This document provides an overview of variable frequency drives (VFDs), including their components, operation, benefits, and applications. A VFD controls the frequency and voltage supplied to an electric motor, allowing it to run at variable speeds. It has three main sections - an input section that draws power, a rectifier that converts AC to DC, and an inverter that converts the DC back to a controlled AC waveform. VFDs provide benefits like energy savings, better process control, and protection for motors. Common industrial applications include fans, pumps, compressors, and chillers in HVAC systems.

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

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

3.  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.

4.  Before semiconductor devices were introduced (<1950):
 AC motors for fixed speed applications
 DC 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 control
Application 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

5. Conventional electric
drives (variable speed)
Modern electric drives (With
power electronic converters)
• Bulky
• Inefficient
• inflexible
 Small
 Efficient
 Flexible

6.  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

7.  Buildings:
◦ Primarily commercial
 Applications:
◦ Air handling
◦ District Heating
◦ Room & Zone
 Operation:
◦ Control fans, pumps,
compressors to reduce
energy consumption

8.  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.

9.  RECTIFIER is that special type of converter that
converts AC to DC

10.  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.

11.  Simplified Inverter Section of a VFD
Pulse-width-modulated voltage and
current waveforms

12. 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
Pulse- width-modulatION (PWM)

13.  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

14.  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

15.  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

16. 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

17. Pressure
Set point
From The Source
reservoir
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 Control
with VFD

18. INDUCTION MOTOR

19.  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.