A Digital Synchronous Rectification Control Strategy With Duty‐Ratio Compensation for LLC Resonant Converters

ABSTRACT Synchronous rectification (SR) technique can significantly enhance the efficiency of LLC resonant converters. However, at high frequencies, SR control strategies based on drain–source voltage suffer from substantial duty ratio loss due to the influence of parasitic inductance, thereby limiting further efficiency improvements. To mitigate duty cycle loss at high frequencies, this paper proposes a digital control strategy for switching timing adjustment by compensating the lost conduction time. To achieve this aim, the mechanism of duty ratio loss at high frequencies is analysed and a mathematical model is developed to quantify the lost conduction time across different loads and frequencies in real time. The synchronous rectifier's conduction time is then compensated and optimized by a digital signal processor. Additionally, the issue of premature turn‐on of the synchronous rectifier under light load conditions is addressed by adjusting the turn‐on timing in real time according to load variations, thereby preventing reverse current flow. The SR control strategy is well‐suited for high‐frequency and wide‐load applications, offering low cost and algorithmic simplicity. Experimental results from a 6kW full‐bridge LLC resonant converter prototype validate the feasibility of the proposed SR control strategy, showing a 0.21% increase in peak efficiency compared to traditional SR control strategy.