Resonance Elimination Method Of Grid-Connected Converter System Based On Active Damper

Recently,as a connection between DG and Grid interface,the flexibility and high efficiency of power electronic grid-connected converter has been widely concerned and researched.However,with the increasing penetration of renewable energy in the grid,PCC(Points of Common Connection)has gradually performed the features of the weak grid,while its impedance cannot be neglected and its variability cannot be denied.In this case,even if the converter itself is designed to be stable,it may still cause serious resonance between the converter and the grid.Meanwhile,the structure of the multi-converter parallel to the PCC is also more widely used,and the resonance generation mechanism of the multi-converter system is more complicated than that of a single converter.Therefore,it is necessary to propose a more accurate model and an effective control structure to deal with these situations,reducing harmonic resonance in the system.This thesis takes the multi-converter system as the research object.By establishing the impedance model of the grid-connected converter system,the stability of the grid converter system is analyzed.According to the impedance analysis method,the mathematical model of the grid-connected converter system is deduced in detail,and the stability conditions of the grid-connected converter system are also obtained.In spite of these,the mechanism of resonance when the grid impedance changes and multiple grid-connected converters are put into parallel operation is theoretically analyzed.In order to solve the resonance generated in the system,an active damper is designed in parallel to the PCC.The damper suppresses the resonance by damping at the resonance frequency,and carries the characteristics of small capacity and high bandwidth.By the method of resonance detection system based on second-order generalized integrator,it not only detects the fundamental signal in the system,but also has better dynamic characteristics and anti-interference ability.In this thesis,the resonant control strategy of multi-grid converter system and active damper is designed,including the current controller,the grid phase synchronization of grid-connected converter,and the resonant detection method of active damper and double closed loop control.Finally,by adapting the simulation platform(Matlab/Simulink)to establish the time-domain simulation,it verifies the effectiveness and correctness in the thesis to elimination the resonance in the system of grid-connected converter.