The Research On High Frequency DC/DC Converter Based On GaN Devices

In application of communication equipment and data center servers,miniaturized power supplies are widely used.High-frequency is an important method to increase the power density of power supplies.However,problems such as switching losses and parasitic parameters caused by high frequencies need to be analyzed and solved.In this regard,it can be considered from the following aspects:(1)Topology,select the topology that can achieve soft switching;(2)Semiconductor device: use semiconductor devices with fast switching speed and low loss.The development of third-generation wide bandgap semiconductor devices has made possible the further innovation of power electronics;(3)Magnetic design: magnetic element design is the core of switching power supply design.Reducing the size and loss of magnetic devices is very important for achieving high frequencies and miniaturization of power supplies.In this paper,according to the requirements of high-frequency and high-efficiency of the system,the half-bridge LLC resonant converter is selected.Taking full consideration of the influence of parasitic parameters at high frequencies,an improved circuit model for LLC considering the secondary side leakage inductance is established.The fundamental wave analysis method is used to analyze the DC characteristics of the improved model,compared with the traditional model,and an analytical method is used to analyze the topology of the model.Due to changes in the voltage gain caused by secondary leakage inductance at high frequencies,the system parameter design has also changed.Therefore,an optimized parameter design method is proposed to ensure the realization of soft switching characteristics of LLC resonant converter.In order to increase the power density of the system,a planar transformer that is small and easy to copy and suitable for high frequencies is used.However,with the increase of frequency,the effects of skin effect and proximity effects make planar transformer modeling difficult.This article uses a systematic modeling method to obtain more circuit parameters based on minimal assumptions.Combined with the analysis of parasitic capacitance and transformer loss theory,the model is optimized.By designing different parameter combinations,the optimal planar transformer structure is selected after analysis and comparison.To achieve good output voltage adjustment,this article adopts the extended description function method to build small-signal model of LLC resonant converter that consider secondary leakage inductance,and simplifies the resonant tank by studying the equivalent circuit of resonant capacitors.According to the obtained transfer function and Bode diagram,a double pole-double zero compensation network is designed to improve the dynamic characteristics of the system.At the same time,in order to overcome the limited frequency resolution of the digital controller at high frequencies,an effective hybrid control strategy combining PWM and PFM is proposed.Finally,in order to verify the accuracy of the theoretical analysis,according to the technical specifications,a prototype with a rated output power of 300 W is designed and built for testing and analysis.The rated input voltage is 48 V and the output voltage is 12 V.The efficiency at full load is as high as 95.2%.The experimental results are consistent with the simulation and theoretical analysis.