Mixed H_2/H_∞ State Feedback Attitude Control of Microsatellite Based on Extended LMI Method

For the appearance of the additive perturbation of controller gain when the controller parameter has minute adjustment at the initial running stage of system,to avoid the adverse effects,this paper investigates the mixed H_2/H_∞ state feedback attitude control problem of microsatellite based on extended LMI method.Firstly,the microsatellite attitude control system is established and transformed into corresponding state space form.Then,without the equivalence restriction of the two Lyapunov variables of H_2 and H∞performance,this paper introduces additional variables to design the mixed H_2/H_∞ control method based on LMI which can also reduce the conservatives.Finally,numerical simulations are analyzed to show that the proposed method can make the satellite stable within 20 s whether there is additive perturbation of the controller gain or not.The comparative analysis of the simulation results between extended LMI method and traditional LMI method also demonstrates the effectiveness and feasibility of the proposed method in this paper.

Predictive control for satellite formation keeping

Based on a Hill equation and a nonlinear equation describing the desired and real dynamics of relative motion separately, a predictive controller is brought forward, which makes the real state track the desired ones to keep satellite formation. The stability and robustness of the controller are analyzed. Finally, comparing the simulation results of the proposed controller with that of the traditional, proportional-differential controller shows that the former one is capable of keeping the satellite formation more favorably, considering the disturbances such as the J2 perturbations.

Research on improved integrated FDD/FTC with effectiveness factors

This paper investigates the integrated fault detection and diagnosis(FDD) with fault tolerant control(FTC) method of the control system with recoverable faults.Firstly,a quasi-linear parameter-varying(QLPV) model is set up,in which effectiveness factors are modeled as time-varying parameters to quantify actuators and sensors faults.Based on the certainty equivalency principle,replacing the real time states in the nonlinear term of the QLPV model with the estimated states,the parameters and states can be estimated by a two-stage Kalman filtering algorithm.Then,a polynomial eigenstructure assignment(PEA) controller with time-varying parameters and states is designed to guarantee the performance of the system with recoverable faults.Finally,mathematical simulation is performed to validate the solution in a satellite closed-loop attitude control system,and simulation results show that the solution is fast and effective for on-orbit real-time computation.

A new method of choosing scales in wavelet transform for damping identification

A systematic study of the method of selecting scales in wavelet transform for damping identification in frequency domain was carried out. A method to select the scale with the modulus at the maximum was developed by extending the range of scales. It is proved that using this method in small damping ratio and linear system, we can achieve better results in identification of the closely-spaced model.

Fault-tolerant control of linear uncertain systems using H∞ robust predictive control

The robust fault-tolerant control problem of linear uncertain systems is studied. It is shown that a solution for this problem can be obtained from a H∞ robust predictive controller (RMPC) by the method of linear matrix inequality (LMI). This approach has the advantages of both H∞ control and MPC: the robustness and ability to handle constraints explicitly. The robust closed-loop stability of the linear uncertain system with input and output constraints is proven under an actuator and sensor faults condition. Finally, satisfactory results of simulation experiments verify the validity of this algorithm.

Predicting test data of aluminum honeycomb sandwich board based on volterra adaptive filters

Random vibration test was done on aluminum honeycomb sandwich board.The result suggested that chaotic behavior is found in the test data.The Volterra expression can not be gained from the input and output data directly in this paper.The state space reconstruction was used to convert the system observed data into the quasi-input/output pairs,and the second-order Volterra adaptive filter was used to predict the test data.It is shown that combining the state space reconstruction with the Volterra adaptive filter,these chaotic series could be accurately predicted.

Integrated modeling of spacecraft relative motion dynamics using dual quaternion

To realize high accurate control of relative position and attitude between two spacecrafts, the coupling between position and attitude must be fully considered and a more precise model should be established. This paper breaks the traditional divide and conquer idea, and uses a mathematical tool, namely dual quaternion to establish the integrated 6 degree-of-freedom(6-DOF) model of relative position and attitude, which describes the coupled relative motion in a compact and efficient form and needs less information of the target. Considering the complex operation rules and the unclarity of the current relative motion model in dual quaternion, necessary mathematical foundations are given at first, followed by clear and detailed modeling process and analysis. Finally a generalized proportion-derivative(PD) controller law is designed. The simulation results show that based on the integrated model established by dual quaternion, this control law can achieve a high control accuracy of relative motion.

Dual-quaternion-based modeling and control for motion tracking of a tumbling target

This paper investigates the problem of controlling a chasing spacecraft(chaser)to track and rendezvous with an uncontrolled target.Based on the actual situation,the torque-free motion of an axisymmetric prolate rigid body is employed to represent the short-term attitude motion of the tumbling target.By taking advantage of the dual quaternion’s compact and efficient description of the general rigid motion,the coupled and integrated model of the 6-degree-of-freedom(6-DOF)relative motion between the chaser and the tumbling target is derived in the chaser’s body fixed frame after taking full consideration of coordinate transformation.Based on the logarithm of dual quaternion,a sliding mode control(SMC)law based on the exponential reaching law and the continuous relay function is brought forward to address the problem of synchronization control of the 6-DOF relative motion.Simulation results illustrate the effectiveness of the proposed method.

Influences of vacancy defects on thermal conductivities of Ge thin films

The effects of vacancy defects on the thermal conductivity of Ge thin films were investigated by employing molecular dynamics(MD) simulations and theoretical analysis based on the Boltzmann equation.Both the MD and theoretical results show that the lattice thermal conductivity dramatically decreases with the increasing of vacancy concentration at 400 and 500 K.In addition,the dependence of vacancy concentration on the thermal conductivity of Ge thin films becomes less sensitive as the temperature increases.Theoretical results also confirm that the major part of the lattice thermal conductivity reduction is associated with the point-defect scattering and phonon-phonon scattering processes.

Dynamics Analysis of Nonlinear Energy Sink for Metal-Rubber Vibration Absorber

Recent advances in the application of the nonlinear energy sink under a sinusoidal excitation make it possible to investigate metal-rubber vibration absorber. To provide such a vibration absorber for the integrated spacecraft platform,we analyze the targeted energy transfer of the simplified model with nonlinear energy sink using the complex-variables averaging method. Theoretical study shows two quasi-periodic responses that are essentially different in this nonlinear system. The steady-state response which is one of two quasi-periodic responses is caused by the linear instability of system,and another one appears as a result of the nonlinear normal modes between the linear and nonlinear oscillators,resulting from the energy transfer of different oscillators,and it can be used to vibration absorber. Secondly,this paper also discusses the performance of the proposed nonlinear absorber by using the phase portraits. All conclusion derived by the analytic model is verified numerically and the results are consistent with numerical simulations.

Multidimensional modal analysis of liquid nonlinear sloshing in right circular cylindrical tank

The multidimensional modal theory proposed by Faltinsen,et al.(2000) is applied to solve liquid nonlinear free sloshing in right circular cylindrical tank for the first time. After selecting the leading modes and fixing the order of magnitudes baaed on the Narimanov-Moiseev third order asymptotic hypothesis,the general infinite dimensional modal system is reduced to a five dimensional asymptotic modal system (the system of second order nonlinear ordinary differential equations coupling the generalized time dependent coordinates of free surface wave elevation).The numerical integrations of this modal system discover most important nonlinear phenomena,which agree well with both pervious analytic theories and experimental observations. The results indicate that the multidimensional modal method is a very good tool for solving liquid nonlinear sloshing dynamics and will be developed to investigate more complex sloshing problem in our following work.

Applying of Switch Strong Tracking UKF in Spacecraft Autonomous Celestial Navigation

Star & Horizon sensor based autonomous navigation methods play an increasingly important role in spacecraft celestial navigation. However,the measurements of star sensors and horizon sensor are frequently affected by uncertain noises from space environment. To improve the estimation precision,a state estimation algorithm named Switch Strong Tracking Unscented Kalman Filter( SSTUKF) is presented. Firstly,the adaptive fading factor is deduced through the adoption of unknown instrumental diagonal matrixes to real time rectify the measurement covariance matrix. Secondly,according to the deduction of Chebyshev law of large numbers,innovation criterion is introduced during estimation to decrease the unnecessary calculation. Finally,SSTUKF is suggested through the adoption of adaptive fading factor and innovation criterion. The filter can switch between the normal filter mode and adaptive filter mode. As the calculation of innovation criterion is less than the adaptive fading factor,SSTUKF improves the estimation efficiency. To demonstrate the effectiveness,SSTUKF is applied to Star & Horizon sensor based autonomous navigation system with uncertain measurement noises. The simulation results verify the proposed algorithm.

Relative navigation for satellite formation flight using a continuous-discrete converted measurement Kalman filter

The present paper develops an approach of relative orbit determination for satellite formation flight.Inter-satellite measurements by the onboard devices of the satellite were chosen to perform this relative navigation,and the equations of relative motion expressed in the Earth Centered Inertial frame were used to eliminate the assumption of the circular reference orbit.The relative orbit estimation was achieved through a continuous-discrete converted measurement Kalman filter design,in which the measurements were transformed to the inertial frame to avoid the linearization error of the observation equation.In addition,the situation of the coarse measurement period(only microwave radar measurements are available)existing was analyzed.The numerical simulation results verify the validity of the navigation approach,and it has been proved that this approach can be applied to the formation with an elliptical reference orbit.

基于有向图的信息拓扑独立的二阶系统一致性判据(英文)

In this paper,consensus seeking of second-order systems without leaders is investigated under possibly switching directed graphs.Two consensus algorithms using different cooperative schemes are proposed and some information topology-independent criteria are obtained.For the first one,an eigenvalue-based analysis is taken to attain a sufficient and necessary condition for consensus seeking under fixed directed graph.For the second one,consensus can be achieved as long as the union of the switching graphs has a directed spanning tree frequently enough.Convergence analysis is presented,which is facilitated by an equivalent model transformation into a cascaded system.A novel sufficient and necessary condition for consensus seeking under switching undirected graph is also obtained using the same strategy.Moreover,robustness of both the algorithms to time-delays is studied under fixed directed graph.Illustrative examples are also provided to show the effectiveness of the theoretical results.

Fault reconstruction observer design for continuous-time systems with measurement disturbances via descriptor system approach

This paper addresses a problem of observer-based sensor fault reconstruction for continuous-time systems subject to sensor faults and measurement disturbances via a descriptor system approach. An augmented descriptor plant is first formulated,by assembling measurement disturbances and sensor faults into an auxiliary state vector. Then a novel descriptor state observer for the augmented plant is constructed such that simultaneous reconstruction of original system states, sensor faults and measurement disturbances are obtained readily. Sufficient conditions for the existence of the proposed observer are explicitly provided, and the application scope of the observer is further discussed. In addition,an extension of the proposed linear approach to a class of nonlinear systems with Lipschitz constraints is investigated. Finally, two numerical examples are simulated to illustrate the effectiveness of the proposed fault-reconstructing approaches.

LMI Approach to Mixed H_/H_∞ Fault Detection Observer Design

To investigate the robust fault detection(RFD) observer design for linear uncertain systems,the H_ index and H ∞ norm are used to describe this observer design as optimization problems.Conditions for the existence of such a fault detection observer are given in terms of matrix inequalities.The solution is obtained by new iterative linear matrix inequality(ILMI) algorithms.The RFD observer design over finite frequency range in which D f does not have full column rank for a system is also considered.Numerical example demonstrates that the designed fault detection observer has high sensitivity to the fault and strong robustness to the unknown input.

Modified super twisting controller for servicing to uncontrolled spacecraft

A relative position and attitude coupled sliding mode controller is proposed by combining the standard super twisting(ST) control and basic linear algorithm for autonomous rendezvous and docking. It is schemed for on-orbit servicing to a tumbling noncooperative target spacecraft subjected to external disturbances.A coupled dynamic model is established including both kinematical and dynamic coupled effect of relative rotation on relative translation, which illustrates the relative movement between the docking port located in target spacecraft and another in service spacecraft. The modified super twisting(MST) control algorithm containing linear compensation items is schemed to manipulate the relative position and attitude synchronously. The correction provides more robustness and convergence velocity for dealing with linearly growing perturbations than the ST control algorithm.Moreover, the stability characteristic of closed-loop system is analyzed by Lyapunov method. Numerical simulations are adopted to verify the analysis with the comparison between MST and ST control algorithms. Simulation results demonstrate that the proposed MST controller is characterized by high precision, strong robustness and fast convergence velocity to attenuate the linearly increasing perturbations.

Relative Attitude and Position Estimation for Spacecraft from Multiple Geometric Features

This paper investigates the pose and motion estimation problem using single camera measurement for spacecraft. The leader spacecraft of three-dimensional shape is observed by a calibrated camera fixed on the follower spacecraft. Based on dual numbers,an integrated observation model is proposed based on a combination of multiple geometric features including points,lines and circles,which can improve the robustness and accuracy of the estimation algorithm. A six-degree-of-freedom relative motion model is proposed by using the dual quaternion representation,in which the rotation-translation coupling effect due to the points deviating from the center of the mass is described. Employing the proposed observation model and dynamics model,an Extended Kalman Filter is presented to estimate the relative state between the two spacecraft. Numerical simulations are performed to evaluate the proposed approaches,showing the convergence of relative estimation errors and superior estimation performance.

Response regimes of narrow-band stochastic excited linear oscillator coupled to nonlinear energy sink

This paper draws attention to the issue of the vibration absorption of nonlinear mechanical system coupled to nonlinear energy sink(NES) under the impact of the narrow band stochastic excitation. Firstly, based on the complex-averaging method and frequency detuning methodology,response regimes of oscillators have been researched under the linear impact of coupling a nonlinear attachment with less relativistic mass and an external sinusoidal forcing, of which results turn out that the quasi-periodicity response regime of system which occurs when the external excitation amplitude exceeds the critical values will be the precondition of the targeted energy transfer.Secondly, basing on the path integration method, vibration suppression of NES has been researched when it is affected by a main oscillator with a narrow band stochastic force in the form of trigonometric functions, of which results show that response regimes are affected by the amplitude of stochastic excitation and the disturbance strength. Finally, all these conclusions have been approved by the numerical verification and coincided with the theoretical analysis; meanwhile, after the comparing analysis with the optimal linear absorber, it turns out that the NES which is affected by the narrow band stochastic force could also suppress the vibration of system with a better effect.