Frequency-coupled impedance model based subsynchronous oscillation analysis for direct-drive wind turbines connected to a weak AC power system

Abstract

Recently, the emerging subsynchronous oscillation (SSO) issue caused by interactions between power electronic converters and weak grids has provoked serious stability concerns. Impedance modelling based method has been widely used to analyse the emerging SSO phenomenon. In this paper, a frequency coupled impedance model (FCIM) is proposed to analyse this interaction. The FCIMs at multiple frequencies are measured and then the transfer function model is identified. The modelling method is then applied to type-4 wind turbine based farms connected to a weak AC grid. The aggregated impedance of the whole system is obtained by combining the FCIMs of all components in the power system. The system stability is then investigated by varying the online number of wind turbines. Time-domain simulations using PSCAD/EMTDC are carried out to verify the proposed methods of impedance modelling and stability analysis.

Keywords

• wind power plants
• transfer functions
• oscillations
• power grids
• power generation faults
• time-domain analysis
• power electronics
• wind turbines
• aggregated impedance
• system stability
• stability analysis
• frequency-coupled impedance model
• subsynchronous oscillation analysis
• direct-drive wind turbines
• weak ac power system
• emerging subsynchronous oscillation issue
• power electronic converters
• weak grids
• serious stability concerns
• impedance modelling based method
• emerging sso phenomenon
• frequency coupled impedance model
• fcim
• multiple frequencies
• transfer function model
• modelling method
• type-4 wind turbine
• weak ac grid