Impedance Modeling And Stability Analysis Of Three-phase PWM Grid-connected Converters

With the development and utilization of fossil fuels,environmental pollution and energy shortages become increasingly serious,so the use of renewable energy by the attention of countries.As the key technology,grid-connected converters' stability problem cannot be ignored.Therefore,this paper studies the stability of grid-connected converters.This paper,we use the small-signal impedance modeling method to establish the impedance model of the three-phase PWM grid-connected converter in the synchronous rotating coordinate system,and judge the influence of control link on system stability by Generalized Nyquist Criterion.In this paper,the impedance model of the main circuit of the parallel converter is deduced in the synchronous rotating coordinate system.Since the system is built in the synchronous rotating coordinate system,the influence of phase-locked loop on the system is taken into account.On this basis,the current loop is considered.The whole impedance model of the system with pll and current loop is built.The influence of the control system parameters on the stability of the system is analyzed.As the LCL filter is widely used in practice,this paper establishes a three-phase PWM grid-connected impedance model with LCL filter.LCL filter is coupled in the synchronous rotating coordinate system.Therefore,decoupling control is added to the current loop.Combined with the phase-locked loop,the main circuit model of the system constitutes a complete impedance model.Furthermore,in order to suppress resonance problems introduced by LCL filter,active damping is added.Based on the established impedance model,the influence of the control system parameters and the active damping effect on the system stability is analyzed by Nyquist.Based on the above model,the impedance model with DC and AC voltage loop is established for three-phase PWM grid-connected converter.The DC and AC voltage loops are used to control the voltage of the DC side and the AC side respectively.Considering the influence of control system,a complete impedance model is established based on the main circuit model.The Nyquist curve and simulink is used to analyze the influence of the system parameters on the system stability.Aiming at the above system model,the stability analysis of the system and the experimental verification of the proposed model are completed on the laboratory three-phase grid-connected converter experimental platform.