Partial Control of Systems in Series

This paper deals with the design of partially controlled SISO plants where the dynamics of a subsystem is not changed either because it is unchangeable or for convenience. This is the case of controlled processes where an input (output) filter is added to smooth the manipulated variable (the measurements). It is also the case when there is an unavoidable delay, either at the process input or output. The open-loop plant may be stable/unstable minimum/non-minimum phase. The state of the plant (including the unchanged subsystem) is assumed to be accessible or estimated. A simple procedure to design the control structure is outlined. Some examples illustrate the control design technique.