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Aiming at enhancing the extent of military automatization and the effectiveness of armed helicopters in complex battlefield environment, integrated fire/flight control (IFFC) coupler connects the fire control system and the flight control system which is used to generate the optimal flight command signals. However, it is difficult to obtain satisfactory flight command signals within a certain firing accuracy due to the unavoidable uncertain information in battlefield environment. In this paper, a new IFFC scheme is proposed for armed helicopters against complex combat by using the idea of distributionally robust optimization combined with the framework of trust region. Initially, a vector equation and coordinate transformation are employed to acquire the relative motion model of the IFFC coupler problem in complex battlefield environment. Moreover, an improved performance index is designed according to the constraints, and the original non-convex problem is handled by the Taylor formula combined with an improved BFGS (Broyden–Fletcher–Goldfard–Shanno) algorithm. Considering the uncertain parameters during optimization, the non-linear distributionally robust optimization is transformed into a linear matrix inequality optimization problem based on the worst-case conditional value-at-risk (WC-CVaR) approximation. Then, an algorithmic framework with a non-monotone adaptive trust region algorithm is given to obtain the optimal flight command signals. Finally, a simulation example is given to illustrate the effectiveness of the proposed approach. [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 proposes a novel strategy to design a suboptimal attitude tracking control law for a near-space hypersonic vehicle (NSHV) based on the Koopman operator and stable manifold theory. The nonlinear vector field of the NSHV attitude model is locally Lipschitz continuous and can be approximated by a high-dimensional linear system over a compact set. Linear and nonlinear parts of the attitude dynamics are determined based on this system. Subsequently, the stable manifold theory is applied to determine the unconstrained approximated optimal control law that is used to further consider the control input constraints of the NSHV attitude model. The suboptimality of the control law is analyzed, and the local exponential stability of the closed-loop system with input constraints is proven. Furthermore, the eigenvalues for the closed-loop nonlinear attitude error dynamics are analyzed. After the control input saturation, the nonlinear closed-loop error dynamics of the NSHV can be approximated by a high-dimensional linear system with a minimal dimension. The eigenvalues of this linear system indicate the stability and time response characteristics of the attitude error dynamics of the NSHV. The numerical simulation results demonstrate the effectiveness and suboptimality of the proposed attitude tracking control law and workflow of the eigenvalue analysis. [ABSTRACT FROM AUTHOR]

This paper presents a novel suboptimal attitude tracking controller based on the algebraic Riccati equation for a near-space hypersonic vehicle (NSHV). Since the NSHV's attitude dynamics is complexly nonlinear, it is hard to directly construct an appropriate algebraic Riccati equation. We design the construction based on the Chebyshev series and the Koopman operator theory, which includes three steps. First, the Chebyshev series are considered to transform the error dynamics of the NSHV's attitude into a polynomial system. Second, the Koopman operator is used to obtain a series of high-dimensional linear dynamics to approximate each of the polynomial system's vector fields. In this step, our contribution is to determine a well-posed linear dynamics with the minimal dimension to approximate the original nonlinear vector field, which helps to design the control law and analyze the control performance. Third, based on the high-dimensional dynamics, the NSHV's attitude error dynamics is separated into the linear part and the nonlinear part, such that the algebraic Riccati equation can be constructed according to the linear part. Then, the suboptimal error feedback control law is derived from the algebraic Riccati equation. The closed-loop control system is proved to be locally exponentially stable. Finally, the numerical simulation demonstrates the effectiveness of the suboptimal control law. [ABSTRACT FROM AUTHOR]

This article deals with the problem of attitude tracking control for flexible satellite under flexible vibration disturbance, actuator fault and time delay. Based on disturbance observer and fault tolerant control techniques, the flexible vibration disturbance and actuator fault are effectively estimated by disturbance observer and fault estimation observer, respectively. Meanwhile, a delay-dependent attitude tracking feedback controller is designed to ensure that the reference attitude is stably tracked. To reduce the conservatism of the designed algorithm, a time delay correlative decomposition factor is introduced to make the flexible satellite have a better performance for attitude tracking control. Finally, the effectiveness of the proposed method is illustrated by numerical simulations. [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]

The complex nonlinearities of hypersonic vehicles can lead to strong couplings between variables, which will bring great challenges to flight control. For this purpose, this paper proposes a novel coupling analysis method for the longitudinal dynamics of a hypersonic vehicle, based on which a coordination controller is designed to reduce the negative effects of the couplings. Initially, according to the coupling characteristics of the hypersonic vehicle, a novel coupling analysis method based on the dynamic equations is proposed to describe the dynamic coupling relationships between variables. Then, a coordination control scheme is designed by combining sliding mode control and the dynamic coupling matrix obtained. Subsequently, the asymptotic stability of the closed-loop system is proved by using Lyapunov theory, and the simulation results are given to verify the effectiveness of the proposed dynamic coupling matrix-based coordination control. [ABSTRACT FROM AUTHOR]

In this paper, the issue of prescribed performance-based fault tolerant control is investigated for the medium-scale unmanned autonomous helicopter with external disturbance, system uncertainty and actuator fault. The altitude and attitude combination unmanned autonomous helicopter model is established. An error transformation function is proposed to guarantee that the tracking error satisfies the prescribed performance. The parameter adaptation method is adopted to handle the external unknown disturbance and the radial basis function neural networks are employed to approximate the interaction functions including the system uncertainty. The auxiliary system is introduced to weaken the effect of actuator fault, which can effectively avoid the singularity. Based on the backstepping control technology, an adaptive neural fault tolerant control scheme is developed to ensure the boundness of all closed-loop system signals and the specified tracking error performance. Simulation studies on the medium-scale unmanned autonomous helicopter are performed to demonstrate the efficiency of the designed control strategy. [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]

The paper analyzes the pros and cons of classical gray relational analysis on solving multi-target and multi-attribute problems, and presents an improved gray relational model to assess the battle damage of surface warship formations. First, with an entropy method and analytic hierarchy process, the subjective and objective weights of the index attributes are determined, respectively, and then they are combined with the product method to obtain the combined weight. Second, to make full use of the information carried by the index attributes, a polygon area formed by the adjacent points of the reference sequence curve and alternative sequence curve is used as gray relational coefficient. Third, by combining with the combined weight and the gray relational coefficients, an improved gray relational degree is thus determined. Finally, the numerical results illustrate that the battle damage assessment is generally consistent with the assessment results of experts, and the achieved result will provide important information to make a correct decision for carrying out a next strike. [ABSTRACT FROM AUTHOR]

In this article, robust attitude control schemes are proposed for the near-space vehicle with the backlash-like hysteresis and the time-varying unknown disturbance using backstepping technique. In the robust attitude control design, the backlash-like hysteresis is described by a dynamic equation which is decomposed as a linear term and a nonlinear term. To handle the nonlinear term in the dynamic equation of the backlash-like hysteresis and the time-varying unknown disturbance, they are treated as a compounded disturbance and the nonlinear disturbance observer is designed to estimate them. Based on the developed nonlinear disturbance observer, the robust backstepping attitude control is firstly developed for the near-space vehicle. Then, the robust sliding mode attitude control scheme is presented for the near-space vehicle to further enhance the robust attitude control performance. The convergence of all closed-loop signals is rigorously proved via Lyapunov analysis method under the developed robust attitude control schemes. Finally, simulation results are presented to illustrate the effectiveness of the proposed attitude control approaches. [ABSTRACT FROM PUBLISHER]