Stable shaft-sensorless control of permanent magnet synchronous motors using a sliding torque observer

Abstract

Two nonlinear sliding observers are developed for speed-sensorless control of permanent magnet synchronous motors. One of the observers estimates the rotor position and velocity based on the measurement of the motor current, while the other estimates load torque as well as rotor position and velocity. The lower bounds of the sliding gain, which guarantee the existence of the sliding manifold, and the upper bounds, which guarantee the stability of the digital implementation of the sliding observers, are also presented. Both theoretical analyses and experimental results demonstrate that, regardless of the observer used for speed-sensorless control, the steady-state velocity error converges even when an external load torque is applied to the rotor. However, when an external load is present, the position estimation error of the control system with torque estimation and compensation is significantly smaller than that of the system without torque estimation and compensation.