Variable Frequency Drives for Industrial Applications

BY:NAILA SHUTTARY BRANCH:EEE ROLL NO:12D21A0213

INTRODUCTION OVERVIEW COMPARISON PURPOSE VFD OPERATION COMPONENTS OF VFD WHY USE VFD? BENEFITS OF VFD INDUSTRIAL APPLICATIONS CONCLUSION

CONTENTS

A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor.

A variable frequency drive is an adjustable speed drive.

VFDs are available in a number of different low and medium voltage AC-AC and DC-AC topologies.

Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, micro drive, and inverter.

INTRODUCTION

Before semiconductor devices were introduced (<1950):

AC motors for fixed speed applicationsDC motors for variable speed applications• After semiconductor devices were introduced (1950s)Variable frequency sources available – AC motors in

variable speed applications Coupling between flux and torque controlApplication limited to medium performance

applications – fans, blowers, compressors – scalar control

High performance applications dominated by DC motors – tractions, elevators, servos, etc

• In 1980s vector controlled semiconductor drives were introduced

AN OVERVIEW

COMPARISON OF VFD AND CONVENTIONAL DRIVES

Conventional electric drives (variable speed)

Modern electric drives (With power electronic converters)

• Bulky• Inefficient• inflexible

Small Efficient Flexible

Energy savings on most pump and fan applications.

Better process control and regulation. Speeding up or slowing down a

machine or process. Inherent power-factor correction Emergency bypass capability Protection from overload currents Safe Acceleration

The Purpose OF USING VFD

Buildings:◦ Primarily commercial

Applications:◦ Air handling◦ District Heating◦ Room & Zone

Operation:◦ Control fans, pumps,

compressors to reduce energy consumption

Where are variable frequency drives used?

Understanding the basic principles behind VFD operation requires understanding the three basic sections of the VFD:

Input section, draws AC electric power from the utility,

Rectifier section, converts the AC into DC power.

Inverter section,

converts DC back into a controllable AC waveform.

VFD OPERATION

RECTIFIER is that special type of converter that converts AC to DC

COMPONENTS OF VFD

Simplified Circuit showing DC bus components

The DC link is an important section of the drive as it provides much of the monitoring and protection for the drive & motor circuit.

COMPONENTS OF VFD

Simplified Inverter Section of a VFD

COMPONENTS OF VFD

Pulse-width-modulated voltage and current waveforms

Pulse- width-modulatION (PWM)

The DC waveform looks more like an AC waveform but the voltage waveform is

much different. The power semi-conductors in the inverter section act as switches, switches of the DC

bus, and therefore, are pulsing the motor with some

voltage.A typical square wave takes its shape on the square-wave

look due to this switching function ( which explains the

sharp rise to peak) rather than a rotational, changing

state of amplitude. This frequency and

amplitude pattern is sometimes called the carrier

frequency of a PWM drive.Pulse-width-modulated voltage and

current waveforms

Saves energy through fan and pump speed control◦ up to 70% energy savings in pump and fan applications

e.g. 32% average savings in a ventilation system → Payback period of 1 year

Decreases mechanical stress due to pressure spikes with direct on-line start & stop◦ VFDs creates a smooth start which reduces the

pressure spikes that reduce system lifetime Reduces the starting current of the motor

◦ VFDs minimize the starting current of the motor, which means electrical installation investments can be lower

Why use variable frequency drives?

As VFD usage in HVAC applications has increased, fans, pumps, air handlers, and chillers can benefit from speed control. Variable frequency drives provide the following advantages:

• energy savings • low motor starting current • reduction of thermal and mechanical stresses on motors and belts during starts • simple installation • high power factor • lower KVA

BENEFITS OF VFD

Typical energy savings with VFD on centrifugal pumps

Flow is proportional to speed

Power varies to the cube of the speed change

20% reduction in speed = 50% reduction in energy

50% reduction in speed = 80% reduction in energy

INDUSTRIAL APPLICATIONS

Fans Applications (E.g.) Odor control Ventilation Cooling towers

Benefits Exact air flow to match demand Energy savings (20% reduction in speed gives ~ 50% saving in energy) Constant pressure &Temperature Less wear (EG: Extends belt life) Reduced audible noise Parallel fan operation possible

INDUSTRIAL APPLICATIONS

INDUSTRIAL APPLICATIONS

The VFD adjusts the pump speed based on a feedback signal from the pressure transmitter to

maintain a constant pressure with changes in flow

Pressure Set point

From The Source

reservoir

Pressure Control with VFD

INDUCTION MOTORINDUSTRIAL APPLICATIONS

Using VFDs, a small reduction in speed can save large amount of energy.

They help to reduce wear and tear. This technology can meet even the

most stringent harmonic standards and reduce backup sizing .

They provide lower KVA,helpin alleviate voltage sags.

They help to save money as well as energy losses are reduced.

CONCLUSION