Fractional order PI control applied to level control in coupled two tank MIMO system with experimental validation

Often in a coupled two tank MIMO system, the level of the first tank is required to be kept at a constant level while the level of the second tank is required to follow a time varying reference signal. Sometimes controllers of the PID family along with conventional feedforward controllers may not be able to maintain the constant level in the first tank rejecting the disturbance due to the change in the level of the second tank without deteriorating the tracking performance of the level of the second tank. This paper shows analytically as well as experimentally that Fractional Order Proportional Integral (FOPI) controllers along with conventional feedforward controllers work better than PI/PID/2DOF-PI/3DOF-PI with feedforward controllers in such situation. FOPI controller is designed using the frequency domain approach. Effectiveness of the controllers is tested to maintain a constant level in the first tank while making the level of the second tank to follow a sinusoidal and square wave reference signals. Experimental results validate the objective of the paper.