Speed control of PIG using bypass flow in natural gas pipeline

This paper introduces a simple nonlinear control method for pipeline inspection gauge (PIG) flow in a natural gas pipeline. The PIG is controlled using the amount of bypass flow across its body. The dynamic behavior of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow and dynamics of the PIG. The method of characteristics (MOC) and Runge-Kutta method are used to solve the dynamics of flow. To control the PIG velocity, a simple nonlinear controller is proposed based on the back-stepping method. The closed loop system is stable in the sense of Lyapunov stability. To derive such a controller, three system parameters should be measured: the PIG position, its velocity and the velocity of bypass flow across the PIG body. To show the effectiveness of the proposed controller, the simulation has been done with three cases: the PIG starts to move at its launcher, the PIG arrives at its receiver and the PIG restarts after stopping in the pipeline. The simulation results show that the proposed controller can be used for controlling the PIG velocity with good performance when it runs in the natural gas pipeline