A comparison between NMPC and LQG for the level control of three tank interacting system

Modern industrial plants consist of many processes occurring simultaneously which are to be monitored and controlled at all time, during plant operation. Typically, industrial plants are multi-input multi-output type and they also exhibit strong non-linear dynamics. Three tank liquid level control is such a laboratory based benchmark multi-variable control problem for modeling, identification, fault detection & diagnosis and fault tolerant control system design. Multi-variable processes make monitoring and control difficult for conventional controllers. To overcome this problem most modern industries, use a model based controller as supervisory controller. However, these controllers are designed based on linear model of the process. Linear models often fail to capture the non-linear dynamics which results in the failure of control systems. In this article, we compared the performance of Linear Quadratic Gaussian Control (LQG) with the Non-linear Model Predictive Control (NMPC) to achieve the servo plus disturbance rejection and regulatory control of a three tank system in presence of changing valve position which serves as the disturbance input. As anticipated, the simulation results reveal better competency of NMPC over LQG in handling disturbances.