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"attitude control"
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Fixed-time control for high-precision attitude stabilization of flexible spacecraft
This is a study of adaptive constraint attitude control for a flexible spacecraft in the presence of inertia uncertainties, unknown disturbance, actuator saturation and faults. The proposed controller is designed by incorporating a Prescribed Performance Control (PPC) and fixed-time sliding mode control. First, a novel Nonsingular Fast Fixed-time Sliding Surface (NFFTSS) is introduced. Not only is the settling time independent of initial conditions, but also it is shorter than existing fixed-time attitude controls. Second, different from the conventional complex PPCs in the literature, a simple structure attitude controller is proposed to satisfy the transient and steady-state performance is proposed through a novel log-type PPC. An inherently continuous adaptive switching control is then presented in order to avoid the a priori not to require accurate information of the fault occurrence. Numerical simulations demonstrate that the proposed controller successfully accomplishes attitude control with high attitude pointing accuracy and stability.
Journal Article
Prescribed performance adaptive attitude tracking control for flexible spacecraft with active vibration suppression
This paper investigates the high-performance attitude control and active vibration suppression problem for flexible spacecraft in the presence of external disturbances. The active vibration control usually depends on additional sensors and actuators, which will highly increase the difficulty of practical application. In order to reduce the implementation complexity, the piezoelectric sensors are not adopted, but instead a modal observer is introduced to estimate the modal information. Based on the observed modal information and the prescribed performance design process, an adaptive attitude controller is developed, which has the capabilities of rejecting disturbances as well as possessing predetermined transient and steady-state control performance. Similarly, an active controller is constructed to deal with the vibrations induced by attitude motions. It can be proved that by constraining the estimations of the modal variables, the actual modal coordinate will also be constrained with expected attenuation characteristics. The stability of the entire closed-loop system is analyzed by the Lyapunov theory. Simulation results in different cases show the effectiveness and performance of the proposed algorithms.
Journal Article
Chattering-free Fault-tolerant Attitude Control with Fast Fixed-time Convergence for Flexible Spacecraft
This paper is mainly dedicated to the challenging issue of fixed-time attitude control for a flexible spacecraft in the presence of actuator faults, external disturbances and coupling effect of flexible modes. The attitude controller is developed by employing a fixed-time nonsingular terminal sliding mode under which the convergence time is bounded and independent of the initial states. This robust attitude controller is able to provide superior properties such as fast fixed-time attitude manoeuvring with high pointing accuracy, singularity avoidance and chattering free. More specifically, a new reaching law is employed to provide convergence rate improvement as well as chattering alleviating simultaneously. The actuator fault problem is also considered and the attitude control is achieved even when the actuators experience severe faults. The proposed controller ensures that the closed-loop attitude system is stable in the sense of fixed-time stability concept. Furthermore, since the upper bound of external disturbances and flexible vibrations acting on the spacecraft is not available, an adaptation mechanism is presented. Numerical simulations demonstrate that the proposed controller is able to successfully accomplish attitude control with high attitude pointing accuracy and stability in spite of the actuator faults, flexible structures vibrations and external disturbances.
Journal Article
Integrated uncertain optimal design strategy for truss configuration and attitude–vibration control in rigid–flexible coupling structure with interval uncertainties
By simultaneously considering the supported truss configuration optimization and optimal attitude–vibration control in rigid–flexible coupling (RFC) structure, this study proposes a novel integrated uncertain optimal structure-control design strategy with interval uncertainties. Based on the principle of energy equivalence, the flexible support truss of the RFC structure is simplified using an equivalent beam model, which can significantly reduce the degree of freedom of the model and improve design efficiency on the premise of satisfying the analysis accuracy of the static and dynamic characteristics of the complete truss structure. The Lagrangian method is applied to establish an RFC structure model including a central rigid body, equivalent flexible truss and free end mass. Given the difficulty of quantifying the multi-source uncertainty encountered by actual RFC structures, the structural optimization and control system design in this study considers them as interval uncertainty. As long as the uncertainty bounds are known, the uncertainty propagation in the integrated design strategy can be quantified using interval dimension-wise analysis. The time-independent interval reliability-based frequency constraint and time-dependent interval reliability-based dynamic response constraint are both constituted for the proposed integrated uncertain optimal design strategy, which is solved using an advanced multi-objective optimization algorithm. One numerical example is applied to verify the proposed method. An optimum integrated design layout with a lightweight truss configuration and a low energy consumption control system is obtained.
Journal Article
Adaptive Fuzzy PID Control Strategy for Spacecraft Attitude Control
In this paper, a novel adaptive fuzzy proportional–integral–derivative (AFPID) controller is designed for geostationary satellite attitude control. In order to design the AFPID controller, first a fuzzy PID (FPID) controller is proposed in which two fuzzy inference engines are used: single-input fuzzy inference engine (SIFIE) and preferential fuzzy inference engine (PFIE). SIFIE has only one input which means a separate SIFIE is assigned to each state variable, and on the other side, PFIE represents the control priority order of each state variable. Consequently, control gains of FPID controller will be adjusted and updated with a sliding mode-based adaptation mechanism. As a result, via numerical simulations, objectives of the AFPID controller in terms of faster convergence time and higher performance are achieved.
Journal Article
Predefined‐Time Fault‐Tolerant Control of Rigid Spacecraft With Prescribed Performance
This paper proposes a predefined‐time fault‐tolerant control strategy to address the attitude tracking problem of rigid spacecraft, considering time‐varying actuator faults, inertia uncertainties and unknown external disturbances. To ensure both transient and steady‐state performance of attitude tracking, prescribed performance functions are introduced, and coordinate transformations are employed to convert constrained tracking errors into unconstrained states. Based on the transformed errors and the command‐filtered backstepping recursive design procedure, a predefined‐time fault‐tolerant controller incorporating radial basis function neural networks (RBFNNs) is systematically developed. RBFNNs are utilized for online estimation and compensation of the system's unknown dynamics, thereby improving control accuracy. The proposed controller guarantees that spacecraft attitude errors converge to minimal neighbourhoods of the origin within a predefined settling time. Finally, comparative simulation results validate the effectiveness of the proposed control approach.
Journal Article
Barrier function-based adaptive integral sliding mode finite-time attitude control for rigid spacecraft
This paper investigates the problem of attitude tracking control with predefined-time convergence for rigid spacecraft under external disturbances and inertia uncertainties. Firstly, the proposed nominal controller is designed to achieve attitude tracking control of the rigid spacecraft in the absence of disturbances and inertia uncertainties, and the convergence of the spacecraft attitude errors can be selected in advance. Then, the integral sliding mode combined with barrier function-based adaptive laws is proposed to reject the disturbances and inertia uncertainties, and at the same time, a barrier function-based adaptive method can also ensure the solutions of the rigid spacecraft system belonging to a stipulated vicinity of the intended variables starting from the initial moment and the uncertainties’ upper bound is not overestimated. Finally, a numerical simulation is provided to illustrate the efficiency of the proposed control protocol.
Journal Article
Mitigating the curse of dimensionality: sparse grid characteristics method for optimal feedback control and HJB equations
We address finding the semi-global solutions to optimal feedback control and the Hamilton–Jacobi–Bellman (HJB) equation. Using the solution of an HJB equation, a feedback optimal control law can be implemented in real-time with minimum computational load. However, except for systems with two or three state variables, using traditional techniques for numerically finding a semi-global solution to an HJB equation for general nonlinear systems is infeasible due to the curse of dimensionality. Here we present a new computational method for finding feedback optimal control and solving HJB equations which is able to mitigate the curse of dimensionality. We do not discretize the HJB equation directly, instead we introduce a sparse grid in the state space and use the Pontryagin’s maximum principle to derive a set of necessary conditions in the form of a boundary value problem, also known as the characteristic equations, for each grid point. Using this approach, the method is spatially causality free, which enjoys the advantage of perfect parallelism on a sparse grid. Compared with dense grids, a sparse grid has a significantly reduced size which is feasible for systems with relatively high dimensions, such as the 6-D system shown in the examples. Once the solution obtained at each grid point, high-order accurate polynomial interpolation is used to approximate the feedback control at arbitrary points. We prove an upper bound for the approximation error and approximate it numerically. This sparse grid characteristics method is demonstrated with three examples of rigid body attitude control using momentum wheels.
Journal Article
Attitude Control for a satellite with inertial wheels based on Attractive Ellipsoids Method
This article presents a robust control law based on the Attractive Ellipsoids Method applied to perform attitude control of a satellite that has inertial wheels and relatively small dimensions such as microsatellites or other similar architectures. The novelty lies in the fact that under certain characterized external and parametric perturbations it is possible to track the desired angular trajectory with an optimization method to determine the computed torque. Additionally, a demonstration of this methodology is carried out with a numerical example.
Journal Article