Control Strategy Of Grid-connected Converters Of Wind Power System Based On Improved Active Disturbance Rejection Control

In recent years,with the growth of global energy demand and the promulgation of relevant regulations on climate and environmental protection,the renewable energy,especially the wind power industry,has developed rapidly.Permanent magnet direct drive wind turbines are widely used because they do not have a variable-speed gearbox and adopt a full-power converter structure,which has the characteristics of higher power generation efficiency,safety and reliability,and higher grid adaptability.Therefore,in order to improve the fault ride-through capability of permanent magnet direct-drive wind power system,it is of great significance to further study its control strategy.In this thesis,the principle of wind power generation is introduced,and the mathematical models of wind generator,machine side rectifier and grid-side inverter in direct-drive permanent magnet wind power system are established and coordinate transformation is carried out.This thesis analyzes the voltage variation process of the DC bus when the power of the grid-connected converter is unbalanced when the wind power system fails,and explains the necessity of maintaining its stability.The different control strategies of the grid-side inverter are briefly described.Aiming at the problem that the traditional PI control technology has weak real-time estimation and compensation capabilities for system disturbances.An improved linear second-order active disturbance rejection control(ADRC)technology based on the lumped disturbance observation error is proposed,and then conducts stability verification and anti-disturbance analysis of the improved control technology in the frequency domain.Aiming at the problem of linear expansion state observer(LESO)in the initial stage of operation control,the output signal is different from the initial value of the system,resulting in a peak phenomenon,which results in poor convergence of the observer.A nonlinear ESO with variable error gain coefficient to weaken the peak phenomenon is proposed in this thesis.Then the sliding mode control is combined with the active disturbance rejection control technology,and the sliding mode control rate is used to replace the linear feedback control rate and the disturbance compensation link to further improve the control accuracy of the system.Finally,use MATLAB & Simulink to build a digital simulation platform for permanent magnet direct drive wind power grid-connected system for verification.The wind power control system adopts a variety of control methods to carry out simulation and comparison analysis,and simulate and verify the fault ride-through capability of the system when the machine side load and reduce and high and low voltage ride-through conditions occur.The results show that the correctness of the two improved control methods proposed in this thesis can better reduce the adverse effects of various disturbances on the DC bus voltage,and effectively strengthen the system’s anti-disturbance ability.