Research On Variable Reluctance Resolver With Asymmetric Teeth On The Stator

As electromagnetic rotor position sensor of motor, variable reluctance (VR)resolver, which has simple structure, small axial dimension, high reliability, highamplitude of output voltage, low cost and relatively high precision, is widely used inAC governor system with high dynamic performance and electric vehicle.Unfortunately, when VR resolvers are applied in a small and narrow space, insertingcoils is of great difficulty because thin copper wires are too fragile and the spaceinside the resolver for inserting coils manually is too limited to accomplish thataccurately and conveniently as a result of too many tooth on the stator. Thus, a novelVR resolver with asymmetric teeth on the stator, which has a minimal number ofactive teeth and the simplest structure, is proposed to reduce the size of the devicewhile simplifying its construction. The principle, numerical analysis, structureoptimization, error analysis and experimental test of the novel VR resolver areresearched.First of all, the working principle of VR resolver with asymmetric tooth on thestator is studied by analytical method in this paper. Based on the principle ofslot-pole combination, the VR resolver with four teeth on the stator is obtained. Inorder to eliminate the effect of the null voltage, the asymmetric tooth andcompensating coils are brought and the VR resolver with asymmetric teeth on thestator is proposed. By deducing the analytical expression, the number of turns of theSIN and COS compensating coils can be calculated theoretically.Based on Finite Element Analysis (FEA), the VR resolver with four teeth onthe stator and VR resolver with asymmetric tooth on the stator is researched. Theair-gap permeance and output voltages of these two resolvers are analyzed. Thecomputing results show that the VR resolver with asymmetric teeth on the stator caninduce two amplitude-equal output voltages in quadrature. The analytical results andcalculations of the turns of SIN and COS compensating coils are nearly identical.Those results prove the validities of analytical method and FEA. The locationchosen for the asymmetric tooth on the stator is arbitrary theoretically.The structure optimization of VR resolver with asymmetric tooth on the statoris studied. Based on FEA, the length of air-gap, the shape of rotor, the width of teethon the stator and the height of compensating tooth are optimized. After each localoptimum is acquired and the relation of local optimum and global optimum areanalyzed, the global optimum of VR resolver with asymmetric tooth on the stator isresearched.Finally, the effects of technology errors of VR resolver with asymmetric tooth on the stator are investigated. Based on FEA, the electric error curves of statoreccentricity, rotor eccentricity, hybrid eccentricity, the move of reference windingsand the move of signal wingdings are computed. The prototype is manufactured andtested. The waveforms of output voltages of signal windings are recored by TEKoscilloscope. The zero-error curve is measured by high-precision digital gratingoptical dividing head.