Practical Study of Mixed-Core High Frequency Power Transformer

Abstract

The design of medium- to high-frequency power electronics transformer aims not only to minimize the power loss in the windings and the core, but its heat removal features should also allow optimal use of both core and copper. The heat removal feature (e.g., thermal conduction) of a transformer is complex because there exist multiple loss centers. The bulk of total power loss is concentrated around a small segment of the core assembly where windings are overlaid. The primary winding is most constrained thermally. For superior use of core and copper, the temperature rise in different segments of the transformer should be well below their respective safe operating limits. In practice, cores of same soft-magnetic materials are traditionally used. To achieve superior temperature profile and for better long-term performance, this article proposes to use the mixed-core configuration. The new core(s) would replace the parent ones from the segment where windings are laid. The characteristic features of new cores would share increased burden of heat removal from the transformer. To obtain the qualitative insight of magnetic and thermal performance, the proposed mixed-core transformer would be thoroughly validated practically in two different high-power applications. In the first case, the core is always energized to its rated value, and in the second one, windings are always energized at respective rated current capacity.