Improved Resonant Converters for Wide Voltage Range, High Current DC-DC and Universal AC-DC Applications
Data centers are the cornerstone of business in modern society and individual lives. Of similar significance to daily life is the external AC-DC power supply exemplified by the cell phone charger. In both applications, power converters play the key role. As the demand for high-performance-and-small-size power converters increases, resonant converters, have become dominant in the data center power systems, and are gaining popularity in the cell phone charging market. This thesis discusses three challenges in both applications – holdup issue, multiphase operation with current sharing in data center application, and universal AC input for the external AC-DC application. Aiming at these issues, several solutions have been proposed. Specifically, sLLC converter is proposed for holdup applications, and LCLC converter can be used in both holdup and wide-input-voltage-range applications. Both technologies can extend the operational input voltage range of the conventional LLC converters, while have no impact on the performance of normal operation. For the high current application, common-inductor and common-capacitor multiphase LLC converters are proposed to achieve current sharing without additional sensing and control. By adding one wire to connect the resonant inductors or the resonant capacitors in the conventional multiphase LLC converter, the current sharing performance can be improved from completely unshared to almost evenly shared. Following the paradigm of the common inductor and common capacitor LLC converters, the impedance matching concept is proposed to model the coupled resonant tank with de-coupled components. With the proposed impedance matching concept, the current sharing mechanism is explained from the input impedance point of view, and more topologies with current sharing ability have been found. For the universal AC-DC power supply, a new series resonant converter with capacitor bypassing method is proposed to significantly reduce the inductor size and loss. Besides, the performance is expected to improve thanks to the removal of switching loss and reduction of conduction loss as compared to existing technologies. In this thesis, the proposed theories are verified by physical and mathematical analysis and computer simulations. Circuit prototypes are built to demonstrate the effectiveness and advantages of the proposed topologies and design methods.