Robust MIMO water level control in interconnected twin-tanks using second order sliding mode control

A novel second order sliding mode control algorithm is presented for a class of MIMO nonlinear systems in input–output (I–O) form. The algorithm produces a dynamic control and does not require the derivative of the sliding variable, thus eliminating the requirement to design observers or peak detectors. The algorithm has been applied for robust control of liquid level in interconnected twin-tanks. The controller is implemented on a laboratory rig and the results presented validate the proposed theory. The implementation results show robustness to parameter variations such as tank area, the admittance coefficients of various pipes, leakage in the tanks and uncertainty in the pump dynamics. In order to contextualise the results obtained with second-order sliding mode control, the results obtained using a classical PI controller are also presented.