Eccentricity Effect on Radial Forces of Bearingless BLDC Motor: Study and Analysis

Abstract

The bearingless BLDC motor gathers all advantages of the BLDC motor and bearingless machine, and this motor is extensively used in blood and artificial heart pumps. In a bearingless BLDC motor, there are two sets of windings, the main winding, responsible for producing the motor torque, and the suspension winding, which keeps the rotor in the center without any contact with the stator. Generally, the suspension system is responsible for the generation of the suspension forces to cancel the pull-out forces (radial forces), which strongly depends on the accurate evaluation of radial forces distribution at different operating conditions. In this paper, a mathematical model based on the finite element method is used to calculate and analyze the radial force of a bearingless blood pump BLDC motor using Ansys/Maxwell. Based on Maxwell equations, the normal and tangential components of the airgap flux density is determined and used to calculate the radial force, magnitude, and direction. In addition, different cases of rotor displacement under eccentricity conditions are covered. The relation between the rotor displacement and radial force is analyzed, accounting for the displacement direction. Finally, the results are analyzed and discussed.