Multi-MHz isolated resonant dc-dc converters in wide-bandgap technology

Modern electronic systems require compact, energy-efficient power supplies, yet passive components - especially inductors and transformers - often dominate converter size. Increasing switching frequency reduces magnetic energy storage needs, but hard-switching losses grow with frequency, limiting efficiency at multi-MHz operation. Resonant topologies achieving zero-voltage switching (ZVS) mitigate these losses, while Wide-Bandgap (WBG) devices such as GaN and SiC enable high-frequency, high-power-density operation due to their superior breakdown field, lower parasitics, and higher thermal tolerance. This thesis explores the design, modelling, and control of isolated dc-dc converters operating at multi-MHz frequencies using WBG devices. A 140 W, 12 MHz isolated Class EF2 converter with an air-core PCB transformer is demonstrated, achieving 80.8% peak efficiency. A parasitic-aware workflow is presented, combining full PCB layout parasitic extraction with electromagnetic simulation to create a lumped equivalent model, accurately predicting performance and detuning from parasitics. Validation against VNA S-parameter measurements shows close agreement. A first-harmonic-approximation model provides the dc-dc voltage gain versus switching frequency, enabling frequency-modulation-based output regulation and supporting closed-loop control. Additionally, a 260 W (36 V, 7 A) 5 MHz Class E2 push-pull converter with a ferrite-cored transformer is designed, achieving 90% efficiency. Closed-loop control is implemented via MCU-based frequency modulation (5–7 MHz) and duty-cycle adjustment to maintain ZVS. Control-to-output transfer functions are estimated from simulated step responses for model-based controller tuning. The system maintains 90% efficiency over a wide load range (35–260 W) with output-voltage recovery under 200 µs and operates safely in regions where open-loop operation would fail. A qualitative analysis investigates the origin of the right-half-plane zero in the control-to-output transfer function and suggests that adopting a finite input-inductor design could eliminate it, enabling higher control bandwidth.