Three key points about the document: 1. The document discusses different types of electric vehicle motors, including DC motors, induction motors, and brushless DC motors. It provides details on the working principles, advantages, and applications of each type of motor. 2. Induction motors are highlighted as being a good choice for electric vehicles due to their low cost, high efficiency, robustness, and ability to provide high starting torque needed for vehicle propulsion. Several electric vehicles that use induction motors are mentioned. 3. Brushless DC motors are also discussed as being well-suited for electric vehicles due to their high efficiency and power density. Outrunner and inrunner BLDC motor configurations are described.

1. “Hybrid Electric Vehicles”
Unit 5 : Electric Drives
Name of Author: Dr. M . I. Ansari
E-Mail ID: miansari@bvucoep.edu.in

2. Content of the Syllabus
• Motor Drives for EV using
1. DC Motor Drives,
2. Induction Motor Drives,
3. Permanent Magnet Brushless and
4. Switched Reluctance Motor Drives,
• Selection of Motor,
• Structural Configuration of motor layout
1. Single motor,
2. Dual motor,
3. in wheel/Hub motor,
4. Planetary-Geared Motors, etc for EV,
• Motor Safety and Maintenance,
• Motor Torque and Power Rating

3. Motor Drives for EV
• The electric propulsion system of EVs is responsible for converting electrical
energy to mechanical energy in such a way that the vehicle is propelled to
overcome aerodynamic drag, rolling resistance drag and kinetic resistance.
• Modern motor drive has, high-torque low-speed and constant-power high-speed
regions can be achieved through electronic control. the EV propulsion design
can be more flexible, namely single or multiple motors, with or without
reduction gearing, with or without differential gearing, and axle or wheel
motors.
• The electric propulsion system consists of the motor drive, transmission device
and wheels. The transmission device sometimes is optional. In fact, the
motor drive, comprising of the electric motor, power converter and electronic
controller, is the core of the EV propulsion system.
The major requirements of the EV motor drive are summarized as follows,
• High instant power and high power density;
• High torque at low speeds for starting and climbing as well as high speed at low
torques for cruising;
• Very wide speed range including constant-torque and constant-power regions;
• Fast torque response;
• High efficiency over wide speed and torque ranges;
• High efficiency for regenerative braking;
• High reliability and robustness for various vehicle operating conditions;
• Reasonable cost.

4. Systems employed for motion control are called drives. Motion control
is required in industrial as well as domestic applications like
transportation system, rolling mills, paper mills, textile mills, machine
tools, fans, pumps, robots, washing machines etc. Motion control
may be translational, rotational or combination of both. Generally, a
drive system is basically has a mechanical load, a transmission system
and a prime mover. The prime mover may be I.C. engine, steam
engine, turbine or electric motors. However, electric motors are
predominantly used employed as prime mover due to certain
advantages.
Advantages of Electric Drives:
• Flexible control characteristics.
• Starting and braking is easy and simple
• Provides a wide range of torques over a wide range of speeds (both ac
and dc motor)
• Availability of wide range of electric power
• Works to almost any type of environmental conditions
• No exhaust gases emitted
• Capable of operating in all 4 quadrants of torque –speed plane
• Can be started and accelerated at very short time.

5. Basic Elements of the Electric Drive Systems:
• Power source: The power source provides the energy to the drive
system. It may be dc or ac (single phase or three-phase).
• Power Converter: The converter interfaces the motor with the power
source and provides the motor with adjustable voltage, current and
frequency.
• Controller: The basic function is to monitor system variables,
compare them with desire values, and then adjust the converter
output until the system achieves a desired performance.
• Electric motor: The basic criterion in selecting an electric motor for a
given drive application is it meets power level and performance
required by the load during steady state and dynamic operation.

6. EV motor's load requirement, performance specification and operating environment are
summarized as follows:
• EV motors need to offer the maximum torque that is four to five times of the
rated torque for temporary acceleration and hill-climbing, while industrial
motors generally offer the maximum torque that is twice of the rated torque for
overload operation.
• EV motors need to achieve four to five times the base speed for highway
cruising, while industrial motors generally achieve up to twice the base speed
for constant-power operation.
• EV motors should be designed according to the vehicle driving profiles
and drivers’ habits, while
industrial motors are usually based on a typical working mode.
• EV motors demand both high power density and good efficiency map (high
efficiency over wide speed and torque ranges) for the reduction of total vehicle
weight and the extension of driving range, while industrial motors generally
need a compromise among power density, efficiency and cost with the
efficiency optimized at a rated operating point.
• EV motors desire high controllability, high steady-state accuracy and good
dynamic performance for
multiple-motor coordination, while only special purpose industrial motors
desire such performance.
• EV motors need to be installed in mobile vehicles with harsh operating
conditions such as high temperature, bad weather and frequent vibration, while
industrial motors are generally located in fixed places.

7. Difference Between a Motor and a Drive
• A motor is the mechanical or electrical device that generates the
rotational or linear force used to power a machine. A drive is the
electronic device that harnesses and controls the electrical energy
sent to the motor. The drive feeds electricity into the motor in varying
amounts and at varying frequencies, thereby indirectly controlling the
motor’s speed and torque.
• There are two types of drives: a standard inverter drive for controlling
speed and torque only; and a servo drive for controlling speed and
torque, as well as positioning machine components used in
applications that require complex motion.
• A motor drive controls the speed, torque, direction, and resulting
horsepower of a motor. Dc drives typically control a shunt-wound dc
motor, which has separate armature and field circuits. Ac drives
control ac-induction motors and, like their dc counterparts, control
speed, torque, and horsepower.

8. Classification of EV motors
• The basic consideration of motor design includes magnetic loading-the peak of
fundamental component of radial flux density in the air-gap of the motor,
electric loading-the total R.M.S.
• Current per unit length of periphery of the motor or ampere-turns per unit
periphery, power per unit volume and weight, torque per unit volume and
weight, flux density at each part of the magnetic circuit, speed, torque and
power, losses and efficiency, and thermal design and cooling.
• The corresponding key issues are better utilization of steel, magnet and copper,
better electromagnetic coupling, better geometry and topology, better thermal
design and cooling, understanding the limits on the motor performance, and
understanding the relationship among geometry, dimensions, parameters and
performance, thus to achieve higher power per unit weight, higher torque per
unit weight and better performance.

9. Classification of EV motors

10. DC Motor Drives:
• DC motor drives have been widely used in applications requiring adjustable speed, good
speed regulation, and frequent starting, braking and reversing.

11. Working
• Whenever a current-carrying conductor placed in a magnetic field then there
will be a force produced in the conductor. The two fluxes oppose each other.
Here, the field flux is produced by the field winding and the armature flux is
produced by the armature winding when the armature is given an electric input.
• The direction of the flux produced by the armature conductor is determined by
the right-hand thumb rule and the direction of the armature conductor can be
determined. armature flux and main field flux will interact with each other by
which the net flux will be increased towards one side and which will be
minimum on the other side.
• The increased flux on one side will be in the shape of an enlarged magnetic
field or flux or like a
stretched rubber band. Therefore, this will exert a force on the surface of the
conductor by which there will be momentum in the conductor.
• As the armature is in a cylindrical shape and has a radius, therefore, a force
will be created on the
surface of the armature which leads to turning or twisting which is called as
production of torque.
• As the flux is zero the speed is infinity and the motor mechanically gets
damaged. The speed of the motor can be varied up to two times. We should not
run the series motor at no-load conditions.
• Under light load conditions, the current drawn by the series motor will be
very very small and
therefore the speed of the motor will be very very high which may lead to
mechanical damage to the
motor. So, the series motor should not be operated under light load or no-load
conditions.

13. Brushless DC Motors
• It is similar to DC motors with Permanent Magnets.
• It is called brushless because it does not have the commutator and
brush arrangement.
• The commutation is done electronically in this motor because of this
BLDC motors are maintenance free.
• BLDC motors have traction characteristics like high starting torque,
high efficiency around 95-98%, etc.
• BLDC motors are suitable for high power density design approach.
The BLDC motors are the most preferred motors for the electric
vehicle application due to its traction characteristics.
• BLDC motors further have two types:
1) Out-runner type BLDC Motor
2) In-runner type BLDC Motor

14. Out-runner type BLDC Motor:
• The rotor of the motor is present outside and the stator is present
inside.
• It is also called as Hub motors because the wheel is directly
connected to the exterior rotor.
• This type of motors does not require external gear system.
• In a few cases, the motor itself has inbuilt planetary gears.
• This motor makes the overall vehicle less bulky as it does not require
any gear system.
• It also eliminates the space required for mounting the motor.
• There isa restriction on the motor dimensions which
limits the power output in the in- runner
configuration.
• This motor is widely preferred by electric cycle manufacturers like
Hullikal, Tronx, Spero, light speed bicycles, etc.
• It is also used by two-wheeler manufacturers like 22 Motors, NDS
Eco Motors, etc.

15. In-runner type BLDC Motor:
• In this type, the rotor of the motor is present inside and the stator is
outside like conventional motors.
• These motor require an external transmission system to transfer the
power to the wheels, because of this the out-runner configuration is
little bulky when compared to the in-runner configuration.
• Many three- wheeler manufacturers like Goenka Electric Motors,
Speego Vehicles, Kinetic
Green, V
oltaAutomotive use BLDC motors.
• Low and medium performance scooter manufacturers also use BLDC
motors for propulsion.
• It is due to these reasons it is widely preferred motor for electric
vehicle application.
• The main drawback is the high cost due to permanent magnets.
• Overloading the motor beyond a certain limit reduces the life of
permanent magnets due to thermal conditions.

16. Advantages Of DC Motor
• DC motors are smaller in size.
• These motors operate on DC supply then they can be used in electronics devices.
• DC motors are suitable for traction systems for driving heavy loads.
• DC series motors have will high starting torque.
• Wide range of speed control.
• DC Shunt motors are best suited for armature control and field control.
• DC motors have quick starting, stopping, reversing, and fast acceleration.
• DC motors are free from harmonics.
Disadvantages Of DC Motor
• DC motors have a high initial cost.
• Maintenance cost is high and increased operation due to the presence of brushes and
commutator.
• Due to sparking at brush DC motors cannot operate in explosive and hazardous
conditions.
• As the speed increases, the shaft gets vibrated and the armature gets damaged.
• We need converters to supply power to the motor.
Applications Of DC Motor
• DC series motors are used where high starting torque is required and variation of
speed is possible. Series motors are used in traction systems, cranes, air compressors,
vacuum compressors, sewing machines, etc.
• Shunt motors are a special type of motor used where constant speed is required.
These motors are used in
blowers, weaving machines, spinning machines, lifts, etc.

17. Summery of DC Motor Drives:
• Brushed DC motors are well known for their ability to achieve high torque
at low speed and their torque–speed characteristics suitable for the traction
requirement.
• The motor speed is adjusted through varying voltage. Being suitable to propel
a vehicle and easy to be controlled, they have been used on EVs. Brushed DC
motors can have two, four or six poles depending on power output and
voltage, and may have series or shunt field windings.
• On the one hand, shunt motors have the better controllability than series
motors. Separately excited DC motors are inherently suited for field
weakened operation, due to its decoupled torque and flux control
characteristics.
• On the other hand, a range of extended constant power operation is obtained
by separate field weakening. However, brushed DC motor drives have a bulky
construction, low efficiency, low reliability, and higher need of maintenance,
mainly due to the presence of the mechanical commutator and brushes.
• It is difficult to downsize brushed DC motors. This makes brushed DC motors
more heavy and expensive. Furthermore, friction between brushes and
commutator restricts the maximum motor speed.

18. Induction Motors
Working principal
• In a DC motor, supply is needed to be given for the stator winding as well as the rotor
winding. But in an induction motor only the stator winding is fed with anAC supply.
• Alternating flux is produced around the stator winding due to AC supply. This
alternating flux revolves with synchronous speed. The revolving flux is called
as "Rotating Magnetic Field" (RMF).
• The relative speed between stator RMF and rotor conductors causes an induced
emf in the rotor conductors, according to the Faraday's law of electromagnetic
induction. The rotor conductors are short circuited, and hence rotor current is
produced due to induced emf. That is why such motors are called as induction
motors.
• (This action is same as that occurs in transformers, hence induction motors can
be called as rotating transformers.)
• Now, induced current in rotor will also produce alternating flux around it. This
rotor flux lags behind the stator flux. The direction of induced rotor current,
according to Lenz's law, is such that it will tend to oppose the cause of its
production.
• As the cause of production of rotor current is the relative velocity between
rotating stator flux and the rotor, the rotor will try to catch up with the stator
RMF. Thus the rotor rotates in the same direction as that of stator flux to
minimize the relative velocity. However, the rotor never succeeds in catching
up the synchronous speed. This is the basic working principle of induction
motor of either type, single phase of 3 phase.

19. • The induction motors do not have a high starting toque like DC
series motors under fixed voltage and fixed frequency operation.
• But this characteristic can be altered by using various control
techniques like FOC or v/f methods.
• By using these control methods, the maximum torque is made
available at the starting of the motor which is suitable for traction
application.
• Squirrel cage induction motors have a long life due to less
maintenance.
• Induction motors can be designed up to an efficiency of 92-95%.
• The drawback of an induction motor is that it requires complex
inverter circuit and control of the motor is difficult.
• In permanent magnet motors, the magnets contribute to the flux
density B. Therefore, adjusting the value of B in induction motors is
easy when compared to permanent magnet motors.
• It is because in Induction motors the value of B can be adjusted by
varying the voltage and frequency (V/f) based on torque
requirements. This helps in reducing the losses which in turn
improves the efficiency.

20. Three PhaseAC Induction Motors
• Tesla Model S is the best example to prove the high performance
capability of induction motors compared to its counterparts.
• By opting for induction motors, Tesla might have wanted to
eliminate the dependency on permanent magnets.
• Even Mahindra Reva e2o uses a three phase induction motor for its
propulsion.
• Major automotive manufacturers like TATAmotors have planned to
use Induction motors in their cars and buses.
• The two-wheeler manufacturer TVS motors will be launching an
electric scooter which uses induction motor for its propulsion.
• Induction motors are the preferred choice for performance oriented
electric vehicles due to its cheap cost.
• The other advantage is that it can withstand rugged environmental
conditions.
• Due to these advantages, the Indian railways has started replacing
its DC motors with AC induction motors.

21. Three Phase AC Induction Motors

22. Advantages of induction motor:
• It is a very cheap cost compare to the other motors.
• This motor is a highly efficient motor. The efficiency of the induction
motor is varying from 85 to 95%.
• Themaintenance of an induction motor is very less
compared to the DC motor and synchronous motor.
• The working of an induction motor is very simple and unique.
• The construction of an induction motor is robust and also sturdy.
• In this motor, only the AC source requires to operate. It does not require
DC excitation like the use of a synchronous motor.
• In this motor, the speed variation from no load to rated load is very less.
• The induction motor is famous for its durability. This makes it the ideal
machine for many of
the uses. This results in the motor run for many years with no cost and
maintenance.
• Due to the absence of brushes, there are no sparks in the motor. It can
also be operated in hazardous conditions.
• Unlike synchronous motors, a 3 phase induction motor has high starting
torque, good speed
regulation, and also reasonable overload capacity.

23. Disadvantages of induction motor:
• The power factor of the motor is very low during light load
conditions.
• During light load conditions, it operates at a very low power factor.
• It has low efficiency.
• Single-phase induction motor is not self-starting.It requires some
auxiliary for stating.
• This motorcannot use in such applications where
the uses of high starting torque is necessary like
traction and lifting weight.
• The change in the speed of the motor is very low loading different
loading conditions, so the
speed control of IM is difficult.
• The speed ofthe motor is very low during
different loading conditioned so, the speed control of
the induction motor is difficult.

24. Applications of single-phase induction
motors
Applications of three-phase induction
motors
• Pumps
• Compressors
• Small fans
• Mixers
• Toys
• High-speed vacuums
• Electric shavers
• Drilling machines
• Lifts
• Cranes
• Hoists
• Large exhaust fans
• Lathe machines
• Crushers
• Oil extracting mills
• Textiles
• Commercial electric and hybrid vehicles

25. Summery of Induction motor drives:
•Induction motors are of simple construction, reliability, ruggedness, low
maintenance, low cost, and ability to operate in hostile environments. The
absence of brush friction permits the motors to raise the limit for maximum
speed, and the higher rating of speed enable these motors to develop high
output.
•Speed variations of induction motors are achieved by changing the frequency of
voltage. Field orientation control (FOC) of induction motor can decouple its
torque control from field control. This allows the motor to behave in the same
manner as a separately excited dc motor.
•This motor, however, does not suffer from the same speed limitations as in the
dc motor. Extended speed range operation beyond base speed is accomplished
by flux weakening, once the motor has reached its rated power capability. A
properly designed induction motor, e.g., spindle motor, with field oriented
control can achieve
field weakened range of 3-5 times the base speed.
•However, the controllers of induction motors are at higher cost than the ones of
DC motors. Furthermore, the presence of a breakdown torque limits its
extended constant-power operation. At the critical speed, the breakdown torque
is reached. Generally, for a conventional IM, the critical speed is around two
times the synchronous one.
•Any attempt to operate the motor at the maximum current beyond this speed
will stall the motor. Although FOC
may extend constant power operation, it results in an increased breakdown
torque thereby resulting in an over- sizing of the motor.
•In addition, efficiency at a high speed range may suffer in addition to the fact
that IMs efficiency is inherently
lower than that of permanent magnetic (PM) motors and switched reluctance
motors (SRMs) due to the absence
of rotor winding and rotor copper losses.

26. Permanent Magnet Brushless Motor:
• By using high energy permanent magnet as the field excitation mechanism a
permanent magnet motor drive can be potentially designed with high power
density, high speed and high operation efficiency for EV and HEV
applications.
• BLDC motor works on the principle similar to that of a Brushed DC motor. The
Lorentz force law which states that whenever a current carrying conductor
placed in a magnetic field it experiences a force. As a consequence of reaction
force, the magnet will experience an equal and opposite force. In the BLDC
motor, the current carrying conductor is stationary and the permanent
magnet is moving.
• When the stator coils get a supply from source, it becomes electromagnet and
starts producing the uniform field in the air gap. Though the source of supply
is DC, switching makes to generate an AC voltage waveform with trapezoidal
shape. Due to the force of interaction between electromagnet stator and
permanent magnet rotor, the rotor continues to rotate.
• With the switching of windings as High and Low signals, corresponding
winding energized as North and South poles. The permanent magnet rotor
with North and South poles align with stator poles which causes the motor to
rotate.

27. Advantages of Brushless DC motor
• Less overall maintenance due to absence of brushes
• Reduced size with far superior thermal characteristics
• Higher speed range and lower electric noise generation.
• It has no mechanical commutator and associated problems
• High efficiency and high output power to size ratio due to the use of permanent
magnet rotor
• High speed of operation even in loaded and unloaded conditions due to
the absence of brushes that limits the speed
• Smaller motor geometry and lighter in weight than both brushed type DC and
inductionAC motors.
• Long life as no inspection and maintenance is required for commutator system
• Higher dynamic response due to low inertia and carrying windings in the stator
• Less electromagnetic interference
• Low noise due to absence of brushes

28. Limitations of Brushless DC motor
• These motors are costly
• Electronic controller required control this motor is expensive
• Requires complex drive circuitry
• Need of additional sensors
Applications of Brushless DC motor
• Brushless DC motors (BLDC) use for a wide variety of application
requirements such as varying loads, constant loads and positioning
applications in the fields of industrial control, automotive, aviation,
automation systems, health care equipments etc.
• Computer hard drives and DVD/CD players
• Electric vehicles, hybrid vehicles, and electric bicycles
• Industrial robots, CNC machine tools, and simple belt driven systems
• Washing machines, compressors and dryers
• Fans, pumps and blowers.

30. Permanent magnet direct current motor: When field windings
and magnetic poles of conventional DCMs are replaced with PMs, a
PM-DCM is established. PM-DCMs show higher power density and
efficiency, but it needs more maintenance and exhibits low life and
torque fluctuation due to the commutator and brush system; these are
still the concerns to be solved for EV applications.
Permanent magnet brushless DC motor: PM-BLDCM is a special
PMSM structurally and theoretically, but its windings are
concentrated normally and the stator current wave shape is
trapezoidal, instead of sinusoidal in SPM. The commutator-brush
system is not required. However, the torque ripple and noise appear
during electrical commutation, and it is difficult to achieve the
maximum speed beyond twice the base speed.
Permanent magnet hybrid excitation motor: By adding excitation
windings to PMSM, the motor has both PMs and excitation windings
and becomes a hybrid excited motor, which is PM-HEM. This motor
has the minimum flux leakage, high flux density in the air gap, high
power density, and good torque-speed characteristics. However, its
topology and control are relatively complex owing to two separate
excitations.

31. Summery of PM BLDC motor drives:
• PM BLDC motor drives are specifically known for their high
efficiency and high power density. Using permanent magnet, the
motors can eliminate the need for energy to produce magnetic poles.
So they are capable of achieve higher efficiency than DC motors,
induction motors and SRMs.
• Furthermore, heat is efficiently dissipated to the surroundings. The
speed range may be extended three to four times over the base speed
if for a PM BLDC motor a conduction- angle control is used .
• PM BLDC motor drives have the other drawbacks in that the magnet
is expensive and that the mechanical strength of the magnet makes
it difficult to build a large torque into the motor. PM BLDC motors
have no brush to limit speed, but questions persist over the fixing
intensity of the magnet because it restricts the maximum speed if the
motors are of an inner- rotor type.
• Furthermore, this motor suffers from a rather limited field weakening
capability. This is due to the presence of the PM field which can
only be weakened through production of a stator field component
which opposes the rotor magnetic field.
• Nevertheless, extended constant power operation is possible through
the advancing of the commutation angle.

32. Switched Reluctance Motors (SRM)
• An electric motor like SRM (switched reluctance motor) runs
through reluctance torque. Different from the types of common
brushed DC motor, power can be transmitted to windings within the
stator instead of the rotor. An alternate name of this motor is VRM
(Variable Reluctance Motor). For a better operation of this motor, it
uses a switching inverter. The control characteristics of this motor
are the same as dc motors which electronically commutated. These
motors are applicable where sizing, as well as horsepower (hp) to
weight, is critical.
• This motor simplifies its mechanical design to restrict the flow of
current toward a rotary part; however, it complicates the design
because some kind of switching system must be employed to
transmit the power toward the different windings. This mechanical
design can also be used for a generator. The load can be switched
toward the coils within the sequence to coordinate the flow of
current through the rotation. So these generators can also run at
high speed as compared with conventional types of motors because
the armature is made like a single piece of magnetizable material
like a slotted cylinder.

33. Switched Reluctance Motors (SRM)

34. Working Principle
• The working principle of the switched reluctance motor is, it works
on the principle of variable reluctance that means, the rotor of this
motor constantly tries to align through the lowest reluctance lane.
• The formation of the rotary magnetic field can be done using the
circuit of power electronics switching.
• In this, the magnetic circuit’s reluctance can mainly depend on the
air gap. Therefore, by modifying the air gap among the rotor as well
as a stator, we can also modify the reluctance of this motor. Here,
reluctance can be defined as resistance toward the magnetic flux. For
Electrical circuits, reluctance is the combination of resistance as well
as the magnetic circuit.
• The operating of SRM (switched reluctance motor) can be done
through switching currents within the stator windings of the motor
by making changes within the magnetic circuit. This circuit can be
formed through the stator as well as the rotor of the motor.
• Once the poles of the stator & the rotor are out of position, then the
magnetic circuit among them includes a high reluctance.

35. • When the pairs of the pole in the stator are switched, the rotor switches to connect
through the activated stator poles to reduce the reluctance of the circuit. When the
stator poles are switched then they should be exactly timed to make sure that it
happens because the rotor pole is moving toward to connect with the activated stator
pole.
• The main difference between SRMs (switched reluctance motors) & stepper
motors is the construction of stator. In an SRM, the phases are autonomous with
each other that means, if one otherwise more phases stop working, then the motor
will operable even though by decreased torque output.
• Switched reluctance motors generate more clear noise as compared with stepper
motors. The main source of
noise can be the distortion of the stator because of the radial forces that happen once
the pairs of stator poles are activated. These pairs are attracted to cause radial forces
to alter the stator.
The characteristics of the switched reluctance motor include the following.
• This kind of reluctance motor is a 1-phase or 3-phase
• Speed control of this motor is simple.
• The triggering circuit can be changed to get high speed
• It operates with a DC supply once used with an inverter.
• Once the firing angle of any switching device can be changed then different speeds
can be achieved.
• Control of one phase is independent of the other two phases.
• The unutilized energy fed to the motor can be retrieved by using the feedback diodes.
This improves efficiency.

36. The advantages of a switched reluctance motor include the
following.
• These motors are very simple & the rotors in this motor are
extremely strong
• These motors are applicable for high-speed applications.
• The VFDs (variable frequency drives) of this motor are somewhat
simpler as compared with conventional VFDs.
• This motor doesn’t use any additional ventilation system when the
stator, as well as rotor slots, is projected. So the airflow can be
maintained among the slots.
• These are less expensive because of the nonexistence of permanent
magnets.
• Fault tolerance is high
• This motor works with a simple two-phase or three-phase pulse
generator.
• Phase losses do not change the operation of the motor.
• Once the phase sequence is changed then the motor direction will be
changed.
• Inertia Ratio or High Torque
• Self-starting without using additional arrangements

37. The disadvantages of a switched reluctance motor include the following.
• Switched reluctance motors have less torque capacity & normally these motors
are noisy.
• While operating this motor at high speed, it creates a torque ripple.
• High noise level
• It uses an external rotor position sensor
• These are applicable for medium to high speed, low-cost applications wherever
controllability & shaft or noise torque ripple are not dangerous.
• This motor generates harmonics when it operates at high speed, so to reduce
this, large size capacitors need to
install.
• Since the nonexistence of a permanent magnet, the SRM has to carry a
high i/p current to increase the necessity of converter KVA.
The applications of switched reluctance motors include the following.
• These types of motors are used as an alternative for induction motors in
different applications wherever the
operating conditions of this motor do not suit them.
• In textile machinery like towel looms, rapier looms, etc
• Used in electric vehicles
• Oilfield machinery like beam pumps, vertical pumps, well testing machinery,
etc.
• Mining machinery like conveyors, shearers, winches, ball mills, boring
machines, coal crushers, etc.
• Used in all kinds of mechanical presses like screw presses.

38. These motors are used in miscellaneous applications which include
the following.
• Machine tools like vertical lathes, planers, drilling machines, etc.
• Coil winding as well as unwinding equipment
• General machinery like pumps, fans, compressors, etc.
• Equipment used in paper mills
• Machinery used for food mixing
• Rolling mill for metals
• Lifting machines such as winches, lifts, conveyors, etc
• Manufacturing of plastic-like extrusion, injection molding devices
• Power generation device like load control using wind turbine rotor
blade
• Used in domestic appliances like vacuum cleaners, washing
machines, fans, etc.
• These motors have many benefits in different applications. At
present, the linear version of this motor has been implemented to
process the same attributes as well as prospects by owing their
design & high force density.

39. Summery of SRM motor drives:
• SRM drives are gaining much interest and are recognized to have a potential for
EV applications. These motor drives have definite advantages such as simple
and rugged construction, fault-tolerant operation, simple control, and
outstanding torque–speed characteristics.
• SRM drives can inherently operate with an extremely long constant-power
range. The torque-speed
characteristics of SRM drives match very well with the EV load characteristics.
• The SRM drive has high speed operation capability with a wide constant
power region. The motor has high starting torque and high torque-inertia ratio.
The rotor structure is extremely simple without any windings, magnets,
commutators or brushes.
• The fault tolerance of the motor is also extremely good. Because of its simple
construction and low
rotor inertia, SRM has very rapid acceleration and extremely high speed
operation.
• Because of its wide speed range operation, SRM is particularly suitable for
gearless operation in EV propulsion.
• In addition, the absence of magnetic sources (i.e., windings or permanent
magnets) on the rotor
makes SRM relatively easy to cool and insensitive to high temperatures.
• The latter is of prime interest in automotive applications, which demand
operation under harsh ambient conditions. An extended range of 2-3 times the
base speed is usually possible using an appropriate control.
• The disadvantages of SRM drives are that they have to suffer from torque
ripple and acoustic noise.
However, these are not potential problems that prohibit its use for Evs
application.

40. Review and Development of Electric Motor Systems and Electric Powertrains for New
Energy Vehicles
Index DC Motor Induction
Motor
Permanent magnet
induction motor
Switched Reluctance
Motor Drives
Efficiency Good Better Best Good
Speed Good Best Better Best
Size Good Better Best Better
Reliability Good Better Best Best
Control
simplicity
Best Better Good Better
Performance Good Better Best Better

41. Comparative analysis of motor drives:
• DC motor drives will continue to be used in EVs because DC motor drives
are available at the lowest cost. From the point of view of efficiency, PM
BLDC motor drives are the best choice. SRM drives have the lowest weight
among four types of motor drives for Evs. If the choice of motor drives for
EVs is determined by three factors that are weight, efficiency and cost, it is
clear that SRM drives are the best choice for EVs. Except for the efficiency,
weight and cost, SRM drives also have the ascendancy in the aspects of
cooling, maximum speed, fault tolerance, and reliability.
• after evaluating tradeoffs between the efficiency, weight and cost, cooling,
maximum speed, fault tolerance, safety and reliability for brushed DC motor
drives, IM drives, PM BLDC motor drives, and SRM drives, SRM drives are
the most appropriate candidate by evaluating an optimal balance.
• In the aspect of efficiency, PM BLDC motor drives are better than SRM
drives, IM drives and brushed DC motor drives; The weight of SRM drives is
lower than PM BLDC motor, IM, and brushed DC motor drives; Brushed DC
motor drives have the lowest cost for these four types of motor drives;
Taking into account the aforementioned three criteria, SRM drives are
superior to other three types of motor drives. Furthermore, SRM drives also
have the ascendancy in the aspects of cooling, maximum speed, fault
tolerance, safety, and reliability. Therefore, SRM drives are ideally suitable for
nowadays EV applications.

42. Selection of Motor
• The electric motors used for automotive applications should have
characteristics like high starting torque, high power density, good
efficiency, etc.
• For selecting the appropriate electric vehicle motors, one has to first
list down the requirements of the performance that the vehicle has to
meet, the operating conditions and the cost associated with it.
• For example, go-kart vehicle and two-wheeler applications which
requires less performance (mostly less than 3 kW) at a low cost, it is
good to go with BLDC Hub motors.
• For three-wheelers and two-wheelers, it is also good to choose
BLDC motors with or without an external gear system.
• For high power applications like performance two-wheelers, cars,
buses, trucks the ideal motor choice would be PMSM or Induction
motors. Once the synchronous reluctance motor and switched
reluctance motor are made cost effective as PMSM or Induction
motors, then
one can have more options of motor types for electric vehicle
application.
• In terms of maturity of technology, induction motor and dc electric
motors has highest mature technology for being used propulsion
system and maturity of technology of these motors are slightly
greater than permanent magnet brushless electric motor and switched
reluctance motor.

43. • Drive requires less maintenance and breakdown should be
minimum.
• From reliability point of view, induction motor and switched
reluctance motors are most reliable motor drive followed by
permanent magnet brushless motor.
• DC drive have least reliability among all other drives. In terms of
power density permanent magnet brushless motor have high power
density as compare to both induction motor and switched reluctance
motor.
• Again DC drive has least power density. Apart from these factors
cost factor is also an important characteristics that should be taken
under consideration.
• Cost factor is most important because its makes things commercially
viable.
• In terms of cost factor, induction motor most cost efficient followed
by dc and switched reluctance motors.

44. Motor selection criteria
• Vehicle characteristics: The properties of the vehicle such as size,
weight, overload and aerodynamics are crucial vehicle
characteristics that will ultimately determine speed, torque and
power requirements of the electric motor. These aspects will help
understand the effects of the operating conditions of the vehicle and
are essential to the selection of the right powertrain.
• Driving cycles: How is the vehicle being used is also very
important. What will be the usual driving cycles of the vehicle?
Will it be driven in an urban area with many stops? Will it be
driven on long distances with only a few stops? All of this will help
to determine the vehicle configuration (series hybrid, parallel
hybrid, all electric) and battery pack size and ultimately impact the
choice of the powertrain.
• Vehicle configuration (electric, hybrid): Is the vehicle hybrid or full
electric? If hybrid, is it parallel hybrid or series hybrid? As a rule of
thumb, if the vehicle routes are not predictable or if it will be driven
on long distances, usually the hybrid architecture is preferred. The
full electric configuration is well suited for in city driving where the
distance is not too long between charging points, the speed is low
and the amount of stops is high.

45. • Maximal speed: What is the targeted maximum speed of the
vehicle? How long does it have to be sustained, maybe it is used
only for passing? What are the gearbox ratios available (if using a
gearbox) and the differential ratio? What is the rolling radius of the
wheel? All of these questions must be answered and used in the
calculations to determine the maximum speed the electric motor has
to reach in your application.
• Maximal torque: The maximum torque enables the vehicle to start in
a given slope. You need to find the highest grade the vehicle will
need to ascend. Using that grade, it is possible to calculate the
highest torque required by the electric motor considering the
differential and gearbox (if using a gearbox!). Maximal weight is
also to be taken into consideration.
• Maximal power: Some grades need to be climbed at a minimum
speed some others don’t. Sometimes the maximum power is found
simply at maximum speed (this is the case where the vehicle as a
large frontal area or goes at very high speed). This translates to
having a motor powerful enough to go through all the different
conditions the vehicle can be submitted to! The maximum power
enables the vehicle to reach and maintain a constant speed under
stringent slope and speed conditions.

46. • Battery Capacity: The battery capacity is typically calculated using a simulator
to go through a reference cycle typical of the usage of the vehicle. The
simulator can output the consumption of the vehicle in kWh/km. From that
value, the capacity of the battery can be calculated by multiplying it with the
desired range.
• Battery Voltage: The battery voltage is dependent on the size of the
vehicle. As the battery
voltage increases, the current output is lowered. So in the cases where the
vehicle continuous power is high like in bigger vehicles, you want to keep the
size of the conductors at a manageable level by increasing the battery voltage.
There are normally two ranges of voltages: 300-450Vdc and 500- 750Vdc.
This is because of the voltage limitation of IGBTs used in the motor controller
and the two main standard voltages available for them: 600Vdc and 1200Vdc.
• Gearbox or direct-drive: Will the powertrain architecture require a gearbox?
Do you want to save the costs related to implementing a transmission or/and
simplify your system? TM4’s SUMO electric powertrain offer a direct-drive
approach: the high torque/low speed of the motor allows it to directly
interface with standard axle differentials without the need for an intermediate
gearbox. While improving system reliability and reducing overall
maintenance costs, removing the transmission in an electric vehicle also
increases the powertrain’s efficiency considerably, allowing optimal use of the
energy stored in the battery pack.
• Cost: Last but not least, what is your budget? In a previous blog post, we
reviewed the different electric motor technologies available on the market,
their pros and cons and their relative usage in electric vehicles.

47. EV configurations
• Previously, the EV was mainly converted from the ICEV, simply replacing the
combustion engine by the electric motor while retaining all the other
components. This converted EV has been fading out because of the drawback
of heavy weight, loss of flexibility and degradation of performance.
• Compared with the ICEV, the configuration of the EV is particularly flexible.
• The energy flow in the EV is mainly via flexible electrical wires rather than
bolted flanges or rigid shafts.
• Different EV propulsion arrangements (such as independent four-wheel
and in-wheel drives)
involve a significant difference in the system configuration.
• Different EV energy sources (such as batteries and fuel cells) have different
weights, sizes and shapes.
• Figure shows the general configuration of the EV, consisting of three major
subsystems-electric
propulsion, energy source and auxiliary.
• The electric propulsion subsystem comprises the electronic controller,
power converter, electric
motor, mechanical transmission and driving wheels.
• The energy source subsystem involves the energy source, energy management
unit and energy refueling unit.
• The auxiliary subsystem consists of the power steering unit, temperature
control unit and auxiliary
power supply.

48. EV configurations

49. EV configurations

50. • 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 devices of the power converter which functions to
regulate power flow between the electric motor and 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.
• most available EV batteries (except some metal/air batteries) as well
as capacitors and flywheels readily accept regenerative energy.
• The energy management unit cooperates with the electronic
controller to control regenerative braking and its energy recovery.
• It also works with the energy refuelling unit to control refuelling 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. Besides the brake and
accelerator, the steering wheel is another key control input of the EV.
• Based on its angular position, the power steering unit can
determine how sharply the
vehicle should turn.

51. • For a modern EV, a three-phase induction motor is typically selected.
• The corresponding power converter is a three-phase PWM inverter.
• In general, the mechanical transmission is based on fixed gearing
and a differential. Also, a nickel-metal hydride (Ni-MH) battery is
also typically selected as the energy
• source.
• The corresponding refueling unit becomes a battery charger.
• The temperature control unit generally consists of a cooler and/or
a heater, depending on the climate of a particular country. This
typical set-up is shown in Figure.
• Atpresent, there are many possible EV
configurations due to thevariations in electric propulsion
and energy sources.
• Focusing on those variations in electric
propulsion, there are six typical alternatives
as shown in Figure.

53. • Figure (a) shows the first alternative which is a direct extension
of the existing ICEV adopting longitudinal front-engine front-wheel
drive. It consists of an electric motor, a clutch, a gearbox and a
differential. The clutch is a mechanical device which is used to
connect or disconnect power flow from the electric motor to the
wheels. The gearbox is another mechanical device which consists of
a set of gears with different gear ratios. By incorporating both clutch
and gearbox, the driver can shift the gear ratios and hence the torque
going to the wheels. The wheels have high torque low speed in the
lower gears and high speed low torque in the higher gears. The
differential is a mechanical device which enables the wheels to be
driven at different speeds when cornering-the outer wheel covering a
greater distance than the inner wheel.
• By replacing the gearbox with fixed gearing and hence removing the
clutch, both the weight and size of the mechanical transmission can
be greatly reduced. Figure (b) shows this arrangement which consists
of an electric motor, fixed gearing and a differential. Notice that this
EV configuration is not suitable for the ICEV as the engine by itself,
without the clutch and gearbox, cannot offer the desired torque-speed
characteristics.

54. • Similar to the concept of transverse front-engine front-wheel drive of
the existing ICEV, the electric motor, fixed gearing and differential
are integrated into a single assembly, while both axles point at both
driving wheels. Figure (c) show this configuration which is in fact
most commonly adopted by modern EVs.
• Besides the mechanical means, the differential action of an EV when
cornering can be electronically provided by two electric motors
operating at different speeds. Figure (d) shows this dual-motor
configuration in which two electric motors separately drive the
driving wheels via fixed gearing.
• In order to further shorten the mechanical transmission path from
the electric motor to the
driving wheel, the electric motor can be placed inside a wheel. This
arrangement is the so- called in-wheel drive. Figure (e) shows this
configuration in which fixed planetary gearing is employed to reduce
the motor speed to the desired wheel speed. It should be noted that
planetary gearing offers the advantages of a high speed-reduction
ratio as well as an inline arrangement of input and output shafts.
• 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. Figure (f) shows this gearless arrangement in which the
outer rotor is directly mounted on the wheel rim. Thus, speed control
of the electric motor is equivalent to the control of the wheel speed
and hence the vehicle speed.

55. • Apart from the variations in electric propulsion, there are other EV
configurations due to the variations in energy sources (batteries, fuel cells,
capacitors and flywheels). Six typical alternatives are shown in Figure 2.
• Figure (a) shows a basic battery-powered configuration that is almost
exclusively adopted by existing EVs. The battery may be distributed around the
vehicle, packed together at the vehicle back or located beneath the vehicle
chassis. This battery should be able to offer reasonable specific energy and
specific power as well as being able to accept regenerative energy during
braking. Notice that both high specific energy and high specific power are
desirable for EV applications as the former governs the driving range while the
latter dictates the acceleration rate and hill-climbing capability. A battery having
a design compromised between specific energy and specific power is generally
adopted in this configuration.
• Instead of using a compromised battery design, two different batteries (one is
optimized for high specific energy while another for high specific power) can
be used simultaneously in an EV. Figure (b) shows the basic arrangement of
this battery & battery hybrid energy source. This arrangement not only
decouples the requirements on energy and power but also affords an
opportunity to use those mechanically rechargeable batteries which cannot
accept regenerative energy during braking or downhill.

56. • Differing from the battery which is an energy storage device, the fuel cell is an
energy generation device. The operating principle of fuel cells is a reverse
process of electrolysis- combining hydrogen and oxygen gases to form
electricity and water. Hydrogen gas can be stored in an on-board tank whereas
oxygen gas is simply extracted from air. Since the fuel cell can offer high
specific energy but cannot accept regenerative energy, it is preferable to
combine it with a battery with high specific power and high energy receptivity.
Figure (c) shows this arrangement which is denoted as a fuel cell & battery
hybrid energy source.
• Rather than storing it as a compressed gas, a liquid or a metal hydride,
hydrogen can be on- board generated from ambient-temperature liquid fuels
such as methanol or even petrol. As shown in Figure (d), a mini reformer is
installed in the EV to produce on line the necessary hydrogen gas for the fuel
cell.
• In contrast to the fuel cell & battery hybrid in which the battery is purposely
selected to offer high specific power and high energy receptivity, the battery in
the battery & capacitor hybrid is aimed to have high specific energy. This is
because a capacitor can inherently offer a much higher specific power and
energy receptivity than a battery. Since the available capacitors for EV
application, usually termed as ultracapacitors, are of relatively low voltage
level, an additional dc-dc power converter is needed to interface between the
battery and capacitor terminals. Figure (e) shows this configuration.

57. • For EVs converted from ICEVs, the use of variable gearing was
claimed to be natural because both gearbox and clutch are already
present and their maintenance costs are minor.
• the use of variable gearing can enhance the electric motor
achieving regenerative braking and high efficiency operation over a
wide speed range.
• Fixed-gearing transmission is usually based on planetary gearing. A
planetary gear set consists of a sun gear, several planet gears, a planet
gear carrier and a ring gear. It takes the advantages of strong,
compact, high efficiency, high speed reduction ratio and in-line
arrangement of input and output shafts over the conventional parallel-
shaft variable gear set.
• Thus, the removal of this variable gearing can significantly reduce
the overall complexity,
size, weight and cost of the transmission. Moreover, modern electric
motors with the use of fixed gearing can readily offer the desired
torque-speed characteristics for vehicular operation.
• Figure shows typical force-speed characteristics of an EV with fixed
gearing, consisting of constant-torque operation for acceleration and
hill climbing as well as constant-power
operation for high-speed cruising. Moreover, the absence of gear
changing (irrespective of whether it is manual or automatic) can
greatly enhance smooth driving and transmission efficiency.
Therefore, modern EVs almost exclusively adopt fixed gearing rather
than variable gearing.

58. • For EVs, output characteristics of electric motors differ from those of
ICEs.
• Typically, the electric motor eliminates the necessity for a motor to be
idle while at a stop, it is allowed to produce large torque at low
speed, and it offers a wide range of speed variations.
• It may be possible to develop lighter, more compact, more efficient
systems by taking advantages of the characteristics of electric
motors.
• The choices of drivetrain systems in an EV include mainly:
propulsion mode, such as front-wheel drive, rear-wheel drive, or
four-wheel drive;
number of electric motors in a vehicle;
drive approach, for instance, indirect or direct drive; and
number of transmission gear levels.
• Therefore, the possible drivetrain systems in EVs have the following
six configurations.
1)Conventional
Type
2)Transmission-
less Type
3)Cascade Type
4)In-wheel Type with Reduction Gears and
Direct-drive Type 5)Four- wheel Direct-drive
Type
6)Planetary gear type

59. Conventional Type Transmission-less Type
Cascade Type In-wheel Type with Reduction Gears and Direct-drive
Four- wheel Direct-drive Type Planetary gear type

60. ICEV force-speed characteristics with five-speed transmission. EV force-speed characteristics with fixed gearing.

61. • Similar to the capacitor, the flywheel is another emerging energy storage device which can
offer high specific power and high energy receptivity. It should be noted that the flywheel for
EV applications is different from the conventional design which is characterized by low
speed and massive size. In contrast, it is lightweight and operates at ultrahigh speeds under a
vacuum environment.
• This ultrahigh-speed flywheel is incorporated into the rotor of an electric machine which
operates at motoring and generating modes when converting electrical energy to and from
kinetic energy, respectively. The corresponding configuration is shown in Figure (f) in which
the battery is selected to offer high specific energy. Since this flywheel is preferably
incorporated into an ac machine which is brushless and can offer a higher efficiency than
that of a dc machine, an additional ac-dc converter is needed to interface between the battery
and flywheel terminals.
FixedAnd Variable Gearing (Planetary gearing)
• Fixed gearing means that there is a fixed gear ratio between the propulsion device (ICE or
electric motor) to the driving wheels.
• In contrast, variable gearing involves shifting between different gear ratios, this can be
accomplished by using a combination of clutch and gearbox.

62. • The purpose of variable gearing is to provide multiple-speed transmission (achieving wide
ranges of speed and torque using different gear ratios).
• Generally, four- or live-speed transmission is used for passenger cars, and up to 16-speed
transmission for trucks.
• When the clutch is engaged, the propulsion device and the gearbox are coupled together and
power transmission is enabled. When it is disengaged manually or automatically, the power
transmission is interrupted so that the gear ratio in the gearbox can be shifted.
• For ICEVs, there is no alternative to the use of variable gearing as the ICE cannot offer the
desired torque-speed characteristics (such as high torque for hill climbing and high speed for
cruising) without using multiple-speed transmission).
• For EVs, the employment of variable gearing to achieve multiple-speed transmission used to
be controversial. For EVs converted from ICEVs, the use of variable gearing was claimed to
be natural because both gearbox and clutch are already present and their maintenance costs
are minor.
• However, the concept of converted EVs is almost obsolete as it cannot fully utilize the
flexibility and potentiality offered by EVs.

63. • It was also claimed that the use of variable gearing can enhance the electric motor achieving
regenerative braking and high efficiency operation over a wide speed range. With the
advances of power electronics and control algorithms, both regenerative braking and high
efficiency operation of electric motors can be easily achieved by electronic means rather than
mechanical means.
• Fixed-gearing transmission is usually based on planetary gearing. A planetary gear set
consists of a sun gear, several planet gears, a planet gear carrier and a ring gear. It takes the
advantages of strong, compact, high efficiency, high speed- reduction ratio and in-line
arrangement of input and output shafts over the conventional parallel-shaft variable gear set.
• Thus, the removal of this variable gearing can significantly reduce the overall complexity,
size, weight and cost of the transmission. Moreover, modem electric motors with the use of
fixed gearing can readily offer the desired torque-speed characteristics for vehicular
operation.
• fixed gearing, consisting of constant-torque operation for acceleration and hill climbing as
well as constant-power operation for high-speed cruising. Moreover, the absence of gear
changing (irrespective of whether it is manual or automatic) can greatly enhance smooth
driving and transmission efficiency. Therefore, modern EVs almost exclusively adopt fixed
gearing rather than variable gearing.

64. Single-And Multiple-motor Drives
• A differential is a standard component for conventional vehicles and this technology can be
carried forward to the LV field.
• When a vehicle is rounding a curved road, the outer wheel needs to travel on a larger radius
than the inner wheel.
• Thus, the differential adjusts the relative speeds or the wheels; otherwise, the wheels will slip
which causes tire wear, steering difficulties and poor road holding.
• For all ICEVs, whether front- or rear-wheel drive, a differential is mandatory.
• Figure shows a typical differential in which pinion spider gears can rotate on their shaft,
allowing axle side gears to turn at different speeds.
• For EVs, it is possible to dispense with a mechanical differential.
• By separately coupling two or even four electric motors to the driving wheels, the speed of
each wheel can be independently controlled in such a way that the differential action can be
electronically achieved when comparing.
• Figure shows a typical dual- motor drive with an electronic differential.

65. • This arrangement is smaller and lighter than the mechanical counterpart.
• Unlike the choice between variable gearing and fixed gearing, the selection of either a
single-motor drive with a differential or a multiple-motor drive without a differential is still
controversial.
• Positively, the removal of a mechanical differential can reduce the overall size and weight
while (he electronic differential can accurately control (he wheel speeds so as to achieve
better performance during cornering.
• Negatively, the use of an additional electric motor and power converter causes an increase in
the initial cost while the reliability of the electronic controller to accurately control two
electric motors at various driving conditions is to be observed.
• In recent years, the reliability of this electronic controller has been greatly improved by
incorporating the capability of fault tolerance.
• For example, the electronic controller consists of three micro processors.
• Two of them are used to separately control the motor speeds for the left and right wheels
while the remaining one is used for system control and coordination. All of them watch one
another by using a watchdog to improve the reliability.

67. In wheel drive configuration:
• By placing an electric motor inside the wheel, the in-wheel motor has the definite advantage
that the mechanical transmission path between the electric motor and the wheel can be
minimized or even eliminated, depending whether the electric motor is a high-speed inner-
rotor type or a low-speed outer-rotor type.
• When it is a high-speed inner-rotor motor, a fixed speed-reduction gear becomes necessary
to attain a realistic wheel speed. In general, a high speed-reduction planetary gear set is
adopted which is mounted between the motor shaft and the wheel rim.
• Typically, this motor is purposely designed to operate up to about 10000rpm so as to give a
higher power density.
• This maximum speed is limited by the friction and windage losses as well as the
transmission tolerance.
• Thus, the corresponding planetary gear ratio is of about 10:l to provide the wheel speed
range from zero to about 1000 rpm.
• On the other hand, the transmission can be totally removed when a low-speed outer-rotor
motor is used.

68. • The key is that this outer rotor itself is the wheel rim and the motor speed is equivalent Lu
the wheel speed, and no gears are required.
• Figure shows these two in-wheel drives, both employing a permanent-magnet brushless
motor.
• Although different types of electric motors can be adopted, the permanent-magnet brushless
machine is most attractive because of its outstanding power density.
• The high-speed inner-rotor motor has the advantages of smaller size, lighter weight and
lower cost, but needs an additional planetary gear set.
• On the other hand, the low-speed outer-rotor motor has the definite advantage of simplicity
and is gearless, but the motor suffers from the drawbacks of increased size, weight and cost
because of the low-speed design.
• Both types of in-wheel motors have been applied to modem EVs (Shimizu. 1995).

70. Motor Safety and Maintenance:
A well and carefully designed motor maintenance program, when correctly used, can be
summed up as preventive maintenance, predictive maintenance and reactive maintenance.
Inspection cycles depend upon the type of motor and the conditions under which it operates.
Motors need maintenance regularly in order.
kinds of maintenance:
• Preventive maintenance – to prevent operating problems and make sure that the motor
continuously provides reliable operation.
• Predictive maintenance – to ensure that the right kind of maintenance is carried out at the
right time.
• Reactive maintenance – to repair and replace the motor when a failure occurs.
Reactive Maintenance
• When motors fail, it is important to examine the motor and find out where in the motor it
happened and why it happened. Normally, good preventive maintenance can prevent failure.
• If the failure is caused by a weak component or inadequate maintenance, then all similar
equipment has to be examined in order to prevent the same failure from occurring elsewhere
inthe motor or in the entire system.

72. Predictive Maintenance
The objective of predictive maintenance of electric motor maintenance is to reduce
maintenance costs by detecting problems at an early stage and deal with them. Observations
of motor temperature, vibrations, etc. are only a few examples of data that can help predict
when the motor needs to be repaired or replaced. Following are some of the tests that provide
the necessary data about the state of the motor.
• Bearing considerations
• Insulation considerations
• Ground insulation test
• Cleaning and drying stator windings
• Surge test
• High potential testing – HIPOT
• DC high potential ground test
• AC high potential phase to ground test and phase-to-phase test
• Motor temperature
• Thermographic inspection

73. Electric Motor Safety:
Maintaining a safe work environment is paramount in industrial settings that involve high-voltage
infrastructure and rapidly moving components. Proper electric motor safety is an essential step
toward achieving trouble-free operation. Safety practices span across motor installation, everyday
operation, and maintenance. It is necessary to develop and consistently follow proper safety
procedures during each phase to achieve the best outcomes for your company and personnel.
With the right approach, the risk of accident can be minimized, and a safe and productive
working environment maintained.
Motor Operation Safety
One of the best ways to spot problems with a motor in advance is for operators to use sight, smell
and temperature to detect abnormal circumstances. However, this can be dangerous unless
operators are properly informed. A motor's surface can be extremely hot during normal operation,
especially after sudden changes in the load that draw unusually high current, and this temperature
can persist well after the motor has been stopped. Correct safety gear should be used around
running motors, and fingers and other objects kept away from ventilation ports and other points
of entry into the motor. Everyone should keep a safe distance from moving or rotating
components of the motor or driven load. When power outages occur, make sure that the motor
power is cut off so that it does not start unexpectedly when power returns.

74. Motor Installation Safety
• Before installing motor or developing electric motor safety procedures for your
application, it is essential to become familiar with local and national safety codes related to
your industry, as well as risk factors specific to the type of motor you have purchased.
• Please read the information provided by the manufacturer and always follow their
recommendations. After developing comprehensive safety procedures for your operation,
ensure that all operators and technicians involved are familiar with the procedures and
apply them consistently. Following the right steps during the installation of the motor
helps prevent accidents that can cause injury and damage to infrastructure.
• Before installing the motor, inspect it thoroughly for defects or damage. If any issues are
found, contact the seller before commencing installation. To reduce the risk of accident,
check that the motor characteristics are adequate for the requirements of the application
and that the voltage and connections on the motor match the power supply.
• When installing the motor, ensure that it is properly grounded and all connections are tight.
This helps protect against electrical shock if the motor connects with the skin.
Install all necessary safety measures such as thermal protection and electrical fuses, which
protect the motor and prevent potential accidents such as fires caused by overheating.

75. • Ensure that the motor is securely mounted and properly aligned and connected to the load.
Before start-up, it is advisable to run the motor in-place without a load to ensure that it has
been installed correctly. This is a good time to review safety procedures for the operator and
relevant personnel, including start-up, shutdown and emergency stop procedures.
• During normal operation of the motor, including start-up and shutdown, it is essential to
develop consistent procedures that protect the safety of not just the motor but any personnel
in the area. When starting a motor, make sure that all personnel in the area are alert and
aware of it.
Motor Maintenance Safety
• Whether routine or not, electric motor maintenance involves repeatedly handling and
testing the motor.
• Maintenance personnel work near hot and rapidly moving components. Besides being
qualified to disassemble and service the motor, maintenance personnel should be trained in
proper power lockout procedures, safety gear, first aid and any relevant safety codes.
• This ensures that maintenance is a low risk operation and productivity can be restored as
quickly and safely as possible when a fault occurs. Locking out power before working on
the motor is extremely important, and it is not enough to simply switch it off.

76. • Power can be suddenly and unexpectedly restored if the motor was stopped by a thermal
protector, which can automatically re-connect power when the motor has cooled down.
• The motor may also be inadvertently switched on by someone unaware. Proper power
lockout involves physically locking the main power switch in the off position, for example,
by enabling each technician to apply their own padlock before working on the motor.
• The main power switch should also be clearly labeled with a warning to ensure that
operators know that maintenance is being performed.
• Before handling the motor, ensure that the work environment is safe and that the motor has
been fully de-energized.
• Capacitors can store a lethal charge and must be properly drained if they are to be handled.
Ensure that the motor has cooled down sufficiently so that it does not present a risk of burn.
Check the work area for pools of liquid or leaked lubricant, increasing the risk of an
accident.

77. Motor Torque and Power Rating
• Power rating for electrical machines indicates the required supply voltage for smooth
running of that machine, it also shows the permissible maximum amount of current which
can easily flows through the machine and there will be a chance of breakdown in the
machine if those parameters goes beyond this limit.
• When the motor have insufficient rating, there will be frequent damages and shut downs
due to over loading.
• if the power rating of a motor is decided liberally, the extra initial cost and then loss of
energy due to operation below rated power makes this choice totally uneconomical.
• Another essential criteria of electrical motor power rating is that, during operation of motor,
heat is produced and it is inevitable due to I2R loss in the circuit and friction within the
motor. So, the ventilation system of the motor should be designed very carefully, to
dissipate the generated heat as quickly as possible.
• the main objectives of selecting and finding out motor power rating are To obtain the
suitable thermal model of motor and design the machine properly and for Finding out motor
duty class, also to Calculating motor ratings for various classes of duty.

78. Selection of Motor Power Rating:
• Selection of power rating is important to achieve economy with reliability.
• Improper selection of motor power rating results extra initial cost and extra loss of energy
due to the operation below rated power makes the choice uneconomical.
• Furthermore, induction and synchronous motors operate at a low power factor when
operating below the rated power.
• During operation of the machine, heat is produced due to losses and temperature rises.
An amount of developed heat is dissipated into the atmosphere. When the dissipation of
heat is equal to the developed heat, then it is said to be equilibrium condition. "Motor
temperature then reaches a steady state value.
• Steady state temperature depends on power loss, which in turn depends on the output power
of the machine. Since temperature rise has a direct relation with the output power, it is
termed thermal loading on the machine.
• Steady state temperature varies in different parts of the machine. It is usually high is the
windings because loss density in conductors is high and dissipation is slow; and the
conductors which are wrapped in insulating material are partly embedded in slots and thus
are not directly exposed to the cooling air.

79. Motor Torque and Power Rating
• Torque is the rotational equivalence of linear force. Power is the rate of doing work. The
relation between torque and power is directly proportional to each other.
• The power of a rotating object can be mathematically written as the scalar product of torque
and angular velocity. i.e. Power P = τ.ω Where, P is the power (work done per unit time),
τ is the torque (rotational ability of a body), ω is the angular velocity(rate of change of
angular displacement).
• By taking the voltage and multiplying it by the associated current, the power can be
determined. A watt (W) is a unit of power defined as one Joule per second. For a DC source
the calculation is simply the voltage times the current: W = V xA.
• To calculate load torque, multiply the force (F) by the distance away from the rotational
axis, which is the radius of the pulley (r). If the mass of the load (blue box) is 20 Newtons,
and the radius of the pulley is 5 cm away, then the required torque for the application is 20
N x 0.05 m = 1 Nm.

80. Assignment No: 1
1. Define motor dives for electric vehicles with its advantage and requirements?
2. Explain Basic Elements of the Electric Drive Systems with neat sketch?
3. Explain EV motor's load requirement, performance specification and operating environment?
4. Classify EV motor drives with its comparative analysis?
5. Explain DC motor drives with its working principal, advantages, disadvantages and applications?
6. Explain Induction motor drives with its working principal, advantages, disadvantages and applications?
7. Explain Permanent Magnet Brushless motor drives with its working principal, advantages, disadvantages and
applications?
8. Explain Switched Reluctance motor drives with its working principal, advantages, disadvantages and
applications?
9. Compare electric motor drives on basis of following,
 Efficiency
 Speed
 Size
 Reliability
 Control stability
 Performance
10.List and explain motor selection criteria for electric vehicles?
11.What do you mean by EV configuration, explain with suitable block diagram?
12.Explain any two EV configurations due to variation in electric propulsion?
13.Explain any two EV configurations due to variation in energy sources?
14.Explain Fixed and Variable Gearing (Planetary gearing)?
15.Explain Single- And Multiple-motor Drives configuration?
16.Explain In wheel drive configuration
17.Explain significance of Motor Safety and Maintenance with its types?
18.Explain the following
 Electric Motor Safety:
 Motor Operation Safety
 Motor Installation Safety
 Motor Maintenance Safety
19.Explain significance of Motor Torque and Power Rating?
20.Explain the Selection criteria of Motor Power Rating?