Electromechanical Coupling Modeling And Load Characteristics Analysis Of Doubly-Fed Wind Turbine Under Virtual Synchronous Generator Control

In the context of a high proportion of wind power grid connection,the grid-supporting control of wind turbines is of great significance for ensuring the safe and stable operation of the power grid.However,grid-supporting control will enhance the electromechanical coupling effect of wind turbines.In addition to wind speed disturbances,frequency and other power grid disturbances will also change the mechanical load characteristics of wind turbines,which may endanger the structural reliability of wind turbines and restrict their grid-supporting capacity,becoming a major obstacle to the design and development of current grid-friendly wind turbines.Virtual synchronous control technology is one of the mainstream technical solutions applied to wind turbines to solve the problem of wind power supporting the grid.This article mainly focuses on the mechanical load problem brought by the electromechanical coupling of doubly-fed wind turbines under virtual synchronous control,and carries out the following research work:(1)Based on the implementation of virtual synchronous control of doubly-fed wind turbines,this paper analyzes the dynamic characteristics of the drive train system of doubly-fed wind turbines under virtual synchronous control.First,the virtual synchronous control of doubly-fed wind turbines is implemented according to the principle of virtual synchronous control.Secondly,based on the model of doubly-fed wind turbines with flexible drive train system,simulations are conducted to compare the dynamic characteristics of the transmission shaft system of doubly-fed wind turbines under virtual synchronous control and traditional vector control under two scenarios: frequency impact disturbance and sustained wind speed disturbance.The key control parameters of virtual synchronous control are analyzed in both time and frequency domains to evaluate their impact on the dynamic characteristics of the drive train system.(2)In order to address the issue that existing models focusing solely on electrical or mechanical aspects have difficulty effectively characterizing the electromechanical coupling under virtual synchronous control,a study on the electromechanical coupling modeling of a doubly-fed wind turbine under virtual synchronous control is conducted.The paper mainly uses the Open-FAST and Matlab/Simulink co-simulation method to construct the electromechanical coupling model of the doubly-fed wind turbine under virtual synchronous control,in which Open-FAST is used to build aerodynamic,mechanical and other models,and Matlab/Simulink is used to build virtual synchronous control,pitch control,motor and inverter control models.Using the established electromechanical coupling model,simulation analysis of the mechanical and electrical characteristics of the doubly-fed wind turbine under step wind conditions is carried out to verify the effectiveness of the model,and simulation analysis of the impact load of the entire wind turbine under grid frequency disturbances is conducted.(3)In order to address the lack of understanding of the impact of virtual synchronous control on the mechanical dynamic loads of doubly-fed wind turbine generators,a study was conducted to analyze the dynamic load response mechanism and quantify the impact of virtual synchronous control on the dynamic loads of doubly-fed wind turbine generators.A linearized multi-body dynamic model of the wind turbine generator was established to analyze the mechanism of the impact of virtual synchronous control on key mechanical components such as blades,tower,and drive train system.Using the established electromechanical coupling model,simulations were conducted to analyze the mechanical loads of the doubly-fed wind turbine generator under turbulent wind conditions during normal operation of the grid according to the IEC wind turbine generator load analysis standard.The concept of equivalent fatigue load was introduced and compared with traditional vector control to quantify the impact of virtual synchronous control on the dynamic loads of doubly-fed wind turbine generators.The above research can provide scientific basis for the development of virtual synchronous control for wind turbines and the design of grid-friendly mechanical structures for wind turbines.It has important practical value in improving the reliability of wind turbines and the safety of grid operation.