Research On Mitigation Of Sub-synchronous Oscillation In Wind Power System By Static Synchronous Series Compensator

With the large-scale grid connection of new energy,the problem of sub-synchronous oscillation(SSO)is becoming a huge potential risk and a prominent problem restricting the development and utilization of new energy.At present,the main suppression devices for sub-synchronous oscillation are parallel type,while the research on series type sub-synchronous oscillation suppression devices is less.Compared with the parallel device,the series device avoids the dilution effect of injected energy,and the suppression effect is less affected by the operation mode,and has better flexibility.In this paper,the mitigation of sub-synchronous oscillation in wind power system by static synchronous series compensator(SSSC)is studied as follows:The mathematical model of SSSC is established,and the correlation formula between output characteristics and device characteristics of SSSC is deduced.Based on the H-bridge cascaded SSSC main circuit topology,the influence of SSSC sub-synchronous oscillation and SSSC input sub-synchronous suppression function time-synchronous signal on the DC capacitor voltage of SSSC is investigated,which provides a basis for the parameter design of SSSC.The control strategies of SSSC at system level,device level and device level are analyzed.According to the topology of H-bridge cascade SSSC,two-stage DC voltage sharing strategy and capacitor charging strategy for SSSC are designed.Based on PSCAD/EMTDC simulation platform,the SSSC simulation model is built and verified by steady-state and transient step simulation.Aiming at the sub-synchronous oscillation caused by doubly fed wind farm sending out through series compensation system,a strategy of using Supplementary Active Resistance Control(SARC)to suppress the sub-synchronous oscillation of wind power is proposed.In this paper,the broadband and time-varying characteristics of oscillation frequency in wind power Grid-connected sub-synchronous oscillation are analyzed,and a method of extracting sub-synchronous signal based on grid-side electrical quantity is proposed,and the corresponding broadband filter is designed.Combining with practical engineering model,the effectiveness of SSSC-SARC in suppressing sub-synchronous oscillation is verified under different working conditions.Based on SSSC-SARC strategy to suppress sub-synchronous oscillation,combined with the actual multi-wind power transmission system,the effects of SSSC centralized and distributed access modes on the suppression of sub-synchronous oscillation are analyzed by time domain simulation.The capacity of SSSC devices with two different access modes under the same suppression effect is explored,and the selection suggestions of SSSC access modes in practical engineering application are given.