JP2011090912A - Fuel cell system, and starting control method of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress local deterioration of a fuel cell when starting at a low temperature, and achieve a long service life of the fuel cell. <P>SOLUTION: In the fuel cell system 100, when the fuel cell 10 is started at low temperature of 0 (°C) or less, while a control unit 50 supplies a fixed amount of hydrogen to an anode 14, it restricts a supply amount of air to a cathode 16 so that a concentration overpotential of the fuel cell 10 becomes a higher value than that in normal starting process. Furthermore, the control unit 50 controls a reflux pump 37 and a shut valve 38 installed in a cathode off-gas reflux piping 36, and supplies air comparatively high in oxygen concentration and air comparatively low in oxygen concentration to the cathode 16 of the fuel cell 10 in pulse alternately, and concentration distribution of oxygen on a surface of the cathode 16 of the fuel cell 10 is changed with the passage of time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a startup control method for a fuel cell system.

  A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas has attracted attention as an energy source. Since this fuel cell has an operating temperature range suitable for power generation, a fuel cell system equipped with a fuel cell is required to quickly raise the temperature of the fuel cell to the above operating temperature range at startup. It is done.

  Therefore, conventionally, various techniques have been proposed for rapidly raising the temperature of the fuel cell at the time of startup in the fuel cell system. For example, at low temperature startup from below freezing point, the supply amount of oxidant gas to the cathode relative to the supply amount of fuel gas to the anode of the fuel cell is made smaller than that during normal power generation, and the supply of oxidant gas to the cathode is delayed. By making the voltage drop (concentration overvoltage (diffusion overvoltage)) caused by the battery to be lower than that during normal power generation and performing low-efficiency power generation, and increasing the amount of heat generation compared to during normal power generation, the temperature of the fuel cell can be quickly increased. Techniques for raising the temperature are known.

JP 2003-197247 A JP-A-2-18868 JP 2007-265910 A JP 2009-59669 A JP 2009-21076 A

  However, in the above-described method for starting the fuel cell system, there is a region where the oxidant gas is locally insufficient on the surface of the cathode of the fuel cell, and the fuel cell may deteriorate intensively in this region. When such local degradation of the fuel cell occurs, the power generation performance of the entire fuel cell is lowered even if other regions are not degraded, and the life of the fuel cell is shortened. .

  The present invention has been made to solve the above-described problems, and has an object to suppress the local deterioration of the fuel cell at a low temperature start-up and extend the life of the fuel cell in the fuel cell system. To do.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A fuel cell system, a fuel cell, a fuel gas supply unit that supplies fuel gas to the anode of the fuel cell, and an oxidant gas supply unit that supplies oxidant gas to the cathode of the fuel cell And a control unit, wherein the control unit is configured to supply the oxidant gas to the cathode with respect to the supply amount of the fuel gas to the anode during startup when the temperature of the fuel cell is equal to or lower than a predetermined temperature. The ratio of the supply amount is limited so that the concentration overvoltage of the fuel cell becomes larger than at the start-up when the temperature of the fuel cell is higher than the predetermined temperature, and the unit of the oxidant gas to the cathode A fuel cell system that performs low-temperature start-up control for controlling the oxidant gas supply unit so that the supply amount per hour repeatedly increases and decreases.

  In the fuel cell system of Application Example 1, at the time of start-up when the temperature of the fuel cell is equal to or lower than a predetermined temperature (for example, at low temperature start-up from below freezing point), the amount of fuel gas supplied to the anode of the fuel cell is supplied to the cathode. The ratio of the supply amount of the oxidant gas is limited as described above. Therefore, the temperature of the fuel cell can be quickly raised by performing low-efficiency power generation and increasing the amount of heat generated compared to when starting when the temperature of the fuel cell is higher than a predetermined temperature. Furthermore, in the fuel cell system of Application Example 1, the supply amount of the oxidant gas per unit time to the cathode of the fuel cell is repeatedly increased or decreased at the start-up when the temperature of the fuel cell is equal to or lower than a predetermined temperature. The concentration distribution of the oxidant gas on the surface changes with time. For this reason, even if a region where the oxidant gas is locally insufficient occurs on the surface of the cathode, this region moves with time. Therefore, in the cathode of the fuel cell, local deterioration of the fuel cell at the time of low temperature start-up due to partial fixing of the region where the oxidant gas is locally insufficient is suppressed, and the life of the fuel cell is extended. be able to.

  In the fuel cell system of Application Example 1, as a mode of repeatedly increasing / decreasing the supply amount per unit time of the oxidant gas to the cathode of the fuel cell at the start-up when the temperature of the fuel cell is equal to or lower than a predetermined temperature, Various modes can be applied. Examples of such modes include pulse-like increase / decrease, sine wave-like increase / decrease, and sawtooth wave-like increase / decrease.

  [Application Example 2] The fuel cell system according to Application Example 1, wherein the fuel gas is hydrogen, the oxidant gas is oxygen, and the oxidant gas supply unit uses air containing oxygen. An air supply pipe for supplying to the cathode; an air pump provided in the air supply pipe; and a cathode off-gas recirculation part for circulating the cathode off-gas discharged from the cathode to the air supply pipe. The fuel cell system performs control of the air pump and the cathode off-gas recirculation unit as the low-temperature start-up control.

  In the fuel cell system of Application Example 2, the air pump and the above-described air pump are configured so that the flow rate of the cathode off-gas recirculated to the cathode of the fuel cell repeatedly increases and decreases during startup when the temperature of the fuel cell is equal to or lower than a predetermined temperature. By controlling the cathode off-gas recirculation part, the supply amount of oxidant gas (oxygen) per unit time to the cathode of the fuel cell is repeatedly increased and decreased, and the concentration distribution of oxidant gas (oxygen) on the surface of the cathode is changed. It can be changed over time.

  In the fuel cell system of Application Example 2, the amount of air supplied from the air pump to the cathode of the fuel cell may be constant or may vary.

  [Application Example 3] The fuel cell system according to Application Example 1, wherein the fuel gas is hydrogen, the oxidant gas is oxygen, and the oxidant gas supply unit uses air containing oxygen. An air supply pipe for supplying to the cathode, an air pump provided in the air supply pipe, a combustor for burning hydrogen with oxygen, and combustion exhaust gas exhausted from the combustor is supplied to the cathode And a combustion exhaust gas control valve for controlling a supply amount of the combustion exhaust gas to the cathode, and the control unit serves as the air pump as the low temperature start control. And a fuel cell system that controls the combustor and the combustion exhaust gas control valve.

  In the fuel cell system of Application Example 3, the above-described fuel exhaust gas supplied from the combustor to the cathode of the fuel cell is repeatedly increased or decreased during startup when the temperature of the fuel cell is equal to or lower than a predetermined temperature. By controlling the air pump, the combustor, and the combustion exhaust gas control valve, the supply amount of oxidant gas (oxygen) per unit time to the cathode of the fuel cell is repeatedly increased and decreased, and the surface of the cathode The concentration distribution of the oxidant gas (oxygen) in can be changed over time.

  In the fuel cell system of Application Example 3, as oxygen introduced into the combustor, for example, oxygen in the air discharged from the air pump can be used. Further, as the hydrogen introduced into the combustor, hydrogen as the fuel gas can be used. The amount of air supplied from the air pump to the cathode of the fuel cell may be constant or may vary.

  [Application Example 4] The fuel cell system according to Application Example 1, wherein the fuel gas is hydrogen, the oxidant gas is oxygen, and the oxidant gas supply unit uses air containing oxygen. A fuel cell system comprising: an air supply pipe for supplying to the cathode; and an air pump provided in the air supply pipe, wherein the control unit controls the air pump as the low temperature start control.

  In the fuel cell system of Application Example 4, the air pump is controlled so that the amount of air supplied to the cathode of the fuel cell repeatedly increases and decreases during startup when the temperature of the fuel cell is equal to or lower than a predetermined temperature. By repeatedly increasing or decreasing the amount of oxidant gas (oxygen) supplied to the cathode of the fuel cell per unit time, the concentration distribution of the oxidant gas (oxygen) on the surface of the fuel cell cathode is changed over time. Can do.

  The present invention can also be configured by appropriately combining the various features described above. Further, the present invention can be configured as an invention of a fuel cell system activation control method 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.

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 starting control process of the fuel cell system 100 of 1st Example. It is explanatory drawing for demonstrating the effect by the starting control process (at the time of low temperature starting) of the fuel cell system 100 of a present 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 starting control process of 100 A of fuel cell systems of 2nd Example. It is explanatory drawing which shows schematic structure of the fuel cell system 100B as 3rd Example of this invention. It is a flowchart which shows the flow of a starting control process of the fuel cell system 100B of 3rd Example. It is explanatory drawing which shows schematic structure of the fuel cell system 100C of a modification. It is a flowchart which shows the flow of the starting control process of the fuel cell system 100C of a modification.

Hereinafter, embodiments of the present invention will be described based on examples.
A. First embodiment:
A1. Configuration of fuel cell system:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system 100 as a first embodiment of the present invention.

  The fuel cell 10 includes an electrolyte membrane 12 having proton conductivity, an anode 14 formed on one surface of the electrolyte membrane 12, and a cathode 16 formed on the other surface of the electrolyte membrane 12. In the present embodiment, a solid polymer membrane such as Nafion (registered trademark) is used as the electrolyte membrane 12. The fuel cell 10 is provided with a temperature sensor 18 for detecting the temperature Tfc of the fuel cell 10.

  For example, hydrogen as fuel gas is supplied to the anode 14 of the fuel cell 10 through a hydrogen supply pipe 20 from a hydrogen tank (not shown) that stores high-pressure hydrogen. The anode off gas discharged from the anode 14 of the fuel cell 10 is discharged to the outside of the fuel cell 10 through the anode off gas exhaust pipe 24. An anode off-gas recirculation pipe for circulating the anode off-gas to the anode 14 of the fuel cell 10 is connected to the anode off-gas exhaust pipe 24 and the hydrogen supply pipe 20 so that unconsumed hydrogen contained in the anode off-gas is contained. May be reused for power generation. In this case, the anode off-gas circulation pipe is provided with a pump for circulating the anode off-gas to the hydrogen supply pipe 20.

  Air containing oxygen as an oxidant gas is compressed and supplied to the cathode 16 of the fuel cell 10 through an air supply pipe 30 by an air compressor 32 provided in the air supply pipe 30. By changing the rotation speed of the air compressor 32, the amount of air supplied to the cathode 16 of the fuel cell 10 can be changed. The cathode offgas discharged from the cathode 16 of the fuel cell 10 is discharged to the outside of the fuel cell 10 through the cathode offgas exhaust pipe 34. The air compressor 32 corresponds to the air pump in [Means for Solving the Problems].

  Further, in the fuel cell system 100 of the present embodiment, the cathode offgas exhaust pipe 34 and the air supply pipe 30 are connected to the cathode offgas circulation pipe 36 for circulating the cathode offgas to the air supply pipe 30. The cathode offgas recirculation pipe 36 is provided with a recirculation pump 37 and a shut valve 38. By switching on / off of the recirculation pump 37 and opening / closing of the shut valve 38, it is possible to switch whether or not the cathode off gas is recirculated to the cathode 16 of the fuel cell 10. Further, by changing the number of revolutions of the recirculation pump 37, the flow rate of the cathode off-gas to the cathode 16 of the fuel cell 10 can be changed. The cathode offgas recirculation pipe 36, the recirculation pump 37, and the shut valve 38 correspond to the cathode offgas recirculation section in [Means for Solving the Problems].

  The operation of the fuel cell system 100 is controlled by the control unit 50. The control unit 50 is configured as a microcomputer having a CPU, a RAM, a ROM, and the like inside, and according to a program stored in the ROM, based on output requests to the fuel cell 10, outputs from various sensors, etc. Control the operation of the system, such as control of the pump and air compressor 32. The control unit 50 corresponds to the control unit in [Means for Solving the Problems]. Hereinafter, the startup control process of the fuel cell system 100 will be described.

A2. Startup control processing:
FIG. 2 is a flowchart showing a flow of start control processing of the fuel cell system 100 of the first embodiment. This process is a process executed by the CPU of the control unit 50 when the fuel cell system 100 is activated. In this embodiment, it is assumed that a certain amount of hydrogen is supplied to the anode 14 of the fuel cell 10 when the startup control process is started.

  The CPU sets the rotational speed of the recirculation pump 37 to zero (step S100), closes the shut valve 38 provided in the cathode off-gas recirculation pipe 36 (step S102), and sets the air compressor 32 provided in the air supply pipe 30. Air is supplied to the cathode 16 of the fuel cell 10 with the rotational speed set to a predetermined rotational speed (step S104). The rotational speed of the air compressor 32 at this time is such that the supply amount of air (oxygen) to the cathode 16 of the fuel cell 10 is smaller than that during normal power generation, and delays in the supply of oxygen to the cathode 16 of the fuel cell 10. A value lower than that during normal power generation is set so that the resulting voltage drop (concentration overvoltage) is greater than during normal power generation. Note that the order of steps S100, S102, and S104 may be changed.

  Then, the CPU acquires the temperature Tfc of the fuel cell 10 detected by the temperature sensor 18, and determines whether or not the temperature Tfc of the fuel cell 10 is 0 (° C.) or less (step S110). When the temperature Tfc of the fuel cell 10 is higher than 0 (° C.) (step S110: NO), the CPU executes a normal activation control process (step S200), and then ends the activation control process. In the present embodiment, the normal activation control processing is performed until the temperature Tfc of the fuel cell 10 rises to a desired temperature, and the supply amount of hydrogen to the anode 14 of the fuel cell 10 and the supply of air to the cathode 16. This is start-up control for generating electricity with a constant amount. In this normal activation control process, the rotation speed of the air compressor 32 is set so that air (oxygen) in an amount that makes the concentration overvoltage equivalent to that during normal power generation is supplied to the cathode 16 of the fuel cell 10. That is, the rotation speed of the air compressor 32 in step S104 is lower than the rotation speed of the air compressor 32 in step S200.

  In step S110, when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less (step S110: YES), the CPU elapses from the start of the start control process, or clears a counter to be described later (step S180). The elapsed time from is counted up (step S120). That is, the CPU stops the recirculation pump 37, closes the shut valve 38, and accumulates the time during which the air compressor 32 is operated without recirculating the cathode off gas to the cathode 16 of the fuel cell 10.

  Then, the CPU determines whether or not the counter is greater than or equal to a predetermined value (step S130). That is, the CPU supplies the cathode 16 with the air discharged from the air compressor 32 without circulating the cathode off-gas to the cathode 16 of the fuel cell 10 for a predetermined time (for example, 1 second) or more. Determine whether or not. When the counter is less than the predetermined value (step S130: NO), the CPU returns the process to step S100.

  On the other hand, if the counter is equal to or larger than the predetermined value (step S130: YES), the CPU clears the counter (step S140), sets the rotational speed of the circulating pump 37 to the predetermined rotational speed (step S150), and shuts the valve 38. Is opened (step S152), and the cathode off-gas is circulated to the cathode 16 of the fuel cell 10. That is, air having a relatively low oxygen concentration obtained by mixing the air discharged from the air compressor 32 and the cathode off gas is supplied to the cathode 16 of the fuel cell 10. Note that the order of steps S150 and S152 may be changed.

  Then, the CPU counts up the elapsed time from step S140 (step S160). That is, the CPU accumulates the time during which the cathode off gas is circulated to the cathode 16 of the fuel cell 10.

  Then, the CPU determines whether or not the counter is equal to or greater than a predetermined value (step S170). That is, the CPU determines whether or not the time during which the cathode off gas is circulated to the cathode 16 of the fuel cell 10 has exceeded a predetermined time (for example, 1 second). When the counter is less than the predetermined value (step S170: NO), the CPU returns the process to step S150. On the other hand, if the counter is equal to or greater than the predetermined value (step S170: YES), the CPU clears the counter (step S180), returns the process to step S100, and returns the cathode off-gas to the cathode 16 of the fuel cell 10. To stop.

  As can be seen from the above description, in the start-up control process of the fuel cell system 100 of the present embodiment, air having a relatively high oxygen concentration (step S100) during low-temperature start-up when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less. To S130) and air with relatively low oxygen concentration (steps S150 to S170) are alternately supplied to the cathode 16 of the fuel cell 10 in a pulsed manner. By doing in this way, the effect demonstrated below can be acquired.

  FIG. 3 is an explanatory diagram for explaining the effect of the startup control process (at the time of low temperature startup) of the fuel cell system 100 of the present embodiment. FIG. 3A schematically shows the distribution of oxygen concentration at the cathode 16 when air having a constant oxygen concentration is supplied to the cathode 16 of the fuel cell 10 with a constant supply amount. The supply amount of air at this time is assumed to be the supply amount in steps S100 to S130 of the startup control process of the fuel cell system 100 of the present embodiment. FIG. 3B shows a case where air having a relatively high oxygen concentration and air having a relatively low oxygen concentration are alternately supplied to the cathode 16 of the fuel cell 10 in a pulse manner, that is, in this embodiment. A distribution of oxygen concentration in the cathode 16 in the case of applying the start-up control process of the fuel cell system 100 is schematically shown.

  As shown in FIG. 3A, when air with a constant oxygen concentration is supplied to the cathode 16 of the fuel cell 10 with a constant supply amount, the oxygen contained in the air is the inlet of the air at the cathode 16. In the vicinity of the air outlet of the cathode 16, there may be a region where oxygen is locally insufficient. In this case, the region where oxygen is locally deficient does not move because the amount of air supplied to the cathode 16 is constant. For this reason, the fuel cell 10 deteriorates intensively in a region near the air outlet where oxygen becomes insufficient. When such local deterioration of the fuel cell 10 occurs, the power generation performance of the fuel cell 10 as a whole is lowered even if other regions are not deteriorated, and the life of the fuel cell 10 is shortened. turn into.

  On the other hand, as shown in FIG. 3B, when air having a relatively high oxygen concentration and air having a relatively low oxygen concentration are alternately supplied to the cathode 16 of the fuel cell 10 in a pulsed manner. In the cathode 16, a region having a relatively high oxygen concentration and a region having a relatively low oxygen concentration can be sequentially moved with time along the air flow direction. This is because air having a relatively low oxygen concentration supplied earlier is scavenged by air having a relatively high oxygen concentration supplied later, and air having a relatively high oxygen concentration supplied earlier is This is because the oxygen concentration supplied from the air is scavenged by relatively low air. By doing so, it is possible to suppress a region where oxygen is locally deficient in the cathode 16 from being partially fixed, and to suppress intensive deterioration of the fuel cell 10.

  In the fuel cell system 100 of the first embodiment described above, the supply amount of air (oxygen) to the cathode 16 of the fuel cell 10 during low temperature startup when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less, Specifically, the ratio of the supply amount of air (oxygen) to the cathode 16 with respect to the supply amount of hydrogen to the anode 14 of the fuel cell 10 is set so that the concentration overvoltage of the fuel cell 10 becomes higher than that during normal startup control processing. Restrict. Therefore, the temperature Tfc of the fuel cell 10 can be quickly raised by performing low-efficiency power generation and increasing the amount of heat generation compared to the normal startup control process. Furthermore, in the fuel cell system 100 of the present embodiment, when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less, at a low temperature start, air having a relatively high oxygen concentration and air having a relatively low oxygen concentration are used. By supplying pulses alternately to the cathode 16 of the fuel cell 10, the oxygen concentration distribution on the surface of the cathode 16 of the fuel cell 10 can be changed over time. For this reason, even if a region where oxygen is locally deficient occurs on the surface of the cathode 16, this region moves with time. Therefore, in the cathode 16 of the fuel cell 10, local deterioration of the fuel cell 10 at the time of low-temperature start-up due to partial fixing of a region where oxygen is locally deficient is suppressed, and the life of the fuel cell 10 is extended. Can be achieved.

B. Second embodiment:
B1. Configuration of fuel cell system:
FIG. 4 is an explanatory diagram showing a schematic configuration of a fuel cell system 100A as a second embodiment of the present invention.

  The fuel cell system 100A of the second embodiment does not include the cathode offgas recirculation pipe 36, the recirculation pump 37, and the shut valve 38 in the fuel cell system 100 of the first embodiment. Instead, the fuel cell system 100A of the second embodiment includes a catalyst combustor 40 that burns hydrogen with oxygen, a hydrogen introduction pipe 42 for introducing hydrogen from the hydrogen supply pipe 20 to the catalyst combustor 40, an air An air introduction pipe 44 for introducing air from the supply pipe 30 to the catalyst combustor 40, and a combustion exhaust gas supply pipe 46 for supplying the fuel exhaust gas exhausted from the catalyst combustor 40 to the cathode 16 of the fuel cell 10. And. The hydrogen introduction pipe 42 is provided with an injector 43 for controlling the amount of hydrogen introduced into the catalytic combustor 40. The air introduction pipe 44 is provided with a shut valve 45 for switching whether to introduce air into the catalyst combustor 40. The other configuration of the fuel cell system 100A is the same as the configuration of the fuel cell system 100 of the first embodiment. The shut valve 45 corresponds to the combustion exhaust gas control valve in [Means for Solving the Problems].

  Note that the fuel cell system 100A of the second embodiment includes a control unit 50A instead of the control unit 50 in the fuel cell system 100 of the first embodiment. Hereinafter, the activation control process of the fuel cell system 100A will be described.

B2. Startup control processing:
FIG. 5 is a flowchart showing a flow of start control processing of the fuel cell system 100A of the second embodiment. This process is a process executed by the CPU of the control unit 50A when the fuel cell system 100A is activated. Also in the present embodiment, as in the first embodiment, when the start control process is started, a certain amount of hydrogen is supplied to the anode 14 of the fuel cell 10. The startup control process of the fuel cell system 100A of the second embodiment is partially different from the startup control process of the fuel cell system 100 of the first embodiment.

  The CPU stops the injector 43 provided in the hydrogen introduction pipe 42 (step S100A), closes the shut valve 45 provided in the air introduction pipe 44 (step S102A), and air provided in the air supply pipe 30. Air is supplied to the cathode 16 of the fuel cell 10 by setting the rotation speed of the compressor 32 to a predetermined rotation speed (step S104). Note that the order of steps S100A, S02A, and S104 may be changed.

  Then, the CPU acquires the temperature Tfc of the fuel cell 10 detected by the temperature sensor 18, and determines whether or not the temperature Tfc of the fuel cell 10 is 0 (° C.) or less (step S110). When the temperature Tfc of the fuel cell 10 is higher than 0 (° C.) (step S110: NO), the CPU executes a normal activation control process (step S200), and then ends the activation control process. On the other hand, when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less (step S110: YES), the CPU determines the elapsed time from the start of the start control process or the counter clear (step S180) described later. The elapsed time is counted up (step S120). That is, the CPU stops the injector 43, closes the shut valve 45, and operates the air compressor 32 without supplying the combustion exhaust gas from the catalytic combustor 40 to the cathode 16 of the fuel cell 10. Accumulate time.

  Then, the CPU determines whether or not the counter is greater than or equal to a predetermined value (step S130). That is, the CPU does not supply the combustion exhaust gas from the catalytic combustor 40 to the cathode 16 of the fuel cell 10 and supplies the air discharged from the air compressor 32 to the cathode 16 for a predetermined time (for example, 1 second) or more is determined. When the counter is less than the predetermined value (step S130: NO), the CPU returns the process to step S100.

  On the other hand, if the counter is equal to or greater than the predetermined value (step S130: YES), the CPU clears the counter (step S140), opens the shut valve 45 (step S150A), and drives the injector 43 (step S150A). In step S152A), the combustion exhaust gas from the catalytic combustor 40 is supplied to the cathode 16 of the fuel cell 10. That is, air having a relatively low oxygen concentration obtained by mixing the air discharged from the air compressor 32 and the combustion exhaust gas from the catalytic combustor 40 is supplied to the cathode 16 of the fuel cell 10. Note that the order of steps S150A and S152A may be changed.

  Then, the CPU counts up the elapsed time from step S140 (step S160). That is, the CPU accumulates the time during which the combustion exhaust gas from the catalytic combustor 40 is supplied to the cathode 16 of the fuel cell 10.

  Then, the CPU determines whether or not the counter is equal to or greater than a predetermined value (step S170). That is, the CPU determines whether or not the time during which the combustion exhaust gas from the catalytic combustor 40 is supplied to the cathode 16 of the fuel cell 10 has exceeded a predetermined time (for example, 1 second). When the counter is less than the predetermined value (step S170: NO), the CPU returns the process to step S150. On the other hand, if the counter is equal to or greater than the predetermined value (step S170: YES), the CPU clears the counter (step S180), returns the process to step S100, and sets the combustion exhaust gas to the cathode 16 of the fuel cell 10. Stop supplying.

  As can be seen from the above description, in the start-up control process of the fuel cell system 100A of the present embodiment, the temperature Tfc of the fuel cell 10 is 0 (° C.) as in the start-up control process of the fuel cell system 100 of the first embodiment. At the time of low temperature start-up as described below, air having a relatively high oxygen concentration and air having a relatively low oxygen concentration are alternately supplied to the cathode 16 of the fuel cell 10 in a pulsed manner.

  In the fuel cell system 100A of the second embodiment described above, similarly to the fuel cell system 100 of the first embodiment, the fuel cell 10 is activated at low temperature when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less. The amount of air (oxygen) supplied to the cathode 16, more specifically, the ratio of the amount of air (oxygen) supplied to the cathode 16 to the amount of hydrogen supplied to the anode 14 of the fuel cell 10 is compared with that during normal startup control processing. Also, the concentration overvoltage of the fuel cell 10 is limited to be high. Therefore, the temperature Tfc of the fuel cell 10 can be quickly raised by performing low-efficiency power generation and increasing the amount of heat generation compared to the normal startup control process. Further, in the fuel cell system 100A of the present embodiment, when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less, at a low temperature start, air having a relatively high oxygen concentration and air having a relatively low oxygen concentration are used. By supplying pulses alternately to the cathode 16 of the fuel cell 10, the oxygen concentration distribution on the surface of the cathode 16 of the fuel cell 10 can be changed over time. For this reason, even if a region where oxygen is locally deficient occurs on the surface of the cathode 16, this region moves with time. Therefore, in the cathode 16 of the fuel cell 10, local deterioration of the fuel cell 10 at the time of low-temperature start-up due to partial fixing of a region where oxygen is locally deficient is suppressed, and the life of the fuel cell 10 is extended. Can be achieved.

C. Third embodiment:
C1. Configuration of fuel cell system:
FIG. 6 is an explanatory diagram showing a schematic configuration of a fuel cell system 100B as a third embodiment of the present invention. In the fuel cell system 100B of the third embodiment, the cathode offgas recirculation pipe 36, the recirculation pump 37, and the shut valve 38 in the fuel cell system 100 of the first embodiment are omitted. The fuel cell system 100B of the third embodiment includes a control unit 50B instead of the control unit 50 in the fuel cell system 100 of the first embodiment. Hereinafter, the activation control process of the fuel cell system 100B will be described.

C2. Startup control processing:
FIG. 7 is a flowchart showing the flow of start control processing of the fuel cell system 100B of the third embodiment. This process is a process executed by the CPU of the control unit 50B when the fuel cell system 100B is activated. Also in the present embodiment, as in the first embodiment, when the start control process is started, a certain amount of hydrogen is supplied to the anode 14 of the fuel cell 10. The startup control process of the fuel cell system 100B of the third embodiment is partially different from the startup control process of the fuel cell system 100 of the first embodiment.

  The CPU supplies air to the cathode 16 of the fuel cell 10 with the rotation speed of the air compressor 32 provided in the air supply pipe 30 as the first predetermined rotation speed Na (step S100B). At this time, the rotation speed (first predetermined rotation speed Na) of the air compressor 32 is such that the supply amount of air (oxygen) to the cathode 16 of the fuel cell 10 becomes smaller than that during normal power generation, and the cathode of the fuel cell 10. A value lower than that at the time of normal power generation is set so that the voltage drop (concentration overvoltage) due to the delay in the supply of oxygen to 16 is larger than that at the time of normal power generation.

  Then, the CPU acquires the temperature Tfc of the fuel cell 10 detected by the temperature sensor 18, and determines whether or not the temperature Tfc of the fuel cell 10 is 0 (° C.) or less (step S110). When the temperature Tfc of the fuel cell 10 is higher than 0 (° C.) (step S110: NO), the CPU executes a normal activation control process (step S200), and then ends the activation control process. On the other hand, when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less (step S110: YES), the CPU counts the elapsed time from the start of the start control process or the counter clear (step S180) described later. Up (step S120). That is, the CPU accumulates the time during which the rotation speed of the air compressor 32 is operated as the first predetermined rotation speed Na.

  Then, the CPU determines whether or not the counter is greater than or equal to a predetermined value (step S130). That is, the CPU determines whether or not the time during which the air discharged from the air compressor 32 operating at the first predetermined rotational speed Na is supplied to the cathode 16 has exceeded a predetermined time (for example, 1 second). To do. When the counter is less than the predetermined value (step S130: NO), the CPU returns the process to step S100.

  On the other hand, if the counter is equal to or greater than the predetermined value (step S130: YES), the CPU clears the counter (step S140) and sets the rotation speed of the air compressor 32 as the second predetermined rotation speed Nb (step S150B). Then, air is supplied to the cathode 16 of the fuel cell 10. The second predetermined rotation speed Nb is lower than the first predetermined rotation speed Na.

  Then, the CPU counts up the elapsed time from step S140 (step S160). That is, the CPU accumulates the time during which the rotation speed of the air compressor 32 is operated as the second predetermined rotation speed Nb.

  Then, the CPU determines whether or not the counter is equal to or greater than a predetermined value (step S170). That is, the CPU determines whether or not the time during which the rotation speed of the air compressor 32 is operated as the second predetermined rotation speed Nb has passed for a predetermined time (for example, 1 second). When the counter is less than the predetermined value (step S170: NO), the CPU returns the process to step S150B. On the other hand, if the counter is equal to or greater than the predetermined value (step S170: YES), the CPU clears the counter (step S180), returns the process to step S100, and sets the rotation speed of the air compressor 32 to the first predetermined rotation. Increase to a few Na.

  As can be seen from the above description, in the start-up control process of the fuel cell system 100 according to the present embodiment, air is supplied to the cathode 16 of the fuel cell 10 at low temperature start-up when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less. Supply by increasing / decreasing the supply amount in pulses.

  In the fuel cell system 100B of the third embodiment described above, similarly to the fuel cell system 100 of the first embodiment, the fuel cell 10 is activated at a low temperature when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less. The ratio of the supply amount of air (oxygen) to the cathode 16 with respect to the supply amount of hydrogen to the anode 14 of the fuel cell 10, in detail, during the normal startup control process The concentration overvoltage of the fuel cell 10 is limited to be higher than that. Therefore, the temperature Tfc of the fuel cell 10 can be quickly raised by performing low-efficiency power generation and increasing the amount of heat generation compared to the normal startup control process. Further, in the fuel cell system 100B of the present embodiment, the amount of air supplied to the cathode 16 of the fuel cell 10 is increased or decreased in a pulse manner at low temperature startup when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less. Thus, the oxygen concentration distribution on the surface of the cathode 16 of the fuel cell 10 can be changed over time. For this reason, even if a region where oxygen is locally deficient occurs on the surface of the cathode 16, this region moves with time. Therefore, in the cathode 16 of the fuel cell 10, local deterioration of the fuel cell 10 at the time of low-temperature start-up due to partial fixing of a region where oxygen is locally deficient is suppressed, and the life of the fuel cell 10 is extended. Can be achieved.

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 a various aspect is possible within the range which does not deviate from the summary. It is. For example, the following modifications are possible.

D1. Modification 1:
FIG. 8 is an explanatory diagram showing a schematic configuration of a fuel cell system 100C as a modification. As can be seen from the comparison between FIG. 8 and FIG. 1, the fuel cell system 100C of the modified example includes a cathode off-gas recirculation pipe 36 and an air supply pipe 30 instead of the shut valve 38 in the fuel cell system 100 of the first embodiment. Is provided with a three-way valve 39. The other configuration of the fuel cell system 100C is the same as the configuration of the fuel cell system 100 of the first embodiment. The fuel cell system 100C according to the modified example includes a control unit 50C instead of the control unit 50 in the fuel cell system 100 according to the first embodiment. Then, the CPU of the control unit 50C executes the following activation control process when the fuel cell system 100C is activated.

  FIG. 9 is a flowchart showing the flow of activation control processing of the fuel cell system 100C according to the modification. As can be seen from the comparison between FIG. 9 and FIG. 2, in the start-up control process of the fuel cell system 100C of the modified example, the open / close state of the shut valve 38 in steps S102 and S152 of the start-up control process of the first embodiment. The third embodiment is the same as the first embodiment except that the three-way valve 39 is switched instead of switching (step S102C and step S152C). The three-way valve 39 may be switched between supplying air discharged from the air compressor 32 or supplying cathode off-gas to the cathode 16 of the fuel cell 10, or discharging from the air compressor 32. It is also possible to switch between supplying the supplied air and supplying the air discharged from the air compressor 32 and the cathode off gas mixed.

  Also in the fuel cell system 100C according to the modified example, similarly to the fuel cell system 100 according to the first embodiment, in the cathode 16 of the fuel cell 10, the region where oxygen is deficient is fixed, so that the fuel cell 10 at the time of low temperature startup is fixed. Local deterioration can be suppressed and the life of the fuel cell 10 can be extended.

D2. Modification 2:
In the first and second embodiments, in step S104 (FIGS. 2 and 5) of the start-up control process of the fuel cell systems 100 and 100A, the rotation speed of the air compressor 32 is set so that the concentration overvoltage of the fuel cell 10 is higher than that during normal power generation. However, the present invention is not limited to this. However, the air (oxygen) of a higher level is set so as to be supplied to the cathode 16 of the fuel cell 10. The ratio of the oxygen supply amount to the cathode 16 with respect to the hydrogen supply amount to the anode 14 of the fuel cell 10 is limited so that the concentration overvoltage of the fuel cell 10 becomes higher than that in the normal startup control process (step S200). That's fine.

D3. Modification 3:
In the first and second embodiments, the rotation speed of the air compressor 32 is made constant in the startup control processing of the fuel cell systems 100 and 100A, but the present invention is not limited to this. For example, the rotational speed of the air compressor 32 may be increased or decreased in a pulse manner.

D4. Modification 4:
In the first and second embodiments, in the start-up control process of the fuel cell system 100, 100A, the air having a relatively high oxygen concentration and the oxygen concentration at the low-temperature start-up when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less. However, the present invention is not limited to this, although the relatively low air is supplied alternately to the cathode 16 of the fuel cell 10 in a pulsed manner. In the third embodiment, in the start-up control process of the fuel cell system 100B, the amount of air supplied to the cathode 16 of the fuel cell 10 is reduced at the time of low-temperature start-up when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less. Although the supply is made by increasing / decreasing in a pulse manner, the present invention is not limited to this. In the start-up control process of the fuel cell system 100, 100A, 100B, the supply amount of oxygen per unit time to the cathode 16 of the fuel cell 10 is repeated at the time of low-temperature start-up where the temperature Tfc of the fuel cell 10 is 0 (° C.) or less. Increase or decrease.

D5. Modification 5:
In the first and second embodiments, as air having a relatively low oxygen concentration, air mixed with air in the atmosphere and cathode offgas is used (first embodiment), air in the atmosphere, and catalytic combustor. Although air mixed with combustion exhaust gas exhausted from 40 is used (second embodiment), the present invention is not limited to this. As the air having a relatively low oxygen concentration, for example, a mixed gas obtained by mixing air in the atmosphere and an inert gas such as nitrogen or argon may be used.

D6. Modification 6:
In the first embodiment, in the start-up control process of the fuel cell system 100, when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less, the circulating pump 37 is turned on / off in pulses and the shut valve 38 is turned on. However, the present invention is not limited to this. For example, the opening degree of the shut valve 38 may be increased or decreased in a pulse manner while the recirculation pump 37 is always operated.

  In the second embodiment, in the start-up control process of the fuel cell system 100A, when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less, the injector 43 is turned on / off in pulses and the shut valve However, the present invention is not limited to this. For example, the opening degree of the shut valve 38 may be increased or decreased in a pulse manner while the recirculation pump 37 is always operated.

D7. Modification 7:
In the second embodiment, the shut valve 45 is provided in the air introduction pipe 44 as a combustion exhaust gas control valve. However, the present invention is not limited to this. The shut valve 45 may be provided in the combustion exhaust gas supply pipe 46 instead of the air introduction pipe 44. Further, shut valves may be provided in both the air introduction pipe 44 and the combustion exhaust gas supply pipe 46.

D8. Modification 8:
In the above embodiment, in the start control process of the fuel cell system, when the temperature Tfc of the fuel cell 10 is 0 (° C.) or less, the amount of air (oxygen) supplied to the cathode 16 of the fuel cell 10 is limited. However, the present invention is not limited to this. When the temperature Tfc of the fuel cell 10 is equal to or lower than a predetermined temperature, that is, a predetermined threshold value, the supply amount of air (oxygen) to the cathode 16 of the fuel cell 10 may be limited. This predetermined temperature can be arbitrarily set within a relatively low temperature range where a rapid temperature increase of the fuel cell 10 is required.

D9. Modification 9:
In the above embodiment, the temperature Tfc of the fuel cell 10 is detected by the temperature sensor 18 provided in the fuel cell 10, but the present invention is not limited to this. A temperature sensor that can indirectly detect the temperature Tfc of the fuel cell 10 may be provided in a portion other than the fuel cell 10.

DESCRIPTION OF SYMBOLS 100,100A, 100B, 100C ... Fuel cell system 10 ... Fuel cell 12 ... Electrolyte membrane 14 ... Anode 16 ... Cathode 18 ... Temperature sensor 20 ... Hydrogen supply piping 24 ... Exhaust pipe for anode off gas 30 ... Air supply piping 32 ... Air compressor 34 ... Cathode off gas exhaust pipe 36 ... Cathode off gas recirculation pipe 37 ... Recirculation pump 38 ... Shut valve 39 ... Three-way valve 40 ... Catalytic combustor 42 ... Hydrogen introduction pipe 43 ... Injector 44 ... Air introduction pipe 45 ... Shut valve 46 ... Combustion Exhaust gas supply pipe 50, 50A, 50B, 50C ... Control unit

Claims (5)

A fuel cell system,
A fuel cell;
A fuel gas supply unit for supplying fuel gas to the anode of the fuel cell;
An oxidant gas supply unit for supplying an oxidant gas to the cathode of the fuel cell;
A control unit,
The control unit, at startup when the temperature of the fuel cell is below a predetermined temperature,
The ratio of the supply amount of the oxidant gas to the cathode with respect to the supply amount of the fuel gas to the anode is the concentration of the fuel cell than at the start-up when the temperature of the fuel cell is higher than the predetermined temperature. Performing low temperature start-up control for controlling the oxidant gas supply unit so as to limit the overvoltage to be large and to repeatedly increase or decrease the supply amount of the oxidant gas to the cathode per unit time.
Fuel cell system. The fuel cell system according to claim 1, wherein
The fuel gas is hydrogen;
The oxidant gas is oxygen;
The oxidant gas supply unit is
An air supply pipe for supplying the oxygen-containing air to the cathode;
An air pump provided in the air supply pipe;
A cathode offgas recirculation section for recirculating the cathode offgas discharged from the cathode to the air supply pipe;
The control unit performs the control of the air pump and the cathode offgas recirculation unit as the low-temperature start-up control.
Fuel cell system. The fuel cell system according to claim 1, wherein
The fuel gas is hydrogen;
The oxidant gas is oxygen;
The oxidant gas supply unit is
An air supply pipe for supplying the oxygen-containing air to the cathode;
An air pump provided in the air supply pipe;
A combustor that burns hydrogen with oxygen;
A combustion exhaust gas supply pipe for supplying combustion exhaust gas exhausted from the combustor to the cathode;
A combustion exhaust gas control valve for controlling a supply amount of the combustion exhaust gas to the cathode,
The control unit controls the air pump, the combustor, and the combustion exhaust gas control valve as the low-temperature start-up control.
Fuel cell system. The fuel cell system according to claim 1, wherein
The fuel gas is hydrogen;
The oxidant gas is oxygen;
The oxidant gas supply unit is
An air supply pipe for supplying the oxygen-containing air to the cathode;
An air pump provided in the air supply pipe,
The control unit performs control of the air pump as the cold start control.
Fuel cell system. A startup control method for a fuel cell system, comprising:
The fuel cell system includes:
A fuel cell;
A fuel gas supply unit for supplying fuel gas to the anode of the fuel cell;
An oxidant gas supply unit for supplying an oxidant gas to the cathode of the fuel cell,
The activation control method includes:
Determining whether the temperature of the fuel cell is below a predetermined temperature;
When the temperature of the fuel cell is equal to or lower than a predetermined temperature, the ratio of the supply amount of the oxidant gas to the cathode with respect to the supply amount of the fuel gas to the anode is expressed as follows. The oxidant gas is limited so that the concentration overvoltage of the fuel cell becomes larger than that at the time of start-up when it is higher, and the supply amount of the oxidant gas to the cathode per unit time is repeatedly increased or decreased. A step of controlling the supply unit;
A start control method for a fuel cell system.

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