JP2017139182A - Fuel battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel battery system capable of suppressing variation in output voltage of a cell stack.SOLUTION: A fuel battery system includes a cell stack 9 having a plurality of fuel battery cells that generate electric power using fuel gas and oxidant gas, temperature adjustment means for adjusting the temperature of the cell stack 9, change indicator acquisition means 20 for acquiring an indicator representing a state of time-dependent change in power generation performance of the cell stack 9, and control means C for performing steady control of controlling the operation of the temperature adjustment means such that the temperature of the cell stack 9 is equal to a reference temperature after the time-dependent change state of the power generation performance acquired by the change indicator acquiring means 20 reaches a predetermined state, and performing initial control of controlling the operation of the temperature adjustment means so that the temperature of the cell stack 9 is higher than the reference temperature before the state of the time-dependent change in power generation performance obtained by the change indicator acquiring means 20 reaches the predetermined state.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system including a cell stack that generates power using fuel gas and oxidant gas.

In the solid oxide fuel cell, the power generation performance changes with the passage of power generation time. For example, the state of the parts constituting the cell stack of the solid oxide fuel cell may change depending on the temperature, and a unique change in power generation performance including a decrease in output voltage may appear. Such a change in the power generation performance of the cell stack appears when the parts begin to be exposed to high temperatures in the initial operation of the cell stack. For example, as the coating, such as a current collector, is exposed to high temperatures, the properties may change and its electrical resistance may change.
Alternatively, there may be a problem that the cell stack deteriorates with the lapse of power generation time, and the output voltage of the cell stack continues to decrease monotonously as the deterioration proceeds.
Even if the power generation performance changes due to any reason, it is possible to forcibly increase the output voltage of the cell stack by increasing the temperature of the cell stack.

  Japanese Patent Application Laid-Open No. H10-228667 describes that a temperature is limited when the cell stack is operating in consideration of deterioration of the cell stack at a high temperature. However, in Patent Document 1, the limit temperature is set to a higher value as the cumulative operation time of the cell stack becomes longer. That is, even if the deterioration of the cell stack progresses over time, the temperature of the cell stack is increased with the progress of the deterioration so that a voltage drop due to the deterioration does not appear.

Japanese Patent No. 5336818

As described in Patent Document 1, when the temperature of the cell stack is increased in order to suppress a decrease in the output voltage, the cell stack deteriorates due to the high temperature, and the durability of the cell stack decreases. There is.
Patent Document 1 deals with the problem that degradation occurs with the lapse of power generation time and the output voltage of the cell stack continues to decrease monotonously. It does not deal with the unusual changes in the power generation performance of the cell stack that appears when it is exposed. Therefore, a peculiar change in power generation performance including a decrease in output voltage appears in the initial operation of the cell stack.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell system capable of suppressing a decrease in durability while reducing a change in output voltage of a cell stack.

In order to achieve the above object, the fuel cell system according to the present invention includes a cell stack having a plurality of fuel cells that generate power using fuel gas and oxidant gas, and
Temperature adjusting means for adjusting the temperature of the cell stack;
Change index acquisition means for acquiring an index indicating a state of change over time of the power generation performance of the cell stack;
After the time-dependent change state of the power generation performance acquired by the change index acquisition unit reaches a predetermined state, steady control is performed to control the operation of the temperature adjustment unit so that the temperature of the cell stack becomes a reference temperature. And the temperature adjustment is performed so that the temperature of the cell stack is higher than the reference temperature before the time-dependent change state of the power generation performance acquired by the change index acquisition unit reaches a predetermined state. Control means for executing initial control for controlling the operation of the means.

According to the above characteristic configuration, by performing the initial control, the temperature of the cell stack is higher than the reference temperature before the time-dependent change state of the power generation performance including a decrease in the output voltage of the cell stack reaches a predetermined state. Temperature. Therefore, during the initial control, at least a decrease in the output voltage of the cell stack is mitigated.
In addition, the temperature of the cell stack is set to the reference temperature by the steady control performed following the initial control. That is, the state in which the temperature of the cell stack is high is limited during the initial control, and in the steady control, the temperature of the cell stack is set to the reference temperature.
Therefore, it is possible to provide a fuel cell system capable of suppressing a decrease in durability while relaxing a change in the output voltage of the cell stack.

  Another characteristic configuration of the fuel cell system according to the present invention is that, when the cumulative power generation period of the cell stack reaches a predetermined period, the change index acquisition unit causes the time-dependent change state of the power generation performance to reach a predetermined state. It is in the point to judge that.

  The tendency of the power generation performance of the cell stack to change over time may be considered to be the same if the cell stack of the same model, for example. Therefore, it is possible to acquire information related to the tendency of the power generation performance of the cell stack over time, for example, information related to the time-dependent change of the output voltage. Then, if the cumulative power generation period of the cell stack is counted, the information on the tendency of the power generation performance of the cell stack that has been acquired in advance is referred to, and the cell stack of the cell stack at the current cumulative power generation period is referred to. The state of power generation performance can be estimated. That is, the change index acquisition means can determine that the state of change in power generation performance over time has reached a predetermined state when the accumulated power generation period of the cell stack reaches a predetermined period.

  Yet another characteristic configuration of the fuel cell system according to the present invention is that the change index acquisition means determines that the state of change of the power generation performance with time when the state of change of the output voltage of the cell stack reaches a predetermined state. The point is that it is determined that a predetermined state has been reached.

  The tendency of the power generation performance of the cell stack to change over time may be considered to be the same if the cell stack of the same model, for example. Therefore, it is also possible to obtain information regarding the tendency of the output voltage of the cell stack over time. Then, if the output voltage of the cell stack is measured, the cell stack at the time of the output voltage of the cell stack at that time is referred to by referring to the previously acquired output voltage of the cell stack and the information on the tendency of power generation performance over time. The state of the power generation performance of the stack can be estimated. That is, the change index acquisition means can determine that the time-dependent change state of the power generation performance has reached the predetermined state when the time-dependent change state of the output voltage of the cell stack reaches the predetermined state.

  According to still another feature of the fuel cell system according to the present invention, in the initial control, the control unit gradually decreases the temperature of the cell stack while maintaining the temperature higher than the reference temperature by the temperature adjusting unit. The lowering process is executed.

  According to the above characteristic configuration, even when the output voltage of the cell stack increases unless initial control is performed, the initial control including this decrease processing is performed while performing the decrease processing, that is, While the output voltage of the cell stack is intentionally lowered, an increase in the output voltage of the cell stack is less likely to appear.

  In another feature of the fuel cell system according to the present invention, in the initial control, the control means gradually increases the temperature of the cell stack by the temperature adjusting means while maintaining a temperature higher than the reference temperature. And an increase process to be performed and a decrease process to gradually decrease the temperature of the cell stack while maintaining the temperature higher than the reference temperature by the temperature adjusting means after the increase process.

  According to the above characteristic configuration, even if the output voltage of the cell stack is suddenly decreased unless initial control is performed, the increase process is performed by performing the initial control including the increase process and the decrease process. During this period, that is, while the output voltage of the cell stack is intentionally increased, a rapid decrease in the output voltage is less likely to appear. In addition, by reducing the temperature of the cell stack, which has become higher than the reference voltage by the increasing process, by the decreasing process after the increasing process, it is possible to avoid the problem that the durability of the cell stack is decreased by the high temperature.

It is a figure which shows the structure of a fuel cell system. It is a figure which shows transition of the output voltage of a cell stack. It is a figure which shows transition of the control temperature of a cell stack. It is a figure which shows transition of the output voltage of a cell stack. It is a figure which shows transition of the control temperature of a cell stack.

<First Embodiment>
The configuration of the fuel cell system according to the first embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a fuel cell system. As shown in the figure, the fuel cell system includes an evaporator 6 that heats and evaporates the supplied water for evaporation, and reforms the supplied raw fuel gas using water vapor generated by the evaporator 6. A cell stack 9 having a reformer 7 that generates reformed gas containing hydrogen, and a plurality of fuel cells 8 that generate power using the reformed gas generated by the reformer 7 and supplied oxygen. A combustion section 10 that can give combustion heat generated by burning reformed gas and oxygen that have not been used in the cell stack 9 to the evaporator 6, the reformer 7, and the cell stack 9; With.

In the present embodiment, the raw fuel gas is supplied to the evaporator 6 through the raw fuel supply path 2. The raw fuel gas is a gas containing hydrocarbon, for example, city gas. The amount of raw fuel supplied to the evaporator 6 through the raw fuel supply path 2 is adjusted by a valve V 1 provided in the middle of the raw fuel supply path 2. Further, evaporation water is supplied to the evaporator 6 through the water supply path 3. The amount of evaporation water supplied to the evaporator 6 through the water supply path 3 is adjusted by a valve V <b> 2 provided in the middle of the water supply path 3. The operation of these valves V1 and V2 is controlled by the control means C. Combustion heat generated in the combustion unit 10 to be described later is transmitted to the evaporator 6, and evaporation water is evaporated by the heat. The evaporator 6 also mixes the generated water vapor and raw fuel gas.
Although not shown in FIG. 1, a desulfurizer for removing sulfur components (for example, an odorant contained in city gas) contained in the raw fuel gas before being supplied to the evaporator 6 is provided. It may be provided.

  The reformer 7 is supplied with a mixed gas of raw fuel gas and water vapor obtained by the evaporator 6. In the reformer 7, steam reforming of the raw fuel gas is performed to generate a reformed gas (a gas containing hydrogen as a main component). In addition, the heat of combustion generated in the combustion section 10 to be described later is transmitted to the reformer 7, and the reforming reaction is promoted by the heat. The reformed gas generated by the reformer 7 is supplied to the gas manifold 12 through the reformed gas supply path 11. A plurality of fuel cells 8 are connected to the gas manifold 12, and the reformed gas supplied to the gas manifold 12 is distributed to each fuel cell 8.

The cell stack 9 includes a fuel flow portion (not shown) through which the reformed gas generated by the reformer 7 flows and an air flow portion (FIG. 5) through which air (that is, an oxidant (oxygen)) flows. A plurality of solid oxide fuel cells 8 provided in a state of being electrically connected in series. Although not shown, the fuel battery cell 8 is configured in a solid oxide form having a solid electrolyte layer between the fuel electrode and the air electrode. In each fuel cell 8, the reformed gas flows upward through the fuel flow part, whereby the reformed gas is supplied to the entire fuel electrode, and the air flows upward through the air flow part. Air is supplied to the entire electrode, and the reformed gas and air are used for the power generation reaction. The exhaust reformed gas after being subjected to the power generation reaction is discharged from the upper outlet of the fuel flow passage, and the exhaust air after being subjected to the power generation reaction is discharged from the upper outlet of the air flow passage. Is done.
In the present embodiment, a cell temperature sensor Tc for measuring the temperature of the cell stack 9 is provided.

  Above the cell stack 9, off-gas (that is, exhaust reformed gas discharged from the fuel flow portion of each fuel cell 8 and exhaust air (that is, oxygen) discharged from the air flow portion) is burned. A combustion space (that is, the combustion part 10) is formed. That is, the combustion unit 10 is realized by the cell stack 9. In addition, the evaporator 6 and the reformer 7 are provided adjacent to the combustion space above the cell stack 9 that functions as the combustion unit 10. As a result, the evaporator 6, the reformer 7 and the cell stack 9 are heated by the combustion heat generated in the combustion unit 10.

  Although illustration is omitted, the cell stack 9 is electrically connected to an inverter as an electric load. The operation of the inverter is controlled by the control means C. That is, the control means C can change the output of the cell stack 9.

The evaporator 6, the reformer 7, the gas manifold 12, the cell stack 9, and the like described above are accommodated in the housing 1. Air (oxygen) is supplied into the housing 1 through the oxygen supply path 4. This oxygen is used for the power generation reaction in the fuel battery cell 8 and for the combustion of the exhaust reformed gas in the combustion unit 10. The amount of oxygen supplied into the housing 1 through the oxygen supply path 4 is adjusted by a blower B as a blower connected to the oxygen supply path 4. The operation of the blower B is controlled by the control means C.
The casing 1 is also connected to an exhaust path 5 for discharging the combustion exhaust gas generated in the combustion unit 10 to the outside.

  When supplying the electric power generated by such a fuel cell system to an electric load, the control means C adjusts the output of the cell stack 9 (for example, the output current), and at the same time, supplies an appropriate amount of raw fuel gas and oxygen and Evaporating water is supplied into the housing 1. That is, the control means C is used for adjusting the amount of hydrogen and oxygen consumed in the cell stack 9, adjusting the amount of hydrogen generated in the reformer 7, and combustion in the combustion unit 10. Adjust the amount of oxygen.

Further, the control means C can adjust the amount of off-gas burned in the combustion unit 10. For example, the control means C does not change the output of the cell stack 9, that is, does not change the amount of reformed gas and oxygen used in the cell stack 9, and the raw fuel gas, oxygen, and evaporating water Increasing or decreasing the supply rate increases or decreases the amount of off-gas. And the quantity of the combustion heat which generate | occur | produces in the combustion part 10 increases or decreases, and the temperature inside the housing | casing 1 (namely, temperature of the cell stack 9) rises or falls.
As described above, in this embodiment, the valve V1 for adjusting the supply amount of the raw fuel gas, the blower B for adjusting the supply amount of oxygen, and the valve V2 for adjusting the supply amount of water for evaporation adjust the temperature of the cell stack 9. Functions as a temperature adjusting means for adjusting.

Next, power generation control of the cell stack 9 performed by the control means C will be described.
FIG. 2 is a diagram showing the transition of the output voltage of the cell stack 9. In this example, it is assumed that power generation is started at time t0. The solid lines in FIG. 2 indicate the supply amount of raw fuel gas and the supply amount of oxygen while operating the temperature adjusting means so that the temperature of the cell stack 9 measured by the cell temperature sensor Tc is constant at the reference temperature Tr. And the transition of the output voltage of the cell stack 9 when the power generation operation is performed such that the output current of the cell stack 9 is constant while the supply amount of the evaporation water is maintained at a predetermined amount. As shown in the figure, the output voltage of the cell stack 9 gradually decreases with time. In particular, between time t0 and time t2, the output voltage decreases at a relatively large decrease rate. On the other hand, after time t2, the output voltage of the cell stack 9 decreases at a relatively low decrease rate. Note that the transition of the output voltage of the cell stack 9 shown in FIG. 2 is described for illustrative purposes only, and the transition of the actual output voltage of the cell stack 9 is not drawn correctly.

  In the present embodiment, the fuel cell system includes a change index acquisition unit 20 that acquires an index indicating a state of a time-dependent change in the power generation performance of the cell stack 9. The change tendency of the output voltage of the cell stack 9 as shown by the solid line in FIG. 2 may be considered to be the same for the cell stack 9 of the same model, for example. Therefore, information related to the transition of the output voltage of the cell stack 9 as indicated by a solid line in FIG. 2, that is, information indicating the relationship of the output voltage of the cell stack 9 with respect to the cumulative power generation period of the cell stack 9 is acquired and stored. It can also be stored in part M. Then, if the change index acquisition means 20 measures the accumulated power generation period of the cell stack 9, the change index acquisition means 20 refers to the information regarding the transition of the output voltage of the cell stack 9 as shown by the solid line in FIG. Thus, it is possible to know the state of the power generation performance of the cell stack 9 over time during the cumulative power generation period. In other words, the change index acquisition unit 20 determines that when the accumulated power generation period of the cell stack reaches a predetermined period, the time-dependent change state of the power generation performance reaches a predetermined state (for example, the power generation performance at time t2 in FIG. 2). Can be judged).

  The control means C controls the operation of the temperature adjusting means so that the temperature of the cell stack 9 becomes the reference temperature after the time-dependent change state of the power generation performance obtained by the change index obtaining means 20 reaches a predetermined state. The temperature control is performed so that the temperature of the cell stack 9 is higher than the reference temperature before the steady-state control is performed and the time-dependent change state of the power generation performance acquired by the change index acquisition unit 20 reaches a predetermined state. An initial control for controlling the operation of the means is executed. Specifically, in the present embodiment, the control means C performs initial control between time t0 and time t2 shown in FIG. 2, and performs steady control after time t2.

  FIG. 3 is a graph showing the transition of the control temperature of the cell stack 9. As shown in the figure, the control means C operates the temperature adjusting means to gradually increase the control temperature of the cell stack 9 measured by the cell temperature sensor Tc from the reference temperature Tr to the temperature T1 between time t0 and time t1. Raise. The period from time t0 to time t1 at this time corresponds to the period (between time t0 and time t1) in which the output voltage of the cell stack 9 decreases at a large decrease rate shown in FIG. Further, the control means C operates the temperature adjusting means to gradually lower the temperature of the cell stack 9 measured by the cell temperature sensor Tc from the temperature T1 to the reference temperature Tr between time t1 and time t2. The period from time t1 to time t2 corresponds to the period (between time t1 and time t2) in which the output voltage of the cell stack 9 decreases at a large decrease rate shown in FIG. Thus, in the initial control, the control means C gradually increases the temperature of the cell stack 9 while maintaining the temperature higher than the reference temperature by the temperature adjusting means, and the temperature adjusting means after the increasing process. A lowering process for gradually decreasing the temperature of the cell stack 9 while maintaining a temperature higher than the reference temperature is executed. Then, by controlling the control temperature of the cell stack 9 by operating the temperature adjusting means, the cell stack 9 that should have been operated at the output voltage as shown by the solid line in FIG. 2 is shown by the broken line in FIG. Initial control for operating at such an output voltage is performed.

  When the control means C performs the initial control to adjust the temperature of the cell stack 9 to the control temperature as shown in FIG. 3 between the time t0 and the time t2, the output voltage of the cell stack 9 is a broken line in FIG. It changes at the value shown in. When comparing the transition of the output voltage “without initial control” indicated by the solid line and the transition of the output voltage “with initial control” indicated by the broken line, the output voltage “with initial control” indicated by the broken line is more rapid. It turns out that it changed in the form close | similar to linear form, without showing a remarkable fall.

  Further, when it is determined by the change index obtaining unit 20 that the time t2 has come, the control unit C stops the initial control and starts the steady control. In the steady control, the control unit C controls the operation of the temperature adjusting unit so that the temperature of the cell stack 9 becomes the reference temperature Tr.

As described above, in the present embodiment, by performing the initial control, the temperature of the cell stack 9 is decreased before the state of power generation performance with time including the decrease in the output voltage of the cell stack 9 reaches a predetermined state. The temperature is higher than the reference temperature Tr. Therefore, during the initial control, at least a decrease in the output voltage of the cell stack 9 is alleviated. In particular, even when the output voltage of the cell stack 9 is rapidly decreased unless initial control is performed, the initial control including the increase process and the decrease process is performed to perform the increase process. That is, while the output voltage of the cell stack 9 is intentionally increased, a rapid decrease in the output voltage is less likely to appear. In addition, by reducing the temperature of the cell stack 9 that has become higher than the reference voltage by the increasing process by the decreasing process after the increasing process, the problem that the durability of the cell stack 9 decreases due to the high temperature is avoided. it can.
In addition, the temperature of the cell stack 9 is set to the reference temperature Tr by steady control performed following the initial control. That is, the state in which the temperature of the cell stack 9 is high is limited during the initial control, and in the steady control, the temperature of the cell stack 9 is set to the reference temperature Tr. Can be avoided.

Second Embodiment
The fuel cell system of the second embodiment is different from the above embodiment in the content of the initial control. The fuel cell system of the second embodiment will be described below, but the description of the same configuration as that of the above embodiment will be omitted.

  FIG. 4 is a diagram showing the transition of the output voltage of the cell stack 9. The solid lines in FIG. 4 indicate the supply amount of raw fuel gas and the supply amount of oxygen while operating the temperature adjusting means so that the temperature of the cell stack 9 measured by the cell temperature sensor Tc is constant at the reference temperature Tr. And the transition of the output voltage of the cell stack 9 when the power generation operation is performed such that the output current of the cell stack 9 is constant while the supply amount of the evaporation water is maintained at a predetermined amount. As shown in the figure, the output voltage decreases at a relatively large decrease rate from time t0 to time t3, and the output voltage increases from time t3 to time t4. After time t4, the output voltage of the cell stack 9 decreases at a relatively low decrease rate. Note that the transition of the output voltage of the cell stack 9 shown in FIG. 4 is described for illustrative purposes only, and the transition of the actual output voltage of the cell stack 9 is not drawn correctly.

  In the present embodiment, the fuel cell system includes a change index acquisition unit 20 that acquires an index indicating a state of a time-dependent change in the power generation performance of the cell stack 9. The change tendency of the output voltage of the cell stack 9 as shown by the solid line in FIG. 4 may be considered to be the same for the cell stack 9 of the same model. Therefore, information related to the transition of the output voltage of the cell stack 9 as indicated by a solid line in FIG. 4, that is, information indicating the relationship of the output voltage of the cell stack 9 to the cumulative power generation period of the cell stack 9 is acquired and stored in advance. It can also be stored in part M. Then, if the change index acquisition means 20 measures the accumulated power generation period of the cell stack 9, the change index acquisition means 20 refers to the information regarding the transition of the output voltage of the cell stack 9 as shown by the solid line in FIG. Thus, it is possible to know the state of the power generation performance of the cell stack 9 over time during the cumulative power generation period. That is, when the cumulative power generation period of the cell stack 9 reaches a predetermined period, the change index acquisition unit 20 determines that the power generation performance has changed over time (for example, the power generation performance at time t4 in FIG. 4). Judgment).

  The control means C controls the operation of the temperature adjusting means so that the temperature of the cell stack 9 becomes the reference temperature after the time-dependent change state of the power generation performance obtained by the change index obtaining means 20 reaches a predetermined state. The temperature control is performed so that the temperature of the cell stack 9 is higher than the reference temperature before the steady-state control is performed and the time-dependent change state of the power generation performance acquired by the change index acquisition unit 20 reaches a predetermined state. An initial control for controlling the operation of the means is executed. Specifically, in the present embodiment, the control means C performs initial control between time t0 and time t4 shown in FIG. 4, and performs steady control after time t4.

  FIG. 5 is a graph showing the transition of the control temperature of the cell stack 9. As shown in the figure, the control means C operates the temperature adjustment means so that the control temperature of the cell stack 9 measured by the cell temperature sensor Tc at a temperature T2 higher than the reference temperature Tr between time t0 and time t3. Keep constant. The period from time t0 to time t3 at this time corresponds to the period (between time t0 and time t3) in which the output voltage of the cell stack 9 decreases at a large decrease rate shown in FIG. Further, the control means C operates the temperature adjusting means to gradually lower the temperature of the cell stack 9 measured by the cell temperature sensor Tc from the temperature T2 to the reference temperature Tr between time t3 and time t4. The period from time t3 to time t4 corresponds to the period (between time t3 and time t4) in which the output voltage of the cell stack 9 increases as shown in FIG. Thus, in the initial control, the control unit C performs a lowering process that gradually decreases the temperature of the cell stack 9 while maintaining the temperature higher than the reference temperature by the temperature adjusting unit. Then, by controlling the control temperature of the cell stack 9 by operating the temperature adjusting means, the cell stack 9 that should have been operated at the output voltage as shown by the solid line in FIG. 4 is shown by the broken line in FIG. Initial control for operating at such an output voltage is performed.

  When the control means C performs the initial control for adjusting the temperature of the cell stack 9 to the control temperature as shown in FIG. 5 between the time t0 and the time t4, the output voltage of the cell stack 9 is a broken line in FIG. It changes at the value shown in. When comparing the transition of the output voltage “without initial control” indicated by the solid line and the transition of the output voltage “with initial control” indicated by the broken line, the output voltage “with initial control” indicated by the broken line is more rapid. It turns out that it changed in the form near a straight line, without showing an increase or decrease. As described above, even if the output voltage of the cell stack 9 increases unless initial control is performed, the initial control including the decrease processing is performed during the decrease processing, that is, the cell. While the output voltage of the stack 9 is intentionally lowered, an increase in the output voltage of the cell stack 9 is less likely to appear.

  Further, when it is determined by the change index obtaining unit 20 that the time t4 has come, the control unit C stops the initial control and starts the steady control. In the steady control, the control unit C controls the operation of the temperature adjusting unit so that the temperature of the cell stack 9 becomes the reference temperature Tr.

<Third Embodiment>
In the fuel cell system of the third embodiment, the function of the change index acquisition means 20 is different from that of the above embodiment. The fuel cell system of the third embodiment will be described below, but the description of the same configuration as that of the above embodiment will be omitted.

  In the present embodiment, the change index acquisition unit 20 constantly monitors the output voltage of the cell stack 9 during the initial control. This output voltage is constant at a predetermined value for the output current of the cell stack 9 in a state where the supply amount of raw fuel gas, the supply amount of oxygen, and the supply amount of evaporation water are maintained at predetermined amounts. It is a conversion value when it is assumed that such a power generation operation is performed. Then, the change index acquisition means 20 determines that the time-dependent change state of the power generation performance has reached the predetermined state when the time-dependent change state of the output voltage of the cell stack 9 reaches a predetermined state. For example, as shown in FIG. 4 of the second embodiment, in “no initial control”, the output voltage of the cell stack 9 starts to rise after the time t3. For this reason, if the control temperature of the cell stack 9 is maintained at the temperature T2, the output voltage in “with initial control” should also start to increase. Therefore, when the change index obtaining unit 20 maintains the control temperature of the cell stack 9 at the temperature T2, when it reaches a predetermined state in which the output voltage increases, there is a time to decrease the control temperature of the cell stack 9. Judge that it has arrived. Then, the control unit C performs a reduction process that starts to lower the control temperature of the cell stack 9 at a constant reduction rate based on the determination result of the change index acquisition unit 20. With this control, between time t3 and time t4, the increase in output voltage over time as indicated by “no initial control” cancels out the decrease in output voltage caused by the decrease in the control temperature of the cell stack 9. Thus, the output voltage in “with initial control” shows a constant value.

  Further, as shown in FIG. 4, in “no initial control”, the output voltage of the cell stack 9 starts decreasing after the time t4. Therefore, if the control temperature of the cell stack 9 is continuously decreased at a constant decrease rate, the decrease rate of the output voltage in “with initial control” should suddenly increase. For this reason, when the rate of decrease of the output voltage in “with initial control” increases beyond the set value, the control means C ends the initial control and starts the steady control similar to the above embodiment. Note that the control means C does not cause the control temperature of the cell stack 9 to be lower than the reference temperature Tr.

<Another embodiment>
<1>
In the said embodiment, although the specific example was given and demonstrated about the structure of the fuel cell system of this invention, the structure can be changed suitably.

<2>
In the above embodiment, an example is shown in which the temperature adjusting means is realized by the valve V1 for adjusting the supply amount of the raw fuel gas, the blower B for adjusting the supply amount of oxygen, and the valve V2 for adjusting the supply amount of evaporation water. However, other devices can also be used as temperature control means. For example, the temperature of the cell stack 9 can be adjusted using an electric heater or the like as temperature adjusting means.

<3>
Note that the configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with the configurations disclosed in other embodiments as long as no contradiction arises, and are disclosed in this specification. The embodiment described above is an exemplification, and the embodiment of the present invention is not limited thereto, and can be appropriately modified without departing from the object of the present invention.

  The fuel cell system of the present invention can be used to suppress fluctuations in the output voltage of the cell stack.

6 Evaporator 7 Reformer 8 Fuel cell 9 Cell stack 10 Combustion unit 20 Change index acquisition means C Control means

Claims (5)

A cell stack having a plurality of fuel cells that generate power using fuel gas and oxidant gas;
Temperature adjusting means for adjusting the temperature of the cell stack;
Change index acquisition means for acquiring an index indicating a state of change over time of the power generation performance of the cell stack;
After the time-dependent change state of the power generation performance acquired by the change index acquisition unit reaches a predetermined state, steady control is performed to control the operation of the temperature adjustment unit so that the temperature of the cell stack becomes a reference temperature. And the temperature adjustment is performed so that the temperature of the cell stack is higher than the reference temperature before the time-dependent change state of the power generation performance acquired by the change index acquisition unit reaches a predetermined state. And a control means for executing initial control for controlling the operation of the means.   2. The fuel cell system according to claim 1, wherein the change index acquisition unit determines that the time-dependent change state of the power generation performance has reached a predetermined state when a cumulative power generation period of the cell stack reaches a predetermined period.   2. The fuel according to claim 1, wherein the change index acquisition unit determines that the time-dependent change state of the power generation performance has reached a predetermined state when the time-change state of the output voltage of the cell stack reaches a predetermined state. Battery system.   The control unit according to any one of claims 1 to 3, wherein in the initial control, the temperature adjusting unit performs a lowering process for gradually decreasing the temperature of the cell stack while maintaining a temperature higher than the reference temperature. The fuel cell system according to item.   In the initial control, the control means gradually increases the temperature of the cell stack while maintaining a temperature higher than the reference temperature by the temperature adjusting means, and the temperature adjusting means after the increasing process. The fuel cell system according to any one of claims 1 to 3, wherein a reduction process for gradually decreasing the temperature of the cell stack while maintaining a temperature higher than the reference temperature is performed.

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