Research On GaN Based Soft Switching Interleaved Totem Pole PFC Converter

In order to meet the growing demand for high-performance power factor correction(PFC)circuit,totem-pole PFC circuit based on gallium nitride(Gallium Nitride,GaN)high electron mobility transistors(High Electron Mobility Transistors,HEMTs)has become the primary choice for single-phase,high-efficiency,and high-power-density PFC converters.On the one hand,the achievement of soft switching at high switching frequency has an important impact on the efficiency of the converter.On the other hand,the current ripple under heavy load limits the further improvement of system power,and the high switching frequency under light load limits the system efficiency and brings about control difficulties.Therefore,this paper focuses on the research of a GaN HEMTs based totem-pole PFC circuit to address the aforementioned issues.This paper first provides a detailed analysis of the operation modes of the softswitching totem-pole PFC converter,obtains the control degree of freedom to ensure its realization of zero voltage switching(ZVS),and the calculation formula for system turnon time control is modified to achieve better input current sinusoidal characteristics while implementing PFC.Subsequently,a control strategy for the soft-switching totem-pole PFC circuit without Zero Current Detection(ZCD)circuit is proposed to eliminate the effects of ZCD circuit transmission delay and false triggering.Furthermore,the off-time dynamic adjustment strategy based on the ZVS detection circuit is used to optimize the input current deterioration problem caused by the non-ZCD circuit and the calculation time of the control loop.Various optimization strategies are also presented to address issues such as the input zero-crossing spike of inductance current and input current phase lead problem.Secondly,the totem-pole PFC circuit operating in Critical Conduction Mode(CRM)suffers from issues such as high current ripple and difficulty in increasing power levels.This paper proposes a two-phases interleaved control for totem-pole PFC circuit to reduce current ripple.Additionally,the proposed technique also enhances the power level of the system.This paper provides an overview of open-loop and closed-loop interleaved control strategies for CRM mode totem-pole PFC circuit and analyzes the proposed control strategy of interleaved control in digital control to ensure stable 180° interleaving of the primary and secondary phase.Then,the switching frequency of the CRM mode totem-pole PFC circuit varies with the AC cycle,inductance value and load.In particular,there is a problem of excessively high switching frequency under light loads.This paper summarizes and analyzes the problems brought about by ultra-high frequency on the converter.It compares and analyzes the light load frequency limiting strategies under traditional Triangle Current Mode(TCM)and Discontinuous Conduction Mode(DCM)strategies,discusses their shortcomings,and proposes a Hybrid Discontinuous-Triangle Current Mode(D-TCM)light load control scheme to solve the problem of ultra-high frequency.Finally,the characteristics of GaN HEMTs are analyzed,and the GaN half-bridge module is optimized and designed.Based on this,an experimental prototype is built to test the proposed control strategy,thus verifying the correctness of the proposed approach.