Eccentricity Error Detection in Axial Flux Resolvers

Mechanical errors are one of the most common errors related to electric machines. Among them, eccentricities have the major share of mechanical errors. Resolvers, as an electric machine, can be affected by eccentricities or the electric motor connected to it. The existence of eccentricities in the resolvers, which can be caused by the rotation of the machine at critical speed, incorrect installation of the rotor and stator, core turning defects, and wear and corrosion of the bearings, leads to an increase in the position estimation error. The position estimation error will eventually increase the torque fluctuations, reduce the efficiency, lose the ideal control of the electric motor, and disrupt the automation process. Therefore, providing indicators to detect the occurrence of eccentricity in the resolver can be a preventive solution. Based on this, in this article, focusing on the inclined eccentricity, the equations describing air gap reluctance, magnetic flux density, and mutual inductance will be presented using the modified winding function method. By using the relationships describing the output voltage, the harmonic spectrum of the output voltage in the static and dynamic eccentricities will be compared with the healthy mode, and an index will be provided to identify static and dynamic mechanical error.