control system lecture notes

1. Chapter one
Introduction of Control Systems
Chapter Contents
1. Introduction
2. Closed-Loop Control Versus open-Loop Control
3. Design of Control Systems

2. 1.1 introduction
Control system play a vital role in our day-to-daily life. Because of that the
development of control system was changed from time to time. This arise the
different theory of control system.
Control system theories commonly used today are:
classical control theory (also called conventional control theory),
modern control theory, and
robust control theory.
But in our case we presents comprehensive treatments of the analysis and design
of control systems based on the classical control theory and modern control theory.
Automatic control is essential in any field of engineering and science. Because of an
important and integral part of space-vehicle systems, robotic systems, modern
manufacturing systems, and any industrial operations involving control of
temperature, pressure, humidity, flow, etc.

3. History
• 18th Century James Watt’s centrifugal governor for the speed control of a steam engine.
• 1920s Minorsky worked on automatic controllers for steering ships.
• 1930s Nyquist developed a method for analyzing the stability of controlled systems
• 1940s Frequency response methods made it possible to design linear closed loop control
systems
• 1950s Root-locus method due to Evans was fully developed
• 1960s State space methods, optimal control, adaptive control and
• 1980s Learning controls are begun to investigated and developed.
• Present and on-going research fields. Recent application of modern control theory includes
such non-engineering systems such as biological, biomedical, economic and socio-economic
systems

4. Comparison of classical and modern control system
Classical control theory, which deals only with single-input,
single-output systems, becomes powerless for multiple-input,
multiple-output systems.
Modern control theory is based on time-domain analysis of
differential equation systems.
It made the design of control systems simpler because the theory is based
on a model of an actual control system.
Easy to analysis complex system

5. Definition of basic terminology
Systems.: is a combination of components that act together and perform a
certain objective. E.g. class room
Control: means measuring the value of the controlled variable of the system
and applying the control signal to the system to correct or limit deviation of the
measured value from a desired value.
Plants.: any physical object to be controlled (such as a mechanical device, a
heating furnace, a chemical reactor, or a spacecraft) a plant. Also called a
process
Processes: any operation to be controlled a process. Examples are chemical,
economic, and biological, industrial processes

6. Cont..
controlled variable(output): is the quantity or condition that is measured and
controlled.
control signal or manipulated variable: is the quantity or condition that is
varied by the controller so as to affect the value of the controlled variable.
Disturbances. A disturbance is a signal that tends to adversely affect the value
of the output of a system.
If a disturbance is generated within the system, it is called internal,
while an external disturbance is generated outside the system (an input)
Feedback Control. an operation that, in the presence of disturbances, tends to
reduce the difference between the output of a system and some reference input
and does so on the basis of this difference

7. • Control system
 It is a combination of different physical elements linked in a such manner so as to regulate,
direct or command itself to obtain a certain objectives.
 It must have :
 Input
 Output
 Ways to achieve input and output objectives
 Control action

8. Classification of control system
Natural control system: the system inside a human being or biological system
Man-made control system: control system that are designed and developed by man.
Example an automobile
Combinational control system: this control system is a combination of natural and
man-made control system. Example a driver driving a car
Continuous Time Control Systems or Discrete time Control Systems :
If the signals in all parts of a control system are continuous functions of time, the system is
continuous time feedback control system.(e.g. speed control of dc by tacho-generator)
If one or more system variables of a control system are know at a certain discrete time ,the
system is discrete time control system (e.g. computer system)
Linear Control Systems or Non-Linear Control Systems: If a system obeys
superposition principle the system is said to be a linear system.
If it does not obey superposition principle is said to be a non-linear system.

9. Cont...
• Time-varying and time invariant control system
• Lumped and distributed control system
• SISO and MIMO control system
• Closed loop and open loop control system

10. 1.2 Open Loop and Closed Loop Control Systems
Open Loop Control Systems
 A system in which the output has no effect on the control action is known as an open loop control
system. For a given input the system produces a certain output.
 If there are any disturbances, the out put changes and there is no adjustment of the input to bring
back the output to the original value.
A perfect calibration is required to get good accuracy and the system should be free from any external
disturbances. No measurements are made at the output.
Examples of open-loop control system
A traffic control system is a good example of an open loop system. The signals change according
to a preset time and are not affected by the density of traffic on any road.
A washing machine is another example of an open loop control system. The quality of wash is not
measured; every cycle like wash, rinse and dry' cycle goes according to a preset timing.

11. Closed loop control system
• If the control action of a system is depends on somehow output value was changed
• A system which maintains a prescribed relationship between the controlled variable and the
reference input, and uses the difference between them as a signal to activate the control
• The output or the controlled variable is measured and compared with the reference input and an
error signal is generated.
• This is the activating signal to the controller which, by its action, tries to reduce the error. Thus the
controlled variable is continuously feedback and compared with the input signal.
• If the error is reduced to zero, the output is the desired output and is equal to the reference input
signal.

12. Example of Closed loop control system
• If any body move away from a desired road with open eyes

13. Open Loop Vs Closed Loop Control Systems
Open Loop Systems
Advantages
1. They are simple and easy to build.
2. They are cheaper, as they use less number of components to build.
3. They are usually stable.
4. Maintenance is easy.
Disadvantages
1. They are less accurate.
2. If external disturbances are present, output differs significantly from the desired value.
3. If there are variations in the parameters of the system, the output changes.

14. Closed Loop Systems
Advantages
1. They are more accurate.
2. The effect of external disturbance signals can be made very small.
3. The variations in parameters of the system do not affect the output of the system i.e.
the output may be made less sensitive to variation is parameters.
4. Speed of the response can be greatly increased.
Disadvantages
1. They are more complex and expensive
2. They require higher forward path gains.
3. The systems are prone to instability. Oscillations in the output many occur.
4. Cost of maintenance is high.

15. 1.3 Design control system
The following table shows the control system design process