Accuracy Improvement in Variable Reluctance Resolvers

Variable reluctance (VR) resolvers are widely used in many industrial applications. The conventional winding method for variable air-gap length resolvers is overlapping, variable turn, on-tooth winding. However, it is not possible to distribute the turn function exactly in accordance with a sinusoidal function. Because, there are a finite number of slots in the stator and only integral number of conductors can be included in each slot. So, in this paper, the influence of rounding off the turn numbers on the accuracy of VR resolvers is investigated. To minimize that error, an initial angle is defined for the starting of the sinusoidal turn function on the teeth. Meanwhile, the effect of maximum number of turns is studied. It is shown that there is an optimal value for the starting angle of the turn function and the maximum turn numbers to minimize the position error. Furthermore, it is proved that considering the stator slot and rotor pole combinations, there is more than two applicable rotors for a wound stator. All the analysis is verified using time stepping finite element method and experimental tests on a prototype resolver.