JPH0118385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring AC active current and reactive current.

It is well known that in order to rationally control or manage an AC power supply and demand system, it is necessary to measure active and reactive power, and for this purpose, measurement of active and reactive current is a prerequisite.

Figure 1 is a block diagram showing an example of a conventional AC current measuring device for effective and reactive components, where TV is an AC voltage input terminal, SW1 is a changeover switch, and PS is an input terminal for AC voltage.
is a π/2 phase shift circuit, and COM is a comparator, which outputs an output voltage only during the positive or negative half cycle of its AC input voltage, for example, during the positive half cycle. TI is an input terminal for alternating current, R1 is a voltage extraction resistor, and SW2 is, for example, an electronic switch whose opening/closing is controlled by the output voltage of the comparator COM. A1 is an amplifier (gain K1), F1 is a filter, and TO is an output terminal.

Switch SW1 to contact B side, apply AC circuit voltage to input terminal TV, and apply current corresponding to the current of the AC circuit to resistor R1 via a current transformer (not shown) and input terminal TI. When the current is applied, the AC voltage V1 applied to the input terminal TV is passed through the contact B of the changeover switch SW1 to the comparator.
The comparator COM outputs an output voltage V2 every positive half period of the AC input voltage V1 as shown in FIG. 2, thereby closing the electronic switch SW2. Further, as shown in FIG. 2 V3, a voltage V3 in phase with the input AC current is generated across the resistor R1, and is introduced into the amplifier A1 via the electronic switch SW2.
Since it closes every positive cycle of the input AC voltage of COM, that is, the AC voltage applied to the input terminal TV,
The output voltage V4 of the amplifier A1 has a waveform shown in FIG. 2 V4. Therefore, when this output voltage V4 is applied to the filter F1, the voltage V appearing at the terminal TO
5 corresponds to the average value of the voltage V4, that is, the effective portion of the AC circuit current.

If the instantaneous value of the AC circuit current introduced into the input terminal TI is i, the effective value is I, the phase angle of the input current with respect to the input voltage is φ, and the effective component of the input current is Ia, then i=√2Isin(ωt+φ)dt …(1) So, when electronic switch SW2 is closed every negative half cycle of AC circuit voltage, Therefore, the output voltage V5 of terminal TO is becomes.

Next, when the changeover switch SW1 is switched to the contact A side, the AC circuit voltage V applied to the input terminal TV
1 is introduced into the phase shift circuit PS through the contact A of the changeover switch SW1, and the phase is shifted by π/2, so that the input voltage V1' and the output voltage V2' of the comparator COM are equal to V1' and V2 in FIG. ' However, since the phase of the voltage V3 across the resistor R1 is the same as the previous time, the output voltage V4' of the amplifier A1 is the second
The waveform V4 shown in the figure is obtained, and the output voltage V5' at the terminal TO corresponds to the reactive component Ir of the AC circuit current.

That is, Or Therefore, the output voltage V5', becomes.

The magnitude of the output voltage in this conventional device is (2)
Equation (3), Equation (5), or Equation (6) corresponds to the magnitude of the integral of only half the period of the AC waveform, and the measurement accuracy of effective and reactive currents is compared. It is inevitable that you will be short-sighted.

An object of the present invention is to realize a device that can measure AC active current and reactive current with high accuracy using a simple circuit configuration.

FIG. 3 is a block diagram showing an embodiment of the present invention, in which A2 is an inverting amplifier, for example, an operational amplifier. A3 is a summing amplifier, for example, an operational amplifier, with input resistors R2 and R3, and a feedback resistor R4.
The following relationships are established between them: 2・R2=R3 and K2・R2=R4. Other symbols are the same as in FIG.

When the changeover switch SW1 is switched to the contact B side and the AC circuit voltage is applied to the input terminal TV, and a current corresponding to the AC circuit current is passed through the resistor R1 via the input terminal TI, the input voltage V1 and the output voltage of the comparator COM are V2 and the voltage V across resistor R1
3 is as shown in the fourth diagram.

In this embodiment, the voltage V3 across the resistor R1 is switched on and off by the electronic switch SW2 and applied to the inverting amplifier A2. If the gain of the inverting amplifier A2 is selected to be 1, the output voltage V4'' of A2 is 4, the voltage has the same amplitude and inverted polarity as the voltage V3, and is applied to the summing amplifier A3 via the input resistor R2.

Also, the voltage V3 across the resistor R1 is directly applied to the summing amplifier A3 via the input resistor R3, but since the resistance value of the input resistor R3 is selected to be twice that of the input resistor R2, the input voltage V3 of the summing amplifier A3 is
The output voltage corresponding to V3' is V3' in Figure 4, and the output corresponding to the input voltage V4'' is V4 in Figure 4, and its amplitude is twice V3', so
The combined output V4''''' of the circuit shown in FIG. 3 has twice the frequency of the circuit shown in FIG.
The same applies when switching the changeover switch SW1 to the contact A side and measuring the reactive current.

The above description is based on a case in which the active and reactive components of the alternating current can be measured by inserting and removing the π/2 phase shift circuit PS at the front stage of the comparator COM by switching the changeover switch SW1. The configuration may be such that SW1 and the π/2 phase shift circuit PS are omitted and the AC circuit voltage is directly introduced into the comparator COM, and only the effective component of the AC current is measured. It may be configured such that only the reactive current is measured by directly introducing the voltage into the π/2 phase shift circuit PS, shifting the phase by π/2, and then applying it to the comparator COM.

As is clear from the above description, the device of the present invention has a simple circuit configuration and can be configured mainly using semiconductor elements, so it can be easily modularized or integrated into an IC, and the output is an electrical signal, making remote measurement possible. ,
It has features such as being able to be used as a control signal as is and improving measurement accuracy, and has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a conventional device, FIG. 3 is a diagram showing an embodiment of the present invention, and FIGS.
The figure is a waveform diagram to explain the operation. TV: AC voltage input terminal, SW1: changeover switch, PS: π/2
Phase shift circuit, COM: Comparator, TI: AC current input terminal, R1: Voltage extraction resistor, SW2: Open/close switch, A1: Amplifier, F1: Filter,
TO: output terminal, A2: inverting amplifier, A3: summing amplifier, R2 and R3: input resistance, R4: feedback resistance.

Claims (1)

[Claims] 1. A comparator that sends out an output only during the positive or negative half period of the input AC voltage, and a circuit that introduces the voltage of the AC circuit into the comparator with a phase shift of π/2, or a circuit that introduces the voltage of the AC circuit into the comparator without phase shifting the voltage of the AC circuit. a changeover switch that selects a circuit to be introduced into the comparator; an open/close switch whose opening/closing is controlled by the output of the comparator; and a circuit that generates a voltage corresponding to the magnitude of the current of the AC circuit;
A summing amplifier to which the voltage generated in this circuit is applied via the on-off switch, an inverting amplifier connected in cascade to the on-off switch, and a first input resistor connected in series to the inverting amplifier; a circuit that applies a voltage generated by a circuit that generates a voltage corresponding to the magnitude to the summing amplifier via a second input resistor having a resistance value twice that of the first input resistor, and an output of the summing amplifier; A device for measuring the effective and reactive components of an alternating current, characterized by comprising a circuit for taking out the active component and a reactive component.