MRFT-based robust and adaptive controller design for gas loop of liquid-gas separator

The Modified Relay Feedback Test (MRFT) was recently proposed as a continuous oscillation method for identification of process parameters and controller tuning. In this research, the MRFT is used for the design of a robust and an adaptive PI controllers for a gas loop in the two-phase separator. The gas normally uncounted in the separator is the natural gas (mostly methane) which is contained in crude oil coming from the reservoir. In this paper, the PI controller is developed based on sixty four modes of operation corresponding to certain ranges of gas inflow and liquid level values - the two parameters that characterize the operating modes. It is shown through the developed model and simulations that these operating modes affect the dynamics of the gas loop. Dynamic properties of the process in each mode are studied through MRFT. A robust and an adaptive PI controllers are designed in order to maintain the pressure during the change of the operating conditions. Performance of the designed control system is studied by simulations.