Semi-analytical loss model for rotary transformers

In modern drive systems, electrically excited machines (ESM) have become an interesting alternative to those excited by permanent magnets. The excitation winding is normally supplied by a slip ring system that (in automotive applications) has to be protected against environmental influences like wetness, oil and dust. To increase the power density of ESM, brushless excitation systems based on rotationally symmetric transformers (fig. 1 b) begin to replace slip rings. Their insusceptibility to environmental influences is their major advantage compared to slip rings. To allow the movement of the secondary against the primary side, air gaps are needed. With the focus on vehicle drive applications, they must be designed with (air) gap widths between 0.5 mm and 1.0 mm, or accommodation of tolerances.