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• There is a phenomenon of secondary opening and closing in the flowering process of a single flower in Magnolia × soulangeana 'Hongyun'. • The synchronism of pollen viability and stigma receptivity suggests that dichogamy might be a morphological concept in 'Hongyun'. • The morphological dichogamy may relate to the breeding system type of 'Hongyun' which is partially self-compatible, outcrossing, and demands pollinators. Magnolia soulangeana 'Hongyun' is an ornamental tree used for landscaping. It has an attractive shape and produces abundant showy flowers. However, the fruit set rate of 'Hongyun' is low under natural pollination condition. In this study, we examined the basic characteristics of its breeding system. The results showed that the flower of 'Hongyun' is hermaphroditic, with both pistil and stamen being fertile. The pollen-ovule ratio (P/O) ranged from 3,205.78 to 6,244.21, and the outcrossing index (OCI) was 4. Comparing with different pollination treatments, we found that there was no fruit set under direct bagging, bagging after emasculation, and no bagging and non-pollination after emasculation. Furthermore, the fruit set rate under the geitonogamy treatment was lower than that under the xenogamy treatment, indicating low self-compatibility. Therefore, when combined with the numerical value of P/O and OCI, we infer that the breeding system of 'Hongyun' is partially self-compatible, outcrossing, and demands pollinators. In particular, 'Hongyun' presents a mass-flowering pattern. Furthermore, there is the phenomenon of secondary opening and closing in the flowering process of a single flower. The stigma receptivity and pollen viability of a flower are the strongest when it is slightly blooming during the first flowering. Strangely, the anther wall dehiscence occurs during the second flowering, which may guarantee that 'Hongyun' maintains a morphological dichogamy status to avoid self-fertilization. Overall, the unique flowering dynamics is closely related to the type of breeding system in 'Hongyun'. Group planting will be the best way to promote better reproductive success of 'Hongyun' under garden planting conditions. [ABSTRACT FROM AUTHOR]

This paper presents a disturbance observer-based robust optimal flight control strategy for near space vehicle (NSV) attitude system with external time-varying disturbance generated by an exogenous system. For the purpose of eliminating the effect of the disturbance, nonlinear disturbance observer (NDO) technique is used and the disturbance estimation error is guaranteed to be globally exponential convergence. Then, based on the disturbance estimation result and desired trajectory signal, a steady state control input is presented and the optimal tracking problem of original system with external disturbance can be converted into the optimal regulation problem of a nominal error system. Furthermore, a single network-based adaptive dynamic programming (ADP) method is applied to obtain the corresponding optimal feedback control law. Finally, all the signals in closed-loop system are proved to be uniformly ultimately bounded (UUB) and the tracking error can converge to a sufficiently small bound. Simulation tests about NSV attitude system are given to verify the effectiveness of proposed robust optimal flight control scheme. [ABSTRACT FROM AUTHOR]

This paper investigates a class of uncertain linear discrete-time systems subject to input rate saturation. A predictive sliding mode control approach is proposed which guarantees the control inputs remain bounded in the input rate saturation. Furthermore, the disturbance observer is developed to compensate for the system uncertainty and disturbance. Finally, the simulations demonstrate the effectiveness of the proposed predictive sliding mode control scheme. [ABSTRACT FROM AUTHOR]

This paper investigates a class of nonlinear time-delayed systems with output prescribed performance constraint. The neural network and DOB (disturbance observer) are designed to tackle the uncertainties and external disturbance, and prescribed performance function is constructed for the output prescribed performance constrained problem. Then the robust controller is designed by using adaptive backstepping method, and the stability analysis is considered by using Lyapunov-Krasovskii. Furthermore, the proposed method is employed into the unmanned helicopter system with time-delay aerodynamic uncertainty. Finally, the simulation results illustrate that the proposed robust prescribed performance control system achieved a good control performance. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive non-affine control scheme for the longitudinal short-period model of a generic hypersonic flight vehicle (HFV). Firstly, the non-affine nonlinear characteristics of the aerodynamic coefficients are analyzed, which have great influence on the flight dynamical behaviors. Secondly, without ignoring the non-affine nonlinear aerodynamics, a fuzzy sliding mode adaptive non-affine controller is designed. Under the existence of external disturbances and unmodeled dynamics, the controller can still ensure that the angle of attack tracks the desired signal robustly and asymptotically. Furthermore, the proposed controller does not require the exact bound values of the external disturbances and unmodeled dynamics, which is very important for hypersonic vehicles because the values usually cannot be obtained at hypersonic flight conditions. Finally, the simulation results are provided to illustrate the feasibility and effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Time delay phenomena exist almost everywhere in the actual world and are especially important in the control of an AHV. The small time delay usually ignored in control may cause quite obvious errors in the flight trajectory tracking, because of the extremely high flight speed. In this paper, a new framework of solving a nonlinear input delay regulation problem is proposed for the first time, which is comprised of nonlinear damping controllers, nonlinear disturbance observers, and a nonlinear time delay predictor-based compensator, under the proved separation principle. Then the attitude tracking control of an AHV with a known time-varying input delay is studied based on the proposed design framework. Simulation results show the advantage of the proposed control method. [ABSTRACT FROM AUTHOR]

A robust adaptive backstepping control scheme is proposed, aiming at the attitude system of near space vehicle with compound disturbances, which needs the good control performance and the strong robustness in the flight. Firstly, an algorithm of disturbance approximation is presented for improving the accuracy of disturbance approximation. Secondly, a rapid-convergent nonlinear differentiator is proposed for avoiding differential expansion problem in the procedure of the backstepping design and is used to rapidly estimate the differential of the desired angular rate. Then, the design of compound controller is given through the algorithm of disturbance approximation, the rapid-convergent nonlinear differentiator and the backstepping method, in which the robust terms can offset the impact of the approximation errors. The closed-loop stability is proved by input and output bounded theory. Finally, the simulation results show the good tracking control performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper studies a discrete-time formation containment tracking control problem of a linear heterogeneous multi-unmanned system under the leader-follower formation with switching directed topology and unknown external disturbance. To solve the containment tracking control of the heterogeneous multi-unmanned system with switching directed topology, distributed containment control strategies are presented in this paper. First, according to practical situation, the discrete-time heterogeneous multi-unmanned system composed of unmanned aerial vehicles and unmanned ground vehicle is given. Then, by using switching directed topology, the distributed state feedback control strategies are proposed for the leaders and followers. An l 2 − l ∞ performance index is introduced to guarantee the tracking performance of the heterogeneous multi-unmanned system under the unknown energy-bounded disturbance. The controller gains of the leaders and followers are solved by a set of linear matrix inequalities (LMIs). Finally, simulation results demonstrate the effectiveness of the designed control strategies. [ABSTRACT FROM AUTHOR]

In this article, an adaptive neural fault-tolerant control (FTC) scheme is proposed for the medium-scale unmanned autonomous helicopter subject to external disturbance, actuator fault, and input saturation. Multiple approximators are constructed to handle the unknown terms and promote the control design. The nonlinear coupled function terms are approximated by virtue of the radial basis function neural networks. The unknown disturbance is tackled by the developed disturbance observer. Meanwhile, two auxiliary systems are introduced to handle the actuator fault and input saturation, respectively. In the framework of the backstepping method, a multiapproximator-based adaptive FTC strategy is presented, which assures the boundedness of all closed-loop system signals. Simulation results are presented to validate the availability of the designed controller. [ABSTRACT FROM AUTHOR]

In this paper, a tracking flight control scheme is proposed based on a disturbance observer for a quadrotor with external disturbances. To facilitate the processing of external time-varying disturbances, it is assumed to consist of some harmonic disturbances. Then, a disturbance observer is proposed to estimate the unknown disturbance. By using the output of the disturbance observer, a flight controller of the quadrotor is developed to track the given signals which are generated by the reference model. Finally, the proposed control method is applied to flight control of the quadrotor Quanser Qball 2. The experimental results are presented to demonstrate the effectiveness of the developed control strategy. [ABSTRACT FROM AUTHOR]

In this paper, based on the integral sliding mode method and adaptive dynamic programming (ADP) algorithm, a robust optimal tracking control scheme is presented for near space hypersonic vehicle (NSHV) system in the presence of unknown modeling error, external disturbance, and input saturation. Firstly, combining neural network, auxiliary system and integral sliding mode methods, an adaptive integral sliding mode control (AISMC) law is designed to guarantee system trajectories tend to a defined integral sliding surface and the effects of modeling uncertainty, external disturbance, and control input saturation are eliminated. Then, the robust optimal tracking control problem of original system is converted into the optimal control problem of a nominal system, and an ADP method with single critic network is utilized to acquire the corresponding optimal controller. Furthermore, Lyapunov analysis method shows that the overall control input which contains AISMC law and optimal controller can ensure all the signals in closed-loop system are stable in the sense of uniform ultimate boundedness (UUB). Finally, simulation results about attitude flight control of NSHV are given to verify the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a disturbance interval estimation approach for nonlinear systems. Distinct from the conventional estimation schemes aiming to estimate the magnitude of the disturbance, the disturbance interval estimation approach is capable of approximating the time-varying upper and lower boundaries for the disturbance. To achieve this, the dynamics of the boundary estimation errors are constructed as positive systems by introducing a time-invariant coordinate transformation. The boundary estimation errors are guaranteed to be nonnegative and bounded. Then, the generated interval is capable of covering all possible values of the current disturbance and the interval width can provide a quantized guidance on the estimation accuracy at any time. Furthermore, a general antidisturbance control scheme is summarized in light of the proposed disturbance interval estimation approach. As an illustrative case, an antidisturbance control method is developed by integrating the proposed estimation approach and the sliding mode control. Finally, the proposed disturbance interval estimation approach and the anti-disturbance control method are demonstrated through both the numerical and the experimental validation. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of adaptive fault tolerant tracking control for uncertain nonlinear systems in the event of external disturbances, actuator faults and input saturation. In order to guarantee the transient and steady-state control performance, the prescribed performance function is employed to impose the anticipant performance criterion on the output tracking error. By using the error transformation, the original inequality error constraint is converted to an unconstrained issue. For the conversion systems, the negative effect resulting from the external disturbances is restrained via the adaptive control approach. The radial basis function neural network (RBFNN) is adopted to handle the unknown nonlinear functions. The Nussbaum gain technique is utilised to deal with the nonlinear terms arising from the actuator faults and input saturation. Combining with the backstepping control strategy, an adaptive neural fault tolerant control (FTC) scheme is developed for the uncertain nonlinear systems. It is rigorously proved that the proposed controller is capable of ensuring the boundness of all closed-loop signals as well as the specified tracking performance. Simulation results on two examples are given to illustrate the effectiveness of the presented control approach. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to present a novel structural reliability analysis scheme with considering the structural strength degradation for the wing spar of a generic hypersonic aircraft to guarantee flight safety and structural reliability. Design/methodology/approach: A logarithmic model with strength degradation for the wing spar is constructed, and a reliability model of the wing spar is established based on stress-strength interference theory and total probability theorem. Findings: It is demonstrated that the proposed reliability analysis scheme can obtain more accurate structural reliability and failure results for the wing spar, and the strength degradation cannot be neglected. Furthermore, the obtained results will provide an important reference for the structural safety of hypersonic aircraft. Research limitations/implications: The proposed reliability analysis scheme has not implemented in actual flight, as all the simulations are conducted according to the actual experiment data. Practical implications: The proposed reliability analysis scheme can solve the structural life problem of the wing spar for hypersonic aircraft and meet engineering practice requirements, and it also provides an important reference to guarantee the flight safety and structural reliability for hypersonic aircraft. Originality/value: To describe the damage evolution more accurately, with consideration of strength degradation, flight dynamics and material characteristics of the hypersonic aircraft, the stress-strength interference method is first applied to analyze the structural reliability of the wing spar for the hypersonic aircraft. The proposed analysis scheme is implemented on the dynamic model of the hypersonic aircraft, and the simulation demonstrates that a more reasonable reliability result can be achieved. [ABSTRACT FROM AUTHOR]

This study proposes a sliding mode fault‐tolerant control (FTC) scheme for the medium‐scale unmanned autonomous helicopter with rotor flapping dynamics in the presence of wind gusts and actuator faults using extended state observer technique. The radial basis function neural networks are employed to tackle the unknown non‐linear interaction functions and adaptive neural network extended state observers are constructed to estimate the unknown wind gusts. Meanwhile, the adaptive fault observers are developed to estimate the fault parameters in position, attitude and flapping motion subsystems. With the aim of obtaining satisfactory trajectory tracking performance, a robust adaptive sliding mode FTC scheme is presented based on the backstepping sliding mode control technique and the closed‐loop system stability is rigorously proved via Lyapunov analysis. Simulation results are carried out to validate the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

An integrated guidance and control scheme is proposed on path following for the unmanned aerial vehicle. It is capable of handling the coupled non-linearities of the path's kinematics and the aircraft's dynamics independently. In the path coordinate, the guidance law is designed based on a nominal model, and the non-linearity of the path's kinematics is taken into full consideration. In the time coordinate, the flight control law is designed as a feed-forward controller, and it can guarantee the robustness of the guidance law with respect to the actual aircraft's dynamics. Instead of only employing Lyapunov method, the concept of immersion and invariance is also applied to explicitly analyse the stability in both time and path coordinates, and the asymptotic stability of the closed-loop system can be guaranteed. What is more, the regulation-based and immersion-based adaptive technologies are synthetically utilised to handle the unknown parameters. Finally, the numerical simulations demonstrate the effectiveness of the developed integrated guidance and control scheme. [ABSTRACT FROM AUTHOR]

This paper addresses the suppressing problem of cable vibration and the positioning control design for a suspension cable system of a helicopter with disturbances. Hamilton's principle is applied to obtain a distributed parameter system for the suspension cable system of a helicopter. Two observers are employed to restrain the effect of unknown external disturbances. Based on the proposed disturbance observers and Lyapunov's direct method, two boundary control laws are designed, which are provided by the actuators at the top and bottom boundaries of the suspension cable, respectively. Under the proposed control laws, the oscillation amplitude and the error between the bottom boundary payload and the desired point are proven to be uniformly ultimately bounded. Moreover, they will converge to a small neighbourhood of zero by selecting proper design parameters. Meanwhile, some sufficient conditions are provided to guarantee the validity of the proposed control laws. Finally, simulation results show the rationality and effectiveness of the control scheme developed in this paper. [ABSTRACT FROM AUTHOR]

Abstract A fuzzy adaptive non-affine attitude tracking control method is proposed for a generic hypersonic flight vehicle (HFV). Due to the complexities of the hypersonic flows and nonlinear dynamics, the aerodynamic coefficients of the HFV are dependent not only on the attack of angle, sideslip angle, angular rates, and Mach number, but also on the deflection angles of the control surfaces. This cause the attitude tracking control problem becomes a non-affine multi-input–multi-output (MIMO) one. By analyzing the characteristics of the aerodynamic coefficients, it can be found that the non-affine terms have a great influence on the attitude dynamics and should not be ignored. Then, a non-affine MIMO attitude tracking controller is designed using fuzzy sliding mode adaptive techniques with consideration of the non-affine nonlinear aerodynamic coefficients. The proposed controller has good practicability because it does not need to know the exact bound values of the uncertainties, unmodeled dynamics, and external disturbances. Finally, simulation results show that the attitude angles can track the desired signals robustly and asymptotically under the control. [ABSTRACT FROM AUTHOR]

The modeling and state tracking control for the conversion mode of tilt-rotor aircraft are investigated with a switching modeling method and a bumpless transfer technique. Based on the Euler equation and the Blade element theory, the nonlinear model of conversion mode is deduced to illustrate the features of the tilting process. Afterward, the switching modeling method settles the linearization problem of the nonlinear control with an uncontrollable nacelle inclination signal. Meanwhile, it also transfers the conversion mode control issue to a reference state tracking control problem of switched linear systems. In addition, the H ∞ control is adopted to restrain the external disturbances, and the controller with bumpless transfer performance is designed to overcome the control jump at switching instants. Finally, an example of XV-15 tilt-rotor aircraft is proposed to illustrate the effectiveness of the developed method. [ABSTRACT FROM AUTHOR]

This paper focuses on the tracking problem for a class of nonstrict-feedback nonlinear systems with mismatched unknown nonlinear functions and external disturbances. First, a disturbance observer is developed to estimate the disturbance generated by an exogenous system. Then, based on the output of the disturbance observer, a constrained adaptive neural controller is developed for the nonstrict-feedback nonlinear system. In the control scheme design, the modified variable separation approach is applied to establish the relationship between the bounded function of nonstrict-feedback nonlinear function and the error variable. Furthermore, the barrier Lyapunov function is applied to guarantee that full state constraints are not violated. As a result, all the signals of the closed-loop system are semi-global uniformly ultimately bounded. Finally, two simulation examples are used to demonstrate the effectiveness of the developed constrained adaptive neural control law. [ABSTRACT FROM AUTHOR]

This paper investigates the tracking control problem for a class of strict-feedback nonlinear uncertain systems in the presence of unknown disturbance, input and output constraints. By using backstepping approach, an adaptive tracking controller is developed on the basis of neural network and disturbance observer. The Nussbaum function is introduced to tackle the problem of the nonlinear term arising from the input saturation, and the barrier Lyapunov function is employed to prevent the outputs from violating the constraints. The disturbance observer is developed to estimate unknown external disturbances. The proposed control scheme can guarantee that all signals of the closed-loop system are bounded by using the Lyapunov analysis method. Finally, the simulation results for three degrees of freedom (3-DOF) model helicopter are given to illustrate the effectiveness of the developed control scheme. [ABSTRACT FROM AUTHOR]

The problem of state feedback stabilization is studied for networked control systems (NCSs) subject to actuator saturation and network-induced delays. To facilitate the controller design, the NCSs are modeled as a class of discrete-time systems with bounded delays and input saturation. Based on Lyapunov-Krasovskii theory and free weighting matrix approach, the sufficient condition is derived in terms of linear matrix inequality for the asymptotic stability. Finally, the effectiveness of the developed control approach is proved through numerical examples. [ABSTRACT FROM AUTHOR]

In this study, the problem of adaptive dynamic surface control (DSC) design is investigated for a class of stochastic non‐linear systems with input saturation. The saturation non‐linearity is modelled via the existing dead zone‐based model of saturation. Furthermore, the packaged unknown functions are tackled using the neural networks. On the basis of the DSC technique, an adaptive controller is designed for stochastic non‐linear systems with input saturation. The proposed control scheme can guarantee the closed‐loop system stability, which shows that all closed‐loop system signals are semi‐globally uniformly ultimately bounded in the sense of probability and the tracking error converges to a small neighbourhood of the origin. Simulation results are provided to demonstrate the effectiveness and performance of the proposed approach. [ABSTRACT FROM AUTHOR]

The reference governor strategy is presented for the flight envelope protection control of the aircraft during high angle of attack maneuvers. Limits of key flight parameters and amplitude saturation of control surfaces are explicitly considered by imposing the output and input constraints on the flight system. Firstly, a nominal flight control scheme is designed using eigenstructure assignment approach. The static and dynamic reference governors are discussed for flight envelope protection control of the aircraft during stability-axis roll maneuver. Then, a new reference governor is presented based on step response model. The performance of these reference governors for flight envelope protection is demonstrated and compared by numerical simulations. Results show that the dynamic reference governor and the proposed step response model based reference governor are valid for the flight envelope protection control and the latter is easier to be realized. [ABSTRACT FROM AUTHOR]

Unmanned autonomous helicopter (UAH) path planning problem is an important component of the UAH mission planning system. The performance of the automatic path planner determines the quality of the UAH flight path. Aiming to produce a high-quality flight path, a path planning system is designed based on human-computer hybrid augmented intelligence framework for the UAH in this paper. Firstly, an improved artificial bee colony (I-ABC) algorithm is proposed based on the dynamic evaluation selection strategy and the complex optimization method. In the I-ABC algorithm, the following way of on-looker bees and the update strategy of nectar source are optimized to accelerate the convergence rate and retain the exploration ability of the population. In addition, a space clipping operation is proposed based on the attention mechanism for constructing a new spatial search area. The search time can be further reduced by the space clipping operation under the path planning result within acceptable changes. Moreover, the entire optimization process and results can be feeded back to the knowledge database by the human-computer hybrid augmented intelligence framework to guide subsequent path planning issues. Finally, the simulation results confirm that a feasible and effective flight path can be quickly generated by the UAH path planning system based on human-computer hybrid augmented intelligence. [ABSTRACT FROM AUTHOR]

The trajectory planning and tracking control problem is studied in this paper based on prescribed performance method (PPM) for the small-scale unmanned autonomous helicopter (UAH) with wind-gust disturbances (WGDs) and unmeasurable states. For the purpose, the nonlinear model with flapping dynamics is established, and the transformation performance function is used to ensure that the errors of trajectory tracking satisfy the corresponding performance. A fractional-order observer is designed for unmeasurable states to estimate the flapping angles in actual flight, and the fractional-order extended state observer (ESO) is constructed to estimate the WGDs, respectively. On the basis of PPM and the designed observers, the fractional-order theory-based backstepping trajectory tracking control scheme is developed for the UAH system, and the three-dimensional trajectory is planned by the improved wolf pack algorithm. Then the stability of the entire system is proven through strict theoretical analysis. Finally, the simulation analysis on the UAH is presented to demonstrate the efficiency of the designed method. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a robust active fault‐tolerant control (AFTC) approach for medium‐scale unmanned autonomous helicopter (UAH) with rotor flapping dynamics in the presence of unknown external disturbances and actuator faults. The robust items are adopted to improve the disturbance rejection capability of the UAH system. The adaptive fault observers are developed to estimate the fault parameters and the fault detection (FD) algorithms are presented to detect the actuator faults in different loops. In order to obtain satisfactory trajectory tracking performance, a backstepping‐based robust AFTC scheme is designed for the simplified 6‐degree‐of‐freedom (DOF) UAH nonlinear dynamics model and the global stability of the closed‐loop system is proved by using the Lyapunov method. Several groups of numerical simulation results are carried out to verify the effectiveness of the developed method. [ABSTRACT FROM AUTHOR]

Abstract Owing to the diverse structures and unique characteristics of MOFs, the combination of magnetic particles with porous MOFs is an attractive way for rapid and efficient extraction of organic pollutions from water. In this work, the magnetic porous composites, Fe 3 O 4 -PSS@ZIF-67 (PSS, poly (sodium-p-styrenesulfonate)), were prepared. The obtained composites exhibit core-shell structure, for which the spherical Fe 3 O 4 particles as core are embedded in ZIF-67 shell. The existence of SO 3 − anions on poly (sodium-p-styrenesulfonate) is the key factor for the uniform coating of ZIF-67 on Fe 3 O 4 particles. Poly (sodium-p-styrenesulfonate) providing enough chelating sites (-SO 3 −) for Co2+ which could further coordinate with 2-methylimidazole to form ZIF-67. This work further studied the adsorption property of 2-nitroresorcinol in aqueous solution, using Fe 3 O 4 -PSS@ZIF-67 as adsorbents. The equilibrium adsorption capacity for 2-nitroresorcinol is up to 52.50 mg g−1. The adsorption kinetics were investigated. The mechanism could be attributed to the electrostatic interaction between 2-nitroresorcinol and Fe 3 O 4 -PSS@ZIF-67 composites. Graphical abstract A new magnetic porous composites (Fe 3 O 4 -PSS@ZIF-67) was prepared, for which poly (sodium-p-styrenesulfonate) links the spherical Fe 3 O 4 core and ZIF-67 coating. The composites perform well on nitrophenol from aqueous solution via magnetic separation operation, mainly owing to the porosity of ZIF-67 and the electrostatic interaction between nitrophenol and composites. The combination of magnetic separation with MOFs is attractive way for efficient removal of nitrophenols from waste water. fx1 [ABSTRACT FROM AUTHOR]

In this study, a robust adaptive neural control is proposed for a fractional‐order rotational mechanical system (FORMS) in the presence of system uncertainties and external unknown disturbances. System uncertainties of the FORMS are handled by the neural network (NN). To tackle unknown disturbances, a non‐linear fractional‐order disturbance observer (FODO) is explored for the FORMS. A robust adaptive control scheme is then developed by combining the NN with the designed FODO. Finally, numerical simulation results further demonstrate the effectiveness of the proposed tracking control scheme for the uncertain FORMS subject to external unknown disturbances. [ABSTRACT FROM AUTHOR]

This paper deals with the attitude control problem of flexible satellite system under time-varying disturbance, actuator fault and input time-delay. Initially, in order to compensate for the negative effects of the disturbance and fault, two observer designs are proposed to obtain their estimations, respectively. Secondly, by combining anti-disturbance control, fault tolerant control and time-delay control approaches, a composite delay-dependent controller is presented and an augmented closed-loop system is derived. Then, based on Lyapunov stability theory and linear matrix inequality (LMI) approach, two sufficient conditions on ensuring the asymptotical stability and H ∞ performance index are established, in which the observer gains and controller one can be computed by resorting to the Matlab LMI Toolbox. Finally, some simulations and comparisons are provided to illustrate the effectiveness and advantages of the proposed control methods. [ABSTRACT FROM AUTHOR]

This paper investigates the tracking control problem of multi-input and multi-output nonlinear systems simultaneously considering the user-specified tracking performance, the asymmetric input saturation, and external disturbances. By introducing the modification signals into the user-specified performance functions, we propose a flexible performance-based control scheme, featuring the capability of avoiding the violation of the resulted modified performance functions (MPFs) due to the input saturation. These modification signals are associated with input saturation errors (the errors between the actual and desired control inputs) and generated by a novel auxiliary system in which all the states are guaranteed to be nonnegative. Consequently, the MPF can degrade the user-specified tracking performance when saturation happens and can recover it when no saturation occurs. Furthermore, the disturbance observer is utilized to estimate external disturbances and relieve the burden on the selection of control gains. With the developed control scheme, it is theoretically shown that the output can always track the reference signal and satisfy the constraints of the MPFs. Finally, the numerical simulation results are presented to show the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]