Chapter 1 Introduction to Electric Drive Systems
© 2000 http://www.ece.umn.edu/groups/electricdrives
1-1
History o Constant frequency AC - essentially constant pump speed o Inefficient - Heat generated in pump and throttling valve o Not amenable to automation Throttling Valve
Outlet
MOTOR Inlet Constant frequency AC
© 2000 http://www.ece.umn.edu/groups/electricdrives
⇒
Essentially Constant Speed
Pump
1-2
Trend : Adjustable Speed Drives (ASDs) Outlet Adjustable Speed Drive (ASD) Constant frequency AC
Inlet Adjustable fequency electric converter
Adjustable Pump speed
o Driven at appropriate speed u High Efficiency
© 2000 http://www.ece.umn.edu/groups/electricdrives
1-3
What is an Electric-Motor Drive? Electric Drive
fixed form
Power Processing Unit (PPU)
Motor speed / position
adjustable form
Electric Source (utility)
Load
Sensors measured speed/ position
Controller
Power Signal
input command (speed / position)
w Role of Electric Drive: Efficient conversion of power from electrical to mechanical w Role of PPU: Delivers appropriate form of frequency to motor (as required by the load) © 2000 http://www.ece.umn.edu/groups/electricdrives
1-4
World Market and Scope
w healthy growth rate ~ 25% per year
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w A very wide range of speed and power
1-5
Factors for Growth o Technical Advances in u Linear ICs and Digital Signal Processors u Power devices o Market Needs u $20 Billion market in 1997 u 25% Growth rate
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1-6
Typical Applications o Process Industry - agitators, pumps, fans, compressors o Machining - planers, winches, calendars, chippers, drill presses, sanders, extruders, grinders, mills, presses o Heating and Air Conditioning - blowers, compressors o Paper and Steel Industry - hoists, rollers o Transportation - elevators, trains, automobiles o Textile - looms o Packaging - shears o Food - conveyors, fans o Oil, Gas , Mining - compressors, pumps, cranes, shovels o Residential - heat pumps, freezers, washing machines © 2000 http://www.ece.umn.edu/groups/electricdrives
1-7
Application for Energy Conservation o Heat Pumps and air-conditioners - cycled operation ideal loss
actual
Compressor Output
t ON
OFF
w 30% improvement in efficiency by running compressor at appropriately reduced speed using an ASD © 2000 http://www.ece.umn.edu/groups/electricdrives
1-8
Energy Conservation in Pumps throttling valve
Pressure (H)
outlet Q2
A
∆H H 2 + ∆H H 2
motor
( H2 + ∆H , Q2 )
( H1 , Q1 )
Q2 full speed
inlet
pump
no throttling valve Adjustable Speed Drive (ASD)
D
pump
( H2 , Q2 ) Pump curve at reduced speed
Q2
Pressure across throttling valve, ∆H
Unthrottled System Curve
H2
reduced speed
C
Throttled System Curve
outlet
Pump curve at full speed
B
inlet
Q2 0
Q2
Q1
Flow Rate (Q)
u Throttling introduces extra pressure drop, ∆H u ASD reduces pump speed to match load requirement © 2000 http://www.ece.umn.edu/groups/electricdrives
1-9
Energy Conservation in Blower Systems Outlet damper
100 80
Power Consumption (% of full flow rate)
Inlet vane
60 40
Electric drive 20 0 100
90
80
70
60
50
40
30
% Flow Rate
o Relative power consumption using three methods to reduce blower flow rate © 2000 http://www.ece.umn.edu/groups/electricdrives
1-10
Harnessing Wind Energy Variable wind
Variable speed
Wind turbine
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Variable speed generator
Variable Frequency AC
Power Processing Unit
Constant frequency AC
Utility
1-11
Hybrid Electric Vehicles
IC Engine
Continuously
Variable
Transmissio n
Electric
Motor
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1-12
Multi-disciplinary Nature of Electric Drives Machine Theory
Utility Interaction
Electric Drives
Sensors
Mechanical system modelling
© 2000 http://www.ece.umn.edu/groups/electricdrives
Power Electronics
Control Theory
Real-time DSP control
1-13
Evolution of Power Processing Unit 200
100 Size (volume)
60
Weight
40 20
150 Components
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
© 2000 http://www.ece.umn.edu/groups/electricdrives
1-14
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 [10].) • How does a heat pump work? • How do ASDs save energy in air conditioning and heat pump systems? © 2000 http://www.ece.umn.edu/groups/electricdrives
1-15
Summary o What is the role of ASDs in industrial systems? o 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? o What is the role of electric drives in electric transportation systems of various types? o List a few specific examples from the applications mentioned in section 1-4 that you are personally familiar with. o What are the different disciplines that make up the study and design of electric-drive systems? © 2000 http://www.ece.umn.edu/groups/electricdrives
