JP2005148028A - Device and method for measuring voltage, current, active power, reactive power, and frequency in power system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring device and method capable of directly measuring, even in case of a change in frequency of a power system that is a measuring object, the voltage, effective value of current, active power, reactive power and frequency of the power system with a minimized error from sampling data without performing a correction operation. <P>SOLUTION: This device comprises an anti-aliasing filter, a sample holding means for sampling and holding the waveform of voltage in an AC signal every predetermined period, an analog/digital conversion means for converting analog data to digital data, a basic wave extraction means for extracting a basic wave component around a commercial frequency, a voltage value temporary storage means for temporarily storing voltage values up to 4 samples before, and a voltage value computing means for substituting the voltage values up to 4 samples before to an arithmetic expression. The effective value of the voltage that is a measuring object is computed with the following arithmetic expression. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a measurement apparatus and a measurement method that are less affected by fluctuations in system frequency when measuring electric quantities such as voltage, current, active power, reactive power, and frequency in a power system such as a power generation / transformation facility.

  There is an amplitude-square method as a widely used technique for calculating effective values of voltage and current in a power system such as a power generation substation. There is also a right-angle 2-sample calculation method for calculating active and reactive power. In both of the square amplitude method and the quadrature two-sample calculation method, a sampling interval corresponding to ¼ period with respect to the alternating current to be measured is essential. As a method for obtaining the effective value of voltage, current, and effective / reactive power at an arbitrary sampling interval, there is a continuous 2-sample calculation method.

The amplitude square method is represented by the following equation.
・ Amplitude square method

無効電力

The right-angle 2-sample calculation method is expressed by the following equation.
Right angle 2-sample calculation method Active power

Reactive power

有効電力

無効電力

Furthermore, the continuous 2-sample calculation method is expressed by the following equation.
・ Continuous 2-sample method Voltage RMS

Active power

Reactive power

  A method widely used for frequency measurement is a method based on detection of a zero cross point. This is a method of calculating an average value of instantaneous values of the AC signal to be measured, detecting a point where the average value and the instantaneous value of the AC signal cross, measuring the interval, and obtaining the frequency.

In addition, as a conventional technique for measuring an AC signal and digitally processing it, there is a technique described in Japanese Patent Laid-Open No. 58-51315.
JP 58-51315 A

  In the amplitude square method and the quadrature two-sample calculation method, the sampling interval S must always be ¼ period of the AC signal to be measured. However, if the frequency of the AC signal to be measured fluctuates, There is a problem that the relationship is broken and the measurement of the AC signal becomes inaccurate.

よって、振幅２乗法により算出される値は

となる。ここでサンプリング間隔Sが、交流信号の１／４周期であるならば、

となり、右辺における[ ]内の第２項は

となる。ゆえに、

となり、電圧値の実効値が求まる。 An amplitude square method will be described as an example. The instantaneous value of the voltage at time t and t−S can be expressed by the following equation.

Therefore, the value calculated by the amplitude square method is

It becomes. Here, if the sampling interval S is ¼ period of the AC signal,

And the second term in [] on the right side is

It becomes. therefore,

Thus, the effective value of the voltage value is obtained.

  However, when the frequency of the power system to be measured fluctuates, the above relational expression does not hold and signal measurement becomes inaccurate. The quadrature two-sample calculation method has a similar problem. The continuous 2-sample calculation method includes the terms sin (2πfS) and cos (2πfS) in the calculation formula, and the system frequency f is used as a known value in the calculation formula. Therefore, when the system frequency fluctuates, the measurement result becomes inaccurate. In addition, in the frequency measurement method based on the detection of the zero cross point, methods such as interpolating between sampling data with a straight line or a curve or performing high-speed sampling are taken in order to improve measurement accuracy, but errors due to interpolation occur.

  The present invention pays attention to such a problem, and even when the frequency of the power system to be measured fluctuates, the voltage and current of the power system with less error are directly calculated from the sampling ring data without performing a correction operation. It is an object of the present invention to provide a measuring device and a measuring method capable of measuring the effective value, active power, reactive power, and frequency.

時刻ｔにおける電圧のサンプリングデータを ｅ（ｔ）
１サンプル前の電圧のサンプリングデータを ｅ（ｔ−S）
２サンプル前の電圧のサンプリングデータを ｅ（ｔ−２S）
３サンプル前の電圧のサンプリングデータを ｅ（ｔ−３S）
４サンプル前の電圧のサンプリングデータを ｅ（ｔ−４S）
として、計測対象となる電圧の実効値を演算するものである。 The measuring apparatus and method according to claims 1 and 6 of the present invention include an anti-aliasing filter used for band limitation of a broadband signal, and a sample holding means for sampling and holding a voltage waveform in an AC signal at predetermined intervals. Analog / digital conversion means for converting analog data output from the sample holding means to digital data, fundamental wave extraction means for extracting fundamental wave components near the commercial frequency from the digital data, and voltage values up to four samples before Voltage value temporary storage means for temporarily storing the voltage value, and voltage value calculation means for calculating the voltage values stored in the voltage value temporary storage means by substituting the voltage values up to four samples before the calculation formula,
The arithmetic expression is

Sampling data of voltage at time t is e (t)
Sampling data of voltage one sample before e (t−S)
Sampling data of voltage 2 samples before e (t-2S)
Sampling data of voltage 3 samples before e (t-3S)
Sampling data of voltage 4 samples before e (t-4S)
As described above, the effective value of the voltage to be measured is calculated.

時刻ｔにおける電流のサンプリングデータを ｉ（ｔ）
１サンプル前の電流のサンプリングデータを ｉ（ｔ−S）
２サンプル前の電流のサンプリングデータを ｉ（ｔ−２S）
３サンプル前の電流のサンプリングデータを ｉ（ｔ−３S）
４サンプル前の電流のサンプリングデータを ｉ（ｔ−４S）
として、計測対象となる電流の実効値を演算するものである。 In addition, the measuring apparatus and method according to claims 2 and 7 of the present invention include an anti-aliasing filter used for band limitation of a broadband signal, and a sample that samples and holds a waveform of a current in an AC signal at a predetermined period. Holding means, analog / digital conversion means for converting analog data output from the sample holding means to digital data, fundamental wave extraction means for extracting a fundamental wave component near the commercial frequency from the digital data, and up to four samples before A current value temporary storage means for temporarily storing a current value; and a current value calculation means for calculating the current value stored in the current value temporary storage means by substituting the current values up to four samples before the calculation formula,
The arithmetic expression is

The current sampling data at time t is i (t)
Sampling data of current one sample before i (t−S)
Sampling data of current 2 samples before i (t-2S)
Sampling data of current 3 samples before i (t-3S)
Sampling data of current 4 samples before i (t-4S)
As above, the effective value of the current to be measured is calculated.

として、計測対象となる有効電力の値を演算するものである。 Moreover, the measuring device and method according to Claims 3 and 8 of the present invention include each voltage value stored in the voltage value temporary storage means according to Claim 1 and the current value temporary storage means according to Claim 2. Active power calculation means for calculating by substituting each current value stored in the calculation formula,
The arithmetic expression is

As described above, the value of the active power to be measured is calculated.

として、計測対象となる無効電力の値を演算するものである。 Further, the measuring device and method according to claims 4 and 9 of the present invention are the voltage values stored in the voltage value temporary storage means according to claim 1 and the current value temporary storage means according to claim 2. Reactive power calculation means for calculating by substituting each current value stored in the calculation formula,
The arithmetic expression is

As described above, the value of reactive power to be measured is calculated.

として、計測対象となる周波数の値を演算するものである。 According to a fifth aspect and tenth aspect of the present invention, there is provided a measuring apparatus and method according to the first aspect of the present invention, wherein a frequency calculation means for calculating by substituting each voltage value stored in the voltage value temporary storage means according to claim 1 into an arithmetic expression. With
The arithmetic expression is

As described above, the frequency value to be measured is calculated.

  According to the measuring apparatus and method of the first and sixth aspects of the present invention, five voltage values (e) up to four samples before only the fundamental wave component near the commercial frequency stored in the voltage value RAM is extracted. By substituting (t) to e (t-4S)) into (Equation 1) and calculating, even if the harmonics of the AC signal are superimposed, the measurement target is not affected by the distorted wave. The effective value of the voltage of the power system can be measured directly from the sampling data without performing the correction calculation even when the effective value E of the voltage being obtained is obtained and the frequency of the power system being measured fluctuates. it can.

  Further, according to the measuring apparatus and method of claims 2 and 7 of the present invention, five current values up to four samples before only the fundamental wave component near the commercial frequency stored in the current value RAM is extracted. By calculating by substituting (i (t) to i (t-4S)) into (Equation 2), even if harmonics are superimposed on the AC signal, the measurement target is not affected by distortion waves. The effective value I of the current is obtained, and even if the frequency of the power system being measured fluctuates, the effective value of the current of the power system can be directly calculated from the sampling data without performing a correction operation. It can be measured.

  According to the measuring apparatus and method of claims 3 and 8 of the present invention, five voltage values up to four samples before only the fundamental wave component near the commercial frequency stored in the voltage value RAM is extracted. (E (t) to e (t-4S)) and three current values (i (1 (1) to 3 samples) from which only the fundamental wave component near the commercial frequency stored in the current value RAM is extracted. By substituting (t−S) to i (t−3S)) into (Equation 3) and calculating, even if harmonics are superimposed on the AC signal, the measurement object is not affected by distortion waves. Even if the active power P is accurately obtained, and the frequency of the power system to be measured fluctuates, the effective power value of the power system can be increased directly from the sampling data without performing a correction operation. It can be measured with high accuracy.

  According to the measuring apparatus and method of the fourth and ninth aspects of the present invention, five voltage values up to four samples before only the fundamental wave component near the commercial frequency stored in the voltage value RAM is extracted. (E (t) to e (t-4S)) and three current values (i (1 (1) to 3 samples) from which only the fundamental wave component near the commercial frequency stored in the current value RAM is extracted. By substituting (t−S) to i (t−3S)) into (Equation 4) and calculating, the harmonics are superimposed on the AC signal and the measurement object is not affected by the distortion wave. The reactive power Q is accurately obtained, and even if the frequency of the power system being measured fluctuates, the reactive power value of the power system can be increased directly from the sampling data without performing a correction operation. It can be measured with high accuracy.

  Moreover, according to the measuring apparatus and method of claims 5 and 10 of the present invention, four voltage values up to three samples before only the fundamental wave component near the commercial frequency stored in the voltage value RAM is extracted. By substituting (e (t) to e (t−3S)) and the sampling interval S into (Equation 5) for calculation, even when a harmonic is superimposed on the AC signal, it is affected by the distorted wave. Therefore, the frequency value f to be measured can be accurately obtained, and the frequency value of the power system can be measured with high accuracy without detecting the zero cross point and performing data interpolation.

  Hereinafter, the best mode for carrying out the present invention will be described.

  Hereinafter, the voltage value measuring apparatus 10 that measures the effective value of the voltage of the power system will be described with reference to FIG. The voltage value measuring apparatus 10 includes an anti-aliasing filter 11, a sample hold circuit 12, an analog / digital conversion means 13, a fundamental wave extraction unit 14, a voltage RAM 15, a voltage value calculation unit 16, and a control circuit 17.

  The anti-aliasing filter 11 is used for band limitation of a wideband signal, and is an analog filter for preventing aliasing (aliasing). The sample hold circuit 12 samples and holds the voltage waveform in the AC signal at predetermined intervals. The analog / digital converter 13 converts analog data output from the sample hold circuit 12 into digital data. The fundamental wave extraction unit 14 extracts only the fundamental wave component near the commercial frequency from the digital data converted by the analog / digital converter 13. The fundamental wave extraction unit 14 has a two-stage connection of a low-pass filter and a band-pass filter. As a result, all harmonic components and direct current components are cut, the S / N ratio (signal-to-noiSe ratio) is improved, and voltage can be measured with higher accuracy. That is, even when a harmonic is superimposed on the AC signal, the voltage can be accurately measured without being affected by the distorted wave. The voltage RAM 15 temporarily stores voltage values up to four samples before. The voltage value calculation unit 16 substitutes the voltage values (e (t) to e (t-4S)) stored up to 4 samples stored in the voltage RAM 15 into the calculation formula shown below, and obtains the effective value of the voltage to be measured. E is calculated. The control circuit 17 controls the sample hold circuit 12, the analog / digital converter 13, the fundamental wave extraction unit 14, the voltage RAM 15, and the voltage value calculation unit 16.

（数１７）により、計測対象である電力系統の周波数が変動した場合でも、影響をほとんど受けずに電力系統の電圧の実効値Ｅを高精度に計測することができる。 Next, the measurement method will be described. The AC voltage signal is input to the anti-aliasing filter 11 to limit the band of the broadband signal, and the sample and hold circuit 12 samples and holds the voltage waveform in the AC voltage signal at predetermined intervals. The analog data of the voltage output from the sample hold circuit 12 is converted into digital data by the analog / digital converter 13, and only the fundamental wave component near the commercial frequency is extracted by the fundamental wave extraction unit 14. In the voltage RAM 15, five voltage values (e (t) to e (t-4S)) up to four samples before are temporarily stored. Thereafter, the voltage value calculation unit 16 calculates the effective value E of the voltage to be measured by substituting and calculating five voltage values up to four samples before in (Equation 17).

According to (Equation 17), even when the frequency of the power system to be measured fluctuates, the effective value E of the voltage of the power system can be measured with high accuracy with almost no influence.

であり、サンプリング間隔をSとすると、

と表すことができる。（１）〜（５）を連立方程式として、ｆ、ｔ、Sを消去し、実効値Ｅを求めることができれば、周波数、時刻、サンプリング間隔に依存することのない電圧の実効値を求めることができる。 Next, how to obtain (Equation 17) will be described.
The instantaneous voltage value at time t is

And if the sampling interval is S,

It can be expressed as. If (1) to (5) are used as simultaneous equations and f, t, and S are eliminated and the effective value E can be obtained, the effective value of the voltage that does not depend on the frequency, time, and sampling interval can be obtained. it can.

となる。
（６）、（７）式の和と差により

（８）、（９）式の、それぞれの平方の差よりｔを消去する。

（１０）式から

（１１）式を整理すると、

（４）、（５）式からも同様にして

が得られる。
（１２）、（１３）式より、

となる。 When (2) and (3) are expanded by the addition theorem,

It becomes.
(6), by the sum and difference of formulas (7)

T is eliminated from the difference between the squares in the equations (8) and (9).

From equation (10)

(11) Organizing the formula,

In the same way from equations (4) and (5)

Is obtained.
From equations (12) and (13),

It becomes.

  Here, since √ is 1 regardless of the frequency f and the sampling interval S, the calculation result gives the effective value E of the voltage regardless of the frequency f and the sampling interval S. If five consecutive data of e (t + 2S) to e (t-2S) are replaced with five consecutive data of e (t) to e (t-4S), the equation (14) is nothing but (Equation 17). The sampling interval S is arbitrary except for an integral multiple of ½ period of the system frequency at which the denominator of equation (14) is zero. However, if the sampling interval is about ¼ of the system frequency, the denominator of Equation (14) becomes maximum, so that the measurement accuracy becomes high. The effective value E of the voltage to be measured is obtained by substituting and calculating the five voltage values stored in the voltage value RAM up to 4 samples before (Equation 17), and is the measurement target. Even when the frequency of the power system fluctuates, the effective value of the voltage of the power system can be measured directly from the sampling data without performing a correction operation.

  Hereinafter, the current value measuring device 20 that measures the effective value of the current of the power system will be described with reference to FIG. In addition, the same code | symbol was attached | subjected to the structure same as the structure shown in Example 1 and Example 2. FIG. The current value measuring device 20 includes an anti-aliasing filter 11, a sample hold circuit 12, an analog / digital conversion means 13, a fundamental wave extraction unit 14, a current RAM 18, a current value calculation unit 21, and a control circuit 17.

  The anti-aliasing filter 11 is used for band limitation of a wideband signal, and is an analog filter for preventing aliasing (aliasing). The sample hold circuit 12 samples and holds the waveform of the current in the AC signal at predetermined intervals. The analog / digital converter 13 converts analog data output from the sample hold circuit 12 into digital data. The fundamental wave extraction unit 14 extracts only the fundamental wave component near the commercial frequency from the digital data converted by the analog / digital converter 13. The fundamental wave extraction unit 14 has a two-stage connection of a low-pass filter and a band-pass filter. As a result, all harmonic components and direct current components are cut, the S / N ratio (signal-to-noise ratio) is improved, and current can be measured with higher accuracy. That is, even when a harmonic is superimposed on the AC signal, the current can be accurately measured without being affected by the distorted wave. The current RAM 18 temporarily stores current values up to four samples before. The current value calculation unit 21 substitutes the current values (i (t) to i (t-4S)) stored in the current RAM 18 up to four samples before into the calculation formula shown below, and obtains the effective value of the current to be measured. I is calculated. The control circuit 17 controls the sample hold circuit 12, the analog / digital converter 13, the fundamental wave extraction unit 14, the current RAM 18, and the current value calculation unit 21.

（数２７）により、計測対象である電力系統の周波数が変動した場合でも、補正演算を施すことなく、サンプリングデータから直接的に電力系統の電流の実効値Ｉを高精度に計測することができる。なお、（数２７）の求め方は（数１７）における電圧値を電流値に置換することにより求まるので説明は省略する。 Next, the measurement method will be described. The alternating current signal is input to the anti-aliasing filter 11, and the sample and hold circuit 12 samples and holds the waveform of the current in the alternating current signal at predetermined intervals. The analog data of the current output from the sample and hold circuit 12 is converted into digital data by the analog / digital converter 13, and only the fundamental wave component near the commercial frequency is extracted by the fundamental wave extraction unit 14. In the current RAM 18, five current values (i (t) to i (t-4S)) up to four samples before are temporarily stored. Thereafter, the current value calculation unit 21 calculates the current value I of the current to be measured by substituting and calculating the five current values up to four samples before (Equation 27).

According to (Equation 27), even when the frequency of the power system to be measured fluctuates, the effective value I of the power system current can be measured with high accuracy directly from the sampling data without performing a correction operation. . Since the method of obtaining (Equation 27) can be obtained by substituting the voltage value in (Equation 17) with a current value, description thereof will be omitted.

（数２８）により、計測対象である電力系統の周波数が変動した場合でも、補正演算を施すことなく、サンプリングデータから直接的に電力系統の有効電力の値を高精度に計測することができる。 Hereinafter, an apparatus and a method for measuring the value of active power will be described with reference to FIG. In FIG. 3, only the active power calculation unit 31 is different from the other figures, and redundant description is omitted. In addition, the same code | symbol was attached | subjected to the structure same as the structure shown in Example 1 and Example 2. FIG. In the active power calculation unit 31, five voltage values e (t) to e (t-4S) up to four samples before only the fundamental wave component near the commercial frequency stored in the voltage value RAM 15 and the current value RAM 18 are extracted. The three current values (i (t−S) to i (t−3S)) from one sample before to three samples before only the fundamental wave component near the commercial frequency stored in FIG. By substituting for calculation, the value P of the active power that is the measurement target is obtained.

According to (Equation 28), even when the frequency of the power system to be measured fluctuates, the value of the active power of the power system can be measured with high accuracy directly from the sampling data without performing correction calculation.

と表すことができる。
（１６）、（１７）式を加法定理により展開すると、

（２）、（１８）式の積より、

上式において Ｐ＝Ｅ・Ｉ・cosθ、Ｑ＝Ｅ・Ｉ・sinθとすると、

となる。更に展開して整理すると、

同様にして、（３）、（１９）式の積より、

また、

（２０）、（２１）および（２２）式からｔ、θを消去する。

（２３）式に（１２）式を代入し、ｆ、Sを消去し、Ｐについて整理する。

Ｅの値として［実施例１］の結果式を用いると、

となる。 Next, how to obtain (Equation 28) will be described.
Assuming that the instantaneous value of the current at time t ± S is delayed by the phase θ with respect to the voltage,

It can be expressed as.
Expanding (16) and (17) by the addition theorem,

From the product of equations (2) and (18),

In the above equation, if P = E · I · cosθ and Q = E · I · sinθ,

It becomes. When further expanded and organized,

Similarly, from the product of equations (3) and (19),

Also,

T and θ are eliminated from the equations (20), (21) and (22).

Substituting equation (12) into equation (23), erasing f and S, and organizing P.

Using the result of [Example 1] as the value of E,

It becomes.

  The above expression is hardly affected by the frequency f and the sampling interval S. The calculation result of equation (25) gives the value P of the active power regardless of the frequency f and the sampling interval S. It should be noted that five consecutive data of e (t + 2S) to e (t-2S) are replaced with five consecutive data of e (t) to e (t-4S), and i (t−S) to i (t + S). ) Is replaced with three consecutive data of i (t−S) to i (t−3S), the equation (25) is nothing but (Equation 28). The sampling interval S is arbitrary except for an integral multiple of a half period of the system frequency at which the denominator of equation (25) is zero. However, if the sampling interval is about ¼ of the system frequency, since the denominator of Equation (25) becomes maximum, the measurement accuracy becomes high. Five voltage values e (t) to e (t-4S) stored in the voltage value RAM 15 up to four samples and three current values stored in the current RAM 18 from one sample to three samples before ( By substituting i (t−S) to i (t−3S)) into (Equation 28), an active power value P to be measured is obtained, and the power system to be measured is calculated. Even when the frequency fluctuates, the value of the active power of the power system can be measured with high accuracy directly from the sampling data without performing correction calculation.

（数３９）により、計測対象である電力系統の周波数が変動した場合でも、補正演算を施すことなく、サンプリングデータから直接的に電力系統の無効電力の値を高精度に計測することができる。 Hereinafter, the apparatus and method for measuring the value of reactive power will be described with reference to FIG. In FIG. 4, only the reactive power calculation unit 41 is different from the other figures, and redundant description is omitted. In addition, the same code | symbol was attached | subjected to the structure same as the structure shown in Example 1 and Example 2. FIG. In the reactive power calculation unit 41, five voltage values (e (t) to e (t-4S)) and currents up to four samples before only the fundamental wave component near the commercial frequency stored in the voltage value RAM 15 is extracted. Three current values (i (t−S) to i (t−3S)) from one sample before to three samples before only the fundamental wave component near the commercial frequency stored in the value RAM 18 is extracted (number By calculating by substituting into 39), the reactive power value Q to be measured is obtained.

According to (Equation 39), even when the frequency of the power system to be measured fluctuates, the value of the reactive power of the power system can be measured with high accuracy directly from the sampling data without performing correction calculation.

同様にして、

（２６）、（２７）式の共通項を消去すると、

また同様に、

（２９）−（３０）より共通項を消去すると、

（２８）−（３１）よりｔ、Ｐを消去すると、

（１３）および（１）を代入し、ｆ、Sを消去し、［実施例１］の結果式を用いると、

となる。 Next, how to obtain (Equation 39) will be described.

Similarly,

Eliminating the common terms in equations (26) and (27)

Similarly,

If the common term is deleted from (29)-(30),

If t and P are deleted from (28)-(31),

Substituting (13) and (1), erasing f and S, and using the result formula of [Example 1],

It becomes.

  The above expression is hardly affected by the frequency f and the sampling interval S. The calculation result of the equation (33) gives the reactive power value Q regardless of the frequency f and the sampling interval S. It should be noted that five consecutive data of e (t + 2S) to e (t-2S) are replaced with five consecutive data of e (t) to e (t-4S), and i (t−S) to i (t + S). ) Is replaced with three consecutive data i (t−S) to i (t−3S), the equation (33) is nothing but (Equation 39). The sampling interval S is arbitrary except for an integral multiple of 1/2 period of the system frequency at which the denominator of equation (33) is zero. However, if the sampling interval is about ¼ of the system frequency, the denominator of Equation (33) becomes maximum, so that the measurement accuracy becomes high. Five voltage values (e (t) to e (t-4S)) stored in the voltage value RAM 15 up to four samples before, and three voltage values stored in the current value RAM 18 from one sample before to three samples before. By substituting the current values (i (t−S) to i (t−3S)) into (Equation 39), the reactive power value Q that is the measurement target is obtained and is the measurement target. Even when the frequency of the power system fluctuates, the value of reactive power can be measured directly from the sampling data with high accuracy without performing correction calculation.

（数４７）により、ゼロクロス点の検出やデータ補間をすることなく、交流信号の周波数の値ｆを高精度に計測することができる。 Hereinafter, an apparatus and method for calculating a frequency value will be described with reference to FIG. In FIG. 5, the configuration different from the other figures is only the frequency calculation unit 51, and redundant description is omitted. In addition, the same code | symbol was attached | subjected to the structure same as the structure shown in Example 1. FIG. In the frequency calculation unit 51, four voltage values e (t) to e (t-3S) up to three samples before only the fundamental wave component near the commercial frequency stored in the voltage value RAM 15 is extracted (Expression 47). By substituting and calculating, the frequency value f of the power system being measured is obtained.

According to (Equation 47), the frequency value f of the AC signal can be measured with high accuracy without detecting the zero cross point and performing data interpolation.

同様に、

（３４）、（３５）の２乗和より

ｆに関して整理すると、

となる。 Next, how to obtain (Equation 47) will be described.

Similarly,

From the sum of squares of (34) and (35)

Organizing with respect to f,

It becomes.

  If four consecutive data of e (t + 2S) to e (t−S) are replaced with four consecutive data of e (t) to e (t−3S), the equation (38) is nothing but (Equation 47). If the sampling interval S is about ¼ of the system frequency, since the denominator of Equation (38) becomes maximum, the measurement accuracy becomes high. The four voltage values (e (t) to e (t-3S)) stored in the voltage value RAM 15 up to three samples before are substituted into (Equation 47) and calculated, thereby being a measurement target. A system frequency value f can be obtained, and the frequency value of the power system can be measured with high accuracy without detecting the zero cross point and performing data interpolation. If the sampling interval S is 5 ms, the frequency that can be calculated is between 0 and 100 Hz.

The block diagram which shows the voltage value measuring device in the electric power system of this invention The block diagram which shows the electric current value measuring device in the electric power system of this invention The block diagram which shows the active power measuring device in the electric power system of this invention The block diagram which shows the reactive power measuring device in the electric power system of this invention The block diagram which shows the frequency measuring device in the electric power system of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Voltage value measuring device 11 Anti-aliasing filter 12 Sample hold circuit (sample holding means)
13 Analog / digital conversion means 14 Fundamental wave extraction unit (fundamental wave extraction means)
15 Voltage RAM (Voltage value temporary storage means)
16 Voltage value calculation part (Voltage value calculation means)
17 control circuit 18 current RAM (current value temporary storage means)
20 Current Value Measuring Device 21 Current Value Calculation Unit (Current Value Calculation Means)
30 active power measuring device 31 active power calculating part (active power calculating means)
40 Reactive Power Measuring Device 41 Reactive Power Calculation Unit (Reactive Power Calculation Unit)
50 Frequency measurement device 51 Frequency calculation unit (frequency calculation means)

Claims (10)

An anti-aliasing filter used for band limitation of a wideband signal, a sample holding unit that samples and holds a voltage waveform of an AC signal at predetermined intervals, and converts analog data output from the sample holding unit into digital data An analog / digital conversion means; a fundamental wave extraction means for extracting a fundamental wave component near the commercial frequency from digital data; a voltage value temporary storage means for temporarily storing voltage values up to four samples before; and a voltage value temporary storage means. Voltage value calculating means for calculating the stored voltage values up to four samples before by substituting them into an arithmetic expression;
The arithmetic expression is

Sampling data of voltage at time t is e (t)
Sampling data of voltage one sample before e (t−S)
Sampling data of voltage 2 samples before e (t-2S)
Sampling data of voltage 3 samples before e (t-3S)
Sampling data of voltage 4 samples before e (t-4S)
A voltage value measuring device that calculates an effective value of a voltage to be measured. An anti-aliasing filter used for band limitation of a wideband signal, a sample holding unit that samples and holds a current waveform in an AC signal at predetermined intervals, and converts analog data output from the sample holding unit into digital data An analog / digital conversion means, a fundamental wave extraction means for extracting a fundamental wave component near the commercial frequency from digital data, a current value temporary storage means for temporarily storing current values up to four samples before, and a current value temporary storage means Current value calculating means for calculating the stored current values up to four samples before by substituting them into an arithmetic expression;
The arithmetic expression is

The current sampling data at time t is i (t)
Sampling data of current one sample before i (t−S)
Sampling data of current 2 samples before i (t-2S)
Sampling data of current 3 samples before i (t-3S)
Sampling data of current 4 samples before i (t-4S)
A current value measuring device that calculates an effective value of a current to be measured. An active power calculated by substituting each voltage value stored in the voltage value temporary storage means according to claim 1 and each current value stored in the current value temporary storage means according to claim 2 into an arithmetic expression. An arithmetic means,
The arithmetic expression is

As an active power measuring device, a value of active power to be measured is calculated. Reactive power calculated by substituting each voltage value stored in the voltage value temporary storage means according to claim 1 and each current value stored in the current value temporary storage means according to claim 2 into an arithmetic expression. An arithmetic means,
The arithmetic expression is

A reactive power measuring device that calculates a reactive power value to be measured. Frequency calculating means for calculating by substituting each voltage value stored in the voltage value temporary storage means according to claim 1 into an arithmetic expression,
The arithmetic expression is

As a frequency measurement device, a frequency value to be measured is calculated. A step of performing band limitation of a wideband signal by an anti-aliasing filter, a step of sampling and holding a voltage waveform of an AC signal at predetermined intervals, a step of converting the sampled analog data into digital data, and digital data Extracting a fundamental wave component in the vicinity of the commercial frequency from the step, temporarily storing voltage values up to 4 samples before, and substituting the voltage values up to 4 samples before into an arithmetic expression,
The arithmetic expression is

Sampling data of voltage at time t is e (t)
Sampling data of voltage one sample before e (t−S)
Sampling data of voltage 2 samples before e (t-2S)
Sampling data of voltage 3 samples before e (t-3S)
Sampling data of voltage 4 samples before e (t-4S)
As a voltage value measuring method, an effective value of a voltage to be measured is calculated. A step of performing band limitation of a wideband signal by an anti-aliasing filter, a step of sampling and holding a waveform of a current in an AC signal at predetermined intervals, a step of converting sampled analog data into digital data, and digital data Extracting a fundamental wave component in the vicinity of a commercial frequency from, temporarily storing a current value up to 4 samples before, and substituting the current value up to 4 samples before into an arithmetic expression,
The arithmetic expression is

The current sampling data at time t is i (t)
Sampling data of current one sample before i (t−S)
Sampling data of current 2 samples before i (t-2S)
Sampling data of current 3 samples before i (t-3S)
Sampling data of current 4 samples before i (t-4S)
As a current value measuring method, an effective value of a current to be measured is calculated. An active power is calculated by substituting each voltage value stored in the step of temporarily storing the voltage value according to claim 6 and each current value stored in the step of temporarily storing the current value according to claim 7 into an arithmetic expression. And having a process of
The arithmetic expression is

As an active power measurement method, a value of active power to be measured is calculated. Reactive power is calculated by substituting each voltage value stored in the step of temporarily storing the voltage value according to claim 6 and each current value stored in the step of temporarily storing the current value according to claim 7 into an arithmetic expression. And having a process of
The arithmetic expression is

As a reactive power measurement method, a reactive power value to be measured is calculated. A step of calculating a frequency by substituting each voltage value stored in the step of temporarily storing the voltage value according to claim 6 into an arithmetic expression,
The arithmetic expression is

As a frequency measurement method, a frequency value to be measured is calculated.

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