Study Of Global Sliding Mode Control Buck Converter

Sliding mode controller is simple in structure and easy to implement, with excellent robustness and dynamics, it is therefore more suitable for the control of switching dc-dc converters which are variable structure systems in natural to achieve better control performance.Conventional sliding mode control switching power converter is a special sliding mode control with control variable (duty ratio) constrained. Consequently, sliding region is closely related to the sliding coefficients and circuit parameters of switching power converter. However, sliding coefficients is in inverse proportion to sliding region, and in proportion to the performance of sliding mode, that make robustness and dynamic response speed become a trade-off and make the selection of sliding coefficients difficult.The design method for switching DC-DC converter with sliding mode control is studied in detail in this thesis. Global sliding mode control is applied to the design of switching dc-dc converter. Two design methods with simple implementation structure have been presented in this dissertation to achieve both excellent robustness and better sliding mode performance of sliding mode control. The main contents of this dissertation are outlined as follows(1) Based on the theoretical analysis for sliding control system with control variable constrained, the relation among the sliding region, the sliding coefficients and the circuit parameters of conventional sliding mode control switching dc-dc converter is investigated. The design method of first-order sliding mode controller is analyzed and the practical design method has been given for conventional sliding mode control switching power converter.(2) Based on the principle of global sliding mode control, major characteristics of global robustness is analyzed and applied to the control of switching DC-DC converters. Buck converter is used as an example to illustrate the application of global sliding mode control to switching dc-dc converters. A cmparison study between global sliding mode control and conventional sliding mode control is performed by way of simulation results. The simulation results show that switching dc-dc converter with global sliding mode control has better dynamic characteristics than with conventional sliding mode control.(3) Due to time varying characteristics of global switching surface of global sliding mode control, switching dc-dc converter with discrete global sliding mode control is studied. Discrete reaching law method and global attenuation law are investigated to provide a design method for global sliding mode controller of switching power converter.(4) To select reasonable sliding coefficients, optimal load step variation transient characteristics are studied and their relations with main circuit parameters are investigated. A simple sliding coefficients design method is investigated. Simulation results verify analysis results.(5) Regarding to the initial value of transient of global switching function, the design method for global switching function is investigated and the seady state performance of switching DC-DC converter with different load is analyzed.