Error treatment in constrained control and its application to MPC of rectifier

A new error treatment was applied to the model predictive control (MPC) of a commercial ethylene-ethane rectifier. The present method simply considers the error as zero if it is in the constrained zone, otherwise, the error is equaled to y_sp-y. There is a jump (0 to y_sp-y) at the constrained boundary. While, the new method presented in this paper avoids the jump at the constrained boundary, and ensures the measure of controlled variables to approach the setpoint in multivariable control. The error exponential coefficient, namely index was estimated by the simulating experiments of ethylene rectifier, ranged from 2 to 4. In the commercial ethylene-ethane rectifier application, the setpoint control of side draw products purity comes true and the concentration of bottom ethylene is controlled within a certain scope. Hence, the optimization of economy can be got from the proper choice of the setpoint and the scope of constrained zone.