Chattering-free Nonsingular fast terminal Sliding-mode Control for Permanent Magnet Synchronous Motor servo system

To overcome the higher order nonlinearity, strong-coupling, parameters time-varying and unknown external disturbance for Permanent Magnet Synchronous Motor servo system, a chattering-free nonsingular fast terminal sliding-mode control is proposed. There are two main problems of the conventional sliding-mode control, the singularity and the chattering. The advantages of the fast terminal sliding-mode control and the dynamic sliding-mode control are combined to solve the two main problems. The singularity is avoided because of the derivatives of terms with fractional powers is not appearing in the sliding-mode surface and the control. And a low-pass filter is designed in the switching control term, so the switching control term becomes smooth and the chattering phenomenon has been solved. It is shown that the proposed method can guarantee the stability and the finite time convergence of the system from Lyapunov stability analysis. The simulation results show the effectiveness of the proposed method. Compared to the traditional PI control strategy, the dynamic performance and the accuracy of steady-state are both improved.