Optimization the LLC resonant converter for achieving maximum efficiency at a predetermined load value

In this paper, a new approach for optimizing the LLC resonant converter for achieving maximum efficiency in a desired load is proposed. Generally, the optimum value of the load is chosen near the full load condition to reduce the converter overall cost and consumption. Beside the inductor and transformer core and copper losses, the conduction and switching losses of the power switches and diodes and the converter capacitors ESR losses are also considered. In the given approach, the switching frequency variation range for regulating the output voltage is minimized, too. To verify the given analyses, a wide variable range input voltage (350-400 Vdc) LLC resonant converter has been simulated. When the converter output load changes from 100 to 500 watts, its switching frequency varies between 1 and 2 MHz to regulate its 50V constant output voltage. Maximum efficiency value of 94% has been achieved for the simulated converter.