Discrete controller design

This chapter discusses the theory and practice of discrete time control (i.e. the sort that is implementable in computers) to achieve closed-loop control of continuous time processes. Thus, we are concerned with the discrete time control of continuous time processes within a hybrid feedback loop. A natural initial question suggests itself: what are the advantages of discrete, as opposed to continuous, controllers? The answer is very disappointing. As far as control theory is concerned, there are no advantages (the proof of this is that every realisable discrete time signal is a continuous time signal, but the converse is false). The reason for studying discrete time control is essentially practical: to allow reliable miniature low-cost digital electronic devices to be used as controllers.