Adaptive output feedback attitude control of a LEO satellite under angular velocity constraints

In this paper, the rest-to-rest reorientation problem of the uncertain spacecraft with multiple attitude constrained zones and angular velocity limitations is studied. In order to deal with attitude and angular velocity constraints concurrently, two types of logarithmic potential functions are proposed, where the ineffective attitude constraints are excluded in the design of attitude potential function by introducing a warning angle. In addition, we also designed a projection operator-based adaptive law to estimate the upper bounds of the inertia uncertain parameters and the environmental disturbances, so that the estimation process conforms to the physical meaning of the parameters. Combining the two potential functions and the parameters adaptation law, an adaptive controller is constructed to asymptotically stabilize the attitude reorientation error while satisfying the attitude and the angular velocity constraints. Simulation example of an uncertain spacecraft with rest-to-rest attitude maneuver subject to constraints on attitude and angular velocity is carried out, and the obtained results verify the effectiveness of the proposed adaptive attitude controller.KeywordsInertia uncertaintyAttitude constraintAngular velocity constraint

This paper develops adaptive output feedback control to reduce stop-and-go oscillations in congested traffic regime. The macroscopic traffic dynamics are governed by Aw-Rascle-Zhang(ARZ) model, consisting of second-order, nonlinear hyperbolic PDEs of traffic density and velocity. We linearize the PDE system around steady states of congested traffic regime. The boundary input through ramp metering is then introduced for the linearized ARZ traffic model. The goal is to stabilize the oscillations in a freeway segment upstream of the ramp, without the knowledge of relaxation time and boundary parameter. Control is applied at the outlet and the measurement is taken from the inlet. In the absence of both parameter knowledge and full-state measurement, we use backstepping method to transform the system into an observer canonical form in which unknown parameters multiply with measured output. We obtain a parametric model based on this form and gradient-based parameter estimators are employed. An explicit state observer involving the delayed values of the input and the output is proposed for state estimation. Using the parameter and state estimates, we develop an adaptive output feedback control law, which achieves convergence to the steady states in the $L^{2}$ sense.

This paper investigates adaptive output feedback control problem for switched uncertain nonlinear systems with input quantization, unmeasured system states and state constraints. Firstly, fuzzy logic systems are introduced to identify system uncertainties, then the fuzzy based observer is constructed to estimate unavailable states. Secondly, combing the backstepping technique and the barrier Lyapunov function method, an adaptive fuzzy output feedback control law is designed, which guarantees that all signals in the closed-loop system are bounded, the system output tracks the reference signal, and system states satisfy their corresponding constraint conditions. Finally, simulation results further show the good performances of the proposed control scheme.

This paper develops a framework of adaptive compensation of actuator nonlinearities with unknown parameters, for output feedback control of unknown multi-input multi-output linear time-invariant dynamic systems. A new controller parametrization is derived to deal with bilinear parameters from the actuator nonlinearity parameters and the dynamic system parameters, which, based on the LDU decomposition of the system high frequency gain matrix, is capable of overcoming the difficulty caused by a nondiagonal high frequency gain matrix and a special actuator nonlinearity parameter structure. The adaptive actuator nonlinearity compensation control scheme is a model reference adaptive control based design, employing an adaptive output feedback control law combined with an adaptive actuator nonlinearity inverse, to deal with parameter uncertainties in the system dynamics and actuator nonlinearities. Simulation results show the desired adaptive control system performance.

Traffic congestion control for Aw–Rascle–Zhang model

This paper is devoted to investigating the fault-tolerant reduced-attitude control problem for boresight reorientation of an uncertain spacecraft subject to pointing and angular velocity constraints. First, the stereographic projection is used to transform this problem to an obstacle avoidance problem on a two-dimensional Euclidean sphere world with circular obstacles. Then, an adaptive fault-tolerant control strategy is proposed to solve the transformed problem, by designing two potential functions for constraint handling in conjunction with a sliding vector containing hyperbolic tangent functions. Stability analysis shows that the derived controller can achieve asymptotic convergence of the gradient of the obstacle avoidance potential and angular velocities, while ensuring the satisfaction of both pointing and angular velocity constraints, despite the presence of unknown time-varying inertia parameters, disturbances, and actuator faults. In particular, benefiting from incorporating the spacecraft principal moments of inertia into the potential field design, the risk of the system losing strong controllability under multiplicative actuator faults is greatly reduced. To accommodate actuator faults under input saturation, the adaptive fault-tolerant controller is further extended to a saturated counterpart, which is capable of making full use of the remaining actuation power to react to actuator faults. Finally, simulation results are presented to demonstrate our theoretical findings.

Nonlinear adaptive control of an underwater towed vehicle

Event-triggered robust cooperative output regulation for a class of linear multi-agent systems with an unknown exosystem

In this paper, the attitude control problem for uncertain spacecraft under angular velocity constraint is addressed. Both parametric uncertainty and external disturbance are considered in the spacecraft's dynamics. The spacecraft's attitude is represented by modified Rodrigues parameter (MRP) for its non-redundancy. A time-varying sliding mode control (TVSMC) algorithm is derived for attitude control system. The proposed control algorithm eliminates the reaching phase of the conventional time-invariant sliding mode control (SMC) and guarantees the sliding mode occurrence all the time. Moreover, the control parameter is adjusted to avoid the angular velocity constraint during the maneuver. Finally, a numerical simulation is employed to verify the proposed control algorithm.

The paper considers rejection of unmatched general periodic disturbances with time-varying gains for a class of nonlinear systems. The period of the periodic disturbances is known, the gains of the disturbances depend on the output of the system, and the coefficient vector of the disturbance input channel is not assumed to be a Hurwitz vector. A novel filtered transformation is presented. Based on the filtered transformation, an adaptive output feedback control law is proposed, which guarantees that the output of the closed loop system converges to zero.

This paper focuses on the problem of adaptive output feedback tracking control for a class of non-strict-feedback nonlinear systems with unknown control coefficients. By employing a linear state transformation, the original system is transformed to a new system for which control design becomes feasible. Then, after the introduction of a simple input-driven observer, an adaptive output feedback controller which contains only one parameter is developed for such systems by using backstepping technique and variable separation method. The designed controller ensures that all the signals in the closed-loop systems are Semi-globally Uniformly Ultimately Bounded (SGUUB).

This paper focuses on the problem of adaptive output feedback tracking control for a class of nonstrict-feedback nonlinear systems with unknown control coefficients and quantized input. The difficulty from the unknown control direction is solved by using the linear state transformation and the Nussbaum gain function(NGF) approach. Based on the combination of input-driven observer, backstepping technique, neural network(NN) parametrization and variable separation method, a novel adaptive output feedback quantized control scheme involving only one adaptive parameter is developed for such systems. The designed quantized controller ensures that all signals of closed-loop systems are semi-globally uniformly ultimately bounded (SGUUB), and the tracking error converges to an adjustable neighborhood of the origin. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed control design.

A time suboptimal method for on-orbit rapid attitude maneuver control of agile spacecraft with attitude angular velocity constraint is proposed, which can generate suboptimal control torque command for real-time application. Spacecraft time-optimal slew maneuver has been studied by many researchers, and most of the interest is focused on formulating and resolving the optimization problem of spacecraft attitude maneuver in proper ways. Pseudospectral method, among most of the existing methods, is feasible to figure out the preferred solution satisfying the control precision, which possesses the values of practical application. However, pseudospectral method consumes much time for planning attitude trajectory making it impossible for on-orbit spacecraft real-time control, especially for observation mission with frequent maneuver. After thorough analysis of the time optimal attitude maneuvering results, several patterns with respect to the generation of attitude control command are summarized that result in an interpolation control method, which is time suboptimal and is capable of on-orbit real-time application for spacecraft with small products of inertia. Closed-loop control is implemented to cancel the final pointing error. Several simulations have been performed to validate the performance of the proposed strategy, and have demonstrated the potential application for small agile spacecraft with limited attitude control ability.

In this paper, an adaptive output feedback control strategy is presented to solve the stabilization problem of nonholonomic systems in chained form with strong nonlinear drifts and uncertain parameters using output signals only. The control law is developed using input-state scaling and backstepping techniques. The objective is to design adaptive nonlinear output feedback laws which can steer the closed-loop systems globally converge to the origin, while the estimated parameters remain bounded. An adaptive output feedback controller is proposed for a class of uncertain chained systems. Simulation results demonstrate the effectiveness of the proposed controllers.

In this study, the fault-tolerant control problem is investigated for a class of non-affine output-constrained multi-input multiple-output non-linear systems with actuator faults. The controlled systems contain unknown non-linear functions, unknown external disturbance and immeasurable states. The fuzzy logic systems and a robust compensation function are employed to deal with the unknown non-linear functions and non-affine non-linear actuator fault problems. Then, the state observer and the non-linear disturbance observer are developed for estimating the immeasurable states and unknown compounded disturbance, respectively. By using the barrier Lyapunov function method and in the unified framework of adaptive backstepping output feedback control design, a novel adaptive fuzzy fault-tolerant controller design scheme is developed. It is shown that all the variables of the closed-loop system are semi-globally uniformly bounded. Moreover, the system outputs cannot violate their predefined bounds in the presence of the non-affine non-linear faults. A simulation is given to validate the effectiveness of the proposed approach.