Disturbance observer based non-singular fast terminal sliding mode control of permanent magnet synchronous motors

The existence of load disturbance can lead to the instability of permanent magnet synchronous motor (PMSM) speed control systems. Therefore, a non-singular fast terminal sliding mode control (NFTSMC) strategy based on a disturbance observer is proposed in this paper. First, a new exponential reaching law is presented to relate the rate of convergence to the state error and switching function, which achieves an improvement of the system convergence speed while reducing system jitter. At the same time, to eliminate system jitter, a new smooth saturation function is introduced in place of the symbolic function. Second, a non-singular fast terminal (NFT) sliding surface is generated by combining a nonlinear function with a linear function, which makes the state error converge rapidly at different stages. Finally, a disturbance observer is built to boost the robustness of the control system by observing the outside disturbance value and feeding it back to the speed controller. The dependability and effectiveness of the proposed control strategy are confirmed by simulation experiments with MATLAB.