High Speed Synchronous Reluctance Motors for Electric Vehicles: a Focus on Rotor Mechanical Design

Abstract

This paper deals with the design of high-speed Synchronous Reluctance motors for electric vehicle applications. The need to enhance power density and lowering costs leads to the design of high speed motors with a reduced amount of rare earth. Pure synchronous reluctance motors potentially operate at high speed and exhibit a low cost rotor compared to PM and induction motors. Nevertheless, they present reduced performances in deep flux weakening operations in particular when the so-called radial ribs are introduced to increase the mechanical robustness of the rotor. In this paper the adoption of the radial ribs in the related design challenges are investigated and discussed. The adoption of a suitable commercial optimization tool able to optimize the placement and the sizing of the radial ribs is presented. The approach leads to an original positioning of the radial ribs able to preserve the performances of the motor at high operating speed enhancing the mechanical integrity of the rotor.

Adopting the Topology Optimization in the Design of High-Speed Synchronous Reluctance Motors for Electric Vehicles

“…In [1] different numbers of poles have been analyzed, optimized and compared (respectively 4, 6, and 8), concluding that the 6-pole design presents the best performance. About the barrier shape, "fluid shape" or "Joukowsky barriers" have been chosen [23].…”

“…-Adoption of high strength electrical steel [24]: usually involves steels with lower magnetic properties; -Adoption of retaining sleeves [25]: it is problematic since it would require a material substantially stiffer than steel to decrease the radial deflection under inertial load; -Novel rotor constructions [26]: they need custom manufacturing process and custom spare parts; -Adopting properly rotor interconnecting end plates or interconnecting shaft (dovetails vs press fit) [27]: it is more effective for compact buried PM rotors; -Adoption of structural non-magnetic materials (epoxy resins, titanium, others) [25], [28], [29]; these are difficult to be interconnected with the rotor laminations and have an additional cost that has to be accurately evaluated; -Adoption of optimized structural ribs [1], [16], [30], [31]:…”

“…The electric machines have become the primary candidate for mobility [1]- [3], adopting motor solutions mainly based on high performance permanent magnets (PM) manufactured with Rare-Earth (RE) materials [4]- [6].…”

A New Design Procedure for Rotor Laminations of Synchronous Reluctance Machines with Fluid Shaped Barriers

“…Even in [12] four fluid shaped barriers have been considered as a basis for different optimization strategies. With a similar purpose, but specifically for the design of high speed SynRM for electric vehicle applications, a new rotor layout with multiple ribs in different positions with respect to the flux barriers is presented in [24]; this geometry is quite unusual compared to those reported in the literature. The original positioning of the radial ribs is able to preserve the performance of the motor at high speed, enhancing the mechanical integrity of the rotor.…”

Finite Elements Model Co-Simulation of an Induction Motor Drive for Traction Application

“…Induction motors and Permanent Magnet (PM) synchronous motors are currently considered the better solutions for traction of EV, [3] [4]. Respect to PM synchronous motors, Induction Motors (IMs) can allow for a better average efficiency in variable load conditions and easier flux-weakening capability useful for speed range extension thanks to the absence of the need for field weakening current.…”