Study On LLC Resonant Converter With Magnetic Control

Due to its characteristics of wide input voltae and output voltage range and soft switching capability,LLC resonant converters have been widely used in many applications like server power supplies,LED drivers,laptop adaptors and on-board battery chargers.Different analysis methodologies will have an influence on the converter's parameter design,and even the practical performance.For LLC resonant converter,it mainly has four analysis methodologies,namely: 1)fundamental harmonic analysis(FHA);2)frequency domain with time domain partial correction;3)frequency domain with time domain complete correction;4)time domain analysis.However,there is no literature focusing on the systematic review and comparison of these different analysis methodologies,and there is no guideline for the applications of these different analysis methodologies.Therefore,the study of these different analysis methodologies of the LLC resonant converter is meaningful.To regulate the output of the converter,the frequency modulation(FM)or phase shift modulation(PSM)techniques are mostly adopted.However,for wide input voltage and wide output power applications,LLC resonant converters are required to operate in a wide switching frequency range,which causes problems to design magnetic components and degrade the system EMI performance.In addition,for the phase shift modulation,high turn-offf current for the primary switches and difficulty to achieve zero voltage turn on will lead to low efficiency.However,magnetic control or variable inductor control can regulate the output by keeping the switching frequency and duty cycle constant,which makes the design of magnetic components simple.However,few publications are focusing on the analysis and design of the LLC resonant converter with magnetic control.In this paper,based on the LLC resonant converter,a detailed analysis and comparision of these four different analysis methodologies have been implemented;then,combined with magnetic control,an optimal design methodology for LLC resonant converter with magnetic control is proposed;in addition,a dual half-bridge LLC resonant converter with magnetic control is proposed for the battery charger application.The followings are the main content of this paper:Firstly,the four different analysis methodologies of LLC resonant converter has been introduced briefly;then,based on the voltage gain error and peak gain frequency error,a detailed comparison among these four methodologies has been presented;finally,according to the theoretical analysis,the recommended applications for different analysis methodologies are summarized.Secondly,based on the time domain analysis and magnetic control,an optimal design methodology for LLC resonant converter with magnetic control is proposed.By adopting the proposed method,the LLC resonant converter's operation mode can be assured;in addition,zero-voltage switching(ZVS)for the primary switches and zero-current switching(ZCS)for the secondary diodes are guaranteed;meanwhile,the resonant network RMS current is limited to further improve the system efficiency.Finally,based on the magnetic control,a dual half-bridge LLC resonant converter is proposed for the battery charger application.The half-bridge inverter is shared between two resonant networks,and the outputs of two rectifiers are connected in series.Then,the operation analysis of the proposed dual half-bridge topology is presented;and the circuit parameter design is implemented by using FHA;finally,the experimental reults from a 320 W prototype are presented and analyzed.