Design Of Attitude Control System For Air-floating Platform Based On Fractional Order Theory

Today in the exploration of outer space, the ground flotation simulation systemis the main means of simulating spacecraft rendezvous and docking, high-precisionattitude control, rail rapid mobility and fault diagnosis technology in space. In thispaper ground flotation simulation platform functionally divides into measurementand control parts. This paper designs simulation system for flotation attitude controlsection to which fractional theory emerging in recent years is applied. Thecontrollers are fractional PI~λD~μ controller and fractional sliding control law.Andthey are verified by simulation for different circumstances.First, the laboratory air-flotating platform is modeled and a simplified dynamicmodel is derived. Then the Modified Rodrigues parameters (MRPs) describeflotation attitude motion equations is derived and the change between MRPs andEuler angles is deduced. Then calculation of the moment of inertia of the actualsystem makes the results more realistic.Then this paper introduces the basicknowledge of the theory of fractional order including the definitions, thefundamental nature and the expression of real fractional order system. Oustaloupfilter with improved methods of fractional calculus operator for discreteapproximation is used as a numerical implementation of MATLAB simulation. Andthen fractional PI~λD~μ controller and fractional sliding control law is designed.Controller with fractional angular velocity feedback and without the feedbackrespectively simulates while spacecraft control implemented as benchmarks.Simulation results shows the attitude control system possesses higher accuracy,faster convergence process and better quality control with whole state information.Fractional PI~λD~μ controller shows robustness when the uncertainty of the inertiamoment and interference control moment is joined. Fractional differential operatoris introduced into the traditional sliding control surface and sliding control law.Fractional sliding mode control for attitude control model is designed usingfractional order systems as well as the advantages of sliding mode control. First, thesystems controlled by integer and fractional order sliding mode are simulated.Analysis of simulation results shows the latter’s control precision and convergencespeed is better than the former. Then the inertia moment of uncertainty and externaldisturbance torques join the system simulation. Simulation results show under thecontrol of fractional order sliding mode the system still have a better control effect.