LLC DC/DC Resonant Converter with PLL Control Scheme

This paper proposes a capacitively loaded loop (LLC) DC/DC resonant converter with phase-locked loop (PLL) control scheme. The PLL control scheme enables the switching frequency of the converter to continuously track the resonant frequency of the LLC resonant tank by detecting the phase signals of the input and transformer secondary output voltages of the LLC resonant tank. Based on this resonant frequency, the switching frequency is adjusted to obtain the required voltage gain. However, because the operating frequency will not be lower than the resonant frequency of the LLC resonant tank, the switches of the inverter are both operated in zero-voltage-switching (ZVS) condition so that the turn-on switching losses are reduced. The proposed 200W LLC DC/DC resonant converter with PLL control scheme is then designed and implemented to validate and demonstrate the performance and feasibility of the proposed DC/DC converter.