22349929 speed control of dc motor using pulse width

8/8/2019 22349929 Speed Control of Dc Motor Using Pulse Width

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SPEED CONTROL OF DC

MOTOR USING PULSE W

MODULATION

Submitted bySHAKTI MOHAN PATNAIK(06-3261)

ABINASH PADHI(06-3273)

RITESH KUMAR LENKA(06-3262)EIE, 7th SEMUnder Guid

Mr. Rakesh Kum


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Content :

Introduction

D.C. motor

xWorking principle

x Types of motor

Method of speed control

x Pulse width modulation

x Circuit diagram & its description

Advantages & Disadvantages

Application

Conclusion


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Introduction :

Almost all the machine in industries operelectrical motors. Among them most of mmotors.

DC series motor is specially used for traclocomotive, trolley systems, cranes and c

All these works require frequent speed copreparation of job.

A PWM (Pulse Width Modulation) wave to control the speed of the motor.


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Working Principle:

A machine that convert d.c power into mpower.

It is based on electromagnetism i.e. whencarrying conductor is placed in the magnthere is some mechanical force exerted ocarrying conductor which is perpendiculaconductor and the magnetic filed.

The most common DC motor types are thwound and series wound types.


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Shunt wound motor :

Shunt wound motor are used for driving speed shafts, centrifugal pumps, blower &

The characteristics of a DC shunt wound very good speed regulation, and it is classconstant speed motor, even though the spslightly decrease as load is increased.

Shunt-wound motors are used in industrautomotive applications where precise cospeed and torque are required.


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Series wound motor : The advantage of a Series Wound Motor

develops a large torque and can be operaspeed.

It is a motor that is well-suited for startinloads; it is often used for industrial crane

winches where very heavy loads must be and lighter loads moved more rapidly.

DC series motor is specially used for traclocomotive, trolley systems, cranes hoistsconveyor


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Speed control of dc motor :

The purpose of a motor speed controlltake a signal representing the required

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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Cont

It is obvious that the speed can be controvarying

flux/pole, * (Flux Control)

resistance Ra of armature circuit (Rheosta

applied voltage V (Voltage Control)


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Cont

The above methods have some demerits i

A large amount of power is wasted incontroller resistance. Hence, efficiencdecreased.

It needs expensive arrangement for dheat produced in the controller resist

It gives speeds below the normal spee


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Electronic Speed Control Method

Motors : compared to the electric and electromech

systems of speed control, the electronic m

higher accuracy

greater reliability

quick response

higher efficiency


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Principle : The main principle is control of power by

duty cycle.

Here the conduction time to the load is c

Let for a time t1, the input voltage appears acros

ON state.

for t2 time the voltage across the load is zero

The average voltage at output is given by

Va = 1/T vodt = t1/T Vs = ft1Vs = kVthe average load current

Ia = Va/R = KVs/R

where T is the total time period =t1+t2

k = t1/T is the duty cycle


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Cont

The rms value of output voltage is

V0 = ( i/T V02 dt ) = k Vs The output power and is given by

Pi = 1/T v0idt = 1/T v02/R dt = kVs2/R

The duty cycle can be varied from 0 to 1 by varyTherefore, the output voltage V0 can be varied controlling k, and the power flow can be contro

As the time t1 changes the width of pulse is varieof control is called pulse width modulation (PW


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Pulse Width Modulation :

Pulse width modulation (PWM) is a methsignals generation, which has 2 signal peand low).

The width (W) of each pulse varies betweperiod (T).

The duty cycle (D) of a signal is the ratio

width to period. D=(t1+t2) / T


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Pictures of the Waveform :

The motor is on formost of the time and

only off a short while,so the speed is nearmaximum

The switch is on 50%

and off 50%. The motor will only

rotate slowly.


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High Speed Signal (90%)

The signal at the rightshows the motor on

for most of the time.

The white dipsindicate when the

motor isnt receivingpower.


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Signal With The Motor Half Spe(50%)

The signal at the rightshows the motorreceiving power halfthe time.


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Low Speed Signal (10%)

The signal at the rightshows the low speedsignal which turns themotor slowly


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Circuit Description :

Power supply

Motor Controller


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Power Supply :


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Circuit Description:

The transformer is a center tap 12-0-12V supply 12v to the circuit.

The i/p sine wave is rectified by using fulrectifier which convert it to one constant

A 1000QFcapacitor is used for filtration p

The three terminal voltage regulators 781regulated DC 12 v outputs for the operaticircuit.


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Circuit Diagram :

(Motor Controller Sections)


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Circuit Description :

The design is based on astable multivibra

output is low for a period determined by for a period set by R2 and P1.

When C1 is discharged, the level at the in

below the lower threshold, so that the oustage is high.

The capacitor is then charged rapidly via and reaches the upper threshold in about

t = ln(2)RC= ln(2).(22k).(100nf)

=1.5 ms


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Cont..

As output of IC1a goes low, whereupon Cdischarged via D2, R2, and P1.

The discharge time could be set between 25ms.

the duty factor of the output signal may bbetween 5% and 90%.

The signal is inverted again and then appinput of transistor BC557 through 4k7.

The transistor Bc557 act as a buffer whichelectrical impedance from one circuit to acircuit i.e. it act as a pre amplifier.


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Cont

The o/p of Bc557 is given to the power tra2N3055 which is used in a circuit as an adetector, or switch.

The diode connected across the motor is

freewheeling purpose i.e. the diode used flyback, the sudden voltage spike seen acinductive load when its supply voltage is reduced or removed.

The resistance of P1(Potentiometer) is atthe rotary speed of the motor is at a maxi


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Advantage :

PWM duty cycle control techniques engreater efficiency of the DC motor .

PWM switching control methods imprcontrol and reduce the power losses insystem.

The pulses reach the full supply voltag

produce more torque in a motor by beovercome the internal motor resistanceasily.


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Disadvantages :

The main Disadvantages of PWM circuadded complexity and the possibility o

generating radio frequency interferenc

It can give speed below the full speed,

It cannot be used for fast controlling


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Applications :

Traction application

Conveyor Belt carrying loads

Various motors requiring smooth speed

DC motors of all range can be controlledused for the production of materials

Electric locomotives

DC motor using precise job preparations


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Conclusion

The present project is practical one anfeasibility according to economic poin

reliability & accuracy. It is programmatherefore it can control various motorsmall one to several hp motors.


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Any

query


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22349929 speed control of dc motor using pulse width

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