Improved sensorless scalar control of induction motors using dual RF-MRAS and stator voltage compensation

Abstract

Abstract: This paper presents an improved sensorless scalar control (SC) scheme for in-duction motor drives, aimed at enhancing speed tracking capability in the low-speed region. The proposed method integrates rotor flux-based model reference adaptive system (RF-MRAS) with dual adaptation to estimate both rotor speed and stator resistance. The rotor flux angle obtained from the current model (CM) is used to compute the synchronous speed, while the slip component is filtered before being injected into the scalar frequency com-mand. In addition, a stator-voltage-drop compensation strategy based on estimated stator resistance is introduced to preserve the air-gap flux during low-voltage operation. Simula-tion studies confirm that the proposed method extends the stable operating range. The min-imum stable speeds are 12.23/12.28 rad/s at 20% load, 10.78/11.59 rad/s at 25% load, and 11.88/11.29 rad/s at 30% load, evaluated using EMAPE/Emax criteria. All cases satisfy EMAPE ≤ 2% and Emax ≤ 6%, showing better low-speed stability than the baseline methods. Laboratory experiments were also performed on an induction motor drive platform. At 300 rpm, online stator resistance estimation strongly reduces speed oscillations under a 20% stator resistance increase. At very low speeds, voltage compensation restores the ef-fective stator voltage and improves steady-state tracking. These results verify that the pro-posed dual RF-MRAS scheme improves robustness without requiring mechanical speed sensors.