Disturbance Observer Based Performance Improvement of H∞ Controller

Disturbance observer proposed in this paper estimates the equivalent input disturbance and modifies control law to reject it. A reduced order observer is used to estimate disturbance from the input-output measurement when subject to large disturbance. Convergence of disturbance estimator is decided by the observer gain, which is selected through sufficient condition for stability. Simulation studies carried out on a satellite launch vehicle model has shown significant improvement on the response. The proposed controller has also shown enhanced disturbance rejection, when analyzed through frequency response of disturbance transfer function.