Output‐feedback control of nonlinear plants

A robust state estimator design for nonlinear plants

“…As it can be seen, there is fast convergence with small offsets. The offsets of the observable-part variables can be eliminated with integral action, and reduced in the unobservable-part variables by incorporating integral action to the estimation scheme, as it was done in the estimator-based nonlinear geometric controller in [4]. h…”

“…This reactor has (at least) three steadystates [4]. To maintain the reactor volume without modifying its detectability structure, there is a proportional volume controller.…”

“…These conditions are met by any free-radical polymerization reactor [ 1,4]. The unobservable dynamics ( 4) are given by the forced motion of the zeroth and second CLD moments:…”

“…The extension of the GO, HG, and SM nonlinear observation techniques to the case of nonlinear detectable plants do not seem straightforward, as it can be seen in [14]. Combining the GO and HG approaches and including a pole-placement tuning procedure, in [4] an estimator with nominal convergence was designed for observable or detectable nonlinear plants subjected to a geometric nonlinear controller. As it stands, this technique cannot be applied to open-loop plants, or to closed-loop plants with non-geometric controllers.…”

“…The extended Kalman filter (EKF) [ l l ] is by far the most widely used nonlinear state estimation technique in chemical engineering (see [4] and references therein), has a simple construction, but has the following drawbacks: lacks stability criteria and systematic tuning procedures, bears the on-line computational burden of a Riccati-type nonlinear matrix equation, and does not apply to detectable (partially observable) plants. There are three main approaches to the design of nonlinear estimators with convergence criteria: the geometric observer (GO) design [lo] which applies to an extremely restrictive class of plants, the high-gain (HG) approach [5,7] which has complex tuning procedures; and the sliding-mode (SM) approach [ 131 which has an elaborated design.…”