Design, analysis and prototyping of a PM-assisted synchronous reluctance machine equipped with new-type of fractional-slot winding

Abstract

PM-assisted synchronous reluctance machines are becoming so attractive for electrical machine designers because of their lower cost due to minor usage of PMs in comparison to IPM and SMPM machines. Besides, they can effectively utilise both the magnetic and reluctance torques, thus, they can play an important role in many industrial applications including electric transportation systems. Up to now, more or less, the conventional distributed-windings are employed in design of the synchronous reluctance machines. However, recent advancements have seen the adoption of fractional-slot concentrated windings (FSCWs) due to their shorter end-winding length, simpler structure, and higher slot fill factor. Although FSCWs offer these advantages, they also suffer from higher magnetomotive force (MMF) space harmonics, which can lead to undesirable effects such as localised iron saturation and increased core losses. The main target of the present research was introducing the winding layouts, which have the benefits of both FSCWs and distributed windings to use in PM-assisted synchronous reluctance machine. To solve the problems related to FSCWs, in this research, the stator slot-shifting has been developed and new types of fractional-slot winding topologies, comprising significantly low MMF harmonics and short-end windings length have been proposed. Based on these proposed winding configurations, a prototype machine was built as case study; and analytical results, finite element analysis, and experimental tests were conducted to validate the machine’s characteristics. Although in the proposed machine the winding is converted to overlapped type and is not concentrated anymore, but the obtained results show significant advantages over the conventional design in terms of air-gap flux density, back electromotive force, torque profile, power factor, power losses, efficiency and flux weakening capability.