Analysis And Suppression For Resonance Of Thr Grid Based On The Grid-connected Multi-inverter System

With widely application of distributed power generation, more and more grid-connected inverters are integrated into the distribution network. The nonlinear grid-connected inverter can present either capacitive or inductive with the change of control strategy and parameters, which is the third element causing resonance besides capacitance and reactance, also, it excites more complex resonant characteristics of system.This paper focuses on the grid-connected inverter and analyzes the resonant characteristics of the grid-connected multi-inverter system. The comparison of the control strategies of grid-connected inverter in αβ stationary coordinate and dq rotating coordinate system is analyzed and the output impedance model of three-phase grid-connected inverter with practical and simply application in αβ stationary coordinate is built for describing external characteristics of grid-connected inverter. Based on which, the influences of the number and composition of grid-connected inverters and power line impedance on the resonant characteristics of system are achieved by analyzing the interactive influences between the multiple inverter systems.Aiming at the resonance problem of the grid-connected multi-inverter system, this paper presents an investigation on parallel resonant using the modal analysis. By analyzing the characteristics of the eigenvalue of node admittance matrix, the resonance mode and frequency are obtained and the location with the highest excitability and highest observability is achieved according to the critical left eigenvector and right eigenvector.For single-inverter system, a resonance suppression module locating in the point of common coupling for suppressing the resonance between the multiple inverter systems is introduced to this paper using an active damping control scheme based on filter capacitor current. The suppression effect of two suppressive styles, which are single resistance and resistance in series capacitance, of resonance suppression module is analyzed. Finally, the applicability of the output impedance modeling, the correctness of resonance characteristics analysis and the effectiveness of the suppression strategy are verified by the simulation.