Design and dynamic simulation of a wind turbine powered electric vehicle charging system

Abstract

These days, electric vehicles (EVs) are popular, and there is a need to increase the number of charging stations for EVs. Newfoundland has considerable potential for wind energy to charge EVs. The design of such a system and its dynamics are described, and simulation results are provided in this paper.

Full text

Presented at 30th IEEE NECEC conference November 18, 2021, St. John's, NL
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Design and dynamic simulation of a wind turbine
powered electric vehicle charging system
Amirhossein Jahanfar
Department of Electrical Engineering,
Faculty of Engineering and Applied Science
Memorial University of Newfoundland
St. John’s, NL, Canada
ajahanfar@mun.ca
M. Tariq Iqbal
Department of Electrical Engineering,
Faculty of Engineering and Applied Science
Memorial University of Newfoundland
St. John’s, NL, Canada
tariq@mun.ca
Abstract— These days, electric vehicles (EVs) are popular, and
there is a need to increase the number of charging stations for EVs.
Newfoundland has considerable potential for wind energy to
charge EVs. The design of such a system and its dynamics are
described, and simulation results are provided in this paper.
Keywords— electric vehicles, wind turbine, charging station,
Homer Pro, Simulink
I. INTRODUCTION
For past decades, humanity faces a wild rise in CO2 and
other greenhouse gas emissions, resulting in irreversible
consequences. One of the most efficient ways to prevent climate
change is replacing fuel cars with electric vehicles(EVs). The
EVs are environmentally friendly, quieter, and easier to operate
compared to conventional vehicles (CVs).
It should be noted that electric vehicles need electrical power
to run, and if conventional power plants are used to provide this
energy, it probably results in more air pollution (due to low
efficiency at a conventional power plant and power loss at the
network). According to what is said, it is wise to use green
energy (like PV and WT) to provide power for EVs. This
research will design a charging system for electric vehicles
based on wind energy for St. John’s to achieve this goal.
It goes without saying that St. John’s is one of the windiest
cities in the world, so it is logical to take advantage of the nature
of this city. The average wind speed of St. John’s for a period of
12 months between Aug 2020 to Aug 2021 is 24.96 km/h [1].
In this paper, first, Wind turbines and wind energy
conversion systems are reviewed. Then, an overview of Electric
Vehicle systems and the standard AC and DC Charging systems
are provided. The proposed scheme and system sizing using
Homer Pro, are discussed in part4. The result of Simulink is
provided in part 5. In the end, essential system protection is
described.
II. WIND TURBINE
A. Wind turbine classification
There is different structure of wind Turbine which are
classified at two types, Horizontal Axis Wind Turbine(HAWT)
and Vertical Axis Wind Turbine (VAWT) :
1. Horizontal Axis Wind Turbine: HAWTs are used
widely because they tap more wind energy (from only
one direction), so make them more economical than
VAWT [2]. The main components of HAWT are
blades, Nacelle, and foundation tower.
2. Vertical Axis Wind Turbine: although HAWTs are
more economical, VAWTs are more portable [2] and
take less space to install. These kinds of wind turbines
tap wind energy from any direction. VAWT is usually
used at stand-alone systems to supply individual
households with electricity, heat, and even pumping
water [4]. Varies designs of VAWTs are available, like
Straight-bladed Darrius VAWT. Table 1 compares the
advantages and disadvantages of HAWTs and VAWTs
Table 1: A comparison of 2 types of wind turbine structure
Turbine
design
Advantages
Disadvantages
HAWT
• Full range from
watt to megawatt
• Yaw control [2]
• Blades pitch
control
• More efficient and
economical [2]
• Emission of the
sound [2]
• It is heavier
and cannot
produce well in
turbulent winds
[2]
VAWT
• Usually are built in
small size, so they
easily can be
mounted on a
rooftop
• Simple design (no
yaw or pitch) [4]
• Gearbox,
generator, etc. are
installed on the
ground (easy to
install and
maintain)
• Usually are
installed low to
ground (wind
speed is low at
ground level)
• Not all of the
blades produce
torque at the
same time
(Pulsating
torque)

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B. Typical wind energy conversion systems
On the basis, there are two categories of wind turbines, 1-
fixed speed wind turbine 2- variable speed wind turbine. Until
the mid-1990s, most of the installed wind turbines were fixed
speed ones, based on squirrel cage induction machines directly
connected to the grid, and the generation was always done at
the constant speed [3]. Today, most of the installed wind
turbines are variable speed ones, which are based on three
typical electrical systems, 1- permanent magnet synchronous
generators (PMSGs), 2- squirrel cage Induction generator
(SCIG) 3- doubly-fed induction generator (DFIG). Table 2
shows these configurations:
Table 2: A comparison of varies electrical generation configure
topologies
Advantages
Disadvantages
PMSG
&
WRSG
• Brushless
(requires less
maintenance)
• Can operate at a
full range of
wind speed (due
to full-scale
converter)
• Full converting
system
DFIG
• Partial
converting
system (needs a
converter to deal
with about 30%
of rated power)
[3]
• Fully Control of
active and
reactive power
independently
• Needs slip-
rings
• Limited speed
( around -
30% to +30%
of synchronous
speed)
III. ELECTRIC VEHICLE(EV) AND CHARGING SYSTEM
A. Electric Vehicles (EVs)
There are four types of EVs, including Battery Electric
Vehicle (BEV), Hybrid Electric Vehicle (HEV), Plug-in Hybrid
Electric Vehicle (PHEV), Fuel Cell Electric Vehicle (FCEV)
[5]:
• Battery Electric Vehicle: BEVs are the fully electric
vehicle which their energy provided only by their
rechargeable battery. It means, once the battery is fully
charged, it can drive until it uses all battery stored
energy. Typically, they can cover 100 km–250 km on
one charge [6].
• Hybrid Electric Vehicle: HEVs use both an internal
combustion engine (ICE) and an electric machine.
There are three different configurations, series,
parallel, and series-parallel [7].
• Plug-in Hybrid Electric Vehicle: In the beginning,
PHEV starts at fully electric mode, and all the
propulsion energy comes from batteries; when battery
energy reaches a specified low level, the ICE starts
until the end of the trip [8]. The batteries can be
charged through both regenerative braking and
plugging in (utility grid).
B. Charging systems
For charging of EVs, DC or AC systems can be used [5].
There is various kind of charging systems for EVs, and they
are categorized as level 1, level 2 and level 3 charging (based
on level of voltage and current) [9].
• AC Charging system: it provides an AC power supply
according to the SAE J1772 standard (Society of
Automotive Engineers). This system usually uses an on-
board charger; it means EV’s charger is installed inside
the vehicle, and EV is plugged into an AC outlet at the
charge station [10]. There is 3 level of AC charging
system [5]:
o Level 1: voltage 120V single phase, the
current between 12A to 16A
o Level 2: voltage between 208V and 240V
single phase, current up to 80A
o Level 3: voltage 208,480 or 600V three-phase,
current up to 400A
• DC Charging system: it provides a DC power supply
according to the SAE EV DC Charging standard. This
system usually uses an off-board charger which is fixed
at the charging station [10]. Similar to AC charging
systems, DC charging systems are at three levels [5]:
o Level 1: voltage 200V-400V, current up to
80A
o Level 2: voltage 200V-400V, current up to
200A
o Level 3: voltage 200V-600V, current up to
400A
IV. PROPOSED SCHEME AND SYSTEM SIZING
So far, the main concepts of wind power systems and EVs
are given. This research is aimed to design an EV charging
station; consists of a wind turbine and its tower, converter, and
battery to provide sufficient power for charging an EV like Kia
e-Soul.
A. Main component and specifications
1) Wind Turbine: Wind turbine is the most important part
of the system because the wind turbine provides the whole
energy. The Bergey EXCEL 10 is selected because:
o A wind turbine with at least 7 KW for its nominal
output power is needed to minimize the battery
bank.
o The Bergey company is one of the professional
companies.
o This is one of the few small wind turbines which
has SWCC Certification.

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Table 3: The Bergey EXCEL 10 specification
specification
Value
Reference Rated Power
10 kW
AWEA Rated Power
8.9 kW at 11.176 m/s
AWEA Rated Annual
Energy
13,800 kWh at 4.9 m/s
average
AWEA Rated Sound Level
42.9 dB (A)
Cut-in Wind Speed
2.2 m/s
Cut-out Wind Speed
none
Peak Power
12.6 kW at 12.5 m/s
Max. Design Wind Speed
59.5 m/s
Design Operating Life
30-50 years
Turbine Rotor Diameter
7 m
Nominal output voltage
240 V AC 1phase
Voltage frequency
60Hz
2) Inverter: The inverter is the heart of the system which
not only converts AC/ DC in both directions, but also controls
the battery's state of charge and adjusts output voltage and
frequency. A hybrid inverter named “Schneider - XW Pro 8.5
kW Hybrid Inverter 230V” is chosen for this project. This
inverter is used to:
o Convert input 200-240V AC to 48V DC for charging
the batteries
o Once the system needs energy from the batteries, it
Converts input 48V DC to 230V AC
o It fixes the output voltage with pure sin waveform
o It controls the battery charging process
3) Battery: To build a 48VDC back-up energy system, a
series of 4 number 12V batteries is needed. So, Trojan SAGM
12 205 battery is used. This battery has a reasonable capacity
and a high lifespan.
4) Load: The aim of this work is that to design a charging
station for Kia e-Soul. This is an EV car that is equipped with
a 39.2KWh or 64KWh battery. This car supports both AC
(Level2) and fast DC charging (Level3) systems.
B. Sizing and analysis
Homer Pro is used for sizing the system. Homer pro is a
powerful software for designing an optimum microgrid that
provides the models of different wind turbines, solar panels,
customized load profiles, and NASA resources data. The
simulation properties are as follow:
1. Location: A spot at the Avalon Mall parking lot is
chosen where it has the least wind obstruction and is
easy to install the tower.
Figure 1: Proposed installation location
2. Load: the assumption is that one of the Avalon mall
employees will charge its EV car for 6 hours, from 9
AM to 2 PM. So the charging station is supposed to
handle this demand every day. As mentioned
previously, the charging station should provide
7.2KWh to charge the Kia e-Soul
3. Wind turbine: as mentioned earlier, Bergey Excel 10
is used which the full model of this WT is available at
Homer Pro. The hub height and lifetime are adjusted to
24m and 30 years, respectively.
4. Battery: As well as the WT model, Trojan SAGM 12
205 is available at Homer Pro. The string size should
be 4 to build a 48V DC bus.
5. Inverter: exact model of Schneider - XW Pro 8.5 kW
Hybrid Inverter 230V was not available at Homer Pro,
So the Schneider Conext XW+8548 is used instead,
which has similar properties.
Figure 2: System scheme at Homer Pro
C. Sizing Result
Homer Pro does the calculation, and the result is as
follow:
Homer proposed a system consisting of one Bergey Excel
10, a 7.8 kW inverter, and 40 Trojan 205 batteries in 10 strings.
The project cost is estimated at 145000 CAD.
Figure 3: Homer pro analysis result
Figure 4: Project estimated expenses
As shown in Figure 4, batteries have a significant share in
expenses, so it is possible to decrease the expenses if they ignore
the system back-up or reduce the back-up power. Figure 5
shows that most electric production is during the winter when
the wind speed in St. John’s is at maximum.

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Figure 5: Electrical power flow
V. DYNAMIC SIMULATION IN SIMULINK
In the previous section, the sizing and steady-state analysis is
done. In this part, we will make a dynamic system model on
Matlab Simulink and provide its results. The simulation is done
with the help of prepared models, customized models, and
modifications on Matlab examples and models.
1) The main components of this system are:
➢ Wind turbine [11]
➢ Gearbox [11]
➢ Permanent magnet synchronous generator [11]
➢ AC/DC/AC inverter
➢ Bidirectional DC/DC converter [12].
Figure 6: Complete system
Figure 7: Wind turbine Subsystem consists of turbine, gearbox, PMSG model
2) The Simulink Result:
The main result of dynamic analysis in Simulink are
depicted as follows:
Figure 8 shows that after transient time when both
electromagnetic and mechanical torque follow each other,
the rotational speed reaches to its nominal speed.
Figure 8: a) Electromagnetic torque (Yellow) and mechanical torque
(Blue) b) Rotational speed
Figure 9: a) Voltage signal of the load b) Current signal of the load
c) Output voltage of inverter d) Voltage of DC bus
Also, Figure 9 depicts that after transient time, the load is
powered by a pure sinusoidal voltage, and voltage at a DC
bus is controlled at a constant value. As a result, the
dynamic study of designed an EVs charging station shows
that this system is reliable and efficient.
VI. SYSTEM PROTECTION AND CONTROL
All electrical systems need to be controlled and protected
to guarantee the system reliability and efficiency. There are
some simple but vital protection tools and control system
which will be addressed in the following:
A. system protection
a) AC and DC fuse: it is a safety device installed in
series to protect the overflow of current.
b) Circuit breaker: A circuit breaker is a safety device
that automatically switches off to protect an electrical circuit
from damage caused by excess current from an overload or
short circuit. It mainly works with electromagnetic principles.
c) Grounding: all standard systems are supposed to
provide a grounded wire to protect both humans and the system.
d) Surge and lightning arrester: this device captures the
lightning to protect the system from a surge voltage.
Figure 10: Scheme of protection system

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B. Control system
the mentioned system is equipped with a small wind turbine and
PMSG generator, so there is not yaw or pitch angle controller.
Since this system has a battery bank, a control system for
batteries is needed; this control system consists of two
subsystems:
1. Bidirectional DC/DC controller: this controller adjusts and
fixes the voltage at the battery side. Even if the DC bus
voltage changes, the battery side voltage remains constant.
Figure 11: Bidirectional DC/DC control system
2. Battery over charge/discharge controller: this part of
the system controls the battery's state of charge to
protect the battery against overcharge or over-
discharge. When the SOC excide 80%, the battery
stops charging, and when the SOC drops under 20%,
it prevents the battery from discharging.
Figure 12: Battery charge control and protection system
Figure 13: Battery charging system
It should be noted that both mentioned control functions are
done by the Schneider hybrid inverter, and figures 11 to 13
depict a simple model of the inverter subsystems.
VII. CONCLUSION
In this research, a charging station for electric vehicles is
designed, and the simulation result is provided. The initial
installation cost seems a bit high, so this project might not be
economical, but it is quite practical and environmentally
friendly. The system consists of a 10 kW wind turbine, an 8.5
kW bidirectional inverter, a battery bank to store energy while
the vehicle is on the road.
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