Study On Nonlinear Behaviors And Control In Parallel DC-DC Converters

DC-DC converter is the basic circuit unit of many other types of power electronic converters,the significance to stability and the reliability of its operational status has important referential analyze the working performance of the power electronic converters.DC-DC converter is also a typical switching nonlinear system,which includes discrete and continuous working states.There are various nonlinear behaviors in DC-DC converters,such as period-doubling bifurcation,boundary collision bifurcation,coexisting attractor and chaos.Bifurcation,chaos and other behaviors will increase the voltage or current altitude,change the ripple and harmonic of the voltage and current,decrease the performance increase the switch loss and electromagnetic interference,decrease the efficiency and reliability and lead the converter to oscillation.In the development of switch converter,the influence mentioned above always exists.Before the nonlinear scientific theory was applied to the nonlinear behavior of switching converters,the bifurcation and chaos in the converters were attributed to the external interference or the design error in the application.Engineers usually ignore the nonlinear behaviors or change them by adding filters to the converter.But this approach increases the size of the converter and the cost of the device.In practice,the effect is very limited.In recent years,scholars at home and abroad have studied a series of subjects such as the discovery of nonlinear phenomena in converters,the modeling of the system,the simulation by using relevant software,the analysis of nonlinear theory,the control and inverse control of nonlinear behavior,and the engineering application of nonlinear behavior.The research on nonlinear behavior of converters has become a hot topic at home and abroad and has become an important research direction and branch of power electronics and nonlinear dynamics theory.However,at present,the research mainly focuses on the discovery,characterization,analysis and control of nonlinear behavior in a single DC-DC converter,and there are few research results of the DC-DC converter with parallel structure,especially the analysis and control of nonlinear behavior in the parallel DC-DC converter is at primary stage.In the design of power electronic circuit,the switch converter often needs parallel structure because of large capacity,large load and low cost.Parallel converter can improve the output of high power.Especially it is suitable for distributed modular power system.It has a wide range of applications in various fields.This paper takes the parallel DC-DC converter as the research object,adopts the thought of modeling,discovery,analysis and control.By using the methods of numerical simulation,experimental verification and theoretical analysis,the paper develops the nonlinear dynamics research.The following work has been completed:(1)The nonlinear model of parallel DC-DC converter is established.Aiming at the complexity of parallel structure and the mixture of continuous and discrete switching,the state variable equation and discrete iterative mapping model are established.Model is based on the circuit structure and working mode.The solution of equation can accurately reflect physical properties and the working state of parallel converter.So it can be used to analysis bifurcation,chaos and the other dynamic behaviors of the parallel converter.Balancing point,the stability of the periodic orbit and dynamics characteristics of the converter can be studied furtherly.By combining the state variable equation with the discrete mapping model,the nonlinear behavior and characteristics of the parallel converter can be comprehensively analyzed.(2)The nonlinear behaviors of parallel DC-DC converter is revealed and analyzed.Taking the parallel Buck converter and parallel Boost converter under the voltage control as examples,through numerical simulation and experimental verification,the paper reveals lots of nonlinear behaviors of parallel converter caused by the change of system parameters and the frequency of sawtooth in the control circuit.It is found that the variation of voltage and current feedback gain in parallel Buck converter can lead to bifurcation and chaos.In parallel Boost converter,the change of parameters causes Hopf bifurcation.The converter goes through limit cycle,quasi-cycle and then enters chaos.In addition,there is some attractors coexist in parallel converter.When two frequencies of sawtooth signals are different,the parallel converter is in intermittent instability,it periodically runs alternately with chaotic or higher harmonics.The characteristics of nonlinear behavior are revealed by time domain diagram and phase diagram.(3)The mapping of parameter bifurcation and time bifurcation is proposed,and the stability of parallel converter is analyzed.Based on the nonlinear dynamics theory of parallel theory,the paper analyze the stability influence of the converter,respectively from the circuit parameters and interference.By parallel converter discrete iterative mapping,the jacobian matrix is constructed,the eigenvalues are solved.The numerical analysis of characteristic value and trajectory reveals the state and instability of the converter.The influence of interference signal on the stability of the parallel DC-DC converter is studied.It is revealed for the first time that coupling interference signal is also the cause of intermittent instability of the converter.The mapping relationship between time bifurcation and parameter bifurcation is established.Mapping can reduces the amount of computation.It is an effective method to analyze the stability of parallel DC-DC converter.(4)The method of control on intermittency of parallel DC-DC converter is proposed.Traditional methods are carried out on the bifurcation and chaos control.Taking the parallel Buck converter and parallel Boost converter as examples,perturbation parameter resonance and delay feedback control technology are implemented.The change of power spectrum and phase diagram indicate the effectiveness of the control technology.Taking the parallel Buck converter and parallel Boost converter as examples,this paper studies the modeling method,nonlinear behavior analysis and control technology,etc.The methods adopted in the research and the existing conclusions can be extended to the nonlinear research of the other kinds of parallel power electronic devices.