Chuang Liu

Robust non-fragile state feedback attitude control for uncertain spacecraft with input saturation

This paper investigates the robust non-fragile state feedback attitude control problem for uncertain spacecraft, and the problem explored here is subject to H∞ performance constraint, quadratic stability, external disturbances, controller perturbation and control input saturation. The model of spacecraft attitude control system is introduced and transformed into a state space form with parameter uncertainty. Based on Lyapunov theory, sufficient conditions for the existence of robust non-fragile state feedback controller are given based on linear matrix inequalities in terms of additive perturbation and multiplicative perturbation. Then, the design of non-fragile controller subject to required constraints can be regarded as a convex optimization problem based on linear matrix inequalities. By solving linear matrix inequalities to obtain an optimal feasible solution which satisfies all the constraints of the problem and optimizes the objective function, the controller gain matrix can be obtained exactly. Based on the obtained controller, the spacecraft attitude control problem can be solved. The simulation results also demonstrate the effectiveness of the proposed control method.

In-orbit estimation of inertia parameters of target satellite after capturing the tracking satellite

After capturing the tracking satellite, the target satellite will turn into a compound satellite, and the inertia parameters of target satellite can produce great changes and greatly affect the attitude control system and its control effect. In order to estimate the inertia parameters of target satellite, two methods including the method based on Angular Momentum Conservation Law and the modified method based on Angular Momentum Conservation Law are proposed. Comparisons are made with the least-square method. Simulation results show that the inertia parameters of compound satellite can be estimated directly within 200s, so the inertia parameters of target satellite can also be estimated. Compared with the once least-square method, the estimation precision of methods based on Angular Momentum Conservation and modified Angular Momentum Conservation Law are higher. But the product of inertia precision of the modified method is the highest of the three. Basically, it can meet the needs of the inertial parameters estimation of target satellite.

Mixed H2/H∞ Control Approach and its Application in Satellite Attitude Control System

In this paper, we address the mixed H2/H∞ control approach for linear time-invariant system based on linear matrix inequality (LMI). First, the problem to be solved is stated, and the satellite attitude dynamics is established and converted into a corresponding state space form. Then, the mixed H2/H∞ controller based on LMIs is designed in order to attain the state feedback gain matrix. To validate the efficiency and practicability of the proposed controller, simulation results based on satellite attitude system are presented, from which we can observe that under the condition of external disturbances, the system will be stable within 150s, and the maximum of control torque will be no more than 0.025Nm. Expanding the controller gain will affect the stabilizing process, but not the stabilization time, and it will increase the control input which will bring pressure to the actuator.

Robust Adaptive Variable Structure Tracking Control for Spacecraft Chaotic Attitude Motion

A continuous globally stable control algorithm is presented to track angular velocity for spacecraft chaotic attitude motion affected by external disturbances using adaptive variable structure controller. Affected by some external disturbances, the spacecraft attitude dynamics system can generate many types of chaotic motion. Once it is required that a spacecraft with chaotic attitude motion should track the other spacecraft chaotic attitude plant to achieve angular velocity synchronization, the design of a robust tracking controller becomes necessary. The controller design is based on adaptive control theory and variable structure control theory, and adopts integral sliding surface and a single vector adjusted dynamically. Numerical simulations are performed to demonstrate the effectiveness and feasibility of the proposed adaptive variable structure controller.

Mixed H 2 /H ∞ approach of full order state observer design for satellite attitude control system

This paper investigates the design method of full order state observer for satellite attitude control system using mixed H₂/H_∞ optimal approach. A linear system described by state space form is introduced first to state the problem of full order state observer design. The designed observer should meet the requirement of H₂ performance and H_∞ performance so that the disturbance would influence the observer as little as possible. Thus, we convert the satellite attitude control system to the same state space form, and deduce the mixed H₂/H_∞ approach based on linear matrix inequalities (LMIs). By solving LMIs, we can obtain the solution of corresponding convex optimization problem. Then, the observer gain can be decided. The simulation results based on satellite attitude control system show that the magnitude of observer error is 10^-6 rad/s within 10000s. We can conclude that the mixed H₂/H_∞ approach of full order state observer design is effective and the external disturbance has little influence on the observation error.

A novel robust non-fragile control approach for a class of uncertain linear systems with input constraints

This paper addresses the non-fragile control problem for a class of uncertain linear systems subject to model uncertainty, controller perturbations, fault signals and input constraints. The controller to be designed is supposed to have additive gain perturbations. A novel state feedback controller is proposed based on the exact available expectation of a Bernoulli random variable, which is introduced to model the feature of the controller gain perturbation that randomly occurs. By using Lyapunov stability theory, new sufficient conditions are derived to design non-fragile controller for a class of uncertain linear systems considering input constraints. Compared with the existing non-fragile state feedback controller methods, the non-fragile property is fully considered to improve the tolerance of uncertainties in the controller, where the conservativeness can be reduced via the Bernoulli random variable. The effectiveness of the proposed control strategy is illustrated by two numerical examples.

Underactuated spacecraft chaotic attitude control based on exponential reaching law

The control problem of underactuated spacecraft chaotic attitude motion is investigated based on exponential reaching law in this paper. First, the underactuated spacecraft chaotic attitude system is written in nonlinear equation form with two controls. Once the trajectory planning of angular acceleration is preset, the dynamics equation of angular velocity error can be obtained. Then, the sliding mode controller based on exponential reaching law and linear matrix inequality is designed, which consists of equivalent control term and switching control term. Finally, simulations are performed to test the performance of the proposed controller.

Dynamics modeling and simulation of space electromagnetic docking for CubeSat

A novel model of space electromagnetic docking is established to solve the problem of traditional plume contamination and short service life in this paper. A new modelling technique regarding space electromagnetic docking for CubeSat is proposed. The mathematical model with four core-containing energized solenoids is derived and simplified to the magnetic dipole far-field model of single-turn coil. Simplifying the magnetic dipole far-field model will yield the model of space electromagnetic docking, and the numerical simulation results also verify the reliability and feasibility of simplification process.