Advances in Very High Frequency Power Conversion

Resonant and quasi-resonant converters operated at frequencies above 30 MHz have attracted special attention in the last two decades. Compared to conventional converters operated at ~100 kHz, they offer significant advantages: smaller volume and weight, lower cost, and faster transient performance. Excellent performance and small size of magnetic components and capacitors at very high frequencies, along with constant advances in performance of power semiconductor devices, suggests a sizable shift in consumer power supplies market into this area in the near future.

To operate dc-dc converter power devices at very high frequencies, switching loss needs to reduced or eliminated, as it would become prohibitively large. In addition, as the frequency increases, hard-switched gate driving becomes less and less of an option, as it embodies the same loss mechanism. A low-loss gate drive methods may need to be applied, especially at low power levels where gating loss becomes a significant percentage of the total loss budget.

Various resonant gate drive methods have been proposed to address this design challenge, with varying size, cost, and complexity. This dissertation presents a self-oscillating resonant gate drive solution, which is applicable in cases when there are at least two power stages, and with minimal additional hardware requirements.

It is experimentally confirmed that the method is suitable for both parallel and serial input configurations. Compared to state-of-the-art solutions, the proposed method provides low complexity and low gate loss simultaneously. A direct design synthesis method is provided for resonant SEPIC converters employing this technique.

Most experimental prototypes were developed using low cost, commercially available power semiconductors. Due to very fast transient response of VHF converters, on/off control schemes are often used for their output control. The options presented so far demonstrated excellent performance, but with very strict timing constraints on all functional blocks in the feedback loop.

Therefore, an on/off control method is proposed which allows the use of conventional ICs, while still providing high control bandwidth and performance comparable to state-of-the-art solutions. Since in many applications of interest galvanic isolation is not a requirement, the thesis proposes a method for providing a DC power path from input to output of a previously galvanic isolated converter.

The method requires connection rearrangement in the existing converter only, and provides higher output power and converter efficiency for the same or lower voltage and/or current stresses in the converter components. iii/xiii Achieved results demonstrated that low-cost solutions, based on silicon power semiconductors and ICs, can achieve formidable performance even when operated at very high frequencies.

The power devices employed in this thesis were not optimized for such operation. With proper optimization and new semiconductor materials, it is expected that VHF converters become frequent occurrence within the power conversion domain, rather than a curiosity