Research On High Frequency LLC Resonant Converter Based On Planar Matrix Transformer

The development of information technology industry puts forward new requirements for the efficiency and volume of data center server power supply.Increasing switching frequency is an important means to improve the power density of the converter.However,increasing switch frequency also brings challenges such as efficiency,and circuit performance.This thesis analyzes and optimizes the LLC resonant converter in terms of topology,magnetic design,closed-loop control and synchronous rectification for the characteristics of low-voltage,high-current and high-frequency operation of the server power supply,to design a high-frequency,high-power-density DC/DC converter,provides a new idea for the design of high frequency converters.Firstly,this thesis uses the description function method to analyze the current-voltage gain of the LLC converter,overcomes the shortcomings of the fundamental wave analysis error,and considers the resonant network to b e inductive and other factors,and analyzes the current voltage gains.This thesis using MATLAB software to draw the converter current and voltage gain curve,provides an important reference for the parameter design of the converter.At the same time,this thesis also analyzes the working mechanism of the converter,and focuses on analyzing the operating mode of the converter below the resonant frequency.It is proposed that the operating frequency range is designed to be lower than the resonant frequency,and the efficiency of the converter should be the highest.The transformer is the core component of the LLC resonant converter.According to the principle of magnetic integration,the structure of the magnetic baffle is inserted into the original secondary side of the transformer.The resonant inductance of the LLC converter is integrated into the transformer,and the magnetic circuit modeling and analysis of the transformer is carried out.The precise control of the leakage inductance of the transformer effectively reduces the number and volume of the magnetic components of the converter.On the other hand,in order to reduce the loss caused by the large current on the secondary side of the transformer,the transformer is designed in the form of a matrix transformer,and the number of cores is reduced by the magnetic flux cancellation.In order to further reduce the loss of the transformer,this thesis also optimizes the structure of the planar transformer winding,and uses finite element simulation software to analyze and design,and obtain a SPPS structure with smaller AC impedance.In this thesis,the extended description function method is used to analyze the small-signal modeling of LLC resonant converter.Based on the transfer function of LLC converter,the 2P2 Z compensator is designed to improve the dynamic performance of the converter.In addition,this thesis also studies the synchronous rectification of LLC converter under high frequency.In order to solve the problem of duty cycle loss caused by synchronous rectifier package inductance,an adaptive synchronous rectification scheme based on pulse counter is proposed,achieving high efficiency synchronous rectification with less CPU resources.Finally,this thesis builds a prototype with a resonant frequency of 1MHz and a rated power of 300 W.After experimental testing,the prototype can achieve soft switching within the full load range,with an efficiency of 95%.