Improved Linear Active Disturbance Rejection Control Of Wind Power Grid Connected Inverter Under Low Voltage Ride Through Condition

With the increasing installed capacity of wind power system,wind turbine operating off the grid under low voltage traverses will have a serious impact on the stability of power system.As the interface between wind turbine and grid,wind power grid-connected inverter ensures its control performance under low voltage crossing condition,which is the key to the wind power system not to be off grid.The main work of this thesis is as follows:Firstly,the basic theory of doubly fed wind power generation system is analyzed,and the mathematical model,control strategy of grid-connected inverter and the operation characteristics of DC bus voltage when grid voltage drops are mainly summarized.Thus,the importance of enhancing the control effect of DC bus voltage of grid-connected inverter to improve the low voltage ride through capability of the system is pointed out.Then,the improved grid-connected inverter double closed loop control strategy is established,which is PI control in the current inner loop and the voltage outer loop is linear active disturbance rejection control(LADRC).LADRC is applied to the outer voltage loop,and the internal and external disturbances in the system are observed and compensated by the linear extended state observer(LESO),so as to improve the stability of DC bus voltage.Secondly,LESO is the core of LADRC.In order to improve the observation accuracy of LESO,the traditional LADRC is improved by introducing the error between DC bus voltage differential and its observed value in LESO.The improved LADRC can not only reduce the observation error of the observer and improve the disturbance estimation ability of the observer,but also reduce the initial differential peak caused by the large initial observation error.From the frequency domain analysis,it is proved that the anti-interference ability and tracking ability of the improved LADRC is better than that of the traditional LADRC.The simulation results of MATLAB & Simulink show that the control strategy proposed in this thesis can significantly improve the control effect of DC bus voltage under low voltage ride through condition compared with traditional LADRC.Finally,because the DC bus voltage can be accurately measured in real time by the measurement link,this thesis removes it from LESO and constructs a reduced order linear extended state observer(RLESO)which only takes the DC bus voltage differential and total disturbance as the observation values,which reduces the phase lag of the observer and enhances the disturbance observation accuracy of the system.At the same time,aiming at the shortcoming of noise amplification effect in RLESO,a correction link is introduced in the total disturbance channel,and the frequency domain characteristics and simulation analysis of LADRC based on improved RLESO are carried out,which proves the effectiveness of the control strategy.