Computationally Efficient Strand Eddy Current Loss Calculation in Electric Machines

• Published in: IEEE transactions on industry applications Vol. 55; no. 4; pp. 3479 - 3489
• Main Authors: Fatemi, Alireza, Ionel, Dan M., Demerdash, Nabeel A. O., Staton, Dave A., Wrobel, Rafal, Chong, Yew Chuan
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.07.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: AC copper loss; Algorithms; Alternating current; Analytical models; Coils (windings); Computational efficiency; Computational modeling; Computer simulation; Conductors; Current loss; Design optimization; eddy current loss; Eddy current testing; Eddy currents; Electric wire; finite element (FE) method; Finite element method; Flux; high-speed permanent magnet (PM) machines; Loss measurement; Mapping; Modelling; Permanent magnets; Qualitative analysis; Stator windings; Stators; Synchronous machines; Winding
• ISSN: 0093-9994; 1939-9367
• DOI: 10.1109/TIA.2019.2903406

A fast finite element (FE) based method for the calculation of eddy current losses in the stator windings of randomly wound electric machines is presented in this paper. The method is particularly suitable for implementation in large-scale design optimization algorithms where a qualitative characterization of such losses at higher speeds is most beneficial for identification of the design solutions that exhibit the lowest overall losses including the ac losses in the stator windings. Unlike the common practice of assuming a constant slot fill factor <inline-formula><tex-math notation="LaTeX">s_f</tex-math></inline-formula> for all the design variations, the maximum <inline-formula><tex-math notation="LaTeX">s_f</tex-math></inline-formula> in the developed method is determined based on the individual slot structure/dimensions and strand wire specifications. Furthermore, in lieu of detailed modeling of the conductor strands in the initial FE model, which significantly adds to the complexity of the problem, an alternative rectangular coil modeling subject to a subsequent flux mapping technique for determination of the impinging flux on each individual strand is pursued. Rather than pursuing the precise estimation of ac conductor losses, the research focus of this paper is placed on the development of a computationally efficient technique for the derivation of strand eddy current losses applicable in design optimization, especially where both the electromagnetic and thermal machine behavior are accounted for. A fractional-slot concentrated winding permanent magnet synchronous machine is used for the purpose of this study due to the higher slot leakage flux and slot opening fringing flux of such machines, which are the major contributors to strand eddy current losses in the windings. The analysis is supplemented with an investigation on the influence of the electrical loading on ac winding loss effects for this machine design, a subject that has received less attention in the literature. Experimental ac loss measurements on a 12-slot 10-pole stator assembly will be discussed to verify the existing trends in the simulation results.