JP3719285B2 - Equivalent impedance estimation method for power system, and distributed power supply isolated operation detection method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an estimation of equivalent impedance of an electric power system, particularly a commercial electric power system , and an electric power system for performing isolated operation detection of a distributed power source such as a private power generation facility linked to the commercial electric power system based on the equivalent impedance thus estimated. It relates to the monitoring method . More specifically, the equivalent line impedance of the power system and / or the equivalent power supply voltage of the power system as viewed from the output terminal of the distributed power source connected to the power system is estimated , and the estimated equivalent impedance and / or equivalent Based on the power supply voltage, with the commercial power system to which the distributed power supply is connected and the circuit breaker at the outlet of the upper system open, the distributed power supply continues to operate (power generation) independently. The present invention relates to a power system monitoring method to be detected.
[0002]
[Prior art]
From the viewpoint of effective use of energy and improvement of the power supply situation, it is approved to link private power generation facilities such as small hydropower generation, garbage incineration power generation, wind power generation, fuel cells, solar cells, etc., that is, distributed power sources, to the commercial power system. It came to be put to practical use. In such an interconnected power system, when an accident occurs in a commercial power system or a higher system connected to a distributed power source, or when maintenance, repair, or restoration of the system is performed, the outlet The circuit breaker is opened. In such a state, if the isolated operation (power generation) is continued in the partial series separated from the commercial power supply without disconnecting the distributed power supply, the commercial power line that should be essentially no voltage is generated. There will be a problem in terms of ensuring safety. Therefore, the isolated operation of the distributed power source during system maintenance, repair, restoration work, etc. must be reliably detected and prevented.
[0003]
In the case of power generation equipment that does not allow power flow from the distributed power source to the power system, that is, interconnection without reverse power flow, reverse power flow is detected by installing a reverse power relay at the receiving point of the distributed power source and automatically Distributed power can be disconnected from the grid. However, in the case of an interconnection that allows reverse power flow, a reverse power relay or the like cannot be used because there is a power flow from the distributed power source to the power system even during steady operation.
[0004]
If the circuit breaker at the outlet of the power system is opened due to a power system accident, maintenance or repair, etc., within the sub-series (for example, the output terminal of the distributed power supply) that includes the distributed power supply disconnected from the main system When the power generation amount and the load amount are different, the frequency and voltage of the partial series fluctuate. Therefore, it can be easily estimated that the isolated operation can be detected by monitoring these and the distributed power source can be disconnected based on this.
[0005]
[Problems to be solved by the invention]
In the method of detecting the frequency and voltage fluctuation in the partial series as described above, the frequency and voltage are increased as the difference between the power generation amount and the load quantity in the partial series including the distributed power source separated from the main series decreases. The fluctuation of the frequency becomes small and it becomes difficult to detect the fluctuation, and in the state where both are balanced, the frequency and voltage fluctuations practically do not occur, so that the isolated operation cannot be detected. Therefore, naturally, the inconvenience that the isolated operation state will continue is expected.
[0006]
The purpose of the present invention, estimates the equivalent impedance and / or equivalent power source voltage of the power system as viewed from the interconnection to power to the power grid, and the power generation amount in the severed portion in a sequence from the main sequence loadings and It is an object of the present invention to provide a power system monitoring method that reliably detects the isolated operation of a distributed power source even when the difference between the two is small as described above, regardless of the balance state.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, firstly, the output voltage Eti and current Igi (i is a positive integer 1 to n) of a distributed power source linked to a main system such as a commercial power system over time. The relational expression Et = Es + Ig (R + jX) between the output voltage Et of the distributed power supply, the current Ig, the system power supply voltage Es, and the system impedance Z = R + jX (where R is the line resistance and X is the line reactance). ) To calculate the terminal voltage estimated value Etif = Es + Igi (R + jX) by substituting the measured current value Igi into the line resistance, and further to minimize the difference between the terminal voltage estimated value Etif and the measured voltage value Eti. At least one of an equivalent impedance composed of R and line reactance X and an equivalent power supply voltage on the main system side viewed from the distributed power supply is estimated and calculated. And when at least one of the estimated change amount and change speed of the equivalent impedance on the main system side exceeds a predetermined value, or when the equivalent power supply voltage on the main system side drops to substantially zero, or the distributed power output frequency When the fluctuation amount / speed of fluctuation exceeds the reference value, a signal indicating the independent operation of the distributed power source is generated.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 2, a load L1 is connected to a main system (commercial power system) power source Es having a power source impedance Z1 and a line impedance Z2, and a load Li is connected to a distributed power source G connected thereto. In the power system, Equation 1 in FIG. 5 is established. In general, the impedances ZL1 and ZLi of the loads L1 and Li are much larger than the power supply impedance and the line impedance. Therefore, when considering the impedance of the distributed power supply G viewed from the main system side, the load impedance can be ignored. . Therefore, in the system of FIG. 2, the formula 2 of FIG. 5 is established between the terminal voltage Et of the distributed power source G and the output current Ig.
[0011]
If the main system power supply Es is cut off at point A in FIG. 2, the main system power supply Es viewed from the distributed power supply G is zero, and the power source impedance Z1 becomes infinite, so Equation 1 changes to Equation 3. . Here, when the fluctuation amount of the terminal voltage Et with respect to the minute fluctuation amount of the current Ig is obtained, the expression 4 is obtained from the differentiation of the expression 2 when connected to the system, and the expression 3 when disconnected from the system. From the differentiation, the relationship of Equation 5 is obtained. As can be seen, Equation 5 ignores the line impedances Z1 and Z2 in consideration of the fact that the line impedances Z1 and Z2 are sufficiently smaller than the load impedances ZL1 and ZL2, and the loads ZLi and ZL1 are connected in parallel to the distributed power source. Corresponding to the state. From the above analysis, it can be seen that the impedance viewed from the distributed power source when viewed from the grid side is expressed by Equation 4 during normal interconnection operation, and suddenly changes to Equation 5 when disconnected and shifted to independent operation.
[0012]
The present invention estimates the equivalent impedance and / or system-side power supply voltage Es as seen from the system side from the distributed power source, or further monitors the amount of change and / or the rate of change of these estimated values, so that the distributed power source is in a single operation state. It tries to detect that it became. For this purpose, consider a case where the output current Ig from the distributed power supply G is changed at a sufficiently lower period than the commercial frequency. In such a system, the capacitance of lines and parallel capacitors can also be ignored, so the equivalent circuit is represented as shown in FIG. Here, R and L are resistance and inductance components of the line, and Lg is an impedance when the distributed power source side is viewed from the output terminal of the distributed power source G. Further, the vector diagram in this case is as shown in FIG. 4, and the relationship of Expression 6 shown in FIG. 5 is obtained.
[0013]
Based on these relationships, when the output current Ig from the distributed power source G is changed gently, the relationship between the measured current Igi and the measured terminal voltage Eti at each time t i (i is a positive integer from 1 to n) Coefficients (parameters) Es, R, and X satisfying 6 are obtained by an appropriate parameter estimation method. As for the parameter estimation method, for example, OHM Co., Ltd., issued on October 30, 1983, edited by the Society of Instrument and Control Engineers, “Automatic Control Handbook, Device / Application”, page 516 “6.3 Parameter Estimation”, Corona, Inc. published on March 25, 1988, "Hyundai Control Series (1)" Signal Analysis and System Identification "" by Nakayoshi Takayoshi, pages 7-17 "Estimation", page 127 "Least Square Estimation" It is stated.
[0014]
As one method of parameter estimation, for example, a typical least square method described in the above-mentioned document can be used. In that case, the difference εi between the estimated terminal voltage E tif (Equation 7) obtained by substituting the measured current Igi into Equation 6 and the measured terminal voltage Eti, ie, ε ² represented by Equations 8 and 9 is minimized. The estimated values of the main system voltage Es, the resistance R of the line, and the reactance component X are obtained. As apparent from FIG. 4, the phase angle (β + θ) of the measured current Igi with respect to the main system voltage Es is uniquely determined when R, X, and θ are given. By the way, since θ can be measured as θi, the phase angle (β + θ) is uniquely determined. Since the estimated terminal voltage Etif and the measured terminal voltage Eti have the same phase angle with respect to the measured current Igi, the difference between Etif and Eti may be an absolute value difference.
[0015]
Es, R, and X thus obtained are estimated values of the power supply voltage and line impedance of the main system within i = 1 to n hours. Since Expression 10 is obtained from the vector diagram shown in FIG. 4, Expression 11 is obtained by substituting it into Expression 9. Es, R, and X in Equation 11 are changed little by little, and by repeated calculation, values of Es, R, and X that minimize Equation 11, that is, values of coefficients Es, R, and X that minimize Equation 8 are obtained. be able to.
[0016]
FIG. 1 is a block diagram showing an example of an apparatus configuration suitable for carrying out the method of the present invention. In the figure, the same reference numerals as those in FIGS. 2 and 3 represent the same or equivalent parts. The output (current Ig, voltage Et) of the distributed power supply G is changed by the output control device 11 in a sinusoidal, M-sequence or irregular (random) manner, preferably at a frequency sufficiently lower than the commercial power supply frequency. The M series (longest series) is described in detail, for example, on page 57 and subsequent pages of “Latest spread spectrum communication system” by Toshin Tateno et al. In addition, naturally occurring output fluctuations can be detected and used as they are without forcibly changing the output current. The output current Igti and voltage Eti of the distributed power source G at time ti are measured and supplied to the parameter estimation calculation unit 12. The parameter estimation calculation unit 12 estimates at least one of the maximum likelihood values of the main system power supply voltage Es, the line resistance R, and the line reactance X by an appropriate method as described above (for example, the least square method). To do.
[0017]
The parameter reference setting unit 13 is a system parameter obtained in advance for each distributed power source or the interconnected system, or for each partial system, in the normal interconnected operation state of each distributed power source, that is, the output terminal of each distributed power source. The main system power supply voltage Es, the line resistance R, the standard value of the line reactance X, and the set values such as the deviation necessary for abnormality determination are stored. The abnormality detection unit 14 is supplied with the main system power supply voltage Esf, the line resistance Rf, and the line reactance Xf estimated by the estimation calculation unit 12, and these are compared with the respective standard values, and each deviation is equal to or more than a predetermined value. If so, an abnormality is detected, and a corresponding abnormality signal is supplied to the isolated operation determination unit 15 to generate a signal indicating the isolated operation. The determination of the isolated operation can be performed based on, for example, the following state continuing for a set time (for example, several seconds to 10 seconds) or longer.
[0018]
(1) When the estimated value of the main system power supply voltage Es becomes zero.
During the grid operation, the estimated value of the main system power supply voltage Es naturally shows a certain value close to the rated value, but when the main system is shut off, the estimated value of the voltage becomes zero as described above. In this way, it is possible to determine the isolated operation.
[0019]
(2) When the equivalent impedance (R and / or X) increases rapidly, and its change width and / or change speed becomes larger than the set value.
While the equivalent impedance during normal interconnection operation is substantially only the line impedance and is very small and small, the interconnection end is opened in the single operation, so that the load as shown in FIG. Even if the load impedance ZL1 is added, the equivalent impedance increases in each stage. In accordance with such a fact, the isolated operation can be determined by monitoring the increase in the equivalent impedance. In this case, the determination criteria vary depending on each system. For example, when an increase of several tens of percent or more is detected within 0.5 seconds and this state continues for several seconds to 10 seconds or more, it is independent. It can be assumed that the operation is determined.
[0020]
(3) When the value of R / X increases to 1 to 1.5 or more.
In a normal transmission / distribution line, the value of R / X is about 0.5 to 1, but when the main system power supply is shut off and the load is connected, the load impedance is added as described above. Therefore, the value increases to 2 or more (because the power factor of the load is usually 90% or more). Therefore, the isolated operation can be determined based on such a change.
[0021]
Furthermore, an abnormal voltage / frequency detecting unit 16 to which the output voltage (and current, if necessary) signal of the distributed power source G is supplied is attached, and abnormal rise and fall of the voltage and frequency seen at the output terminal of the distributed power source are output. When abnormal fluctuations in the phase difference of the current with respect to the voltage occur and these abnormal states continue for a predetermined time (for example, several seconds to 10 seconds) or more, the second abnormal signal or individual abnormal signal is determined as an independent operation determination unit. 15 may be output to generate a signal indicating an isolated operation.
[0022]
That is, the isolated operation determination unit 15 receives the second abnormal signal from the voltage / frequency abnormality detection unit 16 in the form of an analog signal (in this case, the deviation from the standard value of voltage and frequency), and Based on combinations (logical product and logical sum) of deviations (or ratios) from standard values of various parameters (estimated main system power supply voltage Es, resistance R, reactance X) obtained by the abnormality detection unit 14 It is possible to comprehensively judge the single operation state. For example, for each power system cutoff point (for example, point A in FIG. 2), the voltage and frequency deviation amounts (or ratios) at the output terminals of the respective parameters and the distributed power source are estimated or calculated in advance. If these combinations are stored in the table, the combinations of deviation amounts (or ratios) from the abnormality detection unit 14 and the abnormality detection unit 16 such as voltage / frequency are referred to the table to distribute the combinations. The single operation of the power supply can be determined. That is, the generation of a signal indicating the independent operation of the distributed power source may be determined based on a combination of the deviation amounts (or ratios).
[0023]
For frequency fluctuation, for example, if a fluctuation of ± 0.1% to ± 0.3% (0.06 to 0.18 Hz) is detected within 0.5 seconds, an abnormality is detected. If it continues for 10 seconds, it can be determined that it is an isolated operation. For other parameters, it is possible to perform abnormality detection and isolated operation determination based on substantially the same criteria.
[0024]
The input data (terminal voltage Eti, current Igti, phase difference θi) necessary for the arithmetic processing described above can be acquired by the following method.
(1) Measure voltage and current amplitude values and phase difference between them.
(2) The output voltage of the distributed power source is varied at a frequency ωm lower than the commercial frequency ωc to generate an amplitude-modulated waveform current Igi as represented by Equation 12 in FIG. 5, and (ωc + ωm) in the equation The component or (ωc−ωm) component is extracted using, for example, a known correlation filter. The correlation filter (Matched Filter) is, for example, published on March 13, 1986, “Detailed Digital Analog Communication System”, pages 484-491, and published on “Analog / Digital” on June 20, 1982 by Hyundai Engineering. Signal analysis "pages 263-265.
[0025]
【The invention's effect】
According to the present invention, based on the output current and voltage actually measured at the output terminal of the distributed power supply (and the phase difference between them), the impedance and power supply voltage on the main series side viewed from the distributed power supply can be estimated. In this way, by monitoring changes in the estimated impedance and / or power supply voltage, frequency, etc., or by comparing with a standard value prepared in advance, the power generation amount and load amount in the partial series separated from the main series Even when they are balanced or close to the balance, it is possible to reliably detect the isolated operation of the distributed power source and disconnect them as necessary. Furthermore, the stability of the power system can be monitored based on the estimated impedance.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of an apparatus to which a method of the present invention is applied .
FIG. 2 is a diagram showing an example of a power system suitable for applying the present invention.
3 is an equivalent circuit diagram of the power system of FIG. 2. FIG.
4 is a vector diagram of voltage and current in the circuit of FIG. 3;
FIG. 5 is a diagram showing an arithmetic expression used in the present invention.

Claims (6)

Measure the output voltage Eti and current Igi (i is a positive integer 1 to n) of a distributed power source linked to a main system such as a commercial power system over time,
A relational expression between the output voltage Et of the distributed power source, the current Ig, the system power source voltage Es, and the system impedance Z = R + jX (where R is a line resistance and X is a line reactance) Et = Es + Ig (R + jX)
Is substituted with the measured current value Igi to calculate the terminal voltage estimated value Etif = Es + Igi (R + jX), and further the line resistance R to minimize the difference between the terminal voltage estimated value Etif and the measured voltage value Eti. And a power system monitoring method for estimating and calculating at least one of an equivalent impedance composed of a line reactance X and an equivalent power supply voltage on the main system side as viewed from the distributed power supply . The power system monitoring method according to claim 1, wherein the output voltage Eti and the current Igi are measured while varying the output of the distributed power source. A power system monitoring method for estimating and calculating an equivalent impedance composed of the line resistance R and the line reactance X, and at least one of a change amount and a change speed of the line resistance R and the line reactance X exceeds a predetermined value. 3. The power system monitoring method according to claim 1 , further comprising: generating a signal indicating an independent operation of the distributed power source. A power system monitoring method for estimating and calculating an equivalent power supply voltage on the main system side as seen from the distributed power supply, and further generating a signal indicating an independent operation of the distributed power supply when the equivalent power supply voltage drops to substantially zero power system monitoring method according to claim 1 or 2, characterized in that it comprises. The estimation calculation of the equivalent power supply voltage, line resistance R and line reactance X on the main system side as viewed from the distributed power supply is performed by the equivalent circuit composed of the line resistance R and line reactance X and the series circuit of the equivalent power supply outputs the output of the distributed power supply. power system monitoring method according to any one of claims 1 to 4, characterized in that is carried out based on the connected equivalent circuit terminal. Further measuring the output voltage frequency of the distributed power source,
Based on at least one of the equivalent impedance composed of the line resistance R and the line reactance X and the equivalent power supply voltage on the main system side as viewed from the distributed power supply, the amount of fluctuation and / or the speed of fluctuation of at least one of the output voltage and frequency are also considered. to, power system monitoring method according to any one of claims 1 to 5, characterized in that it comprises generating a signal indicating a single operation of the distributed power supply.

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