Control chap1


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Control chap1

  1. 1. CONTROL SYSTEMS THEORY Assessment Mini Project Lab Report Test 20% 20% 20% Final Exam Total 40% 100%
  2. 2. Teaching plan Week Chapter 1 2-3 4 5-7 8 9-10 Introduction to control systems System representation Response analysis in time domain Stability analysis in time domain Test Controller design 11-12 Response analysis in frequency domain 13-14 Stability analysis in frequency domain
  3. 3. CONTROL SYSTEMS THEORY Basic Control Systems Concept Chapter 1 STB 35103
  4. 4. Objectives  To understand the concept of control systems engineering.  To evaluate the characteristic responses of a certain automatically controlled system.
  5. 5. Introduction What is control system? A control systems is an integral part of our society. It is used in an automatically controlled systems Definition: Subsystem Control Control System Output of the process Process A control system consists of subsystems and processes assembled for the purpose of controlling the output of the process
  6. 6. Purpose of building control system We build control systems for four primary reasons 1. Power amplification 2. Remote control 3. Convenience of input form 4. Compensation from disturbances
  7. 7. Figure 1.1 a Elevators Early elevators were controlled by hand ropes or an elevator operator. Here, a rope is cut to demonstrate the safety brake, an innovation in early elevators; Photos courtesy of United Technologies Otis Elevator.
  8. 8. Figure 1.1 b Elevators Modern Duo-lift elevators make their way up the Grande Arche in Paris, driven by one motor, with each car counterbalancing the other. Today, elevators are fully automatic, using control systems to regulate position and velocity.
  9. 9. Other examples  ASIMO-created by Honda
  10. 10. Other examples  Car cruise control Cables Electronicallycontrolled Vacuum actuator
  11. 11. Other examples  Anti-lock braking system (ABS)  Major components of the typical ABS system four speed sensors (one at each wheel)  electronic control unit (ABS computer)  a hydraulic control unit 
  12. 12. Other examples  Vehicle suspension system  a system that will absorb the energy of the vertically accelerated wheel, allowing the frame and body to ride undisturbed while the wheels follow bumps in the road
  13. 13.  Advantages & disadvantages?
  14. 14. Response characteristic Input: Our desired response Output: The actual response that we get from the system E.g. Using the elevator.
  15. 15. Response characteristic Elevator: We need to push the button of our desired floor. Elevator rise to the floor with speed and floorleveling accuracy that is comfortable to the passenger. Input - Push of the floor button - can be represented by a step command - represents what we would like the output to be after the elevator stops
  16. 16. Figure 1.3 Elevator input and output
  17. 17. Response characteristic Transient response: The state changes through a path that is related to the physical device and the way it acquires and dissipate energy. E.g. The elevator undergoes a gradual change as it rises from the ground to our selected floor. We call this part of the response the transient response.
  18. 18. Figure 1.3 Elevator input and output
  19. 19. Response characteristic Steady state response: Approximation to the commanded or desired response. E.g. This response occurs when the elevator reaches our desired floor.
  20. 20. Response characteristic Steady state error: The difference between the input and the output. Often steady-state error is inherent in the designed system. It is up to the engineer to determines whether or not that error leads to significant degradation of systems function. E.g. Accuracy of the elevator’s leveling with the floor.
  21. 21. Type of systems Control system configuration can be categorized into two: 1)Open-Loop Input Control System Output 2)Closed-Loop Input Control System Output
  22. 22. Type of systems Open-loop system A generic open-loop system Input transducer: Converts the form of input to that used by controller Controller: Drives a process or plant
  23. 23. Type of systems Open-loop system A generic open-loop system Plant: Air conditioning system Controller: Remote control Input: ??? Output: ???
  24. 24. Type of systems Open-loop system A generic open-loop system Open loop-system characteristic Cannot compensate for any disturbances that add to the controller’s driving signal. Signal that drives plant is corrupted by disturbance. The output is also corrupted.
  25. 25. Open loop control  Missile launcher system
  26. 26. Type of systems Open-loop system Advantage of Open-loop system Simple Cheap
  27. 27. Type of systems Open-loop system Disadvantage of Open-loop system Sensitive to disturbance Solution Use closed-loop system Inability to correct for disturbance
  28. 28. Type of systems Closed-loop system A generic closed-loop system
  29. 29. Type of systems Closed-loop system Input transducer: Converts the form of the input to the form used by controller. Output transducer (sensor): Measures the output response and converts it into the form used by the controller.
  30. 30. Type of systems Closed-loop system Output transducer (sensor): Measures the output response and converts it into the form used by the controller. E.g. Valves of a temperature control system: Input position + output temperature →electrical signals
  31. 31. Type of systems Closed-loop system Valves of a temperature control system: Input position  potentiometer (variable resistor) output temperature  thermistor Electrical resistance changes with temperature
  32. 32. Type of systems Closed-loop system A generic closed-loop system
  33. 33. Type of systems Closed-loop system First summing junction adds the signal from the input to the signal from the output which arrives via the feedback path (return path from output to summing junction).
  34. 34. Type of systems Closed-loop system Actuating signal: Input and output have different gain Error: Input and output transducers have unity gain (transducers amplifies its input by 1)
  35. 35. Type of systems Closed-loop system Closed-loop system compensates for disturbance by: •Measure output response •Feeding the measurement back to summing junction •If there is difference between two responses, the system drives the plant. If no difference, the system does not drive the plant.
  36. 36. Closed loop feedback control  Missile launcher system
  37. 37. Type of systems Closed-loop system Advantage of Closed-loop system Less sensitive to noise, disturbances and changes in environment Transient response and steady-state error can be controlled easily Transient response and steady-state error can be controlled by redesigning the controller. The process of redesigning is called compensating the system and the resulting hardware is a compensator
  38. 38. Type of systems Closed-loop system Disadvantage of Closed-loop system More complex More expensive
  39. 39. Type of systems Open loop vs. Closed-loop system  How do we choose OL or CL?  Criticality of application The need to monitor output  The need to control the output  The need for reduced error or zero error  Cost / budget  Safety 
  40. 40. Analysis and design objectives 3 major objectives Transient Response Steady-state response Stability
  41. 41. Analysis and design objectives Transient response A very important aspect in control systems. E.g. Elevator. Slow transient response makes passengers impatient. Rapid transient response makes them uncomfortable.
  42. 42. Analysis and design objectives Steady-state response This response resembles the input. We are concerned about the accuracy of the steady-state response. E.g. An elevator must be level enough with the floor for the passengers to exit.
  43. 43. Analysis and design objectives Stability Total response of a system is the sum of natural response and forced response. Total response = Natural response + Forced response c ( t ) = cforced ( t ) + cnatural ( t ) A useful control system has a natural response that 1. Eventually approaches zero, leaving only the forced response. 2. Oscillates.
  44. 44. Design process Determine a physical system and specifications from the requirements Analyze, design and test to ensure requirements are met Draw functional block diagram Reduce block diagrams if necessary Transform physical system into a schematic Obtain block diagram, signal flow diagram, state-space representation