Influence of Construction of High Frequency Air Transformers for SMPS on Parameters of Their Compact Thermal Model

High frequency air transformers for switched-mode power supply (SMPS) are important components of wireless power transfer systems (WPT). This paper describes a compact thermal model of such transformers. This model takes into account self-heating in all components of such a transformer and mutual thermal couplings between these components. Methods of measurement of self- and transfer transient thermal impedances characterizing properties of the considered devices are proposed. The form of the elaborated model is described together with a parameters estimation method. Some results of measurements and calculations illustrating an influence of selected factors on waveforms of self- and transfer transient thermal impedances obtained for different constructions of the tested devices are shown and discussed. Two kinds of constructions of the air transformers are considered—with ferrite plates and without them. Different dimensions of the coils and different distances between them are considered. A good agreement is obtained between the results of measurements and simulations for all the considered constructions of the tested transformers operating in different conditions.