JP2007026678A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a low-temperature starting property of a fuel cell system having a fuel cell stack. <P>SOLUTION: This fuel cell system 100 is provided with selector switches 20 and 22 for switching a current take-out part in the fuel cell stack 10. In low-temperature starting, taking-out of current from a single cell 12 reducing power generation performance due to freezing is stopped, and current is taken out of a single cell 12 not reducing the power generation performance. The single cell 12 reducing the power generation performance due to freezing is heated by heat from the cell 12 not reduced in the power generation performance. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

  Conventionally, a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen has attracted attention as an energy source. This fuel cell includes a fuel cell stack in which a plurality of single cells each having an anode (hydrogen electrode) and a cathode (oxygen electrode) are stacked on both surfaces of an electrolyte membrane having proton conductivity. And in the cathode of a single cell, water (product water) is produced | generated by a cathode reaction.

  When a fuel cell system including such a fuel cell stack is started at a low temperature below freezing point, in some single cells in the fuel cell stack, the generated water is frozen to prevent oxygen diffusion or Since it does not react, the power generation performance may be reduced. Then, when power generation is continued to output the required power in a state where a single cell whose power generation performance has been reduced and a single cell whose power generation performance has not been reduced, a negative voltage is applied to the single cell whose power generation performance has been reduced. This may cause deterioration of the electrolyte membrane of the single cell.

  In view of this, various techniques have been proposed in order to solve the above problems at the time of starting the fuel cell system at a low temperature. For example, Patent Document 1 described below describes a technique for setting the extraction current to the maximum in a range where the voltage of a single cell does not fall below a predetermined voltage when the fuel cell system is started at a low temperature from below the freezing point. Accordingly, the power generation reaction is promoted regardless of the required power, the self-heating of the fuel cell can be promoted, and the warm-up time can be shortened, so that the generated water at the start-up can be suppressed from freezing.

Japanese Patent Laying-Open No. 2005-71626

  However, in the technique described in Patent Document 1, the current taken out from the entire fuel cell stack is lowered in accordance with the single cell having the lowest power generation performance among the plurality of single cells. In some cases, the amount of heat generated in the fuel cell stack also decreases, and the time required for the entire fuel cell stack to rise in temperature cannot be shortened sufficiently.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve low-temperature startability of a fuel cell system including a fuel cell stack.

In order to solve at least a part of the above-described problems, the present invention employs the following configuration.
The fuel cell system of the present invention comprises:
A fuel cell stack in which a plurality of single cells that generate electricity by an electrochemical reaction between hydrogen and oxygen are stacked;
A voltage detector for detecting a voltage of each part of the fuel cell stack divided into a plurality of parts along the stacking direction of the single cells;
A current control unit for controlling a current flowing through each of the parts;
When the voltage detection unit detects that the voltage of any of the plurality of parts has become less than a predetermined value at a low temperature start under freezing point of the fuel cell system, the detected voltage is A low temperature start control unit that controls the current control unit so that a current flowing in the portion that is less than the predetermined value is lower than a current flowing in the other portion;
It is a summary to provide.

  In the present invention, when the fuel cell system is started at a low temperature, the fuel cell stack monitors the voltage of each part divided into a plurality of parts along the stacking direction of the single cells, thereby generating single cells included in the parts. Detects a decrease in power generation performance due to water freezing. And, from the single cell of the part where the power generation performance is not lowered, the almost required current is taken out, and the single cell of the part where the power generation performance is lowered is replaced with the single cell of the other part where the power generation performance is not lowered. Less current than that. In addition, flowing a low value current includes setting the current value to 0, that is, not flowing a current.

  By doing this, at the time of low temperature start, the single cell whose power generation performance has not deteriorated is made to generate power almost as required, and the entire fuel cell stack is quickly heated by its heat generation and heat conduction. Can do. In addition, since the current flowing to the single cell whose power generation performance is reduced due to the freezing of the generated water is limited, it is possible to suppress the negative voltage from being applied to the single cell whose power generation performance has been reduced, and to prevent deterioration of the electrolyte membrane provided in the single cell. Can be suppressed. As a result, the low temperature startability of the fuel cell system can be improved.

In the fuel cell system,
In the control of the current control unit at the time of the low temperature start, the low temperature start control unit is detected by the voltage detection unit that any one of the plurality of portions has become less than a predetermined value. Further, the current flowing through the portion where the detected voltage is less than the predetermined value may be set to zero.

  In the present invention, the current is taken out only from the single cell where the power generation performance is not deteriorated, and no current is passed through the single cell where the power generation performance is deteriorated. By carrying out like this, it can avoid that a negative voltage is applied to the single cell in which the single cell power generation performance in which the power generation performance has not decreased is reduced, and the deterioration of the electrolyte membrane can be suppressed.

In the fuel cell system of the present invention,
In the control of the current control unit at the time of the low temperature start, the low temperature start control unit is detected by the voltage detection unit that any one of the plurality of portions has become less than a predetermined value. Further, for the portion where the detected voltage is less than the predetermined value, the value of the current flowing through the portion is set based on the detected voltage value so that a negative voltage is not applied to the single cell. It may be changed.

  By doing this, while avoiding a negative voltage being applied to the single cell with reduced power generation performance, the single cell with reduced power generation performance also self-heats due to power generation, so the fuel cell while suppressing deterioration of the electrolyte membrane The stack heating time can be shortened.

In any of the above fuel cell systems,
The current control unit may be configured to control only the portion arranged at the end of the fuel cell stack in the stacking direction to reduce the flowing current value.

  In general, since an end plate or the like is disposed at the end in the stacking direction of the fuel cell stack, the single cell disposed at the end is more than the single cell disposed at the center due to heat radiation to the outside. However, it is difficult to raise the temperature, and the power generation performance tends to be reduced due to freezing of the generated water. On the other hand, the single cell arranged in the center part is easily heated because the single cells that generate heat by power generation are in contact with each other, and the generated water is not easily frozen.

  In the present invention, only the single cell, which is disposed at the end of the fuel cell stack and whose power generation performance is likely to deteriorate due to freezing of the generated water, is the target of control for limiting the flowing current. Control at start-up can be simplified.

In any one of the above fuel cell systems,
A temperature detection unit for detecting the temperature of each part;
The low temperature start control unit performs the control of the current control unit at the time of the low temperature start, the temperature detection unit for the portion where the voltage detected by the voltage detection unit is less than the predetermined value When the temperature detected by the above becomes equal to or higher than a predetermined temperature, the control of the current control unit at the low temperature start may be stopped.

  The predetermined temperature can be arbitrarily set within a range where the generated water does not freeze. According to the present invention, the control at the low temperature start described above can be switched to the control at the normal temperature based on the temperature of each part.

  Instead of the temperature detector, a timer for measuring the duration of the control at the low temperature start is provided, and the switching is based on whether the duration of the control at the low temperature start has reached a predetermined time or more. And may be performed. In this case, the predetermined time may be set so that the temperature of all the single cells of the fuel cell stack is sufficiently raised so that the generated water does not freeze.

In the fuel cell system of the present invention,
A part of each of the parts of the fuel cell stack is constituted by a cold start cell for use only during the cold start as the single cell,
The fuel cell system further includes:
A temperature detector for detecting the temperature of the cold start cell;
The current control unit is configured to stop power generation by the cold start cell when the temperature detection unit detects that the temperature of the cold start cell is equal to or higher than a predetermined temperature during the cold start. A power generation control unit for controlling
You may make it provide.

  Here, the cold start cell is a single cell which is suitable for power generation at a low temperature start because the generated water is hard to freeze, but is not suitable for power generation at a normal temperature. Examples of such a cold start cell include those shown below.

In the fuel cell system,
The single cell includes an anode and a cathode on both sides of a predetermined electrolyte membrane,
The cold start cell has high permeability to the anode and at least the cathode among the cathodes, the generated water generated by the power generation is higher than the single cells other than the cold start cell. A layer may be provided.

  Since water generated by power generation is generated by a cathode reaction, freezing of the generated water is more likely to occur at the cathode than at the anode. In the present invention, since at least the cathode of the cold start cell is provided with the high permeability layer having a relatively high permeability of the produced water, the produced water can be discharged relatively quickly. Therefore, in the cold start cell, it is possible to extend the time until the produced water freezes and complete the temperature increase of the entire fuel cell stack before the produced water freezes.

In the fuel cell system,
The single cell is supplied on both surfaces of the electrolyte membrane with a catalyst layer for causing the electrochemical reaction, a water repellent layer for repelling the generated water, and a reaction gas diffused in the catalyst layer. And in this order, a diffusion layer for
The low temperature start cell includes the water repellent layer having a thickness smaller than the water repellent layer of the single cell other than the low temperature start cell, and the single unit other than the low temperature start cell as the high transmission layer. You may make it provide at least one of the said diffusion layers whose thickness is thinner than the said diffusion layer of a cell.

  The generated water generated in the catalyst layer at the time of low temperature starting is supercooled water when discharged out of the catalyst layer. This supercooled water can be easily transmitted by making the water repellent layer thin. In addition, the supercooled water can be easily transmitted by making the diffusion layer thin. Therefore, according to the present invention, the generated water can be quickly discharged.

  In addition, it is preferable to omit a water repellent layer in a highly permeable layer from the viewpoint of the permeability of supercooled water. By carrying out like this, the permeability of supercooling water can be made higher.

In any fuel cell system comprising the cold start cell,
The cold start cell may be provided only in the portion arranged at the end of the fuel cell stack in the stacking direction.

  As described above, the single cell arranged at the end of the fuel cell stack in the stacking direction is less likely to raise the temperature than the single cell arranged in the center, and the power generation performance is likely to deteriorate due to freezing of the produced water. . On the other hand, the single cell arranged in the center part is easy to raise the temperature and the generated water is not easily frozen.

  In the present invention, since the cold start cell is disposed only at the end of the fuel cell stack, the configuration of the fuel cell system and the control during the cold start can be simplified.

The fuel cell system of the present invention is
A fuel cell stack in which a plurality of single cells that generate electricity by an electrochemical reaction between hydrogen and oxygen, and a plurality of low-temperature start cells that are the single cells for use only during low-temperature start under the freezing point of the fuel cell system; ,
A current control unit for controlling a current flowing through each of the parts;
A temperature detector for detecting the temperature of the cold start cell;
The current control unit is configured to stop power generation by the cold start cell when the temperature detection unit detects that the temperature of the cold start cell is equal to or higher than a predetermined temperature during the cold start. A power generation control unit for controlling
You may make it provide.

  By doing this as well, the low temperature startability of the fuel cell system can be improved in the same manner as the fuel cell system described above.

  The present invention does not necessarily have all the various features described above, and may be configured by omitting some of them or combining them appropriately. The present invention can be configured as an invention of a control method of a fuel cell system in addition to the above-described configuration as a fuel cell system. Further, the present invention can be realized in various modes such as a computer program that realizes these, a recording medium that records the program, and a data signal that includes the program and is embodied in a carrier wave. In addition, in each aspect, it is possible to apply the various additional elements shown above.

  When the present invention is configured as a computer program or a recording medium storing the program, the entire program for controlling the operation of the fuel cell system may be configured, or only the portion that performs the function of the present invention is configured. It is good also as what to do. The recording medium includes a flexible disk, a CD-ROM, a DVD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punch card, a printed matter on which a code such as a barcode is printed, a computer internal storage device (RAM or Various types of computer-readable media such as a memory such as a ROM and an external storage device can be used.

Hereinafter, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
A1. System configuration:
A2. Cold start control:
B. Second embodiment:
B1. System configuration:
B2. Cold start control:
C. Third embodiment:
C1. System configuration:
C2. Cold start control:
D. Variation:

A. First embodiment:
A1. System configuration:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system 100 as a first embodiment of the present invention. As illustrated, the fuel cell system 100 includes a fuel cell stack 10, changeover switches 20 and 22, a voltage sensor 30, a temperature sensor 40, a load 50, and a control unit 60.

  The fuel cell stack 10 is a stacked body in which a predetermined number of single cells 12 that generate power by an electrochemical reaction between hydrogen and oxygen are stacked. The single cell 12 is formed by forming an anode (hydrogen electrode) and a cathode (oxygen electrode) on both surfaces of an electrolyte membrane having proton conductivity. The number of stacked single cells 12 can be arbitrarily set according to the required output. In this embodiment, the fuel cell stack 10 is a solid polymer fuel cell using a solid polymer membrane as an electrolyte membrane. Other fuel cells may be used.

  At one end of the fuel cell stack 10 in the stacking direction of the single cells 12, single cells 12a, 12b, and 12c are arranged in this order from the outside. In addition, unit cells 12d, 12e, and 12f are arranged in this order from the outside at the other end in the stacking direction of the unit cells 12 of the fuel cell stack 10. Each of the single cells 12a to 12f is provided with a terminal for taking out a current during power generation.

  The fuel cell stack 10 is connected to a load 50 via a changeover switch 20 and a changeover switch 22. The changeover switch 20 is provided with three terminals a, b, and c. The changeover switch 22 is provided with three terminals d, e, and f. The terminals a, b, and c of the changeover switch 20 are connected to the single cells 12a, 12b, and 12c, respectively. The terminals d, e, and f of the changeover switch 22 are connected to the single cells 12d, 12e, and 12f, respectively. By switching the connection state of the changeover switch 20 and the changeover switch 22, it is possible to switch the portion from which current is extracted during power generation. In the present embodiment, each of the changeover switch 20 and the changeover switch 22 is provided with three terminals and is connected to the three single cells 12, but the present invention is not limited to this. Many terminals may be provided.

  The voltage sensor 30 is provided for each single cell 12 and detects the voltage (hereinafter referred to as cell voltage) Vc of each single cell 12. The temperature sensor 40 is also provided for each single cell 12 and detects the temperature Tc of each single cell 12. By monitoring the cell voltage Vc of each single cell 12 and the temperature Tc, an abnormality of each single cell 12 can be detected.

  The operation of the fuel cell system 100 is controlled by the control unit 60. The control unit 60 is configured as a microcomputer including a CPU, RAM, ROM, and the like inside, and controls the operation of the system according to a program stored in the ROM.

  In the present embodiment, the control unit 60 performs low-temperature start control described later when the fuel cell system 100 is started at a low temperature below the freezing point. At the time of cold start, the generated water generated by the cathode reaction may freeze in the single cell 12 to prevent the reaction gas from being supplied, and the power generation performance of the single cell 12 may be reduced. In the present embodiment, even when the power generation performance of the single cell 12 is reduced due to the freezing of the generated water during the low temperature start-up control, the fuel cell stack 10 is quickly heated to recover the power generation performance. In this low temperature start control, the changeover switch 20 and the changeover switch 22 are controlled based on the outputs of the voltage sensor 30 and the temperature sensor 40 as described below. The control unit 60 corresponds to a low temperature start control unit in the present invention. The changeover switches 20 and 22 correspond to a current control unit in the present invention.

A2. Cold start control:
FIG. 2 is a flowchart showing a flow of low temperature start control in the first embodiment. This process is a process executed by the CPU of the control unit 60 when the fuel cell system 100 is started at a low temperature below the freezing point. In this embodiment, when the fuel cell system 100 is started, this control is executed when the output of any temperature sensor 40 is below freezing point.

  In the initial state at the start of the cold start control, the changeover switch 20 and the changeover switch 22 are connected to the terminals a and d, respectively, and from the single cell 12a and the single cell 12d, that is, from the entire fuel cell stack 10. The requested current is taken out (see FIG. 1).

  After that, the CPU measures the cell voltage Vc of the single cell 12 that is most likely to deteriorate the power generation performance disposed at the end of the fuel cell stack 10 by the voltage sensor 30 (step S100). Immediately after the cold start control, the cell voltages Vc of the single cells 12a and 12d arranged at both ends of the fuel cell stack 10 are measured. As will be described later, when power is not generated by the single cells 12a and 12d, the cell voltage Vc of the single cells 12b and 12e disposed on the outermost side of the single cells 12 that are generating power is measured. .

  Then, the CPU determines whether or not the cell voltage Vc is less than the predetermined voltage Vth (step S110). When the power generation performance of the single cell 12 decreases and the cell voltage Vc becomes less than the predetermined voltage Vth (step S110: YES), the changeover switches 20 and 22 are switched (step S100), and the process returns to step S100. For example, when the cell voltage Vc of the single cells 12a and 12d at both ends where the power generation performance is most likely to deteriorate in the fuel cell stack 10 becomes less than a predetermined voltage Vth, the changeover switch 20 and the changeover switch 22 are respectively connected to the terminals. Switching to b and terminal e, the requested current is taken out from the single cell 12b and the single cell 12e. At this time, no power is generated in the single cells 12a and 12d, and no current flows through the single cells 12a and 12d. When power generation is continued in this state, and then the power generation performance of the single cells 12b and 12e is reduced and the cell voltage Vc becomes less than the predetermined voltage Vth, the connection of the changeover switch 20 and the changeover switch 22 is performed. Are switched to the terminal c and the terminal f, respectively, and the requested current is taken out from the single cell 12c and the single cell 12f. At this time, further, no power is generated in the single cells 12b and 12e, and no current flows through the single cells 12a and 12d.

  In step S110, when the cell voltage Vc is equal to or higher than the predetermined voltage Vth (step S110: NO), the CPU determines that the single cell 12 that is not generating power depends on the connection state of the changeover switch 20 and the changeover switch 22. It is determined whether or not there is (step S130). When the changeover switch 20 and the changeover switch 22 are connected to the terminals a and d, respectively, and there is no single cell 12 that is not generating power (step S130: NO), the CPU 40, the temperature Tc of the outermost unit cell 12 among the unit cells 12 generating power is measured (step S180), and it is determined whether or not the temperature Tc of the unit cell 12 is equal to or higher than the predetermined temperature Tth. (Step S190). As the predetermined temperature Tth, a temperature at which the generated water does not freeze is set. When the temperature Tc of the single cell 12 is equal to or higher than the predetermined temperature Tth (step S190: YES), the low temperature start control is terminated. On the other hand, when the temperature Tc of the single cell 12 is lower than the predetermined temperature Tth (step S190: NO), the process returns to step S100.

  In step S130, when the changeover switch 20 and the changeover switch 22 are connected to terminals other than the terminal a and the terminal d, respectively, and there is a single cell 12 that is not generating power (step S130: YES) The CPU measures the temperature Tc of the single cell 12 that is not generating power (step S140), and determines whether the temperature Tc of the single cell 12 is equal to or higher than the predetermined temperature Tth (step S150). When the temperature Tc of the single cell 12 is lower than the predetermined temperature Tth (step S150: NO), the process returns to step S100. On the other hand, when the temperature Tc of the single cell 12 is equal to or higher than the predetermined temperature Tth (step S150: YES), the changeover switches 20 and 22 are switched (step S160). For example, when the changeover switch 20 and the changeover switch 22 are connected to the terminal c and the terminal f, respectively, and the single cell 12b, (12a, 12d,) 12e is not generating power, the single cell If the temperature Tc of 12b, 12e is equal to or higher than the predetermined temperature Tth, even if power generation is performed using the single cells 12b, 12e, the generated water does not freeze, and no negative voltage is applied to the single cells 12b, 12e. The changeover switch 20 and the changeover switch 22 are changed over to the terminal b and the terminal e, respectively, and the power generation by the single cells 12b and 12e is resumed. When the changeover switch 20 and the changeover switch 22 are connected to the terminals b and e, respectively, and the power generation is not performed in the single cells 12a and 12d, the temperature Tc of the single cells 12a and 12d. Is equal to or higher than the predetermined temperature Tth, even if power generation is performed using the single cells 12a and 12d, the generated water is not frozen and no negative voltage is applied to the single cells 12a and 12d. The changeover switch 22 is switched to the terminals a and d, respectively, and the power generation by the single cells 12a and 12d is resumed.

  Next, the CPU again determines whether or not there is a single cell 12 that is not generating power according to the connection state of the changeover switch 20 and the changeover switch 22 (step S170). If the changeover switch 20 and the changeover switch 22 are connected to terminals other than the terminals a and d, respectively, and there is a single cell 12 that is not generating power (YES in step S170), the process proceeds to step S180. . On the other hand, when the selector switch 20 and the selector switch 22 are connected to the terminals a and d, respectively, and there is no single cell 12 that is not generating power (step S170: NO), that is, all the units When the temperature of the cell 12 becomes equal to or higher than the predetermined temperature Tth and power generation is resumed using all the single cells 12, the low temperature start control is terminated.

  After the cold start control is finished, control is performed to extract current from the entire fuel cell stack 10 at the normal temperature.

  According to the fuel cell system 100 of the first embodiment described above, in the single cell 12 in which the power generation performance is not deteriorated at the time of low temperature start, power generation is performed as requested, and by the heat generation and heat conduction, The temperature of the entire fuel cell stack 10 can be quickly raised. In addition, since no current flows through the single cell 12 whose power generation performance has been reduced due to freezing of the generated water, it is possible to suppress negative voltage from being applied to the single cell 12 whose power generation performance has been reduced, and to suppress deterioration of the electrolyte membrane. it can. As a result, the low temperature startability of the fuel cell system 100 can be improved.

B. Second embodiment:
B1. System configuration:
FIG. 3 is an explanatory diagram showing a schematic configuration of a fuel cell system 100A as a second embodiment of the present invention. As illustrated, the fuel cell system 100A includes a fuel cell stack 10, variable resistors 24a to 24f, a voltage sensor 30, a temperature sensor 40, a load 50, and a control unit 60A. The fuel cell system 100A according to the second embodiment is different from the changeover switches 20 and 22 in the fuel cell system 100 according to the first embodiment except that variable resistors 24a to 24f are provided. Is almost the same.

  The fuel cell stack 10 is connected to a load 50 through variable resistors 24a to 24f. As shown in the figure, the variable resistors 24a to 24f are connected to the single cells 12a to 12f, respectively. By changing each resistance value of the variable resistors 24a to 24f, the current flowing through each part of the fuel cell stack 10, that is, the current value taken out from each part can be changed. In this embodiment, six variable resistors 24a to 24f are used. However, the present invention is not limited to this, and more variable resistors may be provided.

  In the present embodiment, the control unit 60A executes low-temperature start control described later when the fuel cell system 100A is started at a low temperature below the freezing point. In this low temperature start control, the resistance values of the variable resistors 24a to 24f are controlled based on the outputs of the voltage sensor 30 and the temperature sensor 40 as described below. The control unit 60A corresponds to a low temperature start control unit in the present invention. The variable resistors 24a to 24f correspond to the current control unit in the present invention.

B2. Cold start control:
FIG. 4 is a flowchart showing a flow of low temperature start control in the second embodiment. This process is a process executed by the CPU of the control unit 60A when the fuel cell system 100A is started at a low temperature below the freezing point. Also in this embodiment, this control is executed when the output of any of the temperature sensors 40 is below the freezing point when the fuel cell system 100A is started.

  In the initial state at the start of the low temperature start control, the resistance values of the variable resistors 24a, 24d are 0, and the resistance values of the variable resistors 24b, 24c, 24e, 24f are infinite. Then, the requested current is taken out from the entire fuel cell stack 10 (see FIG. 3).

  Thereafter, the CPU measures the cell voltage Vc of each single cell 12 by the voltage sensor 30 (step S200). Then, each resistance value of the variable resistors 24a to 24f is set based on each cell voltage Vc (step S210). At this time, the resistance values of the variable resistors 24 a to 24 f are set so that no negative voltage is applied to each single cell 12. For example, in the single cells 12a and 12d at both ends of the fuel cell stack 10, when the generated water freezes and the power generation performance decreases, the resistance values of the variable resistors 24a and 24d are increased and the variable resistors 24b, 24c and 24e are increased. , 24f is lowered so that no negative voltage is applied to the single cells 12a, 12d, and power generation in the single cells 12a, 12d is continued. Then, a current having a value corresponding to the cell voltage Vc and the resistance value of the variable resistor is taken out from each single cell 12.

  Next, the CPU measures the temperature Tc of each single cell 12a, 12d arranged at both ends of the fuel cell stack 10 by the temperature sensor 40 (step S220). Then, the CPU determines whether or not the temperature Tc of the single cells 12a and 12d arranged at both ends is equal to or higher than a predetermined temperature Tth (step S230). When the temperature Tc of the single cells 12a and 12d is not equal to or higher than the predetermined temperature Tth (step S230: NO), the process returns to step S200. On the other hand, when the temperature of the single cells 12a and 12d is equal to or higher than the predetermined temperature Tth (step S230: YES), the low temperature control process is terminated.

  After the cold start control is finished, control is performed to extract current from the entire fuel cell stack 10 at the normal temperature.

  According to the fuel cell system 100A of the second embodiment described above, in the single cell 12 in which the power generation performance is not deteriorated at the low temperature start, the power generation is performed almost as requested, and the heat generation and heat conduction The temperature of the entire fuel cell stack 10 can be quickly raised. Moreover, since the extraction of the current from the single cell 12 whose power generation performance is reduced due to freezing of the generated water, that is, the current flowing through the single cell 12 whose power generation performance is reduced is limited, a negative voltage is applied to the single cell whose power generation performance is reduced. This can be suppressed and deterioration of the electrolyte membrane can be suppressed. As a result, the low temperature startability of the fuel cell system can be improved. Further, in the fuel cell system 100A of the second embodiment, even in the single cell 12 whose power generation performance has deteriorated, power generation is continued in a state where no negative voltage is applied and self-heating occurs. This can be shortened compared to the fuel cell system 100 of one embodiment.

C. Third embodiment:
C1. System configuration:
FIG. 5 is an explanatory diagram showing a schematic configuration of a fuel cell system 100B as a third embodiment of the present invention. As shown in the figure, the fuel cell system 100 includes B, a fuel cell stack 10B, changeover switches 20B and 22B, a temperature sensor 40, a load 50, and a control unit 60B. The fuel cell system 100B according to the third embodiment includes changeover switches 20B and 22B instead of the changeover switches 20 and 22 in the fuel cell system 100 according to the first embodiment, and a fuel cell instead of the fuel cell stack 10. The fuel cell system 100 is substantially the same as the fuel cell system 100 of the first embodiment except that the stack 10B is provided.

  At both ends in the stacking direction of the single cells 12 of the fuel cell stack 10B, single cells having an internal film configuration different from the single cells 12 arranged at portions other than the both ends are arranged. Hereinafter, the single cells arranged at both ends of the fuel cell stack 10B are referred to as end cells 12edg. The end cell 12 edg and the single cell 12 adjacent to the end cell 12 edg are each provided with a terminal for taking out a current during power generation. The film configuration of the single cell 12 and the end cell 12 edg will be described later. As will be described later, the end cell 12 edg is a single cell used only at the time of cold start, and corresponds to that for cold start in the present invention.

  The changeover switch 20B is provided with two terminals a and b. The changeover switch 22B is provided with two terminals c and d. Each end cell 12edg is connected to a terminal a of the changeover switch 20B and a terminal c of the changeover switch 22B. The single cells 12 adjacent to the end cells 12edg are connected to the terminal b of the changeover switch 20B and the terminal d of the changeover switch 22B, respectively. By switching the connection state of the changeover switch 20B and the changeover switch 22B, it is possible to switch the portion from which current is extracted during power generation.

  In the present embodiment, the control unit 60B executes low-temperature start control described later when the fuel cell system 100B is started at a low temperature below the freezing point. In this low temperature start control, the changeover switch 20B and the changeover switch 22B are controlled based on the output of the temperature sensor 40 as described below. The control unit 60B corresponds to the power generation control unit in the present invention. The changeover switches 20B and 22B correspond to a current control unit in the present invention.

  Here, the film configuration of the end cell 12 edg and the single cells 12 other than the end cell 12 edg will be described. FIG. 6 is an explanatory diagram showing the film configuration of the end cell 12 edg and the single cells 12 other than the end cell 12 edg. FIG. 6A shows a part of the cross section of the single cell 12 other than the end cell 12 edg, and FIG. 6B shows a part of the cross section of the end cell 12 edg.

  As shown in FIG. 6A, in the single cell 12, a catalyst layer 122a, a water-repellent layer 124a, and a diffusion layer 126a are laminated in this order on one surface of the electrolyte membrane 120, whereby an anode is formed. Is formed. Further, a cathode is formed by laminating the catalyst layer 122c, the water repellent layer 124c, and the diffusion layer 126c in this order on the other surface of the electrolyte membrane 120.

  On the other hand, in the end cell 12edg, similarly to the single cell 12, the anode is formed by laminating the catalyst layer 122a, the water repellent layer 124a, and the diffusion layer 126a in this order on one surface of the electrolyte membrane 120. Has been. Further, a cathode is formed by laminating a catalyst layer 122c and a diffusion layer 126c in this order on the other surface of the electrolyte membrane 120. The end cell 12 edg differs from the single cell 12 in that the thickness of the cathode diffusion layer 126 c is thinner than the thickness of the diffusion layer 126 c in the single cell 12 and that the cathode is not provided with a water repellent layer.

  Due to the difference in the film configuration described above, the end cell 12edg has the following characteristics.

  The first feature is that when the power generation is started below freezing point, the generated water generated by the power generation is less likely to freeze in the membrane than the single cell 12. As described above, the end cell 12 edg does not include a water repellent layer on the cathode, and the diffusion layer 126 c is thinner than the diffusion layer 126 c of the single cell 12. For this reason, the end cell 12 edg has higher permeability of the supercooled water in which the produced water generated by the power generation is in the supercooled state than the single cell 12. Accordingly, the supercooled water can be quickly discharged from the membrane.

  The second feature is that the performance at normal temperature is worse than that of the single cell 12. Specifically, the end cell 12 edg is not provided with a water repellent layer on the cathode, so flooding is likely to occur. Flooding hinders the supply of reaction gas and reduces power generation performance. For this reason, it is unsuitable for power generation at normal temperature.

  In consideration of the two characteristics of the end cell 12 edg described above, in this embodiment, the cold start control described below is performed.

C2. Cold start control:
FIG. 7 is a flowchart showing a flow of low temperature start control in the third embodiment. This process is a process executed by the CPU of the control unit 60B when the fuel cell system 100B is started at a low temperature below the freezing point. Also in this embodiment, this control is executed when the output of any of the temperature sensors 40 is below the freezing point when the fuel cell system 100B is started.

  In the initial state at the start of the low temperature start control, the changeover switch 20B and the changeover switch 22B are connected to the terminals a and c, respectively, and take out current from the entire fuel cell stack 10B (see FIG. 5).

  Thereafter, the CPU measures the temperature Tc of the end cell 12edg (step S300), and determines whether or not the temperature Tc of the end cell 12edg is equal to or higher than a predetermined temperature Tth (step S310). If the temperature Tc of the end cell 12edg is not equal to or higher than the predetermined temperature Tth (step S310: NO), the process returns to step 300. On the other hand, when the temperature Tc of the end cell 12edg is equal to or higher than the predetermined temperature Tth (step S310: YES), the connection of the changeover switch 20B and the changeover switch 22B is switched to the terminal b and the terminal d, respectively (step S320), power generation using the end cell 12edg is terminated, and the cold start control is terminated.

  After the end of the low temperature start control, the control is performed at the normal temperature for taking out the current from the fuel cell stack 10B other than the end cell 12edg.

  According to the fuel cell system 100B of the third embodiment described above, since power generation is performed using the end cell 12edg in which the generated water is difficult to freeze at the time of low temperature start, the end cell 12edg generates heat, and the single cells other than the end cell 12edg The temperature of the entire fuel cell stack 10B can be quickly raised by the heat generation of 12 and their heat conduction. As a result, the low temperature startability of the fuel cell system 100B can be improved.

D. Variation:
As mentioned above, although several embodiment of this invention was described, this invention is not limited to such embodiment at all, and implementation in various aspects is possible within the range which does not deviate from the summary. It is. For example, the following modifications are possible.

D1. Modification 1:
In the first and second embodiments, the cell voltage Vc is measured for each single cell 12 to detect a decrease in power generation performance. However, the present invention is not limited to this. The voltage may be measured for each block constituted by a plurality of single cells 12, and a decrease in power generation performance of the single cells 12 included in the block may be detected. In this case, a terminal for taking out the current may be prepared for each block of the single cell 12.

D2. Modification 2:
In the first and second embodiments, the single cell 12 at the end of the fuel cell stack 10 is hard to increase in temperature at the time of low temperature start under freezing point, and the generated water is likely to freeze. The single cell 12 adjacent to both ends is controlled to limit the current to be taken out, but is not limited thereto. The same control may be performed as appropriate for the other unit cells 12 as well.

  In the third embodiment, the cold start cells are disposed at both ends of the fuel cell stack 10B. However, the present invention is not limited to this, and the cold start cells may be disposed in other portions as appropriate. It may be.

D3. Modification 3:
In the third embodiment, the end cell 12edg, which is a cold start cell, does not include a water repellent layer on the cathode, but includes a water repellent layer thinner than the water repellent layer 124c of the single cell 12. Also good. In the end cell 12 edg, the cathode diffusion layer 126 c is thinner than the diffusion layer 126 c of the single cell 12, but it may have the same thickness. The end cell 12 edg, that is, the cold start cell only needs to have higher permeability of the supercooling water than the single cell 12.

D4. Modification 4:
In the third embodiment, the end cell 12edg, which is a cold start cell, is provided with a layer having higher permeability of supercooling water than the single cell 12 at the cathode. It is good also as a thing provided with the layer whose permeability | transmittance is higher than the single cell 12. FIG.

D5. Modification 5:
In the above embodiment, when the temperature Tc of the single cell 12 at the end becomes equal to or higher than the predetermined value Tth by the temperature sensor 40, the low temperature start control is terminated, but the present invention is not limited to this. For example, a timer for measuring the duration of the low temperature start control may be provided, and whether or not to end the low temperature start control may be performed based on the duration of the low temperature start control. In this case, the predetermined time may be set so that the temperature of all the single cells 12 of the fuel cell stack is sufficiently raised so that the generated water does not freeze.

D6. Modification 6:
You may make it combine the said 1st thru | or 3rd Example suitably.

It is explanatory drawing which shows schematic structure of the fuel cell system 100 as 1st Example of this invention. It is a flowchart which shows the flow of the cold start control in 1st Example. It is explanatory drawing which shows schematic structure of 100 A of fuel cell systems as 2nd Example of this invention. It is a flowchart which shows the flow of the cold start control in 2nd Example. It is explanatory drawing which shows schematic structure of the fuel cell system 100B as 3rd Example of this invention. It is explanatory drawing which shows the film | membrane structure of the single cells 12 other than the end cell 12edg and the end cell 12edg. It is a flowchart which shows the flow of the cold start control in 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell stack 10B ... Fuel cell stack 12edg ... End cell 12, 12a-12f ... Single cell 20, 20B, 22, 22B ... Changeover switch 24a-24f ... Variable resistance 30 ... Voltage sensor 40 ... Temperature sensor 50 ... Load 60, 60A, 60B ... Control unit 100, 100A, 100B ... Fuel cell system 120 ... Electrolyte membrane 122a ... Catalyst layer 122c ... Catalyst layer 124a ... Water repellent layer 124c ... Water repellent layer 126a ... Diffusion layer 126c ... Diffusion layer

Claims (9)

A fuel cell system,
A fuel cell stack in which a plurality of single cells that generate electricity by an electrochemical reaction between hydrogen and oxygen are stacked;
A voltage detector for detecting a voltage of each part of the fuel cell stack divided into a plurality of parts along the stacking direction of the single cells;
A current control unit for controlling a current flowing through each of the parts;
When the voltage detection unit detects that the voltage of any of the plurality of parts has become less than a predetermined value at a low temperature start under freezing point of the fuel cell system, the detected voltage is A low temperature start control unit that controls the current control unit so that a current flowing in the portion that is less than the predetermined value is lower than a current flowing in the other portion;
A fuel cell system comprising: The fuel cell system according to claim 1, wherein
In the control of the current control unit at the time of the low temperature start, the low temperature start control unit is detected by the voltage detection unit that any one of the plurality of portions has become less than a predetermined value. Furthermore, the current flowing through the portion where the detected voltage is less than the predetermined value is set to zero.
Fuel cell system. The fuel cell system according to claim 1, wherein
In the control of the current control unit at the time of the low temperature start, the low temperature start control unit is detected by the voltage detection unit that any one of the plurality of portions has become less than a predetermined value. Further, for the portion where the detected voltage is less than the predetermined value, the value of the current flowing through the portion is set based on the detected voltage value so that a negative voltage is not applied to the single cell. change,
Fuel cell system. The fuel cell system according to any one of claims 1 to 3,
The current control unit is a control target for control to reduce the flowing current value only in the portion arranged at the end portion in the stacking direction of the fuel cell stack.
Fuel cell system. The fuel cell system according to any one of claims 1 to 4, further comprising:
A temperature detection unit for detecting the temperature of each part;
The low temperature start control unit performs the control of the current control unit at the time of the low temperature start, the temperature detection unit for the portion where the voltage detected by the voltage detection unit is less than the predetermined value When the temperature detected by the above becomes a predetermined temperature or more, the control of the current control unit at the low temperature start is stopped,
Fuel cell system. The fuel cell system according to claim 1, wherein
A part of each of the parts of the fuel cell stack is constituted by a cold start cell for use only during the cold start as the single cell,
The fuel cell system further includes:
A temperature detector for detecting the temperature of the cold start cell;
The current control unit is configured to stop power generation by the cold start cell when the temperature detection unit detects that the temperature of the cold start cell is equal to or higher than a predetermined temperature during the cold start. A power generation control unit for controlling
A fuel cell system comprising: The fuel cell system according to claim 6, wherein
The single cell includes an anode and a cathode on both sides of a predetermined electrolyte membrane,
The cold start cell has high permeability to the anode and at least the cathode among the cathodes, the generated water generated by the power generation is higher than the single cells other than the cold start cell. With layers,
Fuel cell system. The fuel cell system according to claim 7, wherein
The single cell is supplied on both surfaces of the electrolyte membrane with a catalyst layer for causing the electrochemical reaction, a water repellent layer for repelling the generated water, and a reaction gas diffused in the catalyst layer. And in this order, a diffusion layer for
The low temperature start cell includes the water repellent layer having a thickness smaller than the water repellent layer of the single cell other than the low temperature start cell, and the single unit other than the low temperature start cell as the high transmission layer. Comprising at least one of the diffusion layers having a thickness smaller than the diffusion layer of the cell,
Fuel cell system. A fuel cell system according to any one of claims 6 to 8,
The cold start cell is provided only in the portion disposed at the end of the fuel cell stack in the stacking direction.
Fuel cell system.

Images