Performance Analysis of Robust Averaging Level Control

Frequent inlet flow changes, especially in the same direction, typically cause problems for averaging level controllers. To obtain optimal flow filtering while being robust towards future inlet flow upsets closed loop robust MPC has been used. It differs from other averaging controllers in that it does not return the tank level to a fixed set-point, but rather lets it depend on the current inlet flow. The performance and robustness of this robustly optimal behavior is analyzed and compared to that of the (non-robust) optimal averaging level controller. Both the analysis and the simulation results show that the robust controller obtains comparable flow filtering as the optimal controller even when inlet flow changes are sparse while handling frequent upsets considerably better.