Research On High Frequency Multiresonant DC/DC Converter Based On Planar Magnetic Elements

Achieving high efficiency,high power density,miniaturization,integration and light weight have always been the goals pursued by switch mode power supply.Adopting a resonant soft-switching topology,increasing the converter’s operating frequency and applying planar devices are effective ways to achieve the above goals.Over the years,with the commercialization of silicon carbide and gallium nitride power semiconductor devices and the application of soft switching technology,switching power supplies have successfully embarked on the road of high-frequency development.In terms of applications,aviation secondary power supplies,electric vehicle chargers,etc.not only require high efficiency and high power density,but also need to meet a wide input voltage range.This subject is based on the development and application background of the abovementioned hardware technology,and carried out the research of LLC-LC high frequency multi-resonant DC/DC converter with wide input voltage range function.Resonant converters are widely used in DC/DC converters due to their good soft switching characteristics.Based on the topology of the LLC resonant converter,in order to transmit the fundamental and third harmonic energy at the same time,the LLC-LC multi-resonant DC/DC converter topology is constructed.The impedance characteristics of the two resonant cavities are compared and analyzed,and it is found that the multiresonant cavity has two resonant frequencies and has the natural functions of soft start and overcurrent protection.The fundamental wave analysis method is used to obtain the DC voltage gain curve,and the influences of the quality factor,inductance coefficient and transformer magnetizing inductance on the voltage gain and operating characteristics of the resonant converter are discussed separately,and the effect of variable frequency control is studied.Based on the voltage gain curve,a practical method for parameter selection and optimization of multi-element resonant converters is proposed.It is found through circuit simulation results that this parameter selection method is effective.In order to enable the converter to be used in a high-frequency environment,SiC MOSFET is selected as the power semiconductor switching device of the inverter bridge.In order to ensure the stable and reliable operation of the device,double-pulse test simulation was carried out using LTspice software to explore the influence of drive resistance and parasitic inductance on the drive circuit.The simulation results show that reducing parasitic inductance can significantly reduce the voltage oscillation between gate and source.A drive circuit suitable for SiC MOSFET was designed,and the experiment fully verified the feasibility and stability of the drive circuit.In addition,the use of planar transformers to reduce the volume and weight of magnetic components is conducive to improving the power density of the system.The influence of the winding layout of the planar transformer on the parasitic capacitance is analyzed,and it is found that the winding dislocation distribution can minimize the parasitic capacitance.Using Faraday’s law of electromagnetic induction and other related electromagnetic field principles,a basic process for calculating and designing a planar transformer is given.The equivalent parameters of the designed transformer are extracted by Maxwell 3D eddy current field simulation,and the simulation results are consistent with theoretical calculations.Before the hardware experiment,the open-loop and closed-loop control simulations of the designed converter were carried out using PSIM software and the corresponding results were analyzed.The simulation results are consistent with the conclusions drawn from the theoretical analysis.Finally,an experimental prototype with working frequency of 500 k Hz,input voltage of 270 V and rated output power of 300 W was designed and built.The experimental results were basically consistent with the results of software simulation and theoretical analysis,which fully verified the correctness of theoretical analysis and the feasibility of experiments on this multi-resonant converter.