Research On The Control Strategy Of Grid-forming Inverter

Recently years,the proportion of distributed generation(DG)has greatly improved in the power system,and a large number of distributed energy connect to grid with grid-connect converter(GCC).Because distributed energy has the characteristics of dispersivity,intermittent and unstable,and GCC lacks the damping and inertia characteristics.The traditional GCC,which is based on current control,is difficult to meet the requirements of new grid,as a result,grid-forming converter has received more extensive attention.This thesis focuses on the power ring control strategy and the power decoupling strategy.This thesis analyzes the influence of active and reactive power control parameters on the stability and dynamic performance of traditional VSG.As a result,there is contradiction between the active loop control parameters,which contributed to the stability and dynamic performance cannot be taken into account.Finally,this thesis proved it by simulation.To slove the problem that there are contradictions in the performance of active loop control parameters This thesis analyzes the influence of feedforward coefficients on power loop stability and dynamic energy,and design the adaptive improvement of the traditional VSG control strategy by the adaptive improvement of the feedforward coefficient,and improves the stability and dynamic energy of the voltage controlled parallel inverter,and proves the validity and feasibility of the adaptive improvement control strategy with the forward feed coefficient.In this thesis,the power coupling problem of the power loop control strategy is analyzed,and the two conditions of ideal decoupling are analyzed.A generalized power coupling analysis method is introduced: the relevant gain matrix(RGA).This method analyzes the influence of traditional virtual synchronous machine control parameters on power coupling performance.This thesis analyzes the common decoupling strategy: virtual impedance decoupling(VID),and indicates the reason for the limitation of decoupling performance: the voltage reference value of the d axis is changed.Finally,a multi-input multi-output controller is designed,and the power of the voltage controlled parallel inverter is completely decoupled.