Charge Mode Control For LLC Resonant Converters

High efficiency, high frequency and high power density are the development trend in DC/DC converter applications. Traditional PWM converter operates in hard-switched state. The switching loss increases sharply, the efficiency decreases and the power density is influenced as the switching frequency increases. Resonant converters solve these problems well. LLC resonant converter can realize zero voltage switching (ZVS) of the primary side switches and the zero current switching (ZCS) of secondary rectifier diodes within wide input voltage range and whole load range, solve the loss caused by the increasing frequency and reach more and more attention.The transient response of voltage-mode controlled LLC resonant converter is poor, due to the absence of current in its single voltage control scheme. The control schemes with fast dynamic response are studied in the paper based on voltage-mode contrlled LLC resonant converter. The current-mode control scheme and the charge-mode control scheme are derived by detecting tesonant tank current, so current-mode controlled LLC resonant converter and charge-mode controlled LLC resonant converter are derived. The charge-mode control scheme is researched in this paper. The construction of charge-mode control scheme and its operation principle are analyzed in detail. The operation principle, the dynamic regulation and the design principle of key parameters of charge-mode controlled LLC resonant converter are analyzed in detail.The experimental prototype of charge-mode controlled LLC resonant converter is built. The analysis is verified by the result of experiment. It is verified that charge-mode control scheme has better dynamic response by the experiment results of charge-mode control scheme and voltage-mode control scheme.