JPS63173973A - Quantity of electricity measuring apparatus - Google Patents

Abstract

PURPOSE:To prevent errors due to any frequency deviation, by measuring the frequency of a system when deviated from a fundamental frequency to compute the results of computation of voltage, current and power with the correction thereof by a correction factor determined by a measured frequency. CONSTITUTION:An output of a sampling/holding part S/H which samples and holds a voltage (v) and current (i) obtained from a power system is inputted into an A/D convertor section A/D through a multiplexer MPX. An output of the A/D convertor section A/D is computed at an arithmetic section AL and values of voltage, current, effective power, reactive power and the like are inputted into a correcting/computing section CPE, into which also is inputted a frequency (f) of a voltage of the power system as measured with a frequency measuring section FRS. The correcting/computing section CPE corrects values inputted using the frequency (f) and outputs quantity of electricity - voltage, current, effective power, reactive power and the like - free from errors in variations wit time, phase characteristic and frequency characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to a device that digitally processes voltage and current obtained from a power system to measure electrical quantities such as voltage, current, and power.

B9 Summary of the Invention This invention is a device for measuring electrical quantities such as voltage, current, and power, which measures the frequency when the frequency of the grid deviates from the fundamental frequency, and determines the calculation results of the voltage, current, and power based on the measured frequency. By performing correction calculations using correction coefficients, errors in electrical quantity measurement due to frequency deviations are eliminated.

C6 Conventional technology Figure 4 is a block diagram showing a conventional electrical quantity measuring device. In Figure 4, S/H is a sampling/holding system that samples and holds the voltage V and lightning current obtained from the power system. section, this sampling/hold section S/
The H output is input to the analog/digital converter A/D via the multiplexer MPX. The output of the analog-to-digital converter A/D is calculated by the calculation unit AL, and an electrical quantity measuring device such as voltage, current, active power, and reactive power is obtained as an output.

Note that the sampling frequency f of the above device is normally 4m times the fundamental frequency f0 of the power system (m is a positive integer), and when expressed by the formula, fs=4mfa.

Now, if fo = 50 Hz and m = 3, the sampling frequency will be f = 4 x 3 x 50 = 600 Hz.

Various means have been proposed as means for measuring electrical quantities such as voltage, current, active power, and reactive power from the instantaneous values of voltage and current obtained as described above. One example of conventional calculation means using effective values is shown in Table 1 below.

” Sampling frequency f, = 600Hz sampling interval θ, = 360X50/600 = 30'V (j)
= sin (2yr ・f o ・j /600 + αX The waveform is shown in FIG. 5) D0 The problem to be solved by the invention The calculation results by the above calculation means for ignition will be described below in terms of temporal fluctuations, phase characteristics, and frequency characteristics. .

First, we will discuss temporal fluctuations. Table 2 below shows the amplitude of fluctuations for the algorithms of the five means in Table 1, and FIGS. 6A-F and 7A-F show the temporal fluctuations.

From FIGS. 6A-F and 7A-F' and Table 2, the following problems occur.

(1) When f=50Hz, all algorithms settle on a constant value and can calculate the effective value correctly. However, only in the case of the area method, an error occurs because the calculated value differs depending on the sampling phase α. The calculated value using the area method is α=0°, 30”.

Minimum at 60°, α=15@, 45°, 75@...
・The maximum value of the error occurs at these phases.

(2) When f≠50 Hz, all algorithms oscillate at a period twice the frequency f, and from Table 2, the fluctuation amplitudes of each algorithm are compared as follows.

(a) If the root is taken in the square addition and triple product methods, the fluctuation amplitude becomes smaller.

(b) Between square addition R and triple product R, square addition R has a smaller fluctuation amplitude.

Next, problems with phase characteristics will be explained.

As mentioned above, in the area method, even at f = 50Hz,
Affected by phase angle α. For other means f = 50H
At z, it is not affected by the phase angle α, but f≠50
At Hz, the calculated value (one cycle average value) varies depending on the value of the phase angle α.

Table 3 shows the results of calculating this variation using the case of f=45 Hz as an example.

Table 3 Finally, we will discuss the frequency characteristics. Tables 4 to 6 and FIG. 8 show the frequency characteristics at f=40 to 601-1 z for the algorithms of the five means described above.

Shown in FIGS. 9A and 9H. These Tables 4 to 6 and FIG.

Figure 9A, I3 is V1. The 1-cycle integral values of V2R and V3R are normalized by the calculated value of 50 cycles. In addition, regarding the area method, the average value at f=50 Hz was normalized by 1 (α=0″)+V 1 (α=15°)/2.

Table 4 Comparison of normalized l-cycle average values of frequency characteristics of various algorithms f, = 600H
z α = 0 degrees Table 5 Comparison of normalized 1-cycle average values of frequency characteristics of various algorithms f, = 600 Hz
α=15 degrees Table 6 Frequency characteristics of various algorithms (
Error) Comparison of errors of normalized l-cycle average values f
, = 600 Hz α = 0 degree The following problems arise from the above Tables 3 to 6 and FIGS. 8 and 9 A and B.

(1) In the area method, f = 50 as shown in Figure 1A-C.
The error becomes large even near Hz.

(2) Means other than areal measurement have good accuracy near f=50Hz, but errors increase when the frequency of the system deviates from the fundamental frequency. (B, C in FIG. 1O) Moreover, since the values of these errors vary depending on the sampling phase α, it is also impossible to perform correction based on the frequency.

Means for Solving the E0 Problem This invention provides means for sampling the voltage and current obtained from the power system at a frequency that is 4m times the fundamental frequency of the power system (m: a positive integer), and the voltage and current sampled by this sampling means. means for converting data into a digital quantity; means for calculating peak values of voltage, current, and power from the digital quantity converted by the means; means for measuring a frequency from the voltage of the electric power system; and the calculating means. Calculated voltage.

The calculation results of current and power are input, and at the same time, a correction coefficient determined by the frequency measured by the frequency measuring means is input, and the calculation results of voltage, current, and power are corrected by this correction coefficient, and the output is used to measure the quantity of electricity. and correction calculation means for sending out the results.

F0 Effect In this invention, the frequency is measured from the voltage of the power system, and the calculation result of the calculation section is corrected using the measured frequency. Therefore, errors due to frequency deviation can be eliminated. Since this error correction is not dependent on the sampling phase α, accurate measurements can be made no matter what timing the sample is taken.

G. Example An example of the present invention will be described below with reference to the drawings.
The same parts as in FIG. 4 will be described with the same reference numerals.

In FIG. 4, the voltage V1 obtained at the output of the calculation unit AL
．． Six values, such as current ■, active power Pl, and reactive power Q1, are input to the correction calculation unit CPE. The correction calculation unit CPE also receives the frequency f of the voltage of the power system measured by the frequency measurement unit F'RS. The correction calculation unit CPE receives the input V,, I,, P;.

The six values such as Ql are corrected using the frequency f that is also input, and the output is a voltage vt, current that does not cause errors in temporal fluctuations, phase characteristics, and frequency characteristics! ,,active power Pa
, reactive power Q2, etc. are obtained.

Next, the voltage vl, the current I5. Active power P
To describe the means for calculating and obtaining t and reactive power Q using mathematical formulas, first, the meaning of each symbol is defined as follows.

f: System frequency (e.g. f = 45-55Hz) fo
: Fundamental frequency of the system (fo=50Hz) f, : Sampling frequency (f-=4fO) τ : Sampling interval (τ=2πf/f,) V : Input voltage instantaneous value i : Input terminal instantaneous value v = Vsin(ωL+θv)=VsinAi= l5
in (ω = 10i) = l5inBθ: Phase difference of voltage and current (θ = θV - θi = A - B) vn: Current data shown in Figure 2 V n-+: Shown in Figure 2! Data before sampling Vn-9: Data before two samplings shown in FIG. 2 Voltage v2. obtained at the output of the arithmetic unit AL. Reactive power Q5.
The active power P1 is expressed by the following formulas (1) and (2).

Obtained by calculating equation (3).

Yl""Vn-1"-VnVn-*"" (
1) QI -Vn-11n-Vnln-1"" (2
)P+=Vn-wordn-+-1/2(Vnln-*+Vn
-tln)”” (3) Next 1. : It will be explained below that V In Pr, Q + is determined by the equations (1) to (3). First, when formulas (1) to (3) are expanded, formulas (4) to (6) are obtained.

Vl'=Vn-+"-VnVn-t=V"sin"(A-r)-VsinAXVsin
(A-2r)=V”((sinAcosr-co
sA sinr )”-5inA(sinA cos2r
−cosAsin2r ))= Y” (sin”Ac
os” r +cos”As1n” r-2sinAc
osAs+1nrcos r-sin"Acos' r
+sin”As1n” r+2sinAcosAsi
nτ cosτ )=V”cos(A-A)sin”
r==V"sin'τ・
...(4) Qr = Vn-tIn-Vnln-+=
Vsin(^-r)X1sinB-VsinAXI
sin(Br)=Vl((sinAcost−
cosA sinr) sinB-sinA(sinBc
osr − cosBsinr )) = V, l5in(
A-B) sinr, =VIsinθminτ
...(5)'P+,==Vn-tjn-t
−VnL−t=Vn−lIn−+−1/2(Valn
−t”Vn−tlvi)=Ysin(A−r)Xl
sin(B-r)-1/2(VsinAxlsin(
B-2r)+Vsin(A-2r)XIsinB)
= Vl((sinAcosr −cosAsinr
)(sinBcosr-cosBsinr)-1/
2sinA(sinBcos2r-cosBsin2
r )-1/2sinB(sinAcos2r-co
sA sin2r )) = Vl (sinA sinBc
os"r +cosAcosBsin"r-(sinA
cosB+cosAsinB) sinr cosr-1
/2sinAsinB(cos”r−sin τ)+5
inAcosBsin r cos r-1/2sin
AsinB(cos't-5in"r)+cossi
nBsinτCo1tτ) = VI(cosAcosB
+5inAsinB)sin”r=Vlcos(A-
B) sin”r = VI cos Asin’t”・
(6) Here, the frequency f of the system is f = f o (5
0Hz), then V, I, P, and Q can be determined accurately as follows.

τ=2πf/f, -2πfo/4f, =π/2sinr
= sinyr /2 = 1, and from equation (4), V 1""Vn-1"-Vn"Vn-1=V"
"" From equations (7) and (5), Q r= Vn-3・In-Vn"In-t= Vls
inθ=(1−−−(+3)) From formula (6), P1=Vn−1・tn−+−1/2(V+%・In−*
”Vn-t・tn)=VIcosQ=P
...(9) However, the frequency f of the system
deviates from the fundamental frequency f0, f f−f o (
50Hz) is τ=2πf/f, =2π(/4fo=π
/2-f/f.

5inr=sin(yr/2·f/fo)≠1.

Therefore, from equation (4), V l"= Vn-t-Vn"Vn-*= V"sxn
"r"" (10) From formula (5), Q1=Vn-t・I n-Vn・in-+=Qsinτ
--- From equations (11) and (6), P+-Vn-+"In-+-Vn'In-1= Psi
n”τ ---(12), (10), (11),
Equation (12) is (7).

Equations (8) and (9) are not equal and have errors.

From the above formulas (10), (II), and (12), f f f
In the case of o, the calculation results according to equations (1) to (3) are the system frequency f and the fundamental frequency f. It will have an error determined by This error is not related to the sampling phase α.

For example, let's evaluate the measurement error of reactive power Q.

If the true value of reactive power is Q, the measured value Q is Q1=Qs
int=Qsin(g/2·f/f o ).

Error εQ=(Q, −ψ/QXIQG= (stir −
1) Since XIOQ (%), f = 45 Hz
If Ql = Qsinr = Qsin(z /2X4
5150)=QXo, 9877. Also, the error ε
9 is e Q=(Ql-Q)/QX100= (0,9877
-1)X100=-1,23(%).

Next, finding Q and εQ when f=55Hz, Qr=
Qsint=Qsin(r/2X55150)=
QxO, 9877εo=-1,23 (%).

Here, the tendency of the error εQ for f=45 Hz to 55 Hz is illustrated as shown in FIG. 3.

v obtained as the output of the calculation unit AL as described above,
Since there is no error in I,, Pt, and Qt when f=fo, there is no need for correction in the correction calculation unit CPE, and the outputs thereof can be obtained as electrical quantities of Vt, It, P*, and Qt. However, in the case of ff-fo, (10)2~(
12) Errors sin τ and sin" τ occur as shown in equation 12), so it is necessary to correct this error. Since this error is determined by the frequencies f and f, the system frequency " is determined by the frequency measurement unit FR8. This can be corrected by
Fixed at Hz. As a frequency measuring means, 1 of the voltage V is used.
This is done by converting the cycle into a number of pulses using an IMHz clock pulse and counting the number of pulses with a counter.

Here, when the fundamental frequency fo = 50 Hz, the output of the counter is IXI O''150 = 20,000, so the resolution of frequency measurement is 50/20,0OO = 0.0025 Hz.

Change the measurement frequency obtained as above from 45Hz to 55H.
z is measured in advance and its output F is stored in the correction calculation unit CPE. Table 7 shows the frequency f and the output F of the frequency measuring section, and also shows the errors sinτ and sin″τ.

Table 7 v, , x, , p, obtained at the output of the arithmetic unit AL.

Ql is input to the correction calculation unit CPE. Correction circuit section C
In the PE, correction calculations according to the following equations (13) to (15) are performed to obtain an electrical quantity as an output.

The correction calculation formula is vl-v1' from equations (4) to (6).
/sinτ...(13) Qt = Ql/5inr
”・(14)Pt=P+/sin”r
---(15).

From equation (13) to equation (15), ite,v,,Q,.

P+ is obtained at the output of the calculation unit AL, and sinτ, sin
"Vt", Ql, and Pt can be easily determined because they are determined by f and fo as described above. Especially s
inτ.

Once f and fo have been determined, sin"τ can be easily corrected by storing the values shown in Table 7 in the correction calculation unit CPE in advance. If the frequency f deviates from the fundamental frequency f0, But V t, I t, P t.

The amount of electricity Q can be determined accurately.

In the above embodiment, the sampling frequency f-=4f.

We have described the case of , but as long as the relationship fs = 4mf0 (m is a positive integer) is satisfied, the sampling frequency f may be any value, and V In I In P In Q +
It is sufficient to use every m data for the 'D operation.

For example, if m = 3−, f o = 50 Hz, f
a=4X3X50=600Hz, but at this time vl
The calculation can be performed using every third piece of data as described above.

(From formula (4)) Y r"= Vn-s"-Vn@Vn-sI In P
The same applies to l+Q+. Also, in the above explanation, the fundamental frequency of the system f o = 50 Hz, but F
It is clear that o=60 Hz or other values also hold true.

H8 Effects of the invention As described above, according to the invention, even when the frequency of the grid deviates from the fundamental frequency, by measuring the frequency and performing correction calculations on the measurement results of voltage, current, and power,
Errors due to frequency deviation can be eliminated. Since the error correction at this time does not depend on the sampling phase α, accurate measurements can be made no matter what timing the sampling is performed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a voltage and current waveform diagram showing sampling data, Fig. 3 is a characteristic diagram showing error trends, and Fig. 4 is a block diagram showing a conventional example. Figure 5 is a waveform diagram showing the sampling points, Figure 6 A to F are characteristic diagrams showing temporal fluctuations by the area method, square addition method, and triple product method, Figure 7 A to F are the area method, A characteristic diagram showing temporal fluctuations due to square addition R and triple product R. Figure 8 shows the area method, square addition method, triple product method, square addition R method, and triple product R.
Figures 9A and B are frequency characteristic diagrams based on the area method, square-addition R method, and triple product R method. Figure 1O A to C are frequency characteristics diagrams when α=θ° and α=15°. It is a frequency characteristic diagram of each of the area method, the square addition R method, and the 3 product R method. S/H...sampling hold section, MPX...multiplexer, A/D...analog-to-digital conversion section,
AL...Arithmetic unit, FRS...Frequency measurement unit, CPE
...Correction calculation section. Figure 1] Shishin? Shio 11 70 wrinkle opening Figure 2 Figure 3

Claims (1)

[Claims] (1) A means for sampling the voltage and current obtained from the power grid at a frequency that is 4m times the fundamental frequency of the grid (m: a positive integer), and a means for converting the voltage and current data sampled by the sampling means into a digital quantity. , means for calculating peak values of voltage, current and power from the digital quantities converted by this means; means for measuring frequency from the voltage of the power system; and means for calculating the peak values of voltage, current and power from the digital quantities converted by the means; When the calculation results are input, a correction coefficient determined by the frequency measured by the frequency measuring means is input, and the calculation results of the voltage, current, and power are corrected by this correction coefficient, and the electrical quantity measurement results are sent to the output. An electrical quantity measuring device comprising a correction calculation means.