INS/CNS Deeply Integrated Navigation Method of Near Space Vehicles.

Celestial navigation is required to improve the long-term accuracy preservation capability of near space vehicles. However, it takes a long time for traditional celestial navigation methods to identify the star map, which limits the improvement of the dynamic response ability. Meanwhile, the aero-optical effects caused by the near space environment can lead to the colorization of measurement noise, which affects the accuracy of the integrated navigation filter. In this paper, an INS/CNS deeply integrated navigation method, which includes a deeply integrated model and a second-order state augmented H-infinity filter, is proposed to solve these problems. The INS/CNS deeply integrated navigation model optimizes the attitude based on the gray image error function, which can estimate the attitude without star identification. The second-order state augmented H-infinity filter uses the state augmentation algorithm to whiten the measurement noise caused by the aero-optical effect, which can effectively improve the estimation accuracy of the H-infinity filter in the near space environment. Simulation results show that the proposed INS/CNS deeply integrated navigation method can reduce the computational cost by 50%, while the attitude accuracy is kept within 10" (3 ). The attitude root mean square of the second-order state augmented H-infinity filter does not exceed 5", even when the parameter error increases to 50%, in the near space environment. Therefore, the INS/CNS deeply integrated navigation method can effectively improve the rapid response ability of the navigation system and the filtering accuracy in the near space environment, providing a reference for the future design of near space vehicle navigation systems.

Adaptive path following control for miniature unmanned aerial vehicle confined to three-dimensional Dubins path: From take-off to landing.

This study proposes a method for resolving the challenge of controlling miniature fixed-wing unmanned aerial vehicles (MAVs) along a predetermined three-dimensional (3D) Dubins path while using models with uncertainty and when experiencing external wind disturbances. We provide a multilayered structure that incorporates both guiding and control at the same time. In the guidance layer, a modified vector-field-based approach is presented to enable the MAV to follow a 3D Dubins path, including the takeoff, cruise, and landing processes with three different types of route segments. Then, an adaptive sliding model controller is used for the analysis and management of both wind disturbances and system uncertainties. Finally, both simulated scenarios and in-flight trials demonstrate the applicability of the methodology and the efficiency of the proposed approach.

Backstepping control for a two-link manipulator with appointed-time convergence.

In this paper, a novel backstepping control law is investigated, which guarantees appointed-time convergence for a two-link manipulator. In contrast to other fixed-time controllers or predefined-time controllers, the practical convergence time can be precisely obtained instead of being estimated. By utilizing a novel appointed-time prescribed performance function, the trajectory tracking error of the manipulator can be previously constrained. Furthermore, the external disturbances have been suppressed by introducing a disturbance observer with the convergence time as a prior control parameter and a switching sliding mode control law. The stability of the controller is analyzed by the Lyapunov method. Various numerical simulation results are carried out to demonstrate the efficacy of the proposed control scheme.

Novel anti-saturation robust controller for flexible air-breathing hypersonic vehicle with actuator constraints.

A novel anti-saturation robust control algorithm (NARC) is presented for flexible air-breathing hypersonic vehicle (FAHV) with actuator saturation, including two controllers designed for velocity and height subsystem respectively. Firstly, an anti-saturation finite-time dynamic inversion controller is designed for velocity subsystem, in which an anti-saturation fixed-time compensator (ASFC) is proposed to ensure the stability of saturated system and make it exit saturated region faster. Compared with conventional anti-saturation compensator, the auxiliary variable of ASFC can converge with faster speed and higher precision when actuator is not saturated, which avoids the impact on original system. Secondly, an anti-saturation robust command filtered backstepping controller is designed for height subsystem, combining backstepping control, ASFC and a novel fixed-time filter (FTF). Compared with low pass filter, the FTF proposed can track input signal with faster response speed and higher precision without the need to select a smaller time constant, so as to avoid introducing high-frequency noise. Meanwhile, convergence domain of height subsystem can be reduced as well. Ultimately, simulations on FAHV with actuator constraints, parametric uncertainties and external disturbances are performed using the NARC and conventional anti-saturation controller respectively to demonstrate the superiority of NARC.

Robust fixed-time sliding mode controller for flexible air-breathing hypersonic vehicle.

An improved robust fixed-time sliding mode controller (RFSMC) is presented for flexible air-breathing hypersonic vehicle (FAHV) with actuator faults, composing of a novel fast fixed-time integral sliding surface (FFIS), a continuous fixed-time super-twisting-like reaching law (CFSTL) and a uniformly convergent observer. Firstly, the nonlinear control-oriented model of FAHV is processed via input/output feedback linearization with flexible effects and actuator faults modeling as matched Lipschitz disturbances. Secondly, a novel non-singular FFIS is established based on a fast fixed-time high-order regulator (FFTR), which is improved with two gains incorporating into standard fixed-time high-order regulator via dilation rescaling. The FFTR proposed can accelerate respond speed of system by tuning values of two gains simply without complicated parameters selection and the stability is proved strictly via Lyapunov criteria. Thirdly, a CFSTL is utilized to ensure high-precision convergence of sliding mode vector and its derivative in fixed time. Afterwards, a uniformly convergent observer is applied to estimate lumped disturbances accurately in fixed time. With the estimated values compensated into controller, RFSMC can enhance fault-tolerant performance and attenuate chattering efficiently. Finally, simulations on FAHV are performed to verify the effectiveness and superiority of the method proposed.