Mitigation of background harmonic amplification caused by offshore wind farm long AC cable integration

Abstract

The high voltage alternating current transmission with submarine cables is the common scheme to integrate offshore wind farms close to the land. Due to the capacitive effect of AC cables, the association of the long AC cables and the onshore grid can cause resonances, which may amplify grid background harmonics. This paper focuses on the mitigation of background harmonic amplification caused by offshore wind farm integration. First, the background harmonic amplification mechanism in the offshore wind farm integration system is analysed qualitatively, and the mitigation approaches are given in principle. Then, taking a practical project as a study case, the harmonic modelling methods of the offshore grid and the onshore grid are elaborated, including the harmonic models of wind turbines, transformers, cables, the high voltage and the extra-high voltage transmission grid, and the low voltage distribution network. According to the established harmonic models, the cause of background harmonic amplification is analysed. On this basis, two mitigation methods of installing the series blocking filter and the shunt filter are compared and the recommended mitigation scheme is proposed. Finally, the feasibility of the proposed scheme is verified by calculation results under different grid operating conditions.