Research On Sliding Mode Control For Fractional Order BUCK Converter System

The DC-DC buck converter,which has been high widely used in the consumer electronics,communications equipment,industrial applications,and military and security fields because of its advantages such as simple circuit,high power transfer efficiency and low electronic components,is a DC voltage conversion device that rapidly converts a high amplitude voltage into a low one.Meanwhile,with the high-tech markets demand,the performance of the buck converters put forward higher requirements.In addition,because the buck converter system is a nonlinear switching system with fractional calculus properties,parametric changes and load mutations,as well as external disturbances,can easily lead the system to poor response performance and poor immunity.Thus,in order to obtain the fast response performance and robustness of the buck converter system,a fractional-order terminal sliding mode controller is designed in thesis paper.The main contents of this thesis are as follows:Firstly,the integer-order model is established for pulse-width modulation and hysteresis-modulated DC-DC buck converter.However,since the inductor and the capacitor are fractional-order characteristic elements,the DC-DC buck converter is a fractional-order control system.Therefore,two kinds of fractional order models are established respectively.Meanwhile,the integer-order model and the fractional-order model of the DC-DC buck converter are simulated by MATLAB/Simulink simulation software,and the necessity of fractional order model of DC-DC buck converter is verified by comparing and analyzing the simulation results.Secondly,a fractional-order terminal sliding mode controller which utilized the advantages of sliding mode invariance and strong robustness of the sliding mode control method is designed for the pulse width modulation DC-DC buck converter fractional system.The theoretical derivation and simulation analysis show that the controller can make the output voltage of the converter circuit converge to the desired output voltage in a finite time,and can effectively suppress the ripple of the output voltage.Meanwhile,the simulation analysis of the external disturbance and load mutation of the circuit system also shows that the controller has the characteristics of sliding mode invariance and strong robustness.Thirdly,in order to overcome the problem that the switching frequency of the hysteresis-modulated DC-DC buck converter tends to be infinite,a fractional-order sliding mode controller and a fractional-order terminal sliding mode controller are designed respectively.Based on the comparison and analysis of two different controllers,it is proved that the fractional-order terminal sliding mode controller can make the DC-DC buck converter circuit obtains better dynamic performance and steady-state performance.Meanwhile,the presence of the terminal link can make the DC-DC buck converter circuit has better robustness,and can effectively weaken the controller's buffeting.Finally,the work of the paper is summarized,and the future research direction is forecasted.