Research On Controller For DC-DC Buck Converter Based On Sliding Mode Theory

With the development of power electronic technology,switching power has been widely used in various fields,such as computer,industry,aviation,signal communication and so on.As a branch of switching power,DC-DC converter,which has the advantages of small-size and high output efficiency,has currently become a hot topic in power field.However,traditional control methods may no longer meet the requirements of modern technology for high-performance power supplies.In recent years,some modern practical control methods begin to appear.The main technique used in this thesis is the sliding mode control method and the Buck DC-DC converter is taken as the research object.Several control schemes are designed and implemented for Buck converter and the resulting experimental results are analyzed.In order to improve the anti-disturbance ability and the dynamic performance of the closed-loop system,two kinds of control methods based on sliding mode control technology are introduced in this paper.One is the composite control scheme based on non-singular terminal sliding mode and nonlinear disturbance observation theory.Firstly,a sliding mode controller for the Buck converter is developed by using the terminal sliding mode technique.Then,the nonlinear disturbance observer is designed in combination with the actual model of the converter.Finally,combining the state-feedback controller and the feed-forward compensation to obtain composite control scheme.Compared with the linear controller,the disturbance can be effectively suppressed.The other is the discontinuous second-order sliding mode controller based on the second-order sliding mode theory.Firstly,the mismatching problem existing in the sliding mode control system is considered and the control system with mismatching terms is established.Then,the second order sliding mode controller is designed and its stability is verified by using Lyapunov method.Finally,the comparisons between the second-order controller and the conventional first-order sliding mode controller are also given.This thesis mainly discusses the following contents:(1)The research background of DC-DC converter and the frequently-used control strategies have been introduced,and then the research methods and steps in this thesis are presented.(2)The basic principles of Buck converter are introduced,including the state analysis under three modes and the establishment of the mathematical model for Buck DC-DC converter.(3)The system design of Buck converter based on the DSP platform is introduced.The overall design scheme of the system is described,including hardware circuit design and software design.Then,taking the case of PID control algorithm,the feasibility of the system design and algorithm is verified.(4)On the basis of the establishment of the mathematical model,a state-feedback controller for Buck converter is first designed based on non-singular terminal sliding mode.Then,a nonlinear disturbance observer is further constructed such that a new composite controller can be developed by combining with the previous state-feedback controller and the the disturbance observer,whose performance has been verified by simulation and experiment.These simulation and experimental results show that the composite controller exhibits better performance than the pure state-feedback controller.(5)In order to obtain a better control performance,considering the mismatched problem in the sliding mode control system,a sliding mode control system with mismatched item is established.And then,a second-order sliding mode controller is designed and the stability of the closed-loop system is proved.Finally,the seconder-order sliding mode controller is applied to the Buck converter.Compared with the conventional sliding mode controller,the simulation and experiment show that the proposed second-order sliding mode controller will have a better disturbance rejection and dynamic performance.(6)The thesis is summarized at the end of the paper and the shortcomings and the contents worthy of continuing research is discussed.Finally,the prospects are pointed out.