Observer-based Backstepping liquid level controller for a quadruple tank process

This paper deals with the design of a nonlinear sensorless controller for a quadruple tank process. So to provide an economic liquid level control, a novel output feedback control scheme is developed. In the proposed approach, a model-based Backstepping controller combined with a second order sliding mode observer is designed for the four-tank liquid levels system. In fact, only two sensors are used to measure the liquid levels in the two bottom tanks and the other process´s states are assumed unavailable. The nonlinear Backstepping controller is synthesized in order to ensure globally asymptotical stabilization for this nonlinear system. The super twisting observer converges in a finite time. It leads to a good estimation of the liquid levels in the two top tanks. A good track of the liquid level in the bottom tank with the reference trajectory is achieved by the proposed controller. To highlight the applicability and the efficiency of the proposed control scheme, simulation results are provided and discussed.