JPH1114675A - Power system harmonic measurement method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To determine the admittance of a measured harmonic from a measurement result by injecting a current of a non-integer multiple frequency of a fundamental wave into a power system, the amount of injected current has an adverse effect on a load of the power system. Set the optimum amount not to be given so that it can be obtained accurately. SOLUTION: A current of a non-integer multiple frequency of a fundamental wave of each of upper and lower sides of a measurement harmonic is injected into an injection point 4 of a power system 1 while gradually increasing the current, and the injection point 4 based on the injection current is obtained.
When the distortion voltage at the injection frequency rises to a substantially predetermined upper limit voltage, the injection current stops increasing, and the operation shifts to harmonic measurement, where the injection point 4 based on the injection current on both the upper and lower sides of the measurement harmonic is measured. The admittance of an equivalent circuit for the injection current on the target side of the system 1 is calculated from the measurement result of the voltage and at least one of the currents higher and lower than the injection point 4, and the injection currents on the upper and lower sides of the measurement harmonic are calculated. The admittance of the equivalent circuit for the measured harmonic on the side of interest is obtained and determined by interpolation processing based on the admittance obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring harmonics of a power system for obtaining an admittance or an equivalent circuit of a harmonic (measurement harmonic) 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 integer multiple of the frequency fs of the fundamental wave of the system power supply, and the typical frequency of the fifth harmonic (fifth harmonic) is 5 · fs. is there.

[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 generally regarded as a parallel circuit of an admittance and a current source, of which the admittance is the most important from the viewpoint of 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. , The size and phase of the current source are calculated and estimated.

[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.

[0009] For example, a harmonic current of an integral multiple frequency n · fs (n is an integer) of a fundamental wave (frequency fs) is injected into a connection point of the filter device, and current, voltage, etc. at various points in the system at that time. Even when trying to find an equivalent circuit for the higher harmonics from the measurement results, since the higher harmonics exist in the power system, it is not possible to clarify changes in current, voltage, etc. based on changes in the injected harmonics. The admittance and the equivalent circuit of the power system with respect to the harmonic cannot be obtained accurately.

Therefore, conventionally, it is not possible to individually and accurately obtain the admittance and the equivalent circuit for the higher and lower harmonics such as the connection point of the filter device in the power system, and as a result, when switching the system, etc. Precise prediction of the voltage level of harmonics could not be made.

By the way, assuming that the n-th harmonic is the measurement harmonic, the power system (real system) does not originally have a non-integer multiple frequency component of the fundamental wave above and below the measurement harmonic. From the measurement results based on the injection of the currents at these frequencies, it is conceivable to determine the admittance and the equivalent circuit for the measured harmonics of the power system as follows.

That is, a current having a frequency that is a non-integer multiple of the fundamental wave on both the upper and lower sides of the measured harmonic is injected into the power system, and based on the measurement result, the injected current on the upper and lower sides of the measured harmonic of the power system is measured. Find the admittance of the equivalent circuit for.

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

Further, when obtaining an equivalent circuit, a current source for the measured harmonics of the power system is obtained from the obtained admittance and the measurement results of the current and the voltage for the measured harmonics of the power system, and the admittance and the current source are obtained. To find an equivalent circuit consisting of a parallel circuit with

In this case, the admittance of the power system with respect to the current having a non-integer multiple frequency of the fundamental wave is accurately obtained from the measurement result, so that the admittance and the equivalent circuit of the measured harmonic can be accurately obtained.

From the viewpoint of measurement accuracy and the like, it is desirable to increase the amount of current injection at a frequency that is a non-integer multiple of the fundamental wave. However, the load conditions of the power system differ depending on the system, time zone, and the like. It is extremely difficult to properly set.

Then, an appropriately set constant amount (set amount)
Simply injecting the current into the power system and measuring it, the degree of voltage distortion with respect to the injection frequency of the power system changes according to the change in the load condition, and in some cases, the injection becomes insufficient and the measurement is performed with the desired accuracy. The situation that cannot be done arises.

Further, if the injection frequency coincides with or is close to the resonance point of the power system, the distortion voltage of the power system due to the injection is significantly increased by the resonance. Causes an excessive distortion voltage of
The load on the power system may be adversely affected.

Since the load condition of the power system changes every moment and is unknown and its resonance frequency cannot be grasped, the current of a non-integer multiple frequency of the fundamental wave adversely affects the load of the power system. It is not possible to accurately determine the admittance and the equivalent circuit of the measured harmonic from the measurement result obtained by injecting no optimal amount.

According to the present invention, the injection amount of the current having a non-integer multiple frequency of the fundamental wave on the upper and lower sides of the measurement harmonic is set to an optimum amount which does not adversely affect the load on the power system, and the measurement is performed from the injection result. It is an object to accurately determine an admittance and an equivalent circuit for harmonics.

[0021]

In order to solve the above-mentioned problems, a method for measuring harmonics of a power system according to claim 1 of the present application measures harmonics of an integral multiple of a fundamental wave of a power system. Inject into the power system harmonic injection point currents at non-integer multiples of the fundamental wave on each of the upper and lower sides of the measurement harmonic, while gradually increasing the current. The distortion voltage at the injection frequency at the harmonic injection point based on the injection current is measured, and when the distortion voltage rises to a substantially predetermined upper limit voltage, the injection current stops increasing, and the operation shifts to harmonic measurement. From the measurement results of the voltage at the harmonic injection point based on the injection currents on both the upper and lower sides of the wave and at least one of the currents higher and lower than the harmonic injection point of the power system, the power consisting of the upper and / or lower power Measurement of the line of interest Calculate the admittance of the equivalent circuit for the injection currents on both the upper and lower sides of the wave, and perform interpolation processing based on the calculated admittances for the injection currents on the upper and lower sides of the measurement harmonic to obtain the equivalent of the measured harmonics on the target side. Determined for admittance of the circuit.

Therefore, the current of a non-integer multiple frequency of the fundamental wave on each of the upper and lower sides of the measured harmonic is gradually increased and injected into the power system to repeatedly measure the distortion voltage at the injected frequency. Based on this, the current amount immediately before the generation of an excessive distortion voltage in the power system, that is, the optimum injection amount that does not adversely affect the load of the power system due to the injection is set.

The current injection at the optimum injection amount does not adversely affect the load on the power system, and the power system is capable of injecting a non-integer multiple frequency of the fundamental wave on each of the upper and lower sides of the measured harmonic. The admittance of the attention side is accurately determined, and the admittance of the measurement harmonic of the attention side is accurately determined from the result.

According to a second aspect of the present invention, there is provided a method for measuring harmonics in an electric power system, wherein a harmonic having an integral multiple of a fundamental wave of the electric power system is used as a measurement harmonic, and the measured harmonic is added to a harmonic injection point of the electric power system. The current at a non-integer multiple of the fundamental wave on each of the upper and lower sides is gradually increased and injected, and the distortion voltage of the injection frequency at the harmonic injection point based on the injected current on the upper and lower sides of the measured harmonic is reduced. When the distortion voltage rises to a predetermined upper limit voltage, the injection current stops increasing, and the operation shifts to harmonic measurement. The harmonic injection point is based on the injection current at both the upper and lower sides of the measured harmonic. From the measurement results of at least one of the higher and lower currents of the voltage and the harmonic injection point of the power system, the injection currents on the upper and lower sides of the measurement harmonic on the attention side of the power system consisting of the upper and lower ones About the equivalent circuit The admittance of the equivalent circuit for the measured harmonic on the side of interest is determined and determined by interpolation processing based on the calculated admittance of the injection current on the upper and lower sides of the measured harmonic by calculating the dominance and determining the admittance. Based on the measurement results of the voltage and current of the measured harmonic of the power system at the harmonic injection point, the current source of the equivalent circuit for the measured harmonic of interest is determined and determined, and the admittance between the determined admittance and the current source is determined. An equivalent circuit for the measured harmonic on the side of interest is determined by a parallel circuit.

Therefore, in this case, the admittance of the measured harmonic on the target side of the power system obtained in the same manner as in claim 1 and the measurement results of the voltage and current of the measured harmonic of the power system are obtained by: A current source of the measurement harmonic in parallel with the admittance on the power system's attention side is required, and an equivalent circuit for the measurement harmonic consisting of a parallel circuit of the admittance and the current source on the power system's attention side is a load of the power system. Is accurately determined without adversely affecting the system.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. When measuring the harmonic equivalent circuit of the power system, as shown in FIG.
An appropriate position between the system power supply 2 and the load 3, for example, a position where a filter device for reducing harmonic current is connected is designated as a harmonic injection point 4. Inject current.

By the way, in addition to the fundamental wave of the frequency fs, the power system 1 has harmonics of the frequency n · fs which are integral multiples of the fundamental wave.
The lower part (load side) of the system 1 viewed from the harmonic injection point 4 is almost in a state where the load 3 is connected, and the upper part (power supply side) is connected to the system power supply 2 via a line impedance 6 including a transimpedance of a distribution transformer, for example. Is connected.

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

It should be noted 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 previously known from the line characteristics of the power system 1 and are known.

When the n-th order harmonic is used as a measurement harmonic, and the admittance (circuit constant) that changes every moment in the upper and lower harmonic injection points 4 for the measurement harmonic is obtained,
The voltage at the injection point 4 (system voltage) is measured by the transformer 7,
At least one of the upper and lower parts of the harmonic injection point 4, for example, the upper part of the current is measured by the current transformer 8.

Further, the measurement signal of the voltage of the transformer 7 is
The signal is supplied to a synchronizing signal generator 9 having an L circuit configuration.
As a result, a synchronization control signal synchronized with a fundamental wave of, for example, 60 Hz of the system power supply 2 is formed based on the control signal of the control unit 10.

Then, based on the control of the control unit 10, the injection source signal creating unit 11 to which the synchronization control signal is supplied, as an injection signal of a non-integer multiple frequency of the fundamental wave above and below the measurement harmonic, An injection signal of a non-integer multiple frequency of the fundamental wave synchronized with the fundamental wave between the measurement harmonic (nth harmonic) and each of the n ± 1st harmonics is formed.

Next, the injection signal is amplified by an amplifier 12 to form an injection current on each of the upper and lower sides of the measured harmonic, and this injection current is passed through an injection circuit 13 and a switch 14 to obtain a harmonic injection. Injection is made at a point 4, the system voltage at the harmonic injection point 4 based on the injection is measured by the transformer 7, and at least one of the upper and lower harmonic currents of the harmonic injection point 4, for example, the upper system current is converted to the current transformer 8. Measured by

The injection current at the harmonic injection point 4 is measured by the current transformer 15. The current injection period is set to, for example, 10 periods of the fundamental wave in consideration of measurement accuracy based on frequency analysis and the like described later.

The measurement signal of the voltage of the transformer 7 and the measurement signal of the current of the current transformers 8 and 15 are supplied to the A / D converter 16, which controls the synchronization of the synchronization signal generator 9. Each measurement signal is converted into measurement data by a sampling pulse synchronized with the fundamental wave of the sampling timing control unit 17 based on the signal.

Next, these measurement data are supplied to a signal processing unit 18, which performs DET processing, F
A digital frequency analysis process such as an FT process or an analog frequency analysis process is executed, and based on a result of this analysis, at least one of the upper and lower harmonic injection points 4 of the power system 1;
For example, with the lower side as the target side, the admittances of the injection frequencies on the upper and lower sides of the measurement harmonic on the target side are obtained.

Further, the admittance on the target side of the measured harmonic having an intermediate value is obtained and determined by interpolation processing based on the admittance of the upper and lower injection frequencies.

When obtaining an equivalent circuit for the measured harmonic on the side of interest, the determined admittance and power system 1
A current source in parallel with the determined admittance is also obtained from the measured harmonic current and voltage measurement results.

Next, a method of injecting an injection current on both upper and lower sides of the measurement harmonic will be described. First, as shown in the equivalent circuits 19 and 20 of FIG. 2, the admittances Yn ₁ and Yn ₂ and the current source Gn ₁ are shown in the upper and lower equivalent circuits of the harmonic injection point 4 for the n-th harmonic of the power system 1. , Gn
It can be regarded as a parallel circuit with ₂ .

Further, the equivalent circuit of the power system 1 for the non-integer multiple of the fundamental wave on the upper and lower sides of the n-th harmonic has only admittance because there is no component of this frequency.

Then, the power system 1 is a 1KVA-based small-capacity load circuit model that easily causes voltage distortion due to the injection of harmonics, and the measured harmonic is the fifth harmonic of n = 5. In the case where the injection current of a non-integer multiple frequency of the fundamental wave on both sides is a 5.5th harmonic and a 4.5th harmonic intermediate order harmonic synchronized with the fundamental wave, the current injection was performed based on various experiments. Gives a voltage distortion of about 0.3% with respect to the fundamental voltage, the admittance Yn ₁ , Yn ₂ and the equivalent of the measured harmonic on the attention side can be obtained from the measurement result without adversely affecting the load of the power system 1. It has been found that circuits 19 and 20 can be obtained.

On the other hand, the resonance point of the power system 1 is 5.5 order,
When a 4.5th intermediate order harmonic or a frequency in the vicinity thereof is reached, 5.5% or 4.5th intermediate order harmonic current is injected, and the above 0.3% A large distortion voltage exceeding the above occurs.

Then, the distortion voltage of 0.3% of the fundamental wave voltage is set as a predetermined upper limit voltage (threshold value), and the control unit 10 executes the injection flow rate determination processing of FIG. determining the amount of injected current of the intermediate order harmonics by treatment ₁ to S _5.

That is, when the harmonic order or frequency of the injection current on both the upper and lower sides of the measurement harmonic is given to the control unit 10 by keyboard operation or the like, the control unit 10 firstly operates, for example, on the lower side of the measurement harmonic. 4.5th harmonic frequency [fundamental wave is 60H
270Hz ｛= (240 + 300) /
2｝] is set as the injection frequency, and in step S ₁ , the signal gain of the injection source signal generator 11 is controlled so as to form an injection signal of the initial injection amount (start level) of the injection frequency, and the harmonic injection point 4 is set. Is injected with the current of the initial injection amount of the 4.5th harmonic.

Next, the process proceeds to step S _2, transformer 7
The signal processing unit 18 analyzes and processes the measured data of the voltage of the A / D conversion unit 16 based on the measurement signal of (1), and detects the distortion voltage of the power system 1 based on the 4.5th harmonic current injection.

[0047] The detection result (distorted voltage) is transmitted to the control unit 10, the control unit 10 compares the upper limit voltage distortion voltage transmitted by the step S _3, the transmitted distortion voltage reaches the upper limit voltage until the process returns to step S ₂ via step S _4, the injected current amount small portions, for example, a fixed amount Δ
The process of increasing by I and injecting into the power system 1 is repeated.

When the distortion voltage based on the injection current rises to the upper limit voltage, the process proceeds from step S ₃ to step S ₅ , where the injection current is reduced by a fixed amount ΔI and returned to the immediately preceding magnitude, and the injection current is reduced. The magnitude (implantation amount) at which a distortion voltage of about 0.3% of the fundamental wave is generated is determined, and the current amount determination processing ends.

After completion of the above operation, the operation proceeds to the harmonic measurement, and the current of the 4.5th harmonic of the determined injection amount is injected into the harmonic injection point 4, and the measurement results of the transformer 7 and the current transformers 8, 15 are obtained. From 4.5
The admittance of the attention side of the power system 1 for the next harmonic is determined.

Further, when the admittance of the 4.5th harmonic is obtained, the control unit 10 sets the upper 5.5 of the measured harmonic.
Next harmonic frequency [330Hz if fundamental wave is 60Hz
{= 300 + 360) / 2}] is set as the injection frequency, and the injection amount determination processing of FIG. 3 is executed again. As in the case of the 4.5th harmonic, the injection current of the 5.5th harmonic is set. Is gradually injected into the harmonic injection point 4.

The distortion voltage of the power system 1 based on the 5.5th harmonic injection current is approximately 0.3% of the fundamental wave voltage.
When it becomes larger, the injection current is determined to this value, and the operation shifts to harmonic measurement, and the admittance of the attention side for the 5.5th harmonic is obtained.

Therefore, the injection currents of the 5.5th harmonic and the 4.5th harmonic on the upper and lower sides of the measured harmonic (the 5th harmonic) are respectively substantially applied to the power system 1 by the injection. Is automatically set to the optimal injection amount immediately before the 0.3% distortion voltage occurs. Based on the current injection of the optimal current amount,
The admittance of the 5.5th harmonic and the 4.5th harmonic on the target side of the power system 1 is obtained.

In this case, the frequency of the injected current is
At the resonance point or at a frequency near the resonance point, excessive voltage distortion does not occur in the power system 1 and the load on the power system 1 is not adversely affected. Is determined.

Incidentally, the initial injection amount and the change amount ΔI of the injection current may be the same fixed amount, and may be, for example, an amount that increases or decreases linearly or non-linearly.

The optimum injection amount may be determined by increasing the injection current from zero. However, as described below, the optimum injection amount is determined by increasing the injection amount in consideration of the voltage expansion rate at the resonance point. Is preferable in practical use.

That is, the power system 1 is set to, for example, 10 MVA.
Assuming that the lower side of the harmonic injection point 4 is the target side, the equivalent circuit of the n-th harmonic is, as shown in FIG.
The parallel circuit of the admittance Yn ₂ and the current source _{IGn2 in} FIG. 2 can be represented as admittance Yn, and this admittance Yn is composed of an n-order admittance in which a capacitance component SC and a resistance load component Y are combined in parallel.

At this time, the voltage of the nth harmonic of the system power supply 2 is set to En, and the wiring impedance 6 for the nth harmonic mainly based on the impedance of the distribution transformer is set to jXL.
Assuming that n, the voltage Vn of the nth harmonic at the harmonic injection point 4 is expressed by the following equation (1).

[0058]

## EQU1 ## Vn = En / (1 + jXLn.Yn)

Further, the voltage expansion rate is represented by Vn / En, and based on the equation (1), the voltage expansion rate Vn / En is 1 /
It is obtained from the absolute value of (1 + jXLn · Yn).

For the fifth harmonic (n = 5), when the resistance load component Y is changed to a load of 1000% (1 MW load) and the capacitance component SC is changed to 0 to 100% (0 to 10 MVA), the voltage expansion rate becomes V ₅ / E ₅ changes in the range of approximately 1 to 25 as shown in the actual measurement results in FIG.
It can be seen that it is magnified 5 times.

Next, an intermediate order harmonic that does not exist in the power system 1 on both the upper and lower sides of the nth harmonic is converted into an n ± mth harmonic (0 <m).
When the current In ± m of the n ± m-th harmonic is injected into the harmonic injection point 4, the equivalent circuit of the power system 1 similar to that of FIG. 4 is as shown in FIG.

In FIG. 6, the admittance Yn ± m on the attention side below the harmonic injection point 4 is composed of a parallel combination of the capacitance component SC ′ and the resistance component Y ′. If the wiring impedance 6 is jXLn ± m, Voltage Vn at harmonic injection point 4
± m is expressed by the following equation (2).

[0063]

Vn ± m = (jXLn ± m · In ± m) / (1
+ JXLn ± m ・ Yn ± m)

In the equations (1) and (2), In =
In ± m, Vn = Vn ± m, XLn = XLn ± m, Yn
Assuming that = Yn ± m, the denominator of both equations becomes equal, and the equation of Equation 2 can be expressed by the following Equation 3.

[0065]

## EQU3 ## Vn ± m = (jXLn · In) · Voltage expansion rate

The equation (3) is, for example, the fifth harmonic (n =
5) When injecting the current of the middle order harmonic near the upper and lower sides,
If the voltage expansion rate is 25 (maximum), the voltage expansion rate is 1
(Minimum), the same voltage distortion as when the voltage expansion rate is 1 occurs at a current amount of 1/25, and the power system 1
Indicates that even if a current of the same magnitude is injected, excessive or insufficient voltage distortion occurs.

Therefore, when the measured harmonic is the fifth harmonic and the upper limit voltage (threshold) for injection is 0.3% of the fundamental wave voltage, the intermediate harmonics on both upper and lower sides of the measured harmonic are used. The initial injection amount of the wave injection current is set to an amount such that the distortion voltage due to the injection becomes 1/25 of the 0.3%, and the amount of the injection current is determined by increasing the injection amount.

Next, a specific method of obtaining the admittance of the attention side based on the injection result of the determined injection current will be described.

For simplicity of explanation, the current of the intermediate order harmonic injected into the harmonic injection point 4 is defined as Ix, and this current I
Let Vx be the voltage at the harmonic injection point 4 based on the injection of x, and let Ix be the current flowing through each of the upper and lower harmonic injection points 4.
_1, and Ix _2, higher than the current Ix _1, Ix ₂ harmonic injection point 4 of the power system 1 based on, when the lower admittance and Yx _1, Yx _2, admittance Yx _1, Yx
₂ is obtained from each of the following equations (4) and (5).

[0070]

## EQU4 ## Yx ₁ = Ix ₁ / Vx

[0071]

## 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
When the lower side is set as the attention side, the signal processing unit 18 outputs the A /
The voltage Vx is obtained by analyzing the frequency of the
And current Ix, seek 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.

[0075] Furthermore, based current Ix, the Ix _1, the signal processing unit 18 Ix ₂ = on the calculation of the Ix-Ix ₁ attention side of the measuring harmonics, determine the current Ix ₂ intermediate degree harmonics of the lower 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).

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, the admittance Yn ₂ of the measured harmonic on the target side is given by admittance Yx ₂ (d) where the admittance of the current Ix ₂ on both the upper and lower sides is Yx ₂ (u), Yx ₂ (d). u), Yx ₂ (d).

For this reason, the signal processing section 18 executes an interpolation operation by a simple average or a least square method based on the admittances Yx ₂ (u) and Yx ₂ (d), and obtains an equivalent circuit 20 of FIG. Is determined by obtaining the admittance Yn ₂ of

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

Also, in the case where the upper side of the harmonic injection point 4 is the target side, based on the current Ix ₁ , the current Ix, and the voltage Vx obtained from the measurement or the calculation of Ix−Ix _{2 in} the same manner as described above. 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 measured harmonic by setting both the upper and lower harmonics of the harmonic injection point 4 as the attention side. In this case, current transformers are provided for 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, in order to more completely find an equivalent circuit for a measured harmonic composed of a parallel circuit of the admittance and the current source, not only the admittance but also the signal processing unit 18 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 Yn ₂ on the side of interest for the measured harmonic is determined, the measurement of the transformer 7 and the current transformer 8 with the switch 14 opened after the end of the current injection of the intermediate order harmonic is completed. The frequency (harmonic voltage) and 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 signal.

Then, assuming that the harmonic voltage of the measured harmonic is Vn and the harmonic current is In (the direction from upper to lower is positive),
As is clear from the equivalent circuit diagram of FIG. 2, the following two equations (6) and (7) hold for the lower and upper harmonic injection points 4 respectively.

[0089]

## _EQU6 ## I _Gn1 = In + Vn · Yn ₁

[0090]

## _EQU7 ## I _Gn2 = Vn · Yn ₂ -In

Therefore, when the _target side is below the harmonic injection point 4, the signal processing unit 18 _obtains the current source I _Gn2 of the measurement harmonic on the _target side from the calculation of the equation (7), and obtains the measurement tone of FIG. The attention side equivalent circuit 20 for the wave is determined.

When the target side is higher than the harmonic injection point 4, the equivalent circuit 19 is determined by _{obtaining the} current source I _Gn1 from the calculation of the equation (6).

In this case, the equivalent circuits 19 and 20 for the measurement harmonic on the side of interest are individually and accurately obtained.

[0094] Incidentally, each circuit constant _{Yn 1, Yn 2, I Gn1} , I Gn2 information such as determined attention side of the equivalent circuits 19 and 20 are 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 harmonics are reduced by system switching or the like, the above-described measurements are repeated to grasp the state of the latest equivalent circuits 19 and 20 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.

In this embodiment, the injection current of the intermediate order harmonics on the upper and lower sides of the measurement harmonic is actually gradually injected into the electric power system 1 while the injection amount is increased. , The two injection currents are determined to be the optimum amount of current at which the distortion voltage caused by the injection adversely affects the load of the power system 1, and the power for the measured harmonic is determined based on the result of the injection of the optimum current amount. Admittance Yn _{1 of} system 1,
Since Yn ₂ or the equivalent circuits 19 and 20 have been obtained, the circuit characteristics of the power system 1 with respect to harmonics can be accurately obtained without causing a failure due to so-called harmonic injection of the power system 1.

The injection currents on the upper and lower sides of the measurement harmonic may be currents having an appropriate frequency which is a non-integer multiple of the fundamental wave which is not synchronized with the fundamental wave. Is also good.

When the injection currents on the upper and lower sides of the measurement harmonic are plural, for example, the admittance is obtained for each injection current on both the upper and lower sides, and the average value and the like are obtained. What is necessary is to find the admittance of the wave. The magnitude of the upper limit voltage may be set according to the state of the power system 1 or the like.

[0099]

The present invention has the following effects. First, in the case of claim 1, a current of a non-integer multiple frequency of each of the fundamental waves on both upper and lower sides of the measurement harmonic is injected into the power system 1 while gradually increasing, and a distortion voltage at the injection frequency is measured. Based on the repetition, the current amount immediately before an excessive distortion voltage is generated in the power system 1, that is, the optimum injection amount that does not adversely affect the load of the power system 1 due to the injection can be set.

The current injection at the optimum injection amount does not adversely affect the load of the power system 1 and the power system for current injection at a non-integer multiple frequency of the fundamental wave on each of the upper and lower sides of the measured harmonic. 1, the admittance of the attention side of the power system 1 can be accurately obtained.
The admittance of the measurement harmonic on the side of interest can be accurately determined without causing an obstacle due to harmonic injection.

Also, in the case of claim 2, the admittance of the measured harmonic on the target side of the power system 1 obtained in the same manner as in the case of claim 1 and the voltage of the measured harmonic of the power system 1,
Based on the current measurement result, a current source of a measurement harmonic parallel to the admittance on the target side of the power system 1 can be obtained, and a measurement source including a parallel circuit of the admittance and the current source on the target side of the power system 1 can be obtained. An equivalent circuit for the wave can be obtained accurately without adversely affecting the load of the power system 1.

[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 diagram of the power system of FIG.

FIG. 3 is a flowchart of an injection current determination process of FIG. 1;

FIG. 4 is a first equivalent circuit diagram for explaining the determination of an injection current in FIG. 1;

FIG. 5 is a measurement diagram of resonance characteristics.

FIG. 6 is a second equivalent circuit diagram for explaining the determination of the injection current in FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 power system 4 harmonic injection point 5 measuring device 19, 20 equivalent circuit

Continued on the front page (72) Inventor Shoji Nishimura, 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi Nissin Electric Co., Ltd. Inventor Toshihiko Shikata 47, Umezu Takaune-cho, Ukyo-ku, Kyoto Nissin Electric Co., Ltd.

Claims (2)

[Claims] 1. A harmonic having an integral multiple of a fundamental frequency of a power system as a measurement harmonic, and a non-integer multiple of the fundamental wave on each of the upper and lower sides of the measurement harmonic at a harmonic injection point of the power system. Injecting while gradually increasing the frequency current, measuring the distortion voltage of the injection frequency at the harmonic injection point based on the injection currents on both the upper and lower sides of the measurement harmonic, wherein the distortion voltage is substantially a predetermined upper limit. When the voltage rises to a voltage, the increase of the injection current is stopped, and the operation shifts to harmonic measurement. The voltage of the harmonic injection point based on the injection current on each of the upper and lower sides of the measurement harmonic and the power system From the measurement results of at least one of the higher and lower currents from the harmonic injection point, the measured values of the injection current on the upper and lower sides of the measurement harmonic on the attention side of the power system, which is composed of at least the upper and lower ones, Equivalent circuit Calculating an admittance, and determining and determining an admittance of an equivalent circuit for the measurement harmonic on the side of interest by performing an interpolation process based on the calculated admittance for the injection currents above and below the measurement harmonic. Power system harmonic measurement method. 2. A harmonic which is an integral multiple of a fundamental frequency of a power system as a measurement harmonic, and a non-integer of the fundamental wave on each of upper and lower sides of the measurement harmonic is added to a harmonic injection point of the power system. Injecting while gradually increasing the current of the double frequency, measuring the distortion voltage of the injection frequency at the harmonic injection point based on the injection current on each of the upper and lower sides of the measurement harmonic, wherein the distortion voltage is substantially predetermined. When the voltage rises to the upper limit voltage, the injection current stops increasing and shifts to harmonic measurement. The voltage at the harmonic injection point based on the injection currents on the upper and lower sides of the measurement harmonic and the power system From the measurement results of at least one of the higher and lower currents above the harmonic injection point of the injection current on the upper and lower sides of the measurement harmonic on the side of interest of the power system comprising at least the upper and lower ones The equivalent of The admittance of the path is calculated, and the admittance of the equivalent circuit for the measurement harmonic on the side of interest is determined and determined by interpolation processing based on the calculated admittance of the injection current on the upper and lower sides of the measurement harmonic. The determined admittance of the measured harmonic and the measurement result of the voltage and current of the measured harmonic of the power system at the harmonic injection point, the equivalent circuit of the measured harmonic on the side of interest. A method for measuring harmonics in a power system, comprising determining and determining a current source, and determining the equivalent circuit for the measurement harmonic on the side of interest using a parallel circuit of the determined admittance and the current source.