Wideband Current Transducer for Measuring AC Signals With Limited DC Offset

Abstract

In many applications, a current measurement that can measure ac currents with dc offset is required. This is not possible using conventional current transformers (CTs) due to the core saturation because of the dc offset. In this paper, a new sensor concept is presented, which consists of a wideband CT and a demagnetizing circuit. The sensor concept is capable of measuring ac currents with dc offset, which have periodic zero crossings, as given in power-factor-corrected (PFC) circuits. Using the demagnetization circuit, the core is actively reset during the zero crossing intervals. The operation principle and design equations are discussed in detail in this paper. For validating the presented concept, three sensors have been built using different core materials, and measurements of the transfer functions as well as operation in a PFC system are presented. A bandwidth from dc up to 20 MHz has been achieved.

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