Pilot protection based on voltage and current correlation for DC lines in mesh DC grid without boundary

Abstract

As the scale of DC grids expands, the converter will be connected with multiple outgoing lines. In this context, locating current-limiting reactors at the outlet of the converter can effectively balance the contradiction between current-limiting requirements and construction costs. However, the absence of a clear line boundary poses challenges for DC line protection. In response, a setting-less line pilot protection is proposed for the mesh DC grid without boundary. First, through the analysis of measured impedance characteristics, it is found that for internal faults, the high-frequency voltage and high-frequency current on both ends of the line are negatively correlated. Whereas for external faults, there is at least one end of the line where the high-frequency voltage and high-frequency current are positively correlated. Then, a suitable high-pass filter is designed, and the cosine similarity is utilized to evaluate whether the filtered voltage and current waveforms display a similar trend of change, further providing a comprehensive protection scheme. Finally, numerous simulation results demonstrate that the proposed method exhibits strong endurance to fault resistance and noise environment. The proposed method remains applicable even when system parameters change and does not require complex setting.