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Abstract-- Hybrid Electric Vehicle (HEV) is an emerging

technology in the modern world because of the fact that it

mitigates environmental pollutions and at the same time

increases fuel efficiency of the vehicles. Multilevel inverter

controls electric drive of HEV of high power and enhances its

performance which is the reflection of the fact that it can

generate sinusoidal voltages with only fundamental switching

frequency and have almost no electromagnetic interference. This

paper describes precisely various topology of HEVs and presents

transformer less multilevel converter for high voltage and highcurrent HEV. The cascaded inverter is IGBT based and it is fired

in a sequence. It is natural fit for HEV as it uses separate level of

dc sources which are in form of batteries or fuel cells. Simulation

has been done in PSIM as well as MATLAB and its responses

match the theoretical concept of multilevel inverter.

Index Terms-- Hybrid Electric Vehicle, Cascaded Inverter,Multilevel Inverter, Common Mode Voltage, PWM Converter,

Quasi-square wave, Powertrain.

I. ITCTI

recent years research in hybrid electric vehicle (E)

development has been focused on various aspect of design

such as component architecture engine efficiency reducedfuel emissions material for lighter components power

electronics efficient motors and high power density batteries

[1] [3]. To meet some of the aspect of E cascaded

multilevel inverter is used so as to meet high power demands.

The multilevel voltage source inverters with unique structure

allow them to reach high voltages with low harmonics without

the use of transformers or series-connected synchronized

switching devices [4]. The general function of the multilevel

inverter is to synthesize a desired voltage from several levels

of dc voltages. or this reason multilevel inverters can easily

provide the high power required of a large electric drive. As

the number of levels increases the synthesized output

waveform has more steps which produces a staircase wave

A.K. erma is with Birla Institute of Technology Mesra anchi India (e-mail: [email protected]).

P.. Thakura is with Birla Institute of Technology Mesra anchi India(e-mail:[email protected]).

K.C. ana is with Birla Institute of Technology Mesra anchi India (e-mail: [email protected] ).

.S. Buja is with niversity of Padova Padova Italy (e-mail:[email protected]).

978-1-4244-7882-811$2. 211 IEEE

that approaches a desired waveform. Also as more steps are

added to the waveform the harmonic distortion of the output

wave decreases approaching zero as the number of levels in-

creases. As the number of levels increases the voltage that can

be spanned by summing multiple voltage levels also increases.

The structure of the multilevel inverter is such that no voltage

sharing problems are encountered by the active devices. E

Configurations

This paper elaborates the various configurations of Es

highlighting its advantages and disadvantages. IBT basedcascaded multilevel has been developed and it is interface

with 2k 3-phase induction motors suitable for Es and

simulation result in PSIM as well as MATAB are done and

results are presented in the paper.

II. ECIATIS

Although a number of configurations are used for E

powetrains the main architectures are the series parallel and

series-parallel ones [-]. They are analyzed in this Section

i)by disregarding the losses in the electric and mechanical

devices the power consumption of the auxiliary electric loads

and the presence of gearboxes and clutches and ii) byconsidering the static converters used for the interface of the

electric devices as a whole with the devices themselves.

Moreover the analysis is carried out by assuming that i) the

powers are positive quantities when the associated energy

flows in the direction of the arrows reported in the schemes of

the architectures and ii) the driving requirements for a vehicle

are the speed and the torque at the wheels where the product

of the two variables gives the required propulsion power.

A. Series Architecture

The Powertrain of a Series E (SE) has the

architecture of ig.1. It comprises a genset (i.e. a generation

set) and a drivetrain of electric type which are connectedtogether through a common power Bus (B). To B is also

connected an energy Storage system (S).

ig.1: SE Powertrain architecture (electric and mechanical connections aretraced respectively with single & double lines whereas the fuel path is tracedwith dashed line).

Cascaded Multilevel Inverter for Hybrid

Electric Vehicles

A. K. Verma, P. R. Thakura, K.C.Jana and G.Buja, Fellow Member, IEEE

I

pe

B

S

ICE

M

pw

ps


2/6

In the genset ICE is fed by the uel tank () and delivers

the mechanical power pe to the electric enerator (). The

latter one converts pe into electric form and supplies B. The

energy associated to pe can be either stored in S (in this case

the power ps of ig.1 is negative) or drawn by the electric

drivetrain or both. uring the engine start-up behaves as a

crank motor energized from S.

The electric drivetrain is constituted by one (or more)

electric Motor (M) that draws the propulsion power pw fromB and delivers it to the heels (). ote that in this

architecture the wide speed-torque regulation allowed by M

may make superfluous the insertion of a variable-ratio gearbox

between M and . uring the regenerative braking M

operates as a generator to recover the kinetic energy of the

vehicle into S.

The mechanical separation between genset and electric

drivetrain and the energy buffering action of S give the series

architecture the maximum flexibility in terms of power

management. As a matter of fact SE may be considered as

a purely electric vehicle equipped with a genset that recharges

S autonomously instead of at a recharge station. Sometimes

the genset is undersized with respect to the average propulsionpower absorbed during a typical travel mission. In this case

the genset is used to extend the operating range allowed by S

and SE is referred to as "range extender".

Pros and cons of the series architecture may be summarized

as follows. Pros: i) ICE and are conveniently sized for the

average propulsion power or even less; ii) genset and

electrical drivetrain are mechanically separated thus

permitting to maximize the ICE efficiency with a

consequential substantial reduction of emissions. Cons: i) two

electric machines (i.e. and M) are required; ii) M must be

sized to provide the peak propulsion power; iii) the power

generated by ICE is transferred to by means of at least two

energy conversions (from mechanical to electrical to possibly

chemical inside S and vice-versa) with a lower efficiency

than a direct mechanical connection.

The series architecture is reputed to be more suited for

vehicles mainly used in urban area with rapidly varying

requirements of speed (and power); it is also used in large

vehicles where the lower efficiency of both ICE and the

mechanical transmission make more convenient the electric

propulsion.

B. Parallel Architecture

The Powertrain of a Parallel E (PE) has thearchitecture of ig.2. It comprises two independentdrivetrains namely one of mechanical type and the other oneof electric type whose powers are "added" by a 3-waymechanical devices -the Adder (A)- to provide the propulsionpower As shown in ig.2 the mechanical drivetrain generatesthe part pe of the propulsion power whilst the electricdrivetrain delivers the remaining part pm. The propulsionpower pw is then equal to

mew ppp (1)

ig. 2: PE Powertrain architecture.

The power sum may be done by adding either the speeds or

the torques of ICE and M. In the first case it is

mmeew cc ZZZ ZZ (2)here cwe and cwm are coefficients that depend on the gear

arrangement of A. By (1) the relationships between the

torques are

wee c WW Z wmm c WW Z (3)In the second case it is

mmeew cc WWW WW (4)here cwe and cwm are coefficients that depend again on the

gear arrangement of A. By (1) the relationships between the

speeds are

wee c ZZ W

wmm c ZZ W

()The simplest implementation for A is a torque adder with a

mechanical shaft that couples ICE and M to . ith this

implementation it is

1cc me WW ()ifferently from SE M acts here as generator not only

during the regenerative braking but also during the normal

driving whenever S must be recharged; in the latter

circumstance M draws energy from ICE through A.

As a matter of fact PE may be considered as a

conventional vehicle supplemented with an additional

drivetrain of electric type that overtakes the role of the

traditional generator-battery set by contributing to the

propulsion. Sometimes S is chosen to have small storable

energy but high power capability and M is sized with a wide

overload margin. In this case the electric drivetrain is used as a

power boost to supplement ICE during fast changes of the

propulsion power thus permitting ICE to adapt slowly to the

driving conditions. The resultant PE is often referred to as

power-assist; a commercial example of it is the onda

Insight car [7].

The modifications required to convert a conventional

vehicle into PE may be somewhat moderate and this

makes easier the manufacturing of PEs using the existing

production processes. A vehicle built up accordingly is termed

minimal or mild E depending on the extent of themodifications introduced in the original Powertrain.

Pros and cons of the parallel architecture may be

summarized as follows. Pros: i) only one electric machine is

needed; ii) the peak power requirement for M is lower than in

SE since both M and ICE provide the propulsion power;

iii) the power generated by ICE is transferred to directly

which is more efficient than through a double energy

conversion. Cons: i) an additional 3-way mechanical device is

required to couple together ICE M and ; ii) such coupling

imposes a tighter constraint on the power flow compared to

B

S

ICE

M

A

pepw

pm

ps


3/6

SE possibly turning into worse operation of ICE.

The parallel architecture is reputed to be more suited for

small- and mid-size vehicles mainly traveling along extra-

urban routes where the range for the required propulsion

power is not too wide.

C. Series-Parallel Architecture

The Powertrain of a Series-Parallel E (SPE) has the

architecture of ig.3. It may be viewed as a mix of the SE

and PE architectures obtained by employing a Power split

apparatus (P) with 2 mechanical ports and 1 electric port. The

3 ports are connected to ICE A and B respectively. P divides

the power generated by ICE into two parts i.e. the part pd

which is delivered directly in mechanical form to via A

similarly to PE and the part pb which is delivered in

electric form to B similarly to SE. The task of the power

split apparatus is then twofold; besides dividing the power

generated by ICE it must convert mechanical energy into an

electric form.

The series-parallel architecture has two main features: the

propulsion requirements are decoupled from the ICE operation

and the overall losses are lower since a fraction of the powergenerated by ICE is delivered to without any intermediate

energy conversion. The former feature makes the management

of the power flow very flexible enabling in principle to

optimize the ICE operation in a wide range of driving

conditions

ig. 3: SPE Powertrain architecture.

So splitting of the ICE power is obtained by two ways:

i. an apparatus based on a mechanical devices.ii. an apparatus based on electrical device.

III. CASCAE MTIEE IETE

Among various configurations of multilevel inverters

cascaded multilevel inverter is important. An eleven level

multilevel inverter consists of five -bridge cascaded in

single-phase. ne -bridge consisting of 4 IBTs as shown in

fig. 4(a). So a three phase unit will have 1 -bridge with

IBTs cascaded as shown in fig. . A multilevel inverter

synthesize a desired voltage from several separate dc sources

(SCSs) which may be obtained from batteries fuel cells or

solar cells [8]. Each SCS is connected to a single-phase full-bridge inverter. Each -bridge can generate three different

voltage outputs (vdc and -vdc) by the different combinations

of the four switches (s1 s2 s3 and s4). The fig. 4(b) shows the

switching pattern of four switches in a single -bridge.

dC

fdV

1S

2S

3S

4S

1D

2D

3D

4D

1g 3g

2g4g

A

B

P

ABv

iT iTS

pipi

aiV

0iTS 2 iTS

dcV

dc-V

S

S

0

0 0

0

1

1aip

G

ainG

a ip a in

G G, ="0":lower device on; "1":upper device on.

(a) (b)ig. 4: (a) ne -bridge with 4 IBTs (b) Switching sequence of one -

bridges inverter.

Cascaded waveform can be obtained which is almost

similar to a sinusoidal waveform and in this way we get an ac

output voltage. The ac outputs of each of the different level

full-bridge inverters are connected in series such that the

synthesized voltage waveform is the sum of the inverter

outputs. The number of output phase voltage levels in a

cascade inverter is defined by van vbn vcn given as

1321 ... amaaaan VVVVV (7)

here the number of output phase voltage level is given bym=2s1. heres is the number of -bridges in a leg. Phase

voltage of a -level cascaded inverter can represent in ourier

series as follows [9]:

1 1

/2 /2

( 1)/ 2

1

( 1) /2

1

(8)

4 sin( ) ...... sin( )

4 cos( )

4( ) cos( ) sin( ) (9)

m

dcn

mdc

jj

mdcan j

j

VB n t d t n t d t

V nn

VV t n n t n

D D

Z Z Z Z

D

Z D Z

3 3

3

3

3

DC

DC

DC

DC

DC

DC

DC

DC

DC

DC

DC

DC

DC

DC

DC

Va Vb Vc

3 phase balancedload

n

ig. : Power circuit of three-phase cascaded -bridges multi--level inverter

using IBT.

B

ICA

Pe pd

pmpw


4/6

2

S

S3

2

S

2S

Fundamental

component of VABVAB

Van

1T

2T

3T

4T

5T 5TS

4TS

3TS

2TS

1TS

1p

2p

3p

5p

5p

4p

4p

3p

2p

1p

x5V

x4V

x3V

x2V

x1V

ig. : utput voltages and switching pattern for one leg of the 3-phase

cascaded multilevel inverter.

Inverter with five SSCs and five full bridges is shown in

fig. . The output voltage of the inverter is almost sinusoidal

and it has less than % T with each of the -bridges

switching only at fundamental frequency. Each -bridge unit

generates a quasi-square waveform by phase shifting itspositive and negative phase legs switching timings. ig.

shows the switching timings to generate a quasi-square

waveform. ote that each switching device always conducts

for 18 (or cycle) regardless of the pulse width of the

quasi-square wave. This switching method makes all of the

active devices current stress equal. or a stepped waveform

such as the one depicted in ig. with steps the ourier

transform for this waveform is shown in eq. 8. rom the

magnitudes of the ourier coefficients when normalized as in

eq. (9) gives the conducting angles which can be chosen such

that the voltage total harmonic distortion is minimum.

ormally these angles are chosen so as to cancel the

predominant lower frequency harmonics [1]. or the -levelcase in fig. 1 the th 7th 11th and 13th harmonics can be

eliminated with the appropriate choice of the conducting

angles. ne degree of freedom is used so that the magnitude

of the output waveform corresponds to the reference

amplitude modulation index M which is defined as:

( )

( ) ( )

1

20.8

dc

an peak

cr peak cr peak

mV

VM

V V (1)

ere cr (peak) is the peak value of the carrier wave and

an (peak) is the command voltage. an (peak) is defined as

)()1()( peakcrdcpeakan VVmV (11)

or the harmonics (n=1 3 7 11 13 ) the set of non-

linear transcendental equation (from eq. 9) can be represented

as follows

1 2 3 4 5

1 2 3 4 5

1 2 3 4 5

1 2 3 4 5

1

cos(5 ) cos(5 ) cos(5 ) cos(5 ) cos(5 ) 0




cos(

T T T T TT T T T TT T T T TT T T T T

T

2 3 4 51

) cos( ) cos( ) cos( ) cos( ) (12)2

mMT T T

If the number of levels m=11 (including the zero level) and

modulating index M is .8 then[((m-1)2) M] = .8 = 4

Thus the values of the firing angles can be obtained by

putting the above value in eq. 12 and then solving it by

ewtonaphson iterative method.

q 57.61T q 94.182T q 18.273T q 57.454T q 24.625T

rom the angles followings things can be determined which

areB1=.1% T=.98% =.8%. ereB1 is

fundamental component THD is total harmonic distortion and

DFis distortion factor.

I. ESTSA ISCSSIS

A 3- phase multilevel inverter has been developed using

IBT because IBT is a very popular device among 11 high

power semiconductor switches. Its switching is very easy as

well as it handles high level of power demanded by E

motor drives. The multilevel inverter is loaded with 3-phase

2k induction motor to drive E powertrains. The

simulation has been done in PSIM and MATAB. The phase

voltage line voltage and line current of each bridge are shownin the figure [8-1] for changing load condition which

matches the E load characteristics. oad torque is

proportional to voltage function and it is matched with the

load function of ECE driving cycle of E.

ig. 7: Circuit diagram (sub- system) of a cascaded multilevel inverter on

PSIM attached to an Induction motor whose load can be externally controlled.

The circuit shown in fig. 7 whose load can be controlled

externally. This represents a E which has variable load and

this shows that voltage is proportional to torque. A PSIM

based 11-level inverter is shown in fig.. It consists of 1 -

bridges. The three phase output phase voltages and line

voltages are shown in fig.8.


5/6

ig. 8: 3-phases load voltage of cascade multilevel inverter (a) Three line-line

voltages (b) Three phase voltages.

ig. 9: Input current of SSC of each bridge drawn from bottom to top as

shown in figure 9.

ig. 1: esponse of cascaded multilevel based induction motor (a) 3-phase

stator current (b) Torque by motor and oad torque and (c) Speed of motor.

The converter consist of -bridge and produces 11-level (as it

has five steps above and five steps below the zero level

including the zero level). ig. 9 shows the input current of

each SSC which implies discharging of the batteries. It

shows that as the level increases from bottom to top the

discharging of battery increase. ig. 1 shows the stator

current motor torque and speed of motor. In this as the load

torque changes in unit step correspondingly stator current

speed and motor torque also changes. The rise time of speed islow which shows a good response

(a) (b)ig. 11: T of (a) ine-to-line voltage (b) Phase voltage at modulation index

.9.

ig. 12: T of (a) ine-to-line voltage (b) Phase voltage at modulation index

.8 (using MATAB).

(a)

Modulation index 0.8 Modulation index 0.9

(b)

ig 13: Change of (a) Phase and (b) line voltage respectively at different

modulation index (.8 and .9) using MATAB.

ig. [11-12] shows the T (voltage total harmonic

distortion) of the line to line voltage and phase voltage

respectively and its seen that the voltage waveform are onlydue to the fundamental components and other harmonics

components are negligible. ig. 13 shows the change in the

line to line voltage and phase voltage at different modulating

index (.8 and .9) respectively.

. APPEI

Three phase Squirrel Cage Induction Motor

Power = 2 k ine-ine oltage = 4 requency =

z Stator esistance (s) = .21475RWRU5HVLVWDQFH5r)

= .226WDWRU/HDNDJH,QGXFWDQFH / s+5RWRU


6/6

eakage Inductance (r+0XWXDO,QGXFWDQFH0

4.19 m Moment of Inertia = .12 Kg.m2 riction actor

= .7 ms.

I. CCSI

ybrid electric vehicle is the marriage between electrical

and mechanical engineering and provides two powertrains to

wheels of the vehicle. It is one of the solutions to mitigate

environmental pollutions and depletion of fossil fuels causedby land vehicles. IBT based cascaded multilevel inverter is

connected to star connected 3-phase induction motor. At

various load conditions it is simulated with PSIM and

MATAB. Current voltage speed and torque waveforms are

plotted. It is found that cascaded multilevel inverter reduces

harmonics and produces sinusoidal voltages. So it can be

concluded that cascaded multilevel converter is highly useful

and can be vehemently used in Es.

In this work cascaded multilevel inverter is interfaced

with electric drive of Es because of following special

features:

x The number of components used in cascaded is less thanother types of multilevel inverters like diode clamped and

flyback capacitor multilevel inverter.

x It is suitable for high voltage and high current ratingelectric drives. E has high current and low voltage

rating in order to reduce weight of the batteries.

x Cascaded multilevel inverters are switched at lowfrequency so it will create low noise which can be

suppressed and are comfortable for driving Es.

This converter will have high power factor and also have

less EMI and voltage unbalance problem.

II. EEECES

[1] C C Chan The State of the Art of Electric ybrid and uel Cellehicles proceeding of IEEE 27.

[2] M. Ehsani Y. ao Ali Emadi Modern electric ybrid Electric anduel Cell ehicles; undamentals theory and design 2nd edition CCPress 29.

[3] C C Chan and K.T. Chau Modern Electric ehicles Technologyxford niversity Press 21.

[4] . M. Tolbert and . Z. Peng Multilevel inverters for large automotivedrives All Electric Combat Vehicle 2nd Int. Conf.earborn MI vol.2 pp. 29214 une 812 1997.

[] P..Thakur et.al Technology and role of power split apparatus forhybrid electric vehicles IEEE IEC Taiwan ov. 27 pp 2-21.

[] A.Emadi K.ajashekara S.S.illiamson and S.M.ukic Topologicaloverview of hybrid electric and fuel cell vehicular power systemarchitectures and configurations IEEE Trans. on Vehicular

Technology vol.4 no.3 pp. 73-77 May 2.[7] The Insight-ondas irst ybrid Electric ehicle Special Auto

Technology pp. 14-18 27. Converters used in railways.[8] K.C. ana S. Biswas and P..Thakura A simple and generalized space

vector pulse width modulation of multi-level voltage source inverterIEEE ICIT- Mumbai ec.2.

[9] M..ashid undamental of power electronics Prentice all India 2ndEdition elhi 24.

[1] eon M. Tolbert ang Zheng Peng and Thomas .abetlerMultilevel converters for large electric drives IEEE Trans.Indus. Applicat. vol. 3 no.1 pp. 3-44 an. eb. 1999.

[11] . S. ai and . Z. Peng Multilevel convertersA new breed of powerconverters IEEE Trans. Ind. Applicat. vol. 32 pp. 9-17 Mayune199.

III. BIAPIES

A.K. Verma has received B.Tech. from BengalInstitute of Technology and ManagementSantiniketan est Bengal India in Electronics andCommunication Engineering in the year 29.Currently pursuing his ME in Power Electronics

from Birla Institute of Technology Mesra anchiharkhand India.

P.R. Thakura has received BE ME and Ph fromational Institute of Technology amshedpur BirlaInstitute of Technology and Science Pilaniajasthan and Birla Institute of Technology Mesraanchi India in 198 199 and 28 respectively.

At present he is eader in Electrical andElectronics Engineering epartment and ProfessorIn-Charge of Power Electronics aboratory. e had

been winner of young researcher fellowship andworked in niversity of Padova Padova Italy for one year 2-7. e has3 papers in his credit. ad done review of power electronic book of TMelhi and also review of papers of IEEE Transactions. is area of interest is

Power Electronics and ybrid Electric ehicles. e is ife member of IndianSociety of Technical Education ew elhi and Institution of Engineers[India].

K.C. Jana has received BE and M.Tech fromational Institute of Technology urgapur Indiain Electrical Engineering department in the year2 and 23 respectively. Currently he is

pursuing his Ph in Electrical Engineering fromadavpur niversity Kolkata India.

At present he is Assistant professor inepartment of Electrical and ElectronicsEngineering at Birla Institute of TechnologyMesra anchi harkhand India. e has 8 papers in

referred journal and conference. is area of interest is power electronicsdrives and embedded system. e is life member of Indian Society ofTechnical Education ew elhi and Institute f Engineers [India].

Giuseppe S. Buja (M7SM84 9) e receivedthe aurea degree in Electronic Engineering withhonors from the niversity of Padova PadovaItaly in 197.pon graduation he joined theEngineering aculty of the niversity of Padova.Since 198 he has been a ull Professor of PowerElectronics first at the niversity of Trieste andthen at the niversity of Padova. e has carried outresearch in the fields of electric energy staticconverters electric drives motion control systems

and field buses and has authored or co-authored more than 1 paperspublished in referred journals and international conference proceedings. estarted up the aboratory of Electric rives at the niversity of Trieste andthe aboratory of Industrial Automation at the niversity of Padova the latterof which he is currently the ead. e has directed several research projectsgranted by the university and by private companies. Prof. Buja has served theIEEE in several capacities including eneral Chairman of the 2th AnnualConference of the IEEE Industrial Electronics Society (IEEE IEC94)Associate Editor of the IEEE TAS. ISTIA EECTICSand ice President of the IEEE Industrial Electronics Society (IES).Currently he is a Senior Member of the Administrative Committee of the IESa oted Member of the Executive Council of the Association on PowerElectronics and Motion Control (PEMC).is biography has been included inthe last four editions ofWhos Who in the World.

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