Analysis and Design of an Isolated Resonant Buck-Boost PFC Converter Employing Monolithic Bidirectional GaN Switches

This thesis presents the analysis and optimization of a new and original converter topology: an isolated three-phase resonant four switches buck-boost power factor corrector employing monolithic 650 V bidirectional GaN switches (3Φ − RFSBB). Commonly, the interconnection of three-phase low-voltage AC and 400 V DC buses require buck-type PFC. Thus typical solutions consist in a step-up followed by a step-down stage. The studied converter features limited voltage stress in the grid-side input stage equal to the line-to-neutral voltage, employing simple control scheme and modulation. Since, initially, an experience-based method was adopted to design the converter, a systematic investigation on methodologies for topology and control optimization in power electronics are used for optimizing and exploiting the potential of given technological base. The optimization is performed using a systematic design approach that mathematically maps a multi-dimensional design space into a performance space. The adopted design approach employed steady-state equations in the time domain to find the optimal design in terms of efficiency and converter size by evaluating different parameter combinations. To achieve this, the optimization algorithm was tailored by defining an appropriate model to calculate conduction and switching losses in the semiconductor components of the input and output half-bridges, and for the elements comprising the resonant LC tank. Alongside the electrical model used to determine losses, a thermal model was developed for each component. The algorithm systematically analyzes various degrees of freedom at both the system and component levels, creating a Pareto front that illustrated the best possible compromise between competing performance goals and feasible limits. The converter’s performance was evaluated by analyzing the results and assessing how the various loss components behaved as design parameters were varied. The frequency range analyzed spanned from 50 kHz to 300 kHz, with nominal power ratings between 0.5 kW and 3 kW. The objective was to determine the device’s potential performance and application ranges. A peak efficiency of approximately 98% was observed for a converter with a nominal power rating of around 1 kW; however, the analysis highlights significant operational flexibility across different design configurations.