Study on AC Harmonic Characteristics of Netherland ±525kV/2GW MMC-HVDC System for Offshore Wind Farms Integration

Abstract

At present, Modular Multilevel Converter based High Voltage Direct Current (MMC-HVDC) is the typical solution for large-scale and long-distance offshore wind farms integration. And study on AC harmonic characteristics of MMC-HVDC is one of the important contents to ensure that the system can meet the electric power quality requirement and avoid resonance in power system. In this paper, the method of harmonic amplification factors calculation and resonance analysis on basis of harmonic impedance region is used. The topology of Netherland ±525kV/2GW MMC-HVDC system for offshore wind farms integration is shown. The requirements for evaluation and the detailed research method of AC harmonics including subharmonics, inter-harmonics and integer harmonics are introduced, and the equivalent AC harmonic impedance-frequency characteristics are studied using harmonic linearization method based on PSCAD/EMTDC model. The harmonic amplification factors at Point of Common Coupling (PCC) of AC side are calculated on basis of equivalent AC harmonic impedance of MMC-HVDC and AC system harmonic impedance. At last, adopting the Fast Fourier Transform (FFT) module and writing programs and scripts in MATLAB/SIMULINK, the AC harmonic performances including subharmonics and inter-harmonics at AC side of offshore convertor station when MMC-HVDC system is in different typical operation modes are calculated, and the resonance is analyzed.