JPH09243682A - Method for estimating equivalent impedance of power system and method and apparatus for detecting individual operation of distributed power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sense individual operation of a distributed power source by measuring output voltage and current of the distributed power source and estimation-calculating line resistance and line reactance which minimize difference between a terminal voltage estimated value calculated from the above values and a measured voltage value. SOLUTION: Output current Igti and voltage Eti of a distributed power source G is measured and supplied to a parameter estimation-calculation part 12. The calculation part 12 estimates the most likely values of main system supply voltage Es , line resistance R and line reactance by the minimum square method for example. A parameter reference setting device 13 stores set values such as standard values for main system supply voltage Es , line resistance R and line reactance viewed from an output end during normal interlocked operation of the distributed power source G and deviation amounts required for determining abnormality. The main system supply voltage, line resistance and line reactance estimated in the calculation part 12 are supplied to an abnormality detection part 14, which compares these values with reference values, wherein when deviation values are more than expected values, abnormality is detected, an abnormal signal is supplied to an individual operation detecting part 15 for issuing a signal representing individual operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating an equivalent impedance of a power system, particularly a commercial power system, and a distributed power source such as a private power generation facility connected to the commercial power system based on the thus estimated equivalent impedance. And an isolated operation detection method and device. More specifically, a method of estimating the equivalent line impedance of the power system and / or the equivalent power supply voltage of the power system viewed from the output terminals of the distributed power source connected to the power system, and the estimated equivalent impedance and / or Or, based on the equivalent power supply voltage, the distributed power supply continues to operate (generate electricity) independently with the breaker at the outlet of the commercial power system or the upper system to which the distributed power supply is interconnected open. The present invention relates to a method and an apparatus for detecting a thing.

[0002]

2. Description of the Related Art From the viewpoint of effective use of energy and improvement of power supply conditions, private power generation facilities such as small hydroelectric power generation, refuse incineration power generation, wind power generation, fuel cells, and solar cells, that is, distributed power sources, are connected to a commercial power system. Things have come to be approved and are now being put to practical use. In such an interconnected power system, in the event of an accident in the commercial power system in which the distributed power sources are interconnected, or in the higher level system, or during maintenance, repair, or restoration of the system, The circuit breaker is opened. In such a state, if the isolated operation (power generation) is continued in the sub-series separated from the commercial power source without disconnecting the distributed power source, the commercial power line that should originally have no voltage It will be charged and there is a problem in terms of ensuring safety. Therefore, the isolated operation of the distributed power source is reliably detected during maintenance, repair, and restoration work of the system.
Must be prevented.

In the case of power generation equipment that does not allow power flow from the distributed power sources to the power system, that is, in the case of interconnection without reverse power flow, reverse power flow is detected by installing a reverse power relay or the like at the receiving point of the distributed power sources, Distributed power can be automatically disconnected from the grid. However, in the case of interconnection that allows reverse power flow, a reverse power relay cannot be used because there is a power flow from the distributed power sources to the power system even during steady operation.

When the circuit breaker at the outlet of the power system is opened due to a power system accident, maintenance or repair, etc., within a partial series including the distributed power supply separated from the main system (for example, the output end of the distributed power supply). ) When the amount of power generation differs from the amount of load,
Since the frequency and voltage of the partial series fluctuate, it can be easily inferred that islanding can be detected by monitoring these and the distributed power supply can be disconnected based on this.

[0005]

In the method for detecting the frequency and voltage fluctuations in the sub-series as described above, the power generation amount and the load amount in the sub-series including the distributed power source separated from the main sequence are divided. As the difference becomes smaller, the fluctuations in the frequency and the voltage also become smaller, making it difficult to detect the fluctuations. When the two are in a balanced state, the fluctuations in the frequency and the voltage practically do not occur, making it impossible to detect the islanding operation. Therefore, of course, the inconvenience that the islanding operation state will continue is expected.

A first object of the present invention is to provide a method for estimating an equivalent impedance and / or an equivalent power supply voltage of a power system viewed from a power supply connected to the power system. Another object of the present invention is to ensure independent operation of the distributed power source regardless of the balance between the amount of power generation and the amount of load in the partial series separated from the main series, even when the difference between the two is small as described above. A method and apparatus for detecting

[0007]

In order to achieve the above object, in the present invention, first of all, an output voltage Eti and a current I of a distributed power source connected to a main system such as a commercial power system.
gi (i is a positive integer 1 to n) is measured over time, and output voltage Et of distributed power supply, current Ig, system power supply voltage Es, and system impedance Z = R + jX (where R is line resistance, X is line reactance). The relation between Et = E
Substituting the measured current value Igi into s + Ig (R + jX) to calculate the estimated terminal voltage value Etif = Es + Igi (R + jX) and further minimizing the difference between the estimated terminal voltage value Etif and the measured voltage value Eti. The line resistance R, the line reactance X, and the power supply voltage Es on the main system side are estimated and calculated. Then, when at least one of the estimated change amount and change speed of the equivalent impedance on the main system side exceeds the planned value, or the estimated power supply voltage on the main system side drops to substantially zero, or the distributed power supply output frequency When the variation amount / variation velocity of 1 exceeds a reference value, a signal indicating the isolated operation of the distributed power source is generated.

The distributed power source isolated operation detection apparatus according to the present invention is a means for measuring output voltage and current of a distributed power source connected to a main system such as a commercial power system over time, and a plurality of obtained voltages and currents. Means for estimating at least one of an equivalent impedance and an equivalent power supply voltage on the main system side as seen from the distributed power supply based on a measured value, and a variation amount and / or a variation of at least one of the estimated equivalent impedance and the equivalent power supply voltage. When the speed exceeds a predetermined value, an abnormality detection unit that generates a signal indicating the isolated operation of the distributed power source is provided.

Further, the means for measuring the output voltage frequency of the distributed power supply and the second means when it is detected that the variation amount and / or the variation speed of at least one of the output voltage and the frequency exceed a reference value. An abnormality detecting means for generating an abnormal signal, such as a voltage frequency, and an islanding operation determining section for producing an output signal indicating an islanding operation of the distributed power source based on the signal from the abnormality detecting section and the second abnormality signal are provided. be able to. The abnormality detection unit outputs a deviation from a standard value of at least one of the estimated equivalent impedance and the equivalent power supply voltage, and the abnormality detection unit such as the voltage frequency is an output voltage of the distributed power supply and a standard value of at least one of the frequencies. The deviation is output, and the isolated operation determination unit generates an output signal indicating the isolated operation of the distributed power source based on the combination of the deviations.

[0010]

BEST MODE FOR CARRYING OUT 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 of Z1 and a line impedance of Z2, and is connected to a distributed power source G. In the electric power system to which the load Li is connected, Equation 1 of FIG. 5 is established. Since the impedances ZL1 and ZLi of the loads L1 and Li are usually much larger than the power source impedance and the line impedance, the load impedance can be ignored when considering the impedance viewed from the distributed power source G to the main system side. . Therefore, in the system of FIG. 2, Expression 2 of FIG. 5 is established between the terminal voltage Et of the distributed power source G and the output current Ig.

Now, assuming that the main system power supply Es is cut off at point A in FIG. 2, the main system power supply E seen from the distributed power supply G is shown.
Since s is zero and the power source impedance Z1 becomes infinite, 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 calculated, the formula 4 is obtained from the differentiation of the formula 2 when the system is connected, and the formula 3 is obtained when the system voltage is disconnected. The relationship of Equation 5 is obtained from the differentiation of As is apparent, the equation 5 shows that the line impedances Z1 and Z2 are greater than the load impedances ZL1 and ZL2.
Are neglected in consideration of being sufficiently small, and correspond to a state in which the loads ZLi and ZL1 are connected in parallel to the distributed power source. From the above analysis, it can be seen that the impedance viewed from the distributed power source on the system side is expressed by equation 4 during normal interconnection operation, and changes abruptly to equation 5 when it is disconnected and shifts to isolated operation.

The present invention estimates the equivalent impedance and / or the system side power supply voltage Es when the system side is viewed from the distributed power source, or further, the variation of these estimated values and / or
Alternatively, the rate of change is monitored to detect that the distributed power source is in the independent operation state. For this,
Consider a case where the output current Ig from the dispersed power source G is changed at a cycle sufficiently lower than the commercial frequency. In such a system, the capacitance of the line and the parallel capacitor can be ignored, so that the equivalent circuit is shown in FIG. Here, R and L are the resistance and inductance components of the line, and Lg is the impedance seen from the output terminal of the distributed power supply G to the distributed power supply side. 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.

Based on these relationships, when the output current Ig from the distributed power source G is gently changed, each time ti
The coefficients (parameters) Es, R, and X such that the relationship between the actually measured current Igi and the actually measured terminal voltage Eti at (i is a positive integer of 1 to n) satisfy Expression 6 are obtained by an appropriate parameter estimation method. The parameter estimation method is, for example, published by Ohmsha Co., Ltd. October 30, 1983, edited by the Society of Instrument and Control Engineers, "Automatic Control Handbook, Equipment / Application" 51
Page 6, "6. 3 Parameter estimation" and Corona Co., Ltd. March 25, 1988, "Hyundai Control Series (1)"
“Signal analysis and system identification”, Takayoshi Nakamizo, pages 7 to 17, “estimation”, page 127, “least squares estimation” and the like.

As one method of parameter estimation, for example, the typical least squares method described in the above document can be used. In that case, the difference εi between the estimated terminal voltage Etif (equation 7) obtained by substituting the measured current Igi into the equation 6 and the measured terminal voltage Eti, that is, ε ² expressed by the equations 8 and 9 is minimized. Then, the estimated values of the main system voltage Es, the resistance R of the line and the reactance component X are calculated. Phase angle (β + θ) of the measured current Igi with respect to the main system voltage Es
As is clear from FIG. 4, it is uniquely determined when R, X and θ are given. By the way, since θ can be measured as θ i, 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, Etif and E
The difference with ti may be the difference in absolute value.

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, when this is substituted into Expression 9, Expression 11 is obtained.
Is obtained. Es, R, and X in Eq. 11 are changed little by little, and Es that Eq.
, R, X values, ie the coefficient Es that minimizes Equation 8,
The values of R and X can be obtained.

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 portions. The output (current Ig, voltage Et) of the distributed power source 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 source frequency. Regarding the M series (longest series), for example, Jitec Publishing Co., Ltd. Showa 5
This is described in detail in "Latest spread spectrum communication method", written by Toshi Tateno et al. Further, even if the output current is not forcibly changed, naturally occurring output fluctuation can be detected and used as it is. Time t
output current Igti and voltage Eti of the distributed power source G at i
Are measured and supplied to the parameter estimation calculation unit 12. The parameter estimation calculation unit 12 uses the appropriate method (for example, the least square method) as described above to supply the main system power supply voltage E.
At least one of the maximum likelihood values of s, line resistance R, and line reactance X is estimated.

The parameter reference setting device 13 is a system parameter in a normal interconnection operating state of each distributed power source, that is, each distributed power source, which is obtained in advance for each distributed power source or interconnection system or partial system. The standard values of the main system power supply voltage Es, the line resistance R, and the line reactance X as seen from the output terminal of, and set values such as the deviation amount 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 compares them with their respective standard values, and the respective deviations are equal to or larger 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 isolated operation. The determination of the isolated operation can be made based on, for example, the following state that continues for a set time (for example, several seconds to 10 seconds) or more.

(1) When the estimated value of the main system power supply voltage Es becomes zero. Naturally, the estimated value of the main system power supply voltage Es shows a value close to the rated value during the interconnection operation, but when the main system is shut off, the estimated value of the voltage becomes zero as described above. ,
This makes it possible to determine the islanding operation.

(2) When the equivalent impedance (R and / or X) suddenly increases and its change width and / or change speed becomes larger than a set value. The equivalent impedance during the normal interconnection operation is substantially only the line impedance and is very small and small. On the other hand, the interconnection end is opened in the isolated operation. Therefore, even if the load as shown in FIG. Even if the load impedance ZL1 is added, the equivalent impedance becomes large in each stage. Based on such a fact, islanding can be determined by monitoring the increase in the equivalent impedance. Although there are variations in each system as a criterion in this case, for example, if an increase of several tens% or more is detected within 0.5 seconds, and if this state continues for several seconds to 10 seconds or more, it is considered as an independent criterion. It can be assumed that it is determined to be driving.

(3) When the value of R / X becomes larger than 1 to 1.5 or more. The value of R / X is about 0.5 to 1 in a normal transmission and distribution line, but if the main system power supply is cut off with the load still connected to shift to the independent operation, the load impedance is added as described above. Therefore, the value increases to 2 or more (because the load power factor is usually 90% or more). Therefore, the islanding operation can be determined based on such a change.

Further, a voltage / frequency anomaly detection section 16 supplied with an output voltage (and, if necessary, current) signal of the distributed power source G is additionally provided, and an abnormal rise in voltage or frequency observed at the output end of the distributed power source. If an abnormal change in the phase difference between the output voltage and the output voltage occurs, and if these abnormal states continue for a predetermined time (for example, several seconds to 10 seconds), the second abnormal signal or each individual abnormal signal is used. The signal may be output to the driving determination unit 15 to generate a signal indicating the isolated driving.

That is, the islanding operation judging section 15 receives the second abnormal signal from the voltage / frequency and other abnormality detecting section 16 in the form of an analog signal (in this case, the deviation amount from the standard value of the voltage and frequency), Based on the combination (logical product or logical sum) of this and the deviation amount (or ratio) from the standard value 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 isolated operation state of the distributed power source. For example, the deviation amount (or ratio) of the voltage and frequency at the output end of each parameter and the distributed power source is estimated or calculated in advance for each cutoff point (for example, point A in FIG. 2) of the power system. Then, if these combinations are stored in the table, the variance of each deviation amount (or ratio) from the abnormality detection unit 14 and the voltage / frequency abnormality detection unit 16 can be referred to in the table to obtain the variance. The isolated operation of the power supply can be determined. That is, the generation of the signal indicating the isolated operation of the distributed power source may be determined based on the combination of the deviation amounts (or ratios).

Regarding the frequency fluctuation, for example, within ± 0.5 seconds, ± 0.1% to ± 0.3% (0.06 to 0.18H
If the variation of z) is detected, the abnormality is detected, and this abnormality is 5
If it is continued for 10 seconds, it can be determined to be an isolated operation.
With respect to the other parameters, it is possible to detect an abnormality and determine the islanding operation based on substantially the same criteria.

The input data (terminal voltage Eti, current Igti, phase difference θi) necessary for the above-mentioned arithmetic processing can be taken in by the following method. (1) Measure the voltage and current amplitude values and the phase difference between them. (2) The output voltage of the dispersed power source is varied at a frequency ωm lower than the commercial frequency ωc to generate a current Igi having an amplitude-modulated waveform as represented by the equation 12 in FIG. 5, and (ωc + ωm) in the equation The component or the (ωc −ωm) component is extracted using, for example, a known correlation filter. Regarding the correlation filter (Matched Filter), for example, published by HBJ Publishing Bureau on March 13, 1986, “Detailed Digital Analog Communication System”, pages 484 to 491, and Hyundai Engineering Co. 198.
Published June 20, 2012 "Analog / Digital Signal Analysis"
Pp.263-265.

[0025]

According to the present invention, the output current and voltage (and the phase difference between the two) actually measured at the output end of the distributed power supply.
On the basis of the above, it is possible to estimate the impedance and the power supply voltage on the main series side viewed from the distributed power supply, and in this way, the estimated impedance and / or the change of the power supply voltage, the frequency, etc. can be monitored or prepared in advance. By comparing with the standard value, even when the power generation amount and the load amount in the partial series separated from the main series are in balance or are close to the balance, it is possible to reliably detect the isolated operation of the distributed power source. , Can be disconnected if necessary. further,
It is also possible to monitor the stability of the power system based on the estimated impedance.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing an example of a power system suitable for applying the present invention.

FIG. 3 is an equivalent circuit diagram of the power system of FIG.

4 is a vector diagram of voltage and current in the circuit of FIG.

FIG. 5 is a diagram showing an arithmetic expression used in the present invention.

[Explanation of symbols]

11 ... Output control device 12 ... Parameter estimation calculation unit 1
3 ... Parameter reference setter 14 Abnormality detection unit 15 ... Single operation determination unit 16 ... Abnormality detection unit for voltage, frequency, etc.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akio Tsuji, 4-19-18 Shimizu, Minami-ku, Fukuoka-shi, Fukuoka Prefecture Kyushu Electric Manufacturing Co., Ltd. (72) Inventor Takayuki Torikai 4-chome, Shimizu, Minami-ku, Fukuoka-shi, Fukuoka 19-18 No. 18 in Kyushu Electric Manufacturing Co., Ltd. (72) Yu Yamashita 4-19-18 Shimizu, Minami-ku, Fukuoka City, Fukuoka Prefecture

Claims (13)

[Claims] 1. An output voltage Eti and a current Igi (i is a positive integer 1 to n) of a distributed power source connected to a main system such as a commercial power system.
Of the distributed power supply, the output voltage Et, the current Ig, the system power supply voltage Es
, And system impedance Z = R + jX (however,
R is the line resistance, and X is the line reactance. Substituting the measured current value Igi into the relational expression Et = Es + Ig (R + jX), the estimated terminal voltage value Etif
= Es + Igi (R + jX), and further estimates and calculates the line resistance R and the line reactance X that minimize the difference between the estimated terminal voltage value Etif and the measured voltage value Eti. Equivalent impedance estimation method. 2. The impedance estimation method for a power system according to claim 1, wherein the output voltage Eti and the current Igi are measured while varying the output of the distributed power source. 3. An output voltage and current of a distributed power source connected to a main power system such as a commercial power system is measured with time, and the main voltage seen from the distributed power source is based on the obtained voltage and current measurement values. Estimating the equivalent impedance on the system side, and when at least one of the amount of change and the speed of change of the estimated equivalent impedance exceeds a predetermined value, a distributed power supply that generates a signal indicating the isolated operation of the distributed power supply is generated. An islanding detection method. 4. The output voltage and current of a distributed power supply connected to a mains system such as a commercial power system are measured over time, and the output voltage and current are viewed from the distributed power supply based on a plurality of different voltage and current measurement values. Estimating the main system equivalent power supply voltage, when the estimated equivalent power supply voltage drops to substantially zero,
A method for detecting an isolated operation of a distributed power source, which comprises generating a signal indicating the isolated operation of the distributed power source. 5. The phase difference between the output voltage and the current of the distributed power source is further measured with time, and the main voltage viewed from the distributed power source is based on the plurality of voltage and current measurement values and the measured phase difference. The distributed power source islanding operation detection method according to claim 3 or 4, wherein the equivalent impedance on the system side is estimated. 6. The estimation of the equivalent impedance and the equivalent power supply voltage on the main system side as viewed from the distributed power supply is performed based on an equivalent circuit in which a series circuit of the equivalent impedance and the equivalent power supply is connected to the output terminal of the distributed power supply. The distributed power source isolated operation detection method according to any one of claims 3 to 5, wherein: 7. The output voltage and current of the distributed power supply are measured by changing the output voltage and current of the distributed power supply regardless of the load of the distributed power supply.
The method for detecting isolated operation of a distributed power source according to any one of 1. 8. The output voltage frequency of the distributed power supply is further measured, and a signal indicating the isolated operation of the distributed power supply is generated in consideration of the variation amount and / or the variation speed of at least one of the output voltage and the frequency. The distributed power source isolated operation detection method according to any one of claims 1 to 7, wherein: 9. A means for measuring the output voltage and current of a distributed power source connected to a main system such as a commercial power system over time, and the distributed power source based on the obtained plurality of voltage and current measurement values. And a means for estimating at least one of the equivalent impedance and the equivalent power supply voltage on the main system side when viewed from above, and when the fluctuation amount and / or the fluctuation speed of at least one of the estimated equivalent impedance and the equivalent power supply voltage exceeds a predetermined value. A distributed power source isolated operation detecting apparatus comprising: an abnormality detection unit that generates a signal indicating the isolated operation of the distributed power source. 10. The distributed power source islanding operation detection device according to claim 9, further comprising output control means for changing an output voltage and a current of the distributed power source irrespective of a load. 11. A means for measuring an output voltage frequency of the distributed power supply; and a second means when it is detected that a variation amount and / or a variation speed of at least one of the output voltage and the frequency exceeds a reference value. An abnormality detecting means for generating an abnormal signal, such as a voltage frequency, and an islanding operation determining section for generating an output signal indicating an islanding operation of the distributed power source based on the signal from the abnormality detecting section and the second abnormality signal are further provided. The distributed power source isolated-operation detecting device according to claim 9 or 10, characterized in that. 12. The abnormality detecting section outputs a deviation of at least one of the estimated equivalent impedance and the equivalent power supply voltage from a standard value, and the abnormality detecting means such as a voltage frequency is at least one of an output voltage and a frequency of the distributed power supply. 12. The deviation from the standard value is output, and the isolated operation determination unit generates an output signal indicating isolated operation of the distributed power source based on a combination of the deviations. Distributed power source isolated operation detection device. 13. The distributed power source isolated operation according to claim 12, wherein the standard value is predetermined based on a value when the distributed power source is connected to a grid and is normally operating. Detection device.