Research On Grid-Connected Control Technology Of Full Power Converter For Permanent Magnet Direct-drive Wind Power Generation System

With the increasingly serious environmental problems,countries begin to attach importance to the development of wind power generation in the world,so wind power generation has developed rapidly in recent years.With the increasing capacity of wind turbines connected to the grid,the interaction between the grid and wind turbines becomes more and more important,and the wind turbines are connected to the grid through full-power converters.Therefore,it is of great practical significance and value to study the control technology of full power converter of permanent magnet direct-drive synchronous generators.In this paper,the permanent magnet direct-drive wind power generation system is taken as the research object.Its working principle,system model and control strategy are analyzed.The control strategy of grid-side converter is studied when the grid voltage is normal.A double closed-loop control system is constructed.The control effect of grid-side converter is improved by introducing LADRC in the voltage outer loop.The LVRT technology of permanent magnet direct-driven wind power generation system is further studied when the three-phase symmetrical fault occurs in the grid.The correctness and effectiveness of the improved control strategy are verified by the MATLAB/Simulink.Firstly,the basic working principle of permanent magnet direct-drive wind power generation system is analyzed,its mathematical model is established,and its control strategy is studied.It mainly includes the basic characteristics of wind turbine,the principle of maximum wind energy tracking,the mathematical model of permanent magnet direct-drive generator and zero-d-axis vector control strategy,the mathematical model of grid-side converter and the vector control strategy based on grid voltage orientation.The mathematical model of intermediate DC link is established by analyzing the energy transfer characteristics between full power converters.Secondly,under the normal grid voltage,the grid-side converter based on grid voltage oriented vector control strategy is studied,and the parameters of the double closed-loop control system are designed and tuned.Because the control effect of traditional PI controller is not ideal when disturbance occurs to the system,and LADRC has the advantages of insensitivity to the change of system parameters and disturbance,and strong robustness,this paper proposes a control strategy of first-order LADRC for voltage outer loop,so as to make the control performance of grid-side converter more ideal.The simulation results show that,compared with PI control strategy,the voltage outer loop control strategy based on LADRC has the advantages of fast response,no overshoot and strong robustness.Finally,the LVRT technology of permanent magnet direct-drive wind power generation system is studied when three-phase symmetrical fault occurs in power grid.For the unbalanced power of DC link,Crowbar unloading resistance circuit is used to consume the redundant unbalanced power on DC link,and the grid-side converter runs in STATCOMmode when the grid symmetrical fault occurs,providing reactive power to the grid to improve the LVRT ability of the permanent magnet direct-drive wind power generation system.The effectiveness of control strategy in this paper is verified by simulation.