Ultra-low and zero speed sensorless control of permanent magnet synchronous motor based on sliding mode observer

The ultra-low and zero speed sensorless control of permanent magnet synchronous motor (PMSM) based on observers is a troublesome problem due to the extremely weak back electromotive force (EMF) and unavoidable noises. Faced with this problem, we analyzed the factors that may cause motors rotating inversely, and constructed an equation describing how the given speed, inertia and load torque affect the rotating direction in the ultra-low speed occasions. The results on ultra-low and zero speed simulations show excellent performance and strong robustness of the control system.