Font Size: a A A

On-orbit Active Vibration Control For Flexible Spacecrafts

Posted on:2014-01-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y LiFull Text:PDF
GTID:1262330398997835Subject:Mechanical and electrical engineering
Abstract/Summary:PDF Full Text Request
Since large spacecrafts extensively deployed exhibit strong flexibility, the vibrationgenerated during space work must be depressed to satisfy the task demands. Dynamicmodeling, model updating, nonlinear attitude control and vibration control, robustvibration control and vibration control implementation strategies for flexible spacecraftsare studied in this research and the results can find theoretical and technicalfundamentals for the engineering application of the vibration control for flexiblespacecrafts. The main contributions are described as follows:1. The dynamic model of a flexible spacecraft is derived by a hybrid coordinatemethod and Lagrange equation, and an added mass method is presented to analyze thevibration in the air. With regard to non-linear vibration of a spacecraft flexible structurein ground testing, Green-Lagrange strain is introduced to correct first-order shearingdeformation of its non-linear sheet. Then a finite element model is built by virtual workprinciple. Added mass is gained by calculating the pressure with velocity potentialfunction and Green equation. On this basis, the original structure is modified withadditional mass. The method of updating flexible spacecraft model is proposed usinganalysis result of flexible structure ground vibration. A relatively refined dynamic modelof the in-orbit spacecraft is obtained.2. Based on the piezoelectric smart materials and modal controls method, attitudecontrol and vibration control systems for the three-axis-stabilized flexible spacecraftsare established. Based on a bandwidth insulation method, a positive position feedback(PPF) active vibration controller for the flexible structure is designed. The finiteelement model of piezo-intelligent plate is built, and mode control force and modedisplacement are deduced. Taking account of the attitude determination system andattitude control actuators, a full digital simulation model of the three-axis stabilizedflexible spacecraft is built. Simulation results verify the validity of the proposed modeland control methods.3. In order to improve anti-interference ability of the attitude control system, anovel state-dependent Riccati equation (SDRE)-based attitude controller is designed.The robustness of the control system is enhanced by introducing the idea ofself-adaptation. Since the rate of change of the angular velocity variable and the rate ofchange of angular displacement variable are different, attitude dynamics and kinematicmodel are decomposed into the inside and outside control loops. Nonlinear dynamics is pseudo-linearized, and hence the corresponding integral SDRE controller is designedfor each loop. The characteristics of first-order PPF controller are studied, By means ofan adaptive PPF controller, not only the robustness of the control system is enhanced,but also the tradeoff between control precision and control performance could be solved.Numerical example shows the effectiveness and feasibility of the proposed methods.4. Based on Linear Matrix Inequalities (LMI), a robust control method for nonlinearsystem is proposed, furthermore, a robust second-order PPF controller is designed. Forthe nonlinear systems based on a fuzzy T-S model with control input constraints, theupper bound of the quadratic performance index is derived. Stability constraints andcontrol input constraints are further formulated into LMIs which are easily obtained. AnLMI method is introduced into PPF controller design. In the closed-loop systems withthe PPF controller, by considering the uncertainty of the flexible structure dynamic andthe actuators’ capacity limit, the control problem is transformed into solving theeigenvalue problem with LMI constraints. Therefore, an optimal PPF controller isobtained, and robustness of vibration control is enhanced. The simulation results showthe effectivity of the robust PPF controller.5. Aiming at achieving higher reliability in engineering application, the strategy ofactive vibration control for the flexible structure is presented using multiple active tunedmass dampers (MATMD). For a flexible spacecraft structure, multiple tuned massdampers (MTMD) consisting leaf springs and inertial masses are designed. By using ofdisplacement amplification factor, the parameters of mass, springiness element anddamping element are optimally chosen. The piezoelectric actuators are introduced intoactive control. Combined with the PPF method, a modal control equation withpiezoelectric actuators is deduced. The simulation results with three cases are compared,showing the advantage and reliability of the MATMD.
Keywords/Search Tags:Flexible spacecraft, Vibration control, Positive position feedback, Nonlinear control, LMI method
PDF Full Text Request
Related items