Research On High Voltage Ratio DC/DC Converter Based On LLC Circuit And TSC Buck Circuit

With the continuous updating of power electronic technology,terminal equipment such as DC microgrid,new energy power supply and data center server are also being continuously promoted.Nowadays,the world is generally faced with energy shortages and environmental crises.The cascaded power supply system widely used in data centers that consume more than 10% of electrical energy consumes a lot of energy in the process of electrical energy distribution.Therefore,how to improve the efficiency of power supply systems with high step-down ratios such as data center servers and solve the problems of equipment structural redundancy have become key technical points to be solved urgently.Although many scholars at home and abroad have proposed various highefficiency single-stage DC/DC converter topologies.However,these topologies generally have relatively low input voltages.And the system efficiency and reliability are deteriorated at a higher step-down ratio condition.In this research context,this paper has designed a high step-down ratio DC/DC converter to provide new design ideas for data center to reduce equipment volume and achieve efficient work combined with the lowvoltage and high-current load requirements of the data center.First of all,this paper carries out detailed modal analysis on the two parts of the high step-down ratio DC/DC converter.on the basis of the overall introduction of the topology In addition,for the LLC part responsible for transmitting power,this paper analyzes that the influence of the secondary side leakage inductance on the circuit gain is not negligible under the condition of high step-down ratio.On this basis,MAXWELL Q3 D Extractor is used to optimize the layout of the secondary side devices to reduce the gain error caused by the loop inductance.Regarding the TSC(Tapped series capacitor)Buck circuit,this paper demonstrates that the AC component of the resonant capacitor is much smaller than the DC component when the design leakage inductance is much smaller than the magnetizing inductance through mathematical deduction,and a simplified step-down conversion ratio formula and device stress expression are given on this basis.Finally,this paper gives the design process of key device parameters in the system combines design indicators and theoretical analysis.As the core component of the system,design and optimization of the planar transformer determine the quality of the final prototype.First of all,this paper introduces the brief design process of planar transformers,which provides the duidance for the design of matrix transformers and coupled inductors.After that,this paper gives a detailed description of the magnetic integration process for the matrix transformer of the LLC part.The winding configuration with less influence of parasitic parameters is obtained combined with MAXWELL simulation.An optimized winding method is proposed to reduce the number of vias,AC impedance and occupied area.Besides,the variable width design method is adopted for the coupled inductor in the voltage regulating circuit,and the winding configuration is optimized in combination with MAXWELL simulation.This paper uses the state space averaging method to establish an AC small signal model on the basis of reasonable assumptions regarding the voltage regulating circuit part,and adopts 3P2 Z compensator to design a suitable system compensation network link,which effectively improves the dynamic response capability of the system’s digital control.Finally,an experimental prototype with rated 400 V input and 5V/20 A output was established.It is determined that all switches of the system under the input range of360～440V can meet the soft switching characteristics through experiments,and the corresponding voltage and current waveforms are basically in agreement with theoretical analysis and simulation.The efficiency reaches 91.5% under rated operation.