System interconnection system

Abstract

To implement smooth system interconnection in a system in which many inverter type power generators and power storage equipment are connected, by inhibiting excess current from being generated at the time of connection with another system.SOLUTION: A system interconnection system 11 comprises: a first power system 13 in which a plurality of inverter interconnection power sources 21 are connected to lines 23; a switch 15 that is provided so as to lie between the lines 23 and comprises a normally open contact; a second power system 17 connected to the first power system 13 via the switch 15; a synchronization controller 19 for performing open / close control on the switch 15; a synchronization determination unit 39 that on the basis of a first voltage value V1 associated with the first power system 13 and a second voltage value V2 associated with the second power system 17, determines whether or not a difference Vdf associated with the first voltage value V1 and the second voltage value V2 converges on a predetermined acceptable range Var; an open / close control unit 41 that when the difference Vdf converges on the predetermined acceptable range Var, performs control of closing the normally open contact of the switch 15; and a correction command generation unit 43 for generating an output voltage correction command so that an amplitude and phase of the first voltage value V1 agree with those of the second voltage value V2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a grid interconnection system for interconnecting a plurality of power grids. [Background technology]

[0002] To improve environmental friendliness, the introduction of solar power generation, wind power generation, and storage batteries into power grids is progressing. These power sources are connected to the grid via power converters, rather than via synchronous generators as in the case of thermal and nuclear power plants. Power converters are constructed using semiconductor elements. While power converters have higher responsiveness and greater control flexibility than synchronous generators, they tend to have lower current tolerance due to overcurrent constraints of semiconductor elements.

[0003] Conventionally, the mainstream control method for power converters has been a current source operation control method called grid following, which controls the output current of the power converter in accordance with the power command value based on the voltage of the interconnected system.

[0004] However, grid following control requires that the voltage of the interconnected grid be maintained strong. If grid following control is applied to a system with a small short-circuit capacity and prone to grid voltage fluctuations, the control is likely to become unstable. Also, when charging after a power outage, such as during disaster recovery, grid following does not function properly because there is no reference voltage to begin with.

[0005] Against this background, a control method called Grid Forming (GFM), which operates a power converter as a voltage source like a conventional synchronous generator, is attracting attention. With Grid Forming Control (GFM Control), the converter outputs its own AC voltage independently of the voltage of the interconnected system. This allows stable operation even in systems with small short-circuit capacity, and even in a power outage, it is capable of outputting AC voltage and charging the power system. The series of operations that recharges the power system after a power outage and resumes operation of the power system is called a black start.

[0006] During a black start, the power supply is increased over time. Therefore, it is difficult to charge all equipment and transmission lines at once. One possible method of operation during a black start is to divide the system into appropriate sizes to create multiple grids, and while each grid is charged, the charged range is gradually increased by connecting the multiple grids.

[0007] In this regard, Patent Document 1 discloses an invention of a cooperative autonomous decentralized grid interconnection system in which an entire group of grids (cell grids) divided into multiple parts is managed by a grid interconnection controller, and these are synchronized to enable the cell grids to operate independently, allowing them to always be connected in sync to the main distribution grid. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-4472 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the grid interconnection system disclosed in Patent Document 1, in order to synchronously connect the cell grid system to the main distribution system, all of the cooperative autonomous decentralized devices belonging to the cell grid system must be synchronized with a standard time signal. To ensure synchronization with such a standard time signal, the communication load increases as the number of cell grid systems increases.

[0010] Furthermore, the grid interconnection system disclosed in Patent Document 1 mentions frequency information and phase information of the cell grid system, but does not mention matters related to integrated control of voltage amplitude. In this regard, if the voltage amplitude is not controlled appropriately, a current corresponding to the difference in voltage amplitude will flow when the cell grid is connected to another system. If this current becomes excessive, it may damage equipment or activate protective devices installed in the system. As a result, there is room for improvement in the area of ​​grid interconnection related to black starts, which can cause problems.

[0011] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a grid interconnection system that suppresses the occurrence of overcurrent when connecting a grid to another grid, in a grid to which a large number of inverter-type generators and power storage facilities are connected, and enables smooth grid interconnection. [Means for solving the problem]

[0012] In order to solve the above problems, the grid interconnection system according to the present invention comprises: A grid-connected system comprising: a first power system in which a plurality of inverter grid-connected power supplies are connected to a line; a switch provided on the line and having a normally open contact; a second power system connected to the first power system via the switch; and a synchronous control device that performs switching control of the switch, The synchronization control device includes: an acquisition unit that acquires a first voltage value associated with the first power system and a second voltage value associated with the second power system from the switches; a determination unit that determines whether a difference between the first voltage value and the second voltage value has converged to a predetermined allowable range, based on the first voltage value and the second voltage value acquired by the acquisition unit; a control unit that controls the normally open contact of the switch to close when the determination unit determines that the difference has converged to the predetermined allowable range; and a command generating unit that generates an output voltage correction command to be given to the plurality of inverter-interconnected power supplies provided in the first power system so that the difference converges within a predetermined allowable range; a command transmission unit that transmits the output voltage correction command generated by the command generation unit to the plurality of inverter-interconnected power sources. This is its most important feature. [Effects of the Invention]

[0013] According to the grid interconnection system of the present invention, in a grid to which a large number of inverter-type generators and power storage facilities are connected, when connecting to another grid (second power grid), it is possible to suppress the occurrence of overcurrent and realize smooth grid interconnection. Problems, configurations, and effects other than those described above will be described in detail in the following embodiments. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic configuration diagram of a grid interconnection system according to a first embodiment of the present invention. [Figure 2] 1 is a control block diagram of an inverter grid-connected power supply provided in a grid-connected system according to a first embodiment. FIG. [Figure 3] FIG. 4 is a schematic configuration diagram of a grid interconnection system according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a schematic configuration diagram of a grid interconnection system according to a third embodiment of the present invention. MODE FOR CARRYING OUT THE INVENTION

[0015] A grid interconnection system according to an embodiment of the present invention will be described in detail with reference to appropriate drawings. In the description of the grid interconnection system according to the embodiment of the present invention, components having common functions are denoted by common reference numerals, and duplicated descriptions thereof will be omitted.

[0016] [Schematic configuration of grid interconnection system 11A according to the first embodiment] First, a schematic configuration of a grid interconnection system 11A according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a grid interconnection system 11A according to a first embodiment of the present invention.

[0017] As shown in FIG. 1, the grid-connected system 11A (grid-connected system 11) according to the first embodiment of the present invention is configured to include a first power system 13 in which an inverter grid-connected power supply 21 is connected to a line 23, a switch 15 disposed on the line 23 and consisting of, for example, an electromagnetic switch with normally open contacts, a second power system 17 connected to the first power system 13 via the switch 15, and a synchronous control device 19 that performs opening and closing control of the switch 15.

[0018] The first power system 13 is configured to include an inverter-interconnected power supply 21, a line 23, a bus 25, and a load 27. The inverter-interconnected power supply 21 is connected to the line 23 and the bus 25. The bus 25 is connected to the load 27. The first power system 13 and the second power system 17 are concepts that include all facilities related to the generation to consumption of electricity, including power generation facilities, power transmission facilities, substation facilities, and demand facilities.

[0019] A first voltage sensor 33 is connected to the first power system 13 side of the switch 15 via a first connection point 31. Furthermore, a second voltage sensor 37 is connected to the second power system 17 side of the switch 15 via a second connection point 35.

[0020] The synchronization control device 19 includes a first voltage sensor 33 , a second voltage sensor 37 , a synchronization determination unit 39 , a switching control unit 41 , a correction command generation unit 43 , and a correction command transmission unit 45 .

[0021] The first voltage sensor 33 detects a first voltage value V1 associated with the first connection point 31. The second voltage sensor 37 detects a second voltage value V2 associated with the second connection point 35. The first voltage value V1 detected by the first voltage sensor 33 and the second voltage value V2 detected by the second voltage sensor 37 are sent to the synchronization determination unit 39. The first voltage sensor 33 and the second voltage sensor 37 correspond to the "acquisition unit."

[0022] The synchronization determination unit 39 determines whether the difference Vdf (|V1-V2|) between the first voltage value V1 and the second voltage value V2 has converged to a predetermined allowable range Var based on the first voltage value V1 detected by the first voltage sensor 33 and the second voltage value V2 detected by the second voltage sensor 37. The synchronization determination unit 39 corresponds to a "determination unit." The predetermined allowable range Var is set to an appropriate voltage width in consideration of, for example, obtaining an appropriate effect of suppressing the flow of overcurrent when the switch 15 is turned on (when the switch 15 is connected to the grid).

[0023] When the synchronization determination unit 39 determines that the difference Vdf (|V1-V2|) has converged to a predetermined allowable range Var, the switching control unit 41 controls to close the normally open contact of the switch 15. Preferably, the switching control unit 41 controls to close the normally open contact of the switch 15 in a state where the amplitude and phase of the second voltage value V2 of the first connection point 31 and the second connection point 35 match. With this configuration, no overcurrent flows when the normally open contact of the switch 15 is closed. The opening / closing control section 41 corresponds to the "control section."

[0024] The correction command generator 43 generates an output voltage correction command to be given to the inverter grid-connected power supply 21 in the first power system 13 so that the difference Vdf (|V1-V2|) converges within a predetermined allowable range Var. Preferably, the correction command generator 43 generates an output voltage correction command (amplitude E0 and phase θ0: including information on the second voltage value V2) that takes into consideration that the amplitude and phase between the first voltage value V1 and the second voltage value V2 match.

[0025] The correction command transmitting unit 45 transmits the output voltage correction command (including information on amplitude E0 and phase θ0: second voltage value V2) generated by the correction command generating unit 43 to multiple inverter-connected power sources 21 provided in the first power system 13 via a predetermined communication medium 47.

[0026] [Operation of the grid interconnection system 11A according to the first embodiment] Next, the operation of the grid interconnection system 11A according to the first embodiment will be described with reference to FIG. FIG. 2 is a control block diagram of the inverter grid-connected power supply 21 provided in the grid-connected system 11A according to the first embodiment.

[0027] In an initial state, the first power system 13 is disconnected from the second power system 17 and supplies power in an independent state. At this time, the inside of the first power system 13 and the first connection point 31 are charged. However, the first voltage value V1 associated with the first connection point 31 is not necessarily the same as the second voltage value V2 associated with the second connection point 35.

[0028] In the synchronization control device 19, the first voltage sensor 33 detects (acquires) the first voltage value V1 related to the first connection point 31, and the second voltage sensor 37 detects (acquires) the second voltage value V2 related to the second connection point 35, and transmits the acquired first voltage value V1 and second voltage value V2 to the synchronization determination unit 39.

[0029] When the difference Vdf (|V1-V2|) between the first voltage value V1 and the second voltage value V2 converges to a predetermined allowable range Var, preferably when the difference Vdf becomes zero, the synchronization determination unit 39 sends the determination result to the switching control unit 41. In addition, the synchronization determination unit 39 sends the first voltage value V1 and the second voltage value V2 to the correction command generation unit 43.

[0030] When the synchronization determination unit 39 determines that the amplitudes and phases of the first voltage value V1 and the second voltage value V2 match, the switching control unit 41 performs control to close the normally open contacts of the switch 15. This makes it possible to suppress the flow of overcurrent when the normally open contacts of the switch 15 are closed.

[0031] The correction command generator 43 generates an output voltage correction command including information about the second voltage value V2 so that the amplitude and phase of the first voltage value V1 associated with the first node 31 and the second voltage value V2 associated with the second node 35 match. Here, the information about the second voltage value V2 serves to synchronize the reference voltages Vsd associated with the multiple inverter-connected power supplies 21. This will be described in more detail later.

[0032] As a method for generating the output voltage correction command, for example, the first voltage value V1 associated with the first connection point 31 and the second voltage value V2 associated with the second connection point 35 are each decomposed into amplitude information and phase information. A difference is calculated for each of the decomposed amplitude information and phase information. A proportional-integral control is applied based on the calculated difference to generate the output voltage correction command.

[0033] In the grid interconnection system 11A according to the first embodiment, the correction command generator 43 generates an output voltage correction command by decomposing it into an amplitude E0 and a phase θ0. The decomposition of the output voltage correction command is performed, for example, by the following procedure. First, the phase of the second voltage value V2 associated with the second connection point 35 is detected by a phase locked loop. Next, the first voltage value V1 associated with the first connection point 31 is subjected to coordinate transformation using a dq coordinate transformation. Then, the amplitudes and phases of the d-axis voltage and the q-axis voltage are calculated.

[0034] The correction command transmitting unit 45 transmits the output voltage correction command (including information on the amplitude E0 and phase θ0: second voltage value V2) generated by the correction command generating unit 43 to multiple inverter-connected power sources 21 via a predetermined communication medium 47.

[0035] The inverter-interconnected power supplies 21 in the first power system 13 control their own output voltages based on the output voltage correction command (including information on amplitude E0 and phase θ0: second voltage value V2) sent from the correction command transmitter 45. That is, the switching operations of the plurality of inverter-interconnected power supplies 21 are set based on a predetermined reference voltage Vsd. In this way, the output voltages of the plurality of inverter-interconnected power supplies 21 themselves are controlled. The predetermined reference voltage Vsd is set based on the second voltage value V2 related to the second power system 17.

[0036] As shown in FIG. 2, the inverter-interconnected power supply 21 includes an inverter control unit 51 and a pair of adding units 53 and 55.

[0037] The inverter control unit 51 performs control to output the active power and reactive power of the inverter-interconnected power supply 21 itself. The control performed by the inverter control unit 51 is known control that is applied to a grid-connected inverter for photovoltaic power generation and a storage battery, including feedback control of active power, feedback control of reactive power, and AC current feedback control and AC voltage feedback control that are performed based on the active power and reactive power feedback control. Any configuration may be appropriately adopted as the control system within the scope of the present invention.

[0038] Specifically, for example, GFM control is applied to the inverter grid-connected power supply 21 shown in Fig. 2. In GFM control, the output voltage is set independently of the first voltage value V1 related to the first power system 13, and the output voltage itself is adjusted based on the current flowing due to the difference with the first voltage value V1 related to the first power system 13. In other words, GFM control is a control that does not require a voltage reference.

[0039] Therefore, in the present invention, the concept of a reference voltage Vsd for synchronizing the first voltage value V1 and the second voltage value V2 is introduced, and the reference voltage Vsd related to the inverter grid-connected power supply 21 is utilized to suppress the flow of overcurrent when the switch 15 is turned on (when grid-connected).

[0040] As described above, each of the multiple inverter-interconnected power sources 21 belonging to the first power system 13 has an independent (mutually different) voltage reference. In this state, it is difficult to synchronize the interconnected operations of the multiple inverter-interconnected power sources 21. Therefore, each of the multiple inverter-interconnected power sources 21 synchronizes the reference voltages Vsd of the multiple inverter-interconnected power sources 21 based on the information on the second voltage value V2 sent from the correction command sending unit 45.

[0041] The inverter-connected power supply 21 is a self-excited inverter, and sets the switching operation of the inverter-connected power supply 21 itself by phase modulation control based on the voltage command value (second voltage value V2) and the voltage detection value (first voltage value V1). In the following description, the amplitude of the output voltage command value related to the inverter control unit 51 is referred to as Eref1, and the phase of the output voltage command value is referred to as θref1.

[0042] In the grid-connected system 11A according to the first embodiment, a pair of adders 53, 55 provided in the inverter grid-connected power supply 21 add the output voltage correction command value (amplitude E0 and phase θ0) transmitted from the correction command transmitter 45 to the amplitude Eref1 and phase θref1 of the output voltage command value related to the inverter control unit 51. The amplitude of the corrected command value after the addition is called Eref2 (=Eref1+E0) and the phase of the corrected command value is called θref2 (=θref1+θ0). The inverter grid-connected power supply 21 sets the switching operation of the inverter grid-connected power supply 21 based on the amplitude Eref2 of the corrected command value and the phase θref2 of the corrected command value.

[0043] The present invention is based on the principle that the reference voltage Vsd of the inverter grid-connected power supply 21 is controlled to be equal to the second voltage value V2 (voltage value of the second power system 17) of the second connection point 35, thereby suppressing the flow of overcurrent when the switch 15 is turned on (when the system is connected).

[0044] Based on this principle, the inverter-connected power supply 21 provided in the first power system 13 controls each output voltage based on a reference voltage Vsd according to the second voltage value V2 so as to supply power in the first power system 13. However, when the first power system 13 is in an autonomous operation state, this reference voltage Vsd is set independently of the second voltage value V2 associated with the second connection point 35.

[0045] In the present invention, the reference voltage Vsd of the inverter grid-connected power supply 21 is controlled to be equal to the second voltage value V2 of the second connection point 35, thereby matching the amplitude and phase of the first voltage value V1 and the second voltage value V2. This suppresses the flow of overcurrent when the switch 15 is closed (when the inverter is connected to the grid). In the present invention, since only the reference voltage Vsd related to the inverter grid-connected power supply 21 is controlled, there is no effect on the power supply during the self-sustained operation of the first power system 13.

[0046] According to the grid interconnection system 11A of the first embodiment, in a system (first power system 13) to which a large number of inverter-type generators and power storage facilities are connected, when connecting to another system (second power system 17), it is possible to suppress the occurrence of overcurrent and realize appropriate and smooth grid interconnection. Furthermore, according to the grid interconnection system 11A of the first embodiment, by operating in such a way that grids are interconnected to the power grid in order from small-scale grids, it is possible to eventually construct a large-scale grid, and therefore it is possible to appropriately carry out a black start in consideration of the construction of a large-scale grid.

[0047] [Schematic configuration of grid interconnection system 11B according to second embodiment] Next, a schematic configuration of a grid interconnection system 11B according to the second embodiment will be described with reference to FIG. FIG. 3 is a schematic configuration diagram of a grid interconnection system 11B according to the second embodiment of the present invention. The grid-connected system 11A according to the first embodiment and the grid-connected system 11B (grid-connected system 11) according to the second embodiment have the same configuration of functional parts, except for some functional parts (such as the inverter grid-connected power supply 21 and the synchronous control device 19). Therefore, the following description will focus on differences in some functional units (such as the inverter grid-connected power supply 21 and the synchronous control device 19) instead of describing the configuration of the grid-connected system 11B according to the second embodiment.

[0048] In the grid-connected system 11A according to the first embodiment of the present invention, in the synchronous control device 19, the correction command generating unit 43 generates an output voltage correction command (including information on the amplitude E0 and phase θ0: second voltage value V2), and the correction command transmitting unit 45 transmits the generated output voltage correction command to multiple inverter-connected power sources 21. Each of the multiple inverter-connected power sources 21 provided in the first power system 13 controls the output voltage based on the output voltage correction command transmitted from the correction command transmission unit 45 so that the amplitude and phase of the first voltage value V1 and the second voltage value V2 match.

[0049] In contrast, the grid-connected system 11B according to the second embodiment is provided with a third voltage sensor 38 that detects a second voltage value V2 associated with the second connection point 35 (however, the second voltage value V2 associated with the second voltage sensor 37 may also be used), and the second voltage value V2 detected by the third voltage sensor 38 is transmitted to a plurality of inverter-connected power sources 21 provided in the first power system 13 via a predetermined communication medium 47. Each of the multiple inverter-connected power supplies 21 provided in the first power system 13 calculates output voltage correction information (amplitude E0 and phase θ0) based on the first voltage value V1 and the second voltage value V2 detected by the third voltage sensor 38, taking into consideration that the amplitudes and phases between the first voltage value V1 and the second voltage value V2 are identical, and sets the switching operation of the inverter-connected power supplies 21 so as to match the amplitudes and phases between the first voltage value V1 and the second voltage value V2. The synchronization control device 61 includes a synchronization determination unit 39 and a switching control unit 41, and controls the normally open contact of the switch 15 to close when the amplitude and phase of the first voltage value V1 and the second voltage value V2 match. The other configurations are the same as those of the grid interconnection system 11A according to the first embodiment.

[0050] [Operation of grid interconnection system 11B according to second embodiment] According to the grid interconnection system 11B of the second embodiment, similarly to the grid interconnection system 11A of the first embodiment, in a system (first power system 13) to which a large number of inverter-type generators and power storage facilities are connected, when connecting to another system (second power system 17), it is possible to suppress the occurrence of overcurrent and realize appropriate and smooth grid interconnection. Furthermore, according to the grid-connected system 11B of the second embodiment, compared to the grid-connected system 11A of the first embodiment, the control load of the synchronous control device 61 is transferred to the plurality of inverter-connected power sources 21 provided in the first power system 13, thereby making it possible to expect the effect of balancing the control load.

[0051] [Schematic configuration of grid-connected system 11C according to the third embodiment] Next, a schematic configuration of a grid interconnection system 11C according to the third embodiment will be described with reference to FIG. FIG. 4 is a schematic configuration diagram of a grid interconnection system 11C according to the third embodiment of the present invention. The grid interconnection system 11A according to the first embodiment and the grid interconnection system 11C (grid interconnection system 11) according to the third embodiment have the same configuration of functional units, except for some functional units (transmission paths of output voltage correction commands transmitted from the correction command transmission unit 45). Therefore, the following description will focus on the differences in some functional units (the transmission path of the output voltage correction command) instead of describing the configuration of the grid interconnection system 11C according to the third embodiment.

[0052] In the grid-connected system 11A according to the first embodiment of the present invention, in the synchronous control device 19, the correction command generating unit 43 generates an output voltage correction command (including information on the amplitude E0 and phase θ0: second voltage value V2), and the correction command transmitting unit 45 transmits the generated output voltage correction command to a plurality of inverter-connected power sources 21 via a predetermined communication medium 47.

[0053] In contrast to this, in the grid-connected system 11C according to the third embodiment, the output voltage correction command generated by the correction command generating unit 43 is transmitted offline by the correction command transmitting unit 45 to the plurality of inverter-connected power supplies 21 via the plurality of workers 71, 73. "Transmitting offline" means transmitting the content of the output voltage correction command via telephone or the like at a predetermined interval or at an appropriate timing, for example.

[0054] Here, each of the multiple inverter-connected power sources 21 is configured to be able to receive an output voltage correction command transmitted offline via multiple workers 71, 73. For example, a monitor is provided in the synchronization control device 19, and the output voltage correction command is displayed on the display screen of the monitor, which is then read by the worker 71. The worker 71 transmits the content of the output voltage correction command via telephone or the like to a worker 73 who is located near the multiple inverter-connected power sources 21. The worker 73 inputs the content of the output voltage correction command to the inverter-connected power source 21 via an appropriate input device such as a dial, button, keyboard, mobile terminal, or personal computer. The other configurations are the same as those of the grid interconnection system 11A according to the first embodiment.

[0055] [Operation of grid interconnection system 11C according to the third embodiment] According to the grid interconnection system 11C of the third embodiment, similarly to the grid interconnection system 11A of the first embodiment, in a system (first power system 13) to which a large number of inverter-type generators and power storage facilities are connected, when connecting to another system (second power system 17), it is possible to suppress the occurrence of overcurrent and realize appropriate and smooth grid interconnection. In particular, according to the grid interconnection system 11C of the third embodiment, even if a large-scale power outage occurs due to a disaster such as an earthquake (when online transmission is not working properly due to damage to infrastructure facilities), as long as the contents of the output voltage correction command can be transmitted, it is possible to eventually build a large-scale grid by connecting grids to the power grid in order from small-scale grids. As a result, it is possible to expect the effect of appropriately carrying out a black start based on the construction of a large-scale grid.

[0056] Other Embodiments The above-described embodiments are merely examples of the present invention, and therefore the technical scope of the present invention should not be construed as being limited by them, as the present invention can be embodied in various forms without departing from the spirit or main characteristics thereof.

[0057] In addition, part of the configuration of the embodiment described here can be replaced with the configuration of another embodiment, and the configuration of one embodiment can be added to the configuration of another embodiment. Furthermore, part of the configuration of each embodiment can be added to, deleted from, or replaced with another configuration.

[0058] For example, in the explanation of the first to third embodiments, three inverter-interconnected power supplies 21 are used as the inverter-interconnected power supplies 21 provided in the first power system 13, but the present invention is not limited to this example. Any number of inverter-interconnected power supplies 21 may be used as the inverter-interconnected power supplies 21 provided in the first power system 13.

[0059] Furthermore, in the explanation of the first to third embodiments, an example has been given in which an output voltage correction command is sent to each of the plurality of inverter-connected power sources 21 provided in the first power system 13, but the present invention is not limited to this example. It is also possible to employ an example in which the transmission of an output voltage correction command is omitted to some of the plurality of inverter-connected power sources 21 provided in the first power system 13.

[0060] In this case, the multiple inverter-connected power sources 21 that have received the output voltage correction command operate in accordance with the reference voltage Vsd to set the voltage in the first power system 13, while the other inverter-connected power sources 21 that have not received the output voltage correction command control their output voltages so as to supply the required power for the set voltage in the first power system 13. As a result, the other inverter-connected power supplies 21 that have not received the output voltage correction command can be operated so as to approach the reference voltage Vsd. In other words, even if the synchronism among the multiple inverter-connected power supplies 21 is somewhat impaired, smooth grid interconnection can be achieved. [Explanation of symbols]

[0061] 11 Grid-connected systems 11A Grid-connected system according to the first embodiment (grid-connected system) 11B Grid-connected system according to the second embodiment (grid-connected system) 11C Grid-connected system according to the third embodiment (grid-connected system) 13 1st power system 15 Switchgear 17 Second power system 19 Synchronous control device 21 Inverter-connected power supply 23 railroad track 25 busbar 27 Load 31 First Connection Point 33 First voltage sensor (acquisition unit) 35 Second connection point 37 Second voltage sensor (acquisition unit) 39 Synchronization determination unit 41 Opening and closing control section 43 Correction command generation section 45 Correction command transmitter 47 Communication media 61 Synchronous control device 71, 73 Workers Eref1 Amplitude of output voltage command value θref1 Phase of output voltage command value Eref2 Amplitude of the corrected command value θref2 Phase of the corrected command value V1 First voltage value V2 Second voltage value Vdf difference Vsd Predetermined reference voltage

Claims

1. A grid-connected system comprising: a first power system in which a plurality of inverter grid-connected power supplies are connected to a line; a switch provided on the line and having a normally open contact; a second power system connected to the first power system via the switch; and a synchronous control device that performs switching control of the switch, The synchronization control device includes: an acquisition unit configured to acquire a first voltage value associated with the first power system and a second voltage value associated with the second power system from the switches; a determination unit that determines whether a difference between the first voltage value and the second voltage value has converged to a predetermined allowable range based on the first voltage value and the second voltage value acquired by the acquisition unit; a control unit that controls the normally open contact of the switch to close when the determination unit determines that the difference has converged to the predetermined allowable range; and a command generating unit that generates an output voltage correction command to be given to the plurality of inverter-interconnected power supplies provided in the first power system so that the difference converges within a predetermined allowable range; a command transmission unit that transmits the output voltage correction command generated by the command generation unit to the plurality of inverter-interconnected power sources. A grid-connected system characterized by:

2. 2. The grid interconnection system according to claim 1, The command generating unit of the synchronous control device generates the output voltage correction command taking into consideration that the first voltage value and the second voltage value are equal to each other. A grid-connected system characterized by:

3. 3. The grid interconnection system according to claim 1 or 2, The output voltage correction command includes information for correcting amplitude and phase of output voltages of the plurality of inverter-interconnected power sources. A grid-connected system characterized by:

4. 4. The grid interconnection system according to claim 3, The plurality of inverter-interconnected power supplies have their switching operations set based on a predetermined reference voltage (Vsd), The predetermined reference voltage (Vsd) is set based on a second voltage value (V2) related to the second power system. A grid-connected system characterized by:

5. 5. The grid interconnection system according to claim 4, Any of the plurality of inverter-interconnected power supplies performs control to adjust the output voltage so that the amplitude and phase of the first voltage value and the second voltage value match. A grid-connected system characterized by:

6. 5. The grid interconnection system according to claim 4, Each of the plurality of inverter-connected power supplies performs control to adjust the output voltage so that the amplitude and phase of the first voltage value and the second voltage value match. A grid-connected system characterized by:

7. A grid-connected system comprising: a first power system in which a plurality of inverter grid-connected power supplies are connected to a line; a switch provided on the line and having a normally open contact; a second power system connected to the first power system via the switch; and a synchronous control device that performs switching control of the switch, The synchronization control device includes: an acquisition unit configured to acquire a first voltage value associated with the first power system and a second voltage value associated with the second power system from the switches; a determination unit that determines whether a difference between the first voltage value and the second voltage value has converged to a predetermined allowable range based on the first voltage value and the second voltage value acquired by the acquisition unit; a control unit that controls the normally open contact of the switch to close when it is determined that the difference has converged to the predetermined allowable range as a result of the determination by the determination unit, Any of the plurality of inverter-interconnected power supplies performs control to adjust the output voltage so that the amplitude and phase of the first voltage value and the second voltage value match. A grid-connected system characterized by:

8. 8. The grid interconnection system according to claim 7, Each of the plurality of inverter-connected power supplies performs control to adjust the output voltage so that the amplitude and phase of the first voltage value and the second voltage value match. A grid-connected system characterized by:

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