Hybrid Modulation of Frequency and Phase Minimizing Switching Loss for LC Resonant Converter

Rapidly developing household energy storage systems raise the demand for corresponding DC-DC converters. Although topologies like LLC have already achieved good performance in these large-power and wide-voltage-range applications, they still have shortcomings in dealing with low-voltage battery cells. When converting from low voltage to high voltage, conventional methods can hardly control output current well when the normalized voltage gain is greater than one. Moreover, they cannot ensure a constantly small turn-off current on the low-voltage side over various working conditions, which affects efficiency and stability. To overcome these drawbacks, the paper proposes a hybrid strategy combining frequency and phase modulation for LC resonant converters. First, the theoretical model of the proposed method is constructed and analyzed. Second, a circuit is built and the proposed method is implemented, which is subsequently tested at different working conditions. As the experimental result, the actual output current is close to the expectation and the turn-off current is nearly a small constant at all the working conditions. Hence, the proposed modulation strategy is verified to solve those drawbacks. Furthermore, based on this method, close-loop output current and voltage controller will also be easier to design.