arpit presentation55
TRANSCRIPT
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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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