Design Of Half-bridge LLC Resonant Type AC/DC Converter

Under the impetus of the new power semiconductor device,the switching power supply technology has made a breakthrough progress.Therefore,the switching power supply is applied more and more widely.The demand for switching power supply is becoming more and more stringent.Power equipment is developing in the direction of high efficiency and light weight.The lightening of the power supply can be achieved by increasing the switching frequency.But the increase of switching frequency will cause the decrease of efficiency.And the problem of having a lower power factor and the power grid pollution still exists in power supply.So the high-quality technology on AC/DC transform has become a new research hotspot.In order to achieve green and high efficiency use of electricity,a two-stage AC/DC converter structure which includes power factor corrected as the first stage and a soft-switched DC/DC as the second stage is proposed in this paper.Compared with the single-stage AC/DC converter,the structural performance is more superior.Firstly,compare with the advantages and disadvantages of passive power factor correction and active power factor correction,it is determined that the previous stage adopts the active power factor correction(APFC)program.BOOST circuit is used in active power factor correction,working in critical mode(CRM).In-depth analysis circuit mode of CRM mode and take the method of peak current as the control method by comparing the common control methods of PFC circuit.Secondly,speaking of the development of resonant technique,research on several traditional resonant techniques,and their advantages and disadvantages are given by comparison and analysis to determine the level after the use of LLC resonant converter.The operation principle of the resonant circuit under three different switching frequencies is analyzed.The LLC equivalent model is established based on the fundamental wave equivalent principle,and derive Q and K value expression to analyze its influence on converter performance,then analyze the DC gain characteristics and short circuit characteristics of the converter to determine the conditions of the primary switch to achieve ZVS and secondary rectifier diode to realize ZCS and design the parameters of the resonant tank and the high frequency transformer by calculate the value of K and Q.In addition,we design the control circuit and the front and back main power circuit based on the above programs and principles,the circuit is verified by the saber simulation software.Finally,based on theoretical analysis and simulation research,a prototype of AC/DC converter is built.The different working conditions of the prototype are tested,and the measured data and waveform are analyzed.