Induction motor rotor temperature estimation using superheterodyne receivers

A rotor temperature estimator is proposed in this paper for line-connected squirrel-cage induction motors during dynamic or steady-state operations. The method utilizes a pipelined architecture with two superheterodyne receivers that operate in parallel on a complex current vector. The first superheterodyne receiver detects motor speed by extracting an instantaneous rotor slot harmonic frequency from the complex current vector. The second superheterodyne receiver extracts a complex fundamental current vector from the same complex current vector. A model-reference adaptive system then produces an estimate of the rotor time constant from the superheterodyne receivers´ outputs, plus a complex voltage vector and a few motor parameters. Finally, the rotor temperature is derived from the estimated rotor time constant via a correlation between the rotor temperature and its resistance. Experimental results demonstrate that the proposed method is capable of estimating induction motor rotor temperature on a sample-by-sample basis without using temperature or speed sensors.