Continuous sliding control applied to subsea oil and gas separation

Abstract

Due to the complexity and cost of maintenance in subsea environment, subsea equipments should be designed to be extremely robust. Thus, the robustness of sliding control is used to project a controller of liquid level inside subsea gas–liquid separator system. Subsea separation presents challenges related to nonlinearities of the dynamical system and disturbances on pipelines flow both changing their patterns along the years of operation. The present article proposes a controller capable of treating uncertainties regarding nonlinear effects based on distributed parameters. The controller deal with these uncertainties considering their bounded boundaries. Usual problems linked to the discontinuous control function generated by the sliding strategy are mitigated with a softened stabilization condition. Instead of determining the convergence of the liquid level to a specific point, the sliding control is used to stabilize the liquid level into a recommended operation zone. Inside of this zone, a sigmoid function is used to ensure the continuity and differentiability of control signal. Numerical simulations use characteristics method to represent the pipeline dynamics. Finally, it is presented a case of a trajectory tracking during a severe slug to show control performance.