Digital Computer Process Control Lecture 1

Transcription

1 Digital Computer Process Control Lecture 1 Dr. Jie Yu Department of Chemical Engineering McMaster University Jie Yu Digital Computer Process Control 1

2 Course Outline Introduction Section I: Dynamic Models Continuous Systems Fundamental models Linearization Transfer-function representation State-space representation Conversion between transfer-function and state-space models Section II: Dynamic Models Discrete Systems Model discretization Z-transforms Pulse transfer function Conversion between transfer-function and state-space models Dynamic Responses Jie Yu Digital Computer Process Control 2

3 Course Outline Section III: Systems Identification Least-square formulation and solution to first-order models First-order plus dead-time model General ARMA models Model Diagnostics Input test signal and data pre-processing Section IV: Closed-Loop Analysis Continuous Systems Closed-loop transfer function Stability analysis Controller design using direct synthesis Section V: Closed-Loop Analysis Discrete Systems Closed-loop transfer function of sampled-data systems Stability analysis Jie Yu Digital Computer Process Control 3

4 Course Outline Section VI: Digital Control Design Discretization of continuous-time control laws Direct Approach Section VII: Model Predictive Control Unconstrained MPC SISO systems Unconstrained MPC MIMO systems Closed-loop properties Constrained MPC MPC implementation issues Jie Yu Digital Computer Process Control 4

5 What is control system? Set-point Controlled Variable Feedback Manipulated Variable Jie Yu Digital Computer Process Control 5

6 What is control system? Manipulated Variable - Insulin Injection Set-point Controlled Variable - Blood Glucose Controller pump patient sensor Jie Yu Digital Computer Process Control 6

7 What is digital control? Process parameters and variables sampled at discrete time instants Discrete sample systems Controller sees output responses only at discrete sample points However, the process being controlled may still be in continuous operation Control law computed discretely by digital computer Distributed computer control network used in a plant Jie Yu Digital Computer Process Control 7

8 Digital Computer Control Diagram Jie Yu Digital Computer Process Control 8

9 Pros/Cons of Digital Computer Control Pros Easy data acquisition High speed computation Data storage and retrieval Flexible calculation of control law Cons Potential failure of control systems due to computer malfunction Inability for handle unexpected operation event Security issue on process control computer network may cause plant operation upset or even serious incident Software cost for control systems Jie Yu Digital Computer Process Control 9

10 What you are expected to learn? How to discretize continuous-time control law? How to analyze closed-loop control systems? What is the effect of sampling time on closed-loop stability? How to design discrete-time control law? Regulatory control Model predictive control How to run discrete control law on continuous systems? How to achieve desirable closed-loop behavior? Jie Yu Digital Computer Process Control 10

11 Major Steps of Control System Design Jie Yu Digital Computer Process Control 11

12 Remarks on Digital Control Design Identification of discrete-time dynamic models from plant data Digital signal processing and analysis Control design strategy specifically for discrete-time system Simulation of digital control system Matlab Simulink Performance analysis of digital control system Jie Yu Digital Computer Process Control 12

13 Process Control Basics Specific control objectives Increase product throughput Increase yield of higher valued products Reduce energy consumption Reduce environmental pollution Improve product quality Improve process safety Extend equipment life Improved economic profit Reduce work labor Jie Yu Digital Computer Process Control 13

14 Process Control Basics Controlled Variable (CV) - Variables used to quantify control objectives such as product quality and profit Manipulated Variable (MV) - Variables being adjusted dynamically to keep the controlled variables at set-points Disturbance Variable (DV) - Variables that can cause controlled variables to deviate from set-points DV Controller MV Plant CV Jie Yu Digital Computer Process Control 14

15 Feedback Control Feedback Boiler Level DV Steam Flow MV Feedwater Flow Jie Yu Digital Computer Process Control 15

16 Feedforward Control Feedforward Steam Flow MV Feedwater Flow Jie Yu Digital Computer Process Control 16

17 Feedforward-feedback Control Jie Yu Digital Computer Process Control 17

18 Key Items to Control Design Closed-loop Stability Bounded Inputs Bounded Outputs Controller Performance Setpoint Tracking Disturbance Rejection Process Output Variability Valve Moves System Robustness Model Uncertainty Operation Condition Change Jie Yu Digital Computer Process Control 18