Design, Analysis, and Prototyping of an Axial-Flux Permanent Magnet Motor Based on Genetic Algorithm and Finite-Element Analysis

This paper presents an axial-flux permanent magnet motor optimized by the genetic algorithm (GA)-based sizing equation and the finite-element analysis (FEA). The designed slotted TORUS motor produces sinusoidal back-EMF waveform, maximum power density, and reduced cogging torque. The GA obtained the dimensions of motors with different numbers of slots and the highest possible power density. Electromagnetic field analysis of the candidate motors obtained from GA with various dimensions is subjected through FEA to obtain the motors' characteristics. Based on the GA and FEA results, a candidate motor design is introduced and subjected to FEA for reoptimization and finalization of the motor design. Techniques like modifying winding configuration and permanent magnet skewing are investigated to attain the most sinusoidal back-EMF waveform and reduced cogging torque. FEA and GA simulation results are compared and agreed well to the flux density in various areas of the designed motor at no-load condition. The final designed motor (1 kW, 50 Hz, four poles) is fabricated and tested. Experimental results agree with those of the simulation, both satisfying the desired technical specifications.

I. Introduction

Permanent magnet (PM) motors have garnered increasing interests because of their high performance [1]. The low price of high-energy PMs and electronics used in motor fabrication promote the utilization of motors in a wide range of applications [2]. PM motors have different geometries, among which is the disc-type or axial-flux permanent magnet (AFPM) motor available in various configurations [3]–[7]. The high torque-to-volume ratio, excellent efficiency, and flat structure of the AFPM motor are suited for military and transport applications; these characteristics motivated researchers to develop new approaches in designing AFPM machines [8], [9]. AFPM machines can be single- or double-sided, with or without armature slots/core, have internal/external PM rotors, contain a surface-mounted or interior PM, and are single- or multistaged [10]. The AFPM motors cogging torque is normally much higher compared to conventional motors [11]; however, they can still potentially be applied to high-torque applications such as ship propulsion or elevator direct drive [12], [13]. The double-sided AFPM motor is the most promising and widely used motor type. The topologies for double-sided AFPM machines are the axial-flux one-stator–two-rotor (TORUS) and two-stator–one-rotor (AFIR) [14], while either of the two arrangements (external stator or external rotor) is practical. The external-stator arrangement uses fewer PMs at the expense of winding. The external-rotor arrangement is considered advantageous when space is limited, mechanical robustness is required, and torque-to-volume ratio is crucial [15]. The double-sided slotted TORUS AFPM motors are the most frequently applied among the other configurations, chiefly because they are mechanically stronger and have higher power densities [16]. Therefore, the slotted TORUS AFPM motor is used in this study for modeling and simulation. Using genetic algorithm (GA) and finite-element analysis (FEA) in the design process maximize the motor power density, reduce the cogging torque, and eliminate the undesired back-EMF harmonics, thereby enhancing the operational performance of the initial design.