Axial—Radial Flux Permanent Magnet Synchronous Machines: A Comprehensive Review

Axial–radial flux permanent magnet synchronous machines (ARFPMSMs) are an emerging family of electrical machines that combine radial flux and axial flux topologies within a single electromagnetic structure. By using multiple radial and axial air gaps, they increase the effective torque-producing surface without enlarging the machine envelope, which enables higher torque density and better utilization of active materials than in conventional single-flux topologies. This makes them attractive for traction, aerospace, wind, elevator and other compact high-torque applications. This paper reviews the state of the art of ARFPMSMs and provides four main contributions. First, it proposes a unified topology-oriented classification of classical PM-only, hybrid-excitation and vernier/flux-modulated ARFPMSMs, while clarifying their conceptual boundary with transverse-flux machines. Second, it consolidates published designs and compares key parameters across the three families. Third, it summarizes experimentally validated prototypes, including rated power, torque density, materials and cooling methods. Finally, it identifies open research challenges and outlines future directions, including surrogate models, Bayesian optimization and active cooling strategies.