Research On High Power LLC Resonant Converter Optimization

LLC resonant converter has been widely utilized in DC small and mediumpower supply due to its well known advantages of high efficiency, high powerdensity and low level of EMI emission. With LLC resonant converter being moreand more popular in high power applications, it is very interesting that highpower LLC resonant converter considering parasitic parameters is analyzedcomprehensively. And the research contents in this thesis are as follows.In response to high power applications, topology with full bridge switchnetwork and full bridge rectifier is chosen. With parasitic parameters considered,LLC resonant converter’s non-ideal steady-state model is created, FHA (FirstHarmonic Approximation) is utilized to analyze component voltage stress,current stress and power loss. Converter non-ideal voltage gain characteristic isderived, compared with that in ideal converter, and parasitic parameters’ impacton voltage gain and efficiency is analyzed. An efficiency estimation method isgiven, and corresponding optimal proposals and design guideline are introduced.After popular power conversion modeling methods have been compared,time domain simulation method is chosen to create LLC resonant converter’snon-ideal switching circuit model. Open loop AC frequency sweep utilizingPSIM is carried out for ideal and non-ideal LLC resonant converter in differentload and switching frequency, the corresponding AC small signal characteristicsare obtained and parasitic parameters’ impact is analyzed by comparison betweenideal and non-ideal condition. With AC sweep result and traditional controltheory used, a controller is implemented and its performance is verified byexperimental data of Network Analyzer AC sweep. The reliability of timedomain simulation method is verified too.Power stage including a novel CLC output filter, output rectifier,transformer, resonant tank and switch network, and control stage areimplemented. The output voltage steady characteristic, dynamic response andZVS (Zero Voltage Switching) are verified by experiment, and CLC output filterperformance is verified by simulation. The experimental and simulation results are in agreement with the theoretical analysis and the optimal proposals in thethesis are quite feasible.