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.
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
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.