NVH Study of Axial Flux Motor for Electric Propulsion Systems

The advancement of high-performance electrification for electric vehicle (EV) development is continuously pushing the boundaries of electric motor technology. The axial flux motor (AFM) represents a promising application for high-performance EVs, offering potential advantages including up to twice the torque density and a 50% reduction in weight compared to regular IPM radial flux motors. The distinctive "pancake" configuration and high axial forces inherent to AFMs present notable NVH challenges, yet there is a lack of research exploring NVH analysis and risk assessment. In this paper, a 10-pole and 12-slot AFM motor is designed, prototyped, and tested, demonstrating the capability to deliver 300 Nm of peak torque and 140 kW of peak power. A comprehensive finite-element model is constructed, and the orthotropic stator material properties are evaluated using modal test data. The dominant axial stator modes are identified as the source of resonances in the system responses. A three-dimensional electromagnetic analysis is conducted to calculate the electromagnetic force in the axial, tangential, and radial directions. Subsequently, force excitations are mapped on a structural mesh to predict the dynamic responses of the AFM when integrated into a motor fixture system. Both the analysis and the test capture strong pole-pass orders around the 60th order, and dominant axial vibrations are identified around the resonance frequency corresponding to the stator benching modes. These unique characteristics suggest the importance of considering NVH analysis and optimization in the early design phase for AFM development.