This paper deals with a digital tracking control system subject to change in load condition. It is assumed that the plant is described by a discrete-time state-space model with a time delay and a direct forward link between control input and output. An optimal controller with state feedback plus integral and preview actions is derived by using the LQI technique. It is shown under the stabilizability and detectability conditions that the optimal closed-loop system is stable and achieves a complete output regulation. For a special case where the time delay is unilateral, we present an algorithm for computing feedback gain with less computational effort. The tracking performance of proposed optimal control law is evaluated through a numerical example for a heat exchanger model. Experimental studies using a pilot plant show that the controller gives acceptable tracking performance in the presence of load change.
