JP2940603B2 - Power system harmonic measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring admittance (impedance) or an equivalent circuit of a harmonic (measured harmonic) of a power system, and a method of measuring the harmonics of the power system.

[0002]

2. Description of the Related Art In a technique for suppressing harmonics in power transmission and distribution systems of a power system, it has been regarded as important to reduce harmonics by a so-called system switching technique utilizing harmonic loss.

The frequency of a harmonic generated by system switching or the like is an integral multiple of the frequency fs of the fundamental wave of the system power supply, and the typical frequency of the fifth harmonic is 5 × fs.

[0004] The reduction of harmonics is performed by installing a filter based on prediction of the voltage level of the harmonics by a filter facility attached to the capacitor facility.

At this time, in order to predict the voltage level of the harmonic, for example, the characteristics of the higher (upstream) and lower (downstream) harmonics from the connection point of the filter equipment of the power system are grasped, and the equivalent circuit thereof is determined. Need to ask.

This equivalent circuit can be regarded as a parallel circuit of admittance and a current source or a series circuit of impedance and a voltage source, of which the admittance or impedance is the most important from the viewpoint of understanding the characteristics.

[0007] The Transactions of the Institute of Electrical Engineers of Japan, B, 101, 8
No., p. 451-458, (Showa 56-8) discloses that when obtaining an equivalent circuit for the fifth harmonic of a distribution line, the voltage and current of the fundamental wave of the system are measured, and the admittance of the equivalent circuit with respect to harmonics is obtained from the results. It describes calculating and estimating (impedance), the size and phase of a current source (voltage source), and the like.

[0008]

As described in the above-mentioned documents and the like, when an equivalent circuit for harmonics of a power system is obtained from the measurement results of the voltage and current of the fundamental wave, it cannot be obtained with high accuracy. There is.

For example, a current (voltage) of a harmonic of an integral multiple of the fundamental wave (frequency fs) m × fs (m is an integer of 1, 2,...) Is injected (applied) to a connection point of the filter device. However, even if an attempt is made to obtain an equivalent circuit for the higher harmonics from the measurement results of the current and voltage at various points in the system at that time, since the higher harmonics exist in the power system, the current and voltage based on the injected harmonic changes Equal changes could not be clearly measured, and the admittance (impedance) and equivalent circuit of the power system could not be accurately obtained for the harmonics.

Therefore, conventionally, it is not possible to individually and accurately obtain the admittance (impedance) and the equivalent circuit for the higher and lower harmonics such as the connection point of the filter device in the power system. In this case, it was not possible to accurately predict the voltage level of the harmonic.

By the way, assuming that the m-th harmonic is the measurement harmonic, the electric power system (real system) does not originally have a current or voltage of a non-integer multiple frequency of the fundamental wave above and below the measurement harmonic. Therefore, it is conceivable to obtain an admittance (impedance) and an equivalent circuit for the measured harmonics of the power system from the measurement results based on the injection or application of these currents and voltages in the following manner.

That is, a current (voltage) having a non-integer multiple frequency of the fundamental wave on both upper and lower sides of the measurement harmonic is injected or applied to the power system.
Find the admittance (impedance) on both lower sides.

Then, the admittance (impedance) on the upper and lower sides of the measured harmonic is subjected to interpolation processing such as averaging, and the admittance (impedance) of the power system for the intermediate measured harmonic is obtained.

Further, when an equivalent circuit is obtained, a current source (voltage source) for the measured harmonics of the power system is obtained based on the obtained admittance (impedance) and the current and voltage measurement results for the measured harmonics of the power system. And an equivalent circuit composed of a parallel circuit of the admittance and the current source or a series circuit of the impedance and the voltage source is obtained.

In this case, since the admittance (impedance) of the power system based on the current (voltage) of a non-integer multiple frequency of the fundamental wave is accurately obtained from the measurement result, the admittance (impedance) of the measured harmonic and the equivalent circuit can be accurately determined. You can ask.

However, the measurement of the voltage and current of the power system based on the injection or application of a current (voltage) having a non-integer multiple frequency of the fundamental wave is performed by processing the sampling result by frequency analysis such as digital Fourier analysis (DFT). To do
It is not easy to appropriately determine the frequency of the current (voltage) of the non-integer multiple frequency in consideration of a demand for measurement accuracy and suppression of an analysis error due to a so-called sampling edge.

In particular, a plurality of currents (voltages) of the non-integer multiple frequency on each of the upper and lower sides of the measurement harmonic are set as a plurality, and the respective admittances (impedances) of the upper and lower sides of the measurement harmonic are set as a plurality of measurement results. It is extremely difficult to determine the frequency of the current (voltage) of each non-integer multiple frequency when trying to obtain the current with higher accuracy from the average or the like.

The analysis error due to the sampling edge is an error in the frequency analysis caused by the discontinuity of the start and end of the sampling. To prevent this error, the sampling frequency is set to be sufficiently higher than the frequency of the fundamental wave. Higher makes the measuring device expensive and complicated.

According to the present invention, a current (voltage) having a non-integer multiple of the fundamental wave above and below the measurement harmonic is injected (applied) into the power system, and the measured harmonics of the power system are measured based on the measurement results. When obtaining an admittance (impedance) or an equivalent circuit, the frequency of a current (voltage) having a non-integer multiple of the fundamental wave is determined from a simple calculation formula in consideration of measurement accuracy and the like, and the current ( It is an object of the present invention to prevent an error in the frequency analysis at the time of measurement and to inject the voltage into the power system.

[0020]

In order to solve the above-mentioned problems, a method of measuring harmonics of a power system according to claim 1 of the present application is directed to a method of measuring a harmonic (m times (m) times a fundamental frequency of a frequency fs of a power system).
) Is the m-th harmonic measurement harmonic of the frequency, and when calculating the admittance of the measurement wave of the power system or the equivalent circuit composed of the parallel circuit of the admittance and the current source, the upper and lower sides of the measurement harmonic The current synchronized with the fundamental wave of a non-integer multiple of the fundamental wave is defined as the current of the intermediate harmonic, and the current of the intermediate harmonic between the measured harmonic (mth harmonic) and the m ± 1st harmonic is calculated. The frequency fx of the current is given by fx = (fs × m) ± ｛(fs
/ N) × k} (where n is the measurement accuracy 1 / n (0 <1
/ N <1), and k is an integer of 1, 2,..., N for frequency setting) and determined at the harmonic injection point of the power system. A current of an intermediate order harmonic having a frequency fx on both upper and lower sides of the harmonic is injected for n periods of a fundamental wave,
The voltage at the harmonic injection point based on this injection and at least one of the currents higher and lower than the harmonic injection point of the power system are measured, and at least one of the upper and lower levels is set as the target side, and the result of the measurement is used as the target side. The admittance is calculated for the intermediate order harmonics on both the upper and lower sides of the measured harmonic, and the admittance of the measured harmonic on the side of interest is determined by interpolation processing based on the calculation result.

In the method for measuring harmonics of a power system according to a second aspect of the present invention, an m-th harmonic having a frequency m times (m is an integer) of a fundamental wave of a frequency fs of the power system is set as a measurement harmonic, and When obtaining the impedance of the measurement wave or an equivalent circuit consisting of a series circuit of the impedance and the voltage source, the voltage synchronized with the fundamental wave of a non-integer multiple of the fundamental wave on the upper and lower sides of the measurement harmonic is calculated as an intermediate value. The frequency of the voltage of the intermediate order harmonic between the measured harmonic (m order harmonic) and the m ± 1 order harmonic is fx = (fs ×
m) ± {(fs / n) × k} (where n is an integer of 1, 2,... depending on the measurement accuracy 1 / n (0 <1 / n <1),
k is an integer of 1, 2,..., n for frequency setting) and determined at the harmonic injection point of the power system, the voltage of the intermediate order harmonic of the frequency fx above and below the measured harmonic. Is applied for n cycles of the fundamental wave, and the voltage at the harmonic injection point based on this application and at least one of the currents higher and lower than the harmonic injection point of the power system are measured, and at least one of the upper and lower levels is noted. As the side, the impedance for the intermediate order harmonics on the upper and lower sides of the measurement harmonic on the attention side is calculated from the measurement result on the attention side, and the impedance for the measurement harmonic on the attention side is calculated by interpolation based on the calculation result. To determine.

Therefore, in the case of the harmonic measuring method according to the above claims, the current (voltage) of a non-integer multiple frequency of the fundamental wave on the upper and lower sides of the measured wave can be calculated from a simple formula in consideration of the measurement accuracy. It is obtained as the current (voltage) of the intermediate order harmonic synchronized with the fundamental wave.

Further, the current (voltage) of the intermediate order harmonics
Is injected or applied over n periods of the fundamental wave,
The injection period of the current (voltage) of the intermediate order harmonic is always an integer period (m × n ± k).

Then, the voltage and current of the power system are measured based on the current injection (voltage application) of the intermediate order harmonic of the integer period, and the current and the current of the intermediate order harmonic of the integer period of the power system are measured.
If the voltage is sampled and subjected to frequency analysis or the like, the sampling synchronized with the fundamental wave prevents the frequency analysis error due to the sampling edge without increasing the sampling frequency, and the admittance of the measured harmonic wave with the desired measurement accuracy ( Impedance) is obtained, and from this result, an equivalent circuit is also obtained.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. (First Embodiment) When measuring harmonics of a power system, as shown in FIG. 1, an appropriate position between a system power supply 2 and a load 3 of the power system 1, for example, a filter for reducing a harmonic current. The position where the device is connected is defined as a harmonic injection point 4, and a current (voltage) is injected or applied from the measuring device 5 to the injection point 4.

Incidentally, in addition to the fundamental wave having the frequency fs, the power system 1 has harmonics having a frequency n × fs which is an integral multiple of the fundamental wave.
The lower side (load side) of the system 1 viewed from the harmonic injection point 4 is in a state where the load 3 is almost connected, and the upper side (power supply side) is in a state where the system power supply 2 is connected via the line impedance 6, for example. .

At this time, the harmonic equivalent circuit in which the upper and lower parts are expressed by Norton's theorem can be regarded as a parallel circuit of the admittance and the current source, respectively.

Note that the lower current source does not actually exist but is formed equivalently due to current distortion caused by a load.

The upper line impedance 6 and the like are known in advance from the line characteristics of the power system 1 and are known.

The m-th harmonic, such as the fifth harmonic (m = 5), is used as a measurement harmonic, and the admittance (circuit constant) of the upper and lower harmonic injection points 4 for this measurement harmonic that changes every moment. ), The voltage (system voltage) at the harmonic injection point 4 is measured by the transformer 7, and
At least one of the lower order, for example, the upper order current is measured by the current transformer 8.

Further, the signal of the detection voltage of the transformer 7 is
The signal is supplied to a synchronizing signal generator 9 having an L circuit configuration.
Thus, based on the control signal of the control unit 10, a synchronization control signal of a non-integer multiple frequency (frequency fx) of the fundamental wave synchronized with the fundamental wave of, for example, 60 Hz of the system power supply 2 is formed.

Then, based on the synchronization control signal, a signal of the frequency fx synchronized with the fundamental wave is created as an injection signal of the intermediate order harmonic by the injection source signal creation section 11, and the injection signal is amplified by the amplifier 12. To form a current of an intermediate order harmonic having the frequency fx, and inject the current into the harmonic injection point 4 via the injection circuit 13 and the switch 14.

At this time, for the current of the intermediate order harmonic, the frequency fx and the like are set by the following processing of the control unit 10.

That is, the measurement harmonic is the m-th harmonic, and the measurement accuracy is 1 / n (where n is 0 <1 / n <1).
2, the control unit 10 calculates the m-order measurement harmonic and m ± 1 on both upper and lower sides from the calculation of the following equation (1).
The frequency fx of each intermediate-order harmonic with the second-order harmonic is obtained and determined.

[0035]

Fx = (fs × m) ± {(fs / n) × k}

Here, k is 1, 2,..., N for frequency setting.
When k = 1, 2,..., N−1, the frequency of the intermediate-order harmonic at an interval of fs / n is obtained from Expression 1, and when k = n, fx = fs × ( m ± 1), and the frequency of the equation (1) coincides with the frequencies of the m ± 1 order harmonics on both upper and lower sides of the measured harmonic.

If k = 0, the frequency of the equation (1) becomes fx = fs × m, which coincides with the frequency of the measured harmonic (mth harmonic).

By the way, fs, m, n, k in the equation (1)
Is given to the control unit 10 by a keyboard operation of the operation unit 15 or the like, and the fifth harmonic (5th harmonic) of the 60 Hz power system is provided.
Is used as a measurement harmonic, and its admittance is obtained with a measurement accuracy of 1/10, fs = 60 (H
z), m = 5, n = 10, k = 1, 2,..., 10 are given to the control unit 10.

In this case, at k = 1, fx = 300 ± 6H
fx = 300 ± 12 Hz for z and k = 2, f for k = 3
When x = 300 ± 13 Hz,..., k = 10, fx = 300
± 60 Hz, the fifth harmonic (300 Hz) and above
The frequency fx of the intermediate-order harmonic at intervals of 6 Hz, which is obtained by equally dividing each of the lower sixth harmonic and the fourth harmonic (300 ± 60 Hz) into ten, is obtained.

When the measurement accuracy is reduced to half,
k = 1, 2 and fx = 300 ± 30H at k = 1
When z and k = 2, k = 300 ± 60 Hz (the frequency of the sixth and fourth harmonics) can be obtained from the calculation.

The control unit 10 forms, for all or a part of each of the frequencies fx obtained from the calculation, a transmission control signal composed of, for example, data of the ratio to the frequency of the measured harmonic. Based on the reception of the signal indicating the establishment of synchronization, each transmission control signal is sequentially supplied to the injection source signal creation unit 11.

Based on this supply, the injection source signal generator 11
Forms an injection signal of each frequency fx synchronized with each of the fundamental waves on the upper and lower sides of the measurement harmonic in order, and sequentially forms n periods of the fundamental wave.

Then, each injection signal of the injection signal generator 11 is amplified to form a current of each intermediate order harmonic having a frequency fx synchronized with the fundamental wave on each of the upper and lower sides of the measurement harmonic. A current is sequentially generated for n periods of the fundamental wave and injected into the harmonic injection point 4.

At this time, by injecting n periods of the fundamental wave,
The current of each intermediate order harmonic is: Tx = (n / fs) / (1 /
fx) Period injection is performed, and the injection period Tx always becomes an integer period as shown in the following equation (2).

[0045]

Tx = (n / fs) × fx = (n × m) ± k

The current of each intermediate-order harmonic injected into the harmonic injection point 4 is detected by the current transformer 16.

The voltage at the harmonic injection point 4 based on the injection of the current of each intermediate harmonic is detected by the transformer 7, and the current flowing above the harmonic injection point 4 is changed by the current transformer 8.
Is detected by

The detection signal of the voltage of the transformer 7 and the detection signal of the current of the current transformers 8 and 16 are supplied to an A / D converter 17, which converts the synchronization control signal of the synchronization signal generator 9. By the timing control of the sampling timing creating unit 18 based on the above, each time the current of each intermediate order harmonic is injected,
Each detection signal is sampled while shifting the phase over n periods of the fundamental wave in synchronization with the fundamental wave of the power system.

At this time, the sampling of the A / D converter 17 is started by detecting the establishment of the synchronization of the generator 9 based on the signal indicating the establishment of the synchronization of the synchronization signal generator 9 and then injecting the signal from the controller 10. A together with the wave signal generator 11 and the switch 14
A start (close) instruction is given to the / D converter 17 and set.

Further, since the current (voltage) of each intermediate-order harmonic is synchronized with the fundamental wave, and the sampling period is always an integral multiple of the period of the fundamental wave, the sampling in synchronization with the fundamental wave is performed. Continuity of start and end can be maintained. In this case, a frequency analysis error due to a sampling edge can be prevented without extremely increasing the sampling frequency, and A / D conversion can be performed by a relatively low-frequency and inexpensive and simple sampling circuit. The part 17 can be formed.

Then, the sampling data (measurement data) of the A / D converter 17 is supplied to the signal processor 19, and the signal processor 19 performs a calculation described below to place the data higher than the harmonic injection point 4 of the power system 1. , At least one of the lower levels is set as the target side, and the admittance and the like of the measurement harmonic on the target side are obtained.

First, for the sake of simplicity, assuming that the current of the intermediate order harmonic injected into the harmonic injection point 4 is Ix,
The current Ix is a current having a frequency fx that does not exist in the power system 1, and the power system 1 is in a state where only the admittance Yx exists with respect to the current Ix.

At this time, if the voltage at the harmonic injection point 4 based on the current Ix is Vx, the admittance Yx can be accurately obtained from the following equation (3) without being affected by the harmonics existing in the power system 1. I get it.

[0054]

## EQU3 ## Yx = Ix / Vx

Further, based on the injection of the current Ix, the power system 1
The currents flowing higher and lower than the harmonic injection point 4 are Ix ₁ and Ix _2, and the admittances higher and lower than the harmonic injection point 4 of the power system based on the currents Ix ₁ and Ix ₂ are Yx ₁ and Yx. Assuming ₂ , admittance Yx ₁ ,
Yx ₂ is obtained from each of the following two equations (4) and (5).

[0056]

## EQU4 ## Yx ₁ = Ix ₁ / Vx

[0057]

## EQU5 ## Yx ₂ = Ix ₂ / Vx

If _{one of} the currents Ix ₁ and Ix ₂ is measured, Ix ₁ = Ix−Ix ₂ and Ix ₂ = Ix
The other is obtained by calculation of -ix _1.

Therefore, the harmonic injection point 4 of the power system 1
If the lower side is the attention side, the signal processing unit 19
Voltage Vx and current Ix by frequency analysis of the DFT analysis or the like of the measurement data D converter 17 obtains the Ix _1.

At this time, the injection current is an integer period current synchronized with the fundamental wave of the power system 1, and the sampling start and end continuity is maintained by the sampling synchronized with the fundamental wave. No frequency analysis error such as a DFT error occurs.

[0061] Further, the current Ix, on the basis of the Ix _1, Ix
₂ = on the calculation of the Ix-Ix ₁ attention side of the measuring harmonics, determine the current Ix ₂ intermediate degree harmonics below both sides.

Then, based on the current Ix ₂ and the voltage Vx,
The admittance Yx ₂ for the intermediate order harmonics on the upper and lower sides of the measurement harmonic on the side of interest is calculated from the equation (5).

The frequency fx obtained from the equation (1)
When multiple intermediate degree harmonic current is injected, on the measurement harmonic, per each lower sides, it seeks current Ix ₂ of the plurality of intermediate orders harmonics admittance Yx ₂ for each intermediate orders harmonic Ask for.

At this time, since the current Ix is a current having a frequency that does not exist in the power system 1, the admittance Yx ₂ can be accurately obtained without being affected by harmonics of the power system 1 even if the amount of injected power is minute. I get it.

Even if a harmonic current of the measured harmonic is injected instead of the current Ix, the admittance based on the injected harmonic current cannot be obtained because the harmonic exists in the power system 1. .

Next, assuming that the admittance of the measurement harmonic on the side of interest is Ym, and that the admittance of the current Ix ₂ on the upper and lower sides is Yx ₂ (u) and Yx ₂ (d), The admittance Ym can be obtained as an intermediate value between the admittances Yx ₂ (u) and Yx ₂ (d).

For this reason, the signal processing section 19 executes an interpolation operation by a simple average method or a least square method based on the obtained admittances Yx ₂ (u) and Yx ₂ (d) to obtain the admittance Ym for the measured harmonic. To decide.

At this time, the admittance Yx ₂ (u), Y
If a plurality of x ₂ (d) are determined, for example,
An average value (representative value) is obtained by a simple average, a least squares method, or the like for each of the admittances Yx ₂ (u) and Yx ₂ (d), and the admittance Ym is obtained by performing the above-described interpolation operation using the average value.

At this time, the admittance Yx ₂ (u), Y
Since x ₂ (d) is accurately calculated without being affected by harmonics of the power system 1, the admittance Ym of the measured harmonic can be accurately obtained.

The higher current Ix _{1 at the} harmonic injection point 4
Instead of measuring may measure the current Ix ₂ of the lower, in this case, immediately noticed side current Ix ₂ is obtained from the measured current.

[0071] In the case of a target-side upper harmonic injection point 4 also based current obtained from the operation of the measurement or Ix-Ix ₂ Ix ₁ and the current Ix, the voltage Vx, in the same manner as the Thus, the admittance of the measured harmonic can be accurately obtained without being affected by harmonics of the power system 1.

It is also possible to determine the admittance of each of the measured harmonics by using both the upper and lower harmonics of the harmonic injection point 4 as the attention side. In this case, current transformers are provided in both the upper and lower harmonics. Currents Ix ₁ , Ix flowing in the upper and lower parts
₂ may be measured respectively.

When the admittance of the measurement harmonic on the target side is obtained, the behavior of the measurement harmonic on the target side can be grasped.

By the way, in this embodiment, not only the admittance but also an equivalent circuit for a measurement harmonic composed of a parallel circuit of this admittance and a current source is more completely obtained. After determining and determining the admittance of the target side for the target, the current source of the target side for the measured harmonic is calculated and its equivalent circuit is determined, as described below.

That is, when the admittance of the attention side of the measured harmonic is determined, the transformer 7 and the current transformer 8 with the switch 14 opened after the completion of the current injection of the intermediate order harmonic.
The voltage (harmonic voltage) and the current (harmonic current) of the measured harmonic of the power system 1 are obtained by frequency analysis of the measurement data of the A / D converter 17 based on the detection signal of the above.

Then, the obtained harmonic voltage of the measured harmonic is V
m, the harmonic current is Im (the direction from the upper to the lower is positive), the admittances of the equivalent circuits of the upper and lower measurement harmonics at the harmonic injection point 4 are Ym ₁ and Ym ₂ , and the current sources are I _Gm1 and I _Gm1 .
_{Assuming that Gm2} (the direction flowing to the harmonic injection point 4 is positive), as can be seen from the equivalent circuit of FIG. Holds.

[0077]

[ _Formula 6] I _Gm1 = Im + Vm · Ym ₁

[0078]

[Expression 7] I _Gm2 = Vm · Ym ₂ -Im

Therefore, the signal processing section 19 calculates 2
Determining seeking current source I _Gm1, I _Gm2 measurement harmonics of the target side from either or both of the calculation formulas determined seek equivalent circuits 20 and 21 of the measuring harmonics shown in FIG.

In this case, the equivalent circuits 20 and 21 for the measurement harmonic on the side of interest are individually and accurately obtained.

[0081] Then, each circuit constant Ym ₁ determined attention side of the equivalent circuit _{20,21, Ym 2, I Gm1,} I Gm2 such information is stored in the storage unit of the measuring device 5 (not shown) At the same time, a screen is displayed on a display unit (not shown) in the form of, for example, an equivalent circuit diagram.

When the harmonics are reduced by system switching or the like, the above-described measurements are repeated to grasp the state of the latest equivalent circuits 20 and 21 on the side of interest. The generation of accompanying harmonics is predicted, and the filter capacity of a filter device (not shown) connected to the harmonic injection point 4 is optimally set.

(Other Embodiment) Next, the harmonic equivalent circuit of the power system 1 is a series circuit of an impedance and a voltage source, and the impedance for the measurement harmonic on the target side or the equivalent of this impedance and the voltage source. A case where a circuit is obtained will be described.

In this case, when the voltage of the intermediate order harmonic obtained from the equation (1) of the voltage Vx and the frequency fx is applied to the harmonic injection point 4 for n periods of the fundamental wave and measured, the equation (3) is obtained instead of the equation (3). , Admittance Yx of this equation is represented by impedance Zx
(= 1 / Yx) holds, and the following two equations (8) and (9) hold as equations corresponding to the two equations (4) and (5).

[0085]

[Equation 8] Zx ₁ = Vx / Ix ₁

[0086]

## EQU9 ## Zx ₂ = Vx / Ix ₂

Therefore, the signal processor 19 measures the measured voltage Vx at the harmonic injection point 4 and the lower and upper currents Ix ₁ and Ix.
Based on _2, number 8, on a number 9 expression of the fundamental wave of interest side,
Impedance Zx ₁ for lower-order intermediate order harmonics
(= Zx ₁ (u), Zx ₁ (d), Zx ₂ (= Zx
₂ (u), Zx ₂ (d)).

[0088] Further, on the, the same interpolation processing on the impedance Zx ₁ or Zx ₂ below both sides, determining seeking impedance Zm (= 1 / Ym) for measuring harmonic.

When obtaining an equivalent circuit of the impedance Zm and the voltage source, the voltage Vm and the current Im of the measured harmonic at the harmonic injection point 4 are measured, and the equations corresponding to the equations (6) and (7) are obtained. current source I _Gm1 from operation of FIG. 2, is determined to seek a voltage source which corresponds to I _Gm2.

Instead of applying the voltage of the intermediate order harmonic, the current of the intermediate order harmonic is injected, and the impedances Zx ₁ , Zx ₁ , Z x
seeking x _2, it is also possible to determine the impedance Zm and an equivalent circuit for measuring harmonic.

Then, in both of the above embodiments,
The frequency fx of the current or voltage of the intermediate order harmonics on both the upper and lower sides of the measurement harmonic is determined in consideration of the measurement accuracy and the like by calculating a very simple formula of Equation 1, and particularly, the current or voltage of the intermediate order harmonics It is extremely useful when multiple voltages are injected or applied.

Further, the current (voltage) of each intermediate-order harmonic is synchronized with the fundamental wave, and its injection (application) period is set to n periods of the fundamental wave. Voltage) is always injected as an integral multiple of the fundamental wave,
When frequency analysis such as DFT analysis is performed on a predetermined result based on the injection (applied) to obtain admittance (impedance) for intermediate-order harmonics above and below the fundamental wave on the target side of the power system, the sampling frequency is Sampling synchronized with the fundamental wave without increasing the frequency resolution to a very high level can prevent continuity of sampling start and end points and prevent frequency analysis errors due to sampling edges. Highly accurate measurement can be performed.

[0093]

The present invention has the following effects. The injection current (applied voltage) at a frequency that is a non-integer multiple of the fundamental wave on the upper and lower sides of the measurement harmonic is calculated from a simple formula that takes into account the measurement accuracy. It can be obtained as a current (voltage).

Further, since the current (voltage) of the intermediate order harmonic is injected or applied over n periods of the fundamental wave, the injection period of the current (voltage) of the intermediate order harmonic must be set to an integer period (m × n ± k).

Therefore, the voltage and current of the power system 1 are measured based on the current injection (voltage application) of the intermediate order harmonic of the integer cycle, and the current (voltage) of the intermediate order harmonic of the integer cycle of the power system 1 is measured. Is sampled in synchronism with the fundamental wave and frequency analysis is performed, thereby preventing a frequency analysis error or the like due to a sampling edge without excessively increasing the sampling frequency and preventing the measurement harmonic of the attention side of the power system 1 from being measured. The admittance (impedance) of the upper and lower intermediate harmonics can be obtained.

The admittance (impedance) or the equivalent circuit of the measured harmonic can be obtained with the desired measurement accuracy from the result, and the admittance (impedance) of the higher harmonics of the power system 1 which was conventionally impossible is obtained. Alternatively, accurate measurement of the equivalent circuit can be performed based on a simple signal injection type calculation.

[Brief description of the drawings]

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

FIG. 2 is a harmonic equivalent circuit of the power system of FIG.

[Explanation of symbols]

 Reference Signs List 1 power system 4 harmonic injection point 5 measuring device 20, 21 equivalent circuit

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoji Nishimura, 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi Inside Nissin Electric Machinery Co., Ltd. Inside (72) Inventor Toshihiko Shikata 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi Nissin Electric Machinery Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) G01R 23/20 G01R 31/00 H02J 3/01

Claims (2)

(57) [Claims] 1. An m-order harmonic having a frequency that is m times (m is an integer) a fundamental frequency of a frequency fs of a power system is set as a measurement harmonic, and admittance of the measurement harmonic of the power system or the admittance and a current source are measured. When obtaining an equivalent circuit composed of a parallel circuit with the above, a current synchronized with the fundamental wave of a non-integer multiple of the fundamental wave on the upper and lower sides of the measurement harmonic is defined as a current of an intermediate order harmonic, The frequency fx of the current of the intermediate harmonic between the measurement harmonic (mth harmonic) and the m ± 1st harmonic is given by fx = (fs ×
m) ± {(fs / n) × k)} (where n is an integer of 1, 2,..., n according to measurement accuracy 1 / n (0 <1 / n <1), and k is frequency And an integer of 1, 2,..., N for setting), and at the harmonic injection point of the power system, the current of the intermediate-order harmonic of the frequency fx above and below the measurement harmonic. Inject n cycles of the fundamental wave, measure the voltage at the harmonic injection point based on the injection and at least one of the higher and lower currents than the higher harmonic injection point of the power system, The admittance of each of the intermediate order harmonics on the upper and lower sides of the measurement harmonic on the side of interest is calculated from the result of the measurement using the one side as the side of interest, and interpolation processing based on the calculation result is performed. Determining admittance for the measured harmonics and determining Harmonic measurement method that the power system. 2. An m-order harmonic having a frequency m times (m is an integer) a fundamental frequency of a frequency fs of a power system as a measurement harmonic, and an impedance or the impedance and a voltage source for the measurement harmonic of the power system. When obtaining an equivalent circuit consisting of a series circuit with the following, a voltage synchronized with the fundamental wave of a non-integer multiple of the fundamental wave on the upper and lower sides of the measurement harmonic is defined as a voltage of an intermediate order harmonic, The frequency fx of the voltage of the intermediate order harmonic between the measurement harmonic (mth harmonic) and the m ± 1st harmonic is given by fx = (fs ×
m) ± {(fs / n) × k} (where n is an integer of 1, 2,... depending on the measurement accuracy 1 / n (0 <1 / n <1),
k is an integer of 1, 2,..., n for frequency setting), and is determined at the harmonic injection point of the power system by intermediate order harmonics of the frequency fx above and below the measured harmonic. Is applied for n periods of the fundamental wave, and the voltage at the harmonic injection point based on the applied voltage and at least one of the currents higher and lower than the harmonic injection point of the power system are measured. At least one of the lower order is set as the attention side, and the impedance of the intermediate order harmonic on each of the upper and lower sides of the measurement harmonic on the attention side is calculated from the measurement result on the attention side, and the interpolation processing based on the calculation result, A method for measuring harmonics in a power system, comprising determining and determining impedance of the measurement harmonic on a target side.