Analysiss And Mitigation Of Sub-synchronous Interaction Of Large-scale Wind Farm Transmission System With HVDC

In recent years,the installed capacity of wind power in China has been increasing.Because of the long distance between our country’s wind power generation base and load center,the problem of long-distance transportation of large-capacity wind power resources should be considered.As a new technology,HVDC transmission can realize reasonable optimization of resources between remote areas,so it is widely used for long-distance delivery of large-capacity wind power resources.With the rapid development of HVDC transmission and the integration of renewable energy such as wind power to the power system,the problem of sub-synchronous interaction caused by this has become increasingly come out.Therefore,it is necessary to study the sub-synchronous interaction problem of large-scale wind farm transmission system with HVDC.In this dissertation,the characteristics of the sub-synchronous interaction problem of large-scale wind farm transmission system with HVDC are analyzed.And the mitigation strategies of the sub-synchronous interaction problem of large-scale wind farm transmission system with HVDC are proposed.The research is mainly carried out from the following aspects:1)The characteristics of the sub-synchronous interaction problem of large-scale wind farm transmission system with HVDC are analyzed.Firstly,the small signal model of largescale wind farm transmission system with HVDC for the analysis of SSI problem is built on MATLAB.Based on the small signal model,the eigenvalue analysis and correlation analysis of the studied system are carried out.Based on this,the influence of the control parameters of the wind farm converter and the HVDC transmission system converter on the SSI problem are studied.2)The local gain-varying control strategy is proposed to suppress the SSI problem of the studied system.Firstly,the principle of the local gain-varying controller is analyzed in detail.The parameters of the local gain-varying controller are designed.And the input and output characteristic of the local gain-varying controller is deduced.Through time domain simulation model of large-scale wind farm transmission system with HVDC built on PSCAD/EMTDC,it is verified that the local gain-varying control strategy can effectively suppress the SSI problem without negatively affecting other performance of the system.3)The parameter design method of SSDC is proposed.Firstly,based on the thought of root trajectory design and combined with the characteristics of SSI oscillating mode,the parameter design method of SSDC phase compensation link is provided.And based on the determination of SSDC compensation phase,the parameter design method of proportional link is provided.Secondly,the parameter design method of SSDC is applied to SVC-SSDC and HVDC-SSDC of large-scale wind farm transmission system with HVDC.Through simulation,the rationality of the parameter design method of SSDC is verified.4)The source-grid coordinated damping control strategy is proposed to suppress the SSI problem of the studied system.The principle of the source-grid coordinated damping control strategy is analyzed in detail.And the control strategy is applied to the mitigation of the SSI problem of the large-scale wind farm transmission system with HVDC.Through simulation,it is verified that the source-grid coordinated damping control strategy can better play the role of SVC-SSDC and HVDC-SSDC in suppressing the SSI problem.The rationality of the source-grid coordinated damping control strategy is verified.