Hawassa University, IOT; Department Electromechanical Engineering

BSC Thesis

CHAPTER TWO
LITERATURE REVIEW
2.1 Introduction
Urban mobility has gained importance in the past few years. By 2050, nearly 70% of the
global population is projected to live in urban areas, exacerbating the effects of air
pollution, congestion, noise and greenhouse gas emissions. Moreover, transportation is the
second largest contributor to greenhouse gas emissions and urban air pollution, posing
severe threats to human health and well-being. The vehicles emitting organic compounds,
nitrogen oxide and carbon monoxide have done significant pollution of air. World
population is growing by an extremely high rate so that the vehicle usage is also rising with
the rise of the population. Fossil fuel is the main energy resource of these vehicles. In 21th
century oil production reached a peak. Estimates indicate that petroleum and natural gas
will be run out by the year 2042 [2].

Governments in Europe and other world regions are focused on the greatly reducing the
transport sectors carbon emissions. The European Union (EU) and its member states are
using vehicle and fuel regulations, substantial financial and nonfinancial incentives for
consumes and other policies to replace petroleum with lower carbon alternatives. This put
much pressure on the transportation sector to replace the diesel engine vehicles with the
electric vehicles.

The first electric vehicles were introduced as early as 1838 or 52 years before internal
combustion engine vehicle entered the market. Despite recent growing interest electric
vehicles have remained a relatively small market until today. Overall the market has grown
from just hundreds of electric vehicle sales in 2010 to more than 500,000 sales worldwide
in 2015. The early development of markets for electric vehicles is seen predominantly in
parts of china, Europe, and the United States, where electric vehicle support policies are
helping promote the technology while costs are still relatively high compared with
conventional vehicles.

 TESLA
Founded as Tesla Motors, Tesla Inc. was incorporated in July 2003 by Martin Eberhard and
Marc Trepanning who financed the company until the Series a round of funding. The
founders were influenced to start the company after GM recalled all its EV1 electric cars
in 2003 and then destroyed them [3].
 KIA
The Kia Soul EV is an all-electric subcompact crossover manufactured by Kia motors.
The US Environmental Protection Agency (EPA) official range for the 2015 Kia Soul EV
is 93 miles and 111 miles for 2018 model year.
Designing of a Back Up Power Supply for Page 20
Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis

Deliveries began in South Korea in May 2014. European sales began in July 2014. Sales
started in the U.S. in October 2014; initially it was sold only in California, Oregon, and
several Eastern states, with the largest EV markets and infrastructure including New York,
New Jersey and Maryland. Global sales exceeded the 10,000 unit milestone in January
2016, with Europe as the leading market with 6,770 units sold. Germany is the leading
European market with 3,853 units sold through December 2015 [4].
 BMW
While the BMW brand is better known for its luxury performance sedans than for its
emissions saving technologies, 2012 marks the 40th anniversary of the first all-electric
BMW. To celebrate, BMW has put out a brief primer on its EV efforts, starting way back
in 1972 at the Munich Olympics. The Munich Olympics was BMW’s chance to show to
the world their response to the ongoing oil crisis in the Middle East. To wit, BMW’s
engineers developed the 1602 Electric using a 43 horsepower Bosch electric motor and 12
lead-acid batteries. Alas, with just 19 miles of range, even their limited use during the
Olympics pushed the boundaries of the very limited range. Yet the battery pack was
designed to be swapped out for a fresh one, an idea that is still on the table thanks to Project
Better Place [5].
 NISSAN
Nissan motors has developed several concept car and limited production electric cars, and
launched the production Nissan all electric car in December 2010. As of December 2015,
the Leaf is the world's all-time best selling highway-capable plugged in electrical cars with
over 200,000 units sold since its introduction. The Renault-Nissan alliance committed €4
billion (around US$5.2 billion) into its electric vehicle (EV) and battery development
programs with the aim to become the leader in zero-emission transportation. By mid-2015,
the Alliance ranked as the world's leading electric vehicle manufacturer with global sales
of over 250,000 units delivered since December 2010 [6].
This all companies had been trying to on work how to expand the traveling range of the
electric vehicles. Many studies and researches had been carried out in the past many years.
But still there is no fully satisfying findings discovered. However there are some techniques
that are applied through the life time of the electric vehicle revolution era.
Most of this techniques mainly focus on the battery. All electric vehicle manufacturer
companies tried to upgrade the efficiency of the battery. In addition to this in the recent
period there has been introduced a new technique of charging the vehicle during its
movement. This technique arises from the idea energy neither created nor destroyed, but it
can change to different form.
So from this theory the companies generate electrical energy from the energy which
dissipate by changing in to different form of energy during the brake pedal is applied.
Which is called regenerative braking. This generated electrical energy goes back to the
battery pack of the electric vehicle and charges it.
Designing of a Back Up Power Supply for Page 21
Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis

2.2 Battery Technology

The value chain of electric car batteries consists of seven steps:
I. Component production
II. Cell production
III. Module production
IV. Pack assembly
V. Vehicle integration
VI. Use
VII. Reuse and recycle

Figure 6: Seven Steps of Electric Car Batteries

Lithium ion batteries comprise a family of battery chemistries that employ various
combination of anode and cathode materials. Each combination has distinct advantages and
disadvantages in terms of safety, performance, cost, and other parameters. The most
prominent technologies for automotive applications are lithium-nickel-cobalt-aluminum
(NCA), lithium-nickel-manganese-cobalt (NMC), lithium-manganese spinel (LMO), and
lithium ion phosphate (LFP) [7].

On the technical side, competing lithium ion technologies can be compared along six
dimensions:
1. Safety: is the most important criterion for electric car batteries. Even a single
battery fire could turn public opinion against electric mobility and set back industry
development for months or years. The main concern in this area is avoiding thermal
runaway a positive feedback loop whereby chemical reactions triggered in the cell
exacerbate heat release, potentially resulting in a fire.

Designing of a Back Up Power Supply for Page 22

Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis
While battery safety is indisputably a valid concern, it is useful to put this concern
in context by recalling the significant safety challenges originally associated with
the internal combustion engine (ICE) and with gasoline storage, which were largely
overcome through improvements in design and engineering.

2. Life span: there are two ways of measuring battery life span: cycle stability and
overall age. Cycle stability is the number of times a battery can be fully charged
and discharged before being degraded to 80% of its original capacity at full charge.

3. Performance: the expectation that the owner of an electric vehicle should be able
to drive it both at blisteringly hot summer temperatures and at subzero winter
temperature poses substantial engineering challenges.

4. Specific energy: it is the battery capacity for storing energy per kilogram of weight
is still only 1 percent of the specific energy of gasoline. Unless there is a major
breakthrough, batteries will continue to limit the driving range of electric vehicles
to some 250 to 300 kilometers (about 160 to 190 miles) between chargers.

5. Specific power: it is the amount of power that batteries can deliver per kilogram of
mass, it addresses relatively well by current battery technologies. Specific power is
particularly important in hybrid vehicles which discharge a small amount of energy
quickly.

6. Cost: most source estimate the current cost of an automotive lithium ion battery
pack, as sold at between $1,000 and $1,200 per kWh.

Figure 7: Five Principal Lithium Ion Technology

Designing of a Back Up Power Supply for Page 23
Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis

Improvements in battery technology over the past six years have been impressive. Today’s
battery cells have higher energy densities and are much less expensive on a per kWh basis
than they were just a few years ago. Lithium-ion (Li-ion) cells enjoy the bulk of investment,
and remain the preferred technology for LG Chemistry, Panasonic, and Samsung, the three
largest producers. Lithium-metal technologies with much higher energy densities are in
development, but currently lack the production scale and established supply chain
advantages of Li-ion.

Verifiable information on battery costs is difficult to obtain, owing to both intense

commercial sensitivity and confusion over the definition of “battery” which can apply to
the cost of individual cells, the battery pack, or the battery pack once installed in the vehicle
itself, or indeed the final cost to the consumer once any manufacturer markup is applied.

The sharp downward trend in the cost of Li-ion cells, however, is clear. From a baseline of
about $1,000 per kWh for an installed battery. Cell manufacturing costs have declined
about 70% since 2010 due primarily to economies of scale. This holds across different
configurations and chemical compositions, and is the largest contributor to observed cost
declines, with an average of 8% cost reduction for a doubling in volume every year since
2010. Compounded from 2010-2015, this equates to a 35% real decline in cost due to
economies of scale, accounting for almost half of the total cost reductions seen since 2010
[8].

2.3 Types of EV Charging Equipment

Charging equipment, henceforth denoted by “electric vehicle supply equipment” (EVSE)
comes in two basic varieties. The first, comprising “Level 1” and “Level 2” EVSE, operates
using alternating current (AC), and can draw electricity directly from the local distribution
system. All BEVs and PHEVs carry an on-board inverter with limited capacity, to convert
AC power to direct current (DC), which is required to charge the battery. The second
variety, “Level 3” and above, uses DC charging, which bypasses the need for an inverter
by charging the battery directly and can therefore deliver much more power. There is
otherwise no relevant difference in the AC and DC charging process. Chargers in public or
commercial locations, typically Level 2 and above, (henceforth “commercial chargers”)
may be standalone devices, or stations comprised of multiple chargers.

Level 1 and Level 2: Alternating Current

Level 1, providing 1.4 kW of power in the U.S., is simply a conventional wall socket, and
requires no additional circuitry, aside from the adapters required to connect the EV to the
socket. In theory, Level 1 charging can be used anywhere, although in practice it takes
place primarily at the EV owners’ homes.
Level 2 charging operates on the same upgraded 220-volt outlets, required by washing
machines and clothes driers, and can easily be installed. More modern houses typically
have these outlets, while older houses may require electrical upgrades.

Designing of a Back Up Power Supply for Page 24

Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis
Depending on the home’s electrical infrastructure, this can involve upgraded circuitry,
wiring extensions to reach the charging location, or, even in rare cases, an upgraded
transformer.
Level 2 charging can also be provided at workplace locations, other business locations
(hotels, gas stations, private parking lots), and public locations (on-street parking space,
garages, streets, public parking lots wherever cars are likely to be stationary for hours at a
time).
Level 2 charging starts at a power rating of 6.6 kW, increasing to 19.2 kW depending on
the level of current that the supporting circuitry can sustain. Most home Level 2 charging,
and almost all commercial Level 2 charging, is limited to 6.6 kW because (a) the onboard
inverter on most existing EVs cannot handle significantly more than this level38 and (b)
boosting the current typically requires the installation of more expensive higher-capacity
circuitry.

Level 3 and above: Direct Current

Because direct current charging bypasses an EV’s onboard inverter to charge the battery
directly, it can deliver much higher levels of electrical power. This type of charger is
commonly referred to as a Direct Current Fast Charger (DCFC) and is typically used only
in commercial locations. While studies demonstrate that consistently high DCFC usage can
accelerate deterioration in battery capacity over time, capacity degradation for the vast
majority of users is more closely associated to overall usage than charging patterns.
“Estimated Direct Current Fast Charger utilization rates,” an NREL study concludes, “do
not appear frequent enough too significantly impact battery life,” suggesting that the
thermal management systems of the battery itself are a more important determinant.
Self-reported survey data from Tesla drivers suggests that even for the most frequent users
of fast charging, battery capacity is highly unlikely to fall below 90% of its original rating
even after 150,000 miles of usage.

DCFC charging is classified as follows:

• Level 3 charging is used to refer to a power delivery of 50 kW;
• Level 4 corresponds to 150kW;
• Level 5 (ultra-fast DCFC) corresponds to 350kW.

Most third-party DCFC chargers are Level 3, operating at about 50kW. Tesla’s proprietary
network of Superchargers, with a typical power output of 120 kW, is designed to serve
Tesla vehicles exclusively and corresponds most closely to Level 4. Level 5 ultra-fast
DCFC, which requires heavy duty insulation equipment, has not yet been deployed on a
commercial basis, and no mass-produced EVs can currently handle this level of power.
EVSE operator Charge Point announced a 400kW charging platform in January 2017 and
a consortium of OEMs (Porsche, Ford, Daimler and Volkswagen Group) is involved in a
joint venture aiming to install a 350kW network across Europe.

Designing of a Back Up Power Supply for Page 25

Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis

2.4 Regenerative Braking System

Brakes are employed to stop or retard the motion of any moving body. Thus, in automobiles
the brakes are having the most important function to perform. In conventional braking
system the motion is retarded or stopped by absorbing kinetic energy by friction, by making
the contact of the moving body with frictional rubber pad (called brake liner) which causes
the absorption of kinetic energy, and this is wasted in form of heat in surroundings. Each
time we brake, the momentum of vehicle is absorbed that it has gained by it and to re-
accelerate the vehicle we have to start from the scratch to redevelop that momentum by
using the more power from an engine .Thus, it will ultimately result in huge waste of
energy. As the basic law of Physics says „energy can neither be created nor be destroyed
it can only be converted from one form to another‟. It will be good if we could store this
energy somehow which is otherwise getting wasted out and reuse it next time we started to
accelerate. That's the basic concept of regenerative ("regent") brakes, which provide
braking for the system when needed by converting the available energy to some usable
form. These are widely used in electric trains and the latest electric cars.
Regenerative brake is an energy recovery mechanism which slows a vehicle by converting
its kinetic energy into another form, which can be either used immediately or stored until
needed.
Thus, the generated electricity during the braking is fed back into the supply system (in
case of electric trains), whereas in battery electric and hybrid electric vehicles, the energy
is stored in a battery or bank of capacitors for later use. Energy may also be stored by
compressing air or in a rotating flywheel.
An Energy Regeneration Brake was developed in 1967 for the AMC Amitron. This was a
completely battery powered urban concept car whose batteries were recharged by
regenerative braking, thus increasing the range of the automobile.
Many modern hybrid and electric vehicles use this technique to extend the range of the
battery pack. Examples include the Toyota Prius, Honda Insight, the Vectrix electric maxi-
scooter, and the Chevrolet Volt.
2.4.1 Need For Regenerative Brakes?
The regenerative braking system delivers a number of significant advantages over a car
that only has friction brakes. In low-speed, stop- and-go traffic where little deceleration is
required; the regenerative braking system can provide the majority of the total braking
force. This vastly improves fuel economy with a vehicle, and further enhances the
attractiveness of vehicles using regenerative braking for city driving. At higher speeds, too,
regenerative braking has been shown to contribute to improved fuel economy by as much
as 20%.

Designing of a Back Up Power Supply for Page 26

Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis

Consider a heavy loaded truck having very few stops on the road. It is operated near
maximum engine efficiency. The 80% of the energy produced is utilized to overcome the
rolling and aerodynamic road forces. The energy wasted in applying brake is about 2%.
Also its brake specific fuel consumption is 5%.
Now consider a vehicle, which is operated in the main city where traffic is a major problem
here one has to apply brake frequently. For such vehicles the wastage of energy by
application of brake is about 60% to 65%.

Figure 8: Graphical Representation of Energy usage of two vehicles

2.4.2 Basic Idea of Regenerative Brakes
Concept of this regenerative brake is better understood from bicycle fitted with Dynamo.
If our bicycle has a dynamo (a small electricity generator) on it for powering the lights,
we'll know it's harder to peddle when the dynamo is engaged than when it's switched off.
That's because some of our peddling energy is being "stolen" by the dynamo and turned
into electrical energy in the lights. If we're going along at speed and we suddenly stop
peddling and turn on the dynamo, it'll bring us to a stop more quickly than we would
normally, for the same reason: it's stealing our kinetic energy. Now imagine a bicycle with
a dynamo that's 100 times bigger and more powerful. In theory, it could bring our bike to
a halt relatively quickly by converting our kinetic energy into electricity which we could
store in a battery and use again later. And that's the basic idea behind regenerative brakes.
Electric trains, cars, and other electric vehicles are powered by electric motors connected
to batteries. When we're driving along, energy flows from the batteries to the motors,
turning the wheels and providing us with the kinetic energy we need to move. When we
stop and hit the brakes, the whole process goes into reverse: electronic circuits cut the
power to the motors. Now, our kinetic energy and momentum makes the wheels turn the
motors, so the motors work like generators and start producing electricity instead of
consuming it.

Designing of a Back Up Power Supply for Page 27

Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis

Power flows back from these motor-generators to the batteries, charging them up. So a
good proportion of the energy we lose by braking is returned to the batteries and can be
reused when we start off again. In practice, regenerative brakes take time to slow things
down, so most vehicles that use them also have ordinary (friction) brakes working
alongside (that's also a good idea in case the regenerative brakes fail).That's one reason
why regenerative brakes don't save 100 percent of our braking energy [9].

Figure 9: Basic Idea of Regenerative Brakes

2.4.2.1 The Motor as a Generator
Vehicles driven by electric motors use the motor as a generator when using regenerative
braking, it is operated as a generator during braking and its output is supplied to an
electrical load; the transfer of energy to the load provides the braking effect. Regenerative
braking is used on hybrid gas/electric automobiles to recoup some of the energy lost during
stopping. This energy is saved in a storage battery and used.
Basic Elements of the System
There are four elements required which are necessary for the working of regenerative
braking system, these are:
I. Energy Storage Unit (ESU): the ESU performs two primary functions.
 To recover & store braking energy
 To absorb excess engine energy during light load operation
The selection criteria for effective energy storage includes:
 High specific energy storage density
 High energy transfer rate
 Small space requirement

Designing of a Back Up Power Supply for Page 28

Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis
The energy recaptured by regenerative braking might be stored in one of three devices:
a. An Electrochemical Battery
b. A flywheel
c. Compressed air
a. Batteries
With this system as we know, the electric motor of a car becomes a generator when the
brake pedal is applied. The kinetic energy of the car is used to generate electricity that is
then used to recharge the batteries. With this system, traditional friction brakes must also
be used to ensure that the car slows down as much as necessary. Thus, not all of the kinetic
energy of the car can be harnessed for the batteries because some of it is "lost" to waste
heat. Some energy is also lost to resistance as the energy travels from the wheel and axle,
through the drive train and electric motor, and into the battery. Regenerative Braking
System
When the brake pedal is depressed, the battery receives a higher charge, which slows the
vehicle down faster. The further the brake pedal is depressed, the more the conventional
friction brakes are employed.
The motor/generator produces AC, which is converted into DC, which is then used to
charge the Battery Module. So, the regenerative systems must have an electric controller
that regulates how much charge the battery receives and how much the friction brakes are
used.
b. Fly wheels
In this system, the translational energy of the vehicle is transferred into rotational energy
in the flywheel, which stores the energy until it is needed to accelerate the vehicle.
The benefit of using flywheel technology is that more of the forward inertial energy of the
car can be captured than in batteries, because the flywheel can be engaged even during
relatively short intervals of braking and acceleration. In the case of batteries, they are not
able to accept charge at these rapid intervals, and thus more energy is lost to friction.
Another advantage of flywheel technology is that the additional power supplied by the
flywheel during acceleration substantially supplements the power output of the small
engine that hybrid vehicles are equipped with.
II. Continuously Variable Transmission (CVT)
The energy storage unit requires a transmission that can handle torque and speed demands
in a steeples manner and smoothly control energy flow to and from the vehicle wheels.

Designing of a Back Up Power Supply for Page 29

Electrical Car from a Wind Energy
 Hawassa University, IOT; Department Electromechanical Engineering
BSC Thesis
III. Controller
An “ON-OFF” engine control system is used. That means that the engine is “ON” until the
energy storage unit has been reached the desired charge capacity and then is decoupled and
stopped until the energy storage unit charge fall below its minimum requirement.
IV. Regenerative Brake Controllers
Brake controllers are electronic devices that can control brakes remotely, deciding when
braking begins ends, and how quickly the brakes need to be applied. During the braking
operation, the brake controller directs the electricity produced by the motor into the
batteries or capacitors. It makes sure that an optimal amount of power is received by the
batteries, but also ensures that the inflow of electricity isn't more than the batteries can
handle.
The most important function of the brake controller, however, may be deciding whether
the motor is currently capable of handling the force necessary for stopping the car. If it
isn't, the brake controller turns the job over to the friction brakes. In vehicles that use these
types of brakes, as much as any other piece of electronics on board a hybrid or electric car,
the brake controller makes the entire regenerative braking process possible.
Generally, this method can improve the battery life of the system. It is also possible to
boost the overall efficiency if the system is properly sized and controlled. The energy
efficiency of a conventional car is only about 20 percent, with the remaining 80 percent of
its energy being converted to heat through friction. The miraculous thing about
regenerative braking is that it may be able to capture as much as half of that wasted energy
and put it back to work. This could reduce fuel consumption by 10 to 25 percent [9].

Designing of a Back Up Power Supply for Page 30

Electrical Car from a Wind Energy