Component Synthesis Active Vibration Suppression Method Of Flexible Spacecraft During Attitude Maneuver

With the development of space technology, complication becomes one of the most important characteristics for more and more spacecrafts, for example, the spacecraft with large solar panels or antennas. Solar panels and antennas are called appendages, and most of them are deformable, so they are called flexible appendages usually. The coupling between the vibration of flexible appendages and the rigid motion of the spacecraft greatly affects the accuracy of attitude control and the stability of the system. However, due to the low-damping of the flexible structure, it is difficult to attenuate the vibration to a permissible limit by itself. Therefore, it is necessary to find an active vi-bration suppression method for the flexible structures. The main vibration components should be suppressed rapidly and effectively while the specified attitude motion is being realized.The essential of the component synthesis active vibration suppression method (CSVS) is synthesizing several components as system input. These components are same or similar time-varying and are arranged according to certain rules along the time axis. The synthesized command can realize specified attitude maneuver and, at the same time, suppress the vibration harmonic of arbitrary order. The basic principle of CSVS method, the theorem of robustness and the method of suppressing multi modes simulta-neously are introduced into this thesis in form of theorems. First, by using the Lagrange method to construct the mathematic model of flexible spacecraft, then the vibration equations are discretized by using unconstrained modes series method. Then decoupled attitude dynamic equations of spacecraft and the vibration equations of flexible append-ages are obtained the, which are the basis of numerical simulation later.When the CSVS method is used in the time domain, the number of component will increase extremely if the number of suppressed harmonic increases. The CSVS methods based on the zero-placement, i.e. analyzing CSVS in complex plane, are used to solve the above problem. The essentials of the zero-placement are to collocate enough zeros in the system poles where need to be suppressed to eliminate the vibration and obtain identical time interval components which are easier to realize. By using this method, the number of component will increase linearly when the number of harmonic increases.Considering the spacecraft with jet on-off actuator, two methods applying CSVS to perform large angle maneuver are suggested in this thesis. The first method is to use CSVS and optimization theory at the same time, and the obtained maneuver commands are simple and realizable, but it is not available to CSVS with different amplitude com-ponents and damped structure. The second method is CSVS based on pulse width modulation technique (PWM). That is, first, the maneuver commands to suppress vibra-tions are obtained by applying CSVS method. Then the maneuver commands are trans-formed to regular amplitude maneuver commands by using PWM technique. Due to the minimal pulse width of jet actuator, it should not be switched frequently. By reasonably choosing the minimal pulse period that meets the vibration requirements, the actuator can achieve the maximal pulse width. This method is no longer constrained by the prin-ciple of CSVS and damp of system.The maneuver commands discussed above are open-looped. In fact, CSVS method is a kind of feedforward control method. The system can have certain insensitivity by increasing the robustness of the method and have a stronger anti-interference ability by using closed-loop control. Combining the above two methods and utilizing the respec-tive advantages, the performance index of the control system can be improved signifi-cantly.By applying the Lagrange method and unconstrained mode series method, the at-titude dynamics equations and the vibration equations of flexible appendages are de-coupled. By choosing the appropriate feedback quantity and adding the vibration of flexible appendages and CSVS method as constrain condition when design the closed-loop feedback parameters, the optimum performance solution can be obtained. The va-lidity of this method is proved by designing the proportion add rate feedback controller and PD feedback controller.