The Research Of High Voltage Ride Through Strategy Of Offshore DFIG-Based Wind Turbine

In recent years,large-scale wind turbines out-of-network accidents have occurred frequently with the grid voltage swelling,which seriously affects the power grid stability.Considering the objective environment and long-distance transmission of offshore wind farm,the fault occurrence mechanism is more complicated.The impact on the offshore wind turbines based on Doubly-Fed Induction Generator have increased.Therefore,it's of great practical significance to study the high voltage ride through ability of offshore wind farm.When the voltage swells,there are two problems to be addressed that threaten the safety operation of the DFIG-based wind turbine.One is the rotor overcurrent,and the other is the dc-link overvoltage.Therefore,based on the dynamic model of the DFIG-based wind turbine,this paper studies the above problems and proposes corresponding control strategies.The main work is as follows:The dynamic model of the DFIG-based wind turbine is established,in order to simulate the behaviour of DFIG and investigate high fault ride-through performance of DFIG-based wind turbine.Based on the transient time scale of the grid fault,the corresponding model is established for each subsystem of the DFIG-based wind turbine,which include the simplified model of the pneumatic system and the transmission system,and the detailed model of the power generation system and the control system.In the PSCAD software,a simulation model of DFIG-based wind turbine is built to simulate the transient process under different grid voltage swell amplitudes and verify the feasibility of the fault ride through strategy.Considering the dynamic change of stator flux linkage in the case of three-phase symmetrical voltage swell,a feedforward voltage compensation control strategy for rotor-side converter is proposed.In the ?? coordinate system,the variation law of electromagnetic quantities of DFIG are analyzed and obtained under the grid voltage swell.By quantitatively analyzing the rotor voltage in the dq coordinate system,an accurate voltage compensation amount is obtained.For 2MW DFIG-based wind turbine,Simulation results show that the feedforward voltage compensation control strategy can effectively suppress the rotor current surge compared with the steady-state control strategy.A high voltage ride through strategy based on coordinated control of super capacitor energy storage system and grid-side converter is proposed.Super capacitor energy storage system is used to quickly absorb unbalanced energy to avoid dc-link overvoltage.At the same time,the grid-side converter preferentially emits inductive reactive power to provide reactive power support for the grid.A doubly-fed wind turbine model with a supercapacitor energy storage system is established.The control strategy of super capacitor energy storage system and the reactive power priority control strategy of grid-side converter are respectively proposed.A collaborative control scheme is designed based on coordinated control of super capacitor energy storage system and grid-side converter.Simulation results show that compared with the Chopper protection scheme,the presented strategy has better control effect on restrain the dc-link overvoltage.Based on the dynamic model of DFIG-based wind turbine,this paper respectively proposes the corresponding control strategy for the rotor overcurrent and dc-link overvoltage in the case of high voltage faults.The feasibility and effectiveness of the proposed control strategy are verified by simulation in PSCAD software.