Search

In this paper, a fixed-time adaptive recursive sliding mode (FTARSM) control scheme is addressed for a steer-by-wire (SbW) automated guided vehicle against model uncertainties and disturbances. First, based on a newly constructed faster fixed-time stable system, a fixed-time recursive sliding structure is developed to guarantee the SbW system fixed-time convergence, where the setting time is independent of initial conditions. By making appropriate initialization settings for the recursive structure, the sliding reaching phase is removed and the control robustness is improved. Then, the extreme learning machine (ELM) is incorporated into the FTARSM controller to estimate the lumped uncertainties upper bound, thus not only the requirement for prior bounds information in controller design is eliminated but also the control chattering is suppressed effectively. Rigorous Lyapunov analyses are further employed to ensure fixed-time closed-loop stability. Finally, the superior performance of the derived control law is verified by experimental results. [ABSTRACT FROM AUTHOR]

High-efficiency permanent-magnet synchronous motor (PMSM) is a key technology to improve the driving range of batteries in electric vehicles, while the mismatched disturbance that is caused by external disturbances and parameter perturbation may easily result in speed fluctuations and overshoot of the PMSM, which further deteriorate the performance and efficiency of batteries. To solve the problem, a novel nonlinear disturbance observer-based sliding mode control (NDO-SMC) is proposed. Compared with the traditional SMC method, the NDO-SMC scheme has better disturbance rejection ability in the presence of matched and mismatched uncertainties and disturbances by introducing the estimation value of the nonlinear disturbance observer in the sliding surface. Furthermore, owing to the compensation of the disturbance observer, the switching gain is only required to be greater than the bound of the disturbance estimation error rather than that of the disturbance; thus, the chattering problem is substantially alleviated. A rigorous stability proof of the whole closed-loop system is given in detail using Lyapunov theory by designing an appropriate Lyapunov function. The simulation results demonstrate the feasibility and superiority of the proposed NDO-SMC strategy. [ABSTRACT FROM AUTHOR]

Manipulating crystallization for macromolecule using ionic liquids (ILs) as an additive has received great attention, but how ILs accurately control their formation and crystallization pathway remains unclear. Here, we aim to illuminate the role of ILs on the solution chemistry of macromolecules by investigating their effects on the crystallization of lysozyme. The solubility findings show ILs changed intermolecular contacts, leading to lysozyme supramolecular repulsive interactions being induced or attractive interactions enhanced. Lysozyme was crystallized in the form of tetragonal crystals in the presence of [C4mim]BF4 (1-butyl-3-methylimidazolium tetrafluoroborate), [C4mim]Cl (1-butyl-3-methylimidazolium chloride) and [C4mim]Br (1-butyl-3-methylimidazolium bromide), while it was crystallized in the form of monoclinic crystals in the presence of [dmim]I (1,3-dimethylimidazolium iodine). Compared with that in the absence of ILs, lysozyme in the presence of [C4mim]Cl and [dmim]I contained a decreased α-helix content, but increased β-sheet content. The presence of [dmim]I also caused the β-turn content to increase and random coil content to decrease. This demonstration shows the formation of crystal nucleus is involved in transition at the protein secondary structure level, which may contribute to a better understanding of the role of ILs in the crystallization of bio-macromolecular materials and to developing a strategy to produce new bio-macromolecular materials using ILs. [ABSTRACT FROM AUTHOR]

The fractionation of oils has received considerable research attention, aiming at the modification of the properties of oils. The thermal and crystallization properties of palm kernel oil (PKO) and its olein/stearin (PKOL/PKST) were systematically investigated using differential scanning calorimetry (DSC). Based on the isothermal DSC results, crystallization temperature exerted critical effect on co-crystallization of PKOL and PKST. Moreover, it is reported that PKOL could be further separated by controlling the crystallization temperature, while PKST is hard to be further separated. The PKOL/PKST mixtures with different compositions were prepared and subjected to dynamic DSC analysis. The results illustrated that PKO meets the phase equilibrium of quasi-solid solutions. [ABSTRACT FROM AUTHOR]