High-Speed Synchronous Reluctance Machines: Materials Selection and Performance Boundaries

Abstract

This paper presents a comprehensive comparative design exercise of Synchronous Reluctance (SyR) machines considering different soft magnetic materials and a wide range of speeds. First, a general design methodology able to consider all the consequences of selecting different materials is presented. In fact, magnetic non-linearities, rotor structural limitations and the rise of both stator and rotor iron losses are all considered. The adopted design approach allows achieving optimal stator and rotor geometries balancing all these competitive multi-physics aspects and keeping constant the cooling system capability. Both silicon-iron (SiFe) and cobalt-iron (CoFe) alloys with optimized magnetic and mechanical performance are examined to assess the maximum capabilities achievable with a SyR machine technology. The adoption of CoFe alloys leads to machines that outperform the SiFe counterparts up to a certain speed, above which, machines with SiFe provide better performance. Indeed, in the lower speed range, the effect of the higher saturation flux density of the CoFe materials is dominant, while for higher design speeds, their higher iron losses and lower yield strength, with respect to the SiFe ones, make the latter more convenient. All the design considerations are finally validated by comparing the predicted performance with the experimental test results on a 6.5kW, 80krpm SyR machine prototype.

An Overview of High-efficiency Synchronous Reluctance Machines

“…In [84], a hybrid design approach for the SynRMs suit-able for high-speed operation is proposed. A comparative study on different soft magnetic materials is presented.…”

Synchronous Reluctance Machines: A Comprehensive Review and Technology Comparison

“…High speed (HS) SynRMs have attracted an ever increasing research interest in the last decade. The key publication in that matter are [94], [95], [96], [97], [98], [99], [100].…”

“…In [99], a comprehensive design methodology for HS-SynRM has been introduced and validated against FEAs and experimental findings. Adopting the same design approach, [100] reports a comparative design exercise in order to identify the optimal soft magnetic materials to be used for both stator and rotor of a HS-SynRM.…”

High Speed Permanent Magnet Assisted Synchronous Reluctance Machines – Part I: A General Design Approach

“…The airgap thickness has been selected as a compromise choice between the need of mimizing it (beneficial from the electromagnetic point of view) and practical assembly limits, whereas the selected number of pole pairs allows a lower fundamental frequency beneficial for both control and thermal management. The stator and rotor materials are chosen so to minimize the iron losses and improve the rotor integrity at high-speed (further details about the materials selection can be found in [27]); the iron flux density is a consequence of the selected iron material for the stator lamination.…”