Sensorless control of PM synchronous motors based on LKF estimation of rotor position

Abstract

This paper presents a novel PMSM sensorless control scheme based on a linear Kalman filter (LKF) observer. The LKF algorithm is able to estimate rotor position and current components in the stator reference frame by measuring stator currents, and using a mathematical model based on the voltage equations of motor. The proposed observer is linear but time-varying because the rotor speed is treated as a model parameter to be updated on-line. Estimation of rotor speed is performed in two steps: firstly a rough speed estimation is obtained by processing the estimates of rotor position; then a simple speed observer is used to improve the accuracy of speed estimates. The observer output, i.e. the final speed estimate, is fed back to both the speed control loop and LKF algorithm. Sensitivity to strong stator resistance variations makes this sensorless algorithm unsuitable for operation at very low speed; good performances are obtained in the speed range from 10% of rated speed to full speed.