Enhanced Cascade Sliding Mode Direct Thrust Control for Linear Induction Machine Based on Linear Metro

In this article, a robust cascade sliding mode control is proposed for the direct thrust control (cascade-DTC) to achieve quicker transient response and high tracking capability with lower thrust and flux ripples for the linear induction machine (LIM). First, the fast terminal sliding mode control (FTSMC) method is designed for the speed loop to improve the speed response of LIM under DTC control structure compared to the conventional SMC (CSMC) and proportional integral control methods. Second, a supertwisting sliding mode control (ST-SMC) method is designed for both electromagnetic thrust and primary flux-linkage control loops to further improve the dynamic response in terms of transient response, steady-state response with smaller thrust and flux ripples. Third, combined speed, thrust, and flux controllers are implemented based on the FTSMC and ST-SMC for the LIM, known as the cascade-DTC technique. Afterwards, the close loop stability of the speed loop is checked by the Lyapunov function. Finally, comprehensive simulation and experimental analyses have been carried out based on one prototyped 3 kW arc induction machine to demonstrate the superiority of the cascade-DTC method than those of conventional direct thrust control, CSMC with DTC, and FTSMC based on DTC methods, respectively.