Researchers at NCPRE, IIT Bombay, have developed a medium-frequency transformer (MFT) employing aluminium foil windings for Dual Active Bridge (DAB) converters to improve efficiency and power density for PV systems. While copper is conventionally used in transformer windings because of its high conductivity, its higher density increases transformer weight and limits gravimetric power density. The proposed work demonstrates that aluminium foil windings can offer superior performance in certain regions during medium-frequency operation by reducing eddy-current effects and transformer losses.

The study analytically investigates the influence of winding material on AC resistance and leakage inductance, two critical parameters governing DAB converter performance. It is shown that although aluminium has lower conductivity than copper, the reduced eddy-current generation leads to a more uniform current distribution and lower AC winding losses at medium frequencies. In addition, the aluminium-wound transformer exhibits a slightly higher leakage inductance, which is advantageous for DAB operation for integrating it inside the transformer.

To validate the concept, two 20 kVA, 50 kHz, 110/800 V medium-frequency transformers are designed, fabricated, and experimentally evaluated using aluminium and copper foil windings. Experimental results demonstrated a 17.02% reduction in secondary-winding AC resistance and a 16.8% reduction in primary-winding AC resistance for the aluminium-wound transformer compared to the copper-wound counterpart. The aluminium design also achieved a 0.5% increase in leakage inductance and a 28.1% improvement in gravimetric power density, highlighting its potential for PV systems as well as railway traction, ship propulsion, offshore wind energy systems, and electric aircraft applications.

This work was carried out by Priya under the guidance of Prof. Sandeep Anand, and Prof. Baylon G. Fernandes at the National Centre for Photovoltaic Research and Education (NCPRE), and was presented at the 2026 IEEE Applied Power Electronics Conference and Exposition (APEC) in San Antonio, USA.