| Single-phase AC/DC converters are widely used as the important device in electronic or electrical equipment.When AC/DC converters with only single step-up or step-down capability are used in applications where require wide input or output voltage,the range of output voltage is restricted and the efficiency is relatively low.The single-phase step-up/down AC/DC converter can solve this problem well,so it has been studied a lot.This dissertation combines the fully-controlled H-bridge with the Cuk converter,proposing a new AC/DC converter with low THD,low EMI and high PF,which can realize step-up/down conversion.This converter also has the advantages of less numbers of switches,simple structure and control method,etc.The contents are as follows:Firstly,according to the literature,this dissertation summarizes the structures and characteristics of the existing AC/DC converters with step-up/down capability.In addition,the EMI problems and solutions in AC/DC converters are summarized.Then,the structure of the new single-phase step-up/down AC/DC converter is described in detail,and the working modes of the converter in the DCM state are analyzed.Its circuit characteristics are also analyzed by formula derivation.Through the derivation of the common-mode noise model of the converter,the ability of the converter to suppress EMI is verified.Besides,in view of the zero-crossing problem of the input current of the converter,a new duty ratio compensation method is proposed.The above theoretical analyses are verified by simulation.After that,a dual-loop control is designed by modeling the converter.Considering the second harmonic ripple existing in the output voltage,a method of injecting the third harmonic at the duty ratio is adopted to reduce the ripple,and simulation results are also analyzed.Finally,according to software and hardware design,an experimental setup was built based on TMS320F2812.The experimental results prove the correctness of the theory and simulation results. |
