The recent emerge of wide band-gap powerdevices enables higher switching frequencies in electric motor drives. The subsequent possibility for higher efficiencyand smaller size requires accurate prediction of harmonic losses in motors. Therefore this paper presents an original analysis of harmonic losses arising in inverter-fed 2-pole slotless permanent-magnet machines with axially segmented ring magnets. The developed three-dimensional time-efficient numerical model is successfully validated under high-speed no-load operation using a silicon-carbide based three-phase inverter and rotors carrying a broad range of magnet segment thicknesses (3–12.6 mm). The model enables harmonic loss prediction capability (including loss separation) with an accuracy of 15 % over a wide frequency range (8–120 kHz), which is a unique contribution. The sensitivity analysis primarily emphasizes the importance of taking into account the axial segmentation, and secondarily the rotor-shaft magneto-elasticity effects for accurate modeling of harmonic losses. The conducted case-study demonstrates that wide band-gap transistors effectively can contribute to eliminating the need for inductive filters in motor drives.

In this paper, an inverter with wide bandgap transistors was designed, experimentally evaluated and compared to a conventional IGBT-based inverter in a three-phase slotless PM motor drive. Using the developed inverter, GaN andSiC transistors (650 V) were experimentally tested using switching frequencies up to 48 kHz. Despite operation at significantly higher switching frequencies, the inverter efficiency was increased from approximately 90 to 95 % by using wide band-gap transistors. Furthermore, a system weight reduction of up to 50 % was enabled due to the elimination of the inductive filter and use of a smaller heatsink (due to lower losses). By combining the wide band-gap technology with a new slotless 4-pole motor type, the total system losses can be reduced by more than 30 %.

Abstract—The recent emerge of wide band-gap (WBG) powertransistors enables higher switching frequencies in electricalmotor drives. Their full utilization from a system point ofview requires quantification of the corresponding time-harmonicmotor losses. As an initial step, this paper presents a uniquestudy of stator losses for three different commercially availablenon-oriented silicon-iron (SiFe) steel grades (with laminationthicknesses 0.1, 0.2 and 0.3 mm). The investigations cover awide frequency range (10-100 kHz) at different levels of DC-bias(up to 1.6 T). Iron losses are identified from measurements onfully assembled stators, deploying a novel technique. By utilizingfully assembled stators, no additional samples are required.Manufacturing influence is inherently incorporated. Results showthat measured iron losses are twice as high at 10 kHz comparedto Epstein test results, which emphasizes the need to incorporatemanufacturing influence on iron losses at high frequencies. Thelevel of DC-bias is also observed to have a significant impacton iron losses (up to 30 %). Even though thinner laminationsare known for reducing iron losses, the reduction is much lowerthan anticipated in the studied frequency range due to skin effect.Using 0.1 mm lamination gauge instead of 0.3 mm reduces lossesby 50 % at 10 kHz, while the same substitution at 100 kHz onlyreduces losses by 30 %. Future work includes loss separation incomplete converter-fed machines.

This document presents the results of the project "Eciency of Motor and Drive with SiCtransistors" within SiC Power Center. The project was conducted between 2015-06-01 - 2016-06-30. The purpose of the study is to point out potential system benets of using SiC PowerMOSFET:s instead of conventional IGBT:s in nutrunner systems. The study can conclude thatthe total motor-drive system weight can be more than halved by using SiC technology. The studyalso shows that blanking time and motor inductance are important parameters for optimal useof SiC Power MOSFET:s in electrical nutrunner systems. The project was partly funded by theSwedish Energy Agency, Energimyndigheten and Sweden's innovation agency, Vinnova.

The magnetic properties, namely the iron losses and the relative permeability, of SiFe electrical steel laminations after mechanical and laser cutting are studied. Mechanical cutting with guillotine shears and cutting by means of fiber and CO2 lasers are considered. The magnetic measurements are conducted on the Epstein frame for frequencies of 50, 100 and 200 Hz. The specimens also include Epstein strips with 1, 2 and 3 additional cutting edges along their length, in order to increase the cutting effect and the characterization data. Mechanical cutting results in more than 20% iron loss increase and more than 40% relative permeability reduction at 1 T for 0.5 mm gauge, for a strip width of 10 mm compared with the reference of 30 mm, while corresponding values for laser cutting are 40% and 60%. It is also noted that different steel grades of the same raw material show lower magnetic deterioration with thinner lamination thickness. The influence of welding is also investigated by means of Epstein measurements. Experiments show an iron loss increase of up to 50% with a corresponding 62% reduction in the permeability compared to similar non-welded laminations. A model that incorporates the cutting effect with geometry dependency is developed and implemented in a FEM-based motor design software. Simulations made for an industrial low voltage induction motor indicate a more than 15% increase in the iron losses compared to a model that does not consider the mechanical cutting effect. In the case of laser cutting, this increase reaches 30% to 50%, depending on laser settings.

This paper presents a time-efficient transient numerical method for three-dimensional analysis of rotor losses in a three-phase 2-pole high-speed permanent-magnet synchronous machine. The motor has axially stacked ring shaped permanent magnets (PM). The influence of shaft material properties on rotor harmonic losses and loss distribution between the rotor shaft and magnets is investigated in the frequency range 10100 kHz. It is found that the shaft magnetic properties have a significant impact not only on the total rotor losses, but on the magnet losses and inductance as well.

This article deals with the estimation of magnet losses in a permanent-magnet motor inserted in a nut-runner. This type of machine has interesting features such as being two-pole, slot-less and running at a high speed (30000 rpm). Two analytical models were chosen from the literature. A numerical estimation of the losses with 2D Finite Element Method was carried out. A detailed investigation of the effect of simulation settings (e.g., mesh size, time-step, remanence flux density in the magnet, superposition of the losses, etc.) was performed. Finally, calculation of losses with 3D-FEM were also run in order to compare the calculated losses with both analytical and 2D-FEM results. The estimation of the losses focuses on a range of frequencies between 10 and 100 kHz.

This paper presents a systematic, university--wide approach to creating an encompassing movement towards faculty development. In 2014, KTH Royal Institute of Technology launched the pedagogical developers initiative, appointing part--time pedagogical developers among teachers from all schools of KTH, to implement and strengthen good teaching and learning practices among faculty and students. They are teachers active in different educational programmes, with experience of, and interest in, pedagogical issues. In line with CDIO standard 10, the purpose of the pedagogical developers’ initiative is to facilitate cooperation and knowledge exchange between faculty members, and to establish communities of practice. The paper presents the activities, processes for developing these activities and preliminary results from the initiative’s second year, which focused much on supporting faculty development by putting into place a series of workshops, a format chosen for its combination of active community-building learning and time efficiency. The topics of the workshops emerged to meet faculty needs identified by the pedagogical developers during the first year. The workshops were created by smaller teams of pedagogical developers from different schools of KTH. This enabled a wide array of experiences and perspectives to be incorporated into the workshops. Main focuses of the workshops have been on creating internal discussions in dynamic communities of practice on specific subjects of interest, and on creating forums for exchange of ideas, open to the whole faculty. During Autumn 2015, the workshops have been offered as voluntary add-on parts of the basic course in teaching and learning offered to faculty at KTH. This first round of workshops generated a positive interest from teachers, and participant feedback indicates that they particularly appreciated the opportunity to work directly with their own courses and the opportunity to discuss pedagogical aspects with peers. 

This paper presents an up-to-date magnetic materialinvestigation and overview on magnetic materials used in rotatingelectrical machines. The focus is on small to medium-sizedhigh-performance and high-efficiency permanent-magnet andinduction motors for different application scenarios. The inves-tigated materials include silicon-iron, nickel-iron, and cobalt-iron lamination steels, as well as soft magnetic composites andamorphous magnetic materials. The technical focus is on themagnetic properties and iron losses as well as the manufacturinginfluence and required thermal treatments during the manufac-turing process. A new loss to flux density factor is introducedto compare theBHmagnetization curve and the iron losses ofdifferent materials in the same diagram. The aim of the paper isto give the machine designer an efficient material overview andselection guide during the early machine design process.

Most of the volume in classical electrical machinesis occupied by magnetic materials for creating an as good as possible magnetic path. In machines with planar flux paths (2Dgeometries) the material is laminated to reduce eddy current losses in the core. Manufacturers typically supply reference values from Epstein frame measurements as a material performance specification and an easy way for comparison. However, the magnetic flux path in electrical machines is more complex due to rotating magnetic fields passing through the stator (with or without teeth), the rotor, and the airgap. Therefore, other material characterization methods, such as ring core measurements, are more suitable to characterize the magnetic materials for electricalnmachines. This paper gives a short introduction on different methods to characterize magnetic materials and a detailed de-scription of building up a measurement system for characterizingring core samples or electrical machine stator cores. The system isdeveloped with regard to the IEC standard for measurements on magnetic ring core samples and can easily be build up in any lab with a power amplifier and a standard industrial control system equipped with analog input/output interfaces. Finally, reference measurements demonstrate the performance of the system.