Owing to their soft switching capability, resonant converters are promising candidates for highfrequency operation and converter size reduction. However, as the range of input and output voltages that the converter needs to support gets wider, conventional resonant converters tend to have large amount of circulating currents in their resonant tanks and/or lose soft-switching across some portion of their operating range. To address this challenge, this thesis introduces new resonant converter architectures and control techniques that offer a wide soft-switching range with low circulating currents. For converters that need to support a wide output voltage range, an LCL-T resonant converter is proposed. This converter behaves like a current source and ensures soft-switching of all its inverter and rectifier transistors with low circulating currents at all output voltage levels. An automotive LED driver that needs to deliver a constant 0.5 A output current over a 3.3 V - 49.5 V output voltage range is built using the proposed LCL-T resonant converter topology. This 2-MHz prototype LED driver achieves a peak efficiency of 91.1%. A strategy to improve the dynamic performance of this LED driver is also proposed. An impedance control network (ICN) converter is proposed for applications with wide input voltage variation. The working of this converter is tested in the context of a universal-input adapter that needs to support an input voltage range of 90 Vrms – 265 Vrms. Phase-shift control strategies are devised that allow all the high-voltage transistors in this converter to achieve soft-switching with low circulating current throughout the line cycle across the entire input voltage range. An ICN-based universal-input adapter prototype is built and tested, and this prototype achieves a power density of 37.9 W/in3 and peak efficiencies of 92.2% and 93.2% at 120 Vrms and 230 Vrms input voltages, respectively. To further improve the performance of this converter, a reconfigurable-inverter design is introduced that effectively compresses the range of input voltages seen by the converter by a factor of two, by configuring the two inverters of this converter in parallel at low line and in a stacked fashion at high line. This new design helps reduce current and voltage stresses on the converter’s transistors and the improves the magnetics design. An active voltage balancing strategy for the stacked mode of operation of the reconfigurable inverter- based ICN converter is also introduced. A 300-kHz ICN based adapter prototype is built using the proposed reconfigurable-inverter design. This prototype achieves a peak efficiency of 94% at 120 Vrms and 93.8% at 230 Vrms, which are 23% and 9% better than the basic ICN ac-dc converter prototype, respectively, in terms of overall loss. Moreover, the reconfigurable-inverter prototype achieves a power density of 44.5 W/in3 which is 17% higher than the basic ICN ac-dc converter prototype. This thesis also introduces control strategies for soft-switching of all the inverter and rectifier transistors of the ICN converter. A phasor analysis of the ICN converter is performed to enable easier visualization of the operation of the ICN converter. Through this analysis, the soft-switching regions and minimum current operating point of the ICN converter are derived. Finally, an onboard EV charger is designed using the results of this phasor analysis and the losses in this converter are estimated.