H-infinity control of free-radical polymerisation reactors

This paper examines the problem of controlling a continuous stirred tank re actor (CSTR) in which free-radical polymerisation of styrene takes place. T he continuous polymerisation reactor under consideration is governed by a 6 th order nonlinear differential equation which has three equilibrium states . These equilibrium states are corresponded to low, medium and high monomer conversion rates. However, for economical and practical reasons, it is des irable to operate the reactor at the unstable medium monomer conversion rat e. In general, the problem of designing a robust nonlinear controller for a highly nonlinear system such as chemical reactors is still an ongoing rese arch area. In this paper, it is shown that by combining a nonlinear observe r design procedure, the linear H-infinity control theory and the feedback I /O linearisation technique, a robust nonlinear controller can be developed for the continuous polymerisation reactor. The performances of this control ler have been evaluated through computer simulations and compared to that o f a decentralised PID controller structure. (C) 2001 Elsevier Science Ltd. All rights reserved.