System-forming power conversion device, system-forming power system, system-forming power conversion method, and program

Abstract

To provide a coordinative autonomous distributed system interconnection system that enables each cell grid to operate independently by causing synchronization of a large number of coordinative autonomous distributed appliances, and that enables constant synchronization connection to a main system.SOLUTION: A coordinative autonomous distributed system interconnection system according to one embodiment of the present invention is characterized in that: coordinative autonomous distributed appliances (DGR40) each receive frequency information and phase information transmitted, on the basis of a standard time signal, from the system interconnection controller or a composite signal between the frequency information and the phase information; when the switch (21) is open, each of the coordinative autonomous distributed appliances (DGR40) performs control such that the voltage phase of a cell grid system becomes synchronous with the voltage phase of a main system; and when the switch (21) is closed, each of the coordinative autonomous distributed appliances (DGR40) controls electric power flow flowing between the main system and the cell grid system.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to System-forming power conversion device, system-forming power system, system-forming power conversion method and a program.

Background Art

[0002] In recent years, there has been an increasing demand for on-site consumption of electric power generated by power generation facilities using renewable energy within the region. For this reason, a method called a mini-grid or a micro-grid, which divides and manages a power system including one or more power generation facilities, is known. The AC system in this micro-grid is synchronized by an inverter provided on the output side of the power generation facility.

[0003] Patent Document 1 describes a method of independently managing a micro-grid. In Patent Document 1, inverters provided respectively at the outputs of a plurality of power generation facilities in the micro-grid adjust the output voltage value and the phase based on a time signal obtained from GPS. Also, based on the actual series impedance of the micro-grid, the active power and the reactive power are feedback-controlled. For grid connection with other micro-grids, a central energy management system is required.

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

[0005] Reference 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 power system within the microgrid, and this measured phase information is used as a reference in the synchronous fixed-frequency control of the inverters connected to the outputs of each power generation facility. It is also described that the impedance from the output of each power generation facility to the power system within the microgrid is regarded as a common reference impedance and compensated by a compensating virtual impedance.

[0006] Reference Document 4 describes a method of controlling the current of a power converter within a microgrid. The method regards the converter connected to the AC power source as a virtual voltage source with a virtual impedance, and controls the waveform of the AC voltage by operating the phases of the active current and the reactive current. Also, as a method of operating the instantaneous current, a droop control method is adopted, which is a combination of current limiting and maximum power point tracking (MPPT) methods, etc.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] In order to coordinate with the main system by the method of independently managing the microgrid of the above Patent Document 1, a central energy management system that comprehensively controls the entire separate system is required. For this reason, the system for connecting the in-microgrid system and the main system has become large-scale enough to comprehensively control all systems, and there has been a problem that the communication system has also become large-scale and cannot follow rapid fluctuations due to the communication delay.

[0009] In the power conversion device of the above Patent Document 2, since the microgrid has a fixed frequency, an asynchronous connection power converter that performs AC-DC-AC power conversion is provided to connect the in-microgrid system and the main system. Therefore, synchronization of matching the frequency and phase of the in-microgrid system with the main system is not required during system connection. However, in the asynchronous type system connection device of the above Patent Document 2, since an asynchronous system connection device via an AC-DC-AC converter is used to connect the in-microgrid system and the main system, there is a limit to the connectable power capacity, the current that can be energized is limited, and the device has become large-sized. In addition, the protection measures for consumers in the system of an area including power facilities using renewable energy are set according to the magnitude of the short-circuit current supplied from the main system. Therefore, when an AC-DC-AC converter is interposed, the short-circuit current cannot be sufficiently supplied, and there has been a problem that the protection circuit does not operate even when a short-circuit accident occurs in the consumer's home.

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

[0011] According to the method for controlling the amplitude and phase of the inverter in the above-mentioned Patent Document 4, it is possible to adopt an appropriate droop technique in which the desired active and reactive currents are determined as functions of the voltage and frequency of the system in the microgrid, such as phase shift virtual voltage - virtual impedance droop. However, it is a patent regarding the control method of the inverter connected to the system. The content of making the microgrid independent and operating synchronously by the proposed control method of the inverter is not included, and the method for synchronously connecting to the main system is not mentioned either.

[0012] Therefore, an object of the present invention is to synchronize one or more power conversion devices in a power distribution system (hereinafter referred to as "cell grid" or "cell grid system") in which at least one location is separated by a switch that can separate the main system, so that the cell grid can be independently operated. System-forming power conversion device, system-forming power system, system-forming power conversion method, and program It is to provide the above.

Means for Solving the Problems

[0013] The above object of the present invention can be achieved by the following configuration. That is, in the first aspect of the present invention The system-forming power conversion device Connected to the main system via a switch that can be connected or separated, and one or more are connected in the cell grid system, When a plurality of them are connected in a cell grid system Power conversion is performed so as to be synchronously linked to each other System-forming power conversion device and A voltage detection unit that detects the voltage and phase of the main system using a PLL, and a voltage control unit that controls the output voltage and phase of the system-forming power conversion device to be generated independently of the main system voltage based on the voltage and phase detected by the voltage detection unit, wherein the voltage control unit controls the output voltage and phase of the system-forming power conversion device so that the current flowing between the system-forming power conversion device and the main system satisfies a predetermined relationship, and the predetermined relationship is such that the relationship between the current flowing between the system-forming power conversion device and the main system and the voltage difference between the output voltage of the system-forming power conversion device and the main system voltage matches a predetermined system connection impedance.

Effects of the Invention

[0024] Connected to the main system via a switch that can be connected or separated in the first aspect of the present invention, and one or more are connected in the cell grid system, When a plurality of them are connected in a cell grid system Power conversion is performed so as to be synchronously linked to each other System-forming power conversion device and A voltage detection unit that detects the voltage and phase of the main system using a PLL, and a voltage control unit that controls the output voltage and phase of the system-forming power conversion device to be generated independently of the main system voltage based on the voltage and phase detected by the voltage detection unit, wherein the voltage control unit controls the output voltage and phase of the system-forming power conversion device so that the current flowing between the system-forming power conversion device and the main system satisfies a predetermined relationship, and the predetermined relationship is such that the relationship between the current flowing between the system-forming power conversion device and the main system and the voltage difference between the output voltage of the system-forming power conversion device and the main system voltage matches a predetermined system connection impedance. By doing so, it is possible to synchronize each power conversion device and make the cell grid independently operable System-forming power conversion device, system-forming power system, system-forming power conversion method, and program which can be provided.

Brief Description of the Drawings

[0039]

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Embodiments for Carrying Out the Invention

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

[0041] [Embodiment 1] A collaborative autonomous distributed system connection system according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 4C. FIG. 1 is a block diagram of the collaborative autonomous distributed system connection system according to Embodiment 1 of the present invention.

[0042] [Overall Configuration of Collaborative Autonomous Distributed System Connection System] The electric power generated at the power plant 10 is stepped up to an extra-high voltage by the extra-high voltage substation 11, and then, via the power transmission facility 12, the power further stepped down at the substation 13 is supplied to the distribution facility 15 (hereinafter referred to as the "main system") which is the main grid. 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 600V AC and 7,000V or less), and may be, for example, extra-high voltage (more than 7,000V AC), or conversely, low voltage (600V AC or less).

[0043] In a distribution system (hereinafter referred to as a "cell grid") in which at least one location is separated by a circuit breaker 21 with a synchronization verification function capable of separating the main distribution system (hereinafter referred to as the "main system"), the cell grid 20 includes a circuit breaker 21 with a synchronization verification function, a cell grid system 28 connected to the main system 15 via the circuit breaker 21 with a synchronization verification function, one or more collaborative autonomous distributed devices 40 having a power conversion function (hereinafter sometimes referred to as a Digital Grid Router, "DGR") connected to the cell grid system 28, and various power facilities connected to the cell grid system 28. Note that the cell grid 20 may be, for example, on the scale of a housing complex, one city block, or a power network on the scale of a complex or industrial park. It means a power network that can consume locally the power of distributed power sources such as on-site natural energy power generation facilities within the area without relying on the power of large-scale nuclear power plants or thermal power plants outside the area. In Japan, it may be expressed as a "microgrid", but in the specification, it may also be referred to as a "mini grid" as an English expression. These are used synonymously with the cell grid 20. Also, the system connection controller 30 may be omitted and referred to as "MGC" (Mini Grid Controller).

[0044] When considering a housing complex as a single cell grid 20, its size can be, for example, in Japan, housing complexes with an area of 100 ha or more account for 52% ( "Actual Conditions of Housing Complexes", Ministry of Land, Infrastructure, Transport and Tourism, Housing Bureau, December 2018), and the scale of a single cell grid 20 can be 100 ha or more. For housing complexes of any scale, it is applicable by increasing or decreasing the number of DGR40.

[0045] To DGR40, as power generation equipment 23, for example, a wind power generation device 23a, a solar power generation device 23b, a fuel cell device, a hydrogen power generation device, a biomass power generation device, an internal combustion engine power generation device (for example, diesel or gas engine, etc.) 23d, a gas turbine power generation device, a geothermal power generation device, a hydroelectric power generation device (for example, about 200 kW), etc., various distributed power sources can be connected. Also, to DGR40, it is possible to connect power equipment such as energy storage devices 22b, 23c and an electric vehicle charging / discharging device 22c. DGR40 is provided with a power converter, for example, an inverter, and can convert the DC voltage generated by 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 power to each household equipment 22a as power demand equipment 22. The power demand equipment 22 is not particularly limited, and examples include each household equipment 22a, an energy storage device 22b, an electric vehicle charging / discharging device 22c, and an electric vehicle 22d, etc. Note that since the energy storage device 22b, the electric vehicle charging / discharging device 22c, and the electric vehicle 22d can be charged and discharged, they are power demand equipment 22 during charging, and also have the function as power generation equipment 23 during discharging. Although they are illustrated as power demand equipment 22 in FIG. 1, the present embodiment is not limited to this, and they may be connected to the cooperative autonomous distributed device 40 as power generation equipment 23.

[0047] Each power generation facility 23 such as the wind power generation device 23a, the solar power generation device 23b, and the internal combustion engine power generation device 23d, and the power storage facility 23c are connected to the cell grid system 28 via the DGR40. As will be described later, each DGR40 performs synchronization control of the cell grid system 28 based on, for example, the main system frequency measurement value f and the phase synchronization signal Ncyc_ref_Sync sent from the MGC30, which are provided on the cloud, so as to be synchronized with the frequency and phase of the main system 15. Also, 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 power flow, or reverse power flow, of active and reactive power respectively. That is, when the cell grid system 28 receives power from the main system 15, that is, when the cell grid system receives a power flow, the power flow from the main system to the cell grid system can be increased by decreasing the inter-system phase difference φglobal. Conversely, for example, when surplus power 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, that is, when there is a reverse power flow, the amount of power transmitted to the main system 15 can be increased by increasing the inter-system phase difference φglobal and advancing the phase angle of the cell grid system 28.

[0048] The breaker with a synchronization verification 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 breaker with a synchronization verification 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 the breaker with a synchronization verification function 21 can be closed only when both systems are synchronized. That is, the synchronization verification can also be performed by the PLL.

[0049] The breaker 21 with a synchronous verification function can detect the main system frequency f and the main system rotational phase angle θref. Further, the breaker 21 with a synchronous verification function is 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 rotational phase angle θref, and the phase difference between the main system 15 and the cell grid system 28 detected by the breaker 21 with a synchronous verification function are sent to the DGR40 and used for phase synchronous control. Thus, in the breaker (21) with a synchronous verification function, it is also possible to share a part of the system connection controller (30) by acquiring system voltage information and cell grid voltage information and performing calculations.

[0050] Here, an example in which the main system frequency f, the main system rotational phase angle θref, and a PLL are provided in the breaker 21 with a synchronous verification function has been described, but the present embodiment is not limited to this, and the detectors for the main system frequency f and the main system rotational phase angle θref may be provided separately from the breaker 21 with a synchronous verification function. Also, the PLL may be configured to be provided separately from the breaker 21 with a synchronous verification function.

[0051] Since a plurality of DGR40s are distributed and arranged in the cell grid system 28, the coverage range of one DGR40 can be subdivided, so there is no need to centrally arrange large-scale system connection equipment in the cell grid system 28. Therefore, there are advantages such as a shorter distribution line and a thinner wire diameter. The coverage range of one DGR40 is not particularly limited, but for example, it can be set as a unit of about ten houses. In this case, although not particularly limited, the DC input of the DGR40 can be, for example, 750V, 40kW, the AC output can be, for example, 380V, three-phase, 40kW, and the built-in battery capacity of 20kWh can be 1 to 4 units. Further, in the case of a smaller size, for example, the DC input can be 350V, 20kW, the AC output can be, for example, 200V, three-phase, 20kW, and the built-in battery capacity of 20kWh can be 1 to 4 units.

[0052] When the main system and the cell grid system are not connected, the system of this embodiment synchronizes the frequency and phase of the cell grid by transmitting the frequency and phase on the main system side to all DGR40s in the cell grid by the method described later. When they are connected, the power flow between the two systems is controlled. Furthermore, when the main system experiences a short-term voltage drop while connected, synchronization is maintained continuously (Fault Ride Through: FRT). When the main system experiences a power outage, it disconnects and enables the cell grid to perform a black start. The magnitude of the voltage is information that is closely related to reactive power, and this is also transmitted to all DGR40s in the cell grid in the same way. Since this transmission method is an existing technology, details are not described. By these means, during constant voltage operation, the power flow and reverse power flow of the power generation facilities 23 connected to the cell grid system 28, such as renewable energy power generation facilities, are controlled. The power generated by the power generation facilities 23 in the cell grid system 28 is consumed locally, and autonomous operation can be performed during a power outage of the main system 15.

[0053] The MGC30 comprehensively controls each DGR40 in the cell grid 20 and performs control such as the total power demand of the cell grid 20, the power generation amount of the power generation facilities 23, the associated control of phase and frequency, accident control, system power outage and restoration control, and demand schedule control.

[0054] Synchronization control is performed for each DGR40 based on accurate time information, such as time information by GPS using the artificial satellite 17. Also, information such as the main system frequency f, the phase synchronization signal Ncyc_ref_Sync, and the inter-system phase difference φglobal is transmitted from the MGC30 to each DGR40 as main system synchronization information.

[0055] [Equivalent Circuit of DGR40 in Cell Grid] Figures 2A to 2F are the principle diagrams of the cooperative autonomous distributed system connection system according to Embodiment 1 of the present invention. Figure 2A is a circuit diagram of one cooperative autonomous distributed device 40, which is an equivalent circuit when one DGR40 in the cell grid system 28 is taken out. As shown in Figure 2A, all DGR40s operate as an AC voltage source Vdgr_i having an output impedance. i is a subscript representing the number of DGR40s. Each DGR40 is connected in parallel to the cell grid voltage Vgrid via a system connection resistance RG and an inductance LG, and a current Idgr_i flows out from each DGR40. Since the cell grid voltage Vgrid is common to all DGR40s, each DGR40 can control Idgr_i by changing the internal voltage Vdgr_i. In the normal state, Idgr_i is controlled to be equal for all i to equalize the load sharing of each DGR40. However, depending on the state of the DGR40, there may be cases where the load sharing is changed or Idgr_i is controlled in the inflow direction into the DGR40 to charge the internal battery. These can be controlled depending on how the target value of Vdg_i is set.

[0056] [Vdgr Voltage Control by Current Hysteresis Control] Figure 2B is a detailed circuit diagram of Figure 2A, showing the half-bridge inverter which is a component of the DGR40. Figure 2C is an operation explanatory diagram of Figure 2B, showing the state where IL repeatedly increases and decreases as the upper and lower switches of the half-bridge are alternately turned on. For the target current value Iref, an upper and lower bandwidth is set. 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, and this operation is repeated continuously. This is called current hysteresis control. The details of the hysteresis control will be described in Embodiment 3 below.

[0057] Generally, in hysteresis control, the problem is that the switching period fluctuates, which makes it difficult to design filters and the like. In the present invention, a variable bandwidth method is devised to solve this problem. The lines above and below the target current value Iref in Fig. 2C are bands. If the width of the band is narrowed, the switching period becomes faster, and if it is widened, the switching period becomes slower. Since the reactor current IL of the half-bridge changes in slope due to the difference between Vdc and Vdgr, an operation is added to change the bandwidth according to the difference so that the switching frequency becomes almost constant. Thereby, open-loop control is performed to control the target current value Iref to be equal to Idgr and correct the filter voltage of the half-bridge to be equal to the target Vdgr. Although the control target is current, as a result, high-speed voltage control is enabled. Hereinafter, the description will proceed on the premise that Vdgr is directly controlled by this method.

[0058] Fig. 2D is a circuit diagram of the cooperative autonomous distributed system connection system according to Embodiment 1 of the present invention, showing a state in which N DGR40s represented in Fig. 2A are connected in parallel to the cell grid. The cell grid voltage Vgrid is common, and each DGR40 is connected with a different voltage Vdgr_i through different output impedances ZG_i (i = 1 to N), and currents of Idgr_i are respectively made to flow in. Such parallel connection operation of a plurality of voltage sources requires a synchronization force because a cross current flows between the voltage sources unless voltage synchronization can be achieved with high precision. In the present invention, a means of using a standard time signal as the synchronization signal is adopted. In this embodiment, furthermore, the virtual impedance technique described below is used to virtually equalize ZG_i, equalize Vdgr_i and Idgr_i, and equalize the load sharing. Also, by controlling Vdgr, it is possible to change Idgr and change the load sharing for each DGR40.

[0059] The physical output impedance of the DGR40 varies depending on its installation location, the influence of the outlet transformer, the distance of the distribution line, and the wire thickness. Since these values are not known, it is difficult to equalize the load sharing ratio among multiple DGR40s even by operating the internal voltage Vdgr of the DGR40. As one way to solve this, introducing a virtual impedance that increases the ratio of the known impedance is effective. By defining a virtual impedance including the physical impedance, making its value equal for each DGR40, and taking it into account in the control of Vdgr, it becomes easier to equalize the load sharing ratio.

[0060] Specifically, it is realized by subtracting the voltage drop due to the virtual impedance (=(virtual reactor - physical reactor) × time derivative value of Idgr) from the control target value of Vdgr and performing control. 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. Therefore, it is important to accurately grasp the physical impedance for each installation location of the DGR40 and incorporate it as a control constant.

[0061] To synchronize the frequencies and phases of all DGR40s in the cell grid, the following two synchronization methods are adopted. They are (A) a synchronization method using a GPS time signal and (B) a voltage-based synchronization method. These two methods can complement each other, and it is possible to use them in combination or individually. As a means of obtaining the standard time signal, all DGR40s are equipped with GPS receivers, but it is not limited to GPS as long as the accuracy of the standard time signal can be obtained. When the GPS signal is interrupted, all DGR40s can be operated in synchronization without the standard time signal by the (B) voltage-based synchronization method. Both use a well-known method called Phase Lock Looop (PLL) to detect the frequency and phase from the voltage vector. The following details the two synchronization methods. Regarding the reactive power, voltage correction information is transmitted to all DGR40s via the MGC30, enabling the adjustment of the reactive power by the PI control of the prior art. First, the synchronization method using the (A) GPS time signal will be described.

[0062] [Explanation of the synchronization method using the GPS time signal] Figure 2E illustrates the correlation between the current Idgr of one DGR40 in the GPS time synchronization control, the internal voltage phase Vdgr of DGR40, and the voltage phase Vgrid of the cell grid. Note that the notation of "*" appended to the right shoulder like Vgrid* represents the target value. In the figure, the state where the target and the actual value match is shown. In the following explanations, the actual value is used for representation. Since Vgrid is based on the GPS time signal, all DGR40s are synchronized. Vgrid rotates at the frequency speed based on the global angle reference θref calculated from the GPS time reference. In Figure 2E, this is represented by fixing it as the D-axis (Daxis). Idgr becomes a current delayed by the phase angle φ based on the load in the cell grid and the grid impedance. When Idgr is decomposed into the DQ axes, it becomes ID and IQ. ID is in phase with Vgrid, and IQ is a component delayed by 90°.

[0063] Voltage drops occur in the DQ axes due to Idgr and the virtual impedance including the aforementioned physical impedance. The voltage drop in the D-axis component is ID×RG + IQ×XG, and the voltage drop in the Q-axis component is ID×XG - IQ×RG. In Figures 2E and 2F, the multiplication symbol "×" is represented by ".". Since these voltage drops in the D-axis and Q-axis components correspond to the voltage drop between Vdgr and Vgrid, Vdgr is obtained to compensate for this voltage drop. Let the phase angle between the internal voltage Vdgr and the cell grid system voltage Vgrid generated at this time be δ. Since Vgrid is synchronized in all DGR40s, although there is a phase difference, Vdgr also rotates synchronously. Therefore, by adjusting the phase angle δ, the output sharing of each DGR40 can be changed, or a negative output, that is, it can function as a load, can be used to charge the built-in battery.

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

[0065] However, when the cell grid is separated from the main power system and operates independently, since there is no power adjustment by the main power system, the total output of all DGR40s and the total demand in the cell grid must exactly match. Since the DGR40 does not have demand information, as a result of controlling to match the actual Vdgr with the target internal voltage Vdgr* of the DGR40, an actual current Idgr corresponding to the actual demand flows as shown in Fig. 2F. With this actual Vgrid and actual Idgr, the active and reactive power components of the demand are supplied without shortage or excess. As a result, there is a deviation between the actual current Idgr and the target current value Idgr*. The actual voltage Vgrid also deviates from the target Vgrid*. Let the phase difference between this actual cell grid voltage Vgrid and the target cell grid voltage Vgird* be Δδ. Since the Daxis* axis is synchronized with the frequency of the main power system, to shift the cell grid from independent operation to grid-connected operation, this Δδ can be made close to zero to synchronize with the main power system. Therefore, this is achieved by using a signal called φglobal described later.

[0066] To synchronize all DGR40s, it is necessary to apply an accurate standard time. When a synchronization error occurs, it creates a voltage difference between DGR40s. Due to the impedance between DGR40s, a voltage drop of 10% - 20% occurs. Therefore, even if the allowable voltage error is set at 1%, the control error of the current will be approximately ±10% - ±5%. Thus, it is desirable to minimize the voltage error as much as possible. A voltage error of 1% corresponds to 0.0015 radians in phase angle. In terms of time, this corresponds to an accuracy of 5 μsec. Although there are crystal oscillators with an accuracy of about ±10 μsec, the error between DGR40s will increase without common correction. A relatively inexpensive common time signal that can ensure this accuracy is the GPS time signal. Radio-controlled clocks and network time protocols have insufficient accuracy. Although expensive, atomic clocks are also an option.

[0067] In this embodiment, examples of the standard time signal acquisition device include a GPS clock, an atomic clock, a device that precisely corrects time according to the arrangement of individual cooperative autonomous distributed devices (DGR40), or a device that measures the zero crossing of an AC voltage and its time, transmits the information to individual cooperative autonomous distributed devices (DGR40), and corrects the internal clock by matching the zero crossing time of individual cooperative autonomous distributed devices (DGR40). Regarding the method of measuring a specific zero crossing of an AC voltage and its time to correct the internal clock of individual cooperative autonomous distributed devices (DGR40), for example, a system connection controller (MGC30) acquires a standard time signal from a GPS clock, an atomic clock, etc., accurately grasps a specific zero crossing of an AC voltage and its time, transmits the specific zero crossing and its standard time signal to individual cooperative autonomous distributed devices (DGR40), and in individual cooperative autonomous distributed devices (DGR40), the internal clock can be corrected 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 description has been made assuming that the system connection controller (MGC30) acquires the standard time signal and accurately grasps a specific zero crossing of the AC voltage and its time. However, this embodiment is not limited to this, and a standard time signal acquisition device provided separately from the system connection controller (MGC30) can be used to accurately grasp a specific zero crossing of the AC voltage and its time, and transmit the information to the system connection controller (MGC30) and individual cooperative autonomous distributed devices (DGR40), thereby correcting the internal clocks of the system connection controller (MGC30) and each cooperative autonomous distributed device (DGR40).

[0068] [(A) Block diagram of synchronization control] Figure 3A is a block diagram of the synchronization control of GPS synchronization according to Embodiment 1 of the present invention. Referring to Figure 3A, a synchronization control method based on a GPS time signal will be described. This method is characterized in that each DGR40 can create a phase angle signal θref synchronized with the main system within ±5 μsec by receiving two signals of a phase synchronization signal Ncyc_ref_Sync obtained by applying a main system frequency signal f and a GPS time signal via an MGC30 and combining them with the GPS time signal inside the DGR40. Details are shown below.

[0069] In the arithmetic block of Figure 3A, the arithmetic operation in the system connection controller (MGC) 30 is performed as follows. The main system frequency f is measured by the main system frequency measuring device 31, and in the first time acquisition unit, the GPS time t32 is obtained as the first time information (t). By multiplying these two and applying a "function for extracting the fractional part" shown below, such as the floor function, to the result obtained by subtracting from the main system rotation phase angle θref34 which is sawtooth-shaped for each cycle, the phase synchronization signal Ncyc_ref_Sync39 (corresponding to Δδ) can be calculated. The two signals of the main system frequency signal f and the phase synchronization signal Ncyc_ref_Sync are transmitted from the MGC30 to each DGR40. The transmission means may be a server method or a broadcast method. Also, although the above arithmetic unit is a function inside the MGC30, physically it is built into the breaker 21 with a synchronization test function and calculated, and may be transmitted to each DGR40 via the cloud using a mobile line or power line carrier.

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

[0071] Also, in the arithmetic block of FIG. 3A, the arithmetic operation in the cooperative autonomous distributed device (DGR) 40 is performed as follows. First, in the DGR 40, the main system frequency measurement value acquisition unit 41 in the system connection controller (MGC) 30 receives the main system frequency f acquired from the breaker 21 with a synchronization test function. Also, the second time information (t') is acquired as the GPS time t'42 from the second time acquisition unit. In addition, for each DGR 40, Ncyc_shift_local44 is prepared in case a unique adjustment value according to the location of the DGR 40 is required. Further, the DGR 40 receives Ncyc_ref_Sync39 calculated by the MGC 30 and sets it as Ncyc_ref_Sync45 inside the DGR 40.

[0072] Next, the main system frequency measurement value f41 and the GPS time t'42 are multiplied by the multiplier 43, and f·t' is obtained as a graph with a continuously increasing characteristic. An operation 50 is performed in which the output of the floor function 51 is subtracted from the sum of Ncyc_shift_local44 and Ncyc_ref_Sync45 added by the adder 46 and the adder 47 to this f·t', and Ncyc_ref_bas is obtained as a saw-tooth-shaped graph. The operation 50 by this floor function is not limited to this, and for example, as described above, it can be replaced with a function that extracts other fractional parts.

[0073] In the DGR 40, after the operation 50 by the frac function, a subtractor 53 for feeding back and subtracting Ncyc_ref is provided. Further, in the adder 54, after adding a value of 0.5, an operation 55 by the frac function is performed. In FIG. 3A, the operation 55 by this frac function subtracts the output of the floor function 56 by the subtractor 57, but the present embodiment is not limited to this, and for example, as described above, it can be replaced with a function that extracts the fractional part. Then, an operation of adding a value of -0.5 is performed by the adder 58, and further, by the multiplier 59, f = 2πf0·10 3 (1) Perform the operation of and calculate f + Δf. After passing f through the limiter 60 with f - α and f + α, Ncyc_ref is demodulated by the operation of the integrator 61. Through these operations, the phase of the system phase angle θref34 of the main system 15 and the output system phase angle θref62 of each DGR40 are synchronized, and the frequencies also match.

[0074] The input signal of 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). By providing the limiter 60 for the rate of change part, it becomes a factor that determines the speed and magnitude of the phase tracking of the cell grid. That is, if the width of the limiter 60 is widened, it will quickly follow the phase change of the main system but the phase fluctuation will be slightly larger. If the width of the limiter 60 is narrowed, it will take more time to follow the phase change of the main system, but the phase fluctuation will be smaller.

[0075] In this way, there is a transmission delay in the frequency and phase tracking by the MGC30, and the fact that it can be restricted by the limiter 60 has the effect of suppressing the rate of change of frequency (ROCOF) within a certain range. Instead of the secondary transfer function that simulates the synchronizer of a general grid-forming inverter, it becomes a primary transfer function, so it is a very stable mechanism. Note that the main system rotation phase angle θref is originally a signal of 0 - 2π, but here it is treated as a sawtooth signal between 0 - 1 after dividing by 2π.

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

[0077] [(A) Explanation of system connection, independent operation, and main system power outage state] Next, referring to FIGS. 3B, 3C, and 3D, the following three states will be described. · Main system connection state: Fig. 3B is a control block diagram of the main system connection state of GPS synchronization according to Embodiment 1 of the present invention. · Cell grid independent state: Fig. 3C is a control block diagram of the cell grid system independent state (synchronization control) of GPS synchronization according to Embodiment 1 of the present invention. · Main system power outage · Cell grid independent operation state: Fig. 3D is a control block diagram of the cell grid system independent state (during main system power outage) of GPS synchronization according to Embodiment 1 of the present invention.

[0078] [(A) Main system connection state] In Fig. 3B, the breaker 21 with a synchronization verification function is closed, and the main system 15 and the cell grid system 28 are synchronously linked. 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 MGC30, and the inter-system phase difference signal φglobal is calculated. In the system linked state, φglobal controls the active power and reactive power flow between the two systems. Note that φglobal can transmit different values for each DGR40 without changing the total, and can also produce different outputs.

[0079] The GPS time information tref as the first time information (t) is input to the MGC30 from the GPS receiver 91 as the first time acquisition unit. On the other hand, the tref as the second time information (t') is input to the DGR40a from the GPS receiver 92 as the second time acquisition unit.

[0080] In MGC30, the phase synchronization signal (Ncyc_ref_Sync) is calculated, and two pieces of information, the main system frequency and Fgrid_ref, are transmitted and input to the DGR (GPS-based phase calculation block) 40a. Although these two pieces of information are sufficient for synchronization control, the φglobal signal is also transmitted for power flow control. In DGR40a, the cell grid system rotation phase angle θref of DGR40 is calculated. In the adder 93, θref and φglobal are added to calculate θref_adj. Based on θref_adj, DGR40b is operated, and the output current Idgr of each DGR40 is output. The output currents of each DGR40 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 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 MGC30 to form a stable feedback loop.

[0081] [(A) Cell grid independent state (during main system operation)] In Fig. 3C, the method of phase synchronization between the two systems when the circuit breaker 21 with a synchronization test function is opened and the main system 15 and the cell grid system 28 are disconnected, and the cell grid is in an independent operation state, is explained. When the two systems are disconnected, the main system voltage Vgrid_main is generally different from the cell grid system voltage Vgrid_mini. However, in this GPS time synchronization method, through the transmission of the main system frequency f31 and the phase synchronization signal Ncyc_ref_Sync39 and the calculations in Fig. 3A, the θref of the two systems is always synchronized. During independent operation, the inter-system phase difference signal φglobal can be used for fine adjustment. In this way, since the voltage phase of the cell grid system 28 is synchronized with the voltage phase of the main system 15, it is always possible to connect the cell grid system 28 to the main system 15 by closing the circuit breaker 21 with a synchronization test function.

[0082] [(A) Cell grid independent state (during main system power outage)] Figure 3D explains how to synchronize the DGR40 within the cell grid in the GPS synchronization main system power failure and cell grid system independent state (during main system power failure) of Embodiment 1. When the main system stops, the circuit breaker with synchronization test opens, and the information from the MGC30 is lost. On the other hand, in the DGR40a, tref as the second time information (t') is continuously input from the GPS receiver 92 as the second time acquisition unit.

[0083] Therefore, in the DGR40, if the main system frequency measurement value Fgrid_ref is replaced with the previous value or a predetermined fixed value (such as 50 Hz, etc.), and the phase synchronization signal Ncyc_ref_Sync is also replaced with the previous value or a predetermined fixed value (such as 0, etc.), all DGR40s can obtain θref synchronized with the GPS time as a common index. Also, for the inter-system phase difference signal φglobal, since it is optional, by setting it to a predetermined fixed value (such as 0, etc.), θref_adj is also synchronized. Therefore, even during a main system power failure, the cell grid can operate independently with all DGR40s synchronized. When the main system resumes, resume the GPS time synchronization operation, and when synchronization is achieved, close the circuit breaker with synchronization test to shift to the system connection operation, or continue the cell grid independent operation as it is.

[0084] Despite the power failure of the main system (15), the circuit breaker (21) with a synchronization test function does not open, and the system connection controller (MGC30) has a system connection protection function including single operation detection so that the cell grid cannot continue independent operation. During active single operation detection, the output of the reactive power of each cooperative autonomous distributed device (DGR40) can be adjusted to operate the protection function and open the circuit breaker (21) with a synchronization test function. Also, during a short-term main system power failure, the circuit breaker (21) with a synchronization test function is also equipped with an FRT function to maintain the closed state.

[0085] [(A) Black start operation of the cell grid] When the main system experiences a power outage during system connection, the time from detecting the power outage of the main system to opening the breaker 21 with a synchronization test function, for example, when using a high-voltage vacuum circuit breaker (VCB), is about 3 cycles to 5 cycles at rated conditions, that is, there is a delay of about 0.06 seconds to 0.1 seconds. Also, when the main system experiences a power outage during system connection, it is conceivable that the cell grid system voltage will decrease together with the decrease in the main system voltage and become 0V. Returning to independent operation from here is what is called a black start.

[0086] In this case, if it is determined in advance whether to maintain the previous value of the main system frequency measurement value f41 or replace it with the rated value, and whether to maintain the previous value of the phase synchronization signal Ncyc_ref_Sync45 or replace it with a fixed value prepared in advance, even when the voltage becomes zero, after disconnecting the main system while maintaining synchronization inside all DGR40s, a black start can be performed and the cell grid can shift to independent operation. This is because all DGR40s have the GPS time t'42 (Fig. 3A), that is, tref92 (Fig. 3D), and perform calculations based on it.

[0087] [(A) Time synchronization error] When the main system and the cell grid are in a disconnected state and there is no change in the main system frequency f31 and the phase synchronization signal Ncyc_ref_Sync and they are constant, in this way, the θref (= 2π·Ncyc_ref) obtained by each DGR40 is synchronized with the θref of the main system with an error within 1% of the voltage error (equivalent to within 5 μsec of the time error). In the case of an error of this degree, it can be said that the main system and the cell grid are synchronized, so even if the breaker 21 with a synchronization test function is turned on to connect the two systems, no abnormal current will flow between the two systems.

[0088] [(A) Influence of transmission time] When the main system and the cell grid are disconnected and the frequency or phase in the main system changes, there are time delays such as the transmission delay time from MGC30 to DGR40 that conveys the change to DGR40 and the calculation times in MGC30 and DGR40. Therefore, the synchronization with the main system is temporarily disrupted. Even when attempting to connect the two systems by turning on the breaker with a synchronization test function in this state, the synchronization test function may operate and prevent the breaker from being turned on. However, once the transmission delay time has elapsed, the voltage phase of the cell grid synchronizes with the main system and the breaker is turned on. This transmission delay time is on the order of the delay in network communication and is usually within about 0.1 to 1 second depending on the communication environment.

[0089] [(A) Inertial force and synchronization force] When the main system and the cell grid are connected, since the two systems are physically connected, the frequency f and the rotational phase angle signal θref of the two systems have common values. Here, when a change occurs in the frequency or rotational phase angle of the main system, MGC30 cannot convey the change to each DGR40 during the transmission delay time. Therefore, the follow-up of the frequency and rotational phase angle of each DGR40 is delayed by this delay time. Therefore, from the perspective of the main system side, each DGR40 and the cell grid appear to behave as if they have a strong inertial force as a unit. Furthermore, since they start to follow the main system after this delay time, each DGR40 and the cell grid appear to have a strong synchronization force.

[0090] Also, the frequency fluctuations of the transmitted main system are also limited by the limiter 60 in the controller of the DGR40. If the limit width is narrow, it is difficult to follow the frequency fluctuations of the main system, so it behaves as if the inertial force has increased. If the limit width is wide, it is easy to follow the frequency fluctuations, so it behaves as if the inertial force has become lighter. The same applies even if there are multiple cell grids. In a single system such as an isolated island, even if the scale of the cell grid is small here but it accounts for more than half of the total demand as a whole, by narrowing the limit width of the frequency change rate and making it robust to frequency fluctuations, it is possible to gradually switch the cell grid side to behave like the main system. That is, the cell grid becomes a power system with controllable inertial force.

[0091] Next, among the two synchronization methods for synchronizing the frequencies and phases of all DGR40s in the cell grid, an explanation will be given regarding the "(B) Voltage-based synchronization method".

[0092] [Basic Explanation of the (B) Voltage-based Synchronization Method] The voltage-based synchronization method is a standard method in grid-connected microgrids. This method has been widely implemented, tested, and deployed worldwide. When connected to the main system, the fluctuations on the cell grid side are absorbed by the main system and do not have an adverse impact. However, when the inverter group becomes the center and the cell grid operates independently from the main system, it becomes difficult to maintain the frequency. Also, a simultaneous black start of the cell grid cannot be achieved. Hereinafter, methods for solving these problems will be proposed.

[0093] First, the voltage-based synchronization control method has the following advantages. · The synchronization signal uses the voltage of the distribution line of the cell grid. - No special additional equipment such as GPS signals or receivers is required. - The synchronization signal of voltage is very robust. - The operation can continue as long as there is no fault or damage to the power line. ·The voltage synchronization signal automatically adjusts the following issues. - Voltage changes and phase shifts in the transformer. - Voltage drops and phase shifts due to circuit impedance. ·The DGR40 can be detached without special configuration when connecting to the cell grid. ·The DGR40 is flexible with respect to manual or automatic changes in the cell grid circuit configuration.

[0094] On the other hand, it also has the following demerits. ·Synchronization cannot be achieved during independent operation of the cell grid separated from the main system. - In general frequency droop control, the fluctuations become too large. - The synchronization signal by the proposed MGC30 is required. ·Black start during a cell grid power outage is not possible. - A synchronization signal based on GPS time is required.

[0095] The reason why synchronization cannot be achieved during independent operation of the cell grid separated from the main system will be explained below. When the cell grid is operating independently, the total output of all DGR40s must match the total demand within the cell grid. Therefore, as shown in Figure 2F, the actual current Idgr corresponding to the actual demand flows, resulting in a deviation 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. However, once the balance between the total output and the total demand is disrupted and Δδ becomes positive or negative, |Δδ| will increase.

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

[0097] Conversely, when the DGR40 active power output is smaller than the actual load active power, the actual voltage Vgrid lags in phase behind the target voltage Vgrid*, and Δδ is always negative. The PLL continuously decreases 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 microgrid does not stabilize, nor does the frequency.

[0098] Thus, voltage-based synchronization cannot be used for a cell grid in an independent operating state that does not depend on the grid. This is because there is no robust power source for accepting or providing the actual reactive power difference between DGR40 and the load. Conversely, if there is a robust power source, since the actual voltage Vgrid is stable, even if the target voltage Vgrid* performs control to approach it, it will not fall into a positive feedback loop.

[0099] [(B) Introduction of the inter-system phase difference signal φglobal] Even for a cell grid in an independent operating state that does not depend on the main grid, in order not to fall into such a positive feedback loop, the following method was devised. That is, a method is proposed to stabilize the frequency and phase of the cell grid by transmitting the main grid frequency signal f and the inter-system phase difference signal φglobal to all DGR40s through MGC30. First, as shown in Figure 4B, first, the phase angle signal θref creates φsync through a feedback control Kθctrl85 that reduces the error between the reference angular frequency ωref and the microgrid angular frequency ωgrid. Then, the obtained phase angle signal θpll is added in the adder 86 by the PLL of each DGR40 to create a local system phase angle signal Ncyc_ref89. However, with only this control, the voltage phase of the cell grid undergoes positive feedback as described above and does not stabilize.

[0100] Therefore, as shown in Figure 4B, φglobal80 is further added in the adder 86. φglobal is a signal representing the phase difference between the main grid and the cell grid. Although the main system and the cell grid are disconnected, if the phase of the cell grid is open compared to the phase of the main system, φglobal changes. By adding φglobal, it is possible to suppress the positive feedback loop in which the phase opens, and further suppress the phase and frequency instability of the cell grid. This stabilizes the frequency of the cell grid by using only that information without directly connecting to the main system. As a result, all DGR40s in the cell grid can be synchronized and the frequency can be stabilized even during independent operation without connection to the main system. Also, since both systems are synchronized, the breaker with synchronization test can be switched on at any time to connect the two systems.

[0101] Even when the main system and the cell grid are connected, it is shown using Fig. 4A that φglobal is effective. Since active power flows when the phase difference between the two systems is open, φglobal measures the power flow 17 flowing between the two systems, compares it with the target active and reactive power, creates the necessary phase difference signal φglobal, and transmits it to all DGR40s. As a result, by increasing or decreasing the output of all DGR40s, the power flow between the two systems can be controlled to match the target value.

[0102] Also, when the main system is in a power outage state and the cell grid is operating independently, instead of the voltage phase of the main system, a reference voltage phase based on the internal clock is created, and the phase difference signal with the cell grid voltage phase is transmitted as φglobal to all DGR40s through MGC30, so that the frequency and phase of the cell grid can be synchronized.

[0103] Next, the reason why a standard time signal is required at the time of black start when MGC30 stops and when the cell grid is powered off will be explained. As described above, when the main system and the cell grid are connected, the voltage phase of the main system serves as a reference, and when they are separated, the voltage phase information of the main system can be obtained through MGC30. Also, even when the main system is powered off, the phase based on the clock inside MGC30 can be transmitted as a common reference to all DGR40s through MGC30. However, when MGC30 stops and is in a state separated from the main system, there is no voltage phase information common to all DGR40s. Similarly, when the cell grid stops, there is no voltage phase information common to all DGR40s. In such a case, it is necessary to supply a synchronization signal common to all DGR40s by another means. If DGR40 acquires standard time information, it is possible to create a voltage phase synchronized with all DGR40s by correcting the internal clock based on this information. In this way, a method of stabilizing the frequency and phase of the cell grid using standard time information is proposed for the black start after a cell grid power outage or the independent operation of the cell grid when MGC30 stops.

[0104] [(B) Detailed Explanation of Voltage-Based Synchronization Method] The voltage-based synchronization control method will be described with reference to FIGS. 4A, 4B, and 4C. FIG. 4A is a control block diagram of the main system connection state of voltage synchronization according to Embodiment 1 of the present invention, FIG. 4B is a control block diagram of the cell grid system independent state (synchronization control) of voltage synchronization according to Embodiment 1 of the present invention, and FIG. 4C is a control block diagram of the cell grid system independent state (when the main system is powered off) of voltage synchronization according to Embodiment 1 of the present invention. The block diagrams and their control methods in each state will be described below.

[0105] [(B) Synchronization Method When Connected to the Main System] In the voltage-based synchronization method, when the cell grid is connected to the main system, control is performed so that the difference between the signal based on the frequency of the main system and the signal based on the frequency detected by the PLL of each DGR40 becomes small, and the signal of the phase angle is also detected and taken into account, so that the target voltage Vgrid* and the actual voltage Vgrid are substantially the same. This state is represented in FIG. 2E and is the same as the state when synchronized with GPS and time.

[0106] [(B) Explanation Based on the Block Diagram When Connected to the Main System] Referring to FIG. 4A, a block diagram for calculating Ncyc_ref89 in the cooperative autonomous distributed device (DGR) 40A when the cell grid system is connected to the main system will be described. FIG. 4A is a block diagram of voltage-based synchronization control according to Embodiment 1 of the present invention and serves as a control diagram for the system connection state. It includes an inter-system connection controller (MGC) 30A and a cooperative autonomous distributed device (DGR) 40A. In the inter-system connection controller (MGC) 30A, an inter-system phase difference signal φglobal is generated from the main system active power Pgrid_main and the main system reactive power Qgrid_main measured by the main system active power Pgrid_main measurement unit 98 and the main system reactive power Qgrid_main measurement unit 99 in the inter-system phase difference signal φglobal calculation unit 80, taking into account the power flow between the main system 15 and the cell grid system 28.

[0107] First, the main system frequency meter 31 will be described. The main system voltage acquisition unit 97 acquires the main system voltage Vgrid_main. In the connection state with the main system, since the main system voltage and the cell grid voltage are the same, Vgrid_main = Vgrid_mini.

[0108] The PLL96 calculates the main system frequency measurement value f31 from the main system voltage Vgrid_main and transmits a signal to the DGR40 via the MGC30. The inter-system phase difference signal φglobal80 calculation unit calculates the inter-system phase difference signal φglobal based on the difference between the measured main system active power Pgrid_main and reactive power Qgrid_main flowing between the main system and the cell grid, and their respective target values (not shown in the figure), and transmits a signal to the DGR40 via the MGC30. Assuming that the direction in which the power flow is directed towards the cell grid side is positive, when the inter-system phase difference signal φglobal is increased, the phase angle of the cell grid system lags behind that of the main system, so the power flow from the main system to the cell grid system increases. Also, when the inter-system phase difference signal φglobal is decreased, the phase angle of the cell grid system advances, so the reverse power flow from the cell grid system to the main system increases. In this way, the output of the DGR40 is changed to match the power flow between the two systems to the target value. Regarding reactive power, instead of φglobal80, a voltage correction signal is transmitted to the DGR40 via the MGC30, but the method is the same, and detailed description is omitted.

[0109] The PLL83 of the coordinated autonomous decentralized device (DGR) 40A generates the cell grid system phase angle signal θpll and the 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 meter 31 and calculates the main system angular velocity signal ωref = 2π·f. The PLL83 calculates the cell grid system angular velocity signal ωpll from the cell grid voltage Vgrid_mini. Next, the comparator calculates the inter-system angular velocity error signal ωerr = ωref - ωpll. Next, in the controller kθ_ctrl85, ωerr is input and PI calculation is performed to calculate the control phase signal φsync. 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 to make it less affected by sudden frequency changes and the like.

[0110] In the 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 obtained signal is divided by 2π by a divider, and further, the remainder by the slow calculation using the MOD function is calculated, and only the fractional part is extracted to obtain Ncyc_ref89 which is a sawtooth output. Further, by multiplying Ncyc_ref by 2π, a cell grid system rotation phase angle signal (hereinafter sometimes referred to as "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 fractional part described above.

[0111] In this way, the cell grid system phase angle signal θref = 2π·Ncyc_ref obtained by each cooperative autonomous distributed device (DGR) 40A is synchronized with the main system voltage (= cell grid voltage). In the case of a steady-state stable system, since the PLL frequency is constant, ωref = ωpll, ωerr = 0, and thus φsync = 0. Therefore, θpll created by the PLL of each DGR40 becomes dominant. The inter-system phase angle φglobal is added thereto, and the power flow and reverse power flow between the cell grid system and the main system can be controlled.

[0112] When the system frequency and phase change suddenly, ωref ≠ ωpll and a transmission time delay occurs. However, since the PLL83 looks at the cell grid voltage (= main system voltage) and creates θpll, it immediately follows (about 1 cycle) even in the case of a sudden change. Although the power flow between the main system and the cell grid changes suddenly, a time delay occurs in the transmission of φglobal. Limitations are provided for the rise and fall of φglobal so that sudden changes do not occur. In this way, the synchronization force and inertia force of the cell grid are maintained by the power flow connecting the two systems and the PLL.

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

[0114] φglobal in FIG. 4B has different input contents from φglobal in the case of FIG. 4A. In the case of FIG. 4B, since the two power grids are separated, the purpose is to align the voltage phase of the DGR 40B with the main power grid so that the synchronous test function breaker 21 can be switched on at any time. Therefore, in FIG. 4B, φglobal calculates the voltage phase difference between the two power grids. When both the main power grid and the cell grid are in a steady state and stable during independent operation, by sending a signal of φglobal = 0, the voltage phases of the two power grids are the same, and they are always in a state where they can be connected. When the system frequency and phase change suddenly, ωref ≠ ωpll. However, since the two power grids are separated, the phase angle difference between the main power grid and the cell grid once widens, but after the time of the transmission time delay has elapsed, the voltage phases coincide again, and the connection between the two power grids can always return to a possible state.

[0115] [(B) Adoption of the standard time signal] As described above, the standard time signal is not necessary in the forms of FIGS. 4A and 4B. However, as will be described in detail below, as shown in FIG. 4C, when the MGC 30C stops or during black start, the voltage-based synchronization method cannot be used. This is because even if the target frequency is switched to a fixed value, the common index φglobal regarding the phase is lost. 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 synchronization test is disconnected, the voltage in the cell grid may become zero. The return of the cell grid from zero voltage is what is called a black start. In the present invention, as described above, each DGR40C has a reference voltage vector based on the GPS time inside, and at the time of black start, the DGR40C can be operated with that reference voltage vector as Vgrid* in FIG. 2E, making it possible to perform a black start.

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

[0120] FIGS. 5A to 5N show that the cell grid 20 is connected to both the main system 15a composed of the main systems 15a1 and 15a2 connected to the substation A and the main system 15b composed of the main systems 15b1 and 15b2 connected to the substation B, via the circuit breakers 21a and 21b with synchronization test functions, respectively. The connection of the cell grid 20 connected to the two main systems 15a and 15b in this way is sometimes referred to as a "mid-extracted system".

[0121] Similar to Embodiment 1, a plurality of cooperative autonomous distributed devices (DGRs) 40 are provided in the cell grid 20. Each DGR 40 is controlled by a control signal from the system connection controller (MGC) 30 and can be system-connected to the main system 15a or 15b. The circuit breakers 21a and 21b with synchronization verification functions are also controlled by the control signal from the MGC 30, and the connection and disconnection between the cell grid system 28 and the main systems 15a and 15b are controlled by the control signal from the MGC 30. Note that the MGC 30 physically has a part integrated with the circuit breaker with a synchronization verification function. Two circuit breakers 21a and 21b with synchronization verification functions are provided in the cell grid 20. One circuit breaker 21a with a synchronization verification function is connected to the main system 15a, which is the system of the substation A13a, and the other circuit breaker 21b with a synchronization verification function is connected to the main system 15b, which is the system of the substation B13b.

[0122] In the main system 15a, a power distribution sectionalizer 16a is provided between the circuit breaker 21a with a synchronization verification function and the substation A13a. A main system 15a1 is provided between the circuit breaker 21a with a synchronization verification function and the sectionalizer 16a, and a main system 15a2 is provided between the sectionalizer 16a and the substation A13a.

[0123] In the main system 15b, a power distribution sectionalizer 16b is provided between the circuit breaker 21b with a synchronization verification function and the substation B13b. A main system 15b1 is provided between the circuit breaker 21b with a synchronization verification function and the sectionalizer 16b, and a main system 15b2 is provided between the sectionalizer 16b and the substation B13b.

[0124] [Recovery control from an accident in the main system 15a] Referring to FIGS. 5A to 5K, the state from when an accident occurs in the system 15a2 until the accident is recovered and power supply is restored to the original state will be described. Even when an accident occurs in the system 15a2, the cell grid system 28 is always powered by the power generation equipment 23 in the cell grid 20.

[0125] In the state of FIG. 5A, both the circuit breakers 21a and 21b with synchronization verification functions are open, and the cell grid 20 is operating independently.

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

[0127] In the state of Fig. 5C, an accident, such as a short circuit accident, has occurred in the system 15a2. When it is identified that an accident has occurred in the system 15a2, the sectional disconnector 16a immediately opens as in the state of Fig. 5D.

[0128] In the state of Fig. 5D, since the sectional disconnector 16a is open, no power is supplied to the system 15a1. Even in this case, the circuit breakers 21a and 21b with synchronous testing function are open, and since the cell grid 20 is operating independently, the power supply to the cell grid system 28 is continued by the power generation equipment in the cell grid 20.

[0129] In the state of Fig. 5D, since there is no abnormality in the system 15a1, the MGC30 plans, together with the power supply department of the power company, to control the power of the substation B13b to be supplied to the system 15a1. First, synchronous control of the frequency and phase is performed so that the cell grid system 28 can be synchronously connected to the system 15b1.

[0130] In the state of Fig. 5E, after the cell grid system 28 is synchronized with the system 15b1, the circuit breaker 21b with synchronous testing function is closed, and synchronous connection is made with the system 15b1.

[0131] In the state of Fig. 5F, the cell grid system 28 can be powered by the power of substation B13b through the systems 15b2, 15b1, and the breaker 21b with synchronism checking function by being operated in association with the system 15b1. Thereby, the cell grid system 28 can be charged by the power of substation B13b.

[0132] In the state of Fig. 5G, by closing the breaker 21a with synchronism checking function, the cell grid system 28 is connected to the system 15a1 which is a normal system and has a power outage.

[0133] In the state of Fig. 5H, since the breaker 21a with synchronism checking function is closed and the system 15a1 is powered from substation B13b through the cell grid system 28, the systems 15b2, 15b1, cell grid system 28, and system 15a1 are charged by the power of substation B13b.

[0134] In the state of Fig. 5I, the system 15a2 where an accident occurred has been restored, and power from substation A13a is being supplied to the system 15a2. Here, MGC30 plans to control, in cooperation with the power supply department of the power company, to supply power from substation A13a to the system 15a1 which was being powered from substation B13b through the cell grid system 28 as before.

[0135] In the state of Fig. 5J, the breakers 21a and 21b with synchronism checking function are opened. By opening the breakers 21a and 21b with synchronism checking function, the cell grid 20 operates independently. At this time, the system 15a1 is not powered by any of the substations 13a and 13b.

[0136] In the state of Fig. 5K, by closing the sectionalizer 16a, power from substation A13a is supplied to the system 15a1 through the system 15a2, and the power outage due to the accident that occurred in the system 15a2 is restored.

[0137] [Recovery control at the time of an accident in the cell grid during independent operation] Referring to FIGS. 5L to 5N, the restoration control when an accident occurs in the cell grid 20 during the independent operation of the cell grid 20 will be described.

[0138] In the state of FIG. 5L, the cell grid is in an independent operation state. Each DGR 40 in the cell grid 20 performs synchronization control so as to synchronize with the system 15a1. Suppose an accident occurs in the cell grid 20 at this time. When the cell grid is in independent operation, when an accident such as a short-circuit accident occurs in the cell grid, a large short-circuit current may not be supplied from the power generation facilities in the cell grid to the accident point so as to cut off the protective relay at the accident point. When the protection level of the protective relay is set according to the main system, etc., the protective relay may not operate, and the accident point may not be disconnected. If the accident continues for a certain period of time and the voltage does not return, it will shift to the state of FIG. 5M.

[0139] In the state of FIG. 5M, since the cell grid system 28 and the system 15a1 are synchronized, the breaker 21a with a synchronization detection function can be immediately closed. By closing the breaker 21a with a synchronization detection function, a short-circuit current is supplied from the main system to the accident point in the cell grid. When a short-circuit current equal to or higher than the interruption level is supplied to the accident point, the protective relay at the accident point operates to disconnect the accident point.

[0140] In the state of FIG. 5N, since the accident point in the cell grid 20 is disconnected, the voltage returns. It is possible to continue the system connection operation as it is, or the cell grid 20 can be independently operated by opening the breaker 21a with a synchronization detection function again.

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

[0142] [Embodiment 3] The cooperative autonomous distributed system connection system according to Embodiment 3 of the present invention will be described with reference to FIG. 6. The same reference numerals are used for the configurations common to FIGS. 1-5N, and the description thereof will be omitted. FIG. 6 is a block diagram of the cooperative autonomous distributed system connection system according to Embodiment 3 of the present invention.

[0143] The cooperative autonomous distributed device (DGR) 40 is composed of a common unit 120 and an individual unit 130, and communicates with the system connection controller (MGC) 30 via a mobile circuit. The MGC 30 is provided on the cloud as a cloud for common units. A part of the MGC 30 is built in the control unit of the 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 individual units.

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

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

[0146] Each individual subunit 131 is composed of an ADC (Analog-to-Digital Converter) board 132, a power board 133, an auxiliary power board 134, and an AC or DC filter 135. The ADC board 132 outputs the switching pulse signal transmitted by the 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 the power from the auxiliary power board 134 as the control power supply, outputs a switching pulse according to the switching pulse signal from the ADC board 132, and supplies the switching pulse to the power interface 140 through the AC or DC filter 135.

[0147] The voltage value and current value detected at the power interface 140 are input into the ADC board 132 through the AC or DC filter 135 and the power board 133. In the ADC board 132, the detected voltage value and current value are input as digital signals to the motherboard 123 through the LVDS cable.

[0148] The BMU board 136 communicates with the motherboard 123 via CAN (Controller Area Network). A plurality of, for example, 11 battery units 137 are provided in the individual unit 130. The BMU board 136 and each battery unit 137 are connected by cables.

[0149] The battery unit 137 is composed of a CMU (Cell Management Unit) 138 and battery sub-units 139. The BMU board 136 monitors and controls the states of each battery unit 137 based on command signals from the motherboard 123. The CMU 138 communicates with the BMU board 136 to control and protect the battery sub-units 139. The BMU board 136 controls the entire battery unit and monitors for abnormalities based on information for each CMU 138, and can prevent ignition accidents, for example, in lithium-ion batteries. Note that the BMU board 136 and the battery unit 137 can be provided integrally with the DGR40 or separately.

[0150] In the DGR40, the motherboard 123 of the common unit 120 centrally performs all control operations, and the individual units 130 drive the hardware based on control signals output by the control operations of the motherboard 123.

[0151] The motherboard 123 outputs switching pulses to the ADC board 132 via an LVDS cable, and the ADC board 132 supplies a control signal including the switching pulses of the LVDS cable to the power board 133 via a FLAT cable. The power board 133 uses the auxiliary power board 134 as a control power source and supplies switching pulses to the power interface 140 via an AC or DC filter 135 based on the switching pulses calculated in the motherboard 123. Also, information such as voltage values and current values detected at 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 digital signals at the ADC board 132, collected by the motherboard 123 through communication via the LVDS cable, and used for control operations.

[0152] The motherboard 123 also intensively performs the control operations of the battery unit 137. That is, the BMU board 136 controls, protects, and monitors all battery sub-units 139 via the CMU138 according to the control signals calculated on the motherboard 123.

[0153] In addition, the FPGA and CPU on the motherboard 123 can be freely reprogrammed from the MGC30. Therefore, the DGR40 can be freely configured and changed via the cloud. For example, various settings are possible, such as three-phase settings, single-phase settings, voltage 380V settings, voltage 200V settings, DC settings for solar power, DC settings for batteries, DC settings for fuel cells, etc. Therefore, even with the same hardware, different units can be realized by changing the software via the cloud, and thus the DGR40 can be used not only throughout the country but also around the world.

[0154] The individual unit 130 has no main control device such as a microcomputer, and all control operations are performed by the motherboard 123. The individual unit 130 is driven by the control signals from the motherboard 123. For example, switching pulse signals calculated by the motherboard 123 are supplied to each of the three half-bridges of the three individual sub-units 131, that is, 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 location are acquired as digital data via the LDVS cable, and all control operations of the DGR40 are performed.

[0155] By standardizing the common unit 120 and the board-to-board interface, the individual unit 130 can be provided as various application products. The operation of the system can be realized entirely by the MGC30 in the cloud. Moreover, by updating the software of the motherboard 123 via the cloud using the MGC30, the latest software can always be utilized.

[0156] In addition to information such as power and voltage from the motherboard 123, the DGR controller 122 can also extract information on sunlight, generators, etc. connected to the half-bridge and battery information, send it to the cloud, and use it comprehensively. The information of the DGR40 distributed in a planar manner can also utilize weather information and the like. Also, necessary information can be encrypted and sent to the blockchain ledger, etc., to create a foundation for local currency and the like.

[0157] For the calculation of switching pulses in the motherboard 123, it is desirable to use hysteresis control. Hereinafter, with reference to FIGS. 2B and 2C, hysteresis control will be described. Hysteresis control is current control by a hysteresis current control method, which is different from the generally popular PWM control. In PWM control, when a short-circuit accident occurs during single-cell grid operation, an instantaneous overcurrent flows, so the inverter is stopped for overcurrent protection. In contrast, in hysteresis control, since the current is controlled, the current can be suppressed even when a short-circuit accident occurs.

[0158] The target current Iref for achieving the target voltage Vref is calculated by the following formula (2). JPEG0007708480000001.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. Also, the second term on the right side is the correction current for achieving the target voltage Vref, which corresponds to ΔI = C·dV / dt.

[0159] According to hysteresis control, the current can be directly controlled and Vdgr can be made to follow the target voltage Vref. That is, IL is made to follow the target current Iref by hysteresis control, and further, by controlling Vdgr to be the target voltage Vref, the target power can be obtained in the DGR40.

[0160] In hysteresis control, an upper band Δib and a lower band -Δib are respectively provided above and below the target current Iref. 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, and this operation is repeated.

[0161] In Fig. 2C, at time t0, since IL is below the lower band -Δib, 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, since IL is below the lower band -Δib, 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, as the slope of IL changes according to the voltage difference across Lfilter, the switching frequency fluctuates. Therefore, in order to suppress the fluctuation of the switching frequency, the bandwidths of the upper band Δib and the lower band -Δib are changed according to the following formula (3). JPEG0007708480000002.jpg25170

[0163] When the switching frequency always fluctuates and its band is wide, it is difficult to design the EMC filter. According to the variable bandwidth control, since the switching frequency can be converged to fsw, it becomes easier to design the EMC filter.

[0164] Each of the embodiments described above does not specify the present invention, and can be equally applied to other embodiments included in the claims. Also, each embodiment can be appropriately changed or each embodiment can be appropriately combined.

Explanation of Reference Numerals

[0165] 10 Power plant 11 Extra-high voltage substation 12 Power transmission equipment 13 Substation 15 Main system 16a, 16b Sectional disconnector 17 Artificial satellite 20 Cell grid 21 Circuit breaker with synchronization checking function 22 Power demand equipment 22a Household equipment 22b Energy storage device 22c Electric vehicle charging / discharging device 22d Electric vehicle 23 Power generation equipment 23a Wind power generation device 23b Photovoltaic power generation device 23c Energy storage device 23d Internal combustion engine power generation device 28 Cell grid system 30 System connection controller (MGC) 31 Main system frequency measurement value acquirer 32 GPS receiver 33 Multiplier 34 Main system rotational phase angle 35 Subtractor 36 Arithmetic block 37 floor function 38 Subtractor 39 Phase synchronization signal 40 Cooperative autonomous distributed device (DGR) 41 System frequency measurement value acquisition section 42 GPS receiver 43 Multiplier 44 Adjustment value acquirer 45 Phase synchronization signal 46 Adder 47 Adder 50 Arithmetic block 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 Calculation Unit 81 Multiplier 82 Cell Grid System Voltage Detector 83 PLL 84 Subtractor 85 Controller 86 Adder 87 Multiplier 88 Remainder Operation 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 Cloud for Individual Units 120 Common Unit 121 Common Sub-Unit 122 DGR Controller 123 Motherboard 130 Individual Unit 131 Individual Sub-Unit 132 ADC Board 133 Power Board 134 Auxiliary Power Board 135 DC Filter 136 BMU Board 137 Battery Unit 138 CMU 139 Battery Sub-Unit 140 Power Interface

Claims

1. A system-forming power conversion device that is connected to the main system via a connectable or separable switch, has one or more connections within the cell grid system, and when multiple connections are made within the cell grid system, performs power conversion so as to be synchronously linked to each other, a voltage detection unit that detects the voltage and phase of the main system using a PLL, a voltage control unit that controls the output voltage and phase of the system-forming power conversion device to be generated independently of the main system voltage based on the voltage and phase detected by the voltage detection unit, comprising: the voltage control unit controls the output voltage and phase of the system-forming power conversion device so that the current flowing between the system-forming power conversion device and the main system satisfies a predetermined relationship, the predetermined relationship is that the relationship between the current flowing between the system-forming power conversion device and the main system and the voltage difference between the output voltage of the system-forming power conversion device and the main system voltage is controlled to match a predetermined system linking impedance, and the system-forming power conversion device is characterized by this.

2. The voltage control unit, includes at least one control element of at least inertial force supply for rapid frequency change, frequency droop characteristic control, power damping control, and frequency damping control, and the system-forming power conversion device according to claim 1 is characterized by this.

3. In the system-forming power conversion device according to claim 1 or 2, the voltage control unit controls the current flowing through the filter unit of the system-forming power conversion device in order to form and maintain the output voltage at a predetermined value, by performing this current control by hysteresis control, while forming the output voltage, a variable bandwidth hysteresis control is performed to keep the switching frequency substantially constant by making the bandwidth of the hysteresis control variable, and the system-forming power conversion device is characterized by this.

4. Comprising the system-forming power conversion device according to claim 1, when the switch is in the open state and the cell grid system and the main system are operating independently, a system linking controller is provided that outputs voltage and phase difference information between the cell grid system and the main system to the system-forming power conversion device, and the power system is characterized by this.

5. Comprising the system-forming power conversion device according to claim 1, When the switch is in the closed state, a system connection controller is provided that operates the system-forming power conversion device to perform power flow control between the cell grid system and the main system. A power system characterized by this.

6. The system connection controller uses a cloud server. The power system according to claim 4 or 5, characterized by this.

7. The power system according to claim 4 or 5, characterized by including the case where the cell grid system is sandwiched between a plurality of main systems.

8. During normal operation, it is possible to switch between the coordinated operation of the cell grid system with the switch closed and the main system, and the independent operation of the cell grid system with the switch open, without power interruption. The power system according to claim 4 or 5, characterized by this.

9. When a power outage or accident in the main system or the cell grid system is detected, the cell grid system opens the switch, The power system according to claim 8, characterized in that the cell grid system switches to the independent operation during normal times.

10. When a power outage or accident in the main system or the cell grid system is detected, the cell grid system opens the switch, In the event of an accident within the cell grid system, by closing the switch, an accident current is supplied from the main system to the accident point within the cell grid system, and the accident point is disconnected by the operation of the protective relay at the accident point. The power system according to claim 9, characterized by this.

11. After disconnecting the accident point, the power system according to claim 10, characterized by continuing the coordinated operation with the switch closed.

12. The system-forming power conversion device further includes a time synchronization unit, The power system according to claim 4 or 5, characterized in that the cell grid system can be black-started by the time synchronization unit.

13. The time synchronization unit, The power system according to claim 12, characterized by performing time synchronization using at least one of GPS time information, AC voltage zero-crossing information, and atomic clock information.

14. A system-forming power conversion method using a system-forming power conversion device that is connected to the main system via a connectable or separable switch, one or more are connected within the cell grid system, and when a plurality are connected within the cell grid system, they perform power conversion so as to be synchronously connected to each other. The above system-forming power conversion device is a voltage detection unit that detects the voltage and phase of the main system using a PLL, a voltage control unit that controls the output voltage and phase of the system-forming power conversion device to be generated independently of the main system voltage based on the voltage and phase detected by the voltage detection unit, and includes the voltage control unit controls the output voltage and phase of the system-forming power conversion device so that the current flowing between the system-forming power conversion device and the main system satisfies a predetermined relationship, the predetermined relationship is characterized in that the relationship between the current flowing between the system-forming power conversion device and the main system and the voltage difference between the output voltage of the system-forming power conversion device and the main system voltage is controlled to match a predetermined system connection impedance. A system-forming power conversion method.

15. A program characterized by causing a computer to execute each step of the system-forming power conversion method according to claim 14.

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