JP2007042436A - Fuel cell system and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain degradation of a fuel cell due to output fluctuation, and aim at improvement of durability of the fuel cell. <P>SOLUTION: In the fuel cell system provided with a fuel cell receiving fuel supply and oxidant supply and outputting power and a control unit 50 controlling an output of the fuel cell, the control unit 50 limits the number of fluctuation of output voltage based on an operation history of the fuel cell. That is, the control unit is provided with an operation history storage means 52 storing operation histories of the fuel cell, a fluctuation number limiting means 53 limiting the number of fluctuation of output voltage in accordance with the operation histories stored in the operation history storage means 52, and an output setting part 51 controlling an output of the fuel cell based on the number of fluctuation limited by the fluctuation number limiting means 53 and the requested output from outside. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a method for operating the same, and more particularly to a technique for improving the durability of a fuel cell.

In a fuel cell, if the output voltage changes, for example, switching between the rated output and 1/2 to 1/4 rated output (output fluctuation) is frequently performed, the durable life of the fuel cell is reduced. This decrease in durability life is caused by chemical deterioration due to changes in the water content of the electrolyte membrane in the membrane-electrode assembly (hereinafter referred to as MEA; Membrane Electrode Assembly) provided in the fuel cell, and the electrolyte membrane repeatedly expands and contracts. To occur. In addition, the activity of the catalyst is reduced (elution and aggregation), which also reduces the durability.
JP 2004-103397 A

  As a result of studies by the inventors of the present invention, it has been found that the decrease in the durable life of the fuel cell depends on the cumulative operation time and the number of output fluctuations. This is because the performance degradation due to the output fluctuation is added to the performance degradation accompanying the increase in the cumulative operation time in the steady operation with the constant output. Patent Document 1 describes a technique for providing a fixed upper limit value for the output of a fuel cell. However, since the upper limit value is fixed in this technique, even when the deterioration has progressed, it deteriorates at the same speed. May go on.

  The present invention has been made in view of the above circumstances, and provides a fuel cell system capable of suppressing deterioration of the fuel cell due to output fluctuation and improving the durability of the fuel cell, and an operating method thereof. The purpose is to do.

  In the present invention, the following means are employed in order to solve the above problems. That is, in a fuel cell system including a fuel cell that generates power upon receipt of a fuel supply and an oxidant supply, and a control device that controls the output of the fuel cell, the control device includes an operation history of the fuel cell. Based on this, the number of fluctuations per unit time of the output is limited.

  According to such a configuration, a fixed upper limit value is not provided for the output of the fuel cell, but a limit is imposed on the number of times that output fluctuation is permitted. Therefore, deterioration of the fuel cell due to output fluctuation can be suppressed. “Per unit time” can be set to an appropriate time interval such as per day or per predetermined time.

  The control device may limit the number of output voltage fluctuations.

  The control device includes an operation history storage unit that stores an operation history of the fuel cell, a fluctuation number limiting unit that limits the number of fluctuations of the output according to the operation history stored in the operation history storage unit, It is good also as a structure provided with the output setting part which sets the output target value of the said fuel cell based on the said frequency | count of fluctuation | variation restrict | limited by the fluctuation | variation frequency limiting means and the request | requirement from the outside.

  According to such a configuration, the durable life is determined based on the operation history of the fuel cell, for example, the cumulative number of output fluctuations. When the durable life is shorter than the standard, the number of fluctuations of the fuel cell is restricted by the fluctuation number limiting means, thereby ensuring the durable life.

  The operation history stored in the operation history storage means includes at least the cumulative fluctuation count of the output, and the fluctuation count limit means increases the cumulative fluctuation count, so that the fluctuation count limit value (in other words, The upper limit value) may be reduced.

  As the fuel cell continues to operate, the number of cumulative fluctuations in output increases, and as a result, the deterioration of the fuel cell progresses and the service life decreases. According to the above configuration, as the number of cumulative fluctuations increases, per unit time The number of output fluctuations allowed is reduced. For example, the number of output fluctuations is reduced from 2 to 1 per day.

  Depending on the operating conditions of the fuel cell, there may be a predetermined correlation (composite relationship) between the cumulative number of fluctuations and the cumulative operating time. You may correct | amend according to accumulated operation time.

  In a predetermined case, a fluctuation number changing means for changing the cumulative fluctuation number to a predetermined value may be provided.

  For example, when the maintenance of the fuel cell is performed (predetermined case), the durability life is extended. Therefore, according to the above configuration, the accumulated fluctuation number of the output stored in the operation history storage unit is initialized (returned to a predetermined value). This avoids unnecessary output restrictions. In addition to initializing the cumulative fluctuation count, the cumulative fluctuation count may be returned to a predetermined value according to the cumulative fluctuation count.

  When the operation history storage means is configured to be able to store not only the cumulative fluctuation count but also the cumulative operation time, the cumulative fluctuation count is returned to a predetermined value according to the cumulative fluctuation count and / or the cumulative operation time. You may do it.

  The fluctuation number limiting means may be configured to permit the increase in the output only during a time zone in which the externally requested output is higher than a predetermined value and to limit the output fluctuation in other time zones.

  According to such a configuration, for example, a time measuring unit is provided, and power consumption is increased, for example, in the morning and evening, so that a time zone in which rated power generation is necessary is determined based on the past operation history. Thereby, an optimal restriction pattern can be obtained according to the use environment of the fuel cell system.

  In this case, the priority order may be set higher in a time zone in which the output request is high, and the limit on the number of fluctuations may be tightened according to the priority order as the cumulative number of output fluctuations increases. That is, when the service life is reduced, the increase in output may be limited even in a time zone with a low priority.

  An operation method of a fuel cell system according to the present invention is a fuel cell system operation method comprising: a fuel cell that generates power by receiving fuel supply and oxidant supply; and a control device that controls the output of the fuel cell. The number of fluctuations per unit time of the output is limited based on the operation history of the fuel cell.

  According to such a configuration, it is possible to limit the output fluctuation per unit time to a predetermined number of times when there is a possibility that the durable life of the fuel cell is shortened or when the deterioration is advanced. “Per unit time” can be set to an appropriate time interval such as per day or per predetermined time.

  According to the present invention, deterioration of the fuel cell due to output fluctuation can be suppressed, and the durability of the fuel cell can be improved. Further, when the deterioration of the fuel cell is advanced, the durability can be further effectively improved by tightening the restriction on the output fluctuation.

Next, an embodiment of a fuel cell system according to the present invention will be described. The fuel cell system in the present embodiment is an example in which the fuel cell is applied as a stationary power generation system that is used as a power generation facility for buildings (housing, buildings, etc.). However, the fuel cell system of the present invention is not limited to such an application example, but can be applied to any moving body such as a vehicle, a ship, an aircraft, a train, and a walking robot.
In the present embodiment, the oxidizing gas and the fuel gas are used as the oxidant and the fuel, respectively, but the present invention is not limited to this. For example, liquid fuel such as methanol can be used as the fuel. Furthermore, in the present embodiment, air is used as the oxidizing gas and the reformed gas is used as the fuel gas, but the present invention is not limited to this. For example, hydrogen gas or hydrogen-containing gas may be used as the fuel gas.

  As shown in FIG. 1, air (outside air) as an oxidizing gas is humidified by a humidifier 2 from a stack air supply system 1 including an air pump, an air filter, and the like, and then supplied to a fuel cell (FC stack) 20. . The air off-gas (remaining air) discharged from the fuel cell 20 is exhausted after being recovered by the first condenser 11.

  On the other hand, the reformed gas (hydrogen-containing gas) as the fuel gas supplied to the fuel cell 20 is the city gas (such as 13A) supplied as the raw fuel gas to the reformer 32 of the reformer 30. After being converted to hydrogen-containing gas in the unit 32, the gas is generated through the shift unit 33 and the CO purification unit 34 of the reformer 30. The reformed gas off-gas (residual gas) from the fuel cell 20 is recovered by the second condenser 12 and then introduced into the combustion section 31 of the reformer 30 and combusted to be used as a heat source for the reforming reaction. . The combustion exhaust gas is exhausted after being recovered by the third condenser 13.

  In addition, the stack cooling water is circulated in the fuel cell 20, and the stack cooling water absorbs heat accompanying power generation, and the absorbed heat is transmitted to the heat exchanger 40.

  Hot water from the hot water storage tank 15 is circulated in the first condenser 11 to the third condenser 13 and the heat exchanger 40, absorbs the amount of heat from each, and the hot water is stored in the hot water storage tank 15. This hot water is used for hot water supply. The recovered water obtained by the first condenser 11 to the third condenser 13 is returned to the reforming water supply system 36 and used for the reforming reaction in the reformer 30 as shown by the broken line in FIG. The

  Since the electric output generated by the fuel cell 20 is a direct current, it is converted into an alternating current by the inverter 21 and output. The fuel cell 20 is configured as a fuel cell stack (FC stack) in which a required number of single cells are stacked. The single cell is composed of an MEA and a pair of separators that sandwich the MEA, and has a laminated form as a whole. The separator is made of a gas-impermeable conductive material, and a gas flow path for oxidizing gas or fuel gas is formed on the surface facing the MEA side.

  The MEA includes an electrolyte membrane made of an ion exchange membrane made of a polymer material and a pair of electrodes sandwiching the electrolyte membrane from both sides. The electrode is made of, for example, a porous carbon material bound with a catalyst such as platinum. One electrode is supplied with an oxidizing gas such as air, and the other electrode is supplied with a fuel gas such as a reformed gas.

  The two gases cause an electrochemical reaction in the MEA 11 and the electric power generated by the fuel cell 20 is supplied to a building (house, building, etc.).

  The control unit 50 receives control information from an external request load (not shown) and sensors (not shown) in each part of the fuel cell system, and controls the operation of each part in the system. The control unit 50 is configured by a control computer system (not shown). This control computer system has a known configuration such as a CPU, ROM, RAM, HDD, input / output interface, and display, and is configured by a commercially available control computer system.

  A block diagram of the control unit 50 is shown in FIG. The control unit 50 includes an output setting unit 51 that sets an output target value for the fuel cell 20, an operation history storage unit 52 that stores an operation history of the fuel cell 20, and the fuel cell 20 stored in the operation history storage unit 52. The fluctuation number limiting means 53 for limiting the number of fluctuations of the output voltage, the fluctuation number changing means 54 for changing the cumulative fluctuation number of the output voltage to a predetermined value, and the required output from the outside increase. High load time zone estimating means 55 for estimating the time zone.

  The output setting unit 51 sets the output target value of the fuel cell 20 based on the number of fluctuations restricted by the fluctuation number restriction means 53 and the output requested from the outside. Specifically, the power generation amount of the fuel cell 20 is switched between a first predetermined output and a second predetermined output lower than the first predetermined output. This switching is called output fluctuation. For example, the first predetermined output can be a rated output of 1 kW, and the second predetermined output can be a 1/2 to 1/4 rated output.

  The operation history storage means 52 stores the cumulative fluctuation number of the output voltage of the fuel cell 20, that is, the cumulative number of times of switching from the second predetermined output to the first predetermined output or vice versa, and the cumulative operating time.

  The fluctuation number limiting means 53 obtains the number of fluctuations of the output voltage allowed per day based on the cumulative fluctuation number stored in the operation history storage means 52. The durable life is calculated based on the correlation between the number of fluctuations per day and the durable life shown in FIG. It should be noted that the correlation shown in FIG.

  When it is determined that the durable life is shorter than the standard (for example, 10,000 hours or less), the control is switched to the control (restriction mode) in which the number of fluctuations per day is suppressed, so that the final life is lengthened. For example, the lifetime is set to about 25,000 hours. Specifically, the fluctuation number limiting means 53 switches the power generation of the fuel cell 20 by the output setting unit 51 to the following limiting mode.

  In the limit mode, for example, the output voltage is controlled with a limit pattern in which output fluctuation to a 1 kW rated output (first predetermined output) is limited to once in the morning and once in the night. This is shown in FIG. In the example of the figure, what is indicated by a symbol A is an example of power consumption in a house where a fuel cell is installed, and a symbol B is a restriction pattern.

  In the limit pattern, the rated power generation of 1 kW (first predetermined output) is performed only once each morning and night, which is a time zone in which power consumption increases, and the second predetermined output is 1/2 to 1 at other times. Electric power is generated at / 4 rated output (250 to 500 W). In addition, it will be in a stop state at night. The restriction pattern may be a preset pattern, but can be automatically set based on the driving pattern history as follows.

  The high load time zone estimation means 55 provided with a time measuring means determines a time zone (high output request time zone) in which the power consumption increases and the rated power generation is necessary based on the past power generation history or power consumption. In the example of FIG. 4, power consumption increases in the morning and at night, but may differ from the power consumption pattern of FIG. 4 depending on the installation environment. As in this example, the high load time zone estimation means 55 estimates the high output request time zone, so that an optimal control pattern can be obtained according to the use environment of the fuel cell system.

  As the operation is continued, the cumulative number of fluctuations of the output voltage or the cumulative operation time of the fuel cell 20 increases, whereby the deterioration of the fuel cell 20 progresses and the life is shortened. For this reason, the fluctuation number limiting means 53 further restricts the fluctuation number when the life is reduced. For example, in the limiting pattern of FIG. 4, the rated output is allowed twice per day, but this is reduced to one.

  In order to realize this, the high load time zone estimation means 55 sets a high priority in the high output request time zone in which a high output is required, and the rated output priority is low when the life is reduced. The rated output is limited even during the high output demand period. Note that the power exceeding the limit pattern (power consumption exceeding the shaded portion of the limit pattern) is covered by separately supplied commercial power.

  When the maintenance of the fuel cell 20 is performed, the endurance life of the fuel cell 20 is extended. Therefore, the accumulated number of fluctuations and the accumulated operation time of the output voltage stored in the operation history storage unit 52 are initialized by the variation number changing unit 54. Or return to a predetermined value. By performing such initialization or returning it to a predetermined value, unnecessary output voltage limitation is avoided. Note that the cumulative fluctuation count may be returned to a predetermined value according to the cumulative fluctuation count or / and the cumulative operation time.

  As described above, according to the fuel cell system of the present embodiment, deterioration of the fuel cell 20 due to output fluctuation can be suppressed, and the durability of the fuel cell 20 can be improved. Particularly, when the deterioration of the fuel cell 20 has progressed, the durability can be further effectively improved by tightening the restriction on the number of fluctuations.

1 is a system configuration diagram schematically illustrating an embodiment of a fuel cell system according to the present invention. It is the block diagram which showed the structure of the control unit with which the fuel cell system is provided. It is the figure which showed correlation with the frequency | count of fluctuation | variation of the output voltage per day, and a durable life. It is the figure shown about an example of the power consumption in the household in which the fuel cell was installed, and the power generation pattern (limitation pattern) of a fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Fuel cell, 50 ... Control unit, 51 ... Output setting part, 52 ... Operation history memory | storage means, 53 ... Variation frequency limit means, 54 ... Variation frequency change means, 55 ... High load time zone estimation means,

Claims (7)

In a fuel cell system comprising: a fuel cell that generates power by receiving fuel supply and oxidant supply; and a control device that controls the output of the fuel cell.
The control device limits the number of fluctuations per unit time of the output based on an operation history of the fuel cell.   The fuel cell system according to claim 1, wherein the control device limits the number of times the output voltage fluctuates.   The control device includes an operation history storage unit that stores an operation history of the fuel cell, a fluctuation number limiting unit that limits the number of fluctuations of the output according to the operation history stored in the operation history storage unit, 3. An output setting unit that sets an output target value of the fuel cell based on the number of fluctuations limited by a fluctuation number limiting means and an externally requested output. The fuel cell system described. The driving history stored in the driving history storage means includes at least the cumulative number of fluctuations of the output,
4. The fuel cell system according to claim 3, wherein the fluctuation number limiting means decreases the limit value of the fluctuation number as the cumulative fluctuation number increases.   5. The fuel cell system according to claim 4, further comprising a fluctuation number changing means for changing the cumulative number of fluctuations to a predetermined value in a predetermined case.   The fluctuation number limiting means permits an increase in the output only during a time zone in which a request output from the outside is higher than a predetermined value, and limits the output fluctuation in other time zones. Item 6. The fuel cell system according to any one of Items 3 to 5. In a method of operating a fuel cell system comprising: a fuel cell that generates power upon receipt of a fuel supply and an oxidant supply; and a control device that controls the output of the fuel cell.
An operation method of a fuel cell system, wherein the number of fluctuations per unit time of the output is limited based on an operation history of the fuel cell.

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