Fuel cell power generation system

Abstract

To suppress an increase in the failure rate of cell stacks and other metal parts due to fatigue and deterioration due to repeated and accumulated rapid temperature changes due to sudden fluctuations in power output in a fuel cell while ensuring good response and coverage to a power load.SOLUTION: A fuel cell power generation system includes a fuel cell portion 6 having a cell stack 6B formed by stacking a plurality of solid oxide fuel cells 6A, and outputting the electromotive force of the cell stack 6B as generated power, a power generation output control portion 9A that controls the power generation output of the fuel cell portion 6 according to the power load, and a counting portion 9B that counts sudden fluctuations in the power generation output that meet a predetermined counting condition among the fluctuations in the power generation output of the fuel cell portion 6. The power generation output control portion 9A executes output fluctuation restriction control to limit the power generation output fluctuation of the fuel cell portion 6 when the count state by the counting portion 9B satisfies a predetermined output fluctuation restriction condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell power generation system having a cell stack made up of multiple stacked solid oxide fuel cell cells that generate electricity through an electrochemical reaction between reformed fuel gas obtained by reforming fuel gas in a reforming section and an oxidant gas, and is equipped with a fuel cell section that outputs the electromotive force of the cell stack as generated electricity. [Background technology]

[0002] One such type of fuel cell power generation system is equipped with an output control unit that controls the output of the fuel cell unit in accordance with the power load, thereby performing power load following control (see, for example, Patent Document 1). In such a fuel cell power generation system, the output control unit changes the amount of fuel gas supplied to the reforming unit when varying the power generation output of the fuel cell unit in accordance with the power load, and the temperature of the cell stack and other metal parts also changes as the amount of fuel gas supplied changes.

[0003] For example, when the power generation output of the fuel cell section is to be high, the amount of fuel gas supplied to the reforming section is increased, thereby increasing the amount of reforming in the reforming section and the amount of reformed fuel gas supplied to the cell stack, which in turn increases the temperature of the cell stack and other metal parts. On the other hand, when the power generation output of the fuel cell section is set to low, the amount of fuel gas supplied to the reforming section is reduced, thereby reducing the amount of reforming in the reforming section and the amount of reformed fuel gas supplied to the cell stack, which results in a drop in the temperature of the cell stack and other metal parts in the fuel cell section. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-018884 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a sudden change in power load occurs in the home, for example, when a high-load appliance such as a microwave oven or electric kettle is turned on and off, the fuel cell unit will respond by suddenly fluctuating between low and high power outputs, causing a sudden change in temperature in the cell stack and other metal parts, which will be subjected to large thermal stresses. There is a concern that the failure rate of the cell stack and other metal parts will increase due to fatigue and deterioration caused by the repeated and accumulated large thermal stresses.

[0006] To prevent such adverse effects, it is possible to slow down the rate at which the fuel cell unit's power output fluctuates in advance or to keep the fuel cell unit's power output constant. However, the former approach has the disadvantage of reducing responsiveness to the power load, while the latter approach has the disadvantage of reducing the power load coverage rate (the range of power load that can be handled), resulting in increased utility costs.

[0007] In view of this situation, the main objective of the present invention is to provide a fuel cell power generation system that can suppress an increase in the failure rate of the cell stack and other metal parts due to fatigue and deterioration caused by repeated and accumulated sudden temperature changes associated with sudden fluctuations in power generation output in the fuel cell section, while ensuring good responsiveness and coverage rate to power loads. [Means for solving the problem]

[0008] The first characteristic configuration of the present invention is a fuel cell unit having a cell stack formed by stacking a plurality of solid oxide fuel cell units that generate electric power by an electrochemical reaction between an oxidant gas and a reformed fuel gas obtained by reforming a fuel gas in a reforming unit, and that outputs the electromotive force of the cell stack as generated electric power; a power generation output control unit that controls the power generation output of the fuel cell unit in accordance with the power load; a counting unit that counts sudden power generation output fluctuations that satisfy a predetermined counting condition among the power generation output fluctuations of the fuel cell unit, The power generation output control unit executes output fluctuation limiting control to limit power generation output fluctuations of the fuel cell unit when the counting state by the counting unit satisfies a predetermined output fluctuation limiting condition.

[0009] According to this configuration, the counting unit counts sudden power output fluctuations that satisfy predetermined counting conditions among the power output fluctuations of the fuel cell unit. If the counting state of the counting unit does not satisfy the predetermined output fluctuation limiting condition, the power output fluctuations of the fuel cell unit are not limited, ensuring good responsiveness and coverage rate to the power load. If the counting state of the counting unit satisfies the predetermined output fluctuation limiting condition, the power output control unit executes output fluctuation limiting control to limit the power output fluctuations of the fuel cell unit, thereby mitigating fatigue and deterioration of the cell stack and other metals due to repeated and accumulated sudden temperature changes associated with sudden power output fluctuations of the fuel cell unit. Therefore, it is possible to provide a fuel cell power generation system that can suppress an increase in the failure rate of the cell stack and other metal parts due to fatigue and deterioration caused by repeated and accumulated sudden temperature changes associated with sudden fluctuations in power generation output in the fuel cell section, while ensuring good responsiveness and coverage rate to power loads.

[0010] A second characteristic configuration of the present invention is that the counting condition is a condition that the fluctuation in power generation output is equal to or greater than a set fluctuation amount within a set time period.

[0011] According to this configuration, the counting unit can count output fluctuations that are greater than or equal to a set fluctuation amount within a set time period, which is a period when fatigue of the cell stack and other metals is greatly affected, as abrupt fluctuations in power generation output that satisfy the counting condition, thereby enabling the output fluctuation limiting control by the output fluctuation control unit to be executed at a more effective timing. Furthermore, if the set time period is fixed, it is possible to determine whether the counting condition is satisfied based solely on the set fluctuation amount, making it easy to determine abrupt fluctuations in power generation output.

[0012] A third characteristic configuration of the present invention is that the output fluctuation limiting condition is an occurrence number condition that the number of times counted by the counting unit reaches a set number of times.

[0013] According to this configuration, when the number of occurrences of sudden power generation output fluctuations that satisfy the counting conditions reaches a set number, such as a design upper limit number at which a high failure rate is expected, output fluctuation limiting control can be executed to suppress power generation output fluctuations in the fuel cell unit, thereby preventing failure of the cell stack or other metal parts after the set number of occurrences has been exceeded.

[0014] A fourth characteristic configuration of the present invention is that the output fluctuation limiting condition is an occurrence pace condition that the pace counted by the counting section is faster than a set pace.

[0015] According to this configuration, if the rate at which sudden fluctuations in power generation output that satisfy the counting conditions occur is faster than the set rate at which the failure rate is expected to increase, for example, by exceeding the design upper limit number of times before the design service life has elapsed, output fluctuation limiting control can be executed to suppress fluctuations in power generation output from the fuel cell unit, thereby preventing the cell stack and other metal parts from failing before the design service life has elapsed.

[0016] A fifth characteristic configuration of the present invention is that the power generation output control unit cancels the output fluctuation limit control when the generation pace condition is satisfied and then the cancel condition is satisfied after executing the output fluctuation limit control.

[0017] According to this configuration, when the output fluctuation limiting control is executed after the occurrence pace condition is satisfied, and the release condition is satisfied, for example, when the rate of occurrence of sudden power generation output fluctuations falls below the set pace or a predetermined period of time has passed during which fatigue of the cell stack and other metal parts is alleviated, the output limiting control unit can release the output fluctuation limiting control and return the fuel cell unit to a normal state with good responsiveness and coverage rate to the power generation load.

[0018] A sixth characteristic feature of the present invention is that the output fluctuation limiting control is fluctuation speed limiting control that limits the power generation output fluctuation speed of the fuel cell unit to a speed slower than normal.

[0019] According to this configuration, the output limiting control unit can execute the above-mentioned fluctuation speed limiting control to lengthen the time required for the power generation output fluctuation of the fuel cell unit and make the temperature gradient gentler, thereby suppressing the occurrence of sudden power generation output fluctuations while suppressing a decrease in the coverage rate for the power load due to limiting the power generation output fluctuation range.

[0020] A seventh characteristic feature of the present invention is that the output fluctuation limiting control is a fluctuation range limiting control that limits the fluctuation range of the power generation output of the fuel cell unit to a range smaller than normal.

[0021] According to this configuration, the power generation output limiting control unit can reduce the range of power generation output fluctuations of the fuel cell unit by executing the above-mentioned fluctuation range limiting control, and can suppress the occurrence of sudden power generation output fluctuations while preventing a deterioration in responsiveness to power loads due to limiting the output fluctuation rate. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a fuel cell power generation system. [Figure 2] 1 is a flowchart showing the flow of counting processing executed by a counting unit; [Figure 3] 1 is a flowchart showing a flow of control executed by a power generation output control unit. DETAILED DESCRIPTION OF THE INVENTION

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fuel cell power generation system according to an embodiment of the present invention will be described with reference to the accompanying drawings. As shown in Figure 1, this fuel cell power generation system is equipped with a desulfurization unit 1 that desulfurizes hydrocarbon fuel gas such as city gas, a vaporization unit 3 that heats reforming water supplied from a reforming water tank 2 to generate steam, a reforming unit 4 that uses the steam generated in the vaporization unit 3 to steam reform the fuel gas desulfurized in the desulfurization unit 1, and a fuel cell unit 6 that generates power using the reformed fuel gas obtained in the reforming unit 4 and oxidant gas (oxygen gas) in the air supplied from a blower 5 (an example of an air supply amount adjustment means).

[0024] This fuel cell power generation system also includes a combustion section 7 that mixes the exhaust reformed fuel gas discharged from the fuel cell section 6 after the power generation reaction with exhaust air and burns the combustible components in the exhaust reformed fuel gas, a power conversion section 8 that converts the power generation output of the fuel cell section 6 to the same voltage and frequency as the power received from the commercial power source 17, and a control device 9 that controls the operating state of each section.

[0025] This fuel cell power generation system is configured such that the vaporization section 3, reforming section 4, fuel cell section 6, and combustion section 7 are housed within a storage container 10, and the vaporization section 3 performs a process of generating steam using the combustion heat generated by combustion in the combustion section 7, while the reforming section 4 performs a process of reforming fuel gas using the combustion heat generated by combustion in the combustion section 7.

[0026] Fuel gas is supplied to the desulfurization unit 1 through a fuel gas supply path L1 by operation of a boost pump 11 (an example of a fuel gas supply amount adjusting means). Reforming water in the reforming water tank 2 is supplied to the vaporization unit 3 through a reforming water supply path L2 by operation of a reforming water pump 12 (an example of a reforming water supply amount adjusting means). A downstream portion of the fuel gas supply path L1 from the desulfurization unit 1 merges with a midpoint of the reforming water supply path L2, and the reforming water and fuel gas merged outside the storage container 10 are supplied to the vaporization unit 3 provided inside the storage container 10. The fuel gas containing water vapor produced in the vaporization unit 3 is supplied through a water vapor-containing fuel gas supply path L3 to the reforming unit 4, where the fuel gas is steam reformed to produce a reformed fuel gas mainly composed of hydrogen gas. The reformed fuel gas produced in the reforming unit 4 is supplied to the fuel cell unit 6 through a reformed fuel gas supply path L4.

[0027] The fuel cell section 6 has a cell stack 6B made up of a plurality of stacked solid oxide fuel cell cells 6A that generate electricity through an electrochemical reaction between the reformed fuel gas and the oxidant gas, and is configured to output the electromotive force of the cell stack 6B as generated power. The plurality of fuel cell cells 6A are provided in the cell stack 6B in a state where they are electrically connected in series.

[0028] The fuel cell 6A is provided with a fuel conduit 6a through which the reformed fuel gas flows and an air conduit 6b through which the air flows, and although not shown, a solid electrolyte layer is provided between the fuel electrode and the air electrode, and the reformed fuel gas flows through the fuel conduit 6a to supply the reformed fuel gas to the fuel electrode, and the air flows through the air conduit 6b to supply the air to the air electrode. The cell stack 6B is arranged in the storage container 10 with multiple fuel cell cells 6A arranged in an orientation such that the reformed fuel gas outlet of the fuel conduit 6a and the air outlet of the air conduit 6b face upward.

[0029] 1, the fuel cell section 6 is provided with a gas manifold 6C that receives reformed fuel gas supplied from the reforming section 4 through the reformed fuel gas supply path L4, and the multiple fuel cell units 6A are arranged above the gas manifold 6C, with the gas manifold 6C connected to gas inlets at the lower ends of the fuel flow sections 6a of the multiple fuel cell units 6A. The reformed fuel gas supplied to the gas manifold 6C is supplied to the fuel flow sections 6a of each of the multiple fuel cell units 6A from the gas inlets at the lower ends, flows through each fuel flow section 6a from bottom to top, and is used in the power generation reaction, and the waste reformed fuel gas after being used in the power generation reaction is discharged from the reformed fuel gas discharge port at the top end.

[0030] The storage container 10 is provided with an air inlet 13, and an air supply path L5 is connected to the air inlet 13. By operating a blower 5 (an example of an air supply amount adjusting means), air is supplied into the storage container 10 through the air supply path L5. An air supply hole (not shown) that connects the inside of the storage container 10 to the inside of the air flow section 6b is provided near the lower end of the air flow section 6b in each of the plurality of fuel cell cells 6A. Air from inside the storage container 10 is supplied to the air flow section 6b of each of the plurality of fuel cell cells 6A through this air supply hole, flows through each air flow section 6b from the bottom to the top, and is used for the power generation reaction, and the exhaust air after being used for the power generation reaction is discharged from the air outlet at the top end.

[0031] Within the storage container 10, the space between the cell stack 6B, which is made up of a plurality of stacked fuel cells 6A, and the reforming section 4 arranged above the cell stack 6B, is configured as a combustion section 7 that combusts the exhaust reformed fuel gas and exhaust air discharged from the upper ends of the fuel cells 6A. The combustion heat generated by the combustion of combustible components in the exhaust reformed fuel gas in the combustion section 7 is used to generate steam in the vaporization section 3, and is used for the reforming process in the reforming section 4.

[0032] The storage container 10 has an exhaust section 14 formed on the bottom surface or the like, which exhausts the combustion gas generated in the combustion section 7 to the outside. The storage container 10 is provided with a combustion catalyst section 15 (e.g., a platinum-based catalyst) which removes carbon monoxide gas from the combustion exhaust gas exhausted to the outside from the exhaust section 14.

[0033] The power conversion unit 8 is an inverter or the like electrically connected to the cell stack 6B, and can convert the power output of the cell stack 6B into power of a desired voltage, frequency, and phase and output it. Then, power is supplied to a power load device (not shown) via a power supply line L6 connected to the power conversion unit 8. The power supply line L6 is connected to a commercial power source 17, and power is supplied to the power load device from at least one of the commercial power source 17 and the cell stack 6B.

[0034] The control device 9 is provided with a power generation output control section 9A that controls the power generation output of the fuel cell section 6. This power generation output control section 9A performs power load following control, which controls the power generation output of the fuel cell section 6 in accordance with the power load, as normal power generation output control during operation after startup.

[0035] Specifically, the power generation output control unit 9A acquires the measurement results of the power load measuring unit 16 provided on the power supply line L6, and controls the operation of the boost pump 11, the reforming water pump 12, and the blower 5 according to the acquired measurement results to adjust the amount of fuel gas and reforming water supplied to the vaporization unit 3 and the amount of air supplied into the storage container 10, thereby adjusting the amount of reforming in the reforming unit 4 and the amount of reforming fuel gas and oxidant gas supplied to the cell stack 6B, thereby adjusting the power generation output of the fuel cell unit 6.

[0036] When increasing the power generation output, the power generation output control unit 9A controls the operation of the boost pump 11, the reforming water pump 12, and the blower 5 in accordance with the power load to increase the amount of fuel gas and reforming water supplied to the vaporization unit 3 and the amount of air supplied into the storage container 10, thereby increasing the amount of reforming in the reforming unit 4, the amount of reformed fuel gas supplied to the cell stack 6B, and the amount of oxidant gas supplied. In this case, the temperature of the cell stack 6B and other metal parts rises.

[0037] When reducing the power generation output, the power generation output control unit 9A controls the operation of the boost pump 11, the reforming water pump 12, and the blower 5 to reduce the amount of fuel gas and reforming water supplied to the vaporization unit 3 and the amount of air supplied into the storage container 10, thereby reducing the amount of fuel gas reformed in the reforming unit 4, the amount of reformed fuel gas supplied to the cell stack 6B, and the amount of oxidant gas supplied, thereby reducing the power generation output. In this case, the temperatures of other metal parts, etc. of the cell stack 6B drop.

[0038] Here, when a sudden power load fluctuation occurs in the fuel cell section 6 by turning on and off high-load equipment such as a microwave oven or electric kettle as a power load device, the sudden power load fluctuation causes a sudden fluctuation in the power generation output between low and high output in the fuel cell section 6, resulting in a sudden change in temperature in the cell stack 6B and other metal parts, which in turn places large thermal stress on them. There is a concern that the failure rate of the cell stack 6B and other metal parts will increase due to fatigue and deterioration caused by the repeated and accumulated large thermal stress.

[0039] Therefore, in this fuel cell power generation system, the control device 9 is provided with a counting unit 9B that counts abrupt power generation output fluctuations that satisfy predetermined counting conditions, among the power generation output fluctuations of the fuel cell unit 6, and is configured so that when the counting state by the counting unit 9B satisfies predetermined output fluctuation limiting conditions, the power generation output control unit 9A executes output fluctuation limiting control to limit the power generation output fluctuations of the fuel cell unit 6. By executing output fluctuation limiting control in such cases to limit the power generation output fluctuations of the fuel cell unit 6, fatigue and deterioration of the cell stack 6B and other metals due to repeated and accumulated abrupt temperature changes that accompany abrupt power generation output fluctuations of the fuel cell unit 6 are mitigated.

[0040] The counting unit 9B is configured to monitor the power generation output of the fuel cell unit 6, and count abrupt power generation output fluctuations that satisfy predetermined counting conditions among the power generation output fluctuations of the fuel cell unit 6. For example, the counting unit 9B monitors the power generation output of the fuel cell unit 6 by monitoring the power generation output of the fuel cell unit 6 measured by the power conversion unit 8, or an index that has a relationship with the power generation output (for example, the power load measured by the power load measuring unit 16 or the amount of fuel gas supplied by the boost pump 11).

[0041] In this embodiment, the counting condition is set to a condition that the power generation output fluctuation is greater than or equal to a set fluctuation amount within a set time, for example, a condition that the power generation output fluctuation is greater than or equal to 300 W within 5 minutes.

[0042] Furthermore, as the first output fluctuation limiting condition, an occurrence count condition is set such that the number of times counted by the counting unit 9B reaches a set number, and the set number is set to the design upper limit number (for example, 6000 times) at which a high failure rate is expected. Therefore, when the design upper limit number is reached, output fluctuation limiting control is executed to suppress fluctuations in the power generation output of the fuel cell unit 6, and it is possible to suppress failures of the cell stack 6B and other metal parts, etc., after the design upper limit number is exceeded.

[0043] Furthermore, as a second output fluctuation limiting condition, a set pace condition is set in which the counting pace by the counting unit 9B is faster than the set pace, and the set pace is set to a design pace (e.g., 50 times / month) calculated by dividing the design upper limit number of times (6000 times) by the design service life (e.g., 120 months). Therefore, when the set pace becomes faster than the design pace at which the design upper limit number of times is exceeded before the design service life has elapsed and the failure rate is expected to increase, output fluctuation limiting control can be executed to suppress the power generation output fluctuation of the fuel cell unit 6, and it is possible to prevent the cell stack 6B and other metal parts from breaking down before the design service life has elapsed.

[0044] Here, the power generation output control unit 9A is configured to release the output fluctuation limit control when a predetermined release condition is satisfied after the set pace condition as the output fluctuation limit condition is satisfied and the output fluctuation limit control is executed. The release condition can be set, for example, such that the execution of output fluctuation limiting control after the occurrence pace condition is met reduces the rate of occurrence of sudden power generation output fluctuations to below the design rate (e.g., less than 50 times per month), or such that a predetermined period of time (e.g., one month) has passed during which fatigue of the cell stack 6B and other metal parts, etc. is alleviated. When such a release condition is met, the power generation output control unit 9A can release the output fluctuation limiting control and return the fuel cell unit 6 to normal power load following control that corresponds to the power load and has good responsiveness and coverage rate to the power generation power load.

[0045] The power generation output control unit 9A can employ, as the above-mentioned output fluctuation limiting control, either fluctuation speed limiting control that limits the power generation output fluctuation speed of the fuel cell unit 6 to a speed slower than normal, or fluctuation range limiting control that limits the power generation output fluctuation range of the fuel cell unit 6 to a range smaller than normal, or a combination of these.

[0046] If the above-mentioned fluctuation rate limiting control is executed as the output fluctuation limiting control, the power generation output fluctuation rate of the fuel cell section 6 can be limited to a rate slower than normal (for example, 1 / 10 of normal), thereby lengthening the time required for the power generation output fluctuation of the fuel cell section 6 and making the temperature gradient gentler. This makes it possible to suppress the occurrence of sudden power generation output fluctuations while suppressing a decrease in the coverage rate for the power load due to limiting the power generation output fluctuation range.

[0047] By executing the above-mentioned fluctuation range limiting control as the output fluctuation limiting control, the range of fluctuation in the power generation output of the fuel cell section 6 can be reduced, and the occurrence of sudden fluctuations in the power generation output can be suppressed while suppressing deterioration in responsiveness to the power load due to limiting the output fluctuation speed.

[0048] Examples of this fluctuation range limiting control include control that limits the range of power generation output fluctuation within a set time to a smaller range (e.g., 100W in 5 minutes) than normal (e.g., 300W in 5 minutes), control that limits the maximum power generation output of the fuel cell unit 6 to a lower output (e.g., 500W) than normal (e.g., 700W), or control that keeps the power generation output of the fuel cell unit 6 constant regardless of the power load.

[0049] In addition, when control is being executed to maintain the power generation output of the fuel cell unit 6 at a constant output regardless of the power load, if the power generation output becomes greater than the power load measured by the power load measuring unit 16 and surplus power is generated, the surplus power may be supplied to the commercial power source 17 if reverse flow of power to the commercial power source 17 is possible, or if reverse flow of power to the commercial power source 17 is not permitted, the surplus power may be consumed by an electric heater or the like (not shown) for consuming surplus power that recovers the surplus power in the form of heat.

[0050] The flow of the counting process executed by the counting unit 9B and the flow of the control executed by the power generation output control unit 9A depending on the counting state of the counting unit 9B will be described below with reference to the flowcharts of FIGS.

[0051] As shown in Fig. 2, when a sudden power generation output fluctuation that satisfies the counting condition occurs during execution of normal power load following control according to the power load, the number of occurrences is cumulatively counted by counting unit 9B (if Yes in step #01, if Yes in step #02, step #03). Then, such counting process is repeatedly executed during execution of power load following control. Note that this counting process is not reset even if the fuel cell unit 6 is started or stopped, but is cumulatively counted.

[0052] 3, when the count number of the counting unit 9B reaches the set number (the design upper limit number in this example) and the fluctuation number condition is satisfied, the power generation output control unit 9A executes output fluctuation limiting control to limit the power generation output fluctuation of the fuel cell unit 6 (if Yes in step #11, step #12). Then, the output fluctuation limiting control is continued.

[0053] Even if the number of counts by the counting unit 9B has not reached the set number and the occurrence number condition is not met, if the counting pace of the counting unit 9B is faster than the set pace (design pace in this example) and the set pace condition is met, the power generation output control unit 9A executes output fluctuation limiting control to limit the power generation output fluctuation of the fuel cell unit 6 (if No in step #11, if Yes in step #13, step #14).

[0054] After the output fluctuation limiting control is executed due to the set pace condition being satisfied, the output fluctuation limiting control continues until the release condition is satisfied (if No in step #15), and if the release condition is satisfied, the output fluctuation limiting control is released and the control returns to normal power load following control according to the power load (if Yes in step #15, step #16).

[0055] [Another embodiment] Other embodiments of the present invention will be described below. Note that the configurations of the embodiments described below are not limited to being applied independently, but can also be applied in combination with the configurations of other embodiments.

[0056] (1) In the above embodiment, the counting condition for the counting unit 9B is set to a condition that the power generation output fluctuation is equal to or greater than a set fluctuation amount within a set time. 、 The condition may be that the power generation output fluctuation is equal to or greater than a set output fluctuation rate.

[0057] (2) In the above embodiment, an example was given in which both the occurrence count condition and the occurrence pace condition were set as output fluctuation limiting conditions for the power generation output control unit 9A to execute output fluctuation limiting control, but only one of them may be set, or other conditions may also be set.

[0058] (3) In the above embodiment, the generation output control unit 9A has set one set number of times (design upper limit number of times) as the occurrence count condition for executing the output fluctuation limit control, but multiple set numbers with different numbers may be set. In that case, the content of the output fluctuation limit control may be changed depending on the set number stage, for example, by increasing the limit as the set number stage increases.

[0059] (4) Similarly, the example shows a case where one set pace (design pace) is set as the generation pace condition for the power generation output control unit 9A to execute output fluctuation limiting control, but multiple set paces with different paces may be set. In that case, the content of the output fluctuation limiting control may be changed according to the set pace stage, for example, by increasing the limit as the set pace becomes faster.

[0060] (5) In the above embodiment, an example was given in which the generation pace condition was met and the power generation output control unit 9A executed the output fluctuation limit control, and then the output fluctuation limit control was released when the release condition was met. However, the output fluctuation limit control may also be released even when the release condition (such as a condition that a predetermined period of time has passed) is met after the generation count condition is met and the power generation output control unit 9A executed the output fluctuation limit control. [Explanation of symbols]

[0061] 4. Modification section 6 Fuel cell section 6A fuel cell 6B Cell Stack 9A Power generation output control unit 9B Counting section

Claims

1. a fuel cell section having a cell stack formed by stacking a plurality of solid oxide fuel cell units that generate electricity by an electrochemical reaction between an oxidant gas and a reformed fuel gas obtained by reforming a fuel gas in the reforming section, and that outputs the electromotive force of the cell stack as generated electricity; a power generation output control unit that controls the power generation output of the fuel cell unit in accordance with the power load; a counting unit that counts sudden power generation output fluctuations that satisfy a predetermined counting condition among the power generation output fluctuations of the fuel cell unit, the power generation output control unit executes output fluctuation limiting control to limit power generation output fluctuations of the fuel cell unit when the counting state by the counting unit satisfies a predetermined output fluctuation limiting condition; A fuel cell power generation system, wherein the counting condition is a condition that the power generation output fluctuation is equal to or greater than a set fluctuation amount within a set time period, or a condition that the power generation output fluctuation is equal to or greater than a set output fluctuation rate.

2. A fuel cell unit having a cell stack formed by stacking a plurality of solid oxide fuel cell cells that generate electricity by an electrochemical reaction between reformed fuel gas obtained by reforming fuel gas in a reforming unit and an oxidant gas, and that outputs the electromotive force of the cell stack as generated electricity; a power generation output control unit that controls the power generation output of the fuel cell unit in accordance with the power load; a counting unit that counts sudden power generation output fluctuations that satisfy a predetermined counting condition among the power generation output fluctuations of the fuel cell unit, the power generation output control unit executes output fluctuation limiting control to limit power generation output fluctuations of the fuel cell unit when the counting state by the counting unit satisfies a predetermined output fluctuation limiting condition; The fuel cell power generation system, wherein the output fluctuation limiting control is a fluctuation range limiting control that limits the power generation output fluctuation range of the fuel cell unit to a range smaller than normal.

3. 3. The fuel cell power generation system according to claim 1, wherein the output fluctuation limiting condition is an occurrence number condition that the number of times counted by the counting unit reaches a set number.

4. 4. The fuel cell power generation system according to claim 1, wherein the output fluctuation limiting condition is an occurrence pace condition that the pace counted by the counting unit is faster than a set pace.

5. 5. The fuel cell power generation system according to claim 4, wherein the power generation output control unit cancels the output fluctuation limiting control when a canceling condition is satisfied after the generation pace condition is satisfied and the power generation output control is executed.

6. 6. The fuel cell power generation system according to claim 1, wherein the output fluctuation limiting control is a fluctuation speed limiting control that limits the power generation output fluctuation speed of the fuel cell unit to a speed slower than normal.

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