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To address the challenging issue of automatic carrier landing with disturbances, this paper presents an active anti-disturbance control with integrated direct lift scheme. This control scheme is comprised of three controllers: the attitude controller for maintaining angle of attack and eliminating lateral tracking error, the integrated direct lift controller for eliminating longitudinal tracking error and the auto-throttle controller for maintaining the velocity. To estimate and compensate for the external disturbances, the extended state observer is designed, along with the implementation of sliding mode and nonlinear dynamic inversion methods. The stability of the controllers is proved by the Lyapunov theorem. Based on this control scheme, a novel automatic carrier landing system is developed, consisting of the glide path subsystem, the guidance subsystem, the aircraft subsystem and the control subsystem. To validate the efficacy of the proposed method, numerical simulations are conducted. The comparative results demonstrate that the proposed method is capable of achieving precise and safe carrier landing with external disturbances. Furthermore, the Monte Carlo test results provide compelling evidence of the superiority of the proposed method. [ABSTRACT FROM AUTHOR]

The flight control system of coaxial compound helicopters (CCHs) is a complex multi-variable system characterized by redundant control effectors, strong nonlinear characteristics, and multiple flight modes. This paper presents a unified robust control framework tailored for CCH full-envelope flight, utilizing nonlinear dynamic inversion and extended state observer techniques. The framework is specifically designed to tackle issues arising from a multi-mode nature, parametric uncertainties, and external disturbances. Within the unified framework, the study addresses inherent complexities such as nonlinearities and cross-coupling effects in CCH by leveraging nonlinear dynamic inversion to formulate flight control laws for both inner and outer-loops. To mitigate model uncertainties and external disturbances, the extended state observer is employed to estimate lumped disturbance effectively. Control allocation for both inner and outer-loops is devised to adapt to changes in control effector authorities and flight modes. Furthermore, an exponential control allocation strategy is proposed for the outer-loop to ensure a smooth pitch angle during transition flight. The effectiveness of the proposed control laws and control allocation strategies in achieving precise attitude tracking, transition flight and mission task elements (MTEs), even in the presence of notable model uncertainties and external disturbances, is demonstrated through numerical simulations. • A unified robust nonlinear dynamic inversion control framework is presented for full envelope flight of the CCH. • An outer-loop control allocation strategy is proposed to address the issue of pitch angle command oscillation during transition flight. • A simplified nonlinear dynamic model of CCH is employed to mitigate the effects of model uncertainties during the design of inner-loop control law. [ABSTRACT FROM AUTHOR]

This paper presents an improved nonlinear dynamic inversion control approach for the longitudinal dynamics of a flexible air-breathing hypersonic vehicle. The control design of the approach is based on a control-oriented model that represents the nominal state. By establishing a three inputs and three outputs control system, the control-oriented model in this study has full vector relative degree, without dynamic extension. To maintain tracking performance in the presence of disturbances, a nonlinear disturbance observer is adopted to estimate the disturbances. To achieve good transient performance, an adaptive damping term is proposed to the pitch dynamics. Based on approximate input–output linearization, linear control theory is applied to design a pole placement controller for the equivalent linear system. The damping ratio, natural frequency, and simple pole of the pole placement controller are optimized by the genetic algorithm along with the full nonlinear model of the vehicle. During the optimization, 11 uncertain parameters are introduced to the nonlinear model. Monte Carlo evaluation shows that the optimized pole placement controller provides robust tracking of reference trajectories. Simulation results indicate the effectiveness of the proposed control approach. [ABSTRACT FROM AUTHOR]

Nuclear Power Plants mostly act as base-load stations mainly because of constraints on rate of reactivity addition. In order that such plants operate as commercially viable entities, it is necessary that they are capable of operating as load following stations. The inherently self-regulating nature of a Pressurized Water Reactor (PWR) makes it a natural choice for load followers. However, this entails an associated problem of periodic variation in spatial concentrations of the burnable neutron poison Xenon which alters the spatial flux profile substantially within the reactor core, and this phenomenon is known as Xenon oscillation . This paper proposes a nonlinear controller design methodology based on Nonlinear Dynamic Inversion (NDI) which is coupled with constrained optimization to develop a tracking controller that achieves load following operation of a PWR over a wide range of reactor power with no Xenon oscillations and satisfies the operational constraints of the reactor imposed by reactivity worth of the control devices and allowable fuel and coolant temperatures. [ABSTRACT FROM AUTHOR]

Bacillus thuringiensis is a microorganism that allows the biosynthesis of δ-endotoxins with toxic properties against some insect larvae, being often used for the production of biological insecticides. A key issue for the bioprocess design consists in adequately tracking a pre-specified optimal profile of the dissolved oxygen concentration. To this effect, this paper aims at developing a novel control law based on a nonlinear dynamic inversion method. The closed-loop strategy includes an observer based on a Bayesian Regression with Gaussian Process, which is used for on-line estimating the biomass present in the bioreactor. Unlike other approaches, the proposed controller leads to an improved response time with effective disturbance rejection properties, while simultaneously prevents undesired oscillations of the dissolved oxygen concentration. Simulation results based on available experimental data were used to show the effectiveness of the proposal. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the fault tolerant capabilities of the neural aided sliding mode controller for autolanding under actuator failures and severe winds developed earlier are improved significantly by incorporating a novel anti-windup strategy and a phase compensation scheme. This controller further increases the size of the fault tolerance envelope for various types of control surface stuck faults and provides complete coverage at every point within the envelope boundaries. Earlier work by the authors showed the existence of a neural-aided sliding mode controller which could handle a wide range of actuator stuck faults. One of the major drawbacks of this earlier controller is that it does not ensure that all points within the range of minimum and maximum bounds of the fault tolerance envelope are covered. The anti-windup proposed in this paper is a generalization of the scheme used for proportional-derivative-integral controllers to the cascaded trajectory following controllers designed by the authors. This scheme can handle requirements of state limiting as well as multiple redundant control surface saturation. The proposed anti-wind up design is a simplification over the command filter approach used for adaptive backstepping. The approach is demonstrated for a fixed-wing aircraft undergoing unknown actuator stuck failures and subject to severe wind disturbances during autolanding. An example of three control surface failures (both ailerons and rudder) handled by this controller is also presented. [Copyright &y& Elsevier]

Abstract: This paper deals with the design of a guidance algorithm for the hypersonic phase of a lifting-body vehicle. The guidance strategy is based on a particular kind of nonlinear dynamic inversion, the so-called flatness approach. The main advantage of this approach is that the longitudinal guidance law is in-flight self-adaptive to any feasible hypersonic trajectory and can be written in analytical form with a small set of design parameters. Therefore, the required on-board computational resources are limited, and a reduced off-line design effort is needed for the change of vehicle parameters. Moreover, the closed-loop longitudinal guidance commands are computed on-board in a coupled way without relying on an explicit deceleration profile. Consequently, the approach leads to an efficient management of the degree of freedom associated with the angle-of-attack. PID controllers are then designed based on the longitudinal flat model in order to circumvent uncertainties and parameters dispersions. The crossrange is controlled by a series of bank reversals determined by an azimuth error deadband. The robustness and performance of the proposed guidance law are assessed by performing Monte Carlo runs with various sets of dispersions. [Copyright &y& Elsevier]

• This research emphasizes on an adaptive nonlinear integral-sliding-mode (ISM) controller design for F16 aircraft. The objective is to attain the desired maneuvering subject to the unknown external disturbance and aerodynamical uncertainty effects. • The nonlinear dynamics of F16 aircraft is first partitioned into inner faster and outer slower loop. For each loop, the adaptive ISM control strategy is proposed where the baseline controller is designed using nonlinear-dynamics-inversion (NDI technique) • The aerodynamics coefficients, that are the nonlinear function of angle-of-attack α , and side slip angle β , are estimated using iterative reweighted least square algorithm. The estimated information is available to the controller design where the estimation error is treated as unmatched uncertainty. • A detailed analysis is performed to show that the aircraft internal dynamics are stable for the applicability of NDI controller. • A detailed comparison is performed with NDI controller and ISM/NDI controller to validate the dominant performance of proposed scheme. Aircraft dynamics are highly nonlinear and the traditional linear flight controllers cannot fully utilize the real-time performance ability of aircraft. This paper investigates a nonlinear control approach for high maneuvering fighter aircraft that deployed baseline nonlinear-dynamics-inversion (NDI) control and high-level robust adaptive integral-sliding-mode (ISM) control. The design objective is to maintain the acceptable flight quality at a high angle-of-attack under the influence of unknown disturbance and aerodynamics uncertainties. The nonlinear dynamics of F16 aircraft are divided into two loops by utilizing time-scale separation principle and adaptive ISM/NDI controller is designed for each loop. The aerodynamics coefficients are estimated using the iterative reweighted least square (IRLS) algorithm based on the wind tunnel real-time flight data available at NASA Langlet and Ame Research center. The internal dynamics stability is proven to validate the complete system stability. Simulations are conducted on F16 aircraft and compared the results with the NDI controller and ISM/NDI controller (without adaptive strategy). [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicles (UAVs) are safety-critical systems that often need to fly near buildings and over people under adverse wind conditions and hence require high manoeuvrability, accuracy, fast response abilities to ensure safety. Under extreme conditions, the dynamics of these systems are strongly nonlinear and are exposed to disturbances, which need a robust controller to keep the UAV and its environment safe. In this paper a novel robust nonlinear multi-rotor controller is introduced based on essential modifications of standard dynamic inversion control, which makes it insensitive to payload changes and also to large wind gusts. First a robust attitude controller is established, followed by lateral and vertical position control in a customary outer loop. The controllers take into account thrust limitations of the aircraft and theoretical proof is provided for robust performance. The control scheme is illustrated in simulation with a realistic nonlinear dynamical model of an aircraft that includes rotor dynamics and their speed limitations to show robustness. Lyapunov stability methods are used to prove the stability of the robust control system. [ABSTRACT FROM AUTHOR]