Unit 2

2.1Hybrid Electric Drive-trains

2.2Electric Drive-trains
• Hybrid Electric Drive-trains: Basic concept of hybrid
traction, introduction to various hybrid drive-train
topologies,( 2)power flow control in hybrid drive-train
topologies, fuel efficiency analysis. (2 hrs)

• Electric Drive-trains: Basic concept of electric traction,

introduction to various electric drive-train topologies,
power flow control in electric drive-train topologies,
fuel efficiency analysis.(3 hrs)
 Basic concept of hybrid traction
--necessity---
1) develop sufficient power to meet the
demands of vehicle performance,
(2) carry sufficient energy onboard to support
vehicle driving in the given range,
(3) demonstrate high efficiency, and
(4) emit few environmental pollutants.
 Definition-hybrid vehicle
• Any vehicle that has two or more energy
sources and energy converters is called a
hybrid vehicle.
• A hybrid vehicle with an electrical power train
(energy source energy converters)is called an
HEV.
• More than two power train configurations will
complicate the system. because power flow is
different
 Different power flow
routes.
• a hybrid drive train usually has a bidirectional
energy source and converter.
• The other one is either bidirectional or
unidirectional.
• Figure 5.1 shows the concept of a hybrid drive
train and the possible different power flow
routes.
 9 Types of general power train-
hybrid traction
• There are many available patterns of combining the power flows to meet
load requirements as described below
1. Power train 1 alone delivers power to the load
2. Power train 2 alone delivers power to the load
3. Both power train 1 and 2 deliver power to load at the same time
4. Power train 2 obtains power from load (regenerative braking)
5 Power train 1 chargetheowertrain2duringideal
6. Power train 2 obtains power from power train 1 and load at the same time
7. Power train 1 delivers power to load and to power train 2 at the same time
8. Power train 1 delivers power to power train 2, and power train 2delivers power to
load
9. Power train 1 delivers power to load, and load delivers power to power train 2. :
 Pattern (1) and its function
• In the case of hybridization with a liquid fuel-
IC engine (power train 1) and a battery-
electric machine (power train 2),
• pattern (1) is the engine-alone propelling
mode.
• This mode may be used when the batteries
are almost completely depleted.
• Ic engine will meet the load
 Pattern (2)
• Pattern (2) is the pure electric propelling
mode, in which the engine is shut off.
• This pattern may be used in situations where
the engine cannot operate effectively, such
as very low speed, or in areas where emissions
are strictly prohibited.
 Pattern(3)
• Pattern(3) is the hybrid traction mode and
may be used when a large amount of
power is needed, such as during sharp
acceleration or steep hill climbing
 Pattern (4)
• Pattern (4) is the regenerative braking mode,
by which the kinetic or potential energy of the
vehicle is recovered through the electric
motor functioning as a generator.
• The recovered energy is stored in the batteries
and reused later on.
 Pattern (5)
• Pattern (5) is the mode in which the engine
charges the batteries while the vehicle is at a
standstill, coasting(moving with out power), or
descending a slight grade, in which no power
goes into or comes from the load.
 Pattern (6)
• Pattern (6) is the mode in which both
regenerative braking and the IC engine charge
the batteries simultaneously.
 Pattern (7)
• Pattern (7) is the mode in which the engine
propels the vehicle and charges the batteries
simultaneously
 Pattern (8)
• Pattern (8) is the mode in which the engine
charges the batteries, and the batteries supply
power to the load
 Pattern (9)
• Pattern (9)is the mode in which the power
flows into the batteries from the heat engine
through the vehicle mass.
• The typical configuration of this mode is two
power trains separately mounted on the front
and the rear axle of the vehicle
 advantages
• The varied operation modes in a hybrid
vehicle create more flexibility over a single
power train vehicle.
• With proper configuration and control,
applying the specific mode for each special
operating condition can optimize overall
performance, efficiency, and emissions
2nd topic
 introduction to various hybrid drive-
train topologies/configuration
• Therefore, HEVs are now classified into four kinds: series
hybrid, parallel hybrid, series–parallel hybrid, and
complex hybrid, which are functionally shown in Figure
Complex hybrid
 1.Series Hybrid Electric Drive Trains
• A series hybrid drive train is a drive train where two power sources feed a
single power plant (electric motor) that propels the vehicle. The most commonly
found series hybrid drive train is the series hybrid electric drive train shown in
Figure
• The unidirectional energy source is a fuel tank and the unidirectional
energy converter is an engine coupled to an electric generator.
• The output of the electric generator is connected to an electric power bus
through an electronic converter (rectifier).
• The bidirectional energy source is an electrochemical battery pack,
connected to the bus by means of a power electronics converter (DC/DC
converter).
• The electric power bus is also connected to the controller of the electric
traction motor.
• The traction motor can be controlled either as a motor or a generator, and
in forward or reverse motion.
• This drive train may need a battery charger to charge the batteries by a
wall plug-in from the power network.
 Series hybrid electric drive trains potentially have the
following operation
modes
• 1Pure electric mode: The engine is turned off and the vehicle is propelled only by the
batteries.
• 2. Pure engine mode: The vehicle traction power only comes from the engine-generator,
while the batteries neither supply nor draw any power from the drive train. The electric
machines serve as an electric transmission from the engine to the driven wheels.
• 3. Hybrid mode: The traction power is drawn from both the engine generator
• and the batteries.
• 4. Engine traction and battery charging mode: The engine-generator supplies power to
charge the batteries and to propel the vehicle.
• 5. Regenerative braking mode: The engine-generator is turned off and the traction motor is
operated as a generator. The power generated is used to charge the batteries.
• 6. Battery charging mode: The traction motor receives no power and the engine-generator
charges the batteries.
• 7. Hybrid battery charging mode: Both the engine-generator and the traction motor operate
as generators to charge the batteries
 Series hybrid drive trains offer several
advantages
• The engine is fully mechanical when decoupled from the driven wheels.
• Therefore, it can be operated at any point on its speed–torque
characteristic map, and can potentially be operated solely within its
maximum efficiency region as shown in Figure.
• The efficiency and emissions of the engine can be further improved
by optimal design and control in this narrow region.
• A narrow region allows greater improvements than an optimization across
the entire range.
Furthermore, the mechanical decoupling of the engine from the driven
wheels allows the use of a high-speed engine.
• This makes it difficult to power the wheels directly through a mechanical
link, such as gas turbines or powerplants, with slowdynamics like the
Stirling engine.
• Because electric motors have near-ideal torque–speed
characteristics,they do not need multigear transmissions as
discussed already.
• Therefore, their construction is greatly simplified andthe cost is
reduced.
• Furthermore, instead of using one motor and a differential gear,
two motors may be used, each powering a single wheel.
• This provides speed decoupling between the two wheels like a
differential but also acts as a limited slip differential for traction
control purposes.
• The ultimate refinement would use four motors, thus making the
vehicle an all-wheel-drive without the expense and complexity of
differentials and drive shafts running through the frame.
• Simple control strategies may be used as a
result of the mechanical decoupling provided
by the electrical transmission.
series hybrid electric drive trains have
some disadvantages
• The energy from the engine is converted twice
(mechanical to electrical in the generator and
electrical to mechanical in the traction motor).
• The inefficiencies of the generator and
traction motor add up and the losses may be
significant
• The generator adds additional weight and
cost..
• The traction motor must be sized to meet
maximum requirements since it is the only
powerplant propelling the vehicle
 2.Parallel Hybrid Electric Drive Trains
• A parallel hybrid drive train is a drive train in
which the engine supplies its power
mechanically to the wheels like in a
conventional ICE-powered vehicle.
• It is assisted by an electric motor that is
mechanically coupled to the transmission.
• The powers of the engine and electric motor
are coupled together by mechanical coupling,
as shown in Figure
• The mechanical combination of the engine
and electric motor power leaves room for
several different configurations, detailed
hereafter
• Torque-Coupling
• Speed-Coupling
• Torque speed-Coupling
 2.1Torque-Coupling in
Parallel Hybrid Electric Drive Trains
• The mechanical coupling in Figure 5.5 may be a
torque or speed coupling.
• The torque coupling adds the torques of the
engine and the electric motor together or splits
the engine torque into two parts: propelling and
battery charging.
• a mechanical torque coupling, which has two
inputs. One is from the engine and one is from
the electric motor.
• The mechanical torque coupling outputs to the
mechanical transmission
 torque coupling -types
• There are a variety of configurations in torque coupling hybrid
drivetrains.
• They are classified into two-shaft and one-shaft designs.
• In each category, the transmission can be placed in different
positions and designed with different gears, resulting in
different tractive characteristics.
• An optimum design will depend mostly on the tractive
requirements, engine size and engine characteristics, motor
size and motor characteristics, etc.
transmotor
• Transmotor is an electric motor with a floating stator which
forms a double-rotor machine with stator as outer rotorrotor
and traditional rotor as inner rotor. Through the air gap,
electric power converts into mechanical power as shown in
• in
 4configuration
• 2.1.1two-shaft/ two transmission
configuration design
• 2.1.2)Two -shaft/single transmission
• 2.1.3)single-shaft configuration
• 2.1.4separated axle architecture
 2.1.1)detail
two-shaft/ two transmission configuration
design
 explanation
• This figure two transmissions are used: one is
placed between the engine and the torque
coupling and other is placed between the
motor and torque coupling.
Both transmissions may be single or multi gear
• Figure 5.9 shows the tractive effort–speed profiles of a
vehicle with different transmission parameters.
• It is clear that two multigear transmissions produce many
tractive effort profiles.
• The performance and overall efficiency of the drive train
may be superior to other designs, because two multigear
transmissions provide more opportunities for both the
engine and electric traction system (electric machine and
batteries)to operate in their optimum region.
• This design also provides great flexibility in the design of
the engine and electric motor characteristics.
• However, two multigear transmissions will significantly
complicate thedrive train.
• The multigear transmission 2 is used to overcome
the disadvantages of the IC engine speed–torque
characteristics (flat torque output along speed).
• The multispeed transmission 2 also tends to
improve the efficiency of the engine and reduces
the speed range of the vehicle — in which an
electric machine alone must propel the vehicle —
consequently reducing the battery-discharging
energy.
• In contrast with the above design, Figure
5.9(c) shows the tractive effort–speed profile
of the drive train, which has a single
transmission 1 forthe engine and a multispeed
transmission 2 for the electric motor.
• This configuration is considered to be an
unfavorable design, because it does not use
the advantages of both powerplants.
• Figure 5.9(d) shows the tractive effort–speed profile of
the drive train, which has two single-gear
transmissions.
• This arrangement results in simple configuration and
control.
• The limitation to the application of this drive train is
themaximum tractive effort of the drive train.
• When power of the engine, electric motor, batteries,
and transmission parameters are properly designed,
this drive train would serve the vehicle with
satisfactory performance and efficiency
2.1.2)Two -shaft/single transmission
configuration design
 two-shaft/1 tr
parallel hybrid drive train
• Another configuration of the two-shaft parallel hybrid drive train is
shown in Figure 5.10, in which the transmission is located between the
torque coupling and drive shaft.
• The transmission functions to enhance the torques of both engine
and electric motor with the same scale.
• Designing the constant k1 and k2 in the torque coupling allows the
electric motor to have a different speed range than the engine;
therefore, a high-speed motor can be used.
• This configuration would be suitable in the case when a relatively
small engine and electric motor are used, and where a multigear
transmission is needed to enhance the tractive effort at low speeds
 2.1.3)single-shaft configuration
• The simple and compact architecture of the
torque coupling parallel hybrid is the single-
shaft configuration where the rotor of the
electric motor functions as the torque
coupling (k11 and k21]), as shown
in Figure 5.11 and Figure 5.12
 Pretransmission- posttransmission
• A transmission may be either placed behind an electric motor that
is connected to the engine through a clutch or between the engine
and the electric motor.
• The former configuration is referred to as “pretransmission” (the
motor is ahead of the transmission, Figure 5.11) and the latter is
referred to as “posttransmission” (the motor is behind the
transmission, Figure 5.12).
• In the pretransmission configuration, both the engine torque and
motor torque are modified by the transmission.
• The engine and motor must have the same speed range.
• This configuration is usually used in the case of a small motor,
referred to as a mild hybrid drive train, in which the electric motor
functions as an engine starter, electrical generator, engine power
assistant,and regenerative braking.
• However, in the post transmission configuration as shown
in Figure 5.12, the transmission can only modify the engine
torque while the motor torque is directly delivered to the
driven wheels.
• This configuration may be used in the drive train where a
large electric motor with a long constant power region is
used. The transmission is only used to change the engine
operating points to improve the vehicle performance and
engine operating efficiency.
• It should be noted that the batteries cannot be charged
from the engine by running the electric motor as a
generator when the vehicle is at a standstill and the motor
is rigidly connected to the driven wheels
2.1.4separated axle architecture
• Another torque coupling parallel hybrid drive
train is the separated axle architecture, in
which one axle is powered by the engine and
another is powered by the electric motor
(Figure 5.13).
• The tractive efforts from the two power trains
are added through the vehicle chassis and the
road.
 advantages
• The separated axle architecture offers some of the advantages of a
conventional vehicle.
• It keeps the original engine and transmission unaltered and adds
an electrical traction system on the other axle.
• It also has four wheel drive, which optimizes traction on slippery
roads and reduces the tractive effort on a single tire.
• However, the electric machines and the eventual differential gear
system occupy considerable space and may reduce the available
passenger and luggage space.
• This problem may be solved if the motor transmission is single gear
and the electric motor is replaced by two small-sized electric
motors that can be placed within two driven wheels.
• It should be noted that the batteries cannot be charged from the
engine when the vehicle is at a standstill
2.3Speed-Coupling Parallel Hybrid
Electric Drive Trains
• Figure 5.15 shows two typical speed-coupling devices:
• one is a planetary gear unit and the other is an electric
motor with a floating stator, called a transmotor in this
book.
• A planetary gear unit is a three-port unit consisting of the
sun gear, the ring gear, and the yoke labeled 1, 2, and 3,
respectively.
• The speed and torque relationship between the three ports
indicates that the unit is a speed-coupling device, in which
the speed, the sun gear, and the ring gear are added
together and output through the yoke.
• The constants k1 and k2depend only on the radius of each
gear or the number of teeth of each gear
 transmotor
• Another interesting device used in speed coupling is an electric motor
(called a transmotor in this book),
• in which the stator, generally fixed to stationary frame, is released as a
power-input port.
• The other two ports are the rotor and the air gap through which electric
energy is converted into mechanical energy.
• The motor speed, in common terms, is the relative speed of the rotor to
the stator.
• Because of action and reaction effects, the torque action on the stator and
rotor is always the same and results in the constants k11 and k21. Just like
the torque-coupling device, the speed-coupling units can be used to
constitute various hybrid drive trains.
• Figure 5.16 and Figure 5.17 show two examples of hybrid drive trains with
speed coupling of the planetary gear unit and an electric transmotor.
• In Figure 5.16, the engine supplies its power to
the sun gear through a clutch and transmission.
The transmission is used to modify the speed–
torque characteristics of the engine so as to
match the traction requirements.
• The electric motor supplies its power to the ring
gear through a pair of gears.
• Locks 1 and 2 are used to lock the sun gear and
ring gear to the standstill frame of the vehicle in
order to satisfy the different operation mode
requirements
 following operation modes can be
satisfied:
• Hybrid traction: When locks 1 and 2 are released the sun gear and ring gear can
rotate and both the engine and electric machine supply positive speed and torque
(positive power) to the driven wheels.
• 2. Engine-alone traction: When lock 2 locks the ring gear to the vehicle frame and
lock 1 is released only the engine supplies power to the driven wheels.
• 3. Motor-alone traction: When lock 1 locks the sun gear to the vehicle frame
(engine is shut off or clutch is disengaged) and lock 2 is released only the electric
motor supplies its power to the driven wheels.
• 4. Regenerative braking: Lock 1 is set in locking state, the engine is shut off or
clutch is disengaged, and the electric machine is controlled in regenerating
operation (negative torque). The kinetic or potential energy of the vehicle can be
absorbed by the electric system.
• 5. Battery charging from the engine: When the controller sets a negative
speed for the electric machine, the electric machine absorbs energy from the engine
 The drive train, consisting of the
transmotor as shown in Figure 5.17,
• Figure 5.17, has a structure similar to that in Figure 5.16. Locks 1
and 2 are used to lock the stator to the vehicle frame and the stator
to the rotor, respectively.
• This drive train can fulfill all the operation modes mentioned above.
The operating modes analysis is left to the readers.
• The main advantage of the hybrid drive train with speed coupling is
that the speeds of the two power plants are decoupled;
• therefore, the speed of both the power plants can be chosen freely.
This advantage is important to power plants such as the Stirling
engine and the gas turbine engine, in which their efficiencies are
sensitive to speed and less sensitive to torque.
 2.3Torque-Coupling and Speed-Coupling
Parallel Hybrid Electric(With Optional Coupling
Mode)
Drive Trains
• By combining torque and speed coupling together, one
may constitute a hybrid drive train in which torque and
speed coupling states can be alternatively chosen.
• Figure 5.18 shows such an example. When the torque
coupling operation mode is chosen as the current
mode, lock 2 locks the ring gear of the planetary unit to
the vehicle frame, while clutches 1 and 3 are engaged
and clutch 2 is disengaged.
• The powers of the engine and the electric motor are
added together by adding their torques together and
then delivered to the driven wheels.
•
• Another variation of the drive train in Figure
5.24 is the single-shaft design as shown in
Figure 5.25
• A more compact design of the drive train in
Figure 5.25 is to integrate the transmotor and
the traction motor together as shown in
Figure 5.26. The design and control may be
more complicated than the separated
structure due to correlated magnetic field in
the double air gaps.
 Assignment
• Explain speed coupling, torque coupling and
speed coupling and torque coupling with
suitable diagram
3 rd configuration of drive train
Series parallel
• The configuration introduces an additional mechanical link
(unlike the series hybrid) and an additional generator
(unlike the parallel hybrid) to facilitate the advantages of
both configurations .
• Among various possibilities in series-parallel hybrids, the
general classification includes electric-intensive and engine-
intensive.
• In electric-intensive configuration, electric motor is more
dominating than the ICE. In engine-intensive configuration,
ICE is more dominating than electric motor [10].
• Accordingly, the dominating components are designed.
•
• The operating modes (start, normal driving,
acceleration, deceleration, braking, and battery charging) of
electric-intensive and ICE-intensive are almost the same except for
the normal driving mode.
• In normal driving mode, efforts are made to operate the engine at
its most efficient point.
• Therefore, in ICE-intensive configuration, the engine propels the
wheels solely, and in electric-intensive configuration, the ICE can
assist the electric motor to propel the wheels.
• Although the series-parallel hybrid vehicle incorporates the
advantages of both the series and parallel hybrid, the use of
additional electric and mechanical components (generator
and planetary gear arrangement) adds to the complexity, weight,
and costs.
4th model
Complex Hybrid System
• both the front and rear wheels propel the vehicle. In this
configuration, the front-wheel and rear-wheel axles are decoupled
from each other, and there is no mechanical link between them;
• hence, both the axles are driven independently .
• In complex hybrid vehicle, the electric generator offers bidirectional
power flow, whereas in case of series-parallel, it offers
unidirectional power flow.
• However, both the configurations involve ICE, electric generator,
and motor to propel the vehicle.
• The capability of complex hybrid system, to drive the wheels by
either electric propulsion or hybrid propulsion or combination of
both, offers additional flexibility and reliability.
• The front wheels are propelled by hybrid propulsion system, and
rear wheels are propelled by electric propulsion system or vice
versa. The operating modes for both the scheme are almost
common, except when front wheels are propelled by hybrid system,
all the wheels are driven;
• however, when front wheels are propelled by electric system, only
front wheels are driven at starting . A planetary gear arrangement is
used to coupled ICE, front electric motor, and front axle altogether.
Independent control of front and rear wheels provides
smooth vehicle operation and flexibility in casing.
• This, however, increases complexity and costs. Also, regenerative
braking in all four wheels can significantly improve efficiency of the
system and hence fuel economy
Next topic
 Power flow control in hybrid drive
train
• The following topics are covered in this lecture
• Power Flow Control
• Power Flow Control in Series Hybrid
• Power Flow Control in Parallel Hybrid
• Power Flow Control in Series-Parallel Hybrid
 Need of power flow control
• Power Flow Control Due to the variations in HEV
configurations, different power control strategies
are necessary to regulate the power flow to or
from different components. All the control
strategies aim satisfy the following goals:
• maximum fuel efficiency
• minimum emissions
• minimum system costs
• good driving performance
 Power Flow Control in Series Hybrid
• In the series hybrid system there are four
operating modes based on the power flow:
Mode 1: During startup (Figure 1a), normal
driving or acceleration of the series HEV, both
the ICE and battery deliver electric energy to
the power converter which then drives the
electric motor and hence the wheels via
transmission.
• Mode 2: At light load (Figure 1b), the ICE
output is greater than that required to drive
the wheels. Hence, a fraction of the generated
electrical energy is used to charge the battery.
The charging of the batter takes place till the
battery capacity reaches a proper level
• Mode 3: During braking or deceleration
(Figure 1c), the electric motor acts as a
generator, which converts the kinetic energy
of the wheels into electricity and this, is used
to charge the battery.
• Mode 4: The battery can also be charged by
the ICE via the generator even when the
vehicle comes to a complete stop (Figure 1d)
next
 Power Flow Control in Parallel Hybrid
• The parallel hybrid system has four modes of operation. These four
modes of operation are
• Mode 1: During start up (Figure 2a); both the ICE and the EM
share the required power to propel the vehicle. Typically, the
relative distribution between the ICE and electric motor is 80-20%.

• Mode 2: During normal driving (Figure 2b), the required traction

power is supplied by the ICE only and the EM remains in off mode.
• Mode 3: During braking or deceleration (Figure 2c), the EM acts
as a generator to charge the battery via the power converter.
• Mode 4: Under light load condition (Figure 2d), the traction
power is delivered by the ICE and the ICE also charges the battery
via the EM
 Power Flow Control Series-Parallel
Hybrid
• The series-parallel hybrid system involves the
features of series and parallel hybrid systems.
Hence, a number of operation modes are
feasible.
• Therefore, these hybrid systems are classified
into two categories:
• the ICE dominated
• and the EM dominated.
 ICE dominated
• The various operating modes of ICE dominated system are:
• Mode 1: At startup (Figure 3a), the battery solely
provides the necessary power to propel the vehicle and the
ICE remains in off mode.
• Mode 2: During full throttle acceleration (Figure 3b),
both the ICE and the EM share the required traction power.
• Mode 3: During normal driving (Figure 3c), the required
traction power is provided by the ICE only and the EM
remains in the off state.
• Mode 4: During normal braking or deceleration (Figure
3d), the EM acts as a generator to charge the battery
 ICE dominated
• Mode 5: To charge the battery during driving
(Figure 3e), the ICE delivers the required
traction power and also charges the battery. In
this mode the EM acts as a generator.
• Mode 6: When the vehicle is at standstill
(Figure 3f), the ICE can deliver power to
charge the battery via the EM
 EM dominated
• The operating modes of EM dominated system are:
• Mode 1: During startup (Figure 4a), the EM provides the traction
power and the ICE remains in the off state.
• Mode 2: During full throttle (Figure 4b), both the ICE and EM
provide the traction power.
• Mode 3: During normal driving (Figure 4c), both the ICE and EM
provide the traction power.
• Mode 4: During braking or deceleration (Figure 4d), the EM acts
as a generator to charge the battery.
• Mode 5: To charge the battery during driving (Figure 4e), the ICE
delivers the required traction power and also charges the battery.
The EM acts as a generator.
• Mode 6: When the vehicle is at standstill (Figure 4f), the ICE can
deliver power to charge the battery via the EM
next
 Power Flow Control Complex Hybrid
Control
• The complex hybrid vehicle configurations are
of two types
• : Front hybrid rear electric
• Front electric and rear hybrid
 Front hybrid rear electric
• Both the configurations have six modes of operation:
• Mode 1: During startup (Figure 5a), the required
traction power is delivered by the EMs and the engine
is in off mode.
• Mode 2: During full throttle acceleration (Figure 5b),
both the ICE and the front wheel EM deliver the power
to the front wheel and the second EM delivers power
to the rear wheel.
• Mode 3: During normal driving (Figure 5c), the ICE
delivers power to propel the front wheel and to drive
the first EM as a generator to charge the battery.
• Mode 4: During driving at light load (Figure 5d) first
EM delivers the required traction power to the front
wheel. The second EM and the ICE are in off sate.
• Mode 5: During braking or deceleration (Figure 5e),
both the front and rear wheel EMs act as generators to
simultaneously charge the battery
• Mode 6: A unique operating mode of complex hybrid
system is axial balancing. In this mode (Figure 5f) if the
front wheel slips, the front EM works as a generator to
absorb the change of ICE power. Through the battery,
this power difference is then used to drive the rear
wheels to achieve the axle balancing.
 Assignment num 2
• explain power flow control in various
configuration of hybrid electric vehicle
Next half
 Unit 2.2
ELECTRIC DRIVE TRAINS
Basic concept of electric traction,
introduction to various electric drive-train topologies,
power flow controlling electric drive-train topologies,
fuel efficiency analysis
 What is Electric Traction
• A system which causes the propulsion of
vehicle in which tractive or driving force is
obtained from electric motors, is called as
electric traction system.
 Basic concept of electric traction
• The electric traction system is the most
efficient of all other traction system such as
steam and internal combustion (IC) engine
type systems.
• It offers several benefits over other systems,
including quick start and stop, very efficient,
pollution-free, easy to handle and easy speed
control.
 Traction motor working
• The motor consists of two parts, a rotating armature
and a fixed field .
• The fixed field consists of tightly wound coils of wire
fitted inside the motor case. The armature is another
set of coils wound round a central shaft.
• It is connected to the field through "brushes" which
are spring loaded contacts pressing against an
extension of the armature called the commutator.
• The commutator collects all the terminations of the
armature coils and distributes them in a circular
pattern to allow the correct sequence of current flow
 Advantage of electric traction
No need of clutch
• The ability of electric motors to start from zero
speed and operate efficiently over a wide
speed range makes it possible to eliminate the
clutch that is used in internal combustion
engine vehicles (ICEV).
 No need of multiple gear
• A single gear ratio is sufficient to match the
wheel speed with the motor speed.
• EVs can be designed without a gear
• but the use of a speed reducer allows the
electric motor to operate at much higher
speeds for given vehicle speeds, which
minimizes the motor size because of the low
torque requirement at higher speeds.
MAIN PARTS OF EV
• In Figure the black line represents the mechanical
link, the green line represents the electrical link and
the blue line represents the control information
communication
• Based on the control inputs from the brake and
accelerator pedals, the electronic controller provides
proper control signals to switch on or off the power
converter which in turn regulates the power flow
between the electric motor and the energy source
• The backward power flow is due to regenerative
braking of the EV and this regenerative energy can be
stored provided the energy source is receptive
• The energy management unit cooperates with
the electronic controller to control regenerative
braking and its energy recovery. It also works
with the energy-refueling unit to control refueling
and to monitor usability of the energy source.
• The auxiliary power supply provides the
necessary power with different voltage levels for
all EV auxiliaries, especially the temperature
control and power steering units.
 modern EV’s configuration
• Three phase motors are generally used to
provide the traction force
• The power converter is a three-phase PWM
inverter
• Mechanical transmission is based on fixed
gearing and a differential
• Li-ion battery is typically selected as the
energy source
The typical setup of the EV is shown in
Figure B.
 introduction to various electric drive-
train topologies
• There are many possible EV configurations
based on 1.propulsion motor arrangement
• 2 based on storage arrangement

• based on 1.propulsion motor arrangement six

alternatives are possible as shown in Figure 3.
These six alternatives are
1.Based on electric propulsion
• In Figure 3a a single EM configuration with gearbox (GB)
and a clutch is shown.
• It consists of an EM, a clutch (C), a gearbox, and a
differential (D).
• The clutch enables the connection or disconnection of
power flow from EM to the wheels.
• The gear consists of a set of gears with different gear
ratios. With the use of clutch and gearbox, the driver can
shift the gear ratios and hence the torque going to the
wheels can be changed.
• The wheels have high torque low speed in the lower gears
and high-speed low torque in the higher gears.
• In Figure 3b a single EM configuration
without the gearbox and the clutch is shown.
The advantage of this configuration is that
the weight of the transmission is reduced.
However, this configuration demands a more
complex control of the EM to provide the
necessary torque to the wheels.
• Figure 3c shows a configuration of EV using
one EM. It is a transverse front EM front
wheel drive configuration. It has a fixed
gearing and differential and they are
integrated into a single assembly.
• In Figure 3d a dual motor configuration is
shown. In this configuration the differential
action of an EV when cornering can be
electronically provided by two electric
motors.
• . In order to shorten the mechanical
transmission path from the EM to the driving
wheel, the EM can be placed inside a wheel.
This configuration is called in-wheel drive.
Figure 3e shows this configuration in which
fixed planetary gearing is employed to reduce
the motor speed to the desired wheel speed
• In Figure 3f an EV configuration without any
mechanical gearing is shown. By fully
abandoning any mechanical gearing, the in-
wheel drive can be realized by installing a low
speed outer-rotor electric motor inside a
wheel.
2.Based on Power Source
Configuration
 Configuration 1:

• 1. It is a simple battery powered configuration, Figure 4a.

The battery may be distributed around the vehicle, packed
together at the vehicle back or located beneath the
vehicle chassis.
• The battery in this case should have reasonable specific
energy and specific power and should be able to accept
regenerative energy during braking.
• In case of EVs, the battery should have both high specific
energy and specific power because high specific power
governs the driving range while the high power density
governs the acceleration rate and hill climbing capability
 Configuration 2

• Instead of two batteries, this design uses

two different batteries, Figure 4b. One
battery is optimized for high specific energy
and the other for high specific power
 Configuration 3

• : In this arrangement fuel cell is used, Figure 4c. The

battery is an energy storage device, whereas the fuel cell
is an energy generation device.
• The operation principle of fuel cells is a reverse process of
electrolysis. In reverse and electrolysis, hydrogen and
oxygen gases combine to form electricity and water. The
hydrogen gas used by the fuel cell can be stored in an on-
board tank whereas oxygen gas is extracted from air. Since
fuel cell can offer high specific energy but cannot accept
regenerative energy, it is preferable to combine it with
battery with high specific power and high-energy
receptivity
 Configuration 4

• Rather than storing it as a compressed gas, a

liquid or a metal hydride, hydrogen can be
can be generated on-board using liquid fuels
such as methanol, Figure 4d. In this case a
mini reformer is installed in the EV to
produce necessary hydrogen gas for the fuel
cell.
 Configuration 5:

• In fuel cell and battery combination, the battery is selected

to provide high specific power and high-energy receptivity.
In this configuration a battery and supercapacitor
combination is used as an energy source,
• Figure 4e. The battery used in this configuration is a high
energy density device whereas the supercapacitor
provides high specific power and energy receptivity.
Usually, the super capacitors are of relatively low voltage
levels, an additional dc-dc power converter is needed to
interface between the battery and capacitor terminals.
 next topic
• Power Flow Controlling Electric Drive-train
Topologies
Based on Power Source Configuration
 Energy Consumption/ fuel efficiency
analysis
• In transportation, the unit of energy is usually
kilowatt-hour (kWh) rather than joule or
kilojoules ( J or kJ).
• The energy consumption per unit distance in
kWh/km is generally used to evaluate the
vehicle energy consumption
• However, for ICEVs the commonly used unit is
a physical unit of fuel volume per unit
distance, such as liters per 100 km (L/100 km).
• On the other hand, for battery-powered EVs,
the original energy consumption unit in kWh,
measured at the battery terminals, is more
suitable.
• The battery energy capacity is usually
measured in kWh and the driving range per
battery charge can be easily calculated.
• Similar to ICEVs, L/100 km (for liquid fuels) or
kg/100 km (for gas fuels such as hydrogen) or
mpg or miles per kilogram is a more suitable
unit of measurement for vehicles that use
gaseous fuels
• Energy consumption is an integration of the
power output at the battery terminals.
• For propelling, the battery power output is
equal to the resistance power and power
losses in the transmission and motor drive,
including power losses in the electronics.
• The power losses in transmission and motor
drive are represented by their efficiencies ηt
and ηm, respectively.
• Thus, the battery power output can be
expressed as
• Here, the non traction load (auxiliary load) is
not included.
• In some cases, the auxiliary loads may be too
significant to be ignored and should be added
to When regenerative braking is effective on
an EV, a part of the braking energy—wasted in
conventional vehicles—can be recovered by
operating the motor drive as a generator and
restoring it into the batteries the traction load.
• The regenerative braking power at the battery
terminals can also be expressed as
• The regenerativebraking factor α is a function
of the applied braking strength and the design
and control of the braking system. The net
energy consumption from the batteries is
• The efficiency of a traction motor varies with its
operating points on thespeed–torque (speed–power)
plane as shown in Figure 4.14
• where the most efficient operating area exists.
In power train design, this area should overlap
or at least be as close as possible to the area of
the greatest operation as mentioned in the
previous section.
 questions
• Explain Basic concept of electric traction(5
mark)
• Explain EV TRANSMISSION
CONFIGURATIONS(5 mark
• List the Use of differential ,clutch and break in
ev vehicle(5)
• How to calculate Energy Consumption in ev
vehicle(10)
 Reference
Modern Electric, Hybrid Electric, and
Fuel Cell Vehicles