Research On The Wide Input LLC Resonant Converter

Thanks to LLC topology’s merits of achieving both zero-voltage switching in primary side and zero-current switching in secondary side,it has been widely used in LED lighting and communication power supply.With the development of renewable energy resouces,it makes new demands on DC/DC converter,that is the DC/DC converter can operate on wide input voltage range.The LLC resonant conveter with VF control can not operate on wide input voltage range because of its own characteristics.When the switching frequency is above the resonant converter,the rectified diodes can not realize the ZCS switching.Therefore,many scholars study on it in recent years.Based on this background,the wide input LLC resonant converter will be studied in this paper.The main research objects of this paper are as follows.Firstly,several ways are came to widen the input range based on the research background of the wide input voltage LLC resonant converter.Secondly,a new hybrid control strategy is proposed base on the full bridge LLC resonant converter.This control strategy combines traditional variable frequency control with variable frequency and phase shift control which proposes in this paper and makes the full bridge LLC resonant converter can operate in the wide input-voltage-range.By using this control strategy,all switches can realize the zero-voltage switching,and the rectified diodes can achieve the zero-current switching,in the meanwhile,the current flow through the secondary side rectified diodes operates in the boundary of continuous-discontinuous current mode,which improves the converter efficiency.Thirdly,a multi-level control strategy is proposed based on the dual bridge LLC resonant converter.By changing the bridge arm midpoint voltage level to widen the input voltage range.In this paper,the detail operation principles and characteristics of the two control strategies are discussed.And by using the mathematical tool to get the voltage gain curves of the two control strategies.Finally,a 500W prototype is built to verify the correctness and effectiveness of the strategy respectively.