Online Stator Resistance Estimation Method for a SPMSM Sensorless Drive Using Adaptive Flux Observer in Stationary Reference Frame

When running at low speed and high torque, sensorless drives are highly influenced by the stator resistance error of the motor and sometimes lose synchronization, leading to startup or drive failures. First, this paper analyzes the effect of the stator resistance error on the rotor position estimation in sensorless drives at low speed and high torque with large stator currents. Overestimation of stator resistance increases the loop gain of the rotor position estimator, making it unstable. An underestimated one reduces the loop gain, making it susceptible to disturbances and causing synchronization failure. Then, a real-time stator resistance estimation method in sensorless drive of surface mounted permanent magnet synchronous motors (SPMSMs) is proposed. The proposed method adopts an adaptive flux observer in the stationary reference frame. By integrating the stator voltage after subtracting the ohmic drop in the stationary d-q reference frame and subtracting the stator inductance flux linkage, the rotor permanent magnet flux is estimated. By comparing it with the reference rotor flux linkage, which is predefined or estimated at the beginning of the operation, the proposed method adjusts the estimated resistance. The proposed approach is validated through simulations and experiments, confirming its ability to accurately track time-varying stator resistance and maintain stable control performance under low-speed, high-load conditions.