Frequency-coupled impedance modelling and resonance analysis of DFIG-based offshore wind farm with HVDC connection

Abstract

Motivated by recent years’ resonance incidents in wind-integrated power systems, this paperinvestigates the resonance-induced harmonic distortion and stability issues in doubly fed induction gener-ator (DFIG)-based offshore wind farm (OWF) with high-voltage direct current (HVDC) grid connection.To accurately capture the dynamic characteristics of DFIG-based wind farm, a comprehensive impedancemodelling considering the detailed PI control loop and DC dynamics of wind turbine as well as the cableconnections of the medium-voltage (MV) collector system is conducted. Through stepwise simulationverifications, aggregated modelling of MV collector system is proved to be suitable for wideband resonanceanalysis. On this basis, the resonance analysis regarding grid topology change and controller parametervariation is conducted and the impact of frequency coupling on subsynchronous resonance (SSR), middle-and high-frequency resonances is analyzed using the aggregated models derived from a practical HVDCconnected DFIG-based OWF. The strength or degree of the frequency coupling between the sequenceimpedances of wind farm, which is induced by the asymmetrical converter control of wind turbines, is foundto be dependent on the impedances of all the components of the system. Moreover, case studies are conductedto demonstrate the importance of including the frequency coupling in SSR stability assessment. Simulationsin MATLAB / Simulink validate the modelling and resonance analysis.