Superimposed large-current bias alternative-current (AC) current measuring device

Abstract

The invention provides a superimposed large-current bias alternative-current (AC) current measuring device, which aims at measuring small AC current which is superimposed on large-current bias, is wide in measurement frequency range and capable of accurately measuring a small AC signal under the situation of the large-current bias. The measuring device comprises a current transformer and a direct-current (DC) current measuring device, wherein a closed magnetic core of the current transformer is respectively wound with secondary sensing windings with turns of N2 and DC compensation windings with turns of N1, and the measured current is used as primary current of the transformer to run through the center of the magnetic core; and the DC compensation windings are connected with a DC current measuring device through a DC current drive circuit and a low-pass filter circuit, which are sequentially connected with each other, the DC current measuring device converts the measured current signal to an electric signal, after the AC component is filtered by the low-pass filter circuit, one DC current which can counteract the magnetic sensing strength produced by the DC bias current in the current transformer is outputted through the DC current drive circuit.

Description

technical field [0001] The invention relates to the technical field of current measurement, in particular to a measuring device for superimposing an alternating current with a large direct current bias. Background technique [0002] How to measure current accurately and conveniently has always been a subject of continuous exploration in the field of current measurement. Connect a small resistor (shunt) in series in the measurement circuit, measure the voltage across the shunt, and use Ohm’s law I=U / R to divide the measured voltage by the resistance of the shunt to calculate the required current. value. This measurement method uses less equipment, is convenient and quick, and has been generally welcomed. However, when this method needs to measure the AC current superimposed with a large DC bias, it will have the following disadvantages. First, it is not isolated from the measurement circuit, and there are certain safety hazards. If additional isolation measures are added, t...

AI Technical Summary

Problems solved by technology

The structure of the Hall sensor is simple, the accuracy and linearity of the measurement results are high, and it can measure the current of DC, AC and various waveforms. It seems to meet the needs of measuring small AC signals with large DC bias superimposed, but the analysis It has the following disadvantages: ①Its frequency band is not wide enough, and the Hall devices with relatively wide bandwidths available on the market are about 0 to 200kHz; ②The full range of Hall sensors is generally relatively large (such as tens of Amperes), the resolution of small-amplitude currents (such as a few milliamps) is not enough. Compared with large DC, small AC signals are much smaller, so the measured AC part is very inaccurate and has a large error

Because magnetic materials can only transmit coupled AC signals and cannot transmit DC signals, only AC currents can be measured

If a traditional current transformer directly measures a small AC signal superimposed with a large DC bias, the large DC will saturate the magnetic core and lose the effect of coupling the AC signal, so it is impossible to measure a small AC signal superimposed with a large DC bias. Purpose

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