Analysis and Design for a High Power Density Three-Phase AC Converter Using SiC Devices

The development of a high-power-density three-phase ac converter has been a hot topic in power electronics due to the increasing need in applications like electric vehicles, aircraft and aerospace, where light weight and/or a low volume is usually a must. There are many challenges due to the complicated relationships in a three-phase power converter system. In addition, with the emerging SiC device technology, the operating frequency of the converter can be potentially pushed to tens of kHz to hundreds of kHz at high-voltages and high-power conditions. The extended frequency range brings opportunities to further improve the power density of the converter. The technologies based on existing devices need to be revisited. In this dissertation, a systematic methodology to analyze and design a high-powerdensity three-phase ac converter is developed. All the key factors of the converter design are investigated with the goal of high power density. The dissertation is divided into five sections. Firstly, the criteria for passive filter selection are derived, and the relationship between the switching frequency and the size of the EMI filter is investigated. A functional integration concept is proposed together with the physical design approach. Secondly, a topology evaluation method is presented, which provides insight into the relationships between the system constraints, operating conditions and design variables. Four topologies are then compared with the proposed approach, culminating with a preferred topology under the given conditions. Thirdly, a novel average model is developed for the selected topology, and is used for devising a carrier-based control approach with simple calculations and good regulation performance. Fourthly, the converter failure mode operation and corresponding protection approaches are discussed and developed. Finally, a 10 kW three-phase ac/ac converter is built with the SiC devices. All the key concepts and ideas developed in this work are implemented in this hardware system and then verified by the experimental results.