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Renewable and Sustainable Energy Reviews 47 (2015) 462–475
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Renewable and Sustainable Energy Reviews
journal homepage: www.elsevier.com/locate/rser
Inductively coupled power transfer (ICPT) for electric vehicle charging
– A review
Kafeel Ahmed Kalwar, Muhammad Aamir, Saad Mekhilef n
Power Electronics and Renewable Energy Research Laboratory (PEARL), Department of Electrical Engineering, University of Malaya, Kuala Lumpur, 50603, Malaysia
art ic l e i nf o
a b s t r a c t
Article history:
Received 26 July 2014
Received in revised form
12 January 2015
Accepted 8 March 2015
The deficiency in the availability of petroleum products has given rise to the incorporation of electric vehicles
(EVs) globally as a substitute for the conventional transportation system. Significant research has been pursued
over last two decades in the development of efficient EV charging methods. A preliminary review of few
methods developed for wireless charging revealed that ICPT is a promising and convenient method for the
wireless charging of EVs. This paper includes the equivalent circuit analysis and characteristics of the ICPT
system and focuses on the research progress in respect of the designs for the charging coil, leakage inductance
compensation topologies, power level enhancement and misalignment toleration. The improvement in these
factors has been essential for the implementation of EV charging. A brief discussion over design process and
control of ICPT system has been added. Conclusions have been made on the basis of the information extracted
from the literature and some future recommendations are provided.
& 2015 Elsevier Ltd. All rights reserved.
Keywords:
Electric vehicle (EV)
Wireless charging of electric vehicle
Inductively coupled power transfer (ICPT)
Contents
1.
2.
3.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EV's impact on energy and environment and their advantages and drawbacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EV battery charging technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.
Microwave power transfer (MPT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.
Inductive power transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.
Inductively coupled power transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Operating principle for ICPT system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5. Equivalent circuit analysis of ICPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6. Characteristics of ICPT system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1.
Impact of coupling coefficient and frequency on the efficiency of the ICPT system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.
Impact of quality factor (Q) of coils on the efficiency of ICPT system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7. Development of ICPT system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.1.
Compensation technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2.
Charging distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.
Power level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.4.
Misalignment toleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8. Design criteria of ICPT system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9. Control algorithms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10. Future recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
n
Corresponding author. Tel.: +60 379677611.
E-mail address: [email protected] (S. Mekhilef).
http://dx.doi.org/10.1016/j.rser.2015.03.040
1364-0321/& 2015 Elsevier Ltd. All rights reserved.
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1. Introduction
Petroleum products, including compressed natural gas and
liquefied petroleum gas, have remained the main resources of the
energy demand–supply cycle for transportation [1]. The gradual
increase in energy demand has created a scarcity of these naturally
available resources. Moreover, carbon dioxide emission contributing
global warming and high fuel prices have compelled scientists and
researchers to find a sustainable alternate solution to these depleting natural energy reserves [2–4]. Substantial research and development resources are being devoted towards alternate energy
technologies [5–7].
The incorporation of electric vehicles (EVs) has been considered to
be a suitable replacement for the depleting petroleum resources used
for automotive applications [8,9]. The concept of EV was developed
with the advent of the Hybrid Electric Vehicle (HEV), which later led to
the introduction of plug-in hybrid electric vehicles (PHEVs). But the
PHEV exhibited several disadvantages such as such the need of
connecting cable and plug in charger, galvanic isolation of on-board
electronics, the size and weight of the charger, and more importantly
safety issues concerning their operation in the rain and snow [10]. In
order to incorporate the aforementioned disadvantages in PHEV, pure
EV has been developed [11,12]. Electric vehicles (EV) enable smoke free
transportation, and offer an effective solution to the adverse environmental impacts of the conventional transportation system [13], and are
powered over a large air gap through wireless charging even in bad
weather and harsh environmental conditions without utilizing plugs or
wires [14]. However the EVs are operated by means of electrical energy,
so these are polluting the environment indirectly depending on the
source of energy. They operate with low emissions of greenhouse gases
[15]. Furthermore, they can be used with smart house systems to
supplement the energy storage through bidirectional energy transfer
[16]. Although EV is a possible substitute for depleting energy reserves
and to overcome the environmental issues, the limited mileage and
time needed to recharge, less misalignment toleration and overall cost
involved are still limitations. These issues require special consideration
for the successful implementation of an electrically driven vehicle
system worldwide. The quest for a solution to the aforesaid issues has
led researchers to develop the most useful method of wireless charging
of EVs. Several methods have been pursued to charge both stationary
and moving electric vehicles [17,18]. Static charging of EVs is convenient for the users to utilize at home or office parking [19], while
dynamic charging allows powering the moving EVs. Though the static
charging of EVs has the advantage of low cost compared to dynamic
charging, but these require heavy size batteries so to store more charge
[10], while the dynamic charging makes use of several charging coils
paved in the roadbed at a spaced distance which allows more vehicles
to get charged simultaneously [20]. Thus the dynamic charging has the
main advantage of avoiding the need for a high capacity battery and
reduces the battery cost. Inductively coupled power transfer (ICPT) has
been most successful in consideration for the wireless charging of EV.
Due to reasonable electrical isolation between transmitting coil and
receiving coil, the ICPT system has ability to operate in grimy conditions. It is highly reliable and requires less maintenance. Extensive
research over the span of time, in different technical aspects, has
improved the performance of ICPT in terms of charging distance,
misalignment toleration, high power and high efficiency [21,22].
This paper reviews the methods developed for the wireless
charging of electric vehicles and their deployment as well as the
evolution of ICPT performance. It begins with the impact of electric
vehicles on energy and the environment and a brief comparison of
the different EV charging methods in Sections 2 and 3 respectively.
The operational mechanism of the ICPT method is discussed in
Section 4. The equivalent circuit analysis and characteristics of the
ICPT system are provided in Sections 5 and 6. A discussion on the
research progress of ICPT is presented in Section 7. The discussion on
463
design criteria and control algorithm is presented in Sections 8 and 9
respectively. Few recommendations and a conclusion based on the
information learnt from the literature are provided in Sections 10
and 11.
2. EV's impact on energy and environment and their
advantages and drawbacks
Transportation causes the consumption of 27% world petrolatum energy and 33.7% of greenhouse gas emissions in 2012 [1,8].
To reduce the CO2 emissions, legislation is being introduced in
some countries to limit the emissions from cars and other means.
Substantial use of natural resources has created a scarcity thereof,
and, in future, the world may face the impact of the dependence
on these depleting natural energy resources.
Electricity has proven to be a viable alternative transportation
fuel to replace petroleum products, so the electric vehicle has
paved the path for reducing the dependence on petroleum energy.
The EVs are solely operated by electric power and generates zero
emissions of greenhouse gases. This creates substantial changes to
reduce the air pollution, thus making the populated surroundings
cleaner and gratifying for all livings around. The noise of conventional internal combustion engines is avoided through adoption of
EV and the metropolises becomes noiseless [23].
With the development of wireless charging of EVs, the users do
not need any wires to charge them safely. With automatic
charging, the users simply need to park the EV over the plugless charging pad. Through the development in technology, the
dynamic charging of electric vehicles has been introduced, which
enables the charging of moving vehicles on the roadway. Regular
stops on the roadway offer charging points to avoid disrupting the
timetable of users. The charging system can operate reliably even
in the most adverse weather conditions of snow and rain.
Particularly, the electric vehicles can be connected to the smart
grid of the future. The batteries of EVs have the potential to benefit
both consumers and the overall electrical grid [24] and by feeding
electricity back to the grid during peak demand it helps to keep
the overall electricity cost stable. In addition, the charged vehicle
could also potentially serve as an emergency supply for home or
business in case of power outage.
There is risk of safety during accidents in case of human or
animal presence under the car or bus. Thus, there is a major
concern of electromagnetic field exposure in wireless charging of
electric vehicles. The EMI exposure has to be under limited range
as prescribed safety regulatory authorities during normal as well
as abnormal operation.
The main drawback of EV is requirement of a battery of high
energy density. It corresponds to frequent mileage of electric
vehicle. More the mileage, larger the battery pack will be used.
Lead acid battery is mostly used, which is very expensive.
Escalating demand of EVs will result in the deficit of energy
gradually introducing load management issues in grids.
The provoked concern of environment pollution and energy issues
will rapidly ensure the feasibility of EVs for common commercialization by manufacturing light weight high energy density batteries,
technical advancements to overcome misalignment, low efficiency
during dynamic behavior of the power transfer system.
3. EV battery charging technologies
Different EV battery charging methods have been developed in
the quest to achieve high efficiency, large power transfer and other
attributes. The deployed methods have approached the different
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capabilities in terms of power level, air gap and efficiency. These
methods are discussed in this section.
3.1. Microwave power transfer (MPT)
This technology enables the transmission of power and information by using radio waves whose wavelength range falls into
the category of microwaves. The operation of MPT involves
components including a microwave generator, transmitting
antenna and receiving antenna (also termed as rectenna). The
block diagram shows the mechanism of MPT. Initially, the power
supplied from the 50 Hz grid is converted into DC, which is fed
into a microwave generator. There are resonating cavities in the
microwave generator through which the current passes and
produces microwave electromagnetic radiation. The rectenna
receives the microwave energy and converts it back to DC. The
received DC is utilized as per the requirements of the application.
Kyoto University has been working on the implementation of the
MPT for the charging of EV for some years. In 2000, Kyoto University
developed a MPT system for EV charging and achieved an efficiency of
76% [25]. A 10 kW rectenna array capable of receiving 3.2 kW/m2 at a
circa distance of 4 m with efficiency of 84% has been developed by the
Volvo Technologies Japan and the Nihon Dengyo Kosaku companies
[26]. Although the MPT has the advantage of transferring power over
longer distances, it has the disadvantage of increased cost and antenna
size. In addition, high power transmission using microwaves is not
considered safe for humans as it does not comply with the radio wave
regulation for high power. To overcome the disadvantage of the cost
and antenna size, a new technique “Microwave Building” was introduced in [27]. In this technique, a waveguide is used, which provides a
path for microwaves and does not allow the diffusion of microwaves.
Therefore, the size of antenna and cost are reduced to a great extent
and the technique is considered safe. However, to date, low power has
been transferred using this technique.
3.2. Inductive power transfer
The charging of plugin electric vehicles has always a safety risk
of the direct contact of metal-to-metal. To avoid this concern, the
designs of electric vehicle charging systems were developed based
on inductive power transfer (IPT) [28]. The IPT works on electromagnetic induction phenomena to transfer power through an air
cored transformer with closely spaced primary and secondary coils
[2,14,29]. The coils seem to be connected physically to each other
but are isolated electrically, as shown in Fig. 1(a). The extended
picture in Fig. 1(b) shows a sealed charging pad. The charger is
inserted into the vehicle like fueling a conventional vehicle. The
schematic diagram of IPT is shown in Fig. 2.
Inductive power transfer has been successfully implemented
for EV battery charging. This method showed promising high
power transfer with a smaller air gap, however, when the air
gap between the primary and secondary coils is increased the
performance decreases drastically due to leakage inductance [29].
3.3. Inductively coupled power transfer
The inductive power transfer offers low efficiency when the air
gap is increased between charging coils and also involves wired
chargers, while the designs for full wireless charging systems have
been developed to overcome the deficiencies of IPT and make the
charging system convenient for the users. The inductively coupled
power transfer (ICPT) employs capacitors connected to both the
primary and secondary coils to compensate the leakage flux due to
the increased air gap, as shown in Fig. 3. Both the LC circuits work on
resonance phenomena to enable effective energy transfer at resonant
frequency [31].
The inductively coupled power transfer (ICPT) method is
known worldwide for its high power transfer in many applications, mainly in electric vehicles [5,31]. It provides a rapid charging
process, and optimized power transmission by frequency variation
Fig. 1. (a) EV charging through inductive power transfer [30], (b) charging pad [30].
High Frequency
Inductive Link
From Utility
Source
Battery
Charging station
Vehicle charging system
Fig. 2. Schematic diagram of Inductive Power Transfer.
K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
and control over the loss due to low magnetic coupling. The ICPT
has been used for both stationary and moving electric vehicles
[21]. If the vehicle being charged is stationary, it is said to be
“charging of the battery electric vehicle (BEV)” or “static charging”,
while, if the vehicle is moving, some names given to it are dynamic
charging and online electric vehicle (OLEV). In the OLEV set-up,
the primary coil is placed in the pavement at spaced locations,
thereby establishing a charging roadbed that allows power transfer at several spaced locations throughout the roadbed. Although it
involves high capital cost for infrastructure installation, its feature
of frequent charging can elude the need for high capacity batteries.
The online electric vehicle (OLEV) uses relatively low resonant
frequency as the system is installed for the charging of moving
electric vehicles in an open public area. Therefore, it is necessary to
maintain safety regulations prescribed by safety regulation organizations, such as the International Committee on Electromagnetic
Safety (ICES), and the International Commission on Non-ionizing
C1
V1
C2
M
L1
L2
V2
Fig. 3. ICPT circuit.
Table 1
ICPT applied projects.
Manufacturer/institute
Power rating
Efficiency (%)
Air gap (cm)
2007 [32]
2011 [37]
2011 [38]
2011 [39]
2012 [40]
2012 [26]
2013 [41]
2014 [42]
60 W
1 kW
3.3 kW
60 kW
3.3 kW
30 kW
180 kW
300–600 kW
40
88
84–90
92
90
92
85
83
200
30
10
40
18
14
10
3
465
Radiation Protection (ICNIRP) to avoid the exposure by humans to
the electromagnetic field (EMF).
Many authors have termed this technology as the inductively
coupled power transfer (ICPT), while Kurs et al. [32], and Karalis
et al. [33] termed this method as the strong magnetic coupled power
transfer. Nevertheless, both of these indicate same characteristics
[13,34]. Takanashi et al. [35] split IPT based on the use of the magnetic
core and operating frequency into the inductively coupled power
transfer (ICPT ) method [31] and the magnetic resonant power transfer
method [32,33]. According to [35], the ICPT works on a frequency of
less than 200 kHz and employs a ferrite core, while the magnetic
resonance power transfer works on a frequency higher than 1 MHz
and does not utilize a ferrite core.
The literature suggests that the ICPT is a comparatively efficient,
optimum and light charging system through which power can be
transferred from one part to another part of the system with no
physical contacts, particularly in the electric vehicle application, even
in extreme weather conditions [13]. Inductive power transfer (ICPT)
has been attracting the interest of manufacturers in the last few years
[36]. Cellular phone charging through ICPT is an application that has
already been commercialized. The common commercialization of this
technology is likely to be unveiled soon and may modernize the
automotive industry.
The achievements in research of ICPT technology are tabulated
in Table 1:
A comparison of charging methods with respect to the parameters including efficiency, frequency, cost, power level and
distance is shown in Table 2.
From developed methods of electric vehicle charging, the ICPT
method has enabled the high power transfer.
4. Operating principle for ICPT system
In the ICPT system, unlike the transformers in which the primary
and secondary windings are wound on a magnetic core to avoid the
leakage of inductance, and to produce a good coupling, the windings
Table 2
Comparison of various EV battery charging methods.
Technology
Efficiency
Frequency
Power level
Distance
Cost
Microwave power transfer
Inductive power transfer (Uncompensated)
Inductive coupled power transfer
Medium
High
Medium
1–30 GHz
15–100 kHz
20–200 kHz
Low/medium
High
High
Long
Very low
Medium
High
High
Medium
Rectifier
M
Inverter
Cs
Secondary Coil
Battery
Primary Coil
Cp
High Frequency
Inverter
Fig. 4. Components of wireless power transfer for EV charging.
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K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
are not linked through a common magnetic core but separated over a
large air gap. The inductively coupled power transfer for the EV
charging system is depicted in Fig. 4, which consists of a utility supply,
high-frequency inverter, primary and secondary resonant circuits and
EV load [22]. The primary coil in Fig. 4 is a charging pad that is fixed in
the ground. The EV is parked above the charging pad and a highfrequency AC voltage is applied to the charging pad. The rate of current
flow creates a time variant magnetic field around the primary coil.
Subsequently, by Ampere's Law and Faraday's law, being in the vicinity
of a variant magnetic field, a voltage is induced at the terminals of the
secondary coil, as shown in Fig. 5 [43]. The electrical load of EV is
connected to the secondary coil, which completes the circuit and
enables the power transfer.
As the primary and secondary coils are separated by a large air
gap that results in low mutual inductance and the voltage across
the mutual inductance becomes less [31], which creates a delay
between the current and voltage and thus the reactive power is
produced. To overcome the low power factor due to the reactive
power [44], capacitance is added to both the primary and
secondary coils to achieve the resonance phenomenon. This
strengthens the coupling between the loosely coupled coils. The
schematic diagram of the series–series compensated circuit topology is as shown in Fig. 6. This ensures the high power transfer
when both the primary and secondary circuits are operated at the
same resonant frequency [20,31].
The power output of an ICPT system ðP out Þ can be analyzed by
using two observations in the ICPT system [46]:
Open-circuit test
V OC ¼ jωMI 1
ð1Þ
Short-circuit test
I SC ¼
MI 1
L2
ð2Þ
P ¼ Su Q ¼
P¼
jωM 2 I 1 2
Q2
L2
jωM 2 I 1 2 ωL2
L2
RL
ð4Þ
; Since Q 2 ¼
ωL2
ð5Þ
RL
Therefore, the power transferred at the secondary coil can be
calculated using the following equation:
P¼
ω2 M 2 I 1 2
ð6Þ
RL
where ω is the angular frequency of the transmitting coil, I 1 is the
current through transmitting coil, M is the mutual inductance
between two coils and RL is the load resistance.
5. Equivalent circuit analysis of ICPT
Although the inductively coupled power system has many
configurations to compensate for the effect of leakage flux, a
series–series resonant structure of the ICPT system is selected for
analysis because of its simplicity and moreover it reduces the
parameters that are involved in the optimization of efficiency of
the ICPT system. An ICPT system with a series resonant capacitor is
shown in Fig. 7. Lp , Ls are the self-inductances of the primary and
secondary side and M is mutual inductance. C p , C s are the capacitances of the primary and secondary side capacitors. R1 , R2 are
the resistances of the primary and secondary side and RL is the
load resistance. Fig. 8 shows the T-type of equivalent circuit of the
ICPT system circuit shown in Fig. 7.
The coupling coefficient (k), that defines the extent of coupling
of the primary and secondary coil, is given by:
M
k ¼ pffiffiffiffiffiffiffiffiffi
Lp Ls
ð7Þ
Then power can be calculated as the product of open circuit test
voltage and short circuit test current:
Su ¼ jωMI 1 MI 1 jωM 2 I 1 2
¼
L2
L2
Cp
I1
ð3Þ
R1
I2
Vs
I
Ampere’s Law
Lp
V
I1
Cp
R1
Lp-M
Fig. 5. Basic concept of inductive power transfer [45].
High Frequency
Inverter
Ls
RL
VL
Ls - M
R2
M
Vs
Rectifier
M
Fig. 7. Series–series (SS) resonant ICPT system.
Faraday’s
Law
H
Inductively Coupled
Power Transfer
Mutual
Induction
L 1 Lm
Cs2
L2
Fig. 6. Circuit of inductively coupled power transfer.
Rectifier
Cs
I2
RL
Fig. 8. Equivalent circuit of ICPT system.
Cs1
AC
Cs
R2
Battery
K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
The total impedance of the equivalent circuit for given parameters may be calculated as:
0
1
2 2
1
ω
M
@
A
ð8Þ
Z SS ¼ R1 þ j Lp ω þ
Cpω
R þ j Ls ω 1 þ R
Cs ω
2
467
And, thus, the maximum efficiency can be obtained as:
2
2π f r M 2
ηmax ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ffi
2 pffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2
R1 R2 þ 2π f r M 2 þ ðR1 R2 Þ
ð18Þ
L
The current absorbed from the supply is given by:
Vs
Z SS
I1 ¼ ð9Þ
Vs
1
R1 þj Lp ω C p ω þ
2
ω2 M R2 þ j Ls ω C 1ω þ RL
ð10Þ
s
Now the circuit is operating at a resonant frequency f r and the
LC components cancel out their reactance and I 1 is given by:
I1 ¼
R1 þ
V
s 2 2
ð2 π f r Þ M
ð11Þ
R2 þ RL
The input power can be calculated as:
P IN ¼
R1 þ
V 2
s 2 2
ð2π f r Þ M
ð12Þ
R2 þ RL
Or:
P IN ¼
V s 2 ðR2 þ RL Þ
2
R1 R2 þ R1 RL þ 2π f r M 2
ð13Þ
Likewise, the output power can be obtained as below:
2
V s 2 2π f r M 2 RL
P OUT ¼ 2 2
R1 R2 þ R1 RL þ 2π f r M 2
P OUT
P IN
6.1. Impact of coupling coefficient and frequency on the efficiency
of the ICPT system
The coupling coefficient between the primary and secondary
can be calculated from Eq. (1). If no coupling exists between the
primary and secondary, then M ¼ 0; and, thus k ¼ 0. The general
transformers with cores and no air gap have the highest coupling
coefficient. The coupled coils have k Z 0:5, they are termed as
tightly coupled and those having k r 0:5 are called loosely coupled.
The value of M and thereby k depends on the physical dimensions
and the number of turns of each coil, their relative position to one
another and the magnetic properties of the core on which they are
wound. There is also a probable decrease in the coupling coefficient due to misalignment between the transmitting and pick-up
coils in both the static and dynamic charging of EVs. Fig. 9 depicts
the variation of coupling coefficient and mutual inductance as a
function of variable distance.
Eq. (16) can be simplified to determine the dependence of the
efficiency of the ICPT system on the coupling coefficient. The
relationship between the coupling coefficient (k) and power
100
90
ð14Þ
k=0.2
80
And the efficiency of the system can be represented by the
following equation:
η¼
6. Characteristics of ICPT system
ð15Þ
Or
η¼
k=0.4
70
Efficiency (η)
I1 ¼
k=0.6
60
50
40
30
RL
2
RL þR1 ðR2 þ RL Þ= 2π f r M
þ R2
20
ð16Þ
10
The maximum load resistance for optimized efficiency can be
obtained by:
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
2π f r M 2
RL ¼ 1 þ
ð17Þ
R1 R2
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
Frequency (Hz)
Fig. 10. Efficiency of ICPT system at various coupling coefficient.
4000
0.25
7.00E-05
Mutual Inductance
5.00E-05
0.15
4.00E-05
3.00E-05
0.1
2.00E-05
0.05
1.00E-05
Power Transferred (Watts)
0.2
6.00E-05
Mutual Inductance (Henery)
Coupling Coefficient (k)
3500
Coupling Factor
RL=3 Ω
3000
RL=3.5 Ω
2500
RL=4 Ω
2000
RL=4.5 Ω
1500
RL=4.5 Ω
1000
500
0
0
0.2
0.4
0.6
0.8
1
0.00E+00
Airgap / Distance (Metres)
Fig. 9. The effect of distance upon coupling coefficient (k) and mutual inductance
(M).
0
15000 16000 17000 18000 19000 20000 21000 22000 23000 24000 25000
Frequency (Hz)
Fig. 11. Maximum power transferred at resonant frequencies.
468
K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
100
Table 3
Loaded quality factors of ICPT coils.
Secondary series
compensated
Secondary parallel
compensated
Q1
Q1 ¼
RL L1
ωM 2
Q1 ¼
Q2
Q1 ¼
ωL2
RL
Q1 ¼
95
Maximum Efficiency (η)
Quality
factor
ωL1 L2 2
RL M 2
RL
ωL2
90
80
90
85
80
75
Efficiency (η)
70
70
60
5
25
45
50
65
85
105
kQ
40
Fig. 13. The maximum efficiency of ICPT system against kQ [35].
30
20
10
in [48] and presented by Eq. (21):
0
5000
10000 15000 20000 25000 30000 35000 40000 45000 50000
Q1 4
Frequency (Hz)
Fig. 12. Efficiency during bifurcation phenomenon.
transferred can be represented by Eq. (19):
2
2
R k 2π f r L1 L2
L
η¼
2
2
ðRL þ R2 Þ R1 RL þ R1 R2 þk 2π f r L1 L2
ð19Þ
Fig. 10 shows that the efficiency varies directly with the
coupling coefficient and frequency. The lower air gaps offer higher
efficiency. It is important to select a trade-off between the distance
and efficiency for high power transfer, keeping in view the
necessity of application.
The power transferred can be determined by Eq. (1). Fig. 11
shows the maximum power transferred for different load resistances at certain bandwidth of optimum resonant frequencies. At
these frequencies, the LC components cancel out their reactance
on both sides of the circuit. The power transfer drops considerably
at all other frequencies except the range of bandwidth.
6.2. Impact of quality factor (Q) of coils on the efficiency of ICPT
system
The quality factor quantifies how much the coil is purely
inductive. It signifies its ability to produce a large magnetic field.
Normally, the ICPT system is designed to operate at a fixed
frequency; however, sometimes, due to a change in parameters,
i.e. capacitance or load, the air gap causes the change in system
frequency, so the transfer efficiency drops. Therefore, the system
does not operate at a zero phase angle frequency.
The native quality factor of primary and secondary coil can be
calculated as:
Q1 ¼
ωL1
R1
;
Q2 ¼
ωL2
R2
ð20Þ
The loaded quality of series and parallel compensated ICPT
system are given in Table 3.
A bifurcation phenomenon occurs when a system has more
than one zero phase angle frequency [47]. Fig. 12 shows the
efficiency characteristics during bifurcation phenomenon. It can
be seen that there are more than one resonant frequencies where
the efficiency becomes high. It has been shown in [47,48] that the
bifurcation phenomenon highly depends on the quality factors of
the coils. The condition for bifurcation in SS topology is derived
4Q 2 3
ð21Þ
4Q 2 2 1
To avoid the bifurcation phenomenon in the series–series (SS)
ICPT system, the quality factor of primary coil should always be
greater than the secondary coil and thus the system will operate
on a single zero angle frequency.
The impact of quality factor on the amount of power transferred and its efficiency can be observed from the following
equations [49]:
P ¼ jωL2 I 1 I 1 M2
Q
L2 L1 2
2
P ¼ V 1 I1 k Q 2
ð22Þ
ð23Þ
To determine the maximum efficiency of the ICPT system, an
equation based on the coupling coefficient and Q factor is developed in [35]:
ηmax ¼
1
2
1 þ pffiffiffiffiffiffiffiffiffi
k
ð24Þ
Q 1Q 2
13 shows the results plotted between ηmax and kQ ¼
ffiffiffiffiffiffiffiffiffiffiffiffi
pFig.
k Q 1 Q 2 . It reveals that the higher the values of the coupling
coefficient and quality factors, the greater the efficiency.
7. Development of ICPT system
7.1. Compensation technologies
The increase in air gap between two inductive coils increases
the leakage inductance and magnetizing current, and, accordingly,
the coupling between them weakens. The circuit is operated at a
resonant frequency to compensate the leakage inductance and to
strengthen the coupling between the resonant coils [50]. It has
been analyzed that the primary coil compensation can minimize
the apparent power rating of the power supply of the ICPT system,
while the secondary coil compensation can increase the capability
of the pick-up coil [31]. This is achieved by operating the system at
the zero phase angle frequency, i.e. the angle between the current
and voltage is always kept at zero. The arrangement of the
capacitor connections for compensation on both sides either in
series or parallel makes four topologies – series–series (SS), series–
parallel (SP), parallel–series (PS) and parallel–parallel (PP) – as
shown in Fig. 14. All these four basic topologies have different
merits and demerits that are presented in Table 4. The selection of
K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
Cp
Cs
Cp
I1
I2
V1
Lp
Ls
469
RL
I2
I1
V1
Lp
RL
Ls
Cs
M
M
Series-Series Compensated
ICPT
Series-Parallel Compensated
ICPT
Cs
I1
V1
I1
I2
Lp
RL
Ls
V1
I2
Cp
Lp
Ls
RL
Cs
Cp
M
Parallel-Series Compensated
ICPT
M
Parallel-Parallel Compensated
ICPT
Fig. 14. Compensation topologies (a) SS, (b) SP, (c) PS, (d) PP.
Table 4
Characteristics of compensation topologies.
Topology
Acts as
Independent of changes Power factor at small
in
distance
Power factor at small
distance
Total impedance at resonant
state
Efficiency
Series–series (SS)
Voltage
source
Current
source
Voltage
source
Current
source
C2
Low
Very high
Low
Very high
C2
Low
High
Low
Medium
C1
High
Medium
High
Medium
C1
Very high
Medium
High
High
Series–parallel
(SP)
Parallel–series
(PS)
Parallel–parallel
(PP)
4
1
Series-Parallel
3
Parallel-Series
0.6
I2/I 2r
I2 /I 2r
Parallel-Parallel
0.8
Series-Series
2
1
0.4
0.2
0
0
-100
-90
-50
0
50
90
100
X% Misalignment
Fig. 15. The behavior of SS, SP topologies in absence of secondary [50].
the topologies depends upon their suitability for specific applications satisfying the respective requirements, as SS and SP topologies can transfer higher power than the rated, but these offer an
uncertain behavior to the supply [50], and the PS and the PP
compensated ICPT systems are safe for the supply in the absence of
secondary winding but these are unable to transfer the rated
power if the coils are somewhat misaligned. The behavior of
SS and SP topologies when the secondary is absent is shown
in Fig. 15; the current rises due decrease in impedance with
increase in misalignment. The I 2 is load current and I 2r is rated
load current. However in PS, PP the current decreases as the total
impedance increases due to misalignment as shown in Fig. 16.
-100
-75
-50
0
50
75
100
X% Misalignment
Fig. 16. The behavior of PS, PP topologies in absence of secondary [50].
They require additional series inductor to control the inverter
output current flowing through primary parallel resonant circuit,
however, the size and cost of converter is increased. In [51], a
series-parallel LCL pick-up design was presented that offered
uninterrupted controlled power and smooth power transitions
during switching states but it reflected reactive power back onto
the source [52]. Moreover, the SP topology depends upon the
coupling coefficient and requires a high-value of capacitance for
stronger magnetic coupling [53]. According to [31,54], the SS
topology is considered as the most suitable for EV charging
because the primary and secondary capacitances are unimpeded
from both the magnetic coupling coefficient and the load. It may
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K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
also act as a constant current and voltage source that is desirable
for battery charging.
Besides these four conventional compensation topologies,
other meritorious designs are proposed [21,31,48,55]. In [31] a
design based on a primary compensated circuit was presented that
minimized the effects of frequency shifts to avoid a low coupling
coefficient. In [54], parallel–parallel–series (PPS) topology has
been implemented that offered higher efficiency than PP topology
for same distance of 50 mm and load of 1 Ω. The power factor of
inverter in PPS topology has higher power factor than PP, however
for smaller misalignment the PP topology has good performance
than PPS. Vila et al. [50] presented the SPS design, which offered
better performance for 2 kW prototype in terms of misalignment
toleration and efficiency as compared to the basic compensation
topologies for the load of 1.25 Ω. The selection of PPS and SPS
topologies may done according to application requirement as SPS
would not fit where less misalignment is expected but PPS can be
useful. The Sakamato et al. [56] presented an inductive coupler
design that is capable of providing high self-inductance and less
leakage inductance resulting in 8.3 kW of power transferred at an
air gap of 3 mm with more than 97% efficiency.
7.2. Charging distance
The large air gap has been the main consideration in the
development of EV charging, as a reasonable ground clearance is
required between the EV chassis and the charging pad fixed in the
ground. An air gap of a few hundred millimeters is considered
necessary for EV application [57] and the value of k in the EV
charging ICPT systems has been observed to be between 0.3 and
0.6 [31].
Table 5
ICPT systems using ferrite core.
Ferrite cored ICPT systems
Air cored ICPT systems
Ref
no.
Coupling
coefficient
Ref
no.
Charging
distance (mm)
Coupling
coefficient
0.35
0.25
0.72
[25]
[32]
[60]
200
2000
300
0.16
0.01
0.05
Charging
distance (mm)
[11] 70
[58] 80
[59] 6
In the quest to achieve efficient, optimum and high power
transfer, research has been carried out on various transformers
with a core and without a core (air core). Many designs have been
proposed using an air core [20] and ferrite core [43]. Ferrite cores
have been preferred because of their improved coupling coefficient and lower cost compared to others [14]. Table 5 shows a
comparison between ICPT EV charging systems employing a ferrite
core and an air core. This comparison reveals that the coupling
coefficient in the ICPT systems using a core is higher than in the air
core systems.
Extensive research studies have been conducted and published
over time concerning the optimization of the charging pad by
employing different core shapes. Initially, U cores, E cores and pot
cores were examined but these were incompatible with EV
application due to their greater thickness. The single-sided winding with a circular core shape, as shown in Fig. 17, was considered
and used in the EV charging applications for long spans of time
[31,61]. Mecke and Rathge [57] used circular coils of 400 mm
diameter to transfer 1 kW power with an air gap of 300 mm. They
achieved an overall power transfer system efficiency of more than
80% but misalignment was not focused upon. In [62], a 2 kW 700mm-diameter circular power pad with a 200 mm air gap was
proposed. The single-sided circular core offered both a low leakage
electric field and electromagnetic radiation, which are desirable in
EV charging. Less leakage of an electric field is preferable due to
the surrounding metallic structures in the EV as the pick-up coil is
embedded in the EV chassis. The circular pads exhibited limited
coupling and offered poor tolerance to horizontal offset. In [62], it
was shown that the pick-up coil should be aligned with the
transmitting coil for the charging of the EV using circular coils,
however, when the misalignment attained an offset of around
740%, the output power fell to zero. Budhia et al. [19] proposed a
meritorious solution to overcome the limitations revealed by the
circular pad. They introduced and optimized a new polarized
coupler called a Double D Quadrature (DDQ), as shown in Fig. 18.
Fig. 18. Double-D quadrature magnetic couple design [13].
Fig. 17. Single-sided circular charging pad [13].
Fig. 19. Rectangular H-shaped core [63].
K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
The DDQ produced a flux path height twice that of a circular pad
together with having a single-sided flux path completely interoperable with the traditional circular pads.
According to [63] and [64], the double-sided windings with
rectangular core shape, as shown in Fig. 19, have also have been
considered for EV charging systems. The double-sided rectangular
H-shaped core type was compact and lightweight but resulted in a
low coupling coefficient due to its leakage flux at the back of the
core, however, this leakage flux could be shielded by the
aluminum sheet.
As there is an escalation in both the static and dynamic charging of
EVs, accordingly, such power pads should be developed that can
handle both [19]. In the design of power pads, the winding width
should be sufficient enough to prevent the decrease in k. To decide
upon the optimum winding width, Takanashi et al. [35] determined
the effect of the winding width (w) and magnetic air gap (g) on the
efficiency. It has been analyzed that a larger w/g ratio could observe
maximum efficiency at a w/g ratio of 1.4. However, the large size of
the secondary coil cannot fit on an EV chassis. Thus, it is required to
keep in view the geometry of the secondary coil while designing for
an EV chassis. According to [62], an increase in coil diameter with
centered ferrite core can increase the self-inductance in a greater
proportion than the mutual inductance that reduced the coupling
coefficient. Generally, the magnetic coupling decays at 1=r 3 , r being
the distance from center loop, thus it seems that the size of magnetic
charging pad can be increased but there are some limitations due to
cost [65].
7.3. Power level
The power level for the ICPT system accommodates several
important aspects including charging time, location, and cost [66].
The suitability of ICPT in different applications, charging time and
the cost significantly depends upon the selection of the power
level. A high power level is desirable when more vehicles are being
charged from a single charging track. The static charging of EV
prefers power levels of 2–7 kW with an operational air gap of 100–
250 mm.
Different codes and standards suggest different criteria for the
suitability of the power level selected for EV charging. The Society
of Automotive Engineers (SAE) J1772 code describes the power
level according to three categories that define different amounts of
energy transfer requiring different infrastructure. The power level
may also be classified according to on-board (the charger located
inside the EV) and off-board charging [67]. The charging levels
prescribed in SAE J1772 are summarized in Table 6.
Different OEMs (Original Equipment Manufacturers) manufacture production with different specifications that do not follow a
single standard worldwide. Recently, the SAE international J2954
471
task force for the wireless power transfer (WPT) of light duty
electric and plug-in electric vehicles [68] has proposed a specific
frequency and power level for the interoperability of EV charging
before commercialization. The proposed frequency that may be
used for charging light electric vehicles is 85 kHz, which lies
within an internationally available 81.38–90 kHz frequency band.
The power levels prescribed by this code are presented in Table 7.
7.4. Misalignment toleration
Misalignment is the displacement of the pick-up coil with respect
to the transmitting coil and leads to a decline in both the efficiency
and power transfer of the ICPT system. The ICPT system for EV
charging requires maximum alignment between the coils to avoid
inefficient power transfer due to driver mistake while parking the
vehicle in the desired position [62]. The car weight may slightly
change the air gap between the EV chassis and the ground and
thereby coupling, consequently it would affect the power transfer
efficiency [64]. The ICPT charging system with perfect alignment will
reduce the leakage flux, and, as a result, it reduces the electromagnetic interference emission from the system; however, an ICPT
system that could offer good tolerance for misalignment to give
maximum freedom to the driver, is desirable [31].
Misalignment may be classified as lateral or longitudinal, in
which the lateral misalignment can occur when coils are horizontally misaligned and longitudinal misalignment can occur when
the coils are irregular with respect to their length [70]. Both types
of misalignment may reduce the mutual inductance, and can cause
the ICPT system to operate on a frequency other than what was
designed with a low coupling coefficient k. When the secondary
coil of a single-sided winding transformer with circular core is
displaced 40% from the transmitter coil, the coupling coefficient
becomes zero, as can be observed from Fig. 20. In [43], a polarized
flux pipe was presented that offered better tolerance to misalignment than the circular pad and met the tolerance requirements for
an EV. In [19], a Double D Quadrature (DDQ) coil design was
presented, which offered far greater tolerance than a circular coil
and was also compatible with circular coils. It may be observed
that when the double-sided windings are misaligned to a certain
position, as shown in Fig. 21, they still have good coupling because
the flux linkage path is extended compared to the circular coils, as
shown in Fig. 20 [64]. The ICPT systems can have a variable
coupling coefficient, thus a perfect frequency control that keeps
the ICPT circuit to remain in the state of resonance or coil
geometry optimization that can offer high efficiency with a
reasonable misalignment between coils may be employed, however, the system becomes either complex in terms of frequency
control or costly due to the geometry of the coils [62,71].
Table 6
Power levels defined by code J1772 [69].
Power level type
Charger location
Typical use
Energy supply interface Expected power level Charging time Vehicle technology
Level 1 (Opportunity) On-board 1-phase Charging at home or office
Convenience outlet
120 Vac (US)
230 Vac (EU)
Level 2 (Primary)
On-board 1Charging at private or public outlets Dedicated EVSE
or 3- phase
240 Vac (US)
400 Vac (EU)
Level 3 (Fast)
Off board 3-phase analogous to a filling station
Dedicated EVSE
(280 V-600 Vac
or Vdc)
1.4 kW (12 A)
1.9 kW(20 A)
4–11 h
11–36 h
PHEVs (5–15 kWh)
EVs(16–50 kWh)
4 kW (17 A)
8 kW (32 A)
19.2 kW(80 A)
1–4 h
2–6 h
2–3 h
PHEVs(5–15 kWh)
EVs(16–30 kWh)
EVs(3–50 kWh)
50 kW
100 kW
0.4–1 h
EVs(20–50 kWh)
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K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
Table 7
The Power levels defined by code J2954 [68].
SAE TIR J2954 WPT Power class
Classification
Maximum input WPT power rating
WPT1 house parking
3.7 kW
Secondary Coils (Car)
Position(B)
Position(A)
Primary Coil
(Ground)
Fig. 20. Single-sided winding transformer misalignment [64].
1
Lp C P
fo ¼
Ferrite Cores
Magnetic
Flux
Fig. 21. Double-sided winding transformer misalignment [64].
I1
Cp1
R1
R2
Cs
I2
Cp2
Vs
Lp
M
Ls
VL
RL
Fig. 22. Circuit of SPS topology [50].
I1
Cp
R1
R2
Cs2
I2
Vs
Lp
M
1
Ls C s
ð25Þ
Or
Position
(A)
Primary Transformer
(Ground)
The development of ICPT design is done systematically using
iterative process or experimental analysis. The principal condition
for maximum power in ICPT system is resonant frequency operation. Thus the design of ICPT system primarily corresponds to the
parameters that are necessary for resonant operation. These
parameters are winding inductances (Lp ; Ls ), their respective
capacitances (C p ; C s ) that are connected with them and resonant
frequency ( f o ). Following is resonant condition for inductive
power transfer.
ωo ¼ pffiffiffiffiffiffiffiffiffiffi ¼ pffiffiffiffiffiffiffiffiffi
Secondary Transformer
(Car)
Forward Direction
Position
x
(B)
y
WPT3 L.D. fast charge
22 kW
8. Design criteria of ICPT system
Magnetic
Flux
Lateral
Direction
WPT2 private/public parking
7.7 kW
Ls Cs1
VL
RL
Fig. 23. Circuit of PPS topology [54].
The ICPT compensation circuits play a significant role in misalignment toleration. Throngnumchai et al. [54] pointed out that basic
compensation circuit topologies SS, SP, PS and PP are not suitable for
ICPT systems considering the need for low sensitivity to the misalignment requirements of EVs, high power level and larger air gap. A
meritorious
study
was
conducted
on
the
misalignment performance enhancement of ICPT by selecting a suitable
SPS compensation topology, shown in Fig. 22, that realized the rated
power transfer with the high misalignment of the pick-up coil
without any complex control [62]. In [31], another circuit topology
PPS, shown in Fig. 23, was proposed and validated experimentally,
which resulted in recoverable potency of the circuit to counter the
variation in coupling and thereby permitted power transfer at a
reasonably larger air gap. The circuit topology presented was able to
enhance the power factor of the output of the inverter and that of the
transmitter coil to overcome the low coupling coefficient.
2π
1
1
pffiffiffiffiffiffiffiffiffiffi ¼ pffiffiffiffiffiffiffiffiffi;
Lp C P 2π Ls C s
Since
ωo ¼ 2 π f o
ð26Þ
Considering the overall ICPT system, design process involves
the amount of power to be transferred, load resistance, desired
load voltage. Based upon of the amount of power, the frequency,
inductances, capacitances are selected. The inductance of windings
depends on number of turns and dimensions of coils and may be
varied as per requirement. A meritorious study on design process
has been presented in [21] that provides a flow diagram of ICPT
design process depicted in Fig. 24. This design flow process can be
applied for low to high power level ICPT system. According to this
flow diagram the design process initiates with initial geometry,
number of turns, cross sectional area and current density of coils
and then an iterative process is applied until the fulfilment of
required power level with permissible maximum frequency, geometry of coil. From Eq. (6), it clear that the resonant operating
frequency is related to the amount of power to be transferred;
higher the power to be transferred, higher will be the operating
frequency. But higher frequencies are limited due to switching
speed of inverter. To ensure high efficiency in ICPT system, the
coupling coefficient and quality factors of coils should be high. The
coupling coefficient may be improved by various magnetic shapes
such as combination of ferrite core and litz wire. The coils of high
Q-factor enable protection from electromagnetic interference [72].
Generally ICPT systems are designed for either fixed frequency
operation or variable frequency operation. In variable frequency
operation, the ICPT systems are designed in such a way that their
input VA should be greater than secondary VA to avoid point of
bifurcation and power loss [49].
Nowadays new trends in magnetic coupler designs and electronic are being introduced [46,73].
9. Control algorithms
The variation in air gap and alignment causes the change in
load resistance and magnetic coupling between primary and
secondary coil. There can be a deviation in frequency of inverter
and load can vary over a considerable range. Uncertain characteristics can be expected due to all these issues. The output
voltage of secondary coil may vary excessively from designed
value. To avoid undesirable characteristics under various
K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
473
Fig. 24. Flow diagram of ICPT design [21].
Reference
Current
Controller
(DSP/FPGA)
Gate
Drive
High Frequency
Converter
Zero Current
Crossing detection
Filter
ICPT
Coil
Current
Detection
Magnitude
Detection
Fig. 25. Control block diagram of ICPT Coil Supply.
operating conditions and to maintain a normal operation of
power transfer, a proper control is essential. It will prevent from
output voltage fluctuation, where a constant supply is important.
The control strategy may be applied to different parts of ICPT;
Individually for primary coil power supply control and secondary
coil power control or synchronised control of primary and
secondary coils. The control of secondary coil is more common
in order to get stabilized voltage.
The circuit of inductively coupled power transformer is shown
in Fig. 6. A high frequency inverter is necessary to operate the
resonant circuit and produce high frequency supply for primary coil.
The operating frequency of inverter switches has to match with the
designed frequency of coils but fixed frequency control cannot
manage variation of circuit parameters, and as a result the switches
practice high voltage or current stress, and high energy loss in the
form of heat. Thus variable frequency control has been developed to
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K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
ensure circuit resonance [74]. Proportional–integral (PI) controllers
have been implemented to control the input and output current
through DSP, FPGA and other devices [2,18,53,58,75]. Atypical control
block diagram of input current is shown in Fig. 25. Promoting the
concept of bidirectional power transfer for V2G (vehicle-to-grid)
system and V2H (vehicle-to-home), some coordinated controller
including single-ended quasi resonant high frequency inverter, directional tuning control and synchronised PWM with high frequency
communication system have been implemented [76–78].
10. Future recommendations
Although EVs have huge potential to switch conventional
transport into modern electric transport, they are not commonly
adopted yet due to various technical and commercial obstacles. A
positive approach to these obstacles is expected in the near future
to replace conventional vehicles with EVs.
Besides ferrite cores, the research may be extended to a unique
core material and design that provides high magnetic field
strength and low core losses to allow users to charge freely
regardless of the misalignment issue within permissible limits.
During the optimization process to avoid the copper losses, the
current ratings can be kept at possible low values.
The challenge for future EVs would be the long mileage. The long
mileage by an EV mainly requires a high-energy density battery
that could be charged within a few minutes and last for several
hundred miles. Consideration of the use of graphene material for
batteries and super-capacitors may enhance the mileage issue.
Then a single charging of EV may provide longer mileage.
11. Conclusion
This paper has provided a brief review and comparison of the
different EV charging methods and their deployment. The equivalent circuit analysis and characteristics of the ICPT system were
presented. The progress of the ICPT method for various factors and
benefits from them were reviewed. The implementation of ICPT
was found to be contingent upon the leakage flux compensation
topology, charging distance and proper alignment. A trade-off
between distance, charging pad size and efficiency is necessary for
EV charging application. Advanced flux leakage compensating
topologies SPS and PPS topologies offer efficient power transfer
over large air gaps and better misalignment toleration as compared to basic conventional topologies. Power levels 1 and 2 are
designed for slow and moderate charging at home and public
parking, respectively, however, power level 3 provides off board
quick charging. Rectangular and DDQ coils offer good coupling and
high misalignment consideration. Design criteria is utmost to
develop the overall ICPT system for low to high power level. To
cope with the dynamic behavior of ICPT system many controllers
have been developed to maintain input and output parameters.
Future recommendations supporting the implementation of this
technology are included.
Acknowledgment
The authors would like to acknowledge the financial support
from University of Malaya. This research was carried under the
High Impact Research Grant (UM.C/HIR/MOHE/ENG/24) scheme.
References
[1] Atabani A, Badruddin IA, Mekhilef S, Silitonga A. A review on global fuel
economy standards, labels and technologies in the transportation sector.
Renew Sustain Energy Rev 2011;15:4586–610.
[2] Madawala UK, Thrimawithana DJ. A bidirectional inductive power interface for
electric vehicles in V2G systems. IEEE Trans Ind Electron 2011;58:4789–96.
[3] Saidur R, Abdelaziz E, Demirbas A, Hossain M, Mekhilef S. A review on biomass
as a fuel for boilers. Renew Sustain Energy Rev 2011;15:2262–89.
[4] Mekhilef S, Faramarzi S, Saidur R, Salam Z. The application of solar technologies for sustainable development of agricultural sector. Renew Sustain
Energy Rev 2013;18:583–94.
[5] Boys JT, Elliott GA, Covic GA. An appropriate magnetic coupling co-efficient for
the design and comparison of ICPT pickups. IEEE Trans Power Electron
2007;22:333–5.
[6] Hannan M, Azidin F, Mohamed A. Hybrid electric vehicles and their challenges: a review. Renew Sustain Energy Rev 2014;29:135–50.
[7] Fotouhi A, Yusof R, Rahmani R, Mekhilef S, Shateri N. A review on the
applications of driving data and traffic information for vehicles' energy
conservation. Renew Sustain Energy Rev 2014;37:822–33.
[8] Tie SF, Tan CW. A review of energy sources and energy management system in
electric vehicles. Renew Sustain Energy Rev 2013;20:82–102.
[9] Chau K, Wong Y, Chan C. An overview of energy sources for electric vehicles.
Energy Convers Manag 1999;40:1021–39.
[10] Su W, Eichi H, Zeng W, Chow M-Y. A survey on the electrification of
transportation in a smart grid environment. IEEE Trans Ind Inform
2012;8:1–10.
[11] Ning P, Miller JM, Onar OC, White CP, Marlino LD. A compact wireless charging
system development.
[12] Hori Y. Application of electric motor, supercapacitor, and wireless power
transfer to enhance operation of future vehicles. Industrial Electronics (ISIE).
In: Proceedings of 2010 IEEE international symposium on: IEEE; 2010. p.
3633–5.
[13] Covic GA, Boys JT. Modern trends in inductive power transfer for transportation applications.
[14] Keeling NA, Covic GA, Boys JT. A unity-power-factor IPT pickup for high-power
applications. IEEE Trans Ind Electron 2010;57:744–51.
[15] Hasanzadeh S, Vaez-Zadeh S, Hassanpour Isfahani A. Optimization of a
contactless power transfer system for electric vehicles; 2012.
[16] Brown S, Pyke D, Steenhof P. Electric vehicles: the role and importance of
standards in an emerging market. Energy Policy 2010;38:3797–806.
[17] Choi S, Huh J, Lee W, Lee S, Rim CT. New cross-segmented power supply rails for
roadway-powered electric vehicles. IEEE Trans Power Electron 2013;28:5832–41.
[18] Ning P, Miller JM, Onar OC, White CP, Marlino LD A compact wireless charging
system development. In: Proceedings of twenty-eighth annual IEEE Applied
Power Electronics Conference and Exposition (APEC); 2013. p. 3045–50.
[19] Budhia M, Covic GA, Boys JT, Huang C-Y. Development and evaluation of single
sided flux couplers for contactless electric vehicle charging. In: Proceedings of
2011 IEEE Energy Conversion Congress and Exposition (ECCE), IEEE; 2011.
p. 614–21.
[20] Villa JL, Sallán J, Llombart A, Sanz JF. Design of a high frequency inductively
coupled power transfer system for electric vehicle battery charge. Appl Energy
2009;86:355–63.
[21] Sallán J, Villa JL, Llombart A, Sanz JF. Optimal design of ICPT systems applied to
electric vehicle battery charge. IEEE Trans Ind Electron 2009;56:2140–9.
[22] Hasanzadeh S, Vaez-Zadeh S. Efficiency analysis of contactless electrical power
transmission systems. Energy Convers Manag 2013;65:487–96.
[23] 〈http://primove.bombardier.com/about/benefits/〉 [accessed 15.03.14].
[24] Kempton W, Letendre SE. Electric vehicles as a new power source for electric
utilities. Transp Res Part D: Transp Environ 1997;2:157–75.
[25] Shinohara N. Beam efficiency of wireless power transmission via radio waves
from short range to long range. J Korea Electromagn Eng Soc 2011;10:224–30.
[26] Shinohara N. Wireless power transmission progress for electric vehicle in
Japan. In: Proceedings of 2013 IEEE Radio and Wireless Symposium (RWS),
IEEE; 2013. p. 109–11.
[27] Shinohara N, Niwa N, Takagi K, Hamamoto K, Ujigawa S, Ao J-P, et al.
Microwave building as an application of wireless power transfer. Wirel Power
Transf 2014;1:1–9.
[28] Klontz K, Esser A, Bacon R, Divan D, Novotny D, Lorenz R. An electric vehicle
charging system with 'universal' inductive interface. In: Proceedings of 1993
conference record of the: IEEE power conversion conference, Yokohama; 1993.
p. 227–32.
[29] SangCheol M, Bong-Chul K, Shin-Young C, Gun-Woo M. Analysis and design of
wireless power transfer system with an intermediate coil for high efficiency.
ECCE Asia Downunder (ECCE Asia), IEEE; 2013. p. 1034–40.
[30] 〈http://www.altfuels.org/events/testdriv/farewell.html〉 [accessed 20.05.13].
[31] Wang C-S, Stielau OH, Covic GA. Design considerations for a contactless
electric vehicle battery charger. IEEE Trans Ind Electron 2005;52:1308–14.
[32] Kurs A, Karalis A, Moffatt R, Joannopoulos JD, Fisher P, Soljačić M. Wireless power
transfer via strongly coupled magnetic resonances. Science 2007;317:83–6.
[33] Karalis A, Joannopoulos JD, Soljačić M. Efficient wireless non-radiative midrange energy transfer. Ann Phys 2008;323:34–48.
[34] Ricketts DS, Chabalko MJ, Hillenius A. Experimental demonstration of the
equivalence of inductive and strongly coupled magnetic resonance wireless
power transfer. Appl Phys Lett 2013;102 053904–4.
K.A. Kalwar et al. / Renewable and Sustainable Energy Reviews 47 (2015) 462–475
[35] Takanashi H, Sato Y, Kaneko Y, Abe S, Yasuda T. A large air gap 3 kW wireless
power transfer system for electric vehicles. Energy Conversion Congress and
Exposition (ECCE), IEEE; 2012. p. 269–74.
[36] Kurschner D, Rathge C, Jumar U. Design methodology for high efficient
inductive power transfer systems with high coil positioning flexibility. IEEE
Trans Ind Electron 2013;60:372–81.
[37] Hori Y.Novel EV society based on motor/capacitor/wireless—application of
electric motor, supercapacitors, and wireless power transfer to enhance
operation of future vehicles. Microwave workshop series on innovative
wireless power transmission: technologies, systems, and applications (IMWS),
2012 IEEE MTT-S international: IEEE; 2012. p. 3–8.
[38] 〈http://www.pluginnow.com/sites/default/files/PluglessL2_Specs.pdf〉
[accessed 20.04.14].
[39] Gehm R. Inductive charging gets green flag, truck & bus engineering online,
SAE international; Aug. 2011.
[40] Kesler M. Highly resonant wireless power transfer: safe, efficient, and over
distance. WiTricity Corp; 2013.
[41] 〈http://phys.org/news/2013-08-wireless-online-electric-vehicle-olev.html〉
[accessed 20.04.14].
[42] 〈http://www.businesskorea.co.kr/article/4766/wireless-train-wirelessly-char
ged-high-speed-train-successful-test-run〉 [accessed 30.05.14].
[43] Budhia M, Covic G, Boys J. A new IPT magnetic coupler for electric vehicle
charging systems. In: Proceedings of IECON 2010-36th annual conference on
IEEE industrial electronics society: IEEE; 2010. p. 2487–92.
[44] Keeling NA, Covic GA, Boys JT. A unity-power-factor IPT pickup for high-power
applications. IEEE Trans Ind Electron 2010;57:744–51.
[45] Covic G, Boys J. Inductive power transfer (IPT) powering our future. New
Zealand: Power Electronics Research Group, The University of Auckland; 2010
[Tech Rep].
[46] Budhia M, Boys JT, Covic GA, Huang C-Y. Development of a single-sided flux
magnetic coupler for electric vehicle IPT charging systems. IEEE Trans Ind
Electron 2013;60:318–28.
[47] Lee S-H, Lorenz RD. A design methodology for multi-kW, large air-gap, MHz
frequency, wireless power transfer systems. Energy Conversion Congress and
Exposition (ECCE), IEEE; 2011. p. 3503–10.
[48] Wang C-S, Covic GA, Stielau OH. Power transfer capability and bifurcation
phenomena of loosely coupled inductive power transfer systems. IEEE Trans
Ind Electron 2004;51:148–57.
[49] Covic GA, Boys JT. Modern trends in inductive power transfer for transportation applications. IEEE J Emerg Sel Top Power Electron 2013;1:28–41.
[50] Villa JL, Sallan J, Sanz Osorio JF, Llombart A. High-misalignment tolerant compensation topology For ICPT systems. IEEE Trans Ind Electron 2012;59:945–51.
[51] Huang C-Y, Boys JT, Covic GA, Ren S. LCL pick-up circulating current controller
for inductive power transfer systems. Energy Conversion Congress and
Exposition (ECCE), IEEE; 2010. p. 640–6.
[52] Amjad M, Salam Z, Facta M, Mekhilef S. Analysis and implementation of
transformerless LCL resonant power supply for ozone generation. IEEE Trans
Power Electron 2013;28:650–60.
[53] Moradewicz AJ, Kazmierkowski MP. Contactless energy transfer system with
FPGA-controlled resonant converter. IEEE Trans Ind Electron 2010;57:3181–90.
[54] Throngnumchai K, Kai T, Minagawa Y. A study on receiver circuit topology of a
cordless battery charger for electric vehicles. Energy Conversion Congress and
Exposition (ECCE), IEEE; 2011. p. 843–50.
[55] Pantic Z, Bai S, Lukic S. ZCS-compensated resonant inverter for inductivepower-transfer application. IEEE Trans Ind Electron 2011;58:3500–10.
[56] Sakamoto H, Harada K, Washimiya S, Takehara K, Matsuo Y, Nakao F. Large airgap coupler for inductive charger [for electric vehicles]. IEEE Trans Magn
1999;35:3526–8.
[57] Mecke R, Rathge C. High frequency resonant inverter for contactless energy
transmission over large air gap. In Proceedings of IEEE 35th annual: IEEE power
electronics specialists conference, 2004 PESC 04 2004; 2004. p. 1737–43.
475
[58] Zheng C, Chen R, Faraci E, Zahid ZU, Senesky M, Anderson D., et al. High
efficiency contactless power transfer system for electric vehicle battery
charging. Energy Conversion Congress and Exposition (ECCE), IEEE; 2013. p.
3243–9.
[59] Sibue J, Kwimang G, Ferrieux J, Meunier G, Roudet J, Périot R. A Global Study of
a Contactless Energy Transfer System: Analytical Design, Virtual Prototyping
and Experimental Validation. IEEE Trans Power Electron 2012;28:4690–9.
[60] Lee S-H, Lorenz RD. Development and validation of model for 95%-efficiency
220-W wireless power transfer over a 30-cm air gap. IEEE Trans Ind Appl
2011;47:2495–504.
[61] Wu HH, Gilchrist A, Sealy KD, Bronson D. A high efficiency 5 kW inductive
charger for EVs using dual side control. IEEE Trans Ind Inform 2012;8:585–95.
[62] Budhia M, Covic GA, Boys JT. Design and optimisation of magnetic structures
for lumped inductive power transfer systems. Energy Conversion Congress
and Exposition, 2009 ECCE, IEEE; 2009. p. 2081–8.
[63] Nagatsuka Y, Noguchi S, Kaneko Y, Abe S, Yasuda T, Ida K., et al. Contactless
power transfer system for electric vehicle battery charger. In: Proceedings of
25th world battery, hybrid and fuel cell electric vehicle symposium and
exhibition (EVS-25), Shenzhen China; 2010.
[64] Chigira M, Nagatsuka Y, Kaneko Y, Abe S, Yasuda T, Suzuki A. Small-size lightweight transformer with new core structure for contactless electric vehicle
power transfer system. Energy Conversion Congress and Exposition (ECCE),
IEEE; 2011. p. 260–6.
[65] Rao KS, Nikitin PV, Lam SF. Antenna design for UHF RFID tags: a review and a
practical application. IEEE Trans Antennas Propag 2005;53:3870–6.
[66] Peschiera B, Williamson SS. Review and comparison of inductive charging
power electronic converter topologies for electric and plug-in hybrid electric
vehicles. Transportation Electrification Conference and Expo (ITEC), IEEE;
2013. p. 1–6.
[67] Lukic SM, Saunders M, Pantic Z, Hung S, Taiber J. Use of inductive power
transfer for electric vehicles. IEEE Power and Energy Society General Meeting:
IEEE; 2010. p. 1–6.
[68] 〈http://www.sae.org/servlets/pressRoom?OBJECT_TYPE=PressRe
leaes&PAGE=showRelease&RELEASE_ID=2296〉 [accessed 30.12.13].
[69] SAE electric vehicle and plug-in hybrid electric vehicle conductive charge
coupler, SAE Standard J1772; Jan. 2010.
[70] Prasanth V, Bauer P. Study of misalignment for on road charging. Transportation Electrification Conference and Expo (ITEC), IEEE; 2013. p. 1–8.
[71] Ramos RR, Biel D, Fossas E, Guinjoan F. A fixed-frequency quasi-sliding control
algorithm: application to power inverters design by means of FPGA implementation. IEEE Trans Power Electron 2003;18:344–55.
[72] Trevisan R, Costanzo A. State-of-the-art of contactless energy transfer (CET)
systems: design rules and applications. Wirel Power Transf 2014;1:10–20.
[73] M. B. Scudiere JWM, J.M. Miller. Design of Wireless Power Transfer for
Stationary and Moving Hybrid Electric Vehicles. SAE World Congress. Cobo
Center, Detroit, MI, 2011. p. 2011-01-0354.
[74] Li HL, Hu A, Covic G. FPGA controlled high frequency resonant converter for
contactless power transfer. Power Electronics Specialists Conference, 2008
PESC, IEEE; 2008. p. 3642–7.
[75] Shin J, Shin S, Kim Y, Ahn S, Lee S, Jung G, et al. Design and implementation of
shaped magnetic-resonance-based wireless power transfer system for roadwaypowered moving electric vehicles. IEEE Trans Ind Electron 2014;61:1179–92.
[76] Omori H, Nakaoka M, Iga Y. A new resonant IPT-wireless EV charging system
with single-ended quasi-resonant inverter for home use. 2013 IEEE 14th
workshop on Control and Modeling for Power Electronics (COMPEL), IEEE;
2013. p. 1–7.
[77] Hu AP. Selected resonant converters for IPT power supplies: ResearchSpace@
Auckland; 2001.
[78] Akter MP, Mekhilef S, Tan NML, Akagi H. Model predictive control of
bidirectional AC–DC converter for energy storage system.