A combined PID/adaptive controller for a class of nonlinear systems

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.