Dc-dc Switching Converter Nonlinear Analysis And Topology

The theory of analysis and synthesis of DC-DC switching power converters are studied in this dissertation.(1) Theory of Analysis. First, methods of analyzing switching converters are reviewed. It is demonstrated that nonlinear analysis of switching converters is important to practical designs. Therefore, the thesis focuses on the asymptotic analysis of switching converters, which includes the following:(â… ) A circuit-oriented averaging technique, high-frequency network averaging principle, is proposed. Based on this principle, the characteristics of and relationship between conventional PWM converters and quasi-resonant converters are studied.(â…¡) An improved perturbation technique, equivalent small parameter method, is generalized to the steady-state and transient analyses of switching converters, including quasi-resonant converters. Analytic expressions of DC values and ripples of capacitor voltages and inductor currents can be obtained. It is demonstrated that its first-order approximation is the usual averaging technique (for example the high-frequency network averaging). The method features simplicity and accuracy when compared with other asymptotic methods, such as KBM method or Harmonic Balance method.(â…¢) Conditions for the justification of the usual averaging technique are investigated and stability issues of PWM switching converters are addressed. It is shown that converters in closed-loop operation are systems with complex dynamics. However, closed-loop models, which are critical to simulations and analyses of these time-variant systems, have not been systematically established yet in existing literature. This thesis develops such models through the sliding-mode control theory.(2) Theory of Synthesis. It is shown that soft-switching techniques will dominate the DC-DC power conversion field in the near future. The thesis presents a general method of modeling and synthesizing quasi-resonant converters, including actively-clamped quasi-resonant converters. First, the concept of PWM switch model is generalized to encompass all PWM (non-isolated) converters. Then, by adding LC elements and auxiliary switches into the PWM switch, quasi-resonant converter families are synthesized. DC and small signal analyses can be carried out based on these switch models. Furthermore, the duality relationship between zero-voltage-switching and zero-current-switching quasi-resonant converters is established systematically and rigorously.