On Sliding Mode Control And Chaos Suppression For Buck Converter Based On Fractional Theory

Buck converter is an electric device which can convert direct voltage of the system input to reference lower voltage value fast and effectively.Owing to the advantages of high energy utilization rate and less electronic elements,Buck converter has been widely applied in multiple areas such as office automation,home appliances,and space vehicles,etc.Because it's a kind of time-varying and nonlinear system,the control is nonlinear and discontinuous.And the Buck converter control system has disadvantages of slow dynamic response and poor anti-interference ability.In order to improve the rapidity and robustness of the output response,this thesis do some sliding mode control research for Buck converter respectively in inductance current continuous mode and in inductance current discontinuous mode based on fractional theory,and do some research on the suppression methods for chaos in Buck converter based on fractional theory.The main research contents are as follows:In the first part,an integer order state space averaging model for Buck converter in inductance current continuous mode are established according to state space average method.But Buck converter system is actually a fractional-order system based on the fact that inductance and capacitance are not integer-order but fractional-order.Therefore,the fractional-order models in inductance current continuous mode and in inductance current discontinuous mode are built by using basic operator of fractional-order calculus and state space average method.What's more,the correctness and necessity of the fractional order models of Buck converter are proved through theoretical proof and simulation;the process to chaos state of the voltage-mode control Buck converter with input voltage increasing is proved through simulation.In the second part,the fractional order PID controller and the fractional order backstepping sliding mode controller are designed respectively for Buck converter in inductance current continuous mode and in inductance current discontinuous mode based on fractional theory,which accelerates the response speed of the system and enhances the robustness of the system.The effectiveness of the controller proposed is verified by the simulation results.In the third part,this thesis do some research on the current differential negative feedback suppression of chaos and the output voltage delay negative feedback suppression of chaos for a voltage-mode control Buck converter in chaos caused by extortionate input voltage based on fractional theory,using the perturbation thought.These control methods based on perturbation thoughts effectively suppress the chaotic phenomena in Buck converter,and control the Buck converter to the monocycle status fast,and also retain the inherent characteristics of Buck Converter.At last,conclusions are presented and future research directions are discussed.