Fixed-time trajectory following for quadrotors via output feedback

Cooperative group formation control for multiple quadrotors system with finite- and fixed-time convergence

A multitude of quadrotors cooperatively executing complicated tasks in predefined geometric configurations has attracted arising attention. Accurate and effective formation control laws are essential for completing missions. Finite- and fixed-time group formation control problems for multiple quadrotors are researched in this paper. The quadrotors are first divided into M distinct and non-overlapping subgroups. In each subgroup, quadrotors are driven to form the predefined configuration, with the whole achieving M-group formation meanwhile. Two distributed algorithms for multiple quadrotors system are then designed to realize finite- and fixed-time group formation. Detailed and theoretical analysis of finite- and fixed-time group formation formability is conducted. Sufficient conditions are provided by utilizing the Lyapunov stability and bi-limit homogeneity theory. Two simulations are carried out to verify the effectiveness of proposed algorithms.

Modeling and practical fixed-time attitude tracking control of a paraglider recovery system

The mathematical modeling and the control problem of the paraglider recovery system (PRS) are investigated in this paper. A 9-degree-of-freedom dynamic model describing the paraglider recovery control system is modeled including the inside relative rotation, the apparent mass, and the payload's time-varying inertia. On the basis of the attitude tracking error system, a novel practical fixed-time attitude tracking control approach is then proposed. The attitude tracking error is governed to converge into the small regions of the origin with a fixed-time convergence rate. Moreover, this rate is independent of any initial states. Simulation results are finally presented to illustrate the PRS performance obtained from the proposed control scheme.

Wayset-based guidance of multirotor aerial vehicles using robust tube-based model predictive control

The present paper is concerned with the wayset-based guidance of underactuated multirotor aerial vehicles (MAVs). A hierarchical guidance and control structure is first established, in which the guidance is realized as a supervisory loop. The lower-level stabilizing attitude and position control laws are assumed to be available. On the other hand, the outer-loop guidance is designed based on a fixed-horizon tube-based robust model predictive control (MPC), which conducts the MAV to visit a given sequence of waysets, without violating their state and control bounds, and allowing the vehicle to rest in each wayset for a specified period. The MPC is designed using a reduced-order closed-loop dynamic model describing the vehicle's translation, which is derived considering the stabilizing position and attitude control laws and the assumption of a time-scale separation between the closed-loop translational and rotational dynamics. This model is put into a discrete-time linear state-space representation subject to additive bounded random disturbance and measurement noise. The properties of the proposed method, which includes the MPC recursive feasibility and robust stability as well as the overall guidance feasibility, are analytically studied. The method is also numerically evaluated using a realistic quadrotor dynamic model, showing its effectiveness and confirming its properties.

Fixed-Time Circular Impact-Time Guidance with Look Angle Constraint

A fixed-time nonlinear circular guidance law that satisfies the impact time constraint is proposed. By utilizing the geometric principle that the length of a circular arc connecting the missile and the target can be analytically calculated, the exact expression of time-to-go is obtained. Thus, the impact time error can be shaped to zero, and the missile can intercept the target at the desired time, which is crucial in a salvo attack. The settling time of the impact time error is proved to be bounded by a fixed time, which does not depend on initial conditions, but is only determined by two guidance parameters. Moreover, the criteria for choosing the guidance parameters values are established analytically, rather than by trial-and-error or empirically, which can provide valuable guidelines for guidance law designers. To address the look angle constraint, deviated pure pursuit (DPP) is employed, and switching logic between guidance laws is provided. Unlike many existing impact time control guidance laws, the formulation of the one proposed is based on nonlinear engagement kinematics, and the implementation does not execute numerical calculations, which can improve the guidance accuracy and reduce computation burdens on the guidance system. A series of nonlinear simulations are implemented to verify the effectiveness of the proposed guidance law.

Fixed-time consensus tracking control with connectivity preservation for strict-feedback nonlinear multi-agent systems

This paper deliberates fixed-time consensus tracking control for strict-feedback nonlinear multi-agent systems with limited communication/sensing range constraints. First, both potential function and coordinate error transformation surface are designed to make the constraints implicit. Next, based on the synthesis of neural network and adaptive technology, the fixed-time virtual variable is proposed without the upper bounds of estimation errors and disturbances. Then, a fixed-time distributed consensus tracking protocol is designed under backstepping method with a fixed-time differentiator to avoid singularity. Lyapunov stability analysis demonstrates that the closed-loop system under the designed control strategy can accomplish the convergence within fixed time, simultaneously connectivity preservation can be guaranteed. Finally, numerical emulation corroborates the availability of the designed control strategy.

A Robust Observer—Based Adaptive Control of Second—Order Systems with Input Saturation via Dead-Zone Lyapunov Functions

In this study, a novel robust observer-based adaptive controller was formulated for systems represented by second-order input–output dynamics with unknown second state, and it was applied to concentration tracking in a chemical reactor. By using dead-zone Lyapunov functions and adaptive backstepping method, an improved control law was derived, exhibiting faster response to changes in the output tracking error while avoiding input chattering and providing robustness to uncertain model terms. Moreover, a state observer was formulated for estimating the unknown state. The main contributions with respect to closely related designs are (i) the control law, the update law and the observer equations involve no discontinuous signals; (ii) it is guaranteed that the developed controller leads to the convergence of the tracking error to a compact set whose width is user-defined, and it does not depend on upper bounds of model terms, state variables or disturbances; and (iii) the control law exhibits a fast response to changes in the tracking error, whereas the control effort can be reduced through the controller parameters. Finally, the effectiveness of the developed controller is illustrated by the simulation of concentration tracking in a stirred chemical reactor.