EVS29 Symposium

Montréal, Québec, Canada, June 19-22, 2016

Design and prototyping of a rapid-charge electric bus

for urban passenger transportation
Carlo Villante1, Antonino Genovese2, Franecsco Vellucci2
1
(corresponding author) University of L’Aquila, Italy, carlo.villante@univaq.it
2
ENEA, Italy, antonino.genovese@enea.it, francesco.vellucci@enea.it

Summary
Collective transport means must obviously be designed and used to minimize their environmental impact.
The way to reach this aim, however, is certainly not obvious, since it must consider a number of aspects
connected both with the fulfilment of users’ expectations in terms of number and frequency of vehicle stops,
and with the energetic and economic balances of the service offered.
Taking the lead from these consideration, one of the authors previously developed a easy-to-use tool for the
energetic assessment of alternative transport means to be used on a given route. Here, this tool is put in use
by the authors for the design and prototyping of a rapid-charge electric bus for urban passenger transportation,
within a close cooperation with an Italian Transportation Authority.
Keywords: Electric vehicle, Public transportation, Fast Charge, Lithium-ion battery

1 INTRODUCTION
Collective transport means must obviously be designed and used to minimize their environmental impact.
The way to reach this aim, however, is certainly not obvious, since it must consider a number of aspects
connected both with the fulfilment of users’ expectations in terms of number and frequency of vehicle stops,
and with the energetic and economic balances of the service offered.
Therefore, for a given service, there are a number of possible options to be compared, varying in terms of
vehicle dimension and payload, powertrain design and management, fuel used, and so on [1].
Limiting the attention on road transport means, electric propulsion is one of the most promising alternatives,
but may use a number of different technologies, also including hybrid configurations (using a combination
of an ICE and an electric motor) [2-6], and/or alternative fuels, both based on renewable or fossil sources [7-
9].
Author gained a huge experience modelling all these possible alternative solutions and still are convinced
that electric mobility is certainly the most effective solution in a mid-term future within urban mobility
applications.
A full and effective comparison among the given alternatives is only possible on a Well to Wheel (WTW)
basis, to take into account potential benefits for the community connected with different energy vectors use.
Taking the lead from these consideration, one of the authors previously developed a easy-to-use tool for the
energetic assessment of alternative transport means to be used on a given route [10].

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The tool starts from the definition of vehicle cycle and mission on a GPS web-based interface. Then it
automatically defines vehicle mission and compares possible solutions (among conventional vehicles, BEV,
HEV, FCEV and PHEV) modelling their Tank to Wheel behaviour on the defined mission.
Finally, the comparison is extended on a Well to Wheel basis, making use of numerical and experimental
results about Well to Tank emissions and energy consumption gained by the Joint Research Centre of the
European Union [11], to take into account potential benefits for the community connected with different
energy vectors use.
Here, this tool is put in use by the authors for the design and prototyping of a rapid-charge electric bus for
urban passenger transportation, within a close cooperation with an Italian Transportation Authority.

2 Application frame
The procedure was applied to the design of an urban bus which will make its service within the historical
center of L’Aquila, in Italy. The possible path of the vehicle was designed and georeferenced according to a
simple GPS based procedure. Vehicle stops were positioned as well, according to Figure 1. The developed
SW tool [10] permits the derivation of the altitude profile of the mission: results are reported in Figure 2.

Figure 1 – Service Path Figure 2 – Path altitude profile

Moreover, it was considered that Italian National Government (within a grant with ENEL, the main Italian
electric services company), is setting up in the city of L’Aquila a smart city plan which includes the diffusion
of electric mobility: the plan will lead in the next months to the installation of 50 electric charging points
throughout the city. One of these will be a rapid charge charging station and will be installed at the bus
terminal, just at the start of the path represented in Figure 1. The charging station will have a maximum
charging power of 43 kW and could be used both for AC charging, and for DC Chademo compliant charging.
This occurrence makes it possible to recharge the designed bus (for a limited time) at the end of each service
cycle (whose length is about 5.5 km, according to Figure 2).

3 Mission Definition
According the procedure fully described in [10], the SW tool then proceeds to vehicle cycle and mission
definition, according to some data given from municipal administration (max vehicle speed and acceleration
stops durations and cycle frequency). The Results of these design phase are reported in Figures 3.

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 Figure 3 – Vehicle cycle

Each vehicle cycles lasts about 23 minutes and is repeated 24 times during the daylight vehicle mission.
Between each 2 successive cycles, a period of about 7 minutes is therefore available for rapid charging
operations. These charging phases, in the following simulations, will be realized at 1C max current, leading
to a full charge duration of approximately one hour. Therefore, at each stop of the bus at the terminal stops,
one can imagine to recharge approximately the 10% of max battery pack capacity: the charging power
required, as well as the recharged energy obviously depends on battery size.

4 Vehicle revamping
The present design and prototyping activity has been taken ahead with the cooperation of L’Aquila Municipal
Transportation Authority (called AMA). AMA currently holds 4 series hybrid buses named Horus by EPT.
One of those buses (which were bought in 2008) is no longer making any service since its Diesel-fed turbo-
gas APU needs maintenance and OEM is expired.

Figure 4 – EPT Horus Bus and its OEM power electronics schematic

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Taking the lead from these considerations, a cooperation between AMA, University of L’Aquila and ENEA
has started which will lead in the following months to the realizations of a fully electric rapid charge bus.
This prototype will make use of particular Li-ion cells specifically designed by ENEA for rapid charging
applications and equipped by a Battery Management System originally designed by Pisa University in
cooperation with ENEA [12] (see Figure 5).

Figure 5: Design and final assembly of battery modules by ENEA

The battery system manufactured in ENEA is made by 12.8V modules 12.8 V – 60 Ah, obtained connecting
in series 4 lithium-iron-phosphate cells. These modules may be connected in series and in parallel to have
required drivetrain voltage and power.
The modules were successfully tested by ENEA for rapid charging applications. The results of these activities
are reported in [13].

5 Modelling results
Here the results of modeling activities are reported. Model used was completely developed by one of the
authors and is fully described in [10].
The model was firstly applied to the simulation of the original OEM Diesel-fed series hybrid bus (referred to
as “HYB” Configuration). The results of this modeling activity are reported in Figures 6 to 8.

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 Figure 6: HYB: Cycle simulation Figure 7: HYB: Mission simulation

Figure 8: HYB: Overall energy performances

Then a first full electric version of the vehicle is obtained (referred to as “BEV” Configuration) removing its
APU and its on-board Lead Acid Battery pack and substituting it with standard high capacity Li-ion cells
available on the market. The overall size of the Li-ion battery pack was designed to fulfill the complete daily
mission (24 cycles) of the vehicle: 102 kWh. Slow battery charging (1/8 C max current, with a normal 16
kW power charger) is simulated at the end of bus daily mission. The results are reported in Fig. 9 to 11.

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 Figure 9: BEV: Cycle simulation Figure 10: BEV: Mission simulation

Figure 11: BEV: Overall energy performances

Lastly, the Battery pack was substituted by a number of the Li-ion modules designed by ENEA. Their
dynamical characteristics were simulated in the model making use of the detailed testing results reported in
[13]. The overall size of the Li-ion battery pack was customized for frequent rapid charging applications, so
permitting to save costs, transported weight and therefore energy requirements: 15 kWh. 5 minutes lasting
rapid charging operations (1C max current, largely available at bus terminal, where a 43 KW rapid charger

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will be installed) are simulated at the terminal at the end of each bus cycle): during this charging phases, the
pack approximately recovers 10% of its full capacitance, which almost corresponds to the energy spent during
its 5.5 km elementary cycle. The results of this modeling activity are reported in Figures 12 to 14 (referred
to as “BEVRC” Configuration).

Figure 12: BEVRC: Cycle simulation Figure 13: BEVRC: Mission simulation

Figure 14: BEVRC: Overall energy performances

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Looking at the represented results, one may think that a 15 kWh pack is certainly still a bit over-dimensioned
for the specific application. Anyway, a further reduction in the installed capacity could lead to problems
during a 1C charging, because the energy spent during the elementary cycle may not be recovered during the
stops.
As already underlined, the SW permits the comparison of the performances of the three simulated vehicle
configurations on a Well-To-Wheel (WTW), also making use of reliable and up-to-date data about Well-To-
Tank (WTT) CO2 emissions and energy consumption reported in [11]. Comparison results are reported in
Figures 15 and 16.

Figure 15: Results comparison

Figure 16: Results comparison

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A clear convenience in using a fully electric vehicle instead of a hybrid one for this urban application was
demonstrated.
Rapid charging Battery electric vehicle are fully successful in limiting the installed capacity of the battery
pack to approximately 1/6 of the energy needed for its overall daily mission. Energy losses due to rapid
charging are balanced by the energy saving connected to the lower vehicle weight.
Advantages are clear, on the other end, with respect to the limited costs of the rapid charging solution. Cost
saved for the battery pack are not balanced by the additional costs of the rapid charging infrastructure, which
is certainly compatible with those built for cars’ application, not requiring significant power output (like
those needed for high capacity Electric buses). Moreover, the costs of the infrastructure may be divided by
the number of buses using it and may be depreciated in a much longer period (20 years) with respect to
battery packs (2-3 years for heavy duty transportation applications).

6 Conclusions
A tool for the energetic assessment of alternative transport means to be used on a certain route, developed by
one of the authors was here applied within the frame of a cooperation with L’Aquila Municipal transportation
authority aimed to the design of revamping of a hybrid bus. The tool starts from the definition of vehicle
cycle and mission on a GPS web-based interface and automatically defines vehicle mission and compares
possible solutions (among conventional vehicles, BEV, HEV, FCEV and PHEV) modelling their Tank to
Wheel behaviour on the defined mission.
The comparison is extended on a Well to Wheel basis, to take into account potential benefits for the
community connected with different energy vectors use. Model also makes it possible to obtain detailed
Sankey diagrams individuating energy fluxes on board. Results clearly show the capability of the proposed
tool in vehicle comparison on a WTW basis, as well as the preference for proposed Rapid chargeable bus
configuration with respect to higher mileage solutions, especially in historical city centre applications.

References
[1] G. Pede, C. Villante, Thematic Research Summary on Other alternative fuels for transaportation, Energy Research
Knowledge Centre by the European Commission of the European Union, 2014, setis.ec.europa.eu/energy-
research/content/
[2] D. Di Battista, R. Cipollone, M. Marchionni, C. Villante, Model based design and optimization a fuel cell electric
vehicle. Energy Procedia 45, 71 – 80, 2014
[3] G. Pede, F. Martini, L. Tribioli, C. Villante, 0D- 1D coupling for an integrated fuel economy control strategy for
a hybrid electric bus. SAE Technical Paper, 2011-24-0083, 2011
[4] Di Napoli A. Pede G., Polini C., C. Villante. Energy Management in Hybrid Electric Vehicle with ICE and
Ultracapacitors. IEEE International Conference on Electrical Systems for Aircraft, Railway and Ship Propulsion,
ESARS 2010.
[5] E. Rossi, C. Villante, A Hybrid Car by ENEA for Urban Mobility. 25th Electric Vehicles Symposium, Shenzen
(China), EVS25, 2010
[6] E. Rossi, C. Villante, On Energy performance of an Electrically-driven City-Car. 26th Electric Vehicles
Symposium, Los Angeles (USA), EVS26, 2012
[7] G. Pede, A. Genovese, F. Ortenzi, C. Villante, Hydrogen-CNG blends as Fuel in a Turbocharged SI ICE: ECU
calibration and emission tests. SAE Technical Paper, 2013-24-0109, 2013
[8] A. Genovese, C. Villante, Hydromethane: A bridge towards the Hydrogen economy or an unsustainable promise?
International Journal of Hydrogen Energy, 2012
[9] A. Genovese, C. Villante, Environmental analysis of hydrogen-methane blends for transportation. in: A. Gugliuzza,
A. Basile, Membranes for clean and renewable power applications. Woodhead Publishing Series in Energy No.
13, CAMBRIDGE Woodhead Publishing Ltd, 2012

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[10] C. Villante , A tool for Well-to-Wheels evaluation of alternative public transport means, 28th Electric Vehicles
Symposium, Goyang (Korea), EVS28, May 2015
[11] R. Edwards, J. F. Larive, D. Rickeard, W. Weindorf. JEC Well-To-Wheels Analysis: WellTo-Tank Report Version
4.0. Report EUR 26027 EN, Joint Reaserch Center of the European Commission, July 2013.
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29th Electric Vehicles Symposium, Montreal (Canada), EVS29, June 2016

Authors
Prof. Carlo Villante
Mechanical Engineer, PhD on Thermal Machines. Associate University Professor of Renewable Energy
Sources at the University of L’Aquila - Italy. Previously, Associate Professor at the Sannio University, and
Researcher at the Low Impact Vehicles Lab in ENEA. Author of more than 50 technical papers: his main
research activities are on ICEs and on Renewable Energy Sources.

Dr. Antonino Genovese

Electronic Engineer, Senior researcher at the Low Impact Vehicles Lab of ENEA (Italian National Agency
for New Technologies, Energy and Sustainable Economic Development).
Author of more than 30 technical papers

Dr. Francesco Vellucci

Mechanical Engineer, Researcher at the Low Impact Vehicles Lab of ENEA (Italian National Agency for New
Technologies, Energy and Sustainable Economic Development). Previously, he worked in the field of
industrial combustion and electric traction, especially marine engines electrically propelled.
Author of more than 20 technical papers

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