JPH1123626A - Current injector for measuring harmonic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inject an intermediate harmonic current in a short time by extracting an intermediate harmonic current from the output of an inverter and injecting an intermediate harmonic current outputted from a filter section into a system. SOLUTION: Output from an inverter 20 is transformed through a step-up transformer 21 having turn ratio of 1:5 such that the current is increased from 12A to 60A for example. A set current inverter output is fed from the transformer 21 through a filter section 25 comprising a series resonance circuit of a capacitor 22, a resistor 23 of a coil 24 to the third winding 19c of a coupling transformer 19. Based on the selection of a frequency through resonance, unnecessary frequency components, e.g. the component of system basic frequency or the multiple frequency components of intermediate harmonic, are removed at the filter section 25 and an intermediate harmonic current is extracted from the output of the inverter 20. Furthermore, the intermediate harmonic current at the filter section 25 is injected through the coupling transformer 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a current injection device used for measuring harmonic characteristics of a power system, and more particularly, to miniaturization thereof.

[0002]

2. Description of the Related Art Conventionally, in power transmission and distribution, it is important to reduce harmonics.

[0003] Then, n order (n is 1, 2, 3, ... integer) harmonic is an integer multiple of the system fundamental frequency f _s, a typical fifth order, seventh order harmonics 5 × f _s, 7 is a × f _s.

[0004] The reduction of the harmonics is performed by predicting the harmonic level (voltage level) and attaching filter equipment of the frequency to the capacitor equipment.

When predicting the harmonic level, the lower (downstream) or upper (upstream) harmonic characteristics of the power system, for example, from the connection point of the filter equipment are grasped, and an equivalent circuit thereof (harmonic equivalent circuit) is obtained. ).

When this harmonic equivalent circuit is represented by, for example, Norton's theorem, it can be regarded as a parallel circuit of admittance and a current source.

[0007] The Institute of Electrical Engineers of Japan, B101 Vol.
P. 451-458, (Showa 56-8), when obtaining a harmonic equivalent circuit for the fifth harmonic of the distribution system, measures the voltage and current of the fundamental wave of the system, and from the results, determines the harmonic equivalent circuit. It describes that the admittance, the magnitude of the current source, the phase, and the like are calculated and estimated.

However, in the case of the harmonic measurement method described in the above-mentioned journal, the fundamental voltage and current of the system are measured, and the harmonic admittance, the size and phase of the harmonic current source, etc. are measured from the measurement results. Since the harmonic characteristics are measured by estimation, high-precision measurement cannot be performed.

That is, in the above-described measuring method, the magnitude (vector value) of the fundamental wave is not determined by actually measuring the admittance or current source of the harmonic to be measured, but based on the measurement information of the fundamental wave. Since only the magnitude (vector value) of the harmonic to be measured is estimated from the above, it is not possible to accurately obtain and measure the harmonic characteristic.

For this reason, conventionally, it is not possible to accurately grasp the lower harmonic characteristics of the power system, for example, from the connection point of the filter equipment, and to provide an appropriate filter equipment, thereby reducing the harmonic level satisfactorily. I couldn't do that.

Therefore, the present applicant has filed Japanese Patent Application No. 8-31019.
According to the application of No. 2, currents of two frequencies (intermediate harmonic currents) which are non-integer multiples of the system fundamental frequency above and below the harmonic (measurement harmonic) to be measured are respectively injected into the system harmonic injection points, From the measured results of the voltage and current of each intermediate harmonic, the admittance of the equivalent circuit for each intermediate harmonic lower or higher than the harmonic injection point of the system is obtained, and interpolation is performed using these to determine the harmonic injection point. It has already been invented to determine the admittance of the equivalent circuit for the higher or lower harmonics to be measured and measure its harmonic characteristics.

In this case, the current of each intermediate harmonic above and below the harmonic to be measured is a current of a non-integer multiple of the system fundamental frequency that does not originally exist in the system, and the admittance of their equivalent circuit is present in the system. Since it is accurately determined by actual measurement without being affected by each harmonic, the characteristics of, for example, the fifth and seventh harmonics of the system can be accurately measured and grasped using this result.

[0013]

In order to carry out the harmonic measurement method of the above-mentioned application, an injection device is required, and there is a concern that the entire measurement device becomes large. An important issue is how to generate and inject harmonic currents into the system.

It is an object of the present invention to reduce the capacity and size of a current injection device so that current of each intermediate harmonic can be injected in a short time.

[0015]

In order to solve the above-mentioned problems, a current injection device for measuring harmonics according to the present invention comprises: an inverter whose output frequency continuously changes to the frequency of each intermediate harmonic; It consists of a resonance circuit with a resonance point set almost in the middle of the intermediate harmonics. The filter section extracts the current of each intermediate harmonic from the output of the inverter, and the current of each intermediate harmonic output from the filter section is injected into the system. And a coupling transformer. Therefore, the output of the inverter continuously changes to the frequency of each intermediate harmonic.

Further, the filter unit resonates with the frequency components of the respective intermediate harmonics of the inverter, and based on the selection of the frequency by the resonance, the filter unit converts the components of the system fundamental frequency, the components of the multiplied frequency of the respective intermediate harmonics, and the like. Unnecessary frequency components are eliminated and the current of each intermediate harmonic is extracted from the output of the inverter.

Then, the current of each intermediate harmonic of the filter section is injected into the system via the coupling transformer.

In this case, the current of each intermediate harmonic can be injected into the system from one current injection device.

Moreover, the output of the current injection device continuously changes to the frequency of each intermediate harmonic, and the injection of the current of each intermediate harmonic is completed in a short time. It suffices to be satisfied, and a small capacity and small size can be formed.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
This will be described with reference to FIGS. First, FIG. 2 shows a single-line equivalent circuit of the power system 1 to be measured.
The low-voltage secondary side (660) of the distribution substation 2 of this power system 1
0V side) to measure the harmonic characteristics of the distribution substation 2
The harmonic injection / measurement point a is set on the distribution bus 4 drawn out from the secondary side of the distribution transformer 3.

At the injection / measurement point a, the high-voltage side (6600 V) and the low-voltage side (220
V), a current injection device 6 for harmonic measurement is connected, and the current injection device 6 and the A / D converter 7, the signal processing device 8, the arithmetic processing device 9, the display device 10, and the recording device 11 are connected.
Thereby, the harmonic measuring device 12 is formed.

By the way, (the n 1, 2, ... integer) frequency n × f _s is an integer multiple of the system fundamental frequency f _s is in the power system 1 there are various harmonics, for these harmonics Thus, the equivalent circuit 13 on the lower side (downstream) on the right side of the harmonic injection point a can be expressed by, for example, Norton's theorem.
It can be regarded as a parallel circuit of the admittance 14 and the current source 15.

The current source 15 usually does not actually exist, but is generated due to current distortion or the like due to a load.

Then, for example, a typical fifth harmonic (n =
5), the seventh harmonic (n = 7) is set as a harmonic to be measured (harmonic of interest), and a constantly changing circuit constant of the equivalent circuit 13 for the harmonic of interest is obtained, and its harmonic characteristics are determined. When measuring, first, currents of a plurality of intermediate harmonics of a non-integer multiple of the system fundamental frequency above and below the frequency of the target harmonic are individually applied to the harmonic injection / measurement point a from the current injection device 6. inject.

At this time, the current of each intermediate harmonic is a current of a frequency that does not originally exist in the power system 1,
In an ideal case, the equivalent circuit for each of the lower and upper intermediate harmonics from the measurement point a has only admittance when expressed by Norton's theorem.

The current of each intermediate harmonic injected into the harmonic injection / measurement point a is divided into lower and upper sides according to the admittance of each of the lower and upper intermediate harmonics.

For this reason, the injection current I ( _m ) and the injection voltage V ( _m ) of each intermediate harmonic at the harmonic injection / measurement point a are measured by the measurement current of the current transformer 16 provided on the injection line, Table 17
The current I _x ( _m ) of each intermediate harmonic shunted above the harmonic injection / measurement point a is detected by the pressure measuring instrument current transformer 18 above the harmonic injection / measurement point a. Upon detecting the current, the current I _y of each intermediate harmonics diverted to a lower harmonic injection and measurement point a _(m) is determined from the calculation of _{I y (m) = I (} m) -I x (m) .

If the admittance of the lower equivalent circuit for each intermediate harmonic as viewed from the harmonic injection / measurement point a is Y _y ( _m ), the lower and upper intermediate circuits as viewed from the harmonic injection / measurement point a will be described. since the voltage of the higher harmonics is equal to the respective injection voltage V _(m), admittance Y _{y (m)} is Y _y
(M) = obtained from calculation of _{(I (m) -I x (} m)) / V (m).

For the sake of simplicity, the admittances Y _y ( _m ) of the two intermediate harmonics above and below the harmonic of interest are denoted by Y ₁ ( _m ) and Y ₂ ( _m ). admittance 14 of the equivalent circuit 13 for the harmonics, the simplest _{Y (n) = (Y 1} (m) + Y 2 (m)) / 2 interpolation operation from Y _(n)
Is obtained as

After the current injection by the current injection device 6 is completed, the measured voltage of the instrument transformer 17 and the current transformer 18 are measured.
Voltage from the measured current interest harmonics flowing distribution bus 4 in the downward direction V _(n), by determining the current _{I (n), I G (} n)
= Current source 15 of the equivalent circuit 13 from the operation of _{Y (n) × V (n} ) -I (n) is obtained as I _{G (n).}

Then, an equivalent circuit 1 for the harmonic of interest
When the admittance 14 and the current source 15 of 3 are obtained, it is possible to measure and grasp the characteristic of the target harmonic lower than the harmonic injection / measurement point a.

The current injection device 6 is configured as shown in FIG. 1 in order to sequentially and sequentially inject the current of each intermediate harmonic for a set time and finish the measurement of the harmonic characteristics in a short time. The first winding 19a of the coupling transformer 19 is connected to the low voltage side of the low voltage transformer 5, and the voltage type inverter 20 is connected to the second winding 19b of the coupling transformer 19.

The inverter 20 operates, for example, by a timer operation to generate one of the intermediate harmonics held in a memory such as a ROM.
Alternatively, data of several cycles are read out in a set time sequence for each set time, and based on the read data, a semiconductor switching element having a bridge configuration of an output unit is driven, and continuously changes to the frequency of each intermediate harmonic as shown in FIG. To generate an inverter output (voltage output). Note that t ₁ and t ₂ in FIG. 3 indicate timings at which the frequency of the inverter output changes.

In this embodiment, the output of the inverter 20 is transformed by a step-up transformer 21 with a turns ratio of 1: 5 so that the current increases from 12 A to 60 A, for example. Output of the capacitor 22, the resistor 23, the coil 24
Is supplied to the third winding 19c of the coupling transformer 19 through the filter unit 25 formed by the series resonance circuit of FIG.

At this time, in the present embodiment, the fifth harmonic or the seventh harmonic, which is the most important for the actual harmonic measurement, is set as the target harmonic, and only the current of each intermediate harmonic near the target harmonic is measured. Is injected into the harmonic injection / measurement point a via the coupling transformer 19 and the low-voltage transformer 5, so that the resonance point of the filter unit 25 is set before and after the sixth harmonic, which is substantially intermediate between the intermediate harmonics. The characteristic is set to a flat Q characteristic covering substantially the range of the fifth to seventh harmonics.

For this reason, unnecessary high frequency components of intermediate harmonics are eliminated from the low-voltage transformer 5 to the harmonic injection point a, and the current of each intermediate harmonic above and below the harmonic of interest is set without interruption. Injected sequentially by time, 1
The measurement is completed in a short time with one injection device.

Therefore, the inverter 20 and the like only need to satisfy the rating for a short time, can be formed with a small capacity and a small size, and can omit the radiation fins thereof.

Moreover, the capacitor 22 of the series resonance circuit of the filter unit 25 shares the commercial frequency voltage (voltage of the system fundamental wave) of the power system 1, and from this point, the transformers 19, 2
It is possible to reduce the capacity and size of the first and the like.

Therefore, the current injection device 6 can be formed to have a small capacity, a small size, and a light weight, and can be formed as a portable device.

Next, harmonic injection from the current injection device 6 is performed.
A specific method of measuring the harmonic characteristics based on the current of each intermediate harmonic injected into the measurement point a will be described.

Firstly, in order to simplify the description, the current injection device 6 to harmonic injection and measurement points a, thereon sandwiching the interest harmonic (frequency n × f _s), 2 frequency f ₁ below, f ₂ (F
₁ <n × f _s <intermediate harmonic currents I _y1 of f _{2) (m),} I
_It is assumed that measurement is performed by sequentially injecting _y2 ( _m ) (= _Iyi ( _m ), i = 1, 2).

In this case, at the time of injecting each of the currents Iy ₁ ( _m ) and Iy ₂ ( _m ), the injection current at the harmonic injection / measurement point a is measured by the current transformer 16 for the instrument, and 17, the voltage at the harmonic injection / measurement point a (system voltage) and the current flowing therethrough are measured by the current transformer 18 for the instrument, and the measured signals are digitally converted by the A / D converter 7 of the measuring device 12. To the measured data.

Further, each measurement data of the A / D converter 7 is processed by FFT analysis or the like of the signal processing device 8, and the currents I ₁ ( _m ) and I ₂ ( _m ) injected into the harmonic injection / measurement point a. ) (= I _i (
_m ), i = 1, 2), the voltages V ₁ ( _m ) and V ₂ ( _m ) (= V _i ( _m )) at the harmonic injection / measurement point a and the harmonic injection /
The shunt I _x1 ( _m ), I _x2 ( _m ) (=
A measurement result of I _xi ( _m ), i = 1, 2) is obtained.

Then, the measurement output of the signal processing device 8 is supplied to a subsequent processing device 9, and based on the measured current I _xi ( _m ), I _yi ( _m ) = I _i ( _m ) -I _xi
From the calculation of ( _m ), the shunt I _y1 ( _m ) to the lower order of the harmonic injection point a,
I _{y2 (m) asking, Y yi (m) = I} yi (m) / V current from the calculation of _{i (m) I y1 (m} ), I y2 (m) admittance Y _{y1 (m)} for each, Y _y2 ( _m ) (= Y _yi ( _m )) is obtained.

At this time, since the current I _yi ( _m ) is a current having a frequency that does not exist in the power system 1, the admittance Y _yi ( _m ) is _maintained even if the amount of power injected by the current injection device 6 is very small. It is accurately obtained without being affected by harmonics of 1 or the like.

Even if the harmonic current of the measured harmonic is injected instead of the intermediate harmonic current I _i ( _m ), since this harmonic exists in the power system 1, the injected harmonic current is Admittance based on criterion cannot be sought.

Alternatively, the current flowing below the harmonic injection / measurement point a may be measured, and the current I _yi ( _m ) may be obtained from the measured current.

Then, the arithmetic processing unit 9 calculates, for example, Y _y ( _n ) =
An interpolation operation of (Y _y1 ( _m ) + Y _y2 ( _m )) / 2 is executed to determine and determine the admittance Y _y1 ( _n ) of the focused harmonic lower than the harmonic injection / measurement point a.

At this time, the admittances Y _y1 ( _m ) and Y _y2 ( _m )
Is accurately calculated without being affected by the harmonics of the power system 1, the admittance Y _y (
_n ) (admittance 14) is accurately obtained.

Next, immediately after the current injection by the current injection device 6 is completed, the measured voltage of the instrument transformer 17 and the current transformer 18 are measured.
Voltage of interest harmonics of the system bus 4 from the frequency analysis of the measured current V _(n), obtains a lower direction of the current I _{y (n).}

Then, based on the admittance Y _y ( _n ), the voltage V ( _n ) and the current I _y ( _n ), I _Gy ( _n ) = Y _y ( _n ) × V ( _n )
The current source I _Gy ( _n ) (current source 15) is obtained from the calculation of −I _y ( _n ), the equivalent circuit 13 is identified, and the harmonic characteristics of the target harmonic lower than the harmonic injection / measurement point a are obtained. Make a complete measurement of.

Incidentally, the higher harmonic characteristics than the higher harmonic injection / measurement point a can be simultaneously measured in the same manner as described above.

In this case, the measurement current I _xi ( _m ) and the measurement voltage V (
_m ), I _x1 ( _m ), I _x2 (
_m ) (= I _xi ( _m )), the admittances Y _x1 ( _m ) and Y _x2 ( _m ) of the intermediate harmonic higher than the harmonic injection / measurement point a
(= Y _xi ( _m )) is obtained by the calculation of Y _xi ( _m ) = I _xi ( _m ) / V _i ( _m ).

Further, Y _x ( _n ) = (Y _x1 ( _m ) + Y _x2 ( _m )) / 2
From interpolation operation, admittance Y _y admittance of an equivalent circuit of the interest harmonics higher than a similar harmonic injection and measurement points a and _(n) Y _{x (n)} is obtained.

Further, based on the admittance Y _x ( _n ), the voltage V ( _n ), and the current I _x ( _n ), I _Gx ( _n ) = Y _x ( _n ) × V ( _n )
From the calculation of + I _x ( _n ), the current source _IGx ( _n ) of the equivalent circuit for the target harmonic higher than the harmonic injection point a similar to the current source 15 is obtained.

The admittance Y _x ( _n ) and the current source I _Gx
( _n ), an equivalent circuit for the focused harmonic higher than the harmonic injection / measurement point a similar to the equivalent circuit 13 is identified,
Higher harmonic characteristics higher than the harmonic injection / measurement point a can be measured.

Next, in the above embodiment, the harmonic injection / measurement point a is used for both injection and measurement of the harmonic, but the harmonic injection point and the harmonic measurement point are set separately.
The current injection device 6 is connected to the harmonic injection point, an instrument transformer 17 and an instrument current transformer 18 are provided on the harmonic measurement point side, and an equivalent circuit for the target harmonic lower and higher than the harmonic measurement point is provided. May be identified to measure the harmonic characteristics. In this case,
By improving the portability by reducing the size and weight of the current injection device, there is an advantage that the current injection device can be transported to the harmonic injection point very easily.

When a harmonic measuring point and a harmonic injection point are separately provided, a plurality of harmonic injection points are set on each of the buses or the like branched in the system, and a plurality of current injection devices 6 are provided. The harmonic characteristic can be measured by injecting the current of each intermediate harmonic from the device 6, and in this case, the current injection device 6
However, there is an advantage that it becomes smaller and lighter.

The present invention can of course be applied to any case where the number and position of the harmonic injection points and the harmonic measurement points are set.

Next, for example, when a plurality of intermediate harmonics above and below the target harmonic are respectively provided, or when a plurality of target harmonics are collectively measured, the output frequency of the inverter 20 is set to three or more types. Of course, it is only necessary to continuously switch to a large number of frequencies.

The inverter 20 may have any configuration as long as the output frequency continuously changes to the frequency of each intermediate harmonic set by timer control or the like.

The step-up transformer 21 after the inverter 20 can be omitted when the output current of the inverter 20 is sufficiently large.

Further, the resonance characteristics of the series resonance circuit 25 are as follows.
What is necessary is just to set according to the frequency range of the extracted intermediate harmonic, etc., and it is desirable that the so-called Q value is flat in the required frequency range so that the current of each intermediate harmonic is extracted with the same resonance characteristics as much as possible.

Next, instead of using the equivalent circuit 13 or the like as a parallel circuit of admittance and a current source, the present invention can be similarly applied to a case where a harmonic characteristic is measured as a series circuit of an impedance and a voltage source. Of course.

[0065]

The present invention has the following effects. The output of the inverter 20 continuously changes to the frequency of each intermediate harmonic. Then, the filter unit 25 resonates with the frequency component of each intermediate harmonic of the inverter 20, and based on the selection of the frequency by this resonance, the filter unit 25 causes the component of the system fundamental frequency, the component of the multiplied frequency of each intermediate harmonic, and the like. Unnecessary frequency components can be eliminated, and the current of each intermediate harmonic can be extracted from the output of the inverter 20.

Further, the current of each intermediate harmonic of the filter unit 25 can be injected into the system via the coupling transformer 19.

In this case, the current of each intermediate harmonic can be injected from one current injection device 6 into the system.

Moreover, the output of the current injection device 6 continuously changes to the frequency of each intermediate harmonic, and the injection of the current of each intermediate harmonic is completed in a short time. It suffices to satisfy the rating, and it can be formed with small capacity and small size.

Therefore, the high-accuracy harmonic characteristics can be measured by the small-capacity and small-sized current injection device 6.

[Brief description of the drawings]

FIG. 1 is a circuit connection diagram according to an embodiment of the present invention.

FIG. 2 is a circuit connection diagram of an example of harmonic measurement using the current injection device of FIG.

FIG. 3 is an output waveform diagram of the inverter of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power system 19 Coupling transformer 20 Inverter 25 Filter part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoji Nishimura, 47, Takane-cho, Umezu, Ukyo-ku, Kyoto-shi Inside Nisshin Electric Co., Ltd. (72) Inventor Yoshifumi Minowa 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi Nissin Electric Co., Ltd.

Claims (1)

[Claims] 1. A current having a frequency that is a non-integer multiple of the system fundamental frequency above and below the harmonic to be measured is injected into the system as an intermediate harmonic current, and the measured current and measured voltage of the system are analyzed by frequency analysis. The admittance or impedance of the equivalent circuit for each of the intermediate harmonics of the system is determined by detecting the current and voltage of each of the intermediate harmonics, and the equivalent circuit of the system for the target harmonic is determined from the admittance or impedance of each of the equivalent circuits. The admittance or impedance is determined by interpolation, and when measuring the harmonic characteristics of the harmonics to be measured in the system, the current injection for harmonic measurement is performed by injecting the current of each intermediate harmonic into the system. In the device, an inverter whose output frequency continuously changes to the frequency of each of the intermediate harmonics, and a resonance point is set substantially at the center of each of the intermediate harmonics. And a coupling transformer for injecting the current of each of the intermediate harmonics output from the filter unit into a system. A current injection device for measuring harmonics.