Anlysis Of Ssr In Wind-thermal-bundled Transmission System Via Series-Compensated Lines

In recent years,China has vigorously developed renewable energy and promoted low-carbon energy transformation.The north of China is rich in wind resources,but most of them are far away from the load center of the grid.The wind-thermal-bundled transmission via series-compensated lines is used for long-distance system.However,the series-compensated capacitor will cause potential sub-synchronous resonance(SSR),which seriously affects the stability and safety of the grid.According to the SSR of the large-scale wind-thermal-bundled transmission system via series-compensated lines in the Xilin Gol League area,Inner Mongolia,this paper works on system modeling,mechanism analysis and simulation verification.It provides the basis for SSR prevention and control of the actual engineering project.The basic concepts of SSR are introduced,then it derives the conditions of different types of the SSR frequency.According to the characteristics of time/frequency domain,it classifies the analysis methods of SSR,and compares their application.According to conditions of the project,the equivalent model of the system is established.Then the simulation model is built in PSCAD/EMTDC.The risk of SSR of turbo-generators are analyzed.The frequency scanning method is used to preliminarily screen the mode of the system with SSR.And the time-domain simulation method is used to observe the modal speed and transient torque to verify the scanning result.Then the effect of wind turbines connected to turbo-generators is analyzed through the simulation.Furthermore,the impact on SSR characteristics from many factors was investigated,including the fault type and position,the unit combination,the equivalent impedance,the fault starting/clearing time and the mechanical mutual damping coefficient.The model and influencing factors of SSR of wind turbines are studied.The model of wind turbines is established so that the mechanism and oscillation characteristics of SSR can be analyzed with a standard model.Then the validity of the proposed model is verified.Furthermore,the time-domain simulation method is used to analyze this model,so as to obtain the influence of the change of various factors on the stability of wind turbines,including the wind speed,the number of grid-connected turbines,the DFIG control parameters and the series-compensated degree.