JPH1194881A - Ac current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost current detector with low responsiveness and high reliability. SOLUTION: Relating to the AC current detector wherein AC current is detected with a current transformer(CT) or a zero-phase current transformer(ZCT) 1 and an effective value (Io) of the AC current is converted into DC voltage or DC current using the output from the CT or the ZCT 1 for detection, a maximum value (VMZX or IMAX) and a minimum value (VMIN or IMIN) are detected by a maximum value detecting part 5 and a minimum value detecting part 6 at one cycle of AC signal from the CT or the ZCT 1, and a calculation part 7 converts a difference between the maximum and minimum values into DC voltage or DC current, which is an output signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an AC current detecting device for obtaining an effective value of an AC current using a current transformer (CT) and a zero-phase current transformer (ZCT).

[0002]

2. Description of the Related Art An example of a functional block diagram of a conventional AC current detecting apparatus is shown in FIG.

[0003] CT or ZCT1 is a type of transformer.
By connecting a load resistor 9 to the secondary side (primary and secondary are electrically insulated), the alternating current flowing to the primary side is converted into the primary side current and detected. Product.

The voltage at both ends of the load resistor 9 is amplified by the amplifying unit 2, the DC component is removed by the high-pass filter 10, full rectification is performed by the full-wave rectifier 11, and smoothing (DC conversion) is performed by the low-pass filter 12. ).

[0005] The smoothed output (VOUT1) is represented by the following general formula.

VOUT1 = K1 × I + α1 where K1: conversion constant, α1: offset component, I: primary current.

Since the value of K1 is different due to the variation in sensitivity of CT or ZCT1 and the variation in the amplification unit 2, the amplification unit 13 for amplifying the amplification degree is used to absorb the variation.
Needs the function of. Also, the offset component α1 has all the errors of the function blocks so far added, and requires the function of the offset voltage adjustment 14 to make it a certain value.

In the case of voltage output, the function blocks described so far are sufficient, but in the case of current output, a voltage-current conversion circuit 15 is further required.

[0009]

In the AC current detecting device, the AC voltage is converted to a DC voltage (or a DC current).
Although a low-pass filter 12 is used after the full-wave rectification 11 to convert (smooth) the signal into a signal, there is a considerable response delay.

In particular, at low frequencies such as a commercial power supply (50 or 60 Hz), the response delay is several hundred ms to several seconds, which is a considerable problem in practical use.

An object of the present invention is to provide a highly reliable and inexpensive AC current detecting device with little response delay.

[0012]

Means for solving the problems of the present invention are as follows.

According to the present invention, an AC current is detected by CT or ZCT, and an effective value (Io) of the AC current is converted into a DC voltage or DC current based on an output from the CT or ZCT to detect the AC current. In the detection device, CT or ZC
The maximum value in one cycle of the AC signal from T (VMAX or I
MAX) and a minimum value (VMIN or IMIN), and converts the difference between the maximum value and the minimum value into a DC voltage or a DC current to output an output signal.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An alternating current detecting device according to the present invention will be described.

A load resistor is connected to both ends of the output of the CT or ZCT, and after amplifying the output (AC signal) at both ends of the load resistor, the amplified signal is divided for each period of the AC signal.
The maximum value (VMAX or IMAX) and the minimum value (VMIN or IMIN) in the one cycle are detected, and the difference between the maximum value and the minimum value is converted into a DC voltage or a DC current as an output signal, thereby providing a high-speed response. It is possible to provide a certain alternating current detection device.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram of an AC current detecting device according to the present invention. A load resistor 9 is connected to both ends of the output of the CT or ZCT 1 to amplify the output of both ends of the load resistor 9 (however, due to variations in the sensitivity of the CT or ZCT 1 and variations in the amplifying unit 2, the amplification degree is adjusted to absorb the variation). Function).

In addition to this amplification function, there is a clock oscillator 3 which repeats a certain oscillation, and multiplies the clock frequency by N times so that it becomes one cycle of the AC component of the amplified signal. Clock 4 is set.

At one period interval of the AC component of the amplified signal,
Maximum value (VMAX) and minimum value (VMIN) of the output of the amplifying section
Are detected by the maximum value detection unit 5 and the minimum value detection unit 6, respectively, and the calculation unit 7 calculates (maximum value−minimum value).
The output 8 is a DC voltage or DC current.

The low-pass filter existing in the conventional block is also eliminated, and the large-capacity capacitor and the high resistance required for the low-frequency filter are not required (50 or 60).
In the case of a power line such as a Hz, a filter having a particularly low cut-off frequency is required), and noise resistance and reliability can be improved.

[0021]

As described above, as described above, the alternating current is applied to the CT.
Or an AC current detection device that detects by ZCT and converts the effective value (I0) of the AC current into a DC voltage or a DC current based on the output from the CT or the ZCT,
The maximum value (VMAX or IMAX) and the minimum value (VMIN or IMIN) in one cycle of the AC signal from the CT or ZCT are detected, and the difference between the maximum value and the minimum value is converted into a DC voltage or DC current, and the output signal and By doing so, it is possible to provide an AC current detection device that has a high-speed response.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of an AC current detection device according to the present invention.

FIG. 2 is a functional block diagram of a conventional alternating current detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CT or ZCT 2 Amplification part 3 Clock oscillator 4 N times clock 5 Maximum value detection part 6 Minimum value detection part 7 Operation part 8 Output 8a Constant current output 8b Constant voltage output 9 Load resistance 10 High-pass filter 11 Full-wave rectification 12 Low-pass filter 13 Amplification part for amplification degree adjustment 14 Offset voltage adjustment 15 Voltage-current conversion circuit

Claims (1)

[Claims] An AC current is detected by a current transformer or a zero-phase current transformer, and an effective value of the AC current is converted into a DC voltage or a DC current by an output from the current transformer and a zero-phase current transformer. In the AC current detection device, the maximum value and the minimum value in one cycle of the AC signal from the current transformer and the zero-phase current transformer are detected, and the difference between the maximum value and the minimum value is detected as a DC voltage or a DC current. An alternating current detection device characterized by converting the signal into an output signal.