Feedforward Control of Pure Transport Delay Processes

This paper is concerned with the investigation of a feedforward control approach for a class of industrial systems which can be adequately modeled as a pure transport delay. The feedforward control loop is assumed to contain a sensor and actuator both with appreciable dynamics) as well as the feedforward controller. For this class of problems it turns out that application of the standard feedforward control approach leads to controllers which are, from a practical standpoint, unrealizable. The problem arises because the standard approach is based on an attempt to exactly cancel the effects of input disturbances. An alternate design approach is discussed in which a simple and easily realizable controller structure is assumed, and the controller parameters are chosen so that a suitable measure of system performance achieves a satisfactory value. The performance measure used is based on the frequency function relating the input disturbance spectrum to the output spectrum. This approach leads to some simple guidelines for choosing the feedforward controller parameters.