Piecewise-Approximated Time Domain Analysis of <i>LLC</i> Resonant Converter Considering Parasitic Capacitors and Deadtime
Ziheng Xiao, Zhixing He, Renfeng Guan, An Luo
Abstract
<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converters are widely used in high power density and high efficiency applications. Practically, the parasitic capacitors of <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s and diodes, the stray capacitor of the high frequency transformer, and the dead time will have a great impact not only on the steady state resonant waveforms but also on the zero voltage switching- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> (ZVS- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> ) of the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s. This article presents a piecewise-approximated time domain analysis of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> both considering the parasitic/stray capacitors and the dead time. On this basis, not only the accurate steady state resonant waveforms, but also the ZVS- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> boundary can be obtained, which will guide the parameter design, and switching frequency/dead time configuration instead of slow and cumbersome simulations. The major applications of the presented analysis, including the resonant/switching waveform illustration, the critical dead time calculation, and the optimal converter design are verified by a 500 W asymmetric half bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> experimental prototype.