Opportunities and difficulties with 5 × 5 distillation control
Petter Lundström and Sigurd Skogestad

Journal of Process Control
5, 4, 1995, pages 249-261


Multivariable 5 × 5 distillation control, i.e., control of levels, pressure and compositions by one multivariable controller, provides opportunities to improve the control performance as compared to decentralized control. Multivariable interactions can be counteracted with a 5 × 5 controller. However, the main advantage is automatic constraint handling which cannot be realized by a fixed linear 5 × 5 controller, but requires a solution based on on-line optimization, for example, using a model predictive control (MPC) strategy. A multivariable control scheme also presents some difficulties. Unconsidered model uncertainty may be a severe problem. It may also be difficult to tune the multivariable controller. In this paper the MPC approach is combined with the H/μ framework in order to obtain a robust design.