Testing Method for Wideband Oscillation Transmission Accuracy of Flexible DC Current Transformer Based on AC/DC Multispectral Separation

ABSTRACT

Aiming at the problem of difficulty in effectively evaluating the transmission accuracy of wideband composite signals, including DC, power frequency, and their superimposed high‐frequency oscillation characteristics in the current flexible DC current transformer (FDCCT) transmission accuracy testing methods, a new method for wideband oscillation transmission accuracy testing based on AC/DC multispectral separation is proposed. First, the sensing principle and steady‐state/transient transmission characteristics of FDCCT were analysed in detail, and its wideband equivalent model was established. Second, a ‘wideband oscillation formula’ containing adjustable DC bias, fundamental component, and wideband oscillation component was designed, and a wideband oscillation current excitation system based on a high‐precision linear step current source was developed, achieving millisecond‐level, wideband, and high‐fidelity current waveform generation and amplification. Apply the excitation current to the FDCCT under test, obtain its output signal through a high‐performance digital sampling system, and innovatively apply spectrum separation technology to decouple the composite output signal into DC component, AC component, and oscillation component for independent analysis. Based on this, a multidimensional transmission accuracy evaluation index based on component amplitude, phase, and frequency response characteristics is proposed. Simulation and experimental results show that this method can accurately quantify the wideband oscillation transmission performance of FDCCT under different operating conditions. The DC offset error (± 0.023%), Fundamental ratio error (± 0.121%), Fundamental phase displacement (± 0.071°), fundamental harmonic distortion (± 0.322%), oscillation amplitude error (low frequency ± 0.771%, high frequency ± 2.533%), oscillation gain fluctuation (± 0.832 dB), oscillation phase delay (± 35 µs), oscillation attenuation time constant error (± 3.722%), and wideband composite error (± 0.732%) are all superior to other comparative methods, providing important technical support for equipment selection, quality inspection, and system safety and stable operation.