Elaborate Assessment Of Electromechanical Oscillation Damping Characteristics Of Dfig Based On Energy Dissipation

In recent years,new energy power generation represented by wind power has been developed in full swing.As more and more wind turbines are continuously connected to the power system,some synchronous generators equipped with power system stabilizers in the system may be out of operation,and the wind turbines are connected to the power grid through power electronic converters.The damping characteristics lead to the weakening of the overall electromechanical oscillation damping characteristics of the system,which adversely affects the safe and stable operation of the power grid.Regardless of the online monitoring and early warning of low-frequency oscillations,or the offline damping controller design,damping is regarded as an important monitoring object.Therefore,accurate evaluation of damping is the basis for implementing the above control measures.However,the existing concept of damping ratio as a global damping evaluation index cannot quantitatively analyze the damping contribution of the turbine level and the internal subsystem level of the turbine.Based on this background,how to quantitatively evaluate the local damping contribution provided by the wind turbine and its internal subsystems,It is a key problem that needs to be solved urgently.This paper focuses on the corresponding research and analysis of the doubly-fed induction generator.The main research contents of the paper are as follows:Firstly,according to the basic structure and working principle of DFIG,a mathematical model of DFIG suitable for the electromechanical time scale is established,which simplifies and ensures the accuracy of the model.The established dynamic model is the follow-up chapter of the paper.The derived energy function of the power system with wind power and the energy structure of the conserved doubly-fed wind turbine lay the foundation for the model.Secondly,according to the established dynamic mathematical model of the doubly-fed wind turbine,combined with the relevant theory of energy analysis method,the transient energy function of the power system with wind power is deduced,and the damping contribution factor index is defined by the specific analysis of the time domain expression of the dissipated energy.Based on the Prony analysis,the specific process of the decentralized evaluation method of local damping at the unit level of the power system is proposed.In the DIg SILENT/Powerfactory simulation platform,a four-machine two-zone system with an additional wind farm is built,and simulation analysis of various situations is carried out to verify the effectiveness of the method.It is found that the DFIG without additional control contributes less to the damping provided by the system after connecting to the gird,and this phenomenon can be significantly improved by additional virtual inertia control and damping controller.Finally,the energy function of the established doubly-fed wind turbine is further deduced.According to the energy conservation between the various subsystems inside the wind turbine and the energy conservation at the interface between the wind turbine and the power grid,the specific expressions of the corresponding energy functions of each part of the subsystem are deduced,and the electromechanical time is established.The energy structure of the doubly-fed fan that satisfies the law of energy conservation under the scale.The frequency domain form of the damping contribution factor index is deduced,and according to the distribution law of dissipated energy of each subsystem in the energy structure,the frequency domain analysis and quantitative representation of the local damping evaluation index of each subsystem is established.The specific process of the system-level local damping refinement evaluation method.In a four-machine,two-zone system with an additional doubly-fed wind farm,the conservation of the energy structure of the constructed doubly-fed wind turbine and the effectiveness of the proposed method for refined evaluation of subsystem damping are verified through multi-case simulation analysis.