An Integrated Structure with Economic Optimisation and Constrained Model Predictive Control: an Application to a MIMO pH Reactor

Integration of a Model Predictive Control (MPC) algorithm with economic optimisation, important when dynamics of disturbances and of the process are comparable (the problem encountered in many practical applications), is considered in the paper. The case when the process has more manipulated variables than controlled outputs is especially interesting since additional degrees of freedom are available, e.g. when it is sufficient for some of the output variables to be bounded instead of controlled. The idea of the proposed approach is to integrate the economic optimisation and MPC algorithm into one computationally efficient optimisation problem. The steady-state model of the process is approximated on-line at each algorithm iteration taking into account the current state of the plant. As a result, an easy to solve quadratic programming task is obtained. Linear and linear-quadratic approximations are used.