JPS6151266B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biparabolic multiplier for measuring electrical energy or power.

Many methods are known for measuring electrical energy or power by static means. Therefore, the required product of voltage and current is created using a biparabolic multiplier using the formula (u+i) ² -(u-i) ² =4ui.
Here, u means the instantaneous value of voltage, and i means the instantaneous value of current. In order to form the square of the sum and difference of variables u and i, it is possible to use a square characteristic element that approximates the necessary square characteristic by a polygonal line. It is also known to approximately utilize the square-law characteristic of semiconductor elements. Furthermore, a heat converter and an effective value converter can be used as square characteristic elements.

This biparabolic method has a fundamental drawback in that the multiplication result is formed from the difference between two values. For example, if the supply voltage has a finite value and the load current is zero, the biparabolic multiplier forms the difference u ² −u ² =0. However, the parabolic functions of both square characteristic elements are not practically identical, resulting in large measurement errors.

A parabolic multiplier using only one square characteristic element is also known, and this square characteristic element uses a diode circuit to calculate the sum and difference of variables, more specifically, the sum and difference of the positive half-wave period of the power supply voltage. Each negative half-wave period difference is applied alternately. In this case, voltage drops across the diodes of the diode circuit can cause significant measurement errors. In particular, diode asymmetry causes zero point errors. Furthermore, harmonics in the supply voltage and current are not measured correctly.

The present invention overcomes these drawbacks and aims to provide a biparabolic multiplier without zero point errors.

Next, two embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, 1 indicates a current transformer, the load current flows through its primary winding, and the input 4 of the square characteristic elements 5' and 5'' flows through the secondary winding through lead wires 2 and 3. ' and 4''. Inputs 4' and 4'' are connected to the supply voltage U via resistors 6' and 6''. The outputs 7' and 7'' of the square characteristic elements 5' and 5'' are connected to the lead wire 8,
9 to the inputs 10, 11 of the subtractor 12. A polarity switch 13 is attached to the lead wires 2 and 3.
However, a polarity changeover switch 14 is connected to the lead wires 8 and 9. This polarity switch, which may consist of a CMOS-analog switch, for example, is controlled by a clock generator 15. Clock generator 15 generates a symmetrical rectangular pulse train having half cycles T _a and T _b of the same length as the clock frequency f _t .

Current transformer 1 and resistors 6' and 6'' constitute an adder and a subtracter.

During the half cycle T _a , for the input current I _e1 at the input 4' of the square characteristic element 5' and the input current I _e2 at the input 4'' of the square characteristic element 5'', I _e1a = I _u + I _i I _e2a = I _u −I _i holds true. where I _u means the current in the resistor 6' or 6'', and I _i means the current in the secondary winding of the current transformer 1.

The square characteristic elements 5' and 5'' are connected to the input current I _e1 to I
Generates an output current I _a1 proportional to the square of _e2 .

I _a1a = k ₁・I _e1a ² = k ₁ (I _u + I _i ) ² I _a2a = k ₂・I _e2a ² = k ₂ (I _u −I _i ) ² However, k ₁ and k ₂ mean constants .

For the voltage U _a at the output of the subtractor 12, U _aa = k ₃ (I _a1a - I _a2a ) = k ₃ [k ₁ (I _u + I _i ) ² - k ₂ (I _u - I _i ) ² ] holds true. However, k ₃ is also a constant.

On the other hand, during half-cycle T _b , both square-law characteristic elements 5' and 5'' functionally replace each other, so I _e1b = I _u - _{I i} I _e2b = I _u + I _i I _a1b = k ₁ (I _u - I _i ) ² I _a2b =k ² (I _u +I _i ) ² U _ab =k ₃ [k ₂ (I _u +I _i ) ² −k ₁ (I _u −I _i ) ² ] holds.

The temporal average value _a of the voltage U _a is _a = U _aa + U _ab /2 = 2k ₃ (k ₁ + k ₂ )·I _u ·I _i .

Currents I _u and I _i correspond to instantaneous values of power supply voltage U and current consumption I. Therefore, _a = 2k ₃ (k ₁ +k ₂ )·〓/R·U·I·cos. However, U¨ is the transformation ratio of the granule transformer 1, R is the resistance value of the resistors 6' and 6'', and cos is the phase angle.

Since the square characteristic elements 5' and 5'' are periodically exchanged, no zero point error occurs in the measurement results. There are no special conditions for selecting the clock frequency f _t , and it may be greater or less than the power supply frequency. .The measurement of power supply harmonics is performed correctly because at each point in time, the square of the sum and the square of the difference of the variables are formed.

In FIG. 2, the same reference numerals as those in FIG. 1 indicate the same parts. Here, control inputs 17' and 17'' and outputs 18' and 1 are used as square characteristic elements.
Controllable oscillators 16' and 16'' with 8'' are used. These outputs are connected to the polarity switch 14.
Reversible counter 2 that operates as a subtractor through
1 backward count input 19 and forward count input 2
Connected to 0.

Controllable oscillators 16' and 16'' generate a pulse train whose pulse frequency f _a1 or f _a2 is related to the square of the control signal I _e1 or I _e2 . Such oscillators are well known and will not be described in detail here. For example, in a time-sharing multiplier, an oscillator often used as a mark-space modulator can be used, and the relationship f _a = f ₀ [1-I _e /I _r ) ² ] However, f ₀ means the pulse frequency at I _e =0, and I _r means a constant.

When using this kind of oscillator, half cycle T _a
In between, f _a1a =f ₀₁ [1-(I _u +I _i ) ² /I _ri ² ] f _a2a = f ₀₂ [1-(I _u -I _i ) ² /I _r2 ² ] holds.

The reversible counter 21 forms the difference between the two pulse frequencies f _a2 and f _a1 divided by the frequency division ratio N. A pulse train of pulse frequency s is generated at the output of the reversible counter, and f _sa = f _a2a - _{f a1a} /N holds true for half cycle T _a . On the other hand, during the half cycle T _b , the oscillators 16' and 16'' functionally replace each other, so now f _a1b = f ₀₁ [1-(I _u - I _i ) ² /I _r1 ² ] f _a2b = f ₀₂ [1-(I _u +I _i ) ² /I _r2 ² ] f _sb = f _a1b - f _a2b /N holds true.

The average value f _s of the pulse frequency f _s is _s = f _sa + f _sb /2 = 2/N (f ₀₁ /I _r1 ²
+f ₀₂ /I _r2 ² )·I _u ·I _i , which represents a measure of the effective power, while the current counting state of the reversible counter 21 corresponds to the electrical output. It can be seen that in this case as well, no zero point error occurs in the measurement results.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a biparabolic multiplier with a voltage output according to one embodiment of the present invention, and FIG. 2 is a circuit diagram of a biparabolic multiplier with a frequency output according to another embodiment of the present invention. 1... Current transformer, 5', 5'', 16', 16... Square characteristic element, 13, 14... Changeover switch, 15
...Clock generator, 21...Reversible counter.

Claims (1)

[Claims] 1. An adder and a subtracter for forming the sum and difference of two variables proportional to power supply voltage or current consumption;
A biparabolic multiplier having two square characteristic elements for forming the square of the sum and the square of the difference of this variable, and further having a subtractor for forming the difference of the square of the sum and the square of the difference of this variable. , characterized in that switches 13 and 14 controlled by a clock generator 15 are provided to periodically replace the double-square characteristic elements 5', 5'', 16', and 16'' functionally. Biparabolic multiplier for output measurement. 2. In the biparabolic multiplier according to claim 1, the switches 13 and 14 are connected to the inputs 4', 4'', 1 of the square characteristic elements 5', 5'', 16', 16''.
7', 17'' and a polarity changeover switch connected to outputs 7', 7'', 18', 18''.