Trends in Electric Vehicle Propulsion Technology

Trends in Electric Vehicle Propulsion

Technology

Seminar Report

Submitted by,

ALEX T KARIYIL

19110867

In partial fulfillment for the award of the degree

of

Bachelor of Technology

in

Electrical and Electronics Engineering

of

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

DEPARTMENT OF ELECTRICAL ENGINEERING GOVERNMENT MODEL ENGINEERING COLLEGE

KOCHI – 682 021 NOVEMBER 2013

GOVERNMENT MODEL ENGINEERING COLLEGE

THRIKKAKARA, KOCHI -21

Department of Electrical Engineering

Cochin University of Science and Technology

CERTIFICATE

This is to certify that the seminar report entitled,

...........................................................................................................................................

...........................................................................................................................................

Submitted by

..........................................................................................................................................,

is a bonafide account of the work done by him under our supervision.

Dr. Bindu V Ms. Ansciline Joseph

Head of the Department & Seminar Coordinator Seminar Guide

ACKNOWLEDGEMENT

First of all I thank God Almighty for His blessings throughout this seminar.

I would like to express my sincere gratitude to our respected

Principal, Dr. V.P. Devassia for his whole hearted support and encouragement.

I take this opportunity to express my gratitude to my seminar guide

Asst. Prof. Ansciline Joseph for her valuable guidance, constructive criticism and

support in finishing this venture successfully.

I would also like to express my sincere thanks to Dr. Bindu V, H.O.D., Electrical

Department & seminar coordinator for her constant support and guidance.

I would like to thank all the teaching and non-teaching staff for their help and

valuable suggestions.

Finally, I express my sincere thanks to all my friends for their kind presence and

support.

ABSTRACT

Electric vehicles (EV) have been around since late 1800’s. But the advantages

offered by internal combustion engines over electric propulsion made the former a

popular choice. The ever rising price of fossil fuels coupled with environmental concerns

has sparked a renewed interest in the research and development of electric vehicle

propulsion technologies. Automotive companies have been experimenting with different

types of propulsion motors and energy conversion systems incorporated with advanced

power conversion technologies. With this change in approach the scientific world

foresees major advancements in technology giving birth to a product which will dominate

the global market in the coming years.

The critical subsystem that is required in an electric vehicle is the propulsion

system, which provides the tractive effort to propel a vehicle. The propulsion system in

an electric vehicle consists of:

Propulsion motor

Power electronic system

Energy storage system

Present status and the requirements of primary electric propulsion components-

the battery, the electric motor and the power electronic system are reviewed. The future

trends in electric propulsion system and battery charging are presented. Possible future

electric vehicle systems based on lithium air battery are also discussed.

CONTENTS

LIST OF FIGURES ……….......................................................................................... i

LIST OF TABLES ………………………………………...………………………… ii

1. INTRODUCTION ………………………………………………………………. …..1

1.1. HISTORICAL BACKGROUND ………………………………………………. 1

2. ELECRTIC VEHICLE - RELATED THEORY …………………………………….. 3

2.1. TYPES OF ELECTRIC VEHICLES ……………………………………………3

2.2. ADVANTAGES AND DISADVANTAGES OF ELECTRIC VEHICLES …... 6

2.3. COMPARISON OF IC ENGINED VEHICLES & ELECTRIC VEHICLES...... 7

3. COMPONENTS OF AN ELECTRIC VEHICLE …………………………………... 8

4. PRESENT STATUS & FUTURE TRENDS IN PROPULSION TECHNOLOGY … 9

4.1. ELECTRIC MOTOR …………………………………………………………… 9

4.2. POWER ELECTRONICS SYSTEM …………………………………………. 12

4.3. ENERGY STORAGE SYSTEM ……………………………………………… 14

4.4. BATTERY CHARGING ……………………………………………………… 17

5. CURRENT AND FUTURE ELECTRIC CARS …………………………………... 19

6. CONCLUSION …………………………………………………………………….. 20

REFERENCE ………………………………………………………………………. 21

i

LIST OF FIGURES

Fig 3.1 Typical Propulsion System Components of an EV ……………………… 8

Fig 4.1 Axially Laminated Synchronous Reluctance machine ………………… 11

Fig 4.2 PM-assist Synchronous Reluctance Machine ………………………….. 12

Fig 4.3 Power and energy by battery type …………………………………….. 16

ii

LIST OF TABLES

Table 4.1 Characteristics of commonly used batteries in EVs ……………………... 16

Table 4.2 Electric charging Options ……………………………………………… 17

TRENDS IN ELECTRIC VEHICLE PROPULSION TECHNOLOGY

DEPT. OF ELECTRICAL ENGG. 1 MODEL ENGINEERING COLLEGE

Chapter 1

1. INTRODUCTION An electric vehicle (EV), also referred to as an electric drive vehicle, uses one or

more electric motors or traction motors for propulsion. Three main types of electric

vehicles exist, those that are directly powered from an external power station, those that

are powered by stored electricity originally from an external power source, and those that

are powered by an on-board electrical generator, such as an internal combustion engine

(a hybrid electric vehicle) or a hydrogen fuel cell. EVs include electric cars, electric

trains, electric lorries, electric aero planes, electric boats, electric motorcycles and

scooters and electric spacecraft. Diesel submarines operating on battery power are, for

the duration of the battery run, electric submarines, and some of the lighter UAVs are

electrically-powered. Proposals exist for electric tanks.

The present status and the requirements of primary electric propulsion

components- the battery, the electric motors, and the power electronics system are

reviewed. The future trends in the electric propulsion systems, battery charging, and

the types of power trains are presented. Possible future electric vehicle powertrain

systems based on lithium air battery, and plug-in fuel cell vehicles are also discussed.

1.1. HISTORICAL BACKGROUND

Electric vehicles (EV) have been around since late 1800’s. They were very

popular and a number of EVs have been sold until about 1918. For example in the

year 1900, about 4200 automobiles were on the road, out of which 38% were electric,

22% gasoline powered, and 40% steam. With the advancement of gasoline engines,

low cost gasoline, and the invention of electric starter for the internal combustion

engines, the interest in EVs completely declined. In spite of it, some automotive

companies continued to work on research and advancement of electric vehicle

technologies by experimenting with different types of propulsion motors, energy

storage systems, and also incorporating advanced power conversion technologies.

During the Arab oil embargo (1973-74), electric vehicle development activity was

pushed to the forefront. But when the gasoline prices fell during the late 1970’s, the EV

activity again declined. In 1980’s because of the environmental concerns, the interest in

electrical vehicle resumed. The General Motors IMPACT was developed in early

1990’s out of concern for air quality. The IMPACT design was based on advanced



propulsion system technology and was designed suitable for mass production. This

technology was further improved and in mid 1990s it was commercialized by GM as

EV1 vehicle. The EV1 was a battery operated electric vehicle based on lead acid

batteries with induction motor as propulsion motor. It was offered for lease in 1996 and

was the first mass- produced purpose-designed electric vehicle from a major

automaker, and the first GM car designed to be an electric vehicle from the outset.

Because of the limited range of the lead acid batteries, in 1999 GM switched to nickel

metal hydride batteries that offered a longer range but at a much higher cost. During

1990s, other automotive companies were also developing electric vehicles. For example,

in 1996, Toyota developed a pure electric version of the two doors and four doors

RAV4. It was put on sale in Japan in September 1996 and then in USA in 1998. From

1996 to 2003, Toyota Motor Company sold approximately 1,900 units of the first RAV4

EV. A number of first generation RAV4 EVs are still on the road today. With the

announcement of Prius hybrid vehicle by Toyota in 1997 and its commercial

availability, the interest in pure electric vehicles have again declined. The focus of the

pure electric vehicles has shifted to neighborhood vehicles and other city vehicles

mainly being pursued by nontraditional automotive companies like Think Global, Fiskar,

etc.

In 2003, Tesla Motors announced the development of pure electric vehicles.

The Tesla Roadster is a battery electric vehicle produced by Tesla Motors in California

between 2008 and 2012. More than 2,400 units have been sold worldwide through

September 2012. The Roadster was the first production automobile to use lithium-ion

battery cells and the first production all-electric to travel more than 200 miles per

charge. Toyota and Tesla Motors have jointly announced a development of an all-

electric 2013 Toyota RAV4 EV - claimed to be the world's most aerodynamic SUV.

It is expected to achieve an average range of 100 miles from a full charge and can be

completely recharged in about six hours with a 240V/40A charger. Today, a few other

electric vehicles such as Tesla Model S, Nissan Leaf, Mitsubishi i-MiEV, etc. are

commercially available.

In the last 10 years, plug-in hybrid electric vehicles (PHEV) are attracting

increasing interest in North America and in other countries. A plug-in hybrid could be a

series or a parallel hybrid with its battery restored to full charge by connecting it

through a charger to an external electric power source as in an electric vehicle. This

requires a relatively higher capacity battery compared to the typical state-of-the-art

HEV batteries. Additionally, significant enhancements beyond typical full HEV

powertrain configurations would be required in order to properly handle the increased

thermal management system loading and other factors associated with plug-in HEV

usage. With their larger battery capacity of about 5 to 15 kWh, PHEV can be driven in

pure electric vehicle mode for short distances. In hybrid mode, the battery works as an

HEV battery for power assist. Thus, a PHEV battery needs energy and power

performance, requiring shallow cycle durability similar to that in HEVs and deep cycle

durability like EV batteries. GM’s Chevrolet Volt, Toyota Prius, Ford C-Max Energi

are some of the PHEVs that are readily available in the market. Other auto makers are

also planning to commercialize PHEVs in the very near future.



Chapter 2

2. ELECRTIC VEHICLE - RELATED THEORY

2.1. TYPES OF ELECTRIC VEHICLES

For more than 100 years, the predominant energy choice for cars has been the

internal combustion engine. Electric vehicles being designed today either augment

internal combustion or eliminate the need for it altogether.

Hybrid and electric vehicle system components may include a battery for energy

storage, an electric motor for propulsion, a generator, a mechanical transmission and a

power control system. These components are brought together in different ways by

different systems. There are four main types of electric cars:

Hybrid Electric Vehicle

Plug-in Hybrid Electric Vehicle

Extended-Range Electric Vehicle

Battery Electric Vehicle

Hybrid Electric Vehicle

The hybrid electric vehicle uses a small electric battery to supplement a standard

internal combustion engine and increase fuel efficiency by about 25 percent from

conventional light-duty vehicles.

The electric motor minimizes idling and boosts the car's ability to start and

accelerate, which is important in stop-and-go city driving. Hybrids are dual-fuel vehicles

in which both the electric motor and internal combustion engine can drive the wheels.

The electric motor accelerates the car to about 40 mph, depending on the vehicle,

and then the internal combustion engine takes over.

The battery is recharged by the gasoline engine and regenerative braking.

Regenerative braking converts kinetic energy that otherwise would be lost as heat in the



brake pads into electricity to charge the battery. The Ford Fusion Hybrid and Toyota

Prius are examples of this type of hybrid.

Plug-in Hybrid Electric Vehicle

The plug-in hybrid electric vehicle is also a dual-fuel car in which both the

electric motor and the internal combustion engine can propel the car. It has a larger

battery pack that is charged directly from the power grid, increasing the amount of

electric power available to the car.

This larger battery usually supplements an internal combustion engine smaller

than those used in hybrid or conventional vehicles. Toyota began selling a plug-in hybrid

for the U.S. market in February 2012, though kits to convert other cars into plug-in

hybrids were available before that.

Both the hybrid and plug-in hybrid combine an internal combustion engine with a

battery and electric motor to increase fuel efficiency. The difference is that plug-ins also

can be recharged from an electric outlet, extending the use of electricity as a fuel.

Most plug-in hybrids run on electric power only up to about 40 mph, where the

internal combustion engine takes over. Thus, drivers could commute around a city solely

on electric power without ever engaging the internal combustion engine.

The batteries in these vehicles can be charged by the gas engine, regenerative

braking, and by plugging in at home during off-peak hours. While this reduces the

immediate need for public charging stations, the ideal situation would be to build an

infrastructure of charging stations to provide more options for plug-in hybrid owners.

Extended-Range Electric Vehicle

An extended-range electric vehicle uses an internal combustion engine to power

an electric generator that charges the battery system in a linear process — the engine

powers a generator, which in turn charges the battery.

Unlike dual-fuel hybrid and plug-in hybrids, only the electric motor powers the

wheels of an extended-range electric car. The internal combustion engine only charges

the batteries.

The General Motors Chevrolet Volt, which went on sale in the U.S. in late 2010,

is an extended-range electric vehicle with an electric-only range of about 40 miles. The

Volt extends its range with a small internal combustion engine that charges the batteries.



The Volt also can be recharged by plugging into the grid during periods of low power

use.

Battery Electric Vehicle (BEV)

Battery electric vehicles are all electric. They have no internal combustion engine

and must be plugged into the electric power grid for recharging. To accommodate a

range of 80-plus miles per charge, electric-only vehicles require larger batteries than the

combined electric-petroleum cars — from 18 kilowatt-hours to more than 35 kilowatt-

hours.

To more quickly recharge these larger batteries at night when power demand is

low, most homes and businesses will require special outlets to be installed that provide

240 volts or higher. Nissan began U.S. sales of its 100 percent battery electric vehicle,

the LEAF, in late 2010.



2.2. ADVANTAGES AND DISADVANTAGES OF

ELECTRIC VEHICLES

Electrical automobiles are propelled by an electrical motor powered by

rechargeable battery packs. Electric powered motors own several benefits through

internal combustion engines:

Energy efficient. Electric engines convert 75% of the chemical energy by the

batteries to power the wheels—internal combustion engines just convert 20% of the

energy stored in fuel.

Eco friendly. Electrical cars emit no tailpipe pollution; however the power plant

making the electrical energy could produce them. Electrical energy by nuclear-,

hydro-, solar-, or wind-powered plants causes no air pollutants.

Efficiency benefits. Electrical motors provide quiet, smooth operation and stronger

acceleration and necessitate less maintenance compared to internal combustion

motors.

Minimize energy dependency. Electrical energy is a domestic energy source.

Electrical vehicles face significant battery-related challenges:

Driving range. Most electrical vehicles may just go about 100–200 miles before

recharging—gasoline automobiles can go over 300 miles before refueling.

Recharge period. Fully recharging the battery pack can take 4 to 8 hours. Even a

"quick charge" to 80% capacity may take 30 min.

Battery cost: The great battery packs usually are expensive and could need to be

changed one or more times.

Bulk and weight: Battery packs are large and take up significant vehicle space.



2.3. COMPARISON OF IC ENGINED VEHICLES &

ELECTRIC VEHICLES

ICE EV

Efficiency Converts 20% of the energy

stored in gasoline to power the

vehicle.

Converts 75% of the chemical

energy from the batteries to

power the wheels.

Speed (average

top speed)

124 miles per hour (mph) 30-95 mph

Acceleration (on

average)

0-60 mph in 8.4 seconds 0-60 mph in 4-6 seconds

Maintenance

lights

Does not require as much

maintenance because it does

not use a gasoline engine. No

requirements to take it to the

Department of Environmental

Quality for an emissions

inspection.

Mileage Can go over 300 miles before

refueling. Typically get 19.8

miles per gallon (mpg).

Can only go about 100 to 200

miles before recharging.

Cost (on

average)

$14,000 to $17,000. Extensive range, $6,000 to

$100,000



Chapter 3

3. COMPONENTS OF AN ELECTRIC VEHICLE The critical subsystem that is required in an electric vehicle is the propulsion

system, which provides the tractive effort to propel a vehicle. The propulsion system

in an electric vehicle consists of an energy storage system, the power converter, and

the propulsion motor and associated controllers as shown in Figure 3 .1. The battery

is the most widely used energy storage system and battery charger is an integral

part of the electric vehicle system. In this paper, the current technologies and

future trends for the propulsion of electric vehicles are discussed. These technology

trends are also equally applicable for hybrid and plug-in hybrid vehicles.

Figure 3.1: Typical propulsion System components of an EV

A lot of research on the propulsion technology used in electric vehicle is

going on in order to nullify shortcomings of the current technology. Bulk of the

research on electric vehicle propulsion technology is mainly focused upon four key

areas:

I. Electric motor

II. Energy storage system

III. Power electronics

IV. Battery charging



Chapter 4

4. PRESENT STATUS AND FUTURE TRENDS IN

PROPULSION TECHNOLOGY

4.1. ELECTRIC MOTOR

Electric motor converts the energy supplied by the battery into mechanical

energy to provide traction power to the wheels. It is the motor with the controller

that determines the characteristics of the propulsion system and the ratings of the

power devices in the power converter. The main requirements for propulsion motor

are ruggedness, high torque to inertia ratio, high torque density, wide speed range, low

noise, little or no maintenance, small size, ease of control, and low cost.

Several types of electric machine technologies have been investigated for

automotive propulsion. These include induction, permanent magnet (PM), switched

reluctance, and axial gap machines. Most of the commercially available electric and

hybrid vehicles use either induction or PM machines for propulsion. Automotive

manufacturers and suppliers have significantly improved the electric machine

technologies to be used in electric and hybrid vehicles. Tesla Roadster induction

motor peak power density is more than two times that of the induction motor used in

GM EV1. Today, the interior permanent magnet (IPM) synchronous motor is widely

used in automotive propulsion because of its high efficiency, high torque, high power

density, and relatively ease of field weakening operation. Toyota Prius, Ford Escape,

Chevy Volt are some of the vehicles that use IPM machine. Although the interior

permanent magnet based motors are presently being used in most of the electric and

hybrid vehicles, there is a great concern about the availability of rare earth based

magnets and their increasing cost. A number of companies and researchers are

working on the development of motors that do not use permanent magnets, but to

achieve the same performance as IPM motors. There are at least four options to

achieve this.

a. Induction Motors

The induction motors have been used in several types of electric vehicles in

the past including the General Motors EV1, with reasonably good performance. They

are also being used in Tesla electric vehicles such as Roadster, Model S, and

Toyota/Tesla RAV4. More research and development, increasing the operating

voltage, using copper cage rotor, and tailoring the design for a given application

could further improve the efficiency and performance of these motors.



b. Switched Reluctance Motors

Switched reluctance machine (SRM) is essentially a synchronous machine

operating from inverter driven square wave unipolar currents. Torque is created by

rotor saliency and pulsed currents. The magnetic and electric independence of the

machine phases and absence of permanent magnets provide fault tolerance and also

improve reliability. The mechanical integrity of the rotor permits high speed and high

power density operation. The SRM has the simplest mechanical design. But these

machines are generally extremely noisy during the operation; have higher torque

pulsations, lower efficiency, larger size and weight (than PM machine), and the

design has not been advanced to the same extent as the induction or PM machine.

Automotive companies have made several attempts starting from early 1990s to use

these motors for electric vehicle propulsion. Due to the several problems associated

with SRM and the advancement of interior permanent magnet (IPM) machines, the

interest in the use of SRM for EV applications declined. However, with the cost of

rare earth magnets soaring, there is again a strong interest in advancing the SRM

technology for EV applications. Recently, John Deere introduced two diesel-electric

hybrid construction loaders equipped with switched-reluctance motors and generators.

At EV Japan in January 2012, Nidec exhibited a switched reluctance vehicle

traction motor that could have the lowest cost still achieving the performance close

to IPM machine. Several other companies are also in the process of demonstrating

electric vehicles based on switched reluctance motor for propulsion system.

A significant amount of research work is going on to reduce the torque ripple

and acoustic noise in SR machines. One of the advancements being made is the

introduction of a switched reluctance machine with a double-stator configuration. It

features high torque density, low inertia, and reduced acoustic noise compared with

the conventional SR Motor. The motor has an optimized pattern of magnetic flux

paths within the electrical machine that is claimed to provide at least twice the

torque density of conventional SR machines. Two stators inside machine cancel the

radial force that would minimize the noise during normal operation. To reduce the

inertia, a shell type rotor structure is proposed. The motor maintains the fault tolerance

and the extended speed range capability similar to a regular SR machine.

c. Synchronous Reluctance Motors (SynRM) Synchronous reluctance motor technology combines the benefits of induction

motors and permanent magnet motors, and it operates at synchronous speed. It provides

the robustness of an induction motor and the size, efficiency along with synchronous

speed operation benefits of permanent magnet motor technology while eliminating

concerns related to PM technology. The stator of the SynRM is similar to an induction

motor or a permanent magnet motor with distributed windings. The rotor is designed to

produce the smallest possible reluctance in one direction and the highest reluctance in the

perpendicular direction. These motors are fault tolerant like induction motors because

there is no flux in the rotor when the stator windings are not energized. The control

strategy is almost similar to permanent magnet motor unlike switched reluctance motors

that has very different stator, rotor, and a power converter. A number of papers have



been published on synchronous reluctance motor technology and its application to

electric vehicles. Because of some of the problems related to manufacturing,

controllability, and slightly lower power factor, these motors have not been considered

for EV and other applications. Recently, ABB has further advanced this technology and

already commercialized for several industrial applications. The core innovation is the

rotor design, since the stator side of the motor is identical to an induction motor.

Poor power factor of the synchronous reluctance machine is still disadvantageous

since it increases the size of the motor drive. In order to achieve a high power factor in

this machine, a large saliency ratio is required. This results in a relatively large reactive

power which will cause the size of the inverter to increase. A large saliency can be

achieved by both axial and transversally laminated SynRM rotor structures. The effective

saliency ratio of transversally laminated rotors can be enhanced by the proper placement,

shape and number of flux barriers. Figure 4.1 shows modern axially laminated rotor.

This type of rotor could have a high direct axis inductance, Ld and a low quadrature axis

inductance, Lq and therefore the saliency ratio could be high to enable the SynRM

operate at a better power factor.

Figure 4.1: Axially laminated synchronous reluctance machine

d. PM-assist Synchronous Reluctance Motors

Several researchers have investigated the use of adding a small amount of

permanent magnets to the synchronous reluctance rotor (Figure 4.2) to achieve higher

power factor. This motor is similar to an interior permanent magnet (IPM) machine;

however the amount of permanent magnets used and the permanent magnet flux linkages

are smaller with respect to the conventional IPM. By adding appropriate amount of

magnet into the rotor core, efficiency improves without having significant back-EMF

and without necessary change in the stator design. Demagnetization due to the

machine overloading and high ambient temperature is a significant problem in IPM, but

not in PM-assist synchronous reluctance motors. By selecting the right amount of

permanent magnets and with suitable efficiency optimization control, the performance of



the PM assist synchronous reluctance machine could be made similar to that of an

Interior PM machine.

Figure 4.2: PM-assist Synchronous Reluctance Machine

Using advanced design methodologies, control strategies, thermal design aspects,

and improved manufacturing process, the performance of the SynRm and PM-assist

SynRm can be further improved, and these motors could meet the requirements of

propulsion motors in electric vehicles.

4.2. POWER ELECTRONICS SYSTEM Power electronics is an enabling technology for the development of electric and

hybrid vehicle propulsion systems. The power electronics system consists of power

switching devices, power converter topology with its switching strategy, and the closed

loop control system of the motor as shown in Figure 1. The selection of power

semiconductor devices, converters/inverters, control and switching strategies, packaging

of the individual units, and the system integration are very important for the

development of efficient and high performance vehicles. The challenges are to have a

high efficient, rugged, small size, and low cost inverter and the associated electronics for

controlling a three phase electric machine. The devices and the rest of the components

need to withstand thermal cycling and extreme vibrations. All the present EVs and HEVs

use a three phase bridge inverter topology for converting the dc voltage of the battery to

variable voltage and variable frequency to power a three phase ac motor. Three phase

hard switched bridge inverter has been the inverter topology that is being used in all

the electric and hybrid vehicles. This topology is simple and well proven and

continues to be the technology of future with different types of power devices and the

associated passive components for filtering, EMI reduction, protection, etc.

With the advancement of semiconductor device technology, several types of

power devices with varying degrees of performance are available in the market. The



IMPACT (original prototype version of EV1) used two 3 phase inverters each powering

a front wheel drive induction motor. Each inverter had 24 MOSFETS connected in

parallel resulting in 48 MOSFETS for each phase leg of the inverter (totally 144

MOSFETS per inverter). These 48 MOSFETS were later replaced by a single module

resulting in three IGBT modules per leg. Presently IGBT devices are being used in

almost all the commercially available EVs, HEVs, and PHEVs. The IGBTs will

continue to be the technology in the near future until the Silicon carbide and gallium

nitride based devices are commercially available at a cost similar to that of silicon

IGBTs. A significant progress has already been made in the technology of these

devices for automotive and other power applications.

Silicon Carbide (SiC) has become the choice for most of the next generation

power semiconductor devices and could replace the existing silicon technology.

Advanced features of silicon carbide devices are inherent radiation-resistance, high-

temperature operating capacity, high voltage and power handling capacity, high

power efficiency and flexibility to be used as substrate. The various properties of

silicon carbide such as wider band gap, larger critical electric field, and higher thermal

conductivity enables the SiC devices operate at higher temperatures and higher voltages

offering higher power density and higher current density than the pure Si devices. These

properties allow the SiC devices such as Schottky diodes, MOSFETs, and the other

devices to operate at much higher voltage levels than the Silicon devices. But the

technology of the current SiC switching devices, JFETSs and MOSFETS, is not

sufficiently mature to match the reliability of silicon devices or even of SiC Schottky

diodes to be used in EVs and HEVs. These devices also have significant competition

from SiC BJTs, which seem to offer greater reliability in terms of life test, high-

temperature operation and temperature cycling, plus robustness to shocks and

vibrations.

Gallium Nitride (GaN) devices are projected to have significantly higher

performance over silicon-based devices, and much better performance than SiC

devices, due to their excellent material properties such as high electron mobility, high

breakdown field, and high electron velocity. GaN-based power electronics feature both

low on-resistance and fast switching, leading to substantial reduction in both conduction

and switching losses. Due to its compatibility with high- volume silicon fabs, the GaN-

on-Si technology platform can be produced in large volume, allowing superior

performance and affordable manufacturing. It is higher cost than silicon, but GaN will

always cost less than SiC because GaN is compatible with silicon substrates affording a

large area foundation substrate – SiC is not compatible. Since the requirement of dc

voltage rating of power devices in most of the propulsion inverters is less than 1000V,

the GaN will be more applicable for EVs than the higher voltage SiC devices. System-

level advantages, such as reduced size and weight, reduced generation of

electromagnetic interference (EMI), and reduced system cost can be realized with

GaN power electronics, making this technology viable for future electric and hybrid

vehicles. As with SiC devices, adoption of GaN will not take place until devices have

proven reliability to automotive specifications.

The potential areas for the deployment of wide bandgap devices in hybrid and



electric vehicles are: Propulsion inverter, on-board battery charger (EVs and PHEVs),

and the DC-DC converter for converting the high voltage to 12V DC. These devices

have lower conduction and switching losses, thereby offering higher efficiency in

electronic systems. Use of these devices in the propulsion inverter reduces the size and

weight of the unit because of the need for lower cooling for the same rating of the silicon

based power converter. In HEVs, it would be possible to combine the cooling of the

power converter and the motor with the engine coolant loop operating at 105oC, thus

reducing to one coolant loop leading to further reduction in weight and complexity.

Achieving highest power density and a compact package considering the thermal

aspects and reliability is one of the critical items for the successful deployment of power

electronics systems in electric and hybrid vehicles. The original GM EV1 inverter had

4.8kW/kg, but with the advances in technology and packaging, GM is able to achieve the

power densities of about 26kW/kg. With the use of wide bandgap semiconductors, it

would be possible to further improve the power density of the power converters.

In addition to the power conversion and control of propulsion motor, monitoring

the conditions of the electric machine is very important in EVs and HEVs to detect any

failures such as bearing, rotor, and stator faults. By diagnosing the electric machine

faults as early as possible, the lifetime of an electric machine can be prolonged by

performing maintenance before a catastrophic failure occurs. Therefore, the EVs and

HEVs require embedded fault diagnosis systems both to support critical functions of the

control system and to provide a cost-effective maintenance. Unless the electric machine

and power train components are continuously monitored, motor faults might cause

permanent damage or even accidents, depending on the severity of the fault. The

prognostics and health management is presently not being implemented in most of the

EVs and HEVs. Integration of prognostics in the overall control system could predict the

future performance of the machine by assessing extent of its deviation from its expected

normal operating conditions.

4.3. ENERGY STORAGE SYSTEM Electric vehicle use has been limited due to a restricted range, increased refueling

(or recharging) time, and cost. These three aspects are closely related to the energy

storage system. The main considerations in the selection of a battery for EV applications

are: power density, energy density, weight, volume, cycle life, and cost. The other

considerations are operating temperature range, safety, material recycling, and

maintenance. Power density determines the acceleration ability. Energy gives an

indication of the potential range. Cycle life measures how often the battery can be

recharged to its full capacity, and is related to battery lifetime. Weight and volume can

affect the range as well as efficiency of the total system. Cost is determined by the



availability of resources, technology, and manufacturability. Since EV is driven by

environmental concerns, the recyclability of the material is also an important

consideration. In EV applications, in order to obtain higher voltage, several battery

modules have to be connected in series. Thus, charge equalizing, safety, and

reliability become challenging problems to be addressed.

Till mid-1990s, almost all the electric vehicles used lead acid batteries although

some vehicles used other kinds of batteries such as Nickel Cadmium and Sodium Sulfur

batteries. For example, in 1979 the GM Electrovette used Nickel- Zinc batteries at 120V.

The GM EV1 was using valve-regulated lead acid batteries at 312V and in 1999,

switched to Nickel Metal hydride (NiMH) batteries, and Toyota Prius also uses NiMH

batteries. These NiMH batteries have been used till recently in almost all the commercial

electric and hybrid vehicles. Tesla Roadster was the first production automobile to use

lithium-ion battery cells and the first production electric vehicle to travel more than 200

miles per charge. The battery unit contained 6,831 lithium ion cells (laptop cells)

arranged into 11 "sheets" connected in series; each sheet containing 9 "bricks" connected

in series; each "brick" containing 69 cells connected in parallel. Presently Nissan leaf

electric vehicle and GM’s Chevy Volt plug-in electric vehicle also use lithium ion

batteries. Nissan Leaf has a 24-kWh capacity with 1,800 to 2,000 cells. Integrated

thermal, electrical, and mechanical pack design of battery has significantly increased the

pack metrics of specific power and specific energy of lithium ion battery pack in

combination with electrode and material advancement. Nissan was able to double both

metrics with the combined benefits of using laminated cells in place of cylindrical with a

spinel structure.

Typical values of energy, power, and cycle life for lead acid, NiMH, and lithium

ion batteries are shown in Table 4.1 and Figure 4.3. Lithium based technologies and

lithium ion batteries are leading the way to meet the requirements of EV/HEVs. The

most prevalent chemistry is the carbon/graphite anode and lithium metal oxide cathode,

with the metal being either cobalt, manganese, nickel, or a mixture of these, with

lithium salt dissolved in an organic solvent. Another prevalent chemistry is a lithium

titanate anode with a lithium manganese cathode. Lithium-ion batteries have the

potential to deliver about 400 to 450 watt hours of electricity per kilogram. These

batteries can output high energy and power per unit of battery mass, allowing them to

be lighter and smaller than other rechargeable batteries (Figure 4.3). Other advantages

of lithium-ion batteries compared to lead acid and nickel metal hydride batteries

include high-energy efficiency, no memory effects, and a relatively long cycle life.

Lithium-ion is obviously a better and more efficient way to power modern hybrids and

EVs, but it is presently more expensive.

The future of electric vehicle battery could be based on lithium air technology.

These batteries could significantly increase the range of electric vehicles due to their

high energy density, which could theoretically be equal to the energy density of

gasoline. Researchers estimate that these batteries could hold 5-10 times the energy of

lithium-ion batteries of the same weight, and twice the energy for the same volume.



They have the potential of achieving the energy density in the range of 2000 to 3500

Wh/kg. No other known battery has as high of an energy density as lithium-air

batteries. These batteries have an anode made of lithium and an “air cathode” made of

a porous material that draws in oxygen from the surrounding air. When the lithium

combines with the oxygen, it forms lithium oxide and releases energy. Since the oxygen

doesn’t need to be stored in the battery, the cathode is much lighter than that of a

lithium-ion battery, which gives lithium- air batteries their high energy density.

Table 4.1: Characteristics of commonly used batteries in EVs

Figure 4.3: Power (acceleration) and energy (range) by battery type

Toyota Motor Corp and BMW have announced a joint research program on

lithium–air battery that will be expected to be more powerful than the lithium-ion

batteries used in many electric and hybrid vehicles. The technology is being studied by

several researchers including IBM, which is working to develop a lithium-air battery

that will let electric vehicles run 500 miles on one charge. Researchers have already

demonstrated a coin-sized rechargeable lithium-air battery with a current density of 600

mAh/g, which is much higher than the current densities of 100 to 150 mAh/g of lithium-

ion batteries.

The technology of rechargeable lithium air battery is a challenge but several

companies such as PolyPlus with funding from ARPA-E have already made significant



progress. One of the biggest challenges facing lithium-air batteries is their limited

number of charge/discharge cycles. Although single-use lithium-air batteries are already

being used, for example to power hearing aids, electric vehicles require batteries that

can be recharged thousands of times. Researchers also face challenges in speeding up

the recharging process and in keeping water vapor out of the oxygen, since lithium

reacts violently with water. In addition, the process of charging the lithium air battery is

a relatively slow process as compared with the lithium ion battery.

The rechargeable lithium-air batteries would probably not be commercially

available for several years. It could be about 15 years before they can be deployed in

commercial EVs and HEVs. Lithium ion technology took more than 25 years to reach

the present level of technology. There is no “Moore’s law” in battery technology in

terms of energy density and power density. With adequate funding and focused

research, lithium-air battery could be a major player for the battery systems in future

electric vehicles.

4.4. BATTERY CHARGING It is well known that we will never be able to charge the battery of an electric

vehicle as fast as it is to fill the tank with gasoline of an automobile. Current plug-in and

electric vehicles are designed primarily for home charging using either Level 1 or Level

2 chargers (Table 4.2), which charge using AC supply. These charger units that use

120V or 240V AC are generally installed on the vehicle. Homeowners must install

Electric Vehicle Supply Equipment (EVSE) to link home Energy Management System

(HEMS) with the on-board chargers. The Level 3 chargers are off-board and use DC

charging, and the term DC fast charging is often used to refer to these chargers.

Level

Charger location

Volts/amps

Electricity Delivered

(kW) 1

2

3

On board

On board

Off board

120/15

240/80

480/max 200

1.8

19.2

max 90

Table 4.2: Electric charging Options

Several companies are already developing EV Smart charging, that is the

integration of energy flow and information flow. To date, the design and development of

EVSE has been focused on power protection, security, and billing functions. When



PHEVs and EVs are connected to the grid, its integration into the distribution

infrastructure needs to be managed through bi-directional communications. The charging

infrastructure would also improve by having local wireless network architecture with

connectivity between the EVSE and Home Area Network gateway that will minimize the

communication requirements and cost of the EVSE. The EVSE-to-EVSE communication

networks and Neighborhood Area Networks that do not require any direct connection to

the utility company would be the way of future for the EV charging system.

A number of automotive manufacturers working with SAE and other

organizations have developed a new concept for EV charging known as the “Combined

Charging System”. This system enables integration of AC charging and ultra-fast DC

charging in a single system that will have one combined charging inlet per vehicle, one

integrated controller, and one charging communication. SAE and the ACEA (European

Automobile Manufacturers’ Association) have selected HomePlug Green PHY PLC as

the communication standard for the universal charging system that supports both AC

charging and fast DC charging in electric vehicles. HomePlug Green PHY PLC and

ZigBee wireless communication are emerging as the standards for smart grid and Home

Energy Management Systems (HEMS).

The convenience of charging could be a major factor in purchase decisions of the

electric vehicles. All of the major EV manufacturers have announced partnerships for

developing the technology to address the issue of range anxiety. A number of companies

are developing inductive charging that uses an electromagnetic field to transfer energy to

charge the batteries. This type of wireless charging eliminates the EV power cord with an

automatic charging solution. Automakers like BMW and Nissan are already preparing to

implement wireless charging options on their electric cars, which could allow for

charging stations to be embedded in parking spaces and even the roadway. For example,

Delphi is developing a wireless charging system that will automatically transfer power to

a vehicle providing a convenient, wireless energy transfer. This hands-free charging

technology is based on highly resonant magnetic coupling which transfers electric power

over short distances without physical contact, allowing for safer and more convenient

charging options for consumer and commercial electric vehicles. According to Delphi,

the highly resonant magnetic coupling technology will efficiently transfer power over

significantly larger distances as compared to inductive systems, and will allow more

parking-related vehicle misalignment. The system can fully charge an electric vehicle at

a rate comparable to most residential plug-in chargers, which can be as fast as four hours.

At present, the power rating of the wireless charging systems for EVs is not

sufficient to meet fast charging; and the distance and misalignment is still a problem.

ORNL scientists have developed a suite of technologies to solve the problem of

wirelessly charging electric vehicles while parked or in motion. These include light

weight air-coupled system with operating frequency optimized for maximum power

transfer, nanotechnology improved charging coils for reduced energy loss, and wireless

alignment system to maximize charging efficiency. With further advances in technology,

the wireless charging will be prevalent for the future electric vehicles.



Chapter 5

5. CURRENT AND FUTURE ELECTRIC CARS

Many automakers have plans to produce electric cars--also known as an

electric vehicle (EV). Past EVs never gained popularity and had notoriously poor

performance, short battery life and long recharge times. But automakers are confident

that advances in technology will ensure that the next generation of electric cars will

satisfy the needs of today's drivers.

Tesla Motors

Tesla Motors was founded in 2003 and quickly earned worldwide attention

following the unveiling of the Tesla Roadster in 2006. This two-seater sports car

accelerates from 0 to 60 mph in 3.9 seconds and has a travel range of more than 200

miles on a fully charged battery. The base MSRP is $101,500, which includes a

$7,500 federal electric car tax credit. For those needing more room, Tesla is

currently taking reservations for their upcoming Model S, an electric sedan that the

company says will accommodate seven passengers.

Chevrolet Volt

The Volt is a five-passenger sedan that travels on pure electricity for an

estimated 40 miles per battery charge. For longer trips or when charging is not

possible, the Volt automatically switches to an onboard range extender, a gasoline-

powered generator that creates more electricity to power the car. Chevrolet says the

range extender will allow the Volt to travel an additional 300 miles per tank. The Volt

is in showrooms at around $40,000.

Fisker Karma

Fisker Automotive is another start-up that the Karma, a four-passenger luxury

sedan that uses a system almost identical to the Chevrolet Volt. The Karma has a 50-

mile range on pure electricity before switching to a gasoline-powered generator that

provides power for 300 miles per tank. The base price is around $87,000 (before tax

credits are applied).

Nissan Leaf

The Leaf, a five-passenger sedan with an estimated 100-mile range per charge,

was released in late 2010. The Leaf sells for around $36,000.

You can expect this list of electric cars to grow as more customers look for

alternatives to gasoline due to fluctuating gas prices and concern for the environment.



Chapter 6

6. CONCLUSION

The advancement of propulsion system technology of electric vehicles will

be focused on five areas:

1 ) vehicle range

2 ) vehicle cost

3 ) battery pack replacement cost

4) battery pack life

5) quick and easy recharging

Except for vehicle cost, most propulsion system development work will be on

battery systems. Significant improvement in lithium ion technology has already been

achieved and is being deployed in several EVs and PHEVs. More of the EVs and

PHEVs based on lithium ion battery will be available from various automakers in

the near future. A large research effort is underway to develop lithium air batteries

for automobiles. The advancement of lithium air battery will further improve the

range of EVs and may lead to dominance of pure EVs.

The importance of DC fast charging of EVs and PHEVs is expected to

increase in the near future. The smart charging features with the integration

of energy flow and communications will be incorporated in all the chargers. Next

generation EVSE must adapt to become smarter and more capable. It should support

smart-grid functionality, which holds great promise to lower the system cost of

providing energy to EVs and PHEVs. With smart-grid communications, not only

the distribution grid will be better optimized for lower energy costs, but also the users

can use the EVs and PHEVs at lower electricity costs, and charge faster with higher

efficiency.

There will be more emphasis on the propulsion motors without the permanent

magnets. Although the future emphasis will be on non-rare-earth based motors

such as induction, switched reluctance, and synchronous reluctance motors, the

interior PM motor will continued to be used in the near future. Elimination of the

speed/position sensors would enhance the reliability of the propulsion system. In the

area of power electronics, silicon carbide and gallium nitride based power switching

devices will be the future. The silicon based IGBTs will continue to be used until

these wide bandgap devices are commercially available at the required power rating

and at a lower cost.



REFERENCE [ 1 ] K. Rajashekara, “Present Status and Future Trends in Electric Vehicle

Propulsion Technologies”, IEEE Journal of Emerging and Selected Topics in

Power Electronics, 2013

[ 2 ] K. Rajashekara, “History of electric vehicles in general motors’”, IEEE

Trans. Ind. Appl., Jul.–Aug. 1994

[ 3 ] Purnendu Sinh, Vinod Agarwal, “Evaluation of Electric-vehicle

Architecture Alternatives”, IEEE jan 2011

[ 4 ] Boldea, L. Tutelea, and C. I. Pitic, “PM-assisted reluctance synchronous

motor/generator (PM-RSM) for mild hybrid vehicles: Electromagnetic design”,

IEEE Trans. Ind. Appl., Mar.– Apr. 2004.

[ 5 ] Rony Argueta, “A Technical Research Report: The Electric Vehicle”,

University of California, Santa Barbara College of Engineering

Documents

Trends in Electric Vehicle Propulsion Technology