Temperature-Robust Air-Gapless EE-Type Transformer Rails for Sliding Doors

In this paper, a sliding EE transformer (SEET) rail, which has a strong and independent magnetic coupling to the gap variation between the transmitter (Tx) line and receiver (Rx) coil for powering the sliding door, is newly proposed. In the SEET rail, the Tx line and the Rx coil share a single EE ferrite core, while the winding window of the ferrite core is considered as the gap variation. In the proposed structure, the magnetic coupling can be maintained as strong and constant even though the ferrite core moves along the door rail when the sliding door is closed or opened. Through detailed coil designs based on electric and magnetic circuit analyses, design constraints on voltage, output power, flux density, and zero voltage switching are proposed with a closed-form solution of output voltage and theoretical maximum output power. The SEET rail is successfully designed to provide a maximum load power of 200 W for the sliding door within an ambient temperature range from −40 to 125 °C by following design constraints. Moreover, optimal design parameters such as number of turns, air-gap, and ferrite thickness are provided, which maximize power transfer efficiency of the SEET rail while maintaining its performance in the temperature range. The proof-of-concept prototype shows a strong magnetic coupling, κ = 0.76 at 20 °C and the variation of the magnetizing inductance with respect to the temperature variation was measured as 13.8%. The maximum power transfer efficiency excluding the regulator at a nominal load power of 100 W was 85%, and the efficiency at the maximum load power of 200 W was measured as 82% with a 3%P variation by the temperature variation.