Hybrid control for high efficiency LLC resonant converter

Abstract

As the technology now-a-days advances, high efficiency Switched Mode Power Supplies are needed to deliver the power to the modern electronic devices. One such topology that promises high efficiency is LLC Resonant Converter. In typical DC-DC LLC Resonant Converter, the switching frequency of the Half Bridge Converter is operated around the resonant frequency to deliver the maximum power, as the impedance of the resonant circuit is minimum at the resonant frequency. Conventional resonant converters use Frequency Modulation (FM) for a closed loop feedback control in order to regulate the output voltage. The main drawback of FM is, the switching frequency has to be increased in order to regulate the output DC voltage at poor load conditions. As the converter is operated away from the resonant frequency, the switching losses increase at poor load conditions and efficiency of the converter decreases in this case. Therefore, in order to minimize the switching losses, another voltage control technique, Pulse-Width Modulation (PWM) is employed at poor load conditions to regulate the output voltage. In this typical DC-DC LLC resonant converter, a hybrid control strategy has been proposed where FM is used for heavy loads and PWM is used for poor loads to increase the efficiency of the converter over the entire load range. For this proposed system simulation results are carried out in MATLAB/ Simulink software to analyze the performance.