hybrid electric vehicle regenerative-braking using

UNLV Retrospective Theses & Dissertations

1-1-2000

Hybrid electric vehicle regenerative-braking using ultracapacitors Hybrid electric vehicle regenerative-braking using ultracapacitors

Steven L Pay University of Nevada, Las Vegas

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HYBRID ELECTRIC VEHICLE REGENERATIVE-BRAKING

USING ULTRACAPACITORS

by

Steven L. Pay

Associate of Arts Montgomery Community College

December 1993

Bachelor of Science University of Nevada, Las Vegas

May 1994

A thesis submitted In partial fulfillment of the requirements for the

Master of Science Degree Department of Electrical Engineering

Howard R. Hughes College of Engineering

Graduate College University of Nevada, Las Vegas

December 2000


UMI Number: 1403093

UMIUMI Microform 1403093

Copyright 2001 by Bell & Howell Information and Learning Company. All rights reserved. This microform edition is protected against

unauthorized copying under Title 17, United States Code.

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P.O. Box 1346 Ann Arbor, Ml 48106-1346


UNIV Thesis ApprovalThe G raduate College U niversity o f Nevada, Las Vegas

November 17 ^20 00

The Thesis prepared by

Steven L. Pay

Entitled

Hybrid Electric Vehicle Regenerative-Braking usingUltracapacitors

is approved in partia l fu lfillm ent o f the requirem ents for the degree o f

M a s te r o f S c ie n c e in E le c t r ic a l E n g in e e rin g _______

Examlmtion Committee Memo

Examination Committee Memoer

Examination Committee Chair

Dean o f the Graduate College

GradiMe College F/Kulty Representative

PR/1017-53/1.00 11


ABSTRACT

Hybrid Electric Vehicle Regenerative- Braking Using Ultracapacitors

by

Steven L. Pay

Dr. Yahia Baghzouz, Examination Committee Chair Professor o f Electrical Engineering University o f Nevada, Las Vegas

The concept and application of ultra capacitors for electric load leveling and

regenerative braking is presented. Proposed sizing of an ultracapacitor system

Is presented and discussed based on the available energy and the nominal

operating voltage from a hybrid electric vehicle transit bus.

A control scheme Is required to effectively control the charge and discharge of

the ultracapacitor system. This system Is required to provide for electric load

leveling, effective control and maximization of the regeneratlve-braking system.

In order to optimally control the ultracapacitor system a DC/DC converter Is

required. Alternatively, direct connection of the ultracapacitor system across the

battery bank does not allow for control of energy flow but does assist the battery

system by altering the charge and discharge rate thereby reducing the stress on

the battery system. Both connections of the ultracapacitor system were

Investigated. System Integration using optimal power dispatch from the battery

III


packs and generator was Investigated with the aid of PSPICE and the Advanced

Vehicle Simulator (ADVISOR) developed by the National Renewable Energy

Laboratory (NREL).

IV


TABLE OF CONTENTS

ABSTRACT....................................................................................................................lii

LIST OF FIGURES..................................................................................................... vii

ACKNOWLEDGEMENTS........................................................................................... ix

CHAPTER 1 INTRODUCTION..............................................................................1

CHAPTER 2 HYBRID ELECTRIC VEHICLES.................................................... 6Types o f Hybrid Vehicles...................................................................................... 6Hybrid Electric Vehicles Components................................................................. 7Battery Quasi-Static Model..................................................................................11ADVISOR Simulation Results............................................................................. 14

CHAPTER 3 HYBRID ELECTRIC VEHICLES WITH......................................... 23ULTRACAPACITORS AND DC/DC CONVERTER CONTROL

Available Kinetic Energy.....................................................................................23Sizing o f Ultracapacitors.....................................................................................26Ultracapacitor Quasl-Static Model..................................................................... 30DC-DC Converter Control...................................................................................31PSPICE Simulation Results............................................................................... 38ADVISOR Simulation Results............................................................................45

CHAPTER 4 HYBRID ELECTRIC VEHICLES WITH......................................... 50ULTRACAPACITORS AND DIRECT CONNECTION

Pre-ChargIng the Ultracapacitors..................................................................... 50Pre-ChargIng PSPICE Simulation Results......................................................53Direct Connection Control................................................................................. 55Direct Connection PSPICE Simulation Results.............................................. 62Direct Connection ADVISOR Simulation Results...........................................63

CHAPTER 5 ANALYSIS AND CONCLUSIONS................................................. 71Bus Route Drive Cycle.......................................................................................72Central Business District Bus Route Drive Cycle........................................... 87Conclusions...................................................................................................... 101

APPENDIX I MAXWELL TECHNOLOGIES INC PC 2500 DATA SHEET 103

APPENDIX II ADVISOR SOLVE CURRENT FILE............................................105


REFERENCES......................................................................................................... 107

VITA............................................................................................................................ 110

VI


LIST OF FIGURES

Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 2.5 Figure 2.6 Figure 2.7 Figure 2.8 Figure 3.1

Figure 3.2 Figure 3.3 (a) Figure 3.3 (b)

Figure 3.3 (c)

Figure 3.4 (a) Figure 3.4 (b)

Figure 3.4 (c)

Figure 3.5 (a)

Figure 3.5 (b)

Figure 3.6 (a) Figure 3.6 (b) Figure 3.7 (a) Figure 3.7 (b) Figure 3.8 Figure 4.1 Figure 4.2 Figure 4.3 Figure 4.4 Figure 4.5 Figure 4.6 Figure 4.7 Figure 4.8 Figure 4.9 Figure 4.10

Series Hybrid Electrical Vehicle System...........................................6Parallel Hybrid Electrical Vehicle System.........................................7H2 Fuel Hybrid Bus Vehicle Diagram................................................ 8Quasl-Static Energy Storage Device Model................................... 12Available Kinetic Energy From Braking...........................................16ADVISOR Setup for the H2 Fuel Hybrid B us................................. 17ADVISOR Drive Cycle Simulation Setup........................................18ADVISOR Output Horizon Batteries...........................................19-21Hybrid Electric Vehicle Diagram with DC-DC Converter..............32ControlTypical Buck-Boost Converter.........................................................33Typical Buck-Boost Control Circuit In Boost M ode.......................34Typical Buck-Boost Control Circuit In Boost M ode.......................35Switch ClosedTypical Buck-Boost Control Circuit In Boost M od e .......................36Switch OpenTypical Buck-Boost Control Circuit In Buck M od e ........................36Typical Buck-Boost Control Circuit In Buck M od e ........................37Switch ClosedTypical Buck-Boost Control Circuit In Buck Mode.........................37Switch OpenBuck-Boost Control Circuit for H2 Fuel Hybrid Bus In.................. 39Boost ModeBuck-Boost Control Circuit for H2 Fuel Hybrid Bus In..................40Buck ModeDC-DC Converter Boost Mode Voltage Values...........................41DC-DC Converter Boost Mode Current Va lues...........................42DC-DC Converter Buck Mode Voltage Values............................43DC-DC Converter Buck Mode Current V a lues............................44ADVISOR Output Maxwell Technologies Ultra capacitors 46-48Hybrid Electric Vehicle Diagram with Direct Connection..............52Pre-ChargIng C ircu it......................................................................... 52Pre-ChargIng Circuit Voltage and Current V a lues ........................54Pre-ChargIng Circuit Power Values................................................ 55Parallel Control C ircuit...................................................................... 56Required Power Constant Drive Cycle............................................ 58Ouasl-Static Current Values............................................................ 59Ouasl-Stafic Voltage Values............................................................ 59Ouasl-Static Power Values.............................................................. 60PSPICE Results Constant Load of 3 0 ............................................63

VII


Figure 4.11 Figure 4.12

Figure 4.13 Figure 4.14

Figure 4.15 Figure 5.1 Figure 5.2 Figure 5.3

Figure 5.4

Figure 5.5

Figure 5.6

ADVISOR Initial Block Diagram of the Overall System................ 64ADVISOR Revised Block Diagram of the Energy.........................65Storage SystemModified ADVISOR Voc, RInt Block Diagram............................... 66ADVISOR Compute Current Block Diagram................................. 67Added for Ultracapacitor SystemADVISOR Output Ultracapacitor Direct Control...................... 68-70ADVISOR Bus Route Drive Cycle Simulation Setup.................... 75ADVISOR Output Battery System Bus Route Drive Cycle.... 76-80ADVISOR Output Battery & Ultracapacitor System................81-86Bus Route Drive CycleADVISOR Central Business District Bus Route............................89Drive Cycle Simulation SetupADVISOR Output Battery System Central...............................90-94Business District Bus Route Drive CycleADVISOR Output Battery & Ultracapacitor System............. 95-100Central Business District Bus Route Drive Cycle

VIII


ACKNOWLEDGEMENTS

I would like to thank Dr. Baghzouz for all o f his assistance and guidance as

my advisor in completing this thesis. In addition, for his continued support and

encouragement over the year it took to complete this work. Thanks to Linda Shi

PhD student of the Mechanical Engineering Department for her continued

support, assistance and teaching of ADVISOR to make this work possible.

Thanks to other members of the graduate committee; Dr. Latlfl, Dr. McGaugh,

and Dr. Dalpatadu. In addition, thanks to Gerry Martinez for his assistance with

document reproduction.

I would like to thank my wife Shawna, my mother and my father for giving me

the opportunity and encouragement to pursue both graduate and undergraduate

studies and all of their assistance during the ten years of higher education.

IX


CHAPTER 1

INTRODUCTION

The use of fossil fuels as a source of energy for transportation Is facing

opposition by many environmental agencies. Pollution caused by internal

combustion engines and the limited resources of fossil fuels are driving many

efforts to explore alternative fuel methods. In addition, to the pollution caused by

the current fuels used, there exists a dependency on the United States

government on foreign oil sources. The EPA, Federal and State governments

have mandated certain percentages for the elimination of fossil fuel type vehicles

[14]. In addition, these concerns have caused many government agencies to

mandate alternative fuel sources.

There is a wide range of alternate fuel sources currently being used and

under study for transportation. One of the first alternate fuel sources, researched

for transportation use, was the electric or battery source unit. This source of

energy for transportation has many environmental advantages over traditional

fossil fuel sources. These Include no air or noise pollution released into in the

environment [21]. However, there are limitations on the range of these types of

vehicles.


2

Another alternate source of power for transportation Is the use of compressed

natural gas. This source has recently been accepted and Is In use by many

public transportation vehicles [5]. These Include utility companies, taxicabs and

transit buses. This Is due In large to the mandates In place and certain quotas

for these agencies to reduce the number of traditional fossil fuel vehicles. This

source provides longer travel time without refueling or re-charging. However,

natural gas vehicles still produce small amounts o f hydrocarbon pollution.

Another type of alternate source Is Hydrogen. This source has a wide

number of advantages over the primitive alternative sources. The main

advantage Is near zero pollution released Into the atmosphere. In addition,

hydrogen provides a longer range based on the same volume of fuel than other

sources [2], One disadvantage Is the safety concerns not present with other

alternate sources. Another disadvantage of the use of Hydrogen as a fuel source

Is the required Infrastructure.

One recent development In alternative source vehicles Is a combination of

alternate sources that complement each other, a hybrid electric vehicle’ (HEV).

This type of vehicle has two on-board energy sources. First, an engine or fuel

cell powered from some type of fuel. Second, an electrical system and energy

storage system composed of batteries and other components used to power the

drive shaft [23]. There Is a trade off that must be considered In the relative sizes

of each source, as space on the vehicle Is limited. In order to make transportation

practical.


3

However, the major concern in the use of hybrid electric vehicles Is the range

of travel capable without maintenance. The battery system Is the most prominent

cause of reduction In the vehicle’s range. The battery system also has a finite

number of charge and discharge cycles. The relative size of the battery system

typically consumes a large part available space on the vehicle.

Battery systems also have a finite range of allowable power that can be used

to propel the vehicle. This is a major issue in the infancy of hybrid electric

vehicles. The ability to harness the available energy from the vehicle to charge

the battery system is a very complex issue. There are numerous factors or

variables that define this ability, the drive pattern of the vehicle, the particular

characteristics o f the battery, and the speed, acceleration and braking patterns of

the vehicle [13]. The hybrid electric vehicle Is limited both In Its range of

operation and the space required In the vehicle for both propulsion systems.

There has been research In the kinetic energy available from vehicle braking.

In particular, there has been extensive research on hybrid electric vehicles with

regard to the available kinetic energy, the overall efficiency, and the energy

losses present within the vehicle. The amount of kinetic energy available at the

power train of a vehicle can be re-utlllzed to provide electric energy to the

vehicles electric system. An advantage of electric vehicles and hybrid electric

vehicles over the conventional gasoline engine vehicle Is the ability to utilize this

kinetic energy In a regenerative braking system [13]. A regenerative braking

system allows energy that would ordinarily be lost through heat to be harnessed.


4

captured and reused. This tremendous amount of kinetic energy present In

larger vehicles can now be used to Increase the vehicle’s range.

The University of Nevada, Las Vegas Electrical and Mechanical Engineering

Departments engaged In the renovation and redesign of a hybrid electric vehicle,

the H2 Fuel Hybrid Bus. The vehicle was originally constructed with a hydrogen

engine and an electric battery system. This vehicle was used as an application

and for simulations for this thesis.

Currently, there Is no clear and concise energy storage system to convert the

kinetic energy Into electric energy. The systems employed In today’s hybrid

electric vehicles take the available kinetic energy and dump’ current Into the

battery systems to charge the battery units [2]. This creates severe stress In the

operation of the electric and energy storage systems. The battery systems

cannot handle large currents placed across the terminals for short periods of

time. This reduces the overall life of the battery system and can cause serious

damage to the battery system. This current and voltage used to charge the

electric system Is typically outside the allowable limits the battery system can

safely handle.

For this reason, a major component that must be addressed In the design of

hybrid electric vehicles Is the regenerative braking system. Recent research has

discovered alternative sources to store energy with the hybrid electric vehicle. A

relatively new alternative source of energy storage Is the ultracapacitor or

supercapacitor. Ultracapacitors are similar In operation to conventional

capacitors; however, have much larger capacity and much longer self-


5

discharging rates. This thesis will discuss In detail the operation and application

of ultracapacitors to hybrid electric vehicles.

In addition, this thesis will describe and review the design of the energy

storage systems for hybrid electric vehicles and utilize the H2 Fuel Hybrid bus as

an application. The Ideal and actual energy storage systems proposed both

utilize a combination of batteries and ultracapacitors. This will Include computer

simulations In the PSPICE and ADVISOR software packages. ADVISOR Is a

simulation tool used to model and perform detailed research on several types of

hybrid source vehicles. The National Renewable Energy Laboratory (NREL)

produces ADVISOR.

The research shows the direct connection of the ultracapacitor system across

the battery system provides a more robust electrical system than without

ultracapacitors, but the ideal system for a hybrid electric vehicle utilizes a DC-DC

converter to operate the ultracapacitor energy flow independent of the battery

system.


CHAPTER 2

HYBRID ELECTRIC VEHICLES WITH BATTERIES

This chapter will discuss the different types of hybrid electric vehicles, series

and parallel. Further, this chapter will describe and review the hybrid electric

vehicle components, electric drive system, auxiliary power unit, and battery

system. Finally the quasi-static model of the battery system is introduced and

the ADVISOR simulation results are presented.

2.1 Tvpes of Hybrid Electric Vehicles

There are two basic types of hybrid electric vehicles, series and parallel.

These two systems are as simple as they sound on the surface. The series

system provides an engine, a mechanical/electrical converter, a DC battery

source, and an electrical/mechanical converter to power a drive shaft. Figure 2.1

shows a typical configuration of a series hybrid electric vehicle. This is the type

of system that is utilized for the research within this thesis.

EngineFuel Source Battery

SourceConverter

MectVBec

Transmission

Drive Shaft/

Converter

Elec/Mech

Figure 2.1: Series Hybrid Electrical Vehicle System


Alternatively, the parallel hybrid electric vehicle system provides a

combination of propulsion systems connected in parallel to a common drive

shaft. This type of system requires a more elaborate drive train and converter

system to couple the different sources together. See Figure 2.2 shows a typical

parallel type hybrid vehicle system. This type of hybrid electric vehicle will not be

discussed further in this thesis.

Drive Shaft/ Transmission

i i\ j : 1

i !1

Engine DC Motor

ii1

ii

Fuel SourceBattery

Source

Figure 2.2: Parallel Hybrid Electrical Vehicle System

2.2 Hybrid Electric Vehicle Svstem Components

The overall hybrid electric vehicle system consists of three major

components. These components include: electric drive system, auxiliary power


8

unit, and battery banks. Figure 2.3 shows the diagram of the electrical system

for the initial configuration of the energy storage system of the series type H2

Fuel Hybrid Bus.

DC Bus

PukLcbûAODCCanverter

InductionMotorBattery SoLtœ

/SC Generator

Figure 2.3; H2 Fuel Hybrid Bus Vehicle Diagram

2.2.1 Electric Drive Svstem

The electric drive system is composed of an Insulated Gate Bipolar Transistor

(IGBT) type inverter that converts the DC voltage to a pulse width modulated

three phase AC voltage. This AC voltage is used to power an induction motor.

This electric drive system is the output to the drive shaft and transmission. The

system is provided with DC voltage by the auxiliary power unit and the battery

source. Any combination of the DC sources provides electric energy to the

electric drive system that converts this energy to power the vehicle.


9

2.2.2 Auxiliary Power Unit

The auxiliary power unit consists o f an engine that drives a synchronous

generator. The generator AC voltage is converted using an AC-DC converter

diode rectifier. This system powers the engine by a fuel source, in the H2 Fuel

Hybrid Bus the fuel source is hydrogen. The generator has 4-poles and its rated

voltage, frequency and kVA are 277V, 80 Hz, 70 kVA respectively.

2.2.3 Battery Svstem

The battery system provides a DC voltage directly to the DC bus of the

electrical system. A battery’s present charge rate is described by its state of

charge (SOC), this is a value assigned based on how much energy and the

output voltage of the battery and the number of available battery charge and

discharge cycles is based on the time of discharge and the change in the SOC of

the battery. In the H2 Fuel Hybrid Bus the battery system consists of two parallel

sets of deep-cycle value regulated lead acid (VRLA) batteries. Each string

consists o f 28 units. Each unit is rated 12V, 85 Ah @ C/3. The total battery

system operates at a nominal 336V with a capacity of 170Ah @ C/3. The

equivalent maximum energy storage is 57 kWh, which corresponds to a useable

energy amount of 46kWh, based on the fact the batteries cannot be allowed to

discharge below 20% SOC.

The capacity o f the battery unit varies with the type and time of discharge.

The capacity relationship of the battery with relation to time is described by

Peukert’s equation shown below in equation (2-1) where I is the discharge


10

current and t is the time of the discharge for the Horizon battery units in the H2

Fuel Hybrid Bus [10], where «=1.33 and

(2- 1)

The available capacity also varies with the temperature of the battery.

The following relationship in equation (2-2) describes the capacity with regard to

temperature where C^-is the capacity at temperature T , Tis the temperature in

°F, Cj. is the capacity available at To - 85 Ah at C/3 for the Horizon battery units

in the H2 Fuel Hybrid Bus [10], where «=0.004.

Cr=C^,]i + a (T -T„)] (2-2)

The next relationship is the battery voltage as a function of time. The

following equations (2-3) and (2-4) describe this relationship where T is the

temperature in °F and t is the time of discharge, where OCV is the open

circuit voltage where Æ/=13.05, A3=0.785, P/=6, f 2=0.845, 7*5=1.1 and

P^=0.22 [10].

F(f) = Æ ,-T - t + K.

(2-3)

s o c ^ X % ) =

^o cv

[ 100 (2-4)

In the following chapters, a description of the energy storage system

design used to effectively charge these units will be presented. The design of


11

this system requires a clear understanding of the relationships above. The

proposed system design will eliminate the original careless charging or ‘dumping’

of energy to the battery system. The proposed system provides for a controlled

and ideal charging and discharging pattern of the battery system.

2.3 Batterv Quasi-Static Model

In order to understand the simulation and control techniques implemented in

hybrid electric vehicle design, there must first be a basic understanding of the

quasi-static model. This model is used in the design, operation, and simulation

of hybrid electric vehicles. This type of modeling is greatly apparent in computer

simulation tools used to design hybrid electric vehicles. In particular, this type of

modeling is used with the National Renewable Energy Laboratory (NREL)

ADVISOR simulation tool.

The purpose of the quasi-static approach to modeling in the hybrid electric

vehicle is to simplify and increase the speed of the simulation. In quasi-static

modeling, n-dimensional vectors are defined over constant time intervals. The

time interval for this modeling technique is expanded as a function of k, where

k=0,...n-1 specific discrete data points. The general quasi-static approach

utilizes ‘a priori’ modeling techniques regarding the velocity o f the vehicle, v, and

the elevation of the vehicle, h as function of time. The general declarations of

these variables are v(A:)and h(k) where k = Q,...n-\.

From this general information, the acceleration, the velocity, and distance can

be expressed in quasi-static form as:


12

a(k) = — -(ÿ(k + \)-v{k)), k = Q,...n-2, « (» - !) = 0, (2-5)T

v (J c ) = ~ ( y { k + l ) - > r v { k ) ) , k = 0 , . . . n - 2 ,

(v(A: + l ) + v(A:)).*=0

(2-6)

(2-7)

Because of the discrete calculation method, the formulas of the quasi

static approach do introduce a small error into the results as with any numerical

solution technique. This error is inherent in this type of modeling and must be

considered in the results [16].

In particular, the general quasi-static approach of storage device elements

can be described below in Figure 2.4. This is a general quasi-static model

where the variables F, S, Q, and E take on the variable values for the particular

device being modeled.

FQ

E

Figure 2.4: Quasi-Static Energy Storage Device Model

There are several types of energy storage devices capable of being modeled

with the quasi-static approach. The model for these devices adhere to the same

basic model shown.


13

First, is the fuel tank model where F is the mass flow of fuel, in the case of the

H2 Fuel Hybrid Bus, Hydrogen, Q is the fuel tank’s capacity (which is constant)

and E is the output effort of the energy storage system.

The next energy storage device modeled using this approach is the battery

system. In this case, variable F is the input or charge current into the battery

system, hat, and the output voltage of the battery system is In this approach,

the batteries are modeled using the basic electrical properties of Kirchoff Current

Law (KCL) and Ohm’s Law. The internal battery resistance is defined as Rmt(q)

and the internal voltage source is defined as VimCq). Both variables are functions

of the battery system’s current state of charge (SOC), q. Finally, the value Qmax is

defined as the battery’s nominal capacity or maximum charge. The model of this

system is described below in equation (2-8).

+ /w , (2-8)^max

Equation (2-8) is valid for both the charging and discharging cycles provided

the constraints of the SOC of the battery system hold true. This model is

accurate for SOC ranges of 0.2 < q < 0.8. Equations (2-9) and (2-10) show the

model for and respectively, where c and d represent the respective

values for charge and discharge.

^m(^) = v,^-^ + Vo7 (2-9)

= (2- 10)

The battery voltage is determined by the known open circuit voltage of the

battery system as a function of the state of charge (SOC) of the system. Further,


14

the internal resistance of the battery system is not constant in practice. The

value has a static value and a dynamic value as the system changes. This

change in the internal battery resistance as a function of the SOC of the system

increases the complexity of the calculations. The charge of the battery at the

current SOC is obtained by integrating /f,a,over the time interval [16].

2.4 Advisor Simulation Results

The National Renewable Energy Laboratory (NREL) created a MatLab

application for the research, modeling and simulation of hybrid electric vehicles

called ADvanced Vehicle SimulatOR (ADVISOR). ADVISOR was designed to

assist the U.S. Department of Energy (DOE) in their desire to further the design

of hybrid electric vehicles in November 1994. It is a graphical user interface

created on the MatLab and Simulink engine. It provides a very accurate

empirical model o f HEV operation including fuel economy, emissions, storage

system usage and several other operating parameters. ADVISOR was designed

to meet the following criteria: accurate, fast, flexible, publicly available, capable of

modeling vehicles of any type, and easy to use. The main stumbling block of

simulators prior to the design of ADVISOR was the lack of flexibility. For this

reason ADVISOR was designed utilizing a bi-directional quasi-static approach

[28].

Based on the graphical user interface concept, NREL created Simulink block

diagrams for the various types of vehicles: series, parallel, fuel cell, etc. For the


15

purpose of this project only the series type hybrid vehicle model was considered.

Since this is the type of vehicle being used in the H2 Fuel Hybrid Bus.

Initially, in using ADVISOR, the vehicle block diagram must be selected for

the vehicle to be simulated. Next, the type of vehicle must be determined,

series, parallel, etc. Once this information has been determined then the

individual types of devices can be selected for simulation.

The individual vehicle component information is loaded by the selection of a

*.m file. The allowable component selections for the series type vehicle include:

fuel converter, generator, motor/controller, exhaust after treat, transmission,

wheel/axle, vehicle, energy storage, power train control and accessory. The *.m

file of concern for this project is the energy storage file.

The next step is to determine the simulation setup. This information is stored

in a drive cycle file in MatLab. The key element of this file is a definition of the

speed as a function of time. This defines the interval and time period of

acceleration and deceleration for the simulation and the drive cycle.

Initially, simulations were run in ADVISOR to verify the amount of available

kinetic energy available for use by the energy storage system. Figure 2.5 shows

the ADVISOR results for the available kinetic energy (KJ) for use by the energy

storage system. This shows approximately 1750 KJ of available energy at the

output of the braking system.

Simulations were made for the hybrid bus using only the Horizon Batteries.

The purpose of these simulations was to verify the system operation with only the


16

batteries present. Figure 2.6 shows the ADVISOR setup screen for this

simulation.

Torque Coupling

Hyd. Torque Converter

Clutch

FC braking

Braking

Motor/Controller

Wheel/Axle

Gearbox

Final Drive

Energy Usage(Regen Mode) (kJ)“I--------1--------1--------1-------- 1-------- r

» : _J________ « -1_________L_0 200 400 600 000 1000 1200 1400 1600 1000

Figure 2.5: Available Kinetic Energy From Braking

As stated before, there are two series battery strings on the H2 Fuel Hybrid

Bus with an overall voltage of 336V and a total Amp Hour (Ah) capacity of 170 at

C/3. The simulations using the Horizon Batteries depict how the vehicle operates

in the all-electric mode prior to any modifications to the energy storage system.

Figure 2.7 shows the ADVISOR drive cycle simulation setup for the Horizon

Batteries. The simulation setup used is at a constant elevation and the vehicle

starts from rest to accelerate at t=5 sec and continues to accelerate to 55 mph.

The vehicle speed then remains constant at 55 mph until t=70 sec. The

vehicle then decelerates to 0 mph at t=90 sec. Figure 2.8 (a), (b) and (c) shows

the ADVISOR simulation results for only the Horizon Batteries in the energy


17

storage system. These results are consistent with the expected results. This

confirms the input information into ADVISOR is correct for the H2 Fuel Hybrid

Bus. Please note the battery system provided all the power to the bus for the

operation of the bus. The values of power results are shown in watts (W), the

current results are shown in amps (A), the distance is shown in meters (m) and

the x-axis is time shown in (sec). Table 2.1 shows the energy usage for the

Horizon Battery simulation. Again this information is consistent with the expected

results for the H2 Fuel Hybrid Bus based on the two parallel Horizon battery

strings.

Vducle Input

ImWRCGE

aTfanMTmmonWHllWDBOGENSgâSS

VEHiHYDROGENK%!Fuel Converter Operation - Hydrogen (218kW) 7.5L SI Engine |fEnergTSlo.ag»>

lerÆurPROGENAeçLbCtpHpeEBLij

I'iSnVanabteJSlw «= 100

jOBcjcrtm acc_meeh_e(l acc_mech_pwi acc_mech_lrq acc_piopiiel«iy »cc_vaidalioo scc_v«ftion

-0:25

1000 1500 2000 2500 3000Speed (rpm)

Figure 2.6: ADVISOR Setup fo r the H2 Fuel Hybrid Bus


18

Simulation Setup.CYC CONSTANT

100 key on— trace elevation

I

100time (sec)

|Sp»edÆlevationvv. Tkiie

CuronI Prcoedue Oetciipdaa

Date coucarValene Johnicn,NREL

Date cociTviaaooa

Notex Requestxa constant tpeedof the vehidefa SQl

Daated on: l&NovlSSB

E K l CrC_CONSTANT # :

IT;ŒOCaiection IT CÿdeRÙt

Paramedic Stucti

!| Varisile ' Low

I '/Jriàte:

Hipi ïPch»14S4G

:-g|[ Ï33 I ÔS |~TVanàk:

a2s

LoadS««Se|it4>

OpBÎûsoCyârs IsfHÜMS

Figure 2.7: ADVISOR Drive Cycle Simulation Setup


19

cyc_mph r

ess soc hist

Ck 10 10

esspw r out a

0( 10 10

pb pwr_out_aA10 20 30 40 50 60 70 BO 90

Figure 2.8 (a): ADVISOR Output Horizon Batteries


20

GOcyc_mph_rmpha40

20

10 3020 40 50 BO 70 00 90

ess current2 500

CDO)

-500 30 00

ess_pwr_out_rO

0 10 3020 40 0050 BO 70 90400

m 30003(D

^ 360

3200 10 20 30 40 0050 BO 70 90

Figure 2.8 (b): ADVISOR Output Horizon Batteries


21

eye mph r

ess currentID 5Qu

distance% 1000

5 500

0(10 10

ess_pwr_lDss_a

Figure 2.8 (c): ADVISOR Output Horizon Batteries


22

Enetgr Usage Table p j )POWER MODE REGEN MODE

In Out Litss EfL In Out Loss EM.Fuel 0

Fuel Convertes dutch

HjnL: TnrqueCbnvetter Genesalar

TotqueÊfMHgr Slorage 1795 Enetgv Stored -G294

0

7241 848 0.79

Motar/Conbelef 7191 6240 951 IL87 2095 1808 287 0.86Gearbos G240 6045 195 0.97 2100 2095 5 1

Final Drive 6045 6045 0 1 2100 2100 0 1W heei/Aaie

Braking Aur Loads

Aero RoMerg

6045 5903 143

635251467

0.38 3899 3879 201780

0 J 9

■QveM Siatetn Effciw icy

0.31 E*Oveial enagy efliaency is ca lctlatsd é [aero * ioinal/(FueI in - ess stotagej

Table 2.1: ADVISOR Energy Usage Table Output Horizon Batteries


CHAPTER 3

HYBRID ELECTRIC VEHICLES WITH ULTRACAPACITORS AND

DC/DC CONVERTER CONTROL

This chapter will discuss the available kinetic energy available from a vehicle

for use with the regenerative braking system. In addition, sizing calculations of

ultracapacitors and the quasi-static model for the ultracapacitor is presented.

The DC-DC buck boost converter is presented and its application to the H2 Fuel

Hybrid Bus is shown. A buck boost control circuit is designed for use with the H2

Fuel Hybrid Bus and simulation results are presented with the use of PSPICE

and ADVISOR to validate these results.

3.1 Available Kinetic Enerqv

When a vehicle is operating in traffic the majority of energy is dissipated in

heat and friction in the braking system. The efficiency of the energy storage

system to utilize this energy can be improved in three major areas; operate each

component at its maximum efficiency; reduce the friction; aerodynamic and

transmission losses; and recover the kinetic and potential energies that are lost

in heat through the braking system [13]. The latter is the premise for a

regenerative-braking system.

23


24

The available kinetic energy available for a mass in motion not considering

any losses is described in equation (3-1), the definition of kinetic energy, where m

is the mass and v is the velocity.

(3-1)

This recovery of available kinetic energy is the most effective means to

increase the range and overall efficiency of a hybrid vehicle. This energy

available from the friction losses in the braking system can sometimes exceed

the amount o f energy capable of being recovered by the energy storage system.

Therefore, a more realistic approximation of the available energy must be

considered, taking into account the losses within the vehicle. For utilization by

the energy storage system, we must consider the amount o f usable energy in a

storable capacity. For this reason, we must consider the amount o f power that

can be stored in watts (W) or kilowatts (kW). On level ground, the brake power

of the hybrid vehicle during deceleration can be described by equation (3-2) [13].

/?* = V ■ {m5 ■ (^) - mgf, - ^ ( p ^ C ^ A )) (JV) (3-2)

where: m = the vehicle mass (kg)V = the vehicle speed (m/s)

— = the deceleration o f the vehicle (m/s^) dtf^= the rolling resistance coefficient p„= the air density Cg= aerodynamic drag coefficient ^y= front area of the vehicle


25

This relationship provides an accurate approximation of power available for

use by the energy storage system. Consideration must be given in larger

vehicles to determine if all or only some the available kinetic energy can be

harnessed into re-useable energy. This consideration is based on the physical

size within the vehicle for energy storage devices, the availability o f energy

storage devices capable of handling the energy, and the overall system cost [13].

In the regenerative braking process, the kinetic energy is converted into

storable or potential energy by the use of an electric motor or generator. The

speed of this motor is important in the amount of available energy. If the speed

of this motor is less than the rated speed, then the amount o f recoverable energy

is less than optimal. If the speed of this motor is at rated speed or above then

the amount o f energy capable of being recovered will be optimal. Another

important concept to be considered in the amount of recoverable energy is to

ensure the energy is distributed on the front and rear axles so that the maximum

allowable energy is recoverable [13]. The kinetic energy has been calculated for

the H2 Fuel Hybrid Bus system. This initial information was required to begin the

energy storage system design.

The first step in the design of the regenerative braking system was to first

determine the amount available kinetic energy available from the subject vehicle.

Calculations were made to estimate the available kinetic energy that would be

available during the H2 Fuel Hybrid Bus operation cycle.

The weight of the bus accounting for all of the modifications was determined

to be 33,000 lbs or 14,968kg. Estimates were made to determine the amount of


26

kinetic energy produced by the bus not including any resistances or losses. An

initial estimate was made that 30% of the kinetic energy produced would be

usable by the energy storage system. This estimate was based on the urban

drive cycle for a large vehicle. The drive cycle must consider the maximum

acceleration and deceleration values for the vehicle. The results show an

estimated amount of 1.0 MJ of available kinetic energy at 50 mph based on an

estimate o f 30% useable kinetic energy. The bus has a governor that will not

allow the speed to exceed 55 mph. More detailed estimates and computer

simulations validated this value of 1.0 MJ.

Based on the fact, 1MJ of kinetic energy is available after all losses, friction,

heat, etc. the design of the energy storage system was completed. This energy

amount is the maximum available energy when the bus is at 55 mph and is

stopped over period not less than ten (10) seconds. Solving equation (3-1) for

the H2 Fuel Hybrid Bus yields approximately 1 .G9KJ of available kinetic energy.

Applying the relationship in equation (3-2) estimates approximately 25KW/sec for

the bus.

3.2 Sizing of the Ultracapacitors

The H2 Fuel Hybrid Bus came equipped with a regenerative braking system,

which converted the vehicle kinetic energy to electrical energy during braking.

This type o f feature installed was known to increase driving range by up to 20%.

However, since VRLA batteries are not designed to accept large, short bursts of

power, especially when near full charge, conventional regenerative braking


27

causes them to overcharge and results in battery damage. Thfs original system

was disabled on the H2 Fuel Hybrid Bus until design was completed to replace

this system.

In a hybrid electric vehicle, energy is constantly being stored and utilized.

This constant charging and discharging puts the battery system under a

tremendous strain. This constant fluctuation in the SOC of the batteries reduces

the overall life expectancy [15]. Most batteries in production today are designed

to be charged and discharged over a long period of time while not fully being

discharged. Rather, limiting the SOC of the battery system to a minimum of

20% .

An ultracapacitor provides the same basic energy storage parameters as a

conventional capacitor. However, the amount of energy and the discharge rate

or time constant of the device greatly differs from the conventional capacitor.

Ultracapacitors utilize an electrolyte rather than a common dielectric. When a

voltage is applied across the electrodes charge is accumulated at the electrode

terminals and across the electrolyte material. This electrolyte material has far

greater surface area than that of a common dielectric capacitor. This results in a

much greater capacitance per area than a common capacitor. A conventional

capacitor has a capacitance per area on the order of 1 nF/cm^, while the

ultracapacitor has a capacitance per area on the order of 50 pF/c m^ [6] [12].

Conventional capacitors increase the energy storage properties by increasing

the applied voltage across the electrodes. The limit o f the voltage applied to the

electrodes of a conventional capacitor is limited to the breakdown voltage of the


28

dielectric material. In the case of the ultracapacitor, the solvent or the organic

electrolyte decomposition properties limit the energy storage capacity. This

voltage is usually in the range of 1V to 5V [12].

Ultracapacitors are ideal for storage of energy in hybrid electric vehicles

because of the slow discharge rate and the reduced physical size to obtain the

same energy storage characteristics of conventional capacitors. The energy

storage system of the hybrid electric vehicle is critical to increase the overall

driving range and reducing the cycling on the state o f charge (SOC) of the

batteries.

The ultracapacitors used in early hybrid electric vehicles had extremely high

volumetric capacitances because of large electrode surface areas and extremely

small electrode separations. The expected life of an ultracapacitor is much

greater than that of the battery system. It is now probable the energy storage

system of the hybrid electric vehicle to out last the life of the vehicle. This means

an energy storage system utilizing ultracapacitors is now more reliable than that

of an all-electric vehicle only utilizing batteries. In addition, the ultracapacitors

operate at higher power densities than batteries [15].

Once the available kinetic energy was estimated, the required size for the

ultracapacitors was determined. In order to calculate the energy storage system

sizes the following information was required. Vmax - maximum voltage, Vmin -

minimum voltage, Vw - allowable voltage change during pulse. Power - power of

applied current, time - duration of pulse. The following is the calculation


29

procedure used to determine the ultracapacitor system and the individual unit

size [22].

KE = (3-3)

Solving equation (3-3) for the available kinetic energy of 1.0 MJ and a voltage

of 360 V across the capacitor system at the DC bus of the energy storage system

yields a capacitance of approximately 16F.

The charging and discharging of the ultracapacitors is a very complex issue.

The ultracapacitor selected for use with the H2 Fuel Hybrid Bus project, Maxwell

Technologies, PC 2500 has limited voltage and current characteristics.

Each ultracapacitor unit has a nominal voltage of 2.5V for each 2500F unit.

The overall voltage required for the ultracapacitor system of the H2 Fuel Hybrid

Bus is approximately 360V as stated above. Therefore, a minimum of 144

ultracapacitor units was required for the system. A total of 150 ultracapacitor

units were selected to compensate for the internal resistance within the units.

This provides the system with an overall capacitance of 16.67F and a nominal

voltage 375V and a maximum voltage of 405V.

Table 3.1 shows the electrical characteristics for a single Maxwell

Technologies, Inc. PC 2500 unit and the overall electrical characteristics for the

150-unit string.


30

MAXWELL TECHNOLOGIES, INC. PC2500 ULTRACAPACITOR

Single PC2500 Unit 150 PC2500 UnitsCapacitance (F) 2500 16.67Series Resistance (mO), DC 1 150Series Resistance (mQ), 100 Hz 0.6 90Voltage Continuous (V) 2.5 375Voltage Peak (V) 2.7 405Rated Current (A) 400 400Leakage Current (mA) 6 6

Table 3.1: Maxwell Technologies, Inc PC2500 Data

3.3 Ultracapacitor Quasi-Static Model

The ultracapacitor must be modeled using the quasi-static approach to

complete the required simulations. In the quasi-static approach, ultracapacitors

are very similar in nature to the operation of batteries. For that reason, the same

type of modeling scheme was used by NREL to provide a reasonable quasi-static

model. In figure 2-4, the input F to the model is defined as , the ultracapacitor

current and the effort of the output E is defined as , the ultracapacitor voltage.

Therefore, the model applied to the ultracapacitor is shown in equations (3-4)

and (3-5).

+ (3-4)

(3-5)


31

The capacitance C and the internal resistance Ri„, can be defined as

constants or as functions for the purpose of modeling. Similarly to the battery

model, the charge q for the ultracapacitor is obtained by integrating luc using

equation (2-8). However, this type of modeling can introduce issues within the

simulation tools. Because the ultracapacitor operates in a similar fashion to the

battery, it would be intuitive to simulate both devices with the same model.

However, the ultracapacitor does not have an amp hour (Ah) rating and a voltage

referenced by the SOC. Conversely, the ultracapacitor has an initial voltage

across its terminals and a charging and discharging function with respect to time.

In the simulation section of this chapter, the consequences of this modeling are

discussed in further detail.

3.4 DC-DC Converter Control

A control scheme must be determined that can effectively control the storage

of energy within the electrical system. The DC-DC buck-boost converter is most

logical selection for this type of control. Figure 3.1 shows the ideal configuration

for the energy storage system utilizing a DC-DC control scheme for the

ultracapacitor system.

3.4.1 The DC-DC Buck Boost Converter

The buck-boost converter incorporates both the buck and boost converters

into one converter being able to operate both when the output voltage is higher

or lower than the source voltage. Figure 3.2 (a) shows the typical DC-DC buck-


32

DC Bus

DC/DC OofTwerter

ACVDCCon\«1er

InductionMotor

/>C Generator

Lltracapadtors

Figure 3.1: Hybrid Electric Vehicle Diagram with DC-DC Converter Control

booster converter. Figure 3.2 (b) shows the typical DC-DC buck-booster

converter with the switch closed and figure 3.2 (c) shows the typical DC-DC

buck-boost converter with the switch open [17].

3.4.2 H2 Fuel Hvbrid Bus DC-DC Converter Control

For the H2 Fuel Hybrid Bus the buck-booster converter would operate in the

boost mode during acceleration and would operate in the buck mode during

regenerative-braking. The control of the buck-boost converter is accomplished

by altering the pulse width of the modulated waveform.


33

+ iD <

Figure 3.2 (a): Typical Buck-Boost DC-DC Converter

O Vi vL=VsVo

Figure 3.2 (b): Typical Buck-Boost DC-DC Converter Switch Closed

O VI vL=VoVo

J .

Figure 3.2 (c): Typical Buck-Boost DC-DC Converter Switch Open

Once the size of the ultracapacitor system was determined a buck-boost

circuit was determined to effectively operate the system. The boost mode circuit

is shown in figure 3.3 (a), this circuit is used during the acceleration mode of the

vehicle. The buck mode circuit is shown in figure 3.4 (a), this circuit is used

during deceleration or regenerative braking. The buck-boost control circuit must

limit the current of the system below 300A. This is the rated amount of current


34

that the system can effectively handle. In addition, the control circuit must limit

the overall voltage to less than 405V, which the maximum voltage the

ultracapacitor string can handle.

Vo

Figure 3.3 (a): Typical Buck-Boost Control Circuit in Boost Mode

Figure 3.3 (b) shows the buck-boost control circuit in boost mode with the

switch closed. When the switch is closed there are two circuits resulting. The

first is an RLC circuit with only a natural response and the second circuit is a

simple resistive circuit. The first equation has roots that can be over-damped,

critically damped or under-damped based on the values of the resistors,

capacitor and inductor. The resultant equations for the buck-boost control circuit

in the boost mode with the switch closed are shown in equations (3-6) and (3-7).

In addition, the initial conditions of the energy storage elements must be

considered.

C(3-6)


35

(3-7)

RbRcRo

Vb

+

Vo

Figure 3.3 (b): Typical Buck-Boost Control Circuit in Boost Mode Switch Closed

Figure 3.3 (c) shows the buck-boost control circuit in the boost mode with the

switch open. When the switch is open the circuit results which is a second order

result with a natural and forced response. Again, the response of the circuit is

dependent upon the circuit component values. Equation (3-8) shows the

relationship of the natural response of the circuit where / is the current through

the capacitor. The forced response is described by -Vo. Equation (3-9) shows

the relationship of the output voltage Vo. In addition, the initial conditions for the

energy storage elements must be considered.

(3-8)

(3-9)


36

RbRc

Ro

Vb

Figure 3.3 (c): Typical Buck-Boost Control Circuit in Boost Mode Switch Open

AAA—

Rc

C —

Vo

Figure 3.4 (a): Typical Buck-Boost Control Circuit in Buck Mode

Figure 3.4 (b) shows the buck-boost control circuit in the buck mode with the

switch closed. When the switch is closed a circuit results with a forced and a

natural response. The resulting natural response is the same response as


37

shown previously in equation in equation (3-8) with the exception of the forced

response is described by Vg instead of -Vo.

RcVo

Figure 3.4 (b): Typical Buck-Boost Control Circuit in Buck Mode SwitchClosed

RcVo

Figure 3.4 (c): Typical Buck-Boost Control Circuit in Buck Mode Switch Open

Figure 3.4 (c) shows the buck-boost control circuit in the buck mode when

the switch is open. When the switch is open a circuit results with only a natural


38

response. The resulting natural response is the same as shown previously in

equation (3-6).

Again depending upon the circuit component values the natural response of

the circuits can be in various damping modes. In addition, the duty ratio of the

switch within the circuit, both for the boost mode and the buck mode, play an

important role in the circuit operation. This will determine what conduction mode

the buck-boost circuit operates within.

This type of control system is the ideal option to fully utilize the range of the

ultracapacitor system. This allows the ultracapacitor system to operate from OV

to 375V through its full voltage range and completely charge and discharge. This

operation is independent from the battery system and provides complete control

of the ultracapacitor system.

Due to the extensive cost of the buck-boost DC-DC converter, a decision was

made based on available funding not utilize a DC-DC converter to control the

ultracapacitor system. Therefore, further validation was not sought to pursue the

design shown in Chapter 4.

3.5 PSPICE Simulation Results

Computer simulations were completed using the DC-DC converter designed

above. This is the optimal operation of the ultracapacitor system and the most

available energy can be provided for the full range of the ultracapacitor system

operation.


39

Simulations were conducted using the values o f the elements as shown in figure

3.5 (a) and (b), fo r both the boost and buck mode operation. These elements

were selected based on the design parameters for the buck-boost converter and

confirming the best results with simulations verify the optimal operating

parameters.

PSPICE simulations were completed to confirm the expected results of the

DC-DC converter. Figures 3.6 (a) and 3.7 (a) show the voltage values at the

ultracapacitor system and the battery system during the boost and buck mode

respectively. Figures 3.6 (b) and 3.7 (b) show the battery current, the

ultracapacitor current and the output current at the load during the boost and

buck mode respectively. These results are consistent with the expected results

for the DC-DC control circuit. The voltage across the ultracapacitor system does

1H

.150Vs Vo290

=F 16.67F 360

Figure 3.5 (a): Buck-Boost Control Circuit for H2 Fuel Hybrid Bus in Boost Mode


40

1H

.150290

16.67F 4=

Figure 3.5 (b): Buck-Boost Control Circuit for H2 Fuel Hybrid Bus in Buck Mode

across the ultracapacitor system does not exceed the allowable amount of 405V

for the system. The current through the ultracapacitor system does not exceed

the allowable amount of 300A. In addition, the parameters o f the battery system

are with the allowable constraints discussed in the previous chapter. For these

simulations a constant load resistance of 1.5Q was used. In practice the load

resistance varies with the operation and cannot be assumed to be constant.


41

V b a t

iaau-f■s 10s

: U(C1:1) T U (V 2:*)T in

Figure 3.6 (a); DC-DC Converter Boost Mode Converter Voltage Values


42

le a p

■ « + -es

IL o o d

; I ( L 1 ) « - ICR*»)20s a es

T in e

Figure 3.6 (b): DC-DC Converter Boost Mode Current Values


43

%e#v-

2#eu

Os 18s- U (D 1 * :2 )- U (R 2:2) U(C2:1)

T ine

Figure 3.7 (a): DC-DC Converter Buck Mode Voltage Values


44

I gen

-400A +Os 10s

r I(R 5 ) o I(R 2)20s 30s

Tine

Figure 3.7 (b): DC-DC Converter Buck Mode Current Values


45

3.6 ADVISOR Simulation Results

ADVISOR Simulations were completed using only the ultracapacitor system

without the battery system. NREL had created a modified energy storage file for

ADVISOR created to simulate the ultracapacitor system using the same quasi

static model as the batteries. The energy storage file in ADVISOR was modified

to simulate the parameters of the ultracapacitors. In order to simulate the

ultracapacitor system an Ah value need to be calculated. Although

ultracapacitors are not measured with Ah values, a value of .868 was calculated

based on the conversion from Ah to the available energy of the ultracapacitor.

Once this conversion was completed the simulations were straight forward as

shown in the previous chapter for the battery system only. However, in this

simulation cycle the ultracapacitor does not have nearly enough power to propel

the vehicle by itself. For this reason with this simulation the hydrogen engine

was necessary as shown in the simulation results. The drive cycle shown in

figure 2.7 was again used for the simulation. Figure 3.8 (a), (b) and (c) show the

results for the simulations utilizing only the Maxwell Technologies PC 2500

ultracapacitor system. Table 3.2 shows the energy usage for the Maxwell

Technologies ultracapacitors simulation. The results show kinetic energy of 1.1

MJ at the energy storage system regenerative braking mode. This is consistent

with the expected results for the ultracapacitor system alone. This simulation

depicts an unrealistic situation because the vehicle would never be operated with


46

only the ultracapacitor system. However, it was valid to verify the operating

parameters of the system during acceleration and regenerative braking.

cyc_mph_r

20 30 40 50 60 70 00 90

ess soc hist“ 0.9

S 0.7

0( 10 10

ess_pwr out a

OcIO 10 20 30 40 50 60 70 00 90

pb pwr out a

10 20 30 40 50 60 70 00 90

Figure 3.8 (a): ADVISOR Output Maxwell Technologies Ultracapacitors


47

cyc_mph_r

ess current

Dc 10 10

BSS_pwr_out_r

pb_valtage™ 350

Figure 3.8 (b): ADVISOR Output Maxwell Technologies Ultracapacitors


48

BOcyc_mph_rmpha

20

40500

ess currentC033U

-500(DcnO)

-10001000

40

distance0)L)ra 500 2

COOJ

cncnCD

0 10 20 40 5030 GO 8070 90

Figure 3.8 (c): ADVISOR Output Maxwell Technologies Ultracapacitors


49

Enatgf Usage TobiePclJPOWER MODE REBEN MODE

In Out Loss E lf. In Out Loss EH

Fuel 0 178E8Fuel Convetter 178M 3767 14101 0.21 392

dutchHjrd. Torque Cbnveilat

Gcoeretor 3375 3563 188 1.06To n^C ou pfingEnergp Storage 1098 639 191 0.81Energy Stored 2S9

Motor/Contralar 4019 4137 118 1.03 1137 978 159 0.86Gearfaos 4137 4014 123 0.97 1140 1137 3 1

Final Drive 4014 4014 0 1 1140 1140 0 1WheeUArde 4014 3683 331 0.92 1972 1961 11 0.99

BraUng 821AusLoarh 63

Aetb 326RoBng 1247

"Overs# SyKem Effnency

0.083"OvnaD ene tg j/ e flnenq i tt ra ta ia led « Isem * lo ingV lh iri in - ess storage)

MooNB#:

Table 3.2: ADVISOR Energy Usage Table Output Maxwell TechnologiesUltracapacitors


CHAPTER 4

HYBRID ELECTRIC VEHICLES WITH

ULTRACAPACITORS AND DIRECT CONNECTION

This chapter will discuss the direct connection control o f the ultracapacitor

system. This will include pre-charging the ultracapacitor system with PSPICE

simulation results. Finally, the direct connection of the ultracapacitor system is

presented both with the quasi-static solution and exact solution. PSPICE and

ADVISOR simulation results are presented to confirm these results.

4.1 Pre-Charging the Ultracapacitors

Based on the funding o f the H2 Fuel Hybrid Project and the cost of the DC-

DC converter control system, a decision was made to pre-charge the

ultracapacitor system and place it directly across the battery system. Therefore,

instead of the buck-boost converter or DC-DC converter circuit being used to

control the ultracapacitor system, the system will be pre-charged and

permanently connected across the battery system.

Although this is not the optimal approach to incorporate the ultracapacitor

system into the energy storage of the hybrid electric vehicle, this method should

provide a ‘smoothing’ of the current characteristics across the battery system.

50


51

This will elevate some stress on the battery system. However, this

configuration will not eliminate the ‘dumping’ of energy across the battery system

from the regenerative-braking system. Figure 4-1 shows the block diagram of

the direct connection configuration for the energy storage system.

In order to place the ultracapacitor system directly across the battery

terminals, it must be pre-charged to the open circuit voltage o f the battery

system. In order to accomplish this a series of pre-charging switches within a

circuit was used to establish an initial voltage of 360V. Three switches within the

circuit were required to pre-charge the system while keeping it within the

allowable parameters.

Figure 4.2 shows the series of pre-charging switches required to charge the

ultracapacitor system to the required initial voltage. This circuit charges the

ultracapacitor system to 360V at which time the system is placed directly across

the battery terminals.

The values for the pre-charging circuit, in particular the values across the

switches were based on running the charging process several times determining

where the cycle exceeds the allowable limits of the ultracapacitor system. The

simulation was run to determine the point at which the current or voltage

exceeded the allowable parameters of the ultracapacitor system. That is the

reason for three separate switches closing at t=0, t=t1 and t=t2 respectively. The


52

DC Bus

UKracapacitcts

DOACConverter

AODC ConverterACGeneratcr

Battery SoiToe

Figure 4.1: Hybrid Electric Vehicle Diagram with Direct Connection

tClose=0 R1" vA/V

R2

Rb ^ tClose=t1 tClose=t2

RcVb

Figure 4.2: Pre-Charging Circuit

pre-charging designed for the case of the H2 Fuel Hybrid Bus using component

values of R1=4 ohms, R2=2 ohms and the switches closing at t1 =90 seconds

and t2=180 seconds. Once the system reaches the desired initial voltage the


53

pre-charging circuit Is disabled or disconnected from the system. As this should

be in theory, the only time the system is required to be pre-charged. However,

this circuitry will need to be utilized anytime the battery or ultracapacitor system

has to be replaced. In addition, this circuitry enables the system to be charged

at a faster rate than if the ultracapacitor system was directly connected across

one switch.

Once the system Is pre-charged, circuits were initially designed to review the

operation of the system based on a constant request of power.

4.2 Pre-Charqinq Ultracaoacitors PSPICE Simulation Results

Computer simulations were completed using the pre-chargIng circuit and the

acceleration and regenerative-braking circuits above. Again, this operation of the

ultracapacitor system Is not the optimal way to control the system. PSPICE

simulations were completed to confirm the expected results of the pre-charging

circuit. Figure 4.3 shows the battery voltage, the ultracapacitor voltage and the

current across the ultracapacitor. Figure 4.4 shows the power across the battery

and the power at the load. These results are consistent with the expected

results for the pre-charging circuit. The voltage across the ultracapacitor system

does not exceed the allowable amount of 405V for the system. The current

through the ultracapacitor system does not exceed the allowable amount of

300A. In addition, the parameters of the battery system are within the allowable

constraints discussed In the previous chapter.


54

P b s t

lOKW-i

Pcap

os ses: I (C 1 )- U (R4:1) c I (C D * W(U1:*)

100s

T in e

1SQs

Figure 4.3: Pre-Charging Circuit Voltage and Current Values


55

3tflU

2##U

190U

9U

2

Vbat

Vcap

leap

as ##sQ ] - U(RH:1) v> u (u i:* ) (2] ■ i ( c i )

80s 128s

Tine

Figure 4.4: Pre-Charging Circuit Power Values

4.3 Direct Connection Control

Once the ultracapacitor system is pre-charged to the required initial voltage, it

is permanently connected across the battery system. Figure 4.5 shows the

circuit used for the energy storage system for the H2 Fuel Hybrid Bus project.

This circuit is not the optimal approach to control the ultracapacitor system.

However, this type of connection does allow for increased life of the battery

system and additional energy available during acceleration not present in the

standard system with only batteries. The circuit shown in Figure 4.5 shows that

the battery system is connected in parallel with the ultracapacitor system. This

connection forces the voltage at the output terminals of the ultracapacitor system


56

to equal the voltage across the battery system. This system operation differs

from the buck-boost circuit control, as it does not allow the ultracapacitor system

to be fully discharged to OV across the system.

Rb.19

350V-

Tib

4-Vb

Rc .15

16.67F -L

t i c

Vo

+

VII

i

Load

Figure 4.5: Parallel Control Circuit

Initially, the required power is determined for the present situation of the

vehicle, then this power is provided by the energy storage system and the

hydrogen engine. Once the amount of power required to be provided by the

energy storage system the actual amount of power that the energy storage

system could provide could be determined. Equation (4-1) shows the power

relationship of the control circuit in Figure 4.11.

= (4-1)

The required power, the internal resistance of the battery at a given SOC, the

internal resistance of the ultracapacitor system, the voltage across the battery

system and the initial voltage of the ultracapacitor system are all known values.


57

Equation (4-1) can be solved to obtain the values o f/* and Ic. Equations (4-2)

and (4-3) show the resulting equations.

I I- +h- K -K\2\

i^= 0 (4-2)

(4-3)

Equations (4-2) and (4-3) are used for the quasi-static solution to determine

the SOC of the battery and the voltage across the ultracapacitor system at a

given time interval. Equation (4-3) was solved over the same drive cycle using

quasi-static calculation methods. Once the result for the capacitor current was

found at the iteration, the value was then substituted into equation (4-1) and the

quasi-static value of the battery current was solved. This quasi-static method

was repeated at each step. Figure 4.6 shows the required power for that the

hybrid electrical system is required to provide for the drive cycle in question. The

drive cycle shown in figure 2.7 was used, however, for this simulation the speed

of the vehicle was only taken to 25 mph. This was done so that during the

simulations the hydrogen engine would not be included in the simulations and

resulting calculations.


58

Required Power Constant Drive Cycle

80,000

60,000

40,000

K? 20,000

10 • rrrrrTTTTTT

- 20,000

CO ^ CO t — CO ^ CM CN CO CO

CO V — CO CO T— CO cOTf If) to CD CO b- CO GO o)

-40,000 -L--------- ------ — ------- ---------------- ----------- ---- --------------

Time (sec) : —. - 'Power Required

Figure 4.6: Required Power Constant Drive Cycle

The quasi-static solution for solving for the ultracapacitor, battery and load

current and voltage values yields the results shown in figure 4.7 and figure 4.8.

Figure 4.9 shows the power values for the quasi-static solution.

After a solution was reached for the quasi-static results based on the

calculated value of the battery current first and then the ultracapacitor current,

the set of equations were solved again. This time the solution of the

ultracapacitor current


59

Quasi Static Current Values

250.00

200.00

150.00

100.00

50.00

0.00CO 05 m T— fv*T— T— CN CO CO

03CO 03 "in^ TT m CO CO O '

-50 .00 -

- 100.00Current Bat Current Cap Current Load

-150.00

Time (sec)

Figure 4.7: Quasi-Static Current Values

Quasi Static Voltage Values

390.00

380.00

370.00

360.00 -

350.00

340.00

u 330.00

320.00

310.00

300.00■ m — Voltage Bat

- — Voltage Cap

♦ — Voltage Load

290.00 CO 0505CO sCO CO CO CD

T im e (« e c )

Figure 4.8: Quasi-Static Voltage Values


60

Power Quasi Static Values

100,000

80,000

60,000

5 40,000

Ig 20,000

CO 0 3lO COCO CO

- 20,000

j—• — Power Bat j —■ — Power Cap i - - - Power Load

-40,000

Time (sec)

Figure 4.9: Quasi-Static Power Values

was sought first and then the value of the battery current was calculated at each

discrete data point. Equations (4-4), (4-5), (4-6), (4-7) and (4-8) show the

alternate solution.

(4-4)

(4-5)

V, - I , R , -V , R.

(4-6)


31

P-Y^Yè---R.

K - K + IçRç \ n

V R

. {VtRc)^VÀR, ■^2R,)±^VlRl ^2V,R,V,R^+R,{R,(y^-AR,P)-AR]P

Equation 4-9 shows the solution for the ultracapacitor current. Once this

value was calculated at each data point the result was used to calculate the

battery current as shown in equation 4-5. The solutions obtained with the

second calculation method yielded the same results as the initial solution shown

in figure 4.7, figure 4.8 and figure 4.9.

Once the quasi-static solution was obtained, the exact solution for the set of

equations was sought. Mesh analysis was applied to the circuit shown in figure

4.5. Noting that the load power is a function of time. The following set of

equations 4-9 and 4-10 describe the mesh system. Equation 4-11 shows the

resulting relationship for the ultracapacitor current.

- V, + i , . R, + (/, - 0 -R ^ + C — (/, - 0 = 0 (4-9)at

P Pi = — = ------ (4-10)V ^b~h'Rb

(4-11)at

Solving this set of equations for a function of Vc yields the solution in equation

(4-12).


62

p = v:\Rb J

+ V ,dv^ - C - 2 C ^

Rdv

b J dtVbRçC

V Rb . dt R.

(4-12)

C -2 C

(4-13)

This solution shown in equation (4-13) yields a non-linear first order

differential equation. The non-linear first order differential equation was solved

using the quadratic relationship and the Runge-Kutta method to obtain the

solution for Vc. Fortran code was written to obtain this solution. The exact

solution yields the same results as shown for the quasi-static solutions above [3].

This is further validated with computer simulations.

4.4 Direct Connection PSPICE Simulation Results

PSPICE was used to simulate the circuit shown in figure 4.5 with a constant

load resistance. Attempts were made to validate the results obtained from the

quasi-static solutions of the equations for this circuit. PSPICE simulations were

limited because the load could not be modeled with a constant power, only with a

constant resistance, current or voltage. Simulation results for the direct

connection control circuit are shown in figure 4.10 below.

Reproduced with permission ot the copyright owner. Further reproduction prohibited without permission.

63

The PSPICE results for a constant load situation were useful to verify the

results of the quasi-static equations. However, this simulation was not useful to

confirm the calculations during normal operating conditions of the vehicle.

PSPICE was not as an effectively tool as ADVISOR for the validation of the direct

connection control circuit.

8M

[load

' I b o t

\

\

leap

0 A + -------------------------------r-------------------------------------- 1------Os Ss 10sz I(R b ) O I(RC) V - I(R 3 )

2 8 s

Time

2 5 s 38s 35s

Figure 4.10 — PSPICE Results Constant Load of 30

4.5 Direct Connection ADVISOR Simulation Results

In order to simulate the direct connection control circuit in ADVISOR the

ADVISOR code had to be rnodified from its original form. In normal simulations

with ADVISOR, only one energy storage file could be used to input data for the

energy storage system. This file is the energy storage file or the ess file.

Because it was necessary to simulate both the battery system and the


64

ultracapacitor system as one system, the block diagram control scheme in

MatLab and Simulink had to be modified.

Extensive research and investigation was completed to determine the input

and output variables of the block diagram of the ADVISOR simulation process in

Simulink. Figure 4.11 shows the overall block diagram for ADVISOR, figure 4.12

shows the ADVISOR block diagram for the energy storage system.

There are several sub-block diagrams that were investigated within the

overall energy storage system block diagram. They include the sub block

diagram for the Voc and Rint, the sub block diagram for computing the current,

the sub block diagram to limit the power and the sub block diagram for the SOC.

After extensive research of the block diagrams for the ADVISOR energy

storage system, the necessary revisions were made to the energy storage block

diagram. Modifications were made to overall diagram and a sub block diagram

was added to compute the current and voltage.

vehicle controls

0 —4 3Clock To VUoriGpace

generator/«n rttm tfi» r< g r>

drive cyde <cyo

vehicle <veh> wheel andgytP <wh>

Rnal drive <fd: geaitw <gb> motoi/m n fm lfe r < m g

QSum

series hybrid control aategy

iltSgal

total fuel used@al)

JiisL

powerbus<pb>

converterforaeries

ez_c3Jc I

Htc_emi5|

HC.CO.

eneigy aoiage <ea

exiiaua sys NOx. PM M <ax>

Figure 4.11 : ADVISOR Block Diagram of the Overall System


65

o -power req’d into bus (W)

SOC

Goto <sdo>.

ess_pwr_out_f

To Workspaces

pack Voc, Rint

t .= r

'CS>

max pack pwr(W)

computecurrent

>»

>limit power

^ess_max_pwi

Goto <cs>l

M

SOCalgorithm

t

ess_pwr_out_a

To Workspaces

* ©

»<^bus_voltage

power available to bus (W)

3oto <mc>, <go, <sdpss_^_calc

SOC

stop Sim

jx > f(u)

J1 Tess

Qess_gen T ar

Q ar

I ess_pwr_loss_a[

n ess_mod_&TÏ

^ ess_air_tmp

-W' ess_air_th_pw •

coul eft

Figure 4.12: ADVISOR Revised Block Diagram of the Energy Storage System

These values were calculated in the new sub block diagram and then the

calculated values returned to the original block diagram for the voltage, current

and power. These modifications were made with the assistance of the

Mechanical Engineering Department at UNLV. The modified block diagrams for

the energy storage system are shown in figure 4.13 and figure 4.14. The overall

energy storage system now had a control system that allows the vehicle to utilize

both the batteries and ultracapacitors during acceleration and deceleration.


66

rttZ]--Product open a re u it

voitaoe o f batteiy

V 0C 8(V)

SOC(pr V)

mod tm p

Rb

Œ>To Wbrtopace

M em oryl

f{u)

Dot Prodt a

Pc

Figure 4.13; Modified ADVISOR Voc, Rint Block Diagram

The modified file was simulated using the same simulation setup as used in

the previous ADVISOR simulations and the constant drive cycle shown in figure

2.9. Figure 4.17 (a), (b) and (c) shows the results of the ADVISOR simulations

performed with the modifications discussed. The ADVISOR results after the

modifications are consistent with the results o f calculating the values quasi-

statically as well as the exact solutions obtained.


67

mcmyomn

S

Figure 4.14: ADVISOR Compute Current Block Diagram Added forUltracapacitor System


68

30

eye mph r mpFfa20

0 10 20 30 60 9040 50 70 BO400

load200

-200400

20

200

10 20 30 50 60 9040 70 80

0

-100

-2000 10 20 30 6040 50 70 80 90

Figure 4.15 (a): ADVISOR Output Ultracapacitor Direct Control


69

2D

eye mph r mpha

0 10 20 30 50 GO 70 8040400

300

3B3.B10 20 9ID0 30 50 GO 70 8040

VDCb

“ 3G3.G

3G3.410 20 30 50 GO 70 80 9 0

voce

10 20 30 40 50 GO 70 80

Figure 4.15 (b): ADVISOR Output Ultracapacitor Direct Control


70

eye mph r mpha

pb_pwr_out_aCD

40 60 7030

Pb

(X

70 90

Pc

oQ .

10 20 800 40 50 60 70 9030

Figure 4.15 (c): ADVISOR Output Ultracapacitor Direct Control


CHAPTER 5

ANALYSIS AND CONCLUSIONS

The results produced for the Horizon 12N85 lead-acid battery strings were

consistent with the anticipated results. The ADVISOR file provided accurate

input for two parallel battery strings with 28 individual units with an overall parallel

string voltage of 336V. The results were compared to the calculated results, for

H2 Fuel Hybrid Bus as an all-electric vehicle and produced the same results.

The results produced for the Maxwell Technologies PC 2500 Ultracapacitors

were also consistent with the anticipated results. ADVISOR provided accurate

input for an ultracapacitor energy storage system with 150 individual units with

and overall nominal string voltage of 375V. The results were compared to the

theoretical results expected for the ultracapacitor system and are consistent with

those expectations.

Initially, three solution methods were reached for the same direct connection

system, the first, was calculating the results using the quasi-static method. The

second solution was to calculate the results using the exact solution or time

domain solution of the system. The third solution was to modify the ADVISOR

block diagrams and files to account for the installation o f the ultracapacitor

system with the direct connection control scheme. As shown previously, all three

71


72

solutions produced similar results. The cycles used in the previous chapters

were used only to verify the calculation methods for the simulators. The drive

cycles were not typical for simulating the operation of the vehicle.

Once the ADVISOR calculation method was verified it was sought to

simulation the H2 Fuel Hybrid Bus using drive cycles that were representative of

the vehicle operation. In order to show this operation several drive cycles were

simulated for the H2 Fuel Hybrid Vehicle. The constant drive cycle was ran in

greater detail and the Federal Urban Driving Schedule (FUDS). These result

produced results that were expected for the vehicle but were not representative

of the drive cycle pattern that would be seen by the H2 Fuel Hybrid Vehicle. For

this reason, two drive cycles were studied in great detail to further verify and

quantify the benefits of the installation of the ultracapacitor system. These drive

cycles are the Bus Route Drive Cycle and the Central Business District Bus

Route Drive Cycle. These two drive cycles are discussed in detail in this chapter.

5.1 Bus Route Drive Cycle

The next drive cycle used to perform simulations with ADIVSOR was the Bus

Route Cycle. This cycle is shown in figure 5.1 and performs a series of starts

and stops between 0 mph and 20 mph. There are a total of 28 stops in all for the

cycle. This is the most representative drive cycle for the H2 Fuel Hybrid Vehicle.

This drive cycle utilizes the hydrogen engine to power the vehicle. Figure 5.2 (a)

and figure 5.3 (a) show the hydrogen usage for the respective energy storage

system. The vehicle utilizes the hydrogen engine for situations where the


73

maximum power îthe energy storage system can apply is not sufficient for the

energy required fo r the power bus. This situation is shown in figure 5.3 (a) at

approximately 4 0 0 seconds. These figures also show the battery SOC values

slightly higher for the direct connection system. This is expected for this

configuration.

Figure 5.2 (b) shows the current supplied by the energy storage system

when only the battery system is present (ess_current). Figure 5.3 (b) shows the

current supplied b#y the energy storage system when both the battery system and

the ultracapacitor system are present (I load). These values are the same

through out the drive cycle. Figure 5.3 (b) shows the corresponding battery

current (lb) and uMracapacitor current (Ic). Comparing the graphs for the battery

current between th e two systems shows that the battery system does not need to

provide as much current at each acceleration and deceleration pulse for the

system with ultracapacitor system. This is result is desired and is what is

expected for the system. Figure 5.3 (c) shows the voltages at the power bus,

battery system and the ultracapacitor system. Again, these results are consistent

with the expected results. Finally, figure 5.3 (d) shows the simulation results for

the power at each element in the system. The resulting power at the load

(pb_pwr_out_a) is the sum of the power provided by the battery (Pb) and the

power provided b y the ultracapacitor system (Pc). This shows a smaller amount

of energy required by the battery system than required by the battery system by

itself, shown in figu re 5.2 (c) and figure 5.3 (d). This smoothing of the waveform

at the battery system and at the load is consistent with the expected results for


74

the direction connection with the bus route cycle. Comparing figures 5.2 (e) and

5.3 (f) show the benefit of the ultracapacitor system. These figures show

approximately 25% less power required by the battery system with the

ultracapacitor system than with only the batteries. In addition, the overall fuel

required by the hydrogen engine is less with the ultracapacitor system as

expected, because the required power at the power bus does not exceed the

maximum value of the power that can be provided by the energy storage system

for as long o f duration. The simulation with the ultracapacitor system utilizes

approximately 30% of the hydrogen required by the system with only the

batteries. All of these results confirm the expected results for the respective

systems.

Again, this drive cycle is the most representative of the operation of the H2

Fuel Hybrid Bus. It shows a tremendous advantage for the cycle with

ultracapacitor system installed. It provides the desired results for the system and

validates the installation of the ultracapacitor system reducing the stress placed

on the battery system and increasing the overall vehicle ranges.


75

40

Simiilatioa Setup

CYCBUSRTE

#20

key onirsceelevation

0 500 1000 ome (sec)__________(SpBcd/EfavaliDnva.'nme

QnamProcadtne Detciîpïoa

0 i

1500

jRclaipn-e C'tr fiJSRTE mI Oaia source:Maastrad by KsiSi V/ipka. NREL. on a 16ii Suvot Msil bus n Oanvai CO. Oola conTnnafon:

Notes:This is a 1.65-mile round trip: with the bus stopping oi every biocfc end

LBUSRTE

' " “ ' s s i s a s - '

%

:jTeitP>o6Bdl«aa:jTEST_Crrr'_HWi-

55

O ParametiicSIudy Variable T

#ot'variablesLow Hign SPontï

BMBHigal-IS-'j j 1S3-I2 j 3 1Variable 2mmiiMPi C33 1 G.53 1 3 ;|

Variable 2m m m m 6.25 1 £.25 1 3 1

Figure 5.1: ADVISOR Bus Route Drive Cycle Simulation Setup


76

Q .E

30

20

10

0

cyc_mph_rmpha

200 400 600 800 1000 14001200

ess soc hist.2 0.98

ë 0.96

S 0.94

0.92 I0.2

0 200 400 600 800 1000 14001200

0.15

0.05

&10 200 400 600 800 1000 14001200

pbjDwr_out_r

o .

0 200 400 600 800 1000 14001200

Figure 5.2 (a): ADVISOR Output Battery System Bus Route Drive Cycle


77

30

cyc_mph_rmpha

Cl.

1400800 1200200 400 600 1000400

2 200 3S 0

ess current-200

1400800 1000 12009c 10 200 400 600

essjDwr_out_r

cncnCD

1400800 1200200 400 1000600450

pb_voltageœ 400CJiroÔ 350

c l 300

2501400200 800 1200400 600 1000

Figure 5.2 (b): ADVISOR Output Battery System Bus Route Drive Cycle


78

30

20

10

0QtlO 200

cyc_mph_rmpha

lUi400 600 800 1000 1200 1400

ess_pwr_out_a

a .cncn

& 10 200 400 600 800 1000 1200 1400

cncn

Q .cncn

200 600400 800 1000 1200 14003000

distance2000<D

c_>c rB=5 1000

0 200 600400 800 1000 1200 1400

Figure 5.2 (c): ADVISOR Output Battery System Bus Route Drive Cycle


79

x1012

— - Pb- - - Ph

4 r

1000 1200 14000 200 400 600 800

Figure 5.2 (d); ADVISOR Output Battery System Bus Route Drive Cycle


80

x10

. I

200 220 240 260 280 300

Figure 5.2 (e): ADVISOR Output Battery System Bus Route Drive Cycle


81

cyc_mph r

200 400 600 BOD 1000 1200 140

ess SOC histCO

0.90.04

200 400 BOO 800 1000 1200 140

0(10' 200 400 BOO BOO 1000 1200 140

pb pwr out r ess max pwr apply

0 200 400 BOO BOO 1000 1200 140

Figure 5.3 (a): ADVISOR Output Battery & Ultracapacitor Systems Bus RouteDrive Cycle


82

eye mph_r mpha

600200 400 1000 14C800 1200500

less-500400

400 600200 1000 14C800 1200

200JO

-200200 400 600200 1000 1200800

u-200

-4004000 600 1000 14C200 800 1200

Figure 5.3 (b): ADVISOR Output Battery & Ultracapacitor Systems Bus RouteDrive Cycle


83

eye mph_r

1000 1200pb_voltage

■5 350

300200 800400 BOO 1000 1200 14C

3B4vocb

5 3B3

200 BOO BOO 1200400 1000 14C

voce

300200 400 BOO BOO 1000 1200 14C

Figure 5.3 (c): ADVISOR Output Battery & Ultracapacitor Systems Bus RouteDrive Cycle


84

K 10”CO

o

DC 10 200 400 BOO 800 1000 1200 1400Pb

CL

0( 10 400 600200 800 1000 14001200

CL

400 600200 800 1000 1200 1400

500

200 400 600 800 1000 1200 1400

Figure 5.3 (d): ADVISOR Output Battery & Ultracapacitor Systems Bus RouteDrive Cycle


85

X 101.5

PbPcPh

0.5

-0.5

-1.5 1200 14001000800600200 400

Figure 5.3 (e); ADVISOR Output Battery & Ultracapacitor Systems Bus RouteDrive Cycle


86

X 10

0.8 PbPcPh0.6

0.4

0.2

-0.2

-0.4

-0.6

-0.8

200 210 220 230 240 250 260 270 280 290 300

Figure 5.3 (f): ADVISOR Output Battery & Ultracapacitor Systems Bus RouteDrive Cycle


87

5.2 Central Business District Bus Route Drive Cycle

The next drive cycle used to perform simulations with ADIVSOR was the

Central Business District Bus Route Drive Cycle. This cycle is shown in figure

5.4 and performs a series of starts and stops between 0 mph and 20 mph. There

are a total of 14 stops in all for the cycle. This is an extremely valuable

representative drive cycle for the H2 Fuel Hybrid Vehicle. This drive cycle

utilizes the hydrogen engine to power the vehicle. Figure 5.5 (a) and figure 5.6

(a) show the hydrogen usage for the respective energy storage system. Again,

the vehicle utilizes the hydrogen engine for situations where the maximum power

the energy storage system can apply is not sufficient for the energy required for

the power bus. This situation is shown repeatedly in figure 5.6 (a). These

figures also show the battery SOC values slightly lower for the direct connection

system. This result was expected based on the sharp acceleration and

deceleration rate required by the vehicle. This result is different from the

previous Bus Route Drive Cycle.

Figure 5.8 (b) shows the current supplied by the energy storage system

when only the battery system is present (ess_current). Figure 5.6 (b) shows the

current supplied by the energy storage system when both the battery system and

the ultracapacitor system are present (I load). These values are the same

through out the drive cycle. Figure 5.6(b) shows the corresponding battery

current (lb) and ultracapacitor current (Ic). Comparing the graphs for the battery

current between the two systems shows that the battery system does not need to

provide as much current at each acceleration and deceleration pulse for the


88

system with ultracapacitor system. This is result is desired and is what is

expected for the system. Figure 5.6 (c) shows the voltages at the power bus,

battery system and the ultracapacitor system. Again, these results are consistent

with the expected results. Figure 5.6 (d) shows the simulation results fo r the

power at each element in the system. The resulting power at the load

(pb_pwr_out_a) is the sum o f the power provided by the battery (Pb) and the

power provided by the ultracapacitor system (Pc). This shows a smaller amount

of energy required by the battery system than required by the battery system by

Itself, shown in figure 5.5 (c) and figure 5.6 (d). Comparing figures 5.5 (e) and

5.6 (f) clearly show the advantage of the ultracapacitor system. Less fuel is

required by hydrogen engine with the installation o f the ultracapacitor system.

The charge and discharge cycles of the battery system is less dramatic with the

ultracapacitor system by approximately 20%. This smoothing of the waveform at

the battery system and at the load is consistent with the expected results for the

direction connection with the bus route cycle. In addition, the overall fuel

required by the hydrogen engine is approximately 2% less with the ultracapacitor

system as expected, because the required power at the power bus does not

exceed the maximum value of the power that can be provided by the energy

storage system for as long of duration as the previous drive cycle. All o f these

results confirm the expected results for the respective systems.

Again, this drive cycle is an extremely valuable representative of the

operation of the H2 Fuel Hybrid Bus. This drive cycle shows an advantage for

the cycle with ultracapacitor system installed. It provides the desired results for


89

the system and validates the installation of the ultracapacitor system reducing the

stress placed on the battery system and increasing the overall vehicle ranges.

Simulation. SetupCYC CBDBUS

20

15

10key ontraceelevation

Current Procedure Oetcriptlon:

Data source: Nigel Ouk. West Virginia Universiv

I Data confirmation:

I NtJtes: Central Business District test cyde tor buses.

T

0.5

-.0 .5

100 200 300 400 500 600time (sec)

|Spced/BevBÜon vs Time ^

fofvonablesU Parametric Study

Variable 1 H igh # Points

14543

Venable 2I C - !| IP 3

varebie j

Figure 5.4: ADVISOR Central Business District Bus Route Drive CycleSimulation Setup


90

20cyc_mph_rmpha

a-10

100 300200 400 5001.01

ess soc histcn

cn' 0.99cn

0.98100 300200 400 500

S. 0.5

&10 100 300200 400 500

pb_pwr_out_r

I3000 100 200 400 500 60

Figure 5.5 (a): ADVISOR Output Battery System Central Business District BusRoute Drive Cycle


91

20cyc_mph_rmpha

15

a-10

100 200 500300 400400

ess current200

S -200

-400100 200 300 500400

ess_pwr_out_ro

Q -0 30 3

0 100 200 500300 60400450

pb_voltage® 400C71

sp 350

CL 300

250100 200 300 500400

Figure 5.5 (b): ADVISOR Output Battery System Central Business District BusRoute Drive Cycle


92

cyc_mph_rmpha

g-10

400100 200 300 500 60

ess_pwr_oiit_aO

Q.cncn

100 200 400300 500 60

cncn

100 200 400300 500 604000

3000ss 2000cn

1000 distance

0 100 200 400300 500 60

Figure 5.5 (c): ADVISOR Output Battery System Central Business District BusRoute Drive Cycle


93

5x10

1.5

PbPh

1

0.5

0

-0.5

1100 200 300 400 500 600

Figure 5.5 (d): ADVISOR Output Battery System Central Business District BusRoute Drive Cycle


94

x101.5

Pb— - — Ph

0.5

1 L200 220 240 260 280 300

Figure 5.5 (e): ADVISOR Output Battery System Central Business District BusRoute Drive Cycle


95

20

10

eye mph r mpFa -

200100 300 500 BOO400

ess soc histCD

g 0.98CDCDCD

0.96100 200 300 500 600400

Oc 10' 100 200 300 500 600400

pb pwr out r ess max pwr apply

0 100 200 500300 400 600

Figure 5.6 (a): ADVISOR Output Battery and Ultracapacitor Systems Central Business District Bus Route Drive Cycle


96

2D

g-10

n rITTT

eye mph r mpfTa “

100 200 300 500 600500ess

0

100 200 400 500300 BOO

200

100 200 300 400 500 600

CJ-200

-4000 200100 300 400 500 600

Figure 5.6 (b): ADVISOR Output Battery and Ultracapacitor Systems Central Business District Bus Route Drive Cycle


97

2D

| - 10

500

eye mph r mpfia "

300 400 500 GOO

200

LbA/YVW\fYvWvW ]100 200 BOO300 400 500

3B4voeb

g 3B3.5

100 200 300 400 BOO500

voec

I 400

3002001000 300 400 BOO500

Figure 5.6 (c): ADVISOR Output Battery and Ultracapacitor Systems Central Business District Bus Route Drive Cycle


98

K ID”

CO pb_pwr_out_a

Q_

a 10 100 400 BOO200 300 500

Pb

CL

0( 10 100 400200 BOO300 500

Pc

uCL

0( 10 100 400200 BOO300 500

C73

(JO)

0 100 400 BOO200 300 500

Figure 5.6 (d): ADVISOR Output Battery and Ultracapacitor Systems Central Business District Bus Route Drive Cycle


99

,5X 101-5

PbPcPhPL

0.5

-0.5

600500400300100 200

Figure 5.6 (e): ADVISOR Output Battery and Ultracapacitor Systems Central Business District Bus Route Drive Cycle


100

X 101

0.8 PbPcPh0.6

0.4

0.2

0

- 0.2

-0.4

- 0.6

- 0.8

1 --------------- 1----------------1----------------1_________1_________I_________ I_________ I---------------1_________ I_________200 210 220 230 240 250 260 270 280 290 300

Figure 5.6 (f): ADVISOR Output Battery and Ultracapacitor Systems Central Business District Bus Route Drive Cycle


101

5.3 Conclusions

The results o f the desired energy storage system with the ultracapacitors and

the batteries produced reasonable results based on the data. The results

produced were consistent with what was expected for the DC/DC control system.

The modifications to ADVISOR required to fully verify the calculations for this

was not completed as a part of the scope of this research, in lieu of focusing on

the actual system to be installed in the H2 Fuel Hybrid Bus as a result of

available funding.

The results fo r the directly connected control system yielded the expected

outcome. The ADVISOR simulations after modifications to the block diagrams

yield the expected results for the system accounting for the operational

constraints. ADVISOR has been proven to be an effect tool in modeling and

simulating the performance of hybrid electric vehicles. The overall use of the

program is relatively straight forward along with the required modifications to the

energy storage system. The use of ultracapacitors in the energy storage system

modeling is new to the ADVISOR program. However, ultracapacitors can be

effectively modeled in the energy storage system o f ADVISOR.

Actual field simulations are recommended to further validate the models used

in this research, the combination of batteries and ultracapacitors with DC-DC

converter control is the preferred method for development of hybrid electric

vehicles. The DOE funding for the H2 Fuel Hybrid Bus was not available to

install the optimal DC-DC converter control. However, installing the


102

ultracapacitor system in the direct connection method produces favorable results

for the system. This connection shows the ultracapacitor system eliminates the

stress on the battery system, increases the vehicle range and reduces fuel usage

with the hydrogen engine system. There are limitations with this connection

method that are not present with the DC-DC converter control. This is a viable

solution for hybrid electric vehicles. Actual road testing of the H2 Fuel Hybrid

Bus was not conducted based on the installation time frame for the energy

storage system but will be conducted in the future.


APPENDIX

MAXWELL TECHNOLOGIES INC PC 2500 DATA SHEET

103


104

PC2500 Ultracapacitor Data Sheet

Capacitance F .IO%/»25* 2500Series Resislance (2S*C); OC mohms -20%r*20% 1.0

'00 Hz inohms 0.6Voltage; continuous opetaling V 2.5

peak V 2.7Rated Current" A ' 400DgnenskMGUkeüyeixxionhü ; mm l61it8tSs61SVVaight _____________ _______9 _______ 725

Temperature' Operating •c -20 to 60Storage *c -40 to 65

Leakage Current (altar 72 hrs) milliamps 6Notes:' cacod w r e n ) s l^ .^ ^ c fc w ra n tM p c a k irw a n ta n a o u s p o iw e r ' Dovioo can wAhsand short drcut current if kepc wiMn opoia ling tenipflfalus ’ Suady su» casa lempMattite

PC2S00 Power vs Ouralion; Discharge Bo 112 wAage Lite vs. Average Tetnpetahire-Vdlage1600 j 1201400 25*<

100I 890 £ 600 !

400200

o40 35*C

40i 45*CPafcimunca VS. Température

ESB CapKMwioe6.0 - 3000

205.0 - 2500

65-C- 2000

3.0 2.3 2.4 Z 5 2 .6Average Cpetaling Voltage

2.7

- - 1000 &2.0 —

O pe ra t< iim ife o lin u lra fapac4n r isatndKir>oHhe«»«ragel«rTipetatL4a end voRtge.

500

0.0 • tncydHigappiicalona. use Oa* average voeage over OmmSiteoparaBng cytSe to «Mtrrnirw He.• In Otckup «ppeeatorn. wM 0>e conlirtuou» vciugv to detamiina m.


APPENDIX II

ADVISOR SOLVE CURRENT FILE ADDED FOR ULTRACAPACITOR

SYSTEM DIRECT CONNECTION INSTALLATION

105


106

function y=soive_current(x)

%soive the current of battery and ultracapacitor Vocb=x(1);Rb=x(2);Vocc=x(3);Rc=x(4);P=x(5);

%equations: (1) P=Vocb*lb+Vocc*lc-ib'^2*Rb-lc'^2*Rc; % (2) V=Vocc-lc*Rc=Vocb-lb*Rb

%finai expression %a1 *lb''2+b1 *!b+c1 =0 x1=(Vocc-Vocb)/Rc; y1=Rb/Rc;

a1=Rb+y1^2*Rc;b1 =-Vocb-y1 *Vocc+2*x1 *y1 *Rc;c1 =P-Vocc*x1 +x1 2*Rc;!b=(-b1 -sqrt(b1 2-4*a1 *c1 ))/(2*a1 );

x1 =(Vocc-Vocb)/Rc; y1 =Rb/Rc;

%a2*lb'^2+b2*ib+c2=0x2=(Vocb-Vocc)/Rc; y2=Rc/Rb;a2=Rc+y2^2*Rb;b2=-Vocc-y2*Vocb+2*x2*y2*Rb;c2=P-Vocb*x2+x2'^2*Rb;Ic=(-b2-sqrt(b2''2-4*a2*c2))/(2*a2);

l=lb+ic; y=[!b, Ic];


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http://www.pddnet.com

VITA

Graduate College University of Nevada, Las Vegas

Steven L. Pay, P.E.

Address:1208 Padre Serra Lane Las Vegas, NV 89134

Degrees:Associate of Arts, Engineering Science, December 1993 Montgomery Community College, Rockville, MD

Bachelor of Science, Electrical Engineering, May 1994 University o f Nevada, Las Vegas, Las Vegas, NV

Thesis Title: Hybrid Electric Vehicle Regenerative-Braking Using Ultracapacitors

Thesis Examination Committee:Chairperson, Dr. Yahia Baghzouz, Ph.D., P.E.Committee Member, Dr. Sharham Latifi, Ph. D., P.E.Committee Member, Dr. Eugene McGaugh, Ph.D.Graduate Faculty Representative, Dr. Rohan Delpatadu, Ph.D.

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hybrid electric vehicle regenerative-braking using

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