supercapacitor and battery power management for hybrid vehicle applications

1

A Main-Project Report

On

SUPERCAPACITORS AND BATTERY POWER MANAGEMENT

FOR HYBRID VEHICLE APPLICATIONS USING

MULTI BOOST AND FULL BRIDGE CONVERTERS

Is submitted to

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY ANANTAPUR,

ANANTAPUR.

In partial fulfillment of the requirements

For the award of the degree of

BACHELOR OF TECHNOLOGY

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

During the year 2011-2012

Submitted By

P. GURUNADHAM 084E1A0217

S. JANARDHAN 084E1A0220

K. DILEEP KUMAR 084E1A0211

A. JAYA KRISHNA 084E1A0221

D. HARIBABU 084E1A0218

Under the esteemed mentorship of

Mr. K.MUNIGURU RAJAPRAKASH B.Tech.,

Assistant Professor,

Department of E.E.E., S.I.S.T.K

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

SIDDARTHA INSTITUTE OF SCIENCE & TECHNOLOGY

(An ISO 9001:2000 Certificate Institution)

(Approved by A.I.C.T.E. New Delhi & Affiliated to J.N.T.U.A., Anantapur)

Siddhartha Nagar, Narayanavanam road, Puttur-517583

2

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

SIDDARTHA INSTITUTE OF SCIENCE & TECHNOLOGY

(An ISO 9001:2000 Certificate Institution)

(Approved by A.I.C.T.E. New Delhi & Affiliated to J.N.T.U.A., Anantapur)

Siddhartha Nagar, Narayanavanam road, Puttur-517583

CERTIFICATE This is to certify that the MAIN PROJECT report entitled

SUPERCAPACITORS AND BATTERY POWER MANAGEMENT

FOR HYBRID VEHICLE APPLICATIONS USING

MULTI BOOST AND FULL BRIDGE CONVERTERS

has been submitted by :






In the department of Electrical and Electronics Engineering, SIDDARTHA INSTITUTE

OF SCIENCE AND TECHNOLOGY, Puttur and is submitted to JAWAHARLAL NEHRU

TECHNOLOGICAL UNIVERSITY, ANANTAPUR in partial fulfillment of the requirements

for the award of B.Tech, Degree in Electrical and Electronics Engineering. This work has been

carried out under my guidance and supervision during the year 2011-12.

Project Guide: Head of the Department:

Mr. K.MUNIGURU RAJAPRAKASH B.Tech, Mr. S.RAMESHM.E.,

Assistant Professor, Associate Professor,

Department of E.E.E., S.I.S.T.K, Department of E.E.E., S.I.S.T.K

Submitted for the Viva-Voce held on: _______________

Internal Examiner External Examiner

3

DECLARATION

We here by inform that the main project entitled “SUPERCAPACITORS AND BATTERY

POWER MANAGEMENT FOR HYBRID VEHICLE APPLICATIONS USING MULTI BOOST

AND FULL BRIDGE CONVERTERS” is carried by us during the month of Feb-Mar, 2012 is

an original work submitted by us to the DEPARTMENT OF ELECTRICAL AND

ELECTRONICS ENGINEERING, S.I.S.T.K, PUTTUR.






4

ACKNOWLEDGEMENT

The satisfaction that accompanies the successful completion of any task would

be incomplete without the mention of the people who made it possible, without whose

guidance, encouragement and help this venture would not have been success. The

acknowledgement transcends the reality of formality when we would like to express deep

gratitude and respect to all those people behind the screen who guided, inspired and

helped for me for the completion of my project presentation in time and up to the

standards.

I express out deep sense of gratitude to our project guide

Mr. K.MUNIGURU RAJAPRAKASH, B.Tech, Asst. Professor, for his guidance and

supervision at all levels of my project presentation. I indebted to his valuable suggestions

and sustained help in completion of my project presentation.

I express my deep sense of gratitude to Mr. S. RAMESH, M.E., Head of the

department of Electrical and Electronics Engineering for his valuable guidance and

constant encouragement given to me during this presentation

First and Foremost, I express my sincere gratitude to out honorable chairman

Dr. K.ASHOKA RAJU Ph.D., and also deep sense of gratitude to our honorable

principal Dr. USHAA ESWARAN Ph.D., for having provided all the facilities and

support in completing my project presentation successfully.

. I also thankful to All staff members of EEE department, for helping me to

complete this presentation by giving me valuable suggestions. I express my sincere

thanks to All my friends who have supported me in the accomplishment of this project

presentation.

Last but not the least, the one above all of us, the omnipresent God, for answering

our prayers for giving us the strength to plod on despite our constitution wanting to give

up and throw in the towel, thank you so much Dear Lord. Thank you for showing us the

path . . .

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CONTENTS

Abstract 1 +8

1. Introduction 2

1.1 Energy storage unit 5

1.2 Comparison of supercapacitor with lithium-ion (general capacitor) 7

1.3 Advantages and limitations of supercapacitors 8

1.4 Proposed block diagram 9

1.5 Power Flow 10

2. Effectiveness of battery-supercapacitor combination in electric vehicles 12

2.1. Energy management 14

2.1.1 Energy management functions can be separated into two groups 15

2.2 Component Modeling 16

2.2.1 Battery Bank 16

2.2.2 Supercapacitor Bank 17

2.2.3 Electrical Load 18

2.3 Vehicle energy storage system using supercapacitors 18

2.3.1 System specifications 18

2.3.2. The topology of bi-directional DC/DC converter 20

2.4 Vehicle application requirements 21

3. Ultracapacitor-battery interface for power electronic applications 23

4. DC/DC converters topologies and modeling 26

4.1. Multi boost and Multi full bridge converters modeling 27

5. Design for experimental results 31

5.1 Experimental setup at reduced scale 34

6

6. Simulation results 36

6.1 General 37

6.2 Introduction to Matlab 37

6.3 The Matlab System 38

6.3.1 Desktop tools and development environment 38

6.3.2 The Matlab mathematical function library 39

6.3.3 The Matlab language 39

6.3.4 Graphics 39

6.3.5 The Matlab external interfaces 39

6.3.6 Matlab documentation 39

6.3.7 Matlab online help 40

6.3.8 The role of simulation in design 40

6.3.9 Sim power systems libraries 41

6.3.10 Matlab Library 43

6.4 Full bridge converter simulation circuit for Np = 2 43

6.5 Boost converters simulation results 47

6.5.1 Simulation circuit for boost converter 47

6.6 full bridge converters simulation results 51

Conclusion 55

References 56

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LIST OF FIGURES

1. Converter topologies for ECCE Hybrid Vehicle 4 +8

(a). first solution 4

(b). second solution 4

2. Overview of energy storage unit Battery 5

3. Supercapacitor equivalent circuit 8

4. Electric vehicle/hybrid electric vehicle system using supercapacitors 9

5. Power flow to the ESU 10

6. System configuration of the supercapacitor implemented 19

7. The bi-directional DC/DC converter(full-bridge type topology) 20

8. (a). Multi boost Converter topology 27

(b). Multi full bridge converter topology 28

9. (a). Multi boost control strategy 30

(b). Multi full bridge control strategy 30

10. Full bridge converter with chopping devices 33

11. Boost and full bridge converters experimental setup 34

(a). Boost converters setup for Np = 2 34

(b). Full bridge converter setup for Np = 1 35

12. Full bridge converter simulation circuit for Np = 2 44

13. (a). Super capacitor modules voltages 45

(b). Super capacitor modules currents 45

14. (a). Battery current control result 46

(b). DC-link and active load currents 46

15. Simulation circuit for boost converter 47

16. Super capacitor modules experimental and simulation voltage results 48 (a). First module voltage 48

(b). Second module voltage 48

8

17. Super capacitor modules experimental and simulation current results 49

(a). First module current 49

(b). Second module current 49

18. DC-link voltage and current experimental validation 50

(a) Multi boost output current (IL ) 50

(b) Battery current experimental result 50

19. Simulation circuit for full bridge converter 52

20. (a). Super capacitors module voltage and current 53

(b) DC-link and active load experimental currents 53

21. High frequency planar transformer voltages and currents 54

(a) Transformer input and output voltages 54

(b) Transformer input and output currents 54

9

ABSTRACT

This paper presents supercapacitors and battery association methodology for

ECCE Hybrid vehicle. ECCE is an experimental Hybrid Vehicle developed at L2ES

Laboratory in collaboration with the Research Center in Electrical Engineering and

Electronics in Belfort (CREEBEL) and other French partners. This test bench has

currently lead-acid batteries with a rated voltage of 540 V, two motors each one coupled

with one alternator. The alternators are feeding a DC-bus by rectifiers.

The main objective of this paper is to study the management of the energy

provides by two supercapacitor packs. Each supercapacitors module is made of 108 cells

with a maximum voltage of 270V. This experimental test bench is carried out for studies

and innovating tests for the Hybrid Vehicle applications.

The multi boost and multi full bridge converter topologies are studied to define

the best topology for the embarked power management. The authors propose a good

power management strategy by using the multi boost and the multi full bridge converter

topologies. The simulation results of the two converter topologies are presented.

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CHAPTER-1

INTRODUCTION

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1.INTRODUCTION

In the last few years the pollution problems and the increase of the cost of fossil

energy (oil, gas) have become planetary problems. The car manufacturers started to react

to the urban pollution problems in nineties by commercializing the electric vehicle. But

the battery weight and cost problems were not solved. The batteries must provide energy

and peaks power during the transient states. These conditions are severe for the batteries.

To decrease these severe conditions, the super capacitors and batteries associate with a

good power management present a promising solution. Environmental issues create a

demand for more energy efficient vehicles.

A conventional vehicle with an internal combustion engine (ICE), converts

chemically stored energy (gasoline, ethanol, diesel etc.) into kinetic energy in a process

afflicted with significant power losses. Combining the ICE with an electric energy storage

and drive system can improve the fuel efficiency through several means. The electrical

propulsion system allows the combustion engine to operate closer to its optimal operating

point through supplying the wheels with extra power when needed and absorb power

when the ICE produces excess power. Another benefit with hybrid electric vehicles (HEV)

is that when braking, the energy can be absorbed by the electrical system, instead of

converting all kinetic energy into heat via friction brakes. The electrical energy storage

typically consists of a battery with more or less complex support-electronics for charge

control and error prevention.

The storage unit has to store relatively large amounts of energy and handle high

power. With current battery technology, the energy storage capacity comes at a cost of

decreased power capability and the lifetime of the modern batteries is dependent of the

charge cycles. By introducing a supercapacitor as aid, the battery could be spared from the

power peaks and thus allow the battery to be optimized for energy storage or extend the

lifetime o f a given battery, which in turn could lower the cost of the entire unit. To fully

utilize the supercapacitor, a voltage converter is needed, which naturally should be as

efficient and simple as possible. With the converter it is also possible to have sophisticated

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control of the power flows, which can improve the system if proper strategies are used.

Interesting previous works made before this report include, “Comparing DC-DC

Converters for Power Management in Hybrid Electric Vehicles” (Shupbach & Balda

2003), which is a study of different topologies for supercapacitor handling. An in-depth

report on control strategies and optimizations are Andersson and Groot (2003) M.Sc thesis

report “Alternative Energy Storage System for Hybrid Electric Vehicles”. The work

“Comparison of Simulation Programs for Supercapacitor Modeling” by Andersson and

Johansson (2008) has also been a useful resource for modeling of the supercapacitor.

Doerffel (2007) have studied the ageing and deteriation processes of lithium-ion batteries,

and how to measure the state of health.

To ensure a good power management in hybrid vehicle, the multi boost and multi

full bridge converters topologies and their control are developed. Two topologies

proposed for the power management in ECCE Hybrid Vehicle are presented in Fig.1.

Figure 1 . Converter topologies for ECCE Hybrid Vehicle

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1.1 Energy storage unit:

The energy storage unit (ESU) in a car handles the storage of the electrical energy

and functions as a buffer for the electrical machine (and the generator in the series hybrid

configuration). The ESU has the possibility to either receive or deliver power from or to

the electrical machine (via a DC/AC inverter). Depending on application and

dimensioning parameters, such as hybridization level and size of the vehicle, is it possible

to configure the ESU in different combinations.

It is necessary to have a storage utility, which could be a battery or a

supercapacitor or a combination of the both, to work as the source of energy and power in

this thesis work, a combination consisting of a supercapacitor in parallel with a battery

will be studied. If there is a need to control the power flow or if there is a need to have

different voltage levels (i.e. the voltage over the capacitor is dimensioned to be lower than

the voltage over the battery or vice versa) it can be possible or necessary to install a

converter in series with the battery or the supercapacitor or both. If the converter is

installed in series with the battery it is possible, with the ability of power control, to get a

direct control over the power to the battery.

Another possible combination is to install two converters, one in series with the

supercapacitor and one in series with the battery, but this would lead to an unnecessary

complexity of the system. Therefore, in this paper, a converter has been installed in series

with the supercapacitor. The configuration is presented in Figure-2.

Figure 2. Overview of energy storage unit Battery

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The battery is suitable to provide the energy buffer to the HEV due to that battery

has the ability to store relatively high levels of electrical energy. In the market of today

there exist several model and sizes. The problems with batteries are mainly the cost,

lifetime and size. Supercapacitors also called ultracapacitors and electric double layer

capacitors (EDLC) are capacitors with capacitance values greater than any other capacitor

type available today.

Capacitance values reaching up to 400 Farads in a single standard case size are

available. Supercapacitors have the highest capacitive density available today with

densities so high that these capacitors can be used to applications normally reserved for

batteries. Supercapacitors are not as volumetrically efficient and are more expensive than

batteries but they do have other advantages over batteries making the preferred choice in

applications requiring a large amount of energy storage to be stored and delivered in bursts

repeatedly.

The modern supercapacitor is not a battery per se but crosses the boundary into

battery technology by using special electrodes and electrolyte. Several types of electrodes

have been tried and we focuse on the double-layer capacitor (DLC) concept. It is carbon-

based, has an organic electrolyte that is easy to manufacture and is the most common

system in use today.

A supercapacitor is a component which has relatively high specific power ability

in Comparison to batteries much like a capacitor, while it has much higher specific energy

than a conventional capacitor, more like a battery. In order to have high capacitance, the

isolator is very thin, usually in order of tenths of nm (Lai et al. 1992). The maximum

voltage difference between the electrodes is related to the dielectric breakdown of the

isolator, which in turn is related to its thickness and material.

Due to the thin isolator in supercapacitor, the maximum voltage per cell becomes

relatively low, in order of 2-4V to avoid dielectric breakdown. The supercapacitor can not

only be charged and discharged more than one million times but also be stored with ten

15

times more energy than conventional electrolytic capacitors. In contrast, the

supercapacitor has the merits of a rapid charge and discharge of energy and a longer life

cycle, because of electrostatic nature of capacitor rather than chemical reaction.

1.2 Comparison of supercapacitor with lithium-ion (general capacitor):

Function Supercapacitor Lithium-ion (general)

Charge time

Cycle life

Cell voltage

Specific energy (Wh/kg)

Specific power (W/kg)

Cost per Wh

Service life (in vehicle)

Charge temperature

Discharge temperature

1–10 seconds

1 million or 30,000h

2.3 to 2.75V

5 (typical)

Up to 10,000

$20(typical)

10 to 15 years

–40 to 65°C (–40 to 149°F)

–40 to 65°C (–40 to 149°F)

10–60 minutes

500 and higher

3.6 to 3.7V

100–200

1,000 to 3,000

$2 (typical)

5 to 10 years

0 to 45°C (32°to 113°F)

–20 to 60°C (–4 to 140°F)

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1.3 Advantages and limitations of supercapacitors:

Advantages

Virtually unlimited cycle life; can be cycled millions of time

High specific power; low resistance enables high load currents

Charges in seconds; no end-of-charge termination required

Simple charging; draws only what it needs; not subject to

overcharge

Safe; forgiving if abused

Excellent low-temperature charge and discharge performance

Limitations

Low specific energy; holds a fraction of a regular battery

Linear discharge voltage prevents using the full energy

spectrum

High self-discharge; higher than most batteries

Low cell voltage; requires serial connections with voltage

balancing

High cost per watt

Equivalent circuit of supercapacitor

Figure 3. Supercapacitor equivalent circuit

This equivalent circuit is only a simplified or first order model of a super capacitor.

This causes super capacitors to exhibit behavior more closely to transmission lines than

capacitors. Below is a more accurate illustration of the equivalent circuit for

supercapacitor.

1.4 Proposed block diagram:

Figure 4. Electric vehicle/hybrid electric vehicle system using supercapacitors.

A hybrid vehicle is a vehicle which can run the mechanism by using multiple

sources such as diesel, petrol, gas, elect

components and so that it will provide flexibility, reliability, safe and secured target.

Figure4 shows the operation of hybrid vehicle in two modes. One is motoring

mode and the other is regenerative b

of current in the motoring mode and the red mark indicates the flow of current in the

regenerative braking mode. During the motoring mode the hybrid vehicle takes electric



capacitors. Below is a more accurate illustration of the equivalent circuit for

1.4 Proposed block diagram:

Electric vehicle/hybrid electric vehicle system using supercapacitors.


sources such as diesel, petrol, gas, electricity. A hybrid vehicle is combination of different


shows the operation of hybrid vehicle in two modes. One is motoring

mode and the other is regenerative braking mode. The blue arrow marks indicates the flow



17



capacitors. Below is a more accurate illustration of the equivalent circuit for a

Electric vehicle/hybrid electric vehicle system using supercapacitors.


ricity. A hybrid vehicle is combination of different


shows the operation of hybrid vehicle in two modes. One is motoring

raking mode. The blue arrow marks indicates the flow



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energy from both battery and supercapacitor i.e., the steady state energy is supplied by

battery and energy at peak state (during switching, transient periods) is supplied by both

supercapacitor and battery. During the regenerative mode hybrid vehicle supplies the

electrical energy to both supercapacitor and battery. Since this process is recycled

electrical energy is utilized efficiently. Therefore the weight of the battery decreases and

life gets increased.

1.5 Power Flow:

The load power, coming from the outer parts of the HEV, can be both positive and

negative. A positive load power is in this work defined as that there is a surplus of power

in the outer system and the power is therefore flowing into the ESU (generator reference).

If the load power is negative there is a demand for power in the external system and power

is flowing out from the ESU. Inside the ESU the load power is divided between the power

to the battery and power to the supercapacitor, which is demonstrated in Figure 5.

Figure 5. Power flow to the ESU

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The converter is able to divert power to or from the supercapacitor, depending on

outer Circumstances such as power control strategies. These control strategies are

optimized to give a better system performance and mitigating the battery stresses. In the

last few years th e pollution problems an d the increase of the cost of fossil energy (oil,

gas) have become planetary problems. The car manufacturers started to react to the urban

pollution problems in nineties by commercializing the electric vehicle. But the battery

weight and cost problems were not solved.

The batteries must provide energy and peaks power during the transient states.

These conditions are severe for the batteries. To decrease these severe conditions, the

super capacitors and batteries associate with a good power management present a

promising solution.

A Power management is nothing but efficiently directing power to different

components of a system. Power management is especially important for portable devices

that rely on battery power. By reducing power to components that aren't being used, a

good power management system can double or triple the lifetime of a battery.

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CHAPTER-2

EFFECTIVENESS OF

BATTERY-

SUPERCAPACITOR

COMBINATION IN HYBRID

VEHICLES

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2.EFFECTIVENESS OF BATTERY-SUPERCAPACITOR

COMBINATION IN HYBRID VEHICLES

A significant portion of energy is dissipated in the brakes when driving

conventional gasoline-powered vehicles in urban areas, where periodic acceleration-

deceleration cycles are required. Therefore, recovering this energy through regenerative

breaking is an effective approach for improving vehicle driving range and this can only

be accomplished by electric vehicles (EV) or hybrid-electric vehicles (HEV).

Regenerative breaking in these vehicles captures some of the kinetic energy stored in the

vehicle’s moving mass by operating the vehicle’s traction motor as a generator that

provides braking torque to the wheels and recharges the batteries .

The battery bank of an EV is sized for peak power demand, and this often

compromises the desired weight and space specifications. On the other hand, The

auxiliary power unit (APU) of an HEV is designed to provide the normal average power

required by the vehicle, while the battery is sized to provide power surges needed during

acceleration and hill climbing and to accept momentary powers during breaking. While

EVs and HEVs are more efficient than conventional vehicles in urban areas, the electric

load profile consists ofhigh peaks and steep valleys due to repetitive acceleration and

deceleration.

The resulting current surges in and out of the battery tend to generate extensive

heat inside the battery, which leads to increased battery internal resistance – thus lower

efficiency and ultimately premature failure . The problem of battery overheating and loss

of capacity is more acute when batteries are near full state-of-charge (SOC) since they

cannot accept large busts of current from regenerative breaking without degradation at

this stage.

Supercapacitors (also referred to as ultracapacitors or electrochemical capacitors)

have much greater advantage over batteries when capturing and supplying short bursts of

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power due to their higher power density limits, and ability to charge and discharge very

quickly. Hence adding a supercapacitor bank will assist the battery during vehicle

acceleration and hill climbing, and with its quick recharge capability, it will assist the

battery in capturing the regenerative braking energy. This significant advantage a battery-

supercapacitor energy storage/supply system gained attention in recent years in

transportation systems as well as other applications . Applying supercapacitors also

allows for a smaller battery size, and there is almost no limit to number of their charge-

discharge cycles (since there are no chemical reactions involved in their energy storage

mechanism). Furthermore these devices require no maintenance and do not use toxic

materials.

Special considerations must be taken into account when integrating such a hybrid

energy storage system to achieve optimal performance. While direct connection of the

supercapacitor across the battery terminals does reduce transient currents in an out of the

battery, the best way to utilize the supercapacitor bank is to be able control its energy

content through a power converter. The paper reviews the direct supercapacitor-battery

shunt connection, after a short section addressing component modeling issues. The

desired connection is then addressed by using a DC/DC converter in the boost mode

when discharging, and in the buck mode when charging the supercapacitor bank.

2.1. Energy management:

The expanding functions of the vehicle electric/electronic system call for

significant improvements of the power supply system. A couple of years ago, broad

introduction of a higher system voltage level, 42V, initially in a dual-voltage 14/42V

system, was considered as a viable solution. However, the cost/benefit ratio associated

with this type of configuration in systems operating at 42V or less turned out to be too

low for widespread implementation. Furthermore, the electric propulsion that can be

generated at this voltage level is generally considered too low to make mild-hybrid

electric vehicles attractive.

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At the same time, several hardware components for the conventional 14Vsystem

experienced significant technological progress. For example, enhanced 14V clawpole

(Lundell) alternators were developed that can continuously generate an electric power

output of 3 kW or more. AGM batteries demonstrated at least three-fold longer shallow-

cycle life, compared to conventional SLI batteries. Finally, the introduction of high-level

energy management control strategies can ensure system robustness and optimal energy

efficiency and thus help stretch the boundaries of the 14V system.

2.1.1 Energy management functions can be separated into two groups:

Power Supply Management (PSM): Control of the on-board electric generation, i.e.

control of the alternator set point in conventional electrical systems, aiming at optimizing

all of the following: electrical function availability, battery life, vehicle performance (e.g.

reduced alternator load when maximum acceleration is demanded), or fuel consumption

(e.g. reduce alternator output at idle to allow for lower idle speed). Whereas many of

these functions can be considered state of the art in modern voltage regulation,

particularly the latter has garnered growing attention recently. Electric generation

contributes significantly to fuel consumption, at least in real-world conditions. An

average alternator output of 1 kW involves as much as 1–1.4 l gasoline fuel consumption

per 0 km, depending on vehicle parameters and driving conditions. Decoupling the

electric generation from the loads’ demands can significantly reduce this specific fuel

consumption contribution by optimizing the system efficiency of engine and alternator at

any point in time. This will introduce supply voltage fluctuations into the electrical

system and systematically exploit the battery as a short-term energy buffer. Significantly

more advanced strategies of PSM are of course needed for HEVs, where electric

generation plays a more vital role.

Power Distribution Management (PDM) is used to schedule the allocation of available

power and energy to electric loads on a subsystem or component level. Effectively, it

must ensure the controlled function delivery of individual electric features by

prioritization. Whenever a power deficiency occurs, the PDM algorithm aims at ensuring

rail voltage stability, charge balance and robustness, as well as minimizing battery charge

24

throughput in the case of peak loads. Depending on the definition of electric feature

priorities, a PDM strategy can dictate a temporary functional degradation under

appropriate conditions. Here, a careful balancing of priorities is required, especially for

functions that are directly perceivable by the customer. Advanced PDM algorithms will

schedule electric feature functionalities dynamically rather than statically.

Electric energy management actively uses the energy storage system (battery,

supercapacitor, etc.) and hence relies on precise status information about this device. A

battery monitoring system (BMS) has to deliver these essential inputs to the energy

management control system.

2.2 Component Modeling:

This section reviews the modeling of the main power system components in an

electric vehicle; namely, the battery bank, the supercapacitor bank, and the electrical

load. More details on electrical component modeling can be found in power electronics

textbooks.

2.2.1 Battery Bank:

Batteries are quite difficult to model as they undergo thermally-dependent

electrochemical processes while delivering and accepting energy. Thus the electrical

behavior of a battery is a nonlinear function of a number of constantly changing

parameters, such as internal temperature, state-of charge, rate of charge/discharge, etc. …

The capacity of a battery depends on the discharge rate as wells as temperature. This

relationship is described by Peuket’s equation relating the discharge current I (A) to the

time t (hr) it takes it to discharge, I. Given the battery capacity CTo at temperature To, the

capacity at some other temperature is computed by CT = CTo1 + (T-To) where is

a constant.

25

An approximate model that is often used for batteries is a Thevenins equivalent

circuit that consists of the open circuit voltage in series with an effective internal

resistance. Both voltage and resistance values are functions of the battery SOC, and these

relations are generally supplied the manufacturer. SOC is defined the percentage of

energy left in a battery (after supplying a certain amount of amp-hours) relative to its full

capacity.

The open-circuit voltage is often approximated by a linear function of the

SOC: Voc = a1+ a2 SOC, at some specific temperature (e.g., 80o F). The battery internal

resistance has static and dynamic values that depend of battery SOC, whether the battery

is being charged or discharged and rate of charge/discharge. In short duration studies,

however, the amount of amp-hours in and out of the battery is a small fraction of the

battery capacity. Hence it is fair to assume that battery internal voltage is constant during

such periods, and a quasi-steady state model with fixed open-circuit voltage and internal

resistance constitutes an acceptable battery model . Note that two resistance values are

used in this case, one during charging and another during discharging.

2.2.2 Supercapacitor Bank:

As in conventional capacitors, the resistance and inductance of the terminal wires

and electrodes of supercapacitors are represented by a series R-L circuit. Further, non-

perfect insulation between the device electrodes results in leakage current that is

represented by a large shunt resistance. The difference between conventional and

supercapacitors is that the latter are much more efficient, i.e., the series resistance is a lot

lower and the shunt resistance is much higher in value. The self-discharge time constant

of supercapacitors several orders of magnitude larger than that of conventional

capacitors. More sophisticated models suitable for dynamic studies are found. The study

under investigation is a short-duration analysis of the power (or current) distribution

between the battery bank and supercapacitor bank during acceleration and deceleration.

Hence, the leakage resistance can be ignored without much error, and the supercapacitor

bank can simply be represented by a series R-C circuit.

26

2.2.3 Electrical Load:

The electrical load in electric vehicles consists mainly of an inverter-fed induction

motor for motive power. During regenerative breaking, the motor is turned into a

generator by reducing the frequency of its terminal voltage, thus reversing power flow

and producing braking torque. Detailed modeling of inverter-fed motor drives is found in

standard power electronics and drives textbooks. As far as the power source in

concerned, power demand is sufficient for analysis. Since the DC bus voltage is not

allowed to vary significantly from its nominal value, current demand gives a good

approximation of power demand. Thus the load can be modeled simply by a time-varying

current source that reverses direction as the vehicle switches from coasting or

acceleration to regenerative braking.

2.3 Vehicle energy storage system using supercapacitors:

2.3.1 System specifications:

To control the energy stored in supercapacitor bank, it is need that the voltage of

the supercapacitor bank should be controlled. If not, the supercapacitor voltage depends

on the battery voltage, so that there is no possibility to control the energy stored in

supercapacitor bank. Thus, DC/DC converter is indispensable to regulate the bank

voltage level. Moreover, because the current can flow to supercapacitor when the

supercapacitor is charged and the current can flow from supercapacitor when the

supercapacitor is discharged, the DC/DC converter has to have a bi-directional nature.

Figure 6. shows the system configuration with battery pack and supercapacitor bank as an

energy storage. The DC/DC converter is on boost-mode operation as the inverter supplies

traction power to the motor. On the other hands, the DC/DC converter is on buck-mode

operation as the regenerative energy come to supercapacitor bank.

27

Figure 6. System configuration of the supercapacitor implemented.

Table 1. Specification of system.

From the required specification of Table 1, the number of supercapacitor cell is

designed to be 30, on the basis that the maximum voltage of each supercapacitor cell is

2.3V (92% of continuous voltage rating), and the minimum voltage of each

supercapacitor cell is 1.25V (50% of continuous voltage rating). As a consequence, the

capacitance of the supercapacitor bank used in this study becomes 2700/30=90F and

28

equivalent series resistance (ESR) 1mΩ×30=30mΩ, to make the maximum stored energy

become 210kJ. The the total volume and weight of the supercapacitor bank is 18l and

22kg, respectively.

2.3.2. The topology of bi-directional DC/DC converter:

There can be lots of converter topology for realizing a bi-directional DC/DC

converter; single-stage buck/boost type and full-bridge type as a typical one. Full-bridge

type topology has merits compared to single-stage buck/boost type topology. 1) Electrical

isolation between input and output is guaranteed. 2) Higher boost ratio can be

implemented. 3) System protection is possible when output stage short take place. From

these facts, full-bridge type topology is employed in this study, in spite that the full-

bridge type topology is somewhat bulky, requires more components rather than single

stage buck/boost type.

Figure 7. The bi-directional DC/DC converter(full-bridge type topology).

29

As shown in Fig. 7, the bi-directional full-bridge topology DC/DC converter is

operated on boost mode at the time electric power is supplied from supercapacitor stage

(low voltage stage) to battery stage (high voltage stage), and on buck mode at the time

electric power is absorbed from battery stage to supercapacitor stage. Because the

supercapacitor stage of the DC/DC converter has low voltage level, a current control is

necessary in the cause of reducing current’s burden on semiconductors.

At the battery stage of the DC/DC converter, voltage control is necessary to match

to DC bus voltage of the inverter. Also, soft switching technique of zero voltage-zero

current switching is applied to this system for improving the DC/DC converter efficiency.

2.4 Vehicle application requirements:

The energy storage requirements vary a great deal depending on the type and size

of the vehicle being designed and the characteristics of the electric powertrain to be used.

Energy storage requirements for various vehicle designs and operating strategies are

shown in Table 2 for a mid-size passenger car. Requirements are given for electric

vehicles and both charge sustaining and plug-in hybrids.

These requirements can be utilized to size the energy storage unit in the vehicles

when the characteristics of the energy storage cells are known. In some of the vehicle

designs considered in Table, ultracapacitors are used to provide the peak power rather

than batteries.

For ultracapacitors, the key issue is the minimum energy (Wh) required to

operate the vehicle in real world driving because the energy density characteristics of

ultracapacitors are such that the power and cycle life requirements will be met in most

cases if the unit is large enough to met the energy storage requirement.

30

Table 2. Energy storage unit requirements for various types of electric passenger cars

Type of

electric

driveline

System

Voltage V

Useable

energy

storage

Maximum

pulse power at

90-95%

efficiency kW

Cycle life

(number of

cycles)

Useable

depth of-

discharge

Electric

300-400 15-30 kWh 70-150 2000-3000

deep

70-80%

Plug-in

hybrid

300-400

6-12 kWh

battery 100-

150 Wh

ultracapacitors

50-70 2500-3500

deep

60-80%

Charge

sustaining

hybrid

150-200

100-150 Wh

ultracapacitors

25-35 300K-500K

Shallow

5-10%

Micro-

hybrid

45

30-50 Wh

ultracapacitors

5-10 300K-500K

Shallow

5-10%

31

CHAPTER-3

ULTRACAPACITOR-

BATTERY INTERFACE FOR

POWER ELECTRONIC

APPLICATIONS

32

3.ULTRACAPACITOR-BATTERY INTERFACE FOR

POWER ELECTRONIC APPLICATIONS

The electrical load in electric vehicles consists mainly of an inverter-fed induction

motor for motive power. During regenerative breaking, the motor is turned into a

generator by reducing the frequency of its terminal voltage, thus reversing power flow

and producing braking torque. As far as the power source in concerned, power demand is

sufficient for analysis. Since the DC bus voltage is not allowed to vary significantly from

its nominal value, current demand gives a good approximation of power demand. Thus

the load can be modeled simply by a time-varying current source that reverses direction

as the vehicle switches from coasting or acceleration to regenerative braking.

1. The role of the ultracapacitor is to maintain the battery current as constant as

possible with slow transition from low to high current during transients to limit battery

stress. On the other hand, the ultracapacitor ought to charge as fast as possible without

exceeding maximum current from regenerative breaking, and to discharge most of its

stored energy during acceleration. Energy flow in and out of the ultracapacitor can be

controlled with pulse-with-modulated (PWM) DC/DC converter. Adding a

ultracapacitor bank to a battery- or fuel cell driven vehicle makes sense and advantages

by far outweigh the disadvantages. A direct parallel connection will reduce battery stress

by assisting with transient currents during acceleration and deceleration. The parallel

combination of the battery system and UC bank also exhibits good performance for the

stand-alone residential applications during the steady-state, load-switching, and peak

power demand. Without the UC bank, the battery/fuel cell system must supply this extra

power, thereby increasing the size and cost of the attery/fuel cell system .

2. The ultracapacitor addition removes 20% of the mass of the battery pack of the

electric vehicle. Another method for reducing the size of the capacitor bank would use

some battery power during each shot. If the application were to permit this, the

ultracapacitor stack would still supply most of the power while the load was at its peak,

but the battery would supply a lower, consistent level over the full ten-second duration.

Such a hybrid approach can significantly reduce the size of the ultracapacitor stack.

33

3. Time domain and frequency domain measurements both confirmed that

ultracapacitors are very efficient for low frequency use. Both also show that the

capacitance drops (with corresponding decrease in efficiency) for frequencies greater

than 0.1 Hz is measured by various frequency response of ultracapacitors. The time

domain measurements show that capacitor loss becomes very significant (70% for some

tests) for fast discharge times . As Ultra-capacitors are always used for energy storage or

energy buffer applications, their poor high frequency response makes them completely

unsuitable for high frequency applications and are therefore more suitable for dc

circuits. Thus the Ultracapacitors should be connected to any high frequency charging

converter with a small inductance of about 20µH in series to the converter.

4. The main problem with the application of ultracapacitors is that maximum

voltage of each cell in the stack (2 ,5 V) should not be exceeded. It is probably

reasonable to limit the number of cells in series in batteries, and to match voltages of

interconnected DC links using a converter containing an AC medium frequency link

with transformer.

5. Ultra-capacitors are used as an energy storage buffer by simultaneously charging

and discharging them by paralleling them to an energy source like a battery, fuel cell,

DC-DC converter , etc. and a load. The voltage and current ripple caused by the

charging converter can often cause over charging or temperature rise of the capacitor.

The increasing filter inductance or increasing the switching frequency of the buck

derived DC-DC converter that is usually used for charging will be one solution, they

will significantly either increase both size and cost or increase losses in the converter.

Moreover, increasing inductance requires higher turns and this increases both the

radiated fields from the inductor and the inter-winding capacitance of the inductor.

These radiated fields and the feed through noise through the inter-winding capacitance

from the inductor mainly couple to surrounding circuits and increase EMI. Thus a better

solution would be to use additional filter circuits that attenuate both voltage ripple and

ripple current during charging.

34

CHAPTER-4

DC/DC CONVERTERS

TOPOLOGIES AND

MODELING

35

4. DC/DC CONVERTERS TOPOLOGIES AND MODELING

4.1. Multi boost and Multi full bridge converters modeling

Figure 8(a) shows the multi boost converter topology. The general model for this

topology is given by equation (1); where (α1) and (n) define respectively the duty cycle

and parallel input converter number.

The voltage drops in the Ln and λ inductances are given by equation (2).

Figure 8 (a). Multi boost Converter topology

(1)

(2)

36

Figure 8(b). Multi full bridge converter topology

The converter average model has a nonlinear behavior because of crosses between

α1 control variable and Vbus1 parameter. The Vbus1, Vsc1, Vsc2, Vscn , Ich and Vbat

variables can to disturb the control, they must be measured and used in the estimate of the

control law to ensure a dynamics of control . The multi boost converter topology control

law which results from the boost converter modeling is presented by α1 duty cycle (3);

where Np = max(n) is the maximum number of parallel converters.

The multi boost converter control strategy is presented in Fig.9 (a). It ensures the

super capacitor modules discharge with variable current. The super capacitors reference

current (Iscref) is obtained starting from the power management between batteries and

hybrid vehicle DC-link. This control strategy includes the super capacitors and batteries

current control loops. PWM1 signal ensures the multi boost converters control during

(3)

37

super capacitor modules discharge. These modules being identical, the energy

management between the modules and the hybrid vehicle DC-link enables to write the

super capacitors current references (4).

To simplify the super capacitors current references estimation, the multi boost

converter efficiency (η) was fixed at 85%.

The multi full bridge converter control strategy proposed in this paper consists to

establish the full bridge converters standardized voltage . The control law which result

from the multi full bridge converter modeling is presented by equation(5), where (m)

defines the transformer turns ratio.

This standardized voltage is compared with two triangular carrier waves of

amplitude Vmax = 1V with a switching frequency of 20 kHz. The inverter control

strategy is presented in Fig. 9(b); where Q1, Q2, Q3 and Q4 are the control signals

applied to K1, K2, K3 and K4 switches.

(4)

(5)

38

Figure 9(a) Multi boost control strategy

Figure 9(b) Multi full bridge control strategy

Figure 9. Multi boost and Multi full bridge converters control strategy

39

CHAPTER-5

DESIGN FOR

EXPERIMENTAL RESULTS

40

5. DESIGN FOR EXPERIMENTAL RESULTS

Wiring in power electronic design is a general problem for electrical energy

system and the voltage inverters do not escape to this problem. The switch action of

semiconductors causes instantaneous fluctuations of the current and any stray inductance

in the commutation cell will produce high voltage variations. Semiconductors, when

switching off, leads to high voltage transitions which is necessary to control within

tolerable limits. The energy stored in parasitic inductances, during switching on, is

generally dissipated by this semiconductor.

In the case of the single-phase inverter, each cell includes two switches and a

decoupling capacitor placed at the cell boundaries, which presents a double role. It

enables to create an instantaneous voltage source very close to the inverter. The (C)

capacitor associated to an inductor enables to filter the harmonic components of the

currents which are generated by the inverter. Parasitic inductances staying in the mesh

include the capacitor inductance, the internal inductance of semiconductors and the

electric connection inductances. A good choice of the components with an optimal wiring

enables to minimize parasitic inductances.

Using the semiconductors modules solves the connection problems between

components. All these efforts can become insufficient, if residual inductances remain too

high or if the inverter type is the low voltages and strong currents for which the voltage

variations are much important. In both cases, the use of the chopping devices is

necessary. These devices must be placed very close to the component to avoid any

previous problem.

The parameters used for experimental tests are presented in table 3. and the

principle of such circuits is given in Fig. 10.

41

Table 3: Full bridge experimental parameters

Symbol Value Name

R1= R2=R3 = R4 10Ω Chopping circuits

resistances

C1=C2=C3=C4 220µF Chopping circuits capacitors

λ 25µH Battery current smoothing

inductance

m 3 Planar transformer turns

ratio

Vbus1 60V-43V DC-link voltage

C 6800 µF Super capacitors voltage

smoothing capacitor

L1 50µH Super capacitors currents

smoothing inductance

Figure 10. Full bridge converter with chopping devices

During switching off of the semiconductors, the corresponding current stored in

wiring inductances circulates in the following meshes C1, D1 ; C2 , D2; C3, D3 and C4 , D4

which limits the voltages applied to the switches. When electrical energy is fully

transferred in C1, C2, C3 and C4 capacitors, the current becomes null and the meshes

become closed. The C1, C2, C3 and C4 capacitors are used only for transient energy tank

42

and it is necessary to recycle this switching energy while controlling the voltage at the

semiconductors boundary. This function is ensured by R1, R2, R3 and R4 resistances. R1,

R2, R3 and R4 resistances are identical and C1, C2, C3 and C4 capacitors are also identical.

5.1 Experimental setup at reduced scale:

11(a) Boost converters setup for Np = 2

For reasons of cost components and safety, the experimental test benches were carried

out at a reduced scale .

• The boost converter test bench Fig.11 (a) is made of: a battery module of 4 cells in

series, two super capacitors modules of 10 cells (Maxwell BOOSTCAP2600) in series for

each one, an active load which is used to define power request, two boost converters in

parallel which ensure power management in hybrid vehicle.

43

11(b) Full bridge converter setup for Np = 1

Figure 11. Boost and full bridge converters experimental setup

• For the full bridge converter test bench Fig.11 (b), a batteries module, a super capacitors

module, two high frequency planar transformer, the DC/AC and AC/DC converters have

been designed. The super capacitors modules voltages must be between 27 V and 13.5 V.

The batteries module which imposes the DC-bus voltage presents a rated voltage

of 48 V and the DC link voltage level must be between 43 V and 60 V. The converters

are controlled by a PIC18F4431 microcontroller with 10 kHz control frequencies for

boost converters and 20 kHz for the full bridge converter.

44

CHAPTER-6

SIMULATION RESULTS

45

6.SIMULATION RESULTS

6.1 General:

Simulation has become a very powerful tool on the industry application as well as

in academics, nowadays. It is now essential for an electrical engineer to understand the

concept of simulation and learn its use in various applications. Simulation is one of the

best ways to study the system or circuit behavior without damaging it .The tools for doing

the simulation in various fields are available in the market for engineering professionals.

Many industries are spending a considerable amount of time and money in doing

simulation before manufacturing their product. In most of the research and development

(R&D) work, the simulation plays a very important role. Without simulation it is quiet

impossible to proceed further. It should be noted that in power electronics, computer

simulation and a proof of concept hardware prototype in the laboratory are

complimentary to each other. However computer simulation must not be considered as a

substitute for hardware prototype. The objective of this chapter is to describe simulation

of impedance source inverter with R, R-L and RLE loads using MATLAB tool.

6.2 Introduction to Matlab:

MATLAB is a high-performance language for technical computing. It integrates

computation, visualization, and programming in an easy-to-use environment where

problems and solutions are expressed in familiar mathematical notation. Typical uses

includes

1. Math and computation

2. Algorithm development

3. Data acquisition

4. Modeling, simulation, and prototyping

5. Data analysis, exploration, and visualization

6. Scientific and engineering graphics

7. Application development, including graphical user interface building

46

MATLAB is an interactive system whose basic data element is an array that does

not require dimensioning. This allows you to solve many technical computing problems,

especially those with matrix and vector formulations, in a fraction of the time it would

take to write a program in a scalar non-interactive language such as C or FORTRAN.

The name MATLAB stands for matrix laboratory. MATLAB was originally

written to provide easy access to matrix software developed by the LINPACK and

EISPACK projects. Today, MATLAB engines incorporate the LAPACK and BLAS

libraries, embedding the state of the art in software for matrix computation.

MATLAB has evolved over a period of years with input from many users. In

university environments, it is the standard instructional tool for introductory and

advanced courses in mathematics, engineering and science. In industry, MATLAB is the

tool of choice for high-productivity research, development and analysis.

MATLAB features a family of add-on application-specific solutions called

ToolBoxes. Very important to most users of MATLAB, toolboxes allow you to learn and

apply specialized technology. Toolboxes are comprehensive collections of MATLAB

functions (M-files) that extend the MATLAB environment to solve particular classes of

problems. Areas in which toolboxes are available include signal processing, control

systems, neural networks, fuzzy logic, wavelets, simulation and many others.

6.3 The Matlab System:

The MATLAB system consists of five main parts:

6.3.1 Desktop tools and development environment:

This is the set of tools and facilities that help you use MATLAB functions and

files. Many of these tools are graphical user interfaces. It includes the MATLAB desktop

and Command Window, a command history, an editor and debugger, a code analyzer and

other reports, and browsers for viewing help, the workspace, files, and the search path.

47

6.3.2 The Matlab mathematical function library:

This is a vast collection of computational algorithms ranging from elementary

functions, like sum, sine, cosine, and complex arithmetic, to more sophisticated functions

like matrix inverse, matrix eigen values, Bessel functions, and fast Fourier transforms.

6.3.3 The Matlab language:

This is a high-level matrix/array language with control flow statements, functions,

data structures, input/output, and object-oriented programming features. It allows both

"programming in the small" to rapidly create quick and dirty throw-away programs, and

"programming in the large" to create large and complex application programs.

6.3.4 Graphics:

MATLAB has extensive facilities for displaying vectors and matrices as graphs,

as well as annotating and printing these graphs. It includes high-level functions for two-

dimensional and three-dimensional data visualization, image processing, animation, and

presentation graphics. It also includes low-level functions that allow you to fully

customize the appearance of graphics as well as to build complete graphical user

interfaces on your MATLAB applications.

6.3.5 The Matlab external interfaces:

This is a library that allows you to write C and FORTRAN programs that interact

with MATLAB. It includes facilities for calling routines from MATLAB (dynamic

linking), calling MATLAB as a computational engine, and for reading and writing MAT-

files.

6.3.6 Matlab documentation:

MATLAB provides extensive documentation, in both printed and online format,

to help you learn about and use all of its features. If you are a new user, start with this

Getting Started book. It covers all the primary MATLAB features at a high level,

including many examples. The MATLAB online help provides task-oriented and

48

reference information about MATLAB features. MATLAB documentation is also

available in printed form and in PDF format.

6.3.7 Matlab online help:

To view the online documentation, select MATLAB Help from the Help menu in

MATLAB. The MATLAB documentation is organized into these main topics:

6.3.8 The role of simulation in design:

Electrical power systems are combinations of electrical circuits and electro-

mechanical devices like motors and generators. Engineers working in this discipline are

constantly improving the performance of the systems. Requirements for drastically

increased efficiency have forced power system designers to use power electronic devices

and sophisticated control system concepts that tax traditional analysis tools and

techniques. Further complicating the analyst's role is the fact that the system is often so

nonlinear that the only way to understand it is through simulation.

Land-based power generation from hydroelectric, steam, or other devices is not

the only use of power systems. A common attribute of these systems is their use of power

electronics and control systems to achieve their performance objectives.

Sim Power Systems is a modern design tool that allows scientists and engineers to

rapidly and easily build models that simulate power systems. Sim Power Systems uses

the Simulink environment, allowing you to build a model using simple click and drag

procedures. Not only can you draw the circuit topology rapidly, but your analysis of the

circuit can include its interactions with mechanical, thermal, control, and other

disciplines. This is possible because all the electrical parts of the simulation interact with

the extensive Simulink modeling library. Since Simulink uses MATLAB as its

computational engine, designers can also use MATLAB toolboxes and Simulink block

sets. Sim Power Systems and Sim Mechanics share a special Physical Modeling block

and connection line interface.

49

6.3.9 Sim power systems libraries:

You can rapidly put Sim Power Systems to work. The libraries contain models of

typical power equipment such as transformers, lines, machines, and power electronics.

Mat lab Library

50

Mat lab Library

51

6.3.10 Matlab Library:

American utility located in Canada, and also on the experience of Ecole de

Technologies superiors and Universities Laval. The capabilities of Sim Power Systems

for modeling a typical electrical system are illustrated in demonstration files. And for

users who want to refresh their knowledge of power system theory, there are also self-

learning case studies.

The Sim Power Systems main library, powerlib, organizes its blocks into libraries

according to their behavior. The powerlib library window displays the block library icons

and names. Double-click a library icon to open the library and access the blocks. The

main Sim Power Systems powerlib library window also contains the powerguide block

that opens a graphical user interface for the steady-state analysis of electrical circuits.

6.4 Full bridge converter simulation circuit for Np = 2:

The simulation has been made for Np = 2 as shown in figure 12. The maximum

and minimum voltages of the super capacitor modules are respectively fixed at 270V and

135V. The hybrid vehicle requested current (Ich) is respectively fixed at 100A from 0 to

0.5s, 400A from 0.5s to 18s and 100A from 18s to 20s. Battery reference current (Ibatref)

is fixed at 100A independently of the hybrid vehicle power request. Super capacitor

modules voltages (Vsc1, Vsc2) presented in Fig.13 (a) are identical. The currents

amplitudes (Isc1, Isc2) presented in Fig.13 (b) are also identical.

Control enables to maintain the battery current (Ibat) at 100A; but around 0.5s and

18s the battery current control loop has not enough time to react Fig.14 (a). The

important power of the transient states is ensured by the super capacitors modules (IL)

Fig. 14(b). Simulation parameters are presented in table 4.

52

Figure 12. Full bridge converter simulation circuit for Np = 2

Table 4. Full bridge topologie simulations parameters

Symbol Value Name

λ 25µH Battery current smoothing inductance

m 3 Planar transformer turns ratio

Vbus1 604V-432V DC-link voltage

L1=L2 50µH Super capacitors currents smoothing inductances

53

Figure 13 (a). Super capacitor modules voltages

Figure 13(b). Super capacitor modules currents

54

Figure 14. (a): Battery current control result

Figure 14(b): DC-link and active load currents

55

6.5 Boost converters simulation results:

6.5.1 Simulation circuit for boost converter:

The boost converters experimental test is carried out in the following conditions:

During the super capacitors discharge, the batteries current reference (Ibatref) is fixed at

13A so that, the super capacitors modules provide hybrid vehicle power request during

the transient states. For these tests, the hybrid vehicle request (Ich) was fixed at 53A. The

experimental and simulations results of the modules voltage are compared in Fig.16 (a)

and Fig.16 (b). The (Isc1) and (Isc2) experimental currents are not identical Fig.17 (a),

Fig.17 (b) because the super capacitors dispersion and the power electronic circuits

(boost converters) inequality.

The first boost converter ensures 50% and the second ensures also 50% of the

DC-link current (IL). In other words the two super capacitors modules ensure a (IL)

current of 40A to hybrid vehicle as presented in Fig.18 (a), and 13A only is provided by

the batteries Fig.18 (b).

Figure 15. Simulation circuit for boost converter

56

16(a) First module voltage

16(b) Second module voltage

Figure 16. Super capacitor modules experimental and simulation voltage results

57

17(a) First module current

17(b) Second module current

Figure 17. Super capacitor modules experimental and simulation current results

58

18(a) Multi boost output current (IL )

18(b) Battery current experimental result

Figure 18. DC-link voltage and current experimental validation

59

6.6 full bridge converters simulation results:

The Q1, Q2, Q3 and Q4 control signals applied to K1, K2, K3 and K4

semiconductors. For electric constraints reasons of the available components,

(transformer, IGBT, active load), the full bridge experimental test conditions are different

to that of boost converters topology. The super capacitors module maximum voltage

(Vsc1) is fixed at 22V because of battery module voltage (48V), the transformer turns

ratio (m=3) and active load which is limited to 80V. The battery current reference

(Ibatref) and active load current request (Ich) are respectively fixed at 5A and 15A.

The super capacitors power is not constant (Vsc1, Isc1) because of the consumed current by

R1, R2, R3 and R4 resistances Fig.12 (a). The battery current experimental result is

presented in Fig.12 (b). The voltages and currents ripples which appear in Fig. 11 (b),

Fig.12 (a) and Fig. 12 (b) are caused by leakage inductances of the transformer and

wiring of the power electronics devices.

The voltages and currents of the high frequency planar transformer are

respectively presented in Fig. 13 (a) and Fig. 13 (b). The transformer secondary voltage

(Vs2) transient which corresponds to the change of sign of the current (Is2) is caused by

the transformer leakage inductance.

60

Figure 19.simulation circuit for full bridge converter

61

Figure 20 (a). Super capacitors module voltage and current

20(b): DC-link and active load experimental currents

62

Figure. 21(a) Transformer input and output voltages

Figure 21(b) Transformer input and output currents

Figure 21. High frequency planar transformer voltages and currents

63

CONCLUSION

In this paper, multi boost and multi full bridge converter topologies and their

control strategies for batteries and super capacitors coupling in the hybrid vehicle

applications were proposed. For reasons of simplicity and cost, the multi boost converter

is the most interesting topology regarding the multi full bridge converter topology. It

enables a good power management in hybrid vehicle.

Full bridge experimental tests conditions were different from that of boost

converter topology, so at this time it is not easy to make a good comparison between the

two topologies. However, multi full bridge converter topology is well suitable to adapt

the level of available voltage to the DC-link. For low voltage and high current

applications such as super capacitors, the full bridge converter seems to be less

interesting because of its higher cost (many silicon and passive components), and a lower

efficiency.

64

REFERENCES

[1] J.M Timmermans, P. Zadora, J. Cheng, Y. Van Mierlo, and Ph. Lataire. Modelling

and design of super capacitors as peak power unit for hybrid electric vehicles. Vehicle

Power and Propulsion, IEEE Conference, 7-9 September, page 8pp, 2005.

[2] Huang jen Chiu, Hsiu Ming Li-Wei Lin, and Ming-Hsiang Tseng. A multiple- input

dc/dc converter for renewable energy systems. ICIT2005, IEEE, 14-17 December, pages

1304–1308, 2005.

[3] M.B. Camara, H. Gualous, F. Gustin, and A. Berthon. Control strategy of hybrid

sources for transport applications using supercapacitors and batteries. IPEMC2006, 13-16

August, Shanghai, P.R.CHINA, 1:1–5, 2006.

[4] L. Solero, A. Lidozzi, and J.A. Pomilo. Design of multiple-input power converter for

hybrid vehicles. IEEE transactions on power electronics, 20, Issue 5, 2005.

[5] Xin KONG and A. KHA. Analysis and implementation of a high efficiency,

interleaved current-fed full bridge converter for fuel cell system. IEEE, 28-01 Nov,

1:474–479, 2005.

[6] M.B. Camara, F. Gustin, H. Gualous and A. Berthon. Studies and realization of the

buck-boost and full bridge converters with multi sources system for the hybrid vehicle

applications. Second European Symposium on Super capacitors and Applications,

ESSCAP2006, Lausanne, Switzerland,2-3 November, 2006.

[7] Huang-Jen Chiu, Hsiu-Ming, Li-Wei Lin, Ming-Hsiang Tseng. A Multiple-Input

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supercapacitor and battery power management for hybrid vehicle applications

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