The Challenge of Thermal Runaway in Soft Magnetic Materials for Inductive Power Transfer

This paper investigates the thermal runaway effect in soft magnetic materials (SMCs). The SMCs are essential for modern power electronics and are used in applications such as inductors, transformers, and wireless power transfer systems. Despite their importance, the thermal runaway of the SMCs poses a significant challenge to the reliability and safety of these applications, particularly with inductive power transfer (IPT). To address this challenge, the paper compares two materials: a benchmark MnZn ferrite and a Fe-based nanocrystalline material. The core losses of these materials were measured inside a thermal chamber to determine their relationship with different ambient temperatures. The findings reveal that both materials exhibit a valley temperature point where the core loss density is minimized. However, this valley temperature varies with different flux densities and shows distinct behaviors for ferrites and nanocrystalline materials. Furthermore, the thermal runaway effect is mathematically explained based on thermal radiation and convection calculations of an example IPT system. The analysis can be used to estimate and prevent thermal runaway during the pre-design stage.