Design Methodology for an Ultra-High Efficiency Coreless Resonant Power Transformer

Abstract

Coreless resonant power transformers, operating at high frequency, have several advantages over the traditional iron core transformer. They have a simple structure, are lighter, cheaper, and more efficient due to the elimination of core losses. For a given cooling capacity, pushing the efficiency of these devices by as little as a fraction of a percent can lead to a substantial increase in power throughput capability. In order to achieve ultra-high efficiency designs, several advanced conductor topologies are explored with the development of corresponding experimentally validated modeling techniques to capture extra losses due to non-ideal conductor construction and elliptically rotational magnetic fields. In consideration of industrial economics, care is taken throughout this work to minimize conductor complexity. The variety of modeling techniques developed in this work allow for fast design space exploration as well as accurate loss predictions for down-selected conductors. An optimization is performed to choose a final design for an ultra-high efficiency (>99%) 40 kW transformer with a x4 voltage ratio. The transformer was constructed and thermal comparisons at partial load were made with a lower efficiency transformer of the same magnetic design built using solid conductors. Results demonstrate a >2x reduction in loss and a subsequent coil efficiency >99%.