Research On Low Voltage Ride Through Control Strategy Of Double-fed Induction Generators Based On Virtual Synchronous Control

With the progress of society and the development of science and technology,energy issues have become a key factor constraining human development.The unreasonable exploitation and use of resources in history has brought serious environmental pollution problems.As one of the cleanest energy sources,wind power technology has developed rapidly.However,the gradual increase of wind power grid-connected capacity also leads to the absence of equivalent inertia and the reduction of frequency stability in traditional power system.In order to solve this problem,domestic and foreign scholars have proposed virtual synchronous control schemes with different structures.In this paper,the mathematical model of the side and the net side of the doubly-fed generator is established firstly,based on this,the virtual synchronous control strategy of current control type and voltage control type are derived respectively.Based on traditional power decoupling current vector control,a virtual inertia control strategy based on model predictive control is proposed,and verified by simulation.Because the voltage control type is more adaptable under weak grid,this paper takes the virtual synchronous control of voltage-controlled doubly-fed generator as an example,and focuses on the analysis of the problems related to the low voltage ride through of the virtual synchronous control wind turbine under the voltage symmetric sag fault of the power grid.Different from the traditional grid fault through,this paper first divides the fault traversal under virtual synchronous control into two phases,namely,the fault instant and the fault recovery.Aiming at the current impact caused by the intense electromagnetic transient process inside the doubly-fed induction generator excited by the transient voltage sag of the fault,a stator transient flux compensation scheme was proposed to effectively suppress the rotor current and torque shock caused by the transient fault of the doubly-fed induction generator;In view of the active power and frequency pulsation caused by voltage transients during fault recovery,based on the analysis of the causes of pulsation,this paper improves the dynamic response characteristics by adding differential compensation to the first-order inertia link,the frequency pulsation after fault recovery is effectively suppressed,and the capability of low voltage ride through of the doubly-fed induction generator under virtual synchronous control is enhanced.Finally,this paper verifies the effectiveness of the proposed control strategy by constructing the corresponding experimental platform.It shows that the control strategy can improve the low voltage ride through capability of the doubly-fed generator under virtual synchronous control,which has certain research significance.