Mission-profile based reliability framework for medium-frequency transformers

This paper proposes a theoretical framework for assessing the reliability of medium-frequency transformers, combining random failure modeling with wear-out analysis of dielectric insulation. The method decomposes the transformer into discrete dielectric regions and estimates their lifetime based on thermal and electrical stress profiles derived from a specified mission-profile. A case study on a 170 kW, 15 kHz dual active bridge converter demonstrates the approach, using cycle counting, electrothermal modeling, and Monte Carlo simulations to predict regional insulation degradation. Results show that for the studied mission-profile, the medium-frequency transformer achieves a wear-out lifetime well beyond 25 years, with minimal electric stress observed under normal operating conditions. The framework helps identify critical insulation zones and supports more informed design and lifetime risk evaluation in high-frequency power electronic systems.