High-Frequency Characterization of Losses in Fully Assembled Stators of Slotless PM Motors

Abstract

PostprintThis is the accepted version of a paper published in IEEE transactions on industry applications. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. IEEE transactions on industry applicationsAccess to the published version may require subscription. N.B. When citing this work, cite the original published paper. © © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Abstract-The recent emerge of wide band-gap (WBG) power transistors enables higher switching frequencies in electrical motor drives. Their full utilization from a system point of view requires quantification of the corresponding time-harmonic motor losses. As an initial step, this paper presents a unique study of stator losses for three different commercially available non-oriented silicon-iron (SiFe) steel grades (with lamination thicknesses 0.1, 0.2 and 0.3 mm). The investigations cover a wide frequency range (10-100 kHz) at different levels of DC-bias (up to 1.6 T). Iron losses are identified from measurements on fully assembled stators, deploying a novel technique. By utilizing fully assembled stators, no additional samples are required. Manufacturing influence is inherently incorporated. Results show that measured iron losses are twice as high at 10 kHz compared to Epstein test results, which emphasizes the need to incorporate manufacturing influence on iron losses at high frequencies. The level of DC-bias is also observed to have a significant impact on iron losses (up to 30 %). Even though thinner laminations are known for reducing iron losses, the reduction is much lower than anticipated in the studied frequency range due to skin effect. Using 0.1 mm lamination gauge instead of 0.3 mm reduces losses by 50 % at 10 kHz, while the same substitution at 100 kHz only reduces losses by 30 %. Future work includes loss separation in complete converter-fed machines.

Investigation of Harmonic Losses in a Two-Pole Slotless Permanent-Magnet Motor Due to Wide Bandgap Inverter Supply

“…The developed model is experimentally evaluated at no-load for rotors of different magnet segment thickness (3-12.6 mm) over a wide frequency range (8-120 kHz) using a SiC based three-phase inverter. The developed model completes the previously developed stator loss model in [13], enabling harmonic loss prediction capability within 15 %, including the previously unprecedented separation of harmonic losses in the complete frequency range. Polarization (due to rotor magnets) and non-uniform magnetic field (due to skin effect) in the stator core are considered by deploying the frozen complex permeability method [26], [27].…”

“…Tightening losses are dominated by copper conduction losses while rundown losses mainly consist of magnetic losses, such as eddy-current and iron losses [31]. Small signal simulations of the investigated motor show that the inductances decrease less than 2 % at full load in the complete frequency range (due to the large effective air-gap [13]). The simulated d and q-axis inductances at 50 kHz, using a rotor carrying magnet segments of 6.3 mm thickness, are displayed in Fig.…”

“…The laminations are of 0.2 mm thickness and are supported by 8 axially oriented welding seams. The stator steel [13], [29] contains 3 % silicon and 0.4 % aluminum per weight unit. The motor phases are Yconnected, and the Y-point is buried inside one of the endwindings.…”

“…Therefore, minimization of rundown losses is gaining emphasis for improved nutrunner performance. The rundown losses can be approximated by the no-load losses [13]. The no-load losses are comprised of fundamental (P 0 ) and harmonic losses (P h ) according to P no-load = P 0 + P h .…”

“…However, the recent emerge of wide band-gap (WBG) transistors enables significantly higher switching frequencies than their traditional silicon-based counterparts [12]. This may enable a smaller filter, or its complete elimination [13], leading to smaller and less complex systems. Subsequently, a full utilization of WBG-technology in electric drives requires accurate prediction capability of harmonic losses in the motor during the design stage [14].…”