A New Variable Reluctance PM-Resolver

Abstract

Resolvers as position sensors need a high frequency AC excitation voltage, and the induced voltage in their 2-phase perpendicular windings are amplitude modulated (AM) signals. For calculating the position, it is required to demodulated the output signals and calculate their envelopes. Then, inverse tangent can be used for calculating the position. Despite the advantages of resolvers, there are some drawbacks in their application. Calculating the envelopes is always one of the deep concerns in using resolvers. Furthermore, due to low-amplitude of the excitation flux, the performance of the resolvers is strongly affected by electromagnetic interference by the stray fields of motor and brake. Complicated winding process is the next challenge of resolvers. The last concern is referred to the high speed applications where to maintain the accuracy of the sensor it is required to increase the excitation frequency. While, the maximum frequency of excitation is limited by the frequency response of the employed ferromagnetic core and the employed resolver to digital converter (RDC). To overcome all the mentioned worries, a new permanent magnet (PM) resolver is proposed in this paper. The presented resolver has no copper winding and no need to the high frequency excitation. It is equipped by low-price Hall Effect sensors to measure the magnetic flux density and has a robust performance in high electromagnetic disturbance environments. All the analysis is done using time stepping finite element method (TSFEM) and verified by experimental measurements on a built prototype.