Bus converter employing LLC converter operating with variable switching frequency

In this paper, a bus converter employing LLC converter operating variable switching frequency is proposed. Resonant tank devices have a tolerance with manufacturing process and operating that could induce a lower efficiency converter. To keep an optimal operating, switching frequency should track the resonant frequency by tracking control. In this technique, the voltage across secondary rectifier diode compare with the output voltage to control the switching frequency. The validity of this study is confirmed by the experimental results from a prototype with 1.35kW, 385V input, and 54V output.