A sensorless rotor temperature estimator for induction machines based on current harmonic spectral estimation scheme

This paper proposes a sensorless rotor temperature estimator for small to medium size mains-fed Induction machines. With measurements obtained from only current and voltage sensors, the proposed estimator can capture the rotor temperature in an online fashion. First the rotor speed is extracted from the current harmonic spectrum based on the estimated rotor slot and eccentricity harmonic frequencies. Then the inductances are estimated from the induction machine equivalent circuit. The stator winding resistance at ambient temperature is the only motor parameter needed at this stage. Once the inductances are obtained, they are fed into the rotor resistance estimation algorithm to yield an estimate of the rotor resistance. Finally the rotor temperature is calculated from the linear relationship between temperature and rotor resistance. Experimental results from different motors are shown to validate the proposed scheme. The whole scheme Is accurate and reliable and is therefore suitable to be Implemented in a rotor thermal protection relay or a motor drive employing vector control scheme to compensate for the detuning effects.