Study Of Sliding-mode Control And Chaotic Dynamics Of DC-DC Converters

In this dissertation, sliding-mode control (SMC) technique and chaotic dynamics of DC-DC converters are studied intensely.1. Study on sliding-mode control technique.(1) Firstly, this thesis gives a whole introduction to many kinds of linear and nonlinear control techniques (chapter 2), and describes the advantages of sliding- mode control technique. Up to the present, the studies of applications of SMC to DC- DC converters generally aim at only one type of converters, lacking of unified design procedure and having no good closed-loop performance. For this reason, chapter 3 presents an approach of unified synthesis of time-varying SMC. This approach is suitable not only for hard-switching converters, but also for bilinear switched networks. As examples, some applications to four basic hard-switching converters(Buck, Boost, Buck-Boost and Cuk converters) are given. Becaues of the particular structure, every converter has its particular performances and advantages when the time-varying SMC is applied, such as the rapid start-up response and tracking behavior, robust transient response, or invariance performance when meeting the matching condition.(2) An extension of the SMC to phase-shifted(PS) full-bridge(FB) zero-voltage- switched(ZVS) converter is proposed. PS FB ZVS converter, which has found many applications to higher-power supplies, possesses better performance owing to its high switching frequency up to several hundred kilohertz, and the reduction of switching losses and stresses. But the converter has a more complicated circuit topology with four switching devices, which makes the research on control techniques of the converter more difficult. In order to utilize the control technique of SMC, chapter 4 studies the circuit topology and operation process of the converter in detail, and concludes that the PS FB ZVS converter has its correspond equivalent circuit topology of Buck converter. Based on this equivalence condition, an approach of applying SMC to PS FB ZVS converter is proposed, which can achieve good control results. 2. Study on chaotic dynamic state.(1) Chaos can occur only in autonomous systems with no less than three orders, so among four basic hard-switching(non-PWM) converters, only the autonomous Cuk converter can generate chaos. In chapter 6, a SMC system of Cuk converter (hysteristic current-controlled Cuk converter) is discussed. By the method of equivalent control, the sliding-mode state equations on switching surface are established. In addition, the stability of 1-periodic orbit is studied qualitatively on the basis of the sliding-mode state equations, which proves that the instable process is a Hopf bifurcation, and all circuit parameters(such as capacitor, inductor and load) make important influence on the stability of 1-periodic orbit. Then, for the operations after Hopf bifurcation,only numerical simulation is alternative to describe all kinds of periodic, quasi-periodic and chaotic states.(2) The method of resonant parametric perturbations is introduced for the chaos control of DC-DC converters in chapter 7, with the advantages and disadvantages are given. To suppress the disadvantages, an improved method of resonant parametric perturbations based on Logistic map is presented in chapter 8, in which the parameter is perturbed by a periodic sine signal, and a additional disturbance of Logistic map is used. Thus, the converters operating under chaotic dynamics can be controlled to all kinds of periodic dynamics, and the quick switching of periodic states can also be achieved. Furthermore, in accordance to the same idea for chaotic control, an approach to chaotifying converters is proposed for the improvement of electromagnetic inference(EMI) in chapter 8, by which robust chaos can be achieved.The results of the studies in this dissertation are confirmed via circuit simulation or numeric simulation. Furthermore, two experimental circuits are built to verify the time-varying SMC in chapter 3, and the results prove the feasibility of the approach.This dissertation is supported by Guangdong Natural Science Fund (No. 990585) and Doctoral Education Fund of state Education Commission (No. 00056107).