4
Self-tuning PID Controllers
This chapter is devoted to PID digital controllers and how they may be made
self-tuning.
Experience in implementing adaptive control systems indicates that users
in industrial practice are mistrustful of adaptive digital controllers based on
the optimal theory of automatic control, mainly because understanding the
algorithms involved requires in-depth knowledge of the theory of automatic
control. The common factor to all successful applications of this kind of adap-
tive controller has been the availability of a sufficiently qualified person in
industrial practice both capable of absorbing the results of scientific research
and well acquainted with the technology in use. It is for this reason that we
have been able to see a trend over recent years towards research into simple
adaptive controllers which can be implemented not only by theoreticians in
the field of adaptive control but also by users in industrial applications.
It is clear that the vast majority of controllers (around 90%) currently
used in industry are PID type controllers because, provided these are well ad-
justed, they show very good control results. They are also user-friendly in that
they are simple, generally well known and easy to implement. Provided the
parameters have been well chosen they are capable of controlling a significant
portion of continuous-time technological processes.
The use of continuous-time PID controllers has a tradition going back
many years. A number of adjustment approaches and methods of optimization
have been developed in which users and manufacturers of control technology
have wide practical experience. Understandably they wish to put this knowl-
edge to work along with their experience with analogue techniques and apply
this also to digital control systems.
The aim of this chapter is to acquaint the reader with problems of dis-
cretization of continuous-time PID type controllers. A survey of particular
digital PID type algorithms which are suitable for design of their self-tuning
versions is also proposed. Especially emphasized are the additional versions of
PID type controllers which have a number of advantages from the point of view
of their practical implementation. The proposed algorithms are partly taken