On the Effects of Position Sensor Resolution in Variable Speed Drives

The aim of this paper is to further the knowledge on the inherent limitations imposed on variable speed drives by the resolution of the rotor position sensor. Starting from the well-known spatial harmonic formulation of quantized rotor position measurement, time harmonic formulations of both quantized position and speed are derived, which are valid under generic periodic torque disturbances. These formulations, based on modulation theory, justify the presence of otherwise unexplained additional rotor speed harmonics that are induced by the drive when subjected to torque disturbances. Simulations are provided to verify the correctness of the proposed mathematical representations.