Introduction for Process Control Systems 过程控制系统概论

Introduction forProcess Control Systems过程控制系统概论

Institute of Industrial Control, Zhejiang University

2013/03/06

About Myself Research interests:

Process Modeling & Control, Advanced Process Control, Optimization etc.

Contact me:Email: [email protected]: 87952233-8237(O)

13071847893Address: 玉泉校区控制系教 18-237

助教：郭子旭邮箱： [email protected] 地址：教 18-107 手机： 15088719355

课程的参考资料主要参考资料

C. A. Smith ， Automated Continuous Process Control. New York ： John Wiley & Sons ， Inc., 2002戴连奎主编，过程控制工程（第三版） . 北京 : 化学工业出版社 , 2012 年 12 月

考核说明考核：平时成绩 50% ，包括课堂提问、平时练习、综合练习；期末考试（闭卷） 50% 课堂提问

满分 20 分。缺课 1 次扣 5 分。平时练习

满分 10 分。平时作业的平均分 (随堂作业 ) 综合练习 20 分

综合练习说明每位同学在给出的题目中任选 1 题进行仿真研究，也可自行选题，但选题内容必须与本课程相关。报告应包含以下内容，缺一不可：

所选的题目以及主要研究内容；本人采用的控制方法以及仿真过程和结果；仿真结果的比较和分析。

报告以 PDF 文档的形式提交，同时提交仿真文件综合练习的评分标准是：工作量、正确性、创新性、难度、文档规范性等

综合练习的时间安排春学期第 8 周 (4 月 23 日 ) 前公布选题夏学期第 5 周 (6 月 5 日 ) 前上交报告夏学期第 6 周 (6 月 12 日 ) 确定做报告名单夏学期第 7 周 (6 月 8 日 ) 做报告

课程教学目的使学生了解过程控制系统的设计目的与设计步骤以及具体实现掌握控制系统过程对象建模方法与方块图描述法面向工业过程的常规 PID 控制策略，掌握控制系统的分析、设计与实施技术了解先进控制算法，掌握其设计思想、概念、特点及适用场合

Contents （概论） Origin of Process Control Systems （过程控制系统的由来） Important Terms and Objective of Process

Control Systems （过程控制的术语与目标） Description of Process Control Systems （过程控制系统的描述） Types of Control Strategies （控制策略分类） Course Tasks （课程任务）

Concept of Systems and Control Systems （系统与控制系统的概念）

Systems

U

D

Z

Y

Control Systems

有若干要素以一定结构形式联接构成的具有某种功能的有机整体

Inputs

Outputs

Control system examples ?

Origin of Process Control Systems （过程控制系统的由来）Manual Operation: (1) Measure the level by a water

gauge ( 水位表 );(2) Compare the level to its desired

value;(3) Based on this comparison,

decide what to do to correct for any deviation ( 偏差 );

(4) Manipulate the outlet valve (输出阀 ) to correct for the deviation.

Purpose: To maintain the level at a desired operating value, when the inlet flow（输入流量） changes.

Limitations with Manual Control（手动控制的局限性）

Require the operator to look frequently at the level to take corrective action whenever it deviates from the desired value;

Different operators would make different decisions as to how to move the outlet valve, resulting in inconsistent operation ( 操作的不一致性 );

Require a large number of operators to maintain hundreds of variables in most process plants at a desired value.

Solution ?

Automatic Control SystemSolution: Design a control system to accomplish this control automatically without requiring intervention from the operator.

Three basic components of all control systems:• a sensor / transmitter: the “eye” of the control system, • a controller: the “brain” of the control system,• final control element: often a control valve.

h

hsp

Qi

Qo

LT21

LC21

Feedback Control Process（反馈控制过程）1. Measure the level by a sensor ( 传感器 ) and convert the

output from the sensor to an electric signal by a transmitter ( 变送器 ) ;

2. The controller （控制器 / 调节器） then receives the signal and compares it with the value desired;

3. Depending on this comparison, the controller decides what to do to correct for any deviation;

4. Based on this decision, it sends a signal to the final control element （执行单元） , e. g., a control valve.

h

hsp

Qi

Qo

LT21

LC21

Three basic operations （三个基本操作） in every type of control system

Measurement (测量， M)Measuring the variable to be controlled is usually done by the combination of sensor and transmitter.

Decision (决策， D)Based on the Measurement the controller decides what to do to maintain the variable at its desired value.

Action ( 动作 /执行， A)As a result of the controller’s decision, the system must then take an action. This is usually accomplished by the final control element. The action taken must come back and affect the measurement.

Important Terms （重要术语）of Automatic Process Control

Controlled Variable (CV, 被控变量 /受控变量 )The variable that must be maintained or controlled at some desired value.

Setpoint (SP, 设定值 /给定值 )The desired value of the controlled variable.

Manipulated Variable (MV, 操纵变量 /操作变量 )The variable used to maintain the controlled variable at its setpoint.

Disturbance (DV,扰动 /扰动变量 )Any variable that causes the controlled variable to deviate away from its setpoint.

Objective of Process Control Systems（过程控制系统的设计目标）

The objective of an automatic process control system is to adjust the manipulated variable to maintain the controlled variable at its set point in spite of disturbances.

Why automatic control is important:1) Safety. Prevent injury to plant personnel and damage to the process equipment, and protect the environment by minimizing wastes. 2) Product Quality.3) Minimum Cost.

Example 1.1

For the above pressure control system, please describe its CV, SP, MV, DVs, control diagram as well as control objective.

2211 FKFKdtdPV

PPfKF V 1111

2222 PPfKF V

Variable relations are as follows:

Discuss the solution ?

P

P1

P2Psp Pm

u

f1

f2

F1

F2PC51

PT51

uf 1001

Control Diagram #1 for Example 1.1

Point out its MV, DVs ?

PC51

Psp e(t)

+_

Pm

PT51

Control Valve

P(t)u(t)

222 PPfKV

PPfKV 111

f1

P1

F1

2211 FKFKdtdPV

P

P2

F2

f2

P

Controlled Process


PC51

Psp

+_

Pm

PT51

Control Valve

P(t)u(t) f1

P2

Controlled Process

++

Disturbance Path

(干扰通道)

Control Path(控制通道)

P1

f2


PC51

Psp

+_

Pm

PT51

Control Valve

P(t)u(t) f1

Controlled Process

++

Disturbance Path

Control Path

P1, P2, f2

Discuss its correctness

Ex. 1.2: Temperature Control System for a Heat Exchanger (换热器 )

Problem: point out CV, SP, MV, DVs, its block diagram and objective ?

Steam

Tsp

Tm

T

RV

RF , Ti

u(t)

Condensate

Process Fluid

TC22

TT22

Block Diagram for Heat Exchanger

Tsp

+_

Tm

++ T(t)RV (t)

RF (t), Ti (t)Disturbance

Path

TT22

Steam Valve

Control Path

TC22

Heat Exchanger

u(t)

General Feedback Control Systems

CV: temperature, pressure, flow, level, composition(成份含量 ) and property(属性 ) of process fluid ；

yspu(t)

(OP)+

_

ym(t)

++ y(t)MV

DVs Disturbance

Path

Sensor & Transmitter

Final Control Element

Control PathController

Controlled Plant

General Control Systems

Controller: Hardware & Software

Control Strategies / Algorithms (控制策略与算法 )

ysp u(t)

+_

ym(t)

++ y(t)MV

DVs Disturbance

Path




Controlled Plant

Hardware of Controllers Analog control instruments (DDZ-II, III) Digital control instruments (数字控制器 ) Programmable logic controllers ( 可编程逻辑控制器， PLC) Distributed control systems （集散控制系统或称分布式控制系统， DCS ） Fieldbus control system （现场总线控制系统， FCS ） Ethernet for Process Automation ( 过程自动化以太网， EPA)

Types of Control Systems（控制系统分类） Regulatory Control （“定值控制”或“调节控制”） and Servo Control （”伺服控制”或“跟踪控制”）

Examples ： continuous processes and batch processes or flight control.

Feedforward Control （前馈控制） and Feedback Control （反馈控制）Examples ： temperature control system in a heat exchanger.

Feedforward Control & Feedback Control

T

RV

RF

Tsp

Tm

u(t)

Ti

Feedforward Controller

Condensate

Process Fluid

Steam

TT22

FT31

TT32

RFm Tim

Compare the advantages and disadvantages of both strategies.

Steam

Tsp

Tm

T

RV

RF , Ti

u(t)

Condensate

Process Fluid

TC22

TT22

Feedforward Feedback Control

T

RV

Tm

u(t)Steam

Condensate

Process Fluid

Feedforward ControllerTsp

TC22

TT22 RF Ti

FT31

TT32

RFm Tim

Types of Control Systems Switch Control （开关量控制） and

Continuous Control （连续量控制）Examples: air conditioner control

Continuous-Time Control （连续时间控制） and Discrete-Time Control （离散时间控制 , 也称“采样控制” , Digital Control, “数字控制”）Examples: control systems based on computers or analog instruments

Types of Control Systems (cont.)

Multi-input-multi-output Control （ MIMO,多输入多输出控制 , or “多变量控制” ), Single-input-single-output Control （ SISO, 单输入单输出控制） and Multi-loop Control （多回路控制）Examples: distillation column control

Linear Control （线性控制） and Nonlinear Control （非线性控制）Examples: pH control

Multi-loop Control for Distillation

LC

TC

LC

FC

FC

DistillationColumn

SteamResidue

ProcesssFluid

Product

Basic Process Control Strategies

Single-loop PID ( 单回路 PID 控制 ) Cascade Control (串级控制 ) Ratio Control ( 比值控制 ) Override or Selective Control (超驰或选择控制） etc.

Features: PID based, simple, no model needed, easy tuning, and for SISO systems.

Advanced Process Control ( 先进控制， APC) Strategies

Feedforward Control ( 前馈控制 ) Dead-time Compensation (纯滞后补偿 ) Decoupling ( 解耦 ), Predictive Control (预测控制） Adaptive Control ( 自适应控制 ), etc.

Features: Model based, complicated, computer needed, and most for MIMO or SISO systems with long dead-time.

Primary Tasks of the Course( 课程的基本任务 )

To analyze, design and implement the control strategies or controller for continuous controlled processes

ysp u(t)

+_

ym(t)

++ y(t)MV

DVs Disturbance

Path




Controlled Plant

Techniques Correlative to Process Control Engineering

Process Control Engineering

Control Theory Optimization

Chemical Engineering

Measuremental & Control Instruments

Computer & Networks

System Simulation

Problem 1.1

h

Lsp

Qi

Qo

LT21

LC21

A

Lm

u

oi QQdtdhA

,02 hhfKQ VVo

For the level control system, if the following relations are satisfied:

Please describe its CV, SV, MV, DVs, control objective as well as its control diagram.

where A represents the sectional area of the tank, KV2 and fV represent the flow coefficient and relative flow area of the control valve, respectively.

)(ugfV

Introduction for Process Control Systems 过程控制系统概论

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