1 Introduction to Control System CHAPTER 1

2   Basic terminologies.   Open-loop and closed-loop.   Block diagrams.   Control structure. .  Advantages and Disadvantages of closed-loop. Chapter Objective.

3 Definition of a control system;   The control system consists of subsystems and process (or plant) assembled for the purpose of controlling the output with desired performance, given a specified input. 1.1 Introduction.

4 Cont’d… Advantages of control systems;   Can move large objects with precision; for example (i) elevator, (ii) radar antenna to pickup strong radio signal and (iii) robot to operate in the dangerous environment.   Example: (i) Elevator When pressed fourth-floor from first floor, the elevator rises to the fourth floor with a speed and floor-leveling accuracy design for passenger comfort.

5 (a) Sub-system and System subsystem subsystemsubsystem   Subsystem is part of the system that is grouped for a certain function   System is a combination of physical and non-physical components that are configured to serve certain tasks to maintain the output (b) Plantsubsystem inputoutput   Plant is a subsystem where an output signal is derived from the input signal blower room thermostat plant 1.2 Basic Terminologies.

6 (c) Input and Output   Input = Stimulus   Output = Response Cont’d…

7 Cont’d… (d) System Response  Ability of system to achieve desired result is measured in terms of system response: comparison of output versus input.  Transient response.  Steady State Response.  Steady State Error.

8   Disturbance is the unwanted signal that may sway the output.   Controller is a subsystem that is used to ensure the output signal follows the input signal.   The Open-Loop System cannot compensate for any disturbance that add to the system.   Example; bread toaster. 1.3 Open Loop System.

9   The Close-Loop (feedback control) System can overcome the problem of the Open Loop System in term of sensitivity to disturbance and inability to correct the disturbance. 1.4 Close-Loop System.

10 The design of a control system follows these steps; Step 1: Transform Requirement into a Physical System. Step 2: Draw the Functional Block Diagram. Step 3: Create the Schematic. Step 4: Develop the Mathematical Model or Block Diagram. Step 5: Reduce the Block Diagram. Step 6: Analyze and Design. 1.5 The Design Process.

11   Transfer function is the ratio of the output over the input variables.   The output signal can then be derived as; C = GR (a) Multi-variables. 1.7 Block Diagram.

12 (b) Block Diagram Summing point. Cont’d… Figure 1.7: Block Diagram of Summing Point.

13 (c) Linear Time Invariant System. Cont’d… Figure 1.8: Components of a Block Diagram for a Linear, Time- Invariant System.

14 Cont’d… Figure 1.10: Parallel System and the Equivalent Transfer Function. Figure 1.9: Cascade System and the Equivalent Transfer Function. (d) Cascade System.

15 (e) Summing Junction. (f) Pickoff Points. Cont’d… Figure 1.12: Block diagram algebra for pickoff points— equivalent forms for moving a block (a) to the left past a pickoff point; (b) to the right past a pickoff point. Figure 1.11: Block diagram algebra for summing junctions: equivalent forms for moving a block (a) to the left past a summing junction; (b) to the right past a summing junction.

16 Cont’d… Figure 1.13: Block diagram reduction Example 1. (a) collapse summing junctions; (b) form equivalent cascaded system in the forward path and equivalent parallel system in the feedback path; © form equivalent feedback system and multiply by cascaded G1(s)

17   E(s) error signal R(s) reference signal Y(s) output signal C(s) output signal B(s) output signal from feedback   Feed forward transfer function,   Feedback transfer function,   Open-loop transfer function, 1.8 Control Signal.

18   Close-Loop transfer function,   Assume give   Variable difference,   Characteristic equation, Cont’d….

19   Physical model.   Graphical model.   Mathematical model. (a) Current-voltage relationship v = ir. v – voltage in Volt (V). i – current in Ampere (A). r – resistance in Ohm. (b) Force-deflection relationship f – force in Newton (N). k – spring constant x – displacement in meter (m). (c) Mass-spring model f o - applied force x - displacement f s - reaction force 1.9 Model.

20 Transient state   A state whereby the system response after a perturbation before the response approach to a steady condition Steady state   A state whereby the system response becomes steady after a transient state. Stability   The condition of the steady state. If the response converges to a finite value then it is said to be in a stable condition and if the response diverges, it is known to be unstable.   A system must be stable in order to produce the proper transient and steady state response.   Transient response is important because it effects the speed of the system and influence human patience and comfort Design Analysis.

Design. Analogue controller  A controller that used analogue subsystem. Digital Controller  A controller that used computer as its subsystem. Figure 1.14: Controller in Computer Subsystem. computerdriveplant sensor _ + Referene input Actual output

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