Oriented to the position tracking and attitude control problem of quadrotors, an analytic optimal strategy is proposed based on iterative sequential action control, considering the applicability and computing efficiency. To begin with, the nonlinear dynamics of quadrotors are described using quaternions. Then, the iterative sequential optimization strategy generates candidate actions based on the coupled 6-Degree-of-Freedom (6-DoF) model. Each action is a triplet consisting of the amplitude, application occasion and duration. After selection and synthesis, the optimal sequences in the flight are determined. The advantages of the proposed strategy are energy conservation and accurate tracking, owing to the application of discrete signals. Finally, forward simulations of the quadrotor are conducted in various, with detailed analysis, to demonstrate the efficiency of the strategy.

Addressing external disturbances has been a critical issue for control design to ensure reliable operation of systems. This article investigates the tracking control problem for the uncertain nonlinear systems with the strong external disturbance and the prescribed performance. The flexible performance-based control scheme is developed by introducing an external disturbance criterion into the prescribed performance. It is capable of guaranteeing the prescribed performance if the external disturbance is less than a specified threshold and degrading that in light of the user-appointed rule otherwise. Particularly, the disturbance interval observer is synthesized to generate the boundaries of the external disturbances and realize the judgment of that criterion. With the generated boundaries, the interval-type auxiliary system is designed to provide the modified performance functions (MPFs) that characterize performance requirement and degradation rule simultaneously. Based on the positive system theory and the Lyapunov method, it is theoretically shown that the system output can always track the reference signal and satisfy the constraints of MPFs. Finally, both the numerical simulation and the application of flight control design verify that the results are effective and valid.

Since the classical barrier Lyapunov function (BLF) suffers from the restriction on the availability of constrained signals, this work proposes the concept of the interval BLF through introducing the nonlinear interval observer (NIO) technology. Specifically, the velocity-constrained tracking control design of the wheeled mobile robot (WMR) is studied without the linear velocity measurement. To accomplish the constraint objective on the unmeasured linear velocity, the NIO is developed to estimate the upper and lower boundaries of that. Through tactfully using these boundaries and designing the interval BLF, the tracking control scheme is developed for the WMR to accomplish the velocity constraint objective for both the linear and angular velocities. Finally, the proposed control scheme is demonstrated through numerical validation.