Fixed-time Tracking Control Research Articles

6-DOF fixed-time adaptive tracking control for spacecraft formation flying with input quantization

This paper addresses fixed-time tracking control problems for spacecraft formation flying (SFF) with model uncertainties, external disturbances, and input quantization. Firstly, a coupled model based on dual quaternions is introduced to describe the six-degrees-of-freedom (6-DOF) relative motion of spacecraft formation flying. Secondly, hysteretic quantized control input is implemented to reduce the required communication rate and to avoid the oscillations caused by the logarithmic quantizer. Thirdly, a fast terminal sliding mode tracking controller with adaptive updating laws is proposed to guarantee that the resulting closed-loop system is fixed-time stable, and that the relative motion tracking errors converge to a neighborhood around the origin in a fixed time, despite the presence of model uncertainties, external disturbances, and input quantization. Finally, a simulation example is presented to show the effectiveness of the proposed control design scheme.

Adaptive fixed-time relative position tracking and attitude synchronization control for non-cooperative target spacecraft fly-around mission

In this paper, the problem of adaptive fixed-time tracking control for non-cooperative target spacecraft fly-around mission in the presence of the parameter uncertainties and external disturbances is investigated. Firstly, a novel and effective 6 DOF relative motion dynamic model constructed by relative position motion model expressed in the LOS frame and attitude dynamic model described by Modified Rodriguez parameters (MRPs) is firstly established. Subsequently, a new modified nonsingular fast terminal sliding mode (MNFTSM) with bounded convergence time in regardless of the initial states is designed, which not only can circumvent the singularity problem effectively, but also has the advantages of FTSM. By employing MNFTSM and adaptive techniques, two continuous adaptive fixed-time nonsingular fast terminal sliding mode (AFNFTSM) control laws are proposed, which can eliminate the chattering phenomenon and do not require precise knowledge of the mass, inertia matrix. Rigorous proofs show that both of two AFNFTSM control laws can guarantee that the relative position and attitude errors can converge to the small regions containing the origin in fixed time. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed control schemes.

Fixed‐time backstepping control design for high‐order strict‐feedback non‐linear systems via terminal sliding mode

In this study, the state feedback fixed-time control problem is addressed for a class of high-order strict-feedback non-linear systems (SFNSs) with mismatching system uncertainties. Based on the fixed-time control technique and uniform exact difference method, a new fixed-time tracking control algorithm via the backstepping method in conjunction with a novel second-order sliding mode super-twisting-like structure adaptive fixed-time disturbance observer is proposed. Compared with many existing finite-time control results in which the convergence time grows unboundedly when the system initial conditions grow, the fixed-time control provides faster convergence rate by using high-degree terms and the settling time function derived only with controller parameters, is allowed to be adjusted independently of the system initial conditions. Moreover, to avoid the computation explosion, the singularity problem and to relax the assumption on the mismatching system uncertainties, the dynamics surface control method is employed based on a novel non-linear non-smooth first-order filter. Then the semi-globally uniformly fixed-time convergent performance of the high-order SFNSs is achieved. Finally, theoretical results are supported by simulation and experimental results.

Nonlinear feedback design for fixed-time tracking of a class of nonlinear systems

ABSTRACTFixed-time control is more preferable than finite-time control in practical applications since the settling time is independent of the system initial condition in a fixed-time control problem. Moreover, systems in real world usually suffer from unfavourable factors, such as unknown control coefficients and external disturbance. In this paper, we consider the fixed-time tracking control for a class of nonlinear systems by considering the aforementioned two points. A strategy for specifying the control input is established by the method of adding a power integrator. The designed control law guarantees that the reference signal can be followed in a fixed time. As an application, the bank-to-turn missile system is used to show the efficiency of the proposed fixed-time tracking scheme.