Week 1 Introduction to Control System PDF

Chapter 1: Introduction to Control System Ts Dr Mohamad Heerwan Bin Peeie Introduction What is a control system? Why do we need to learn control systems? How important is a control system in our daily life? 2 Introductio...

Chapter 1: Introduction to Control System Ts Dr Mohamad Heerwan Bin Peeie Introduction What is a control system? Why do we need to learn control systems? How important is a control system in our daily life? 2 Introduction to Linear Time-Invariant (LTI) 3 4 Properties LTI Linearity is defined As relationship between input x(t) and the output y(t) both considered as function in which if a is a constant then the system output to ax(t) is ay(t). Time invariance is defined By applying input to the system now or T seconds from now, the output will be identical except for a time delay of T seconds. If output due to input x(t) is y(t) → output due to input x(t-T) is y(t-T). The system is time invariant as the output does not depend on the particular time the input is applied. 5  Chapter 1 Basic Control System Concepts 6 Lesson outcomes: ❑Define a control system and describe some applications ❑Describe the basic features and configurations of control systems ❑Describe control system analysis and design objectives ❑Describe a control system’s design process ❑Describe the benefit from studying control system 7 Introduction Control system are an integral part of modern society. Numerous applications are all around us. Mechanical Engineering Computer Science Electrical Engineering Instrumentation Engineering Chemical Engineering and so on. 8  Discuss one example of control system in your daily life. 9 Example of Control System 10 Control system definition A control system consists of subsystems and processes (or plants) assembled for the purpose of obtaining a desired output with desired performance, given a specified input. 12 Example Consider an elevator, when the fourth-floor button is pressed on the first floor, the elevator rises to the fourth floor with a speed and floor-leveling accuracy designed for passenger comfort. The push of the fourth-floor button is an input represent the output. The performance of the elevator can be shown in the figure 1.2 (next slide). 13 Control Performance 14 Elements of a control system Any control system consist of four elements: 1. The input is the desired response of a control system 2. The output is the actual response of a control system 3. Subsystem is any system that helps controlling the output of the control system 4. A plant is a system in which its output is the one to be controlled or a set of machine parts functioning together, the purpose of which is to perform particular operation. 15 Definition of a Control System Control means measuring the value of the controlled variable of the system and applying the manipulated variable to the system to correct of the measured value from a desired value. A system is a combination that act together and perform a certain objective. “A control system consists of subsystems and plant assembled for the purpose of controlling the outputs of the plants.” -> Norman S. Nise 16 Control system types Two types: 1. Open-loop control system 2. Closed-loop control system. Also called Feedback control system or Automatic control system 17 OPEN-LOOP VERSUS CLOSED-LOOP SYSTEMS Open-Loop 1. The output is not compared with the reference input. 2. The accuracy of the system depends on calibration. 3. In the presence of disturbances, an open loop control system will not perform the desires task. Example: Washing machine operate on a time based. The machine does not measure the cleanliness of the clothes. Closed-Loop 1. The difference between the input/reference signal and the output signal is fed to the controller so as to reduce the error and bring the output of the system to a desired value. 18 Differences between open-loop and closed-loop control systems 1. Additional subsystem call sensor 2. Error signal (e) is the command to the controller subsystem not the desired input (set point) e sensor 19  Open-loop control system: Sun Light or Blocked light Desired On-Off Actual light Bulb Room Switch Light Closed-loop control system: Sun Light or blocked light Desired light On-Off Actual Bulb Room Switch Light Light sensor 20 21 Example Simple Control System Desired Actual light On-Off Light Bulb Room Switch Room is the process or plant Actual light intensity is the output Desired light intensity is the desired input The switch and the bulb are the subsystems The bulb is the actuator An actuator is the mechanism by which a control systems acts upon an environment. (Motor, hydraulic, pneumatic, etc.) 22  Control System Desired Actual temp On Temp temp Air Off Setting Room Conditioned Switch knob What is the process or plant? What is the output? What is the desired input? What are the subsystems? What is the actuator? 23 24 The design process Step 1: Transform requirements into a physical system Step 2: Draw a functional block diagram Step 3: Create schematic Step 4: Develop mathematical model (block diagram) Step 5: Reduce the block diagram Step 6: Analyze and design the system to meet specified requirements and specifications that include stability, transient response and steady state response. 25 The design process 26 Case study Antenna azimuth A position control system converts a position input command to a position output response. 27 Detail layout 28 Schematic 29 Block diagram 30 Response of position control system Underdamped: more Damping ratio 1 31 Definitions Rise time: time required for a signal to change from a specified low value to specified high value. Range [10-90%] (tr) Overshoot: when a signal/function exceeds its target. (Mp) Settling time: time taken for a measuring to get within a certain distance of a new equilibrium value Delay time: time required for the response to reach half the final value of the very 1st time. (td) Peak time: time required for the response to reach the first peak of the overshoot. (tp) Steady-state error: the difference between the desired final output and the actual one when it reach steady state. 32 Question & Answer 33 THANK YOU 34