Supply frequency tracking in resistance-based induction motor rotor temperature estimation

In resistance-based rotor temperature estimation schemes, a rotor temperature is derived from a resistance quantity based on an induction motor equivalent circuit model. This temperature is susceptible to fluctuations in the motor´s supply frequency. In this paper, a complex adaptive phase discriminator is proposed to track supply frequency fluctuations for grid-connected induction motors. A frequency-selective digital filter is applied to attenuate harmonics and interferences in a complex voltage vector. The complex adaptive phase discriminator then iteratively adapts the phase of a complex exponential to align a complex reference signal with a complex primary 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 an increased accuracy.