Study On Nonlinear And Switching Control Methods For DC-DC Converters

DC-DC converters are typical variable structure systems. With the rapid development of electrical power and electronics technology, DC-DC converters are the critical technique for electrical power and electronics equipments. Good dynamic performance and steady state performance are required, especiacally the output tracking for DC-DC converters. Therefore, maintaining tracking of high degree of accuracy, desirable steady output and better dynamical performance is of great importance which has become a hot topic.Based on mathematical models of DC-DC converters, this dissertation studies the problems of output tracking, dynamic performance, steady-state performance, and guaranteed cost control using adaptive control, backstepping control, sliding mode control, and switching control. The main contributions are summarized as follows.Chapter1gives a brief review of DC-DC converters including definitions, applications, working priciples and classification. Common control methods and switching control strategy in the study of DC-DC converters are also surveyed.In chapter2, the output tracking problem for a class of Buck converters with unknown constant parameter uncertainty is studied. The designed controller for such a Buck converter can guarantee asymptic stablility by adding sliding mode surface in the last step of the adaptive backsteeping design. The designed controller is not only continuous, but also provides good tracking performance.In chapter3, a controller is designed for a Buck converter by adopting adaptive smooth sliding mode control method with backstepping, when the load R is time-varying uncertainty with a known bound. The designed controller is not only continuos, but also has good rubustness against the uncertainty. The adaptive smooth sliding mode control brings out bounded tracking, but the bound can be designed to be arbitrarily small. This can fully meet the engineering requirements.Chapter4proposes a new adaptive dynamical surface control method with Fourie series approximation which avoids the explosion of computation caused by repeated differentiation in the process of backstepping design. This chapter also deals with the ability of time-varying uncertainty with an unknown bound. The method is applied to Buck converters. The output can track the reference output with arbitrarily small bound.Chapter5deals with the problem of guaranteed cost control for a class of switched systems with affine vector fields by using multiple Lyapunov function method. The multiple Lyapunov functions are constructed from a set of auxiliary functions with quadratic and linear terms for each subsystem of the switched system. The switching rule is determined to enforce the state of the switched system to a desired equilibrium point by making use of a multiple Lyapunov function, and make a guaranteed cost performance hold. The guaranteed cost control of uncertain polytopic systems is also considered, and the designed results are applied to Boost and Buck converters.In chapter6, according to the characteristics of Buck converter, we consider the existence of parasitic resistances in electric circuit and build up a mathematic model when the Buck converter is working in the continuous current mode. Based on the method of switching controller, we study the output track problem of the system. First, we design two classes of controllers by backstepping:one is for regulation time being less than any given time; the other is for the asymptotical track with non-overshooting. Then, we design a switching signal based on the designed two classes of controllers. Finally, the control objective is achieved.Finally, the results of the dissertation are summarized and further research problems are pointed out.