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In this paper, the terminal guidance problem of unpowered lifting reentry vehicle to stationary target is studied. Based on the requirement of attacking the target with high precision and high impact angle constraint, a fractional-order theory combined sliding mode guidance law is proposed. Its sliding surface is specially designed to satisfy the requirements in the terminal guidance phase. The novel fractional-order sliding mode guidance law is established in both two-dimensional environment and three-dimensional environment; then, the systems are proved to be asymptotically stable according to the Lyapunov stability principle. Finally, compared with the one without fractional-order term, experiments show the novel guidance law has better stability. Monte Carlo simulation verifies that the designed guidance law is more robust against the disturbance of random noise and ensures higher precision in terms of impact angle error and miss distance.

This paper proposes a novel fractional-order P I λ D sliding mode controller for a n th-order nonlinear system with compound disturbance. The novel method contains a fractional-order term in the sliding mode surface compared with the traditional sliding mode controller. The n th-order nonlinear system with disturbance is firstly investigated. Then the effects of the fractional-order P I λ D sliding mode controller with different fractional-orders are studied and the effect is compared with PID controller. Finally, the fractional-order sliding mode controller is designed for hypersonic vehicles. Moreover, in order to combine the advantage of fractional-order sliding mode control with neural network, a fractional-order sliding mode controller with neural network observer is proposed for hypersonic vehicles in this study. The neural network observer is introduced to approximate the compound disturbance and relax the requirement of the switching gain. Based on Lyapunov stability theory, the attitude-tracking errors are shown to be asymptotically stable. The simulation results show that the proposed control scheme achieves satisfactory control performance compared with PID controller and is robust against compound disturbance.

This paper presents an adaptive high-order sliding mode control scheme targeting for uncertain minimum phase nonlinear single-input-single-output (SISO) systems, which can be equivalently formulated as the finite-time stabilization of high-order input-output dynamics subject to the uncertainties of parameters such as a chain of integrators. The proposed controller is derived from the concept of integral sliding mode and consists of two parts, one part of which achieves the finite-time stabilization of the high-order input-output dynamics without uncertainties by solving a finite-horizon optimal control problem with a free-final-state. The other part adopts the adaptive sliding mode control technique considering the practical bounded uncertainties, by which a modified switching gain adaptation algorithm is developed so that the on-line switching gain selection can be executed and the upper bounds of the uncertainties are not requisite in advance. As a result, a high-order sliding mode is established, ensuring the sliding variables and its high-order derivatives converge to an arbitrarily small vicinity of the origin in finite time. Therefore, the proposed controller achieves fixed convergence time and further improves strong robustness against bounded uncertainties with lower chattering and the easy implementation. Simulation results are presented in detail to verify the effectiveness and feasibility of the proposed algorithm.

This work investigates the attitude control of reentry vehicle under modeling inaccuracies and external disturbances. A robust adaptive fuzzy PID-type sliding mode control (AFPID-SMC) is designed with the utilization of radial basis function (RBF) neural network. In order to improve the transient performance and ensure small steady state tracking error, the gain parameters of PID-type sliding mode manifold are adjusted online by using adaptive fuzzy logic system (FLS). Additionally, the designed new adaptive law can ensure that the closed-loop system is asymptotically stable. Meanwhile, the problem of the actuator saturation, caused by integral term of sliding mode manifold, is avoided even under large initial tracking error. Furthermore, to eliminate the need of a priori knowledge of the disturbance upper bound, RBF neural network observer is used to estimate the disturbance information. The stability of the closed-loop system is proved via Lyapunov direct approach. Finally, the numerical simulations verify that the proposed controller is better than conventional PID-type SMC in terms of improving the transient performance and robustness.

In this paper, a predefined-time fractional-order time-varying sliding mode controller is proposed for a class of second-order systems. The state errors are converged to zero at a predefined time, which can be set in advance by an explicit parameter. The stability is proved by Lyapunov second method and the predefined-time convergence is directly proved by solving the analytical formula for the state errors with squeeze theorem and mean value theorem. The sliding mode arrival phase caused by the initial state errors is eliminated in the designed controller, which has stronger robustness. Compared with the integer-order ones, the predefined-time fractional-order time-varying sliding mode controller proposed in this paper has stronger anti-interference ability. The controller is applied to the design of terminal guidance law for hypersonic vehicles. The simulation results show that the designed guidance law can ensure high precision in terms of impact angle error and miss distance under severe interference.

In this paper, the impact angle constrained guidance problem, focusing on the nonlinear engagement dynamics, is considered. In order to fulfill the terminal constraints, a novel function-based finite-time sliding mode control methodology is introduced to design the guidance law. The main feature of this guidance law is that it achieves the desired impact angle exactly at the time of interception. In addition, it is capable of ensuring a continuous and smooth control action. To improve the tolerance of initial heading errors and broaden the application, a feasible guidance logic is also developed. Numerical simulations in various scenarios have shown that the proposed guidance scheme can realize all-aspect interception against stationary, constant-velocity and maneuvering targets. Furthermore, comparison studies with respect to nonsingular terminal sliding mode control-based methods demonstrate the superiority of the proposed method.

In this paper, a time-varying nonsingular terminal sliding mode (T-NTSM) controller is proposed and modified for the rigid robot manipulators with parametric uncertainties and external disturbances. First, in order to eliminate the reaching phase, a novel T-NTSM manifold is proposed by incorporating a piecewise defined function of time into a nonsingular terminal sliding mode manifold. Then a T-NTSM controller is derived from such a sliding surface, by which the robustness is ensured during the entire response of the system, and the convergence time can be chosen in advance. An especially effective method is provided for parameter selection to meet the convergence time requirement. Subsequently, a modified T-NTSM controller is proposed to enhance performance by introducing a time-varying gain in the proposed T-NTSM manifold. The modified controller ensures faster convergence rate and smaller control input amplitude. Finally, the proposed controllers are applied in the control of a two-link manipulator. All of the simulation results demonstrate the effectiveness of the proposed control methods.

The paper presents a gauss pseudospectral solution for the trajectory optimization problem of a hypersonic vehicle. Determination of optimal trajectory of a hypersonic vehicle is of great interest due to the different path and boundary conditions that need to be met for high accuracy. Recent researches show that pseudospectral methods are capable of providing high accuracy in computationally efficient manner. The hypersonic vehicle optimized here is accelerated through solid rocket propulsion to mach 3.5 and after ejection of the rocket motor it is accelerated to mach 6 where it starts cruise for reaching target. The flight profile which is divided into boost, ascent, cruise and dive phase is optimized using multi-phase implementation programme of gauss pseudospectral method GPOPS. The optimization is carried out in 2D assuming non-rotating flat earth assumption and considering propulsion, dynamic and atmospheric constraints. The results are then analyzed for max range and max final velocity and hit angle. The results are found to be feasible.

Purpose – The purpose of this paper is to design a global robust and continuous control scheme for the attitude tracking control problem of the reentry vehicle with parameter uncertainties and disturbances. Design/methodology/approach – First, feedback linearization is applied to the model of reentry vehicle, resulting in three independent uncertain subsystems. Then a new second-order time-varying sliding function is proposed, based on which a continuous second-order time-varying sliding mode control (SOTVSMC) law is proposed for each subsystem. The global robustness and convergence performance of the closed-loop reentry vehicle control system under the proposed control law are proved. Findings – Simulation is made for a reentry vehicle through the assumption that there is external disturbance to aerodynamic moment and the aerodynamic parameters as well as the atmospheric density are perturbed. The results verify the validity and robustness of the proposed strategy. Originality/value – The SOTVSMC attitude controller based on feedback linearization is proposed for the reentry vehicle. The advantages of the proposed SOTVSMC are twofold. First, the global second order sliding mode is established, which implies that the closed-loop system is global robust against matched parameter uncertainties and disturbances in reentry. Second, the chattering problem is significantly alleviated.