Unformatted text preview: 1-1 Chapter 1
Introduction to Electric
Drive Systems Exit 2001 by N. Mohan Print TOC " ! 1-2 History
❏ Constant frequency AC - essentially constant pump
❏ Inefficient - Heat generated in pump and throttling
❏ Not amenable to automation
Valve Outlet MOTOR
AC Exit 2001 by N. Mohan ⇒ Essentially
Constant Speed Pump TOC " ! 1-3 Trend : Adjustable Speed Drives (ASDs)
electric converter Adjustable Pump
speed ❏ Driven at appropriate speed
x High Efficiency Exit 2001 by N. Mohan TOC " ! 1-4 What is an Electric-Motor Drive?
Unit (PPU) Motor
form Electric Source
(utility) Load Sensors
speed/ position Controller Power
Signal input command
(speed / position) ! Role of Electric Drive: Efficient conversion of power
from electrical to mechanical
! Role of PPU: Delivers appropriate form of frequency
to motor (as required by the load)
Exit 2001 by N. Mohan TOC " ! 1-5 World Market and Scope ! healthy growth rate
~ 25% per year
Exit 2001 by N. Mohan ! A very wide range of
speed and power
TOC " ! 1-6 Factors for Growth
❏ Technical Advances in
x Linear ICs and Digital Signal Processors
x Power devices
❏ Market Needs
x $20 Billion market in 1997
x 25% Growth rate
Exit 2001 by N. Mohan TOC " ! 1-7 Typical Applications
❏ Process Industry - agitators, pumps, fans, compressors
❏ Machining - planers, winches, calendars, chippers, drill
presses, sanders, extruders, grinders, mills, presses
❏ Heating and Air Conditioning - blowers, compressors
❏ Paper and Steel Industry - hoists, rollers
❏ Transportation - elevators, trains, automobiles
❏ Textile - looms
❏ Packaging - shears
❏ Food - conveyors, fans
❏ Oil, Gas , Mining - compressors, pumps, cranes, shovels
❏ Residential - heat pumps, freezers, washing machines
Exit 2001 by N. Mohan TOC " ! 1-8 Application for Energy Conservation
❏ Heat Pumps and air-conditioners - cycled operation
ideal loss actual Compressor
Output t ON OFF ! 30% improvement in efficiency by running
compressor at appropriately reduced speed
using an ASD
Exit 2001 by N. Mohan TOC " ! 1-9 Energy Conservation in Pumps
valve Pressure (H) outlet
H 2 + ∆H motor A ( H 2 + ∆ H , Q2 ) ( H 1 , Q1 ) H2
Q2 full speed inlet pump pump C ( H 2 , Q2 )
Pump curve at
reduced speed Q2 Pressure across
throttling valve, ∆H Unthrottled
Curve H2 reduced
speed Pump curve at
full speed B Throttled
Curve outlet no throttling
(ASD) D inlet Q2
0 Q2 Q1 Flow Rate (Q) x Throttling introduces extra pressure drop, ∆H
x ASD reduces pump speed to match load requirement
Exit 2001 by N. Mohan TOC " ! 1-10 Energy Conservation in Blower Systems Outlet damper 100 80 Power Consumption
(% of full flow rate) Inlet vane 60
40 Electric drive
100 90 80 70 60 50 40 30 % Flow Rate ❏ Relative power consumption using three methods
to reduce blower flow rate
Exit 2001 by N. Mohan TOC " ! 1-11 Harnessing Wind Energy
AC Utility Wind turbine Exit 2001 by N. Mohan TOC " ! 1-12 Hybrid Electric Vehicles IC
Engine Continuously Variable
Motor Exit 2001 by N. Mohan TOC " ! 1-13 Multi-disciplinary Nature of Electric Drives
Drives Sensors Mechanical
modelling Exit 2001 by N. Mohan Power
DSP control TOC " ! 1-14 Evolution of Power Processing Unit
Size (volum e) 60 Weight 40
Com ponents 100 Functions 50 Year 1998 1998 1993 1988 1988 1968 1983 0 0 1968 % 80 Relative unit 120 Year 4kW Danfoss VLTR power processing unit Exit 2001 by N. Mohan TOC " ! 1-15 Summary
• What is an electric drive? Draw the block diagram and
explain the roles of its various components.
• What has been the traditional approach to controlling flow
rate in the process industry?
• What are the major disadvantages which can be overcome
by using adjustable speed drives?
• What are the factors responsible for the growth of the
adjustable-speed drive market?
• How does an air conditioner work?
(Consult a handbook such as .)
• How does a heat pump work?
• How do ASDs save energy in air conditioning and heat
2001 by N. Mohan ! 1-16 Summary
❏ What is the role of ASDs in industrial systems?
❏ There are proposals to store energy in flywheels for load
leveling in utility systems. During the off-peak period
for energy demand at night, these flywheels are charged
to high speeds. At peak periods during the day, this energy
is supplied back to the utility. How would ASDs play a role
in this scheme?
❏ What is the role of electric drives in electric transportation
systems of various types?
❏ List a few specific examples from the applications mentioned
in section 1-4 that you are personally familiar with.
❏ What are the different disciplines that make up the study
and design of electric-drive systems?
Exit 2001 by N. Mohan TOC " ! ...
View Full Document
- Fall '06
- Electric motor, Variable-frequency drive, Adjustable-speed drive, N. Mohan