Design of Fuzzy Controller

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Design of fuzzy controller for two tank interacting system
Mohamed sabith KT
Second year Dept of Electrical Engineering NIT Calicut Calicut, India Dr. Abraham T Mathew Professor, Dept of Electrical Engineering NIT Calicut Calicut, India

Abstract—The control of liquid level in tanks and flow between tanks is a basic problem in the process Industries. Vital industries such as Petro-chemical industries, Paper making industries, Water treatment industries have the coupled tanks processes. The level of fluid in the tanks and interaction between tanks must be controlled. The aim of the project is to model the the coupled two tank liquid level system and to design a fuzzy controller. For coupled tank systems with non linear and complex characteristics classical PID is difficult to achieve the desired response. Fuzzy logic control is a classic method by which dynamic performance and strong robustness is guaranteed. The project compares the performance of the two tank system with classical PID and fuzzy logic control. Index Terms—PID, fuzzy logic, steady state Introduction

through two separate pumps whose output is throttled using a control valve. Separate disturbance are made to both the tanks using hand valves. The two tanks are connected by means of hand valve, so the level of tank 1 will affect the tank 2 and vice versa. So this is a highly non linear system. Flow transmitters and pressure transmitters are there which give indication of flow and level respectively in a scale of 4-20 mA. The input from this sensors are taken to a computer which is process by a software in which controller is implemented which will give necessary control signal to throttle the control valve to get the necessary level.

A Coupled tanks process is found in the many industries. Generally, The TITO processes have the problems to control their systems because of the existence of interactions between input and output variables. Many control methods such as 2DOF PID [1], Auto tuning PID [2], CDM [3] and Decoupling [4] have been applied to coupled tanks processes for solving their problems. This paper presents control of two tank interacting system with the help of classical PID and Fuzzy control. The paper is organized as follows. The next section gives details about Coupled-tank process. Section 3 explains about modeling of two tank interacting system. Section 4 explains PID based control. Section 5 explains an implementation of Fuzzy Controller for coupled tank process. Section 6 shows experiment process and results. Finally, conclusions are given in section 7. COUPLED TANK SYSTEM

MODELLING OF A TWO TANK INTERACTING SYSTEM Consider the coupled tank, two-input two-output process . The target is to control level of two tanks by the inlet water flow from two pumps P1and P2. The process inputs are flow rate of two pumps u1(t)and u2(t) which is throttled using control valves. The nonlinear plant equations can be obtained by mass balance equation The overall material balance on the cylindrical tank is: Rate of mass accumulation in the system = rate of mass entering in the system- rate of mass leaving the system There for the dynamics of the tank system can be written as

The coupled tank apparatus is shown in the Figure 1.1. The apparatus is a model consisting of a pump, two cylindrical tanks made of plexiglas, two control valves, and two level transmitters .The two tanks are installed in a manner as shown in the fig 2.1The water input to both the tank is provided

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