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ABSTRACT

y Energy conservation means more efficient use ofenergy without reducing production levels and withoutsacrificing product quality, safety or environmentalstandards.

y VFDs help to limit demand and electrical consumptionof motors by reducing the amount of energy theyconsume

.

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INTRODUCT

IO

Ny Variable Frequency Drive (VFD)

y A VFD can be used to control both the speed andtorque of a standard induction AC electric motor.

y

It varies both the frequency and amps of the ACwaveform being delivered to the motor saving moneyin electricity.

y Basic components of a VFD:y Input section, draws AC electric power from the utility,

Rectifier section, converts the AC into DC power.y Inverter section, converts DC back into a controllable AC

waveform.

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OPERATING PRINCIPLE

y The synchronous speed of AC motor is determinedby the frequency of the AC supply and number of

poles in the stator winding according to therelation:

n = (120 x f)/p

where

n=revolutions per minute(rpm)f=AC power frequency(Hz)

p=Number of poles per phase

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CLASSIFICATION

y Constant voltage converter: Intermediate DC link voltage remainsapproximately constant during each output cycle.

y Constant current drives: Large inductor is placed between the inputrectifier and the output bridge, so the current delivered is nearlyconstant.

y Cycloconverter: No input rectifier or DC link and instead connects

each output terminal to the appropriate input phase.

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MODE OF CONTROL

y The most common type of packaged VF drive is the

constant-voltage type.

y Uses pulse width modulation to control both thefrequency and effective voltage applied to the motor

load

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CIRCUIT DIAGRAM

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VFD CONTROLLER

They are solid state electronic power conversiondevices.

First converts AC input power to DC intermediate

power using a rectifier or converter bridge.Rectifier: usually 3-phase, full wave diode bridge.

DC intermediate power is then converted to quasi-sinusoidal AC power using an inverter switching

circuit.

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y Inverter circuit is probably the most importantsection of the VFD - changes DC energy into threechannels of AC energy that can be used by an AC

motor.

y In order to get the desired frequency we use the pulsewidth modulation technique in the inverter section.

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What is pulse width modulation?y Pulse width modulation is a modulation technique for

generating variable width pulses to represent the amplitudeof an input analog signal or wave.

y Pulse Width Modulation (PWM) techniques is commonlyused in a variable frequency drive scheme to control therotational speed of an induction motor.

y The basic PWM control principle is the Volt/Hertz ratio

which reflects the inductance properties of the motorwindings.

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ADVANTAGES

Potential power factor improvement up to .98

Improved system efficiency (Example, Cooling Tower).

Reduced audible noise.

Reduced wear on motors, belts, and other components,fewer revolutions per year.

Greatly reduce maintenance cost of mechanical flow

controls.

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THANK YOU