A. Stoecker

Bio: A. Stoecker is an academic researcher from Freiberg University of Mining and Technology. The author has contributed to research in topics: Electrical steel & Blanking. The author has an hindex of 2, co-authored 3 publications receiving 19 citations.

Effect of the Interdependence of Cold Rolling Strategies and Subsequent Punching on Magnetic Properties of NO Steel Sheets

Abstract: Nowadays, optimization of non-oriented (NO) electrical steels toward lower iron-loss, improved, and isotropic magnetizability is critical to the improvement of rotating electrical machines. The whole production process chain adjusts the microstructure evolution, e.g., grain size and crystallographic texture, determining the magnetic properties. In particular, the interdependence of raw material properties and the resulting mechanical stress distribution during final assembly, e.g., punching, leading to magnetic property deterioration is crucial for the optimization of NO steel properties of rotating machines. This paper studies the effect of different cold rolling strategies, annealing treatments, and sheet metal blanking (punching) regarding microstructure evolution, magnetic properties, and deterioration.

Grain Size Influence on the Magnetic Property Deterioration of Blanked Non-Oriented Electrical Steels.

Abstract: Non-oriented electrical steel sheets are applied as a core material in rotors and stators of electric machines in order to guide and magnify their magnetic flux density. Their contouring is often realized in a blanking process step, which results in plastic deformation of the cut edges and thus deteriorates the magnetic properties of the base material. This work evaluates the influence of the material’s grain size on its iron losses after the blanking process. Samples for the single sheet test were blanked at different cutting clearances (15 µm–70 µm) from sheets with identical chemical composition (3.2 wt.% Si) but varying average grain size (28 µm–210 µm) and thickness (0.25 mm and 0.5 mm). Additionally, in situ measurements of blanking force and punch travel were carried out. Results show that blanking-related iron losses either increase for 0.25 mm thick sheets or decrease for 0.5 mm thick sheets with increasing grain size. Although this is partly in contradiction to previous research, it can be explained by the interplay of dislocation annihilation and transgranular fracturing. The paper thus contributes to a deeper understanding of the blanking process of coarse-grained, thin electrical steel sheets.

More Robust and Reliable Optimized Energy Conversion Facilitated through Electric Machines, Power Electronics and Drives, and Their Control: State-of-the-Art and Trends

Abstract: According to the special section entitled ‘Robust design and analysis of electric machines and drives’, to be published in IEEE Transactions on Energy Conversion, the authors present an introduction to tolerance analysis, robust optimization, and measures to improve the reliability of electric machines, power electronics and drives, and their robust control in general. A comprehensive review of modeling uncertainties and evaluating robustness and reliability based measures is presented. In addition, techniques facilitating solving dedicated optimization scenarios are introduced. The most recent research activities will be illustrated. The article thus enables to easily catch up with the state-of-the-art in these fields and to take notice of ongoing and future work.

Effect of Punching the Electrical Sheets on Optimal Design of a Permanent Magnet Synchronous Motor

Abstract: Cutting the electrical steel sheets to form the shape of the stator and the rotor affects the magnetic properties of the sheets. The increase of the magnetic losses as well as the drop of the magnetic permeability can impact on the design of electrical devices. This paper investigates this deterioration effect on the optimal design of the stator of a high-speed permanent magnet synchronous motor. The deterioration due to punching is phenomenologically analyzed based on measurement of strips of steel sheets with various widths on an enlarged Epstein frame. The losses are computed with a Bertotti model whose coefficients depend on the width of the sheets. The optimization of a synchronous machine is then carried out with this magnetic losses model.

Degradation of Static and Dynamic Magnetic Properties of Non-Oriented Steel Sheets by Cutting

Abstract: The performances of non-oriented iron-silicon (NO Fe-Si) alloys, which are among the most commonly used materials for soft magnet applications, suffer because of mechanical stresses, whose intensity depends on the cutting technology applied, when these materials are used in the shape of strips in the magnetic core manufacture. This paper presents a detailed analysis of the influence that the stresses, arising from mechanical punching technology, have on the energy losses and normal magnetization curves, measured on NO Fe-Si samples. High-quality Cogent NO20 Hi-Lite and M300-35A samples, having a thickness of 0.2 and 0.35 mm, respectively, with a length of 300 mm, were cut by guillotine shear method to obtain strips with widths varying from 5 to 60 mm. The attained strips having different widths were characterized using a hysteresisgraph-wattmeter to measure ac energy losses and hysteresis cycles in the frequency range from 3 to 1500 Hz for NO20 and up to 400 Hz in the case of M300-35A. The dynamic loss behavior is presented in accordance with the statistical theory of losses, while a low to moderate increase is observed with the sample width decrease. The measured total energy losses were then decomposed into the hysteresis and dynamic components, including the classical and excess energy losses. The energy losses’ behavior as a function of the strip width was, eventually, analyzed and modeled, considering that cutting process induces local hardening on the borders of the samples. The experimental results put also in evidence a hyperbolic variation of the hysteresis losses versus strip width in both cases. As a remarkable result of these considerations, we observe that the evolution of the hysteresis energy losses can be predicted from the very wide, almost undamaged, to narrowest, fully degraded width strips.

Life cycle analysis of electrical motor-drive system based on electrical machine type

Abstract: Nowadays a lot of attention is paid on the issues of global warming and climate change. Human impact on the environment is noticeable from the aspect of resource life cycles. Energy efficiency requirements have led to the research and development of alternative technologies for the rotating electrical machines. The life cycle assessment brings out important procedures which can help to reduce machines’ impact on the environment, being therefore an instrument for the assessment of the influence of particular products on the environment from cradle to grave – beginning with working out the materials, followed by manufacturing, transporting, marketing, use, and recycling. Three types of electrical machines have been chosen for comparison: synchronous reluctance motor, permanent magnet assisted synchronous reluctance motor and induction motor. The article presents a life cycle assessment case study based on experimental results of motors designed by the research group.