Research On Subsynchronous Oscillation Of Doubly Fed Wind Farm Connected To The Grid Through Flexible And Direct Connection

In response to the requirements of the "dual carbon" development goal,more and more new energy power generation devices are replacing thermal power and integrating into the power grid.Most of these devices are based on power electronics technology,and their integration brings a series of risks and challenges to the safe and stable operation of the power grid.Among them,the oscillation problem caused by long-distance wind power grid connection often occurs in practical engineering at home and abroad,and the subsynchronous oscillation problem of doubly fed wind farms connected to the grid through flexible and direct connection is a typical case.Due to the fact that doubly fed wind turbines are one of the mainstream wind turbine models,and wind farms are often far from the load center,and flexible direct current has its unique advantages in long-distance transmission,it can be foreseen that doubly fed wind farms will become one of the main wind power grid connection methods through flexible direct connection.However,the problem of sub synchronous oscillation caused by this will become an obstacle to its promotion and application.In this context,this article establishes a simulation model of a doubly fed wind farm connected to the flexible and direct grid system in PSCAD,studies the parameters related to the subsynchronous oscillation phenomenon of the doubly fed wind farm connected to the flexible and direct grid system,and analyzes the oscillation reasons based on the stability criteria of the measured impedance.Then,based on artificial neural networks(ANN),a prediction method for the parameters related to the subsynchronous oscillation under stable system conditions is proposed.The main work of this article can be divided into the following two parts:(1)Establish a mathematical model for the flexible and direct grid connection of a doubly fed wind farm,and establish a corresponding PSCAD simulation model to study the relevant parameters that affect the sub synchronous oscillation of the system;Propose a dq impedance measurement method based on small disturbance signal injection,and use the measurement impedance to provide the reasons for the occurrence of subsynchronous oscillation from the perspective of the impact of changes in parameters related to subsynchronous oscillation on system impedance characteristics.(2)A prediction method for the parameters related to the next synchronous oscillation of the system under stable operating conditions based on ANN was proposed.A BP neural network mathematical model was established from impedance characteristics to the parameters related to the system’s sub synchronous oscillation.The operational process of the neural network was proposed and implemented in MATLAB.Finally,three sets of examples were used to verify the accuracy of the neural network model.