Control method, control device, and power generation system

Abstract

The present invention provides a control method for a fuel cell system that enables more appropriate control than conventional methods in response to the ratio of heat demand to electricity demand of a customer or changes in the customer's heat demand. [Solution] The control method is a control method for a fuel cell system comprising a plurality of fuel cell units, and switches between a first operating mode and a second operating mode in which the power generated by the fuel cell units is greater than that of the first operating mode and the number of fuel cell units generating power is smaller, based on the ratio of the heat demand to the power demand of the customer or the heat demand of the customer.

Description

Technical Field

[0001] The present disclosure relates to a control method for a fuel cell device, a control device for a fuel cell device, and a power generation system including the fuel cell device.

Background Art

[0002] In order not to waste the heat generated during power generation of a fuel cell, a power generation system has been devised that supplies not only the electricity generated by the fuel cell but also the energy of the heat to consumers. Regarding such a technology, Patent Document 1 below discloses a cogeneration system that operates a combined heat and power device (i.e., a fuel cell) at maximum output when a heat shortage state is predicted and stores surplus power in power storage means.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the cogeneration system described in Patent Document 1, the appropriate control of the fuel cell with respect to the ratio of the heat demand to the power demand of the consumer or the change in the heat demand of the consumer has not been sufficiently studied.

[0005] An object of the present disclosure is to provide a control method for a fuel cell device, a control device for a fuel cell device, and a power generation system that can perform more appropriate control than in the past with respect to the ratio of the heat demand to the power demand of the consumer or the change in the heat demand of the consumer.

Means for Solving the Problems

[0006] To solve the above problems, a control method according to one aspect of the present disclosure is a control method for a fuel cell system comprising a plurality of fuel cell units, which switches between a first operating mode and a second operating mode in which the power generated by the fuel cell units is greater than that of the first operating mode and the number of fuel cell units generating power is smaller, based on the ratio of the heat demand to the power demand of the customer or the heat demand of the customer.

[0007] Furthermore, a control device according to one aspect of the present disclosure is a control device for a fuel cell system comprising a plurality of fuel cell units, comprising: a memory for storing the ratio of a customer's heat demand to their electricity demand or the customer's heat demand; and a controller for switching between a first operating mode and a second operating mode in which the power generated by the fuel cell units is greater than that of the first operating mode and the number of fuel cell units generating power is smaller, based on the ratio or the customer's heat demand.

[0008] Furthermore, a power generation system according to one aspect of the present disclosure comprises a fuel cell device having a plurality of fuel cell units and the control device described above. [Effects of the Invention]

[0009] A control method, control device, and power generation system according to one aspect of this disclosure have the effect of reducing the surplus or deficit of energy generated by the fuel cell device in response to changes in the ratio of heat demand to electricity demand of the customer or the customer's heat demand, compared to conventional methods. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a block diagram of the power generation system. [Figure 2] Figure 2 is a graph showing the relationship between the power generated by the fuel cell unit and the thermoelectric ratio (ratio of heat output to power generated). [Figure 3] Figure 3 is a flowchart of the power generation control program. [Figure 4] Figure 4 is a flowchart of the power generation control program in a modified example. [Modes for carrying out the invention]

[0011] Fuel cell systems, which consist of multiple fuel cell units, generate electricity through a chemical reaction between a fuel such as hydrogen-containing gas or methanol and an oxidizing agent such as oxygen. This chemical reaction also generates heat. By supplying both the electricity and heat generated from the fuel cell system to consumers, and allowing consumers to utilize these energies, the overall energy utilization efficiency can be improved.

[0012] On the other hand, the electricity and thermal energy required by consumers change depending on the situation. Therefore, the ratio of heat demand to electricity demand, or the consumer's heat demand, also changes depending on the situation. If the ratio of thermal output to generated power of the fuel cell system can be changed in response to this change in the ratio of thermal demand to electricity demand, or the consumer's heat demand, then the surplus or deficit of energy (electricity and heat) generated by the fuel cell system relative to the consumer's electricity and heat demand can be reduced.

[0013] Here, the inventors focused on the fact that the ratio of heat output to power generated by a fuel cell unit changes depending on the magnitude of the power generated by the fuel cell unit. They realized that by adjusting the ratio of heat output to power generated by the fuel cell unit in response to changes in the ratio of heat demand to power demand of the customer or changes in the customer's heat demand, and by adjusting the number of fuel cell units according to the increase or decrease in power generated, it is possible to reduce the surplus or deficit of energy (power and heat) generated by the fuel cell device in relation to the customer's power demand and heat demand when the ratio of heat demand to power demand of the customer or the customer's heat demand changes.

[0014] In other words, the control method in the first aspect of the present disclosure is a control method for a fuel cell system comprising a plurality of fuel cell units, wherein the method switches between a first operating mode and a second operating mode in which the power generated by the fuel cell units is greater and the number of fuel cell units generating power is smaller than in the first operating mode, based on the ratio of the heat demand to the power demand of the customer or the heat demand of the customer.

[0015] As mentioned above, the ratio of heat output to power generated by a fuel cell unit changes depending on the magnitude of the power generated by the fuel cell unit. Therefore, by switching between the first operating mode and the second operating mode, as in the control method of the first embodiment, the ratio of heat output to power generated by the fuel cell device can be adjusted when the power generated by the fuel cell unit changes. Thus, the ratio of heat output to power generated by the fuel cell device can be changed in accordance with the ratio of heat demand to power demand of the customer or changes in the customer's heat demand. Furthermore, as in the control method of the first embodiment, the number of power generation units of the fuel cell unit is changed when switching between the first operating mode and the second operating mode, so that the surplus or deficit of power and thermal energy generated by the fuel cell device relative to the customer's power demand and heat demand can be reduced.

[0016] In the control method of the second aspect of the present disclosure, when the ratio increases, the control method of the first aspect switches from the first operating mode to the second operating mode.

[0017] In the control method of the second embodiment, when the ratio of heat demand to electricity demand of the customer increases, the system switches from the first operating mode to the second operating mode in which the fuel cell unit generates more power. This increases the ratio of heat output to power generated by the fuel cell unit, thus increasing the ratio of heat output to power generated by the fuel cell system. Therefore, according to the control method of the second embodiment, the ratio of heat output to power generated by the fuel cell system can be increased in accordance with the increase in the ratio of heat demand to electricity demand of the customer. Furthermore, since the second operating mode has fewer power generators than the first operating mode, the surplus or deficit of power and thermal energy generated by the fuel cell system due to the increase in power generated by the fuel cell unit when switching to the first operating mode can be reduced. As a result, the surplus or deficit of power and thermal energy generated by the fuel cell system relative to the customer's electricity demand and thermal demand can be reduced when the ratio of heat demand to electricity demand of the customer increases.

[0018] The control method according to the third aspect of the present disclosure is that in the control method according to the first aspect, when the heat demand of the consumer increases, the operation mode is switched from the first operation mode to the second operation mode.

[0019] In the control method according to the second aspect described above, when the ratio of the heat demand to the power demand of the consumer increases, the operation mode is switched from the first operation mode to the second operation mode. In contrast, in the control method according to the third aspect, when the "heat demand of the consumer" increases, the operation mode is switched from the first operation mode to the second operation mode. Further, an increase in the heat demand of the consumer leads to an increase in the ratio of the heat demand to the power demand of the consumer. Therefore, the control method according to the third aspect has the same operational effects as the control method according to the second aspect.

[0020] The control method according to the fourth aspect of the present disclosure is that in the control method according to the second aspect, after switching to the second operation mode, when the ratio decreases, the operation mode is switched from the second operation mode to the first operation mode.

[0021] In this control method, when the ratio of the heat demand to the power demand of the consumer decreases, the operation mode is switched from the second operation mode to the first operation mode where the power generation power of the fuel cell unit is small. As a result, the ratio of the heat output to the power generation power of the fuel cell unit decreases, so that the ratio of the heat output to the power generation power of the fuel cell device also decreases. Thereby, the ratio of the heat output to the power generation power of the fuel cell device can be decreased in response to a decrease in the ratio of the heat demand to the power demand of the consumer. Further, since the number of power generation units in the first operation mode is larger than that in the second operation mode, it is possible to reduce the excess or deficiency of the power and heat energy generated by the fuel cell device due to a decrease in the power generation power of the fuel cell unit when switching to the first operation mode. As a result, it is possible to reduce the excess or deficiency of the power and heat energy generated by the fuel cell device with respect to the power demand and heat demand of the consumer when the ratio of the heat demand to the power demand of the consumer decreases.

[0022] The control method according to the fifth aspect of the present disclosure is that in the control method according to the third aspect, after switching to the second operation mode, when the heat demand of the consumer decreases, the operation mode is switched from the second operation mode to the first operation mode.

[0023] In the control method of the fourth aspect described above, when the "ratio of heat demand to power demand of the consumer" decreases, the operation mode is switched from the second operation mode to the first operation mode. In contrast, in the control method of the fifth aspect, when the "heat demand of the consumer" decreases, the operation mode is switched from the second operation mode to the first operation mode. Further, the decrease in the heat demand of the consumer leads to a decrease in the ratio of heat demand to power demand of the consumer. Therefore, the control method of the fifth aspect has the same operational effects as the control method of the fourth aspect.

[0024] In the control method of the sixth aspect of the present disclosure, in the control method of the fourth or fifth aspect, when switching from the first operation mode to the second operation mode, the fuel cell unit that is stopped from generating power to reduce the number of power generation units of the fuel cell unit is less deteriorated than the fuel cell unit that continues to generate power.

[0025] In this control method, when the ratio of heat demand to power demand of the consumer or the heat demand of the consumer increases and the operation mode is switched from the first operation mode to the second operation mode, the power generation of the fuel cell unit that is not deteriorating is stopped. That is, the fuel cell unit that is deteriorating is preferentially used for power generation. Here, as the fuel cell unit deteriorates, the ratio of heat output to power generation power increases. Therefore, if the fuel cell unit that is deteriorating is preferentially used for power generation, the ratio of heat output to power generation power of the fuel cell device will increase. Thus, according to the control method of the sixth aspect, the ratio of heat output to power generation power of the fuel cell device can be increased in response to an increase in the ratio of heat demand to power demand of the consumer.

[0026] Furthermore, the fuel cell unit has the characteristic that the decrease in power generation efficiency due to deterioration is rapid in the initial stage of deterioration, while the decrease in power generation efficiency due to deterioration becomes gentle when the deterioration progresses to a certain extent. Therefore, if the fuel cell unit that is deteriorating is preferentially used for power generation as in the control method of the sixth aspect, the decrease in power generation efficiency of the fuel cell device due to deterioration can be suppressed.

[0027] In the control method of the seventh aspect of this disclosure, in the control method of the fourth or fifth aspect, when switching from the second operating mode to the first operating mode, the fuel cell units that are started to generate power in order to increase the number of power generation units of the fuel cell units are less deteriorated than the fuel cell units that are not started to generate power.

[0028] In this control method, when the ratio of heat demand to electricity demand of the customer or the customer's heat demand decreases and the system switches from the second operating mode to the first operating mode, power generation is started in fuel cell units that have not deteriorated. In other words, power generation is prioritized for fuel cell units that have not deteriorated. As mentioned above, the ratio of heat output to power generated increases as a fuel cell unit deteriorates. Therefore, if power generation is prioritized for fuel cell units that have not deteriorated, the ratio of heat output to power generated by the fuel cell system will decrease. Thus, according to the control method of the seventh embodiment, the ratio of heat output to power generated by the fuel cell system can be reduced in accordance with the decrease in the ratio of heat demand to electricity demand of the customer.

[0029] A control device according to an eighth aspect of the present disclosure is a control device for a fuel cell system including a plurality of fuel cell units, comprising: a memory for storing the ratio of a customer's heat demand to their power demand or the customer's heat demand; and a controller for switching between a first operating mode and a second operating mode in which the power generated by the fuel cell units is greater than that of the first operating mode and the number of fuel cell units generating power is smaller, based on the ratio or the customer's heat demand.

[0030] According to this control device, for the same reasons as the control method of the first embodiment, the ratio of heat output to power generated by the fuel cell device can be changed in response to the ratio of heat demand to power demand of the customer or a change in the customer's heat demand.

[0031] A power generation system according to the ninth aspect of this disclosure comprises a fuel cell device including a plurality of fuel cell units and a control device according to the eighth aspect.

[0032] According to this power generation system, for the same reasons as the control method of the first embodiment, the ratio of the heat output to the power generated by the fuel cell device can be changed in response to the ratio of the heat demand to the electricity demand of the customer or to changes in the heat demand of the customer.

[0033] The following describes specific examples of the above embodiments of this disclosure with reference to the attached drawings. The specific examples described below are all examples of the above embodiments of this disclosure. Therefore, the shapes, numerical values, components, arrangement positions of components, and connection configurations shown below do not limit the scope of the claims unless they are described in the claims.

[0034] Furthermore, among the components described below, those not described in the independent claim representing the highest-level concept of this disclosure will be described as optional components. Also, in the drawings, components with the same reference numeral may not be described. The drawings are schematic representations of each component for ease of understanding, and the shape and dimensional ratios may not be accurately represented.

[0035] Furthermore, in the operation of the apparatus, the order of the processes may be changed or known processes may be added as needed.

[0036] (Power generation system configuration) First, the device configuration of the power generation system 100 according to this embodiment will be described. Figure 1 is a block diagram of the power generation system 100. The power generation system 100 according to this embodiment is a system that supplies electricity and thermal energy to a customer 101 in accordance with the customer's electricity demand and heat demand. The customer 101 is, for example, a house, a shop, a factory, etc.

[0037] As shown in Figure 1, the power generation system 100 includes a fuel cell device 10 and a control device 20. The fuel cell device 10 and the control device 20 will be described in detail below.

[0038] <Fuel cell device> The fuel cell device 10 is a device that generates electricity using a fuel cell. As shown in Figure 1, the fuel cell device 10 has a plurality of fuel cell units 11. The number of fuel cell units 11 that the fuel cell device 10 has is not limited, but the fuel cell device 10 may have, for example, several to several hundred fuel cell units 11.

[0039] In the fuel cell unit 11, electricity is generated by a chemical reaction between a fuel such as hydrogen-containing gas or methanol and an oxidizing agent such as oxygen, and heat is generated in conjunction with this chemical reaction. The electrical and thermal energy generated in the fuel cell unit 11 is supplied to the consumer 101. Figure 2 is a graph showing the relationship between the power generated by the fuel cell unit 11 and the ratio of the heat output to the power generated by the fuel cell unit 11 (hereinafter referred to as the "generated thermoelectric ratio"). The horizontal axis of Figure 2 represents the power generated by the fuel cell unit 11, and the vertical axis represents the generated thermoelectric ratio of the fuel cell unit 11.

[0040] As shown in Figure 2, the thermoelectric ratio of the fuel cell unit 11 decreases as the power generated by the fuel cell unit 11 increases when the power generated by the fuel cell unit 11 is small, but after reaching the lowest point, it increases as the power generated increases. Thus, the thermoelectric ratio of the fuel cell unit 11 changes with the power generated by the fuel cell unit 11, and generally increases as the power generated by the fuel cell unit 11 increases. However, when the fuel cell unit 11 deteriorates, the curve shown in Figure 2 shifts to a higher thermoelectric ratio. In other words, the thermoelectric ratio of the fuel cell unit 11 increases as it deteriorates.

[0041] <Control device> The control device 20 is a device that controls the fuel cell device 10. The control device 20 includes a processor, volatile memory, non-volatile memory, and an I / O interface. Various programs, including the power generation control program described later, are stored in the non-volatile memory of the control device 20, and the processor performs calculations using the volatile memory based on each program. The control device 20 may consist of one device or multiple devices. The control device 20 may consist of multiple devices connected by a network, for example.

[0042] As shown in Figure 1, the control device 20 of this embodiment includes a controller 21 and a memory 22.

[0043] The controller 21 is a device that performs calculations. The controller 21 may be, for example, the processor of the control device 20. The controller 21 is communicatively connected to each fuel cell unit 11. The controller 21 can start power generation in a fuel cell unit 11 that is stopped by sending a power generation instruction signal to that fuel cell unit 11. The controller 21 can also stop power generation in a fuel cell unit 11 that is generating power by sending a stop instruction signal to that fuel cell unit 11. The power generation instruction signal or stop instruction signal from the controller 21 is received by a controller (not shown) installed in the fuel cell unit 11, and this controller executes the power generation and power generation stop of the fuel cell unit 11.

[0044] Furthermore, the controller 21 can acquire power generation information of each fuel cell unit 11 from the controller provided in each fuel cell unit 11. The power generation information in this embodiment includes, for example, the voltage during power generation of the fuel cell unit 11, the cumulative power generation time, and the cumulative number of power generation cycles. Based on the power generation information, the controller 21 can determine or calculate the degree of deterioration of each fuel cell unit 11 and store it in the memory 22.

[0045] The controller 21 may calculate the degree of degradation based on the voltage of the fuel cell unit 11 during power generation, the cumulative power generation time of the fuel cell unit 11, the cumulative number of power generation cycles of the fuel cell unit 11, or a numerical value obtained from a formula in which at least one of the voltage during power generation, cumulative power generation time, and number of power generation cycles is a variable. The controller 21 may determine that the lower the voltage of the fuel cell unit 11 during power generation, the higher the degree of degradation, the longer the cumulative power generation time of the fuel cell unit 11, or the more cumulative number of power generation cycles of the fuel cell unit 11, the higher the degree of degradation.

[0046] The memory unit 22 is a device that stores various types of information. The memory unit 22 may be, for example, the volatile memory or non-volatile memory of the control device 20. The memory unit 22 is communicated with the customer 101 (more precisely, the control device or other equipment installed by the customer 101). In Figure 1, the memory unit 22 is directly connected to the customer 101, but the memory unit 22 may also be connected to the customer 101 via the controller 21.

[0047] The memory unit 22 can acquire and store the power demand and heat demand from the customer 101. It can also store the ratio of heat demand to power demand (hereinafter referred to as the "demand-heat-electricity ratio") calculated by the controller 21. Here, "power demand" is the amount of electricity requested by the customer 101, and "heat demand" is the amount of thermal energy requested by the customer 101. The power demand and heat demand of the customer 101, as well as the demand-heat-electricity ratio, fluctuate depending on the customer 101's circumstances. In addition to the actual power demand and heat demand acquired from the customer 101, the memory unit 22 can also store predicted power demand and heat demand predicted by the controller 21 based on these actual values.

[0048] Furthermore, the memory unit 22 is connected to the controller 21 in a communicative manner. The controller 21 can obtain the power demand and heat demand of the customer 101 from the memory unit 22. The controller 21 also calculates the demand-thermoelectric ratio based on the power demand and heat demand obtained from the memory unit 22. As described above, in this embodiment, the memory unit 22 stores the demand-thermoelectric ratio calculated by the controller 21. However, the memory unit 22 may also obtain the demand-thermoelectric ratio from the customer 101 and store it.

[0049] (Operation of the power generation system) Next, we will explain a specific example of the operation of the power generation system 100. Below, we will explain a specific example of the operation of the power generation system 100 by describing the flow of the power generation control program executed by the controller 21.

[0050] Figure 3 is a flowchart of the power generation control program. As shown in Figure 3, when the power generation control program starts, the controller 21 obtains the power demand and heat demand of customer 101 from the memory 22 (step S1). As mentioned above, the memory 22 stores the power demand and heat demand of customer 101. The memory 22 also stores the demand-to-heat ratio calculated by the controller 21 based on the power demand and heat demand. The power demand and heat demand of customer 101 described here may be measured values ​​or predicted values.

[0051] Next, the controller 21 calculates the demand-thermocouple ratio based on the power demand and heat demand stored in the memory 22, and determines whether this demand-thermocouple ratio is less than a first threshold (step S2). The first threshold is the thermocouple ratio value that serves as the basis for switching the operating mode. The first threshold may be set to any value between 0.8 and 1 (for example, 0.9) depending on the performance of the fuel cell device 10.

[0052] If the controller 21 determines in step S2 that the demand-thermoelectric ratio is less than a first threshold (YES in step S2), it operates the fuel cell device 10 in a first operating mode (step S3). Specifically, the controller 21 operates the fuel cell device 10 so that the power generated by each fuel cell unit 11 is the first power. At that time, it causes the number of fuel cell units 11 to generate power such that the total power generated by the fuel cell units 11 (i.e., the power generated by the fuel cell device 10) is equal to or greater than the power demand of the customer 101. Alternatively, it causes the number of fuel cell units 11 to generate power such that the total thermal energy generated by the fuel cell units 11 (i.e., the thermal energy generated by the fuel cell device 10) is equal to or greater than the heat demand of the customer 101. However, if the power demand or heat demand of the customer 101 cannot be met even if all fuel cell units 11 generate power at the first power, the controller 21 increases the power generated by at least some of the fuel cell units 11 in the fuel cell device 10 to be greater than the first power.

[0053] The "first power" mentioned above is a power less than the maximum power generated by each fuel cell unit 11. The first power may be, for example, 50% of the rated power. However, the first power may not be a fixed value, but may be set based on the demand-thermoelectric ratio of the consumer 101 obtained in step S1. For example, the first power may be set to decrease as the demand-thermoelectric ratio of the consumer 101 decreases. After executing step S3, the controller 21 returns to step S1 and repeats the steps from step S1 onward.

[0054] On the other hand, if the controller 21 determines in step S2 that the demand-thermoelectric ratio is not less than the first threshold (i.e., greater than or equal to the first threshold) (NO in step S2), it operates the fuel cell system 10 in the second operating mode (step S4). Specifically, the controller 21 operates the fuel cell system 10 so that the power generated by each fuel cell unit 11 becomes the second power. In this case, it causes the number of fuel cell units 11 to generate power such that the total power generated by the fuel cell units 11 (i.e., the power generated by the fuel cell system 10) is equal to or greater than the power demand and heat demand of the customer 101. Alternatively, it causes the number of fuel cell units 11 to generate power such that the total thermal energy generated by the fuel cell units 11 (i.e., the thermal energy generated by the fuel cell system 10) is equal to or greater than the heat demand of the customer 101. However, if the power demand or heat demand of the customer 101 cannot be met even if all fuel cell units 11 generate power at the second power level, the controller 21 increases the power generated by at least some of the fuel cell units 11 of the fuel cell system 10 to be greater than the second power level. Furthermore, if the second power source is operating at its rated power and is unable to meet the electricity or heat demand of customer 101, the power generated by each fuel cell unit will be maintained at the level of the second power source.

[0055] The "second power" mentioned above is a power greater than the first power. The second power may be, for example, the rated power. However, the second power may not be a fixed value, but may be set based on the demand thermoelectric ratio of customer 101 obtained in step S1. For example, the second power may be set to increase as the demand thermoelectric ratio of customer 101 increases. After executing step S4, the controller 21 returns to step S1 and repeats the steps from step S1 onward.

[0056] As mentioned above, the second power in the second operating mode is greater than the first power in the first operating mode. Therefore, if the power generated by the fuel cell device 10 is the same in the first and second operating modes, the number of fuel cell units 11 generating power in the first operating mode will be greater than the number of fuel cell units 11 generating power in the second operating mode. For example, if five fuel cell units 11 are operated at the first power when the first power is rated power, and if ten fuel cell units 11 are operated at the second power when the second power is 50% of the rated power, the power generated by the fuel cell device 10 will be the same.

[0057] As described above, when the demand thermoelectric ratio of customer 101 increases and changes from a state below the first threshold to a state above the first threshold, the system switches from the first operating mode to the second operating mode. At this time, the power generated by the fuel cell unit 11 increases from the first power to the second power, which is greater than the first power. Here, assuming that the first power and second power are set as shown in Figure 2 (the second power is greater than the first power), the generation thermoelectric ratio of the fuel cell unit 11 in the second operating mode will be higher than the generation thermoelectric ratio of the fuel cell unit 11 in the first operating mode. Therefore, when the system switches from the first operating mode to the second operating mode, the generation thermoelectric ratio of each fuel cell unit 11 increases, and thus the generation thermoelectric ratio of the fuel cell device 10 increases.

[0058] Therefore, according to this embodiment, the heat-power ratio generated by the fuel cell device 10 can be increased in accordance with the increase in the heat-power ratio demanded by the consumer 101. When switching from the first operating mode to the second operating mode, the power generated per fuel cell unit 11 decreases, but the number of power-generating fuel cell units 11 increases, thus reducing the shortage of power and thermal energy generated by the fuel cell device 10 in relation to the electricity and heat demands of the consumer 101.

[0059] On the other hand, when the demand-to-heat-coefficient ratio of customer 101 decreases and changes from being above the first threshold to being below the first threshold, the system switches from the second operating mode to the first operating mode. At this time, the power generated by the fuel cell unit 11 decreases from the second power to the first power, which is smaller than the second power. As shown in Figure 2, when the system switches from the second operating mode to the first operating mode and the output of the fuel cell unit 11 decreases from the second power to the first power, the heat-coefficient ratio of the fuel cell unit 11 decreases, and therefore the heat-coefficient ratio of the fuel cell device 10 decreases.

[0060] Therefore, according to this embodiment, the heat-power ratio generated by the fuel cell device 10 can be reduced in accordance with the decrease in the heat-power ratio demanded by the consumer 101. When switching from the second operating mode to the first operating mode, the power generated per fuel cell unit 11 increases, but the number of fuel cell units 11 decreases, so the surplus of power and thermal energy generated by the fuel cell device 10 relative to the electricity and heat demands of the consumer 101 is reduced.

[0061] As described above, when switching from the first operating mode to the second operating mode, the number of power-generating fuel cell units 11 is reduced, which means that some of the fuel cell units 11 that are currently generating power will be stopped. At this time, the controller 21 may stop the power generation of fuel cell units 11 that are less deteriorated from among the fuel cell units 11 that are currently generating power, and prioritize the power generation of fuel cell units 11 that are more deteriorated. In other words, the fuel cell units 11 that are stopped from generating power do not need to be more deteriorated than the fuel cell units 11 that continue to generate power.

[0062] Here, as the fuel cell unit 11 deteriorates, its power generation efficiency decreases and its heat recovery efficiency increases. In other words, a deteriorated fuel cell unit 11 has a higher heat-generating ratio than a fuel cell unit 11 that has not deteriorated. Therefore, when the demand heat-generating ratio of the consumer 101 increases and the system switches from the first operating mode to the second operating mode, the heat-generating ratio of the fuel cell device 10 can be increased in accordance with the increase in the demand heat-generating ratio of the consumer 101 by prioritizing the generation of power from the deteriorated fuel cell unit 11, i.e., the fuel cell unit 11 with a high heat-generating ratio.

[0063] Furthermore, the fuel cell unit 11 exhibits a rapid decrease in power generation efficiency due to degradation in the initial stages of deterioration, but the decrease in power generation efficiency due to degradation becomes more gradual once a certain level of degradation has progressed. Therefore, as described above, by prioritizing the generation of power from the more degraded fuel cell unit 11, the decrease in power generation efficiency due to the degradation of the fuel cell device 10 can be suppressed.

[0064] On the other hand, when switching from the second operating mode to the first operating mode, some of the fuel cell units 11 that are not currently generating power will be started to generate power in order to increase the number of power-generating fuel cell units 11. At this time, the controller 21 may start generating power from among the fuel cell units 11 that are not currently generating power, selecting those with a lower degree of degradation, and prioritizing the generation of power from fuel cell units 11 that have not deteriorated further. In other words, the fuel cell units 11 that are started to generate power do not need to be more deteriorated than the fuel cell units that are not started to generate power.

[0065] As described above, the fuel cell unit 11 that is deteriorating has a higher heat-generating ratio than the fuel cell unit 11 that is not deteriorating. Therefore, when the heat-generating ratio of the customer 101 decreases and the system switches from the second operating mode to the first operating mode, the heat-generating ratio of the fuel cell device 10 can be reduced in accordance with the decrease in the heat-generating ratio of the customer 101 by prioritizing the generation of power from the fuel cell unit 11 that is not deteriorating, i.e., the fuel cell unit 11 with a low heat-generating ratio.

[0066] (Variable example of a power generation system) Next, a modified version of the power generation system 100 will be described. In the power generation system 100 described above, the controller 21 selects the operating mode in the power generation control program based on the "demand-heat-power ratio" of the customer 101 (see steps S2, S3, and S4 in Figure 3). In contrast, in the modified power generation system 100, the operating mode is selected based on the "heat demand" of the customer 101. In all other respects, it is the same as the power generation system 100 described above. Here, the power generation control program in the modified version will be described, and other explanations will be omitted.

[0067] Figure 4 is a flowchart of the power generation control program in the modified example. As shown in Figure 4, when the power generation control program in the modified example is started, the controller 21 obtains the power demand and heat demand from the memory 22 (step S11). The power demand and heat demand of the customer 101 described here may be measured values ​​or predicted values.

[0068] Next, the controller 21 determines whether the heat demand is below a second threshold (step S12). The second threshold is a value that serves as a criterion for switching the operating mode. The second threshold is set based on the size of the customer 101 and the capacity of the fuel cell device 10.

[0069] If the controller 21 determines in step S12 that the heat demand is less than the second threshold (YES in step S12), it operates the fuel cell device 10 in the first operating mode (step S13). On the other hand, if the controller 21 determines in step S12 that the heat demand is not less than the second threshold (is greater than or equal to the second threshold) (NO in step S12), it operates the fuel cell device 10 in the second operating mode (step S14). The first and second operating modes are the same as in the embodiment described above. After executing step S13 or step S14, the controller 21 returns to step S11 and repeats steps S11 onward.

[0070] The above is a description of the modified power generation system 100. In the modified power generation system 100, the operating mode is selected based on heat demand, rather than the heat-to-power ratio. Even in this case, the same effects and advantages as the power generation system 100 according to the embodiment described above can be achieved.

[0071] From the above description, many improvements and other embodiments of the disclosure will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the disclosure. The details of its structure and / or function can be substantially modified without departing from the spirit of the disclosure. [Industrial applicability]

[0072] One aspect of this disclosure can be used in a control method for a fuel cell device, a control device for a fuel cell device, and a power generation system that can perform more appropriate control than conventional methods in response to the ratio of heat demand to electricity demand of a customer or changes in the heat demand of a customer. [Explanation of Symbols]

[0073] 10:Fuel cell device 11: Fuel cell unit 20: Control device 21: Controller 22:Memory 100: Power generation system 101: Consumer

Claims

1. A control method for a fuel cell system comprising multiple fuel cell units, A control method for switching between a first operating mode and a second operating mode in which the power generated by the fuel cell unit is greater and the number of fuel cell units used is smaller than that of the first operating mode, based on the ratio of the heat demand to the electricity demand of the customer or the heat demand of the customer.

2. The control method according to claim 1, wherein when the ratio increases, the system switches from the first operating mode to the second operating mode.

3. The control method according to claim 1, wherein when the heat demand of the customer increases, the control method switches from the first operating mode to the second operating mode.

4. The control method according to claim 2, wherein after switching to the second operating mode, if the ratio decreases, the control method switches from the second operating mode to the first operating mode.

5. The control method according to claim 3, wherein, after switching to the second operating mode, if the heat demand of the customer decreases, the control method switches from the second operating mode to the first operating mode.

6. The control method according to claim 4 or 5, wherein, when switching from the first operating mode to the second operating mode, the fuel cell units that are stopped generating power in order to reduce the number of power-generating fuel cell units are less deteriorated than the fuel cell units that continue to generate power.

7. The control method according to claim 4 or 5, wherein when switching from the second operating mode to the first operating mode, the fuel cell units that are started to generate power in order to increase the number of power-generating fuel cell units are less deteriorated than the fuel cell units that are not started to generate power.

8. A control device for a fuel cell system comprising multiple fuel cell units, A memory device that stores the ratio of a customer's heat demand to their electricity demand, or the customer's heat demand. A control device comprising a controller that switches between a first operating mode and a second operating mode in which the power generated by the fuel cell unit is greater than that of the first operating mode and the number of fuel cell units used for power generation is smaller, based on the ratio or the heat demand of the customer.

9. A fuel cell system comprising multiple fuel cell units, A power generation system comprising the control device described in claim 8.

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