Control of Coupled Tank Liquid Level System Using Sliding Mode Control

Author Name(s): B.Amarendra Reddy, G. Ananda Rao, K. Anusha, B. Pavan Kumar
Author Email: bamarendrareddy@yahoo.com

Abstract

Designing a controller for coupled tank liquid level system under tracking conditions is a challenging task.  First order sliding mode controller is designed and implemented for liquid level coupled tank system under distinct tracking signals. The proposed controller was designed by using tracking error approach.  The designed non-linear controller is capable of tracking the desired water level for all set points with high degree of accuracy, with less rise time and with less significant overshoot. The controller shows robustness against the disturbance in the plant and produced an appropriate control signals for the motive of controlling the liquid level in the coupled-tank system. A simulation is carried out using MATLAB to control this system for different tracking signals.

Introduction

The control of a liquid level in tanks is a basic problem in process industries, where often it is required to store some amount of liquid in tanks and after that transferred to other one[1]. For regulating liquid level in coupled tank system requires an efficient and robust controller. One particular approach to robust controller design is so called sliding mode control (SMC) methodology. This type of liquid level systems are used in various industries like steel industries, thermal plants, food processing industries, chemical industries, etc.

In this paper a robust control strategy to control the liquid level of 2nd tank in coupled tank system was designed. This can be achieved by using Sliding Mode Control (SMC) which is belong to the Variable Structure Control Systems (VSCS). Variable Structure Control System (VSCS) is a grade of systems whereby the control law changes during the control process according to some defined produce which depends on the state of the system [4]. The most distinguished feature of VSC is its ability towards robust control systems and using VSC in many cases results invariant control systems. The term “invariant” means that the system is completely insensitive to parametric uncertainty and external disturbances.[5]

This paper is organized as follows. System description of a coupled tank is discussed in section II. Mathematical modeling of the coupled tank system is discussed in the section III. Sliding Mode aspects and Control strategy derivation for generalized system is discussed in section IV. SMC design for a coupled tank system is discussed in Section V. Simulation results are discussed in section VI. Conclusion presented in section VII.

Conclusions

First order sliding mode control was designed successfully under various initial conditions of a non linear coupled tank liquid level system. The switching surface and sliding mode control law was designed for tracking various input signals like step, square wave, saw tooth, sinusoidal, and random signals and also under disturbance conditions.  The tracking performance, error signal and control signals are plotted in time domain in the MATLAB environment.

1,187 total views, no views today

Download PDF File

About the author: admin