A new design procedure for variable structure control systems

In this dissertation two methods are presented for solving the existing control chattering problem. The "plant augmentation" and "adaptive VSC" methods provide robust systems with greatly reduced chattering. Augmenting the plant by a pure integrator places control chattering at the augmented plant input instead at the original plant input. The variable structure control (VSC) technique is then applied to the augmented system. The design procedure of VSC systems consists of three coupled steps. This VSC design procedure provides a robust and stable system in the presence of parametric uncertainties and external disturbances. For a further reduction in control chattering the "adaptive VSC" method is then applied where the magnitude of the signum term is adaptively adjusted according to an estimate of the parametric uncertainties and external disturbances present in a system. An n+1 order Luenberger observer is required to estimate these uncertainties and disturbances. Two cases for estimating these uncertainties and disturbances are considered. Both methods are then applied to control systems with time delay in the presence of parametric uncertainties and external disturbances. Being able to estimate these unknown uncertainties and disturbances makes the Smith prediction technique applicable to variable structure system (VSS) method. The simulation results show that both methods are effective in greatly reducing control chattering, and are effective in making the Smith prediction technique applicable to VSS. Besides, the designed VSC makes the system robust and stable in the presence of parametric uncertainties and external disturbances.