Fuel cell system and control method thereof

Abstract

A fuel cell system (110) includes a fuel cell unit (120) and a control device (130). The fuel cell unit (120) includes a plurality of fuel cells (125). The control device (130) controls unit output power. The unit output power is output power of the fuel cell unit (120). The control device (130) is capable of executing a predetermined control. The predetermined control, in changing the unit output power, controls output power of each fuel cell (125) such that the number of fuel cells (125) activated or the number of fuel cells (125) deactivated takes a minimum value according to an output power range of each fuel cell (125).

Description

FUEL CELL SYSTEM AND CONTROL METHOD THEREOF

[0001] The present disclosure relates to a fuel cell system and a control method thereof.

[0002] Patent Literature 1 discloses a fuel cell system including a plurality of fuel cells. In this system, fuel cells to be activated and fuel cells to be deactivated are determined based on the number of activations of each fuel cell. Patent Literature 1 states an effect that it is possible to inhibit some fuel cells from being degraded earlier than the other fuel cells.

[0003] JP 2023-047079 A

[0004] The present disclosure provides a technology suitable for reducing the cost per power generation of a fuel cell system.

[0005] The present disclosure provides a fuel cell system including: a fuel cell unit including a plurality of fuel cells; and a control device that controls unit output power that is output power of the fuel cell unit, wherein the control device is capable of executing a predetermined control, and in changing the unit output power, the predetermined control controls output power of each fuel cell such that the number of fuel cells activated or the number of fuel cells deactivated takes a minimum value according to an output power range of each fuel cell.

[0006] In another aspect, the present disclosure provides a control method for a fuel cell system including a fuel cell unit including a plurality of fuel cells, the method including executing a predetermined control, wherein assuming that output power of the fuel cell unit is indicated as unit output power, the predetermined control, in changing the unit output power, controls output power of each fuel cell such that the number of fuel cells activated or the number of fuel cells deactivated takes a minimum value according to an output power range of each fuel cell.

[0007] The technology according to the present disclosure is suitable for reducing the cost per power generation of the fuel cell system.

[0008] Fig. 1 illustrates a configuration of a fuel cell system according to an embodiment.Fig. 2 is a time chart illustrating a control by a control device.Fig. 3 is a time chart illustrating a first deactivation control.Fig. 4 is a time chart illustrating a second deactivation control.Fig. 5 is a time chart illustrating a reduction stop control.Fig. 6 is a time chart illustrating a situation in which the reduction stop control is effective.Fig. 7 is a time chart illustrating a first example of operation plan correction.Fig. 8 is a time chart illustrating a second example of operation plan correction.Fig. 9 is a time chart illustrating a third example of operation plan correction.Fig. 10 is a time chart illustrating a control using an operation plan.

[0009] (Findings and the like on which the present disclosure is based) Patent Literature 1 describes that, when a fuel cell is operated at output power that is about 50% of the maximum output power of the fuel cell, power generation efficiency of the fuel cell becomes maximum. However, studies by the present inventors revealed that the operation method of Patent Literature 1 is not always suitable for reducing the cost per power generation of the fuel cell system, for the following reasons. That is, if fluctuation in the output power of the fuel cell system is significant, each fuel cell frequently repeats activation and deactivation. This may cause a situation in which the fuel cell uses up the number of lifetime activations before it uses up the lifetime operation period. The fact that the fuel cell cannot use up the lifetime operation period is disadvantageous in terms of increasing the lifetime power generation of the fuel cell, and therefore is disadvantageous in terms of reducing the cost per power generation of the fuel cell system. Thus, the present inventors have studied the technology suitable for reducing the cost per power generation of the fuel cell system.

[0010] An embodiment will be described in detail below with reference to the drawings. However, an unnecessarily detailed description may be omitted. For example, a detailed description of the matters already well known and a repeated description of substantially the same configuration may be omitted.

[0011] The accompanying drawings and the following description are provided for those skilled in the art to fully understand the present disclosure, and thus are not intended to limit the subject matters recited in the claims to these.

[0012] (Embodiment) [1-1. Configuration] Fig. 1 illustrates a configuration of a fuel cell system 110 according to an embodiment. The fuel cell system 110 includes a fuel cell unit 120 and a control device 130. The fuel cell unit 120 includes a plurality of fuel cells 125.

[0013] The fuel cell system 110 supplies power to a load 140. The load 140 is, for example, a factory, a hospital, a school, a commercial facility, an office building, or the like.

[0014] Each fuel cell 125 is capable of performing rated power generation and partial-load power generation. The rated power generation generates rated generation power. Hereinafter, the output power at the time of rated power generation is sometimes referred to as rated output power. The partial-load power generation generates power less than the rated generation power. The output power at the time of partial-load power generation is less than the rated output power. The fuel cell 125 is, for example, a polymer electrolyte fuel cell (PEFC), a solid oxide fuel cell (SOFC), or the like.

[0015] The fuel cell 125 reaches the end of service life through operation. Here, it is assumed that operating the fuel cells 125 is accompanied by power generation. Specifically, a lifetime operation period and the number of lifetime activations are provided for each fuel cell 125.

[0016] The lifetime operation period of the fuel cell 125 is a cumulative period in which the fuel cell 125 is operable, counted from when the fuel cell 125 is new. In the fuel cell system 110, a fuel cell 125, whose cumulative operation period counted from when it was new has reached the lifetime operation period, is not operated anymore.

[0017] The number of lifetime activations of the fuel cell 125 is a cumulative number of times the fuel cell 125 can be activated, counted from when the fuel cell 125 is new. In the fuel cell system 110, a fuel cell 125, whose cumulative number of activations counted from when it was new has reached the number of lifetime activations, is not operated anymore.

[0018] In the present embodiment, the fuel cells 125 have the same specification. The fuel cells 125 have the same lifetime operation period, and the same number of lifetime activations. The fuel cells 125 may be degraded at the same speed if being used in the same manner.

[0019] The control device 130 is, for example, a computer including a memory and a processor. Programs required for control are stored in the memory. The processor reads out a program from the memory and executes the program.

[0020] The control device 130 controls output power of the fuel cell unit 120 (hereinafter referred to as unit output power). Specifically, the control device 130 controls the unit output power so as to follow request power requested by the load 140 connected to the fuel cell system 110. More specifically, the control device 130 controls the output powers of the fuel cells 125 such that the unit output power follows the request power of the load 140.

[0021] In a typical example, the fuel cell unit 120 includes a plurality of power converters (not shown). The power converters are one-to-one corresponding to the fuel cells 125. The output power of each fuel cell 125 is DC output power. The DC output power of a fuel cell 125 is converted to AC power by a power converter corresponding to the fuel cell 125. Thus, the AC power is outputted by the combination of the fuel cell 125 and the power converter. AC powers from one or a plurality of the combinations are supplied to the load 140 as the unit output power.

[0022] [1-2. Operation] Each of the fuel cells 125 in the fuel cell unit 120 has an output power range. In the present embodiment, the output power ranges of the fuel cells 125 are based on the specification of the fuel cells 125. The output power ranges of the fuel cells 125 may be nominal values. The output power ranges of the fuel cells 125 are described in, for example, the specification of the fuel cells 125. The output power range of each of the fuel cells 125 is stored in the memory of the control device 130.

[0023] In the present embodiment, a lower limit of the output power range (hereinafter referred to as minimum output power) of each fuel cell 125 is larger than zero. The minimum output power of each fuel cell 125 is, for example, a value of 10% or more and 90% or less of the rated output power of the fuel cell 125. The minimum output power may be a value of 20% or more and 60% or less of the rated output power, or a value of 30% or more and less than 50% of the rated output power. An upper limit of the output power range of each fuel cell 125 is the rated output power of the fuel cell 125. The fuel cells 125 have the same minimum output power. The fuel cells 125 have the same rated output power.

[0024] The control device 130 is capable of executing a predetermined control. The predetermined control is as follows. That is, in changing the unit output power, the predetermined control controls the output power of each fuel cell 125 such that the number of fuel cells 125 activated or the number of fuel cells 125 deactivated takes a minimum value according to the output power range of each fuel cell 125. In this configuration, a situation in which a fuel cell 125 frequently repeats activation and deactivation can be easily avoided. This makes a situation, in which a fuel cell 125 uses up the number of lifetime activations before it uses up the lifetime operation period, hard to occur. This is advantageous in terms of increasing the lifetime power generation of each fuel cell 125, reducing the cost per power generation of the fuel cell system 110, and realizing inexpensive power supply.

[0025] Decreasing the number of fuel cells 125 deactivated realizes decreasing the number of activations of the fuel cells 125 after the deactivations. Therefore, not only the configuration in which the number of fuel cells 125 activated takes the minimum value according to the output power range of each fuel cell 125 but also a configuration in which the number of fuel cells 125 deactivated takes the minimum value according to the output power range of each fuel cell 125 is also advantageous in terms of reducing the cost per power generation of the fuel cell system 110.

[0026] Here, the lifetime power generation of each fuel cell 125 is, specifically, the total amount of power (“amount of power” is also referred to as “electrical energy”) that the fuel cell 125 generates from when it is new to when it is discarded. The cost per power generation (“cost per power generation” is also referred to as “unit price of power generation”) of the fuel cell system 110 is, specifically, a value obtained by dividing the total of equipment costs of the fuel cells 125 in the fuel cell unit 120 by the total lifetime power generation of the fuel cells 125 in the fuel cell unit 120.

[0027] Hereinafter, the control by the control device 130 will be further described with reference to Fig. 2. Fig. 2 is a time chart illustrating the control by the control device 130. In Fig. 2, the horizontal axis represents time, and the vertical axis represents power. A solid line 171 represents the unit output power. The size of a diagonal line hatching 175 in the vertical axis direction schematically indicates the magnitude of the output power of the fuel cell 125.

[0028] In the example shown in Fig. 2, the control device 130 controls the unit output power and the output power of each fuel cell 125 for each control cycle CS.

[0029] Specifically, the control device 130 creates an operation plan for the fuel cell unit 120. The operation plan indicates the unit output power and the output power of each fuel cell 125 for each control cycle CS. The control device 130 controls the unit output power and the output power of each fuel cell 125 according to the operation plan.

[0030] In a typical example, the control device 130 repeatedly executes a set of creation of an operation plan and control according to the created operation plan. The operation plan represents a plan of operation of the fuel cell unit 120 for a predetermined period. In the example shown in Fig. 2, the predetermined period is 24 hours.

[0031] Creating the operation plan is not essential. For example, the control device 130 may be caused to perform a control for sequentially changing the unit output power and the output power of each fuel cell 125 while monitoring the request power of the load 140.

[0032] In the present embodiment, the predetermined control is executed in units of the control cycle CSof thecontrol device 130. Specifically, the predetermined control in the present control cycle CSis executed based on the number of operating fuel cells 125 in the previous control cycle CSand on a value to be taken by the unit output power in the present control cycle CS. Thus, the predetermined control in the present control cycle CSsets the number of operating fuel cells 125 in the present control cycle CSto a value based on the number of operating fuel cells 125 in the previous control cycle CSand on the value to be taken by the unit output power in the present control cycle CS.

[0033] Specifically, the predetermined control is described as follows. In the following description, ・ The rated output power of each fuel cell 125 is expressed as WRAT. ・ The minimum output power of each fuel cell 125 is expressed as WMIN. ・ The number of operating fuel cells 125 before change in the unit output power is expressed as M1. ・ The number of operating fuel cells 125 after change in the unit output power is expressed as M2. ・ M2-M1is expressed as ΔM. ・ The unit output power after change in the unit output power is expressed as W2. ・ A natural number not smaller than 1 is expressed as X.

[0034] In the case of increasing the unit output power, the predetermined control controls the output power of each fuel cell 125 such that ・when W2≦WRAT×M1is satisfied, ΔM becomes zero, and ・when there is a value for X that satisfies WRAT×(M1+X-1)＜W2≦WRAT×(M1+X), ΔM becomes X. In the case of increasing the unit output power, M1is an integer not less than 0. M2is a natural number not less than 1. ΔM is an integer not less than 0.

[0035] In the case of reducing the unit output power, the predetermined control controls the output power of each fuel cell 125 such that ・ ΔM becomes zero when WMIN×M1≦W2, and ・ ΔM becomes X×(-1) when there is a value for X that satisfies WMIN×(M1-X)≦W2＜WMIN×(M1-X+1). In the case of reducing the unit output power, M1is a natural number not less than 1. M2is an integer not less than 0. ΔM is an integer not more than 0.

[0036] The case of increasing the unit output power and the case of reducing the unit output power can be summarized as follows. That is, in the case of changing the unit output power, the predetermined control controls the output power of each fuel cell 125 such that ・ when WMIN×M1≦W2≦WRAT×M1is satisfied, ΔM becomes zero, ・ when there is a value for X that satisfies WMIN×(M1-X)≦W2＜WMIN×(M1-X+1), ΔM becomes X×(-1), and ・ when there is a value for X that satisfies WRAT×(M1+X-1)＜W2≦WRAT×(M1+X), ΔM becomes X.

[0037] In the present embodiment, the control device 130 is capable of executing an operation stop control. The operation stop control deactivates each fuel cell 125 according to a continuous operation period of the fuel cell 125. In the present embodiment, the predetermined control and the operation stop control are executed such that the operation stop control is prioritized over the predetermined control. Here, the expression “the predetermined control and the operation stop control are executed such that the operation stop control is prioritized over the predetermined control” is described. This expression means that when the operation stop control and the predetermined control are incompatible, the operation stop control is executed while the predetermined control is not executed. This expression means that when the operation stop control and the predetermined control are compatible, both the operation stop control and the predetermined control are executed.

[0038] In the present embodiment, the operation stop control includes a first deactivation control and / or a second deactivation control. The first deactivation control and the second deactivation control will be described with reference to Fig. 3 and Fig. 4.

[0039] Fig. 3 is a time chart illustrating the first deactivation control. Fig. 4 is a time chart illustrating the second deactivation control. In Fig. 3 and Fig. 4, the horizontal axis represents time, and the vertical axis represents output power of a fuel cell 125. In Fig. 3 and Fig. 4, only a temporal change in output power of one fuel cell 125 is shown for convenience of description. In Fig. 3 and Fig. 4, the level of the rated output power WRATis shown by a block arrow.

[0040] The first deactivation control shown in Fig. 3 deactivates a fuel cell 125 whose continuous operation period is longer than a first upper limit period pUL1. Firstly, this control makes a situation, in which the fuel cell 125 uses up the number of lifetime activations before it uses up the lifetime operation period, hard to occur. This is advantageous in terms of increasing the lifetime power generation of the fuel cell 125, and reducing the cost per power generation of the fuel cell system 110. Secondly, even if the fuel cell 125 is being operated at low output power, this control avoids a situation in which this state continues over a long time. For these reasons, the first deactivation control can contribute to reduction in the cost per power generation of the fuel cell system 110.

[0041] Specifically, the first upper limit period pUL1takes a value obtained by dividing the lifetime operation period by the number of lifetime activations. Thus, a situation, in which the cumulative operation period of the fuel cell 125 becomes short with respect to the cumulative number of activations of the fuel cell 125, can be easily avoided. This makes a situation, in which the fuel cell 125 uses up the number of lifetime activations before it uses up the lifetime operation period, hard to occur.

[0042] In the example shown in Fig. 3, time t1, time t2, and time t3are arranged in time sequence. A control cycle next to a control cycle CScorresponding to time t2is a control cycle CScorresponding to time t3. In a control cycle CScorresponding to time t1, the control device 130 transmits an activation instruction to the fuel cell 125, whereby the fuel cell 125 is activated. This also applies to the example shown in Fig. 4.

[0043] In the example shown in Fig. 3, the first upper limit period pUL1is longer than the length of a period from time t1to time t2, and is shorter than the length of a period from time t1to time t3.

[0044] In the example shown in Fig. 3, in the control cycle CScorresponding to time t2, the control device 130 determines that the continuous operation period of the fuel cell 125 is shorter than the first upper limit period pUL1. Therefore, the control device 130 does not deactivate the fuel cell 125 in the control cycle CScorresponding to time t2. In the control cycle CScorresponding to time t3, the control device 130 determines that the continuous operation period of the fuel cell 125 is longer than the first upper limit period pUL1. Based on this determination, the control device 130 deactivates the fuel cell 125 in the control cycle CScorresponding to time t3. Thus, the first deactivation control is achieved.

[0045] The second deactivation control shown in Fig. 4 deactivates a fuel cell 125 whose mean value of continuous operation period is longer than a second upper limit period pUL2. The second deactivation control can contribute to reduction in the cost per power generation of the fuel cell system 110.

[0046] Specifically, the second upper limit period pUL2is equal to the first upper limit period pUL1. That is, the second upper limit period pUL2takes a value obtained by dividing the lifetime operation period by the number of lifetime activations.

[0047] Specifically, the mean value of continuous operation period is a value obtained by dividing the cumulative operation period of the fuel cell 125 counted from when the fuel cell 125 was new, by the cumulative number of activations of the fuel cell 125 counted from when the fuel cell 125 was new.

[0048] In the example shown in Fig. 4, it is assumed that the first activation, second activation, …, N-2th activation, and N-1th activation of the fuel cell 125 have been performed in advance of the area shown in Fig. 4. In addition, it is assumed that the continuous operation period of the fuel cell 125 from the first activation is p1, the continuous operation period of the fuel cell 125 from the second activation is p2, …, the continuous operation period of the fuel cell 125 from the N-2th activation is pN-2, and the continuous operation period of the fuel cell 125 from the N-1th activation is pN-1. The present activation of the fuel cell 125 shown in Fig. 4 is the Nth activation. At time t3, the present continuous operation period of the fuel cell 125 has reached pt13. At time t3, the mean value of continuous operation period of the fuel cell 125, i.e., (p1+p2+…+pN-1+pt13) / N is larger than the second upper limit period pUL2.

[0049] In the example shown in Fig. 4, in the control cycle CScorresponding to time t2, the control device 130 determines that the mean value of continuous operation period of the fuel cell 125 is shorter than the second upper limit period pUL2. Therefore, the control device 130 does not deactivate the fuel cell 125 in the control cycle CScorresponding to time t2. In the control cycle CScorresponding to time t3, the control device 130 determines that the mean value of continuous operation period of the fuel cell 125 is longer than the second upper limit period pUL2. Based on this determination, the control device 130 deactivates the fuel cell 125 in the control cycle CScorresponding to time t3. Thus, the second deactivation control is achieved.

[0050] Here, a case where the lengths of continuous operation periods of the fuel cell 125 in the respective stages vary, is considered. In this case, if the first deactivation control is adopted, the mean value of the continuous operation period may become shorter than expected. Meanwhile, according to the second deactivation control, a situation, in which the mean value becomes short due to such variations, hardly occurs. This makes a situation, in which the fuel cell 125 uses up the number of lifetime activations before it uses up the lifetime operation period, hard to occur.

[0051] In the present embodiment, in the case of reducing the unit output power, the control device 130 is capable of executing a reduction stop control. Fig. 5 is a time chart illustrating the reduction stop control. In Fig. 5, the horizontal axis represents time, and the vertical axis represents output power of the fuel cell 125. In the example shown in Fig. 5, only a temporal change in output power of one fuel cell 125 is shown for convenience of description.

[0052] The reduction stop control controls the output powers of the fuel cells 125 under a reduction stop constraint. Here, a threshold smaller than the rated output power of the fuel cells 125 is indicated as a first threshold WTH1. The reduction stop constraint is a constraint that when the output power of a fuel cell 125 is reduced, the output power should be reduced so as not to be less than the first threshold WTH1. According to the reduction stop control, deactivation of the fuel cell 125 can be avoided. This can reduce the cumulative number of activations of the fuel cell 125. This makes a situation, in which the fuel cell 125 uses up the number of lifetime activations before it uses up the lifetime operation period, hard to occur. This is advantageous in terms of increasing the lifetime power generation of the fuel cell 125, and reducing the cost per power generation of the fuel cell system 110.

[0053] Specifically, the reduction stop control is performed as follows. That is, in the case where the unit output power is reduced when the fuel cell 125 is present whose reduction of the output power has bottomed out at the first threshold WTH1due to the reduction stop constraint, the output power of a fuel cell 125 other than the fuel cell 125 whose reduction of the output power has bottomed out, is reduced so as not to be less than the first threshold WTH1. Thus, a required reduction in the unit output power can be ensured by a reduction in the output power of the other fuel cell 125.

[0054] In the example shown in Fig. 5, the first threshold WTH1is larger than the minimum output power WMIN. However, the first threshold WTH1may be equal to the minimum output power WMIN.

[0055] A situation in which the reduction stop control is effective will be described with reference to Fig. 6. Fig. 6 is a time chart illustrating the situation in which the reduction stop control is effective. In Fig. 6, the horizontal axis represents time, and the vertical axis represents unit output power.

[0056] In the example shown in Fig. 6, the unit output power takes a peak value at 10 o’clock, a bottom value at 12 o’clock, and a peak value at 18 o’clock. In a period from 10 o’clock to 15 o’clock, the unit output power temporarily decreases and thereafter increases. In other words, in the graph showing the unit output power, a portion corresponding to a period pVALfrom 10 o’clock to 15 o’clock has a valley-like shape. A case where the reduction stop control is not executed is considered. In this case, at the valley-like portion of the period pVAL, one or more fuel cells 125 may be temporarily deactivated and then reactivated. According to the reduction stop control of the present embodiment, such temporal deactivation and reactivation can be avoided. This can reduce the cumulative number of activations of the fuel cell 125. This makes a situation, in which the fuel cell 125 uses up the number of lifetime activations before it uses up the lifetime operation period, hard to occur. This is advantageous in terms of increasing the lifetime power generation of the fuel cell 125, and reducing the cost per power generation of the fuel cell system 110.

[0057] The control device 130 can execute the reduction stop control while executing the predetermined control. In addition, the control device 130 can execute the reduction stop control without executing the predetermined control.

[0058] In the present embodiment, the operation plan is sometimes corrected. Correction of the operation plan will be described with reference to Fig. 7, Fig. 8, and Fig. 9. Fig. 7 is a time chart illustrating a first example of correction of the operation plan. Fig. 8 is a time chart illustrating a second example of correction of the operation plan. Fig. 9 is a time chart illustrating a third example of correction of the operation plan. In Fig. 7, Fig. 8, and Fig. 9, (a) shows the operation plan before correction, and (b) shows the corrected operation plan. In (a) and (b) of Fig. 7, Fig. 8, and Fig. 9, the horizontal axis represents time, and the vertical axis represents output power of a fuel cell 125. In Fig. 7, Fig. 8, and Fig. 9, only a temporal change in output power of one fuel cell 125 is shown for convenience of description. Specifically, a temporal change in output power of a specific fuel cell is shown. The specific fuel cell is clarified in the following description.

[0059] In the example shown in Fig. 7, Fig. 8, and Fig. 9, the control device 130 corrects the operation plan when a constraint cancel condition has been established in the operation plan. Here, a threshold that is equal to or larger than the first threshold WTH1and is less than the rated output power of the fuel cell 125 is indicated as a second threshold WTH2. A fuel cell 125, which is continuously operated with its output power being equal to or less than the second threshold WTH2for a period longer than a specific period pX, is indicated as a specific fuel cell. A starting time point of the period longer than the specific period pXis indicated as a first specific time point tX1. A time point after the specific period pXfrom the first specific time point tX1is indicated as a second specific time point tX2. In this case, the constraint cancel condition is that the specific fuel cell is present in the operation plan. Correction of the operation plan is executed such that the reduction stop constraint is not imposed on the specific fuel cell and the specific fuel cell is deactivated at a deactivation time point tSTOP. The deactivation time point tSTOPis a time point before the second specific time point tX2. In this configuration, a situation, in which the fuel cell 125 is continuously operated for a long time with its output power being low, can be avoided. This can contribute to increase in the lifetime power generation of the fuel cell 125, and reduction in the cost per power generation of the fuel cell system 110.

[0060] The second threshold WTH2may be larger than the first threshold WTH1, or equal to the first threshold WTH1. In the first example shown in Fig. 7, the second threshold WTH2is larger than the first threshold WTH1. In the second example shown in Fig. 8 and the third example shown in Fig. 9, the second threshold WTH2is equal to the first threshold WTH1.

[0061] Specifically, in the examples shown in Fig. 7 and Fig. 8, the deactivation time point tSTOPis the first specific time point tX1. In modifications of the first example and the second example, the deactivation time point tSTOPis a time point tY. The time point tYis a time point before the first specific time point tX1. In Fig. 7 and Fig. 8, a temporal change in output power of the specific fuel cell in the modifications is indicated by an alternate long and three short dashes line. In the third example shown in Fig. 9, the deactivation time point tSTOPis a time point tZ. The time point tZis a time point after the first specific time point tX1and before the second specific time point tX2.

[0062] An example of numerical values in the first example shown in Fig. 7 is as follows. ・ The rated output power WRATof the fuel cell 125 is 10 kW. ・ The minimum output power WMINof the fuel cell 125 is 4 kW. ・ The first threshold WTH1is 5 kW. ・ The second threshold WTH2is 6 kW. ・ The request power of the load 140 at the first specific time point tX1is 19.5 kW. At the first specific time point tX1in the operation plan before correction, the number of operating fuel cells 125 is three. Out of them, the output power of two fuel cells 125 is 7 kW, and the output power of the remaining one fuel cell 125 is 5.5 kW. The operation plan is corrected such that the number of operating fuel cells 125 at the first specific time point tX1is changed from three to two. At the first specific time point tX1in the corrected operation plan, the output power of one of the two fuel cells 125 is 10 kW, and the output power of the other fuel cell 125 is 9.5 kW.

[0063] An example of numerical values in the second example shown in Fig. 8 is as follows. ・ The rated output power WRATof the fuel cell 125 is 10 kW. ・ The minimum output power WMINof the fuel cell 125 is 4 kW. ・ The first threshold WTH1and the second threshold WTH2are each 5 kW. ・ The request power of the load 140 at the first specific time point tX1is 19 kW. At the first specific time point tX1in the operation plan before correction, the number of operating fuel cells 125 is three. Out of them, the output power of two fuel cells 125 is 7 kW, and the output power of the remaining one fuel cell 125 is 5 kW. The operation plan is corrected such that the number of operating fuel cells 125 at the first specific time point tX1is changed from three to two. At the first specific time point tX1in the corrected operation plan, the output power of the two fuel cells 125 is 9.5 kW.

[0064] An example of numerical values in the third example shown in Fig. 9 is as follows. ・ The rated output power WRATof the fuel cell 125 is 10 kW. ・ The minimum output power WMINof the fuel cell 125 is 4 kW. ・ The first threshold WTH1and the second threshold WTH2are each 5 kW. In the example of numerical values, the time point tS1, the first specific time point tX1, the time point tS3, the time point tZ, and the time point tS5are arranged in this order. In addition, ・ The request power of the load 140 at the time point tS1is 28 kW. ・ The request power of the load 140 at the first specific time point tX1is 24 kW. ・ The request power of the load 140 at the time point tS3is 23 kW. ・ The request power of the load 140 at the time point tZis 20 kW. ・ The request power of the load 140 at the time point tS5is 19.5 kW.

[0065] In the operation plan before correction, the number of operating fuel cells 125 is three in a period from the time point tS1to the time point tS5. Specifically, ・ At the time point tS1, the output powers of the three fuel cells 125 are 8 kW, 10 kW, and 10 kW, respectively. ・ At the first specific time point tX1, reduction of the output power of one fuel cell 125 has bottomed out at 5 kW, and the output powers of remaining two fuel cells 125 are 9 kW and 10 kW, respectively. ・ At the time point tS3, reduction of the output power of one fuel cell 125 has bottomed out at 5 kW, and the output powers of remaining two fuel cells 125 are 8 kW and 10 kW, respectively. ・ At the time point tZ, reductions of the output powers of two fuel cells 125 have bottomed out at 5 kW, and the output power of remaining one fuel cell 125 is 10 kW. ・ At the time point tS5, reductions of the output powers of two fuel cells 125 have bottomed out at 5 kW, and the output power of remaining one fuel cell 125 is 9.5 kW.

[0066] In the corrected operation plan, at the time point tZ, the number of operating fuel cells 125 is changed from three to two. In a period from the time point tS1to this change, the number of operating fuel cells 125 is three. In a period from this change to the time point tS5, the number of operating fuel cells 125 is two. Specifically, ・ At the time point tS1, the output powers of the three fuel cells 125 are 8 kW, 10 kW, and 10 kW, respectively. ・ At the first specific time point tX1, the reduction stop constraint is not imposed on one fuel cell 125 and the output power of this fuel cell 125 is 4 kW, and the output powers of remaining two fuel cells 125 are 10 kW and 10 kW, respectively. ・ At the time point tS3, the reduction stop constraint is not imposed on one fuel cell 125 and the output power of this fuel cell 125 is 4 kW, and the output powers of remaining two fuel cells 125 are 9 kW and 10 kW, respectively. ・ At the time point tZ, one fuel cell 125 is deactivated and enters the deactivated state, and the output powers of remaining two fuel cells 125 are 10 kW and 10 kW, respectively. ・ At the time point tS5, one fuel cell 125 is in the deactivated state, and the output powers of remaining two fuel cells 125 are 10 kW and 9.5 kW, respectively.

[0067] As is understood from the example of numerical values of the third example, in the state where the reduction stop constraint regarding the specific fuel cell is canceled, the output power of the specific fuel cell is reduced to the minimum output power WMINaccording to a reduction in the request power of the load 140, and thereafter, the specific fuel cell can be deactivated. Specifically, the specific fuel cell can be deactivated at a timing when the request power of the load 140 can be ensured even when the specific fuel cell is deactivated and the number of operating fuel cells decreases.

[0068] Fig. 10 is a time chart illustrating a control using an operation plan. In Fig. 10, the horizontal axis represents time in the operation plan, and the vertical axis represents unit output power in the operation plan. In Fig. 10, the number of operating fuel cells 125 is parenthesized.

[0069] In the operation plan according to the example shown in Fig. 10, ・ at a reference time point tREF, the number of operating fuel cells 125 is MREF, here, MREFis a natural number not less than 2, ・ at time point tLATElater than the reference time point tREF, the number of operating fuel cells 125 is MPEAKthat is a peak value and is less than MREFby δM, here, MPEAKand δM are a natural number not less than 1, ・ in a post period pLATEon and after the time point tLATE, the number of operating fuel cells 125 is maintained at MPEAKor less, and ・ in a middle period pMIDafter the reference time point tREFand before the time point tLATE, operations of the MPEAKfuel cells 125 are continued, and the δM fuel cells 125 are deactivated without the reduction stop constraint being imposed thereon.

[0070] In the example shown in Fig. 10, in the post period pLATE, the unit output power can be ensured without the δM fuel cells 125. Therefore, in the middle period pMID, the δM fuel cells 125 are deactivated. Meanwhile, in the middle period pMID, operations of the MPEAKfuel cells 125 are continued. Therefore, in the middle period pMID, there is no situation in which some or all of the MPEAKfuel cells 125 are temporarily deactivated and thereafter reactivated. This can reduce the cumulative number of activations of each fuel cell 125. This makes a situation, in which the fuel cell 125 uses up the number of lifetime activations before it uses up the lifetime operation period, hard to occur. This is advantageous in terms of increasing the amount of lifetime power generation of the fuel cell 125, and reducing the cost per power generation of the fuel cell system 110.

[0071] Specifically, in the example shown in Fig. 10, the unit output power at the time point tLATEis (MREF-1)×WRATor less. The number of operating fuel cells MREFat the reference time point tREFis a peak value. During the reduction of the unit output power in the middle period pMID, the number of operating fuel cells 125 decreases each time the unit output power decreases so as to cross an integer multiple of the rated output power WRATand reaches MPEAK.

[0072] [1-3. Effects and the like] The fuel cell system 110 according to one example of the present disclosure includes the fuel cell unit 120 and the control device 130. The fuel cell unit 120 includes a plurality of fuel cells 125. The control device 130 controls the unit output power. The unit output power is the output power of the fuel cell unit 120. The control device 130 is capable of executing the predetermined control. In changing the unit output power, the predetermined control controls the output power of each fuel cell 125 such that the number of fuel cells 125 activated or the number of fuel cells 125 deactivated takes a minimum value according to the output power range of each fuel cell 125. This configuration is suitable for reducing the cost per power generation of the fuel cell system 110.

[0073] The aforementioned operation stop control, reduction stop control, operation plan correction, continuous operation of fuel cells 125 during the middle period, and the like can also contribute to reduction in the cost per power generation of the fuel cell system 110.

[0074] A control method according to one example of the present disclosure is a method for controlling the fuel cell system 110. The fuel cell system 110 includes the fuel cell unit 120. The fuel cell unit 120 includes a plurality of fuel cells 125. The control method includes executing the predetermined control. Here, the output power of the fuel cell unit 120 is indicated as unit output power. In this case, in changing the unit output power, the predetermined control controls the output power of each fuel cell 125 such that the number of fuel cells 125 activated or the number of fuel cells 125 deactivated takes a minimum value according to the output power range of each fuel cell 125.

[0075] A program according to one example of the present disclosure, when being executed by a processor, includes an instruction that causes the processor to execute the above control method. A storage medium according to one example of the present disclosure is a computer-readable storage medium in which the above program is stored. In one example, the program is installed in the fuel cell system 110. Specifically, the program is installed in the control device 130. The processor is, for example, a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. The storage medium is, for example, a semiconductor storage medium, a magnetic storage medium, a magneto-optical storage medium, an optical storage medium, or the like. The semiconductor storage medium is, for example, a secure digital (SD) card, a universal serial bus (USB) memory, a solid state drive (SSD), or the like. The magnetic storage medium is, for example, a hard disk drive (HDD), a flexible disk, or the like. The magneto-optical storage medium is, for example, a magneto-optical (MO) disk or the like. The optical storage medium is, for example, a compact disc (CD), a digital versatile disc (DVD), or the like.

[0076] The present disclosure provides a fuel cell system comprising: a fuel cell unit including a plurality of fuel cells; and a control device that controls unit output power that is output power of the fuel cell unit, wherein in changing the unit output power, the control device is capable of executing a predetermined control, and (A) the fuel cells have the same rated output power, assuming that the rated output power of the fuel cell is expressed as WRAT, the number of operating fuel cells before the unit output power is changed is expressed as M1, the number of operating fuel cells after the unit output power has been changed is expressed as M2, M2-M1is expressed as ΔM, the unit output power having been changed is expressed as W2, and a natural number not less than 1 is expressed as X, in a case of increasing the unit output power, the predetermined control controls the output power of each fuel cell such that when W2≦WRAT×M1is satisfied, ΔM becomes zero, and when there is a value for X that satisfies WRAT×(M1+X-1)＜W2≦WRAT×(M1+X), ΔM becomes X, and / or (B) the fuel cells have the same minimum output power that is larger than zero, assuming that the minimum output power of the fuel cells is expressed as WMIN, the number of operating fuel cells before the unit output power is changed is expressed as M1, the number of operating fuel cells after the unit output power has been changed is expressed as M2, M2-M1is expressed as ΔM, the unit output power having been changed is expressed as W2, and a natural number not less than 1 is expressed as X, in a case of reducing the unit output power, the predetermined control controls the output power of each fuel cell such that when WMIN×M1≦W2is satisfied, ΔM becomes zero, and when there is a value for X that satisfies WMIN×(M1-X)≦W2＜WMIN×(M1-X+1), ΔM becomes X×(-1).

[0077] The present disclosure provides a control method for a fuel cell system including a fuel cell unit including a plurality of fuel cells, assuming that output power of the fuel cell unit is indicated as unit output power, the method comprising , in changing the unit output power, executing a predetermined control, wherein (A) the fuel cells have the same rated output power, assuming that the rated output power of the fuel cell is expressed as WRAT, the number of operating fuel cells before the unit output power is changed is expressed as M1, the number of operating fuel cells after the unit output power has been changed is expressed as M2, M2-M1is expressed as ΔM, the unit output power having been changed is expressed as W2, and a natural number not less than 1 is expressed as X, in a case of increasing the unit output power, the predetermined control controls the output power of each fuel cell such that when W2≦WRAT×M1is satisfied, ΔM becomes zero, and when there is a value for X that satisfies WRAT×(M1+X-1)＜W2≦WRAT×(M1+X), ΔM becomes X, and / or (B) the fuel cells have the same minimum output power that is larger than zero, assuming that the minimum output power of the fuel cells is expressed as WMIN, the number of operating fuel cells before the unit output power is changed is expressed as M1, the number of operating fuel cells after the unit output power has been changed is expressed as M2, M2-M1is expressed as ΔM, the unit output power having been changed is expressed as W2, and a natural number not less than 1 is expressed as X, in a case of reducing the unit output power, the predetermined control controls the output power of each fuel cell such that when WMIN×M1≦W2is satisfied, ΔM becomes zero, and when there is a value for X that satisfies WMIN×(M1-X)≦W2＜WMIN×(M1-X+1), ΔM becomes X×(-1).

[0078] A program according to one example of the present disclosure, when being executed by a processor, includes an instruction that causes the processor to execute the above control method. A storage medium according to one example of the present disclosure is a computer-readable storage medium in which the above program is stored. In one example, the program is installed in the fuel cell system 110. Specifically, the program is installed in the control device 130. The processor is, for example, a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. The storage medium is, for example, a semiconductor storage medium, a magnetic storage medium, a magneto-optical storage medium, an optical storage medium, or the like. The semiconductor storage medium is, for example, a secure digital (SD) card, a universal serial bus (USB) memory, a solid state drive (SSD), or the like. The magnetic storage medium is, for example, a hard disk drive (HDD), a flexible disk, or the like. The magneto-optical storage medium is, for example, a magneto-optical (MO) disk or the like. The optical storage medium is, for example, a compact disc (CD), a digital versatile disc (DVD), or the like.

[0079] The technology according to the present disclosure is applicable to factories and the like.

Claims

1. A fuel cell system comprising: a fuel cell unit including a plurality of fuel cells; and a control device that controls unit output power that is output power of the fuel cell unit, wherein the control device is capable of executing a predetermined control, and in changing the unit output power, the predetermined control controls output power of each fuel cell such that the number of fuel cells activated or the number of fuel cells deactivated takes a minimum value according to an output power range of each fuel cell.

2. The fuel cell system according to claim 1, wherein an upper limit of the output power range is rated output power, and the fuel cells have the same rated output power.

3. The fuel cell system according to claim 2, wherein assuming that the rated output power of the fuel cell is expressed as WRAT, the number of operating fuel cells before the unit output power is changed is expressed as M1, the number of operating fuel cells after the unit output power has been changed is expressed as M2, M2-M1is expressed as ΔM, the unit output power having been changed is expressed as W2, and a natural number not less than 1 is expressed as X, in a case of increasing the unit output power, the predetermined control controls the output power of each fuel cell such that when W2≦WRAT×M1is satisfied, ΔM becomes zero, and when there is a value for X that satisfies WRAT×(M1+X-1)＜W2≦WRAT×(M1+X), ΔM becomes X.

4. The fuel cell system according to any one of claims 1 to 3, wherein minimum output power that is a lower limit of the output power range is larger than zero, and the fuel cells have the same minimum output power.

5. The fuel cell system according to claim 4, wherein assuming that the minimum output power of the fuel cells is expressed as WMIN, the number of operating fuel cells before the unit output power is changed is expressed as M1, the number of operating fuel cells after the unit output power has been changed is expressed as M2, M2-M1is expressed as ΔM, the unit output power having been changed is expressed as W2, and a natural number not less than 1 is expressed as X, in a case of reducing the unit output power, the predetermined control controls the output power of each fuel cell such that when WMIN×M1≦W2is satisfied, ΔM becomes zero, and when there is a value for X that satisfies WMIN×(M1-X)≦W2＜WMIN×(M1-X+1), ΔM becomes X×(-1).

6. The fuel cell system according to any one of claims 1 to 5, wherein minimum output power that is a lower limit of the output power range is larger than zero, an upper limit of the output power range is rated output power, the fuel cells have the same rated output power, and the fuel cells have the same minimum output power.

7. The fuel cell system according to claim 6, wherein assuming that the rated output power of the fuel cells is expressed as WRAT, the minimum output power of the fuel cells is expressed as WMIN, the number of operating fuel cells before the unit output power is changed is expressed as M1, the number of operating fuel cells after the unit output power has been changed is expressed as M2, M2-M1is expressed as ΔM, the unit output power having been changed is expressed as W2, and a natural number not less than 1 is expressed as X, in a case of changing the unit output power, the predetermined control controls the output power of each fuel cell such that when WMIN×M1≦W2≦WRAT×M1is satisfied, ΔM becomes zero, when there is a value for X that satisfies WMIN×(M1-X)≦W2＜WMIN×(M1-X+1), ΔM becomes X×(-1), and when there is a value for X that satisfies WRAT×(M1+X-1)＜W2≦WRAT×(M1+X), ΔM becomes X.

8. The fuel cell system according to any one of claims 1 to 7, wherein the control device is capable of executing an operation stop control, and the operation stop control deactivates the fuel cell according to a continuous operation period of the fuel cell.

9. The fuel cell system according to claim 8, wherein the predetermined control and the operation stop control are executed such that the operation stop control is prioritized over the predetermined control.

10. The fuel cell system according to claim 8 or 9, wherein the operation stop control includes a first deactivation control, and the first deactivation control deactivates the fuel cell whose continuous operation period is longer than a first upper limit period.

11. The fuel cell system according to any one of claims 8 to 10, wherein the operation stop control includes a second deactivation control, and the second deactivation control deactivates the fuel cell whose mean value of continuous operation period is longer than the second upper limit period.

12. The fuel cell system according to any one of claims 1 to 11, wherein in a case of reducing the unit output power, the control device is capable of executing a reduction stop control, the reduction stop control controls output powers of the fuel cells under a reduction stop constraint, a threshold smaller than the rated output power of the fuel cells is indicated as a first threshold, and the reduction stop constraint is a constraint that when the output power of the fuel cell is reduced, the output power should be reduced so as not to be less than the first threshold.

13. The fuel cell system according to claim 12, wherein in a case of reducing the unit output power when the fuel cell is present whose reduction of the output power has bottomed out at the first threshold due to the reduction stop constraint, the reduction stop control reduces the output power of the fuel cell, other than the fuel cell whose reduction of the output power has bottomed out, so as not to be less than the first threshold.

14. The fuel cell system according to claim 12 or 13, wherein the control device creates a first operation plan of the fuel cell units, controls the fuel cells according to the first operation plan, and corrects the first operation plan when a constraint cancel condition is satisfied in the first operation plan, and assuming that a threshold that is equal to or larger than the first threshold and is smaller than the rated output power is indicated as a second threshold, the fuel cell that is continuously operated with the output power being equal to or less than the second threshold for a period longer than a specific period, is indicated as a specific fuel cell, a starting time point of the period longer than the specific period is indicated as a first specific time point, and a time point after the specific period from the first specific time point is indicated as a second specific time point, the constraint cancel condition is a condition that the specific fuel cell is present in the first operation plan, and the first operation plan is corrected such that the reduction stop constraint is not imposed on the specific fuel cell, and the specific fuel cell is deactivated at a time point before the second specific time point.

15. The fuel cell system according to any one of claims 12 to 14, wherein the control device creates a second operation plan, and controls the fuel cells according to the second operation plan, and in the second operation plan, the number of operating fuel cells is MREFat a reference time point, the number of operating fuel cells is MPEAKthat is a peak value and is less than MREFby δM, at a time point after the reference time point, the number of operating fuel cells is maintained to be MPEAKor less in a post-period on and after the time point after the reference time point, and in a middle period after the reference time point and before the time point after the reference time point, operations of the MPEAKfuel cells are continued, and the δM fuel cells are deactivated without the reduction stop constraint being imposed thereon.

16. The fuel cell system according to any one of claims 1 to 15, wherein the predetermined control is executed in units of control cycles of the control device.

17. The fuel cell system according to any one of claims 1 to 16, wherein the control device controls the unit output power so as to follow a request power that a load connected to the fuel cell system requests.

18. A control method for a fuel cell system including a fuel cell unit including a plurality of fuel cells, the method comprising executing a predetermined control, wherein assuming that output power of the fuel cell unit is indicated as unit output power, the predetermined control, in changing the unit output power, controls output power of each fuel cell such that the number of fuel cells activated or the number of fuel cells deactivated takes a minimum value according to an output power range of each fuel cell.

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