Surge Current Analysis and Reduction in LLC Resonant Converter With a New Hybrid Control Strategy of Pulse-Frequency Modulation and Phase-Shift Modulation

Fast charging of high-capacity battery packs contributes to more disruptions in ac-powered systems, thereby increasing the demand for intelligent converters that are both efficient and low in distortion. Therefore, it is crucial to have a battery charger that can respond to the battery's current condition and modify the charging procedure accordingly. To accommodate a wide battery voltage range in on-board battery charger (OBC) applications utilizing LLC resonant converters, a hybrid control technique that combines pulse-frequency modulation (PFM) with phase-shift modulation (PSM) has been proposed. It is. assumed that the input voltage of the LLC converter experiences a 100-Hz fluctuation as a result of power factor correction at the front-end power rectifier. When the control modes change between PSM and PFM due to input voltage fluctuations, a surge current is observed in the output current, which causes heat generation and battery deterioration. In addition to that, a change in the output gain of the main circuit has been confirmed. To mitigate this issue, a novel control state transition strategy known as overlapping mode of operation is proposed for the LLC resonant converters employing PSM and PFM. The experimental findings validated the reduction in surge current and showed that the proposed control method is effective in comparison to the conventional hybrid method.