Analysis And Suppression Of Sub-synchronous Oscillation Of DFIG Wind Farm

In recent years,with the rapid development of my country’s economy,the scale of the power system has gradually expanded.In order to solve the problems of fossil energy depletion and environmental pollution,wind power generation has developed rapidly in my country.The regions with abundant wind energy are generally far away from the load center,which makes wind power face the problem of large-scale longdistance transmission.Series compensation technology can effectively improve the transmission capacity of the line,so it is widely used in wind power transmission lines.However,when the series compensation line is in operation,it sometimes causes sub-synchronous oscillation of the wind power generation system,which threatens the safe operation of the system.In order to solve this problem,a corresponding study has been carried out on the problem of sub-synchronous oscillation that occurs when large-scale wind farms are sent over long distances via series-compensated lines.Firstly,in order to analyze the cause of subsynchronous oscillation of wind power generation system,a grid-connected model of doubly-fed wind farm via seriescompensated lines was established.Combined with specific examples,the eigenvalue analysis of sub-synchronous oscillation of doubly-fed wind power generation system was carried out,and the oscillation was obtained.Modal and main influencing factors.The simulink simulation model was built to perform time-domain simulation on the system,and the results of eigenvalue analysis were verified.On this basis,the specific impact of system string compensation on subsynchronous oscillation is analyzed and discussed to provide support for subsequent design of suppression strategies.Secondly,in order to effectively suppress the sub-synchronous oscillation of the system,according to the analysis results of the eigenvalues,the oscillation suppressors on the rotor side and the stator side are designed according to the main factors affecting the oscillation.Due to the complex structure of the wind power generation system,it is impossible to establish an accurate mathematical model,so a fuzzy damping control strategy with self-adjusting factors is designed,which is applied to the rotor side and stator side of the fan respectively as an additional control in conjunction with the original controller of the fan Work and simulation analysis show that the designed controller effectively improves the system’s ability to suppress sub-synchronous oscillation,and can increase the series compensation degree to improve the system’s delivery capacity.Finally,in order to better suppress the sub-synchronous oscillation of the system,the internal fuzzy cooperative control strategy of the fan with the rotor side as the main and the grid side as the auxiliary is proposed,through the cooperation of the additional fuzzy damping controller on the rotor side of the fan and the grid side,Further improving the dynamic performance of the system.At the same time,the fuzzy damping control strategy is introduced into the control link of SVG,and on the basis of maintaining the system bus voltage,auxiliary synchronous oscillation suppression is carried out.The simulation results prove that the designed control strategy has good control performance,suppresses the sub-synchronous oscillation of the system more quickly,reduces process fluctuations,and is more stable after returning to a stable operating state.