Research On Isolated Buck-boost Converter With Active Rectifier

Wide voltage range isolated DC/DC converters have been widely applied to renewable power supply system,aerospace power supply system and electric vehicles.Comparing with isolated Buck or Boost converters,Buck-Boost converters can achieve higher efficiency in wide voltage range.However,traditional isolated Buck-Boost converters suffer from high voltage stress,high loss and limited soft-switching range.In order to solve these problems,the solution of isolated Buck-Boost converters based on active-boost-rectifiers are studied in this paper.In this paper,the method of developing the topology of isolated Buck-Boost converters with active rectifiers is studied.By integrating non-isolated Boost converters in isolated Buck converters with high-frequency diode-rectifier,the active-boost-rectifier is developed and a family of isolated Buck-Boost converters with active rectifiers is developed.The full-bridge converter with voltage-doubler is taken as an example to introduce the characters of converters of this family.The operating principle and characteristics of the converter under single-phase-shifting control are analyzed in detail.To improve the efficiency of the converter and achieve the ability to adjust the output power in the whole range,a dual-phase-shifting control strategy is proposed in this paper.Comparing with single-phase-shifting control strategy,the dual-phase-shifting control strategy can adjust power in the whole voltage range and load range and achieve soft-switching of all the MOFETs and diodes in the whole range,so the efficiency is improved.Afterwards,the active-boost-rectifiers are applied to LLC resonant converters which lead to a phase-shifting-controlled LLC resonant converter.The wide-voltage conversion is achieved by adopting phase-shifting control in this converter in which the operating frequency is fixed.So,the design of magnetizing inductance will not be restrict by the conversion ratio and the effect of current-circulation loss introduced by the magnetizing inductance on efficiency will be removed.The phase-shifting-controlled LLC resonant converters are well suited for front-end power server.The operating principle and characteristics of the converter under dual-phase-shifting control are analyzed and a 500 W prototype is built which verifies the analysis.