Design of fuzzy-PID controller for first order non-linear liquid level system

This paper deals with a controlling of first order non-linear liquid system to desired level. Mathematical model[1] of non- linear liquid level system is derived using basic principles of science. Different control strategies are applied on level system like conventional Proportional -Integral-derivative (PID) controller which gave unsatisfactory response when used alone. Fuzzy controller[2] was used, which is based on set of empirical rules to meet the desired set-point .Fuzzy control worked better than PID control but there were several drawbacks of fuzzy controller which were addressed by combining the both the controllers and introducing that in level control loop. This paper compares the response of all three controllers-PID, Fuzzy and Fuzzy-PID[4] after simulation in LabVIEW[3]. Integral of Time-Weighted Absolute value of Error (ITAE) was calculated and it was found that for fuzzy-PID, value of ITAE was best. Fuzzy-PID control was best suited for non-linear liquid level system with water as the process liquid, as it had the best set point tracking, least oscillations and the value of ITAE was the least.