Analytical Iron Loss Evaluation in the Stator Yoke of Slotless Surface-Mounted PM Machines

Abstract

One of the attractive benefits of slotless machines is low losses at high speeds, which could be emphasized by a careful stator core loss assessment, potentially available already at the pre-design stage. Unfortunately, mainstream iron loss estimation methods are typically implemented in the finite element analysis (FEA) environment with a constant-coefficients dummy model, leading to weak extrapolations with huge errors. In this paper, an analytical method for iron loss prediction in the stator core of slotless PM machines is derived. It is based on the extension of the 2-D field solution over the entire machine geometry. Then, the analytical solution is combined with variable- or constant-coefficient loss models, which can be efficiently computed by vectorized post-processing. Our case study compares different approaches to predict the loss phenomena. Moreover, the paper proposes a lookup-table-based (LUT) solution as an alternative approach. For validation purposes, the models are matched against a sufficiently dense dataset of 180 measured loss points for a lamination sample in the Epstein frame, covering a wide range of frequencies and flux density levels, which are usually not available from commercial datasheets. Finally, all the methods are compared for the slotless machine case, highlighting that the LUT method depends on a sufficiently dense experimental dataset to achieve satisfactory accuracy.

Analytical Iron Loss Evaluation in the Stator Yoke of Slotless Surface-Mounted PM Machines