As renewable energy systems and energy storage applications continue to expand, the demand for high-efficiency, high-power-density power converters capable of operating across wide voltage and power ranges has become increasingly critical. This thesis addresses these requirements by developing converter architectures, control strategies, and design methodologies to ensure compactness and high efficiency under wide operating conditions. First, to enable efficient energy harvesting from a solar thermoelectric generator (TEG), a multi-mode four-switch buck-boost dc-dc converter is proposed. Designed for a 5-15 V input, it efficiently delivers power to 3.7-V lithium-ion batteries and 5-V loads across four operational modes: buck, boost, buck with boost passthrough, and combined buck-boost. A 50-W prototype achieves an overall peak efficiency of 98.15%, utilizing optimized magnetics and robust gate drive circuitry. To enhance power density in ac-dc converters, a merged energy buffer architecture is also introduced in this thesis. This design incorporates series-stacked switchable capacitors for twice-line-frequency energy buffering. A simple control strategy, relying on the voltage of a single capacitor, ensures stable operation. A systematic optimization method reduces buffer volume by 17% in a 50-W/in³ 150-W LED driver. The thesis further investigates Impedance Control Network (ICN)-based converters for high-performance dc-dc and ac-dc power conversion applications. A bidirectional ICN-based dc-dc converter with a 200-400-V input and 12-V output employs a phase-shift control strategy to achieve near zero-current switching (ZCS), zero-voltage switching (ZVS), and output regulation. A 300-W converter prototype demonstrates a power density of 41 W/in³ with peak efficiencies of 93.7% and 93.3% during forward and reverse operation, respectively. A generalized phase shift control strategy is also developed for bidirectional ICN-based ac-dc converters to achieve power factor correction (PFC) and reactive power control. A 1.7-kW, universal input, 200-500-V output single stage ICN-based onboard electric vehicle charger prototype achieves a power density of 75 W/in³ and a peak efficiency of 93.5% and 92.4% during forward and reverse operation, respectively. Finally, the design and control of a dual-output ICN-based ac-dc converter is presented, enabling power delivery to both high-voltage and low-voltage output ports. The design methodology to optimally design this dual-output ICN converter is also presented. A 2-kW, universal input, prototype dual-output ICN-based ac-dc converter with 200-500 V and 9-15 V outputs achieves a power density of 60 W/in³.