Fault Tolerant Control For Large Strap-on Launch Vehicle’s Servomechanism

The engine servomechanism is the actuator of large strap-on launch vehicle’s attitude control system, which is related to the success of the launch mission. With the research object of China’s new generation of strap-on launch vehicle, this dissertation studies the tolerant control technologies for servomechanism fault during boost phase flight of the launch vehicle. The fault effect on the control system is analyzed, two different fault-tolerant control methods are proposed. The main contens are summarized as follows:1. The attitude controller is designed for normal flight conditions. Firstly, the attitude dynamics model is established for the new strap-on launch vehicle. Secondly, the attitude controller on non- fault condition is desighed. Lastly, a time-domain simulation platform with variable coefficients is built.2. The servomechanis m fault effect on the control system is analyzed. The influence of servomechanism fault is analyzed in frequency-domain and time-domain, the performance of fault control system is studied. The closed- loop stability of fault attitude control system is analyzed using frequency-domain method; In the time-domain, fault simulation platform is built to prove the validity of frequency-domain analysis.3. The reconstruction method based on the engine function redundancy is proposed. Considering the strap-on launch vehicle’ servomachanism number is large, the control instruction deallocation is carried out by the normal working engine swing angle, thus the control moment is reconstructed. Firstly, a independent reconstruction method is proposed by merely using core stages or booster engines, through which the control moment is compensated at a certain extent; To solve the limitation of independent reconstruction, a new reconstruction control method combined core-stage and booster Engines is proposed, and the loss control moment is compensated completely.4. An adaptive fault-tole rant control method based on reference model is studied. Because of the fault information on- line identification is difficult to be realized, an adaptive fault-tolerant controller is designed based on model following thinking. Firstly the fault model is simplified and deformed reasonably, through witch a second-order control model is obtained. In consideration of the attitude model parameters change in large-scale during lauch vehicle boost phase, a time-varying reference model is designed. O n this basis, an adaptive control law is designed, which reduces the fault influence on control system effectively.From the view of engineering practice, the fault tolerant control technology is applied to the lauch vehicle’s attitude control in this paper, the scope of application of fault tolerant control theory is expand. O n the other hand, the study conclusion has a certain practical value for future large strap-on launch vehicle’s attitude control system design.