Robustness Evaluation of Voltage and Current Model-Based Rotor Flux Estimation under Resistance Variations in FOC Systems

Abstract

This study examines how two rotor flux estimators, the voltage model and the current model, behave when used within the same field-oriented control (FOC) structure for a three-phase induction motor drive. Particular attention is given to the effect of stator and rotor resistance variations, since these parameters directly enter the voltage and current model calculations and may change during operation due to heating. In the simulation study, both estimators are tested under low-, medium-, and high-speed conditions. A 30\% increase in stator and rotor resistance is introduced while the drive is operating, and the resulting speed response and flux estimation behavior are then compared. The assessment is based on four time-domain error criteria: Integral of Absolute Error (IAE), Integral of Time multiplied Absolute Error (ITAE), Integral of Squared Error (ISE), and Integral of Time multiplied Squared Error (ITSE). The results show that the voltage model depends on the accuracy of the stator resistance, while the current model depends on the rotor resistance. This effect is most severe in the low-speed region, where the resistive voltage drop becomes significant relative to the applied stator voltage. At higher speeds, the voltage model error decreases, and the difference between the two estimators becomes smaller. These results indicate that the current model is a more reliable option when the drive is expected to operate under uncertainty in stator and rotor resistance, particularly at low speed.