Robust control of a steam header letdown system

The Syncrude Utility plant is a cogenerating power plant where steam is usually a more important quantity than power. Steam is distributed through a multiply-connected header system at four different pressures, with letdown valve stations providing some regulatory control. The existing letdown valve controllers work well for most operating conditions, but during plant upsets controller interaction may occur, which can put some of the letdown flows and consequently header pressures into undesirable oscillatory modes. A multivariable state feedback controller was designed to improve overall letdown coordination and damp out the oscillatory modes. Kharitonov´s Theorem was employed to ensure the robustness of this controller for a reasonable range of operating conditions. The controller was simulated with encouraging results.