Core-as-a-Sensor: Ferrite DC-Resistance-Based Core Temperature Measurement of Magnetics

Future power electronic systems should feature continuous in-situ monitoring of components to facilitate, e.g., predictive maintenance and lifetime prognostics. Temperatures of magnetic components (i.e., transformers and inductors) are typically measured with thermocouples attached to the core surface. It is known from literature that the electrical conductivity of ferrite, typically used as core material of high-frequency magnetics, is temperature dependent. Hence, this paper proposes a method to observe the magnetic component temperature based on a ferrite core resistivity measurement, advantageously allowing to track the average core temperature (which is typically above the core surface temperature). First, methods for electrically contacting the core surface are discussed and common magnetic materials (MnZn ferrites) are characterized. Possible disturbance factors such as dc and ac magnetic flux occurring during operation of power electronic converters are experimentally found to have little impact on the measured resistivity. Finally, a smart inductor prototype with core-resistivity-based temperature estimation is presented and experimentally verified, and the applicability of the method to high-frequency NiZn and powder cores is indicated.