Research On Virtual Synchronous Motor Decoupling Technology Of DC Charging Pile Based On Complex Vector Model

With the widespread use of clean energy,the development of electric vehicles and related industrial chains is getting faster and faster.At present,the energy supply of electric vehicles is mainly carried out through charging piles.However,when a large number of electric vehicles are integrated into the grid for charging,it will inevitably have a certain impact on the smooth operation of the grid and reduce the efficiency of the grid.Since synchronous motors can provide inertial support for the grid and are friendly to the grid,virtual synchronous motors(virtual synchronous generator VSG)can simulate the operation of synchronous motors by changing the control algorithm to control the inverter.Applying this technology to the AC/DC of the DC charging pile of electric vehicles can provide inertia to the grid like a synchronous machine.Support,thereby improving the stability of the grid.However,the virtual synchronous motor will have a power coupling phenomenon during power adjustment,which is manifested as a steady state error when the power setting value reaches a steady state,and a dynamic coupling overshoot will occur when it is in the dynamic adjustment stage.Coupling overshoot will have an serious impact on dynamic performance,and the occurrence of steady-state errors will cause control failure.Aiming at this problem,this paper studies the coupling problem of VSG,and establishes a complex vector model of VSG to point out the reasons for coupling,introduces complex vector analysis tools to study the coupling characteristics,and proposes the decoupling of complex vector PI current controllers.The method achieves complete elimination of steady-state errors and reduces coupling overshoot.The specific content is as follows:(1)The topology structure of the DC charging pile using VSG is proposed,and then the circuit structure of VSG is introduced by analogy with synchronous motor,the control algorithm of VSG is deduced and the main circuit diagram of VSG is proposed.(2)The scalar modeling is introduced,and the complex vector model of the system is established by introducing the concept of complex vector and the modeling process is deduced.Through the comparison between the scalar model and the complex vector model,the unique advantages of the complex vector model to simplify system analysis and to retain system information are explained.Then the complex vector theory is introduced into the traditional frequency response characteristic curve and pole-zero diagram,the bilateral frequency characteristic curve and the complex vector zero-pole diagram are introduced,and the analysis principle of the complex vector analysis tool is explained.(3)Use the complex vector analysis tool to analyze the coupling characteristics of the system,point out the reasons that cause the power coupling of the system,and point out the characteristics that the ideal decoupling system should have on the image.Subsequently,the decoupling method of the complex vector PI current controller is proposed and compared with other decoupling strategies.(4)Based on the Matlab/Simulink simulation tool,the method described in this article was simulated and verified,and the inverter model was built for experimental verification.