Tuning of feedback controllers for SISO systems often starts from
information about the
intersection of the Nyquist curve and the negative real axis. In
standard autotuning this point
is identified by a relay feedback experiment. For many processes,
however, it would be
advantageous to identify a point on the Nyquist curve somewhere in the
third quadrant. The
aim of this paper is two-fold. First, a noniterative procedure is
suggested for identification of
an arbitrarily chosen point in the third quadrant by the use of a
two-channel relay. The two-channel relay consists of two relays operating in parallel on the
process output and on the integral
of the process output, respectively. Secondly, general a
priori plant knowledge, often available,
is utilized for the choice between PI and PID control and for
amplitude-and-phase-margin based
controller tuning.
The chemical engineering literature on t h e control of inverse response processes is reviewed and found to be in a state of confusion. Suggested "compensation control schemes" are actually, for setpoint changes a s well a s for disturbance rejection, equivalent to series compensation networks of lead-lag character a n d generally offer no significant advantage over standard-tuned PID-controllers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.