Cooperative autonomous decentralized grid interconnection system, grid interconnection method, and program

Abstract

To provide a cooperative autonomous distributed type system-interconnection system that enables independent operation of a cell grid by synchronizing a large number of cooperative autonomous distributed type devices and enables continuous synchronous connection to a main system.SOLUTION: In a cooperative autonomous distributed type system-interconnection system of one aspect of the present invention, each of the cooperative autonomous distributed type devices (DGR40) receives frequency information and phase information or a composite signal of frequency information and phase information transmitted from a system-interconnection controller based on a corrected or acquired standard time signal, each of the cooperative autonomous distributed type devices (DGR40) controls a voltage phase of a cell grid system to be synchronized with a voltage phase of the main system when a switch (21) is open, and each of the cooperative autonomous distributed type devices (DGR40) controls a power flow flowing between the main system and the cell grid system when the switch (21) is closed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cooperative autonomous decentralized grid interconnection system, a grid interconnection method, and a program. [Background technology]

[0002] In recent years, there has been an increasing demand for local production and consumption of electricity, where electricity generated by power generation facilities using renewable energy is consumed within the region. For this reason, a system known as a mini-grid or micro-grid is known, in which a power system including one or more power generation facilities is divided and managed. The AC system in this mini-grid is synchronized by an inverter installed on the output side of the power generation facility.

[0003] Patent Document 1 describes a method for independently managing a microgrid. In Patent Document 1, the inverters provided at the outputs of multiple power generation facilities in the microgrid adjust the output voltage value and phase based on a time signal obtained from a GPS. In addition, the effective power and reactive power are feedback-controlled based on the actual series impedance of the microgrid. A central energy management system is required for system interconnection with other microgrids.

[0004] Cited Document 2 describes a power conversion device in which inverters provided at the outputs of multiple power generation facilities in a microgrid are controlled to be in phase with each other by time-correcting the internal clock based on a time signal obtained from a GPS or the like. In Cited Document 2, since the microgrid has a fixed frequency, an asynchronous grid-connected power converter that performs AC-DC-AC power conversion is provided to connect the system in the microgrid to the main system.

[0005] Cited Document 3 describes a method of independently controlling a microgrid at a fixed frequency using a PMU (Phasor Measurement Unit). The PMU measures the voltage phase and current phase of the system in the microgrid, and the measured phase information is used as a reference for synchronous fixed frequency control of the inverter connected to the output of each power generation facility. It also describes that the impedance from the output of each power generation facility to the system in the microgrid is regarded as a common reference impedance, and compensation is performed by a compensation virtual impedance.

[0006] Cited Document 4 describes a method for controlling the current of a power converter in a microgrid. In this method, the converter connected to the AC power source is regarded as a virtual voltage source with a virtual impedance, and the AC voltage waveform is controlled by manipulating the phase of the active current and the reactive current. In addition, a droop control method is adopted as a method for manipulating the instantaneous current, and is combined with a current limit and a maximum power point (MPPT) method. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Publication No. 2016 / 0329709 [Patent Document 2] Patent No. 6863564 [Patent Document 3] LU 500171 B1 [Patent Document 4] U.S. Patent No. 10008854 Summary of the Invention [Problem to be solved by the invention]

[0008] In order to link the microgrid with the main grid using the method of independently managing the microgrid described in Patent Document 1, a separate central energy management system that controls the entire system is required. As a result, the system for interconnecting the microgrid with the main grid becomes large enough to control the entire system, and the communication system also becomes large, causing communication delays that make it difficult to follow sudden fluctuations.

[0009] In the power conversion device of the above Patent Document 2, since the microgrid has a fixed frequency, an asynchronous grid-connecting power converter that performs AC-DC-AC power conversion is provided to connect the microgrid system to the main system, so that synchronization is not required to match the frequency and phase of the microgrid system to the main system when connecting to the system. However, in the asynchronous grid-connecting device of the above Patent Document 2, an asynchronous grid-connecting device via an AC-DC-AC converter is used to connect the microgrid system to the main system, so there is a limit to the power capacity that can be connected, and the current that can be passed is limited, leading to an increase in the size of the device. In addition, since the protection measures of consumers in the system of the area including the power equipment using renewable energy are set according to the magnitude of the short-circuit current supplied from the main system, if an AC-DC-AC converter is inserted between them, the short-circuit current cannot be sufficiently supplied, and there is a problem that even if a short-circuit accident occurs in the consumer, the protection circuit does not operate in some cases.

[0010] In the synchronous fixed frequency control method of the above-mentioned Patent Document 3, the system in the microgrid is independently operated synchronously at a fixed frequency. However, since the main system frequency fluctuates within a range of 50 Hz ± 0.2 Hz in Japan, for example, if the frequency of the system in the microgrid is fixed, there is a problem that it cannot be interconnected with the main system.

[0011] According to the method of controlling the amplitude and phase of the inverter in the above Patent Document 4, it is possible to adopt an appropriate drooping technique, such as phase-shifted virtual voltage-virtual impedance droop, in which the desired effective phase and reactive phase currents are determined as a function of the voltage and frequency of the system in the microgrid, but the patent is related to a control method for an inverter connected to a system.The proposed inverter control method does not include any content such as making the microgrid independent and operating it synchronously, and there is no mention of a method for synchronizing with the main system.

[0012] Therefore, the object of the present invention is to provide a cooperative autonomous decentralized grid interconnection system in which a large number of cooperative autonomous decentralized devices are synchronized in a distribution system (hereinafter referred to as a "cell grid") in which at least one point is isolated from the main system by a circuit breaker that can be separated, enabling the cell grid to operate independently and always being synchronously connected to the main system. [Means for solving the problem]

[0013] The above object of the present invention can be achieved by the following configuration. That is, a cooperative autonomous decentralized grid interconnection system according to a first aspect of the present invention is a cooperative distributed grid interconnection system including a circuit breaker (21) with a synchronism test function capable of connecting or disconnecting a main grid (15) and a cell grid grid (28), a grid interconnection controller (MGC30) that detects power information of the main grid (15) and power information of the cell grid grid (28), and one or more cooperative autonomous decentralized devices (DGR40) that are connected in the cell grid grid system and perform power conversion so as to be synchronously interconnected with each other, in which the grid interconnection controller (MGC30) and each of the cooperative autonomous decentralized devices (DGR40) are connected to a standard time signal from which a standard time signal is obtained. The system is characterized in that it is equipped with a time signal acquisition device, and each of the cooperative autonomous distributed devices (DGR40) receives frequency information and phase information, or a composite signal of frequency information and phase information, transmitted from the grid interconnection controller (MGC30) based on the standard time signal, and when the circuit breaker with synchronism detection (21) is open, each of the cooperative autonomous distributed devices (DGR40) controls the voltage phase of the cell grid system to be synchronized with the voltage phase of the main system, and when the circuit breaker with synchronism detection (21) is closed, each of the cooperative autonomous distributed devices (DGR40) controls the power flow between the main system and the cell grid system.

[0014] A cooperative autonomous decentralized grid interconnection system of a second aspect of the present invention is characterized in that, in the cooperative autonomous decentralized grid interconnection system of the first aspect, the grid interconnection controller (MGC30) generates an inter-system phase difference signal (φglobal) and transmits it to each of the cooperative autonomous decentralized devices (DGR40), and when the circuit breaker with synchronism testing function (21) is closed, each of the cooperative autonomous decentralized devices (DGR40) controls power flow and reverse power flow using the inter-system phase difference signal (φglobal), and even when the circuit breaker with synchronism testing function (21) is open and information cannot be received from the grid interconnection controller (MGC30), each of the cooperative autonomous decentralized devices (DGR40) can synchronously control the cell-grid system based on the standard time signal.

[0015] A cooperative autonomous decentralized grid interconnection system according to a third aspect of the present invention is the cooperative autonomous decentralized grid interconnection system according to the first or second aspect, wherein the standard time signal acquisition device includes a first standard time acquisition unit (32) that acquires a first standard time signal, and a second standard time acquisition unit (42) that acquires a second standard time signal, and the grid interconnection controller (MGC30) is equipped with the first standard time acquisition unit (32), and applies the first standard time signal (t) to a main grid frequency (f) and a main grid rotation phase angle (θref) as a composite signal of the frequency information and phase information. a phase synchronization signal (Ncyc_ref_Sync) is generated by the second standard time acquisition unit (42), and the second standard time signal (t') is applied to the phase synchronization signal (Ncyc_ref_Sync) and the main system frequency (f) output by the system interconnection controller (MGC30), thereby demodulating a cell grid system rotation phase angle signal (θref') synchronized with the main system rotation phase angle (θref).

[0016] A cooperative autonomous decentralized grid interconnection system of a fourth aspect of the present invention is characterized in that, in the cooperative autonomous decentralized grid interconnection system of the first or second aspect, the grid interconnection controller (MGC30A) receives power information of the main grid and / or power information of the cell grid grid as an input, measures a main grid frequency measurement value (f), generates an inter-system phase difference signal (φglobal), and outputs it to the cooperative autonomous decentralized device (DGR40A), and the cooperative autonomous decentralized device (DGR40A) generates a cell grid grid phase angle signal (θpll) and a cell grid grid angular velocity signal (ωpll) from the cell grid system voltage (Vgrid_mini), and calculates a cell grid system rotation phase angle signal (θref) from the cell grid system phase angle signal (θpll), the cell grid system angular velocity signal (ωpll), the main grid frequency measurement value (f), and the inter-system phase difference signal (φglobal).

[0017] A fifth aspect of the cooperative autonomous decentralized grid interconnection system of the present invention is characterized in that, in the cooperative autonomous decentralized grid interconnection system of the fourth aspect, the grid interconnection controller (MGC30B) measures the main grid frequency measurement value (f) using a first phase synchronization circuit (96a), the cooperative autonomous decentralized device (DGR40B) generates the cell grid grid phase angle signal (θpll) and the cell grid grid angular velocity signal (ωpll) using a second phase synchronization circuit (83), and the standard time signal acquisition device includes a first standard time acquisition unit (32) that inputs a first standard time (t) to the first phase synchronization circuit (96a), and a second standard time acquisition unit (42) that inputs a second standard time (t') to the second phase synchronization circuit (83).

[0018] A sixth aspect of the cooperative autonomous decentralized grid interconnection system of the present invention is characterized in that, in the cooperative autonomous decentralized grid interconnection system of the first or second aspect, the cell grid system (28) can be connected to a plurality of the main systems (15a, 15b) via the circuit breakers (21a, 21b) with synchronization testing function, and when an abnormality occurs in a first main system (15a) among the main systems, the cell grid system (28) is interconnected with a second main system (15b) other than the first main system (15a) and is capable of transmitting power to an area (15a1) in the first main system (15a) where no abnormality occurs.

[0019] A seventh aspect of the cooperative autonomous decentralized grid interconnection system of the present invention is characterized in that, in the cooperative autonomous decentralized grid interconnection system of the first or second aspect, when the circuit breaker with synchronism test function (21) is closed and the main system (15) experiences a power outage, the circuit breaker with synchronism test function (21) is switched from closed to open, and each of the cooperative autonomous decentralized devices (DGR40) independently operates the cell grid system (28), and when the circuit breaker with synchronism test function (21) is open and an accident occurs in the cell grid system, the circuit breaker with synchronism test function (21) is closed, and a power flow is controlled to supply a fault current to a fault point, and a protective relay at the fault point is operated to isolate the fault point.

[0020] An eighth aspect of the cooperative autonomous decentralized grid interconnection system of the present invention is characterized in that, in the cooperative autonomous decentralized grid interconnection system of the first or second aspect, the cooperative autonomous decentralized device includes a common unit (120) having a motherboard (123) and one or more individual units (130), and the motherboard (123) performs control calculations including pulse wave generation.

[0021] A ninth aspect of the cooperative autonomous decentralized grid interconnection system of the present invention is characterized in that, in the cooperative autonomous decentralized grid interconnection system of the eighth aspect, hysteresis control is used for the calculation of pulse wave generation in the motherboard (123).

[0022] A system interconnection method by a cooperative autonomous decentralized system interconnection system according to a tenth aspect of the present invention is a system interconnection method by a cooperative distributed system interconnection system including a circuit breaker (21) with a synchronism test function capable of connecting or disconnecting a main system (15) and a cell grid system (28), a system interconnection controller (MGC30) that detects power information of the main system (15) and power information of the cell grid system (28), and one or more cooperative autonomous decentralized devices (DGR40) that are connected in the cell grid system and perform power conversion so as to be synchronously interconnected with each other, the system interconnection method comprising the steps of: the system interconnection controller (MGC30) and each of the cooperative autonomous decentralized devices (DGR40) acquiring a standard time signal; The system includes a step in which each of the cooperative autonomous decentralized devices receives frequency information and phase information, or a composite signal of frequency information and phase information, transmitted from the grid interconnection controller (MGC30) based on the standard time signal; a step in which, when the circuit breaker with synchronism testing function (21) is open, each of the cooperative autonomous decentralized devices (DGR40) controls the voltage phase of the cell grid system (28) to be synchronized with the voltage phase of the main system; and a step in which, when the circuit breaker with synchronism testing function (21) is closed, each of the cooperative autonomous decentralized devices (DGR40) controls the power flow between the main system (15) and the cell grid system (28).

[0023] A program according to an eleventh aspect of the present invention is characterized in that each step of the grid interconnection method by the cooperative autonomous decentralized grid interconnection system according to the tenth aspect is executed by a computer. Effect of the Invention

[0024] According to the first aspect of the cooperative autonomous decentralized grid interconnection system of the present invention, the cooperative autonomous decentralized devices are distributed in the cell grid, function as voltage sources that are synchronously interconnected with each other, and can establish the voltage of the cell grid. In addition, the cell grid system (28) can always be synchronized in frequency and phase with the main system (15), and each cooperative autonomous decentralized device can be synchronized even if there are a large number of devices, so that it can be made compact. Since the capacity of each cooperative autonomous decentralized device is set according to the power generation equipment to which it is connected, a protective operation due to a short-circuit current in an abnormality is also appropriately performed. Moreover, since the power capacity in the cell grid can be arbitrarily adjusted depending on the number of installed cooperative autonomous decentralized devices, a protective operation due to a short-circuit current in an abnormality is also appropriately performed by the current limiting function, time-limited cutoff function, etc. of the cooperative autonomous decentralized device (DGR 40) after securing sufficient power capacity. Furthermore, even if some of the cooperative autonomous decentralized devices (DGR 40) are cut off by a protective operation due to a fault, the remaining cooperative autonomous decentralized devices (DGR 40) can continue to distribute power to the cell grid system (28). In addition, by connecting the cell grid system (28) to the main system (15) via the circuit breaker (21) with a synchronism test function, the cell grid system (28) can be connected to the main system (15) when the main system (15) and the cell grid system (28) are synchronized, and the cell grid system (28) cannot be connected to the main system (15) when the main system (15) and the cell grid system (28) are not synchronized, so that the cell grid system (28) can be reliably synchronized with the main system (15). The system interconnection controller (30) can be provided as, for example, a cloud. In addition, the circuit breaker (21) with a synchronism test function can acquire system voltage information and cell grid voltage information and perform calculations to share part of the system interconnection controller (30).

[0025] In addition, if the main system (15) experiences a power outage during system interconnection, the power outage in the main system (15) is detected and the circuit breaker with synchronism test function (21) is opened, so that the cell-grid system (28) can be operated independently. For example, when a high-voltage vacuum circuit breaker (VCB) is used, the time from closing to opening the circuit breaker with synchronism test function (21) is rated to have a delay of 3 to 5 cycles, i.e., about 0.06 to 0.1 seconds. Therefore, if the main system experiences a power outage during system interconnection, the cell-grid system voltage (Vgrid_mini) may drop together with the main system voltage (Vgrid_main). For this reason, even if the circuit breaker with synchronism test function (21) is quickly opened from closed when the main system (15) experiences a power outage during system interconnection, there is a possibility that the cell-grid system voltage (Vgrid_mini) will rise from a state close to 0V, which is called a black start.

[0026] Therefore, by using the standard time signal acquired from the standard time signal acquisition device, it is possible to black start each cooperative autonomous distributed device (DGR40) based on the standard time signal from, for example, a GPS clock (42) or the like. For standard time signals, the highest level for a typical crystal oscillator is ±10 μsec, and there is a possibility that errors in each cooperative autonomous distributed device (DGR40) may accumulate. The standard time signal acquisition device is required to satisfy the accuracy that keeps the time error between the cooperative autonomous distributed devices (DGR40) within ±5 μsec. For example, there is a standard time signal acquisition method that includes a means for precisely correcting the time based on distance according to the location of a GPS clock, atomic clock, or individual cooperative autonomous distributed device (DGR40), or measuring the zero crossing of AC voltage and its time, transmitting that information to each cooperative autonomous distributed device (DGR40), and comparing it with the zero crossing time of each cooperative autonomous distributed device (DGR40) to correct the internal clock.

[0027] According to the cooperative autonomous decentralized grid interconnection system of the second aspect of the present invention, when the circuit breaker with synchronism test function (21) is closed, each of the cooperative autonomous decentralized devices (DGR40) can control the power flow and reverse power flow using the inter-system phase difference signal (φglobal), and even when the circuit breaker with synchronism test function (21) is open and information cannot be received from the grid interconnection controller (MGC30), each of the cooperative autonomous decentralized devices (DGR40) can synchronously control the cell-grid system based on the standard time signal. Therefore, each of the cooperative autonomous decentralized devices (DGR40) can continue the independent operation of the cell-grid system even during a power outage in the main system, a failure in the grid interconnection controller (MGC30), a communication failure with the grid interconnection controller (MGC30), etc.

[0028] According to the cooperative autonomous decentralized grid interconnection system of the third aspect of the present invention, a phase synchronization signal (Ncyc_ref_Sync) generated by applying a first standard time signal (t) to a main grid frequency (f) and a main grid rotation phase angle (θref) generated by a grid interconnection controller (MGC30) is transmitted to each cooperative autonomous decentralized device (DGR40), and each grid interconnection controller (DGR40) applies a second standard time signal (t') to the phase synchronization signal (Ncyc_ref_Sync) and the main grid frequency (f) to demodulate a cell grid system rotation phase angle signal (θref') synchronized with the main grid rotation phase angle (θref), so that the cell grid system (28) is always synchronized with the main grid (15). Therefore, the cell grid system can be connected or disconnected from the main grid at any time via a circuit breaker (21) with a synchronization test function. Even if an accident occurs in the main system (28), the cell grid system (28) can continue to supply power from the power generation equipment in the cell grid system by opening the circuit breaker (21) with a synchronism test function.

[0029] According to the fourth aspect of the present invention, the grid interconnection controller (MGC30) receives power information of the main grid (15) and / or power information of the cell grid grid, such as the main grid voltage, the main grid active power, and the main grid reactive power, measures a main grid frequency measurement value (f), generates an inter-system phase difference signal (φglobal), and outputs it to the cooperative autonomous decentralized device (DGR40). The cooperative autonomous decentralized device (DGR40) calculates the cell grid phase difference signal (φglobal) from the cell grid system voltage (Vgrid_mini). The cell grid system phase angle signal (θpll) and the cell grid system angular velocity signal (ωpll) are generated, and a cell grid system rotation phase angle signal (θref) is calculated from the cell grid system phase angle signal (θpll), the cell grid system angular velocity signal (ωpll), the main system frequency measurement value (f), and the system phase difference signal (φglobal), thereby appropriately controlling the frequency and phase of the power converters, such as inverters, of each cooperative autonomous decentralized device (DGR40), and performing synchronization control of the cell grid system (28). In this embodiment, since only voltage information is used, a standard time signal is not necessarily required.

[0030] When the first phase-locked loop (96a) measures the main system frequency measurement value (f) and the second phase-locked loop (83) generates the cell-grid system phase angle signal (θpll) and the cell-grid system angular velocity signal (ωpll), phase information and frequency information are generated from the voltage signal by a PLL or the like, so even if a Y-Δ converter is connected to the cooperative autonomous decentralized device (DGR40) and there is a phase shift of 30 degrees, or even if the impedance connected to the cooperative autonomous decentralized device (DGR40) is large and there is a phase shift, these problems of phase shift are eliminated because they are based on the voltage signal itself. Furthermore, when the phase information and frequency information are generated from the detected voltage by a PLL or the like from the voltage signal, they always operate based on the voltage signal, so the cooperative autonomous decentralized device (DGR40) easily complies with the protection function required as an islanding detection and protection device.

[0031] According to the fifth aspect of the cooperative autonomous decentralized grid-connected system of the present invention, the first phase locked loop (96a) and the second phase locked loop (83) periodically use the standard time signal from the standard time signal acquisition device, and it is only necessary to synchronize, for example, a PLL clock or the like, using the standard time signal at a frequency of, for example, about once per second. Since the standard time signal is not always required, the calculation load is reduced, and the PLL clocks of each cooperative autonomous decentralized device (DGR40) can always be synchronized.

[0032] In addition, since each of the cooperative autonomous decentralized devices (DGR 40) is synchronized, it becomes possible to perform a black start of the cell grid system (28). Even if a signal cannot be obtained from the grid interconnection controller (MGC 30), for example, when the grid interconnection controller fails, a phase difference signal between the grids cannot be obtained and φglobal=0, when the grid interconnection controller (MGC 30) fails, or when communication with the grid interconnection controller (MGC 30) is abnormal, the synchronization of each of the cooperative autonomous decentralized devices (DGR 40) can be maintained. In addition, when a main grid frequency measurement value cannot be obtained from the grid interconnection controller (MGC 30), each of the cooperative autonomous decentralized devices (DGR 40) generates a fixed signal equivalent to the main grid frequency value, for example, f=50 Hz if the main grid frequency is 50 Hz, thereby allowing the cell grid system to continue independent operation.

[0033] According to the sixth aspect of the cooperative autonomous decentralized grid interconnection system of the present invention, when the cell grid is an intermediate grid, even if an abnormality occurs in the first main grid (15a), the cell grid grid system can continue to supply power independently and can continue grid interconnection with the normal second main grid. Moreover, power can be transmitted to an area (15a1) in the jurisdiction of a substation included in the first main grid where no abnormality occurs. In this case, the cell grid system (28) can transmit power from the normal second main grid (15b) to the area (15a1) in the jurisdiction of a substation included in the first main grid (15a) where no abnormality occurs.

[0034] (Response in the event of a main grid power outage or a cell grid accident) According to the cooperative autonomous decentralized grid interconnection system of the seventh aspect of the present invention, when the cell grid system (28) is interconnected with the main system (15), if a power outage occurs in the main system (15), the cell grid system (28) can be operated independently to continue power supply from the power equipment in the cell grid system. Also, if an accident occurs in the cell grid system (28) while it is operating independently, the circuit breaker (21) with synchronism test function is closed to supply a short-circuit current to the accident point from the main system (15), and the protective relay at the accident point is operated to isolate the accident point, so that power supply to normal parts in the cell grid system can be continued.

[0035] According to the grid interconnection method using the cooperative autonomous decentralized grid interconnection system of the eighth aspect of the present invention, all control calculations including pulse wave generation for one or more individual units (130) can be performed by the motherboard (123). As a result, by standardizing the common unit (120) and standardizing the interface between the boards, the individual units (120) can be provided as various application products. The operation of the system can be realized in the cloud by the grid interconnection controller (MGC30). Moreover, by updating the software of the motherboard via the cloud by the grid interconnection controller (MGC30), the latest software can always be used.

[0036] According to the grid interconnection method by the cooperative autonomous decentralized grid interconnection system of the ninth aspect of the present invention, the motherboard (123) can appropriately calculate pulse waves for all the individual units (130) by hysteresis control.

[0037] According to the grid interconnection method by the cooperative autonomous decentralized grid interconnection system of the tenth aspect of the present invention, it is possible to provide a grid interconnection method that achieves the same effects as the cooperative autonomous decentralized grid interconnection system of the first aspect.

[0038] According to the program of the eleventh aspect of the present invention, it is possible to provide a program that exhibits the same effects as the cooperative autonomous decentralized grid interconnection system of the first aspect. [Brief description of the drawings]

[0039] [Figure 1] 1 is a block diagram of a cooperative autonomous decentralized grid interconnection system according to a first embodiment of the present invention. [Figure 2A] This is a circuit diagram of one cooperative autonomous distributed device. [Figure 2B] FIG. 2B is a detailed circuit diagram of FIG. 2A. [Figure 2C] FIG. 2C is an explanatory diagram of the operation of FIG. 2B. [Figure 2D] 1 is a circuit diagram of a cooperative autonomous decentralized grid interconnection system according to a first embodiment of the present invention. [Figure 2E] FIG. 2E is an explanatory diagram of the rotation phase angle of FIG. 2D. [Figure 2F] FIG. 2E is an explanatory diagram of the rotation phase angle after adjustment in FIG. 2D. [Figure 3A] FIG. 2 is a block diagram of synchronization control for GPS synchronization according to the first embodiment of the present invention. [Figure 3B] FIG. 2 is a control block diagram of a main system connection state in GPS synchronization according to the first embodiment of the present invention. [Figure 3C] FIG. 2 is a control block diagram of a GPS-synchronized cell grid system independent state (synchronization control) according to the first embodiment of the present invention. [Figure 3D] FIG. 2 is a control block diagram of a GPS-synchronized cell grid system independent state (during a main system power outage) according to the first embodiment of the present invention. [Figure 4A] FIG. 2 is a control block diagram of a main system connection state of voltage synchronization according to the first embodiment of the present invention. [Figure 4B] FIG. 2 is a control block diagram of a voltage-synchronized cell grid system independent state (synchronization control) according to the first embodiment of the present invention. [Figure 4C] FIG. 2 is a control block diagram of a voltage-synchronized cell grid system independent state (during a main system power outage) according to the first embodiment of the present invention. [Figure 5A] FIG. 11 is an explanatory diagram of a first state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5B] FIG. 11 is an explanatory diagram of a second state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5C] FIG. 11 is an explanatory diagram of a third state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5D] FIG. 11 is an explanatory diagram of a fourth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5E] FIG. 13 is an explanatory diagram of a fifth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5F] FIG. 13 is an explanatory diagram of a sixth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5G] FIG. 13 is an explanatory diagram of a seventh state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5H] FIG. 13 is an explanatory diagram of an eighth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5I] FIG. 13 is an explanatory diagram of a ninth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5J] FIG. 13 is an explanatory diagram of a tenth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5K] FIG. 11 is an explanatory diagram of an eleventh state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5L] FIG. 12 is an explanatory diagram of a twelfth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5M] FIG. 13 is an explanatory diagram of a thirteenth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 5N] FIG. 15 is an explanatory diagram of a fourteenth state of the cell-grid connection configuration according to the second embodiment of the present invention. [Figure 6] FIG. 11 is a block diagram of a cooperative autonomous decentralized grid interconnection system according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Hereinafter, a cooperative autonomous decentralized grid interconnection system according to an embodiment of the present invention will be described with reference to the drawings. However, the embodiments shown below are merely examples of a cooperative autonomous decentralized grid interconnection system for embodying the technical concept of the present invention, and the present invention is not limited to these, and may be equally applied to other embodiments included in the scope of the claims.

[0041] [Embodiment 1] A cooperative autonomous decentralized grid interconnection system according to a first embodiment of the present invention will be described with reference to Fig. 1 to Fig. 4C. Fig. 1 is a block diagram of the cooperative autonomous decentralized grid interconnection system according to the first embodiment of the present invention.

[0042] [Overall configuration of a cooperative autonomous decentralized grid interconnection system] Electricity generated in a power plant 10 is stepped up to extra-high voltage by an extra-high voltage substation 11, and then, via a power transmission facility 12, the power is further stepped down at a substation 13 and supplied to a power distribution facility 15 (hereinafter referred to as the "main system"), which is a main system. A plurality of cell grids 20 are connected to the main system 15. The voltage distributed to the main system 15 is not limited to high voltage (more than 600 V AC and not more than 7,000 V AC), but may be, for example, extra-high voltage (more than 7,000 V AC), or conversely, may be low voltage (not more than 600 V AC).

[0043] In a power distribution system (hereinafter referred to as a "cell grid") in which at least one location is separated by a circuit breaker 21 with a synchronism test function capable of isolating a main power distribution system (hereinafter referred to as a "main system"), the cell grid 20 includes the circuit breaker 21 with a synchronism test function, a cell grid system 28 connected to the main system 15 via the circuit breaker 21 with a synchronism test function, one or more cooperative autonomous distributed devices 40 (hereinafter referred to as a Digital Grid Router, or "DGR") having a power conversion function connected to the cell grid system 28, and various power facilities connected to the cell grid system 28. The cell grid 20 may be, for example, a power network of a scale of an apartment complex, a city block, or a petrochemical complex or industrial complex, and means a power network that can locally produce and consume power from distributed power sources such as natural energy power generation facilities within the area without relying on power from large-scale nuclear power plants or thermal power plants outside the area. In Japan, it is sometimes expressed as a "microgrid", but in the specification, it is sometimes referred to as a "mini-grid" in English. These are used as synonyms for the cell grid 20. Furthermore, the grid interconnection controller 30 may be abbreviated to "MGC" (Mini Grid Controller).

[0044] If we consider a housing complex as one Cell Grid 20, its size will be, for example, 52% of housing complexes in Japan are 100 ha or larger ("On the Actual State of Housing Complexes", Housing Bureau, Ministry of Land, Infrastructure, Transport and Tourism, December 2018), so the size of one Cell Grid 20 can be 100 ha or larger, and it can be applied to housing complexes of any size by increasing or decreasing the number of DGRs 40.

[0045] The DGR 40 can be connected to various distributed power sources as the power generation equipment 23, such as a wind power generation device 23a, a solar power generation device 23b, a fuel cell device, a hydrogen power generation device, a biopower generation device, an internal combustion engine power generation device (e.g., diesel or gas engine) 23d, a gas turbine power generation device, a geothermal power generation device, and a hydroelectric power generation device (e.g., about 200 kW). In addition, the DGR 40 can also be connected to power equipment such as the power storage devices 22b, 23c and the electric vehicle charging / discharging device 22c. The DGR 40 is provided with a power converter, such as an inverter, and can convert the DC voltage generated by, for example, the solar power generation device 23b into an AC voltage and supply it to the cell grid system 28.

[0046] The cell grid system 28 distributes electricity to each household equipment 22a as the power demand equipment 22. The power demand equipment 22 is not particularly limited, but may be each household equipment 22a, a power storage device 22b, an electric vehicle charging / discharging device 22c, an electric vehicle 22d, etc. Note that the power storage device 22b, the electric vehicle charging / discharging device 22c, and the electric vehicle 22d are capable of charging and discharging, and therefore function as the power demand equipment 22 when charging, and also function as the power generation equipment 23 when discharging. Although the power demand equipment 22 is exemplified in FIG. 1, the present embodiment is not limited thereto, and may be connected to the cooperative autonomous decentralized device 40 as the power generation equipment 23.

[0047] Each power generation facility 23, such as the wind power generation device 23a, the solar power generation device 23b, the internal combustion engine power generation device 23d, and the power storage facility 23c, are connected to the cell grid system 28 via the DGR 40. As described later, each DGR 40 performs synchronization control of the cell grid system 28 so as to synchronize with the frequency and phase of the main system 15 based on the main system frequency measurement value f and the phase synchronization signal Ncyc_ref_Sync, etc., sent from the MGC 30, which is provided on the cloud, for example. In addition, by adjusting the inter-system phase difference φglobal between the main system 15 and the cell grid system 28, it is possible to control the flow or reverse flow of active and reactive power. That is, when the cell grid system 28 receives power from the main system 15, i.e., when the cell grid system receives a power flow, the inter-system phase difference φglobal can be reduced to increase the power flow from the main system to the cell grid system. Conversely, when surplus electricity generated by a power generation facility 23, such as a solar power generation device in the cell grid 20, is transmitted to the main system 15, i.e., when reverse power flow is performed, the amount of electricity transmitted to the main system 15 can be increased by increasing the phase difference between the systems φglobal and advancing the phase angle of the cell grid system 28.

[0048] The circuit breaker with synchronism testing function (DG breaker) 21 can connect the cell grid system 28 to the main system 15 when the main system 15 and the cell grid system 28 are synchronized, and cannot connect the cell grid system 28 to the main system 15 when the main system 15 and the cell grid system 28 are not synchronized. In this way, the circuit breaker with synchronism testing function 21 is equipped with a PLL and can also detect the phase difference between the main system 15 and the cell grid system 28, and can close the circuit breaker with synchronism testing function only when both systems are synchronized. In other words, synchronism testing can also be performed by the PLL.

[0049] The circuit breaker with synchronism test function 21 can detect the main system frequency f and the main system rotation phase angle θref. The circuit breaker with synchronism test function 21 is also equipped with a PLL and can also detect the phase difference between the main system 15 and the cell grid system 28. The main system frequency f, the main system rotation phase angle θref, and the phase difference between the main system 15 and the cell grid system 28 detected by the circuit breaker with synchronism test function 21 are sent to the DGR 40 and used for phase synchronization control. In this way, the circuit breaker with synchronism test function (21) can acquire system voltage information and cell grid voltage information and perform calculations, thereby sharing part of the function of the system interconnection controller (30).

[0050] Here, an example has been described in which the main system frequency f, the main system rotation phase angle θref, and the PLL are provided in the circuit breaker with synchronism testing function 21, but the present embodiment is not limited to this, and detectors for the main system frequency f and the main system rotation phase angle θref may be provided separately from the circuit breaker with synchronism testing function 21. In addition, the PLL may also be configured to be provided separately from the circuit breaker with synchronism testing function 21.

[0051] Since the DGRs 40 are distributed and arranged in the cell grid system 28, the area covered by one DGR 40 can be subdivided, and there is no need to centralize large-scale grid-connection equipment in the cell grid system 28, which has the advantage of shortening the distribution line and reducing the diameter of the electric wire. The area covered by one DGR 40 is not particularly limited, but can be, for example, about ten houses. In this case, although not particularly limited, the DC input of the DGR 40 can be, for example, 750V, 40kW, the AC output can be, for example, 380V, three-phase, 40kW, and the built-in battery capacity can be 20kWh, for example, for one to four units. In the case of a smaller size, the DC input can be, for example, 350V, 20kW, and the AC output can be, for example, 200V, three-phase, 20kW, and the built-in battery capacity can be 20kWh, for example, for one to four units.

[0052] In the system of this embodiment, when the main system and the cell grid system are not connected, the frequency and phase of the cell grid are synchronized by transmitting the frequency and phase of the main system to all DGRs 40 in the cell grid by a method described later, and when connected, the power flow between the two systems is controlled. Furthermore, when the main system voltage drops for a short period of time while connected, the system continues to maintain synchronization (Fault Ride Through: FRT), and when the main system is powered out, it is disconnected and the cell grid can be black started. The magnitude of the voltage is information closely related to reactive power, and this is also transmitted to all DGRs 40 in the cell grid. This transmission method is an existing technology, so the details are not described here. As a result, when the voltage is constant, the current and reverse current of the power generation equipment 23 connected to the cell grid system 28, such as a renewable energy power generation equipment, can be controlled, the electricity generated by the power generation equipment 23 in the cell grid system 28 can be produced and consumed locally, and independent operation can be performed when the main system 15 has a power outage.

[0053] The MGC 30 controls each DGR 40 in the cell grid 20, and performs control of the total power demand of the cell grid 20, the power generation amount of the power generation facilities 23, interconnection control of phase and frequency, control during accidents, power outage and restoration control of the grid, and demand schedule control.

[0054] Synchronization control is performed on each DGR 40 using accurate time information, for example, time information from a GPS using an artificial satellite 17. In addition, the MGC 30 transmits to each DGR 40 main system synchronization information, such as a main system frequency f, a phase synchronization signal Ncyc_ref_Sync, and an inter-system phase difference φglobal.

[0055] [Equivalent circuit of DGR40 in cell grid] 2A to 2F are diagrams illustrating the principle of the cooperative autonomous decentralized grid-connected system according to the first embodiment of the present invention. FIG. 2A is a circuit diagram of one cooperative autonomous decentralized device 40, and is an equivalent circuit when one DGR 40 is taken out of the cell grid system 28. As shown in FIG. 2A, all DGRs 40 operate as AC voltage sources Vdgr_i having an output impedance. i is a subscript representing the number of DGRs 40. Each DGR 40 is connected in parallel to the cell grid voltage Vgrid via a grid-connection resistance RG and an inductance LG, and a current Idgr_i flows out from each DGR 40. Since the cell grid voltage Vgrid is common to all DGRs 40, each DGR 40 can control Idgr_i by changing the internal voltage Vdgr_i. Under normal conditions, Idgr_i is controlled to be equal for all i, so that the load sharing of each DGR 40 is equal. However, depending on the state of the DGR 40, the load sharing may be changed, or Idgr_i may be controlled to flow into the DGR 40 in order to charge the internal storage battery. These can be controlled depending on how the target value of Vdg_i is set.

[0056] [Vdgr voltage control by current hysteresis control] FIG. 2B is a detailed circuit diagram of FIG. 2A, showing a half-bridge inverter that is a component of the DGR 40. FIG. 2C is an explanatory diagram of the operation of FIG. 2B, showing how IL repeatedly increases and decreases as the upper and lower switches of the half-bridge are alternately turned on. An upper and lower limit band width is set for the target current value Iref, and when the measured current value IL exceeds the upper band, the upper switch of the half-bridge is turned off and the lower switch is turned on. When the measured current value IL falls below the lower band, the lower switch is turned off and the upper switch is turned on. This operation is repeated. This is called current hysteresis control. Details of the hysteresis control will be described in the following embodiment 3.

[0057] In general, hysteresis control has a problem that the switching period fluctuates, making filter design difficult. In this invention, a fluctuating bandwidth method is devised to solve this problem. The lines above and below the target current value Iref in FIG. 2C are the bands, and narrowing the width of the bands makes the switching period faster, and widening the width makes the switching period slower. The slope of the reactor current IL of the half bridge changes depending on the difference between Vdc and Vdgr, so the bandwidth is changed according to the difference to make the switching frequency almost constant. This controls the target current value Iref to be equal to Idgr, and performs open loop control to correct the half bridge filter voltage to be equal to the target Vdgr. Although the controlled object is the current, as a result, high-speed voltage control is possible. The following explanation will be given on the assumption that Vdgr is directly controlled by this method.

[0058] FIG. 2D is a circuit diagram of the cooperative autonomous decentralized grid interconnection system according to the first embodiment of the present invention, and shows a state in which N DGRs 40 shown in FIG. 2A are connected in parallel to the cell grid. The cell grid voltage Vgrid is common, and each DGR 40 is connected to the cell grid through a different output impedance ZG_i (i=1 to N) at a different voltage Vdgr_i, and a current Idgr_i flows into each DGR 40. In this way, in the parallel connection operation of multiple voltage sources, if the voltage synchronization cannot be realized with high accuracy, cross currents will flow between the voltage sources, so the synchronization ability has been considered important. In the present invention, a means is adopted in which a standard time signal is used as the synchronization signal. In this embodiment, the virtual impedance technology described below is further used to virtually equalize ZG_i, and to equalize Vdgr_i and Idgr_i to equalize the load sharing. In addition, by controlling Vdgr, it is also possible to change Idgr and change the load sharing for each DGR 40.

[0059] The physical output impedance of the DGR40 varies depending on the installation location, the effect of the outlet transformer, the distance of the distribution line, the wire thickness, etc. Because these values ​​are unknown, it is difficult to equalize the load sharing ratio between multiple DGR40s even if the internal voltage Vdgr of the DGR40 is manipulated. One method to solve this problem is to introduce a virtual impedance that increases the ratio of known impedance. By defining a virtual impedance that includes the physical impedance, making its value equal for each DGR40, and taking Vdgr control into account, it becomes easier to equalize the load sharing ratio.

[0060] Specifically, this is achieved by subtracting the voltage drop due to the virtual impedance (= (virtual reactor - physical reactor) x time derivative of Idgr) from the control target value of Vdgr. As an example of the setting value of the virtual impedance, it is set so that a voltage drop of about 15% of the rated voltage occurs when the rated current flows, including the physical impedance. For this reason, it is important to accurately grasp the physical impedance for each installation location of the DGR40 and incorporate it as a control constant.

[0061] The following two synchronization methods were adopted to synchronize the frequency and phase of all DGR40 in the cell grid. They are (A) a synchronization method using GPS time signals, and (B) a synchronization method based on voltage. These two methods can complement each other, and can be used in combination or alone. All DGR40 are equipped with GPS receivers as a means of obtaining standard time signals, but any method that can obtain the accuracy of the standard time signal is not limited to GPS. When the GPS signal is lost, all DGR40 can be operated in synchronous mode without a standard time signal by using (B) the synchronization method based on voltage. Both methods detect the frequency and phase from the voltage vector using a well-known method called Phase Lock Loop (PLL). The two synchronization methods are described in detail below. Regarding reactive power, voltage correction information is sent to all DGR40 via MGC30, and reactive power can be adjusted using conventional technology such as PI control. First, (A) the synchronization method using the GPS time signal will be described.

[0062] [(A) Explanation of the synchronization method using GPS time signals] FIG. 2E illustrates the interrelationship between the current Idgr of one DGR 40, the internal voltage phase Vdgr of the DGR 40, and the voltage phase Vgrid of the cell grid under GPS time synchronization control. Note that the notation "*" on the right hand side, such as Vgrid*, indicates the target value. In the figure, it shows the state where the target and actual values ​​match. In the following explanation, it will be expressed as actual values. Vgrid is based on the GPS time signal, so it is synchronized across all DGRs 40. Vgrid rotates at a frequency based on the global angle reference θref calculated from the GPS time reference, but in Figure 2E this is fixed and represented as the Daxis. Idgr is a current that lags with a phase angle φ based on the load in the cell grid and the grid impedance. Idgr can be broken down into DQ axes to become ID and IQ, with ID being in phase with Vgrid and IQ being a 90° lagging component.

[0063] A voltage drop occurs on the DQ axis due to a virtual impedance that includes Idgr and the physical impedance mentioned above. The voltage drop on the D axis component is ID×RG+IQ×XG, and the voltage drop on the Q axis component is ID×XG-IQ×RG. Note that in Figures 2E and 2F, the multiplication symbol "×" is represented as a "." Since the voltage drops of these D-axis and Q-axis components correspond to the voltage drops between Vdgr and Vgrid, Vdgr is required to compensate for this voltage drop. The phase angle between the internal voltage Vdgr and the cell grid system voltage Vgrid that occurs at this time is δ. Since Vgrid is synchronized in all DGRs 40, Vdgr also rotates in sync, although there is a phase difference. Therefore, by adjusting the phase angle δ, it is possible to change the output share of each DGR 40, or to function as a negative output, i.e., a load, to charge the built-in storage battery.

[0064] In the GPS time synchronization method, when the cell grid is connected to the main system, the target Vgrid* vector is created based on the frequency of the main system, and the DGR40 internal voltage target Vdgr* and current target Idgr* are as shown in Figure 2E according to the virtual impedance. The actual cell grid voltage Vgrid, DGR40 internal voltage Vdgr, and current Idgr are controlled to converge to their respective target values ​​Vgrid*, Vdgr*, and Idgr*, and are almost equal. Any power surplus or shortage resulting from an imbalance between the total output of all DGR40s and the total demand within the cell grid is supplied from the main system or flows back toward the main system.

[0065] However, when the cell grid is separated from the main system and operates independently, there is no power adjustment by the main system, so the total output of all DGRs 40 and the total demand within the cell grid must match exactly. Since the DGR 40 does not have information on demand, as a result of control to match the actual Vdgr to the target DGR 40 internal voltage Vdgr*, the actual current Idgr flows according to the actual demand as shown in Fig. 2F, and the active power and reactive power of the demand are supplied without surplus or deficiency by this actual Vgrid and actual Idgr. As a result, a deviation occurs between the actual current Idgr and the target current value Idgr*. The actual voltage Vgrid also deviates from the target Vgrid*. The phase difference between this actual cell grid voltage Vgrid and the target cell grid voltage Vgird* is defined as Δδ. Since the Daxis* axis is synchronized with the frequency of the main grid, in order to transition the cell grid from isolated operation to interconnected operation, this Δδ should be brought close to zero to synchronize with the main grid. This is achieved by using a signal called φglobal, which will be described later.

[0066] To synchronize all DGR40, an accurate standard time must be used. If a synchronization error occurs, it will create a voltage difference between the DGR40. The impedance between the DGR40 will cause a 10% to 20% voltage drop, so even if the allowable voltage error is 1%, the current control error will be about ±10% to ±5%, so it is best to keep the voltage error as small as possible. A voltage error of 1% is equivalent to a phase angle of 0.0015 radians. This corresponds to an accuracy of 5 μsec in terms of time. There are crystal oscillators with an accuracy of about ±10 μsec, but if a common correction is not applied, the error between the DGR40 will increase. A GPS time signal is a common time signal that ensures this accuracy and is relatively inexpensive to obtain. Radio-controlled clocks and network time protocols lack the accuracy. Although expensive, atomic clocks are also an option.

[0067] In this embodiment, the standard time signal acquisition device may include a standard time signal acquisition method having a means for precisely correcting the time by distance according to the arrangement of, for example, a GPS clock, an atomic clock, or each of the cooperative autonomous distributed devices (DGR40), or measuring the zero crossing of the AC voltage and its time, transmitting the information to each of the cooperative autonomous distributed devices (DGR40), and comparing it with the zero crossing time of each of the cooperative autonomous distributed devices (DGR40) to correct the internal clock, etc. Regarding the method for measuring a specific zero crossing of the AC voltage and its time and correcting the internal clock of each of the cooperative autonomous distributed devices (DGR40), for example, the grid interconnection controller (MGC30) acquires a standard time signal using a GPS clock, an atomic clock, etc., accurately grasps the specific zero crossing of the AC voltage and its time, transmits the specific zero crossing and its standard time signal to each of the cooperative autonomous distributed devices (DGR40), and each of the cooperative autonomous distributed devices (DGR40) can correct the internal clock by comparing the standard time corresponding to the specific zero crossing with the time of the internal clock corresponding to the specific zero crossing. Here, the grid interconnection controller (MGC30) has been described as acquiring a standard time signal and accurately grasping specific zero crossings of the AC voltage and their times, but this embodiment is not limited to this. A standard time signal acquisition device provided separately from the grid interconnection controller (MGC30) may be used to accurately grasp specific zero crossings of the AC voltage and their times, and the information may be transmitted to the grid interconnection controller (MGC30) and each of the cooperative autonomous distributed devices (DGR40) to correct the internal clocks of the grid interconnection controller (MGC30) and each of the cooperative autonomous distributed devices (DGR40).

[0068] [(A) Block diagram of synchronous control] Fig. 3A is a block diagram of the GPS-synchronized synchronization control of the first embodiment of the present invention. A synchronization control method based on the GPS time signal will be described with reference to Fig. 3A. This method is characterized in that each DGR 40 can generate a phase angle signal θref synchronized to the main system within ±5 μsec by receiving two signals, the main system frequency signal f and the phase synchronization signal Ncyc_ref_Sync obtained by applying the GPS time signal, via the MGC 30 and combining them with the GPS time signal inside the DGR 40. Details are shown below.

[0069] In the calculation block of FIG. 3A, the calculation in the grid connection controller (MGC) 30 is performed as follows. The main grid frequency f is measured by the main grid frequency measuring device 31, and the GPS time t32 is obtained as the first time information (t) in the first time acquisition unit. The two are multiplied, and the result is subtracted from the main grid rotation phase angle θref34, which is a sawtooth shape per cycle, and then a "function for extracting a decimal part" such as a floor function shown below is applied to the result to calculate a phase synchronization signal Ncyc_ref_Sync39 (corresponding to Δδ). Two signals, the main grid frequency signal f and the phase synchronization signal Ncyc_ref_Sync, are transmitted from the MGC 30 to each DGR 40. The transmission means may be a server method or a broadcast method. Although the above calculation unit is a function inside the MGC 30, it may be physically built into the circuit breaker with synchronization test function 21 and calculated, and transmitted to each DGR 40 via a cloud using a mobile line or a power line carrier.

[0070] As a function for extracting the decimal part, the floor function can be replaced with the frac function, ceil function, round function, MOD function, etc. The two signals, the main system frequency signal f and the phase synchronization signal Ncyc_ref_Sync, change slowly, so they can be treated as if they were constants compared to the calculation speed and the signal transmission time from MGC30 to DGR40. The communication rate between MGC30 and DGR40 is allowed to be about 0.1 to 10 seconds.

[0071] 3A, the calculation in the DGR 40 is performed as follows. First, in the grid interconnection controller (MGC) 30, the main grid frequency f acquired from the circuit breaker 21 with a synchronization test function is received by the main grid frequency measurement value acquisition unit 41. Second time information (t') is acquired as GPS time t' 42 from the second time acquisition unit. Each DGR 40 is provided with Ncyc_shift_local 44 in case a unique adjustment value according to the location of the DGR 40 is required. The DGR 40 receives Ncyc_ref_Sync 39 calculated by the MGC 30, and sets it as Ncyc_ref_Sync 45 inside the DGR 40.

[0072] Next, the main system frequency measurement value f41 and the GPS time t'42 are multiplied by a multiplier 43 to obtain f·t' as a graph of a continuously increasing characteristic. When an operation 50 is performed in which Ncyc_shift_local 44 and Ncyc_ref_Sync 45 are added to this f·t' by adders 46 and 47, and the output of a floor function 51 is subtracted by a subtractor 52, Ncyc_ref_bas is obtained as a sawtooth graph. The operation 50 using this floor function is not limited to this, and can be replaced with, for example, another function that extracts a decimal part as described above.

[0073] In the DGR 40, after the calculation 50 using the frac function, a subtractor 53 is provided which feeds back and subtracts Ncyc_ref. Furthermore, in an adder 54, a value of 0.5 is added, and then a calculation 55 using the frac function is performed. In this calculation 55 using the frac function, in FIG. 3A, the output of a floor function 56 is subtracted by a subtractor 57, but this embodiment is not limited to this, and for example, as described above, it can be replaced with a function that extracts the decimal part. After that, an calculation of adding a value of -0.5 is performed by an adder 58, and further, a multiplier 59 calculates f=2πf0 10 3 (1) To calculate f+Δf, f is passed through a limiter 60 using f-α and f+α, and then Ncyc_ref is demodulated by an integrator 61. Through these operations, the phases of the system phase angle θref34 of the main system 15 and the output system phase angle θref62 of each DGR 40 are synchronized, and the frequencies also match.

[0074] The input signal to the limiter 60 is f+Δf, that is, the sum of the frequency and the rate of change of frequency (ROCOF: Rate of Change of Frequency), and the provision of the limiter 60 for the rate of change portion is an element that determines the speed and magnitude of the phase tracking of the cell grid. In other words, if the width of the limiter 60 is widened, it will quickly track the phase changes of the main system, but the phase fluctuation will be somewhat large. If the width of the limiter 60 is narrowed, it will take longer to track the phase changes of the main system, but the phase fluctuation will be small.

[0075] In this way, there is a transmission delay in frequency and phase tracking by the MGC 30, and being able to restrict it with the limiter 60 has the effect of keeping the rate of change of frequency (ROCOF) within a certain range. Since it is a first-order transfer function rather than a second-order transfer function that mimics the synchronous machine of a general grid forming inverter, it is an extremely stable mechanism. Incidentally, the main system rotation phase angle θref is originally a 0-2π signal, but here it is divided by 2π and treated as a sawtooth signal between 0 and 1.

[0076] The block from subtractor 53 to integrator 61 acts as a low-pass filter and has the role of removing noise contained in Ncyc_ref_bas, such as so-called whisker-like noise, but this embodiment is not limited to this block and it is also possible to configure it as discontinuous time control using, for example, 1 / Z conversion.

[0077] [(A) Explanation of grid interconnection, isolated operation, and main grid blackout conditions] Next, the next three states will be described with reference to Figures 3B, 3C and 3D. Main system connection state: FIG. 3B is a control block diagram of the GPS-synchronized main system connection state according to the first embodiment of the present invention. Cell grid independent state: FIG. 3C is a control block diagram of a GPS-synchronized cell grid system independent state (synchronization control) according to the first embodiment of the present invention. Main grid power outage / cell grid independent operation state: FIG. 3D is a control block diagram of the GPS-synchronized cell grid independent state (at the time of main grid power outage) according to the first embodiment of the present invention.

[0078] [(A) Main system connection status] In FIG. 3B, the circuit breaker 21 with synchronism test function is closed, and the main system 15 and the cell grid system 28 are synchronously interconnected. Therefore, the main system voltage Vgrid_main is equal to the cell grid system voltage Vgrid_mini. The main system active power Pgrid_main and the main system reactive power Qgrid_main are input to the MGC 30, and the MGC 30 calculates the inter-system phase difference signal φglobal. In the system interconnection state, φglobal controls the flow of active power and reactive power between the two systems. It is also possible to transmit a different value for each DGR 40 without changing the total value of φglobal, causing each DGR 40 to output a different output.

[0079] GPS time information tref is input as first time information (t) from a GPS receiver 91 serving as a first time acquisition unit to the MGC 30. Meanwhile, tref is input as second time information (t') from a GPS receiver 92 serving as a second time acquisition unit to the DGR 40a.

[0080] The MGC 30 calculates a phase synchronization signal (Ncyc_ref_Sync) and transmits two pieces of information, including the main system frequency Fgrid_ref, and inputs them to the DGR (GPS-based phase calculation block) 40a. These two pieces of information are sufficient for synchronization control, but the φglobal signal is also transmitted for power flow control. The DGR 40a calculates the cell grid system rotation phase angle θref of the DGR 40. An adder 93 adds θref and φglobal to calculate θref_adj. The DGR 40b is operated based on θref_adj, and the output current Idgr of each DGR 40 is output. The output currents of each DGR 40 are summed and flow into the cell grid (represented as an adder 94 in the figure). The inflow current Igrid_main from the main system is also added, and the current is supplied to the cell grid system load 90. As a result, the cell grid system voltage Vgrid_mini (=cell grid system load voltage Vload) is established. This voltage is input to the MGC30 to create a stable feedback loop.

[0081] [(A) Cell grid independent state (main grid operation)] FIG. 3C describes a method of phase synchronization of both systems when the circuit breaker with a synchronism test function 21 is opened, the main system 15 and the cell grid system 28 are separated, and the cell grid is in an isolated operation state. When both systems are separated, the main system voltage Vgrid_main is generally different from the cell grid system voltage Vgrid_mini. However, in this GPS time synchronization method, the θref of both systems is always synchronized by the transmission of the main system frequency f31 and the phase synchronization signal Ncyc_ref_Sync39 and the calculation of FIG. 3A. During isolated operation, the inter-system phase difference signal φglobal can be used for fine adjustment. In this way, the voltage phase of the cell grid system 28 is synchronized with the voltage phase of the main system 15, so that the cell grid system 28 can be connected to the main system 15 at any time by closing the circuit breaker with a synchronism test function 21.

[0082] [(A) Cell grid isolation state (when the main grid is blacked out)] 3D explains how to synchronize the DGR 40 in the cell grid in the GPS-synchronized main system power outage and cell grid system independent state (at the time of main system power outage) in the first embodiment. When the main system stops, the circuit breaker with synchronism test is turned off and information from the MGC 30 is lost. On the other hand, tref as the second time information (t') is continuously input to the DGR 40a from the GPS receiver 92 as the second time acquisition unit.

[0083] Therefore, in the DGR 40, if the main system frequency measurement value Fgrid_ref is replaced with the previous value or a predetermined fixed value (for example, 50 Hz), and the phase synchronization signal Ncyc_ref_Sync is also replaced with the previous value or a predetermined fixed value (for example, 0), all the DGRs 40 can obtain θref synchronized with the GPS time as a common index. In addition, since the inter-system phase difference signal φglobal is optional, θref_adj is also synchronized by setting it to a predetermined fixed value (for example, 0). Therefore, even during a main system power outage, the cell grid can operate independently with all the DGRs 40 synchronized. When the main system is restored, the GPS time synchronized operation is resumed, and when synchronization is achieved, the circuit breaker with synchronization test is closed to switch to grid-connected operation, or the cell grid independent operation can be continued as it is.

[0084] In order to prevent the breaker with synchronism detection function (21) from opening and the cell grid from continuing independent operation even when the main system (15) is powered off, the grid interconnection controller (MGC30) has a grid interconnection protection function including islanding operation detection, and when active islanding operation is detected, it is possible to operate the protection function and open the breaker with synchronism detection function (21) by adjusting the reactive power output of each cooperative autonomous distributed device (DGR40).In addition, during a short-term main system power outage, the grid interconnection controller (MGC30) is also provided with an FRT function to keep the breaker with synchronism detection function (21) closed.

[0085] [(A) Black start operation of cell grid] If the main system experiences a power outage during system interconnection, the time it takes to detect the power outage in the main system and switch the circuit breaker 21 with synchronization verification function from closed to open is rated at 3 to 5 cycles, i.e., a delay of about 0.06 to 0.1 seconds, when using a high-voltage vacuum circuit breaker (VCB), for example. Also, if the main system experiences a power outage during system interconnection, the cell grid system voltage may drop together with the drop in the main system voltage, and may even reach 0V. Returning to independent operation from this point is called a black start.

[0086] In this case, if it is decided in advance that the main system frequency measurement value f41 should be maintained at its previous value or replaced with the rated value, and the phase synchronization signal Ncyc_ref_Sync45 should be maintained at its previous value or replaced with a fixed value prepared in advance, even if the voltage becomes zero, it is possible to maintain synchronization inside all DGRs 40, perform a black start after isolating the main system, and transition to independent operation of the cell grid. This is because all DGRs 40 have GPS time t'42 (Fig. 3A), i.e. tref92 (Fig. 3D), and perform calculations based on that time.

[0087] [(A) Time synchronization error] When the main system and the cell grid are separated, and the main system frequency f31 and phase synchronization signal Ncyc_ref_Sync remain constant without change, θref (= 2π · Ncyc_ref) obtained in this way by each DGR 40 is synchronized with the main system's θref with a voltage error of within 1% (corresponding to a time error of within 5 μsec). With an error of this magnitude, the main system and the cell grid can be said to be synchronized, so even if the circuit breaker with synchronization test function 21 is closed and the two systems are connected, no abnormal current will flow between the two systems.

[0088] [(A) Impact of transmission delay time] When the main system and the cell grid are separated, if the frequency or phase in the main system changes, there is a time delay, such as a transmission delay time from MGC 30 to DGR 40, which transmits the change to DGR 40, and a calculation time in MGC 30 and DGR 40, and the main system becomes temporarily out of synchronization. In this state, even if an attempt is made to connect the two systems by closing the circuit breaker 21 with a synchronism detection function, the synchronism detection function may operate and the circuit breaker may not be able to be closed. However, once the transmission delay time has elapsed, the voltage phase of the cell grid will be synchronized with the main system and the circuit breaker will be closed. This transmission delay time is about the same as the delay in network communication, and although it depends on the communication environment, it is usually within about 0.1 to 1 second.

[0089] [(A) Inertial force and synchronizing force] When the main system and the cell grid are connected, the two systems are physically connected, so the frequency f and the rotation phase angle signal θref of both systems are the same value. Here, when a change occurs in the frequency or rotation phase angle of the main system, the MGC 30 cannot transmit the change to each DGR 40 during the transmission delay time. Therefore, the tracking of the frequency and rotation phase angle of each DGR 40 is delayed by this delay time. Therefore, when viewed from the main system side, each DGR 40 and the cell grid appear to behave as if they have a strong inertial force as a whole. Furthermore, since they start to track the main system after this delay time, each DGR 40 and the cell grid appear to have a strong synchronizing force.

[0090] In addition, the frequency fluctuations of the transmitted main system are also limited by the limiter 60 in the DGR 40 controller. If this limit width is narrow, it is difficult to follow the frequency fluctuations of the main system, so it behaves as if the inertial force is large. If the limit width is wide, it is easier to follow the frequency fluctuations, so it behaves as if the inertial force is lighter. The same is true even if there are multiple cell grids. In an isolated system such as an isolated island, the size of the cell grid may be small, but when it accounts for more than half of the total demand as a whole, it is possible to gradually replace the cell grid so that it behaves like the main system by narrowing the limit width of the frequency change rate and making it robust against frequency fluctuations. In other words, the cell grid becomes a power system with controllable inertia.

[0091] Next, of the two synchronization methods for synchronizing the frequency and phase of all DGRs 40 in a cell grid, “(B) Voltage-based synchronization method” will be explained.

[0092] [(B) Basic explanation of voltage-based synchronization methods] Voltage-based synchronization is the standard approach for grid-connected microgrids. It has been widely implemented, tested, and deployed around the world. When connected to the main grid, the cell grid fluctuations are absorbed by the main grid and have no adverse effect. However, if the cell grid is operated independently from the main grid by inverters, it becomes difficult to maintain the frequency. Also, simultaneous black start of the cell grid is not possible. Below, we propose a method to solve these problems.

[0093] First, the voltage-based synchronous control method has the following advantages. The synchronization signal uses the voltage of the grid's power distribution lines. -No special additional equipment such as GPS signals or receivers is required. -The voltage synchronization signal is very robust. - Operation can continue as long as the power lines are not disturbed or damaged. The voltage synchronization signal automatically adjusts for the following issues: -Voltage changes and phase shifts in transformers. -Voltage drop and phase shift due to circuit impedance. · The DGR40 can be attached and detached without any special configuration when connecting to the cell grid. · The DGR40 is flexible for manual or automatic changes of cell grid circuit configuration.

[0094] On the other hand, there are also the following disadvantages: · Synchronization is not possible when the cell grid is operating independently from the main grid. -General frequency droop control causes excessive fluctuations. A synchronization signal from the MGC 30 proposed here is required. -Black start is not possible during a cell grid power outage. - A GPS time synchronization signal is required.

[0095] The reason why synchronization cannot be achieved during cell grid isolated operation separated from the main system is explained below. When the cell grid is operating independently, the total output of all DGRs 40 must match the total demand within the cell grid, so as shown in Figure 2F, the actual current Idgr flows according to the actual demand, and a deviation occurs from the target Idgr*. As a result, a phase difference of Δδ occurs between the actual cell grid voltage Vgrid and the target Vgrid*. If Δδ is zero, the frequency and phase are stable, but once the balance between the total output and total demand is lost and Δδ becomes positive or negative, |Δδ| increases.

[0096] For example, when the DGR40 active power output exceeds the actual load active power, the actual voltage Vgrid leads the target voltage Vgrid* in phase, and Δδ is always positive. The target voltage Vgrid* moves to match the actual voltage Vgrid by the PLL, so positive feedback is applied and the phase of θref is increased. As a result, the PLL frequency increases continuously.

[0097] Conversely, if the DGR40 active power output is smaller than the actual load active power, the actual voltage Vgrid lags behind the target voltage Vgrid* in phase, and Δδ is always negative. The PLL continuously reduces the phase of θref in a positive feedback loop. As a result, the PLL frequency continuously decreases. In either case, the phase difference between the PLL and the mini-grid is not stable, and the frequency is not stable either.

[0098] Thus, voltage-based synchronization cannot be used for grid-independent, isolated cell grids because there is no robust source to accept or provide the actual reactive power difference between the DGR 40 and the load. Conversely, if there is a robust source, the actual voltage Vgrid is stable, so the target voltage Vgrid* does not fall into a positive feedback loop even if it is controlled to approach it.

[0099] [(B) Introduction of inter-system phase difference signal φglobal] In order to avoid falling into such a positive feedback loop even when placed in a cell grid in an isolated operation state that is not dependent on the main grid, the following method was devised. That is, a method is proposed in which the frequency and phase of the cell grid are stabilized by transmitting the main system frequency signal f and the inter-system phase difference signal φglobal to all DGRs 40 via the MGC 30. First, as shown in Fig. 4B, the phase angle signal θref creates φsync by feedback control Kθctrl 85 that reduces the error between the reference angular frequency ωref and the mini-grid angular frequency ωgrid. The phase angle signal θpll obtained by the PLL of each DGR 40 is added to this in an adder 86 to create a local grid phase angle signal Ncyc_ref 89. However, with this control alone, the voltage phase of the cell grid generates positive feedback as described above, and is not stable.

[0100] Therefore, φglobal 80 is further added in adder 86 as shown in FIG. 4B. φglobal is a signal that represents the phase difference between the main system and the cell grid. Although the main system and the cell grid are decoupled, φglobal changes when the cell grid phase opens up compared to the main system phase. By adding φglobal, it is possible to suppress the positive feedback loop that causes the phase to open, and to suppress instability in the cell grid phase and therefore frequency. This is intended to stabilize the cell grid frequency by using only that information, even if it is not directly connected to the main system. This makes it possible to synchronize all DGR40 in the cell grid and stabilize the frequency even during independent operation without being connected to the main system. In addition, since both systems are synchronized, a circuit breaker with a synchronization test can be closed at any time to connect the two systems.

[0101] Figure 4A shows that φglobal is effective even when the main system and cell grid are connected. If the phase difference between the two systems is increased, active power will flow, so φglobal measures the power flow 17 flowing between the two systems, compares it with the target active power and reactive power, creates the required phase difference signal φglobal, and sends it to all DGRs 40. This makes it possible to increase or decrease the output of all DGRs 40 and control the power flow between the two systems to match the target value.

[0102] In addition, when the main system is in a state of power outage and the cell grid is operated independently, a reference voltage phase is created using an internal clock instead of the voltage phase of the main system, and the phase difference signal with the cell grid voltage phase is transmitted as φglobal to all DGRs 40 via MGC 30, thereby synchronizing the frequency and phase of the cell grid.

[0103] Next, the reason why a standard time signal is required when the MGC 30 is stopped and when a black start occurs due to a power outage in the cell grid will be described. As described above, when the main system and the cell grid are connected, the voltage phase of the main system is the reference, and when they are separated, the voltage phase information of the main system can be obtained through the MGC 30. Even if the main system is experiencing a power outage, the phase based on the clock inside the MGC 30 can be transmitted to all DGRs 40 as a common reference through the MGC 30. However, when the MGC 30 stops and is isolated from the main system, there is no common voltage phase information for all the DGRs 40. Similarly, when the cell grid stops, there is no common voltage phase information for all the DGRs 40. In such a case, it is necessary to use another means to supply a common synchronization signal to all DGRs 40. If the DGRs 40 acquire standard time information, it is possible to create a voltage phase synchronized with all DGRs 40 by correcting the internal clock based on that information. In this way, we propose a method to stabilize the frequency and phase of the cell grid using standard time information during black start after a cell grid power outage or when MGC30 is stopped for cell grid independent operation.

[0104] [(B) Detailed explanation of voltage-based synchronization method] The voltage-based synchronization control method will be described with reference to Figures 4A, 4B, and 4C. Figure 4A is a control block diagram of the main system connection state of voltage synchronization according to the first embodiment of the present invention, Figure 4B is a control block diagram of the cell grid system independent state (synchronization control) of voltage synchronization according to the first embodiment of the present invention, and Figure 4C is a control block diagram of the cell grid system independent state (during a main system power outage) of voltage synchronization according to the first embodiment of the present invention. The block diagrams and their control methods in each state will be described below.

[0105] [(B) Synchronization method when connecting to the main grid] In the voltage-based synchronization method, when the cell grid is connected to the main system, the difference between the signal based on the main system frequency and the signal based on the frequency detected by the PLL of each DGR 40 is controlled to be small, and the phase angle signal is also detected and taken into account, so that the target voltage Vgrid* and the actual voltage Vgrid almost match. This state is shown in Figure 2E, and is the same as when time is synchronized with GPS.

[0106] [(B) Explanation using a block diagram when connected to the main system] With reference to FIG. 4A, a block diagram for calculating Ncyc_ref89 in the cooperative autonomous decentralized device (DGR) 40A when the cell grid system is in a connected state with the main system will be described. FIG. 4A is a block diagram of the synchronization control based on the voltage in the first embodiment of the present invention, and is a control diagram of the system-connected state. The system-connected controller (MGC) 30A and the cooperative autonomous decentralized device (DGR) 40A are included. In the system-connected controller (MGC) 30A, the inter-system phase angle φglobal is generated in the inter-system phase difference signal φglobal calculation unit 80 from the main system active power Pgrid_main and the main system reactive power Qgrid_main measured by the system active power Pgrid_main measurement unit 98 and the main system reactive power Qgrid_main measurement unit 99, taking into account the power flow between the main system 15 and the cell grid system 28.

[0107] First, a description will be given of the main system frequency measuring instrument 31. The main system voltage acquisition unit 97 acquires the main system voltage Vgrid_main. In a state of connection with the main system, the main system voltage and the cell grid voltage are the same, so Vgrid_main=Vgrid_mini.

[0108] The PLL 96 calculates the main system frequency measurement value f31 from the main system voltage Vgrid_main, and transmits the signal to the DGR 40 via the MGC 30. The system phase difference signal φglobal 80 calculation unit calculates the system phase difference signal φglobal based on the difference between the measured main system active power Pgrid_main and main system reactive power Qgrid_main flowing between the main system and the cell grid and their respective target values ​​(not shown), and transmits the signal to the DGR 40 via the MGC 30. If the direction of the power flow toward the cell grid side is positive, when the system phase difference signal φglobal is increased, the phase angle of the cell grid system lags relative to the main system, and the power flow from the main system to the cell grid system increases. Also, when the system phase difference signal φglobal is decreased, the phase angle of the cell grid system advances, and the reverse flow power from the cell grid system to the main system increases. In this way, the output of the DGR 40 is changed to match the power flow between both systems to the target value. Regarding reactive power, a voltage correction signal is sent to the DGR 40 via the MGC 30 instead of the φglobal 80, but the method is similar and detailed description is omitted.

[0109] The PLL 83 of the cooperative autonomous decentralized device (DGR) 40A generates a cell grid system phase angle signal θpll and a cell grid system angular velocity signal ωpll from the cell grid voltage Vgrid_mini. The main system frequency measurement value acquisition unit 41 receives the main system frequency measurement value f measured by the main system frequency measurement device 31 and calculates the main system angular velocity signal ωref = 2π · f. The PLL 83 calculates the cell grid system angular velocity signal ωpll from the cell grid voltage Vgrid_mini. Next, the inter-system angular velocity error signal ωerr = ωref - ωpll is calculated by a comparator. Next, the controller kθ_ctrl 85 receives ωerr as an input, performs PI calculation, and calculates the control phase signal φsync. The kθ_ctrl has a proportional gain and an integral gain, but the gain is constant for low frequency components and small for high frequency components, making it less susceptible to the effects of sudden frequency changes, etc.

[0110] In an adder 86, the cell grid system phase angle signal θpll and the inter-system phase angle φglobal are added to the control phase signal φsync, the resulting signal is divided by 2π by a divider, and the remainder of the division using a MOD function is calculated to extract only the decimal part, thereby obtaining a sawtooth output Ncyc_ref 89. Furthermore, by multiplying Ncyc_ref by 2π, a cell grid system rotation phase angle signal (hereinafter sometimes referred to as the "cell grid system phase angle signal") θref=2π·Ncyc_ref is obtained. Although the MOD function is used in this embodiment, it can be replaced with a function that extracts the decimal part as described above.

[0111] In this way, the cell-grid system phase angle signal θref=2π·Ncyc_ref obtained by each cooperative autonomous decentralized device (DGR) 40A is synchronized with the main system voltage (=cell grid voltage). In the case of a stable system in a steady state, the PLL frequency is constant, so ωref=ωpll, and ωerr=0, and therefore φsync=0. For this reason, θpll created by the PLL of each DGR 40 becomes dominant. By adding the inter-system phase angle φglobal to this, it is possible to control the power flow and reverse power flow between the cell-grid system and the main system.

[0112] If the system frequency or phase changes suddenly, ωref ≠ ωpll, but a transmission time delay occurs. However, the PLL 83 monitors the cell grid voltage (= main system voltage) and creates θpll, so it follows even sudden changes instantly (within about one cycle). The power flow between the main system and the cell grid changes suddenly, but a time delay occurs in the transmission of φglobal. Limits are placed on the rise and fall of φglobal to prevent sudden changes. In this way, the power flow connecting the two systems and the PLL maintain the cell grid's synchronization force and inertia force.

[0113] [(B) When cell grid is independent] With reference to FIG. 4B, a block diagram for calculating Ncyc_ref in the cooperative autonomous decentralized device (DGR) 40B in the cell grid isolated state will be described. FIG. 4B is a block diagram of the synchronization control based on the voltage in the first embodiment of the present invention, and is a control diagram of the cell grid isolated operation state in which the grid is separated from the grid. It includes a grid interconnection controller (MGC) 30B and a cooperative autonomous decentralized device (DGR) 40B. The same components as those in FIG. 1 to FIG. 4A are given the same reference numerals, and the description thereof will be omitted. The inter-system phase difference signal φglobal calculation unit 80 calculates the measured main system voltage Vgrid_main and cell grid voltage Vgrid_mini by the PLL 96b, and calculates the difference in phase angle between them as the inter-system phase difference signal φglobal.

[0114] The input contents of φglobal in FIG. 4B are different from those of φglobal in FIG. 4A. In FIG. 4B, since both systems are separated, the purpose is to align the voltage phase of DGR 40B with the main system so that the circuit breaker 21 with synchronization test function can be turned on at any time. For this reason, in FIG. 4B, φglobal calculates the voltage phase difference between both systems. When both the main system and the cell grid system are in a steady state and stable during independent operation, the voltage phases of both systems match by sending a signal of φglobal=0, and the system is ready to be connected at any time. If the system frequency or phase suddenly changes, ωref≠ωpll. However, since both systems are separated, the phase angle difference between the main system and the cell grid will temporarily widen, but after the transmission time delay has elapsed, the voltage phases will match again, and the system will return to a state where it is ready to be connected at any time.

[0115] [(B) Adoption of standard time signals] As described above, the configuration of Figures 4A and 4B does not require a standard time signal. However, as will be described in detail below, when the MGC 30C is stopped or during a black start, the voltage-based synchronization method cannot be used, as shown in FIG. 4C. This is because the common index φglobal related to the phase is lost, even if the target frequency is switched to a fixed value. In this case, a target voltage signal Vgrid* having a common phase for all DGRs 40C is required. A standard time signal can be used for this purpose. Based on the standard time, it is possible to ensure a common voltage phase for all DGRs 40C. In this manner, even in the case of synchronous control based on voltage, this embodiment is characterized in that Vgrid* is synchronized in all DGRs 40 by internal clock correction using a standard time signal.

[0116] [(B) When the main grid is blacked out and the cell grid is isolated] Fig. 4C explains a method for realizing cell-grid independent operation by all DGRs 40C continuing synchronous operation when the main system is stopped. When the main system is stopped, the circuit breaker with synchronism test is turned off and information from the MGC 30C is lost. In this case, the main system frequency measurement value f41 is maintained at its previous value or replaced with a rated value, and the inter-system phase difference signal φglobal is maintained at its previous value or replaced with a fixed value (including zero) prepared in advance, whereby the cell-grid independent operation can be continued while all DGRs 40C maintain synchronization.

[0117] [(B) When MGC30C is stopped] Even if the main system voltage is not lost, the MGC30C may stop. In that case, as described above, by storing the voltage vector and rated frequency information based on GPS time inside each DGR40C, and operating the DGR40C at the rated frequency with the voltage vector set as Vgrid* in Figure 2E, continuous operation is possible. Even when the MGC30C is operating and some of the DGR40C (less than 20% in terms of capacity) are unable to receive information from the MGC30C, the remaining DGR40C make the cell grid as a whole robust, so the DGR40C that are unable to receive information from the MGC30C can continue to operate synchronously by switching to a synchronization method based on the normal voltage.

[0118] [(B) Achieving a Black Start] When the voltage of the main system is lost, even if the circuit breaker with synchronism verification is disconnected, the voltage in the cell grid may become zero. The recovery of the cell grid from zero voltage corresponds to a so-called black start. In the present invention, as described above, a reference voltage vector based on GPS time is stored inside each DGR 40C, and during a black start, the DGR 40C is operated with the reference voltage vector set to Vgrid* in FIG. 2E, thereby enabling a black start.

[0119] [Embodiment 2] A cooperative autonomous decentralized grid-connected system according to a second embodiment of the present invention will be described with reference to Figs. 5A to 5N. Figs. 5A to 5N are explanatory diagrams of the first to fourteenth states of the cell-grid connection configuration according to the second embodiment of the present invention. The same reference numerals are used for configurations common to Figs. 1 to 4C, and descriptions thereof will be omitted. The configuration of the cell grid 20 is the same as that of the first embodiment. The second embodiment is an example in which a cell-grid system 28 is connected to a plurality of main systems 15.

[0120] 5A to 5N, a cell grid 20 is connected to both a main system 15a consisting of a main system 15a1 and a main system 15a2 connected to a substation A, and a main system 15b consisting of a main system 15b1 and a main system 15b2 connected to a substation B, via circuit breakers 21a and 21b with a synchronism test function. The connection of the cell grid 20 connected to the two main systems 15a and 15b in this manner is sometimes called a "disconnected system."

[0121] As in the first embodiment, a plurality of distributed cooperative devices (DGRs) 40 are provided in the cell grid 20, and each DGR 40 is controlled by a control signal from a grid interconnection controller (MGC) 30 and can be interconnected with the main system 15a or 15b. The circuit breakers 21a and 21b with a synchronism test function are also controlled by a control signal from the MGC 30, and the connection and disconnection between the cell grid system 28 and the main system 15a and the main system 15b are controlled by a control signal from the MGC 30. Note that the MGC 30 is physically integrated with some parts of the circuit breakers with a synchronism test function. The cell grid 20 is provided with two circuit breakers with a synchronism test function 21a and 21b, and one circuit breaker with a synchronism test function 21a is connected to the main system 15a, which is the system of the substation A 13a, and the other circuit breaker with a synchronism test function 21b is connected to the main system 15b, which is the system of the substation B 13b.

[0122] In the main system 15a, a power company sectional switch 16a is provided between the circuit breaker with synchronization testing function 21a and the substation A 13a, a main system 15a1 is provided between the circuit breaker with synchronization testing function 21a and the sectional switch 16a, and a main system 15a2 is provided between the sectional switch 16a and the substation A 13a.

[0123] In the main system 15b, a power company sectional switch 16b is provided between the circuit breaker with synchronization testing function 21b and substation B13b, a main system 15b1 is provided between the circuit breaker with synchronization testing function 21b and the sectional switch 16b, and a main system 15b2 is provided between the sectional switch 16b and substation B13b.

[0124] [Recovery control from the main system 15a accident] 5A to 5K, a state from when an accident occurs in the grid 15a2 until the accident is restored and power supply is resumed as before will be described. Even if an accident occurs in the grid 15a2, the cell grid system 28 continues to supply power by the power generation facility 23 in the cell grid 20.

[0125] In the state of FIG. 5A, the circuit breakers with synchronism checking function 21a and 21b are both open, and the cell grid 20 is performing independent operation.

[0126] In the state of Fig. 5B, the circuit breakers with synchronism test function 21a and 21b are both open, and the cell grid 20 is operating independently. The sectioning switch 16a is closed, and power from the substation A13a is supplied to the system 15a1 via the system 15a2, and both the system 15a1 and the system 15a2 are charged with the power from the substation A13a. Similarly, the sectioning switch 16b is closed, and power from the substation B13b is supplied to the system 15b1 via the system 15b2, and both the system 15b1 and the system 15b2 are charged with the power from the substation B13b.

[0127] In the state of Fig. 5C, an accident, such as a short circuit accident, occurs in the system 15a2. When it is determined that an accident has occurred in the system 15a2, the section switch 16a is immediately opened as in the state of Fig. 5D.

[0128] In the state of Fig. 5D, the sectional switch 16a is open, so that power is not supplied to the grid 15a1. Even in this case, the circuit breakers 21a and 21b with synchronism checking function are open, and the cell grid 20 is operating independently, so that the cell grid grid system 28 continues to receive power from the power generation equipment in the cell grid 20.

[0129] 5D, since there is no abnormality in the grid 15a1, the MGC 30 plans, together with the power supply department of the power company, a control for supplying power from the substation B 13b to the grid 15a1. First, the frequency and phase synchronization control is performed so that the cell grid system 28 can be synchronously connected to the grid 15b1.

[0130] In the state of FIG. 5E, after the cell-grid system 28 is synchronized with the system 15b1, the circuit breaker with synchronism test function 21b is closed, and synchronous interconnection with the system 15b1 is performed.

[0131] In the state of Fig. 5F, the cell grid system 28 is interconnected with the system 15b1, so that the power of the substation B13b can be supplied to the cell grid system 28 via the system 15b2, the system 15b1, and the circuit breaker with synchronism test function 21b. This makes it possible to charge the cell grid system 28 with the power of the substation B13b.

[0132] In the state of FIG. 5G, the circuit breaker with synchronism test function 21a is closed, thereby connecting the cell-grid system 28 to the system 15a1 which is a normal system and experiencing a power outage.

[0133] In the state of Figure 5H, the circuit breaker with synchronization test function 21a is closed, and power is supplied to the system 15a1 from the substation B13b via the cell grid system 28, so that the system 15b2, the system 15b1, the cell grid system 28, and the system 15a1 are charged with power from the substation B13b.

[0134] In the state of Fig. 5I, the system 15a2 where the accident occurred has been restored, and power is being supplied from the substation A 13a to the system 15a2. Here, the MGC 30 cooperates with the power supply department of the power company to plan control so that the system 15a1, which had been supplying power from the substation B 13b via the cell grid system 28, is again supplied with power from the substation A 13a.

[0135] In the state of Fig. 5J, the circuit breakers 21a and 21b with a synchronism test function are opened. By opening the circuit breakers 21a and 21b with a synchronism test function, the cell grid 20 performs an independent operation. At this time, the system 15a1 is not supplied with power from either the substations 13a or 13b.

[0136] In the state of FIG. 5K, the section switch 16a is closed, and power is supplied from the substation A13a to the system 15a1 via the system 15a2, thereby recovering from the power outage caused by the accident that occurred in the system 15a2.

[0137] [Restoration control in the event of an accident occurring within a cell grid during isolated operation] With reference to Figs. 5L to 5N, restoration control will be described when an accident occurs in the cell grid 20 during independent operation of the cell grid 20.

[0138] In the state of FIG. 5L, the cell grid is in an isolated operation state. Each DGR 40 in the cell grid 20 performs synchronous control to synchronize with the grid 15a1. Assume that an accident occurs in the cell grid 20 at this time. When the cell grid is in an isolated operation state, when an accident such as a short circuit occurs in the cell grid, a short-circuit current large enough to trip the protective relay at the accident point may not be supplied from the power generation equipment in the cell grid to the accident point. If the protection level of the protective relay is set to match the main grid, the protective relay may not be able to operate and the accident point may not be isolated. If the accident continues for a certain period of time and the voltage does not return, the state transitions to FIG. 5M.

[0139] In the state of Fig. 5M, the cell grid system 28 and the system 15a1 are synchronized, so the circuit breaker with synchronization test function 21a can be closed immediately. By closing the circuit breaker with synchronization test function 21a, a short-circuit current is supplied from the main system to the fault point in the cell grid. If a short-circuit current equal to or greater than the tripping level is supplied to the fault point, the protective relay at the fault point operates to isolate the fault point.

[0140] In the state of Fig. 5N, the voltage is restored because the fault point in the cell grid 20 has been cut off. The grid-connected operation can be continued in this state, or the cell grid 20 can be operated independently by opening the circuit breaker with synchronism test function 21a again.

[0141] Here, it has been described that by interconnecting the cell grid system 28 and system 15a1, a short-circuit current is supplied to the accident point in the cell grid 20 and the protective relay at the accident point is shut off. However, this embodiment is not limited to this. For example, instead of system 15a1, the cell grid system 28 and system 15b1 may be interconnected to supply a short-circuit current to the accident point in the cell grid 20 and shut off the protective relay at the accident point.

[0142] [Embodiment 3] A cooperative autonomous decentralized grid interconnection system according to a third embodiment of the present invention will be described with reference to Fig. 6. The same reference numerals are used for configurations common to Figs. 1-5N, and descriptions thereof will be omitted. Fig. 6 is a block diagram of the cooperative autonomous decentralized grid interconnection system according to the third embodiment of the present invention.

[0143] The DGR 40 is composed of a common unit 120 and an individual unit 130, and communicates with a grid controller (MGC) 30 via a mobile circuit. The MGC 30 is provided on a cloud as a cloud for the common unit. A part of the MGC 30 is also built into the control unit of the circuit breaker 21 with a synchronization test function. The MGC 30 can acquire various information of the individual unit 130 by communicating with the cloud 110 for the individual unit.

[0144] The common unit 120 has the same configuration in all DGRs 40. The common subunit 121 provided in the common unit 120 is composed of a DGR controller 122 and a motherboard 123, and communication is performed between the DGR controller 122 and the motherboard 123 via a LAN. The motherboard 123 is equipped with a CPU and an FPGA (Field Programmable Gate Array). The FPGA is an LSI that can be programmed from the MGC 30 and is rewritable, so that the common unit 120 can be commonly used for all kinds of DGRs 40.

[0145] The individual unit 130 is composed of an individual subunit 131, a BMU (Battery Management Unit) board 136, and a battery unit 137. The individual unit 130 is provided with a plurality of individual subunits 131, for example, three individual subunits 131, and each of the individual subunits 131 is connected to the motherboard 123 by an LVDS (Low Voltage Differential Signaling) cable.

[0146] The individual subunit 131 is composed of an ADC (Analog-to-Digital Converter) board 132, a power board 133, an auxiliary power supply board 134, and an AC or DC filter 135. The ADC board 132 outputs a switching pulse signal transmitted by an LVDS cable to the power board 133. The power board 133 is connected to the ADC board 132 by a FLAT cable. The power board 133 uses power from the auxiliary power supply board 134 as a controlled power supply, outputs a switching pulse in response to the switching pulse signal from the ADC board 132, and supplies the switching pulse to the power interface 140 via the AC or DC filter 135.

[0147] The voltage and current values ​​detected by the power interface 140 are input to the ADC board 132 via the AC or DC filter 135 and the power board 133, and the ADC board 132 inputs the detected voltage and current values ​​as digital signals to the motherboard 123 via an LVDS cable.

[0148] The BMU board 136 communicates with the motherboard 123 via a CAN (Controller Area Network). A plurality of, for example, eleven, battery units 137 are provided in the individual unit 130. The BMU board 136 and each battery unit 137 are connected by a cable.

[0149] The battery unit 137 is composed of a CMU (Cell Management Uni) 138 and a battery subunit 139. The BMU board 136 monitors and controls the state of each battery unit 137 based on a command signal from the motherboard 123. The CMU 138 communicates with the BMU board 136 to control and protect the battery subunit 139. The BMU board 136 controls the entire battery unit and monitors for abnormalities based on information for each CMU 138, and can prevent, for example, fire accidents of lithium ion batteries, etc. The BMU board 136 and the battery unit 137 can be provided integrally with the DGR 40 or can be provided separately.

[0150] In the DGR 40 , the motherboard 123 of the common unit 120 centrally performs all control calculations, and the individual units 130 drive the hardware based on control signals output by the control calculations of the motherboard 123 .

[0151] The motherboard 123 outputs a switching pulse to the ADC board 132 via the LVDS cable, and the ADC board 132 supplies a control signal including the switching pulse of the LVDS cable to the power board 133 via the FLAT cable. The power board 133 supplies a switching pulse to the power interface 140 via the AC or DC filter 135 based on the switching pulse and the like calculated in the motherboard 123, using the auxiliary power board 134 as a control power source. Information such as a voltage value and a current value detected in the power interface 140 is transmitted to the ADC board 132 via the AC or DC filter 135 and the power board 133, converted into a digital signal in the ADC board 132, collected by the motherboard 123 through communication via the LVDS cable, and used for control calculation.

[0152] The motherboard 123 also centrally performs control calculations for the battery unit 137. That is, the BMU board 136 controls, protects, and monitors all the battery subunits 139 via the CMU 138 in response to control signals calculated in the motherboard 123.

[0153] In addition, the FPGA and CPU on the motherboard 123 can be freely reprogrammed from the MGC 30. Therefore, the settings of the DGR40 can be freely changed via the cloud, and various settings are possible, such as settings for three-phase, single-phase, 380V voltage, 200V voltage, direct current for solar power, direct current for storage batteries, and direct current for fuel cells. Therefore, even with the same hardware, different units can be realized by changing the software via the cloud, and the DGR40 can be used not only in various places in Japan but also around the world.

[0154] The individual units 130 do not have any main control device such as a microcomputer, and all control calculations are performed by the motherboard 123, and the individual units 130 are driven by control signals from the motherboard 123. For example, a switching pulse signal calculated by the motherboard 123 is supplied to three half bridges in each of the three individual subunits 131, i.e., a total of nine half bridges. The number of these units and half bridges can be increased or decreased. Also, on the motherboard 123 side, detection signals such as voltage values ​​and current values ​​from the power interfaces 140 at each point are obtained as digital data via an LDVS cable, and all control calculations for the DGR 40 are performed.

[0155] By standardizing the common unit 120 and the interface between the boards, the individual units 130 can be provided as products with a variety of applications. All system operations can be realized in the cloud by the MGC 30. Moreover, by updating the software on the motherboard 123 via the cloud by the MGC 30, the latest software can always be used.

[0156] The DGR controller 122 can extract information on the solar panels and generators connected to the half bridge and battery information from the motherboard 123, in addition to information on power and voltage, and send it to the cloud for comprehensive use. Weather information can also be used from the DGR 40 information distributed over a surface area. In addition, the necessary information can be encrypted and sent to a blockchain ledger, creating a foundation for a local currency, for example.

[0157] It is desirable to use hysteresis control for the calculation of the switching pulse in the motherboard 123. Hysteresis control will be described below with reference to Figs. 2B and 2C. Hysteresis control is current control using a hysteresis current control method, which differs from the commonly used PWM control. In PWM control, if a short circuit occurs during isolated operation of the cell grid, an overcurrent flows instantaneously, and the inverter is stopped for overcurrent protection. In contrast, hysteresis control controls the current, so that the current can be suppressed even if a short circuit occurs.

[0158] A target current Iref that achieves the target voltage Vref is calculated by the following equation (2). JPEG0007628328000001.jpg19170Here, Tsw=1 / fsw is the switching period. Idgr is the current flowing through the load of the cell grid, and the target current Iref changes according to the load current Idgr. The second term on the right-hand side is: This is the correction current to achieve the target voltage Vref, and corresponds to ΔI=C·dV / dt.

[0159] According to the hysteresis control, the current can be directly controlled and Vdgr can be made to follow the target voltage Vref. That is, the target power can be obtained in the DGR 40 by making IL follow the target current Iref through the hysteresis control and further controlling Vdgr to the target voltage Vref.

[0160] In hysteresis control, an upper band Δib and a lower band -Δib are set above and below the target current Iref, respectively. When IL exceeds the upper band Δib, the switch of the upper arm is turned off and the switch of the lower arm is turned on. When IL falls below the lower band -Δib, the switch of the lower arm is turned off and the switch of the upper arm is turned on. This operation is repeated.

[0161] In FIG. 2C, at time t0, IL falls below the lower band -Δib, so the switch of the lower arm is turned off and the switch of the upper arm is turned on, so +Vdc is applied to Lfiler. Next, at time t1, when IL exceeds the upper band Δib, the switch of the upper arm is turned off and the switch of the lower arm is turned on, so -Vdc is applied to Lfiler. Next, at time t2, IL falls below the lower band -Δib, so the switch of the lower arm is turned off and the switch of the upper arm is turned on, so +Vdc is applied to Lfiler. The time from time t0 to t2 is the switching period Tsw.

[0162] At this time, the switching frequency fluctuates as the slope of IL changes according to the voltage difference between both ends of Lfilter. Therefore, in order to suppress the fluctuation of the switching frequency, the bandwidth of the upper band Δib and the lower band -Δib is changed according to the following equation (3). JPEG0007628328000002.jpg25170

[0163] When the switching frequency is constantly fluctuating and its band is wide, it is difficult to design an EMC filter. Variable bandwidth control makes it easier to design an EMC filter because it allows the switching frequency to converge to fsw.

[0164] The above-described embodiments do not limit the present invention, and the present invention can be equally applied to other embodiments included in the scope of the claims. In addition, the embodiments can be appropriately modified or combined. [Explanation of symbols]

[0165] 10. Power Plant 11. Extra-high voltage substation 12 Power transmission facilities 13. Substation 15 Main system 16a, 16b section switch 17 Satellite 20 Cell Grid 21 Circuit breaker with synchronous detection function 22 Electricity demand equipment 22a Household equipment 22b Energy storage device 22c Electric vehicle charging and discharging equipment 22d Electric car 23 Power generation facilities 23a Wind power generation equipment 23b Solar power generation equipment 23c Energy storage device 23d Internal combustion engine power plant 28 Cell Grid System 30 Grid-connected controller (MGC) 31 Mains frequency measurement device 32 GPS receiver 33 Multiplier 34 Main system rotation phase angle 35 Subtractor 36 Calculation Block 37 Floor Function 38 Subtractor 39 Phase Synchronous Signal 40 Cooperative autonomous decentralized equipment (DGR) 41 System frequency measurement value acquisition unit 42 GPS receiver 43 Multiplier 44 Adjustment value acquisition device 45 Phase Synchronous Signal 46 Adder 47 Adder 50 Calculation Blocks 51 Floor Function 52 Subtractor 53 Subtractor 54 Adder 55 Calculation Block 56 Floor Function 57 Subtractor 58 Adder 59 Multiplier 60 Limiter 61 Integrator 62 Output system phase angle 80 Arithmetic section 81 Multiplier 82 Cell Grid System Voltage Detector 83 PLL 84 Subtractor 85 Controller 86 Adder 87 Multiplier 88 Modular arithmetic 89 System phase angle signal 90 Cell Grid System Load 91, 92 GPS receiver 93, 94, 95 96 PLL 97 System voltage acquisition unit 97b PLL 98 System Active Power 99 System reactive power 110 Individual Unit Cloud 120 Common Unit 121 Common Subunit 122 DGR Controller 123 Motherboard 130 individual units 131 Individual Subunits 132 ADC board 133 Power Board 134 Auxiliary Power Board 135 DC Filter 136 BMU Board 137 Battery Unit 138 CMU 139 Battery Subunit 140 Power Interface

Claims

1. A switch capable of connecting or disconnecting the main system and the cell grid system; a grid interconnection controller for detecting power information of the main grid and power information of the cell grid; One or more cooperative autonomous decentralized devices are connected in the cell grid system and perform power conversion so as to be synchronously interconnected with each other; A cooperative distributed grid interconnection system comprising: Transmitting the acquired standard time signal to each of the cooperative autonomous distributed devices and correcting the internal time signal of the cooperative autonomous distributed device, or Each of the cooperative autonomous distributed devices is provided with a standard time signal acquisition device for acquiring a standard time signal, Each of the cooperative autonomous decentralized devices receives frequency information and phase information, or a composite signal of frequency information and phase information, transmitted from the grid interconnection controller based on the standard time signal; When the switch is open, each of the cooperative autonomous distributed devices controls the voltage phase of the cell grid system to be synchronized with the voltage phase of the main system; A cooperative distributed grid interconnection system, characterized in that, when the switch is closed, each of the cooperative autonomous distributed devices controls the flow of power between the main grid and the cell grid grid.

2. The grid interconnection controller generates an inter-grid phase difference signal and transmits it to each of the cooperative autonomous decentralized devices; When the switch is closed, each of the cooperative autonomous distributed devices controls power flow and reverse power flow using the inter-system phase difference signal; The cooperative distributed grid interconnection system according to claim 1, characterized in that even when the switch is open and information from the grid interconnection controller cannot be received, each of the cooperative autonomous distributed devices can synchronously control the cell grid system based on the standard time signal.

3. The standard time signal acquisition device includes a first standard time acquisition unit that acquires a first standard time signal, and a second standard time acquisition unit that acquires a second standard time signal, the grid interconnection controller includes the first standard time acquisition unit, and generates a phase synchronization signal as a composite signal of the frequency information and the phase information by applying the first standard time signal to a main grid frequency and a main grid rotation phase angle, and outputs the phase synchronization signal to the cooperative autonomous decentralized device; The cooperative distributed grid interconnection system according to claim 1 or 2, characterized in that the cooperative autonomous distributed device includes the second standard time acquisition unit, and demodulates a cell grid grid rotation phase angle signal synchronized with the main grid rotation phase angle by applying the second standard time signal to the phase synchronization signal and the main grid frequency output by the grid interconnection controller.

4. The grid interconnection controller receives power information of the main grid and / or power information of the cell grid grid, measures a main grid frequency measurement value, generates an inter-system phase difference signal, and outputs the signal to the cooperative autonomous decentralized device; The cooperative autonomous decentralized grid interconnection system according to claim 1 or 2, characterized in that the cooperative autonomous decentralized device generates a cell-grid grid phase angle signal and a cell-grid grid angular velocity signal from the cell-grid grid voltage, and calculates a cell-grid grid rotation phase angle signal from the cell-grid grid phase angle signal, the cell-grid grid angular velocity signal, the main grid frequency measurement value, and the inter-system phase difference signal.

5. The grid interconnection controller measures the main grid frequency measurement value by a first phase locked loop; the cooperative autonomous decentralized device generates the cell-grid system phase angle signal and the cell-grid system angular velocity signal by a second phase locked loop; The coordinated autonomous decentralized grid interconnection system according to claim 4, characterized in that the standard time signal acquisition device includes a first standard time acquisition unit that inputs a first standard time to the first phase synchronization circuit, and a second standard time acquisition unit that inputs a second standard time to the second phase synchronization circuit.

6. The cooperative autonomous decentralized grid interconnection system according to claim 1 or 2, characterized in that the cell grid system can be connected to a plurality of the main systems via the switch, and when an abnormality occurs in a first main system among the main systems, the cell grid system is interconnected with a second main system other than the first main system, and is capable of transmitting power to an area in the first main system where no abnormality is occurring.

7. (Response in the event of a main grid power outage or a cell grid accident) When the switch is closed and the main system is powered out, the switch is switched from closed to open, and each of the cooperative autonomous decentralized devices independently operates the cell grid system; The cooperative distributed grid interconnection system according to claim 1 or 2, characterized in that when the switch is open and an accident occurs within the cell grid system, the switch is closed and the power flow is controlled to supply a fault current to the fault point, thereby activating a protective relay at the fault point to isolate the fault point.

8. The cooperative distributed grid interconnection system according to claim 1 or 2, characterized in that the cooperative autonomous distributed device includes a common unit having a motherboard and one or more individual units, and the motherboard performs control calculations including pulse wave generation.

9. A switch capable of connecting or disconnecting the main system and the cell grid system; a grid interconnection controller for detecting power information of the main grid and power information of the cell grid; One or more cooperative autonomous decentralized devices are connected in the cell grid system and perform power conversion so as to be synchronously interconnected with each other; A cooperative distributed grid interconnection system comprising: When the switch is open, each of the cooperative autonomous distributed devices controls the voltage phase of the cell grid system to be synchronized with the voltage phase of the main system; When the switch is closed, each of the cooperative autonomous distributed devices controls a power flow between the main system and the cell grid system; The cooperative autonomous decentralized device has a pulse waveform calculation device that performs control calculations including pulse wave generation, A cooperative distributed grid interconnection system characterized in that the target current calculated from the target voltage is hysteresis-controlled using a fluctuation bandwidth in the calculation of pulse wave generation in the pulse waveform calculation device, thereby suppressing the current in the event of a grid accident.

10. A switch capable of connecting or disconnecting the main system and the cell grid system; a grid interconnection controller for detecting power information of the main grid and power information of the cell grid; One or more cooperative autonomous decentralized devices are connected in the cell grid system and perform power conversion so as to be synchronously interconnected with each other; A system interconnection method for a cooperative distributed system interconnection system comprising: a step of transmitting the acquired standard time signal to each of the cooperative autonomous distributed devices and correcting the internal time signal of the cooperative autonomous distributed devices, or a step of each of the cooperative autonomous distributed devices acquiring the standard time signal; each of the cooperative autonomous decentralized devices receiving frequency information and phase information, or a composite signal of frequency information and phase information, transmitted from the grid interconnection controller based on the standard time signal; When the switch is open, each of the cooperative autonomous distributed devices controls the voltage phase of the cell grid system to synchronize with the voltage phase of the main system; When the switch is closed, each of the cooperative autonomous distributed devices controls a power flow between the main grid and the cell grid; A system interconnection method using a cooperative distributed system interconnection system, comprising:

11. A program for executing, by a computer, each step of the grid interconnection method for the cooperative autonomous decentralized grid interconnection system according to claim 10.

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