Power supply system

Abstract

To provide a power supply system capable of improving followability of power supply to a demand change without reducing power generation efficiency.SOLUTION: A power supply system 1000 comprises a plurality of power generation units 100 operated in a parallel state to a commercial power source system 500 and a system controller 18 which supervises control states of the power generation units 100. The power generation unit 100 includes a power generation module 20, a power conditioner 16, and a local controller 17. The system controller divides the power generation unit 100 into any one of a first group of maximum output fixed machines, a second group of minimum output fixed machines, a third group of output adjustment machines, and a fourth group of output standby machines and controls total output power of the system by selecting a combination of groups on the basis of purchase power information from the commercial power source system 500.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a power supply system using a fuel cell or the like. [Background technology]

[0002] It is expected that consumers will be able to reduce carbon dioxide emissions by switching some of the commercial electricity they purchase from power companies to self-generated electricity. For example, while the primary energy efficiency of thermal power plants fueled by coal or LNG is around 40%, the primary energy efficiency of solid oxide fuel cells (SOFCs), which generate electricity by reforming city gas, which is primarily composed of methane, is expected to be 50% to 65%. Therefore, increasing the proportion of self-generated electricity can contribute to reducing the environmental burden.

[0003] Furthermore, by realizing a system that can independently maintain the power supply during power outages caused by natural disasters, it is expected that the adverse effects on social life and economic activity can be reduced. For example, solid oxide fuel cells (SOFCs) can independently generate electricity and supply power to the outside world as long as the city gas supply is not cut off. In the case of an earthquake, depending on its scale, gas infrastructure may be damaged, but in the case of a typhoon, there is almost no impact on the gas infrastructure, so the power supply can continue.

[0004] Patent Documents 1 and 2 disclose a power supply system (fuel cell system) that operates in parallel with a commercial power system and supplies power to power demand facilities. When there is a high demand during operation, such as in a power demand facility such as a factory, the power supply system is made up of multiple power generation units (for example, fuel cell units).

[0005] Furthermore, the power supply system does not allow reverse power flow to the commercial power grid, regardless of the number of power generation units installed, so it is necessary to purchase electricity from the commercial power grid at all times. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-019430 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-019431 Summary of the Invention [Problem to be solved by the invention]

[0007] Demand from electricity-consuming facilities fluctuates depending on the operating status of factories, etc., with demand increasing during operating hours and decreasing during non-operating hours. If some of the power generation units are shut down to prevent reverse power flow during periods of low demand, not only will the ability of the power supply to respond to demand changes deteriorate, but the benefit of self-generation, such as reducing the environmental impact, will be lost.

[0008] The present invention has been made in view of the above-mentioned problems, and aims to provide a power supply system that can improve the ability of power supply to follow demand changes while contributing to reducing environmental load. [Means for solving the problem]

[0009] The power supply system of the present invention comprises a plurality of power generation units operated in parallel to a commercial power system, and a system controller that oversees the control state of the plurality of power generation units, each of the plurality of power generation units having a power generation module, a power conditioner that converts the power generated by the power generation module into output power equivalent to the AC power of the commercial power system, and a local controller that controls the output power by controlling the power generated by the power generation module, and in the plurality of power generation units, each of the local controllers is configured to be able to perform output adjustment control that adjusts the output power heteronomously and / or autonomously, and the system controller classifies each of the power generation units into one of a first group of fixed output machines that fix the output power to an upper limit value, a second group of fixed output machines that fix the output power to a lower limit value, a third group of output adjustment machines that adjust the output power within a range from the upper limit value to the lower limit value, and a fourth group of standby output machines that fix the output power to zero, and controls the total output power of the system by selecting a combination of the groups based on purchased power information from the commercial power system. [Effects of the Invention]

[0010] According to the present invention, there is provided a power supply system that can improve the ability of power supply to follow demand changes while contributing to a reduction in environmental load. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram showing the configuration of a power generation unit. [Figure 2] FIG. 1 is a schematic diagram illustrating a configuration of a power conditioner. [Figure 3] FIG. 1 is a schematic diagram illustrating a configuration of a power supply system. [Figure 4] 1 is an explanatory diagram showing the relationship between actual purchased power from a commercial power supply system and reference purchased power and target purchased power in output adjustment control. [Figure 5] 10 is a flowchart of overall control in a system controller. [Figure 6] FIG. 2 is a state transition diagram of the overall control in the system controller. [Figure 7] FIG. 2 is a state transition diagram of the overall control in the system controller. [Figure 8] FIG. 10 is another state transition diagram of the overall control in the system controller. [Figure 9] 10 is a flowchart of output adjustment control in the local controller. [Figure 10] 10 is a flowchart of output adjustment control in the local controller. [Figure 11] 10 is a flowchart of output adjustment control in the local controller. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] 1.1 Overview of the power generation unit configuration First, an outline of the configuration of a power generation unit used in a power supply system according to this embodiment will be described. Fig. 1 is a schematic diagram showing the configuration of a power generation unit according to this embodiment. As shown in Fig. 1, the power generation unit 100 is a type that uses fuel cells, and includes a plurality of cell stacks 1, a reformer 2, a burner 3, an evaporator 4, an air preheater 5, an anode off-gas cooler 6, an anode off-gas condenser 7, a CO oxidizer (carbon monoxide oxidizer) 8, a condensed water recovery tank 9, a first raw fuel blower 10, a first air blower 11, a water pump 12, a second raw fuel blower 13, a second air blower 14, a third air blower 15, a power conditioner 16, and a local controller 17.

[0014] In this embodiment, a total of eight cell stacks 1 are provided, including those not shown in FIG.

[0015] The power generation unit 100 also has the following lines (pipes): a raw fuel line La, a mixed gas line Lb, an anode fuel line Lc, an anode offgas line Ld, a cathode air line Le, a cathode offgas line Lf, a combustion gas line Lg, a burner cooling air line Lh, a reforming water line Li, a start-up air line Lj, ​​a cooling air line Lk, and a condensed water recovery line Lw.

[0016] The anode fuel line Lc includes a first distribution manifold Ma that serves as a main pipe for introducing anode fuel, and the cathode air line Le includes a second distribution manifold Mb that serves as a main pipe for introducing cathode air. These distribution manifolds Ma and Mb have an inlet and multiple outlets corresponding to each cell stack 1, and allow the fluid that flows into the inlet to flow out from each of the outlets.

[0017] The anode offgas line Ld includes a first collection manifold Mc that serves as a mother pipe for the anode offgas, and the cathode offgas line Lf includes a second collection manifold Md that serves as a mother pipe for the cathode offgas. These collection manifolds Mc and Md have multiple inlets and outlets corresponding to the cell stacks 1, and allow fluids that flow into each inlet to flow out from the outlet.

[0018] The combustion gas line Lg includes a heat radiation tube Za and a combustion gas pipe Zb, and the cooling air line Lk includes a cooling pipe Zc and a collection pipe Lk1.

[0019] The raw fuel line La is a pipe connecting the fuel inlet E1 and the burner 3, and a second raw fuel blower 13 is disposed in this pipe. The second raw fuel blower 13 is a device that pressurizes the raw fuel gas (e.g., methane-containing gas such as city gas 13A) Gf taken in from the fuel inlet E1 and sends it to the downstream side of the raw fuel line La, and is typically driven during start-up operation of the power generation unit 100.

[0020] The mixed gas line Lb is a pipe connecting the fuel inlet E2 and the reformer 2, and in this pipe, from upstream to downstream, are arranged a first raw fuel blower 10, an evaporator 4, and a first bellows-type expansion joint B1. The first raw fuel blower 10 is a device that pressurizes the raw fuel gas Ga taken in through the fuel inlet E2 and sends it to the downstream side of the mixed gas line Lb, and is typically driven when the power generation unit 100 is in power generation operation.

[0021] The anode fuel line Lc is a pipe that connects the reformer 2 and the anode of each cell stack 1. More specifically, the anode fuel line Lc has, in order from the upstream side, a pipe that connects the reformer 2 and the inlet of the first distribution manifold Ma, the first distribution manifold Ma, and eight pipes (branch pipes of the first distribution manifold Ma) that connect each outlet of the first distribution manifold Ma to the anode of each cell stack 1.

[0022] The anode offgas line Ld is a pipeline connecting the anode of each cell stack 1 to the burner 3. More specifically, the anode offgas line Ld has, from the upstream side, eight pipelines (branch pipes of the first collecting manifold Mc) connecting the anode of each cell stack 1 to each inlet of the first collecting manifold Mc, the first collecting manifold Mc, and a pipeline (hereinafter referred to as "pipe line Ld1") connecting the outlet of the first collecting manifold Mc to the burner 3. Arranged along the pipeline Ld1, from the upstream side, are a second bellows-type expansion joint B2, an anode offgas cooler 6, an anode offgas condenser 7, and an air-water separator Sa.

[0023] The cathode air line Le is a pipe connecting the air intake E3 and the cathode of each cell stack 1. More specifically, the cathode air line Le has, from the upstream side, a pipe (hereinafter referred to as "pipe Le1") connecting the air intake E3 and the inlet of the second distribution manifold Mb, the second distribution manifold Mb, and eight pipes (branch pipes of the second distribution manifold Mb) connecting each outlet of the second distribution manifold Mb with the cathode of each cell stack 1.

[0024] Along the pipeline Le1, a first air blower 11, an anode off-gas cooler 6, an air preheater 5, and a third bellows expansion joint B3 are arranged, in that order from the upstream side. The first air blower 11 is a device that pressurizes air Aa taken in through an air inlet E3 and sends it to the downstream side of the cathode air line Le, and is typically driven during power generation operation of the power generation unit 100. Furthermore, a bypass path Le2 that bypasses the anode off-gas cooler 6 and the air preheater 5 is provided in the pipeline Le1, connecting the midpoint between the air inlet E3 and the anode off-gas cooler 6 and the midpoint between the air preheater 5 and the third bellows expansion joint B3.

[0025] The cathode offgas line Lf is a pipe connecting the cathode of each cell stack 1 to the burner 3. More specifically, the cathode offgas line Lf has, in order from the upstream side, eight pipes (branch pipes of the second collection manifold Md) connecting the cathode of each cell stack 1 to each inlet of the second collection manifold Md, the second collection manifold Md, and a pipe (hereinafter referred to as "pipe Lf1") connecting the outlet of the second collection manifold Md to the burner 3.

[0026] The combustion gas line Lg is a pipeline connecting the burner 3 and the gas exhaust port E6. More specifically, the combustion gas line Lg has, in order from the upstream side, a heat radiation tube Za, a pipeline connecting the heat radiation tube Za and the combustion gas pipe Zb, the combustion gas pipe Zb, and a pipeline connecting the combustion gas pipe Zb and the gas exhaust port E6 (hereinafter referred to as "pipe line Lg1"). In the middle of the pipeline Lg1, in order from the upstream side, a fourth bellows-type expansion joint B4, an air preheater 5, a CO oxidizer 8, and an evaporator 4 are arranged.

[0027] The burner cooling air line Lh is a pipe that connects the pipe Le1 and the startup air line Lj, ​​and is provided with a flow rate adjusting means (such as an orifice, not shown) in this pipe. More specifically, the burner cooling air line Lh is a pipe that branches off at the midpoint of the pipe Le1 that connects the first air blower 11 and the anode off-gas cooler 6, and merges with the startup air line Lj downstream of the second air blower 14, and is configured so that a minute flow rate of air Ab flows toward the burner 3 when the first air blower 11 is driven.

[0028] The cooling air line Lk is a pipe that connects the air intake E5 with a predetermined location on the pipe Lg1 (a location between the evaporator 4 and the gas outlet E6), and in this pipe, a third air blower 15 and a cooling pipe Zc are arranged in this order from the upstream side. The third air blower 15 is a device that increases the pressure of the cooling air Ad taken in from the air intake E5 and sends it to the downstream side of the cooling air line Lk.

[0029] The reforming water line Li is a pipe that connects the condensed water recovery tank 9 and the evaporator 4, and a water pump 12 is disposed in this pipe. The water pump 12 is a device that sends the condensed water Wb stored in the condensed water recovery tank 9 to the downstream side of the reforming water line Li as reforming water Wa.

[0030] The startup air line Lj is a pipe connecting the air intake E4 and the pipe Lf1, and is provided with a second air blower 14. The second air blower 14 is a device that pressurizes the air Ac taken in from the air intake E4 and sends it to the downstream side of the startup air line Lj, ​​and is typically driven during start-up operation of the power generation unit 100.

[0031] The condensed water recovery line Lw connects the water-air separator Sa, located midway along the pipeline Ld1, to the condensed water recovery tank 9. The water-air separator Sa separates the condensed water Wb generated in the anode off-gas condenser 7 from the anode off-gas Gd, and the separated condensed water Wb flows down the condensed water recovery line Lw. The end of the condensed water recovery line Lw is open to the gas phase without being immersed in the aqueous phase of the condensed water recovery tank 9 to prevent the amount of condensation from increasing or decreasing due to the temperature of the stored condensed water Wb. The reason for not immersing the end of the condensed water recovery line Lw in the aqueous phase is to prevent changes in the flow rate of the anode off-gas Gd sent to the burner 3. This configuration is particularly effective when the anode off-gas Gd after separation of the condensed water Wb is recycled to the primary side of the cell stack or used for power generation in a subsequent cell stack. The water-air separator Sa is, for example, a T-shaped pipe with a horizontally oriented straight pipe section and a downwardly oriented branch pipe section. Also, a small-capacity cylindrical container that is erected vertically can be used as the water-air separation section Sa.

[0032] The cell stack 1 is a power generating unit made up of solid oxide fuel cells (SOFC). A solid oxide fuel cell is a high-temperature operating fuel cell in which the solid electrolyte, anode, and cathode that make up the power generating cell are all made of ceramics, and a power generating unit in which a certain number of power generating cells are integrated via a metal interconnect material (also called a separator material) is called a cell stack. The battery output of the cell stack 1 is adjusted by a power conditioner 16 before being supplied.

[0033] The reformer 2 uses steam to reform the raw fuel gas Ga, generating reformed gas Gc, which is sent to the downstream side. The reformer 2 has a catalyst for steam reforming, and reacts methane contained in the raw fuel gas Ga with steam to generate reformed gas Gc containing carbon monoxide and hydrogen. Although steam reforming is an endothermic reaction, the heat supply from the burner 3 enables the reformer 2 to stably generate reformed gas Gc.

[0034] The burner 3 combusts the incoming gas to generate heat and discharges the combustion gas Gg produced by the combustion into the combustion gas line Lg. The evaporator 4 is a device that performs indirect heat exchange between the reforming water Wa and the combustion gas Gg (heat source fluid), and serves to evaporate the reforming water Wa and heat the raw fuel gas Ga at the same time by exchanging heat with the combustion gas Gg.

[0035] The air preheater 5 and the anode off-gas cooler 6 are both heat exchangers that perform indirect heat exchange between a low-temperature fluid and a high-temperature fluid. The air preheater 5 serves to preheat the air Aa in the cathode air line Le by heat exchange with the combustion gas Gg, and the anode off-gas cooler 6 serves to cool the anode off-gas Gd by heat exchange with the air Aa in the cathode air line Le.

[0036] The anode off-gas condenser 7 cools the anode off-gas Gd using a fan 7a to condense the water vapor contained in the anode off-gas Gd. Although the anode off-gas condenser 7 in this embodiment is an air-cooled heat exchanger, a water-cooled heat exchanger may be used instead, forming a cogeneration type power generation unit in which heat recovery is performed.

[0037] The CO oxidizer 8 is a device that brings harmful carbon monoxide contained in the combustion gas Gg into contact with a catalyst and converts it into harmless carbon dioxide. The CO oxidizer 8 does not operate when the oxidation reaction in the burner 3 is complete, and operates only when the oxidation reaction in the burner 3 is incomplete.

[0038] The condensed water recovery tank 9 serves to recover the condensed water Wb discharged from the air-water separation section Sa and make it reusable as reforming water Wa. The condensed water recovery tank 9 is provided with a water level detector Sb and a drain valve Sc to adjust the level of the stored reforming water Wa within a predetermined range. When the water level detector Sb detects an upper limit water level, the drain valve Sc opens, and when the water level detector Sb detects a lower limit water level, the drain valve Sc closes. In this way, the required amount of reforming water Wa is secured in the condensed water recovery tank 9. Note that to prevent anode off-gas Gd from leaking to the outside during the draining operation of the reforming water Wa, the drain position of the drain valve Sc is set near the bottom of the condensed water recovery tank 9.

[0039] As shown by the dashed line in FIG. 1 , the cell stacks 1, the reformer 2, the burner 3, the manifolds Ma to Md, the heat radiation tube Za, the combustion gas pipe Zb, and the cooling pipe Zc are arranged in a first region R1. The first region R1 is maintained at a temperature exceeding 600°C during power generation operation of the power generation unit 100, and independently maintains a heat balance between heat absorption and heat generation. Meanwhile, the evaporator 4, the air preheater 5, the anode off-gas cooler 6, and the CO oxidizer 8 are arranged in a second region R2. The second region R2 is maintained at a temperature lower than that of the first region R1 but higher than room temperature during power generation operation of the power generation unit 100. The first region R1 and the second region R2 are each surrounded by an insulating box, and the two insulating boxes are integrated to form a power generation module 20. The anode off-gas condenser 7, condenser fan 7a, condensed water recovery tank 9, blowers 10, 11, 13, 14, and 15, water pump 12, power conditioner 16, and local controller 17 are arranged outside (in the room temperature region) of the power generation module 20. The above-mentioned bellows-type expansion joints B1 to B4 are used to absorb the expansion and contraction of the piping caused by temperature changes between when the system is cold and when it is operating.

[0040] 2 is a schematic diagram showing the configuration of the power conditioner 16 according to this embodiment, illustrating the internal configuration of the power conditioner 16 and the state of connection to peripheral devices. As described above, the power generation module 20 is configured to include elements such as the cell stack 1. Furthermore, the auxiliary equipment 30 for operating the power generation module 20 is configured to include components such as the raw fuel blowers 10 and 13, air blowers 11, 14 and 15, the water pump 12, and the fan 7a of the anode off-gas condenser 7.

[0041] The power conditioner 16 converts the power generated by the power generation module 20 into output power equivalent to AC power of the commercial power supply system 500. The power conditioner 16 includes DC / DC converters 16a and 16b, a smoothing capacitor 16c, a grid-connected inverter 16d, switches 16e and 16f, and control circuits 16g and 16h.

[0042] The DC / DC converter 16a converts the DC power from the power generation module 20 into a boost circuit. The smoothing capacitor 16c smoothes the output power of the DC / DC converter 16a. The grid-connected inverter 16d converts the output power of the DC / DC converter 16a into AC power equivalent to that of a commercial power system.

[0043] The output side of the grid-connected inverter 16d is electrically connected to, for example, a distribution panel 610 for receiving commercial power that is installed within a building. The grid-connected inverter 16d and the distribution panel 610 can be switched between a parallel state and a disconnected state via a switch 16e. The distribution panel 610 is electrically connected to a commercial power system 500 and power demand equipment 600. The power demand equipment 600 includes a plurality of distribution panels, and each distribution panel is electrically connected to load equipment such as lighting fixtures, power units, or outlets used within the building.

[0044] The grid-connected inverter 16d is also electrically connected to an independent outlet 300. The grid-connected inverter 16d and the independent outlet 300 can be switched between a connected state and a disconnected state via a switch 16f. The independent outlet 300 is made up of a plurality of outlets into which power plugs of various power-using devices can be inserted.

[0045] The DC / DC converter 16b and the control circuit 16g function as a drive power supply unit that supplies drive power to the auxiliary equipment 30. The DC / DC converter 16b adjusts the DC voltage boosted by the DC / DC converter 16a to a DC voltage suitable for driving the auxiliary equipment 30. The control circuit 16g supplies the DC voltage adjusted by the DC / DC converter 16b to the auxiliary equipment 30 to appropriately drive the auxiliary equipment 30. The auxiliary equipment 30 is driven using commercial power during startup operation and shutdown operation of the power generation unit 100, and is driven using generated power during power generation operation of the power generation unit 100.

[0046] The DC / DC converter 16a and the control circuit 16h function as an operating power supply unit that supplies operating power to the load module 40. The load module 40 includes an electric heater 41 and a heat dissipation fan 42. In the load module 40, when the power generation unit 100 is in an independent operation mode, the electric heater 41 generates heat to consume the surplus power generated by the cell stack 1, and the heat dissipation fan 42 sends airflow to the electric heater 41 to promote heat dissipation. The load module 40 is disposed, for example, inside or outside the housing of the power generation unit 100.

[0047] The local controller 17 controls the operation of the power generation unit 100 in accordance with a control program that has been created and stored in advance. The local controller 17 is provided with a communication unit 17a that communicates with the outside of the power generation unit 100. A current sensor 200, which will be described later, is also connected to the local controller 17. Details of the local controller 17 will be described later as appropriate.

[0048] 1.2 Overview of the operation of the power generation unit Next, an overview of the operation of the power generation unit 100 will be described with reference to Fig. 1. The raw fuel gas Ga supplied from the fuel inlet E2 into the mixed gas line Lb is sent to the downstream side by the action of the first raw fuel blower 10. In parallel with the supply of the raw fuel gas Ga, the reforming water Wa supplied from the condensed water recovery tank 9 into the reforming water line Li has its amount adjusted by the water pump 12 and flows into the mixed gas line Lb.

[0049] The reforming water Wa flows into the evaporator 4 together with the raw fuel gas Ga in the mixed gas line Lb, and is heated by heat exchange in the evaporator 4 to become water vapor (superheated steam). The water vapor is mixed with the heated raw fuel gas Ga and flows into the reformer 2 as a mixed gas Gb.

[0050] The reformer 2 reforms the raw fuel gas Ga using the steam in the mixed gas Gb to generate the reformed gas Gc, which is then sent to the downstream side. The reformed gas Gc sent from the reformer 2 passes through the anode fuel line Lc and is distributed to the anodes of each cell stack 1.

[0051] Meanwhile, in parallel with the supply of the raw fuel gas Ga described above, air Aa is supplied from the air intake E3 into the cathode air line Le. The air Aa in the cathode air line Le is sent to the downstream side by the action of the first air blower 11. This air Aa is heated by heat exchange in the anode off-gas cooler 6, and is further heated by heat exchange in the air preheater 5, and then distributed to the cathodes of each cell stack 1. Note that, in order to adjust the temperature of the air Aa, it is also possible to flow a portion of the air Aa, that is, air Aa1, into the cathodes of each cell stack 1 via a bypass path Le2.

[0052] Furthermore, in synchronization with the supply of air Aa to the cathode, air Ab is supplied into the burner cooling air line Lh. The air Ab in the burner cooling air line Lh is sent to the burner 3 by the action of the first air blower 11. This air Ab acts as a coolant to lower the combustion temperature of the burner 3.

[0053] Each cell stack 1 generates electricity using the reformed gas Gc that flows into the anode and the air Aa that flows into the cathode. When the reformed gas Gc and air Aa are supplied to the cell stack 1 and a current sweep is performed by the power conditioner 16, electricity generation (electrochemical reaction between the reformed gas and oxygen) in the cell stack 1 begins. During the power generation operation of the cell stack 1, anode offgas Gd is discharged from the anode to the anode offgas line Ld, and cathode offgas Ge is discharged from the cathode to the cathode offgas line Lf. The anode offgas Gd contains reformed gas that did not react at the anode, and the cathode offgas Ge contains oxygen that did not react at the cathode.

[0054] The anode off-gas Gd discharged from each cell stack 1 to the anode off-gas line Ld is collected in the first collection manifold Mc, cooled by heat exchange in the anode off-gas cooler 6, and flows into the anode off-gas condenser 7. In the anode off-gas condenser 7, the anode off-gas Gd is cooled to a temperature below the dew point temperature, and the water vapor contained in the anode off-gas Gd is condensed.

[0055] The anode off-gas Gd that has passed through the anode off-gas condenser 7 is sent to the water-vapor separation section Sa where it is separated into water and vapor, and the condensed water Wb is collected in the condensed water recovery tank 9. The condensed water Wb collected in the condensed water recovery tank 9 is reused as reforming water Wa, as described above. The uncondensed portion of the anode off-gas Gd (anode off-gas Gd after water-vapor separation) is sent to the burner 3.

[0056] The cathode offgas Ge discharged from each cell stack 1 to the cathode offgas line Lf is collected in the second collection manifold Md, and then mixed in a pipe Lf1 with air Ab that flows in via the burner cooling air line Lh, and sent to the burner 3. Depending on the operating state of the power generation unit 100, raw fuel gas Gf supplied from a fuel inlet E1 is sent to the burner 3 via the raw fuel line La, and air Ac supplied from an air inlet E4 is sent to the burner 3 via the start-up air line Lj.

[0057] The burner 3 receives the first burner gas Gx, which is raw fuel gas Gf and / or anode offgas Gd, and the second burner gas Gy, which is air Ac and / or cathode offgas Ge, and combusts them to generate heat. Specifically, the first burner gas Gx is either a mixture of raw fuel gas Gf and anode offgas Gd, or either raw fuel gas Gf or anode offgas Gd, which state can vary depending on the operating state of the power generation unit 100, etc. The second burner gas Gy is either a mixture of air Ac and cathode offgas Ge, or either air Ac and cathode offgas Ge, which state can vary depending on the operating state of the power generation unit, etc. Specifically, the state of the gas supplied to the burner 3 changes appropriately depending on the startup operation, power generation operation (full load operation or partial load operation), shutdown operation, etc. of the power generation unit 100.

[0058] The raw fuel gas Gf is a type of hydrocarbon-containing gas, while the air Ac is a type of oxidant-containing gas. During combustion operation of the burner 3, air Ab is continuously supplied from the burner cooling air line Lh to adjust the combustion temperature.

[0059] The combustion gas Gg generated by combustion in the burner 3 is sent to the combustion gas line Lg, passes through the heat radiation tube Za, combustion gas pipe Zb, air preheater 5, CO oxidizer 8, and evaporator 4 in that order, and is discharged from the power generation module 20 through the gas outlet E6. The heat radiation tube Za and combustion gas pipe Zb are positioned so that the combustion gas Gg can be used to effectively heat the reformer 2. Furthermore, the combustion gas Gg in the combustion gas line Lg is used for heat exchange as it passes through the air preheater 5 and evaporator 4, and if it contains carbon monoxide, the carbon monoxide is converted to carbon dioxide as it passes through the CO oxidizer 8.

[0060] Furthermore, the cooling air Ad supplied from the air intake port E5 to the cooling air line Lk serves to cool the inside of the power generation module 20 as it passes through the cooling pipe Zc. As will be described later, the cooling pipe Zc is installed near the cell stack 1, and the cooling air Ad can effectively cool the cell stack 1. The cooling air Ad then passes through the collection pipe Lk1 and is finally discharged to the outside of the power generation module 20 from the gas discharge port E6 together with the combustion gas Gg.

[0061] Furthermore, in the power generation unit 100, the amount of heat (temperature) inside the power generation module 20 is controlled by adjusting the flow rate of the cooling air Ad introduced into the cooling pipe Zc. As an example, when the discharge temperature of the cathode offgas Ge flowing out from the cell stack 1 exceeds an upper limit temperature, the local controller 17 drives the third air blower 15 and controls the rotation speed of the third air blower 15 so that the discharge temperature of the cathode offgas Ge becomes a target temperature (a temperature that is a predetermined temperature lower than the upper limit temperature). As the rotation speed of the third air blower 15 increases, the flow rate of the cooling air Ad introduced into the cooling pipe Zc increases. Furthermore, the local controller 17 stops the third air blower 15 when the rotation speed remains below the lower limit for a predetermined period of time.

[0062] The cooling pipe Zc installed near the cell stack 1 can also be used to heat the cell stack 1 during startup operation of the power generation unit 100. Specifically, during startup operation of the power generation unit 100, the second raw fuel blower 13 and the second air blower 14 are first driven to combust the burner 3. The combustion gas Gg generated by this combustion flows through the heat radiation tube Za and the combustion gas pipe Zb, heating the cold reformer 2 from the outside by radiant heat transfer and raising its temperature. The combustion gas Gg also serves as a heat source for the evaporator 4, generating steam from the reforming water Wa. This steam flows sequentially through the cold reformer 2 and the cell stack 1, heating these devices from the inside by thermal conduction and raising their temperatures. If there is residual heat in the combustion gas Gg discharged from the evaporator 4, the combustion gas Gg is allowed to flow from the pipe Lg1 into the collection pipe Lk1. As a result, the combustion gas Gg flows through the cooling pipe Zc, and the temperature of the cold cell stack 1 can be increased by heating it from the outside by radiant heat transfer.

[0063] In the power generation operation of the power generation unit 100, balancing the heat balance among the heat generated by the electrochemical reaction of the reformed gas Gc and oxygen in the cell stack 1, the heat generated by the combustion reaction of the anode off-gas Gd and cathode off-gas Ge in the burner 3, and the heat absorbed by the steam reforming reaction of the raw fuel gas Ga and steam (reforming water Wa) in the reformer 2 is called "thermal self-sustaining." In addition, recovering the water (reforming water Wa) generated by the electrochemical reaction of the reformed gas Gc and oxygen and repeatedly using it for the steam reforming reaction is called "water self-sustaining."

[0064] During the power generation operation of the power generation unit 100, the output power of the grid-connected inverter 16d is equal to the value obtained by subtracting the sum of the power loss due to the operation of the auxiliary equipment 30, the power loss due to the operation of the power conditioner 16, and the power loss due to the operation of the load module 40. The load module 40 is operated in an isolated operation mode, which will be described later.

[0065] When the power generation unit 100 is operated at full load with rated output power, the local controller 17 sets the sweep current value for the cell stack 1 to the rated current value and supplies an amount of raw fuel gas Ga corresponding to this. When the power generation unit 100 is operated at partial load with less than the rated output power but not less than the minimum output power, the local controller 17 sets the sweep current value for the cell stack 1 to a range less than the rated current value but not less than the lower limit current value and supplies an amount of raw fuel gas Ga corresponding to this. When the power generation unit 100 is put into standby with zero output power, the local controller 17 sets the sweep current value for the cell stack 1 to be equivalent to the operating power of the auxiliary equipment 30 and supplies a minimum amount of raw fuel gas Ga while keeping the power generation module 20 warm. The state in which the power generation unit 100 is put into standby with zero output power is referred to as "hot standby."

[0066] The power generation operation of the power generation unit 100 includes a grid-connected operation mode and an isolated operation mode. In the grid-connected operation mode, as shown in FIG. 2, the switch 16e is controlled to be in the on state and the switch 16f is controlled to be in the off state. As a result, the power generation unit 100 is operated in a parallel state with respect to the commercial power system 500. In the isolated operation mode, contrary to FIG. 2, the switch 16e is controlled to be in the off state and the switch 16f is controlled to be in the on state. As a result, the power generation unit 100 is operated in a parallel-off state with respect to the commercial power system 500.

[0067] The local controller 17 constantly monitors whether or not there is a power outage in the commercial power system 500, and when a power outage is detected, the local controller 17 shifts the power generating unit 100 from the grid-connected operation mode to the independent operation mode. In the independent operation mode, when a power consuming device is connected to the independent outlet 300, the output power of the grid-connected inverter 16d can be supplied to the power consuming device as independent operation power. When the commercial power system 500 recovers from the power outage, the local controller 17 shifts the power generating unit 100 from the independent operation mode to the grid-connected operation mode.

[0068] When the supply of independent operation power exceeds the consumption in the independent operation mode, the power generation unit 100 causes the load module 40 to consume the surplus independent operation power. The power consumption of the load module 40 can be adjusted by adjusting the heat generation amount of the electric heater 41 (for example, by adjusting the number of heaters to be energized or the on / off duty ratio of the power supply).

[0069] 2.1 Overview of the power supply system configuration Next, an outline of the configuration of the power supply system according to this embodiment will be described. Fig. 3 is a schematic diagram showing the configuration of the power supply system according to this embodiment. As shown in Fig. 3, the power supply system (fuel cell system) 1000 includes a plurality of power generation units 100 operated in parallel (grid-connected mode) with respect to a commercial power system 500, and a system controller 18 that controls the control state of each unit. The power supply system 1000 supplies a total output power, which is the sum of the output power of each power generation unit 100, to a power demand facility 600.

[0070] In this embodiment, the power supply system 1000 includes a first power generating unit 101, a second power generating unit 102, a third power generating unit 103, and a fourth power generating unit 104. Each of the power generating units 101 to 104 has the same rated output power. For example, if the rated output power of each is 6 kW, the power supply system 1000 can supply a maximum total output power of 24 kW.

[0071] <Number of power generating units installed> The number N of installed power generating units 100 is determined so as not to generate a reverse power flow when all of the power generating units 100 are operating at their rated output power (i.e., when the power supply system 1000 is operating at its maximum available power). Specifically, the number N is determined so as to satisfy the following formula (1), where Qr [W] is the rated output power of each power generating unit 100, Qs [W] is the preset reference purchased power that is always purchased from the commercial power supply system 500, and D [W] is the minimum power demand for a predetermined period at the power demand facility 600, and n is a natural number obtained by rounding down the decimal point of the number obtained by the calculation (D-Qs) / Qr. 2≦N≦n …(1)

[0072] For example, if the rated output power Qr = 6 kW, the standard purchased power Qs = 2 kW, and the minimum demand power D = 27 kW, then n = 4 is calculated, and therefore, using formula (1), the number of units N to be installed can be estimated to be 2 to 4. Here, in order to take advantage of the benefit of private power generation, which is minimizing purchased power costs, it is desirable to select the maximum number n, which is 4 units, from the estimated range of the number of units N to be installed.

[0073] When the actual number of installed units N is the maximum number n, the standard purchased power Qs is set to a predetermined positive value that is less than the difference obtained by subtracting the maximum supplyable power H, which is the maximum number of units n multiplied by the rated output power Qr, from the minimum demand power D.

[0074] The predetermined period for determining the minimum power demand D should be at least one week, and at most one year, and should not include low demand periods (nighttime or holidays) when the factory or other facility is not operating. By determining the minimum power demand D for high demand periods when the factory or other facility is operating, it becomes possible to operate the four power generation units 100 at the rated output power during high demand periods.

[0075] <Operation as an output adjuster or output fixed device> As described above, the power generating unit 100 can be operated at full load with rated output power, at partial load below the rated output power but above the minimum output power, or in hot standby with zero output power. That is, each of the power generating units 101 to 104 can be operated as an output regulator that operates in a range below the rated output power but above the minimum output power. Note that, since the power generating module 20 in this embodiment includes an SOFC cell stack, the minimum output power during partial load operation is set based on the minimum fuel supply amount that allows the power generating module 20 to maintain thermal independence and the minimum fuel utilization rate that allows the power generating module 20 to maintain water independence.

[0076] The minimum output power in grid-connected operation mode is the lower limit of the output power at which the power generation module 20 achieves both thermal and water independence and at which there is no substantial decrease in power generation efficiency during partial load operation compared to full load operation. Here, if the power generation efficiency during full load operation at 100% output is ηa and the power generation efficiency during partial load operation at 1-99% output is ηb, then it can be considered that there is no substantial decrease in power generation efficiency if the ratio [ηb / ηa] is 0.95 or greater. The minimum output power of a power generation unit 100 using SOFCs is, for example, equivalent to 50% (3 kW) of the rated output power (6 kW).

[0077] In this embodiment, in the grid-connected operation mode, the multiple power generating units 100 are divided into a first group of fixed maximum output units that fix the output power to an upper limit, a second group of fixed minimum output units that fix the output power to a lower limit, a third group of output adjustment units that adjust the output power between the upper limit and the lower limit, and a fourth group of standby output units that fix the output power to zero. Specifically, the fixed output units belonging to the first group are operated at a fixed rated output power (100% output). The fixed output units belonging to the second group are operated at a fixed minimum output power (50% output). The output adjustment units belonging to the third group are operated in a range from the rated output power to the minimum output power (100% to 50% output). The standby output units belonging to the fourth group are in a hot standby state. Note that in order to utilize the fixed maximum output units, fixed minimum output units, output adjustment units, and standby output units to enable the power supply to follow demand changes, at least four power generating units must be installed.

[0078] The output adjusters belonging to the third group adjust the output power from the power conditioner 16 by increasing or decreasing the output current from the grid-connected inverter 16d. The local controller 17 increases the sweep current value for the cell stack 1 in parallel with an increase in the output current, and increases the supply amount of raw fuel gas Ga. Furthermore, the local controller 17 decreases the sweep current value for the cell stack 1 in parallel with a decrease in the output current, and decreases the supply amount of raw fuel gas Ga. As a result, the power generated by the power generation module 20 increases or decreases as the output current increases or decreases.

[0079] <Local Controller> Each of the local controllers 17 mounted on each of the power generating units 101 to 104 is configured by a programmable logic controller (PLC). The PLC has a calculation device, a storage device, an input device, an output device, and a power supply device, and executes required calculations and sequence control using a processing program that has been created and stored in advance. A current sensor 200, which will be described later, is connected to the input device of the PLC.

[0080] Each of the local controllers 17 is configured to be able to execute output adjustment control that adjusts the output power of the power conditioner 16 within a range that is equal to or less than the rated output power and equal to or greater than the minimum output power, based on purchased power information (hereinafter referred to as "first information") from the commercial power system 500. The output adjustment control includes heteronomous output adjustment control that heteronomously adjusts the output power, and autonomous output adjustment control that autonomously adjusts the output power. The heteronomous output adjustment control and autonomous output adjustment control will be described in detail below.

[0081] <System Controller> Each of the local controllers 17 mounted on each of the power generation units 101 to 104 has a system control section that can function as a system controller 18. This system control section is a functional block incorporated in a PLC.

[0082] In this embodiment, each of the power generating units 101 to 104 is divided into one parent unit and the remaining child units. Specifically, the first power generating unit 101 is the parent unit, and the second power generating unit 102, the third power generating unit 103, and the fourth power generating unit 104 are child units.

[0083] The system control unit in the first power generating unit 101 designated as the parent unit is enabled as the system controller 18. On the other hand, the system control units in the second power generating unit 102, the third power generating unit 103, and the fourth power generating unit 104 designated as the child units are disabled as the system controllers 18. As a result, the system controller 18 of the parent unit is configured to oversee the control status of its own unit and the child units.

[0084] <Information and communication functions> The system controller 18 of the parent device and the local controller 17 of the parent device can exchange information with each other within the PLC. The system controller 18 of the parent device and the local controller 17 of the child device can also communicate with each other via a communication unit 17a attached to the PLC.

[0085] Each of the local controllers 17 continuously transmits information about its own control state and output state (for example, the sweep current value for the cell stack 1, the output power of the grid-connected inverter 16d, etc.) to the system controller 18. The system controller 18 uses this information received from each of the local controllers 17 to supervise the heteronomous output adjustment control and autonomous output adjustment control of the output adjuster.

[0086] <Current sensor> The power supply system 1000 includes a current sensor 200 that detects a forward flow current flowing from the commercial power supply system 500 to the power demanding facility 600. The current sensor 200 includes a first current sensor 201 associated with the first power generating unit 101, which is the parent unit, a second current sensor 202 associated with the second power generating unit 101, which is the child unit, a third current sensor 203 associated with the third power generating unit 103, which is the child unit, and a fourth current sensor 204 associated with the fourth power generating unit 104, which is the child unit. The detection units of the current sensors 201-204 are disposed on the power transmission cable from the commercial power supply system 500 to the power demanding facility 600, on the power transmission cable upstream of connection points P1-P4 of the output cables of the power generating units 101-104.

[0087] The detection information (current value information) of each of the current sensors 201 to 204 is input to the local controller 17 of the corresponding power generating unit 101 to 104. In the master unit, the detection information is shared between the local controller 17 and the system controller .

[0088] 2.2 Overview of Power Supply System Control The power supply system 1000 causes each of the power generating units 101-104 to execute output adjustment control using setting information related to the reference purchased power and the target purchased power. Fig. 4 is an explanatory diagram showing the relationship between the actual purchased power Qm from the commercial power supply system 500 and the reference purchased power in output adjustment control. When the actual purchased power Qm is on the positive side, it indicates that a forward flow current is flowing from the commercial power supply system 500 to the power demand facility 600, and when the actual purchased power Qm is on the negative side, it indicates that a reverse flow current is flowing from the power supply system 1000 to the commercial power supply system 500.

[0089] A first reference purchase power Q1 and a higher second reference purchase power Q2 are set for each local controller 17. Furthermore, a target purchase power Qt is set for each local controller 17 within the range from the first reference purchase power Q1 to the second reference purchase power Q2.

[0090] The first reference purchased power Q1 is a marginal amount for preventing reverse power flow even when some of the power generating units 100 are operating at partial load, and is a set value for determining a relatively sudden decrease in demand below the minimum demand power D. The first reference purchased power Q1 is set to a value (e.g., 200 W) that ensures a time margin before reverse power flow occurs, even if there is a slight response delay in suppressing the output of the power generating units 100.

[0091] The second reference purchased power Q2 is a set value for determining an increase in demand when some of the power generating units 100 are operating at partial load. The second reference purchased power Q2 may be equal to or less than the reference purchased power Qs (2 kW) used to determine the number of power generating units 100 to be installed, but from the viewpoint of quickly restoring the output power, it is set to a value (for example, 600 W) equivalent to several times the first reference purchased power Q1.

[0092] The target purchasing power Qt is a target value when the output power of the power generating unit 100 is decreased to increase the actual purchasing power Qm, and a target value when the output power of the power generating unit 100 is increased to decrease the actual purchasing power Qm. In this embodiment, the target purchasing power Qt is set to the median value (e.g., 400 W) between the first reference purchasing power Q1 and the second reference purchasing power Q2.

[0093] Hereinafter, the heteronomous output adjustment control and autonomous output adjustment control executed by each of the local controllers 17 will be described with reference to the state transition diagrams and flowcharts shown in Fig. 5 to Fig. 11. Figs. 5 to 8 are flowcharts and state transition diagrams of the overall control in the system controller 18. Figs. 9 to 11 are flowcharts of the output adjustment control in the local controller 17.

[0094] <Overall control of system controller> First, the overall control of the system controller 18 will be described with reference to the flowchart in Fig. 5. In step ST101, the system controller 18 controls each of the power generating units 101 to 104 to an initial grid-connected state. The initial grid-connected state is, for example, a state in which each of the power generating units 101 to 104 is operating at its rated power output (a state in which actual purchased power Qm exceeds reference purchased power Qs).

[0095] In step ST102, the system controller 18 calculates in real time a monitor value of actual purchased power Qm from the commercial power supply system 500 based on the detection information (current value information) input from the current sensor 201 connected to the parent device and the AC voltage value (e.g., 100 V) of the commercial power supply system 500. This actual purchased power Qm is used as first information for controlling the total output power of the system.

[0096] In step ST103, the system controller 18 determines whether a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1. If the answer is YES in step ST103, the process proceeds to step ST104. On the other hand, if the answer is NO in step ST103, the process proceeds to step ST105.

[0097] In step ST104, the system controller 18 shifts the interconnection state Z to a side that reduces the total output power of the system. Specific control of the shift of the interconnection state Z will be described later.

[0098] In step ST105, the system controller 18 determines whether a predetermined time T2 has elapsed in a state in which the actual purchased power Qm has exceeded the second reference purchased power Q1. If the answer is YES in step ST105, the process proceeds to step ST106. On the other hand, if the answer is NO in step ST105, the process returns to step ST102.

[0099] In step ST106, the system controller 18 shifts the interconnection state Z to the side that increases the total output power of the system.

[0100] In steps ST104 and ST106, the system controller 18 generates an adjustment permission signal that permits the power generation units classified into the third group to execute autonomous output adjustment control, and transmits this adjustment permission signal to each of the local controllers 17. The system controller 18 also generates an adjustment prohibition signal that prohibits the power generation units classified into the first and second groups from executing autonomous output adjustment control, and transmits this adjustment prohibition signal to each of the local controllers 17. The system controller 18 also generates a standby instruction signal that instructs the power generation units classified into the fourth group to transition to hot standby, and transmits this standby instruction signal to each of the local controllers 17. By receiving the adjustment permission signal, each of the local controllers 17 becomes able to execute output adjustment control in a range below the rated output power and above the minimum output power.

[0101] The reason for providing the predetermined time T1 for status confirmation is to indirectly determine whether the output regulator has reached its minimum output power when the system includes an output regulator that autonomously executes output adjustment control according to the actual purchased power Qm.Similarly, the reason for providing the predetermined time T2 for status confirmation is to indirectly determine whether the output regulator has reached its maximum output power.

[0102] Next, the transition control of the grid-connection state Z executed in the above-mentioned steps ST104 and ST106 will be described. Each of the power generation units 101 to 104 is heteronomously controlled by the system controller 18 so as to transition among the grid-connection states Z1 to Z7 shown in Figures 5 and 6 in accordance with a predetermined event condition. The system controller 18 constantly monitors the monitor value of the actual purchased power Qm to determine whether the event condition is met.

[0103] First, in the initial interconnection state described above, the system controller 18 classifies the first power generating unit 101, the second power generating unit 102, and the third power generating unit 103 into a first group. The system controller 18 also classifies the fourth power generating unit 104 into a third group. This results in an interconnection state Z1 in which the first power generating unit 101, the second power generating unit 102, and the third power generating unit 103 are designated as maximum output fixed units, and the fourth power generating unit 104 is designated as an output adjuster. In this interconnection state Z1, assuming that the rated output power of the power generating unit 100 is 100% output, the total output power of the four units can be increased or decreased within a range of 400 to 350% output. In the interconnection states Z1 to Z7, the number of power generating units designated as output adjusters is always one.

[0104] In the grid-connected state Z1, when an event X1 occurs (YES in step ST103) in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1, the system controller 18 transitions each of the power generating units 101-104 to the grid-connected state Z2. Due to the occurrence of event X1, the system controller 18 reclassifies the fourth power generating unit 104, which belongs to the third group, into the second group. Furthermore, among the power generating units belonging to the first group, the third power generating unit 103 is reclassified into the third group. This results in the grid-connected state Z2 in which the first power generating unit 101 and the second power generating unit 102 are designated as maximum output fixed units, the fourth power generating unit 104 is designated as a minimum output fixed unit, and the third power generating unit 103 is designated as an output adjustment unit. In this grid-connected state Z2, assuming that the rated output power of the power generating unit 100 is 100%, the total output power of the four units can be increased or decreased within a range of 350-300% output.

[0105] In the grid-connected state Z2, if an event X2 occurs (YES in step ST103) in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z3. Due to the occurrence of event X2, the system controller 18 reclassifies the third power generating unit 103, which belongs to the third group, into the second group. Furthermore, among the power generating units belonging to the first group, the second power generating unit 102 is reclassified into the third group. This results in a grid-connected state Z3 in which the first power generating unit 101 is designated as a maximum output fixed unit, the third power generating unit 103 and the fourth power generating unit 104 are designated as minimum output fixed units, and the second power generating unit 102 is designated as an output adjustable unit. In this grid-connected state Z3, assuming that the rated output power of the power generating unit 100 is 100%, the total output power of the four units can be increased or decreased within a range of 300 to 250% output.

[0106] In the grid-connected state Z3, if an event X3 occurs (YES in step ST103) in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z4. Due to the occurrence of event X3, the system controller 18 reclassifies the second power generating unit 102, which belongs to the third group, into the second group. Furthermore, the system controller 18 reclassifies the first power generating unit 101, which belongs to the first group, into the third group. This results in the grid-connected state Z4 in which the second power generating unit 102, the third power generating unit 103, and the fourth power generating unit 104 are designated as minimum output fixed units, and the first power generating unit 101 is designated as an output adjustable unit. In this grid-connected state Z4, if the rated output power of the power generating unit 100 is 100%, the total output power of the four units can be increased or decreased within a range of 250 to 200% output.

[0107] In the grid-connected state Z4, if an event X4 occurs (YES in step ST103) in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1, the system controller 18 transitions each of the power generating units 101-104 to the grid-connected state Z5. Due to the occurrence of event X4, the system controller 18 reassigns the fourth power generating unit 104, which belongs to the second group, to the fourth group. This results in the grid-connected state Z5 in which the fourth power generating unit 104 is designated as an output standby unit (0% output), the second power generating unit 102 and the third power generating unit 103 are designated as minimum output fixed units, and the first power generating unit 101 is designated as an output adjustment unit. In this grid-connected state Z5, if the rated output power of the power generating unit 100 is 100% output, the total output power of the four units can be increased or decreased within a range of 200% to 150% output.

[0108] In the grid-connected state Z5, if an event X5 occurs (YES in step ST103) in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z6. Due to the occurrence of event X5, the system controller 18 reassigns the third power generating unit 103, which belongs to the second group, to the fourth group. This results in the grid-connected state Z6 in which the third power generating unit 103 and the fourth power generating unit 104 are designated as standby power units (0% output), the second power generating unit 102 is designated as a minimum output fixed unit, and the first power generating unit 101 is designated as an output adjustment unit. In this grid-connected state Z6, if the rated output power of the power generating unit 100 is 100%, the total output power of the four units can be increased or decreased within a range of 150% to 100% output.

[0109] In the grid-connected state Z6, if an event X6 occurs (YES in step ST103) in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1, the system controller 18 transitions each of the power generating units 101-104 to the grid-connected state Z7. When the event X6 occurs, the system controller 18 reassigns the second power generating unit 102, which belongs to the second group, to the fourth group. As a result, the second power generating unit 102, the third power generating unit 103, and the fourth power generating unit 104 are designated as output standby units (0% output), and the grid-connected state Z7 is entered in which the first power generating unit 101 is designated as an output adjuster. In this grid-connected state Z7, if the rated output power of the power generating unit 100 is 100% output, the total output power of the four units can be increased or decreased within a range of 100 to 50% output.

[0110] In the grid-connected state Z7, when an event Y1 occurs (YES in step ST105) in which a predetermined time T2 has elapsed while the actual purchased power Qm is above the second reference purchased power Q2, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z6. When the event Y1 occurs, the system controller 18 reassigns the second power generating unit 102, which belongs to the fourth group, to the second group. As a result, the grid-connected state Z6 is established in which the third power generating unit 103 and the fourth power generating unit 104 are designated as output standby units (0% output), the second power generating unit 102 is designated as a minimum output fixed unit, and the first power generating unit 101 is designated as an output adjustment unit.

[0111] In the grid-connected state Z6, when an event Y2 occurs (YES in step ST105) in which a predetermined time T2 has elapsed while the actual purchased power Qm is above the second reference purchased power Q2, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z5. When the event Y2 occurs, the system controller 18 reassigns the third power generating unit 103, which belongs to the fourth group, to the second group. As a result, the grid-connected state Z5 is entered, in which the fourth power generating unit 104 is designated as an output standby unit (0% output), the second power generating unit 102 and the third power generating unit 103 are designated as minimum output fixed units, and the first power generating unit 101 is designated as an output adjustment unit.

[0112] In the grid-connected state Z5, when an event Y3 occurs (YES in step ST105) in which a predetermined time T2 has elapsed while the actual purchased power Qm is above the second reference purchased power Q2, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z4. When the event Y3 occurs, the system controller 18 reclassifies the fourth power generating unit 104, which belongs to the fourth group, into the second group. As a result, the second power generating unit 102, the third power generating unit 103, and the fourth power generating unit 104 are designated as minimum output fixed units, and the first power generating unit 101 is designated as an output adjustment unit, entering the grid-connected state Z4.

[0113] In the grid-connected state Z4, when an event Y4 occurs (YES in step ST105) in which a predetermined time T2 has elapsed while the actual purchased power Qm is above the second reference purchased power Q2, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z3. When the event Y4 occurs, the system controller 18 reclassifies the first power generating unit 101, which belongs to the third group, into the first group. Furthermore, among the power generating units belonging to the second group, the second power generating unit 102 is reclassified into the third group. As a result, the grid-connected state Z3 is entered, in which the first power generating unit 101 is designated as a maximum output fixed unit, the third power generating unit 103 and the fourth power generating unit 104 are designated as minimum output fixed units, and the second power generating unit 102 is designated as an output adjustment unit.

[0114] In the grid-connected state Z3, when an event Y5 occurs (YES in step ST105) in which a predetermined time T2 has elapsed while the actual purchased power Qm is above the second reference purchased power Q2, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z2. When the event Y5 occurs, the system controller 18 reclassifies the second power generating unit 102, which belongs to the third group, into the first group. Furthermore, among the power generating units belonging to the second group, the system controller 18 reclassifies the third power generating unit 103 into the third group. As a result, the grid-connected state Z2 is entered, in which the first power generating unit 101 and the second power generating unit 102 are designated as maximum output fixed units, the fourth power generating unit 104 is designated as a minimum output fixed unit, and the third power generating unit 103 is designated as an output adjustment unit.

[0115] In the grid-connected state Z2, when an event Y6 occurs (YES in step ST105) in which a predetermined time T2 has elapsed while the actual purchased power Qm is above the second reference purchased power Q2, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z1. When the event Y6 occurs, the system controller 18 reclassifies the third power generating unit 103, which belongs to the third group, into the first group. Also, it reclassifies the fourth power generating unit 104, which belongs to the second group, into the third group. As a result, the grid-connected state Z1 is entered, in which the first power generating unit 101, the second power generating unit 102, and the third power generating unit 103 are designated as maximum output fixed units, and the fourth power generating unit 104 is designated as an output adjustment unit.

[0116] When events X1 to X3 occur, it is desirable that the number of units reassigned from the third group to the second group be equal to the number of units reassigned from the first group to the third group. Furthermore, when events Y4 to Y6 occur, it is desirable that the number of units reassigned from the third group to the first group be equal to the number of units reassigned from the second group to the third group. Furthermore, it is desirable that the number of units reassigned from the second group to the fourth group when events X4 to X6 occur, and the number of units reassigned from the fourth group to the second group when events Y1 to Y3 occur be equal to the number of units in the third group. By performing this replacement, a specified number of power generation units (e.g., one or two) are always operated as output regulators. An example of operating two power generation units as output regulators will be described later.

[0117] In addition to the above-described interconnection states Z1 to Z7, the system controller 18 may be configured to execute a grid-connected state Z8 in which all of the power generating units 101 to 104 are in a zero power generation state. Specifically, when an event XY1 occurs in the grid-connected state Z7, in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1 (YES in step ST103), the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z8. When the event XY1 occurs, the system controller 18 reclassifies the first power generating unit 101, which belongs to the third group, into the fourth group. This results in the grid-connected state Z8 in which all of the power generating units 101 to 104 are designated as standby units (0% output). In this grid-connected state Z8, all of the power demand is met by purchased power.

[0118] There are two exemplary routes for returning from the grid-connected state Z8 to another grid-connected state. The first route is a return from the grid-connected state Z8 to the grid-connected state Z7, and is triggered by the occurrence of event XY2. The condition for the occurrence of event XY2 is, for example, when the actual purchased power Qm exceeds the sum (5 kW) of the reference purchased power Qs (2 kW) and the 50% output value (3 kW) of one power generating unit 100. The second route is a return from the grid-connected state Z8 to the grid-connected state Z1, and is triggered by the occurrence of event XY3. The condition for the occurrence of event XY3 is, for example, when the actual purchased power Qm exceeds the sum (26 kW) of the reference purchased power Qs (2 kW) and the 100% output value (24 kW) of four power generating units 100.

[0119] From the viewpoint of equalizing the life span of each of the power generation units 101 to 104, it is desirable to rotate the power generation units classified into the third group in the grid-connected state Z1. For example, the power generation unit with the largest cumulative output power amount is given priority in being designated as the output regulator.

[0120] Furthermore, from the viewpoint of maintaining water independence of the power generation modules 20, it is desirable to determine which power generation units 100 are divided into the second, third, or fourth group based on the water level in the condensed water recovery tank 9. Since the amount of condensed water collected tends to decrease during partial load operation or hot standby, by prioritizing the power generation units 100 with a high water level in the condensed water recovery tank 9 to be divided into the second, third, or fourth groups, water independence can be reliably maintained.

[0121] [Another interconnection status control example A] 8 shows a state transition diagram when the number of power generation units designated by the output regulator is two. Each of the power generation units 101 to 104 is heteronomously controlled by the system controller 18 so as to transition between the grid-connected states Z1' to Z4' in accordance with a predetermined event condition.

[0122] First, in the initial interconnection state described above, the system controller 18 classifies the first power generating unit 101 and the second power generating unit 102 into a first group. The system controller 18 also classifies the third power generating unit 103 and the fourth power generating unit 104 into a third group. This results in an interconnection state Z1' in which the first power generating unit 101 and the second power generating unit 102 are designated as maximum output fixed units, and the third power generating unit 103 and the fourth power generating unit 104 are designated as output adjustable units. In this interconnection state Z1', if the rated output power of the power generating unit 100 is set to 100%, the total output power of the four units can be increased or decreased within a range of 400 to 300% output. In this interconnection state Z1', if the rated output power of the power generating unit 100 is set to 100%, the total output power of the four units can be increased or decreased within a range of 400 to 300% output.

[0123] In the grid-connected state Z1', when an event X1' occurs (YES in step ST103) in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z2'. When the event X1' occurs, the system controller 18 reclassifies the third power generating unit 103 and the fourth power generating unit 104, which belong to the third group, into the second group. Also, the system controller 18 reclassifies the first power generating unit 101 and the second power generating unit 102, which belong to the first group, into the third group. As a result, the first power generating unit 101 and the second power generating unit 102 are designated as output adjusters, and the third power generating unit 103 and the fourth power generating unit 104 are designated as minimum output fixed units, resulting in the grid-connected state Z2'. In this interconnection state Z2', if the rated output power of the power generating unit 100 is 100% output, the total output power of the four units can be increased or decreased within the range of 300 to 200% output.

[0124] In the grid-connected state Z2', if an event X2' occurs (YES in step ST103) in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z3'. When the event X2' occurs, the system controller 18 reassigns the third power generating unit 103 and the fourth power generating unit 104, which belong to the second group, to the fourth group. As a result, the first power generating unit 101 and the second power generating unit 102 are designated as output adjusters, and the third power generating unit 103 and the fourth power generating unit 104 are designated as output standby units, resulting in the grid-connected state Z3'. In this grid-connected state Z3', if the rated output power of the power generating unit 100 is 100%, the total output power of the four units can be increased or decreased within a range of 200 to 100% output.

[0125] In the grid-connected state Z3', when an event Y1' occurs (YES in step ST105) in which a predetermined time T2 has elapsed while the actual purchased power Qm is above the second reference purchased power Q2, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z2'. When the event Y1' occurs, the system controller 18 reclassifies the third power generating unit 103 and the fourth power generating unit 104, which belong to the fourth group, into the second group. As a result, the first power generating unit 101 and the second power generating unit 102 are designated as output adjusters, and the third power generating unit 103 and the fourth power generating unit 104 are designated as minimum output fixed units, resulting in the grid-connected state Z2'.

[0126] In the grid-connected state Z2', when an event Y2' occurs (YES in step ST105) in which a predetermined time T2 has elapsed while the actual purchased power Qm is above the second reference purchased power Q2, the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z1'. When the event Y2' occurs, the system controller 18 reclassifies the first power generating unit 101 and the second power generating unit 102, which belong to the third group, into the first group. Also, the system controller 18 reclassifies the third power generating unit 103 and the fourth power generating unit 104, which belong to the second group, into the third group. As a result, the grid-connected state Z1' is entered, in which the first power generating unit 101 and the second power generating unit 102 are designated as maximum output fixed units, and the third power generating unit 103 and the fourth power generating unit 104 are designated as output adjustment units.

[0127] In addition to the above-described interconnection states Z1' to Z3', the system controller 18 may be configured to execute a grid-connected state Z4' in which all of the power generating units 101 to 104 are set to zero power generation. Specifically, when an event XY1' occurs in the grid-connected state Z3', in which a predetermined time T1 has elapsed while the actual purchased power Qm is below the first reference purchased power Q1 (YES in step ST103), the system controller 18 transitions each of the power generating units 101 to 104 to the grid-connected state Z4'. When the event XY1' occurs, the system controller 18 reclassifies the first power generating unit 101 and the second power generating unit 102, which belong to the third group, into the fourth group. This results in the grid-connected state Z4' in which all of the power generating units 101 to 104 are designated as standby units (0% output). In this grid-connected state Z4', all of the power demand is met by purchased power.

[0128] There are two routes for returning from the grid-connected state Z4' to another grid-connected state. The first route is a return from the grid-connected state Z4' to the grid-connected state Z3', and is triggered by the occurrence of event XY2'. The condition for the occurrence of event XY2' is, for example, when the actual purchased power Qm exceeds the sum (8 kW) of the reference purchased power Qs (2 kW) and the 50% output value (6 kW) of two power generating units 100. The second route is a return from the grid-connected state Z4' to the grid-connected state Z1', and is triggered by the occurrence of event XY3'. The condition for the occurrence of event XY3' is, for example, when the actual purchased power Qm exceeds the sum (26 kW) of the reference purchased power Qs (2 kW) and the 100% output value (24 kW) of four power generating units 100.

[0129] [Another interconnection status control example B] The state transition diagrams in Figures 6 to 8 show examples in which the system controller 18 controls the total system output power by combining the first, second, and third groups, and examples in which the system controller 18 controls the total system output power by combining the first, second, third, and fourth groups. Alternatively, the system controller 18 can be configured to control the total system output power by combining the first, second, and fourth groups. In this configuration, since there is no output adjuster in the system, when the total system output power is reduced, the power generating units 100 responsible for output adjustment transition from maximum output fixed unit to minimum output fixed unit to standby output unit in this order. Conversely, when the total system output power is increased, the power generating units 100 responsible for output adjustment transition from standby output unit to minimum output fixed unit to maximum output fixed unit in this order.

[0130] [Another interconnection state control example C] Instead of the above-described interconnection state control examples A and B, the system controller 18 can also be configured to control the total output power of the system by combining the first group and the fourth group. In this configuration, since there are no output adjusters or minimum output fixing units that perform partial load operation in the system, when the total output power of the system is to be reduced or increased, the power generating units 100 that are responsible for output adjustment will transition between the maximum output fixing unit and the output standby unit.

[0131] <Local controller output adjustment control based on first information> Next, the output adjustment control will be described with reference to the flowcharts of Figures 9 to 11. This output adjustment control is an autonomous control executed by the output adjusters classified into the third group. In step ST201, local controller 17 calculates in real time a monitor value of actual purchased power Qm from commercial power supply system 500 based on the detection information (current value information) input from corresponding current sensors 201 to 204 and the AC voltage value (e.g., 100V) of commercial power supply system 500. This actual purchased power Qm is used as first information for the output adjustment control.

[0132] In step ST202, the local controller 17 determines whether or not an adjustment permission signal has been received from the system controller 18. If the signal has been received (YES in step ST202), the process proceeds to step ST203. On the other hand, if the signal has not been received (NO in step ST202), the process proceeds to step ST211.

[0133] In step ST203, the local controller 17 recognizes itself as an output adjuster classified into the third group.

[0134] In step ST204, the local controller 17 designated as the output adjuster determines whether the actual purchased power Qm is below the first reference purchased power Q1. If it is below the first reference purchased power Qm (YES in step ST204), the process proceeds to step ST205. On the other hand, if it is not below the first reference purchased power Qm (NO in step ST204), the process proceeds to step ST214.

[0135] In step ST205, the local controller 17 executes output decrease control. The output decrease control is an autonomous output adjustment control that does not depend on a request from the system controller 18, and decreases the output current from the grid-connected inverter 16d in a stepwise manner by a predetermined adjustment amount.

[0136] In step ST206, local controller 17 determines whether actual purchased power Qm has reached target purchased power Qt due to the output reduction operation of its own device. If it has reached target purchased power Qt (YES in step ST206), local controller 17 ends the output reduction control and fixes the output current. On the other hand, if it has not reached target purchased power Qt (NO in step ST206), the process proceeds to step ST207.

[0137] In step ST207, the local controller 17 determines whether the minimum output power has been reached. If it has been reached (YES in step ST210), the local controller 17 ends the output decrease control and fixes the output current. If it has not been reached (NO in step ST207), the process returns to step ST205, and the output decrease control continues.

[0138] In step ST208, the local controller 17 determines whether or not an adjustment prohibition signal has been received from the system controller 18. If the signal has been received (YES in step ST208), the process proceeds to step ST209. On the other hand, if the signal has not been received (NO in step ST208), the process proceeds to step ST212.

[0139] In step ST209, the local controller 17 determines whether or not its own device is operating at the rated output power. If it is operating at the rated output power (YES in step ST209), the process proceeds to step ST210. On the other hand, if it is not operating at the rated output power, that is, if it is operating at the minimum output power (NO in step ST209), the process proceeds to step ST211.

[0140] In step ST210, the local controller 17 recognizes the local controller 17 as a maximum output fixed machine classified into the first group. Then, the local controller 17 fixes the output from the grid-connected inverter 16d to the rated output power (maximum output current) and ends the process.

[0141] In step ST211, the local controller 17 recognizes the local controller 17 as a minimum output fixed machine classified into the second group. Then, the local controller 17 fixes the output from the grid-connected inverter 16d to the minimum output power (minimum output current), and ends the process.

[0142] In step ST212, the local controller 17 determines whether or not a standby instruction signal has been received from the system controller 18. If the signal has been received (YES in step ST212), the process proceeds to step ST213. On the other hand, if the signal has not been received (NO in step ST212), the process returns to step ST201.

[0143] In step ST213, the local controller 17 recognizes itself as an output standby device classified into group 4. Then, the local controller 17 stops the output from the grid-connected inverter 16d, transitions to hot standby, and ends the process.

[0144] In step ST214, the local controller 17 designated as the output adjuster determines whether the actual purchased power Qm exceeds the second reference purchased power Q2. If it does (YES in step ST214), the process proceeds to step ST215. On the other hand, if it does not (NO in step ST214), the process returns to step ST201.

[0145] In step ST215, the local controller 17 executes output increase control. The output increase control is an autonomous output adjustment control that does not depend on a request from the system controller 18, and increases the output current from the grid-connected inverter 16d stepwise by a predetermined adjustment amount.

[0146] In step ST216, local controller 17 determines whether actual purchased power Qm has reached target purchased power Qt as a result of the output increase operation of its own device. If it has reached target purchased power Qt (YES in step ST216), local controller 17 ends the output increase control and fixes the output current. On the other hand, if it has not reached target purchased power Qt (NO in step ST216), the process proceeds to step ST217.

[0147] In step ST217, the local controller 17 determines whether the rated output power has been reached. If it has been reached (YES in step ST217), the local controller 17 ends the output increase control and fixes the output current. If it has not been reached (NO in step ST217), the process returns to step ST215, and the output increase control continues.

[0148] The output decrease control described above is executed in a situation where there is a relatively sudden decrease in demand below the minimum demand power D. When an unexpected sudden decrease in demand occurs, the local controller 17 designated as the output regulator performs autonomous output adjustment to quickly restore the actual purchased power Qm, thereby avoiding the occurrence of reverse power flow.

[0149] <Local controller output adjustment control based on second information> Each of the local controllers 17 can be configured to be able to execute autonomous output adjustment control based on second information regarding the cooperative state between the local controller 17 and the commercial power system 500. Control based on the second information takes priority over control based on the first information.

[0150] [Control example A based on second information] When the terminal voltage on the output side of the local power conditioner 16 exceeds a set value, the local controller 17 executes constant power factor control, which outputs reactive power so that the operating power factor is constant relative to the power generated (active power) of the power generation module 20. This constant power factor control is an operation for suppressing an increase in the grid voltage. If the terminal voltage does not become equal to or lower than the set value even after executing constant power factor control for a predetermined time, the local controller 17 executes the above-mentioned output reduction control, and forcibly shifts the power generation unit 100 to partial load operation. The condition for ending the output reduction control is when the terminal voltage becomes equal to or lower than the set value.

[0151] [Control example B based on second information] When the corresponding current sensor 201-204 detects a reverse power flow current (for example, when Qm≦−200 [W]), the local controller 17 transitions the power generating unit 100 to the above-mentioned hot standby. In this embodiment, reverse power flow due to an unexpected sudden decrease in demand is basically avoided by the above-mentioned output reduction control. Therefore, transitioning to hot standby is an emergency measure when the output reduction control does not function sufficiently.

[0152] <Local controller output adjustment control based on third information> Each of the local controllers 17 can be configured to be able to execute autonomous output adjustment control based on third information related to the internal temperature of the power conditioner 16 that is exclusively owned by that local controller 17. The control based on the third information takes priority over the control based on the first information.

[0153] [Example of control based on the third information] The grid-connected inverter 16d has a function for monitoring abnormal temperatures of the switching elements, such as IGBTs, that constitute the power module, to prevent them from being damaged by overheating. When the internal temperature of the power conditioner 16, i.e., the temperature of the switching elements, exceeds an upper limit, the local controller 17 executes the above-mentioned output reduction control and forcibly shifts the power generation unit 100 to partial load operation. The output reduction control is terminated when the internal temperature falls below the upper limit.

[0154] <Local controller output adjustment control based on the fourth information> Each of the local controllers 17 can further be configured to be able to execute autonomous output adjustment control based on fourth information related to the thermal balance of the power generation module 20 exclusively owned by that local controller. The control based on the fourth information takes priority over the control based on the first information.

[0155] [Control example A based on fourth information] During power generation operation of the power generation module 20, the local controller 17 adjusts the rotation speed of the fan 7a so that the cooling temperature of the anode off-gas Gd flowing out from the anode off-gas condenser 7 reaches a target temperature below the dew point at which water vapor condenses. If this rotation speed exceeds an upper limit, the local controller 17 executes the above-mentioned output reduction control and forcibly shifts the power generation unit 100 to partial load operation. The output reduction control ends when the rotation speed of the fan 7a falls below the upper limit.

[0156] If the temperature of the cooling air (outside air) sent by the fan 7a is high and the anode off-gas Gd cannot be cooled below the dew point, the amount of condensed water Wb produced will decrease and water independence will not be maintained. Therefore, by reducing the power generation output of the power generation module 20, the discharge temperature of the anode off-gas Gd flowing out of the cell stack 1 will be lowered, making it possible to cool the anode off-gas Gd below the dew point even when the temperature of the cooling air is high.

[0157] [Control example B based on the fourth information] During power generation operation of the power generation module 20, the local controller 17 adjusts the rotation speed of the third air blower 15 so that the discharge temperature of the cathode off-gas Ge flowing out from the cell stack 1 becomes a target temperature. If this rotation speed exceeds an upper limit, the local controller 17 executes the above-mentioned output reduction control and forcibly shifts the power generation unit 100 to partial load operation. The output reduction control is terminated when the manipulated variable falls below the upper limit.

[0158] The discharge temperature of the cathode off-gas Ge flowing out from the cell stack 1 reflects the operating temperature of the cell stack 1. If the operating temperature of the cell stack 1 is too high even when cooling air Ad is flowing through the cooling pipe Zc, this could result in a deterioration in fuel utilization rate or accelerated deterioration of the power generation cells. Therefore, by lowering the power generation power of the power generation module 20, the heat of reaction between the reformed gas and oxygen is reduced, thereby lowering the operating temperature of the cell stack 1.

[0159] <Exclusion process from output adjuster> When there are power generating units 100 that are executing autonomous output adjustment control based on any of the second information, the third information, and the fourth information, the system controller 18 classifies the remaining power generating units 100 into the above-mentioned first to fourth groups. Note that the output power of the power generating units 100 excluded from the groups is left to the discretion of the output adjustment control led by the local controller 17, and therefore is not subject to management of the above-mentioned grid connection states Z1 to Z7, etc.

[0160] 3. Other Modifications The cell stack 1 constituting the power generation module 20 may be a molten carbon dioxide fuel cell (MCFC) instead of a solid oxide fuel cell (SOFC). Like SOFC, MCFC is a high-temperature operating fuel cell and has high power generation efficiency.

[0161] The power generation module 20 using a fuel cell is not limited to a type that generates power using a single cell stack 1, but may also be a type that generates power using two or more cell stacks 1. Specifically, water vapor is removed from the anode off-gas discharged from the previous cell stack to generate regenerated gas, and this regenerated gas is supplied to the anode of the next cell stack. When generating the regenerated gas, carbon dioxide contained in the anode off-gas may be removed using a separation membrane, an absorption liquid, or the like. By configuring the power generation module to generate power using two or more cell stacks, the fuel utilization rate can be significantly increased.

[0162] The fuel cell-based power generation module 20 is not limited to a configuration that supplies reformed gas to the cell stack, but may also be configured to supply pure hydrogen gas. Specifically, hydrogen gas supplied from an external hydrogen production site via transportation infrastructure is introduced into the anode of the cell stack. When hydrogen gas is used as the raw fuel, the components required for steam reforming and water self-sustaining (such as the reformer 2, evaporator 4, anode off-gas condenser 7, steam-water separator Sa, condensed water recovery tank 9, and water pump 12) can be omitted.

[0163] The power generating unit 100 is not limited to a type that uses a fuel cell, and can be changed to other types. The power generating unit may be a type that uses a solar cell, or a type that uses an organic Rankine cycle, a steam turbine, a gas turbine, or a gas engine to rotate a generator.

[0164] The system controller 18 may be a functional block incorporated in the local controller 17 (PLC), or may be an independent controller separated from the local controller 17. In this case, each of the local controllers 17 is connected to the system controller 18 via a communication unit 17a.

[0165] The power supply system 1000 may also include an additional second current sensor in addition to the first current sensors 201-204 connected to the local controller 17 of each of the power generation units 101-104. This additional second current sensor is connected to the system controller 18 of the parent unit.

[0166] Some of the control functions executed by the local controller 17 (PLC) can also be configured to be executed by an internal controller provided in the power conditioner 16. In this case, the internal controller is essentially a component of the local controller 17. For example, the control examples A and B based on the second information and the control example based on the third information described above may be control functions executed by the internal controller. Furthermore, monitoring power outages and power restorations and issuing instructions for transitioning between the grid-connected operation mode and the independent operation mode may be control functions executed by the internal controller.

[0167] The power supply system 1000 of this embodiment described above provides the following advantages.

[0168] (1) The power supply system 1000 includes a plurality of power generating units 100 operated in parallel with a commercial power supply system 500, and a system controller 18 that controls the control state of the plurality of power generating units 100. Each of the plurality of power generating units 100 includes a power generating module 20, a power conditioner 16 that converts the power generated by the power generating module 20 into output power equivalent to AC power of the commercial power supply system 500, and a local controller 17 that controls the output power by controlling the power generated by the power generating module 20. In the plurality of power generating units 100, each of the local controllers 17 is a heteronomous and and / or is configured to be capable of performing output adjustment control that autonomously adjusts the output power, and the system controller 18 classifies each of the power generation units 100 into one of a first group of fixed output machines that fix the output power to an upper limit value (rated output power), a second group of fixed output machines that fix the output power to a lower limit value (minimum output power), a third group of output adjustment machines that adjust the output power within a range from the upper limit value to the lower limit value, and a fourth group of standby output machines that fix the output power to zero, and controls the total output power of the system by selecting a combination of groups based on first information on purchased power Qm from the commercial power supply system 500.

[0169] During high-demand periods when a factory or other facility is operating, the system controller 18 adjusts the total system output power to the rated value (maximum value) by dividing all of the power generating units 100 into the first group and operating them at full load. Meanwhile, during low-demand periods when the factory or other facility is not operating (nighttime or on holidays), the system controller 18 adjusts the total system output power to less than the rated value by dividing some or all of the power generating units 100 into the second or third group and operating them at partial load, or into the fourth group and operating them in standby mode. This maximizes the use of privately generated power, contributing to a reduction in environmental impact, while improving the responsiveness of the power supply to demand changes. Furthermore, the adjustment range of the system's total output power can be varied by changing the group combination. Therefore, selecting the optimal group combination depending on the magnitude of demand changes at the consumer can contribute to a reduction in environmental impact while preventing reverse power flow.

[0170] (2) In the power supply system 1000 of (1), a current sensor 200 is provided to detect the forward flow current flowing from the commercial power supply system 500 to the power demand facility 600, and the system controller 18 is configured to control the total output power of the system by combining the first group, the second group, and the third group, and calculates the actual purchased power Qm from the detection information of the current sensor 200 as purchased power information, and adjusts the number of power generation units 100 assigned to each group according to the actual purchased power Qm, thereby increasing or decreasing the total output power of the system.

[0171] In one example of an operation mode for increasing or decreasing the total output power of the system, the system controller 18 assigns the power generating units 100 to groups of maximum output fixed units, minimum output fixed units, and output adjusters, and then causes the output adjusters to perform autonomous output adjustment control. As a result, some of the power generating units 100 are operated at partial load with output adjustment, improving the responsiveness of the power supply to demand changes. In particular, the greater the number of output adjusters, the better the responsiveness of the power supply. Because some of the power generating units 100 are output adjusters, the power supply system 1000 in this operation mode is suitable for supplying power to power demand facilities 600 with a relatively small fluctuation in power demand.

[0172] (3) In the power supply system 1000 of (1), a current sensor 200 is provided to detect the forward flow current flowing from the commercial power supply system 500 to the power demand facility 600, and the system controller 18 is configured to control the total output power of the system by combining the first group, the second group, the third group, and the fourth group, and calculates the actual purchased power Qm from the detection information of the current sensor 200 as purchased power information, and adjusts the number of power generation units 100 assigned to each group according to the actual purchased power Qm, thereby increasing or decreasing the total output power of the system.

[0173] In one example of an operation mode for increasing or decreasing the total output power of the system, the system controller 18 assigns the power generating units 100 to groups of maximum output fixed units, minimum output fixed units, output adjustment units, and output standby units, and then causes the output adjustment units to perform autonomous output adjustment control. As a result, some of the power generating units 100 are operated at partial load with output adjustment, improving the power supply's ability to respond to demand changes. In particular, the greater the number of output adjustment units, the better the power supply's ability to respond. Furthermore, because output standby units are present as needed, the system can also respond to power demand facilities 600 where power demand suddenly drops, such as at night.

[0174] (4) In the power supply system 1000 of (1), a current sensor 200 is provided to detect the forward flow current flowing from the commercial power supply system 500 to the power demand facility 600, and the system controller 18 is configured to control the total output power of the system by combining the first group, the second group, and the fourth group, and calculates the actual purchased power Qm from the detection information of the current sensor 200 as purchased power information, and adjusts the number of power generation units 100 assigned to each group according to the actual purchased power Qm, thereby increasing or decreasing the total output power of the system.

[0175] In one example of an operation mode for increasing or decreasing the total output power of the system, the system controller 18 assigns the power generating units 100 to groups of fixed maximum output units, fixed minimum output units, and standby output units. The output adjustment control of each power generating unit 100 has three positions (e.g., 100%, 50%, or 0%), so the adjustment range of the total output power of the system becomes fairly coarse, but the ability of the power supply to respond to changes in demand is sufficiently ensured. Furthermore, because the standby output units can be quickly restored to fixed minimum output units, the utilization rate of self-generated power can be quickly increased when demand is recovering.

[0176] (5) In the power supply system 1000 of (1), a current sensor 200 is provided to detect the forward flow current flowing from the commercial power supply system 500 to the power demand facility 600, and the system controller 18 is configured to control the total output power of the system by combining the first group and the fourth group, and calculates the actual purchased power Qm from the detection information of the current sensor 200 as purchased power information, and adjusts the number of power generation units 100 assigned to each group according to the actual purchased power Qm, thereby increasing or decreasing the total output power of the system.

[0177] In one example of an operation mode for increasing or decreasing the total output power of the system, the system controller 18 assigns the power generation units 100 to groups of fixed maximum output units and standby output units. Since the output adjustment control of each power generation unit 100 is limited to two positions (100% / 0%), the adjustment range of the total output power of the system is quite rough. However, since the transition from rated power generation to zero power generation can be done instantly by interrupting the output of the power conditioner 16, it is possible to respond quickly to sudden drops in demand. Furthermore, since no power generation units 100 are operating at partial load, the power generation efficiency of the entire system can be maintained at a high level.

[0178] (6) In the power supply system 1000 of (1) to (5), each of the power generation modules 20 includes a cell stack 1 in which solid oxide fuel cells are integrated.

[0179] The power supply system 1000 generates electricity privately using a power generation unit 100 that uses an SOFC, and supplies the privately generated electricity to consumers. Because SOFC has higher primary energy efficiency than thermal power generation, consumers can reduce carbon dioxide emissions by switching a portion of the commercial electricity they purchase from power companies to privately generated electricity.

[0180] Furthermore, the multiple power generation units 100 can switch from grid-connected operation mode to independent operation mode in the event of a power outage in the commercial power system 500. By realizing a system that can independently maintain power supply in the event of a power outage caused by a natural disaster or the like, it is possible to reduce the adverse effects on social life and economic activity.

[0181] Although the embodiments of the present invention have been described above, the configuration of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. In other words, the above embodiments are illustrative in all respects and should be considered not to be limiting. The technical scope of the present invention is defined by the claims, not by the description of the above embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0182] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] The power generation unit and power supply system disclosed herein reduces carbon dioxide emissions by improving primary energy efficiency, and can contribute to achieving Goal 13 of the Sustainable Development Goals (SDGs), "Take urgent action to combat climate change." In addition, the power generation unit and power supply system disclosed herein can independently maintain power supply during power outages caused by natural disasters, and can contribute to achieving Goal 11 of the SDGs, "Make cities and towns inclusive and sustainable." [Explanation of symbols]

[0183] 1 Cell stack 2 Reformer 3 Burner 4. Evaporator 5. Air preheater 6 Anode off-gas cooler 7. Anode off-gas condenser 7a Fan 8 CO oxidizer (carbon monoxide oxidizer) 9 Condensate recovery tank 10. First raw fuel blower 11 No. 1 air blower 12 Water pump 13 Second raw fuel blower 14 Second air blower 15 Third air blower 16 Power Conditioner 16a, 16b DC / DC converter 16c smoothing capacitor 16d Grid-connected inverter 16e,16f switches 16g, 16h control circuit 17 Local Controller 17a Communication unit 18 System Controller 20 Power generation module 30 Auxiliary Machinery 40 Load Module 41 Electric heater 42 Heat dissipation fan 100 generating units 101 First Power Generation Unit 102 Second Power Generation Unit 103 Third Power Generation Unit 104 No. 4 Power Generation Unit 200 Current Sensor 201 First current sensor 202 Second current sensor 203 Third current sensor 204 4th current sensor 300 Freestanding outlet 500 Commercial power system 600 Electricity demand equipment 610 Switchboard 1000 Power Supply System Aa, Ab, Ac Air Ad Cooling air B1 First bellows type expansion joint B2 Second bellows type expansion joint B3 Third bellows type expansion joint B4 No. 4 Bellows Expansion Joint E1,E2 fuel intake E3, E4, E5 air intakes E6 Gas outlet Ga, Gf raw fuel gas Gb mixed gas Gc reformed gas Gd anode off-gas Ge cathode offgas Gg Combustion gas La raw fuel line Lb mixed gas line Lc anode fuel line Ld Anode off-gas line Le cathode air line Lf Cathode off-gas line Lg combustion gas line Lh Burner cooling air line Li reformed water line Lj Starting air line Lk Cooling air line Lk1 collection tube Lw Condensate recovery line Ma 1st distribution manifold Mb Second distribution manifold Mc 1st Collection Manifold Md Second collection manifold R1 1st area R2 2nd area Sa air / water separation section Sb Water Level Detector Sc drain valve Wa modified water Wb Condensed water Za Heat Radiator Zb Combustion gas pipe Zc cooling pipe

Claims

1. a plurality of power generation units operated in parallel with a commercial power system; a system controller that controls the control state of the plurality of power generating units, Each of the plurality of power generation units comprises: a power generation module; a power conditioner that converts the power generated by the power generation module into output power equivalent to AC power of the commercial power supply system; a local controller that controls the output power by controlling the power generated by the power generation module, In the plurality of power generation units, each of the local controllers is configured to be able to execute output adjustment control that heteronomously and / or autonomously adjusts the output power, The system controller each of the power generating units is divided into one of a first group of output fixing machines that fix the output power to an upper limit value, a second group of output fixing machines that fix the output power to a lower limit value, a third group of output adjusting machines that adjust the output power within a range from the upper limit value to the lower limit value, and a fourth group of output standby machines that fix the output power to zero; The total output power of the system is controlled by selecting a combination of the groups based on purchased power information from the commercial power supply system. Power supply system.

2. a current sensor for detecting a forward flow current flowing from the commercial power supply system to the power demand facility; The system controller configured to combine the first group, the second group, and the third group to control the total output power of the system; As the purchased power information, actual purchased power is calculated from the detection information of the current sensor; The total output power of the system is increased or decreased by adjusting the number of power generating units allocated to each group according to the actual purchased power. The power supply system according to claim 1 .

3. a current sensor for detecting a forward flow current flowing from the commercial power supply system to the power demand facility; The system controller configured to combine the first group, the second group, the third group, and the fourth group to control the total output power of the system; As the purchased power information, actual purchased power is calculated from the detection information of the current sensor; The total output power of the system is increased or decreased by adjusting the number of power generating units allocated to each group according to the actual purchased power. The power supply system according to claim 1 .

4. a current sensor for detecting a forward flow current flowing from the commercial power supply system to the power demand facility; The system controller configured to combine the first group, the second group, and the fourth group to control the total output power of the system; As the purchased power information, actual purchased power is calculated from the detection information of the current sensor; The total output power of the system is increased or decreased by adjusting the number of power generating units allocated to each group according to the actual purchased power. The power supply system according to claim 1 .

5. a current sensor for detecting a forward flow current flowing from the commercial power supply system to the power demand facility; The system controller configured to combine the first group and the fourth group to control the total output power of the system; As the purchased power information, actual purchased power is calculated from the detection information of the current sensor; The total output power of the system is increased or decreased by adjusting the number of power generating units allocated to each group according to the actual purchased power. The power supply system according to claim 1 .

6. In the plurality of power generation units, each of the power generation modules includes a cell stack in which solid oxide fuel cells are integrated. The power supply system according to any one of claims 1 to 5.

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