JPS5851224B2 - Static measuring device for measuring the power of AC power supplies - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a static measuring device for measuring power in an alternating current circuit.

Static measuring devices for measuring the power in alternating current circuits usually operate according to the so-called time-shared measuring method.

Such a measuring device is for example CH-PS462953
It is more well known.

This device has a transformer and a current transformer to provide floating supply voltage and current.

The measured voltage taken on the secondary side of the transformer produces a pulsed voltage such that the ratio of the duration of the pulse to the sum of the differences between the periods and periods is proportional to the measured voltage and therefore to the instantaneous value of the supply voltage, the so-called mark, Control the space modulator.

The voltage proportional to the supply current, captured by the current transformer load, changes polarity in synchronization with the pulse voltage generated by the mark and space modulators.

The temporal average value of the AC amount obtained in this way corresponds to the product of the power supply voltage and the power supply current, that is, the AC power.

Transformers and current transformers require relatively large magnetic cores made of high quality materials and are therefore expensive.

In addition, current transformers have phase errors that adversely affect the measuring accuracy of the measuring device and are brought to values that can be tolerated, for example, by electronic error compensation in the current circuit or by phase shifters acting in the opposite direction in the voltage measuring circuit. It has to be made smaller.

Furthermore, measuring devices with time-sharing multipliers are known that do not require the use of a transformer in the voltage measuring circuit, but require a current transformer to electronically compensate for errors.

Also known are static measuring devices which operate according to the static coincidence method, in which a mark, space modulator, controlled by the supply voltage and controlled by the supply current, generates two pulsed voltages, the temporal coincidence of which represents a measure for the power. (CH-PS5
51013 and 538122).

Finally, a direct time-coded direct current floating measurement method is known (DT-O82112315) in which a magnetizable iron core with at least three different windings is The second winding, i.e. the measuring winding, conducts the current to be measured, and the winding of the force tube 3, i.e. the induction winding, supplies the induced voltage via the magnetic flux density changes of the iron core. do.

This induced voltage is differentiated, and the time shift of the zero series vertices of the differential induced voltage appearing in the iron core due to the influence of the measured current is used as a measure of the strength and direction of the current to be measured.

SUMMARY OF THE INVENTION The present invention relates to a static measuring device for measuring the power of an AC circuit with a simple and highly accurate configuration that does not require expensive transformers and current transformers.

This object is achieved by the features specified in the patent claims.

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

In FIG. 1, 1 designates a mark-space modulator, which comprises a magnetic core 2 having a first winding 3 and a second winding 4.
, a triangular wave current generator 5, a differentiator 6, and a zero threshold switch 7.

The current ■ of the AC power supply passes through the winding 3.

One terminal 8 of the winding 4 is connected by a lead 9 via a capacitor 10 to the non-inverting input of an operational amplifier 7 which operates as a zero threshold switch.

The inverting input of the operational amplifier 7 is connected to ground via a lead 11 and to the other terminal 13 of the winding 4 via a lead 12.
connected to.

A resistor 14, which together with the capacitor 10 forms the differentiator 6, has one terminal connected to the non-inverting input of the amplifier 7 and the other terminal grounded.

A resistor 15 is inserted into the lead wire 11 and a capacitor 16 is inserted into the lead wire 12, which form a second differentiator 17.

The triangular wave current generator 5 is connected to the terminals 8, 13 of the winding 4 in this example.
connected to.

However, it is also possible to connect the triangular current generator 5 to the third winding of the magnetic core 2.

The second differentiator 17 is necessary for potential separation when the output 19 of the generator 5 has a potential different from zero potential, as is the case in the embodiment of the triangular wave current generator illustrated in FIG.

The output 20 of the zero threshold switch 7 represents the output of the mark-space modulator 1, which output is connected on the one hand to the control electrode of the transistor 21 and on the other hand to the input resistor 23 and the feedback line. It is connected to the control electrode of a transistor 25 via an inverting amplifier 22 having a resistor 24 .

The push-pull controlled transistor 21.25 acts as a polarity converter of the amplitude modulator 26.

The voltage U of the transformer power supply is supplied via a resistor 27 to an amplifier 28 having a resistor 29 in the feedbar line.

An inverting amplifier 30 having a resistor 31 on the input side and a resistor 32 on the feedback line is connected to the output of the amplifier 28.

The output of the amplifier 28 is connected via a resistor 33 and the transistor 21 to a node 35 of the outputs of the transistors 21 and 25, and the output of the inverting amplifier 30 is connected to the node 35 via a resistor 34 and a transistor switch 25. .

The current flowing to the connection point 35 is connected to the resistor 36 and the capacitor 37.
an operational amplifier 38 which acts as a filter with negative feedback;
reach.

The resistor 36, capacitor 37, and amplifier 38 constitute a current-voltage converter.

A DC voltage measuring device 39 is connected to the output of this amplifier 38 to display AC power, and a voltage-frequency converter 4 that operates a pulse counter 41 is connected to display the power.
0 is connected.

The connection point 35 is therefore a current-to-voltage converter 36.37.38
and directly connected to the input of the current-to-frequency converter from the voltage-to-frequency converter 40.

The operation of the described measuring device is as follows.

The triangular wave current generator 5 supplies the winding 4 with a triangular alternating current 1 (Fig. 2a), whose frequency is higher than the power supply frequency, and the alternating current 1 moves the magnetic core 2 in one direction or the direction of magnetization. Control and saturate alternately in the other direction.

When the supply current ■ has a value of zero, a symmetrical alternating current voltage U1 (Fig. 2b) is induced in the winding 4, and the alternating current voltage is generated from successive positive and negative needle pulses separated by the same time interval. Become.

At the output of the differentiator 6 or at the input of the zero-threshold switch 7, a voltage U2 (FIG. 2c) is generated which intersects the time axis t at the time of the maximum or minimum value of the voltage U1, respectively.

The zero threshold switch 7 changes its state each time the voltage U2 passes through zero.

Its output triangular pulse voltage U3 (FIG. 2d) has a pulse duration Ta that is as large as the above-body period Tb.

On the other hand, when the instantaneous value i1 of the alternating current ■ is greater than zero, the voltage U1 moves to the left for negative voltage pulses and to the right for positive voltage pulses, as shown by the dotted line in Figure 2b. So, the AC power supply current ■1 helps the magnetizing effect of the current ■1.

The effect is to increase the pulse duration Ta and decrease the on-body period Tb.

In short, 1 is a constant. During the pulse duration, transistor switch 21 is conductive and transistor switch 25 is conductive.
is blocked.

The resistor 33 carries a current proportional to the instantaneous value of the power supply AC voltage U.
i2 flows.

On the other hand, during the body period Tb, the transistor switch 2
1 is cut off and the transistor switch 25 is conductive, so a current + proportional to the instantaneous value of the power supply AC voltage flows through the resistor 34.
t2 flows.

The average value of the current i3 at the connection point 35 is the product 12・(-i2')
, and therefore corresponds to electric power.

Since the voltage-frequency converter 40 generates a pulse frequency corresponding to the power, the pulse counter 41 records the power.

The advantages of the described measuring device are easily understood.

Instead of a precise measuring transformer, only a simple magnetic core with two windings is required, which operates in the saturation region and has a very small cross section compared to the measuring transformer.

Since the current transformer can be omitted, the problem of phase error compensation, which has been necessary up to now, does not arise at all.

The best measurement results are obtained when the current (1) generated by the triangular wave current generator 5 has an ideal symmetrical triangular waveform.

The triangular current curve preferably has rounded corners as shown in Figure 2a.

As a result, a rapid magnetic flux change occurs at the maximum and minimum values of the current flow 1 of the magnetic core 2, and as a result, a jump occurs in the voltage U1 at that point, preventing the acicular pulse of the voltage U2 from being disturbed. .

FIG. 3 shows a circuit diagram of a triangular wave current generator that satisfies these requirements in a simple manner.

In FIG. 3, reference numeral 42 indicates an oscillator, and the oscillator 42 includes a so-called Miller integrator having an amplifier 43 and a capacitor 44 connected in parallel to the amplifier 43, and Miller integrators 43, 44.
It consists of a threshold switch 45 connected to the output of the mirror integrator, and a switch 46 controlled by this switch, which controls the polarity of the current source connected to the input of the Miller integrator.

In the illustrated position of switch 46, a constant current +■ flows from current source 47 to Miller integrator 43, 44, and the voltage at the output of the integrator decreases linearly in the negative direction.

When this voltage reaches a threshold below threshold switch 45, this switch is reversed and switch 46 switches.

This time, a constant current -■ is applied to the inputs of the Miller integrators 43 and 44.
, so this output voltage rises linearly and positively.

The outputs of the mirror integrators 43 and 44 are connected to a differentiator consisting of a capacitor 48 and a resistor 49, whose role is to make the triangular wave voltage produced by the oscillator 42 symmetrical, i.e. to visually detect the DC component present. It is to raise the level.

The voltage of the output of the differentiators 48 and 49 is the voltage of the output of the diode circuit 51.
is applied to the amplifier 50 belonging to the .

Amplifier 50 controls current source 53 via resistor 52 .

Current source 53 consists of an amplifier 54 whose output is output 18
and its inverting input, which is grounded via a resistor 55, is the output 19 of the triangular wave current generator 5.

Diode circuit 51 has a series circuit consisting of diodes 56, 57 and Zener diodes 58, 59, and the series circuit is connected between the connection point between resistor 52 and the non-inverting input of amplifier 54 and ground.

The connection point between the diode 56 and the Zener diode 58 is connected to the voltage source -U via a resistor 60.

diode 57 and Zener diode 59
The connection point with is connected to the voltage source +Uo via a resistor 61.

The triangular wave voltage at the input of the amplifier 54 is connected to the Zener diode 5.
When the breakdown voltage of 9 is exceeded, the diode 57 becomes conductive.
The voltage is more limited.

Similarly, when the triangular wave voltage falls below the breakdown voltage of the Zener diode 58, the diode 56 connected with the opposite polarity to the diode 57 becomes conductive.

In FIG. 4, 1' and 1'' indicate two mark-space modulators, the internal configuration of which corresponds to mark-space modulator 1 of FIG.

The AC power supply current ■ is supplied to the winding 3' of the modulator 1', and the AC power supply voltage U is supplied to the winding 3' of the modulator 1' through a high resistance 60.
connected to.

The outputs 20', 20'' of both scalers are connected to a matching circuit 61.

A sample circuit 62 is connected to the output of the matching circuit 61 and to a sample generator 63, which generator has a pulse frequency Fr.
generates a narrow sample pulse of

The output of the sample circuit 62 is connected to a forward counter input of a reversible counter 64, whose inverse counter input is connected via a frequency divider 65 to a sample generator 63.

The division ratio of the frequency divider 65 is 4=1 or 2:1, depending on whether the matching circuit 61 only checks the coincidence of pulses or the coincidence of pulse interruptions of the pulsed voltages applied to both of its inputs. It is.

By correspondingly designing the triangular wave current generators of both mark-space modulators 1' and 1'' so that their pulse voltages have different pulse frequencies, the reversible counter 64 records the power and its output The average value of frequency Fa corresponds to power.

[Brief explanation of the drawing]

Figure 1 is a principle circuit diagram of a measuring device with a time-sharing multiplier;
Figure 2 is a waveform diagram, Figure 3 is a circuit diagram of a triangular wave current generator,
FIG. 4 is a principle circuit diagram of a measuring device with a multiplier operating according to the static matching method. 1...Mark-space modulator, 5...
・Triangular current generator, 6...Differentiator, 7...
... Zero threshold switch, 39 ... DC voltage measuring device, 40 ... Voltage frequency converter, 41 ...
... Pulse counter, 42 ... Oscillator, 5
1... Diode circuit, 61... Match circuit, 62... Sample circuit, 63...
・Sample generator.

Claims (1)

[Scope of Claims] 1. A magnetic core having a first winding to which a current of the AC power source or a voltage of the AC power source is applied via resistance, and a second winding, the frequency being higher than the frequency of the AC power source. an oscillator that generates a frequency output signal and applies it to the magnetic core to saturate the magnetic core; a differentiator whose input is connected to the second winding of the magnetic core; and a pulse voltage input with the output of the differentiator. an integrator having one input connected to the output of the zero threshold switch and the other input connected to the AC power source to input the voltage or current of the AC power source; , the magnetic core, the oscillator, the differentiator, and the zero-threshold switch constitute a mark-space modulator, and the pulse voltage from the zero-threshold switch is equal to the difference between its duration and the body period. is proportional to the instantaneous value of the current or voltage of the AC power source, and the integrator controls conduction of the voltage or current of the AC power source in response to the output pulse voltage of the zero threshold switch. A static measuring device for measuring the power of an AC power source, characterized in that it outputs a signal indicating the product of the voltage and current of the AC power source. 2. In claim 1, the oscillator generates a triangular voltage by controlling a current source directly connected to the second winding of the magnetic core, and the oscillator generates a triangular wave voltage between the oscillator and the current source. The static measuring device is characterized in that a diode circuit is connected to round the corners of the triangular wave voltage. 3. The static measuring device according to claim 2, characterized in that a polarity switch of an amplitude modulator of a time division multiplier is connected to the output of the zero threshold switch.