JPH0664098B2 - Digital phase meter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital phase meter for measuring a phase difference of AC electric quantities such as voltage and current having a constant frequency and displaying the result as a digital value. .

(Prior Art) Conventionally, as a phase measurement method of this kind, a cathode ray tube method using a Lissajous diagram, a two-phenomenon cathode ray tube method that draws both waveforms compared to a two-phenomenon type oscilloscope, and two sine waves are shaped into a square wave. Then, a square wave method that generates a square wave corresponding to the temporal overlap and averages the phase difference, other counting method, vector meter method (synchronous rectification method), and the like are known.

(Problems to be Solved by the Invention) However, few of these methods can directly calculate the required phase difference and digitally display it,
A lot of labor and time are required because the phase difference cannot be obtained without variously processing each measured value by a mathematical formula or the like. Further, there is a possibility that a measurement error or the like may occur due to a data reading error.

Furthermore, these methods require a dedicated phase meter, and when measuring the phase difference of the AC electricity of the power system, such a phase meter must be brought to an electric station or the like and connected to the target. Was accompanied by. In addition, deterioration of performance due to secular change of components of the phase meter may cause deterioration of measurement accuracy.

The present invention has been proposed to solve the above problems, and an object of the present invention is to perform various calculations and processes by using digital data indicating the instantaneous values of two AC electric quantities, and By calculating the phase difference of the amount of electricity, the phase difference can be measured accurately, easily and directly,
Another object of the present invention is to provide a digital phase meter in which hardware common to the digital relay can be used to reduce the cost and simplify the measurement work.

(Means for Solving Problems) In order to achieve the above object, the present invention samples a plurality of instantaneous values of two alternating-current electric quantities having the same frequency but different phases, and A / D these instantaneous values. In a digital phase meter for obtaining the phase difference between the two AC electric quantities based on the digital data obtained by the conversion, means for calculating the sine value and cosine value of the phase difference between the two AC electric quantities using digital data. , A sine value table storing virtual phase angles from 0 ° to 45 ° and values obtained by multiplying the sine values of these virtual phase angles by a coefficient, respectively, and the absolute values of the calculated sine value and cosine value. Taking a value, comparing the magnitudes of these absolute values, referring to the sine value table based on the smaller value, means for obtaining a virtual phase angle, and judging from the sign of the calculated sine value and cosine value Depending on the attribution quadrant of phase difference, in which a means for converting the virtual phase angle to the true phase difference.

(Operation) In the present invention, first, a plurality of instantaneous values of two AC electric quantities are sampled, respectively, and digital data is obtained by A / D conversion. Next, the sine value and cosine value of the phase difference are calculated by applying the product-add method of the operation principle in the digital relay.

Then, the virtual phase angle corresponding to these sine value and cosine value is obtained from the sine value table. After that, the virtual phase angle is converted into a true phase difference by a predetermined conversion formula according to the belonging quadrant of the true phase difference determined from the sign of the sine value and the cosine value, and thereafter this position is converted by a well-known means. The phase difference is digitally displayed.

(Example) An example of the present invention will be described below with reference to the drawings. In this embodiment, a voltage and a current are input from a power system to obtain a phase difference between them, and as shown in FIG.
Here, the AC voltage v and the current i having the same frequency are the current i
If the phase lags the voltage v by θ °, it can be generally expressed by the following equation.

v = Vmsin (ωt) (1) i = Rmsin (ωt−θ) (2) Further, these waveforms are as shown in FIG.

In processing block 1, for v and i
Sampling at 12 times frequency (sampling interval 30
.Degree.), And A / D-converts this to obtain a digital data string vn, in (n = 0,1,2,3, ...) Related to the instantaneous values of v and i. If these data orders are defined as shown in FIG. 2, for example, v ₀ = Vmsin (ωt) v ₁ = Vmsin (ωt + π / 6) v ₂ = Vmsin (ωt + 2π / 6) :: i ₀ = Imsin (ωt −θ) i ₁ = Imsin (ωt−θ + π / 6) i ₂ = Imsin (ωt−θ + 2π / 6) :: In general, vn = Vmsin (ωt + nπ / 6) (3) in = Imsin (ωt−θ + nπ) / 6) ... (4).

Now, according to the product addition formula as the operation principle of the digital relay, Vm ² = (Vn) ² + (vn _{− 3} ) ² Im ² = (in) ² + (in _{− 3} ) ² ie It is also known that there is a relation of vn ・ in ＋ vn _{− 3}・ in _{− 3} = Vm ・ Imcosθ …… (7) vn ・ in _{− 3} + vn _{− 3}・ in = Vm ・ Imsinθ …… (8) ing. Therefore, (5)-
From equation (8), Becomes The calculation of the equations (9) and (10) for obtaining cos θ and sin θ is performed in the processing block 2 in FIG. 1, but since | cos θ | ≦ 1 and | sin θ | ≦ 1, only fixed point arithmetic can be performed. Since the calculation result is 0 in a microcomputer, it is actually 2 ⁸ cos θ, 2 ⁸ sin
Calculate the value of θ.

After the values of cos θ and sin θ are obtained in this way, the virtual phase angle θ ′ corresponding to | cos θ |, | sin θ |
Calculate (0 ° ≦ θ ′ ≦ 45 °). That is, as is well known, 1) sin θ = cos (90 ° −θ) = cos θ ″ (where 0 ° ≦ θ ≦ 360 °) 2) 0 ° ≦ θ ≦ 45 ° between cos θ and sin θ If cosθ> sinθ ≧ 0 θ = 45 °, then there is a relation of 0 ≦ cosθ <sinθ within the range of cosθ = sinθ 45 ° <θ ≦ 90 °, that is, | cosθ |, | sinθ Since | can be represented by the value of cosine cos θ ′ or sine sin θ ′ of the virtual phase angle θ ′ in the range of 0 ° ≦ θ ′ ≦ 45 °, cos θ, sin θ (2 ⁸ cos θ, 2 ⁸ sin θ) to cos θ ′
If (2 ⁸ cos θ ') or sin θ' (2 ⁸ sin θ ') is found, the corresponding θ'is obtained, and then the true phase difference θ is calculated from θ'by a conversion formula according to the sign of cos θ, sin θ. Good.

At this time, the table for obtaining θ ′ may be composed of 46 sets of numerical values as shown in Table 1 below.

Then, when the phase difference θ is obtained from the value of cos θ or sin θ, | cos θ | and | sin θ | are compared and a table search is performed using the smaller value. That, | sin [theta | when using, the | sinθ | 2 ⁸ sin values in Table 1
Compare from the upper value in the column of θ ′ = 2 ⁸ cos θ ″, | si
At some point when the value of nθ | becomes larger, θ'is some angle. When using | cosθ |, θ'is obtained by subtracting θ ″ similarly obtained from 90 °.

On the other hand, cosθ, si is used when performing the calculations of equations (9) and (10).
The sign of nθ is recognized, and the processing block 4 determines the quadrant to which θ belongs based on FIG.
The phase angle processing is executed by the conversion formula for each quadrant in the table, and the true phase difference θ (0 ° ≤ θ ≤ 360
゜) is asked.

The phase difference θ calculated in this way is displayed by the processing block 5 of FIG. 1 via a well-known digital display.

According to this embodiment, the phase difference θ in the range of 0 ° to 360 ° can be measured only by having the virtual phase angle θ ′ of 0 ° to 45 ° as the sine value table. There is an advantage that the capacity is small.

(Effect of the invention) As described in detail above, according to the present invention, the phase difference is calculated and displayed based on the digital data.
Since the phase difference can be measured and displayed quickly, the labor and time required for the measurement can be significantly reduced.

Further, since the phase difference can be directly read, there is no room for a reading error, and there is very little possibility of an error due to aging of component parts or the like, so that normal measurement can always be performed.

Furthermore, since the present invention can use the hardware common to the digital relay in principle, it is not necessary to prepare a separate phase meter and the cost can be reduced. It has an advantage that it is free from the complicated work of connecting to the power system every time the phase difference is measured.

Further, in the present invention, the sine value table for the virtual phase angle of 0 ° to 45 ° is provided, and the phase difference θ in the range of 0 ° to 360 ° is directly measured by referring to this table and performing a simple calculation. In addition, the phase difference can be accurately measured even when a fixed-point type microcomputer is used.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is a block diagram showing a data processing procedure, FIG. 2 is a waveform diagram of voltage and current to be measured, and FIG. 3 is a sign of sine value and cosine value. FIG. 5 is an explanatory diagram showing a quadrant belonging to a phase difference according to FIG. 1-5 ... Processing block

Claims (1)

[Claims] 1. A plurality of instantaneous values of two alternating-current electric quantities having the same frequency and different phases are sampled, respectively, and based on digital data obtained by A / D converting these instantaneous values, the two alternating-current electric quantities are calculated. In a digital phase meter for obtaining a phase difference, means for calculating the sine value and cosine value of the phase difference between the two AC electric quantities by using digital data, a virtual phase angle from 0 ° to 45 °, and these virtual phases The sine value table that stores the values obtained by multiplying the sine value of the angle by a coefficient, respectively, and the calculated absolute values of the sine value and cosine value are compared, and the smaller of these absolute values is compared. Means for obtaining a virtual phase angle by referring to the sine value table based on the value of, and a virtual phase angle of true according to the quadrant belonging to the phase difference determined from the signs of the calculated sine value and cosine value. Rank Digital phase meter, characterized in that it comprises means for converting the difference, the.