JPS622271B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a parabolic 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 parabolic multiplier using the formula (u+i) ² -(u-i) ² =4ui. Here, u means an instantaneous value of voltage, and i means an 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. 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 positive half-wave periods 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. In addition, large measurement errors occur due to deviations from the sine wave (power supply harmonics, distortion due to nonlinear loads).

SUMMARY OF THE INVENTION An object of the present invention is to provide a parabolic multiplier that does not require a diode in the input circuit of a square characteristic element and can accurately measure energy or output even when the wave deviates from a sine wave.

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

In FIG. 1, 1 means a current transformer, the load current I flows through its primary winding, and the input 4 of the square characteristic element 5 and the reference potential ( connected to ground). Lead wire 2,
3 is connected to a polarity changeover switch 6. The input 4 of the square characteristic element 5 is connected to the power supply voltage U via a resistor 7.
while its output is connected directly to an output resistor 10 in one position of the changeover switch 8 and via an analog inverter 9 in the other position.

The polarity changeover switch 6 and the changeover switch 8, which are composed of CMOS-analog switches, are controlled by a clock generator 11. This clock generator generates a symmetrical rectangular pulse train with half cycles T _a and T _b of the same length as the pulse frequency _t .

The current transformer 1 and the resistor 7 operate as an adder or a subtracter depending on the position of the polarity switch 6.
During the half cycle T _a , the input 4 of the square characteristic element 5
For input current I _e at , I _ea = I _u + I _i holds true, and I _eb = I _u - _{I i} holds true during half cycle T _b . Here, I _u means the current in the resistor 7 and I _i means the current in the secondary winding of the current transformer 1.

The square-law characteristic element 5 generates an output current I _a whose value corresponds to the square of the input current I _e . Output resistance 10
For the voltage U _a in half cycle T _a , U _aa = K ₁ · I _ea ² = K ₁ (I _u + I _i ) ² holds, and during half cycle T _b , U _ab = -K ₁ · I _eb ² = −K ₁ (I _u −I _i ) ² holds true. However, K ₁ means a constant.

The average value _a of the voltage U _a is _a = U _aa + U _ab /2 = 2K ₁ · I _u I _i . The currents I _u and I _i correspond to the instantaneous values of the power supply voltage U and the load current I.

Therefore, _a = 2K ₁・U/R・U・I・cos. However, U¨ means the transformation ratio of the current transformer 1, R means the resistance value of the resistor 7, and cos means the phase angle.

The method described does not require diodes and voltage drops across the diode do not introduce errors in the measurement results. The pulse frequency _t of the clock generator 11 can be chosen sufficiently high compared to the power supply frequency or can be chosen independently so that deviations from the sine wave do not result in measurement errors.

In FIG. 2, the same reference numerals as those in FIG. 1 indicate the same parts. A controllable oscillator 12 with a control input 13 is used here as a square-law characteristic element. The output of this oscillator is connected to a count input 14 of a reversible counter 15, whose count direction control input 16 is connected to a clock generator 11.

A controllable oscillator 12 generates a pulse train whose pulse frequency _a is related to the square of the control signal _Ie . Such oscillators are well known and will not be described in detail here. For example, oscillators often used as mark-space modulators in time-sharing multipliers can be used. The relationship satisfies _a = _p [1-( _Ie / _Ir ) ² ]. However, _p means the pulse frequency at I _e =0, and I _r means a constant.

When using this type of oscillator, half a cycle T
Between _a , _aa = _p [1-(I _u +I _i /I _r ) ² ] holds, and between half cycles T _b , _ab = _p [1-(I _u -I _i /I _r ) ² ] holds.

A reversible counter 15 counts the oscillator pulses between half cycles T _b in the forward direction and between half cycles T _a in the reverse direction.

Pulse frequency at the output of the reversible counter
_s is _s = _sb - _aa /2N=2 _p /N・I _r ²・
I _u・I _i . However, N means the frequency division ratio of the counter 15. When the pulse frequency _a is sufficiently large compared to the mains frequency and thus corresponds to the instantaneous value of the input signal I _e , the pulse frequency _s represents a measure of the effective power, while the current count of the reversible counter 15 The state corresponds to the electrical output.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a parabolic multiplier with a voltage output according to one embodiment of the invention, and FIG. 2 is a circuit diagram of a parabolic multiplier with a frequency output according to another embodiment of the invention. 1... Current transformer, 5, 12... Square characteristic element, 6
...Selector switch, 11...Clock generator, 1
5...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;
An electrical energy or power measurement having a square characteristic element for forming alternately the square of the sum and the square of the difference of this variable, and a subtractor for forming the difference between the square of the sum and the square of the difference of this variable. In the parabolic multiplier for, the inputs 4; 13 of the square characteristic element 5; 12 are connected to a switch 6, of which in one position the sum of the variables and in the other position the difference thereof 12, said switch 6 is controlled by a clock generator 11 which generates a symmetrical rectangular pulse train with a pulse frequency _t that is large compared to or independent of the mains frequency. The parabolic multiplier as described above. 2. In the parabolic multiplier according to claim 1, the output of the square characteristic element 5 is directly when the switch 8 controlled by the clock generator 11 is in one position and in the other position. When the output resistor 10 is connected via the analog inverter 9
Said parabolic multiplier, characterized in that said parabolic multiplier is connected to. 3. In the parabolic multiplier according to claim 1, the square characteristic element 12 is a controllable oscillator whose frequency is related to the square of the control signal I _e and whose output is the count of the reversible counter 15 A parabolic multiplier as described above, characterized in that the count direction control input 16 of the reversible counter 15 is connected to the clock generator 11.