A composite sliding-mode observer with PLL structure for a sensorless SPMSM system

To achieve high-precision speed and position control for the surface-mounted permanent magnet synchronous motor (SPMSM), this paper proposes a sensorless vector control strategy based on a composite sliding-mode observer (SMO) and an improved phase-locked loop (PLL) structure. Different from the existing sensorless methods, the proposed control strategy can further improve the accuracy of observation position and speed. First, a new sliding-mode function and the equivalent control are introduced to weaken the chattering and accelerate the reaching rate. Then, a sliding-mode current observer based on an adaptive law control is designed to observe the back electromotive force (back EMF). Meanwhile, the adaptive law can ensure the stability of the system in different states and reduce the system chattering. Second, an adaptive back EMF observer is presented to accurately observe the estimated back EMF. Furthermore, the stability of the two observers is proved by employing the Lyapunov second method. Next, the variable gain PLL with the signal suppressor is used to obtain an accurate rotor position and speed. Finally, the simulations and experiments are implemented to validate the performance of the proposed control strategy, in terms of speed and position tracking as well as anti-disturbance ability.