NONLINEAR IMC OF SYSTEMS WITH INPUT MULTIPLICITIES

Non-linear internal model control (NIMC) of non-linear systems with in put multiplicities is analyzed. The system is a continuous stirred tan k reactor (CSTR) carrying out Van de Vusse reaction schemes and exhibi ting input multiplicities in the manipulated variable (u) on the produ ct yield (y). The system having two values of u to get a desired value pf y (one value of u has a positive gain and the other value of u has a negative gain) poses problem in the design of conventional PI contr ollers. Non-linear IMC designed based on the original state variable m odel equations drives the system input to a larger value rather than t o a smaller value. Whereas the non-linear IMC designed based on a pseu do dynamic model equation drives the system input to either a larger v alue or to a lower value depending on the designer choice. The perform ance of the non-linear IMC is compared with that of the conventional P I controller.