Supply Frequency Tracking in Resistance-Based Induction Motor´s Rotor Temperature Estimation

In resistance-based rotor temperature estimation schemes, a grid-connected induction motor´s rotor temperature is derived from a resistance quantity based on an equivalent circuit model. This temperature is susceptible to fluctuations in the motor´s supply frequency. In this paper, the relationship between supply frequency fluctuations and accuracy in resistance-based rotor temperature estimates is analyzed, and a complex adaptive phase discriminator is proposed to track the supply frequency fluctuations for grid-connected induction motors. A complex voltage vector is constructed from polyphase voltage measurements and passed through a frequency-selective digital filter to attenuate harmonics and interference. The complex adaptive phase discriminator then operates on the filtered voltage signal, iteratively adapting a complex reference signal´s phase to align it with the filtered voltage signal. The power grid´s supply frequency is directly estimated from the adapted phase on a sample-by-sample basis. Experimental results demonstrate that the proposed complex adaptive phase discriminator helps produce rotor temperature estimates with increased accuracy.