State Trajectory Control of Burst Mode for LCC Resonant Converters With Capacitive Output Filter

LCC resonant converters have been widely adopted to achieve high power density and high efficiency. Due to high switching frequency and large reactive power in the resonant tank, the efficiency of LCC converters at light load decreases dramatically. Burst mode, which is commonly used in dc-dc converters to improve efficiency at light load, has not been applied to LCC resonant converters due to the oscillation of resonant tank during the burst off-time of burst mode. In this article, a simplified state model, which has only two state variables that can easily describe its state trajectory in the state plane, is proposed for LCC resonant converters with a capacitive output filter. Then, optimal state trajectory control of LCC converters for burst mode is proposed based on the state model, which can eliminate the resonance during the burst off-time. In addition, the transition from start-up mode to burst mode is proposed based on state trajectory control, which can complete this transition in one switching cycle. Finally, the proposed optimal trajectory control in burst mode is verified by an LCC converter prototype.