Study On Subsyrichronous Oscillation Stability Criterion And Control Optimization For Grid-Connected Full-Converter Wind Turbines Based On Impedance Model

Recently,with the rapid development of China's economy,energy demand is increasing day by day.In order to adjust the energy structure and respond to environmental pollution and climate change problems,a large number of new energy generation,represented by wind power and photovoltaic power,are connected to the power grid,significant changes have taken place in the form and operation characteristics of power grids,Subsynchronous Oscillation(SSO)caused by the interaction between wind turbines and power grid has threatened the security of power grid operation.In this paper,the SSO problem were researched by impedance-based analysis for grid-connected full-converter wind farm.(1)Quantitative analysis of SSO for grid-connected wind farms was realized.The positive-sequence impedance and negative-sequence impedance model of wind farm were established in the phase domain by harmonic linearization technique,the shortcomings of impedance-based Nyquist stability criterion and aggregated RLC circuit model in quantitative SSO analysis of system were pointed out.A quantitative impedance-based stability criterion by means of fractional polynomial function fitting was proposed,and the equivalent impedance of grid-connected wind farm was fitted by fractional polynomial function,the oscillation frequency and damping of system were obtained and the stability characteristics of the system were analyzed quantitatively by the zeros of the fitting polynomial.The correctness of the proposed method was verified by simulation.(2)The SSO dominant influence factors of grid-connected wind farm were identified and the SSO suppression scheme based on optimization and adjustment of wind turbine control parameters were proposed.The concept of frequency-domain sensitivity was introduced based on impedance-based analysis method,the influence of parameter on system impedance curve is reflected directly by calculating the impedance sensitivity based on impedance model of wind farm and grid,and the leading factors affecting SSO characteristics were identified.The parameter adjustment scheme with SSO suppression were developed by combining with impedance-based stability criterion.The correctness of the proposed scheme was verified by simulation.(3)The positive-sequence impedance and negative-sequence impedance model of static var generator(SVG)were established and the SSO suppression scheme based on optimization and adjustment of SVG control method and control parameters were proposed.The influence of SVG on the SSO characteristics of grid-connected wind farm were researched based impedance models.And the dominant factors affecting SSO stability of grid-connected wind farm in SVG control parameters were identified by impedance sensitivity,and the control method and control parameters adjustment scheme with SSO suppression of SVG were developed by combining with impedance-based stability criterion.The correctness of the proposed scheme were verified by simulation.