Influence of Airgap Length on Performance of High Power PM-Assisted Syn-Rel Machines

Abstract

In recent years, synchronous reluctance (Syn-Rel) machines are research hotspots in variable speed motor drives due to their robust rotor structure and wide constant power speed range (CPSR). More practically, when kVA limitation is considered, embedded permanent magnets (PMs) have been widely adopted in Syn-Rel rotors to further increase power density as well as power factor. In this paper, the authors have investigated the potential of PM-assisted Syn-Rel machine to be the next generation electrical propulsion motor topology for automotive application, with special attention put on a key geometric parameter, i.e., airgap length. In MTPA region, the influence of airgap length on different torque components has been analyzed in detail based on the frozen permeability method. In field weakening region, the variation trend of several key performance such as peak power, iron loss and torque ripple have been investigated along with airgap length. It is found that with specifically high level of electric and magnetic loading, there exists optimal value of airgap length to achieve high power density based on specific cooling and kVA limitation. Numerical FEA and experimental tests are associated to validate the conclusions.

Airgap Length Analysis of a 350 kw PM-Assisted Syn-Rel Machine for Heavy Duty EV Traction

“…Due to the relatively complex rotor structure, extensive efforts have been made in analytical sizing of PM-assisted Syn-Rel machines to rapidly establish the relationship between geometric parameters and basic machine performance, such as average torque [7], torque ripple [8], losses [9] and rotor antidemagnetization capability [10]. Detailed electromagnetic design has been combined with FEA tools to increase calculation accuracy as well as for specific performance requirements [15][16]. In addition, research interests on this machine topology have been extended to multi-physics domains such as mechanical stress on the rotor [17,18], thermal [19] and noise, vibration, harshness (NVH) aspects [20] for reliability improvement in high speed, high power applications.…”