Hysteretic control of LLC resonant converter for solar and dc-dc applications

Abstract

The growing popularity of LLC resonant converter in half-bridge implementation is due to its high efficiency and ability to achieve high power density. Zero Voltage Switching (ZVS) technique minimizes the turn-on loss of the MOSFETs. However, as switching frequency increases, the converter efficiency will suffer due to the increased turn-off loss and gate charge loss. These effects are especially problematic at light load conditions, where the switching frequency has to be further increased in order to regulate the output. A new hysteretic control scheme is proposed in this paper. By fixing the switching frequency equal to the resonant frequency and skipping pulses proportional to the load condition, the switching losses are reduced and the light load efficiency is improved. Moreover, the switching frequency range is limited and therefore wider line and load range can be achieved.