Research On Stability Analysis Method Of Multi-module Cascading System For Power Electronic Converter

With the wide application of power electronics technology,power electronic systems are gradually becoming more modular,and parallel or series connection of multiple modules can flexibly constitute more complex and diverse power electronic devices,but it also brings difficulties to the stability analysis of the system.Module serial cascade structure is one of the basic structures of complex power electronic systems.This thesis focuses on the stability analysis method of multi-module cascade system of power electronic converter.Based on the existing two-stage source-source module stability analysis method,it is proposed to convert the multi-stage cascade module into a two-level source-load module,and then use the existing impedance ratio criterion to analyze,or consider the multi-level cascade module as a whole,and find the open-loop or closed-loop transfer function,then use the Nyquist diagram to analyze the stability of the system.First,the cascading sub-module is equivalent to a two-port network,which defines the small-signal model and model parameters of a single sub-module,including the input-output impedance and the transmission relationship between input and output voltage or current.Based on the impedance ratio characteristics of the small-signal model,the stability of the traditional two-stage cascade system is analyzed,and the equivalence relation between the impedance ratio analysis method and the classical feedback system transfer function analysis method is pointed out.For the stability analysis of multi-module serial cascade system,three analysis approaches are given:using the sub-module small-signal model and its cascade relationship,the transfer function of the whole cascade system is derived,and then the classical control theory is used for stability analysis;or multi-level cascading system through sub-module integration,re-divided into source-load two-level system,using impedance ratio function for stability analysis;or using sub-module small-signal model to derive equivalent to system open-loop signaling Impedance matching expression.The equivalent model parameter calculation method when two cascaded submodules are equivalent to one submodule is proposed,and then the multi-cascade modularization can be simplified into an equivalent module by the small signal model parameters of each submodule.The equivalent model parameters provide a method for analyzing the stability of multi-stage cascade systems using impedance ratio criteria.The PSIM simulation model and RT-LAB experimental platform of DC-DC cascade system and AC-DC cascade system are established.For the specific application examples,the sub-module small-signal model is established,and the theoretical analysis results and simulation results of the stability of the cascaded system under different parameters are given.The simulation results are basically consistent with the theoretical analysis results,indicating the correct feasibility of the proposed multi-stage cascade system stability analysis in this thesis.