Basic Control System_EC

8/12/2019 Basic Control System_EC

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Basic Electronics

Ch-7

Basic Control Systems


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FEEDBACK CONTROL SYSTEMS

An open-loop system is one in which the

control action is independent of the output or

desired result


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FEEDBACK CONTROL SYSTEMS

A closed-loop (feedback) system is one in

which the control action is dependent upon

the output


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Feedback System Classification

According to the method of analysis and

design

Linear versus nonlinear control systems

Time-invariant versus time-varying systems

According to the types of signal found in the

system

Continuous-data and discrete-data systems

Sampled-data and digital control systems


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According to the type of system components

Electromechanical control systems

Hydraulic control systems

Pneumatic control systems

Biological control systems

According to the main purpose of the system

Position control systems

Velocity control systems

Regulators

Servomechanisms

Feedback System Classification


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Transfer Functions and Block

Diagrams

The transfer function is a mathematical formulationthat relates the output variable of a device to the inputvariable

Properties

A transfer function is defined only for a linear time-invariant system. It is meaningless for nonlinear systems

The transfer function between an input variable and anoutput variable of a system is defined as the ratio of theLaplace transform of the output to the Laplace transform

of the input All initial conditions of the system are assumed to be zero

The transfer function is independent of the input


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The block diagram is a pictorial representationof the equations of the system. Each blockrepresents a mathematical operation, and the

blocks are interconnected to satisfy thegoverning equations of the system


Diagrams


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Diagrams


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The expression for the output quantity with

negative feedback is given by

The transfer function M of the closed-loop

system is then given by


Diagrams


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Diagrams


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Diagrams


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EFFECT OF FEEDBACK ON SENSITIVITY TO

PARAMETER CHANGES

The sensitivity S of a closed-loop system to a

parameter changep in the direct transmission

function G is defined as


Diagrams


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Dynamic Response of Control Systems


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Maximum (or peak) overshoot A is the largest

deviation of the output over the step input during

the transient state. It is used as a measure of the

relative stability of the system.

The percentage maximum overshoot is given by

the ratio of maximum overshoot to final value,

expressed in percent. Delay time td is defined as the time required for

the step response to reach 90% of its final value.



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Rise time tr is defined as the time needed for

the step response to rise from 10% to 90% of

its final value.

Settling time ts is the time required for the

step response to decrease and stay within a

specified percentage (usually 5%) of its final

value.



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Steady-State Error of Linear Systems

If the steady-state response of the outputdoes not agree exactly with the steady state ofthe input, the system is said to have a steady-

state error

Applying the final-value theorem, the steady-state error of the system is


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Classification of Feedback Control

Systems by Control Action


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DIGITAL CONTROL SYSTEMS

Discrete-data and digital control systems differfrom the continuous-data or analog systems inthat the signals in one or more parts of thesesystems are in the form of either a pulse train or

a numerical (digital) code. Digital control systems refers to the use of a

digital computer or controller in the system;digital data usually refers to signals that are

generated by digital computers or digitaltransducers and are thus in some kind of codedform.


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Sampled data and digital control offer severaladvantages over analog systems:

More compact and lightweight

Improved sensitivity Better reliability, speed, and accuracy

More flexibility and versatility (in programming)

Lower cost

More rugged in construction no drift

Less effect due to noise and disturbance



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Adaptive Control



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Basic Control System_EC