| Under the background of “double carbon”,the exploitation and utilization of wind energy resources is one of the effective ways to solve the problems of energy shortage and environmental contamination.However,wind power is greatly influenced by natural factors,and the randomness and uncertainty of wind units output are intense.After extensive wind units are integrated into the power grid,the power quality problem has become increasingly prominent.With the continuous expansion of wind power grid-connected scale in China,it is imperative to deal with the voltage and reactive power problems prompted by wind power oscillation in the wind power grid-connection system.In order to resolve this problem validly,this paper has launched a series of research work firmly around the reactive voltage problem of the grid-connected system of doubly-fed wind turbines:Firstly,according to the working mechanism,mathematical model and control framework of the doubly-fed fan,the adjustment mechanism of reactive power output of the doubly-fed fan is broke down.In view of the theoretical calculation method of reactive power limit of doubly-fed fan,the reactive power limit output of the fan is deduced,and the simulation model of doubly-fed wind farm with 1.5*6MW capacity is built in the MATLAB/Simulink simulation environment,and the active and reactive power output graphs of doubly-fed fan under different wind velocities are drawn.Secondly,this paper recommends the commonly used reactive power compensation equipment and configuration criteria of wind power grid connection system,and the output characteristics of different compensation equipment are obtained through simulation analysis,which provides a basis for the formulation of voltage and reactive power regulation strategy of doubly-fed wind power grid connection system in the future.The static var generator(SVG)is studied,which is a general used reactive power compensation device in wind farms.Aiming at the problem that the static var generator based on PI control is greatly affected by disturbance and difficult to adjust parameters,based on the mathematical model of SVG and Euler-Lagrange model,a compound control strategy of static var generator combining sliding mode variable structure control and passive control is proposed in view of the passivity theory,which optimizes the energy function of traditional passive control and effectively reduces the control parameters.The simulation model is built in the MATLAB/Simulink simulation environment to verify its reactive power compensation and three-phase unbalance control ability.The simulation results indicate that the control strategy has favorable dynamic compensation properties.Finally,Aiming at the problem of voltage and reactive power control of wind power grid-connected system,considering the reactive power support ability of the wind units,a voltage and reactive power control method of the wind power grid-connection system with the cooperation of the doubly-fed wind turbine and SVG is proposed.This method can not only significantly improve the voltage quality of wind power grid-connected points,but also make full use of the reactive power output ability of doubly-fed wind turbines and reduce the investment cost of reactive power compensation equipment in wind farms.A reactive power optimization model of IEEE33-node system with wind turbines and SVG is established.The objective function is to minimize the network loss and voltage offset,and the reactive power output constraints of reactive power equipment and wind turbines are considered.The nonlinear time-varying factors,random learning strategy and Cauchy mutation strategy are used to improve the convergence performance of the Whale algorithm.Based on the improved Whale algorithm,various scenarios in which wind turbines are connected to different locations are optimized.The simulation results show that this method can effectively reduce the network loss,improve the node voltage and improve the economy of system operation. |
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