Research On Analysis And Suppression Of Subsynchronous Oscillation In Wind Power System Based On Generalized Short Circuit Ratio Method

As the installed capacity of wind farms increases,the randomness and fluctuation of wind farms will affect the stability of the system.Large-scale wind power connected to weak AC systems through power electronic equipment may cause subsynchronous oscillation.Therefore,this thesis is devoted to studying the analysis and suppression methods of subsynchronous oscillation in wind power systems.Firstly,a wind farm dynamic model based on a permanent magnet direct drive wind turbine is established.The model mainly includes a wind farm model and a direct-drive wind turbine grid-connected model,which lays the foundation for subsequent analysis of subsynchronous oscillations in wind power systems.Secondly,based on the generalized short-circuit ratio index,an uncertainty evaluation model of wind power subsynchronous oscillation is proposed.The established multi-wind farm grid-connected model is decoupled into multiple single-wind farm grid-connected models.Based on the definition of single-wind farm short-circuit ratio,a generalized short-circuit ratio index that can reflect the stability of multi-wind farms’ grid connection is proposed.Aiming at the generalized short-circuit ratio index,an uncertainty evaluation model for sub-synchronous oscillation of wind power systems including stability index,risk evaluation index and probability index is proposed.On this basis,the wind speed correlation is modeled based on the Latin hypercube sampling method,and a wind farm output with correlation is generated according to the wake effect model.Combining Monte Carlo simulation and stability evaluation,a method for stability analysis of subsynchronous oscillation in wind power systems is proposed.Then an additional damping controller is designed based on the generalized short circuit ratio probability stability assessment.In order to improve the strength and dynamic performance of the AC grid,an additional damping controller is designed in the system phaselocked loop.Through analysis,it is found that under the same generalized short circuit ratio,as the coefficient of the additional damping controller changes,the weakest damping ratio of the system has an optimal value.Therefore,the quantum behavior particle swarm optimization algorithm is introduced in this thesis,and the optimal solution of the damping coefficient is solved by taking the minimum critical generalized short circuit ratio of system oscillation stability as the objective function.Finally,in this thesis,through MATLAB programming and time-domain simulation,the sub-synchronous oscillation characteristics of three wind farm grid-connected models are simulated and analyzed.The simulation results show that the proposed method based on the generalized short circuit ratio method for the subsynchronous oscillation probabilistic stability analysis and suppression method of wind power systems can effectively reflect and improve the system’s probabilistic stability.