Accurate ZVS boundary in high switching frequency LLC converter

Due to the realization of zero voltage switching (ZVS) under the full load range, LLC resonant converter is widely adopted in the telecom, battery charger and several applications, characterized with high efficiency, high frequency and high power density, to realize DC conversion. Recently, by using Gallium Nitride (GaN) HFETS, switching frequency of LLC converters is further increased. However, ZVS failure cannot be predicted accurately in the high switching frequency condition by only considering traditional constraints generally applied in the low frequency design. The traditional constraints result in a too optimistic estimation of the dead time to obtain ZVS without considering the reverse resonance under the dead time and the design of resonant parameters at high resonant frequency and high load condition. The experiment shows the LLC converter loses ZVS even through the converter satisfies the ZVS constraints proposed by previous paper. In this paper, the failure mode will be investigated in detail and an accurate ZVS boundary is proposed for high frequency LLC converter design. The proposed theory was verified on a 1 MHz, 1500 W LLC prototype.

[1]  Fred C. Lee,et al.  LLC Resonant Converter With Matrix Transformer , 2014 .

[2]  T. Duerbaum,et al.  ZVS investigation of llc converters based on FHA assumptions , 2013, 2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference and Exposition (APEC).

[3]  Hui Chen,et al.  Analysis on the influence of the secondary parasitic capacitance to ZVS transient in LLC resonant converter , 2014, 2014 IEEE Energy Conversion Congress and Exposition (ECCE).

[4]  R. Elferich,et al.  General ZVS half bridge model regarding nonlinear capacitances and application to LLC design , 2012, 2012 IEEE Energy Conversion Congress and Exposition (ECCE).

[5]  T. Ninomiya,et al.  5MHz PWM-controlled current-mode resonant DC-DC converter using GaN-FETs , 2014, 2014 International Power Electronics Conference (IPEC-Hiroshima 2014 - ECCE ASIA).

[6]  E. Janssen,et al.  Design of a 1-MHz LLC Resonant Converter Based on a DSP-Driven SOI Half-Bridge Power MOS Module , 2007 .

[7]  Yan Liang,et al.  Optimal design methodology for LLC resonant converter , 2006, Twenty-First Annual IEEE Applied Power Electronics Conference and Exposition, 2006. APEC '06..

[8]  Weimin Zhang,et al.  Evaluation of 600 V cascode GaN HEMT in device characterization and all-GaN-based LLC resonant converter , 2013, 2013 IEEE Energy Conversion Congress and Exposition.

[9]  Jee-hoon Jung,et al.  Theoretical analysis and optimal design of LLC resonant converter , 2007, 2007 European Conference on Power Electronics and Applications.