Dc-dc Switching Converter Modeling Analysis And Variable Structure Control Method

DC - DC switching converters are time-variable nonlinear circuits. The power electronic specialists have constantly paid close attention to their modeling, steady-state analysis and control. The main purpose in this dissertation is to study DC - DC converters from a point of unified analytic view. Important aspects such as modeling, steady-state analysis with equivalent small parameter ( ESP ) method which can calculate the converter's ripples and DC value as well, and the application of sliding-mode control method are studied in this dissertation. A summation of the research is presented as follows:1. According to the circuit theory, a general and unified model is proposed for PWM DC-DC converters at continuous conduction mode ( CCM) and discontinuous conduction mode (DCM ), and mathematics expressions describing the converters are conveniently derived. In the model, the active switch and the diode are modeled by a time-variable nonlinear voltage source and a current source, respectively, which almost has the same topology as that of the switching converter under investigation. The physical explanation for the equivalent sources is given in the previous part.2. When the ESP method is applied to PWM DC-DC converters, a unified symbolic analysis algorithm is proposed by setting a mark which features the nonlinear function. The algorithm is simple and straightforward in comparison with other symbolic analysis. In addition, it is easy for computer programming.3. Based on the operation characteristic of half bridge series resonant converter, the modeling approach and algorithm previously proposed are extended to this type of DC-DC converter. A unified model is derived for CCM and DCM. Then the results of symbolic analysis are obtained.4. After the revision of various control schemes for PWM converters, a novel unified control scheme is proposed by using sliding-mode control for PWM converters at CCM. After compensating the sliding-mode errors and adjusting one of the control parameters in each period, the steady-state errors and chatting can be substantially reduced. A sliding-mode controlled Boost converter is used as an example to show the improvement of the converter start-up behavior. It proves to be stable even for large supply and load variations.In this dissertation, the results of numerical simulation verify those obtained by the symbolic analysis.The dissertation was supported by Guangdong Natural Science Fund, under Grant 940089; by the Doctoral Education Fund of the State Education Commission, under Grant 9456102.