Designing for Conductor Lay and AC Loss Variability in Multistrand Stator Windings

Abstract

Vehicle electrification places significant pressures on electric machine design due to the need for increased power densities and mass production. These two requirements couple when designing multistrand stator windings, which exhibit significant AC loss variability as a result of the random nature of the conductor lay within the stator slot caused by automated insert winding. This paper presents two prediction methods for AC loss variability to be deployed at the winding design stage. The first consists of an analytical approach, whilst the second constructs a 2D finite element analysis geometry that captures conductor lay characteristics. Comparison of predictions from both approaches to experimental AC loss measurements established that the proposed models capture the experimentally observed AC loss variability characteristics and that the analytical method is suitable for early design stages whilst the finite element approach should be adopted once the winding configuration is finalised.

AC Losses in Windings: Review and Comparison of Models With Application in Electric Machines

“…Models of circulating currents in the literature are mainly developed for circular wires [18], [19], [20], [21] since the effect of circulating currents is less remarkable for rectangular conductors thanks to predefined locations in the slots [52]. In this section, preliminary formulas related to windings used in the literature are presented.…”

“…Further models were developed to consider magnetic field due to rotation of permanent magnets (PM) [14], [15] and tooth tips [16], [17]. Circulating currents is receiving increased interest [18], [19], [20], [21] because of the use of parallel strands to reduce losses due to the previous effects. Analytical models were developed accounting for neighbouring conductors' effect [22], [23] and for PM rotation assuming equal induced voltage in strands of same slot [24].…”

Verifying Strand Transposition in Stator Windings via X-ray Computed Tomography derived Three-Dimensional Models

“…The most evident exploitation opportunity for the strand and turn assignments derived from 3D models is the use of such information in the modelling of multistrand windings that are subject to variable conductor lays. For example, knowledge of the typical conductor lays and strand paths in coils of a given manufacturing process can improve existing 2D Finite Element Analysis (FEA) estimates of AC losses as previously described by the authors [5].…”

“…Prior work has defined various idealised strand transpositions, and these are routinely assumed during the design and analysis of electrical machine windings [4], [5]. To date however, there have been limited studies into the characterisation of strand transposition in as-manufactured windings, and the identification of complete three-dimensional strand paths around a coil has yet to be performed [6].…”

“…To date however, there have been limited studies into the characterisation of strand transposition in as-manufactured windings, and the identification of complete three-dimensional strand paths around a coil has yet to be performed [6]. Consequently, for coil winding technologies that result in significant mechanical strand-to-strand and strand-to-tool interactions (such as random windings [5] and compressed coils [7]), existing AC loss…”