A dynamic model for the frictional power loss analysis of a synchronous motor rotor-bearing system

Permanent magnet synchronous motors (PMSMs) are broadly adopted as the power sources of the electric underwater vehicles. However, the frictional forces of supporting bearings for PMSMs result in power loss, which can significantly affect the sail range and duration of the vehicle. This work presents a novel approach to quantitatively evaluate the frictional power loss of a PMSM by developing an electromechanical dynamic model. The model considers the lateral and rotational degrees of freedom of inner raceway and rolling balls in supporting angular contact ball bearings (ACBBs). The external loads on the PMSM rotor, including unbalanced magnetic pull (UMP), electromagnetic torque, nonlinear supporting forces, and mixed elastohydrodynamic lubrication (EHL) friction forces of ACBBs, are also considered. The dynamic modelling method is validated by Simpack and JMAG. Based on the simulation results, the mechanisms of the bearing clearance and raceway surface roughness influencing the frictional power loss of the PMSM are investigated. This study can provide effective guidance for the design of high-efficiency PMSMs for underwater vehicles.