SMART BATTERY CHARGER FOR ELECTRIC MOBILITY
IN SMART GRIDS
Vítor Monteiro
1
, João C. Ferreira
2
and João L. Afonso
3
1,3
Centro Algoritmi, Univ. of Minho, Guimarães, Portugal
2
ADEETC, ISEL, Lisboa, Portugal
Keywords: Smart Grids, Electric Vehicles, Smart Batteries Charging, Vehicle-to-grid, Grid-to-vehicle, Electric
Mobility, Power Quality.
Abstract: In this paper is presented the development of a smart batteries charger for Electric Vehicles (EVs) and
Plug-in Hybrid Electric Vehicles (PHEVs), aiming their integration in Smart Grids. The batteries charging
process is controlled by an appropriate control algorithm, aiming to preserve the batteries lifespan. The main
features of the equipment are the mitigation of the power quality degradation and the bidirectional
operation, as Grid-to-Vehicle (G2V) and as Vehicle-to-Grid (V2G). During the charging process (G2V), the
consumed current is sinusoidal and the power factor is unitary. Along the discharging process (V2G), when
the equipment allows delivering back to the electrical power grid a small amount of the energy stored in the
batteries, the current is also sinusoidal. The V2G mode of operation will be one of the main features of the
Smart Grids, both to collaborate with the electrical power grid to increase stability, and to function as a
distributed Energy Storage System (ESS). The functioning of the smart batteries charger is shown through
simulation and experimental results, both during the charging (G2V) and the discharging (V2G) modes of
operation. Also in this paper are shown and briefly described the roles of the key concepts related with the
Smart Grids in terms of Systems and Functional Areas, Power Electronics Systems, and Electric Mobility.
1 INTRODUCTION
The upcoming reality of smart grids and electrical
power markets will raise a diversity of advantages to
the end-user, because he isn’t longer a passive client.
However, it will require several developments and
studies aiming the integration of smart grid, users,
electricity markets and others. The Electric Vehicles
(EVs) and the Plug-In Hybrid Electric Vehicles
(PHEVs) are seen as one of the most promising
means in order to improve the sustainability of the
transportation and energy sectors in near-term
(Bradley, 2009).
In an overview, the smart grid is a conjunction of
technologies that allows the application of the
Information and Communication Technology (ICT)
to the electrical power grid, allowing predict the
energy demand and control the production. It
consists in transform the electrical power grid
through information technology using advanced
communication techniques and control algorithms,
transforming the grid on a coordinated,
collaborative, and automatic infra-structure
(Sekyung et al., 2010), (Ferreira et al., 2011). The
European Technology Platform Smart Grids
(ETPSG) defines the Smart Grid as “an electricity
network that can intelligently integrate the actions of
all users connected to it – generators, consumers and
those that do both, in order to efficiently deliver
sustainable, economic and secure electricity supply”
(ETPSG, 2010).
Specifically, the Smart Grid involves the
installation of different devices, tools and
technologies in the electric power grid in order to
establish a bidirectional flux of information’s about
the operation and performance of the grid, from the
generation to the transmission and distribution grid,
improving in this way, the reliability, the security
against to physical and cyber-attacks and major
natural phenomena (e.g. hurricanes, earthquakes,
and tsunamis), and the efficiency.
In a Smart Grid, one of the main features is the
efficiency, which to the concessionary companies
implies less energy losses to have the same level of
the service quality provided to the clients. Increasing
the efficiency, it is also possible reduce the costs and
101
Monteiro V., C. Ferreira J. and L. Afonso J..
SMART BATTERY CHARGER FOR ELECTRIC MOBILITY IN SMART GRIDS.
DOI: 10.5220/0003954301010106
In Proceedings of the 1st International Conference on Smart Grids and Green IT Systems (SMARTGREENS-2012), pages 101-106
ISBN: 978-989-8565-09-9
Copyright
c
2012 SCITEPRESS (Science and Technology Publications, Lda.)
reduce the emission of greenhouse gases. With a
great amount of information about the generation
and distribution system and the customers habits it is
possible define operation strategies and control
algorithms to the electrical power grid in order to
control the system demands and costs, while
increasing energy efficiency and assuring an optimal
power quality for all clients.
Aiming the reliability in the electrical power
grid, with the constant monitoring of the grid, it is
possible detects and identifies when the Smart Grids
equipment’s are starting to fail or the performance is
in decline, and with this allows correct the problems
avoiding damages to the electrical power grid and to
the clients. In a Smart Grid scenario it will also be
possible detect a failure and locate it with precision,
allowing repair the problem fast or isolating the
impact of the problem protecting the maximum
number of clients possible.
Through a smart control and smart meters in
Smart Grids, will allow the integration in large scale
of renewables reducing the environmental impact of
production, and the integration of EVs and PHEVs
(Clement, 2009), that can interact with the electrical
power grid as isolated loads or as Energy Storage
Systems (ESS). Nowadays, with the increase bet in
EV and PHEV, the actual electrical power grid is
facing new challenges, forcing to a wide efforts of
investigation in different directions aiming the
electric mobility. In this context, the electric power
industry is also facing a challenge motivated by the
need to adopt policies to reducing the impacts of
global climate change, and the need for energy
security reached with the reduction of imbalances
between the supply and demand. Thereby, aiming
this challenge, in this paper is presented a smart
batteries charger, that can be implemented in EVs or
PHEVs, and that allows mitigate problems
associated with power quality (as distorted current
consumption and low power factor), contributing to
the efficiency and reliability of the electric mobility
in Smart Grids. This smart batteries charger, unlike
typical chargers, consumes sinusoidal current with
unitary power factor, and allows bidirectional
functioning as Vehicle-to-Grid (V2G).
2 SMART GRIDS
In Figure 1 are shown three technological areas
associated to Smart Grids: Systems and Functional
Areas (Carvalho, 2011); Power Electronics Systems
(Bollen et al., 2010); and Electric Mobility.
Figure 1: Smart Grids: Systems and Functional areas;
Power Electronics Systems; and Electric Mobility.
2.1 Systems and Functional Areas
In a Smart Grid context with the increasing of the
energy efficiency in the production, in the
transmission and distribution system, as well as in
the consumption, results in a significant reduction of
energy consumption. To achieve this goal several
systems and functional areas in Smart Grids should
be taken into account.
2.2 Power Electronics Systems
The currently electrical power grid consists in the
conventional sources of energy and some sources of
renewables. However, in a Smart Grid context, this
scenario will be integrated with thousands sources of
renewables through the microgeneration, allowing
reduce the use of the energy transmission and
distribution system and the losses associated. It will
be also capable of autonomous operation with
communication with the grid or as an isolated grid.
To integrate the microgeneration in a Smart Grid
context it is necessary the use of equipment’s based
on power electronics, in order to converter the
energy from the renewables into energy to be
delivered to the electrical power grid.
With the advancements in the field of power
electronics, combined with proper control
algorithms to the integration on the electrical power
grid, there are a large variety of operations and
options to the Smart Grid, aiming an efficient
management. In Figure 2 is shown an application
example of power electronics in Smart Grids,
considering typical houses with or without EV and
renewables, typical industries, industries with
SMARTGREENS2012-1stInternationalConferenceonSmartGridsandGreenITSystems
102
Figure 2: Power Electronics in Smart Grids.
interface to renewables, parking to EV charging with
interface with renewables and ESS, and the a data
center to collect the data from the monitors in each
point of consumption. The power flux with the
electrical power grid can be unidirectional or
bidirectional. Then are defined some of the most
important low power equipment’s associated with
power electronics in Smart Grids.
2.3 Electric Mobility
The EV smart charging technology, essentially, will
allow the communication of EVs with local utilities
to ensure that the batteries are charged when the
electricity is cheapest and the impact on the grid is
smallest. The use of computerized charging stations
which constantly monitor the EV charging process
to optimize the charging rate it will be extremely
important to preserve the batteries lifespan.
The concept Grid-to-Vehicle (G2V) is the
simplest process to integrate the EV and PHEV in
the electrical power grid. It is not absolutely required
communication between both and only exist flow of
energy from the electrical power grid to the vehicles.
Nowadays, this is the most common procedure to
charge the batteries of EV and PHEV, and it will be
the first approach to the massive integration of these
vehicles.
The concept V2G consists in the bidirectional
flux of energy between EV and PHEV and the
electrical power grid. With the massive adoption of
EV and PHEV, the batteries charging process needs
assistance of an intelligent process in order to find
the periods with cheaper prices to charge batteries,
to identify the available charging slots (in public
areas), and to provide other useful information to the
drivers, as their historic use. The Mid-Atlantic Grid
Interactive Cars Consortium (MAGICC) defines
V2G as a technology that utilizes the stored energy
in the EV batteries to contribute with electricity back
to the grid when the grid operators request it
(MAGICC, 2011). This technology makes an
interaction between vehicles and grid, in order to
control the needs of both.
The concept Vehicle-to-Home (V2H) is similar to
the V2G concept; however it can avoid the grid
infrastructure and the electricity tariff problems
associated with V2G, because the bidirectional flux
of energy is between the vehicle and the house.
Thereby, V2H can be used to manage and regulate
the profile of electricity demand in the house,
controlling the use of the loads and the stored energy
available in the vehicle.
A specific version of V2G, denominated Vehicle-
to-Building (V2B), is a concept that consists in use
the stored energy in the batteries of EV and PHEV
as an energy source of back-up to compensate the
energy consumption profile in commercial scale
(e.g. when the vehicle is parked to the driver go
work or go shopping).
3 PROPOSED SMART CHARGER
EVs and PHEVs are becoming a part of the electric
power grid day by day, and consequently, the
chargers for these vehicles have the ability to make
this interaction better for the consumer and for the
grid. A battery charger is a device that is composed
of one or more power electronics circuits used to
convert the AC electrical energy into DC with an
appropriate voltage level so as to charge a battery. It
has the potential to increase charging availability of
the EVs and PHEVs since it can operate as universal
converter accepting different voltage and power
levels. An advanced charger performs several
functions in addition to the charging operation for
better grid integration, mainly taking into account
the power quality. Independently the level of the
charging, to the integration of the EVs and PHEVs
in a Smart Grid context aiming the power quality,
the chargers should consume sinusoidal current with
unitary power factor.
To single-phase converters, the most common
converter with a sinusoidal current consumption and
unitary power factor is implemented with the boost
converter with proper control algorithms. In (Wei,
1998) are compared the basic converter topologies
for Power Factor Correction (PFC) (buck, boost,
buck-boost, flyback, forward, cuk, sepic, and zeta).
On other hand, there are also three-phase solutions
with PFC capability.
Focusing the EVs and PHEVs converters with a
bidirectional mode of operation, in (Wiedemuth et
al., 2007) are presented single-phase bidirectional
SMARTBATTERYCHARGERFORELECTRICMOBILITYINSMARTGRIDS
103
Figure 3: Schematic of the developed batteries charger.
AC-DC converters for PHEVs applications, and in
(Kisacikoglu, 2010) is made an examination of a
PHEV bidirectional charger (on-board) system for
V2G reactive power compensation, however, this
compensation only have interest for particular cases,
because the main goal of the V2G is delivering to
the electrical power grid active power.
The bidirectional power converter proposed to
charge the batteries is composed by two power
electronics converters, one AC-DC and other
DC-DC. In Figure 3 is presented the schematic of
the EV batteries charger developed. This charger
consumes sinusoidal current with unitary power
factor, has fewer components when compared to
more complex topologies, and allow the
bidirectional functioning.
The control system has as main function
implement the control algorithms. For this purpose,
the input current, the voltage in the DC bus, and the
voltage and current in output are the main variables
to be controlled by the control algorithm. The
system control receive these signals from the
conditioning circuit (used to adjust the voltage levels
of the signals), and through the microcontroller
(Texas Instruments DSP), are processed the control
signals to the command circuit (which as a function
adapt the microcontroller signals to the IGBTs
drivers and control the signal of the errors detector
circuit), and then are generated the pulses to the
IGBTs.
4 SIMULATIONS RESULTS
In order to analyse the behaviour of the proposed
converter was made different simulations using the
simulation tool PSIM. For all simulations was used
an electric model of the AGM (Absorbed Glass Mat)
batteries with nominal voltage 204 V and nominal
capacity 33 Ah, making a 6.7 kWh bank of batteries.
The results obtained in simulation during the
charging process are shown in Figure 4. As shown,
the consumed current is sinusoidal and in phase with
the voltage.
The results obtained in simulation during the
discharging process are shown in Figure 5. As
shown the current is sinusoidal and in phase
opposition with the voltage.
5 EXPERIMENTAL RESULTS
The principle of functioning of the proposed
bidirectional batteries charger was demonstrated in
simulations in the previous item. Thus, in this item,
is presented the developed prototype and is
described its hardware, mainly the bidirectional
power converter and its control system, and are
shown experimental results of the developed
prototype obtained with the oscilloscope Yokogawa
DL708E. These results were obtained with AGM
(Absorbed Glass Mat) batteries with nominal
voltage 204 V and nominal capacity 33 Ah, making
a 6.7 kWh bank of batteries, which are in a
prototype of an EV.
Figure 4: Simulation results: voltage and current in the
electrical power grid during the charging process (G2V).
Figure 5: Simulation results: voltage and current in the
electrical power grid during the discharging process
(V2G).
5.1 Developed Prototype
A prototype of the bidirectional batteries charger
was developed in laboratory. It consists in two
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104
bidirectional power converters, one AC-DC and
other DC-DC. The bidirectional power converter is
composed by IGBTs modules (two modules to the
AC-DC converter and the other one to the DC-DC
converter). The IGBTs drivers, the snubber
capacitors, the heatsink, and the current and voltage
filters, are also part of the bidirectional power
converters. The control system is composed by the
DSP TMS320F28335, the command circuit which
receive the signals from the microcontroller and
through a control logic combined with the errors
signals process the signals to the IGBTs drivers, and
the signal conditioning circuit to adjust the signals
from the sensors and to detects errors.
In Figure 6 is shown the prototype of the
bidirectional batteries charger that was developed in
laboratory. Currently, this prototype is under test at
an EV. To charge the batteries, was used the
algorithm presented in the flowchart of the Figure 7
and which consist in 3 distinct stages of voltage and
current. As shown in Figure 8, in steady state, the
consumed current (i
i
) is sinusoidal and in phase with
the voltage (v
i
). As intended the output voltage (v
o
)
is constant. To discharge the batteries, in order to
preserve their lifespan, they were only discharged
until 20% of their SoC, which correspond to an 80%
of Depth of Discharge (DoD). In Figure 9 is shown
the obtained results to the electrical power grid
voltage (v
i
), to the consumed current (i
i
), and to the
discharging voltage of the batteries (v
o
), during a
short period, when part of the stored energy in the
batteries is delivered back to the electrical power
grid. As shown in figure the injected current is
sinusoidal and in phase opposition with the electrical
power grid voltage.
Figure 1: Developed prototype of the smart bidirectional
batteries charger.
Figure 7: Flowchart of the algorithm (with 3 distinct
stages of voltage and current) used to charge the batteries.
Figure 8: Experimental results: batteries charging process
(G2V): electrical power grid voltage (v
i
), consumed
current (i
i
), and charging voltage at the batteries (v
o
).
SMARTBATTERYCHARGERFORELECTRICMOBILITYINSMARTGRIDS
105
Figure 9: Experimental results: batteries discharging
process: electrical power grid voltage (v
i
), consumed
current (i
i
), and discharging voltage at the batteries (v
o
).
6 CONCLUSIONS
In this paper was presented a smart batteries charger
for Electric Mobility, which can be used with
Electric Vehicles (EVs) and Plug-in Hybrid Electric
Vehicles (PHEVs), aiming their integration in Smart
Grids, allowing mitigate the power quality
degradation and functioning in bidirectional mode.
During the charging process the consumed
current is sinusoidal with unitary power factor, and it
is possible to control the voltage and the current in
the batteries through an appropriate control
algorithm, in order to preserve the batteries lifespan.
Beyond the charging process, it is also possible to
discharge a small part of the stored energy in the
batteries back to the electrical power grid, which in
the near future, taking into account the Vehicle-to-
Grid (V2G) concept in Smart Grids, can be an
interesting solution during short periods of times
when occur peaks of energy demand in the electrical
system, as well as to work as a distributed Energy
Storage System (ESS). The operation of the smart
batteries charger is shown through simulation and
experimental results.
Also in this paper was briefly described and
shown the key concepts related with the Smart Grids
in terms of Systems and Functional Areas, Power
Electronics Systems, and Electric Mobility.
ACKNOWLEDGEMENTS
This work is financed by FEDER Funds, through the
Operational Programme for Competitiveness Factors
– COMPETE, and by National Funds through FCT –
Foundation for Science and Technology of Portugal,
under the project PTDC/EEA-EEL/104569/2008 and
the project MIT-PT/EDAM-SMS/0030/2008.
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