Power systems and power control devices

Abstract

The present invention aims to provide an electric power system and electric power control device that can improve fuel efficiency compared to conventional systems. To address the above-mentioned issues, an electric power system according to an embodiment includes n (n is an integer greater than or equal to 2) fuel cells and a control unit. The fuel cells generate electricity through electrochemical reactions. The control unit sets the operating mode of each of the fuel cells to any one of a plurality of modes, based on a request output corresponding to the power to be consumed by a load. The plurality of modes includes a first power generation mode that repeatedly starts and stops power generation, a second power generation mode that continues power generation, and a stop mode that stops power generation.

Description

Technical Field

[0001] The present invention relates to an electric power system and an electric power control device. Background Art

[0002] There is a vehicle equipped with multiple fuel cells, in which the multiple fuel cells operate simultaneously.

[0003] [Prior Art Literature]

[0004] (Patent Document)

[0005] Patent Document 1: Japanese Patent Application No. 2011-503812 Summary of the Invention

[0006] [Problems to be solved by the invention]

[0007] However, when multiple fuel cells are operated simultaneously, fuel efficiency is poor in the low-load output range. This is because when the fuel cells are operated at low load, the efficiency deteriorates due to the influence of the load of the auxiliary machines.

[0008] An object of the embodiments of the present invention is to provide an electric power system and an electric power control device that can improve fuel efficiency compared to conventional systems.

[0009] [Technical means to solve the problem]

[0010] An electric power system according to an embodiment includes n (n is an integer greater than or equal to 2) fuel cells and a control unit. The fuel cells generate electricity through electrochemical reactions. The control unit sets the operating mode of each of the fuel cells to any one of a plurality of modes, including a first power generation mode in which power generation is repeatedly started and stopped, a second power generation mode in which power generation is continued, and a stop mode in which power generation is stopped, based on a requested output corresponding to power consumption by a load.

[0011] (Effects of the Invention)

[0012] The present invention can improve fuel efficiency compared with the past. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a block diagram illustrating an example of the structure of a main portion of a vehicle according to the embodiment.

[0014] Figure 2 It is a drawing Figure 1 A flowchart of an example of processing performed by the control unit in .

[0015] Figure 3 It is a drawing Figure 1A graph showing the relationship between the output and efficiency of a fuel cell system (FCS) in FIG.

[0016] Figure 4 It is a drawing Figure 1 A diagram showing an example of an FCS waveform in FIG.

[0017] Figure 5 It is a drawing Figure 1 A graph showing the relationship between the output and efficiency of the FCS. DETAILED DESCRIPTION

[0018] The following describes a vehicle according to an embodiment using the accompanying drawings. The scales of various parts of the drawings used in the following description of the embodiment may be appropriately altered. Furthermore, for ease of explanation, the drawings used in the following description of the embodiment may sometimes omit components. The same reference numerals in the drawings and this specification represent the same components.

[0019] Figure 1 This is a block diagram illustrating an example of the structure of the main parts of the vehicle 1 according to the embodiment.

[0020] Vehicle 1 is a vehicle such as a fuel cell vehicle (FCV) that uses a fuel cell as a power source for propulsion (travel). Vehicle 1 includes, for example, a control unit 11, a fuel cell system (FCS) 12, a battery 13, a motor 14, and a load 15. Vehicle 1 is an example of an electric power system.

[0021] The control unit 11 is, for example, a computer that performs the calculations and control processes required for the operation of the vehicle 1. Based on programs such as firmware, system software, and application software stored in a main storage device or auxiliary storage device, the control unit 11 controls various components to implement the various functions of the vehicle 1. Furthermore, the control unit 11 executes the processes described below based on these programs. Furthermore, some or all of these programs may be incorporated into the circuitry of the control unit 11. The control unit 11 is an example of a load that consumes the power generated by the FCS 12. The control unit 11 is an example of a power control device.

[0022] Vehicle 1 includes multiple FCSs 12. FCSs 12 include, for example, a fuel cell stack and various devices used to operate the fuel cell stack. A fuel cell stack is composed of multiple stacked fuel cells. The fuel cell stack generates and outputs electricity through, for example, an electrochemical reaction between fuel gas and oxidant gas. This electricity is supplied to various components of vehicle 1 and used to operate various components of vehicle 1, such as charging battery 13 and driving motor 14.

[0023] Furthermore, the FCS 12 may include auxiliary equipment for supplying fuel gas and oxidant gas to the fuel cell stack as devices for operating the fuel cell stack.

[0024] Vehicle 1 includes one or more batteries 13. Batteries 13 are secondary batteries that supply power to various components of vehicle 1, such as motor 14. Specifically, vehicle 1 operates using power output from FCS 12 and power output from batteries 13. Batteries 13 are charged, for example, using power generated by FCS 12.

[0025] Vehicle 1 includes one or more motors 14. Motor 14 is, for example, an electric motor that converts input electricity into rotational force and outputs it. Motor 14 operates using electricity output from FCS 12 and battery 13. The rotational force output by motor 14 rotates wheels and other components, for example, via gears and shafts. Motor 14 is an example of a load that consumes the electricity generated by FCS 12.

[0026] The load 15 is a component other than the control unit 11 and the motor 14 that consumes the power generated by the FCS 12. Examples of the load 15 include lighting, air conditioning, vehicle-mounted devices, monitors, displays, and speakers.

[0027] The following is based on Figure 2 The operation of the vehicle 1 according to the embodiment will be described below. The contents of the processing in the following operation description are merely examples, and various processing that can achieve the same result can be used as appropriate. Figure 2 This is a flowchart showing an example of processing performed by the control unit 11 of the vehicle 1. The control unit 11 executes, for example, based on a program stored in a main storage device or an auxiliary storage device. Figure 2 In addition, Figure 2 The illustrated processing is performed when the number of FCSs 12 included in the vehicle 1 is three.

[0028] exist Figure 2 In step ST11, the control unit 11 waits for a change in the requested output. The control unit 11 controls the vehicle 1 so that the total output voltage of the FCS 12 is greater than the requested output. The requested output varies depending on the state of the vehicle 1, etc. If the requested output has changed, the control unit 11 determines "Yes" in step ST11 and proceeds to step ST12.

[0029] In step ST12, the control unit 11 determines whether the requested output is less than threshold value P1. If the requested output is greater than threshold value P1, the control unit 11 determines "No" in step ST12 and proceeds to step ST12. On the other hand, if the requested output is less than threshold value P1, the control unit 11 determines "Yes" in step ST12 and proceeds to step ST17.

[0030] In step ST13, the control unit 11 determines whether the requested output is less than threshold value P2. If the requested output is greater than threshold value P2, the control unit 11 determines "no" in step ST13 and proceeds to step ST14. In contrast, if the requested output is less than threshold value P2, that is, if the requested output is greater than P1 but less than P2, the control unit 11 determines "yes" in step ST13 and proceeds to step ST19.

[0031] In step ST14, the control unit 11 determines whether the requested output is less than threshold value P3. If the requested output is greater than threshold value P3, the control unit 11 determines "no" in step ST14 and proceeds to step ST15. In contrast, if the requested output is less than threshold value P3, that is, if the requested output is greater than P2 but less than P3, the control unit 11 determines "yes" in step ST14 and proceeds to step ST21.

[0032] In step ST15, the control unit 11 determines whether the requested output is less than threshold value P4. If the requested output is greater than threshold value P4, the control unit 11 determines "no" in step ST15 and proceeds to step ST16. In contrast, if the requested output is less than threshold value P4, that is, if the requested output is greater than P3 but less than P4, the control unit 11 determines "yes" in step ST15 and proceeds to step ST24.

[0033] In step ST16, the control unit 11 determines whether the requested output is less than the threshold value P5. If the requested output is less than the threshold value P5, that is, if the requested output is greater than or equal to P4 but less than P5, the control unit 11 determines "yes" in step ST16 and proceeds to step ST26. On the other hand, if the requested output is greater than or equal to the threshold value P5, the control unit 11 determines "no" in step ST16 and proceeds to step ST28.

[0034] use Figure 3 To explain each threshold value. Figure 3 is a graph showing the relationship between the output and efficiency of the FCS 12. Figure 3 , which shows the output-efficiency characteristics of each of the cases where 1 to 3 FCS 12 are operated. Figure 3 In the diagram, the point with the highest efficiency when operating with one FCS 12 is Q1, the point with the highest efficiency when operating with two FCS 12 is Q2, and the point with the highest efficiency when operating with three FCS 12 is Q3. The magnitude relationship between thresholds P1 to P5 and the outputs at points Q1 to Q3 is P1 < Q1 < P2 < P3 < Q2 < P4 < P5 < Q3.

[0035] The output at point Qx is the total output of x FCSs 12 when operating them most efficiently. For example, if x = 1, Qx is Q1. The output at point Q1 is the output of one FCS 12 when operating it most efficiently. x is an integer greater than 1 and less than n. n will be described below.

[0036] Furthermore, the output at point P(2x-1) is a specific value less than the output at point Qx, and the output at point P(2x) is a specific value greater than the output at point Qx. That is, the output at point P1 is a specific value less than the output at point Q1, and the output at point P2 is a specific value greater than the output at point Q1. Furthermore, the output at point P3 is a specific value less than the output at point Q2, and the output at point P4 is a specific value greater than the output at point Q2. Furthermore, the output at point P5 is a specific value less than the output at point Q3. Furthermore, these specific values ​​may be different or the same.

[0037] like Figure 3 As shown, it is generally believed that when the requested output is P1-P2, using one FCS 12 for power generation achieves good efficiency. Furthermore, when the requested output is P3-P4, using two FCSs 12 for power generation achieves good efficiency. Furthermore, when the requested output is P5 or higher, using three FCSs 12 for power generation achieves good efficiency. Furthermore, when the requested output is less than P1, using one FCS 12 with its output reduced for power generation achieves good efficiency. Furthermore, when the requested output is P2-P3, using two FCSs 12 with their output reduced for power generation achieves good efficiency. Furthermore, when the requested output is P4-P5, using three FCSs 12 with their output reduced for power generation achieves good efficiency.

[0038] return Figure 2 Description.

[0039] In step ST17, the control unit 11 operates one FCS 12 in a repetitive operation mode. Repetitive operation is an operation that suppresses output by repeatedly turning on and off power generation. In other words, repetitive operation is an operation that suppresses output by repeatedly starting and stopping power generation. Figure 4 The waveform W2 shows an example of a waveform in a state of repeated operation. Figure 4 1 is a diagram showing an example of a waveform of the FCS 12. The repetitive operation is an example of the first power generation mode.

[0040] exist Figure 2In step ST18, the control unit 11 stops the power generation of the remaining two FCSs 12. Figure 4 The waveform W3 shows an example of a waveform in a state where power generation is stopped. After the process of step ST18, the control unit 11 returns to step ST11. The state where power generation is stopped is an example of a stop mode.

[0041] By Figure 2 According to the processing of step ST17 and step ST18, one of the three FCSs 12 enters the repeated operation state, and the other two enter the power generation stop state.

[0042] In step ST19, the control unit 11 operates one FCS 12 in efficiency-point operation. Efficiency-point operation is an operation in which power generation is continued at an output greater than a specific level within a high power generation efficiency range. Examples of high power generation efficiency ranges include a range with a specific efficiency or higher, or a range in which the output of the FCS 12 is within a specific range. Furthermore, during repeated operation, the output when power generation is enabled is, for example, the same as or equivalent to the output during efficiency-point operation. Figure 4 The waveform W1 shows an example of a waveform in the state of efficiency point operation. In addition, efficiency point operation is an example of the second power generation mode. In addition, the first power generation mode, the second power generation mode, and the stop mode are each an example of an operation mode.

[0043] In step ST20, the control unit 11 stops power generation by the remaining two FCSs 12. After the processing of step ST20, the control unit 11 returns to step ST11.

[0044] By the processing of step ST19 and step ST20, one of the three FCSs 12 enters the state of efficient point operation, and the other two enter the state of power generation stop.

[0045] In step ST21 , the control unit 11 operates one FCS 12 at the efficiency point.

[0046] In step ST22 , the control unit 11 operates one of the remaining two FCSs 12 in a repetitive operation.

[0047] In step ST23, the control unit 11 stops power generation of the remaining one FCS 12. After the processing of step ST23, the control unit 11 returns to step ST11.

[0048] By the processing of steps ST21 to ST23 , one of the three FCSs 12 enters the state of efficient point operation, one enters the state of repeated operation, and one enters the state of power generation stop.

[0049] In step ST24 , the control unit 11 operates the two FCSs 12 at the efficiency point.

[0050] In step ST25, the control unit 11 stops power generation of the remaining one FCS 12. After the process of step ST25, the control unit 11 returns to step ST11.

[0051] By the processing of step ST24 and step ST25, two of the three FCSs 12 are in the state of efficient point operation, and one is in the state of power generation stop.

[0052] In step ST26 , the control unit 11 operates the two FCSs 12 at the efficiency point.

[0053] In step ST27, the control unit 11 operates the remaining one FCS 12 in a repetitive manner. After the processing of step ST27, the control unit 11 returns to step ST11.

[0054] By the processing of step ST26 and step ST27, two of the three FCSs 12 are put into the state of efficient point operation, and one is put into the state of repeated operation.

[0055] In step ST28, the control unit 11 operates the three FCSs 12 at the efficiency point. After the processing of step ST28, the control unit 11 returns to step ST11.

[0056] Furthermore, in steps S17 to S27, the control unit 11 can use various methods to determine whether the FCS 12 is to be operated at the efficiency point, to be operated repeatedly, or to be stopped. For example, the control unit 11 can set a predetermined FCS 12, a randomly determined FCS 12, an FCS 12 determined based on the amount of operating time or the degree of degradation, or an FCS 12 determined by other methods to be operated at the efficiency point, to be operated repeatedly, or to be stopped. For example, the control unit 11 can prioritize the FCS 12 with the lowest degree of degradation for the efficiency point or repeated operation.

[0057] In addition, an example of a case where FCS 12 is 4 is shown in FIG. Figure 5 . Figure 5 is a graph showing the relationship between the output and efficiency of the FCS 12. Figure 5 , which shows the output-efficiency characteristics when operating 1 to 4 FCS 12. When there are 4 FCS 12, in addition to the thresholds P1 to P5, the control unit 11 also uses the thresholds P6 and P7 to control the FCS 12. Figure 5In addition to points Q1 to Q3, point Q4 is also shown, which is the most efficient point when operating four FCSs 12. The magnitude relationship between thresholds P1 to P7 and the outputs of points Q1 to Q4 is P1 < Q1 < P2 < P3 < Q2 < P4 < P5 < Q3 < P6 < P7 < Q4.

[0058] When there are four FCSs 12 and the requested output is less than P5, the control unit 11 controls the FCSs 12 in the same manner as when there are three FCSs 12. However, when there are four FCSs 12, the number of FCSs 12 in the power generation stop state is one more than when there are three FCSs 12. Furthermore, when the requested output is greater than P5 and less than P6, the control unit 11 causes three FCSs 12 to operate at the efficiency point and one FCS 12 to stop operating. Furthermore, when the requested output is greater than P6 and less than P7, the control unit 11 causes three FCSs 12 to operate at the efficiency point and one FCS 12 to operate in a repetitive mode. Furthermore, when the requested output is greater than P7, the control unit 11 causes four FCSs 12 to operate at the efficiency point.

[0059] Furthermore, when there are n FCSs 12, if the requested output is greater than or equal to P(k-1) and less than Pk, the control unit 11 causes (floor(k / 2)) FCSs 12 to operate at the efficiency point, causes (k mod 2) FCSs 12 to operate in a repetitive mode, and causes (n-ceil(k / 2)) FCSs 12 to stop generating power. Furthermore, if the requested output is less than P1, one FCS 12 is operated in a repetitive mode, and (n-1) FCSs 12 are stopped. Furthermore, if the requested output is greater than or equal to P(k+1), the control unit 11 causes n FCSs 12 to operate at the efficiency point. Here, k is an integer satisfying 2≦k≦(2n-1). Floor represents a ceiling function, ceil represents a floor function, and mod represents a modulo operator. In addition, P(k-1) represents the (k-1)th threshold value P, and Pk represents the kth threshold value P. For example, if k=3, Pk represents the third threshold value P, that is, threshold value P3.

[0060] Furthermore, when k is an even number, P(k-1)<Q(k / 2)<Pk, and when k is an odd number, Q((k-1) / 2)<P(k-1)<Pk<Q((k+1) / 2).

[0061] Furthermore, m is set to an arbitrary integer between 1 and n. In this case, if the requested output is greater than or equal to P(2m-2) and less than P(2m-1), the control unit 11 operates the (m-1) FCSs 12 at the efficiency point, puts one FCS 12 into repetitive operation, and stops power generation by the (n-m) FCSs 12. Furthermore, if the requested output is greater than or equal to P(2m-1) and less than P(2m), the control unit 11 operates the m FCSs 12 at the efficiency point and stops power generation by the (n-m) FCSs 12. If m = 1, and the requested output is greater than or equal to 0 and less than P(2m-1), the control unit 11 puts one FCS 12 into repetitive operation and stops power generation by the (n-m) FCSs 12. Furthermore, if m = n, and the requested output is greater than or equal to P(2m-1), the control unit 11 operates the m FCSs 12 at the efficiency point.

[0062] The output at point P(2m-1) is smaller than the output at point Qm by a specific value, and the output at point P(2m) is larger than the output at point Qm by a specific value. This specific value may be different for each point P.

[0063] Threshold value P(2m-1) in the relationship 1≦m≦(n-1) is an example of threshold value A, and threshold value P(2m) is an example of threshold value B. For example, when m=3, threshold value P5 is threshold value A, and threshold value P6 is threshold value B.

[0064] In addition, the threshold value P(2n-1) is an example of the threshold value C. As an example, when n=4, the threshold value P7 is the threshold value C.

[0065] In addition, the threshold value P1 is an example of a first threshold value, the threshold value P2 is an example of a second threshold value, and the threshold value P3 is an example of a third threshold value.

[0066] The vehicle 1 of the embodiment determines the operating mode of the FCS 12 based on the requested output. This allows the vehicle 1 of the embodiment to generate power at a higher efficiency than when the n FCSs 12 are operated with their outputs suppressed. Furthermore, the vehicle 1 of the embodiment improves fuel efficiency due to this increased efficiency.

[0067] Furthermore, the vehicle 1 of the embodiment operates one FCS 1 in a repetitive manner when the requested output is less than P1. This allows the vehicle 1 of the embodiment to generate power at a higher efficiency than when the n FCSs 12 are operated with their outputs suppressed.

[0068] Furthermore, the vehicle 1 of the embodiment operates one FCS 1 at the efficiency point when the requested output is P1-P2. This allows the vehicle 1 of the embodiment to generate power at a higher efficiency than when the n FCSs 12 are operated with their outputs suppressed.

[0069] Furthermore, when the requested output is P(2m-2) to P(2m-1), the vehicle 1 of the embodiment operates (m-1) FCSs 12 at the efficiency point and repeatedly operates one FCS 12. This allows the vehicle 1 of the embodiment to generate power at a higher efficiency than when n FCSs 12 are operated with their outputs suppressed.

[0070] Furthermore, when the required output is P(2m-1) to P(2m), the vehicle 1 of the embodiment operates the m FCSs 12 at the efficiency point. This allows the vehicle 1 of the embodiment to generate power at a higher efficiency than when the n FCSs 12 are operated with their outputs suppressed.

[0071] Furthermore, the vehicle 1 of the embodiment operates n FCSs 12 at the efficiency point when the requested output is P(2n-1) or greater. This ensures that the efficiency of the vehicle 1 of the embodiment does not decrease compared to conventional vehicles even when high-output power generation is required.

[0072] Furthermore, the vehicle 1 of the embodiment stops power generation in FCSs 12 other than those operating at the efficiency point or performing repetitive operation. Thus, the vehicle 1 of the embodiment can generate power at a higher efficiency than before by stopping power generation in FCSs 12 not required for the requested output.

[0073] Furthermore, the vehicle 1 of the embodiment determines the FCS 12 for performing the efficiency point operation and the FCS 12 for performing the repetitive operation based on the degree of degradation.

[0074] The above-mentioned embodiment can also be modified as follows.

[0075] The control unit 11 can also determine the output of the FCS 12 based on the charge state of the battery 13. For example, if the remaining charge of the battery 13 is low, the control unit 11 controls the timing of starting and stopping power generation to shorten the ratio of the length of time during which power generation is stopped during repeated operation. The control unit 11 then uses the excess power generated by the FCS 12 to charge the battery 13.

[0076] An FCS may also have multiple fuel cell stacks.

[0077] The control unit 11 may also control a combination of multiple FCSs 12 as if it were a single FCS. For example, assume that vehicle 1 has six FCSs 12, FCS 12-1 through FCS 12-6. In this case, as an example, the control unit 11 controls three combinations: a combination of FCS 12-1 and FCS 12-2, a combination of FCS 12-3 and FCS 12-4, and a combination of FCS 12-5 and FCS 12-6. The control unit 11 controls the same combination of FCSs 12 in the same operating mode.

[0078] The operation mode of the FCS 12 may be a mode other than the repetitive operation, the efficiency point operation, and the power generation stop.

[0079] In the above embodiments, vehicles are used as an example. However, the power system of the embodiments can also be applied to fuel cell-powered vehicles other than vehicles, such as vehicles or drones. For example, the power system of the embodiments can be applied to fuel cell-powered aircraft, ships, submarines, or railway vehicles.

[0080] Furthermore, the power system according to the embodiment can also be applied to stationary systems such as power generation facilities and cogeneration systems, or to vehicles such as robots and machines other than drones.

[0081] The control unit 11 may implement part or all of the processing implemented by the program in the above-mentioned embodiment by a hardware configuration of a circuit.

[0082] The program that implements the processing of the embodiment is transferred, for example, while stored in a device. However, the device may also be transferred without storing the program. The program may then be transferred separately and written to the device. In this case, the program transfer may be achieved, for example, by recording it on a removable storage medium or downloading it via a network such as the Internet or a local area network (LAN).

[0083] While the embodiments of the present invention have been described above, these are merely examples and do not limit the scope of the present invention. The embodiments of the present invention can be implemented in various forms without departing from the spirit of the present invention.

[0084] Reference numerals

[0085] 1: Vehicle

[0086] 11: Control Department

[0087] 12: FCS

[0088] 13: Battery

[0089] 14: Motor

[0090] 15: Load

Claims

1. A power system comprising: n fuel cells, generating electricity through electrochemical reactions, where n is an integer greater than 2; and, a control unit that sets the operation mode of each of the fuel cells to any one of a plurality of modes, based on a requested output requested according to power to be consumed by a load, the plurality of modes including a first power generation mode in which power generation is repeatedly started and stopped, a second power generation mode in which power generation is continued, and a stop mode in which power generation is stopped; The aforementioned control unit, When the requested output is equal to or greater than a threshold value A, the operation mode of the m fuel cells is set to the second power generation mode. The threshold value A is smaller than the total output of the m fuel cells when the fuel cells are operated at the highest efficiency. m is an integer greater than or equal to 1 and less than or equal to n-1.

2. The power system according to claim 1, wherein: The aforementioned control unit, When the requested output is greater than or equal to a threshold value B, the operation modes of the m fuel cells are set to the second power generation mode, and the operation mode of one fuel cell is set to the first power generation mode. The threshold value B is a specific value greater than the total output of the m fuel cells when the fuel cells are operated at the highest efficiency. m is an integer greater than or equal to 1 and less than or equal to n-1.

3. The power system according to claim 1, wherein: Also includes a secondary battery charged with the electricity generated by the above fuel cell, The control unit controls timings of starting and stopping power generation in the first power generation mode according to a charge state of the secondary battery.

4. The power system according to claim 1, wherein: The control unit determines whether the fuel cell is to be operated in the first power generation mode or the second power generation mode based on the degree of degradation.

5. A power system comprising: n fuel cells, generating electricity through electrochemical reactions, where n is an integer greater than 2; and, The control unit sets the operation mode of each of the fuel cells to any one of a plurality of modes based on a requested output requested according to power to be consumed by a load, the plurality of modes including a first power generation mode in which power generation is repeatedly started and stopped, a second power generation mode in which power generation is continued, and a stop mode in which power generation is stopped, wherein: The control unit sets the operation mode of the n fuel cells to the second power generation mode when the requested output is equal to or greater than a threshold value C. The threshold value C is smaller by a specific value than the total output value of the n fuel cells when the fuel cells are each operated at the highest efficiency.

6. A power system comprising: n fuel cells, generating electricity through electrochemical reactions, where n is an integer greater than 2; and, The control unit sets the operation mode of each of the fuel cells to any one of a plurality of modes based on a requested output requested according to power to be consumed by a load, the plurality of modes including a first power generation mode in which power generation is repeatedly started and stopped, a second power generation mode in which power generation is continued, and a stop mode in which power generation is stopped, wherein: The aforementioned control unit, When the requested output is less than the first threshold, the operation mode of one of the fuel cells is set to the first power generation mode. When the requested output is greater than or equal to the first threshold value and less than a second threshold value, the operation mode of one of the fuel cells is set to the second power generation mode; When the requested output is greater than or equal to the second threshold value and less than a third threshold value, the operation mode of one of the fuel cells is set to the second power generation mode, and the operation mode of one of the fuel cells is set to the first power generation mode. The first threshold is a specific value smaller than the output of the fuel cell when the fuel cell is operated most efficiently. The second threshold is a specific value greater than the output of the fuel cell when the fuel cell is operated most efficiently. The third threshold value is larger than the second threshold value and is smaller by a specific value than the total output of the two fuel cells when the two fuel cells are operated at the highest efficiency.

7. A power control device comprising a control unit that sets an operating mode of n fuel cells that generate electricity by electrochemical reaction to any one of a plurality of modes based on a request output according to power to be consumed by a load, the plurality of modes including a first power generation mode that repeatedly starts and stops power generation, a second power generation mode that continues power generation, and a stop mode that stops power generation, wherein n is an integer greater than or equal to 2. The aforementioned control unit, When the requested output is equal to or greater than a threshold value A, the operation mode of the m fuel cells is set to the second power generation mode. The threshold value A is smaller than the total output of the m fuel cells when the fuel cells are operated at the highest efficiency. m is an integer greater than or equal to 1 and less than or equal to n-1.

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