Online Estimation of Stator Resistance In Induction Machines Using the Zero-Sequence Component of the Stator Current

Monitoring the energy consumption and efficiency of line-connected induction motors is an important task in industry to ensure economical operation and for condition monitoring purposes. Motor efficiency which is the application intended in this paper, is conveniently obtained from airgap torque and rotational speed. Torque is easily calculated from stator voltages and currents and depends on only one machine parameter, the stator resistance. Among the existing stator resistance estimation methods that require these variables, this work is focused on the one that uses zero-sequence components of stator voltages and currents. It is easily applicable to induction machines connected directly to the mains. Zero-sequence current circulation requires the center terminal of the machine winding be connected to the neutral terminal of the voltage source for a short period of time. This work proposes the use of the zero sequence component existing in the voltage supply as the voltage to be injected. The addition of a simple pulse generator circuit to obtain a more controllable voltage is also evaluated. Implementation issues and performance characteristics of these methods are presented and discussed. Computer simulations and experimental results were obtained on a 15 hp motor test bench and used to validate the method.