Servo-type output tracking control via variable structure technique

A design method of a servo-type output tracking system by variable structure control (VSC) is proposed for a class of nonlinear systems. This VSC system requires neither model following structure nor high order differential of a reference signal for output tracking. The VSC system is completely decoupled into a set of VSC subsystems with single-input and single-output. Two types of dynamic compensators which are composed of a set of dynamic subcompensators and a set of switching hyperplanes are introduced in this VSC system. One of the dynamic compensators is a feedforward one which improves the transient response of the output. The other being in the closed loop path contains the internal model of a reference signal generator in order to realize output tracking with no steady state error. The VSC system is stabilized by suitably designing the dynamic compensators and the switching hyperplane. The projection of the trajectory into a subspace in the state space stays in the hyperplane during sliding mode caused by VSC. The subspace is chosen so that the internal model and the feedforward compensation do not become invalid when the VSC is applied. How to design the dynamic compensators and the hyperplane are studied for a servomechanism and a repetitive control system. It is possible to achieve good performance in the transient response and the steady state of the output of the servomechanism. The repetitive control system effectively reduces the tracking error if the same pattern is periodically repeated in the reference signal. The robustness against parameter uncertainties and unknown disturbances is still valid for the VSC systems. The simulation results indicate that the proposed control strategy is extremely useful