Research On Grid-connected Control Strategy Of Full Power Permanent Magnet Synchronous Wind Turbine Under Weak Power Grid

With the comprehensive development of social economy and technology,wind power technology has also shown vigorous development,and its proportion in new energy sources is increasing.However,the high wind power penetration rate reduces the stability of the power grid system,and problems such as oscillations caused by the connection of wind turbines to weak grids continue to occur.This paper takes the full power permanent magnet synchronous wind turbine as the research object.Aiming at the problem of reducing the system inertia caused by the wind turbine connected to the power grid,the virtual inertia control and additional frequency control are analyzed and proposed.Aiming at the problems such as the oscillation caused by the weak power grid connection of wind turbines and the decrease in operation stability,strategies such as robust control and virtual synchronous control were analyzed and proposed.The specific work done by the text is as follows:(1)A mathematical model of a permanent magnet synchronous generator and a fullpower back-to-back converter is established.The conventional control strategies of the full-side PMSG wind turbine generator-side converter and grid-side converter are introduced.At the same time,the position sensorless control strategy of PMSG motor based on full-order state sliding mode observer is studied in detail.(2)The inertia of the grid system of conventional thermal power generating units is analyzed.Based on this,the principle and structure of virtual inertia control of a full power PMSG wind turbine are proposed.The parameter design of the virtual inertia control is analyzed in detail,and the influence of the parameters on the stable operation of the unit is studied.(3)Sequential impedance modeling of a conventionally controlled direct-drive fullpower wind turbine,focusing on the phase-locked loop,current loop,and main circuit of the grid-side converter.Based on the sequence impedance of the unit,the cause of oscillation of the PMSG fan connected to the weak grid under conventional control was analyzed.A set of high-power PMSG fan parameters is used as an example to verify the correctness of the sequence impedance stability analysis.(4)Research and propose a robust AC bus voltage controller based on ? synthesis to improve the grid-connected stability of the unit.Small-signal modeling of PMSG wind turbine grid-side converter was performed.The principle and design method of robust controller are introduced.A comparison is made between the robust control of PMSG fans and conventional control.(5)Propose a virtual synchronous control strategy for full-power PMSG wind turbines,namely the PMSG-VSG control strategy.First,the components of the PMSGVSG control strategy are introduced,including PMSG machine-side control DC voltage,grid-side voltage and current inner loop control,active-power angle and reactive-voltage control,pre-synchronization control,and virtual impedance control.Then,the design of parameters such as inertia time constant,damping coefficient,filter time constant,voltage loop PI,etc.,as well as grid connection characteristics such as virtual inertia and primary frequency adjustment in PMSG-VSG control are analyzed.