Control Systems. Introduction to Control System.

Transcription

1 Introduction to Control System

2 Lecture Outline History of automatic control Examples of control systems Types of controller

3 Control System Control system: An interconnection of components forming a system configuration that will provide a desired system response Target Temperature Controller Temperature Sensor Heater Rood Relay/SCR

4 History of automatic control Feedback control can be said to have originated with the float valve regulators of the Hellenic and Arab worlds Mead s sped regulator Boulton & Watt steam engine with centrifugal governor

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7 Example of Control Automobile driving

8 Example of Control National Economy

9 Example of Control Boiler Generator system

10 Types of controller Typical controllers Embedded Controller : Specially designed controller for specified systems MPU, MCU, DSP, FPGA Cost for development useful for mass production PC Controller Easy development, costly, easy access PLC (Programmable Logic Controller) Widely used in general automation systems, sequence control Use Ladder diagram, Modular composition

11 Lecture Outline Control system terminology Signals and Systems Closed vs. open-loop control

12 Control System Terminology Systems A physical set of components that takes a signal, and produces a signal Signals A function representing some variable that contains some information about the behavior of a system. signal A System signal B

13 Control System Terminology Systems Plant: The physical object to be controlled. Terminology comes from chemical process plants like oil refineries or power plants. Sensor: The device that allows you to measure variables for plant monitoring and for a variety of other purpose In mechanical systems, it measures pressure, force, speed, position, etc. Cf) Actuator: The device that causes the process to provide the output. The device that provides the motive power to the process 13

14 Control System Terminology Systems Controller: The device or operation that gives commands to the plant. These commands are usually based on the current performance of the plant compared to the desired performance of the plant. The controller may or may not include the actuator, the device that enforces the controllers commands on the plant. Controller Plant Sensor 14

15 Control System Terminology Signals Reference: What you d like the measured output of your controlled plant to be. e.g. speed setting for your cruise control. Feedback (Measured output): Variables that are coming out of your plant that are being compared to your reference. e.g. speed measurement of your car from wheel speed sensors

16 Control System Terminology Signals (Feedback) Error: Difference between your reference and your feedback signals. e.g. 10 km/h difference between reference and feedback. (Plant) Input: The signal that is passed from the controller to the plant to affect some action. e.g. Throttle variation. (Plant) Output: all the signals coming out of the plant. Note: not all outputs are used in feedback

17 Control System Terminology Systems and Signals Plant, Controller, and Sensor all systems. usually have some dynamic or differential equation description. transfer function representation for these systems. Signals carry information between these elements. reference error input output Controller Plant feedback Sensor

18 Case Study: Cruse Control Cruise Control ECU Electronic throttle body reference error input output Controller Plant feedback Sensor vehicle speed sensor

19 Case Study: Cruse Control

20 Case Study: Cruse Control more on cruise control adaptive cruise control

21 Control System Terminology Disturbance Disturbance: An unwanted signal that is not accessible to the controller and tends to adversely affect the systems output System or signal??? disturbance Controller Plant Sensors

22 Control System Terminology Control system diagram with disturbance and noise Control system diagram with inner and outer loop

23 Closed vs. Open loop control Closed loop control The difference of reference and feedback are used as a means of control. G c G p Closed-loop (with feedback) Open loop control The output has no effect on control action usually simpler with fewer components G c G p Examples would be timers; e.g. toaster. Open-loop (without feedback)

24 Closed vs. Open loop control Open-loop example

25 Closed vs. Open loop control Closed-loop example

26 Closed vs. Open loop control Comparison Cost Stability Performance Open-loop system no sensors simple and less expensive a stable plant cannot go unstable Disturbances or modeling mismatch can cause errors recalibration are needed Closed-loop system a stable plant can go unstable, but an unstable plant can go stable more robust to disturbances and uncertainty They usually have better performance

27 Closed vs. Open loop control Open loop Closed loop + - with model uncertainty % error 0.01% error

28 Case Study: Insulin dispensing

29 Control design procedure 1. Study the plant and the control objectives. 2. Model the plant (if necessary, simplify the model.) 3. Decide the variables to be controlled (controlled outputs), the measurements(sensor) and manipulated variables (actuators) 4. Select the control configuration and the type of controller. 5. Decide on performance specifications 6. Design a controller. 7. Analyze the resulting controlled system 8. Simulate the resulting controlled system 9. Choose hardware and software and implement the controller. Software labs 10. Test and validate the control system Hardware labs