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Fractional slot concentrated winding (FSCW) is a kind of winding structure with few‐slots/coils multi‐poles. FSCW has the potential value of high torque density due to its short end‐winding and high slot fill ratio and is widely used in low‐speed direct‐drive application situations. However, compared with integral slot winding (ISW), the back EMF coefficient of FSCW is smaller, which leads to smaller output torque under the same condition. To improve the back EMF coefficient of FSCW, equidirectional toroidal winding (ETW) is proposed and applied to the dual rotor slotless axial flux permanent magnet motor (AFPM), in which the unit structure is three slots/coils two poles, and the ideal back EMF coefficient is the same as that of ISW. In this paper, firstly, the structure of ETW is introduced and its operating principle is analyzed. Then, compared with the AFPM with ISW, the open circuit and load characteristics of the AFPM with ETW under two conditions of the same wire gauge and the same coil width are analyzed respectively. The back EMF coefficient and output torque of ETW‐AFPM are similar to that of ISW‐AFPM under the same coil width. The back EMF coefficient and output torque of ETW‐AFPM are a little lower than that of ISW‐AFPM under the same wire gauge. Finally, the experimental results also validate the feasibility of AFPM with ETW and the correctness of the analysis results. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

In this paper, a dual-rotor slotless axial-flux permanent magnet (AFPM) motor with equidirectional toroidal winding (ED-TW) is proposed and compared with the AFPM motor with traditional toroidal winding (T-TW) with the same dimensions, number of coils and poles. Different from the T-TW, only the positive sides of coils of the ED-TW are left on one side of the stator core, the return sides of the coils are all removed to the other side of the stator core. Firstly, the structure and operation principle of the two motors are introduced and analyzed. To clarify the features of the ED-TW, the synthetic electromotive force (EMF) vector and armature reaction field of the ED-TW and T-TW are studied. Secondly, the main size equations of the AFPM motors with toroidal windings are presented. Subsequently, the electromagnetic characteristics of the AFPM motors with ED-TW and T-TW are analyzed and compared based on the three-dimensional finite element method (3D-FEM). The comparison results indicate that the AFPM motor with ED-TW has superiority in torque density and efficiency. Finally, a prototype of the AFPM motor with ED-TW is manufactured and tested, which validates the feasibility of the proposed motor and the correctness of the analysis of the 3D-FEM. [ABSTRACT FROM AUTHOR]

The three‐phase permanent magnet synchronous motor (three‐phase PMSM) has gained much popularity in many applications due to its various advantages. In addition, due to the good fault tolerance, simple inverter circuit structure and high torque density, the six‐phase PMSM has better prospects than three‐phase PMSM in biomedical devices, electric vehicles and other fields with high reliability requirements. In this study, a six‐phase axial‐flux PMSM inherently without cogging torque is proposed to improve torque density, which equips the 60° phase‐belt toroidal winding (60°TW) and slotless stator core. Based on the same effective volume, permanent magnet material, power grade and the other major motor parameters, two six‐phase PMSMs with 30° phase‐belt toroidal winding (30°TW) and 60°TW are designed, respectively. The armature reaction field, air gap magnetic density, back‐electromotive force, output torque, loss characteristic and torque‐speed characteristic are compared by using three‐dimensional (3D) finite‐element models in detail. Finally, the experimental test is carried out using the prototype of three‐phase PMSM with 120° phase‐belt toroidal winding. The experimental results indirectly verify the feasibility of 60° phase‐belt toroidal winding and correctness of 3D FEM. The 3D FEM analysis results are presented to show that torque density of the proposed six‐phase PMSM with 60°TW is improved in comparison to the six‐phase PMSM with 30°TW. Index Terms—60° phase‐belt toroidal winding, axial flux, six‐phase permanent magnet synchronous motor, torque density [ABSTRACT FROM AUTHOR]