Lecture2-Basics of Control

8/4/2019 Lecture2-Basics of Control

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Control SystemsControl Systems

Part 1: Basics of Control Systems


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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.


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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.


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Control loops in a power plant


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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.


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Watts fly ball governor


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This photograph shows a

flyball governor used on asteam engine in a cottonfactory.


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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.


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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


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Simple water level control system


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Block diagram representation


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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


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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.


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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,...)


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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.


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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.


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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.


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In summary, one can say that:

Sensors provide the eyes andactuators the muscle, but controlscience provides the finesse.

Overall control systems


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Better Control

Provides more finesse by combining sensors andactuators in more intelligent ways

Better ActuatorsProvide more Muscle

Better Sensors

Provide betterVision

Lecture2-Basics of Control

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