Fault location for collection lines in DC series-parallel offshore wind systems using multiscale Sobel gradient algorithm

DC series-parallel systems are a critical technology to the development of distant offshore wind power. Unlike in conventional DC networks, collection lines in DC series-parallel systems are short and have uneven segmented structures in which DC transformer (DCT) capacitors are connected in series with submarine cables, which exerts tough challenges to existing fault location methods. To overcome the limitations, this paper proposes a single-ended traveling wave fault location method using the multiscale Sobel gradient (MSG) algorithm. Firstly, this paper elaborates on the configuration of a DC series-parallel system and discusses the specificity issues. Then, the impact of series DCT capacitors on the boundary characteristics and the wave propagation paths in collection lines are analysed. On this basis, the MSG algorithm is utilised to identify the traveling wavefronts with distinct polarity and the fault location is determined accordingly. Finally, the proposed location method is evaluated on the MATLAB/Simulink platform. The results verify that the method can acquire accurate fault distance regardless of fault type and fault resistance, and is robust against noise interference.