A novel online rotor temperature estimator for induction machines based on a cascading motor parameter estimation scheme

This paper proposes a cascading motor parameter estimation scheme to obtain an online estimate of the rotor temperature for a small to medium size mains-fed induction machine. The stator winding resistance at ambient temperature is the only motor parameter needed as an input. First the inductances are estimated according to the equivalent circuit developed from the rotor flux field orientation. Then the estimated inductances are fed into the rotor resistance estimation algorithm to yield an estimate of the rotor resistance. The rotor speed, obtained from the rotor slot harmonics detection algorithm, is also used as an input to the rotor resistance estimation algorithm. Finally the rotor temperature is calculated from the linear relationship between the temperature and the rotor resistance. Experimental results are shown to validate the proposed scheme with accurate tracking of the rotor temperature rises at different load levels. The whole scheme is fast and reliable and is therefore suitable to be incorporated into an existing rotor thermal protection system.