Modified Smith Predictor with a Periodic Disturbance Reduction Method for Linear Small Delay Systems

A modified Smith predictor with a periodic disturbance reduction method for linear systems with small time delays is proposed in this paper. With this method it is not necessary to estimate unknown disturbance frequencies. The main control structure is provided by Astrom's modified Smith predictor. The proposed method consists of a disturbance reduction controller (DRC) and a residual disturbance observer (RDO). The DRC, which is composed of an inverse plant model and an integrator with a nonnegative gain, compensates for unknown load disturbances and exhibiting uncertainties in stable or unstable systems. The disturbance reduction performance of the proposed method is enhanced by combining the DRC with the RDO to suppress undesired residual signals including residual disturbances and residual uncertainties. Simulation examples demonstrate the effectiveness of the proposed periodic disturbance reduction method for linear uncertain systems with time delays, under periodic or non-periodic unknown load disturbances.