Research On Modeling And Nonlinear Bifurcation Of Multi-module Parallel Inverter

Due to the use of devices with fast switching functions,power electronic converters are typical nonlinear systems.When the parameters of the converter are changed or disturbed,nonlinear phenomena such as subharmonic oscillation,bifurcation and chaos will occur,which seriously affects the stability of the system.Therefore,in the recent hundred years,the research of nonlinear dynamic analysis and chaos control based on basic switching converters have gradually become one of the hotspots in the field of power electronics.However,most scholars have focused on the research of DC-DC converters,rather than the nonlinear dynamics and chaos control of DC-AC converters.And this thesis focus on the inverter and study the nonlinear characteristics of the two different inverter circuit systems,including synchronous parallel inverters and interleaving parallel inverters.Moreover,a solution to improve the stability of the system is proposed.The main work is as follows.(1)Taking the double-loop controlled Sinusoidal Pulse Width Modulation(SPWM)single-phase H-bridge inverter as the basic module,a multi-module synchronous parallel inverter system is constructed.The working principle of the system is investigated and the mathematical model is established.The fast-scale instability of the system is analyzed by the system waveforms,phase diagram,etc.Then,according to the output formula of the system,the multi-module synchronous parallel inverter system is equivalent to a single-phase H-bridge inverter.And it is verified by Simulink simulation experiment.Finally,the discrete iterative mapping model of the system is established,which provides a theoretical basis for the chaotic control design of the following inverter.(2)On the basis of the multi-module synchronous parallel inverter system,the switching control signal of each basic module is sequentially added with a delay of 1/n cycles.Therefore,a multi-module interleaved parallel inverter system is constructed.The process is observed that the system from stable periodic state bifurcates to chaotic state,and then returns to the stable periodic state.It is indicated that the fast-scale bifurcation phenomenon still exists in the multi-module interleaved parallel inverter system.(3)Based(1),an equivalent chaotic control method of slope compensation for single-phase H inverter is proposed to suppress the fast-scale bifurcation of the system.In addition,a compensation signal amplitude expression with circuit parameters is determined by two methods.Then,the system is more stable by applying the compensation signal to the inverter system.At the same time,it is shown that the amplitude of the sawtooth wave compensation signal needs to change immediately following the change of multiple parameters in the circuit.Finally,the method is extended to multi-module synchronous parallel inverter system and multi-module interleaved parallel inverter system and is also verified by experiments.