Barrier function-based adaptive nonsingular terminal sliding mode control technique for a class of disturbed nonlinear systems.

In this article, an adaptive non-singular terminal sliding mode controller (NTSMC) is designed based on a barrier function for the robust stability of a category of non-linear dynamic systems in the existence of the external disturbances. The planned approach implements a non-singular terminal sliding mode controller (NTSMC) to ensure robust performance with finite time convergence and singularity-free dynamics. It also uses Barrier Functions (BFs) as an adaptation approach for the NTSMC to attain the tracking errors' convergence to a pre-defined neighbourhood of origin, with a controller gain that is not over-estimated and without requiring any knowledge about the upper bounds of disturbances. The Lyapunov-based stability analysis is carried out to confirm the asymptotic convergence of tracking errors to a pre-defined neighbourhood of zero. The effectiveness and performance of the planned approach is illustrated through simulations and experiments.

H∞-based control of multi-agent systems: Time-delayed signals, unknown leader states and switching graph topologies.

The paper investigates a leader-following scheme for nonlinear multi-agent systems (MASs). The network of agents involves time-delay, unknown leader's states, external perturbations, and switching graph topologies. Two distributed protocols including a consensus protocol and an observer are utilized to reconstruct the unavailable states of the leader in a network of agents. The H∞-based stability conditions for estimation and consensus problems are obtained in the framework of linear-matrix inequalities (LMIs) and the Lyapunov-Krasovskii approach. It is ensured that each agent achieves the leader-following agreement asymptotically. Moreover, the robustness of the control policy concerning a gain perturbation is guaranteed. Simulation results are performed to assess the suggested schemes. It is shown that the suggested approach gives a remarkable accuracy in the consensus problem and leader's states estimation in the presence of time-varying gain perturbations, time-delay, switching topology and disturbances. The H∞ and LMIs conditions are well satisfied and the error trajectories are well converged to the origin.

Smooth super-twisting sliding mode control for the class of underactuated systems.

In this article, Smooth Super-twisting Sliding Mode Control (SSTWSMC) is investigated for the class of underactuated system. In underactuated systems, the control design is not directly applicable as for other systems (known as fully actuated systems). Therefore, at initial step, a nonlinear uncertain model of systems is transformed into the controllable canonical form, and then Smooth Super Twisting (SSTW) based Sliding Mode Control (SMC) is devised for the control design purpose for the considered class. In addition, closed loop stability of the proposed technique is presented in a fascinating way. The effectiveness and supremacy of the proposed control technique is proven by extensive analysis between conventional Sliding Mode Control (SMC), Super twisting (STW) sliding mode control and Smooth Super-twisting Sliding Mode Control (SSTWSMC). The comprehensive analysis evaluates the attributes like robustness enhancement, settling time, control effort, chattering reduction, overshoot, sliding mode convergence, etc. and is supported by simulations as well as practical implementation on ball and beam balancer (which is considered as application example).