Application of Short-Time Fourier Transform for Harmonic-Based protection of Meshed VSC-MTDC Grids

TLDR: This work studies the application of short-time Fourier transform to extract current harmonics of various fault types to design a protection method for meshed multi-terminal voltage source converter-high-voltage direct current grids and shows the accurate detection and discrimination between faulty sections using the proposed harmonic-based method.

Abstract: This work studies the application of short-time Fourier transform (STFT) to extract current harmonics of various fault types to design a protection method for meshed multi-terminal voltage source converter-high-voltage direct current (VSC-HVDC-MTDC) grids. The frequency spectrum of fault current harmonics is used to detect internal and external faults, the faulty pole and fault type. The method does not need the implementation of series inductance on the sides of the DC lines and it is also effective for lines combining overhead lines and cables. The window function and hop size play the primary role in STFT, which are investigated in a sensitivity analysis. A modified version of CIGRE meshed DC grid system is simulated in PSCAD in order to show the robustness of the method, and further signal processing analysis is done in MATLAB. The results show the accurate detection and discrimination between faulty sections using the proposed harmonic-based method and how important the STFT parameters are in order to have a robust protection algorithm.