Research On DC-DC Converter Control Strategy Based On Hybrid Switching System Theory

With the development of modern society and economy,the demand for power electronic devices and systems is increasing day by day,it is a serious challenge to carry out standardized design and fine analysis.With the development of new energy generation,electric vehicle,DC motor and other fields,high-order DC-DC converter,as an important part of building high-performance DC converter system,has been widely used.As a nonlinear time-varying system,the power electronic converter consists of discrete switching variables and continuous state variables,its modeling method and control strategy is a long-term research direction of power electronics technology.According to the working characteristics of power electronic converter,the model and control of high-order DC-DC converter were researched based on hybrid switching system theory.The research content of this thesis mainly includes the following aspects.Firstly,according to the structure characteristics of power electronic converter,the working process of high-order DC-DC converter is analyzed in detail,and the possible circuit phenomena in the whole working process are explored.For different circuit phenomena,the working mode and working mode are unified and classified.Secondly,based on the theory of hybrid switching system,the switching conditions of high-order DC-DC converters in different working modes and the self-restraint conditions of each operating mode are thoroughly studied.The equivalent transformation between propositional logic and mixed integer inequality is explained by Cartesian coordinate system.Based on the principle of equivalent transformation,the mixed integer inequality is used to express the state constraints of high-order DC-DC converters under different operating modes.Thus,the unified hybrid switching model of high-order DC-DC converter running in CCM(continuous transmission mode)and DCM(discontinuous transmission mode)is established.Thirdly,according to the hybrid switching modeling method,the hybrid switching models of Cuk Converter,Sepic converter and zeta converter are established.The analysis shows that the unified expression of hybrid switching model of high-order DC-DC converter is only related to the operation mode,so that the model has simplicity.There are no approximate assumptions in the modeling process,which ensures the accuracy of the converter model.The simulation of Cuk,Sepic and zeta converters with different duty cycle,switching frequency and load proves the correctness of the proposed modeling method.Compared with the state space average model and the discrete-time model,the hybrid switching model is more accurate and more consistent with the actual operation.Finally,based on the hybrid switching model,a hybrid switching control method is designed.According to the changing process of current,voltage and energy in the working process of high-order DC-DC converter,the inductance current,switch off time and critical value of switching operation mode under different operation modes are calculated.After judging the operation mode according to the critical value,the corresponding current and time are selected as the control conditions,so as to achieve fine control process and accurate output results.Through simulation and comparison with other control methods,the correctness and effectiveness of the control method are proved.