A Novel Synchronous Rectification Scheme With Low Computational Burden for <i>LLC</i> Resonant Converter in EV Charger Applications
Chenghao Sun, Rui Wang, Qiuye Sun, Huaguang Zhang
Abstract
In EV charger applications, high voltage level and high computational burden caused by multiple charging modes bring serious challenges to the synchronous rectification (SR) of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter. Conventional SR schemes can be classified as current sensing-based, voltage sensing-based, and sensorless, which are limited by high cost of current sensing, difficulty of high voltage sensing, narrow operating range, or high computational burden, respectively. To deal with these problems, this article proposes a novel SR scheme for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant converter in EV charger applications. In this scheme, SR control signals are tuned only by main control signal, output voltage, and output current, which are naturally available from main controller in EV charger. To this end, no additional signal sensing is required and the cost for SR is reduced. Moreover, the SR tuning principle is on the basis of Kirchhoff's law and phase relationship between main control signal and secondary-side current, which no longer needs to calculate complicated models. Meanwhile, the foresaid tuning process of SR control signals can be implemented by analog circuits. With these effects, this scheme can tune SR control signals effectively over a wide operating range with low computational burden. Furthermore, a virtual current injection strategy is designed to suppress the inversion current of synchronous rectifier. It can guarantee no inversion current and low body diode conduction (BDC) loss. A 600-V input 200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 300-V output <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> prototype converter is built to verify the proposed SR scheme.