Automatic Resonant Frequency Tracking in Parallel LLC Boost DC–DC Converter

This paper proposes an automatic resonant frequency tracking scheme for resonant converters. A plant modeling approach is presented based on realistic ramp variation of resonant frequency due to slowly varying environmental conditions. The drift in resonant frequency is detected by observing the phase relationship of an electrical variable pair. A rigorous analysis is carried out to select the most suitable variable pair for phase comparison. The effects of circuit nonidealities on the proposed phase detection technique have been detailed. The proposed control technique has been implemented using low cost analog circuitry and is applied to a parallel LLC tank-based resonant boost dc-dc converter. Experimental results are presented on a 160-W prototype to validate the analytical predictions.