Photovoltaic power generation system

Abstract

To prevent excessive restrictions on photovoltaic power generation due to output control from the grid side.SOLUTION: A photovoltaic power generation system is connected to the grid via the same service line, together with a power consumption facility. The system includes solar cells, a power conditioner that converts power between the solar cells and the grid, a reverse power relay that stops the operation of the power conditioner when reverse power flowing from the service line to the grid is detected, and a control device that receives an output control signal transmitted from a business operator that manages the grid. The control device normally disables the reverse power relay, and enables the reverse power relay when it receives the output control signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a photovoltaic power generation system, and more particularly to a grid-tied photovoltaic power generation system connected to a power grid. [Background technology]

[0002] In an electric power system (also simply called a system), it is necessary to maintain a balance between the amount of electricity used (demand) and the amount of electricity generated (supply), and when the amount of electricity used exceeds the amount of electricity generated, output control is performed on the power generation equipment. Output control means prohibiting or restricting the power generation of the power generation equipment. Traditionally, output control has been performed mainly on thermal power generation, which has sufficiently maintained the balance of supply and demand.

[0003] However, in recent years, with the spread of solar power generation, output control on thermal power generation alone is no longer sufficient, and output control is also being implemented on solar power generation. Output control on solar power generation is not desirable in terms of further promoting renewable energy, including solar power generation. For this reason, for example, government agencies in Japan are also considering measures to curb output control on solar power generation (Non-Patent Document 1).

[0004] Furthermore, the use of grid storage batteries (large-scale stationary storage batteries connected to the grid) is being considered as one means of suppressing output control of solar power generation. Specifically, when output control is required, the general electricity transmission and distribution company that manages the grid issues a charge command to the grid storage batteries present in the grid. However, because grid storage batteries are relatively small in size and a large number of them are expected to be introduced in the future, it is considered unrealistic for general electricity transmission and distribution companies to manage all of them (Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Handouts for the 48th Grid Working Group of the New Energy Subcommittee of the Energy Conservation and New Energy Subcommittee / Electricity and Gas Basic Policy Subcommittee of the Electricity and Gas Business Subcommittee of the Comprehensive Energy and Resources Advisory Committee of the Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry, held on October 16, 2023: Document 1: "Initiatives to Curb Renewable Energy Output Controls" [Non-patent document 2] Handouts for the 48th Grid Working Group of the New Energy Subcommittee of the Energy Conservation and New Energy Subcommittee / Electricity and Gas Business Basic Policy Subcommittee of the Comprehensive Resources and Energy Advisory Committee of the Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry, held on October 16, 2023: Document 3 "Connection and Use of Grid Storage Batteries" Summary of the Invention [Problem to be solved by the invention]

[0006] It is preferable that output control be performed in real time according to the actual supply-demand balance. Therefore, online output control is also becoming more widespread in output control for photovoltaic power generation. In online output control, a photovoltaic power generation system is connected online to a general electricity transmission and distribution company, and when output control becomes necessary, an output control signal is sent from the general electricity transmission and distribution company to the photovoltaic power generation system. Then, in the photovoltaic power generation system that receives the output control signal, the operation of the power conditioner is forcibly stopped.

[0007] By stopping the operation of the power conditioner, reverse power flow from the solar power generation system to the grid is reliably prevented. On the other hand, since the solar power generation system is unable to generate power, it is also prohibited to consume the power generated by the solar power generation system. This results in excessive loss of opportunities to use the solar power generation system, and could be a factor in hindering the further spread of solar power generation.

[0008] In view of the above, the present specification provides a technique for avoiding excessive restrictions on solar power generation in output control for solar power generation (particularly, online output control). [Means for solving the problem]

[0009] The technology disclosed in this specification is embodied in a photovoltaic power generation system, particularly a photovoltaic power generation system (hereinafter sometimes simply referred to as a system) that is connected to a grid together with a power consumption facility via the same service line. This system includes solar cells, a power conditioner that converts power between the solar cells and the grid, a reverse power relay that stops operation of the power conditioner when reverse power flowing from the service line to the grid is detected, and a control device that receives an output control signal transmitted from a utility that manages the grid. The control device normally disables the reverse power relay, and enables the reverse power relay when it receives the output control signal.

[0010] The purpose of output control of a power generation facility is to maintain the supply-demand balance in the grid, and not to restrict the power generation itself by the power generation facility. In other words, even if the power generation facility continues to generate power, the purpose of output control is fully achieved as long as the power supply from the power generation facility to the grid (i.e., reverse power flow) is reliably prohibited. Based on this knowledge, the solar power generation system according to the present technology is provided with a reverse power relay (also called RPR), even though it is a grid-connected system.

[0011] A reverse power relay is a means for preventing reverse power (i.e., reverse power flow) from a solar power generation system to the grid, and has traditionally only been provided in self-consumption systems. In other words, a grid-connected solar power generation system is premised on supplying power to the grid, and if a reverse power relay were present, power supply to the grid would be impossible. For this reason, in the solar power generation system according to the present technology, the reverse power relay is disabled under normal circumstances, thereby allowing power supply to the grid. On the other hand, when an output control signal is sent from a grid management company (e.g., a general electricity transmission and distribution company), the reverse power relay is enabled, thereby preventing reverse power (i.e., reverse power flow) to the grid. Note that even if the reverse power relay is enabled, the operation of the power conditioner is not immediately stopped. In other words, as long as the self-consumption power of the power consumption facility exceeds the power generated by the solar cells, the operation of the power conditioner is allowed, and solar power generation can continue. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing the configuration of a solar power generation system 10 according to an embodiment and a power grid storage system 50 adjacent thereto. [Figure 2] 1 shows an operating state when the solar power generation system 10 of the embodiment receives an output control signal. [Figure 3] 10 shows an operating state when the photovoltaic power generation system 10 of the embodiment receives an output control signal, and further shows a case where the bypass breaker 32 is closed. [Figure 4] 1 shows the change over time in power A generated by the photovoltaic power generation system 10 and the change over time in power consumption B by a power consuming facility under normal conditions. [Figure 5] 1 shows the change over time in the power A generated by the photovoltaic power generation system 10 and the change over time in the power consumption B by the power consuming facility at the time when an output control command is issued. DETAILED DESCRIPTION OF THE INVENTION

[0013] In one embodiment of the present technology, the solar power generation system may further include a power meter that measures forward power flowing from the grid to the service line. In this case, the control device may command the power conditioner to suppress power generation when it receives an output control signal. Then, when commanded to suppress power generation, the power conditioner may control the power generated by the solar cell so that the forward power measured by the power meter does not become zero. With this configuration, it is possible to avoid activation of the reverse power relay and continue solar power generation for a long period of time.

[0014] In one embodiment of the present technology, when a command to suppress power generation is received, the power conditioner may control the power generated by the solar cell so that the forward power measured by the power meter is maintained at or above a predetermined value greater than 0. With this configuration, it is possible to more reliably avoid the occurrence of reverse power to the grid, i.e., the activation of the reverse power relay and the prohibition of operation of the power conditioner.

[0015] In one embodiment of the present technology, the photovoltaic power generation system may further include a bypass wiring that electrically connects the power conditioner to an external grid storage system, and a bypass circuit breaker that electrically connects and disconnects the bypass wiring. In this case, the control device may keep the bypass circuit breaker open under normal conditions, and close the bypass circuit breaker when it receives an output control signal. With this configuration, when the photovoltaic power generation system is subject to output control, it can supply power generated by the solar cell to the grid storage system without going through the grid.

[0016] In addition, with the above configuration, the grid storage battery system can also contribute to improving the supply and demand balance of the grid by charging the power generated by the solar power generation system without receiving signals from the grid management company. In other words, the system manager will no longer need to manage all of the grid storage batteries that are expected to be introduced in large numbers.

[0017] In the above embodiment, the photovoltaic power generation system may further include a transformer interposed between the grid and the power conditioner. In this case, the bypass wiring may branch off from between the grid and the transformer and be electrically connected to the grid storage system. With this configuration, the photovoltaic power generation system can boost the AC power output from the power conditioner and supply it to the grid storage system. This can reduce power transmission loss and allow the grid storage system to receive the AC power supplied from the photovoltaic power generation system in the same way as AC power supplied from the grid.

[0018] In the above embodiment, the control device may transmit a predetermined notification signal to the grid storage system before closing the bypass breaker. With this configuration, when the photovoltaic power generation system starts supplying power to the grid storage system, the photovoltaic power generation system can notify the grid storage system in advance of this. This allows the grid storage system to perform in advance the processes and operations required for receiving power from the photovoltaic power generation system. [Example]

[0019] A solar power generation system 10 (hereinafter sometimes abbreviated as system 10) according to an embodiment will be described with reference to the drawings. The system 10 according to this embodiment is electrically connected to a grid 2 via a service line 4 together with a power consuming facility. The power consuming facility is, for example, a relatively large facility such as a factory, warehouse, airport, school, hospital, government facility, or large-scale retail store. The system 10 according to this embodiment is attached to such a power consuming facility, and the generated power is consumed by the power consuming facility itself. The system 10 is also a grid-connected solar power generation system, and can supply part or all of the power generated by solar power generation to the grid 2.

[0020] There is no particular limitation on the power generation scale (power generation amount) of the system 10. The power generation scale of the system 10 may be several kilowatts or may exceed 1 megawatt. Furthermore, there is no particular limitation on the voltage of the grid 2 to which the system 10 is connected. The voltage of the grid 2 may be, for example, extra-high voltage (20 kilovolts or more) or high voltage (6000 volts).

[0021] As shown in Fig. 1, a system 10 of this embodiment includes a plurality of solar panels 12, a power conditioner 14, and a grid-connected device 16. The solar panels 12 are an example of solar cells, and are panels in which a plurality of solar cells are arranged in a matrix. The power conditioner 14 is provided between the plurality of solar panels 12 and the grid 2, and converts DC power output from the plurality of solar panels 12 into AC power. As will be described in more detail below, the power conditioner 14 is configured to be able to control the power generated by the plurality of solar panels 12.

[0022] The grid interconnection device 16 is a device that electrically connects the system 10 to the grid 2. The grid interconnection device 16 is connected to the grid 2 via a drop line 5. The grid interconnection device 16 also intervenes between the grid 2 and the power conditioner 14, electrically connecting the two. The grid interconnection device 16 may be, for example, a grid interconnection cubicle.

[0023] The grid interconnection device 16 has a first circuit breaker 18 and a transformer 20. The service line 4 is connected to the first circuit breaker 18. As a result, the first circuit breaker 18 can electrically connect and disconnect between the photovoltaic power generation system 10, including the power conditioner 14, and the grid 2. The transformer 20 is interposed between the first circuit breaker 18 and the power conditioner 14, and is configured to boost the AC power output from the power conditioner 14 and output it to the grid 2 side. The transformer 20 is also configured to lower the AC power supplied from the grid 2 and output it to power consuming facilities.

[0024] The system 10 further includes a power meter 22, a reverse power relay 24, and a control device 26. These devices 22, 24, and 26 are arranged in, but are not limited to, the grid interconnection device 16. The power meter 22 measures the magnitude and direction of power flowing through the drop line 4. That is, the power meter 22 can distinguish between power flowing from the grid 2 to the grid interconnection device 16 (forward power) and power flowing from the grid interconnection device 16 to the grid 2 (reverse power). The measurement value by the power meter 22 is transmitted to the power conditioner 14 wirelessly or via a wire. The power meter 22 may be, for example, a smart meter, and the measurement value may be transmitted to the outside wirelessly or via a wire.

[0025] The reverse power relay 24 monitors reverse power (reverse power flow) flowing from the service line 4 to the grid 2, and is configured to stop operation of the power conditioner 14 when the reverse power is detected. However, in this embodiment, the reverse power relay 24 is configured to be able to switch between enabling and disabling its function. That is, when the reverse power relay 24 is disabled, operation of the power conditioner 14 is permitted even when reverse power flows from the service line 4 to the grid 2. On the other hand, when the reverse power relay 24 is enabled, operation of the power conditioner 14 is stopped when reverse power flows from the service line 4 to the grid 2.

[0026] The control device 26 controls the operation of the reverse power relay 24. For example, the control device 26 issues a command to the power conditioner 14 to enable / disable its function. Normally, the control device 26 disables the reverse power relay 24. This allows power generated by the multiple solar panels 12 to be supplied to the grid 2. Note that even when the control device 26 enables the reverse power relay 24, operation of the power conditioner 14 is not necessarily prohibited. After the reverse power relay 24 is enabled, operation of the power conditioner 14 is prohibited when reverse power (reverse power flow) flows from the service line 4 to the grid 2.

[0027] The control device 26 also controls the operation of the power conditioner 14. For example, the control device 26 can issue a power generation curtailment command to the power conditioner 14. When the power conditioner 14 receives the power generation curtailment command from the control device 26, it performs power generation curtailment on the solar power generation by the multiple solar panels 12. In this power generation curtailment, the power generated by the multiple solar panels 12 is controlled so that the forward power measured by the power meter 22 is maintained within a predetermined range greater than zero.

[0028] As shown in Fig. 2, the control device 26 is configured to be able to receive an output control signal from outside. The output control signal is a signal transmitted online from a general electricity transmission and distribution company that manages the grid 2. When the general electricity transmission and distribution company determines that output control for photovoltaic power generation is necessary for the purpose of maintaining the supply and demand balance in the grid 2, it transmits an output control signal to photovoltaic power generation facilities (including the system 10 of this embodiment) present in the corresponding area.

[0029] Upon receiving the output control signal, the control device 26 issues a command to the power conditioner 14 to enable the power conditioner 14. This reliably prevents reverse power from the system 10 to the grid 2 after the output control command is issued. In addition, the control device 26 issues the power generation suppression command to the power conditioner 14. This causes the power conditioner 14 to control the power generated by the multiple solar panels 12 so that the forward power measured by the power meter 22 is maintained at or above a predetermined value greater than zero (or so that it is maintained at the predetermined value). By the power generation suppression performed by the power conditioner 14, the generation of reverse power from the system 10 to the grid 2 is prevented in advance. This prevents or suppresses the operation of the reverse power relay 24. In other words, even when the general electricity transmission and distribution company issues an output control command, the operation of the power conditioner 14 is not prohibited, and the system 10 can continue generating power.

[0030] However, it is also possible that reverse power may be generated from the system 10 to the grid 2 due to, for example, a power shortage. In such a case, the reverse power relay 24 is activated, the operation of the power conditioner 14 is immediately prohibited, and the reverse power to the grid 2 is quickly stopped. In this way, the photovoltaic power generation system 10 of this embodiment can continue to generate photovoltaic power and supply power to power consumption facilities while responding to a request for output control from the general electricity transmission and distribution company.

[0031] As an example, the system 10 may include a bypass wiring 30 electrically connected to an external grid storage system 50. The grid storage system 50 functions as a regulating power for the grid 2 by being charged and discharged via the grid 2. In general, the grid storage system 50 includes one or more grid storage batteries 52, a power conditioner 54, and a grid interconnection device 56 (for example, a grid interconnection cubicle). The grid interconnection device 56 includes a second circuit breaker 58 for connecting to and disconnecting from the grid 2, a transformer 60 according to the voltage of the grid 2, and the like.

[0032] The bypass wiring 30 electrically connects the photovoltaic power generation system 10 and the grid storage system 50 without going through the grid 2. The connection position of the bypass wiring 30 is not particularly limited. The bypass wiring 30 may be any wiring that electrically connects the power conditioner 14 of the photovoltaic power generation system 10 to the grid storage system 50. The bypass wiring 30 is provided with a bypass circuit breaker 32. The bypass circuit breaker 32 can electrically connect and disconnect the bypass wiring 30.

[0033] The operation of the bypass circuit breaker 32 is controlled by the control device 26. The control device 26 normally keeps the bypass circuit breaker 32 open (see FIG. 1). On the other hand, as shown in FIG. 3, when the control device 26 receives an output control signal, it closes the bypass circuit breaker 32, thereby electrically connecting the photovoltaic power generation system 10 and the grid storage system 50. With this configuration, the photovoltaic power generation system 10 can generate more power even when it is subject to output control. The power generated by the photovoltaic power generation system 10 is supplied to the grid storage system 50 without passing through the grid 2. Therefore, the supply and demand balance of the grid 2 is not affected, and output control requests from the general electricity transmission and distribution company can be met. The grid storage system 50 can also contribute to improving the supply and demand balance of the grid 2 without requiring management by the general electricity transmission and distribution company.

[0034] Note that the control device 26 transmits a predetermined notification signal to the grid storage system 50 before closing the bypass circuit breaker 32 (for example, when receiving an output control signal). As a result, when the photovoltaic power generation system 10 starts supplying power to the grid storage system 50, it notifies the grid storage system 50 in advance. Upon receiving the notification signal from the photovoltaic power generation system 10, the grid storage system 50 opens the second circuit breaker 58 to disconnect itself from the grid 2. This prevents the photovoltaic power generation system 10 and the grid storage system 50 from being connected to the grid 2 by two or more paths.

[0035] As an example, the bypass wiring 30 in this embodiment branches off between the first circuit breaker 18 and the transformer 20 in the grid interconnection device 16 of the photovoltaic power generation system 10. Then, in the grid interconnection device 56 of the grid storage system 50, the bypass wiring 30 is connected to between the second circuit breaker 58 and the transformer 60. With this configuration, the photovoltaic power generation system 10 can boost the AC power output from its power conditioner 14 and supply it to the grid storage system 50. This makes it possible to suppress power transmission loss, and the grid storage system 50 can receive the AC power supplied from the photovoltaic power generation system 10 in the same way as AC power supplied from the grid 2.

[0036] As described above, the solar power generation system 10 of this embodiment can normally supply power to power consuming facilities and also supply surplus generated power to the grid 2. That is, as shown in Fig. 4, in a time period when the generated power A by the solar power generation system 10 exceeds the consumed power B by the power consuming facilities, the surplus generated power can be supplied to the grid 2. Therefore, forward power or reverse power flows in the service line 4 of the solar power generation system 10 (and the power consuming facility) depending on the magnitude relationship between the generated power A and the consumed power B.

[0037] On the other hand, when an output control signal is received from the general electricity transmission and distribution company, the control device 26 activates the reverse power relay 24 and issues a power generation suppression command to the power conditioner 14. For example, in FIG. 5 corresponding to FIG. 4, it is assumed that the output control signal is received at time t1. At this time, if the power consumption B exceeds the power generation A and a sufficient amount of forward power is flowing through the service line 4, the operation of the power conditioner 14 is not prohibited. Furthermore, power generation suppression by the power conditioner 14 is not performed.

[0038] Thereafter, as the generated power A increases, the forward power flowing in the service line 4 decreases. Then, when the forward power reaches a predetermined value D at time t2, power generation suppression by the power conditioner 14 begins at that timing. That is, the power generated by the solar panel 12 is controlled so that the forward power flowing in the service line 4 is maintained at or below the predetermined value D. As a result, even when the general electricity transmission and distribution company issues an output control command, the operation of the power conditioner 14 is not prohibited, and the system 10 can continue generating power.

[0039] The control device 26 may close the bypass circuit breaker 32 at time t1 to start the supply of power from the solar power generation system 10 to the grid storage system 50. Alternatively, the control device 26 may close the bypass circuit breaker 32 at time t1 to start the supply of power from the solar power generation system 10 to the grid storage system 50. In either case, the power generated by the solar power generation system 10 can be increased by increasing the power consumption B in Fig. 5 .

[0040] As a modification of this embodiment, it is not always necessary to suppress power generation by the power conditioner 14. In this case, operation of the power conditioner 14 is prohibited at time t2 shown in Fig. 5, but operation of the power conditioner 14 is permitted at least from time t1 to time t2. In other words, even after output control is issued, the system 10 can continue solar power generation as long as the power consumption B exceeds the power generation A. [Explanation of symbols]

[0041] 2: Grid, 4: Lead-in line, 10: Photovoltaic power generation system, 12: Solar panel, 14: Power conditioner, 16: Grid interconnection device, 18: First circuit breaker, 20: Transformer, 22: Wattmeter, 24: Reverse power relay, 26: Control device, 30: Bypass wiring, 32: Bypass circuit breaker, 50: Grid storage system, 52: Grid storage battery, 54: Power conditioner, 56: Grid interconnection device, 58: Second circuit breaker, 60: Transformer

Claims

1. A photovoltaic power generation system that is connected to a grid together with an electricity consumption facility via the same service line, A solar cell and a power conditioner that converts power between the solar cell and the grid; a reverse power relay that stops operation of the power conditioner when detecting reverse power flowing from the service line to the grid; a control device that receives an output control signal transmitted from a business operator that manages the grid; Equipped with The control device normally disables the reverse power relay, and enables the reverse power relay when the control device receives the output control signal. Solar power generation system.

2. Further provided is a power meter for measuring forward power flowing from the grid to the drop line; When the control device receives the output control signal, the control device commands the power conditioner to suppress power generation; 2. The solar power generation system according to claim 1, wherein the power conditioner controls the power generated by the solar cell so that the forward power measured by the power meter does not become zero when the power generation suppression command is received.

3. 3. The solar power generation system according to claim 2, wherein the power conditioner, when instructed to suppress power generation, controls the power generated by the solar cell so that the forward power measured by the power meter is maintained at or above a predetermined value greater than zero.

4. a bypass wiring that electrically connects the power conditioner to an external grid storage system; a bypass circuit breaker that electrically connects and disconnects the bypass wiring, The photovoltaic power generation system according to claim 1 , wherein the control device keeps the bypass circuit breaker open during normal operation, and closes the bypass circuit breaker when the control device receives the output control signal.

5. Further comprising a transformer interposed between the grid and the power conditioner, The photovoltaic power generation system according to claim 4 , wherein the bypass wiring branches off from between the grid and the transformer and is electrically connected to the grid power storage system.

6. The photovoltaic power generation system according to claim 5 , wherein the control device transmits a predetermined notification signal to the grid energy storage system before closing the bypass breaker.

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