Higher-order nonsingular terminal-sliding-mode observer for permanent-magnet synchronous motor

We proposed a higher-order nonsingular terminal-sliding-mode (NTSM) observer for estimating the rotor position and speed of a permanent-magnet synchronous motor (PMSM) for its control system. This observer produces a smooth estimate of the back electromotive-force (EMF), without the need of an additional low-pass filter. Solving the equation of the back EMF, we obtain the position and the speed of the rotor. Compared with the conventional sliding mode observer, the high-order NTSM observer avoids the phase lag in the back EMF signals, thus improving the estimation precision of the rotor position and speed. Simulation results show that high-order NTSM observer provides fast convergence and high precision in position tacking with less oscillation.