An Electric Vehicle Charging Station: Monitoring
and Analysis of Power Quality
R. J. C. Pinto, J. Pombo, M. R. A. Calado and S. J.P S. Mariano
IT – Instituto de Telecomunicações
Department of Electromechanical Engineering
University of Beira interior
Covilhã, Portugal
rpinto@ubi.pt, jose_p@portugalmail.com, rc@ubi.pt, sm@ubi.pt
vehicle to the grid (regeneration). If properly designed and
controlled, EVs can provide ancillary services and support the
supply network, such as supply/demand matching and reactive
power support. This type of operation is part of a new concept
in power systems called the ‘smart grid’ [3].
Abstract—Electric vehicles are a relatively recent technology
that is seeking for its place in the market. It has several
advantages, such as the reduced greenhouse emissions, fuel
savings and its ease of use. The increase of the electric vehicles in
the roads raises issues about their impact on the grid, in terms of
power quality. This paper presents the main considerations about
power balance and the impact of an electric vehicle charge in the
voltage, current, and total harmonic distortion. An experimental
charging station prototype for Modes 2 and 3 is used to acquire
data of voltage, current and active and reactive power for
different charging profiles and battery state of charge.
EV interface devices may operate from a three-phase or
single-phase supply points. Single phase supply is widely
available and hence it is anticipated that chargers on EVs
would largely be powered from a single-phase supply in user’s
homes. On the other hand, three-phase supply provides a
larger power and hence faster charging, but the availability of
three-phase supply points is currently limited.
Keywords— charging stations, electric vehicles, power quality,
three-phase electric power, total harmonic distortion
Various developments have led to a different view at the
power system. These developments are strongly interrelated,
but the three main ones are, according to [4]: the electricity
deregulation (there is no longer one single system but a number
of independent companies with costumers); customers have
become more aware of their rights and demand low-cost
electricity of high reliability for different customers; electricity
generation is shifting away from large power stations
connected to the transmission system towards smaller units
connected at lower voltage levels.
I. INTRODUCTION
Environment protection and energy conservation have
urged the development of cleaner mobility technologies, as
Hybrid
Electric
Vehicles (HEV),
Plug-in
Electric
Vehicles (PEV), such as Plug-in Hybrid Electric
Vehicles (PHEV) and all Electric Vehicles (EV).
EVs are a new technology known as a zero emissions in its
use [1], and it is known for helping to reduce the air pollution
of the environment. The stringent constraints on energy
resources and environmental concerns will attract EVs and
HEVs and increase the interest from the automobile industry
and the consumer [2]. The demand of using rechargeable
batteries makes the development of battery chargers increase.
Battery chargers are highly non-linear devices due the presence
of switching power semiconductor elements and its operation
principles. The harmonic contents of the input current
generated from EV chargers are generally quite high and may
have adverse effect on electrical supply network or its
associated equipment.
PHEVs are a new and upcoming technology in the
transportation and power sector. As they are defined by the
IEEE, these vehicles have a battery storage system of 4 kWh or
more, a means of recharging the battery from an external
source, and the ability to drive several kilometers in all-electric
mode. These vehicles are able to run on fossil fuels, electricity,
or a combination of both leading to a wide variety of
advantages including reduced dependence on foreign oil,
increased fuel economy, increased power efficiency, lowered
greenhouse gas (GHG) emissions and vehicle-to-grid (V2G)
technology [5].
The growing of the utilization of the recent technologies
and the implementation of fast charging stations for EVs make
raise issues about the impact of those technologies. That is why
it is important to evaluate the power quality of the EV charging
station resulting from a vehicle charging process. Electric
power systems generate electrical energy to supply equipment
at an acceptable voltage. The term power quality came is use
refers to the other characteristics of the supply voltage, i.e.
EV employs use power electronics controllers that
interface the vehicle electric power system to the grid. These
controllers usually include an on-board Alternating Current
(AC) to Direct Current (DC) converter which is coupled to the
grid via a single or three-phase connector. The converter can
be either a diode bridge rectifier for charging the battery or a
switch-mode converter which not only controls the charging
of the battery, but is also capable of feeding power from the
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other than long interruptions occurred. Many authors are trying
to conceptualize the impact of a large scale EV implementation
in terms of battery costs [6] and in term of changing the quality
of grid power supply [7]–[9]
power in the circuit, and is a dimensionless number in the
closed interval of -1 to 1. Active power is the capacity of the
circuit for performing work in a particular time. In an electric
power system, a load with a low power factor draws more
current than a load with a high power factor for the same
amount of useful power transferred.
This paper shows the most important aspects of power
quality and presents the analysis of the obtained data from a
fast charging station. In the section II are exposed the most
important aspects to analyze in power quality of EV chargers.
The section III presents the obtain results showing graphical
information about power characteristics analyzed, and section
IV provides a conclusion.
C. Harmonics
The harmonics are a sinusoidal component of a periodic
waveform having a frequency that is an integer multiple of the
fundamental power frequency. Harmonic distortion of the
power waveform occurs when the fundamental, second, third
and other harmonics are combined. The result is voltage and
current contaminations on the sinusoidal waveform.
Harmonics are generated when nonlinear equipment draws
current in short pulses. The harmonics in the load current can
sometimes result in overheated transformers, overheated
neutrals, blown fuses and tripped circuit breakers (or breakers
failing to trip in some cases) [12].
II. POWER QUALITY
Power quality is an important consideration in the
reliability and security of the grids and more recently of the
smart grids which is likely to be heavily impacted by the
growth of PEVs over the coming years. EV interface devices
use power electronic converters and these are highly nonlinear devices due to their operating principles and the
presence of switching power semiconductor elements [10].
Therefore, the input current of the converter generally contains
high levels of harmonics and these are usually dealt with by
using PWM control and filtering. Manufacturers claim that
their converters produce good power quality (mainly with
regard to harmonics and power factor), both in charging and
regeneration modes [3].
Depending on the charging profile or mode of one or
multiple EV users, the harmonic levels may rise to drastic
levels that can increase stresses on grids. In addition to
harmonic distortions, EV charging may lead to unacceptable
voltage deviations, and additional fundamental and harmonic
power losses. EV charging is likely to take place in either
public or corporate car parks, electric charging stations, or at a
customer’s premises [8]. The total harmonic distortion, or
THD, of a signal is a measurement of the harmonic distortion
present and is defined as the ratio of the sum of the power of
all harmonic components to the power of the fundamental
frequency. THD is used to characterize the linearity of audio
systems and the power quality of electric power systems.
The most important aspects of power quality are the values
of voltage, current, active and reactive power, and the
harmonic content for voltage and current. To assume that the
energy has a good power level, these values should be
between the limits imposed by the standards.
III. PROCEDURE AND EXPERIMENTAL RESULTS
A. Voltage
Voltage quality is the quantitative form of describing
power quality and includes both steady-state power quality
variations and momentary disturbances that may impact loads.
Categories of voltage quality include: power frequency,
magnitude of the supply voltage, harmonics and
interharmonics, voltage unbalance, flicker, dips, swells,
momentary interruptions, and transients
Two collaborating research organizations in Covilhã,
Portugal, the University of Beira Interior and the company
Enforce – Engenharia da Energia, S.A., joined efforts to
develop a charging station and design a system with concepts
that are presently undergoing testing. It may be used to run
tests, and analyze different modes of operation (Charging
Modes 2 and 3). With this experimental setup was possible to
verify the impact on the connection point to the grid of the
charging station by analyzing voltage variation, current
variation, active power and reactive power variation and
harmonic contents.
Every country has different rules regarding distribution of
electricity for portable appliances and lighting. Voltage,
frequency, and plug type vary widely, but large regions may
use common standards. For Portugal, as well as in Europe, the
frequency of the voltage supply is 50 Hz and the voltage rated
value is 230 V. The EN 50160 [11] is the European standard
that defines the frequency, amplitude, waveform and the
symmetry of the three phase voltage, as well as other aspects
such as harmonic levels.
A. Materials
The vehicle used in the tests was the Renault ZOE.
According to the manufacturer's specification, this vehicle has
a tare of 1428 kg including the driver, the engine is a 65 kW
synchronous electric motor, the maximum torque is 220 Nm
with a top speed of 135 km/h; the payload capacity of the
battery is 22 kWh lithium-ion battery pack, and these features
give the vehicle an estimated range in suburban use of around
100 km in cold weather and 150 km in temperate
conditions [13].
B. Active and Reactive Power
The power system requires both types of power - real and
reactive - in order to operate properly. Reactive power flow is
needed in an AC transmission system to support the transfer of
real power over the network. In electrical engineering, the
power factor of an AC electrical power system is defined as
the ratio of the real power flowing to the load, to the apparent
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The charging station has the particularity of making use of
renewable energy with 20 photovoltaic panels installed in the
facility structure with 3.68 kW of connection power. This
micro generation is connected to the grid in order to partially
cover the load demand on charging.
B. Charging Station
C. Acquisition system
The Fluke 434 Series II was the analyzer chosen for the
tests. It is composed by four thin and flexible current probes,
capable of measuring up to 600 A in each phase and voltage
values up to 1000 V between phase and neutral. The device can
display data such as power factor, active and reactive power.
Fig. 1.
D. Methodologies
The fast charge of the vehicle battery was monitored in
terms of level of battery and elapsed time, as shown in Table I,
relative to the expected time for the complete charge as
indicated by the vehicle.
Charging station architecture.
The experimental tests were defined to analyze the behavior
of charging station for different initial battery state of charge.
The vehicle charge 2 stopped at 72 % of the battery capacity by
its action. An error occurred during the load and the vehicle
stopped the flow of current. This information was given by the
vehicle in its dashboard, and this might be security mechanism,
because of the high current values registered just before the
vehicle stopped the communication. This data was seen in the
acquisition data provide by the Fluke analyzer.
The charging station, as referred, is a prototype developed
by the University of Beira Interior and a private company,
which is located in the Health Science Faculty and it is
connected to a low voltage grid point with the architecture seen
in Fig. 1.
In the case of all electric vehicles and PEVs, the battery
capacity is still limited and thy must be recharged regularly.
The European Standards [14]–[17] establish the procedure for
EV charge and in what conditions by setting modes, as they are
described in Table I.
TABLE I.
Mode
Connection
1
Direct
2
Direct
In this work the charge 2 and charge 3 will be considered
due to their meaning in the power quality analysis. Particularly,
they allow understanding the impact to the grid of the first
period of charge (battery almost empty), with constant current,
and second period of charge (almost full), when the current
begins to decrease in steps. The other charges listed in Table II
have presented similar power quality characteristics.
ELECTRIC VEHICLE CHARGING MODES
Sockets
Power
Current
Local
Common
use
Common
with
special
cables
3.711kW
16A per
phase
Home
7.4-22
kW
16A 32A per
phase
3
Direct
Specific
sockets
4
Indirect,
using an
external
charger
Specific
sockets
14.843 kW
64A per
phase
DC
Home or
Public
Facilities
TABLE II.
Charge
Public
Facilities
only
Public
Facilities
only
1
2
3
4
5
6
The charging station follows the standards EN 61851-1 of
2011 and NP 61851-22 of 2013. The voltage does not exceed
690 V and the frequency is 50 Hz±1%. The station is able to
operate with temperatures between -30 ºC and 50ºC and a
relative humidity between 5% and 95%. The position of the
plug is 1m from the floor. The protection index of the charging
station is IP44 and it is prepared to work in Mode 3. This mode
implies a direct connection and control communication
between the vehicle and the grid, through specific charging
stations and it provides a maximum current of 64 A per phase
(14.8 – 43 kW). Due to technical requirements of the vehicle
the tests here presented were performed with a maximum
current of 32A in Mode 2.
VEHICLE CHARGES
Battery State of Charge (%)
Charging Time
(min)
Start of charging
End of charging
Real
Expected
63
11
49
67
79
91
100
72
98
98
98
98
71
43
38
34
19
9
30
65
40
25
20
10
IV. RESULTS
With the performed test were analyzed the active and
reactive power, the voltage and current evolution, and the
voltage and current harmonic contents.
A. Voltage and current
The Fig. 2 and Fig. 3 represent the line to neutral voltages
of charge 2 and charge 3, respectively. The values are near the
nominal voltage and the impact of the EV charging in voltage
was equivalent in all tested charges. The minimum and the
maximum values of each single phase are in the interval
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near the end of the charge, about 85 % of full charge, due to the
OCV–SOC battery characteristics.
imposed by EN 50160 [11], where the minimum value is the
nominal voltage supply (Un) minus 15 % and the maximum is
the nominal value plus 10 % ([Un-15 %; Un+10 %]). Once
one has the single phases in the standard levels is guaranteed
the values for the voltage measured between two phases are
also in standard levels. This voltage behavior was expected
since the charging station is located near a 1600 kVA power
transformer that supplies the Health Science Faculty.
Fig. 5. Current of fast charge 3.
B. Active and reactive power
The Fig. 6 and Fig. 7 represent respectively the behavior of the
active power and the reactive power during the battery
charge 2. The power profiles follow the charging current and it
is important to point out that a significant amount of reactive
power is delivered to the grid representing about 20 % of the
active power consumption.
Fig. 2. Voltages of charge 2.
Fig. 3. Voltages of charge 3.
The Fig. 4 shows the currents of the charge 2. As it is
possible to observe, the current is limited by the technical
requirements of the vehicle with a maximum current value of
32 A. As can be seen all the line currents have similar values.
In this case the charging process was forced to stop by the
vehicle (near 72 % of full charge) and the current immediately
goes to zero.
Fig. 6. Active power of fast charge 2.
Fig. 7. Reactive power of fast charge 2.
The Fig 8 and Fig. 9 represent respectively the behavior of
the active power and the reactive power during the battery
charge 3. Once more, the power profiles follow the charging
current, and the active power also decreases in steps, starting
from the 85 % of the full charge. Contrarily, the reactive power
increases in steps (the amount of reactive power delivered to
the grid increases). This means that for charges until 85 % of
full charge there is no significant differences in power profiles.
The power remains constant during all this period,
independently of the percentage of the battery charge in the
beginning of the charging process. In every charge, the data of
the reactive power shows that the charging station delivers
reactive power to the grid in about 20 % of the active power.
Fig. 4. Current of fast charge 2.
The Fig. 5 shows the currents of the charge 3. Also, the
current is limited by the technical requirements of the vehicle
with a maximum current value of 32 A, and all the line currents
have similar values. In this case, the current decreases in steps
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3 %, where the maximum value is 8 % imposed by the
standard. For the individual harmonics, all the values are under
the standard maximum value.
Fig. 8. Active power of fast charge 3.
Fig. 11. Voltage harmonics of fast charge 3.
The Fig. 12 and Fig. 13 show the histogram of the
harmonic contents of the currents in charge 2 and charge 3,
respectively. International studies have collected data resulting
in an estimation of typical harmonic contents often encountered
in electrical distribution networks. According to the opinion of
many utilities, a number of THD values for the current
correspond to some phenomena in the installation, as follows
[18]: THD under 10 % is considered as a normal situation, with
no risk of malfunctions; THD between 10 % and 50 % is a
significant harmonic pollution with a risk of temperature rise
and the resulting need to oversize cables and sources; THD
higher than 50 % is a major harmonic pollution and
malfunctions are probable and in-depth analysis and the
installation of attenuation devices are required. For the two
considered charges, the current THD registered high values in
all lines, near 20 %. Thus, both charges are with a significant
harmonic pollution. For the individual harmonics, the H5 and
H7 are in the range of significant harmonic pollution, but in the
border line of the normal situation, while the remaining
harmonics are in normal situation.
Fig. 9. Reactive power of fast charge 3.
With the increase of the reactive power delivered to the
grid, in the last 15 % of the charge, the associated power factor
significantly decreases. This way we can conclude that the
behavior of the charger has a much resistive character in the
beginning, while the power factor value stays near to 1, and a
strong capacitive character when the power factor decreases its
value to near zero.The decreasing of the value of the active
power makes the charging more slow to minimize the
deterioration of the battery capacity to store energy.
C. Voltage and current harmonics
The Fig. 10 and Fig. 11 represent the harmonic content of
voltage, respectively for charge 2 and charge 3. The harmonics
present harmonic content up to the 49th order. However, from
the 9th in voltage and from the 17th order in current, the
harmonics have residual values and so, they are not significant.
For the voltage harmonics, the THD has registered less than
Fig. 12. Current harmonics of fast charge 2.
Fig. 10. Voltage harmonics of fast charge 2.
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REFERENCES
Fig. 13. Current harmonics of fast charge 3.
When comparing the THD of the two charges it is observed
that the charge 3 is more pollutant than the charge 2. This way
we can conclude that the most influent period with respect to
the harmonic pollution is the end of the charge (above 85 % of
full charge).
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V. CONCLUSIONS
This paper presented the main considerations about power
balance and the impact of an electric vehicle charge in the
voltage, current, active and reactive power, and total harmonic
distortion, based on experimental data.
When the battery comes close to the complete charge is
possible to identify the increase of reactive power delivered to
the grid and the charger has a much resistive character in the
beginning, while the power factor value stays near to 1, and a
strong capacitive character when the power factor decreases its
value to near zero. This way we can conclude that an EV fast
charging station could be a good power factor compensator in
big industries. The oscillations in the final part of the charging
are noticeable. This is trying to tell us this vehicle can come to
operate within the recent technology of V2G once it easily can
deliver power to the grid.
For the voltage harmonics, the THD and all the individual
harmonic contents have registered values less than 3 %, which
are very good values. For the current harmonics, the THD
registered high values, near 20 %, a significant harmonic
pollution. For the individual harmonics, the H5 and H7 are in
the range of significant harmonic pollution, but in the border
line of the normal situation, while the remaining harmonics
are in normal situation. This scenario has a risk of temperature
rise and the resulting need to oversize cables and to establish
requirements for the station grid connection.
ACKNOWLEDGMENT
The authors would like to thank Eng. João Nuno Serra,
CEO of Enforce – Engenharia da Energia SA, Portugal, for its
collaboration and making available the electric vehicle and the
power quality analyzer.
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