolyte membrane between a fuel electrode and an oxidant electrode, and a plurality of unit cells are divided into units. A stack structure is used in which the cells are stacked via a separator in which a reaction gas flow path for supplying reaction gas (fuel gas or oxidant gas) to the cell is formed. And in a fuel cell system comprising such a solid polymer electrolyte fuel cell having a stack structure, generally operating conditions of around 70 ° C. are assumed, but when the system is started, the fuel cell is in a state equal to the ambient temperature. Since the temperature is raised, the temperature of the unit cell located in the center of the fuel cell having a stack structure is likely to rise, whereas the unit cell located near the end is less likely to rise due to heat dissipation. For this reason, the unit cell located near the end is lower in temperature than the unit cell located in the center, the saturated vapor pressure is low, and the liquid water remains and flooding prevents the reaction gas from being supplied to the catalyst layer. The phenomenon called is easy to occur.

  In particular, in a fuel cell system used as a power source for a mobile object such as a vehicle, the mobile object may be exposed to a cryogenic temperature environment such as below freezing point, and moisture remaining inside the fuel cell may freeze during power generation. is assumed. In that case, not only does the frozen water completely prevent the supply of the reaction gas, but there is also a concern that the fuel cell may be structurally destroyed due to the volume expansion of the water.

  In order to avoid the above problems, in a fuel cell system, in particular, a fuel cell system including a stack-structure fuel cell in which a temperature difference is likely to occur between a unit cell located in the center and a unit cell located near the end. Until the temperature of the fuel cell rises to a temperature suitable for operation, it is required to suppress heat dissipation from the end of the fuel cell and promote the temperature rise.

From this point of view, various methods for reducing the heat radiation at the end of the fuel cell have been proposed (see, for example, Patent Document 1 and Patent Document 2). For example, Patent Document 1 discloses a configuration in which a heating element using an electric resistance material is provided at an end portion of a fuel cell. Further, in Patent Document 2, a heating element is provided at the end of the fuel cell, a circuit in which a current flows through the heating element at the time of start-up is formed, and a circuit that bypasses the heating element is formed after the temperature rises sufficiently. Proposals have been made to prevent the loss of power due to power.
JP-A-8-167424 JP 2003-308863 A

  However, if a heating element using an electric resistance material is provided at the end of the fuel cell as in the invention described in Patent Document 1, it is effective to raise the temperature of the end cell during cold start, but during normal operation, However, there is a problem that electric power is consumed due to the presence of the heating element, resulting in power loss.

  Further, as in the invention described in Patent Document 2, in the method of forming a circuit that bypasses the heating element provided at the end of the fuel cell after the temperature has sufficiently increased, not only the volume of the stack system increases but also the heat generation. In order to form a circuit that bypasses the body, the area of the current extraction portion is reduced, which causes a problem that power loss occurs during normal operation.

  The present invention has been proposed in order to eliminate such drawbacks of the prior art, and is a fuel that can promote a temperature rise at the time of cold start and can suppress power loss as much as possible during normal operation. The object is to provide a battery system.

  In the fuel cell system of the present invention, a current extraction plate is provided in a fuel cell system in which a current extraction plate is disposed adjacent to a polymer electrolyte fuel cell and current taken out from the fuel cell via the current extraction plate is supplied to a load. The object is achieved by making the current extraction area from the fuel cell according to the above variable. As a specific configuration, the current extraction plate is provided with a current extraction plate that is divided or insulated into at least two parts in the plane direction, and the current extraction plate connected to a load is a part of the divided or insulated extraction plate. It was set as the structure provided with the electric current extraction control means selected from part or all.

  In the fuel cell system configured as described above, when power generation is performed in a state where only a part of the current extraction plate is connected to the load, that is, in a state where the current extraction area from the fuel cell by the current extraction plate is reduced, Since the current generated in the entire area of the power generation effective surface of the fuel cell is extracted to the outside from a part of the current extraction plate, it flows in the in-plane direction inside the separator. Here, the separator is usually manufactured using graphite or the like as a material, and has a higher electric resistance than a current extraction plate generally made of metal. Accordingly, most of the current flowing in the in-plane direction inside the separator is converted into heat energy in the process.

  On the other hand, when many or all of the current extraction plates are connected to the load, that is, when the current extraction area from the fuel cell by the current extraction plate is increased, the current generated in the power generation effective surface of the fuel cell Since most of the current flows into the nearest current extraction plate, the amount of current that flows in the separator surface and is converted into thermal energy is small, and the loss of power is reduced accordingly.

  According to the fuel cell system of the present invention, the temperature rise can be promoted by reducing the current extraction area from the fuel cell by the current extraction plate at low temperature start, and the fuel by the current extraction plate can be increased during normal operation. By increasing the current extraction area from the battery, power loss can be minimized.

  Hereinafter, embodiments of a fuel cell system to which the present invention is applied will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view showing the structure of a unit cell of a solid polymer electrolyte fuel cell provided in the fuel cell system of this embodiment. A unit cell of a solid polymer electrolyte fuel cell includes an electrolyte membrane 1 made of a solid polymer membrane and two electrodes (a fuel electrode 2 and two electrodes) disposed on both surfaces of the electrolyte membrane 1 so as to sandwich the electrolyte membrane 1. The gas flow path 4 through which the fuel gas flows and the gas flow path 5 through which the oxidant gas flows are in contact with the fuel electrode 2 and the oxidant electrode 3, respectively.

  The electrolyte membrane 1 is formed as a proton-conductive membrane by using a solid polymer material such as a fluorine-based resin. The two electrodes 2 and 3 arranged on both surfaces of the electrolyte membrane 1 are composed of catalyst layers 2a and 3a made of platinum or platinum and other metals and gas diffusion layers 2b and 3b, and the surface on which the catalyst exists. It is formed in contact with the electrolyte membrane 1. The gas flow paths 4 and 5 are formed as gaps between a large number of ribs arranged on one side or both sides of a separator made of a dense carbon material or the like that is impermeable to gas. The gas is supplied from the gas inlet formed in the gas and is discharged from the gas outlet.

  A solid polymer electrolyte fuel cell usually has a stack structure in which a plurality of unit cells as described above are stacked. That is, separators 6 and 7 are arranged on both sides of each unit cell as shown in FIG. 2, and adjacent unit cells are stacked via the separators 6 and 7. Current take-out plates 8 and 9 for taking out current from the solid polymer electrolyte fuel cell are arranged so as to be in contact with the separators 6 and 7 located at the ends in the stacking direction.

  Here, the current extraction plate for extracting current from the solid polymer electrolyte fuel cell is usually configured as a single member for each electrode, but in the present embodiment, the current extraction plate 8, 9 includes two divided current extraction plates 8a and 9a located in the downstream area of the gas flow paths 4 and 5, and two divided current extraction plates 8b and 9b located in other areas. It is configured. The flow direction of the reaction gas (fuel gas or oxidant gas) in the gas flow paths 4 and 5 is indicated by an arrow A in FIG. In FIG. 2, the divided current extraction plate 9 a is not shown because the division position of the current extraction plate 9 is hidden by the separator 7, but the current extraction plate 9 is also divided in the same shape as the current extraction plate 8. ing.

  In order to increase the temperature rising effect at the time of low temperature startup, as described above, it is possible to divide both the current extraction plates 8 and 9 of each electrode disposed at both ends of the solid polymer electrolyte fuel cell. Although it is preferable, it is not necessarily limited to this, and only one of the current extraction plates may be divided. Further, the divided current extraction plates 8a, 8b, 9a, and 9b do not need to be separated from each other. If the insulation between the divided current extraction plates 8a, 8b, 9a, and 9b is ensured, these are used. You may comprise integrally.

  FIG. 3 is a schematic view showing a state of current flowing in the planes of the separators 6 and 7 when only smaller divided current extraction plates 8a and 9a located in the downstream area of the flow path are connected to the load. In this case, the current generated in the entire area of the power generation effective surface of each unit cell of the solid polymer electrolyte fuel cell flows into the current extraction plates connected to the loads, that is, the divided current extraction plates 8a and 9a. As indicated by the arrow B in the middle, it flows through the separators 6 and 7 in the in-plane direction. In the separators 6 and 7, the current flowing in the in-plane direction is converted into heat energy and generates heat.

  Since the efficiency of power generation in each unit cell of the solid polymer electrolyte fuel cell depends on the partial pressure of the reaction gas, if the reaction gas is consumed for power generation in the upstream region of the gas flow paths 4 and 5, in the downstream region The reaction gas partial pressure decreases and the power generation amount decreases. Therefore, if current is extracted from the divided current extraction plates 8a and 9a located in the downstream area of the gas flow paths 4 and 5, a large current generated in the upstream area passes through the planes of the separators 6 and 7, and A lot of heat energy can be generated. In addition, since a gas containing a large amount of water vapor flows into the downstream area in the upstream area of the gas flow paths 4 and 5, it is difficult to remove moisture in the downstream area, and the moisture is often excessive. Therefore, by extracting current from the divided current extraction plates 8a and 9a located in the downstream area of the gas flow paths 4 and 5, the current generated in the entire power generation effective surface is concentrated in the separators 6 and 7 in the downstream area. It will flow in and the temperature in the downstream area will rise. An increase in temperature leads to an increase in saturated water vapor pressure, resulting in more water removal.

  FIG. 4 is a diagram showing a main configuration of the fuel cell system according to the present embodiment. In the fuel cell system of this embodiment, current extraction plates 8 and 9 are disposed at both ends of a solid polymer electrolyte fuel cell 11, and a load 12 is connected thereto. As described above, the current extraction plates 8 and 9 are each composed of the divided current extraction plates 8a and 9a located in the downstream area of the gas flow path and the divided current extraction plates 8b and 9b having a large area. Has a circuit configuration connected to the load 12 in parallel.

  Here, the cut-off switches 13 and 14 are provided on the wirings for taking out current from the divided current take-out plates 8b and 9b having a large area, respectively. The state of current extraction from the fuel cell 11 by the plates 8 and 9 can be switched. Specifically, when the cutoff switches 13 and 14 are turned on (connected state), the current is taken out from both the divided current take-out plates 8a and 9a and the divided current take-out plates 8b and 9b, and the current is taken out in a large area. It becomes. On the other hand, when the cut-off switches 13 and 14 are OFF (cut-off state), the current is taken out only from the divided current take-out plates 8a and 9a, and the current is taken out in a limited area in the downstream area of the gas flow path.

  Further, in the fuel cell system of the present embodiment, a control unit 15 that controls operation of the entire system is provided, and this control unit 15 functions as current extraction control means. That is, the current extraction state from the fuel cell 11 by the current extraction plates 8 and 9 is switched by turning on and off the cutoff switches 13 and 14 based on an instruction from the control unit 15. The fuel cell 11 is connected to a temperature sensor 16 for detecting the temperature of the fuel cell 11, specifically, for example, the temperature in the vicinity of the end of the fuel cell 11 having a stack structure. The detected value is input to the control unit 15. The control unit 15 determines the system activation status based on the detected value of the temperature sensor 16, that is, the temperature near the end of the fuel cell 11, and instructs the on / off of the shut-off switches 13 and 14 to extract the current. The state of current extraction from the fuel cell 11 by the plates 8 and 9 is switched.

  FIG. 5 is a flowchart showing an example of a startup process executed by the control unit 15 when the system is started in the fuel cell system of the present embodiment. Hereinafter, with reference to FIG. 5, the flow of processing when the fuel cell system of this embodiment is started will be described.

  At the initial start of the fuel cell system, the temperature of the fuel cell 11 is lower than the temperature suitable for system operation. Therefore, in order to suppress the heat radiation from the vicinity of the end of the fuel cell 11 and promote the temperature rise, the control unit 15 Turns off the cut-off switches 13 and 14, and connects only the small area divided current extraction plates 8a and 9a located in the downstream area of the gas flow path to the load 12 (step S1). In this state, power generation of the fuel cell 11 is started (step S2). As a result, in the vicinity of the end of the fuel cell 11, a current component flowing in the in-plane direction of the separators 6 and 7 is generated, and heat is generated. Here, the power generation efficiency is lower in the downstream area of the gas flow path than in the upstream area, and most of the current is concentrated in the upstream area, but this large current flows in the plane of the separators 6 and 7 toward the downstream area. It is possible to obtain a large calorific value.

  After the start of power generation of the fuel cell 11, the temperature of the fuel cell 11 gradually increases with the passage of time due to the above-described self-heating of the fuel cell 11 and the heat when an external heater or the like is provided. Therefore, the control unit 15 reads the detection value of the temperature sensor 16 connected to the fuel cell 11 (step S3), and compares the detection value of the temperature sensor 16 with a predetermined value, so that the system activation status is It is determined whether or not it has reached a stage where it can shift to normal operation, that is, whether or not the fuel cell 11 has reached a temperature suitable for operation by the system activation process (step S4). When it is determined as a result of the determination in step S4 that the fuel cell 11 has reached a temperature suitable for operation (when the detection value of the temperature sensor 16 exceeds a predetermined value), the control unit 15 The switches 13 and 14 are switched on to connect the divided current extraction plates 8b and 9b having a larger area to the load (step S5). In this state, the operation shifts to the normal operation. Thereafter, the fuel cell 11 performs normal power generation while improving the system efficiency by avoiding the energy loss due to the current flowing in the planes of the separators 6 and 7. (Step S6).

  As described above, in the fuel cell system according to the present embodiment, the current extraction plates 8 and 9 for extracting current from the fuel cell 11 are divided or insulated in the in-plane direction, and depending on the startup status of the system. Thus, the current extraction area from the fuel cell 11 by the current extraction plates 8, 9, that is, the divided current extraction plates 8 a, 8 b, 9 a, 9 b connected to the load 12 of the current extraction plates 8, 9 are changed. Therefore, in the stage before the temperature of the fuel cell 11 reaches a temperature suitable for operation, the temperature increase can be promoted by reducing the current extraction area from the fuel cell 11 by the current extraction plates 8 and 9. Moreover, during normal operation, power loss can be suppressed as much as possible by increasing the current extraction area from the fuel cell 11 by the current extraction plates 8 and 9. Kill.

  That is, since the temperature of the fuel cell 11 is low at the time of starting the system and it is desired to quickly raise the temperature of the fuel cell 11 in order to quickly shift to normal operation, Only a part of the take-out plates 8 and 9 is used to generate more in-plane current of the separators 6 and 7, and the heat generation amount is increased to positively raise the temperature of the fuel cell 11. On the other hand, after the system activation state reaches a certain stage, the heat generated in the separators 6 and 7 results in energy loss. Therefore, in the fuel cell system of the present embodiment, the larger area of the current extraction plates 8 and 9, Alternatively, by connecting all the divided current extraction plates 8 and 9 to the load 12, heat generation in the separators 6 and 7 is suppressed, and energy loss is minimized.

  Further, in the fuel cell system of the present embodiment, as information for determining the switching timing of the current extraction plates 8 and 9, the detected value detected by the temperature sensor 16 when the system is started, that is, the end of the fuel cell 11 is determined. The temperature information in the vicinity of the part is used. Thereby, when the temperature of the fuel cell 11 is low at the time of starting the system, the temperature rise rate of the fuel cell 11 is increased using the heat generated in the separators 6 and 7, and after the temperature has sufficiently increased, the heat generated in the separators 6 and 7 is generated. It is possible to appropriately perform switching that suppresses power loss and suppresses power loss, and it is possible to appropriately improve the efficiency of the entire system. When information on the temperature of the fuel cell 11 is used as information for determining the switching timing of the current extraction plates 8 and 9 as described above, not only the temperature of the fuel cell 11 directly detected by the temperature sensor 16 but also the outside air temperature. It is also possible to estimate the temperature of the fuel cell 11 and use the information.

  In the present embodiment, the current extraction plates 8 and 9 of each pole are each composed of two divided current extraction plates 8a, 8b, 9a and 9b, and the current extraction plates connected to the load 12 are divided into these. Although an example is shown in which the current extraction plates 8a, 8b, 9a, and 9b are selectively switched, the current extraction plates 8 and 9 of each pole are configured by three or more divided current extraction plates, respectively. The same effect can be obtained even when the current extraction plate connected to the load 12 is selectively switched from among three or more divided current extraction plates. In addition, the current extraction plates 8 and 9 of each pole are divided here, but even when only one of the electrode extraction plates is divided and the connection is switched, the same is true for that pole. An effect can be obtained.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The fuel cell system of the present embodiment has the same basic system configuration as that of the first embodiment described above, but differs in the manner of dividing the current extraction plates 8 and 9 from the first embodiment described above. . Hereinafter, only the part relating to the division of the current extraction plates 8 and 9 characteristic of the present embodiment will be described with reference to FIG.

  FIG. 6 is a schematic view showing a divided state of the current extraction plates 8 and 9 in the fuel cell system of the present embodiment. In the present embodiment, the current extraction plates 8 and 9 are divided current extraction plates 8c and 9c located at the outer peripheral portion of the power generation effective surface in the fuel cell 11, and a divided current having a larger area located at the central portion of the power generation effective surface. It consists of take-out plates 8d and 9d. In FIG. 6, the divided current extraction plate 9 d is not shown because the division position of the current extraction plate 9 is hidden by the separator 7, but the current extraction plate 9 is also divided in the same shape as the current extraction plate 8. ing.

  In the fuel cell 11, not only the heat radiation from the end in the stacking direction but also the heat radiation from the outer peripheral portion occurs, so the temperature of the outer peripheral portion is often lower than that of the central portion. Therefore, in the fuel cell system of the present embodiment, only the divided current extraction plates 8c and 9c located on the outer peripheral portion of the power generation effective surface are used as the load 12 until the system activation state reaches a predetermined state at the time of system activation. Connecting. As a result, as indicated by an arrow C in FIG. 6, a current that flows from the inside to the outside of the separators 6 and 7 is generated, and a larger amount of heat is generated at the outer peripheral portion. It becomes possible to reduce the temperature gradient resulting from the heat dissipation from.

(Third embodiment)
Next, a third embodiment of the present invention will be described. The fuel cell system of the present embodiment has the same basic system configuration as that of the first embodiment described above, and the method for determining the system activation state is different from that of the first embodiment described above. That is, in the fuel cell system of the present embodiment, as shown in FIG. 7, instead of the temperature sensor 16 used in the first embodiment, the output of at least one unit cell located near the end of the fuel cell 1 is used. A voltmeter 17 for detecting voltage is installed. The control unit 15 reads the detection value of the voltmeter 17 when the system activation process is being performed, determines the activation state of the system, and controls the on / off operation of the cutoff switches 13 and 14 based on the read value. Thus, the current extraction state from the fuel cell 11 by the current extraction plates 8 and 9 is switched.

  Hereinafter, an example of a startup process executed by the control unit 15 characteristic of the present embodiment will be described with reference to the flowchart of FIG.

  In the initial startup of the fuel cell system, the temperature of the fuel cell 11 is lower than a temperature suitable for system operation, and the output voltage of the fuel cell 11 at this time is generally lower than the output voltage of rated condition operation. . At this time, in order to suppress heat dissipation from the vicinity of the end of the fuel cell 11 and promote a temperature rise, the control unit 15 turns off the shut-off switches 13 and 14 and has a small divided current located in the downstream area of the gas flow path. Only the take-out plates 8a and 9a are connected to the load 12 (step S11). In this state, power generation of the fuel cell 11 is started (step S12). As a result, in the vicinity of the end of the fuel cell 11, a current component flowing in the in-plane direction of the separators 6 and 7 is generated, and heat is generated. Here, in the downstream area of the gas flow path, the power generation efficiency is lower than in the upstream area, and most of the current is concentrated in the upstream area, but this large current flows in the separators 6 and 7 toward the downstream area. A calorific value can be obtained.

  After the start of power generation of the fuel cell 11, the temperature of the fuel cell 11 gradually increases with the passage of time due to the above-described self-heating of the fuel cell 11 and the heat generated when an external heater or the like is provided. Accordingly, the output voltage of the fuel cell 11 approaches the value at the rated condition. Therefore, the control unit 15 reads the detected value of the voltmeter 17 installed in the vicinity of the end of the fuel cell 11 (step S13), and compares the detected value of the voltmeter 17 with a predetermined value. It is determined whether or not the starting state of the fuel cell 11 has reached a stage where it can shift to normal operation, that is, whether or not the fuel cell 11 has reached a temperature suitable for operation by the system starting process (step S14). When it is determined as a result of the determination in step S14 that the fuel cell 11 has reached a temperature suitable for operation (when the detected value of the voltmeter 17 exceeds a predetermined value), the control unit 15 13 and 14 are switched on, and the divided current extraction plates 8b and 9b having a larger area are connected to the load (step S15). In this state, the operation shifts to the normal operation. Thereafter, the fuel cell 11 performs normal power generation while improving the system efficiency by avoiding the energy loss due to the current flowing in the planes of the separators 6 and 7. (Step S16).

  As described above, in the fuel cell system of the present embodiment, when the temperature of the fuel cell 11 is low at the time of starting the system and the heat generation at the end is desired, the output voltage of the fuel cell 11 is also lower than the rated value. The control unit 15 reads the detection value of the voltmeter 17 that detects the output voltage of at least one unit cell located in the vicinity of the end of the fuel cell 1 to determine the system activation status, and accordingly Since the divided current extraction plates 8a, 8b, 9a and 9b connected to the load 12 are changed, the temperature of the fuel cell 11 reaches a temperature suitable for operation as in the first embodiment described above. In the previous stage, the temperature increase can be promoted by reducing the current extraction area from the fuel cell 11 by the current extraction plates 8 and 9, and in the normal operation, Ri out plates 8 and 9 to increase the current extraction area of the fuel cell 11 by, it is possible to suppress the power loss as much as possible.

  In the present embodiment, the output voltage detected by the voltmeter 17 is the output voltage of one or several unit cells located near the end of the fuel cell 11. The temperature in the vicinity of the end of the fuel cell 11 is lower than that in the central portion, and the output voltage also decreases accordingly. Therefore, the output voltage of at least one unit cell located in the vicinity of the end is detected and based on the detected value. By determining whether the temperature of the fuel cell 11 has risen sufficiently and switching the temperature so as to suppress power loss after the temperature has risen sufficiently, it is possible to appropriately improve the efficiency of the entire system. it can.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. The fuel cell system of the present embodiment has the same basic system configuration as that of the first embodiment described above, and the method for determining the system activation state is different from that of the first embodiment described above. That is, in the fuel cell system of this embodiment, as shown in FIG. 9, instead of the temperature sensor 16 used in the first embodiment, a timer 18 that measures the elapsed time from the start of startup of the fuel cell system is provided. is set up. Then, the control unit 15 reads the measured value of the timer 18 to judge the system activation state when performing the system activation process, and controls the on / off operation of the cutoff switches 13 and 14 based on the read value. Thus, the current extraction state from the fuel cell 11 by the current extraction plates 8 and 9 is switched.

  Hereinafter, an example of the startup process executed by the control unit 15 characteristic of the present embodiment will be described with reference to the flowchart of FIG.

  At the initial stage of starting the fuel cell system, the temperature of the fuel cell 11 is lower than the temperature suitable for system operation. Therefore, in order to promote the temperature rise of the fuel cell 11, the control unit 15 turns off the shut-off switches 13 and 14. Only the small-area divided current extraction plates 8a and 9a located in the downstream area of the gas flow path are connected to the load 12 (step S21). In this state, power generation of the fuel cell 11 is started (step S22). As a result, in the vicinity of the end of the fuel cell 11, a current component flowing in the in-plane direction of the separators 6 and 7 is generated, and heat is generated. Here, in the downstream area of the gas flow path, the power generation efficiency is lower than in the upstream area, and most of the current is concentrated in the upstream area, but this large current flows in the separators 6 and 7 toward the downstream area. A calorific value can be obtained.

  Since the temperature of the fuel cell 11 gradually rises with time, the timer 18 measures the elapsed time from the start of the system. Then, the control unit 15 reads the measured value of the timer 18 (step S23), and compares the measured value of the timer 18 with a predetermined value, thereby reaching a stage where the system startup status can shift to normal operation. That is, it is determined whether or not the fuel cell 11 has reached a temperature suitable for operation by the system activation process (step S24). Then, when it is determined that the fuel cell 11 has reached a temperature suitable for operation as a result of the determination in step S24 (when the measured value of the timer 18 exceeds a predetermined value), the control unit 15 causes the cutoff switch 13 to , 14 are switched on, and the divided current extraction plates 8b, 9b having a larger area are connected to the load (step S15). In this state, the operation shifts to the normal operation. Thereafter, the fuel cell 11 performs normal power generation while improving the system efficiency by avoiding the energy loss due to the current flowing in the planes of the separators 6 and 7. (Step S26).

  As described above, in the fuel cell system of the present embodiment, the elapsed time since the system startup is measured by the timer 18, and the control unit 15 reads the measured value of the timer 18 to determine the system startup status, and accordingly Since the divided current extraction plates 8a, 8b, 9a, and 9b connected to the load 12 are changed, the temperature of the fuel cell 11 becomes a temperature suitable for operation as in the first embodiment described above. In the stage before reaching, the temperature rise can be promoted by reducing the current extraction area from the fuel cell 11 by the current extraction plates 8 and 9, and in the normal operation, the fuel cell by the current extraction plates 8 and 9 can be promoted. By increasing the current extraction area from 11, power loss can be suppressed as much as possible.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described. The fuel cell system of the present embodiment has the same basic system configuration as that of the first embodiment described above, and the configuration of the separator of the fuel cell 11 is different from that of the first embodiment described above. Hereinafter, only the part relating to the separator of the fuel cell 11 which is characteristic of the present embodiment will be described with reference to FIG.

  FIG. 11 is a schematic diagram showing the structure of the fuel cell 11 in the fuel cell system of the present embodiment. In the present embodiment, among the separators 21 arranged in the stacking direction of a large number of unit cells constituting the fuel cell 11, the separators 21a and 21c positioned near the end in the stacking direction have a higher electrical conductivity than the other separators 21b. It is formed using a low material and has a high electric resistance.

  The amount of heat generated in the separator 21 of the fuel cell 11 is proportional to the electrical resistance when the current flowing in the surface of the separator 21 is equal, and the amount of heat generated increases as the electrical resistance increases. Therefore, in the fuel cell system according to the present embodiment, among the separators 21 arranged in the stacking direction of a large number of unit cells constituting the fuel cell 11, the separators 21a and 21c located near the end in the stacking direction have high electrical resistance. By adopting the configuration, the amount of heat generated in the vicinity of the end of the fuel cell 11 where the temperature is likely to decrease due to heat dissipation is increased. As a result, the temperature of the fuel cell 11 can be increased more rapidly when the system is started.

(Sixth embodiment)
Next, a sixth embodiment of the present invention will be described. The fuel cell system according to the present embodiment corresponds to a modification of the fifth embodiment described above, and has a feature in the configuration of the separator of the fuel cell 11. Hereinafter, only the part relating to the separator of the fuel cell 11 which is characteristic of the present embodiment will be described with reference to FIG.

  FIG. 12 is a schematic view showing the structure of the fuel cell 11 in the fuel cell system of the present embodiment. In the present embodiment, among the separators 31 arranged in the stacking direction of a large number of unit cells constituting the fuel cell 11, the thickness of the separators 31a and 31c located near the end in the stacking direction is the thickness of the other separator 31b. Compared to the above, it is formed thinner and has a high electric resistance. As described above, in the fuel cell system according to the present embodiment, among the separators 31 arranged in the stacking direction of a large number of unit cells constituting the fuel cell 11, the thicknesses of the separators 31a and 31c located near the end in the stacking direction are set. By making it thin and having a high electrical resistance, the amount of heat generated in the vicinity of the end of the fuel cell 11 where a temperature drop is likely to occur due to heat dissipation is increased. As a result, similar to the fifth embodiment described above, the temperature of the fuel cell 11 can be increased more rapidly when the system is started.

(Seventh embodiment)
Next, a seventh embodiment of the present invention will be described. The fuel cell system of the present embodiment has the same basic system configuration as that of the first embodiment described above, but differs in the manner of dividing the current extraction plates 8 and 9 from the first embodiment described above. . Hereinafter, only the part relating to the division of the current extraction plates 8 and 9 characteristic of the present embodiment will be described with reference to FIG.

  FIG. 13 is a schematic view showing a divided state of the current extraction plates 8 and 9 in the fuel cell system of the present embodiment. In the present embodiment, the current extraction plates 8 and 9 of both poles are composed of divided current extraction plates 8e to 8j and 9e to 9j that are divided into six parts. When the system is started, the control unit 15 sequentially switches the divided current extraction plates connected to the load 12 to disperse the heat generated in the planes of the separators 6 and 7 and prevent the temperature gradient from occurring. ing.

  That is, since the current flowing through each region in the plane of the separators 6 and 7 gradually increases along the streamline of the in-plane current, a large current is generated in the vicinity of the divided current extraction plate connected to the load 12. Although it flows and generates a lot of heat, the current value decreases and the amount of heat generation decreases as the distance from the divided current extraction plate connected to the load 12 increases. Therefore, if the state where only one divided current extraction plate is connected to the load 12 is continued, only the peripheral portion of the divided current extraction plate is heated, resulting in a temperature gradient in the plane of the separators 6 and 7. .

  In order to avoid this, in the present embodiment, the current extraction plates 8 and 9 are each divided into six divided current extraction plates 8e to 8j and 9e to 9j, and these divided current extraction plates 8e to 8j and 9e to 9j are sequentially arranged. By connecting to the load 12 and sequentially changing the current extraction position, the heat generation in the surfaces of the separators 6 and 7 is dispersed to prevent the temperature gradient in the surfaces of the separators 6 and 7 from being generated. .

  The switching judgment of the divided current extraction plate connected to the load 12 may be changed every predetermined time, or the temperature of the area can be detected for each area and connected to the load 12. The connection may be changed to another divided current extraction plate when the temperature in the vicinity of the divided current extraction plate reaches a predetermined value. It is also possible to calculate the temperature difference from the temperature information of each region and change the connection when the predetermined temperature difference is reached.

  Further, as the order of the divided current extraction plates connected to the load 12, the connection may be switched in accordance with a predetermined order, or the division to be connected next from the obtained temperature information of each region. The current extraction plate may be determined.

  In the present embodiment as well, after the temperature of the fuel cell 11 has been raised to a temperature that satisfies a predetermined operating condition, all of the divided current extraction plates 8e to 8j and 9e to 9j are connected to the load 12. Thus, it is possible to suppress power loss due to heat generation as much as possible, as in the case of other embodiments.

It is sectional drawing which shows the structure of the unit cell of the polymer electrolyte fuel cell with which the fuel cell system to which this invention is applied is provided. It is a perspective view which shows an example of the divided | segmented current extraction board. It is a perspective view which shows typically the mode of the electric current which flows through a separator surface, when a part of division | segmentation electric current extraction board is connected to load. It is the schematic which shows the principal part structure of the fuel cell system of 1st Embodiment. 4 is a flowchart illustrating an example of a startup process executed by a control unit at the time of system startup in the fuel cell system according to the first embodiment. It is a figure explaining the fuel cell system of 2nd Embodiment, and is a perspective view which shows the other example of the division | segmentation state of an electric current extraction board. It is the schematic which shows the principal part structure of the fuel cell system of 3rd Embodiment. In the fuel cell system of 3rd Embodiment, it is a flowchart which shows an example of the starting process performed by the control unit at the time of system starting. It is the schematic which shows the principal part structure of the fuel cell system of 4th Embodiment. In the fuel cell system of 4th Embodiment, it is a flowchart which shows an example of the starting process performed by the control unit at the time of system starting. It is a figure explaining the fuel cell system of 5th Embodiment, and is the schematic which shows the other example of the structure of a fuel cell. It is a figure explaining the fuel cell system of 6th Embodiment, and is the schematic which shows the further another example of the structure of a fuel cell. It is a figure explaining the fuel cell system of 7th Embodiment, and is a perspective view which shows the further another example of the division | segmentation state of an electric current extraction board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2 Fuel electrode 3 Oxidant electrode 4,5 Gas flow path 6,7 Separator 8,9 Current extraction plate 8a-8j, 9a-9j Divided current extraction plate 11 Fuel cell 12 Load 13, 14 Shut-off switch 15 Control unit 16 Temperature Sensor 17 Voltmeter 18 Timer 21a-21c Separator 31a-31c Separator

Claims (17)

A plurality of unit cells in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an oxidant electrode are stacked via a separator in which a reaction gas channel for supplying a reaction gas to the unit cell is formed. In a fuel cell system having a solid polymer electrolyte type fuel cell and a current extraction plate disposed adjacent to the fuel cell, and supplying a current extracted from the fuel cell via the current extraction plate to a load,
The fuel cell system is characterized in that a current extraction area from the fuel cell by the current extraction plate is variable. A plurality of unit cells in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an oxidant electrode are stacked via a separator in which a reaction gas channel for supplying a reaction gas to the unit cell is formed. In a fuel cell system having a solid polymer electrolyte type fuel cell and supplying a current taken from the fuel cell to a load,
A current extraction plate disposed adjacent to the fuel cell as a medium for extracting current from the fuel cell and divided or insulated in at least two planes;
A fuel cell system comprising: current extraction control means for selecting a current extraction plate connected to a load from a part or all of the divided or insulated extraction plates.   3. The fuel cell system according to claim 2, wherein at least one of the divided or insulated current extraction plates is arranged to be located downstream of a reaction gas flow path in the fuel cell.   3. The fuel cell system according to claim 2, wherein at least one of the divided or insulated current extraction plates is disposed so as to be positioned on an outer peripheral portion of a power generation effective surface of the fuel cell.   The fuel cell system according to any one of claims 2 to 4, wherein the current extraction control means changes a current extraction plate connected to a load in accordance with a startup state of the system. Temperature detecting means for detecting the temperature of the fuel cell or the ambient environment temperature,
6. The fuel cell system according to claim 5, wherein the current extraction control unit changes a current extraction plate connected to a load based on a detection value of the temperature detection unit.   The fuel cell system according to claim 6, wherein the temperature detection unit detects a temperature in the vicinity of an end of the fuel cell.   The current extraction control unit performs current extraction from the fuel cell by connecting only a part of the current extraction plate to a load until the detection value of the temperature detection unit reaches a predetermined value. The fuel cell system according to claim 6 or 7, characterized in that An output voltage detecting means for detecting the output voltage of the fuel cell;
6. The fuel cell system according to claim 5, wherein the current extraction control unit changes a current extraction plate connected to a load based on a detection value of the output voltage detection unit.   The fuel cell system according to claim 9, wherein the output voltage detection means detects an output voltage of at least one unit cell located in the vicinity of an end of the fuel cell.   The current extraction control unit performs current extraction from the fuel cell by connecting only a part of the current extraction plate to a load until the detection value of the output voltage detection unit reaches a predetermined value. The fuel cell system according to claim 9 or 10, wherein: With a timer that measures the elapsed time from the start of system startup,
6. The fuel cell system according to claim 5, wherein the current extraction control unit changes a current extraction plate connected to a load based on a measurement value of the timer.   The current extraction control unit is configured to extract current from the fuel cell by connecting only a part of the current extraction plate to a load until the measured value of the timer reaches a predetermined value. The fuel cell system according to claim 12.   The current extraction control means, when only a part of the current extraction plate is connected to a load, connects the current extraction plate located on the downstream side of the reaction gas flow path to the load. The fuel cell system according to any one of 11 and 13.   The fuel cell system according to any one of claims 2 to 14, wherein a separator located in the vicinity of an end of the fuel cell has a higher electric resistance than a separator located in another portion.   16. The fuel cell system according to claim 15, wherein the separator located in the vicinity of the end of the fuel cell is made of a material having lower electrical conductivity than the separator located in the other part.   The fuel cell system according to claim 15, wherein the thickness of the separator located in the vicinity of the end of the fuel cell is made thinner than the thickness of the separator located in the other portion.

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