Variable structure model-following control of flight dynamics

The design of model-following control systems has received considerable attention in recent years. The design objective for flight control systems is to develop a controller which forces the aircraft dynamics to follow the dynamics of an ideal model. Various approaches using stability criteria have been developed. The problem is considered using the variable structure control approach and a CAD design package, VASSYD, with a robust eigenstructure algorithm. The basic philosophy of variable structure control design is that the structure of the feedback control is altered as the state crosses surfaces in the state space. The control in the sliding mode yields total or selective invariance to system parameter variations and disturbances, and precise closed-loop eigenvalue placement in time-varying and uncertain systems. The designer of model-following variable structure systems first specifies the stable eigenvalues of the closed-loop error system by the choice of sliding hyperplanes and then chooses a suitable control law to ensure sliding motion. The design technique ensures that the desired error transients are obtained for a wide range of flight conditions