Induction motor model selection criterion for parameter estimation in speed sensorless drive

In the parameter estimation algorithm of speed sensorless induction motor drive, the complete model of induction motor is replaced with its reduced order model by many researchers. However, no guideline is available in the literature for the selection of appropriate model under various operating conditions. In this paper, a detailed investigation is done regarding the possibility of such replacement for machines of any power rating and under different working conditions. A systematic comparative analysis is carried out which includes eigenvalue study on four machines of different power ratings with respect to changes in input frequency, slip and winding resistances. This is followed by Kalman's observability test and a computer simulation to demonstrate the relative performance of reduced order model when fed separately from an AC voltage source and then from a sinusoidal PWM inverter circuit. The study presented in this paper reveals that the selection of reduced order model should be made after considering various factors like motor power rating, ratio of leakage reactance to winding resistance, magnetising reactance, range of input frequency, range of operating slip depending upon the load and possible variation in the winding resistances. A comparative guideline is proposed in this regard which was found missing in the available literature.