Finite element analysis of edge-slotted magnets and axial rotor channels for low-speed wind power applications

Abstract

Permanent magnet generators are widely used in small-scale wind energy conversion systems because they offer high efficiency, a compact structure, and direct-drive capability. However, their operation under low-wind-speed conditions is often constrained by cogging torque and rotor inertia, which can reduce self-starting capability and rotational stability. This study presents a finite element magnetic analysis of a 24-slot/10-pole permanent magnet generator by combining magnet-edge slotting and axial rotor-channel modification. The generator was modelled using the Finite Element Method Magnetics (FEMM) 4.2 under a two-dimensional magnetostatic formulation. Three magnet-edge configurations were evaluated: the initial magnet structure, one-step slotting, and two-step slotting. Cogging torque was calculated under no-load conditions using the Maxwell Stress Tensor method. The initial design produced a peak cogging torque of 0.2363933 N·m. One-step slotting reduced the peak cogging torque to 0.0110195 N·m, corresponding to a 95.34% reduction. Two-step slotting further reduced the peak cogging torque to 0.0018320 N·m, corresponding to a 99.23% reduction relative to the initial design. In addition, five axial channels reduced the effective rotor-core area from 0.00810916 m2 to 0.0053815 m2, corresponding to a 33.64% area reduction. These findings indicate that two-step magnet-edge slotting combined with axial rotor channels can improve torque quality and reduce rotor-core area, providing a practical design approach for low-speed permanent magnet generators in wind power applications.