Date post: | 07-Apr-2018 |
Category: |
Documents |
Upload: | golriz-nourani |
View: | 219 times |
Download: | 0 times |
of 19
8/4/2019 Lecture2-Basics of Control
1/19
Control SystemsControl Systems
Part 1: Basics of Control Systems
8/4/2019 Lecture2-Basics of Control
2/19
Learning objectives
To state the basic concept of feedback control
To differentiate sensors from the actuators
To clarify the roles that sensors, actuators andcontrollers play in a feedback control loop.
8/4/2019 Lecture2-Basics of Control
3/19
Motivations for control engineering
Feedback control has a long history which beganwith the early desire of humans to harness thematerials and forces of nature to their advantage.
It involves the use of sensed environmentalinformation to aid in the manipulation of systeminputs to achieve the desired system behaviours.
Modern industrial plants, such as a nuclear power
plant, have sophisticated control systems which arecrucial to their successful operation.
8/4/2019 Lecture2-Basics of Control
4/19
Control loops in a power plant
8/4/2019 Lecture2-Basics of Control
5/19
Impact of control systems
Control Engineering has had a major impact onsociety.
For example, Watts Fly Ball Governor had a majorimpact on the industrial revolution.
Indeed, most modern systems (aircraft, high speedtrains, CD players, ) could not operate without the
aid of sophisticated control systems.
8/4/2019 Lecture2-Basics of Control
6/19
Watts fly ball governor
8/4/2019 Lecture2-Basics of Control
7/19
Watts fly ball governor
This photograph shows a
flyball governor used on asteam engine in a cottonfactory.
8/4/2019 Lecture2-Basics of Control
8/19
Watts fly ball governor
This particular governor was
used to regulate the speed of a
water wheel driven by the flowof the river. The governor is
quite large as can be gauged by
the outline of the door frame
behind the governor.
8/4/2019 Lecture2-Basics of Control
9/19
Procedure for control system design
Design of a practical control system usually takesseveral different stages and each requires a slightlydifferent approach.
Initial "grass roots" design
Commissioning and Tuning
Refinement and Upgrades Forensic studies
8/4/2019 Lecture2-Basics of Control
10/19
Simple water level control system
8/4/2019 Lecture2-Basics of Control
11/19
Block diagram representation
8/4/2019 Lecture2-Basics of Control
12/19
Control system integration
Success in control engineering needs to examine thefollowing issues:
plant, i.e. the process to be controlled
objectives sensors
actuators
communications
computing
architectures and interfacing algorithms
accounting for disturbances and uncertainty
8/4/2019 Lecture2-Basics of Control
13/19
Plant: The process to be controlled
The physical layout of a plant is an intrinsic partof control problems. Thus a control engineerneeds to be familiar with the "physics" of the
process under study.
This includes a rudimentary knowledge of thebasic energy balance, mass balance andmaterial flows in the system.
8/4/2019 Lecture2-Basics of Control
14/19
Control design objectives
Before selecting sensors, actuators or controllerarchitectures, it is important to know the goal of theclosed-loop control system: for example,
what does one want to achieve (energy reduction,yield increase,...)
what variables need to be controlled to achievethese objectives
what level of performance is necessary (accuracy,speed,...)
8/4/2019 Lecture2-Basics of Control
15/19
Sensors
Sensors are the eyes of control enabling oneto see what is going on.
Indeed, one statement that is sometimesmade about control is:
If you can measure it, you may beable to control it.
8/4/2019 Lecture2-Basics of Control
16/19
Actuators
Once sensors are in place to report on the stateof a process, then the next issue is the ability to
affect, or actuate, the system in order to movethe process from the current state to a desiredstate.
8/4/2019 Lecture2-Basics of Control
17/19
Controller architecture and algorithm
Finally, we come to the real heartof control engineeringi.e. the algorithms that connect the sensors to theactuators. One should never underestimate this final
aspect of the problem.
As a simple example from our everyday experience,consider the problem of playing tennis at top internationallevel. One can readily accept that one needs good eye
sight (sensors) and strong muscles (actuators) to playtennis at this level, but these attributes are not sufficient.Indeed eye-hand coordination (i.e. control) is also crucialto success.
8/4/2019 Lecture2-Basics of Control
18/19
In summary, one can say that:
Sensors provide the eyes andactuators the muscle, but controlscience provides the finesse.
Overall control systems
8/4/2019 Lecture2-Basics of Control
19/19
Better Control
Provides more finesse by combining sensors andactuators in more intelligent ways
Better ActuatorsProvide more Muscle
Better Sensors
Provide betterVision