Optimal design of 2-DOF digital controller for sampled-data tracking systems with preview

The design of optimal sampled-data tracking controllers with two and 2 1/2 degrees of freedom (DOF) are considered for the case when future values of the reference signal are known over an interval /spl tau/. A rigorous solution is given in the frequency domain on basis of Laplace transforms in continuous time. Limiting properties of the solution for for /spl tau/ /spl rarr/ /spl infin/ are investigated. It is shown that the use of a reference controller makes it possible to circumvent fundamental limitations on the achievable tracking precision caused by unstable poles of the plant.