This paper presents a robust control method for a class of nonlinear system
s, based on a mixed PID/adaptive algorithm. The nonlinear system is conside
red as a second-order linear dominant model with an unmodeled dynamics that
is possibly nonlinear and time-varying. The PID part of the controller is
applied to stabilize the dominant model. The adaptive part of the controlle
r is used to compensate for the deviation of the system characteristics fro
m the dominant linear model for performance enhancement. The advantage of o
ur controller is that it can cope with strong nonlinearities in the system
without abandoning the PID controller which is well-known to many engineers
. The proposed control scheme guarantees the boundedness of the system stat
es and parameter estimation. An example is given to illustrate the effectiv
eness of the proposed controller. (C) 2001 Elsevier Science Ltd. All rights
reserved.