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A new approach to battery powered electricvehicles: A hydrogen fuel-cell-based rangeextender system

Roberto �Alvarez Fern�andez*, Fernando Beltr�an Cilleruelo,I~naki Villar Martınez

Universidad Nebrija, Pirineos 55, 28040 Madrid, Spain

a r t i c l e i n f o

Article history:

Received 27 November 2015

Received in revised form

8 January 2016

Accepted 8 January 2016

Available online 4 February 2016

Keywords:

Hydrogen

Electric vehicle

Fuel cell

Extended range

Simulation

Model

Abbreviations: BEV, Battery Electric VehicHybrid Electric Vehicle; RE, Range Extender;Vehicles; SoC, State of Charge; PEM, Proton* Corresponding author. Tel.: þ34 914521100E-mail address: ralvarez@nebrija.es (R.�A.

http://dx.doi.org/10.1016/j.ijhydene.2016.01.00360-3199/Copyright © 2016, Hydrogen Energ

a b s t r a c t

Sometimes technology and development of society run slightly different roads. This situ-

ation is now happening in the case of hydrogen as an energy carrier in the automotive

world. In the article presented here, the authors propose a change in the structure of the

power plant of Battery Electric Vehicles (BEV). The objective is that these vehicles can be

presently used until the development of an electric and/or hydrogen recharge/refuel

network allows being useful with the current status. In this paper a new concept of

Extended Range Electric Vehicle (EREV) based in a Fuel Cell Electric Vehicle (FCEV) set

model is presented. A study is then developed in order to determine the working condi-

tions that will lead to better efficiency and performance, referring to capacity of both en-

ergy sources: electricity stored in a Lithium-Ion battery and hydrogen gas in high pressure

tanks. The possibilities here shown open the door to strategic advantages and innovation

for car designers in the future.

Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

Introduction

Nowadays, when the traditional transport model has become

to its depletion, manufacturers and governments are betting

hard on newer and greener technologies as a solution. Not

only the progressive depletion of fuel reserves, but also the

environment evolution indicate that the mobile fleet must

probably change in no more than the next twenty e thirty

le; EREV, Extended RangICE, Internal Combustio

Exchange Membrane; NE; fax: þ34 914521111.Fern�andez).35y Publications, LLC. Publ

years [1,2]. Many manufacturer companies agree that the

Battery Electric Vehicle (BEV) is the one to beat [3,4], but differ

on the specific way [5]. This has much to do with the charac-

teristics of the different technologies of energy storage avail-

able. It is known that batteries offer a good dynamic response,

while their discharge time, shorter than desired, and the

recharge time, longer than desired, makes consequently that

BEVs available in the market today are not suitable for many

customers.

e Electric Vehicle; FCEV, Fuel Cell Electric Vehicle; PHEV, Plug-inn Engine; PDU, Power Distribution System; AFV, Alternative FuelDC, New European Driving Cycle.

ished by Elsevier Ltd. All rights reserved.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 4 8 0 8e4 8 1 9 4809

A temporary solution may be the Plug in Hybrid Electric

Vehicle (PHEV), as it can be charged with electricity like BEVs,

run on gasoline with an Internal Combustion Engine (ICE) and

use batteries to improve fuel efficiency [6]. The combination

offers increased driving range with potential large fuel cost

savings and emission reductions. There are two main PHEV

technologies: parallel hybrids, in which both, the electric

motor and the combustion engine, are mechanically coupled

to the wheels through a transmission (i.e. Toyota Prius), and

series hybrids, also known as Extended Range Electric Vehi-

cles (EREV), in which the electric motor is directly coupled to

the wheels and the combustion engine is only used to charge

the batteries (i.e. BMW i3). Although PHEVs possess many

advantages, they also have certain limitations. The main

concerns include increased cost due to the introduction of

engines, energy storage systems, and power converters [7],

and also, fossil fuels are used. At best, a 2 to 2.5 fold fuel ef-

ficiency gain can be hoped for the world car fleet out to 2030.

Most of this gain would be the result of a switch to hybrid

technologies [8], and depending on the percentage of elec-

tricity derived from renewable energy that could replace most

petroleum-based fuels.

On the other hand, Fuel Cell Electric Vehicles (FCEVs) are

powered by gaseous hydrogen, stored onboard in high pres-

sure tanks, which is converted into electricity by multiple

individual cells serial connected (fuel cell stack). A small bat-

tery pack is still used. It is typically smaller than BEV's one and

it is charged by an excess of energy from the hydrogen fuel cell

or through regenerative braking techniques (also often avail-

able on BEVs) which returns energy from the kinetic force

when braking, by switching the motor to operate in reverse,

flipping the route of the electricity and charging the battery.

Hyundai Tucson ix35 Fuel Cell and Toyota Mirai are two ex-

amples of FCEVs: both are zero tailpipe emissions and enjoy

good characteristics when it comes to range, as it is deter-

mined by the capacity of the tank, which can be refilled as

simply and fast as a gasoline tank.

Several policy initiatives have been adopted in order to

promote the development of a hydrogen refuelling network:

i.e. California State has committed funding for the develop-

ment of 100 hydrogen fuelling stations, Japan's government

proposed $71 million to build hydrogen fuelling stations, the

U.K. announced over $752 million of new capital investment

between 2015 and 2020 in support of ultra-low emission ve-

hicles, including FCEVs [9]. Germany, alone, expects to have

400 hydrogen fuelling stations in 2020. Norway, Sweden and

Denmark are developing the ScandinavianHydrogenHighway

to make the Scandinavian region the first in Europe where

hydrogen is commercially available in a network of refuelling

stations [10]. Italy is establishing a similar highway, designed

to connect the country in a hydrogen way to Germany and

Scandinavia. Nevertheless the slow development of refuelling

infrastructure and current vehicle cost are clearly the most

important hurdles keeping FCEVs from storming the market

en masse [11].

In the present paper the authors have started to combine

both vehicle concepts, EREV and FCEV, in order to solve these

particular problems and obtain a mixed response and an

improved vehicle range with easy refill.

Problem statement

A configuration scheme for an EREV and a FCEV is very similar.

An EREV is characterized by a powertrain composed by an

electric engine, a power converter and an energy storage

battery pack, that compound the vehicle propulsion subsys-

tem (see Fig. 1). It also has a second subsystem, Range

Extender (RE), composed by an Internal Combustion Engine

(ICE), a fuel tank and an electric generator. That subsystem it

is exclusively used to charge the batteries [7].

FCEV configuration is that similar. Like Battery Electric

Vehicles, Fuel Cell Electric Vehicles use electricity to power an

electric engine, but in contrast to other electric vehicles,

FCEVs produce their primary electricity using the fuel cell

powered by hydrogen. The vehicle uses the fuel cell as a

generator to powerwhat is otherwise a battery electric car (see

Fig. 2). The power plant has also a small battery pack that

helps the fuel cell to boost and also to recover energy during

regenerative braking periods. Energy flow is controlled by a

Power Electronic Distributor Unit (PDU). See the arrows inside

the box in Fig. 2: when the vehicle is in a transient of hard

acceleration, the PDU distributes the power generated from

the onboard fuel cell and the battery to cover the power de-

mand. When this transient finishes, the PDU allows the en-

ergy flowing from the fuel cell stack to the primary motor

through the power converter and, at the same time, the bat-

tery could be recharged. In case of braking, the PDU manages

the regenerative braking. This recovered electricity is stored in

the battery.

There are few models of FCEV available currently in the

market but with limited distribution. Details of these

models’ specifications, shown in Table 1, illustrate the effi-

ciency of FCEVs. The models are: Midsize Car Honda FCX

Clarity, Mercedes B Class FCell, Toyota Mirai and Hyundai

Tucson (ix35 Fuel Cell in Europe) respectively. All these ve-

hicles have similar characteristics. Similar power levels

(about 100 kW) and hydrogen gas/electrical energy storage

systems technologies are similar too, fuel tank and battery

technologies. Nickel Metal Hydride and Lithium-Ion battery

packs, two hydrogen pressures: 350 bar and 700 bar with

fibre wrapped composite tanks. But the most important

common characteristic is that all of them use a very low

capacity battery storage and also that no one of them is plug-

in. This is obvious, as the batteries have capacities lower

than 2 kWh, and it creates an auto-generated product design

drawback to commercialize these vehicles, as consumers

will not feel comfortable without the availability of a full

refuelling infrastructure before purchasing a hydrogen fuel

cell vehicle.

Refuelling has been a historical problem for Alternative

Fuel Vehicles (AFV) [11], but this problem is more pronounced

for those AFVs that operate exclusively on a single alternative

fuel, such as hydrogen fuel cell vehicles or battery electric

vehicles [12].

EREVs were born as one possible solution to cope with

some of the BEV limitations in this sense. Some studies have

explored and compared different EREVs taking into account

their energy consumption [13] or the different range

Fig. 1 e Schematic of an EREV.

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extender technologies [14] and it is demonstrated that an

EREV will consume, on average, less than half of the oil of a

PHEV in the real world, if overnight charging is assumed,

reducing regulated emissions by more than 70% when

compared to a PHEV [15]. But oil is still used as fuel. Opel

Vauxhall Ampera and BMW i3 are the most popular/sold

EREVs in the market today.

Table 2 resumes the main characteristics of these two

concepts of EREV, BMW i3 has significant weight advantage,

better electric range (50 km upper) and 14 g. CO2 emissions

less per kilometre, but the achieved range is 120 km, so it is

ideal for city use. For consumers that want to jump into

electric car ownership, but to only want one car, then the

Ampera is the model to go for. Its 35 L fuel tank allows a

500 km all-electric range. Nevertheless Ampera's total range is

close to FCEVS’.

The production of hydrogen through a home unit, which

sits outside a house and reforms natural gas to produce

hydrogen to power the car is today a utopia. Refuelling the

vehicles through a network of charging stations is a complex

but closer idea. See the example of California, the state in

which there is a remarkable refuelling infrastructure for such

vehicles [18,19].

Table 3 summarizes the hydrogen fuelling station in the

United States. It is important to remark that 18 of the global 40

Fig. 2 e Schemat

stations are located in California. The number of stations in

Europe (36), Japan (21) and Korea (13) are not very encouraging,

but referring to the EU situation, a recent studies [21,22] show

that deploying a 25% share of FCEVs in road transport by 2050

can contribute up to 10% of all cumulative transport-related

carbon emission reductions and concludes that by the end

of 2025 an appropriate number of hydrogen refuelling stations

needs to be in place within those Members States which

adopted the use of hydrogen for road transport as one of their

national policies.

Therefore, in the near future two hypothetical scenarios

can be posed:

� A first optimistic scenario in which a large network of

hydrogen refuelling will be developed.

� A second and less optimistic scenario in which the

hydrogen refuelling network is not fully developed or

development occurs very slowly.

None of these scenarios is good for the commercialization

of hydrogen-powered vehicles. In scenario one there would be

a refuelling network similar to the current fossil fuel one, but

the possibility of electric charging at home would not exist. In

the second scenario it is evident that the hydrogen-powered

vehicle would be infeasible or with a negligible market

ic of a FCEV.

Table

1e

Tech

nicalsp

ecifica

tionsofco

mm

ercialFCEVs.

Model

Electricenginepower

Electricenergystorage

Drivingrange(Cycle)

Fuel

capacity

(massepressureevolume)

Fuelce

llpower

Fuel

consu

mption

(kghydro

gen/100km

)

HondaFCX

Clarity

DCPerm

anent

Magnet100kW

Lithium-Ion(Li-Ion)

386km

(EPA

Test

Data)

3.92kge350bar

100kW

1015

MercedesBClass

FCell

100kW

Lithium-Ion-1.4

kW

h385km

(NEDC)

3.7

kg-700bar

100kW

0.97

Toyota

Mirai

114kW

Nickel-Metal-Hydride(N

iMH)-1.6

kW

h483km

(EPA

Test

Data)

5kg-700bar�1

22.4

L100kW

1.03

Hyundaiix35

ACInduction100kW

Lithium-IonPolymer(Li-Po)e

0.95kW

h525km

(NEDC)

5.64kg�7

00bare

144L

100kW

1.07

Table 2 e Main characteristics of the best-selling EREVs[16,17].

BMW i3 Opel Ampera

Electric engine power 125 kW 111 kW

Lithiumeion battery

capacity/weight

18.8 kWh/230 kg 16 kWh/198 kg

Extended range oil tank 9 L 35 L

Range exender petrol

engine power

647 cc 2-cylinder

(25.4 kW)

1.4i 16v (63 kW)

Electric-only range 131 km 83 km

All electric range 250 km 580 km

CO2 emissions 13 g/km 27 g/km

Unladen weight 1390 kg 1715 kg

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penetration rate. Part of this problem could be solved with a

change in the vehicle power plant architecture design,

including a higher capacity battery and plug-in technology. A

power plant based on an EREV concept that used electric en-

ergy storage in a high electric battery and an extended range

fuel cell stack system powered by hydrogen would allow the

vehicle to be used in both scenarios successfully. In scenario

one, the vehicle could be recharged with electricity at home

and refuel hydrogen using the network refuelling points. The

second scenario would allow the driver to preferably recharge

batteries at home with electricity and using the poorly

developed network of hydrogen refuelling for long trips.

So the authors of the present paper, aiming to optimize the

design of two current concepts: EREV and FCEV, and propose a

power plant architecture that mixes the following concepts:

Plug-in battery, ER (Extended Range), FC (Fuel cell stack) and

EV (Electric Vehicle) shown in Fig. 3. The aim of Plug-in ERFC-

EV vehicles is to satisfy the customer specifications defined by

today's car user profile in order to cover two specific re-

quirements of vehicle's customers: Range and refuel.

This power plant structure is not a novelty formedium and

heavy duty vans, trucks and buses. Renault Kangoo ZE H2

model is an example of adaptation of the standard Kangoo Z.E.

electric van featuring the same 22 kW on-board battery pack

and 44 kW electric motor, but also including a small range

extender using a hydrogen fuel cell and hydrogen fuel tank.

However in light duty vehicles this approach is novel and

especially designing a switching control method on the range-

extender strategy, allowing the driver to manage hydrogen

consumption versus battery charge depletion is a novelty.

Methodology

A Matlab/Simulink vehicle model has been developed to es-

timate the energy consumption in battery range attending to

the comparison of different FCEV Plug-in configurations. The

purpose of the study is to find out trends on the range of the

Table 3 e Alternative fuelling station counts in U.S.A [20].

Electric(stations/charging outlets)

Hydrogen

Public 10708/26623 12

Public þ private 12642/30826 40

Fig. 3 e Plug-in ERFC-EV power train.

Table 4 e Battery parameters.

Energy content 16 kWh

Capacity (per cell) 40 Ah

Technology LieIon

Number of cells 108

Nominal voltage 400 V

Max. voltage 448 V

Min. voltage 324 V

Discharge cont. (power) 200 A (80 kW)

Discharge peak (power) 400 A (160 kW)

Max. charging current 80 A (32 kW)

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vehicle with the new power plant architecture working.

Matlab-Simulink block set series allowsmodelling, in a unique

simulation environment, both the electrical and mechanical

systems. The Plug-in ERFC-EV proposed is based on a recent

topology, such as the Hyundai ix35, as starting point.

The electric power plant consists of five major compo-

nents: Battery model, Fuel Cell Stack model, Power Mixture

Management System, Vehicle Dynamics and Electric Engine.

The preliminary design of these components is described

below, with emphasis on the available state of the art in each

one and challenges related to the present application.

Battery model

A battery is characterized by having a capacity, measured in

ampere-hours, which indicates the strength that is capable of

providing per hour from the full State of Charge (SoC 100%) to

the point at which the voltage at its terminals reaches the

limit called “cut-off voltage” for defining the state of charge

0%. A battery has different capacity in ampere-hours

depending on the intensity with which it is discharged: with

less capacity demand for high intensities, whereas for small

currents the capacity increases. Considering the working

conditions of the battery packs on BEVs, the selected

Fig. 4 e Battery mo

methodology to estimate State of Charge is the Coulomb

Counting (known as Ah method too), which is widely used.

The model, shown in Fig. 4, calculates the SoC by measuring

the battery current and integrating it in time. One of the most

important and indispensable parameters of a Battery Model is

an accurate estimation of the State of Charge as it is a classic

method to estimate the range of the vehicle. Battery model

presented by the authors of this paper have been tested in

previous works [23e26].

The model returns every relevant curve representing the

performance of the battery, including the State of Charge

del overview.

Fig. 6 e Unified model overview.

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(SoC) per time, device voltage per time and per SoC, intensity

running through the battery per time, power per time and

effective energy delivered in the cycle. In this paper, the

modelled battery has bigger capacity than the one installed in

the Hyundai ix35 FCEV, because the power plant will work as a

plug-in EREV. The characteristics of the battery are summa-

rized in Table 4. This battery has to achieve a minimum range

value in battery mode driving: 100 km.

Fuel cell stack model

Modelling and control for a Proton Exchange Membrane (PEM)

fuel cell stack system follows textbook procedures [27e29].

The equivalent circuit is shown in Fig. 5.

The model gives data about the stack efficiency and con-

sumption, and therefore the one able to be used in combina-

tion with a fuel tank subsystem, whose capacity is 142 L,

pressured at 700 bar, the same characteristics than Hyundai

ix35's. Themodel is fit to the data proceeding from datasheets

[30] such as voltage at 0A, voltage at 1A, voltage and intensity

of the nominal operating point and the maximum operating

point, stack efficiency, operating temperature, air flow rate,

supply pressure and nominal composition. As outcomes it

offers voltage produced at a determined current, consumption

and efficiency.

Power Mixture Management System

The unified model consists of both, the battery and the fuel

cell stack models, connected through a Power Mixture Man-

agement System (PMMS). The developed PPMS essentially

works as follows: power demand arrives from the vehicle or

from the complete dynamic plus the electric motor model; a

converter adjusts that demand according to the battery

instant working voltage and transforms it into a current; the

PMMS decides whether the depletion of the battery requires a

demand of energy coming from the fuel cell stack system or

not; if it is required this intensity is derived and the corre-

sponding power delivered by the fuel cell is reflected in a

hydrogen consumption. The only input of the unified model,

which is presented in Fig. 6, is therefore the drive cycle, and it

offers the following outcomes: SoC evolution in the battery;

current through the battery; voltage produced in the battery;

power delivered by the battery; effective energy delivered by

Fig. 5 e Fuel cell stack model overview.

the battery; voltage produced in the fuel cell; intensity

through the fuel cell; consumption of the stack; power

delivered by the fuel cell; effective energy delivered by the

fuel cell; fuel reserve remaining; total power delivered by the

set and an estimation about how many driving cycles would

the configuration stand. In the present paper, the New Euro-

pean Driving Cycle (NEDC) has been used as a driving cycle in

the tests. NEDC cycle is composed of two parts: ECE-15 (Urban

Driving Cycle), repeated 4 times, is plotted from 0 s to 780 s;

EUDC (Extra Urban Driving Cycle) is plotted from 780 s to

1180 s. The complete cycle is shown in Fig. 7.

The Power Mixture Management System architecture has

been developed as a block which presents several working

options. It takes into account demanded current, SoC and

capacity of the battery. In the present paper the PMMS system

prioritizes the battery range. It decides when the demand

should start the fuel cell and its amount, considering the

limits in the battery operation. The vehicle initially operates in

battery-only mode and switches to Extended Range Fuel Cell

powered after the battery reaches a low state of charge

threshold. In this phase, the fuel cell supplies the power

needed to recharge the battery vehicle and increase the SoC.

To prevent the battery from supplying current above the

maximum discharge current, a protection circuit will be

considered. This solution can be used to control, not only the

discharge current, but also the charge current. The maximum

discharge and charge currents are provided by battery man-

ufacturer's datasheets. The overcharge effect can be avoidable

by applying an upper limit to the state of charge of the battery.

According to previous documentation [31] this limit can be

located in the 90% of SoC. The PMMS disconnects the fuel cell

when the 80% of the SoC is reached, to give a margin to a

possible energy recovering. It would even be possible that

users can handle this limit according to their preferences.

The regenerative braking charge can be regulated by the

use of the brake system. When the SoC reaches the upper

Fig. 7 e New European Driving Cycle.

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limit, the hydraulic break system takes over the braking

needs, avoiding an overcharge of the battery. Appropriate

safety measures could also be incorporated to handle real-

world situations about fails or underperformance.

Vehicle dynamics

This block calculates the required torque and the speed of the

electric motor. Themodel considers the rolling resistance, the

aerodynamic drag and the gravitational resistance to calculate

the resistance force, according to equation, deduced from the

one-directional movement fundamental equations and New-

ton's second law. However, the regenerative braking is limited

in order to prevent the front wheels from becoming locked

[23]. The optimal braking energy in the front wheels depends

on the acceleration requirement and the dynamic weight

distribution. Using this resistance force, it is possible to

calculate the power and torque. The torque and the speed in

the drive shaft are essential for the determination of the

electric motor operational point. Table 5 shows the Hyundai

ix35 vehicle dimensions needed to complete the simulation

requirements of this block [32].

Electric engine

Hyundai ix35 2015's configuration includes a powerful electric

engine rated at 100 kW (134 horsepower). It is an induction

engine, bigger than the 80 kW one included in the Tucson test

Table 5 e Hyundai ix35 vehicle dynamics data set [32].

Overall Length (mm) 4410

Overall Width (mm) 1820

Overall Height (mm) 1650

Wheelbase (mm) 2640

Front Wheel Tread (mm) 1585

Rear Wheel Tread (mm) 1586

Front Over Hang (mm) 880

Rear Over Hang (mm) 890

Cargo Area (VDA) (litre) 551

Lightest Curb Weight (kg) 2250

Heaviest Curb Weight (kg) 2290

Gross Vehicle Weight (kg) 2290

fuel cell vehicle for Hyundai's 2nd generation hydrogen fuel

cell in 2005. This engine offers constant maximum torque

200 Nm (0e2000 rpm) and constant power 100 kW

(3600e7200 rpm) [32]. An adjustable-frequency drive has been

chosen to control the rotational speed of the electric motor.

This drive controls the slip by changing the frequency of the

supply of the motor. When changing the frequency, the

parameter (V/f) is constant until it reaches the nominal speed.

During this phase, the torque produced by the electricmotor is

constant. At speed greater than the nominal speed, the

voltage cannot be increased and it is fixed to its nominal value,

but the frequency could still be changed. In this second phase

the torque decreases but the power produced by the electric

motor is constant.

These two electric engines have been modelled in the

present paper to establish a comparison in terms of range. A

power converter unit converts voltage direct current from the

fuel cell stack into alternating current, which is then used to

operate the electric motor. It also controls the rotating speed

and torque of the motor.

Results

Therefore, the unified model will be run using a continuous

repetition of NEDC cycles, firstly as a current demand and as a

power demand afterwards. The objective of the study is to

determine which working conditions, in terms of dimensions,

will lead to a better efficiency and performance in the com-

bined energy storage system in this vehicle. It has been

considered interesting to carry out the test divided in the two

fundamental dimensions of both devices, battery capacity and

recharge power, with the aim of observe how the proposed

variations in each one affects system range. The results sec-

tion has been structured as follows: First, a test is performed

without using the range extender (battery mode). The goal is

to achieve the battery capacity that allows 100 km of range

using only the energy stored in the battery. Secondly, the

range extender is connected performing different recharging

strategies based on the variation of the recharging amperage:

beginning with high values (80 A) up to low values (10 A). The

amperage will be analysed to find the better result for vehicle

Fig. 9 e SoC evolution in pure electric mode.

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range. NEDC speed profile will be used as input data for the

vehicle in both tests. Finally, a real-world driving cycle is

considered to study the behaviour of the powertrain when

performing a driving cycle different to NEDC.

a) Performing the tests without considering the effects of fuel

cell range extender.

As a reference model shape and behaviour of discharge

curve of the battery, Fig. 8 presents the variation of battery

voltage obtained using a vehicle operating in pure electric

driving (batterymode) and performing a continuous repetition

of NEDC combined cycle. It can be seen that the voltage varies

in the urban part of the cycle with slightest variations and in

the extra-urban part of the cycle with greater ones. This is

caused due to the high power demand, which concludes in a

high discharge current. There are some existing recharge

notable points produce by regenerative braking (points A and

B in the graph).

Fig. 9 shows the variation in SoC for a battery mode

working operation. It can be clearly seen how the simulation

of SoC exceeds nine NEDC cycles. Each cycle NEDC covers

11023 m.

b) Performing the test considering the effects of fuel cell

range extender.

Fig. 10 shows the evolution of SoC when the vehicle is

working in an EREV mode. As the battery is drained and the

SoC reaches its minimum value (30%), the fuel cell starts

working and the battery is charged until the SoC reaches the

upper limit (80%). In this workingmode, the power supplied by

the fuel cell must be lower than the power of the modelled

electric engine (80 and 100 kW), because the battery is

designed to charge at 80 Amaximum, so only a fuel cell power

of 32 kW is needed. Most of the batteries in the market will

happily charge/discharge at a rate of less than 1C A. This

would translate into a 1 h charge/discharge process. In prac-

tice, the charging/discharging processes may require/reduce

up to twice/half the time. Most batteries can safely be used at

rates above 1C, up to the rating specified by themanufacturer.

However, a reduction in the battery life is surely expected,

although it is difficult to quantify [31]. Fig. 10 then shows the

Fig. 8 e Battery voltage (volts) v

results of the EREV's driving mode when recharging at 80, 40,

20 and 10 A.

Fig. 11 shows the all-electric range in each studied case: a

two engine powertrain configuration (80 kW and 100 kW

nominal power) and different recharging amperage. It can be

observed that the Li-Ion battery provides higher range than

100 km design requirement for battery working mode. When

driving as an EREV, the fuel cell stack is capable of providing

electricity to the battery and recharge it at different amperage

levels: from 80 A (high level) to 10 A (low level). The range

observed in Fig. 11 shows that the range decreases when

increasing the recharging Amps used. This happens when the

charging current exceeds 40 A value. This figure also shows

the variation in nominal power for the fuel cell stack needed.

The fuel cell stack dimensions in terms of power are clearly

influenced by the power plant architecture and this fact is

relevant, because current FCEVs (summarized in Table 1)

power plants must use a 100 kW fuel cell stack as this is the

main energy source. Fig. 11 shows (see the point marks) the

different sizing for the fuel cell stack in terms of power. The

fuel cell stack needed would achieve a maximum power of

ersus time (seconds) plot.

Fig. 10 e SoC vs time plots (Engine 80 kW configuration).

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 4 8 0 8e4 8 1 94816

32 kW, about a third part of the power required in current

FCEV designs.

Fig. 12 shows the hydrogen tank consumption for two

different range extender recharge management strategies

(80 A and 40 A). One can see that the hydrogen tank con-

sumption begins at the same time, but the recharge is faster

when increasing the recharge current. It is not possible to

establish a pattern for linking hydrogen consumptionwith the

Fig. 11 e Range results and fuel cell stack power for diffe

Amps used for recharging the battery, because there exists a

strong influence of the driving cycle: the point in the cycle

where charging starts can match high power demand or,

otherwise, be a drop zone speed. Clearly, if the fuel cell was

always supplying the same amperage and also the Li-Ion

battery always had the same power demand this pattern

could be easily established, but when driving a car this

behaviour does not usually happen.

rent electric engine power and recharging strategies.

Fig. 12 e Hydrogen tank consumption.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 4 8 0 8e4 8 1 9 4817

c) Real-World performing fuel cell range extender

Fig. 13 shows a daily driving profile for people in a road trip

inMadrid (Spain). ThesedatahavebeenobtainedusinganOBD

II data collector, placed in a vehicle running on the way be-

tween a point on the centre of the capital (Madrid) and a border

town (Alcala de Henares). It is a 64 km round commute that

thousandsofdriversdoeachday.As it canbeseen inFig. 14, the

vehicle canperfectly cover the 64 km journeydriving in battery

mode, but if the driver need to cover this distance two times in

one day, a recharge of the vehicle could be necessary with

current BEVS to avoid driver's range anxiety.

However, with the new Plug-in ERFC-EV powertrain here

presented, this problem is avoided. Fig. 14 shows how the range

extender starts working when the SoC falls below the limit set

for theminimum value. Once the initial charge of the battery is

depleted (PointA)and reaches theminimumvalueallowed (30%

Fig. 13 e Real-World driving profile (64 km).

SoC in this case), the range-extending process will seamlessly

activate the on-board electric charge drive system to continue

feeding the car for the additional kilometres, streaming power

to the battery and recharging it until the end of the journey. See

how the different amperage affects the recharging plot graph.

With lower Amps (30 A and 40 A) the SoC continues to drop

under 30% value due to the power demanded from the electric

engine. The driving cycle is in a high acceleration phase and the

depletion of the battery is higher than the recharge process at

these amperage. This does not occurs when recharging at 80 A.

In terms of storage energy, the SoC values are different

when the journey is finished: if the recharge is done at 40 A,

the final value of SoC grows up to 46.5%, while if the used

recharging amperage are lower (30 A) or higher (80 A) the

achieved values in SoC achieved are 34% and 77.4% respec-

tively. The hydrogen fuel consumption is also different: the

hydrogen tank has a consumption of 12% when recharging at

40 A, 9.58% at 30 A and 20% at 80 A.

It is interesting to remark that it is possible to design the

system to recharge the battery between other margins (not

only 30%e80% SoC), or even to only sustain the battery in the

minimum designed 30% SoC value, so that it does not fully

discharged during the trip. It is a manufacturer design/driver

decision: prioritizing hydrogen consumption is an option if

the owner of the vehicle has an electric recharge station at

home. It would be necessary to design a switching control

method on the range-extender strategy with a power

following control method.

It is obvious that the mission of the vehicle will dictate the

type of control to be employed, but summarizing the results,

the vehicle presented here achieves:

� 105 km range using the electric battery only.

� Near 600 km all-electric range NEDC cycle (525 km is the

FCEV NEDC current range).

� It can be refuelled with hydrogen in less than 10 min.

� It could be rechargedat homewith electricity (from1 to 8 h).

� Fuel cell stack with lower power than current FCEV's.

The sizing of the components and the drivetrain architec-

ture and control will be capable of handling real-world situa-

tions within the limits of design requirements and will

improve the current BEV and FCEV architectures, allowing

longer trips and easy refuelling at the same time.

Conclusions

Most of today's battery electric powered vehicles show a

realistic electric range of less than 200 km. It is enough for

most daily drives. Nevertheless, experience shows that this

approach does not satisfy all customers' expectations. Thispaper presents the results in energy consumption of a pow-

ertrain based in the use of a fuel cell range-extender system.

The vehicle drivetrain components have been sized and the

suitability of this electric vehicle has been analyse in this

paper. The range and fuel consumption with different energy

management strategies has been studied. A vehicle homolo-

gation cycle and real world city driving cycle has been used for

the analysis. As far as energy consumption is concerned, it

Fig. 14 e Real-World driving SoC evolution plot.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 4 8 0 8e4 8 1 94818

appears that the benefits of this power train configuration are

clearly better than other powertrains, allowing higher global

range (near 600 km) and also a minimum value of range in

battery mode (100 km). The results presented show a power-

train concept that could avoid the commercialization problem

associated to current FCEVs and BEVs powertrains and open

the door for car design optimization, because the discussed

powertrain could be the starting point for a driver oriented

management battery system and also for a new research

about sizing and managing each fuel storage system. So, in

terms of optimization design, it would be possible to:

(1) reduce/increase hydrogen tanks and/or reduce battery

capacity, understood as the storage hydrogen in litres in

the case of the fuel cell and as the cell capacity in

Ampere-hours in the case of the battery,

(2) recharge the battery at higher/lower C-rates and also,

(3) change the lower/upper limits toSoCdepletion/recharge.

These possibilities will be strategic advantages and inno-

vation for car designers in the future.

Acknowledgements

The authors gratefully acknowledge generous assistance of

Javier Arboleda, Service Senior Manager at Hyundai Motor

Spain and Gema Marıa Rodado Nieto, Engineer at National

Hydrogen Centre (CNH2) Spain.

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