CHEE 319 Process Dynamics and Control

Transcription

1 CHEE 319 Process Dynamics and Control Winter 2012 Instructor: M.Guay TAs: S. Dougherty, D. Park and E. Moshksar 1

2 Organization Instructor: Dr. Martin Guay Office: Dupuis 406 Phone: Web: 2

3 Schedule Lectures: (DUN 14 (for today only), JEF 127) Monday 10:30 11:20 Wednesday 9:30 10:20 Friday 8:30 9:20 Tutorials: Section A (DUP 244) Friday 9:30 10:20 Section B (DUP 244) Friday 10:30 11:20 Office Hours (MG): Monday 15:30 17:00 (Tentative) Tuesday 15:30 17:00 3

4 References All lectures will be available online Derivations will be done on the board Powerpoint slides are to support lectures Textbook (highly recommended) D.E. Seborg,, T.F. Edgar, D.A. Mellichamp, Process Dynamics and Control (2nd or 3rd Edition),, Wiley, NJ (2003, 2009). 4

5 Grading Grading Midterm (TBDIC) 25% Assignments 15% Final Exam 60% 5

6 Guidelines i) Assignments Problems will be assigned every week. Although they will not be marked, weekly tutorials will be concentrated on the solution of the problems and on questions that may arise from the course. Collaboration is encouraged throughout the course. It is recommended that the students develop their own individual solutions. There will be a set of assignments that will be marked. They are to be completed in groups of 4-5. With one assignment per group. ii) Exams Midterm exam will be open-book. Textbooks, course notes and assignments will be allowed. The final will be closed-book. The timing of the midterm exam will be decided in class. (Likely to be after reading week.) 6

7 Course Objectives By the end of this course the student should be able to: derive transfer function models from process models and process data recognize important process dynamic features of SISO linear dynamical systems apply modern control theory to design a controller for uncertain SISO linear dynamical systems understand the trade-off in performance that arise in the design of a controller 7

8 Teaching Approach and Expectations Each student is ultimately responsible for learning the material in a course. Every professor is responsible for presenting the course material in a manner that facilitates learning as much as possible for the class as a whole. 8

9 Teaching Approach and Expectations In fulfilling this contract, I expect that you will actively and constructively participate in the course. ask questions whenever something is not clear, help each other understand the course material, perform all assigned reading on time, arrive on-time for class, be courteous to each other and myself, provide me with feedback / suggestions as to how the course and my delivery can be improved. 9

10 Teaching Approach and Expectations In return you should expect me to: treat each of you with courtesy and respect, be committed to help you understand and master the course material, by being available for out of class assistance, by providing competent teaching assistants, by working to continually improve the course, treat each question or concern seriously and answer these to the best of my ability. Class discussions and student participation are encouraged as much as possible, in and out of the classroom 10

11 Course Outline 1. Introduction 2. Modeling for control 3. Solution of Linear ODEs using Laplace transforms 4. Transfer function models of mechanical systems 5. Analysis of Continuous-time Linear Systems 6. SISO Control System Analysis 7. Synthesis of SISO Controllers 8. SISO Controller Design 11

12 Introduction Feedback systems are commonplace in almost every aspect of life Standing, walking, running etc are all forms of control systems where the central nervous system reacts to various biosensor mechanisms Gene regulation is controlled by complex responses that trigger various biological mechanisms In engineering applications, feedback systems arise in the design of control systems Aircraft flight control, satellite s altitude control Automotive control Communication systems Robotics Manugfacturing systems and industrial process cotnrol Control is the hidden technology It s s everywhere, but hidden by the machinery. 12

13 Introduction Feedback systems: Interconnection of two systems System 1 System 2 E.g. Glucose concentration regulation: System 1 is the liver System 2 is the pancreas the output of interest,, is glucose concentration the input of interest,, is insulin release rate 13

14 Control What is a feedback controller? Process Controller A controller is a system designed to regulate a given process Process typically obeys physical and chemical conservation laws Controller obeys laws of mathematics and logic (sometimes intelligent) e.g. - Riding a bike (human controller) - Driving a car - Automatic control (computer programmed to control) 14

15 Control A controlled process is a system which is comprised of two interacting systems: e.g. Most controlled systems are feedback control systems Disturbances Process Outputs Action intervene Controller Observation monitor The controller is designed to provide regulation of process outputs in the presence of disturbances 15

16 Classical Feedback Control Control is meant to provide regulation of process outputs about a reference, r, despite inherent disturbances d r + - e Controller u Process y Classical Feedback Control System The deviation of the plant output, e=(r-y), from its intended reference is used to make appropriate adjustments in the plant input, u 16

17 Feedforward Control Feedforward control is used to remove the effect of measurable disturbances Disturbance M Nominal Input + + C ff Input Correction A Corrected Input P 17

18 Open-loop vs. Closed-loop Feedback control is an example of closed-loop control: The process output is sent back to the controller before affecting the process Process Control Open-loop control Control Process Controller affects the behavior of Process in a non reactive way 18

19 Control goes back to the 19th century Central theme in many important areas Major impact in flight f control We know how to construct airplanes. Men also know how to build engines. Inability to balance and steer still confronts students of the flying problem.. When one feature has been worked out, the age of flying will have arrived, for all other difficulties are of minor importance. Wilbur Wright (1901) 19

20 Historical Perspective History of flight control is a testament to the importance of control theory Wright Brothers 1903 Sperry s s Autopilot 1912 V1 and V2 (A4) 1942 Robert E. Lee 1947 Sputnik 1957 Apollo 1969 Mars Pathfinder

21 Examples e.g. Landing on Mars 21

22 Historical Perspective The feedback amplifier Invented by Black (1928) to improve signal strength Enables telephone calls over long distances Input + Output - Open-loop amplification Becomes Amplification of the feedback amplifier depends on feedback gain 22

23 Historical Perspective The invention of the feedback amplifier is fundamental Forms the basis for the design of world wide telephone/television networks Confirms the importance of feedback system design Nyquist stability theorem 1932 Bode s work on feedback design 1940 Provides the framework for modern control system theory and control system design 23

24 Historical Perspective By 1940, the magic of feedback was understood An extra component to be considered for process design to: Keep key variables constant Stabilize unstable systems Reduce the effects of disturbances and process variations Main drawback: can de-stabilize stable processes Principles of feedback applied in: Power electronics Industrial process control Flight control Telecommunications But, the similarities between all applications were not understood yet. 24

25 Historical Perspective From 40s, a new field emerges Similarities between applications are understood leading to the unification of Solid theoretical framework Sound design methodology Design principles Applications Modern Control systems Well established body of ideas, concepts, theory and design methods. Wide and growing scope of applications Remains a very active area of research and development 25

26 Introduction In engineering applications, the design of a control system is essential to ensure: Good Process Operation Process Safety Product Quality Minimization of Environmental Impact 26

27 Introduction What is the purpose of a control system? To maintain important process characteristics at desired targets despite the effects of external perturbations. Perturbations Plant Processing objectives Market Economy Climate Upsets... Safety Make $$$ Environment... Control 27

28 Introduction Dynamics: Study of the transient behavior of processes Control: the use of process dynamics for the improvement of process operation and performance the use of process dynamics to alleviate the effect of undesirable (unstable) process behaviors 28

29 What do we mean by process, plant or system? Introduction A process (plant or system),, is an operation that takes an INPUT or a DISTURBANCE and gives an OUTPUT Information Flow INPUT: ( ) Something that you can manipulate DISTURBANCE: ( ) Something that comes as a result of some outside phenomenon OUTPUT: ( ) An observable quantity that we want to regulate 29

30 Examples The speed of an automobile Inputs Friction Engine Aerodynamic Friction Process Force of Engine Output Speed 30

31 Examples Stirred tank heater T in, w M Inputs T in w Q Q Process T, w Output T 31

32 Block representations Block diagrams are models of the physical systems Input variables Process Output variables System Physical Boundary Transfer of fundamental quantities Mass, Energy and Momentum Physical Operation Abstract 32

33 Introduction What is required for the development of a control system? 1. Process Understanding Required measurements Dynamic model Required actuators Understand design limitations 2. Process Instrumentation Appropriate sensor and actuator selection Integration in control system Communication and computer architecture 3. Process Control Appropriate control strategy 33

34 Examples Measure, adjust Controller Heater + - C A M P Tank Thermocouple Feedback control Controller: where Q: Is this positive or negative feedback? 34

35 Example Cruise Control Friction Engine Process Speed Controller Human or Computer 35

36 Classical Control Control is meant to provide regulation of process outputs about a reference, r, despite inherent disturbances d r + - e Controller u Process y Classical Feedback Control System The deviation of the plant output, e=(r-y), from its intended reference is used to make appropriate adjustments in the plant input, u 36

37 Control Process is a combination of sensors and actuators Controller is a computer (or operator) that performs the required manipulations d r + - e Computer C Actuator A P y Process M Sensor e.g. Classical feedback control loop 37

38 Examples Driving an automobile r + - e Driver C Steering A M P Automobile y Visual and tactile measurement Desired trajectory r Actual trajectory y 38

39 Examples Stirred-Tank Heater T in, w Heater Q T, w T R + - e Controller C TC Thermocouple Heater A M T in, w P Tank y Thermocouple 39

40 Examples Measure T i, adjust Q T i M C A P Q i + + ΔQ Q Feedforward Control 40

41 Feedforward Control Feedforward control is used to remove the effect of measurable disturbances Disturbance M Nominal Input + + C ff Input Correction A Corrected Input P 41

42 Identification of all process variables Control Nomenclature Inputs Outputs (affect process) (result of process) Inputs Disturbance variables Variables affecting process that are due to external forces Manipulated variables Things that we can directly affect 42

43 Control Nomenclature Outputs Measured speed of a car Unmeasured acceleration of a car Control variables important observable quantities that we want to regulate can be measured or unmeasured Disturbances Manipulated Process Other Control Controller 43

44 Examples The speed of an automobile Friction Variables Engine force: u Car speed: v Friction force: f fric Aerodynamic forces: f aero Road inclination: Force of Engine 44

45 Example Variables Inputs Outputs Disturbances Manipulated Measured Unmeasured Control Task: Classify the variables 45

46 Example w i, T i P c L w c, T ci h T P o wc, Tco Variables w i, w o : T i, T o : w c : P c : P o : T ci, T co : h: Tank inlet and outlet mass flows Tank inlet and outlet temperatures Cooling jacket mass flow Position of cooling jacket inlet valve Position of tank outlet valve Cooling jacket inlet and outlet temperatures Tank liquid level T w o, T o 46

47 Example Variables Inputs Outputs Disturbances Manipulated Measured Unmeasured Control w i T i T ci w c h w o T o P c P o Task: Classify the variables 47

48 Process Control and Modeling In designing a controller, we must Define control objectives Develop a process model Design controller based on model Test through simulation Implement to real process r Tune and monitor e Controller u d Process y Model Design Implementation 48

49 Control System Development Control development is usually carried out following these important steps Define Objectives Develop a process model Design controller based on model Test by Simulation Implement and Tune Monitor Performance Often an iterative process, based on performance we may decide to retune, redesign or remodel a given control system 49

50 Control System Development Objectives What are we trying to control? Process modeling What do we need? Mechanistic and/or empirical Controller design How do we use the knowledge of process behavior to reach our process control objectives? What variables should we measure? What variables should we control? What are the best manipulated variables? What is the best controller structure? 50

51 Control System Development Implement and tune the controlled process Test by simulation incorporate control strategy to the process hardware theory rarely transcends to reality tune and re-tune Monitor performance periodic retuning and redesign is often necessary based on sensitivity of process or market demands statistical methods can be used to monitor performance 51