Research Of Fault Ride Through And Power Support Technology For Large Doubly Fed Wind Power Generators

With the wide use of doubly-fed wind turbines and the increasing proportion of wind power,wind turbines are interacting more with the grid.Due to the structural characteristics that the stator is directly connected to the grid and the converter has limited capacity,the overvoltage and overcurrent of the winding will occur when the grid fails,which threatens the safety of the wind turbine.The protection shutdown of the wind turbine will cause active power lack and inactive power mismatch,threatening grid stability.For large doubly-fed wind turbines with MW-scale capacity,fault ride through is an urgent and challenging task.When the conventional rotor crowbar protection circuit is put into operation,the machine-side converter loses its control ability.It is a passive protection and is difficult to adapt to the new environment of high wind power ratio.In this paper,a fault ride through solution with stator series impedance and dynamic reactive power support is proposed,which can improve the uninterrupted operation capability of high and low voltage integrated faults and actively supporting the power grid.The key contents and main work of this paper are:Firstly,the basic composition and control principle of doubly-fed induction wind power generation system are analyzed.The mathematical model of induction motor underi dq synchronous rotation coordinate is established.The transient response of doubly-fed induction motor under three-phase grid voltage drop is studied.The protection focus and control objectives of the fault ride through strategy are introduced.According to the DFIG stator power boundary during the grid fault,the method and basis for determining the reactive power support capacity are given.By comparing various series protection schemes,the stator series impedance is selected as the main protection,and the theoretical basis of the impedance to suppress the rotor overcurrent is given.A complete solution of stator series impedance and dynamic reactive support is designed.The complete compensation of the stator outlet voltage is realized,and the method of setting the series impedance is given.The method realizes the high-and low-voltage fault-safe ride through of the grid from 0.2 to 1.3p.u,which can simultaneously protect the stator and rotor windings and provide the reactive current required by the guideline.In view of the rapid input requirements of stator series impedance,the,the requirements for the switch are analyzed,and the advantages and shortages of the existing switch are studied.The series impedance input switch with ultra-fast breaker and commutation circuit is designed.It has the advantages of low loss under normal working conditions and fast action when fault occurs.It can meet the requirements of stator series impedance protection and has practical value in engineering.A real-time simulator-based 2MW parallel converter DFIG hardware-in-loop simulation platform is established for reasearching fault ride through technology,and the software and hardware components of the platform are elaborated.The platform verifies the effectiveness of thedynamic reactive power support strategy for low voltage ride through and high voltage ride through,and tests the reactive power support capability of the proposed scheme.