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i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 7 ) 1e1 2
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Design and analysis of a wireless power transfersystem with alignment errors for electrical vehicleapplications
Sakir Kuzey a, Selami Balci b, Necmi Altin c,*
a Giresun University, Sebinkarahisar Vocational Schools of Technical Sciences, Electricity and Energy Department,
28400, Giresun, Turkeyb Ministry of National Education, Ankara, Turkeyc Gazi University, Faculty of Technology, Electrical and Electronics Engineering Dept., 06500, Ankara, Turkey
a r t i c l e i n f o
Article history:
Received 8 November 2016
Received in revised form
18 March 2017
Accepted 22 March 2017
Available online xxx
Keywords:
Inductively coupled power transfer
(ICPT)
Wireless power transfer
Electric vehicles
Alignment error
* Corresponding author.E-mail address: [email protected] (N. Alt
http://dx.doi.org/10.1016/j.ijhydene.2017.03.10360-3199/© 2017 Hydrogen Energy Publicati
Please cite this article in press as: Kuzey S,electrical vehicle applications, Internationa
a b s t r a c t
In this study, a 15 kWwireless power transfer system with high frequency and large air gap
for electrical vehicle battery charge systems is designed and co-simulations with ANSYS-
Maxwell and Simplorer software are performed. The air gap between the primary and
the secondary windings are determined as 20 cm for the 15 kW wireless power transfer
system. Operation of the designed system for different operation conditions such as
completely aligned windings (ideal condition) and windings with alignment errors, which
can occur because of user error or another reason, are analyzed and obtained results are
reported. The resonant frequency of the designed system which has a 60 � 60 cm sec-
ondary winding and a 60 � 100 cm primary winding is 17.702 kHz, and the maximum ef-
ficiency of the system is obtained as 75.38% for completely aligned windings. The
distribution and density of the electromagnetic flux, and variation of efficiency versus load
level of the system and responses of the system in case of different alignment errors are
also investigated and reported for both ideal operation conditions and in case of alignment
errors.
© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction
Nowadays, reasons such as increase in the price of oil and its
derivatives, extinction of fossil fuels and global warming in-
crease the attention on electrical vehicles (EVs). Environ-
mental friendly EVs have become the main driving force for
automotive industry with their zero emission feature [1e3].
While the battery bank of the conventional EV is charged
through the grid with a power cable and a plug, more safe
in).60ons LLC. Published by Els
et al., Design and analysl Journal of Hydrogen Ene
wireless charge systems have become to use for the same
purpose with the improvements in technology.
Similar to electrical machines and transformers, power
transmission from one winding to the other one, which are
magnetically coupled, is essentially known method. The
overall objective of the inductively coupled power transfer
(ICPT) systems is to provide wireless power transfer effi-
ciently. The inductive coupling coefficient is one of the most
important parameter of these systems. Since the power is
transferred form primary winding to the secondary winding
evier Ltd. All rights reserved.
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 7 ) 1e1 22
through the air gap according to the magnetic induction
principle, the electromagnetic coupling coefficient is decisive
variable that affects the system performance. Therefore,
many studies have been proposed on determining optimal
coupling coefficient and power factor compensation to obtain
efficient power transfer [4].
Effects of ICPT systems on human body is an important
issue and should be examined. These systems should comply
with standards defined by International Commission on Non-
Ionizing Radiation Protection (ICNIRP). Many studies have
been performed to analyze effects of electromagnetic systems
on human body. Although the operation frequency of
communication systems is in range from MHz to GHz, the
operating frequency values of the ICPT systems are usually
lower than a few kHz because of efficiency and power level
limitations. It is reported that, a proper designed ICPT system
comply with the standards and they do not have hazardous
effects on the human health [5].
ICPT systems are usually designed as spiral circles and
rectangle geometries. The mutual inductance value of a ICPT
systemwith spiral circles is also 45e50% higher than the ICPT
system with rectangle geometries. Although, magnetic
coupling value of the ICPT system with the spiral circles is
higher, the ICPT systemwith rectangle geometries have better
performance under alignment errors. Therefore, rectangle
geometries are more common in EV applications [6]. In addi-
tion, ferrite core can be used in primary and secondary
windings to increase the coupling coefficient [7]. In this con-
dition, windings can be designed in different forms to ob-
tained maximum efficiency. However, in this case, increasing
core temperature triggers some disadvantages such as
decreasing on coupling coefficient and linearity reduction on
system control [8e10].
Enlarging size of the primary winding will not increase the
system efficiency. In addition, this increases the system cost
because of increasing conductor length and size of mechani-
cal design. At this point, concordance between primary and
secondary windings has come to the forefront. Themaximum
system efficiency is obtained with optimum inductive
coupling coefficient, proper compensation topology, and
providing operation at resonant frequency [11,12].
Since these ICPT systems are supplied with high frequency
voltage, resonant converters, which are commonly used in
different applications such as induction heating, electronic
ballasts, power supplies, etc., are used at the converter stage
to obtain higher efficiency values [13,14]. Therefore, there are
Fig. 1 e Electrical equivalent
Please cite this article in press as: Kuzey S, et al., Design and analyselectrical vehicle applications, International Journal of Hydrogen Ene
number of studies on electromagnetic design of the ICPT
system [15,16], converter and resonator circuit design issues
[17,18]. In addition, the placement of the ICPT system receiver
and transmitter windings directly affects the system perfor-
mance. Alignment errors are very common in a practical
wireless power transfer system for EV applications Therefore,
some studies on auto-alignment of the EVs are also proposed
[19]. However, effects of different alignment errors on system
performance are rarely analyzed.
In this study, a 15 kW ICPT system with 20 cm air gap is
designed. Then the designed system is simulated with finite
element analysis software. The model of the ICPT system is
also co-simulated with inverter and compensation circuits to
obtain more realistic results. Besides the ideal operation
conditions without any alignment error, presence of different
alignment errors between thewindings are also analyzed. The
flux distribution, and efficiency of the ICPT system are inter-
preted. In addition, efficiency variation versus load is also
analyzed. It is seen from the simulation results that the pro-
posed system is low magnetic coupled systems with 0.1556
electromagnetic coupling coefficient. In addition, the
maximum efficiency value of the ICPT system is obtained as
75.38% for ideal condition, and 33.35% and 46% for alignment
error and 2-degree gradient alignment error conditions,
respectively.
Inductive magnetic coupled power transfersystems
Uncompensated circuit model of inductive magnetic coupled
power transfer system, which makes understanding the sys-
tem easy is seen in Fig. 1. This is the most fundamental figure
[20]. Here, Vp is rms value of sinusoidal signal applied to pri-
mary winding. Assuming that voltage and current are sinu-
soidal, the induced voltage in secondary winding due to the
primary current Ip is juMIp, reflected voltage in the primary
winding due to the secondary current Is is�juMIs where “M” is
on themutual inductanceandu is theoperation frequency [21].
Mathematical equation of system's equivalent circuit must
be derived in order to follow power flow of ICPT system. Ac-
cording to equivalent circuit, Eq. (1) can be written for input
voltage Vp [7,8,11].
Vp ¼�Rp þ j
�uLp
��Ip � juMIs ¼
�Rp þ jXp
�Ip � juMIs
¼ ZpIp � juMIs (1)
circuit of ICPT system.
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
Fig. 2 e Windings with rectangular geometry.
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 7 ) 1e1 2 3
ICPT systems provides high efficiency at low power, low
frequency such as 50e60 Hz and at high mutual inductance
[7]. However, when high power is concern, power trans-
mission becomes more difficult. System must have an
appropriate magnetic coupling coefficient at high resonance
frequency. Furthermore, it is realized that losses which may
occur in the system affect the efficiency of the system. For this
reason, these systems are operated at resonance frequency in
order to minimize the losses. Despite this, the operating fre-
quency is usually under 100 kHz for high power applications
due to switching losses [21]. Besides, Litz wire is used to
reduce skin effect and proximity effect losses which occur in
windings [8,11].
The magnetic coupling coefficient (k) is a value which
shows how much of the magnetic flux created by the primary
is transferred to the secondary circuit. Therefore, the effi-
ciency of the power transferred from the primary to the sec-
ondary depends on the magnetic coupling coefficient. The
magnetic coupling coefficient is given in Eq. (2).
k ¼ MffiffiffiffiffiffiffiffiLpIs
p (2)
It can be seen that themutual inductance and themagnetic
coupling coefficient have a strong impact on each other. But, it
does not mean that an increase at mutual inductance in-
creases the magnetic coupling coefficient. Other determining
parameters are the primary and the secondary inductance
values. According to this, it is understood that the windings
must have optimal parameter values.
Themagnetic coupling coefficient must be within a certain
range depending on the compensation topology. There must
be a strong magnetic connection between the primary and
secondary windings in order to provide high efficient power
transfer. Increase in air gap between the windings decreases
the magnetic coupling coefficient and systems which have
magnetic coupling coefficient under 0.2 are accepted as low
magnetic coupled systems. In addition, the air gap distances
between the windings must be homogenous and the winding
conductors must be aligned. In the absence of this alignment
themagnetic connectionwill not be strong and this reduce the
system efficiency.
In air-gapped transformers, the coupling coefficient and
the quality factors (Q) of the windings are two important pa-
rameters. The quality factor reflects a largemagnetic field and
minimal loss creation capacity of the windings. The relation-
ship between the secondary reactive and active power has
been given in Eq. (3) which is considered to be equal to the
secondary winding quality factor [11].
Qs ¼ VArsPs
(3)
ICPT system with rectangle geometry
In the scaling of the windings the width and the lengths of the
primary and the secondary windings, are denoted as a1, a2, b1and b2, respectively. Following equations given by Sall�an et al.,
the single side lengths created by the windings (r1 and r2 given
in Fig. 2) are given by Eq. (4) and Eq. (5) [8].
Please cite this article in press as: Kuzey S, et al., Design and analyselectrical vehicle applications, International Journal of Hydrogen Ene
r1 ¼ffiffiffiffiffiffiffiffiffiffiffiNpSp
p
r(4)
r2 ¼ffiffiffiffiffiffiffiffiffiffiNsSs
p
r(5)
The ‘c’ and ‘e’ given in Fig. 2 are alignment errors and they
must be zero to obtain high efficient ICPT system. The primary
and secondary windings resistances (Rp and Rs, respectively)
are given in Eq. (6) and Eq. (7), respectively [8].
Rp ¼ rcuNp2ða1 þ b1Þ
Sp(6)
Rs ¼ rcuNs2ða2 þ b2Þ
Ss(7)
Since the Litz wire is used in windings, the skin effect and
the proximity effect is neglected. The primary and secondary
winding impedances are given in Eq. (8) and Eq. (9) [8].
Lp¼m0
pN2
p
26664a1ln
2a1b1
r1
�a1þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�a21þb2
1
r þb1ln2a1b1
r1
�b1þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�a21þb2
1
r
�2
�a1þb1�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffia21þb2
1
q þ0:25ða1þb1Þ
37775:
(8)
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 7 ) 1e1 24
Ls¼m0
pN2
s
26664a2ln
2a2b2
r2
�a2þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�a22þb2
2
r þb2ln2a2b2
r2
�b2þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�a22þb2
2
r
�2
�a2þb2�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffia22þb2
2
q þ0:25ða2þb2Þ
37775:
(9)
Assuming that the primary and secondary windings are at
the same dimensions and the alignment error is zero (ideal
case), the mutual inductance value is calculated as shown in
Eq. (10).
M ¼ m0
pNsNp
2664a1ln
�a1 þ
� ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ a2
1
p � ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ b2
1
q �a1 þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ a2
1 þ b21
q h
þ b1ln
�b1 þ
� ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ a2
1
p � ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ b2
1
q �b1 þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ a2
1 þ b21
q h
� 2
�h�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ a2
1
q
þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ b2
1
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ a2
1 þ b21
q 3775
(10)
It can be seen that when Eq. (8), Eq. (9) and Eq. (10) are
analyzed, the primary and secondary impedance and mutual
impedance value calculations change depending on distances
between the windings and the properties of the magnetic
material, numbers of turn of the primary and secondary
windings, windings' cross-sectional area and dimensions of
the windings. Besides, these calculations are independent to
the electrical circuit equations. When the primary and the
secondary windings are considered to be non-aligned and
have different dimensions, mutual inductance value calcula-
tion becomes different as given in Appendices [8].
Fig. 3 e Compensation topologies
Please cite this article in press as: Kuzey S, et al., Design and analyselectrical vehicle applications, International Journal of Hydrogen Ene
Compensation topologies
Disadvantages of the inductive magnetic coupling can be
removed by adding compensation capacitors to both primary
and secondary sides and thus total system efficiency can be
improved [22]. Compensation capacitors are used to increase
the power transfer efficiency and system capacity in ICPT
systems. Compensation capacitors have different effect at
both sides. They help to decrease the input current when they
added to the primary side, while they are used to increase the
power transfer capacity of the ICPT system at secondary side.
There are four basic compensation topologies such as Serial-
eSerial (SS), SerialeParallel (SP), ParalleleParallel (PP) and
ParalleleSerial (PS). These topologies are depicted in Fig. 3 [11].
Each topology has some advantages and disadvantages in
terms of transfer capacity, cost etc. and has different appli-
cation areas according to their specifications.
The secondary side of the Serial compensation has voltage
source specifications, while the secondary side of the Parallel
compensation has current source specifications [18,23]. SS
and SP compensation topologies provide an advantageous
power transfer. Besides, PS and PP topologies can operatewith
larger air gaps for same operation frequency at low power
levels where winding specifications are not an important
parameter [24]. When capacitor requirement of the deter-
mined topology is not considered, parallel compensation to-
pologies bring out the result of operation at lower frequency,
higher current and lower voltage values. This constitutes
higher current requirements at low operating frequency
values [24]. In addition, in case of horizontal axis alignment
errors, the leakage inductance of the primarywindingmust be
higher to minimize the supply side VA ratings [25]. This cri-
terion should not be ignored while the primary side
compensation topology is selected. In the secondary side, the
compensation topology is used to improve the power transfer
capability. The VA rating is completely a function of the ge-
ometry and material properties of the secondary winding.
Thus, VA rating of a certain geometry is obtained as a function
of operating frequency [23]. Optimum topology can be selected
used in ICPT system design.
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 7 ) 1e1 2 5
by analyzing these topologies for specifications of the
application.
ICPT system with SerialeSerial (SS) compensation
The structure of the SS compensation topology is simple.
The primary side capacitor is independent from magnetic
coupling and load [8,26]. Values of the compensation ca-
pacitors and quality factor can be obtained from equations
presented by Wang et al. [8,11]. Secondary side capacitor is
used to operate the system at resonant, thus to obtain
maximum power transfer capacity, while the primary side
capacitor is used to keep the reactive power demand at zero.
The size and volume of the windings in SS topology are
lower than other topologies, and the winding size is not
linear with the transferred power. A general circuit model of
the ICPT system with SS compensation topology is given in
Fig. 4. This circuit can be analyzed in two parts as primary
circuit and secondary circuit. Power is transferred from the
primary side to the secondary side at the desired quality and
the load which is depicted as RL is supplied. In addition, all
parameters and their effects can be obtained by transferring
secondary side components to primary side. Here, Vp is
output voltage of the power converter and input voltage of
the ICPT system [27].
By using Eq. (7) and Eq. (10), Vp can be obtained as given
below:
Vp ¼�Rp þ j
�uLp � 1
uCp
�Ip � juMIs ¼
�Rp þ jXp
�Ip � juMIs
¼ ZpIp � juMIs (11)
where ZS is the impedance of the secondary side circuit and it
can be written as:
Zs ¼ Rs þ RL þ j
�uLs � 1
uCs
(12)
The primary side impedance ZP is obtained as follows:
Zp ¼ Rp þ j
�uLp � 1
uCp
þ Zr (13)
The secondary side impedance Zr transferred to the pri-
mary side can be written as given below:
Zr ¼ u2M2
ZS(14)
By substitution Eq. (14) into Eq. (13), Eq. (15) is obtained:
Fig. 4 e ICPT sys
Please cite this article in press as: Kuzey S, et al., Design and analyselectrical vehicle applications, International Journal of Hydrogen Ene
Zp ¼ Rp þ j
�uLp � 1
uCp
þ u3CsM2
uCsðRs þ RLÞ þ jðu2LsCs � 1Þ (15)
Similarly, by substituting Eq. (12) into Eq. (14), real and
imaginal components of the Zr is obtained as given Eq. (16)
and Eq. (17), respectively:
ReZr ¼ u4C2sM
2RL
ðu2CsLs � 1Þ2 þ ðuCsRLÞ2(16)
ImZr ¼ �u3CsM2ðu2CsLs � 1Þðu2CsLs � 1Þ2 þ ðuCsRLÞ2
(17)
The resistance transferred to the primary side at resonant
frequency can be obtained by using Eq. (18) and Eq. (19):
ReZr0 ¼ ReZrðu¼u0Þ (18)
ReZr0 ¼ uo2M2
RL(19)
The imaginal component of the impedance that trans-
ferred to the primary side should be zero to obtain resonant
mode operation. The input voltageVp can be obtained as given
with Eq. (20) by using above equations:
Vp ¼ ZpIp (20)
Thus, root mean square (rms) value of the input voltage
that should be generated by the power converter is deter-
mined. In addition, the secondary side current IS can be ob-
tained as given in Eq. (21):
Is ¼ juMIpZs
(21)
The load voltage, VL, can be obtained by subtracting resis-
tive and inductive voltages from secondarywinding voltage as
given in Eq. (22):
VL ¼ juMIp ��Rs þ j
�uLs � 1
uCs
�Is (22)
The power value (P) that transferred from primary side to
secondary side is given as below:
P ¼ Re½Zr�I2p (23)
If the system is operating at secondary side resonant fre-
quency, there is not any limit about its power transfer ca-
pacity. Then, the angular resonant frequency, uo, is given in
Eq. (24) [11]:
tem model.
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
Table 3 e Calculated ICPT system parameters.
Symbol 15 kW system
N1 6
N2 6
S1 (mm2) 38
S2 (mm2) 28
R1 0.0085
R2 0.0073
Rp (ohm) 0.0089
Rs (ohm) 0.0090
L1 (mH) 91.217
L2 (mH) 67.103
M 12.175
k 0.1556
f (kHz) 17.702
C1 (mF) 0.88619
C2 (mF) 1.2046
VLh 133.7968
PLh 14.734
Qp 6.7225
Qs 6.1428
h (efficiency) 0.986
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 7 ) 1e1 26
uo ¼ 1ffiffiffiffiffiffiffiffiffiffiLsCs
p ¼ 1ffiffiffiffiffiffiffiffiffiffiLpCp
p (24)
Therefore, the condition that given in Eq. (25) should be
realized to obtained maximum system efficiency [8].
uo[
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiRpðRs þ RLÞ
pM
(25)
When RL ¼ 0, in other words at no load condition, since the
primary current is assumed as constant, the secondary
resistance transferred to the primary side and the power
transfer capacity is to infinity [11]. When the quality factor
equation given in Eq. (3) is rearranged according to the SS
compensation topology, Eq. (26) is obtained [11]:
Qs ¼ uoLsRL
(26)
Design of ICPT system
In this study, 15 kW ICPT system is designed. The method
proposed by Kalwar et al [28]. is used but the windings di-
mensions are kept constant. TheMATLAB code is designed for
this aim, and system parameters are calculated for predefined
design considerations. The initial values in MATLAB code are
used as zero. The geometric specifications of the ICPT system
given in Table 1 are used as input data, and then the
maximum number of turns value which is an important
parameter in terms of desired maximum power and total
system cost is determined. In the MATLAB code, some con-
ditions which are given in Table 2 are used to ensure the al-
gorithm to work properly [8]. All conditions are given in Table
2 are analyzed, and the parameters of the ICPT system which
are valid for all these conditions are calculated and given in
Table 3. While these values are calculated, the transformer is
Table 1 e Dimensions of the ICPT system.
Symbol 15 kW system
h (cm) 20
a1 (cm) 60
a2 (cm) 60
b1 (cm) 100
b2 (cm) 60
c (cm) 0
e (cm) 0
V1 (volt) 150
RL (ohm) 1.215
Table 2 e Defined conditions for the ICPT system.
Parameter Condition
Power PLðN1;N2Þ ¼ PloadVoltage VLðN1;N2Þ ¼ Vload
Frequency fopðN1;N2Þ � fmax
Quality factor QpðN1;N2Þ>QsðN1;N2ÞPrimary winding current d1ðN1;N2Þ � d1maxðN1;N2ÞSecondary winding current d2ðN1;N2Þ � d2maxðN1;N2Þ
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considered to operate in ideal conditions and inverter losses
are neglected.
Simulation results
After parameters of the system have been determined, the
ICPT system is modelled with ANSYS-Maxwell according to
the calculated parameters, and co-simulation studies are
performed with electrical circuits such as compensation cir-
cuits and inverter, which are designed with Simplorer. The
ANSYS-Maxwell model of the proposed ICPT system designed
with parameters given in Tables 1 and 3 is depicted in Fig. 5.
Here, the alignment error between windings is assumed as
zero and simulation studies of the system is performed for
20 cm air gap between the primary and the secondary wind-
ing. As it is seen from the figure, while dimensions of the
secondary winding are 60 � 60 cm, dimensions of the primary
winding are 60 � 100 cm for 15 kW ICPT system. The system is
loaded with a 1.215 U resistor and supplied with a AC supply
voltage of 150 V (rms). The ANSYS-Simplorer circuit used in
co-simulation studies is shown in Fig. 6. The ICPT system
designed with ANSYS-Maxwell is linked to the Simplorer cir-
cuit, and thus two models are simulated together, and the
designed ICPT system is tested under conditions closer to real
operation conditions.
The designed ICPT system is supplied with single phase H-
bridge inverter which is operated in resonant via the
compensation circuits connected to the primary and second-
ary windings. The electromagnetic flux distribution and effi-
ciency values obtained from simulation studies are
investigated. The electromagnetic flux distribution for full
load condition is given in Fig. 7. While the flux density is 1 mT
on thewindings, it ismeasured as 0.54mT at the air gap. Since
the air gap between the windings of the proposed wireless
power transfer system is large as 20 cm, the electromagnetic
flux density value is low. In addition, the electromagnetic
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
Fig. 5 e ANSYS-Maxwell model of the proposed ICPT
system.
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 7 ) 1e1 2 7
coupling coefficient is 0.1556, and therefore this system is
grouped into low magnetic coupled systems. In order to
transfer high power levels, the ICPT system must be operated
at high frequencies. This increases the primary side imped-
ance value and decrease the power factor. This also causes
high VA ratio at inverter side and reduces the power transfer
efficiency. The system efficiency can also be increased by
decreasing the air gap length. However, since the system
designed for battery charger of electrical vehicles, decreasing
air gap length is not a desired situation.
In simulation studies, the resistance, which is representing
the battery, is increased parametrically and the efficiency
variation with the load level is analyzed. Low load, rated load
Fig. 6 e The ANSYS-Simplorer mo
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and overload operation conditions are analyzed, and variation
of the efficiency with load level is depicted in Fig. 8. As it is
seen from the figure, maximum efficiency value is obtained as
75.38%. In addition, it is seen that, in overload conditions,
system efficiency decreases quickly. In the past studies higher
and lower efficiency values have been reported (40%e92%)
with different coupling coefficient, air gap and operation fre-
quency values. However, one should consider the distance
between primary and secondary windings which greatly af-
fects the coupling coefficient. Since the coupling coefficient of
the designed ICPT system is 0.2, by considering this value, it
can be said that a high efficiency design is obtained [4,27 and
28].
The designed 15 kW ICPT system is also analyzed with
alignment errors both on width (c) and length (e) of windings
by using ANSYS-Maxwell and Simplorer software. The align-
ment error on width and length of windings are 10 cm and
15 cm respectively. Side and top views of the ANSYS-Maxwell
model of the proposed system with alignment errors are
depicted in Fig. 9. The flux distribution of the ICPT system
obtained from ANSYS-Maxwell while there are alignment er-
rors are shown in Fig. 10. The flux density on windings is
measured as 0.84 mT, while the flux density at the air gap is
measured as 0.36 mT. It is seen that, the flux density of the
analyzed 15 kW ICPT systemdecreaseswhen alignment errors
occur. Thus, it can be easily said that, alignment errors will
affect the system efficiency.
The variation of the efficiency versus load is also investi-
gated for the system with alignment errors. The obtained ef-
ficiency variation curve is shown in Fig. 11. The efficiency
variation of both operation conditions (with and without
alignment errors) are depicted in Figure. It is seen that align-
ment errors cause a significant decrease on the maximum
efficiency value. The maximum efficiency of the system with
alignment errors is obtained as 33.35%. Although alignment
errors do not change the air gap value, which is 20 cm, they
cause a decrease in mutual inductance value and thus a
decrease in efficiency.
The modelled 15 kW ICPT system is also analyzed with
non-uniform air gap with ANSYS-Maxwell and Simplorer
software. The primary and the secondary windings are placed
with 2-degree gradient alignment error. The side and top
views of the windings' placement are depicted in Fig. 12. This
ICPT system is also co-simulated via Simplorer with power
del of the proposed system.
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
Fig. 7 e Flux distribution on windings.
Fig. 8 e The efficiency versus percentage of the load curve.
Fig. 9 e The 15 kW ICPT system with alignment errors, (a) Side view of windings, (b) Top view of windings.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 7 ) 1e1 28
Please cite this article in press as: Kuzey S, et al., Design and analysis of a wireless power transfer system with alignment errors forelectrical vehicle applications, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
Fig. 10 e Flux distribution of windings with alignment errors.
Fig. 11 e The efficiency versus load curve of the system with alignment errors.
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 7 ) 1e1 2 9
electronics converter. The flux distribution of the ICPT system
with non-uniform air gap is shown in Fig. 13. The flux density
is measured as 0.1 mT in the air gap that the distance between
the windings is smaller, and it is measured as 0.046 mT in the
air gap that the distance between the windings is larger. The
efficiency variation versus load level of the ICPT system with
2-degree gradient alignment error is given in Fig. 14. The
maximum efficiency is obtained as 46% for this operation
Fig. 12 e 15 kW ICPT system with 2-
Please cite this article in press as: Kuzey S, et al., Design and analyselectrical vehicle applications, International Journal of Hydrogen Ene
condition. Since the parameters are defined for a set of di-
mensions and ideal operation condition, the resonant opera-
tion cannot be achieved and therefore efficiency of the system
decreases. Although the efficiency of the system can be in-
crease by changing the system parameters, but this is not
possible in a practical system. The overload operation condi-
tion also decreases the system efficiency both ideal and non-
ideal operation conditions.
degree gradient alignment error.
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
Fig. 14 e The efficiency characteristics of the system with gradient alignment error.
Fig. 13 e Flux distribution of the 15 kW ICPT system with 2-degree gradient alignment error.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 7 ) 1e1 210
In Table 4, inductance values obtained for three different
operation conditions are given. As it is seen from Table 4,
values of the primary winding inductance (L1), the secondary
winding inductance (L2) and the mutual inductance (M)
decrease when alignment errors occur. Since compensation
circuit is designed for ideal condition, resonant frequency of
the system is also determined for ideal operation condition.
Therefore, in case of alignment errors, phase difference oc-
curs and VA ratings of the system increases and thus, effi-
ciency of the systemdecreases. If alignment errors are defined
in the MATLAB code and then parameters such as the number
of turns, the diameter of the windings, the operation fre-
quency and capacitor values are calculated, maximum
Table 4 e Inductance values of the 15 kW ICPT system fordifferent operation conditions.
Inductancevalues
Idealcondition
Misalignmentcondition(c ¼ 10 cm,e ¼ 15 cm)
Misalignmentcondition (2-degreegradient alignment
error)
L1 (mH) 91.217 70.01 78.15
L2 (mH) 67.103 49.65 54.60
M (mH) 12.175 9.15 10.72
Please cite this article in press as: Kuzey S, et al., Design and analyselectrical vehicle applications, International Journal of Hydrogen Ene
efficiency for these conditions can be obtained. However, this
is not practical for EV battery charge system.
Conclusions
In this study, design and simulation of the 15 kVA ICPT system
with a large air gap for wireless EV charge system is proposed.
The compensation topology which is an important parameter
in ICPT system design is evaluated and optimal topology is
determined. A MATLAB code is generated to calculate the
system parameters depending on the winding dimensions
and compensation topology, and system parameters are
calculated. According to calculated parameters, the ICPT
system model is generated with ANSYS-Maxwell. The gener-
ated model is linked to ANSYS-Simplorer and co-simulation
studies of both ICPT system model and power converter are
performed. The electromagnetic flux distribution and the
system efficiency are investigated in simulation studies.
Despite the large air gap, the maximum efficiency of the
proposed system for ideal operation conditions is obtained as
75.38%. Some effects such as switching losses, magnetic los-
ses are not considered in MATLAB code, therefore a difference
occurs between two efficiency values obtained from simula-
tion studies and calculated by MATLAB code. In addition,
is of a wireless power transfer system with alignment errors forrgy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.03.160
i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 7 ) 1e1 2 11
modeled 15 kVA ICPT system is simulated for different
alignment errors and effect of these errors are analyzed. The
system efficiency is obtained as 33.35% and 46% for alignment
error and 2-degree gradient alignment error conditions,
respectively. Besides, the maximum flux density values in the
air gap is obtained as 0.54 mT for all operation conditions, and
then it is seen that, the magnetic field that human body may
expose is in the limits of international standards.
Appendices
In case of misalignment, mutual inductance value can be
calculated as follows:
M ¼ m0
4pNpNs
2666666666666664
26666666664
d lndþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�tÞ2 þ d2
q
dþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ d2 þ q2
q þ h lngþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ q2 þ g2
q
gþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ g2 þ ð�tÞ2
q þ c ln�cþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ q2 þ c2
q
�cþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ c2 þ ð�tÞ2
q þm ln�mþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�tÞ2 þm2
q
�mþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þm2 þ q2
q þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ q2 þ d2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ q2 þ g2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ q2 þm2
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ q2 þ c2
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�tÞ2 þ g2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�tÞ2 þ d2
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�tÞ2 þm2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�tÞ2 þ c2
q
37777777775
�
2666666666664
d lndþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�pÞ2 þ d2
q
dþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ d2 þ e2
p þ g lnhþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ g2
q
gþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ h2 þ ð�pÞ2
q þ c ln�cþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ c2
p�cþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ c2 þ ð�pÞ2
q þ
m ln�mþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�pÞ2 þm2
q
�mþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þm2 þ e2
p þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ d2
p�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ g2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þm2
pþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ c2
pþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�pÞ2 þ g2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�pÞ2 þ d2
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�pÞ2 þm2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�pÞ2 þ c2
q
3777777777775
þ
26666666664
t lntþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�gÞ2 þ t2
q
tþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ t2 þ c2
p þ p lnpþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ p2 þ c2
q
pþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�gÞ2 þ p2
q þ e ln�eþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ c2
p�eþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ ð�gÞ2
q þ q ln�qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�gÞ2 þ q2
q
�qþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ c2 þ q2
q þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ c2 þ t2
p�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ c2 þ p2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ c2 þ q2
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ c2
pþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�gÞ2 þ p2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�gÞ2 þ t2
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�gÞ2 þ q2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�gÞ2 þ e2
q
37777777775
�
2666666664
t lntþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�dÞ2 þ t2
q
tþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ t2 þm2
p þ p lnpþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þm2 þ p2
q
pþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�dÞ2 þ p2
q þ e ln�eþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þm2
p�eþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þ ð�dÞ2
q þ q ln�qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�dÞ2 þ q2
q
�qþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þm2 þ q2
q þ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þm2 þ t2
p�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þm2 þ p2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þm2 þ q2
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ e2 þm2
pþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�dÞ2 þ p2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�dÞ2 þ t2
qþ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�dÞ2 þ q2
q�
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffih2 þ ð�dÞ2 þ e2
q
3777777775
3777777777777775
where
d ¼ a1 � a2 � c
m ¼ a2 þ c
q ¼ b2 þ e
g ¼ a1 � c
Please cite this article in press as: Kuzey S, et al., Design and analyselectrical vehicle applications, International Journal of Hydrogen Ene
p ¼ b1 � e
t ¼ b1 � b2 � e:
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