Arithmetic unit, power transmission and distribution system, arithmetic method, and program

Abstract

To provide an arithmetic unit, a power transmission and distribution system, an arithmetic method, and a program with which it is possible to calculate power flow without direct measurement of a system impedance.SOLUTION: An arithmetic unit of an aspect of the present invention is an arithmetic unit that operates at least one of the power flow and impedance of a power transmission and distribution system, and comprises measuring units that measure the voltages in a main system and branched systems, branched power, and time, and a summing unit that sums up measurement information from measuring instruments. The arithmetic unit operates the voltage phase difference between the measuring units from information on the time, operates at least one of the power flow and the impedance, and controls power transmission and distribution by using a result of the operation.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a computing device, a power transmission and distribution system, a computing method, and a program. [Background technology]

[0002] In recent years, there has been an increasing demand for local production and consumption of electricity, where electricity generated by power generation facilities using renewable energy is consumed within the region. In such power transmission and distribution systems, it is necessary to understand the power flow in order to control the supply and demand of generated electricity.

[0003] Patent Document 1 discloses a power transmission and distribution system monitoring system that includes a power transmission and distribution line voltage estimation means that performs a power flow calculation based on the impedance of the power transmission and distribution line from a power transmission and distribution substation to a measurement point, the total value of the power amount of consumers at the measurement point, and the power amount and voltage on the secondary side of the power transmission and distribution substation, and estimates the voltage of the power transmission and distribution line.

[0004] Patent Document 2 discloses a phase detection system for detecting the phases of AC voltage and AC current in a power system network, which is composed of one or more slave stations equipped with a phase detection device having a time synchronization means, and a master station equipped with a database that stores system component equipment of the power system and impedance information of the component equipment, and the master station collects phase values ​​measured by the phase detection devices of the slave stations, performs correction calculations for the measured phase values ​​using impedance information of the component equipment that has been stored in advance in the database, and stores the calculated results in an estimated phase value database.

[0005] Patent Document 3 discloses a power system management device that includes input means for inputting signals related to the power system, calculation means for substituting the input signal of the input means into a calculation formula related to the power system and calculating unknowns included in the calculation formula as solutions, determination means for determining whether a solution exists for the calculation formula from the input signal of the input means, and output means for outputting the solution calculated by the calculation means and the determination result of the determination means.In Patent Document 3, the unknowns of the calculation formula are line impedances R and X, and voltage Er at the load point, and R, X, and Er that result in the smallest total difference are calculated as the solution. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-233154 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-247086 [Patent Document 3] Japanese Patent Application Laid-Open No. 2018-570962 Summary of the Invention [Problem to be solved by the invention]

[0007] In the power transmission and distribution system monitoring system of Patent Document 1 and the phase detection system of Patent Document 2, accurate impedance information is required in advance to calculate the power flow, and it is difficult to obtain accurate impedance information.

[0008] In the power system management device of Patent Document 3, in order to calculate the power flow, the solution is calculated to be R, X, and Er that minimizes the total error between impedances R and X and voltage Er at the load point, but this method has problems such as complicated calculations, modeling errors in simultaneous equations, and the influence of characteristic fluctuations.Furthermore, in order to calculate the power flow in conventional power transmission and distribution systems, devices that directly measure the voltage and current of transmission and distribution lines, such as voltage transformers VT and current transformers CT, and their calculation devices are required.

[0009] Therefore, an object of the present invention is to provide a calculation device, a power transmission and distribution system, a calculation method, and a program that can calculate power flow without directly measuring system impedance. [Means for solving the problem]

[0010] The above object of the present invention can be achieved by the following configuration: That is, a calculation device according to a first aspect of the present invention is a calculation device that calculates at least one of a power flow and an impedance in a power transmission and distribution system, and is characterized in that it comprises a measurement unit that measures voltages in a main system and branch systems, branched power, and time, and a compilation unit that compiles measurement information from the measurement devices, and calculates a voltage phase difference of the measurement unit from the time information, calculates at least one of the power flow and the impedance, and controls power transmission and distribution using the calculation results.

[0011] A second aspect of the present invention provides a computing device according to the first aspect, characterized in that the computing device calculates a target power for power generation based on the calculated power flow and impedance.

[0012] A third aspect of the present invention is a calculation device according to the first aspect, characterized in that the calculation device determines a fault location based on the calculated power flow and impedance.

[0013] A fourth aspect of the present invention provides a power transmission and distribution system including the arithmetic device of the first aspect.

[0014] A fifth aspect of the calculation method of the present invention is a calculation method for calculating at least one of the power flow and impedance of a power transmission and distribution system, which uses measuring instruments that measure voltages in a main system and branch systems, branched power, and time, and a calculation unit that calculates measurement information from the measuring instruments, calculates a voltage phase difference based on the time, calculates at least one of the power flow and impedance from information on the voltage at a branch point of the branch system, the power branched at the branch point, and the time, and controls power transmission and distribution using the calculation results.

[0015] A sixth aspect of the present invention provides a program for causing a computer to execute the calculation method of the fifth aspect. [Effects of the Invention]

[0016] According to a first aspect of the present invention, a calculation device can calculate power flows and estimate impedance without directly measuring system impedance. This reduces the cost and time required for monitoring and managing the power system and improves the operational efficiency and stability of the power system. For example, by using a voltage transformer (VT) at a consumer's site and measuring the power received by the consumer using a current transformer (CT) typically installed at the consumer's site, it is not necessary to separately install a voltage transformer (VT) or a current transformer (CT) on the transmission and distribution line to calculate power flows, as in conventional technology. When estimating impedance, for example, the impedance of each part of the real system can be accurately calculated by performing statistical processing after repeated impedance calculations multiple times. An impedance map of the real system can be created from the calculated impedance of each part, and power flow distribution can be mapped using information on the voltage in the main system and branch systems, the branched power, and time. The power flows that can be grasped using this aspect include active power flows, reactive power flows, or both.

[0017] According to the calculation device of the second aspect of the present invention, the available capacity of the power transmission and distribution system can be grasped in real time based on the power flow and impedance. This can be applied to suppression of renewable energy power generation and supply and demand control of power generation, and can calculate the target power of power generation so as to maximize the amount of renewable energy power generation while maintaining system stability.

[0018] According to the third aspect of the present invention, the calculation device can determine the location of a fault based on the calculated power flow and impedance. Furthermore, according to the calculation device of this aspect, by determining the location of the fault, the protection operation is limited to the internal fault, and by identifying only the fault location, the range in which the protection operation is performed is limited to only the fault location, thereby narrowing the scope of the power outage. This enables a new type of protection coordination not available in conventional technology.

[0019] According to the power transmission and distribution system of the fourth aspect of the present invention, it is possible to provide a power transmission and distribution system that achieves the same effects as the arithmetic device of the first aspect.

[0020] According to the calculation method of the fifth aspect of the present invention, it is possible to provide a calculation method that achieves the same effects as the calculation device of the first aspect.

[0021] According to the program of the sixth aspect of the present invention, it is possible to provide a program that executes a calculation method that achieves the same effects as the calculation device of the first aspect. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 2 is a vector diagram illustrating the basic principle of the arithmetic device according to the first embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram of the basic principle of a computing device according to a first embodiment of the present invention. [Figure 3] FIG. 2 is an explanatory diagram of phase detection by the arithmetic unit according to the first embodiment of the present invention. [Figure 4] 3 is a vector diagram of reactive power flow relating to the basic principle of the arithmetic device of embodiment 1 of the present invention. FIG. [Figure 5] 1 is an explanatory diagram of a reactive power flow relating to the basic principle of the arithmetic device according to the first embodiment of the present invention. [Figure 6] FIG. 10 is a vector diagram illustrating the basic principle of the arithmetic device according to the second embodiment of the present invention. [Figure 7] FIG. 10 is an explanatory diagram of the basic principle of a computing device according to a second embodiment of the present invention. [Figure 8] 10 is a modified example of a vector diagram illustrating the basic principle of the arithmetic device according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, a computing device, a power transmission and distribution system, a computing method, and a program according to embodiments of the present invention will be described with reference to the drawings. However, the embodiments shown below are merely examples of a computing device, a power transmission and distribution system, a computing method, and a program for embodying the technical concept of the present invention, and are not intended to limit the present invention to these, and may be equally applicable to other embodiments included in the scope of the claims.

[0024] [Embodiment 1] A calculation device, a power transmission and distribution system, a calculation method, and a program according to a first embodiment of the present invention will be described with reference to FIGS.

[0025] [Basic principles of power flow and impedance measurements] Fig. 1 is a vector diagram illustrating the basic principle of a computing device according to a first embodiment of the present invention. Let P be the active power flow (e.g., 500 kW), V1 and V2 be the voltages at the upstream and downstream ends, respectively (e.g., 6.6 kV), I be the current, X be the impedance of the power transmission and distribution system, δ be the voltage phase difference between V1 and V2, and φ be the phase difference between V2 and I. Note that while the impedance of the power transmission and distribution system is X, this applies when the resistance R of the power transmission and distribution system can be ignored. That is, in this embodiment, an example will be described in which Z can be approximated as Z = R + jX ≒ X. JPEG2025187433000002.jpg97165

[0026] The active power flow P is given by equation (1). From the relationship in Figure 1, it can be seen that equation (2) holds true, and by transforming equation (2), equation (3) is obtained. By substituting equation (3) into equation (1), equation (4) is obtained. Furthermore, equation (4) can be transformed into equation (5). Furthermore, when δ is sufficiently small, sinδ≒δ Therefore, equation (5) can be approximated to equation (5').

[0027] Fig. 2 is an explanatory diagram of the basic principle of the arithmetic device of the first embodiment of the present invention. Fig. 2 shows a power transmission and distribution system in which branch systems B1, B2, and B3 are branched from a main system M. L0 is a voltage measurement point of the main system M as the upstream end, and L1, L2, and L3 are branch points from the main system M to the branch systems B1, B2, and B3, respectively. In Fig. 2, the voltage of the main system is V0 [V], the voltage at the branch point of branch system B1 is V1 [V], the voltage at the branch point of branch system B2 is V2 [V], the voltage at the branch point of branch system B3 is V3 [V], the active power flow from M to B1 is P1S [W], the active power flow from B1 to B2 is P2S [W], the active power flow from B2 to B3 is P3S [W], the active power flowing into branch system B1 is P1L [W], The active power flowing into branch system B2 is P2L [W], the active power flowing into branch system B3 is P3L [W], the impedance between V0 and V1 is X1, the impedance between V1 and V2 is X2, the impedance between V2 and V3 is X3, the phase difference between V0 and V1 is δ1 [rad], the phase difference between V1 and V2 is δ2 [rad], and the phase difference between V2 and V3 is δ3 [rad].

[0028] The basic equation for the active power flow between two points is equation (4), which can be calculated by multiplying the product of the voltages at both points by the sine of the voltage phase difference between the two points and dividing the result by the impedance between the two points. Using this principle, impedance can be estimated if the active power flow and voltage are known and the voltage phase difference can be measured. The voltage phase difference can be calculated on the cloud by combining the clock time of the voltage measuring device at each point and the voltage zero-crossing point. Note that this time must be sufficiently accurate, as described below. This method makes it possible to determine the values ​​of impedances X1, X2, and X3, which was previously difficult to do. At the same time, active power flows P1S, P2S, and P3S can also be calculated.

[0029] From FIG. 2, the active power flow P3S from V2 to V3 is equal to the active power P3L flowing into the branch system B3, and therefore the following equation (6) holds. P3S=P3L (6)

[0030] Since V2, V3, P3L=P3S, and δ3 are measurable, substituting these into equation (5) gives equation (7). X3=(V2×V3)·sinδ3 / P3L (7)

[0031] The active power flow P2S from V1 to V2 is given by equation (8). P2S=P2L+P3L (8) Here, V1, V2, P2L, P3L, and δ2 are measurable, so substituting these into equation (5) yields equation (9). X2=(V1×V2)·sinδ2 / (P2L+P3L) (9)

[0032] Next, the active power flow P1S from V0 to V1 is given by equation (10). P1S=P1L+P2L+P3L (10) Here, V0, V1, P1L, P2L, P3L, and δ1 are measurable, so substituting these into equation (5) yields equation (11). X1=(V0×V1)·sinδ1 / (P1L+P2L+P3L) (11)

[0033] From the above, the active power flows P1S, P2S, and P3S can be calculated using equations (6), (8), and (10), respectively, and the impedances X1, X2, and X3 can be calculated using equations (11), (9), and (7), respectively. In practice, δ1, δ2, and δ3 are sufficiently small values, so sinδ1 ≒ δ1, sinδ2 ≒ δ2, sinδ3 ≒ δ3 can be approximated as follows:

[0034] [Real system for measuring active power flow and impedance] As described above, theoretically, the active power flows P1S, P2S, and P3S can be calculated using equations (6), (8), and (10), respectively, and the impedances X1, X2, and X3 can be calculated using equations (11), (9), and (7), respectively. However, these measurements change from moment to moment. To measure the impedances X1, X2, and X3 in a single measurement, the voltages V0, V1, V2, and V3 at measurement points L0, L1, L2, and L3, the active powers P1L, P2L, and P3L branched to each branch system, the active power flows P1S, P2S, and P3S, and the phase differences δ1, δ2, and δ3 all change from moment to moment. Therefore, the impedances are calculated multiple times, and the results of each calculation of the impedances X1, X2, and X3 are tallied and statistically processed to estimate the true values ​​of the impedances X1, X2, and X3.

[0035] FIG. 3 is an explanatory diagram of phase detection by the arithmetic device according to the first embodiment of the present invention. Measurement units 10 and 20 are provided at points L0, L1, L2, and L3. The measurement units 10 and 20 include grid-connection controllers MGC11 and μGC21. The MGC11 and μGC21 are equipped with GPS receivers for receiving GPS time from a GPS 40. The MGC11 and μGC21 are controllers for performing coordinated, autonomous, and decentralized control of a power transmission and distribution system, for example, a cell grid (sometimes referred to as a "mini-grid"; the same applies below) that is a power transmission and distribution system separated from a main power transmission and distribution system by circuit breakers. The MGC11 and μGC21 acquire phase information from, for example, GPS time, and can also obtain information such as voltages in the main system and branch systems, and branched power. The aggregation unit 30 aggregates the measurement information from each measurement unit 10 and 20 and may be implemented as, for example, a cloud server. The MGC11 is provided on the transmission and distribution system side and performs, for example, opening and closing control of a circuit breaker (not shown) of the transmission and distribution system. On the other hand, the μGC21 is provided on the branch system side (for example, the cell grid system, the consumer side, or the site side) and performs, for example, opening and closing control of a circuit breaker (not shown) of the cell grid system. As will be described later, the calculation device of Fig. 3 can control the power supply and demand of the power generation equipment in the cell grid by grasping the available capacity of the transmission and distribution system, and can accurately determine the fault point and perform protective coordination control such as isolating only the branch system where a short-circuit fault has occurred using the MGC11 and μGC21.

[0036] Phase angles δ1, δ2, and δ3 are measured using GPS time and zero crossings. The voltage values ​​at points L0, L1, L2, and L3 are read using the mini-grid controllers (MGC11 and μGC21) at each point. MGC11 and μGC21 are equipped with GPS receivers and voltage measurement devices, allowing them to measure the exact time at each point and the voltages V0, V1, V2, and V3 at points L0, L1, L2, and L3. For example, μGC21 is installed next to each customer's power receiving circuit breaker, allowing the customer's voltage transformer (VT) to be used to measure the grid voltage at that point. Furthermore, the MGC11 and μGC21 can measure the power received by the customer using a current transformer (CT) typically installed at the customer's site, enabling the power P1L, P2L, and P3L branched to the branch grid shown in Figure 2 to be measured.

[0037] The MGC installed on the upstream side of the transmission and distribution system in FIG. 3 (left side in FIG. 3) measures the voltage of the transmission and distribution system and simultaneously acquires GPS time. The microgrid controller (μGC21) installed on the downstream side of the transmission and distribution system (right side in FIG. 3) measures the voltage at the power receiving point of the consumer and simultaneously acquires GPS time. Here, the μGC21 is assumed to have almost the same functions as the MGC11. While the example shown here illustrates acquiring GPS time as time information, this embodiment is not limited to this. Any time acquisition device can be used as long as it can obtain sufficient accuracy to determine phase information, for example, the difference between zero crossings of voltage at frequencies of 50 Hz or 60 Hz. For example, an atomic clock can also be used. The accuracy of GPS time information can be improved by fixing location information such as the latitude and longitude of the measurement point. Furthermore, phase information is not limited to the zero crossing method. Methods using PLLs (Phase Lock Loops) have also been proposed, allowing arbitrary phase timing to be acquired and compared in conjunction with accurate time information.

[0038] The current flowing through the transmission and distribution system causes a voltage drop commensurate with the system impedance, which causes a slight phase shift in the transmission and distribution voltage. The phase shift is reflected in the difference in the voltage zero cross timing, and although the magnitude is very small, it can be calculated meaningfully if accurate time measurement is possible. For example, if there is a CVT400 distribution line on a 6kV high voltage system, its allowable current is 750A, the reactance per km is 0.09Ω, and the resistance is 0.043 ohms. If the power factor of the current flow is 0.9, when the rated current flows in a 1km distribution line, X×I×cosφ=0.09×750×0.9=60V This results in a voltage drop of about 1% of the q-axis component for a 6000V rating. This corresponds to a phase angle of 0.01 rad, or 32 x 10 -6 The time accuracy of GPS and atomic clocks is 10 -9 Since it is at the second level, it is clearly at a level that can be detected. As the distance increases, the phase angle widens further.

[0039] Because there is a phase difference between the voltages at each point L0, L1, L2, and L3, when the zero-cross timing of the voltage at each point is accurately measured based on GPS time, there is a slight difference in the zero-cross timing of the voltage at each point. In Figure 3, the zero-cross timings of the rising edge of the voltage at point L0 are t0, t1, and t2, the zero-cross timings of the rising edge of the voltage at point L1 are t0_1, t1_1, and t2_1, the zero-cross timings of the rising edge of the voltage at point L2 are t0_2, t1_2, and t2_2, and the zero-cross timings of the rising edge of the voltage at point L2 are t0_3, t1_3, and t2_3.

[0040] For example, in FIG. 3, if a voltage zero crossing, such as a rising voltage zero crossing, occurs at time t0 in the upstream L0, and if a voltage zero crossing corresponding to L0 occurs at time t0_1 in the downstream L1, the phase difference δ [rad] can be calculated using equation (12). δ1=(t0_1-t0)×(2πf) (12)

[0041] Similar calculations hold for t1 and t1_1, and t2 and t2_1. Here, f is the frequency; for example, the voltage frequency f = 50Hz = Const. When δ is very small, it can be approximated as sinδ ≒ δ, so δ can be used instead of sinδ. Note that if δ1 is positive, V1 will lag in phase with respect to V0, and if δ1 is negative, V1 will lead in phase with respect to V0.

[0042] Similarly, for example, between t0_1 and t0_2, there is a time difference (t0_2 - t0_1) depending on the phase difference between V1 and V2, so the following equation holds between the time difference and phase difference δ2: If δ2 is positive, V2 lags behind V1, and if δ2 is negative, V2 leads behind V1. δ2=(t0_2-t0_1)×(2πf) (13)

[0043] Similarly, for example, between t0_2 and t0_3, there is a time difference (t0_3-t0_2) depending on the phase difference between V2 and V3, so the following equation holds between the time difference Δt02-t03 and the phase difference δ3. If δ3 is positive, V3 leads V2 in phase, and if δ3 is negative, V3 lags V2 in phase. δ3=(t0_3-t0_2)×(2πf) (14)

[0044] By substituting the exact zero-cross timing of the voltage rise at each point based on GPS time and the voltage frequency f into equations (12), (13), and (14), the phase differences δ1, δ2, and δ3 can be calculated.

[0045] In this way, the GPS time of the voltage zero-cross timing is recorded, and the impedance calculation is repeated multiple times on the cloud, followed by statistical processing to calculate the impedances X1, X2, and X3 of each part of the real system. An impedance map of the real system is created from the calculated impedances X1, X2, and X3 of each part of the real system. Once the impedance map of the real system is created, it does not change significantly under normal operating conditions. By fixing the impedance map in this way, we provide a method and system that can map the power flow distribution using only the voltage and voltage phase difference. By being able to visualize instantaneous power flow, this system contributes to solving the issue of available capacity for distributed power sources such as solar power. Furthermore, because this method can simultaneously grasp the voltage distribution, it is also useful for resolving voltage issues in power transmission and distribution systems caused by distributed power sources.

[0046] Once the transmission and distribution system impedance map is obtained, it is possible to visualize the power flow. However, because the phase difference is very small, it is necessary to improve the accuracy of the GPS time. Generally, GPS time is calculated by processing information from four or more GPS satellites and calculating the position and time every fixed interval (for example, one second). Because the position of a power system is fixed, recording each position information in the MGC or μGC is expected to improve the time accuracy. Furthermore, because each power and voltage information changes from moment to moment, continuous statistical processing can improve the accuracy of the impedance map, which is a fixed value. When an abnormal step change is observed in the transmission and distribution impedance, it can be assumed that some kind of abnormality has occurred in the power transmission and distribution system, making it possible to take early action.

[0047] However, with conventional technology, a current transformer must be installed in a transmission and distribution system to measure the active power flows P1S, P2S, and P3S that flow through the system. Installing a current transformer in a transmission and distribution system requires expensive equipment, so current transformers are not generally installed in transmission and distribution systems. As a result, with conventional technology, information on system flow is usually not obtained, resulting in inefficient operation of the transmission and distribution system.

[0048] [Reactive power flow measurement] FIG. 4 is a vector diagram of reactive power flow relating to the basic principle of the arithmetic device of the first embodiment of the present invention, and FIG. 5 is an explanatory diagram of reactive power flow relating to the basic principle of the arithmetic device of the first embodiment of the present invention. Information on power flows in a power transmission and distribution system was obtained using basic equations (1) to (5). Here, calculation of reactive power flow Q in a power transmission and distribution system will be described with reference to FIGS. 4 and 5. Reactive power flow Q is expressed as equation (15). From the relationship in FIG. 1, it can be seen that equation (16) holds, and by modifying equation (16), equation (17) is obtained. Substituting equation (17) into equation (15) yields equation (18). Furthermore, equation (18) can be transformed into equation (19). Here, in practice, δ is a sufficiently small value, and the value of cosδ is actually close to 1. Therefore, if cosδ ≈ 1, equation (19) can be approximated to equation (19′).

[0049] Since the reactive powers Q1L, Q2L, and Q3L branched into each branch system can be measured by each μGC, the reactive power flow can be calculated in the same way as the power flow described above by using the basic equations (15) to (19) for reactive power flow. JPEG2025187433000003.jpg81168

[0050] [Embodiment 2] A calculation device, a power transmission and distribution system, a calculation method, and a program according to a second embodiment of the present invention will be described with reference to Figs. 6 to 8. The same reference numerals are used for components similar to those in Figs. 1 to 5, and their description will be omitted. Fig. 6 is a vector diagram illustrating the basic principle of the calculation device according to the second embodiment of the present invention. In the first embodiment, when the resistance R of the power transmission and distribution system can be ignored, the impedance Z of the power transmission and distribution system is set to Z≈X. However, in this embodiment, the resistance R component of the power distribution system is taken into account and Z=R+jX is set. For example, in a high-voltage power transmission and distribution system, R and X are of the same order of magnitude. In this embodiment, the power flow includes an active power flow and a reactive power flow.

[0051] From the relationship in Figure 6, the following equation can be obtained. JPEG2025187433000004.jpg98167

[0052] P and Q can be calculated from equations (20) and (21), similarly to equations (1) and (15). From the vector diagram in Figure 6, equation (22) holds. Transforming equations (20) and (21) yields equation (23). Substituting equation (23) into equation (22) yields equation (24). Transforming equation (24) yields equation (25). Transforming equation (25) further yields equation (26). Here, since δ is actually sufficiently small, if we approximate cosδ≈1, equation (26) can be transformed to yield equation (27).

[0053] Data sets of V1, V2, sinδ, P, and Q can be measured, and the resistance R and reactance X of the power transmission and distribution system can be calculated from two or more data sets. Once the power transmission and distribution system impedance Z is specified, sinδ can be specified from the phase difference because V1 moves along the dashed line in Figure 6 when V2 is constant. Therefore, if V1 and V2 can be measured, P and Q can be calculated without installing a CT in the power transmission and distribution system.

[0054] Figure 7 is an explanatory diagram of the basic principle of a calculation device according to a second embodiment of the present invention. In the power transmission and distribution system of Figure 7, there is a power flow S1 from L0 to L1, an impedance Z1 between L0 and L1, a power flow S2 from L1 to L2, an impedance Z2 between L1 and L2, a power flow S3 from L2 to L3, and an impedance Z3 between L2 and L3. The impedances Z1, Z2, and Z3 and the power flows S1, S2, and S3 of the power transmission and distribution system of Figure 7 can be calculated based on the above equation (27) in the same way as in the first embodiment.

[0055] Fig. 8 is a modified vector diagram of the basic principle of the arithmetic device of embodiment 2 of the present invention. From the relationship in Fig. 8, it is also possible to calculate equations (28) to (32), and equations (27) and (32) can also be used in combination, which further improves the accuracy of the calculation. JPEG2025187433000005.jpg74168

[0056] From the vector diagram in Figure 8, equation (28) holds. Equation (29) is similar to equation (23). Substituting equation (29) into equation (28) gives equation (30). Transforming equation (30) gives equation (31). Here, since δ is actually sufficiently small, sinδ≒δ By approximating this, equation (31) can be transformed to equation (32).

[0057] [Embodiment 3] A calculation device according to a third embodiment of the present invention will be described. Descriptions of configurations similar to those in FIGS. 1 to 8 will be omitted. The description of the calculation device according to the first embodiment applies to one line of a power transmission and distribution system. By performing this independently for each of the three lines, it is expected that accuracy will be improved. Normally, the power flows in the three lines are balanced. If a ground fault occurs in one line, an imbalance in the power flows will occur, making it possible to detect a ground fault. The direction of the power flow in this case can also be determined by whether the phase difference is positive or negative.

[0058] A similar determination can be made for a two-wire short circuit. Since the voltage drops rapidly during a three-phase short circuit, it is difficult to determine the fault point. However, in this embodiment, if the voltage drops rapidly during a three-phase short circuit, it becomes difficult to measure the zero-cross timing. However, since the time of the voltage drop differs depending on the location, this method contributes to determining the fault point even in such cases.

[0059] [Functions that can be achieved] In this embodiment, we will explain functions that can be realized using the impedance maps and power flows (including active power flows and reactive power flows) measured in Embodiments 1 and 2. In this embodiment, the following functions (1) to (6) can be realized.

[0060] (1) Creating an impedance map of the power transmission and distribution network As in the first embodiment, it is possible to create an impedance map of the power transmission and distribution network based on the impedance estimation, and also to detect the power flow.

[0061] (2) Identifying available capacity in the transmission and distribution system As mentioned in (1) above, the power flow and reactive power flow in the power transmission and distribution network can be grasped, making it possible to grasp the available capacity of the power transmission and distribution system in real time. This can be applied to suppressing renewable energy power generation and controlling supply and demand in power generation control, thereby maximizing renewable energy power generation while maintaining system stability.

[0062] (3) Accident detection Measuring voltage phase fluctuations at each point allows for accurate fault location. For example, a short-circuit fault disrupts the power flow. Therefore, even though power is normally flowing from upstream to downstream, a short-circuit fault can result in current flow toward the point where the short-circuit fault occurred, resulting in observed voltage phase changes. For example, while power flows across three lines are normally balanced, a ground fault in one line can cause an imbalance in the power flow, making it possible to detect a ground fault. The direction of the power flow can be determined by the positive / negative change in the phase difference. A similar determination can be made for a two-line short circuit. A three-phase short circuit causes a rapid voltage drop, making fault location difficult. However, in this embodiment, when a three-phase short circuit occurs, it is difficult to measure the zero-crossing timing. However, because the time of the voltage drop varies depending on the location, this method contributes to fault location even in such cases.

[0063] (4) Understanding the power transmission and distribution network Impedance calculation is possible even for complex power transmission and distribution networks, making it possible to create impedance maps of the power transmission and distribution network. Furthermore, by monitoring voltage phase in real time, it is possible to accurately determine whether the location of a fault is upstream or downstream.

[0064] (5) Protection coordination Utilizing the above (4) enables a new type of protection coordination not found in conventional technology. Conventional technology involves first opening a distribution circuit breaker to isolate the fault, regardless of the fault location, and then completely shutting down the distribution system under that circuit breaker. Then, sectioning switches are closed from upstream. When the fault point is reached, the distribution circuit breaker is opened again, thereby identifying the fault point. After identifying the fault point, sectioning switches are closed up to the nearest section to restore power and isolate the faulted section. However, this method requires at least two complete section outages and the supply of fault current to the fault point, raising concerns about the expansion of damage at the fault point. In contrast, the new type of protection coordination proposed in this study can quickly calculate the impedance to the fault point, identify only the fault point, and limit the scope of protective action to the fault point. If this method can be established, it may be possible to identify the fault section and narrow the scope of the outage while avoiding unnecessary power outages and the expansion of damage caused by the supply of unnecessary fault current.

[0065] (6) Understanding current distribution If the approximate impedance can be determined in the power transmission and distribution network, the power flow distribution P1S, P2S, P3S, Q1S, Q2S, Q3S, S1, S2, and S3 can be determined simply by measuring the voltage and voltage phase at the branch system, for example, at a consumer's facility.

[0066] The computing device of this embodiment makes it possible to calculate power flow and estimate impedance without directly measuring system impedance. This reduces the cost and time required for monitoring and managing the power system and improves the operational efficiency and stability of the power system. It can measure the available capacity of the transmission and distribution system in real time and apply it to suppressing renewable energy power generation and power generation control. This makes it possible to maximize renewable energy power generation while maintaining system stability. Furthermore, it is possible to estimate the location of a fault, such as a short circuit, by measuring the distribution of voltage values ​​at the time of the fault. This can be implemented even in complex transmission and distribution networks, and it can also determine whether the fault is located upstream, downstream, or an internal fault, enabling unprecedented protection coordination.

[0067] The above-described embodiments do not limit the present invention, and the present invention can be equally applied to other embodiments included in the scope of the claims. Furthermore, the embodiments can be appropriately modified or combined.

[0068] While FIG. 3 shows an example in which the timing of the voltage zero crossing at the rising edge is measured as the zero crossing timing of the voltage, this embodiment is not limited to this, and any measurement is possible as long as the zero crossing timing can be accurately determined. For example, the timing of the voltage zero crossing at the falling edge of the voltage may be measured. Furthermore, it is also possible to measure the zero crossing timing of both the rising and falling edges of the voltage, but from the viewpoint of accurate zero crossing measurement, this embodiment shows an example in which the timing of the voltage zero crossing at one of the rising edges, for example, the rising edge of the voltage, is measured.

[0069] 3 and 4 show examples of parts of an actual power transmission and distribution network, and the power transmission and distribution network of this embodiment is not limited to this. For example, the number and arrangement of branch systems B1, B2, and B3 are arbitrary, and the present invention can also be applied to more complicated power distribution networks, such as those in which further branch sub-systems exist from the branch systems.

[0070] FIG. 3 illustrates an example of a computing device that performs autonomous decentralized control of a power transmission and distribution system using μGC and MGC, but this embodiment is not limited to this and can be applied to any computing device as long as it accurately measures the zero-cross timing of voltage at an upstream point, a lower end point, and a branch point of a branch system. [Explanation of symbols]

[0071] 10 Measuring part 11 MGC 20 Measuring part 21 μGC 30 Counting Unit 40 GPS CT instrument current transformer VT Voltage Transformer B1, B2, B3 branch lineage M Main system MGC Grid Connected Controller P1L, P2L, P3L Active power branched to branch systems P1S, P2S, P3S active power flow P Active power flow Q1L, Q2L, Q3L Reactive power branched to branch systems Q1S, Q2S, Q3S reactive power flow Q reactive power flow S1,S2,S3 Power flow V0, V1, V2, V3 Voltage at each measurement point X1, X2, X3 reactance R1,R2,R3 resistance Z1, Z2, Z3 impedance f voltage frequency δ phase difference

Claims

1. A computing device that computes at least one of a power flow and an impedance of a power transmission and distribution system, a measuring unit for measuring voltages in the main system and the branch system, branched power, and time; a counting unit that counts measurement information of the measuring device; Equipped with calculating a voltage phase difference of the measuring unit from the time information; Calculating at least one of power flow and impedance; A computing device that controls power transmission and distribution using the computation results.

2. 2. The computing device according to claim 1, wherein a target power for power generation is calculated based on the calculated power flow and impedance.

3. 2. The computing device according to claim 1, wherein a fault location is determined based on the calculated power flow and impedance.

4. A power transmission and distribution system comprising the arithmetic device according to claim 1.

5. A calculation method for calculating at least one of a power flow and an impedance of a power transmission and distribution system, comprising: Using measuring instruments that measure voltages in the main system and branch systems, branched power, and time, and a counting unit that counts measurement information from the measuring instruments, calculating a voltage phase difference based on the time; calculating at least one of a power flow and an impedance from information on a voltage at a branch point of the branch system, power branched at the branch point, and time; A calculation method characterized by controlling power transmission and distribution using the calculation results.

6. A program for causing a computer to execute the calculation method according to claim 5.

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