Circuit Topology And Control Technique Of Isolated Buck-Boost Converter With Clamped Inductor

The voltage of power devices, such as the solar array, fuel cell, thermoelectric cell,battery and capacitors, change in a wide range. The DC-DC converter which can operate in a wide voltage range has attracted the attention of scholars. Isolated buck-boost (IBB) converter has advantages such as input and output isolation, wide operating voltage range and soft switching. The converter contains switches in both primary-side and secondary-side, and its clamped inductor current changes linearly.There are various control strategies of IBB converter. The topology derivation and three control strategies of IBB converter are studied.Recently, several types of IBB topologies have been proposed and the basic derivation method of IBB converter has been reported in some papers recently, but they are imperfect in a sense. Based on the basic structure of IBB converter, the derivation rules and generation methods of primary-side and secondary-side circuits are proposed,and the synthesizing method of IBB converter is given. A series of IBB topologies are derived, and theses topologies cover all kinds of topologies in the previous and have some new topologies. And the converter topology can be generated according to the actual design requirements. The voltage levels of IBB converters are classified, and the appropriate control strategies are proposed.IBB converter contains full bridge circuit in the primary-side, and full bridge rectifier with switch-leg in the secondary-side. Under dual-phase-shift control,the converter can achieve soft switching and regulation in full voltage range and load range.In order to analyze the operational principle clearly, the division of operational areas and three-dimensional graphs of the output current versus two control variables are given. Before providing the optimal dual-phase-shift control strategy, theoretical analysis of and peak current RMS current of the clamped inductor are investigated. The optimal operating point is determined by the peak current of the clamped inductor, and shown as trajectories in the three-dimensional graphs. Furthermore, the parameter design method deriving from the lowest peak current of the clamped inductor is presented. Finally, the performances of the converter are improved.With variable switching frequency, IBB converter can operate at boundary current mode (BCM) mode or discontinuous current mode (DCM) in full range. The converter can achieve good soft-switching performance, and can avoid the current flowback in continuous current mode (CCM), and can improve the efficiency. The variable frequency control strategy contains three control variables is proposed. Three control variables are simplified by replacing as two variables. The optimal operating point with the lowest peak current of the clamped inductor is given. Full range control strategy with variable frequency BCM, constant frequency BCM and variable frequency DCM can realize smooth transition of IBB converter. Moreover, the parameter design method is put forward.Hybrid three-level full-bridge IBB converter is the new derivate topology, which contains hybrid three-level full-bridge circuit in primary-side and full bridge rectifier with switch-leg in secondary-side. The voltage levels of the new converter are increasing, and the operational principle and the control strategy of the new converter both need to be studied. The operational modes are limited to BCM and DCM, and the direct control variables are declined, and the analysis is simplified. The optimal operating point with the lowest peak current of the clamped inductor is proposed. In addition, the switching performance, the output characteristics, and design considerations of the proposed converter are presented in detail. Finally, the operating voltage range of the converter with high efficiency is widened.The realization methods of the three control strategies are put forward separately,and the experimental results are given to verify the effectiveness of the proposed control strategies. These control strategies can be used into other IBB converter derivations.