Modelling, simulation and control of quadruple tank process

Simple processes with only one output that may controlled by one input (variable) are known as single input single output process. But many processes are not such simple. They have more than one input (variable) and one output, which are called Multi Input-Multi Output (MIMO) processes. Common MIMO systems have some difficulties, such that they are large and complex. In addition, they have nonlinearities and also loop interactions which are between inputs and outputs. On the purpose of studying multivariable systems and designing controllers, the quadruple tank process (QTP) is chosen as a benchmark. This system is suitable for studying linear and nonlinear controllers and exhibits minimum and non-minimum system behaviors by simply changing configuration valve positions. We linearize nonlinear process model, than apply various control methods and compare the controlled system performance results.

1. Introduction

Multivariable system involves more than one control loop, These loops interact with each other, in such a manner that single input not only affects its own output but also affects other process outputs. [1], [2] QTP has four tanks and two pumps, this benchmark is simply a water level control problem. The aim of the process is to keep the liquid level in the lower tanks at the desired values. Related laboratory process introduced by Johansson in Figure 2.1. [3], the process is used to show multivariable interactions which are also known as coupling and it limits performance in multivariable control systems. Multivariable interactions in a QTP are each output (water levels) of the system has affected by two pumps. Due to these reasons, it can be regarded as a prototype for many MIMO control applications in industry such as paper production processes, chemical processes, metallurgy and biotechnological areas, medical industries.