Oil Refining - Paper Manufacturing - Chemicals - Power Plants - Automation in Food Processing | Control System Modelling Case Study

Case Study Assignment

The case study is a Research Paper and is to be used as a tool to assist you in developing new skills in research, analysis and technical communication. The case study report is intended to encourage the development of your ability to critically review a chosen topic relevant to the unit of Control Systems and your ability to prepare a formal research report on an assigned topic. These skills will be very valuable for your professional development and will greatly assist you in taking on the responsibilities of a professional engineer.

You are provided with an opportunity to practice and develop your skills in critical thinking, develop a better understanding of the subject content in the unit being studied, and to develop ways of improving your study methods. You are expected to write a technical report which expresses these ideas in a formal way. As a result you will also be able to develop and practice your technical writing skills.

At the end of the case study you will submit a completed report on the ‘Blackboard’ that will be assessed by your lecturer and this assessment will form a part of the assessment for the unit.

What is expected in the case study report You will prepare a report of about six pages (do not exceed 10 pages including figures, tables etc):

• On a topic assigned to you.
• You will explain the problem with the help of a block diagram and develop a transfer function fully documenting all aspects of the mathematical modelling.
• Provide a block diagram of multiple loops if necessary and show a single block or closed-loop system which is simplified from the multi-loop diagram.
• Explain the above process with the help of references and list the references at the end of the report.
• You are not required to create an original mathematical model. You can use available resources (textbook, online research articles or published industrial case studies) and summarize the modelling process in your own words.

Introduction

A control system is typically defined as shown in figure no 1-

Fig 1a: Here actuator along with Process model defines as plant

Figure 1: A typical control system ( Clarity of noise input just before the Plant model)

The first step is defining the plant in the form of a transfer function.

A typical plant is represented here in Laplace domain

Here the plant is second order system

Let us make the transfer function different for each student

K= day of birth = 23

T= month of birth= 10

For detail analysis the transfer function becomes

Now we model the plant using SIMULINK modeling

The value of K and T can be either defined in MATLAB command window

or we can explicitly define in the model as follows

Part 1 : Plant behavior without incorporating any control

The simulated plant with its output is shown below

For demand of 100 at time = 2 sec , we get a peak of 140 at around 9 sec , and the response settles down to 95 giving an steady state error of 5 %

Part 2: To improve the plant behavior Ist stem is to add an integral gain after error signal gets computed.

When we introduce proportional gain and set gain to 2

We find reduction in steady state error, from 5% to just 2%, but overshoot rises to 160

Part 3: Next improvement can be got if we introduce Integral gain along with proportional gain.

PI controller

Typically using PI controller steady state error can be further reduced but peak further rises to 170.

Part 4 and part 5: Finally we get more improvement if we implement PID controller and now we can also demonstrate the noise also gets fully taken care off.

To improve further we use a PID control

Here we have introduced derivative gain as 10, P=10 and integral gain as 0.2

We can see that there is no steady state error and overshoot is also reduced less than 20%

Let us now introduce a disturbance in the form of stem input, of 100 at time = 30 sec is introduced.

From the output we can see that plant has good disturbance removal property.