Elevator Drives
Past, Present and Future
As Presented
at
NAVTP Annual Forum
Atlanta, Georgia
May 3, 2007
Elevator Drives - Discussion
 History
 Requirements
 Motor and Control Types
 Industry Trends
 Future Drives
History
 236 BC – First Passenger Lift,
Archimedes
 1853 – Safe Elevator Demo,
Elisha Otis
 1857 – First Safe Elevator
Installation,
Cooper Union, NYC
 1861 – Otis Elevator Patent
Otis Patent 1861
History
 1873 – First Modern DC Motor
 1874 – J. W. Meaker Door Opener Patent
 1880 – First Electric Motor Controlled
Elevator Siemens / Sprague
 1882-1889 – Tesla AC Induction Motor
3-Phase Squirrel Cage Design
 1889 – Otis Elevator Uses DC Motor
Otis
DC
Elevator
Motor
Circa 1889
History
 1891 – Ward Leonard Variable
Speed Control
– AC Induction Motor Turning DC Dynamo
– Rheostat to Control Generated Voltage
– DC Voltage Controls DC Motor Speed
 1900-1970’s – Ward-Leonard M-G Sets
and DC Motors Used for
Variable Speed Elevators
 AC Motors Used 1 and 2 Speed Starters
Otis No. 1 Geared DC Machine
with DC Motor
Circa 1915
Otis Gearless DC Machine
Circa 1919
M-G Set Controls
(Otis Elevator, 1920’s)
Otis Type 84
26 Broadway,NYC
Circa 1930’s
History
 1975-Present
– Thyristor (SCR) DC Drives
Control Elevators
– All Analog Components in the 70’s
– Replaces Aging M-G Sets
 1980’s – Microprocessors Improve
– Car Dispatch and Motor Drive Controllers
Otis type 84,NYC
with Encoder
Westinghouse #205
with Encoder
History
 Late 1980’s –
– Variable Frequency Inverters AC Induction
Motors, Geared Applications Only
 Early 1990’s –
– More AC Inverters and Motors Begin to Displace
Small DC, 3-15 HP
 Mid-1990’s –
– Vector Control AC Inverters 10-40 HP Almost as
Good as SCR-DC.
– KONE Introduces PM EcoDisc AC Machine
History
 Late 1990’s –
–
–
–
–
Custom Gearless AC Induction Machines
First Fully Regenerative AC
Elevator Drives
Much Discussion on PM-AC and MRL
SCR-DC Still Used for Medium and
Large Building Mods
History
2000-Present –
–
–
–
–
–
–
More PM-AC Motor Manufacturers. PM Gearless
Begins to Replace AC Geared
EU Focus on Efficiency and Harmonics/EMC
Lower Cost IGBT Inverter Components
North America Begins to Focus on Energy Reduction
New Construction Leaning toward AC
SCR-DC Still Used on Medium-Large Building Mods
Elevator Drive
Requirements
Elevator Duty Cycle
2.5
P
O
W
E
R
K
I
L
O
W
A
T
T
S
FULL CAR
EMPTY CAR
1.0
0
-1.0
-2.5
EMPTY CAR
FULL CAR
Four Quadrant Operation
What Customers Want
 Repeatable Elevator Performance
 Smooth Operation
 Reliable Operating Life
 Effortless Installation
 Custom Control Interface
 High Efficiency
 Conformance to All Codes
 Low Installed Cost
Elevators vs. Industrial Applications
 Infinitely Variable Speed Range
 Infinitely Variable Torque Range with
Smooth Bump Less Operation
 Millions of Repeated Operating Cycles
with High Peak Torque
 High Inertia Resonant Load
 Accurate Stopping Position
 Unattended Operation 24/7/365
Elevators vs. Industrial Applications
 Quiet Operation
 Long Operating Life
 Long-Term Product Support
Types of Motors
 DC Shunt Field
– High Speed Geared
– Low Speed Gearless
– Full HP Range 5 – 600 HP
– 89–94% Efficient
– High Torque Capacity Accel/Decel
– In Elevator Service for 70+ Years
– Requires DC Generator, SCR or Other AC-DC
Power Conversion from AC Utility Power
– DC Motor Can Act Like a Generator
Types of Motors
 AC Induction
–
–
–
–
–
High Speed Geared, 2–75 HP
Few Low Speed Designs for Gearless
85–94% Efficient
Many with Single or 2 Speed Starters
Can be Variable Speed by Inverter Control
of Frequency
– Torque Strength Derived from Out of Phase
Excitation Current
– Requires Flux Vector Control for Wide
Operating Speed Range
– Can Act Like a Generator
Types of Motors
 AC Permanent Magnet (PM)
– New Designs for Compact Gearless Machines
– Torque Strength from Permanent Magnets
– 90–95% Efficient
– Compatible with Inverters to Control Speed
– Requires Synchronous Flux Vector / Angle Control
to Regulate / Modulate Torque
– Supply Limited to Specialty Machine Builders
– Not Suitable for High rpm Speed Geared Designs
– Can Act Like a Generator
Modernization
 Why keep a DC machine?
– Many large DC machines cannot be
easily replaced with AC.
– Large Installed Base of DC Machines
Worldwide
– DC Motors and Machines are in Good
Working Order and Provide Excellent
Ride Quality
Large DC Machines
Otis 72
and 269
Types of Motor Drives
For DC Motors
For AC Motors
 M-G Set
 SCR-DC
 PWM-DC
 Variable Voltage
 V V V F Inv. (V/Hz)
Open/Closed Loop
 Vector Control Inv.
Open/Closed Loop
 Synchronous PM Inv.
Closed Loop
 Regen or Non-Regen
Elevator Power Consumption
…the need for Regeneration
 Horsepower = Torque x Speed
 Gearless Friction Losses are 10-20% of Elevator
HP Rating
 Moving inertia absorbs energy during acceleration
that must be removed during deceleration.
 Mechanical, electric and electronic losses are
proportional to torque or current flow.
 Energy Wasted / Dissipated During Deceleration
= Heat
 Excessive heat in control rooms must be removed.
Practical Energy Considerations
 Low Speed Elevators 50–150 fpm
– Almost Always Geared… or PM Gearless
– Low Speed Usually Means Low Power
2-35 HP / 2-25 kW
– Most power is consumed by frictional losses.
– True regeneration is not critical.
– High Gearbox Losses During Regeneration
– Drive type makes little difference in overall
energy consumption.
– If DC, Good Candidate for Conversion to AC by
Replacing Motor
– Low Installed Cost is Usual Critical Issue
Practical Energy Considerations
 Medium Speed Elevators 150–450 fpm
– Geared and Some Gearless… Including PM
– 15-60 HP / 12-45 kW
– Lower Frictional Losses in Gearbox
– Recovery of inertia energy becomes important,
particularly with gearless.
– Resistive Braking Still Possible but Need to Perform
Heat Load Calculations for Equipment Room
Practical Energy Considerations
 High Speed Elevators 500-1,600+ fpm
– Low Friction Gearless
– 45-600 HP / 34-450 kW or Larger
– True Regeneration is Mandatory
Industry Trends
 Energy Consumption Reduction
– kW-hrs / Month
– Harmonics, Power Factor
 Performance
– Reduced Floor–Floor Time
– Reduced Vibration
 Low Maintenance
– Cleanliness
 Larger PM Machines
– More Gearless Applications
Energy Consumption
 Elevator Speed and Payload
 Frequency of Use
 Hoist Way Efficiency
 Motor Efficiency
 Power Conversion Efficiency
 Idle Losses
 Regeneration
Drive Type Comparison
Desired
Feature
Diode –
SCR-DC PWM Inv
Installed
Cost
PWM PWM

Smallest
vol. Wt.
External
XFMR
Pwr conv
efficiency
90%
w/ XFMR

93-96%
92-94%
Drive Type Comparison
SCR-DC
Diode –
PWM Inv
PWM PWM
Regeneration

No

Low
Harmonics
No
No

Unity
Pwr Factor
No
No

Desired
Feature
Drive Type Comparison
SCR-DC
Diode –
PWM Inv
PWM PWM
Flexible
Motor V
With
XFMR
Below
Vac input

Stand-by
Friendly
No


AC / DC
Motor
No
No

Desired
Feature
Future Expectations
 More PM Gearless
– Low and High Power
 More Interest in Energy Conservation
– Overall Efficiency
– Regeneration
 More Restrictions on Harmonics and EMC
– Sinusoidal High pf Utility Line Current
– All Inclusive Drive Units with Filters
Future Elevator Drives
 PWM-PWM Double Converter-Inverter
– Regulated Harmonics
– Unity pf
– Fully Regenerative
– Compatible with DC Stand-by Power
 PM Operation without Resolver
– Electronic Alignment Sensing
 Compact All Inclusive Packaging
 Works with AC Ind. or PM or DC Motors
World’s Tallest Buildings
Magnetek has Elevator Drives in 17 of
the 30 tallest buildings in the world.