Distance protection scheme based on control characteristics of power electronic-based power sources for low-frequency transmission system of offshore wind farm

The performance of conventional distance protection is degraded by the source characteristics of power electronic-based power sources (PEPS) in the low-frequency transmission system (LFTS) of offshore wind farm. Furthermore, as a dual-terminal PEPS system, offshore LFTS facing the inadaptability of improved distance protection scheme originally proposed for general single-terminal PEPS system. To address this, a novel distance protection scheme based on control characteristics of PEPS is proposed for offshore LFTS. The source characteristics of both PEPSs in LFTS are derived from their control strategies and expressed as constraints between output voltages and currents. Building on this, a calculation method for fault electrical quantities is proposed to quantify the influence of PEPS on distance protection. Subsequently, the apparent impedances representing the source characteristics are precomputed and stored in a data matrix using the proposed calculation method. Finally, the proposed protection scheme estimates the fault distance and distinguishes between internal faults and external faults by searching for the best matching values in the data matrix against the actual measured values of apparent impedances. The performance of proposed protection scheme is tested via a simulation model in PSCAD/EMTDC. Simulation results demonstrate that the proposed protection scheme exhibits a high tolerance to fault resistance under different fault types, control strategies and operating states of wind farm.