Design And Eifficiency Optimization Of Planar Magnetics In 1-kV 6.6-kW SiC LLC Converters

Tethered UAVs are powered by special cables.Compared with other kinds of UAVs,they can achieve longer endurance time and capability of carring large load.In order to reduce the transmission loss and cable weight,the power supply bus voltage is rising constantly,so the airborne device needs to realize the transformation of high input voltage to low voltage required by the equipment,and realize high power density.LLC converter can meet the requirements of high power density and high reliability because it can realize ZVS of primary side and ZCS of secondary side.As the most important factor affecting the power density of LLC topology,the design of magnetic components is very important.Compared with traditional Si devices,SiC devices have higher withstand voltage,smaller on resistance and junction capacitance,which makes it convenient to realize high efficiency and high power density of LLC converter.However,with the introduction of SiC devices,the voltage and current level of the converter will increase rapidly.The parasitic capacitance of planar magnetic components and the negative effect of insulation on the winding area will greatly limit the improvement of converter performance.Therefore,the main topic of this paper is to deal with the negative effects and to design the planar magnetic components for high voltage,medium and high power applications.In view of the reduction of parasitic capacitance between turns,this paper analyzes the influence of dv/dt on the realization of soft switch caused by displacement current in this capacitance.The topology of LLC with separated resonant tank is adopted to balance the impedance of two conduction paths of displacement current,which effectively suppresses the current distortion and improves the realization of ZVS.In view of the negative effect of insulation distance on the effective winding area in high voltage situation,this paper analyzes the relationship between the number of turns required for the winding of magnetic components and the change of power and input voltage,and proposes an interleaved winding connection scheme.By setting the winding connection points in an interleaved way,the number of insulation gaps required for the winding group is effectively reduced,and the power density of magnetic components is improved.Aiming at the problem of LLC topology efficiency optimization,this paper summarizes the existing LLC topology design methods and proposes a resonant parameter design method,which can make LLC topology work at the highest efficiency point.A prototype of SiC LLC with 1 kV input and 48 V/4.4 kW output was built to verify the effectiveness of the separated resonant tank LLC topology.The full load efficiency of the prototype can reach 95.9%,and the power density is 63.4 W/in~3.Based on the 4.4 kW prototype,the SiC LLC prototype with 1 kV input and 48 V/6.6 kW output is built,which verifies the feasibility and effectiveness of the interleaved winding connection scheme.The efficiency of the prototype at 1 kV input and 6.6 kW output is 95.64%,and the power density is close to 100 W/in~3.