Research on onboard charger experimental platform based on GaN devices and magnetic integration technology
[Objective]With the development and increasing popularity of electric vehicles,portable onboard charger technology based on household power supply systems is receiving growing attention.Achieving high power factor,high efficiency,miniaturization,and high power density in onboard chargers is a critical challenge.At present,traditional Si metaloxide-semiconductor field-effect transistors(MOSFETs)are used as the main power tubes in onboard chargers,and magnetic elements are usually independent wire-wound magnetic elements,which limit the improvement of efficiency and power density.[Methods]This paper presents the structural design of a two-stage vehicle charger that utilizes a totem pole bridgeless PFC converter and a CLLC resonant converter.The totem pole PFC converter operates in continuous conduction mode,leveraging the excellent reverse recovery characteristics of GaN devices.Additionally,the fast switching speed of GaN devices increases the overall operating frequency,thereby reducing component size.Simultaneously,planar magnetic integration technology is utilized to design and produce a magnetic integrated planar transformer with controllable leakage inductance.This transformer utilizes the leakage inductance of its primary and secondary edges to replace the resonant inductance of the primary and secondary edges of the CLLC converter,thereby reducing the number of components and the size of the CLLC converter.This paper presents the design of the peripheral circuits and controller resources required for the experimental prototype of an onboard charger.A soft-start strategy is employed to achieve multiple control processes,from startup to stable operation.The overall system logic was designed,and a 2-kW onboard charger prototype was constructed.During the prototype start-up,we validated the effectiveness of the system's soft-start strategy by observing the recovery of the bus voltage and current overshoot when the PFC converter transitions from a no-load to a load state.The study examined the steady-state waveforms of the PFC converter at various input voltage frequencies and compared the critical experimental waveforms of the CLLC resonant converter at three output voltage levels to verify that the designed onboard charger meets the design specifications.Finally,the onboard charger's ability to regulate sudden load variations and its efficiency under constant voltage and constant current modes were validated.[Results]The experimental test results show that:1)GaN devices significantly enhance the power level of the totem pole bridgeless PFC converter,improving the efficiency and power density of the vehicle charger;2)the designed controllable leakage magnetic integrated planar transformer meets the design requirements;3)the designed vehicle charging system demonstrates good steady-state characteristics and dynamic regulation capability,with the performance of the entire machine meeting the design specifications.[Conclusions]This experimental platform helps students better understand the working principles,characteristics and applications of power electronic devices.It provides diversified and practical hands-on learning opportunities,integrating knowledge into teaching,injects new impetus and vitality into the school's teaching quality and ability,and cultivates excellent electrical engineering talents with all-round development.
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