Simple robust estimation of load torque in induction machines for application in real plants

Abstract

The load torque information on three-phase induction motor shaft has been widely used in several researches and industrial applications, such as machinery design, optimization of control systems, incipient fault detection, among others. Torque estimation must have accurate response and affect minimally the motor drive. In this paper, a nonintrusive method for in-service torque estimation of induction motors is reported. The technique is based on the RMS value of signals, which are usually found on the machine control panel (current, voltage, and power). As a consequence, the proposed method is suitable for industrial applications. Firstly, computer simulations were performed considering motors with different power ratings in order to analyze the robustness of the proposed method. Later, experimental tests were carried for different operating conditions to validate the technique. The results were compared to those provided by a torque sensor installed on the motor shaft and to the measurements of a commercial equipment. The proposed method presented errors smaller than 2% for all points above 30% of the rated load and errors smaller than 4% below 30% of the rated load.