Liquid Level Tracking Control of Three-tank Systems

In this paper, a liquid level tracking controller composed of a feedforward controller and a feedback controller is proposed for three-tank systems. Firstly, the flat property of three-tank systems is verified and a feedforward controller is designed accordingly to track the ideal trajectories. Secondly, in order to eliminate the tracking errors introduced by model uncertainties or unknown disturbances, a nonlinear model predictive controller is designed in which a terminal equality constraint is added for ensuring asymptotic convergence. In addition, an improved cuckoo search algorithm is adopted to solve the optimization problem involved in the nonlinear model predictive control. Finally, the control performance is confirmed by both simulation and experiment results.