Synchronous Rectification Strategy of CLLC Resonant Converter Based on Accurate Time-Domain Model

Synchronous rectification (SR) is an effective method to improve the operating efficiency of CLLC resonant converter. However, implementing accurate SR directly in a CLLC resonant converter is challenging due to its complex mathematical model. To achieve high precision and low computational complexity SR in the CLLC resonant converter, this article proposes an SR strategy based on an accurate time-domain model. This SR strategy not only provides high accuracy but also exhibits low algorithmic complexity. The first step is to establish the time-domain model of the CLLC resonant converter for each operating mode and calculate the precise values of the SR angle. Then, the fitting formulas for the SR angle with respect to switching frequency and load resistance are derived based on the previously calculated SR angle values. Moreover, after analyzing the sensitivity of the proposed SR angle calculation method, the closed-loop control system of the CLLC resonant converter is designed using the aforementioned fitting formulas for the SR angle. Finally, the experimental results on a 2-kW CLLC resonant converter prototype are presented to validate the feasibility of the proposed SR strategy.