ABSTRACT of M.Tech Thesis

Industries such as petro-chemical industries, paper making industries, waste

management and others are the vital industries where liquid level and flow control are

essential. Liquids will be processed by chemical or mixing treatment in the tanks, but always

the level fluid in the tanks must be controlled, and the flow between tanks must be regulated

in the presence of nonlinearity and inexact model description of the plant. In process control

systems nonlinearity is the rule rather than the exception. Most control loops such as

pressure, temperature, composition, etc., are significantly nonlinear. This may be because of

nonlinearity due to control valves, or on account of variations in process gain, time constant,

and dead time. The control problem becomes more complex if water level and air pressure

control are considered in one system.

The fuzzy logic controller is basically nonlinear and adaptive in nature. This

gives a robust performance in the cases where the effects of parameter variation of controller

are also taken into consideration. It is a well established fact that the fuzzy logic controller

yields results that are superior as compare to those obtained through conventional controllers

such as PI and PID because of the fact that fuzzy logic controller is based on linguistic

variable set theory and does not require a mathematical model. Generally, the input variables

are error and rate of change of error. If the error if coarse, the fuzzy controller provide coarse

tuning to the output variable and if the error is fine it provides fine tuning of the output

variable. The fuzzy logic technique is applied to the single tank, liquid level system. The

single tank system, firstly control with the PID controller and the parameters of the PID

controller are tune with the help of Ziegler-Nichols method. Fuzzy controller provides better

result as compare with conventional controller i.e. PID controller.

The backstepping technique used to develop nonlinear controllers for precise

liquid level tracking in a state-coupled, two-tank system. To serve a stepping stone, a model-

based controller was initially designed that ensured exponential tracking of liquid level.

Simulation studies are then conducted based on the developed model using Matlab

and simulink. A series of tracking performance tests, disturbance rejection and plant

parameter changes are conducted to evaluate the controller performance in comparison to

PID controller.