| Abstract |
LLC resonant converters with high switching frequency can show high power density by reducing thesize of passive components, such as the output capacitor and transformer. However, it is difficult tooperate the PWM generator and at a high switching frequency. Moreover, soft start operation requiresmuch higher switching frequency than the nominal one. Therefore, this paper proposes a new soft startalgorithm to suppress high inrush current with limited switching frequency. In addition, stableoperation of the LLC converter at the high switching frequency is considered. GaN E-HEMTs areselected to achieve the high switching frequency operation due to its small drain-source resistance andsmall parasitic capacitance. However, GaN E-HEMTs also have different switching operationcharacteristics t. In this paper, the design and implementation of a 1 MHz LLC resonant converter areproposed to verify the improvement of power density reducing the passive component size. The softstart algorithm for high switching frequency is analyzed for small inrush currents at the cold startcondition. Simulation and implementation are used to verify the validity of the soft start algorithm.The side effects of high switching frequency operation are analyzed to design the power componentsand PCB. The high speed switching characteristics of the GaN E-HEMT are also analyzed to obtainproper operation for a half-bridge type LLC resonant converter using a boostrap circuit. Simulationand experimental results are presented to show the validity of the proposed analysis and designmethods with a 1 MHz prototype converter using GaN E-HEMTs. |
