A reliable rotor eccentricity detection scheme for induction machines in the presence of a position dependent load torque oscillation

Single phase stator current spectrum is usually monitored to examine rotor eccentricities in mains-fed induction motors. However, a rotor-position-dependent load torque oscillation introduces exactly the same side-band harmonics in the stator currents with larger magnitudes, leading to an ambiguity in the online rotor eccentricity diagnostics in the presence of a load torque oscillation. This paper develops a reliable scheme to eliminate load oscillation effects from rotor eccentricity detection by monitoring eccentricity-only related normalized negative sequence harmonic information in the stator current space vector spectrum. A significant advantage of this method lies in its independence on motor parameters. Extensive experimental results demonstrate the efficacy and convenience of the proposed technique.