This work is on deriving precise lumped parameter thermal networks for modeling the transient thermal characteristics of electric machines under variable load conditions. The goal is to facilitate an accurate estimation of the temperatures of critical machines' components and to allow for running the derived model in real time to adapt the motor control based on the load history and maximum permissible temperatures. Consequently, the machine's capabilities can be exhausted at best considering a highly-utilized drive. The model shall be as simple as possible without sacrificing the exactness of the predicted temperatures. Accordingly, a specific lumped parameter thermal network topology was selected and its characteristics are explained in detail. The measurement data based optimization of its critical parameters through an evolutionary optimization strategy, and the therefore utilized experimental setup will be described in detail here. Measurement cycles were recorded for modeling and verification purposes including both static and dynamic test cycles with changing load torque and speed requirements. Applying the proposed hybrid approach for determining the model's parameters through involving physics-based equations as well as numerical optimization followed a significant improvement of the preciseness of the predicted motor temperatures compared to solely determining the networks's coefficients based on expert knowledge. Thereby, the validation included both the original measurement data as well as extra measurement runs. The proposed and applied strategy provides an excellent basis for future thermal modeling of electric machines.

The first of this two-part article illustrates the state-of-the-art in soft magnetic materials characterization starting with very early developments and giving a retrospective view of research carried out in this field. One famous measurement setup is the Epstein frame, named after Josef Epstein. Around 1900, he published a German article about “The magnetic testing of laminated steel”. As it is highly likely interesting to researchers worldwide, the authors reconsidered his contributions in English language. Consequently, the most common measurement setups are introduced. Besides the Epstein frame, these are the single sheet tester and setups analyzing ring-shaped specimens. These setups allow for a 1-D characterization of the material, while it usually features anisotropic properties and cross-coupling of the magnetization axes. For this reason, 2-D and even 3-D setups are considered and presented here. This article provides a thorough introduction to the field of material characterization. It is the basis for modeling the material characteristics, which is presented in the second part, which also includes recent developments for considering manufacturing impact. It is of particular interest when dealing with mass-produced electric machines. Eventually, these articles shall constitute valuable references for both engineers new to this field as well as experienced researchers.

The first part of this two-part article is about a retrospective view of material characterization, starting with the work of J. Epstein around the year 1900 and respective basic explanations. Consequently, the work presented herein is about the current state-of-the-art, recent developments, and future trends in characterization of ferromagnetic materials. Modeling is in fact a type of characterization, in a phenomenological and mathematical sense, and therefore it is treated with due attention in this article. Quantifying the properties of soft magnetic materials retains significant scientific attention. Thanks to new optimization techniques and advances in numerical evaluation, modern electromagnetic devices feature high utilization. Classical models exhibit assumptions that do not allow modern machine or device characterization with high accuracy. In this manuscript, typically applied techniques and recent incremental improvements, as well as newly developed models are introduced and discussed. Moreover, the significant impact of manufacturing on the materials’ characteristics and its quantification is illustrated. Within this article, a broad overview of the state-of-the-art as well as recent advances and future trends in soft magnetic material characterization is presented. Thus, it is a valuable reading for beginners and experts, from academia and industry alike.

This study presents a computational and experimental verification of a measurement system using slotted ring specimens for electromagnetically characterizing uncompressed, i.e., weakly magnetic, powders, which are promising materials for modern electric drives. Metrological challenges in characterizing weak magnetic bulk materials, such as the stray flux compensation, are addressed. Therefore, a new signal model is analytically derived and validated using 3D finite element analysis, ensuring an accurate indirect determination of the specimen’s averaged field quantities. A Monte Carlo analysis validates the sensitivity of geometric parameters and the achievable estimation accuracy compared to conventional setups using a closed ring-shaped specimen. Additionally, the novel setup and the introduced signal model are verified using 12 samples made of different iron powders.