LOT 30
ECO-DESIGN OF ELECTRIC MOTORS
Final Meeting
Anibal De Almeida
ISR – University of Coimbra
Brussels, February 10, 2014
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Task 6
Technical Analysis of BAT
Provides general inputs for the identification of
improvement potential when compared to the
BaseCases.
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Small induction motors – IR2 Losses
• Increasing the cross-section of stator windings - This
modification is where the largest gains in efficiency are
achieved. High efficiency motors typically contain
about 20% more copper than standard efficiency
models of equivalent size and rating.
• Increasing the cross-section of the rotor conductors.
• Use copper rotor bars – Due to the excellent electrical
conductivity of copper (57 MS/m compared to 37
MS/m), replacing the aluminium in a rotor's conductor
bars with die-cast copper can produce a significant
improvement in the efficiency of an electrical motor.
• Increase size of the end rings.
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Small induction motors – IR2 Losses
• Reduce rotor bar skew - rotor bars are slightly skewed
which helps reduce harmonics Reducing the skew will help
reduce the rotor resistance and reactance, thereby
providing gains in efficiency. However, care must be taken
not increase harmonics. Odd harmonics, particularly the
third harmonic, can originate cogging.
• Reduce the air gap between the stator and rotor - A smaller
air gap lowers the magnetizing current the motor draws to
maintain the magnetic field across that gap. The motor will
then require less current to drive the load and thereby
reduce I2R losses.
• For single-phase motors, adding a secondary “run”
capacitor
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Small induction motors - Magnetic losses
• Lengthening the lamination stack - reduces the flux
density within the stack, therefore reducing core
losses.
• Use of magnetic steel with better magnetic properties
hysteresis losses and Eddy currents are reduced
because the resistivity of the laminations is higher,
reducing the magnitude of the currents.
• Reduce the laminations’ thickness - using thinner
laminations decreases the cross-sectional area through
which the eddy currents are produced, reducing the
magnitude of the eddy currents.
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Small induction motors - Magnetic losses
• Ensuring adequate insulation between laminations,
thus minimizing the flow of current (and I²R losses)
through the stack and reducing eddy current losses.
• Annealing the core steel - After being annealed, the
material becomes much easier to magnetize, which
means the magnetic domains reorient more easily
reducing hysteresis losses.
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Small induction motors - Mechanical losses
• Use low friction bearings – These bearings take advantages
of better geometry, materials and lubricant to reduce
friction by more than 30% when compared to standard
bearings
• Improved cooling – properly designed cooling systems, such
as optimized fans, can help reduce ventilation losses.
Improved air flow can also help reduce the power required
to move the fan.
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Small synchronous PM Motors
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Small synchronous PM Motors
Source: „Untersuchungen zur Energieeffizienz von Ventilatorsystemen“ (Analysis about the energyefficiency of ventilator
systems)
Institute of Air Handling and Refrigeration (ILK), Dresden/Germany, Fachbericht ILK-B-31-13-3839, Dated 24th June.2013
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Super-Premium Motors
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LSPM
• Hybrid motor with squirrel cage rotor fitted
with high energy permanent magnets (NeFeB)
making it suitable for direct on line start
• Interchangeable with induction motors (same
output x frame ratio) and similar starting
torque
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LSPM
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LSPM
• It is worth noting that the starting “kick” of
LSPMs is quite violent, which can lead to
accelerated mechanical wear of the motor and
load bearings and/or gears (if any). This can be
particularly critical in application with
frequent start/stop cycles.
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Medium Synchronous PM Motors
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Medium Synchronous PM - Motors
Part-Load Efficiency
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Switched Reluctance Motors
An SR motor is a doubly salient design
with phase coils mounted around
diametrically opposite stator poles.
Energisation of a phase will cause the
rotor to move into alignment with the
stator poles, so minimizing the
reluctance of the magnetic path. As a
high performance variable speed drive,
the motor's magnetics are optimized for
closed-loop operation. Rotor position
feedback is used to control phase
energisation in an optimal way to
achieve smooth, continuous torque and
high efficiency.
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SR Motor: Rotor
• Simple and robust laminated steel construction: no brushes,
windings, rotor bars or magnets
• Minimal losses in rotor
– no cage or rotor bars
– indefinite stall possible, no limit to frequency of starts
– reduced shaft temperatures and prolonged bearing life
The simple SR Drive® rotor has many
advantages over conventional types
which utilise magnets or conductors
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SR Motor: Stator
• No magnets: straightforward laminated iron construction
• Simple coil windings: absence of phase overlaps significantly
reduces the risk of inter-phase shorts
• Compact and short coil overhangs make efficient use of active
coil area
Compact end-windings permit
construction of high-performance
motors with unusually flat aspect
ratios.
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SR Motor
• APPLICATIONS UP TO 75 kW: High speed centrifugal
machines, compressors, washing machines, vacuum
cleaners, vacuum pumps, HVAC, variable-speed drive
systems, machine-tools, automation, traction, etc.
Torque Speed Curve
T(N.m)
ideal
a
c
b
n(rpm)
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Synchronous Reluctance Motors
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Synchronous Reluctance Motors
The rotor design eliminates rotor I2R losses. These
motors require an electronic controller (VSD) to operate.
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Synchronous Reluctance Motors
Potential efficiency increase due to rotor
loss reduction in SynR Motors
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Synchronous Reluctance Motors
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VSD Efficiency
Typical percent of losses for
passive front-end converters
30 to 50
Factors affecting these losses
Line-rectifier
20 to 25
Forward losses (output stage)
Internal control circuit
Losses (microcontroller, internal
power supply, display,
keyboard, buscommunication,
digital and analogue ins/outs…)
15 to 20
5 to 20
losses Line-current
(nearly proportional to motor
power).
Motor current.
Nearly constant.
Switching losses (line-side
converter / active front-end only)
-
Compound losses
(line-side converter / active frontend only)
-
Switching losses
(output stage)
Motor-current and switchingfrequency.
Line-current and switchingfrequency
(nearly proportional to motor
power).
Line-current
(nearly proportional to motor
power).
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VSD Efficiency
• VSD losses are mainly influenced by the switching
frequency (the higher the switching frequency, the
higher the losses in the drive) and the output current
(which is function of output power and load). However
low switching frequency can cause torque ripple.
• Transistors - IGBTs (Insulated Gate Bipolar Transistors)
and MOSFETs (Field Effect Transistors) - have nearly
completely replaced thyristors in inverter circuits
below 1 MW. Overall losses, parts count, and driver
cost are markedly reduced with these devices resulting
in an increasingly competitive product.
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VSD Efficiency
It must be noted that the energy benefits from using a
VSD always come from decreasing the losses of the
system on the load side and that if this benefits can be
achieved they surpass the losses in the drive itself.
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Harmonic Generation within VSDs
Typical input current waveform for a 1.5 kW three-phase drive (with supply
voltage) and corresponding harmonic spectrum
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Harmonic Generation within VSDs
Typical input current waveform for a 1.5 kW single-phase drive (with supply
voltage) and corresponding harmonic spectrum
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Harmonic Losses
• Motors fed from a converter present
additional losses, higher than during
operation on a sinusoidal system. These
additional losses depend on the harmonic
spectrum of the impressed supply quantity
(either current or voltage) from the converter.
• Additionally, harmonics may cause significant
damage to the motor by producing bearing
currents and insulation voltage stress.
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