Design of Controllers for Three Tank System

Abstract

The important part of a process industry is the analysis of chemical processes and controlling process variables by applying various control strategies. Different types of controllers are available nowadays, still conventional Proportional-Integral-Derivative (PID) controller is the most preferred one. As PID has three different tuning parameters, so it’s perfect tuning is an issue till today. Many researchers have proposed different methods for tuning the controller parameters to control and fulfil needs of a process. Ziegler Nichols closed-loop method, Ziegler Nichols open-loop method, Cohen-coon method are some of the tuning methods to tune PID controller. Further, the level control of three tank system has been analysed. In level process control, three tanks are connected in different fashions like they are purely non-interacting, purely interacting and some are combinations of interacting and non-interacting system. First, mathematical modelling of three tank system is done using basic principle of conservation of mass. The liquid level in third tank is controlled at setpoint by varying the manipulated variable which affects the first tank. Step response of each combinations of three tanks are obtained using P, PI and PID controller and process performances are compared. Internal model controller (IMC) and IMC-based PID controller are also developed for each combinations and their responses are compared with that of conventional feedback controller. The implementation of IMC and IMCbased PID controller is very difficult in case of third or higher order system. So, half rule method is used to reduce higher order transfer function into first-order plus time delay transfer function. Process performance like offset, overshoot and settling time in each cases have been analysed. Laboratory Virtual Instrumentation Engineering Workbench (LabVIEW) is used for simulation of above processes.