Grid-connected fuel cell system and power receiving control method

Abstract

To provide a grid-connected fuel cell system and a received power control method for reducing communication delays.SOLUTION: According to one embodiment, a grid-connected fuel cell system includes a plurality of fuel cell systems that drop output power on the basis of a value of power received from a power grid. The grid-connected fuel cell system further includes a comparator that is connected to the plurality of fuel cell systems by wiring, compares the value of the power received from the power grid with a setting value, and outputs a power drop signal to the plurality of fuel cell systems. Furthermore, the plurality of fuel cell systems drop the output power on the basis of a value of the power drop signal.SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] Embodiments of the present invention relate to an interconnected fuel cell system and a power reception control method.

Background Art

[0002] There is a technique for discriminating between reverse power flow during the independent operation of a distributed power source such as a fuel cell system and temporary reverse power flow other than independent operation, and continuously and stably operating the distributed power source in the power system. Reverse power flow refers to the power generated on the customer side flowing back into the power system. For example, when the power generated on the customer side is greater than the power consumed on the customer side, the surplus power flows back into the power system. Temporary reverse power flow occurs, for example, in association with rapid load fluctuations occurring within the customer's premises.

[0003] Also, in self-consumption type power generation, in a conventional fuel cell system, in order to prevent reverse power flow, the power transmission is adjusted to maintain it within a certain range. For example, a conventional fuel cell system calculates the power reception point power value at the connection point with the power system and the power transmission end power value of the fuel cell system using a control circuit, and adjusts the power transmission with respect to changes in the load.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, in an interconnected fuel cell system in which a plurality of fuel cell systems are interconnected, when communication is performed between a control circuit and each fuel cell system via a network such as a LAN (Local Area Network), the communication delay due to signal conversion becomes large. In an interconnected fuel cell system, due to the communication delay, the adjustment of the power transmission is delayed, which causes reverse power flow to occur.

[0006] Therefore, embodiments of the present invention provide a grid-connected fuel cell system and a power receiving control method that reduce communication delay. [Means for solving the problem]

[0007] According to one embodiment, a grid-connected fuel cell system comprises a plurality of fuel cell systems that reduce output power based on the value of power received from the power grid. Furthermore, the grid-connected fuel cell system comprises a comparator connected to the plurality of fuel cell systems by wiring, which compares the value of power received from the power grid with a set value and outputs a power reduction signal to the plurality of fuel cell systems. Furthermore, the plurality of fuel cell systems reduce the output power based on the value of the power reduction signal. [Brief explanation of the drawing]

[0008] [Figure 1] This is an overall configuration diagram of the interconnected fuel cell system in the first embodiment. [Figure 2] This is an overall configuration diagram of a grid-connected fuel cell system of a comparative example of the first embodiment. [Figure 3] This is an example of a flowchart illustrating the operation of the comparator in the first embodiment. [Figure 4] This is an example of a flowchart of the logic circuit of the fuel cell system in the first embodiment. [Figure 5] This is an example of reverse power flow prevention control in the first embodiment. [Figure 6] This is an overall configuration diagram of the interconnected fuel cell system in the second embodiment. [Figure 7] This is an example of a flowchart of the logic circuit of the fuel cell system in the second embodiment. [Modes for carrying out the invention]

[0009] Embodiments of this disclosure will be described below with reference to the drawings. These embodiments are not intended to limit the present invention. The drawings are schematic or conceptual, and the proportions of each part may not necessarily be the same as those of actual objects. In the specification and drawings, elements similar to those described above with respect to previously shown drawings are denoted by the same reference numerals, and detailed descriptions are omitted as appropriate.

[0010] (First Embodiment) Figure 1 is an overall diagram of the interconnected fuel cell system in the first embodiment.

[0011] The grid-connected fuel cell system 1 is installed, for example, in a plant such as a factory. The grid-connected fuel cell system 1 supplies the generated electricity to loads 4, etc., within the factory, thereby covering the factory's power consumption. The grid-connected fuel cell system 1 may also be used in combination with a PV (photovoltaic) power generation device 5. By supplying the electricity generated by the grid-connected fuel cell system 1 and PV 5 to loads 4, the factory's power consumption is covered.

[0012] In this example, PV5 was chosen as the renewable energy power generation system to be combined with the grid-connected fuel cell system 1, but other power generation methods may also be used. For example, the grid-connected fuel cell system 1 may be used in combination with other renewable energy power generation devices such as wind power generators or biomass power generators. Furthermore, the grid-connected fuel cell system 1 may be used in combination with an emergency generator. The same applies to the following examples.

[0013] Furthermore, for the sake of simplicity, the following explanation assumes that PV5 does not supply power to load 4. Also, for the sake of explanation, in the overall configuration diagram, power supply systems are represented by solid lines and communication systems by dashed lines for each connection.

[0014] In operation, the interconnected fuel cell system 1 does not rely solely on the output power of the fuel cell system 9 to meet all load capacities, but supplements its power supply with power from the power grid 3, providing a margin against reverse power flow. For example, if the maximum output power of the interconnected fuel cell system 1 is 1 MW and the total load of load 4 is 1 MW, it is conceivable that the power supplied from the interconnected fuel cell system 1 to load 4 would be 800 kW, and the power supplied from power grid 3 to load 4 would be 200 kW. This ensures that even if the load capacity of load 4 decreases slightly, the unused power will not flow back into power grid 3. The interconnected fuel cell system 1 needs to implement reverse power flow prevention control to ensure that the value of this received power does not become negative.

[0015] Another method to prevent reverse power flow is to connect a dummy load (not shown) to the output side of the interconnected fuel cell system 1. For example, if the maximum output power of the interconnected fuel cell system 1 is 1 MW and the total load of load 4 is 800 kW, a 200 kW dummy load is connected to the output side of the interconnected fuel cell system 1, and the difference in power is supplied to the dummy load. This prevents power not consumed by load 4 from flowing back into the power grid 3. Even if the load capacity of load 4 decreases, the dummy load can take on some of the output power of the interconnected fuel cell system 1, providing a margin against reverse power flow. In this case as well, the interconnected fuel cell system 1 needs to perform reverse power flow prevention control so that the value of the received power does not become negative.

[0016] The interconnected fuel cell system 1 in this embodiment comprises multiple fuel cell systems 9, a power transmission sensor 6, and a control circuit 8. These devices receive the power necessary for their operation through a distribution board 7. Under normal circumstances, the power generated by the fuel cell systems 9 is supplied to the load 4 via the power line 40 and the distribution board 7, while the control circuit 8 adjusts the transmitted power to prevent reverse power flow to the power grid 3. Hereinafter, the adjustment of transmitted power by the control circuit 8 will be referred to as normal reverse power flow prevention control.

[0017] In addition, the interconnected fuel cell system 1 in the present embodiment includes a comparator 11 that outputs a power drop signal based on the value of a power reception sensor 2 that monitors the power received from the power grid 3. When the value of the received power approaches 0 W and the margin becomes small due to a change in the load capacity of the sudden load 4 or the like, the interconnected fuel cell system 1 switches to high-speed reverse power flow prevention control based on the power drop signal of the comparator 11 and reduces the output power. In this example, the interconnected fuel cell system 1 shows an example in which two comparators 11 are provided. Thereby, the interconnected fuel cell system 1 can adjust the output power from the fuel cell system 9 step by step based on the output of the power drop signal of each comparator 11. For the sake of explanation, the comparator 11 that outputs a power drop signal based on the set value of the first stage is called the comparator 11a, and the comparator 11 that outputs a power drop signal based on the set value of the second stage is called the comparator 11b. Further, the comparator 11a is an example of the first comparator, and the comparator 11b is an example of the second comparator.

[0018] FIG. 2 is an overall configuration diagram of an interconnected fuel cell system of a comparative example of the first embodiment.

[0019] The interconnected fuel cell system 1 of the comparative example includes a plurality of fuel cell systems 9, a power transmission sensor 6, and a control circuit 8. In the interconnected fuel cell system 1 of the comparative example, only normal reverse power flow prevention control by the control circuit 8 is performed. Therefore, when a transmission delay due to signal conversion or the like occurs during communication between the control circuit and each fuel cell system via a network such as a LAN, the adjustment of the power transmission of the fuel cell system 9 may not be in time, and reverse power flow may occur.

[0020] Hereinafter, in order to describe an example of the interconnected fuel cell system 1 including three fuel cell systems 9, each fuel cell system will be described as the fuel cell systems 9a, 9b, and 9c. Further, in order to describe an example in which the interconnected fuel cell system 1 supplies power to two loads 4, each load will be described as the loads 4a and 4b.

[0021] Here, each device will be described again using FIG. 1.

[0022] The fuel cell system 9 generates electricity through a chemical reaction between hydrogen and oxygen. The generated electricity is supplied, for example, to a load 4 within a factory premises via a power line 40 and a distribution board 7.

[0023] The power receiving sensor 2 measures the instantaneous value of the power received from the power system 3. The power receiving sensor 2 also transmits the measured value as an analog signal to the control circuit 8. The power receiving sensor 2 is, for example, a power meter.

[0024] The power transmission sensor 6 measures the instantaneous value of the power transmitted by the fuel cell system 9. The power transmission sensor 6 also transmits an analog signal of the measured value to the control circuit 8. The power transmission sensor 6 is, for example, a power meter. Although the power transmission sensor 6 measures power at a different location than the power receiving sensor 2, a similar power meter may be used.

[0025] The distribution board 7 distributes power received from the power system 3 via the grid power line 20 and power generated by the fuel cell system 9 to each device. The power line 40 connecting the distribution board 7 and the fuel cell system 9, and the cables connecting the distribution board 7 and the control circuit 8, are power cables such as CV cables.

[0026] The control circuit 8 adjusts the power transmitted from the fuel cell system 9 to prevent reverse power flow from the fuel cell system 9 to the power grid 3. To prevent reverse power flow, the control circuit 8 generates a control signal to adjust the output power of the fuel cell system 9 based on a comparison between the value of the power received from the power grid 3 obtained by the power receiving sensor 2 and the value of the power transmitted from the interconnected fuel cell system 1. The control signal is transmitted to the fuel cell system 9 via the communication line 30. The control circuit 8 also receives power from the distribution board 7 via the power cable.

[0027] After transmitting a control signal to the fuel cell system 9, the control circuit 8 compares the value obtained by the power receiving sensor 2 with the value obtained by the power transmitting sensor 6 at a predetermined timing. If this comparison indicates that it is necessary to further reduce the power transmitted by the fuel cell system 9, the control circuit 8 generates another control signal and transmits it to the fuel cell system 9.

[0028] Thus, the control circuit 8 may transmit control signals to the fuel cell system 9 multiple times in order to adjust the output power of the fuel cell system 9.

[0029] The communication lines 30 consist of metal communication lines and optical communication lines. The description of the network equipment necessary for communication is omitted. The control signals are transmitted to the fuel cell system 9 after, for example, protocol conversion during transmission. Transmission via these communication lines 30 involves signal conversion to absorb the differences in communication methods described above, resulting in transmission delays.

[0030] The setting device 10 holds a setting value that serves as a reference value to be input to the comparator 11. The comparator 11 compares the value of the received power with this setting value. The setting value is also set as the value of the received power required to start high-speed reverse power flow prevention control. In this example, the second setting value set by setting device 10b is set to a smaller value than the first setting value set by setting device 10a. The first setting value is an example of the first setting value. The second setting value is an example of the second setting value. These setting values ​​may be set in hardware or in software. For example, a board that allows setting values ​​to be set using DIP switches or the like may be implemented, and the analog value of the setting value may be input to the comparator 11. Alternatively, a board that can be connected to a PC (Personal Computer) via a network interface may be implemented, and the setting value may be input via a user interface or the like. In addition, various setting devices 10 may be used to input setting values ​​to the comparator 11.

[0031] Comparator 11 receives the value of the power received from the power system 3 as an analog signal from the power receiving sensor 2. Comparator 11 also receives the analog signal of the set value as input from the setter 10. Comparator 11 compares the value of the power received with the set value and outputs a power drop signal. The power drop signal is, for example, a "Hi (High)" or "Lo (Low)" signal. Comparator 11 may output a "Hi" signal if the value of the power received is lower than the set value, and a "Lo" signal otherwise. Comparator 11 may also output a "Hi" signal when the value of the power received and the set value are equal. Comparator 11 may also have the output conditions for the "Hi" signal and the "Lo" signal reversed from the above. The value that comparator 11 compares may also be a current value. Comparator 11 receives power from the distribution board 7 via a power cable.

[0032] For example, if the value of the power receiving sensor 2 is 80kW and the value of the first setting is 100 In cases such as kW, the value of the power received from power system 3 is small, so comparator 11a outputs a "Hi" signal.

[0033] Furthermore, the comparator 11 periodically performs the determination of the output of the power drop signal described above at predetermined timings. For example, the comparator 11 performs the determination at intervals such as a 1-second period or a 1-millisecond period.

[0034] The wiring 50 is made of, for example, metal wire. The comparator 11 and the fuel cell system 9 are connected by wiring 50. This type of wiring connection between the comparator 11 and the fuel cell system 9 is also called a hardwired connection. Alternatively, the comparator 11 and the fuel cell system 9 may be electrically connected by a control cable, such as a CVV cable. The power drop signal output from the comparator 11 is input to the fuel cell system 9 via wiring 50. The wiring 50 connecting comparator 11a and each fuel cell system 9a to 9c is called the first wiring, and the wiring 50 connecting comparator 11b and each fuel cell system 9a to 9c is called the second wiring. In this embodiment, the first wiring and the second wiring are implemented as different wirings to avoid transmission delays of the power drop signals output from each comparator 11a and 11b.

[0035] It is preferable that the comparator 11 and the fuel cell system 9 are directly connected via wiring 50. By directly connecting the comparator 11 and the fuel cell system 9, the grid-connected fuel cell system 1 can achieve low-latency signal transmission without protocol conversion.

[0036] The comparator 11 and the fuel cell system 9 may be physically far apart. The interconnected fuel cell system 1 may install a signal amplifier in the power drop signal transmission section to prevent signal attenuation of the power drop signal. The interconnected fuel cell system 1 will experience a transmission delay due to the signal amplification processing performed by the signal amplification circuit, but even when the distance between the comparator 11 and the fuel cell system 9 is large, signal attenuation can be prevented and the power drop signal can be reliably transmitted to the fuel cell system 9.

[0037] The fuel cell system 9 accepts a power drop signal as input. When the fuel cell system 9 receives a "Hi" signal as input for the power drop signal, it detects this using a logic circuit within the fuel cell system 9 and switches from normal reverse power flow prevention control to high-speed reverse power flow prevention control. The fuel cell system 9 has control values ​​and target values ​​set in advance for high-speed reverse power flow prevention control. The fuel cell system 9 continues to reduce the transmitted power at a reduction amount determined by the control value per unit time until the measurement value of the power receiving sensor 2 reaches the target value. In this embodiment, the fuel cell system 9 continuously reducing the transmitted power at a predetermined reduction amount per unit time is called high-speed reverse power flow prevention control.

[0038] The target value is the power value that will be handled as a margin. In addition, the power transmitted by the fuel cell system 9 is continuously reduced by the control value so that the measurement value of the power received by the power received sensor 2 reaches the target value. For example, if the maximum output of the interconnected fuel cell system 1 is 1 MW, and the power received value is set as a margin of 200 kW, then the target value is 200 kW. In other words, the fuel cell system 9 will continue to reduce the power transmitted by the control value so that it reaches 800 kW.

[0039] The control value represents, for example, the power to be reduced per unit time, and is expressed in values ​​such as kW / s or kW / ms.

[0040] In this example, the fuel cell system 9 performs normal reverse power flow prevention control by the control circuit 8 in the manner described above while a "Lo" signal is input from each comparator 11. When a "Hi" signal is input from comparator 11a or 11b, the fuel cell system 9 switches to high-speed reverse power flow prevention control.

[0041] Furthermore, when the measurement value of the power receiving sensor 2 reaches the target value, the comparator 11 outputs a "Lo" signal. Upon receiving the "Lo" signal, the fuel cell system 9 switches from high-speed reverse power flow prevention control to normal reverse power flow prevention control.

[0042] In this example, as described above, the grid-connected fuel cell system 1 is equipped with two comparators 11. In the grid-connected fuel cell system 1, comparators 11a and 11b can output two types of power drop signals, a "Hi" signal and a "Lo" signal, respectively. As a result, each fuel cell system 9 can accept four types of power drop signals as input. For example, if fuel cell system 9 receives a "Hi" signal from comparator 11a and a "Lo" signal from comparator 11b, it may switch to the first stage of high-speed reverse power flow prevention control. Alternatively, if fuel cell system 9 receives a "Hi" signal from comparator 11a and a "Hi" signal from comparator 11b, it may switch to the second stage of high-speed reverse power flow prevention control. The power drop signal output from comparator 11a is an example of the first power drop signal, and the power drop signal output from comparator 11b is an example of the second power drop signal.

[0043] Since the fuel cell system 9 is connected to two comparators 11a and 11b, two control values ​​are set. In this embodiment, the control value in the first stage of high-speed reverse power flow prevention control is called the first control value. The control value in the second stage of high-speed reverse power flow prevention control is called the second control value. During the first stage of high-speed reverse power flow prevention control, the fuel cell system 9 continues to reduce the transmitted power at the first control value. During the second stage of high-speed reverse power flow prevention control, the fuel cell system 9 continues to reduce the transmitted power at the second control value. In other words, the first control value and the second control value reduce the output power by a predetermined reduction amount per unit time that is different for each.

[0044] For example, by setting the first control value to 100 kW / s and the second control value to 150 kW / s, the fuel cell system 9 can reduce the transmitted power by a larger amount when using the second control value compared to when using the first control value.

[0045] The fuel cell system 9 in Figure 2 shows an example in which normal reverse power flow prevention control is performed based on calculations by the control circuit 8, and high-speed reverse power flow prevention control is performed based on the output of the power drop signal from the comparator 11. If either the control circuit 8 or the comparator 11 fails, the interconnected fuel cell system 1 may be configured to continue operating the fuel cell system 9 by performing reverse power flow prevention control using only the other.

[0046] Alternatively, the interconnected fuel cell system 1 may not include a control circuit 8, and may only perform high-speed reverse power flow prevention control of the fuel cell system 9 based on the power drop signal from the comparator 11.

[0047] Figure 3 is an example of a flowchart showing the operation of the comparator in the first embodiment.

[0048] Since comparators 11a and 11b operate similarly, this section will describe the flow when only one comparator 11 is operating.

[0049] In step S11, the comparator 11 receives an analog signal of the received power from the power sensor 2 as input. In step S12, the comparator 11 receives an analog signal of the set value from the setter 10 as input. The flow of steps S11 and S12 may be reversed, and these flows may be executed simultaneously.

[0050] In step S13, the comparator 11 compares the value of the received power with the set value. If the result of the comparison in step S13 is that the value of the received power is less than the set value, in step S14 the comparator 11 outputs a "Hi" signal. If the result of the comparison in step S13 is that the received power is equal to or less than the set value, in step S15 the comparator 11 outputs a "Lo" signal.

[0051] Figure 4 is an example of a flowchart of the logic circuit of the fuel cell system in the first embodiment.

[0052] Since the logic circuits of fuel cell systems 9a to 9c operate similarly, this section will describe the flow when one fuel cell system 9 is in operation.

[0053] In step S21, the logic circuit of the fuel cell system 9 detects a power drop signal received from comparator 11a. In step S22, the logic circuit of the fuel cell system 9 detects a power drop signal received from comparator 11b. Steps S21 and S22 may be performed in reverse order, and these steps may be performed simultaneously.

[0054] In step S23, the logic circuit of the fuel cell system 9 determines whether the power drop signal received from comparator 11a is a "Hi" signal. If the power drop signal received from comparator 11a is not a "Hi" signal, the logic circuit of the fuel cell system 9 terminates processing because it does not need to perform high-speed reverse power flow prevention control. If the power drop signal from comparator 11a is a "Hi" signal in step S23, in step S24, the logic circuit of the fuel cell system 9 determines whether the power drop signal received from comparator 11b is a "Hi" signal.

[0055] If the power drop signal received from comparator 11b in step S24 is not a "Hi" signal, in step S25 the logic circuit of the fuel cell system 9 continues to reduce the transmitted power by a first control value. If the power drop signal received from comparator 11b in step S24 is a "Hi" signal, in step S26 the logic circuit of the fuel cell system 9 continues to reduce the transmitted power by a second control value.

[0056] Figure 5 shows an example of reverse power flow prevention control in the first embodiment.

[0057] In Figure 5, the horizontal axis represents the time axis (hours), and the vertical axis represents the fluctuation of load capacity (MW) or the required control amount (MW) in the interconnected fuel cell system 1.

[0058] The solid line graph in Figure 5 shows the change in the amount of output power control in a grid-connected fuel cell system 1 with an output power of 1 MW, in response to load fluctuations. The dashed line graph shows the change in load capacity at each time point for load 4. The solid line graph also shows the amount of output power control at each time point for the grid-connected fuel cell system 1.

[0059] Furthermore, the load in Figure 5 represents the total load capacity of loads 4a and 4b, and the maximum load capacity of this load is 1 MW. For the sake of simplicity, the explanation will use an example where all load capacities are supplemented by the interconnected fuel cell system 1.

[0060] For example, if the output of the interconnected fuel cell system 1 is 1 MW, the load power at 6:00 is 0.9 MW, which means that the amount of control required for reverse power flow prevention control in the interconnected fuel cell system 1 is 0.1 MW.

[0061] Figure 5 shows that the load fluctuates rapidly from 8:00 to 9:00, becoming 0.3 MW lighter. In such cases, a control amount of 0.3 MW of transmission power is required in the interconnected fuel cell system 1 to prevent reverse power flow. Figure 5 shows an example where a "Hi" signal is output from comparator 11a between 8:00 and 9:00, in which case the fuel cell system 9 performs high-speed reverse power flow prevention control at the first control value.

[0062] In this embodiment, the difference between the amount of power transmission controlled at the setpoint and the amount of power transmission controlled at the target point is called the reverse power control amount (load following amount).

[0063] Figure 5 shows that the load fluctuates sharply between 10:00 and 11:00, becoming 0.35 MW lighter. In such cases, a control amount of 0.35 MW of transmission power is required in the interconnected fuel cell system 1 to prevent reverse power flow. Figure 5 shows an example where a "Hi" signal is output from comparator 11b between 10:00 and 11:00. In this case, the fuel cell system 9 performs high-speed reverse power flow prevention control using the second control value.

[0064] According to this embodiment, the grid-connected fuel cell system 1 reduces transmission delay by wiring the comparator 11 to the fuel cell system 9 and transmitting the power drop signal to the fuel cell system 9 without signal conversion to absorb differences in communication methods. In particular, the grid-connected fuel cell system 1 can further prevent transmission delay of the power drop signal by directly connecting the comparator 11 to the fuel cell system 9 with wiring 50.

[0065] Furthermore, according to this embodiment, the interconnected fuel cell system 1 can avoid multiple comparison operations using the control circuit 8 by continuously reducing the power transmission power of the fuel cell system 9 based on the power drop signal. As a result, the interconnected fuel cell system 1 can perform reverse power flow prevention control at high speed and prevent the occurrence of reverse power flow to the power grid 3.

[0066] Furthermore, according to this embodiment, the interconnected fuel cell system 1 can adjust the transmitted power in stages using multiple control values ​​by controlling the fuel cell system 9 using multiple comparators 11.

[0067] (Second Embodiment) Figure 6 is an overall diagram of the interconnected fuel cell system in the second embodiment.

[0068] In this embodiment, the interconnected fuel cell system 1 includes comparators 11a, 11b, and 11c. Comparator 11c, like comparators 11a and 11b, accepts the value of the received power from the power receiving sensor 2 as an analog signal input. Comparator 11c also accepts an analog signal of the third setting value from the setter 10c as input. In this example, the second setting value is set to a smaller value than the first setting value, and the third setting value is set to a smaller value than the second setting value. The third setting value is an example of a third setting value.

[0069] The wiring 50 connecting comparator 11c and each fuel cell system 9a to 9c is called the third wiring. In this embodiment, the first to third wirings are implemented as different wirings to avoid transmission delays of power drop signals output from each comparator 11a, 11b, and 11c.

[0070] In the interconnected fuel cell system 1, comparators 11a, 11b, and 11c can each output two types of power drop signals: a "Hi" signal and a "Lo" signal. This allows each fuel cell system 9 to accept eight types of power drop signals as input. For example, if fuel cell system 9 receives a "Hi" signal from comparator 11a, a "Lo" signal from comparator 11b, and a "Lo" signal from comparator 11c, it may switch to the first stage of high-speed reverse power flow prevention control. Alternatively, if fuel cell system 9 receives a "Hi" signal from comparator 11a, a "Hi" signal from comparator 11b, and a "Lo" signal from comparator 11c, it may switch to the second stage of high-speed reverse power flow prevention control. Furthermore, if fuel cell system 9 receives a "Hi" signal from comparator 11a, a "Hi" signal from comparator 11b, and a "Hi" signal from comparator 11c, it may switch to the third stage of high-speed reverse power flow prevention control. The power drop signal output from comparator 11c is an example of a third power drop signal.

[0071] Since the fuel cell system 9 is connected to three comparators 11a, 11b, and 11c, three control values ​​are set. In this embodiment, the control value in the first stage of high-speed reverse power flow prevention control is called the first control value. In this embodiment, the control value in the second stage of high-speed reverse power flow prevention control is called the second control value. In this embodiment, the control value in the third stage of high-speed reverse power flow prevention control is called the third control value. During the first stage of high-speed reverse power flow prevention control, the fuel cell system 9 continues to reduce the transmitted power at the first control value. During the second stage of high-speed reverse power flow prevention control, the fuel cell system 9 continues to reduce the transmitted power at the second control value. During the third stage of high-speed reverse power flow prevention control, the fuel cell system 9 reduces the transmitted power until the output stops, putting the fuel cell system 9 into an idle state. For example, the third control value may be set to a value that reduces the output power by a much larger amount than the first or second control values, such as 1 MW / s or 1 MW / ms, to achieve the cessation of the transmitted power output.

[0072] Furthermore, the number of comparators 11 is not limited to three. The interconnected fuel cell system 1 may have N comparators 11 (where N is a natural number). For example, the interconnected fuel cell system 1 may perform N-1 stage high-speed reverse power flow prevention control, continuously reducing the power transmission of the fuel cell system 9 based on the power drop signals of N-1 comparators 11 out of the N comparators 11. Alternatively, the interconnected fuel cell system 1 may perform high-speed reverse power flow prevention control by reducing the power transmission output of the fuel cell system 9 until it stops, based on the power drop signal of one comparator 11.

[0073] For example, if N=2, the interconnected fuel cell system 1 controls the transmission power of the fuel cell system 9 by continuously reducing it by a predetermined amount based on the power drop signal from one comparator 11, according to a first control value. Furthermore, based on the power drop signal from the remaining comparator 11, the interconnected fuel cell system 1 reduces the transmission power output of the fuel cell system 9 until it is stopped. If N=4, the interconnected fuel cell system 1 controls the transmission power of the fuel cell system 9 by continuously reducing it by first to third control values ​​based on the power drop signals from three comparators 11. Furthermore, based on the power drop signal from the remaining comparator 11, the interconnected fuel cell system 1 reduces the transmission power output of the fuel cell system 9 until it is stopped.

[0074] Figure 7 is an example of a flowchart of the logic circuit of the fuel cell system in the second embodiment.

[0075] Since the logic circuits of fuel cell systems 9a to 9c operate similarly, this section will describe the flow when one fuel cell system 9 is in operation.

[0076] In step S31, the logic circuit of the fuel cell system 9 detects a power drop signal received from comparator 11a. In step S32, the logic circuit of the fuel cell system 9 detects a power drop signal received from comparator 11b. In step S33, the logic circuit of the fuel cell system 9 detects a power drop signal received from comparator 11c. The order of steps S31 to S33 may be reversed, and these steps may be executed simultaneously.

[0077] In step S34, the logic circuit of the fuel cell system 9 determines whether the power drop signal received from comparator 11a is a "Hi" signal. If the power drop signal received from comparator 11a is not a "Hi" signal, there is no need to perform high-speed reverse power flow prevention control, and the process ends. If the power drop signal from comparator 11a is a "Hi" signal in step S34, in step S35, the logic circuit of the fuel cell system 9 determines whether the power drop signal received from comparator 11b is a "Hi" signal.

[0078] If, in step S35, the power drop signal received from comparator 11b is not a "Hi" signal, then in step S36, the logic circuit of the fuel cell system 9 performs control to reduce the transmitted power by the first control value. If, in step S35, the power drop signal received from comparator 11b is a "Hi" signal, then in step S37, the logic circuit of the fuel cell system 9 determines whether or not the power drop signal received from comparator 11c is a "Hi" signal.

[0079] If, in step S37, the power drop signal received from comparator 11c is not a "Hi" signal, then in step S38, the logic circuit of the fuel cell system 9 controls the transmission power to decrease by a second control value. If, in step S37, the power drop signal received from comparator 11c is a "Hi" signal, then in step S39, the logic circuit of the fuel cell system 9 controls the output of the transmission power to stop.

[0080] When the fuel cell system 9 stops outputting power and enters an idle state, the interconnected fuel cell system 1 resumes outputting power when all power drop signals received from comparators 11a to 11c become "Lo". Because the fuel cell system 9 is in an idle state, it can resume outputting power more quickly than when the power supply to the fuel cell system 9 is off.

[0081] According to this embodiment, the interconnected fuel cell system 1 can perform stepwise high-speed reverse power flow prevention control based on power drop signals from multiple comparators 11. Furthermore, since each comparator 11 transmits power drop signals to each fuel cell system 9 in parallel via wiring 50, transmission delay can be further reduced.

[0082] Furthermore, according to this embodiment, the interconnected fuel cell system 1 can stop the output of the power transmission from the fuel cell system 9 if reverse power flow is likely to occur immediately.

[0083] Although several embodiments have been described above, these embodiments are presented only as examples and are not intended to limit the scope of the invention. The novel interconnected fuel cell system 1 described herein can be implemented in a variety of other forms. Furthermore, various omissions, substitutions, and modifications can be made to the embodiments of the interconnected fuel cell system 1 described herein, without departing from the spirit of the invention. The appended claims and equivalents are intended to include such forms and modifications included in the scope and spirit of the invention. [Explanation of Symbols]

[0084] 1: Grid-connected fuel cell system, 2: Power receiving sensor, 3: Power grid, 4: Load, 4a: Load, 4b: Load, 5: PV, 6: Power transmission sensor, 7: Distribution board, 9: Fuel cell system, 9a: Fuel cell system, 9b: Fuel cell system, 9c: Fuel cell system, 10: Setting device, 10a: Setting device, 10b: Setting device, 10c: Setting device, 11: Comparator, 11a: comparator, 11b: comparator, 11c: comparator, 20: grid power line, 30: Communication lines, 40: Power lines, 50: Wiring

Claims

1. Multiple fuel cell systems that reduce output power based on the value of power received from the power grid, The system includes a comparator that is hardwired with metal wires to the plurality of fuel cell systems, compares the value of the power received from the power grid with a set value, and outputs a power drop signal to the plurality of fuel cell systems without signal conversion based on the result of the comparison. The plurality of fuel cell systems are interconnected fuel cell systems that reduce the output power based on the value of the power drop signal.

2. The fuel cell system according to claim 1, wherein the fuel cell system receives the input of the power drop signal via the metal wire.

3. The interconnected fuel cell system according to claim 1, wherein the fuel cell system reduces the output power by a predetermined amount per unit time.

4. The interconnected fuel cell system according to claim 1, wherein the comparator outputs the power drop signal based on the value of the received power in the analog signal.

5. Multiple fuel cell systems that reduce output power based on the value of power received from the power grid, A first comparator is hardwired with the plurality of fuel cell systems by metal wires, compares the power received from the power grid with a first set value, and outputs a first power drop signal to the plurality of fuel cell systems without signal conversion based on the result of the comparison. The system comprises a plurality of fuel cell systems and a second comparator that is hardwired with the metal wire, compares the power received from the power grid with a second set value, and outputs a second power drop signal to the plurality of fuel cell systems without signal conversion based on the result of the comparison. The plurality of fuel cell systems reduce the output power based on the value of the first power drop signal and the value of the second power drop signal. Grid-connected fuel cell system.

6. The interconnected fuel cell system according to claim 5, wherein the fuel cell system receives input of the first and second power drop signals via the metal wire.

7. The aforementioned fuel cell system Based on the value of the first power drop signal, the output power is reduced by a predetermined reduction amount determined by the first control value at each unit time. Based on the value of the second power drop signal, the output power is reduced by a predetermined reduction amount determined by a second control value different from the first control value, at each unit time interval. The interconnected fuel cell system according to claim 5.

8. The aforementioned fuel cell system Based on the value of the first power drop signal, the output power is reduced by a predetermined reduction amount determined by the first control value at each unit time. Based on the value of the second power drop signal, the output power is reduced until the output power stops. The interconnected fuel cell system according to claim 5.

9. The interconnected fuel cell system according to claim 5, wherein the first and second comparators output the first and second power drop signals based on the value of the received power in the analog signal.

10. The system further comprises a third comparator that is hardwired with the plurality of fuel cell systems by metal wires, compares the power received from the power grid with a third set value, and outputs a third power drop signal to the plurality of fuel cell systems without signal conversion based on the result of the comparison. The plurality of fuel cell systems reduce the output power based on the value of the first power drop signal, the value of the second power drop signal, and the value of the third power drop signal. The interconnected fuel cell system according to claim 5.

11. The interconnected fuel cell system according to claim 10, wherein the fuel cell system reduces the output power until the output power stops, based on the value of the third power drop signal.

12. Multiple fuel cell systems reduce their output power based on the power received from the power grid. A comparator, hardwired with the aforementioned fuel cell systems by metal wires, compares the power received from the power grid with a set value based on the comparison result, and outputs a power drop signal to the aforementioned fuel cell systems without signal conversion. The plurality of fuel cell systems reduce the output power based on the value of the power drop signal. A method for controlling received power, including the following.

13. The power receiving control method according to claim 12, wherein the fuel cell system receives the power drop signal input via the metal wire.

14. The power receiving method according to claim 12, wherein the fuel cell system reduces the output power by a predetermined amount per unit time.

15. The power receiving control method according to claim 12, wherein the comparator outputs the power drop signal based on the value of the received power in the analog signal.

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