Investigation of DELPHI-inspired compact thermal model for modeling planar transformer — Network concept

Planar Magnetic Components, as called PMC, are now interesting alternatives to classic high frequency transformers. Based on the combination of a low profile magnetic core and Printed Circuit Board (PCB), these devices allow large reduction in terms of weight and size, which exacerbates power density constraints. In order to circumvent the potential thermal issues of a multi-layer embedding of flatten high-current-density copper windings at the heart of a PCB substrate, an investigation is conducted to define the proper way for building a simple thermal model that can take into account the electro-thermo-magnetic combined effects. At first, to better understand the mutual interactions of conjugated copper and iron losses as well as the heat conduction capability of the core structure, a set of numerical simulations were performed to calibrate a fine Detailed Thermal Model (DTM). Then the concept of Compact Thermal Model dedicated to planar transformer devices, inspired by DELPHI'S method, is defined for minimizing the computation time while keeping a high accuracy level to monitor the sensitive temperatures of primary and secondary windings as well as those of core structure. The presented results demonstrate the ability to deduce such a resistor network from time-consuming simulations. Designers can then perform trivial calculations to analyse the thermal impact of planar transformers.