Inertia Uncertainties Research Articles

Intelligent Attitude Fault-Tolerant Control of Space Tumbling Target Fly-Around Based on RBF Neural Network

The flying around monitoring task of space tumbling target is one of the key links of its on-orbit service. Considering the practical constraints of system inertia uncertainty, external disturbance, actuator saturation, and fault in engineering practice, a robust composite controller based on radial basis function (RBF) neural network is proposed. First, in a new line of sight rotation (RLOS) coordinate system, the relative attitude kinematics and dynamics equations between the tracker and tumbling target based on the error quaternion are established; second, the RBF neural network is used to estimate the additive and multiplicative faults of the system, and the fast nonsingular terminal sliding mode surface (FNTSMS) is combined with the active disturbance rejection control (ADRC) technology to design a finite-time fault-tolerant control (FTC) strategy with high accuracy, strong robustness, and anti-saturation based on the RBF neural network. It is proven that the designed robust fault-tolerant controller can ensure that the system state error converges to a small region containing the origin in a limited time under the Lyapunov framework. Finally, the effectiveness and superiority of the control strategy were verified by numerical simulation.

Adaptive predefined-time prescribed performance control for spacecraft systems.

The high-accuracy attitude maneuvering problem for spacecraft systems is investigated. A prescribed performance function and a shifting function are first employed to ensure the predefined-time stability of attitude errors and eliminate the constraints on tracking errors at the incipient stage. Subsequently, a novel predefined-time control scheme is developed by combining prescribed performance control and backstepping control procedures. Radial basis function neural network and minimum learning parameter techniques are introduced to model the function of lumped uncertainty including inertial uncertainties, actuator faults and virtual control law derivatives. According to the rigorous stability analysis, the preset tracking precision can be achieved within a predefined time and the fixed-time boundedness of all closed-loop signals is established. Finally, the efficacy of the propounded control scheme is manifested through numerical simulation results.

Distributed adaptive neural network fixed‐time leader‐follower attitude consensus control for multiple rigid spacecraft

SummaryIn this paper, the problem of fixed‐time attitude consensus control is addressed for a group of rigid spacecraft in the presence of inertia uncertainties and external disturbances. By applying the adaptive technique and neural network approximation technique to handle the disturbances and uncertainties, an adaptive neural network‐based distributed protocol is proposed to achieve attitude consensus control for multiple rigid spacecraft. The proposed distributed attitude consensus protocol is composed of a group of distributed fixed‐time observers for followers to estimate the leader's information and an adaptive neural network‐based fixed‐time sliding mode control law to realize attitude tracking control. Rigorous proofs are provided to demonstrate that the estimation errors of the proposed observers are convergent in a fixed time. Further, it is also proven that attitude tracking errors reach some adjustable regions in a fixed time under the proposed attitude consensus protocol. Numerical simulations are conducted to illustrate the performance of the proposed distributed attitude consensus protocol.

Satellite Attitude Control Using Double-Gimbal Variable-Speed Control Moment Gyro with Unbalanced Rotor

Attitude dynamics of a rigid satellite actuated using a double-gimbal variable-speed control moment gyro (DGVSCMG) with an unbalanced rotor is derived in the framework of geometric mechanics. The proposed formulation accounts for dynamics of the gimbal motors and the rotor motor for finding the required motor torque to actuate the satellite along with the DGVSCMG for achieving high-precision attitude control. The satellite attitude control is accomplished using a proposed cascaded adaptive fixed-time sliding mode control to ensure bounded finite-time convergence. A sliding manifold is also designed to ensure convergence of gimbals angular rates to the desired values. Actuator saturation, system uncertainties such as intrinsic disturbance torques due to the gimbals and rotor bearing friction, extrinsic disturbances due to the environmental factors, and uncertainty in inertia of the satellite bus are accounted for designing the controller. Lyapunov stability analysis is carried out to prove bounded finite-time stability of the proposed system. Simulation results are presented to substantiate the claim made assuming the rigid satellite to be equipped with only one DGVSCMG.

Composite adaptive attitude control for combined spacecraft with inertia uncertainties

This paper examines the attitude control problem of the combined spacecraft subject to inertia uncertainties. A composite adaptive finite-time control scheme with guaranteed parameter convergence is proposed to address this challenging problem, in the absence of persistent excitation. As a stepping stone, the attitude dynamics of the combined spacecraft is first established with explicit consideration of the center-of-mass variation and thruster reconfiguration. Then, a composite adaptive finite-time controller is developed based on a constructive time-varying sliding manifold, and in particular, the concurrent learning technique is used in conjunction with the dynamic regressor extension and mixing procedure to achieve parameter convergence under finite excitation that is strictly weaker than the persistent excitation. Lyapunov stability analysis shows that the derived adaptive controller can simultaneously guarantee finite-time convergence of the attitude tracking and parameter estimation errors; moreover, its robustness against inertia variations and external disturbances is also analyzed. Finally, a set of numerical simulations under ideal and practical scenarios are performed to validate the effectiveness and outperformance of the proposed method.

Optimal Solution for Frequency and Voltage Control of an Islanded Microgrid Using Square Root Gray Wolf Optimization

Voltage and frequency deviation in the islanded operation of a microgrid (MG), due to the uncertainty and lack of inertia in the selection of optimal proportional integral (PI) controller gain, is a challenging task. Although various optimization algorithms have been proposed to achieve this task, most of them require a large number of iterations and are time intensive, making them inefficient for real-time applications. Gray wolf optimization (GWO), a new meta-heuristic algorithm, addresses these issues and has many advantages, including simplicity due to fewer control parameters, flexibility, and globalism. This paper proposes a simple and efficient modified algorithm, called square root gray wolf optimization (SRGWO) algorithm, to realize superior hunting performance. SRGWO is verified using twenty-three benchmark test functions. The algorithm is applied for optimal voltage and frequency regulation of a photovoltaic-based microgrid system operating in the islanded mode during distributed generation insertion and load change conditions. The voltage and frequency gain parameters of the PI controller are optimized. A comparison of the simulation results of the SRGWO algorithm with those of the original gray wolf algorithm (GWO), particle swarm optimization (PSO), augmented gray wolf optimization (AGWO), enhanced gray wolf optimization (EGWO), and gravitational search algorithm (GSA) reveal that the proposed SRGWO algorithm significantly improves system performance while maintaining its simplicity and easy implementation. Furthermore, the SRGWO algorithm obtains the minimum fitness function value in fewer iterations than other algorithms. Moreover, it improves the power quality of the system with regard to minimum total harmonic distortion.

Output-feedback asymptotic tracking control for rigid-body attitude via adaptive neural backstepping

In this note, a novel neural adaptive output-feedback control (NAOC) with asymptotic tracking performance for rigid-body attitude is investigated subject to inertia uncertainty, unavailability of the angular velocity and unknown external disturbance. First, by virtue of the combination of the first-order filter and the coordinate transformation, the original output feedback system with immeasurable angular velocity and unknown dynamics is converted into the full-state strict feedback system with mismatched disturbance. Second, aided by infinitely integrable inequality with saturation function, an innovative neural network (NN) based adaptive control scheme is proposed via backstepping technique. By adopting the model transformation and proposed algorithm, the asymptotic tracking performance of the transformed system and the attitude tracking system without angular velocity can be achieved simultaneously. Finally, comparative numerical simulations illustrate the efficacy of the developed algorithm.

Hybrid Adaptive Dynamic Inverse Compensation for Hypersonic Vehicles with Inertia Uncertainty and Disturbance

This paper studies an intelligent hybrid compensation scheme for the uncertain parameter and disturbance of hypersonic flight vehicles (HFV). For the longitudinal model of HFV with modeling errors, a nominal nonlinear dynamic inverse (NDI) controller ensures that the system output can accurately track the reference command. In the presence of rotational inertia uncertainty, a multi-learning law adaptive NDI controller is proposed to directly compensate for its impact on tracking performance, making the system robust to the uncertainty and reducing high maneuvering attitude angles and velocities vibration. Then, an improved adaptive NDI controller with a sliding mode disturbance observer is designed to actively compensate for the elastic mode disturbance, and continuously ensure the system’s anti-disturbance flight quality. Ultimately, this active–passive hybrid control scheme compensates for both high maneuvering inertia uncertainty and global disturbance. The Lyapunov functions prove the system’s stability, and the semi-physical simulation platform verifies the effectiveness of the method.

Fractional‐order sliding mode attitude coordinated control for spacecraft formation flying with unreliable wireless communication

This paper investigates the coordinated attitude control problem with fractional order sliding mode control theory for spacecraft formation flying by considering of unknown disturbance, inertia uncertainty, partial loss of actuators, and communication delay. Two types of fractional order sliding mode control laws are proposed to solve the considered design problem. The first one is based on the Chebyshev neural network technique, and the second one is involved with the integral-type and super-twisting sliding mode control methods. Compared to traditional sliding mode control methods, the developed fractional order sliding mode control strategies can achieve a faster convergence speed. Simulation results based on a group of three spacecrafts are presented to demonstrate the performance of the proposed coordinated attitude control approaches.

Adaptive sliding mode fault-tolerant control for satellite attitude tracking system

In this paper, an adaptive modified sliding mode control approach is developed for attitude tracking of a nano-satellite with three magnetorquers and one reaction wheel. A sliding variable is chosen based on finite-time convergence of the nano-satellite attitude tracking error and avoiding the singularity of the control signal. The control gain of the proposed method is developed adaptively to reduce the tracking error and improve the closed-loop control performance. The sliding variable and adaptive parameter are also employed in the reaching phase of the control law to decrease the chattering phenomenon. In addition, the finite-time convergence of attitude variables in the presence of actuator faults, inertia uncertainty, and external disturbances is proved using the extended Lyapunov theorem. The simulations are conducted to evaluate the performance of the proposed method according to different evaluation criteria. Monte Carlo simulations are also used to survey the reliability of the system in the presence of the mentioned condition.

Centralized/decentralized indirect robust adaptive control for spacecraft attitude and robotics

AbstractThe diffuse presence of robotic subsystems in new space mission concepts introduces variations and uncertainties in system mass and inertia, imposing stringent constraints to orbital and attitude control. The required performance can be achieved through several paradigms like robust or adaptive controllers and sometimes a combination of the two. In this work, a novel indirect controller, belonging to the robust‐adaptive controllers class, is developed, with the core idea of requiring just one adaptive gain with consequent lower sensitivity and easier tunability. The algorithm is developed both in centralized and decentralized formulation and tested for reliability and parameter sensitivity.

Fixed‐time fault‐tolerance attitude tracking control for spacecraft without unwinding

In this paper, the attitude tracking control problem is investigated for rigid spacecraft subjected to external disturbance, inertia uncertainties, and actuator faults. The rotation matrix is used to model the spacecraft attitude control system which can get rid of the unwinding problem. A nonlinear observer is developed to achieve a high accuracy estimation for the lumped disturbance in fixedtime without the awareness of the boundary of disturbance. To restrain measurement noise, a tracking differentiator is used in the observer to construct signals instead of using the polluted measurement values. Based on the estimation provided by the disturbance observer, a fixed-time attitude tracking controller is proposed by backstepping technique to stabilize attitude tracking errors in fixed time regardless of initial values. The singularity problem in traditional fixed-time controllers based on signal function is eliminated with the help of the arctangent function in the proposed controller. The feature of the designed fixed-time attitude controller is that it can suppress actuator faults, measurement noises and has no unwinding problem. Theoretical analysis based on Lyapunov theory and numerical simulations are presented to illustrate the robustness and effectiveness of the proposed control strategy.

Research on Semi-physical Simulation of Direct Drive Fan Based on ADPSS

A high proportion of new energy equipment brings problems such as increased power source uncertainty and weaker moment of inertia to the power grid. Through large-scale grid simulation with refined models of new energy equipment, potential grid risks can be discovered and grid security can be effectively improved. The modeling accuracy of the new energy equipment model affects the simulation accuracy of the large power grid. In order to solve the accuracy problem of the new energy equipment model, a semi-physical simulation platform close to the actual equipment is used to carry out simulations of different working conditions. Based on ADPSS, a semi-physical simulation electromagnetic model of a dual-motor dual-power unit two-level direct-drive fan was built, and simulation data of different working conditions were obtained. The direct frequency control method is adopted to optimize the motor model, which reduces the steady-state fluctuation of the semi-physical simulation and improves the simulation accuracy.

Wobble of a spin stabilized satellite with cross products of inertia and magnetic attitude control

Asymmetrical spin stabilized satellite dynamics in the vicinity of the required motion is considered. The principal axis of the maximum moment of inertia slightly deviates from its assumed direction in the satellite reference frame. This is formalized in the cross products of inertia. This inertial uncertainty results in a wobble, that is undesired angular velocity components perpendicular to the rotation axis, and oscillations of this axis near the required direction. The torque-free motion is investigated first. Expressions that explicitly relate satellite inertia parameters to wobble are provided. Wobble evolution under the action of magnetic damping control is analyzed next. Its amplitude approximate exponential decay behavior and residual unavoidable wobble level are derived. These expressions are compared with numerical simulation results of nonlinear equations of motion including various disturbance sources.

Barrier function-based adaptive integral sliding mode finite-time attitude control for rigid spacecraft

This paper investigates the problem of attitude tracking control with predefined-time convergence for rigid spacecraft under external disturbances and inertia uncertainties. Firstly, the proposed nominal controller is designed to achieve attitude tracking control of the rigid spacecraft in the absence of disturbances and inertia uncertainties, and the convergence of the spacecraft attitude errors can be selected in advance. Then, the integral sliding mode combined with barrier function-based adaptive laws is proposed to reject the disturbances and inertia uncertainties, and at the same time, a barrier function-based adaptive method can also ensure the solutions of the rigid spacecraft system belonging to a stipulated vicinity of the intended variables starting from the initial moment and the uncertainties’ upper bound is not overestimated. Finally, a numerical simulation is provided to illustrate the efficiency of the proposed control protocol.

Coordinated Attitude Control of Spacecraft Formation Flying via Fixed-Time Estimators under a Directed Graph

This paper mainly studies the distributed fixed-time coordinated attitude tracking control problem of spacecraft formation with a dynamic leader spacecraft under directed communication topology. Follower spacecraft cannot communicate directly with the leader spacecraft; therefore, in order to enable them to obtain the target attitude information, a fixed-time state estimator that can be applied to directed graphs is designed. Based on the estimators, a distributed fixed-time attitude tracking control law is proposed. The settling time of the fixed-time algorithm is only related to the parameters of the control law and independent of the initial state; thus, the proposed control law can reduce the influence of the dynamic leader attitude on the spacecraft formation-coordinated attitude tracking control system. Moreover, external disturbances and spacecraft inertia uncertainty were also considered in the design of the control law. The stability of the system was verified by Lyapunov stability theory, and the effectiveness of the control law was verified by numerical simulation.

Explicit Near-Optimal Guidance and Pulse-Modulated Control for Lunar Descent and Touchdown

This research considers the descent path of a space vehicle, from periselenium of its operational orbit to the lunar surface. The trajectory is split in two arcs: (a) approach, up to a specified altitude, and (b) terminal descent and soft touchdown. For phase (a), a new locally flat near-optimal guidance is used, which is based on iterative projection of the spacecraft position and velocity, and availability of closed-form expressions for the related costate variables. Attitude control is aimed at pursuing the desired spacecraft orientation, and uses an adaptive tracking scheme that compensates for the inertia uncertainties. Arc (b) is aimed at gaining the correct vertical alignment and low velocity at touchdown. For phase (b) a predictive bang-off-bang guidance algorithm is proposed that is capable of guaranteeing the desired final conditions, while providing the proper allocation of side jet ignitions. Actuation of side jets is implemented using pulse width modulation, in both phases. Monte Carlo simulations prove that the guidance and control architecture at hand drives the spacecraft toward safe touchdown, in the presence of non-nominal flight conditions.

Fixed-time attitude cooperative fault-tolerant control with prescribed performance for heterogeneous multiple satellite

This paper mainly investigates the fixed-time cooperative fault-tolerant control problem for heterogeneous satellite attitude control systems with external disturbances, actuator faults, and unknown inertia uncertainties. Firstly, the asymmetric prescribed performance mechanism is utilized to impose desired performance functions on satellite attitude tracking errors. Then, the fixed-time neuroadaptive technique is adopted to approximate unknown system uncertainties, and a novel fixed-time fault-tolerant controller is thus proposed to ensure that the transformed tracking errors converge to a small neighborhood of origin within a fixed time. Moreover, the Lyapunov theory is employed to validate that the closed-loop system is fixed-time stability under the control scheme. Finally, simulations results are carried out to verify the effectiveness of proposed strategy.

NI-based static output feedback control for attitude stabilization of post-capture flexible spacecraft

This paper investigates the attitude stabilization problem of post-capture flexible spacecraft with non-cooperative target in the presence of input fault and saturation. In modeling, these non-cooperative characteristics are often manifested in uncertain and unknown inertia, model parameter uncertainty, input faults, etc. In this paper, aiming at the attitude stabilization problem of such post-capture flexible spacecraft, the attitude dynamics modeling is completed by introducing the nominal inertia to construct the comprehensive disturbance term including external disturbance, inertia uncertainty and actuator failure. Then, a static output feedback controller is applied to convert the closed-loop attitude control system to a stable negative imaginary system with H∞ performance constraints according to negative imaginary theory. As long as the optimization variables approach zero, the iterative algorithm can find such a static output feedback controller to achieve attitude stabilization of post-capture flexible spacecraft. It is worth mentioning that an event-triggered mechanism is introduced into the control scheme to reduce the communication pressure. Finally, the numerical simulation is performed in the presence of model parameter uncertainty and controller gain perturbations. Simulation results demonstrate the effectiveness, robustness and non-fragility of the control method.

Cascade-based tracking control for dynamic positioning vessels under unknown sea loads

This paper investigates the trajectory tracking control problem of a dynamic positioning vessel (DPV) subject to tracking performance, time-varying sea loads and inertia uncertainties. Firstly, a novel cascade model of the DPV is built to describe the dynamics. Then, in order to guarantee the performance constraints of the trajectory tracking, a new-type fixed-time performance function is proposed, which can not only guarantee the transient and steady-state performance during task execution, but also achieve convergence at a fixed time. In addition, an adaptive neural network is introduced to handle the problem of parameter uncertainty and unknown sea loads in the system. Furthermore, it is proved by the Lyapunov stability theory that all signals in the closed-loop system are bounded . Finally, numerical simulation results verified the effectiveness of the proposed method and ensure that the tracking error is stable in the interval of 2 m or less within a given time.