An IMC-PI based Level Control with Gain Scheduling and Set Point Weighting

This paper considers the problem of liquid level control in a conical tank system that regularly arises in process industries. Traditional linear controllers applied to such system, exhibit unsatisfactory performance due to the high non-linear cross-sectional area of the tank. In this paper, a set of linear controllers are employed through gain scheduling technique to achieve the desired response. At first, to approximate the original nonlinear dynamics, the conical tank system is linearized at various operating points. For each of these linearized systems, an Internal Model Control based Proportional-Integral (IMC-PI) controller is designed. The proposed strategy generates control action at any instance of time by simultaneously selecting two controllers whose associated linearization points are least distant from the liquid level in the tank at that time instance. Further improvement in the system performance is achieved by incorporating set point weighting along with the proposed control method. Simulation results and comparative study of various performance measures are provided to show efficacy of the proposed control scheme.