Research On Half-Bridge LLC Resonant Converter

With the development of power supply technology,the requirements on volume,weight,efficiency and power density has also increased for power supplies in low and medium power applications.The high frequency conversion is an effective way to achieve the goals related to power supplies.However,with the increase of operating frequency,the traditional switching power supply technologies have problems such as low efficiency,large switching loss,high switching stress,and large EMI noise,which is a hurdle in making switching power supplies smaller and lighter.Because of the advantages of soft switch,the resonant converter has become a hot research topic.This thesis summarizes the topologies of commonly used resonant converters and analyzes the advantages and disadvantages and applications of various resonant converters.The LLC resonant converter has the advantages some advantages such as soft switching in the full load range,no reverse recovery of the secondary rectifier,wide range of input voltage,and easy to implement magnetic design.The other converters do not match these characteristics.The LLC resonant converter has high research value based on the requirement of high power density and efficiency in low and medium power switching power supplies.Firstly,the topology of double-resonant capacitive half-bridge LLC resonant converter is introduced.The specific working process of the converter in different frequency ranges is analyzed in detail.The process of charging and discharging of two resonant capacitors is explained in detail.For the purpose of analysis and calculation the equivalent steady state model of the converter is established using the fundamental wave approximation method.Based on these calculations a normalized voltage gain expression is acquired and a gain curve diagram is drawn.The effect on converter function while changing different parameters is analyzed.The influence of voltage gain on the performance of converter is also analyzed,that shows,that the inductor inductance has a greater influence on the gain of the converter than the quality factor.This conclusion provides the basics for the parametric design of the converter.Secondly,the basic control strategy of the converter is studied and the implementation of frequency conversion and voltage regulation technology is analyzed and verified by simulation.In order to improve the efficiency of converter,synchronous rectification technology is used in the drive circuit.For low-voltage and high-current applications,the pulse transformer push-pull drive circuit is finally selected to reduce the design of the secondary side driver power supply,which is conducive to the realization of high power density converter.In the end by considering all the theoretical analysis and specific design requirements an experimental prototype is designed.The parametric design flow,hardware circuit design and debugging process is elaborated in detail.The experimental results obtained from prototype match the theoretical analysis.