Research On Transformer Main Protection Based On Model Recognition And Its Application In Power Electronics Dominated Power System

With the advancement of power electronic technology and the large-scale development and utilization of new energy sources,the traditional power system is transforming to a power system dominated by diversified power electronic equipment.In this process,because power transformers play an important role in grid interconnection and power exchange of different voltage levels,their safe and reliable operation is vital to the stability of the grid.In recent years,many transformer-related accidents have occurred in renewable energy bases,high-voltage DC converter stations and other places in power systems at home and abroad,which have brought challenges to the reliable operation of power systems.The problems of transformer protection have become increasingly prominent under the trend of power electronics in power systems,and it is necessary to conduct in-depth research.In previous studies,transformer protection is basically divided into two categories,one is the current feature identification method,and the other is the electromagnetic parameter identification method.The current feature identification method uses signal analysis methods to study the characteristics of transformer current waveforms,thereby distinguishing different working conditions,such as using wavelet analysis to study the singularity of the excitation inrush current.Such methods usually do not have a clear physical meaning,and the extracted mathematical features are easily disturbed by complex scenes.The electromagnetic parameter method introduces the voltage quantity,obtains the equivalent excitation inductance,magnetic flux and other transformer electromagnetic quantities,and sets the protection according to the changes of the electromagnetic parameters.This kind of method can reflect the changes of transformer physical parameters to a certain extent,but the existing research often adopts simplified methods such as power frequency circuit model and broken line magnetization characteristics,it is difficult to achieve accurate analysis of the transformer transient process,and fails to make full use of the transformer electromagnetic model.The results of the research.This paper analyzes and studies the basic problems of transformer model identification.First,analyze the parameters’ identifiability,parameter sensitivity,and computational complexity,and choose an electromagnetic model suitable for transformer protection.Then study the electromagnetic modeling method using voltage and current on the single-phase transformer,consider the physical constraints and mathematical constraints to construct the model parameter identification function with the goal of minimizing the error of the fitting curve,and screen out the excellent intelligent algorithm for the model parameters Identify.Finally,the special problems of modeling and parameter identification in different connections,different structures and three-phase transformers used in converter stations are studied,and corresponding solutions are given.A transformer protection method is proposed based on model identification.The method is based on the electromagnetic model that completes the parameter identification,uses voltage and current to perform online model matching analysis,and judges internal faults based on the matching degree.The magnetization characteristics described by the electromagnetic model are affected by the remanence,and the value is difficult to measure.The online model matching analysis adopts the differential form to eliminate the influence of the remanence and ensure the reliability of the algorithm.From the perspective of practicability,the proposed transformer protection method is studied.Based on the voltage and current,the magnetization curve of the transformer under different working conditions is obtained,and the feasibility and superiority of the algorithm are qualitatively analyzed.Build simulations of various transformer disturbance and fault conditions in PSCAD and MATLAB/Simulink software,and compare and verify the protection scheme proposed in this paper with the traditional differential protection.The results show that the transformer protection based on model identification can respond well to various working conditions and has higher accuracy in internal fault identification.Build a power electronic power system simulation platform in PSCAD software to simulate three working conditions,including transformer DC bias,wind farm output transformer frequency deviation and rectifier side converter transformer fault surge current,and analyze the traditional protection of transformers.Using the protection algorithm proposed in this paper to verify in the above three scenarios,the results show that the algorithm still has good reliability in the complex scenarios of power electronic power system,which is beneficial to ensure the safe and stable operation of the transformer under the new situation of the power system.