Improved LLC Resonant Converter with Rectifier Operating in Three Operation Modes for Wide Voltage Range Applications

When the input or output voltage range of the LLC converter is wide, the switching frequency must extend its range to cover the required voltage, and the magnetizing inductance needs to be reduced to increase the voltage gain. This leads to reduced efficiency due to increased conduction losses. Consequently, this paper proposes an LLC resonant converter with a wide voltage range based on a reconfigurable voltage rectifier for high-DC bus applications. Owing to the reconfiguration of the rectifier by two active switches, the rectifier can operate in three operation modes— voltage-doubler rectifier, a voltage-tripler rectifier, and a voltage-quadrupler rectifier. The proposed converter extends its voltage gain by changing the rectifier structure while the switching frequency operates near the resonant frequency. All MOSFET switches are turned on with zero-voltage switching, and all secondary diodes are turned off with zero-current switching. As a result, the performance efficiency is improved compared to that of the conventional LLC converter. A laboratory prototype was designed and experimentally tested to validate the operation and advantages of the proposed converter.