ARPIT PRESENTATION55

8/7/2019 ARPIT PRESENTATION55

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SPEED CONTROL OF DC

MOTOR USING PULSE WIDTH

MODULATION

Submitted by

ARPIT SHARMA

EIC, 8th SEM

Under Guidance of

Mr. SURRENDRA DUA


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Content :

Introduction

D.C. motor

x Working principle

x Types of motor Method of speed control

x Pulse width modulation

Advantages & Disadvantages Application

Conclusion


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Introduction :

Almost all the machine in industries operated usingelectrical motors. Among them most of motors are DCmotors.

DC series motor is specially used for traction, electriclocomotive, trolley systems, cranes and conveyor belt.

All these works require frequent speed control forpreparation of job.

A PWM (Pulse Width Modulation) wave can be usedto control the speed of the motor.


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Working Principle:

A machine that convert d.c power into mechanicalpower.

It is based on electromagnetism i.e. when a currentcarrying conductor is placed in the magnetic fieldthere is some mechanical force exerted on the currentcarrying conductor which is perpendicular to both the

conductor and the magnetic filed.

The most common DC motor types are the shuntwound and series wound types.


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Shunt wound motor :

Shunt wound motor are used for driving constantspeed shafts, centrifugal pumps, blower & pumps etc.

The characteristics of a DC shunt wound motor give itvery good speed regulation, and it is classified as aconstant speed motor, even though the speed does

slightly decrease as load is increased.

Shunt-wound motors are used in industrial andautomotive applications where precise control of

speed and torque are required.


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Series wound motor : The advantage of a Series Wound Motor is that it

develops a large torque and can be operated at lowspeed.

It is a motor that is well-suited for starting heavyloads; it is often used for industrial cranes andwinches where very heavy loads must be moved slowly

and lighter loads moved more rapidly.

DC series motor is specially used for traction, electriclocomotive, trolley systems, cranes hoists and

conveyor


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Speed control of dc motor :

The purpose of a motor speed controller is to

take a signal representing the required speed,and to drive a motor at that speed.

Motor speed can be controlled by

controlling-- Armature voltage (Va)

- Armature current (Ia)


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FACTORS AFFECTING SPEED

It is obvious that the speed can be controlled byvarying

flux/pole,* (Flux Control)

resistance Ra of armature circuit (Rheostatic Control)

applied voltage V (Voltage Control)


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DEMERITS

The above methods have some demerits i.e

A large amount of power is wasted in thecontroller resistance. Hence, efficiency is

decreased.

It needs expensive arrangement for dissipation ofheat produced in the controller resistance.

It gives speeds below the normal speed.


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Electronic Speed Control Methods for DC

Motors : compared to the electric and electromechanical

systems of speed control, the electronic methods have

higher accuracy

greater reliability

quick response

higher efficiency


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Cont

The duty cycle can be varied from 0 to 1 by varyingt1, T or f. Therefore, the output voltage V0 can bevaried from 0 to Vs by controlling k, and the power

flow can be controlled.

As the time t1 changes the width of pulse is varied

and this type of control is called pulse widthmodulation (PWM) control.


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Pulse Width Modulation :

Pulse width modulation (PWM) is a method for binarysignals generation, which has 2 signal periods (highand low).

The width (W) of each pulse varies between 0 and theperiod (T).

The duty cycle (D) of a signal is the ratio of pulsewidth to period.

D=(t1+t2) / T


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Pictures of the Waveform :

The motor is on for

most of the time andonly off a short while,so the speed is nearmaximum

The switch is on 50%and off 50%.

The motor will onlyrotate slowly.


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High Speed Signal (90%)

The signal at the right

shows the motor onfor most of the time.

The white dips

indicate when themotor isnt receivingpower.


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Signal With The Motor Half Speed(50%)

The signal at the rightshows the motorreceiving power half

the time.


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Low Speed Signal (10%)

The signal at the rightshows the low speedsignal which turns the

motor slowly


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Advantage :

PWM duty cycle control techniques enable

greater efficiency of the DC motor . PWM switching control methods improve speedcontrol and reduce the power losses in thesystem.

The pulses reach the full supply voltage and willproduce more torque in a motor by being able toovercome the internal motor resistances moreeasily.


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Disadvantages :

The main Disadvantages of PWM circuits are the

added complexity and the possibility ofgenerating radio frequency interference .

It can give speed below the full speed, not above.

It cannot be used for fast controlling of speed.


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Applications :

Traction application

Conveyor Belt carrying loads

Various motors requiring smooth speed control

DC motors of all range can be controlled, which areused for the production of materials

Electric locomotives

DC motor using precise job preparations


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Conclusion

The present project is practical one and high

feasibility according to economic point of view,reliability & accuracy. It is programmable onetherefore it can control various motors.


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Any query


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Documents

ARPIT PRESENTATION55