A novel nonsingular terminal sliding mode observer for sensorless control of permanent magnet synchronous motor

Aiming at the accurate estimation of rotor position and speed of permanent magnet synchronous motor for the sensorless vector control system, a novel nonsingular fast terminal sliding mode observer based on tracking differentiator, named NFTSMO, is proposed. First, a nonsingular fast terminal sliding mode surface in form of integration is constructed, which makes the observation error of currents converge to zero in finite time and avoids the singular problem as well as the noises produced by the conventional nonsingular terminal sliding mode surface. Then, the sliding control law is developed with low chattering switching control combined with terminal attractor. The smooth estimation of the back electromotive-force is obtained through the tracking differentiator, and the phase lag caused by the low-pass filter in traditional sliding mode observer is decreased. Finally, the information of rotor position and speed is modulated from the observed back electromotive-force by the phase-locked loop. The simulation results show that the proposed nonsingular fast terminal sliding mode observer can accurately estimate the rotor position and speed of permanent magnet synchronous motor. The maximum error of speed estimation is between ±1 r/min, and the estimated rotor position has no phase lag. The system has good dynamic and static performances. Compared with the traditional sliding mode observer, the proposed observer has advantages of faster convergence rate, higher tracking accuracy, lower chattering of back electromotive-force. Besides, the proposed observer has strong robustness in the presence of load disturbances and parameter perturbations.