Download High efficiency electric drives for EV

Erasmus LLP Intensive Programme
High efficiency electric
machines for EV
Associated professor
Phd Jonas Valickas
KUT, Panevėžys division
[email protected]
Powering the Future With Zero Emission and Human Powered Vehicles – Terrassa 2011
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References
1. Efficiency trends in electric machines and drives B.C.
Mecrow, A.G. Jack;
2. Theodore Wildi. Electrical Machines, Drives, and
Power Systems. Sixth Edition. Pearson Prentise Hall.
2006. 934 p.
3. Vedam Subrachmanyam. Electric Drives. USA.
McGraw – Hill. 2006. 715 p.
4. William Bolton. Mechatronics. Pearson Education
Limited. Forth edition. 2008. 593 p.
Powering the Future With Zero Emission and Human Powered Vehicles – Terrassa 2011
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Electric Engine History
 The first car electric engine was made by
James Starley in 1888.
(was an English inventor and "Father of the Bicycle
Industry." )
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Electric Engine History
 First satisfactory results were achieved by Raeford
and Jantoe only in 1893.
 They constructed an automobile with two batteries
located in the rear; Each of them was 200Ah with total
weight 420 kg.
 The engine power amounted 2.5 kilowatt by 1300 rpm.
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Electric Engine History
 By 1912 there were about 20 thousands automobiles
with electric drive.
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Electric cars history
1935 - 1960
dead years for electric vehicle development and for use
as personal transportation.
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Electric cars history
The CitiCar was produced between 1974 and 1977
by a U.S. company called Sebring-Vanguard, Inc. ,
based in Florida.
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Electric cars motors
 Electric cars are driven by large electric motors usually
rated between 3.5 and 40 horsepower.
1 horsepower = 745.699872 watts
The rating systems used for gas engines and electric
motors are so different.
Gas engines are rated at their peak hp.
Electric motors are rated at their continuous hp.
The peak hp of an electric motor is usually 8
to 10 times its continuous rating.
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Classification
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Electric cars motors
Electric vehicle drive motors can be
divided into two basic groups:
 DC or direct current motors;
 AC or alternating current motors.
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DC motors
 Have a long history in EV use
 The most commonly used version is what is known as
- series-wound motor, which means the armature and
field windings are wired in series;
- shunt-wound motors;
- compound-wound motors;
- permanent magnet motors.
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AC motors
At the present time AC motors are most commonly
found in commercially built EVs.
An important condition:
They require more sophisticated and
systems than DC motors.
complex control
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What is a motor efficiency?
Electrical motor efficiency (ηm) is the ratio between the
shaft output power - and the electrical input power.
If power output is measured in Watt (W),
efficiency can be expressed as:
ηm = Pout / Pin
where:
ηm = motor efficiency
Pout = shaft power out (Watt, W)
Pin = electric power in to the motor (Watt, W)
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Power in rotational motion (Pout )
Power in rotational motion (Pout ) can be written as:
Pout    ,
where:
τ - torque (moment);
ω - rotational speed or angular velocity.
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Torque (moment)
 Torque, also called moment or moment of force is
the tendency of a force to rotate an object about an
axis.
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Rotational speed or angular velocity
 When we supply the specified voltage to a motor, it
rotates the output shaft at some speed. This rotational
speed or angular velocity, is typically measured in
radians/second {rad/s}, revolutions/second {rps},
or revolutions/minute {rpm}.
1 revolution = 360°
1 revolution = (2*π) radians
1 radian = (180/π)°
1° = (π/180) radians
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Electrical power (Pin)
Pin  V  I ,
where:
power Pin is in watts (DC);
voltage V is in volts;
current I is in amperes.
If there is AC, look also at the power factor
PF = cos φ , where φ = power factor angle
(phase angle) between voltage and current.
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Power units
 UNITS of POWER SI English Watts {W}
newton-meters per second {N·m/s}
1 W = 1 N·m/s
1 W = 0.738 ft·lb/s
1 W = 1.341E-03 hp foot-pounds per second {ft·lb/s}
horsepower {hp}
1 ft·lb/s = 1.818E-03 hp
1 ft·lb/s = 1.356
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Electric motors
Motors are devices that convert
electrical energy into mechanical
energy.
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Lorentz force
 The Lorentz force is the force on a point charge due to
electromagnetic fields. It is given by the following
equation in terms of the electric and magnetic fields:
where:
F is the force (in newtons)
E is the electric field (in volts per
metre)
B is the magnetic field (in teslas)
q is the electric charge of the particle
(in coulombs)
v is the instantaneous velocity of the
particle (in metres per second)
× is the vector cross product
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Fleming's left hand rule (for electric motors)
shows the direction of the thrust on a
conductor carrying a current in a magnetic
field.
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DC ( Direct - current) MOTORS
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Two-pole DC Motor Rotation
(Permanent magnet DC motor)
When the coil is
powered, a magnetic
field is generated
around the armature.
The left side of the
armature is pushed away
from the left magnet and
drawn toward the right,
causing rotation.
When the armature becomes
horizontally aligned, the
commutator reverses the
direction of current through
the coil, reversing the
magnetic field. The process
then repeats.
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DC motors design
A: shunt
B: series
C: compound
f = field coil
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Permanent Magnet DC Motor
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DC Motor with wound stator
The most popular brands of DC motors for EVs are Advanced DC and NetGain.
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Brushless DC Motor
 As such they have no commutator, and tend to be more
efficient and more powerful than commutated motors.
They do require a more complicated motor controller,
although as the technology matures and costs come
down they are becoming increasingly popular,
particularly for smaller EV.
 The main disadvantage for EV use is the cost of the
large permanent magnet(s) required for the rotor,
and the added expense of the speed controller.
Unfortunately, at prasent there are no economically
viable BLDC options available for EV use.
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Brushless DC Motor
("in-runner" type)
Two example manufacturers currently producing good
brushless motors are UQM and Aveox.
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DC motor speed –torque
characteristics
maximum power occurs at the point
where
=½
, and
=½
.
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DC motors speed control
Speed of the DC motor is directly proportional to armature supply:
60 Ea
n
,
Z
where:
- n – speed of rotation ( r/min);
- Ea – armature voltage (V);
- Z – total number of armature conductors;
- Ф magnetic flux per pole.
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Stopping of DC motors
 Dynamic bracing;
 Plugging ( reversing the direction of rotation).
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DC Motors application features
 There are four main types of DC motor, namely permanent
magnet, series, shunt and seperately excited.
 Currently series DC are the most economical and commonly used
type of motor in electric vehicles.
 Being a tried-and-tested technology, they are actually quite good
– with efficiencies up to 90% and only needing servicing every
100,000kms or so.
 However using a commutator is restrictive and a source of
inefficiency. Also, with series DC motors regenerative braking is
very difficult to do.
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AC motors
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AC motors
 In 1882 Nikola Tesla identified the rotating magnetic
induction field principle used in alternators and
pioneered the use of this rotating and inducting
electromagnetic field force to generate torque in
rotating machines. He exploited this principle in the
design of a poly-phase induction motor in 1883. In
1885, Galileo Ferraris independently researched the
concept. In 1888, Ferraris published his research in a
paper to the Royal Academy of Sciences in Turin.
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,,Cage – rotor” inventor
 Mikhail Osipovich Dolivo-Dobrovolsky
Michail Osipovich Dolivo-Dobrovolsky
invented a three-phase "cage-rotor" in
1890. This type of motor is now used
for the vast majority of commercial
applications.
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Diagram of the squirrel-cage
(showing only three laminations)
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Stator and rotor
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Vector sum of the magnetic field vectors of the stator
coils produces a single rotating vector of resulting
rotating magnetic field
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Sine wave current in each of the coils produces sine
varying magnetic field on the rotation axis. Magnetic
fields add as vectors.
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Magnetic field vectors of the stator
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Rotor magnetic field production
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AC Induction Motor
The most popular brands for AC induction motors suitable for EVs are Siemens
and Azure Dynamics.
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Slip
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NEMA
 NEMA -National Electrical Manufacturers Association
 NEMA is responsible for several electric motor industry
"standards"
 ►Motor ratings (1/4 hp, 1/2 hp, 1 hp, etc.)
 ►Frame size
 diameter, length, shaft size, etc.
 ►Service factors
 ►Housing/protection types and ratings
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Characteristics of the different design
of the motor
The torque-speed characteristic of an induction motor can be significantly
changed by designing different resistance values within the rotor bars. Figure
shows the impact of different rotor resistance values.
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Typical torque - speed curve of a 3
phase squirrel-cage induction motor
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AC motors speed control
AC motor shaft rotation speed can being calculated:
n  n0 (1 - s)  f(1 - s)/p
where:
120 f
n0 – synchronous speed, r/min; n0 
p
s – slip;
f – AC current frequency, Hz;
p – the number of pairs of motor poles.
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Stopping of DC motors
Plugging ( reversing the direction of rotation).
Dynamic bracing;
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The efficiency of an electrical
machine
The efficiency of an electrical machine is a complex
function of:
 machine type,
 size,
 speed of operation,
 loadings,
 materials,
 operating regime.
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How to increase efficiency?
 Variable-speed drives are created when a motor is
combined with a power electronic converter.
 By introducing variable speed to the driven load, it is
possible to optimise the efficiency of the entire system,
and it is in this area that the greatest efficiency gains
are possible.
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Understanding Regeneration
Electrical motors are reversible machines; they
can function as motors or as generators.
A motor receives electrical power from a
battery and transforms it in torque developing a
Counter Electromotive Force CEMF, which
opposes the battery.
A generator receives mechanical power from a
mechanical actuator and transforms it in
electrical power developing a Counter Torque,
which opposes the actuator.
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Electric motors efficiency
 Induction fixed-speed motor efficiency typically ranges
is 76.2%;
 Commutator machines efficiency is typically 50% or
less
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The principal sources of loss in a
induction machine are:
Stator winding loss. It is the dominant source of loss in small machines. It comprises around 60% of the
total full-load loss in the sub-1kW range, falling to 25% at 1MW and above.
lamination iron loss. It rice due to hysteresis and eddy currents, which accounts for approximately 20%
of full-load loss. This loss does not generally decrease during operation at reduced load.
Rotor winding loss. It is due to losses in the aluminium cage rotor, which are strongly load-dependent
and amount to approximately 20 % of full-load loss.
Stray losses. Are due to a number effects, including induced eddy currents in the stator frame.
These are insignificant in machines of less than10kW.
Friction and windage. includes bearing loss, which is less than 5% of total loss in machines
of 10kW
European CommissionJointResearchCentreonElectricMotorEfficiency,2004:
/http://re.jrc.ec.europa.eu/energyefficiency/S (accessed June2008).
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Motor energy balance flow diagram
Air gap
Input power
Psup
Air gap
power Pag
Developed power
Pdev=3Irot2Rrot(1-s)/s
Output power
Pout
Ventilation
and
friction losses
Rotor Copper loss
3 Irot2 Rrot
Stator Copper loss
3Ista2Rsta
Stator Iron loss
3 Vsta2/Rc
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Future advances to 2050 and
beyond
 The function of an electrical drive is to transfer electrical energy to
mechanical energy and vice versa.
 This is currently achieved almost exclusively via a magnetic field.
Question is: ‘‘Are there any new processes of energy conversion
that may replace this method in the next one hundred years?’’
The answer is simple: none are known of at the time of writing.
Competing systems, such as electric fields are several orders
of magnitude less power-dense or, in the case of ultrasonic
motors, very inefficient.
Electric motors will continue to use the same basic concepts for
the foreseeable future.
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Key challenges:
 increase the adoption of variable-speed, high-efficiency
systems, with a revision of efficiency bands and
possibly legislation replacing voluntary agreements;
 extend the application areas of variable-speed drives
through reduction of power electronic and control costs;
 integrate design of the drive and the driven load to
maximise system efficiency;
 increase the efficiency of the electrical drive.
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Drive efficiency improving
The key to improving motor efficiency lies in new
materials and construction methods.
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Winding loss reduction
Winding loss is reduced by increasing the conductivity of the winding.
In the case of induction machines, recent advances in production
methods are starting to allow the replacement of aluminium rotor
cages with copper reducing machine losses by around 8–10%
 Copper is already used for stator windings and is unlikely to be
replaced by a more conductive material at room temperature.
 Superconducting electrical machines have been researched for
over 30 years, but with the advent of high-temperature
superconductors, they are now close to introduction.
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Iron loss reduction
Air-gap windings are employed, with an ironless stator,
thereby also eliminating iron loss.
However, substantial eddy currents are induced in
the AC windings because they sit in the full
magnetic field.
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Eddy current losses reduction
Current losses in the soft iron material of a machine’s
core can be reduced by either increasing the resistivity
of the core material or reducing the amount of flux,
which eddy currents can enclose.
The former is achieved by the introduction of up to 6%
silicon into the lamination material, which also reduces
the coercivity and hence hysteresis loss.
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Amorphous iron
 Amorphous iron reduces the thickness of the
laminations and therefore the eddy current loss.
 Because of the crystal structure resulting from very
rapid cooling, the hysteresis loss is also exceptionally
low.
 However, the material is expensive to produce and
limited in flux density.
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Soft magnetic composites
 Soft magnetic composites replace the laminations with100 μm
diameter iron particles,which are pressed together.
 This material has very low eddy current loss, but current products
have greater hysteresis loss.
 Soft magnetic composites have, however, been shown to offer
significant efficiency gains because of their three-dimensional
shaping properties.
 New tooth shapes are possible, with much shorter winding lengths,
thereby reducing winding loss.
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Hysteresis loss diminution possibility of
the soft magnetic composites
 Future soft magnetic composites will incorporate
special high-temperature powder coatings, which will
lower hysteresis loss and make the material more
attractive for energy-efficient systems.
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Electromagnetic design tools
 Electromagnetic design tools have advanced greatly
with the application of the finite element method.
 Greater understanding of stray loss mechanisms is
required at the design stage
Improved understanding and modelling of iron loss
mechanisms within the machine are also needed to
replace the empirical scaling that continues to be
adopted by manufacturers
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Key engineering and scientific
advances are required:
 1. New soft magnetic materials giving lower iron loss at low cost;
 2. Low-cost, high-temperature, high-energy magnets;
 3.High-temperature insulation and magnets sytems (>400˚C).
 4. New construction methods, including segmented stators, and
cast copper rotors where appropriate.
 5. Bearing systems for ultra-high-speed operation. Reliable hightemperature superconducting designs at moderate cost.
 6. Improved design tools.
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Power electronics and control cost
reduction.
 New devices, materials and technology to produce
increased switching speeds and reduced conduction
drops.
 Increased integration.
 Reduced size of passive components.
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Electric dives trends in future
 In the future, electric drives will become integral to the
propulsion of road transport vehicles, and so the need
for maximising their efficiency will become even more
pressing than it is today
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,,For internal combustible engine the time for retirement!”
Thanks for attention
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Questions
 What types of motors used in EV ?
 How works DC motors ?
 How works an induction motors ?
 How to control the speed of the DC and AC motor ?
 How to stop DC and AC motor ?
 What is the motor efficiency ?