Introduction to Control Systems - Study Guide and Course Details

Course Material and Tutorial Blocks

During this module, you will be introduced to the study of Control Systems. Control Systems are prevalent in almost all engineering systems and as such makes its study inevitable for anyone inter- ested in understanding how modern engineering systems are designed or analysed. The discipline of Control is often greeted with apprehension from students because of the subjects ‘perceived’ difficulty and its mathematical nature. By following this study guide and paying attention to the course material this perception will prove to be unfounded.

The course will begin with a basic introduction to Control Engineering with definitions of such con-cepts as ‘open-loop’ and ‘closed-loop’ and a brief discussion of their advantages and disadvantages. As you progress through the module you will begin to appreciate the need for ‘a good mathematical model of the system’ this is why we will concentrate in the early stages of the module on obtaining such models and then later refining and expanding the modelling process into what is called state space modelling.

Describe the module contains all the information you need to understand the subject to the level presented Each part of the course notes contains a lecture block with some worked examples followed by an appropriate tutorial block. It is important you complete each tutorial block before you proceed to the next block as each tutorial contains information that will enhance your understanding of the other blocks. Although you will have the solutions to the questions it is important to try the question first before looking at the solution, some questions may only contain answers these are intended to be checked by simulation (more on this later) and various techniques you should pick up during the module. NOTE that is what is intended no solutions to this type of problem will be provided.

The course work for this module is a simulation study with MATLAB (or software of your choice e.g.LabVIEW, Python etc.)Also included in your notes and course folder on GCULearn are past exam papers with solutions. Again, you will be directed to these past papers when you have enough information to try each ques-tion or part of a question. Again, try these questions without looking at the solution in the first instance. I hope that by the end of the module you will be able to use the analytical tools as well as the numerical simulation tools to solve a fair range of systems and control problems.

Assessment and Passing the Module

Assessment and passing the module The assessment of this module is in two parts Part I is a course work, that is attached at the end of these notes, it is worth 30% of the module mark. This should be approximately 15 pages long there will be marks allocated for effective and concise communication.Do some solid work, get the course work in and start studying for the exam! Part II is a formal exam worth 70% of the module mark, examples of which are at the end of these notes.

The exam will be over two hours in the next trimester exam diet (TBA) and will consist of FOUR question and you must answer them all. The questions are designed in such a way that the initial questions are easier leading to the last question that is a little more difficult. Of course, “easier” all depends on how well you have studied and understood the material.

The pass mark for the module is 50%.
But one component may be at 45% if the other is higher, for example look at the following scenarios:
50% in exam and 50% course work = 0.7*50 + 0.3*50 = 50% = pass
55% in exam and 45% course work = 0.7*55 + 0.3*45 = 52% = pass
45% in exam and 60% course work = 0.7*45 + 0.3*60 = 49.5% = pass (normal rounding applies) But
43% in exam and 60% course work = 0.7*43 + 0.3*60 = 48.1% = Fail – resit exam component

There are other scenarios but best advice is aim for above 50% in exam I am working to make the notes for this module self-contained so I have included some appendices on the major mathematics you will need for this module (work in progress). I am also working to include more examples and exercises. As a consequence of this the notes are quite long but hopefully we can work together to get them into a form where you hardly ever need to go outside of them for information.

I will keep you informed during the module mainly by email on GCULearn. I will also post additional material on GCULearn as it requested, e.g. additional tutorials and tutorial solutions. If you feel there are other, reasonable things I can include please let me know.

The general aims and structure of an automatic control system can be seen from shows the schematic representation of a domestic heating system. Here the ‘thing’ or ‘process’ we want to have some control over is the temperature of the house and in general this is called the ‘plant’ or ‘system under control’. The main objective of the control system is to maintain the temperature of the house at some desired or pre-determined temperature, which is termed the output. We see that that actual temperature of the house is measured and compared, through the thermostat, to that of the de- sired temperature. If an error exists between these two values, the gas valve is opened and the furnace turned on to put more heat into the house to raise the temperature towards the desired temperature.

 

In this case, the thermostat-gas valve combination is the controller and the furnace is termed the actuator – that is the ‘physical process’ that causes the change in the controlled variable i.e. the temperature of the room.The other main point to note is that there are disturbances in the system. Those mechanisms will move the system away from the desired set point or desired output. In this case, the disturbance may be someone opening a door or a window thus allowing heat to escape from the system. from the bottom trace of the graph in Figure 1.1 that the furnace is either on or off with no setting in between. This type of control is termed bang-bang control. We will mainly develop what are called continuous controllers, which give a varying output to the actuator depending on the error signal.This domestic heating system control-loop can be generalised as shown in to give the general structure of a closed-loop control system.

From the above discussion, we can extract four main objectives the control loop should achieve:
• Maintain a system output value in the face of disturbances – this is called regulation.
• Make sure the output of the system follows a certain path – trajectory.
• Reduce steady-state errors (SSE)
• Maintain stability

Before we describe in detail the properties of a closed-loop control system let us look at the disadvan-tages of a simpler type of control called an open-loop control system. This is illustrated in where a valve can let liquid into a tank of fixed volume. If we know the volume of the tank and the rate at which the valve lets liquid into the tank we could simply open the valve for a fixed time to let the liquid fill the tank to a set level.