A Fault Detection Method for Multiterminal Flexible DC Grids Based on Current Transient Energy Rate Ratio

Abstract

To address the challenge of weak fault transient characteristics in multiterminal flexible DC grids caused by transition resistance, DC reactors, and noise interference, which render traditional single-electrical-quantity detection methods ineffective, this paper proposes a fault identification scheme for flexible DC transmission systems based on the current transient energy rate ratio. Initially, it examines the distribution of energy release sources from a transient energy perspective, compares transient energy traits across different fault types, and derives fault current expressions. Subsequently, a virtual grounding point is used to simplify the postfault equivalent circuit, analyzing fault characteristics and distinguishing between internal and external faults. Based on these analyses, the concept of the current transient energy rate ratio is introduced, and a dual-terminal nonsynchronous protection strategy is developed. Additionally, Savitzky–Golay filtering is applied to denoise voltage and current signals from CTs and PTs at converter exits, effectively suppressing white noise interference and preventing false fault detection. Simulations in PSCAD/EMTDC validate its effectiveness in a four-terminal system, achieving rapid and accurate fault identification within 1 ms at a 10-kHz sampling frequency, with protection performance analyzed from multiple aspects.