Study On The Mechanism Of Sub-synchronous Oscillation Caused By Wind Power

The renewable energy power generation technology represented by wind power has developed rapidly in recent years.After the access of a large number of new energy units in the source area,the power electronic trend of the system dynamic characteristics is obvious,and a series of system stability problems have arisen.Among them,sub-synchronous oscillation(SSO)of wind power is a hot issue that needs to be solved urgently.This paper describes the structure of the wind power grid-connected system.Including wind turbines,network structures and commonly used dynamic reactive power compensation devices.The structure of different types of wind turbines,the control measures of the converter and the function of the dynamic reactive power compensation device are analyzed and compared,and the target model studied in this paper is clarified.Firstly,by analyzing the response process of the wind turbine side converter to the sub-synchronous frequency harmonics,the analytical expression of the output voltage command value at the port of the wind turbine is obtained.The output component and the original harmonic component are superimposed at the outlet of wind field.When the two parts satisfy a certain phase relationship,the harmonics will exist for a long time and be amplified due to the formation of positive feedback,make the system under the risk of SSO.Secondly,by using the response process of wind turbines to harmonics,this paper deduces the analytical expression of output harmonics.And use the phase relationship to calculate the conditions for the formation of SSO,and forms the criterion for judging the stability of the system.This criterion was compared with the actual data.The influence of converter controller,phase-locked loop and grid strength impact on the sub-synchronous oscillation characteristics of the system is analyzed by using the criterion and simulation results.Finally,the static var generator(SVG)is taken as an example to analyze the influence of dynamic reactive power compensation device on wind-based SSO.The influence of SVG on system stability was analyzed by numerical analysis.The influence of SVG output reactive power and control system parameters on system stability was further analyzed.Voltage-sensitivity is used to explain the rise bus voltage caused by SVG during the off-grid process of the wind units.The theoretical analysis was verified by simulation and measured data.