Adaptive Stator Resistance Estimation for Sensorless Direct Torque Control of Synchronous Reluctance Motors with MTPA

The maximum torque per ampere (MTPA) based direct torque control (DTC) method directly controls the elec-tromagnetic torque and flux in AC machines by dynamically adjusting the stator flux reference in line with the reference torque and draws the minimum stator current. Neglecting the stator resistance variation can lead to an increase in stator current and lead to drive instability. This paper proposes a new sensorless MTPA-based DTC of SynRM under stator resistance variation. The proposed approach focuses on accurately estimating the changes in stator resistance by analyzing variations in the angles between the estimated and reference of stator flux and current vectors, without the need for any speed sensor. Utilizing this estimation methodology, the sensorless MTPA-based DTC adapts to variations in stator resistance, ensuring optimal motor performance across diverse operating conditions and disturbances. The proposed sensorless MTPA-based DTC approach improves the stator current, torque, and speed performance of the SynRM. In contrast, the existing MTPA-based DTC approach struggles significantly under stator resistance variations, leading to increased stator current and looses stability.