Due to superior robustness characteristic of sliding-mode control techniques, this study proposes a multiple sliding-mode control (MSMC) strategy based on the stator flux oriented vector scheme for speed control of three-phase AC induction motor (IM) drives in the presence of an external disturbance and uncertainties. At first, the dynamic model of a three-phase IM drive is transformed into two-axe orthogonal model (i.e. d and q axes) in the synchronously rotating frame so that vector control can be applied. Then, based on the stator flux oriented scheme (i.e. zero stator flux at q-axis and constant at d-axis), the proposed MSMC causes mechanical angular speed and stator current at q-axis reach toward predefined sliding surfaces. Moreover, stator flux and current at d-axis are respectively indirect and direct controlled such that tracking errors approach toward designed sliding surfaces. The closed-loop stability of the proposed MSMC is proved to possess uniformly ultimately bounded (UUB) performance by Lyapunov stability criteria. Furthermore, the simulation results reveal that the proposed MSMC strategy has a high level of robustness despite addition of an external load and random uncertainties on system parameters. In the meantime, the simulations for comparing the baseline controller (i.e. conventional PI control) are also conducted to verify the superiority of the proposed control scheme.

Nanoparticles were added to improve the tribological performance of the biopolymer-based composite films. Aluminum and alumina were used as additives. The matrix of the composite was MoS2/hydroxypropyl methylcellulose (HPMC). The ternary additive/MoS2/HPMC hybrid composites were successfully prepared via solvent evaporation. The surface morphology, thickness, microstructure, and wear scars were analyzed using scanning electron microscopy. X-ray diffraction was used to analyze the crystal structures of the nanoparticles in the composite films. Finally, a wear test was conducted to determine the tribology behavior and was discussed using the third-body theory. Because of the high surface-area-to-volume ratio of the additives, nanoparticles were exposed and densely distributed on the composite surface. Disclosed nanoparticles caused peaks and valleys and showed more significant undulations, prompting a highly rough surface. The addition of nanoparticles enhanced the load capacity of the composite films by 155%. In the meantime, nanoparticle additives significantly reduced the coefficient of friction by 50% and improved anti-wear performance by five times. The nanoparticles in the wear scar exhibited an excellent third-body mechanism during the wear process, coordinating the velocity accommodation mode between the two rubbing surfaces and the transfer load.