Hilbert-Huang Transform Based Transient Analysis in VSC Interfaced DC System

Due to the rapid discharging of the dc-link capacitors, the short-circuit fault normally results in a fastgrowing transient current in the voltage source converter (VSC) based dc power system. Therefore, a fast and sensitive fault detection method is required. In this paper, the feasibility of Hilbert-Huang transform (HHT) for fault detection in VSC-HVDC systems is analyzed. The instantaneous energy density level is used as the fault detection criterion, which emphasizes the fault characteristics in a predefined frequency range and suppresses the effect of steady-state ripple components. The theory of the proposed HHT based fault detection method is presented in detail. Its effectiveness is tested on an OPAL-RT based multi-terminal dc system and a point-to-point experimental dc system. A response delay within 2 ms after the fault inception is achieved. The comparison with other popular frequency-domain based fault detection methods including the wavelet transform, the short time Fourier transform, the S transform and the existing HHT based analysis, using amplitude frequency coefficient as detection criterion underline the performance of the proposed method.