Electrical vehicles: state of art and issues for their
connection to the network
Eduardo Valsera-Naranjo1, Andreas Sumper1,2, Pau Lloret-Gallego1, Roberto Villafáfila-Robles1, Antoni SudriàAndreu1,2
1. Electrical Engineering Department, Universitat Politècnica de Catalunya (UPC)
Centre d'Innovació Tecnològica en Convertidors Estàtics i Accionaments (CITCEA),
Barcelona, Spain
2. Institut de Recerca en Energia de Catalunya (IREC)
eduard.valsera@citcea.upc.edu, sumper@citcea.upc.edu, lloret@citcea.upc.edu, roberto.villafafila@citcea.upc.edu,
sudria@citcea.upc.edu
Abstract— The recent awareness about fossil fuels and the
environment has arisen more sustainable alternatives regarding
means of transport. The first alternative of green transport has
been hybrid vehicles. This kind of vehicles reduces significantly
the CO2 emission but not totally. Nowadays, the current trend is
the utilization of a unique motor for vehicle. i.e. an electrical
motor. It seems that the electric vehicles (EV) will become the
cars of the future.
Moreover, one kind of such vehicles, the plug-in electric vehicles
(PHEV), will not only charge their batteries, but PHEV will also
be able to inject power to the network when required. This fact
suggests that EV penetration will affect current power system
performance. Then, it is necessary to study some scenarios of
penetration of such vehicles into the electrical network in order
to maintain security and quality of power supply.
Electrical vehicles, Plug-in Electrical vehicles, network
performance
I.
INTRODUCTION
A combustion engine uses only about a 30 % of fuel of its
fuel tank while (the rest is lost in gases and in heat losses). An
electrical motor has efficiency greater than an 80 %. This
advantage was well known since the 19th century; in 1889
Thomas Edison built the first electrical vehicle powered by
nickel alkaline batteries. However, electricity had not become
the main energy source to power vehicles due primarily to the
batteries. Since the beginning of the electrical vehicle batteries
were a limiting factor. Indeed, this limiting factor led to giving
up the concept of electrical car to move to the combustion
engine car as the main vehicle.
This trend continued until the end of 1990. In this year, the
growing awareness for the environment caused an action from
the public entities. The CARB (California Air Resources
Board) adopted the Zero Emission Vehicle (ZEV) mandate.
The ZEV required the automakers California market share
include 2% ZEVs in 1998, 5% ZEVs in 2001 and 10% ZEVs in
2003. Unfortunately, the protests of the vehicle manufacturers
and the pressure exercised by the oil industry caused the
abandon of the ZEV.
However, some groups remained and the research in the
electrical vehicle field was not completely forgotten. Little
independent companies lead the research and propose real
alternatives to the combustion vehicle. In addition, important
cities of the world have implemented charge points in their
electrical local network to promote the use of the electrical
vehicle as a real alternative to others ways of transport.
There can be distinguished two types of vehicles which
may require charging points: pure electrical vehicle (EV) and
plug-in hybrid electric vehicle (PHEV) which have the capacity
of charging the battery from an external power source. The
pure EV have only batteries as power source for powering the
electric motor. There are various settings for the layout of the
electric motor in the vehicle: a single electric motor (Fig. 1 (a)),
an electric motor in each of the guide wheels (Fig. 1 (b)), a
motor for each rear wheel ((Fig. 1 (c)) and one motor per wheel
(Fig. 1 (d)). The PHEV’s have one or more electric motors and
a combustion engine. Before the apparition of PHEV’s,
common hybrid vehicle used a combustion engine to charge
their batteries to feed the electric motor. Current PHEV’s allow
starting from an initial situation of charged batteries; thus it
reduces the fuel used by the combustion engine.
Figure 1. Possibilities for the layout of the electric motors in EV’s
Figure 3. Equivalent circuit of an electric battery
Nowadays, there is under discussion the possibility of using
the EVs and the PHEVs in combination with renewable
energies. Specifically, it is proposed to charge the EV when
there is an excess energy from renewable sources. In addition,
it is also proposed to go a step further and use the batteries
from the EV connected to the grid as a power reserve and inject
power to the grid when it is needed. In order to make this
possible it is necessary to study the batteries of the electric
vehicles, chargers, the location of the charge points and the
standardization of the connectors (Fig. 2 shows a proposed
standard for a connector). The present paper makes a review of
all this items.
As Fig. 2 shows, the battery voltage decreases if it is
delivering power and the voltage increases if the battery is
charging.
B. Capacity
The capacity of a battery is the most important parameter
and it is usually expressed in Amphour. If a battery is of 10
Amphours, this means that it can provide 1 A for 10 hours.
However, the same battery would not deliver 10 A in 1 hour
because the capacity of a battery depends directly in the way
the energy is extracted; the quickest the energy is extracted the
less capacity the battery has.
C. Energy stored
One of the most important parameters of the batteries in
the field of the EVs is the energy stored because this
parameter is the responsible of the autonomy of the vehicle.
The energy stored in a battery depends on its voltage and on
its capacity. The unit for this parameter is Joules, but this is an
inconveniently small unit, so Watthour is used instead.
D. Specific energy
Specific energy is the quantity of energy stored in the
battery for every kilogram. The specific energy is typically
given in Wh·kg-1.
Figure 2. Connector of an electrical vehicle
II.
BATTERY PARAMETERS
Batteries were the limiting factor that led the electric
vehicle to disappear from the transport field; the component
that was the only energy storage was the component with the
highest cost, weight and volume. In addition, autonomies
reached by batteries were significantly lower than autonomies
of fuel powered vehicles. Below, a review of batteries and its
main parameters are presented in this section.
A. Battery voltages
The nominal voltage of a battery can be expressed by the
electric equivalent circuit of Fig. 3.
E. Specific power
Specific power is the amount of power obtained for each
kilogram of the battery and is measured in W·kg-1. It is
important to differentiate the specific power from the specific
energy: a high specific energy means that the battery can store
a high energy but this does not imply that the same battery can
provide the energy in a fast way which means it has a high
specific power. In Fig. 4 a Ragone plot shows the relationship
between the specific power and the specific energy of two of
the most used types of batteries (adopted from [1]).
A. Definitions
The main components of the charging station installation
are defined below.
1) Link Station
The link station links the General Protection Panel (GPP)
with the user installation. Therefore, the Link Station begins at
the end of the electrical connection
2) Charging Station
All the equipment designed to provide ca to electric
vehicles. It contains the plugs to connect the electric vehicle.
3) Control Center
Centralized system responsible for manage statistical data
and incidents of all the charging stations of the whole
installation.
Figure 4. Ragone plot two types of batteries
III.
REVIEW OF BATTERIES
V.
This section presents a review of batteries and the main
characteristics of each type.
The main types of batteries for commercial use that can be
considered to power an EV are (Table I) [2]: Lead – Acid
batteries, Ni – Cd batteries, Ni – MH batteries and Li ion
batteries. The cheapest type of battery is the Lead-Acid type.
However, its low specific energy makes this type of battery
inadequate for using them in EVs and PHEVs. The Ni-Cd
battery type has a better cycle number than the Lead-Acid type
but its specific energy is not high enough to use in EV’s and
PHEV’s. The Ni-MH and Li ion battery types have a good
specific energy (specially Li ion type) but they have a high
cost.
TABLE I.
Cost
Specific Energy (Wh·kg-1)
Voltage per cell
Charge current
Cycle number
(charge/discharge)
Autodischarge per month
(% of total)
Minimum time for charge
(h)
Activity requirement
Environmental warning
TYPES OF BATTERIES
Lead - Acid
Low
30 -50
2
Low
Ni - Cd
Medium
50 -80
1.25
Very Low
Ni - MH
High
40 -100
1.25
Moderate
Li ion
Very High
160
3.6
High
200 - 500
1000
1000
1200
Low (5%)
ModerateHigh (20%)
High (30%)
Low (10%)
8 - 16
1 – 1.5
2-4
2-4
180 days
High
30 days
High
90 days
Low
None
High
As it is mentioned in section 1, one of the biggest
challenges that arise in the introduction of electric vehicles in
cities is the standardization of the charging stations. The fact
that there are still no national laws governing standardization
makes difficult the implementation of the electrical vehicles.
The group CITCEA-UPC, in collaboration with the Energy
Agency of Barcelona (AEB), has developed a project to define
standard specifications for electric vehicle charging stations.
The specifications are mainly based on European [3] and [4].
One of the significant outcomes of this project was the
definition of charging points for underground parking and
charging points for surface parking because of the different
charging needs of the two locations
Another conclusion from the project is the need to create a
Europe standard which defines the type of connector to be
used by electric vehicles. Until a new standard gets develop, it
is proposed to use a SCHUKO (CEE 7/4) connector type for
currents up to 16A. In addition, to slow charging, the output
values of the charging station are up to 16 A per plug, 230 V ±
10%, and 50 Hz ± 1%.
REFERENCES
[1]
IV.
CONNECTION ISSUES
In order to achieve a good implementation of the electric
vehicle a definition of a standard charging station is needed.
The standardization process should guaranty:
Easy replication of the charging stations
Easy expansion of functions through a modular design
Safety for people and for the equipment
Interoperability between charge stations and electric
vehicles from different manufacturers
IMPLEMENTATION OF CHARGING POINTS FOR
ELECTRICAL VEHICLES IN BARCELONA
[2]
[3]
[4]
J. Larminie, J. Lowry, “Electric Vehicle Technology Explained”. John
Wiley & Sons Ltd, 2003.
Battery University.com: http://www.batteryuniversity.com/
Conductive charge system for electric vehicles (“Sistema conductivo de
carga para vehículos eléctricos”) (UNE-EN 61851)
Reglamento electrotécnico de baja tensión (Real Decreto 842/2002, 2 de
agosto de 2002)