Enhanced Fast Terminal Sliding Mode Observer for Wide-Speed Sensorless Control of PM Vernier Ship Propulsion Machine Drives

This paper proposes an enhanced fast terminal sliding-mode observer (FTSMO) for the wide-speed sensorless control of a vernier machine used in ship-propulsion system. The method enables speed and position estimation in the dq frame, where, unlike the back-electromotive force (EMF) estimationbased methods, the need for the phase lock loop (PLL) block is eliminated. This not only reduces the control system's computational burden, but also relieves the designer of the adversity of setting PLL design parameters. To overcome the challenges of speed estimation, and especially position estimation at reverse running speeds, an adaptation law is designed to directly estimate the machine speed. Furthermore, a new terminal sliding surface is utilized to improve the reaching phase of sliding surface, which can enable a faster convergence rate with higher precision for estimations compared with the traditional terminal sliding method. The finite-time convergence of the proposed estimation scheme is proved through the Lyapunov theorem, which guarantees that the estimation errors converge to zero in a beforehand time interval without dependence on the initial conditions. The proposed sensorless method is evaluated using MATLAB/Simulink simulation for a 5-MW ship-propulsion permanent magnet vernier motor (PMVM). The outcomes demonstrate a faster convergence time than the conventional terminal sliding observer.