JP2002022783A - Method and device for measuring harmonic characteristics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve measuring performance by precisely removing the noises of existing order-to-order harmonies in a system from measured values for a voltage and a current of the order-to-order harmonies in the power system during filling. SOLUTION: The noises of the existing filling frequency of the system are found from the digital frequency analysis of a voltage and a current in the power system sampled in synchronization with the system fundamental waves during non-filling at least either before or after filling. The noises are subtracted from the measured values by correcting the phase of the noises during non-filling to the phase during filling or the phase of the measured values during filling to the phase during non-filling. An equivalent circuit constant for the order-to- order harmonies of the filling frequency is calculated by removing the noises from the measured values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for injecting a current of an interharmonic having a frequency that is a non-integer multiple of a system fundamental wave into a power system, and obtaining a harmonic equivalent circuit of the power system based on the measurement result. The present invention relates to a harmonic characteristic measuring method for measuring the harmonic characteristics.

[0002]

2. Description of the Related Art Conventionally, in a power system, home electric appliances,
One of the important issues is to suppress harmonic currents generated from OA equipment, industrial equipment, etc., and to reduce voltage distortion in the system. Therefore, it is necessary to measure the momentary harmonic characteristics of the power system. There is.

The n-th harmonic of the power system is a frequency n · fs which is an integral multiple of the frequency (system fundamental) fs synchronized with the system fundamental wave, and is a typical fifth and seventh harmonic. The waves have frequencies of 5 · fs and 7 · fs.

In order to measure the characteristics (harmonic characteristics) of the power system with respect to these harmonics, the applicant of the present application has already proposed a method for measuring harmonic characteristics described below in Japanese Patent Application No. Hei 8-3101.
No. 92 and Japanese Patent Application No. 9-180570.

[0005] The measurement of the harmonic characteristics of these patent applications is based on measuring a current having a frequency that is a non-integer multiple of the fundamental wave above and below the harmonic to be measured in the power system as an intermediate harmonic, ie, an interharmonic. Is injected into the power system as a current, and the frequency and the current of the power system sampled at the time of the injection in synchronization with the system fundamental wave are analyzed by digital frequency analysis of the Fourier operation of the FFT and the DFT to obtain the order harmonics of the injection frequency of the power system. Current,
The voltage is detected, the measured value is obtained, and the admittance or impedance, which is the equivalent circuit constant for the inter-order harmonic of each injection frequency of the power system, is calculated from the voltage and current of the measured value, and the admittance or impedance is calculated. , The admittance or impedance of the power system for the harmonic to be measured is determined by interpolation.

In the case of this harmonic measurement, since the current of the inter-order harmonics above and below the harmonic to be measured is a current of a non-integer multiple of the system fundamental frequency fs which does not originally exist in the power system, the power system The admittance or impedance with respect to the inter-order harmonics can be accurately determined by injecting a small amount of current.
There is an advantage that the momentary harmonic characteristics of the seventh harmonic can be accurately measured and grasped.

However, in the case of the above-described method of measuring the harmonic characteristics, if a frequency component of the interharmonic exists in the power system, the existing component becomes noise and causes a measurement error.

[0008] Therefore, a large capacity for injection of inter-order harmonics,
A large current injection device is required, and the harmonic characteristics of the power system cannot be measured with a small injection capacity.

Therefore, the applicant of the present application has filed Japanese Patent Application No. 9-340.
According to the application of No. 676, the voltage and current of the frequency of each inter-harmonic of the power system before and after the injection of the current of each inter-harmonic are converted into the voltage of the noise of the existing inter-harmonic,
The measured voltage and measured current of each interharmonic of the power system based on the injection of the interharmonic current are measured as current.
The voltage and current of the noise are subtracted and corrected respectively,
Eliminating those effects has already been filed.

[0010]

As described above, the measured values of the voltage and current of each interharmonic of the power system before and after the injection of each interharmonic current before and after the injection of each interharmonic current are used as the conventional noise. When this noise is subtracted from the measured values of the voltage and current of each interharmonic of the power system at the time of injection and removed as it is, sampling at the time of non-injection and at the time of injection is started in synchronization with the system fundamental wave. Also, since the interharmonic frequency is a non-integer multiple of the frequency of the system fundamental wave, and the periodic fluctuation of the system fundamental wave cannot be ignored, the phase of the noise sampled during non-injection and the measured value during injection , The phase of the noise included in the non-injection differs from the phase of the noise during the non-injection.

Therefore, it is impossible to accurately remove the existing noise in the system from the measured values of the interharmonics at the time of the injection, and there is a problem that it is not possible to measure the harmonic characteristics with high accuracy.

An object of the present invention is to improve the measurement performance by accurately removing the noise of the inter-order harmonics existing in the system from the measured values of the voltage and current of the inter-order harmonics of the power system at the time of injection. I do.

[0013]

According to a first aspect of the present invention, there is provided a method for measuring harmonic characteristics, comprising the steps of:
For each interharmonic of each injection frequency, digital frequency analysis of the voltage and current of the power system sampled in synchronization with the system fundamental wave at least one of before and after non-injection at the time of injection, and Find noise,
Correction of the phase of the noise at the time of non-injection to the phase at the time of injection or correction of the phase of the measurement value at the time of injection to the phase at the time of non-injection, subtracting the noise from the measurement value, and subtracting the noise from the measurement value After removal, the equivalent circuit constant for the interharmonic of the injection frequency is calculated.

Therefore, the phase of the noise of the inter-order harmonic of the power system measured and measured at the time of non-injection and the noise included in the measured value of the inter-harmonic of the power system measured and measured at the time of injection are determined. The phase of the noise or the measured value is corrected so that it matches the phase of the noise, the noise is subtracted from the corrected measured value, and the existing noise is accurately removed from the measured value at the time of injection, resulting in a high-precision harmonic. Wave characteristics can be measured.

Further, in the harmonic characteristic measuring method according to the present invention, one of a phase of a noise at the time of non-injection and a phase of a measured value at the time of injection is set as a phase to be corrected.

The phase to be corrected is added to or subtracted from the phase to be corrected by the phase angle of the sampling interval and the product of the product of the sampling number during non-injection or injection and the order of the interharmonic, thereby correcting the phase to be corrected. Apply.

In this case, even if the period during the injection and the period during the non-injection change every moment due to the periodic fluctuation of the system fundamental wave, the phase angle of the sampling interval is constant and does not change. The correction amount (phase shift amount) of the inter-harmonic phase can be accurately determined from the product of the inter-harmonic order and the product of the inter-harmonic order. The phase of the noise of the measured value obtained at the time matches the phase of the noise with high accuracy, and the existing noise of the system is extremely accurately removed from the measured value at the time of injection.

Further, in the harmonic characteristic measuring apparatus according to the third aspect, PLL pulse generating means for outputting a sampling pulse synchronized with the system fundamental wave;

On the basis of the sampling pulse, the voltage of the power system sampled before and / or after the non-injection of at least one of the interharmonics of each injection frequency,
Means for determining the noise of the existing injection frequency from the digital frequency analysis of the current,

Either the noise at the time of non-injection or the phase of the measured value at the time of injection is taken as the phase to be corrected, and the phase angle of the sampling pulse interval and the sampling at the time of non-injection or injection are taken as the phase to be corrected. Means for correcting the phase to be corrected to a phase at the time of injection or a phase at the time of non-injection by adding or subtracting a phase shift amount of a product of the number of pulses and the order of the interharmonic.

Therefore, it is possible to provide a specific harmonic characteristic measuring apparatus which realizes the measuring methods of the first and second aspects.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
This will be described with reference to FIGS. FIG. 1 is a single-line system diagram showing the configuration of the harmonic characteristic measuring device, which is formed by an inverter or the like of the harmonic characteristic measuring device 2 at an injection point a of the inter-order harmonic current of the power system 1 to be measured. The connected current injection device 3 is connected.

Then, the harmonic to be measured is converted to a frequency n · f
Assuming that the s is the n-th harmonic, the current injection device 3 sequentially generates currents of inter-order harmonics having a frequency of a non-integer multiple of the upper and lower harmonics of the harmonic and injects the current into the injection point a. To do it periodically.

The injection current at the injection point a is measured by the current transformer 4 for the meter, the voltage of the power system 1 is measured by the transformer 5 for the meter, and the current on the load side of the injection point a of the power system 1 is measured. Is measured by the current transformer 6 for the instrument.

Then, the analog measurement outputs of the current transformers 4 and 6 and the transformer 5 are supplied to the A / D current transformer 7 of the measuring device 2, and the measurement output of the transformer 5 is also supplied to the PLL pulse generator 8. Supplied.

The PLL pulse generator 8 forms PLL pulse generating means, forms a sampling pulse of, for example, 3.9 MHz synchronized with the voltage of the system fundamental wave of the power system 1, and converts this sampling pulse to an A / D converter. 7 and the subsequent signal processing device 9 and arithmetic processing device 10.

The A / D converter 7 performs the injection current measured by the converters 4 and 6 by the converters 4 and 6 based on the sampling pulse, the current of the power system 1, and the power system measured by the transformer 5. 1 is sampled and converted into digital signals, and these digital signals are sent to the signal processing device 8.

Next, the signal processing device 9 performs a digital frequency analysis of the Fourier operation of the FFT and the DFT on the digital signals, and obtains the current and voltage (vector values) of the interharmonics of each injection frequency of the power system 1. ) Is detected and determined.

Further, the vector values of the voltage and the current as an analysis result of the signal processing device 7 are sent to the arithmetic processing device 10, and this processing device 10 executes the subtraction of the existing noise of the system and the calculation of the harmonic characteristic which will be described later. Then, for example, an equivalent circuit (harmonic equivalent circuit) 11 for the harmonic to be measured on the downstream side (load side) of the injection point a is obtained and determined.

By the way, the voltage and current of the noise of each inter-order harmonic existing in the system are usually very small, and the injection frequency of the injection frequency obtained from the analysis of the digital frequency before and after the injection of the current of each inter-harmonic is usually small. The voltage and the current become the voltage and the current of the noise of each inter-order harmonic existing in the system.

That is, assuming that the frequencies of the inter-harmonics sequentially injected are f ₁ , f ₂ , f ₃ ,..., For example, the frequency f before and after the injection of the current of the inter-harmonic of frequency f _{2 1,} the measurement result of the voltage of the frequency f ₂ obtained from the digital frequency analysis of the infusion period interharmonic current of f _3, the voltage of the current strains existing frequency f ₂ noise becomes current.

[0032] At this time, the system fundamental and interharmonic waveform of the injection frequency f ₂ of the frequency fs, for example, as shown in FIG. FIG. 2 shows the phase relationship, and the respective amplitudes are different from the actual ones.

[0033] Then, the solid line b in FIG. 2 is a system fundamental frequency fs, the solid line b is interharmonic frequency f _2.

Further, ta, tb and tc in the figure are the frequencies f
Between ₂ orders before injection of the harmonic, the time of injection, a timing of the measurement starting point after injection, current Lifetime or interharmonic frequency f ₁ to a part of the period of ta~tb is injected, t
Current Lifetime or interharmonic of frequency f ₂ in a part of the period is the injection of B～tc. Although the system fundamental wave is continuous, its phase changes due to periodic fluctuations and the like.

Further, since the inter-order harmonics do not coincide with the existing phase of the system and the injection phase, they become discontinuous at the time of injection and before and after the injection, and are the components of the inter-order harmonics existing in the system. However, for example, the phases of ta and tb are different.

On the other hand, the phase of the sampling pulse of the PLL pulse generator 8 is shifted by 360 degrees in one cycle of the system fundamental wave, and P sampling pulses (for example, 3.9 × 10 ⁶ ) in one cycle of the system fundamental wave.
), The interval (sampling interval)
The phase angle per τ does not depend on the period variation of the system fundamental wave, etc.
It becomes a constant value of 360 degrees / P.

If the order of the interharmonic of the injection frequency is m, the number of sampling pulses before the injection of ta to tb is P1, and the sampling number at the time of injection of tb to tc is P2, the time of ta to tb Is obtained from (360 degrees / P) · P1 · m, and the phase shift amount during the time from tb to tc is obtained from (360 degrees / P) · P2 · m.

Therefore, ta to tb, tb to tc,...
Whatever the time is, the injection frequency at those times, for example, f ₂ , is obtained from the product of the phase angle of the sampling interval (interval of the sampling pulse), the number of samples in the interval, and the order of the interharmonic. Is obtained.

For the interharmonics of the frequency f ₂ , the phase at ta of the noise before injection obtained from the voltage and current vector values obtained by digital frequency analysis is θa, and the measured value at injection is tb at tb. Is assumed to be θb, and the phase of the noise after injection at tc is θc.

At this time, the phases θa and θc of the noise advance and lag the phase shift amount at the time of injection.
Phase θ at the time of injection of phases θa and θc of noise before and after injection
Correction to a ′ and θc ′ can be performed by the following two equation addition / subtraction operation of the following equation (1).

[0041]

Equation 1 θa ′ = θa + (360 ° / P) · P1 · m θc ′ = θc− (360 ° / P) · P2 · m

Then, by this correction operation, the phase of the existing noise in the system obtained from the measurement before and after the non-injection is corrected to the phase at the time of the injection, and the corrected noise at the time of the non-injection is corrected. By subtracting from the measured value, unnecessary existing components in the system are accurately removed from the measured value of the interharmonic at the time of injection.

At this time, the noise to be subtracted from the measured value at the time of the injection may be noise obtained from one of the measurements before and after the injection. , It is desirable to average the noises obtained from both measurements after injection. Specifically, the noises obtained from both the measurements before injection and after injection are phase-corrected by the calculation of Equation 2 and then averaged. Preferably, the noise obtained by the averaging process is subtracted from the measured value on the injection side as the corrected non-injection noise.

Further, the phases θa and θc of the noises during non-injection
Are the phases θa ′, θ at the time of injection as phases to be corrected.
Instead of correcting to c ', the phase θb of the measured value at the time of injection
May be corrected to the phase θb ′ at the time of non-injection as a phase to be corrected.

When the phase θb of the measured value is corrected to the phase θb ′ before the injection, the phase θc of the noise after the injection is also corrected to the phase θc ″ before the injection, and the phase θa of the noise before and after the injection is corrected. , Θc and the phase θb of the measured value at the time of injection may be corrected to the phase before the injection in the lag direction, and the phases θb ′, θ
c ″ is obtained from the following operation of the two equations of Expression 2.

[0046]

Θb ′ = θb− (360 ° / P) · P2 · m θc ″ = θc− (360 ° / P) · (P1 + P2) · m

The phase θb of the measured value is used as the phase θb after the injection.
When correcting in the leading direction to b ″, the phase θa of the noise before the injection may be corrected in the leading direction to the phase θa ″ after the injection. In this case, the phases θa ″ and θb ″ are expressed by the following equation (3). From the calculation of

[0048]

Equation 3 θa ″ = θa + (360 ° / P) · (P1 + P2) · m θb ″ = θb + (360 ° / P) · P2 · m

[0049] Then, the measuring apparatus 2 operates as shown in the flowchart of the procedure of FIG. 3, the injection of the step S _1, a series of injection frequency f ₁ by the measurement, f _2, f _3, ... current rank of During the injection, the voltage and current of the power system 1 are measured and sampled during the injection, collected, and stored in the storage device 12.

Next, the process proceeds to step S _2, where the digital frequency analysis of the sampling result is executed by the signal processing device 9 based on the sampling pulse of the PLL pulse generator 8 based on the sampling result held in the storage device 12. For example, with respect to the interharmonics of the injection frequency f ₂ , the voltages and currents before and after the non-injection and after the injection are obtained, and the interharmonics of the other injection frequencies are also calculated during the non-injection and the non-injection, respectively. Find the voltage and current at the time of injection.

Next, the process proceeds to the operation of the arithmetic processing unit 10.
In step S _3, interharmonic current of each injection frequency, per voltage, phase θ of the respective non-injection when the noise
a, θc are detected, and in step S ₄ , the phases θa ′, θc when the phases θa, θc are injected are calculated based on the calculation of the two equations in Equation 1.
Correct to c '.

[0052] Further, in step S _5, per interharmonic each injection circuit, phase .theta.a ', .theta.c' obtains the average of the noise, the time of injection the average noise as noise of the system between existing orders harmonics Is subtracted (vector operation) from the measured values of (1) and (2), and the voltage and current of each interharmonic based on the injection of the power system 1 are obtained without the influence of the existing noise of the system.

By calculating the harmonic characteristics in step S ₆ , first, the admittance of each inter-harmonic of the power system 1 is obtained from the voltage and current of each inter-harmonic obtained in step S _5. Alternatively, the impedance is calculated as an equivalent circuit constant, and the constant (equivalent circuit constant) of the equivalent circuit 10 for the harmonic to be measured, that is, the admittance Y _(n) is interpolated from the admittance or impedance of these equivalent circuit constants, and the current is calculated. The source _{IG (n)} is also determined to determine the harmonic characteristics.

The measurement results are stored in the storage device 12 and displayed on a display device 13 such as a CRT.

Also, on the upstream side of the injection point a, the admittance and the current source for the harmonic to be measured can be obtained by the same method to measure the harmonic characteristics.

The existing noise of each injection frequency measured before and after the injection is corrected to the phase at the time of injection, and the phase is corrected from the measured values of the currents and voltages of the interharmonics of each injection frequency at the time of injection. Since the noise is subtracted, the existing noise in the system can be accurately removed from the measured value of each interharmonic at the time of injection, and the harmonic characteristics can be measured with high accuracy.

In this case, since the S / N of the measured value of each interharmonic at the time of injection increases and the frequency resolution increases, the current of each interharmonic injected by the power system 1 is reduced. In addition, there is an advantage that the current injection device 3 can be further reduced in capacity and size, and the measurement device 2 can be reduced in weight and size.

[0058] By the way, in step S ₄ in FIG. 2,
The same effect as described above can of course be obtained by performing the operation of the expression 2 or the expression 3 to correct the phase instead of the operation of the expression 2 of the expression 1.

In the above-described embodiment, the time immediately before the injection and the time when the other inter-harmonics are injected and measured at the subsequent stage are the time when the inter-harmonics are not injected. The time of non-injection is not limited to immediately before and immediately after injection.

In addition, at least one inter-order harmonic may be set above and below the harmonic to be measured.

Further, the transformer 5 and the current transformer 6 are connected to the injection point a.
Is provided in a system other than the injection system such as a system higher than the system provided with (injection system) or another system of the same level branched from the higher system, so that the injection system of the intermediate harmonic and the measurement system are different. It goes without saying that the present invention can be similarly applied to the case where the measurement is performed by using the above method.

[0062]

The present invention has the following effects. First, in the case of the harmonic characteristic measuring method and the harmonic characteristic measuring device according to claim 1, the phase of the noise of the inter-order harmonic of the power system 1 determined by measuring at the time of non-injection is measured at the time of injection. Since the phase of the noise or the measured value was corrected so that the phase of the noise included in the measured value of the inter-order harmonic of the power system 1 was found, and the noise was subtracted from the measured value after this correction, the injection was performed. The existing noise in the system can be accurately removed from the measured value at the time, and the measurement performance of the harmonic characteristics can be improved.

In the case of the method of measuring harmonic characteristics according to claim 2, the phase of the noise of the inter-order harmonics of the power system 1 measured at the time of non-injection and the measured value of the power system 1 at the time of injection are measured. One of the phases is set as a phase to be corrected, and the phase angle of the sampling interval, the sampling number during non-injection or injection, and the phase shift amount of the product of the order of the interharmonic and the product are added to or subtracted from this phase. Since the phase to be corrected is corrected, the phase angle of the sampling interval is constant even if the period during injection and the period during non-injection change every moment due to the periodic fluctuation of the system fundamental wave. The number of pulses and
A phase correction amount (phase shift amount) of the inter-harmonic phase is accurately obtained from a product of the inter-harmonic order and the order of the inter-harmonic harmonic. The phase of the noise of the measured value at the time can be accurately matched with the phase of the noise, and the existing noise of the system can be removed very accurately from the measured value at the time of injection.

Next, in the case of the harmonic characteristic measuring device according to the third aspect, PLL pulse generating means (PLL pulse generator 8) for generating a sampling pulse synchronized with the system fundamental wave.
Means for calculating the noise of the existing injection frequency of the system from digital frequency analysis of the voltage and current of the power system sampled at the time of non-injection based on the sampling pulse (arithmetic processing device 9); Correction is made by adding or subtracting the phase shift of the product of the phase angle of the sampling pulse interval and the number of sampling pulses during non-injection or injection and the order of the interharmonic to one of the phases of the measured value during injection. (Operation processing device 10)
According to the first and second measuring methods, a harmonic characteristic measuring apparatus for measuring harmonic characteristics can be provided.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram of inter-order harmonics of the power system of FIG.

FIG. 3 is a flowchart for explaining the process of FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 power system 3 current injection device 8 PLL pulse generator 9 signal processing device 10 arithmetic processing device 11 equivalent circuit 12 storage device 13 display device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masakazu Tsukamoto 1 Higashi-Shinmachi, Higashi-ku, Nagoya-shi Inside Chubu Electric Power Company (72) Inventor Toshihiko 47-47 Umezu-Takaune-cho, Ukyo-ku, Kyoto-shi F-term ( Reference) 2G028 BF03 CG08 DH01 DH04 GL07 MS01

Claims (3)

[Claims] 1. A Fourier operation on a voltage and a current of a power system sampled at the time of injection in synchronization with the system fundamental wave by injecting a current of an interharmonic having a frequency that is a non-integer multiple of the system fundamental wave into the power system. From the digital frequency analysis of the above, the measured values of the voltage and current of the interharmonic of the injection frequency of the power system are obtained, and the equivalent of the interharmonic of the injection frequency of the power system based on the injected current from the measured values of voltage and current is obtained. The circuit constants are calculated, and the equivalent circuit constants for the harmonics to be measured in the power system are interpolated from the equivalent circuit constants for the inter-order harmonics of the upper and lower harmonics of the measurement target. In the harmonic characteristic measurement method to be determined, for each inter-order harmonic of each injection frequency, sampling is performed in synchronization with the system fundamental wave when at least one of before and after injection is not injected. The noise at the existing injection frequency of the system is obtained from the digital frequency analysis of the voltage and current of the power system, and the phase of the noise is corrected to the phase at the time of injection or the phase of the measured value at the time of injection is determined Correcting the phase at the time of injection, subtracting the noise from the measured value, removing the noise from the measured value, and calculating an equivalent circuit constant for the interharmonic of the injection frequency. Harmonic characteristics measurement method. 2. One of a noise phase at the time of non-injection and a phase of a measured value at the time of injection is set as a phase to be corrected. 2. The harmonic characteristic measuring method according to claim 1, wherein the phase to be corrected is corrected by adding or subtracting a phase shift amount of a product of the number of samplings and the order of the inter-harmonic. 3. An electric current of an interharmonic having a frequency that is a non-integer multiple of a system fundamental wave is injected from a current injection device into a power system, and the voltage and current of the power system sampled at the time of injection in synchronization with the system fundamental wave. From the digital frequency analysis of the Fourier operation of the signal processor of the power system, obtains the measured value of the voltage and current of the interharmonic of the injection frequency of the power system, and calculates the injection frequency of the power system based on the injected current from the voltage and current of the measured value. Calculate the equivalent circuit constants for the inter-order harmonics, and calculate the equivalent circuit for the harmonics to be measured in the power system from the equivalent circuit constants for the inter-order harmonics of the injection frequencies above and below the harmonics to be measured. In a harmonic characteristic measuring apparatus that determines a constant by interpolation, a sampling pulse synchronized with a system fundamental wave is output.
LL pulse generating means; and a system based on the digital frequency analysis of the voltage and current of the power system sampled at least one of before and after non-injection of each interharmonic of each injection frequency based on the sampling pulse. Means for determining noise at an existing injection frequency; and one of the noise at the time of non-injection and the phase of the measurement value at the time of injection as a phase to be corrected. The phase to be corrected is corrected to the phase at the time of injection or the phase at the time of non-injection by adding or subtracting the phase shift amount of the product of the angle and the number of the sampling pulses at the time of non-injection or at the time of injection and the order of the interharmonic. Means for measuring harmonic characteristics.