Analysis and design considerations of an axial‐flux dual‐rotor consequent‐pole Vernier‐PM machine for direct‐drive energy conversion systems

The Vernier permanent‐magnet (VPM) machine is known as high‐torque and low‐speed drive solution suitable for direct‐drive applications such as electric‐vehicles and wind‐turbines. This study presents a high‐efficiency axial‐flux VPM machine with dual‐rotor of consequent‐pole topology and one yoke‐less concentrated‐winding stator. The consequent‐pole VPM machine is a special VPM structure that introduces high torque‐density as the conventional‐VPM machine incorporating a significantly lower volume of PM material. The proposed machine represents desirable features of higher efficiency, improved reliability and lower weight and axial‐length compared to the traditional motor‐gearbox approach. These advantages are achieved due to: dual‐PM rotors for appropriate forming the magnetic flux lines and increasing torque‐to‐weight ratio, yokeless‐stator for reducing flux path, concentrated winding with no overhang for reducing copper‐loss, using rectangular‐shaped copper conductors for increasing winding fill factor and selecting the core material from high‐performance grain‐oriented magnetic steel for reducing core‐loss. After presenting the structure, the operating principles are discussed based on the magnetic flux behaviour and a quasi‐3D magnetic‐equivalent‐circuit model is extracted. The accuracy of the analytical model is validated by comparing the results with the FE results. Finally, the effects of the design parameters on electro‐magnetic performance are analytically investigated by studying a 10 kW machine.