Improved S Transform-Based Fault Detection Method in Voltage Source Converter Interfaced DC System

The short circuit fault in the voltage source converter-based dc power system typically generates rapidly rising transient current which may have serious repercussions on dc grid operation and health of the integrated power electronic devices. Thus, the dc grid requires a high speed and robust fault detection for reliable system operation. With this regard, this article proposes a fault detection method based on the S transform (ST) with adaptive adjustment. This improved ST is based on frequency-domain and is able to detect the fault condition within 0.3 ms. It consists of high-frequency detection, which is responsible for fast response due to high time resolution, and low-frequency screening which is used to differentiate faults from other transient conditions. Introducing a correction factor into a Gaussian function when computing ST could extract the high-frequency spectrum, while the low frequency spectrum information is still retained. The proposed method is validated with the multiterminal dc system developed in the OPAL-RT-based real-time simulator. Additionally, its performance is tested with the point-to-point experimental dc test bed. Comparative analysis with other popular frequency-domain fault detection methods, namely, wavelet transform and short-time Fourier transform substantiates the effectiveness of this method.