A novel method to estimate speed for the induction motor at wide range speed

A novel estimation technique of rotor speed of induction motor is proposed. The new estimation method is to estimate directly rotor speed using stator flux and rotor flux. Speed adaptation law in Model Reference Adaptive System (MRAS) or Speed Adaptive Flux System (SAFO) is not employed because the proportional and integral gains in the adaptation law are difficult to determine for wide operation region. In the proposed method, the stator and the rotor flux is estimated based on the dynamic model of the induction motor and the speed of the motor is then calculated using the estimated flux. The speed can be calculated well at very low speed even very close to zero speed.

I. Introduction

In most drive systems, the speed information is usually obtained from a shaft encoder. The precision of the shaft encoder influences the smoothness of the measured speed, especially in the lower speed range. In order to avoid this drawback, one may use a higher precision shaft encoder, which however, increases the overall price of the AC drive system. Moreover, it has reduced reliability and robustness and susceptibility to noise and vibration. Therefore, emphasis is placed on removing the position sensor from the induction motor drive to enhance the robustness and reliability of the drive systems. If the rotor speed can be estimated from the measured variables, it will not only eliminate the cost of the speed sensor, but also increase the reliability of the drive. In the existing literature, many algorithms have been suggested for the estimation of the rotor speed of the induction motor such as Model Reference Adaptive System Flux Estimators (MRASFE), Speed Adaptive full order Flux Observer (SAFO) and Inherently Stator Flux Estimators (ISFE) [1]–[10].