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0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2682793, IEEETransactions on Industry Applications
Bidirectional Current-Fed-Half-Bridge (C)(LC) –
(LC) Configuration for Inductive Wireless Power
Transfer System
Suvendu Samanta, Student Member IEEE, Akshay K. Rathore, Senior Member IEEE,
and Duleepa J. Thrimawithana, Member IEEE
Abstract -- This paper contributes to analysis and development
of a new power electronics system for bidirectional wireless power
transfer. The major focus is analysis and implementation of a new
current-fed resonant topology with current-sharing and voltage
doubling features. A new bidirectional wireless power transfer
system with current-fed half-bridge voltage doubler circuit is
proposed and analyzed with series-parallel and series resonant
networks. Traditionally used parallel L-C resonant tank in
transmitter circuit with current-fed WPT topology causes higher
voltage stress across the inverter devices to compensate the
reactive power consumed by the loosely coupled coil. In the
proposed topology, this is mitigated by adding a suitably designed
capacitor in series with the transmitter coil thus developing a
series-parallel CLC tank. Detailed analysis and design is reported
for both, grid-to-vehicle and vehicle-to-grid operations. The
power flow is controlled through variable frequency modulation.
Soft-switching of the devices is obtained irrespective of the load
current. A proof-of-concept experimental hardware prototype
rated at 1.2kW is developed and tested. Experimental results are
presented to verify the analysis and demonstrate the performance
of the system with bidirectional power flow.
Index Terms—Wireless power transfer, Voltage doubler,
Current-fed converter
I. INTRODUCTION
ireless power transfer (WPT) systems are capable of
transferring power over a large distance without any physical
contact. Various WPT applications are electric vehicles (EV)
[1]-[20], electronic gadgets, lighting, material handling and
biomedical implants. Capacitive WPT is usually implemented
for low power applications whereas the wireless inductive
power transfer (IPT) technology has been developed for both
low and medium power applications [8], [21].
Recently, research and development on IPT technology
for EV battery recharging application has grown tremendously
[1]. The IPT technology promises a convenient and safer way
of recharging the EV batteries. Ongoing research has proved
that the opportunistic charging with IPT technology reduces
the requirement on battery capacity significantly for a given
travel distance [8], [11] and is promising for local
transportation. A typical Inductive WPT system is shown in
Fig. 1. Generally, the front-end grid side ac-dc stage is chosen
as boost-type power factor correction (PFC) rectifier. For a
mid-range (100-300 mm) WPT, the IPT frequency is generally
selected around 20 kHz to 150 kHz to balance the converter
size, efficiency and cost [10], [19]. Voltage source inverter
(VSI) topologies in the inversion stage are commonly used and
reported in literature mainly because the ac-dc PFC output is a
voltage source [1]-[3]-[5], [11]. To reduce the number of
power conversion stages, direct ac-ac converters have also
been reported in [14].
AC-DC
Active
Rectifier
AC-DC
Coverter
200-300mm Air-gap
Transmitter
Coil
Receiver
Coil
120/230V
60/50Hz
Battery
Bank
On-BoardOff-Board
DC-AC
Convert
-er
Compensat
-ion/
Resonance
Network
Compensat
-ion/
Resonance
Network
Fig. 1. General IPT power conversion stages for EV battery charging
To compensate the reactive power in IPT system, the
simple method is to connect capacitor in both transmitter coil
(TC) and receiver coil (RC) circuits. It develops four types of
compensation networks such as series-series, series-parallel,
parallel-series and parallel-parallel. Transmitter side series
compensation is quite common when the inversion stage is
VSI topology [1]-[3], [11], [16], [21]. In addition, VSI
topologies with LCL [4], [10], [13] and CLCL [5], [10]
compensation networks have also been used for improved
power factor and better performance.
Transmitter side parallel compensation with current
source inverter (CSI) topologies is reported [12], [13]. The
merit of parallel resonant tank is that the capacitor provides the
required reactive power to the coil without flowing through the
inverter switches. In addition, the parallel capacitor provides
much lower impedance to the higher order harmonics and
hence, the coil voltage and current profiles are almost
harmonics free. However, at medium power level, the
requirement of higher voltage rated inverter devices is a major
limitation of transmitter side parallel LC tank. This is because
the parallel capacitor alone provides high volume of reactive
power consumed by the TC. To overcome this issue, in this
paper, a new IPT topology with current-fed converter is
proposed and analyzed. A capacitor is added in series with the
TC to develop CLC tank that reduce the voltage stress across
the inverter switches. Proposed IPT topology is capable of
conducting bidirectional power, thus enabling both grid-to-
vehicle (G2V) and vehicle-to-grid (V2G) operations.
This is the first attempt to implement bidirectional IPT
with current-fed topology with current-sharing voltage doubler
configuration [22]. This is an enhanced version of the paper
presented in [22] with additional results and detailed analysis
and design. DC link inductor provides natural short circuit
protection and also limits the peak and circulating current
through the components. Current sharing (half-bridge)
configuration further reduces the average and peak current
through the components resulting into reduced conduction
losses. Current-fed circuit also offers voltage gain and the
voltage doubler add 2x additional gain. Proposed converter is
analyzed and detailed design procedure is reported.
W
0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2682793, IEEETransactions on Industry Applications
It should be noted that the focus and contribution of this
research is on power electronics, not on the coils or magnetics
design. The objective of this paper is to analyze a bidirectional
current-sharing voltage doubler current-fed topology with new
CLC series-parallel resonant network. The objectives are
realized in various sections. Section II introduces the proposed
bidirectional topology and explains detailed G2Voperation.
Section III studies V2G operation in detail. Systematic design
and components’ selection of the converter are presented in
Section IV. Section V demonstrates experimental results for
both G2V and V2G operations.
II. PROPOSED BIDIRECTIONAL IPT TOPOLOGY
Fig. 2 shows the proposed bidirectional IPT topology where
the transmitter side high-frequency (HF) inverter is current-fed
half-bridge and receiver side HF rectifier is a voltage doubler.
During G2V operation, i.e., EV battery recharging operation,
the switches S1 and S2 are modulated while the switches S3
and S4 are kept permanently off. Compared with conventional
parallel LC tank network, an extra capacitor is added in series
with the TC to reduce the effect of high leakage of the coil to
form CLC series-parallel resonant circuit. The detailed
comparison of parallel LC and CLC tank network with the
inverter as half bridge and full-bridge current-fed converter is
presented in [23].
Transmitter Receiver
Off-Board
S2S1
Cp
vd
id
Ld1L1 i1
jωMi2
v1
Cs
vsvi
S3 S4
Ld2
ii
On-Board
vo
io
Co1
C2L2i2
jωMi1
v2
S5
S6
Co2
vr
Fig. 2. Bidirectional WPT topology using current-fed half bridge converter.
An appropriate size capacitor is connected in series with
receiver coil to compensate the reactive power consumed by
the receiver coil. The series compensation network is most
common in IPT application due to simple structure and load
independent resonance. However, series compensation both in
the transmitter and receiver sides leads to insatiably during no
load condition. However, in this paper only the receiver side
compensation is series LC type; therefore, this instability issue
does not arise here. The detail design considerations of series-
series compensated IPT topology are elaborately described in
[24]-[29]. During G2V operation the voltage doubler network
is used as an uncontrolled rectifier whereas during V2G
operation, this converter acts as an inverter. The voltage across
and current through the switches are named as vS1 ~ vS6 and iS1
~ iS6, respectively and these signals for their body diodes are
named as vD1 ~ vD6 and iD1 ~ iD6, respectively.
A) Steady state operation of G2V
To explain the steady-state operation of the proposed
converter, the switches S1 and S2 are operating at fixed duty
cycle and power is controlled by variable frequency
modulation. Ideally the duty cycle of S1 and S2 are 0.5 and
their gating signals are complimentary. However, to make sure
the continuity of stiff dc link current, Id, a slight overlap in
gating signals of S1 and S2 is given. The operating power
factor at the output of the half bridge current fed inverter is
considered to be lagging to achieve zero-voltage switching
(ZVS) at device turn-on. However, soft-switching at device
turn-off is also possible if this power factor at inverter output is
leading. The steady state analysis, operating waveforms and
equivalent circuits for G2V operation of this converter are
reported in [30]. This paper reports steady state operation and
analysis for V2G operation and it is discussed next.
B) Steady state operation of V2G
During V2G operation the vehicle side converter acts as a
voltage-fed half-bridge inverter and grid side converter acts as
a current-doubler rectifier. To achieve soft switching of the
inverter switches irrespective load, the duty cycle of vehicle
side converter is kept fixed to 0.5 and power flow is controlled
by varying switching frequency. A slight dead band is always
maintained between switches S5 and S6 such that the dc bus
voltage, vo never gets shorted. Grid side current fed converter
switches S3 and S4 are kept on permanently and body diodes
D1 and D2 act as rectifier diodes. Fig. 3 shows the V2G
operating waveforms during steady state and Fig. 4 shows
equivalent circuit diagram of each switching intervals. During
steady state the operating power factor of the vehicle side
converter is considered to be lagging to achieve ZVS turn on
of switches S5 and S6.
Interval I (t0-t1): In this interval, switch S5 is closed and S6
is open. A positive voltage of 0.5Vo appears at the output of
vehicle side converter and due to presence of series resonant
tank a sinusoidal current flows through the receiver coil as
shown in Fig. 3 and 4a. In this duration the voltage and current
expressions of RC side components are given as
𝑣𝑆6 = 𝑣𝑜1 + 𝑣𝑜2, (1)
𝑖𝑆5 = 𝑖2, (2)
𝐶𝑜1𝑑𝑣𝑜1
𝑑𝑡= 𝑖𝑜−𝑖2, 𝐶𝑜2
𝑑𝑣𝑜2
𝑑𝑡= 𝑖𝑜, (3)
where, vo1 and vo2 are the voltages across capacitors Co1 and
Co2. During this interval ac side voltage of grid side converter
is positive and body diode D2 is forward biased. Thus the dc
link inductor current, Id1 passes through the TC tank network
as shown in Fig. 4a equivalent circuit. The TC side voltage and
current expressions are given as
𝑖𝐷2 , 𝑖𝑆4 = 𝑖𝑑1 + 𝑖𝑑2, (4)
𝐿𝑑1𝑑𝑖𝑑1
𝑑𝑡= 𝑣𝑑 − 𝑣𝑖, 𝐿𝑑2
𝑑𝑖𝑑2
𝑑𝑡= 𝑣𝑑, (5)
where, id1 and id2 are currents through inductors Ld1 and Ld2.
Interval II (t1-t2-t3): Interval t1-t2 is dead band period of the
switches S5 and S6. Because the power factor is lagging the
RC current, I2 does not change polarity at instant t1. Thus at t1
instant I2 starts flowing through the body diode of S6 as shown
in Fig. 4b. After the dead time i.e. at t2 instant the switch S6 is
turned on at zero voltage. However, the body diode of S6 i.e.
D6 keeps on conducting till the coil current I2 changes polarity
at instant t3. Throughout this interval the RC side voltage and
current expressions are given as
𝑣𝑆5 = 𝑣𝑜1 + 𝑣𝑜2, (6)
𝑖𝐷6 = 𝑖2, (7)
𝐶𝑜1𝑑𝑣𝑜1
𝑑𝑡= 𝑖𝑜, 𝐶𝑜2
𝑑𝑣𝑜2
𝑑𝑡= 𝑖2 + 𝑖𝑜, (8)
0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2682793, IEEETransactions on Industry Applications
S6t
S5
id
t4t3 t5
t6t2 t7 t8 t9
iS5=i2
S5
i2
vr
vS5
iS5
ii
vi
is3
t1
S6
vS6
iS6
0.5vo
vo
0.5id
vo
iS6=-i2
vS1+vS3
t0
Fig. 3. Steady state waveforms of the converter during vehicle to grid operation.
Interval III (t3-t4-t5): At instant t3 the polarity of RC current, I2
changes and switch S6 starts conducting. For the interval t3-t4
the equivalent circuit is shown in Fig. 4c. Throughout the
period t0-t4, the body diode D2 of switch S2 conducts because
the magnitude of voltage Vi is positive. At instant t4 the
polarity of voltage Vi changes and becomes negative. Thus the
body diode D2 is reverse biased and D1 becomes forward
biased and takes complete dc link current Id. From instant t4
onwards the TC side switch voltage and current expressions
are given as
𝑖𝑆3 , 𝑖𝐷1 = 𝑖𝑑1 + 𝑖𝑑2, (9)
𝐿𝑑1𝑑𝑖𝑑1
𝑑𝑡= 𝑣𝑑, 𝐿𝑑2
𝑑𝑖𝑑2
𝑑𝑡= 𝑣𝑑 − 𝑣𝑖 . (10)
At instant t5 switch S6 is turned off and dead time of S5 and S6
begins. The switch S5 turns on at instant t6 when voltage
across it is zero, thus this switch also achieves ZVS at turn on.
This sequence of operation repeats in each switching cycle.
III. DESIGN PROCEDURE AND CONSIDERATIONS
A) Component ratings of G2V operation
Fig. 5a shows ac side equivalent circuit of the proposed
converter where the input and output are modeled as current
source and voltage source, respectively. The detailed design
equations, ZVS conditions and components’ rating for G2V
operation are reported in [30]. To achieve ZVS at device turn
on during G2V operation the current-fed converter output
power factor has to be lagging. If this power factor is leading
then the current-fed converter switches experiences soft
switching at device turn-off.
Cp
id
id1L1 i1
Cs
vi
D1 D2
id2
iiC2
L2i2
vr
(a)
(b)
(c)
vo
io
Co1S5
Co2
S6
id
C2L2i2
vr
vo
io
Co1S5
Co2
S6
id
C2L2i2
vr
vo
io
Co1S5
Co2
S6
Cp
id
id1L1 i1
Cs
vi
D1 D2
id2
ii
Cp
id1L1 i1
Cs
vi
D1 D2
id2
ii
Fig. 4. Equivalent circuit diagrams for different switching intervals during V2G operation (a) t0-t1 interval, (b) t1-t2- t3 interval and (c) t3-t4 interval.
Transmitter Coil Receiver Coil
Cp
C2
vr
iiL1i1 i2
jωMi2 jωMi1
ip
viv2
vs
v1
Cs
vc2
Transmitter Coil Receiver Coil
Cp
C2
vr
iiL1-M L2-Mi1 i2
M
ip
viv2
vs
v1
Cs
vc2
iM
(a)
(b)
Fig. 5. AC side equivalent circuit of the proposed topology. The wireless coil
is modelled as (a) coupled inductor (b) transformer.
To derive the voltage gain of the converter during G2V
operation, a transformer equivalent circuit of the tank network
is drawn as shown in Fig. 5b. Form Fig. 5b the voltage across
magnetizing inductance is derived as
𝑉𝑀 = 𝑉𝑟 − 𝐼2𝑍2 = 𝑉𝑟 −𝑉𝑟
𝑅𝑒𝑜𝑍2 , (11)
where, Reo is equivalent load resistance at the input of voltage
doubler circuit. Applying power balance at the input and
0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2682793, IEEETransactions on Industry Applications
output of voltage doubler circuit, Reo in terms of output
resistance is calculated as
𝑅𝑒𝑜 = 2
𝜋2 .𝑉𝑜
𝐼𝑜=
2
𝜋2 𝑅𝑜, (12)
𝑍2 = 𝑠(𝐿2 − 𝑀) +1
𝑠𝐶2, (13)
and 𝑠 = 𝑗𝜔. Therefore, using (11) the current fed converter
output voltage is derived as
𝑉𝑖 = 𝑉𝑀 + 𝐼1𝑍1 = 𝑉𝑟 (1 +𝑍2
𝑅𝑒𝑜) + 𝑉𝑟
1
𝑠𝑀(1 +
𝑍2
𝑅𝑒𝑜) +
1
𝑅 𝑍1,
(14)
where,
𝑍1 = 𝑠(𝐿1 − 𝑀) +1
𝑠𝐶𝑠, (15)
During G2V operation the voltage gain expression is (Vr/Vi).
However, the input to the tank network is actually Ii. Thus, the
gain of the converter is (Vr/Ii) and it is derived as
𝐼𝑖 = 𝑠𝐶𝑝𝑉𝑖 + 𝐼1 = 𝑉𝑖 [(1 + 𝑠𝐶𝑝𝑍1) 1
𝑠𝑀(1 +
𝑍2
𝑅𝑒𝑜) +
1
𝑅 +
𝑠𝐶𝑝 (1 +𝑍2
𝑅𝑒𝑜)] . (16)
Fig. 6 shows the gain (Vr/Ii) and phase (∠Vr/Ii) plot of the
proposed converter during G2V operation.
Gai
n (
Vr/
I i)
in d
BP
has
e in
deg
Ro = 95 Ω
0
90
135
45
-45
36
40
28
32
20
24
-90
-135
Ro = 200 Ω
Ro = 150 Ω
Ro = 125 Ω
104.61 104.63104.65 104.67 104.69 104.71 104.73 104.75
Frequency in Hz
104.77
Ro = 95 Ω
Ro = 200 ΩRo = 150 Ω
Ro = 125 Ω
Fig. 6. Gain (Vr/Ii) and phase (∠Vr/Ii) plot of the proposed converter during G2V operation.
B) Derivation of component ratings of V2G operation
The ac side equivalent circuit of the converter remains same
during V2G operation as shown in Fig. 5a. Applying power
balance and considering active power flows in ac side due to
fundamental component only, rms values voltage and current
expressions are given as
𝐼𝑖 = 2√2
𝜋.
𝐼𝑑
2=
√2
𝜋. 𝐼𝑑 , (17)
𝑉𝑖 = 𝜋
√2. 𝑉𝑑, (18)
𝑅𝑒𝑖 = 𝑉𝑖
−𝐼𝑖=
𝜋2
2.
𝑉𝑑
−𝐼𝑑 , (19)
where, Rei is the equivalent load resistance during V2G
operation. Like the G2V operation, in V2G operation also the
rectifier side i.e. TC side converter input voltage Vi and Ii are
in same phase and their phasors are considered as reference
phasor. Using (18) the parallel capacitor, Cp current is derived
as
𝐼𝑝 =𝑉𝑖
(1
𝑗𝜔𝐶𝑝)
= 𝑗𝜋
√2𝜔𝐶𝑝𝑉𝑑. (20)
Applying KCL and using (17) and (20) the TC current and
series capacitor, Cs voltage are derived as
𝐼1 = −√2
𝜋. 𝐼𝑑 − 𝑗
𝜋
√2𝜔𝐶𝑝𝑉𝑑 , (21)
𝑉𝑠 = −𝜋
√2
𝐶𝑝
𝐶𝑠𝑉𝑑 + 𝑗
√2
𝜋
𝐼𝑑
𝜔𝐶𝑠 . (22)
Applying KVL at TC tank network the voltage across TC and
current through the RC are derived as
𝑉1 = −𝜋
√2𝑉𝑑 (1 +
𝐶𝑝
𝐶𝑠) − 𝑗
√2
𝜋
𝐼𝑑
𝜔𝐶𝑠 , (23)
𝐼2 =1
𝜔𝑀[
√2
𝜋𝐼𝑑 (𝜔𝐿1 −
1
𝜔𝐶𝑠) − 𝑗
𝜋
√2𝑉𝑑 (1 +
𝐶𝑝
𝐶𝑠− 𝜔2𝐿1𝐶𝑝)] .
(24)
Using (21) and (24) and applying KVL at the receiver side the
rms value of voltage across RC is derived as
𝑉2 =𝜋
√2𝑉𝑑 [𝜔2𝑀𝐶𝑝 +
𝐿2
𝑀 (1 +
𝐶𝑝
𝐶𝑠− 𝜔2𝐿1𝐶𝑝)] +
𝑗√2
𝜋𝐼𝑑 [
𝐿2
𝑀(𝜔𝐿1 −
1
𝜔𝐶𝑠) − 𝜔𝑀] .
(25)
Using (24) the RMS voltage across capacitor C2 is derived as
𝑉𝐶2 = −1
𝜔2𝑀𝐶2[
𝜋
√2𝑉𝑑 (1 +
𝐶𝑝
𝐶𝑠− 𝜔2𝐿1𝐶𝑝) + 𝑗
√2
𝜋𝐼𝑑 (𝜔𝐿1 −
1
𝜔𝐶𝑠)]. (26)
The peak blocking voltage of voltage doubler switches are
same as given in (24). The rms current rating of this switches
are given as
𝐼𝑆5 , 𝐼𝑆6 =1
√2𝐼2 , (27)
During this V2G operation the peak blocking voltage of
current fed converter switches are same as peak of ac side
voltage vi. The body diode average current of these switches
are given as
𝐼𝐷1 , 𝐼𝐷2
= 0.5𝐼𝑑 . (28)
Again, Fig. 5b transformer equivalent circuit is used to
derive voltage gain during V2G operation. The voltage across
magnetizing impedance branch is calculated as
𝑉𝑀 = 𝑉𝑖 + 𝐼1𝑍1 = 𝑉𝑖 + 𝑉𝑖𝑍1 (1
𝑅𝑒𝑖+ 𝑠𝐶𝑝). (29)
The voltage at the ac side of voltage doubler circuit is
calculated as
𝑉𝑟 = 𝑉𝑀 + 𝐼2𝑍2 = 𝑉𝑖 [(1 + 𝑍1𝑌) (1 +𝑍2
𝑠𝑀) + 𝑍2𝑌], (30)
where,
𝑌 =1
𝑅𝑒𝑖+ 𝑠𝐶𝑝. (31)
Fig. 7 shows the voltage gain (Vi/Vr) and phase (∠Vi/Vr) plot
during V2G operation for different loads.
0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2682793, IEEETransactions on Industry Applications
G
ain
(V
i/V
r) i
n d
BP
has
e in
deg
0
45
-45
-90
15
20
5
10
0
-135
-180104.71
104.73 104.79104.75
Frequency in Hz
104.77
Rei=20
Rei=24
Rei=28
Rei=32
Rei=20
Rei=24Rei=28
Rei=32
Fig. 7. Voltage gain (Vi/Vr) and phase (∠Vi/Vr) plot of the proposed
converter during V2G operation.
C) ZVS conditions during V2G operation
To achieve soft switching of all the inverter switches
irrespective of load, variable frequency fixed duty cycle
control technique is used during V2G operation. From Fig. 5a
equivalent circuit the impedance at the ac side of voltage
doubler circuit i.e. Vr/I2 is derived as
Zero Phase angle line
Lagging power factor
soft-switching at device
turn-on
Leading power factor
Soft-switching at
device turn-off
Rei=20
Rei=24
Rei=28
104.71 104.73 104.75 104.77 104.79
Frequency in Hz
15
20
25
30
0
45
-45
Imp
edan
ce i
n o
hm
, Z
oP
ow
er f
acto
r an
gle
in
deg
, φ
o
UPF line
soft switching both at
turn-on and turn-off
Rei=32
Fig. 8. Plot of impedance (|𝒁𝒐|) and phase angle (∠𝒁𝒐) plot for different
Vd/Id ratio.
𝑍𝑜 =𝑉𝑟
𝐼2=
1
𝑗𝜔𝐶2+ 𝑗𝜔(𝐿2 − 𝑀) + 𝑗𝜔𝑀// [𝑗𝜔(𝐿1 − 𝑀) +
1
𝑗𝜔𝐶𝑠+ (𝑅𝑒𝑖//
1
𝑗𝜔𝐶𝑝)] . (32)
Fig. 8 shows the plot of the magnitude and phase of this
impedance for different equivalent load impedances. The
power injected from the voltage doubler circuit is given as,
𝑃𝑣2𝑔 = 𝑉𝑟
2
𝑅𝑒(𝑍𝑜)=
𝑉𝑟2
|𝑍𝑜|𝑐𝑜𝑠𝜑𝑜=
1
|𝑍𝑜|𝑐𝑜𝑠𝜑𝑜(
√2
𝜋𝑉𝑜)
2
. (33)
From Fig. 8, it is clear that around the resonant point the power
flow is maximum and power flow reduces when operating
frequency deviates from the resonant point. Keeping the
operating switching frequency higher than the resonance
frequency ensures lagging power factor operation. This leads
to ZVS turn on of the switches S5 and S6 irrespective of load.
D) Design example
To implement this bidirectional converter, appropriate
values of tank capacitors and coil inductance are required to be
determined. The total power transfer between the coupled coils
is derived as
𝑆 = 𝑗𝜔𝑀𝐼1𝐼2 = 𝑗𝜔𝑀 ×𝜋
√2𝐼𝑜 ×
1
𝜔𝑀[
𝜋
√2𝐼𝑜 (𝜔𝐿2 −
1
𝜔𝐶2) −
𝑗√2
𝜋𝑉𝑜] (34)
TABLE 1: SPECIFICATIONS FOR THE DESIGN EXAMPLE
Parameters Selected Values
Rated output power 1.2 kW
Switching frequency range 40 kHz - 60 kHz
Rated switching frequency 50 kHz
CSI input dc current, Id 7.0 A
Output/ battery voltage, vo 325 V (rated)
TABLE 2: CIRCUIT PARAMETERS
Components G2V
Rating
V2G
Rating
Selected devices/
Prototype Rating
Mutual
inductance
42 µH 42 µH 43 µH
TC current,
self-inductance
11A
211 µH
12
211 µH
12 A
211 µH
RC current,
self-inductance
8A
211 µH
10A
211 µH
12 A
211 µH
MOSFET
(CSI side)
Body diode
533V peak
4.9A RMS
-
530V peak
-
3.5A(Avg.)
Part no.-SCT2160KE
1.2 kV, 22 A, Rdson=
208mΩ
MOSFET
(vehicle side)
Body diode
325V peak
-
3.7A(avg.)
325V peak
8.4A RMS
-
Part no.-15EWL06FNTR
600V, 15A, Vf=1.05 V @
15 A
Capacitor, Cs 96 nF,
360 V RMS
96 nF,
390 V RMS
500V ac Cornel Doubler
film, 100 nF
Capacitor, Cp 96 nF,
375 V RMS
96 nF,
377 V RMS
500V ac Cornel Doubler
film, 100 nF
Capacitor, C2 48 nF,
530 V RMS
48 nF,
660 V RMS
2×500V ac Cornel
Doubler film, 48 nF
DC link
inductor Ld1, Ld2
1.7 mH
1.7 mH
1.2 mH
1.2 mH
1.2 mH
1.2 mH
Output caps,
Co1, Co2
224µF,
224µF
224µF,
224µF
300 µF, 300 µF
At close to resonant point the part [𝜔𝐿2 − 1/𝜔𝐶2] in (34)
becomes close to zero and complex part becomes zero. In this
condition the real power transfer from TC to RC is given as
𝑃 =𝜋
√2𝜔𝑀𝐼𝑜𝐼1 (35)
For easier explanation a design example of a 1.2 kW IPT
system is presented and this system is used for experimental
verification. The specifications of the target system are listed
in Table 1. In the 1.2kW experimental prototype the battery
voltage and rated charging currents are considered 325V and
3.7A respectively. Also the switching frequency corresponding
0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2682793, IEEETransactions on Industry Applications
to the resonant point is considered approximately 50 kHz.
From (35), it is clear that to design the converter, I1 (RMS) has
to be considered. For the prototype it is considered as 11A
(RMS). Thus for 1.2kW power the required mutual inductance,
M is calculated to be 42 µH. From G2V operation in [30] it is
clear that with the given M the magnitude of TC voltage, V1
increase with higher value of TC self-inductance, L1. Also the
magnitude of Vi increases with the increase of TC self-
inductance where Vi directly determines switch voltage rating.
This indicates that the lower value the self-inductance i.e.
higher coupling factor leads to lower coil voltage. However,
there needs to be a trade- off between IPT coil size and coil
voltage because higher TC to RC coupling indicates larger coil
size. In the prototype IPT coil with 20% coupling is used and
this determines self-inductance of TC around 211µH. Since the
operating principle of the coupled coils are similar to two
winding transformer, therefore, TC to RC turns ratio near unity
provides better performance. In the porotype, TC to RC turns
ratio is selected to be unity.
The TC and RC side tank capacitors are calculated using
following expression derived in [30] as
𝜔𝑜1 =1
√𝐿1(𝐶𝑝𝐶𝑠
𝐶𝑝+𝐶𝑠)
, 𝜔𝑜2 =1
√𝐶2𝐿2 . (36)
Table 2 lists the selected circuit parameter values for both
during G2V and V2G operations. The voltage and current
ratings of the switches and body diodes are calculated from
[30] and (27), (28) for both G2V and V2G operations
respectively. The inductances of dc link inductors at close to
unity power factor of CSI is given as
𝐿𝑑1 , 𝐿𝑑2 =𝑉𝑑×𝑇𝑠
2Δ𝐼𝑑1 , (37)
where, 𝑇𝑠 = 1/𝑓𝑠 and Δ𝐼𝑑1 is peak to peak current ripple in
inductor Ld1 current. Also, the capacitances of output
capacitors are calculated as
𝐶𝑜1 , 𝐶𝑜2 =𝑇𝑠/2× 𝐼𝑜
Δ𝑉𝑜1 , (38)
where, Δ𝑉𝑜1 peak to peak voltage ripple across capacitor Co1.
The dc link inductor values Ld1 and Ld2 are calculated
considering a 20% ripple in inductor current and output
capacitors Co1 and Co2 are calculated considering 5% voltage
ripple at output voltage, Vo.
IV. EXPERIMENTAL RESULTS
A proof-of-concept hardware prototype rated at 1.2kW is
developed to verify the analysis and operation of the proposed
converter. Selected components are listed in Table 2. Fig. 9
shows the picture of the prototype. SKHI 61(R) is used as
MOSFET gate driver and DSP TMS320F28335 is used to
implement variable frequency digital control. During G2V
operation, an electronic load set at fixed voltage mode is used
to emulate 325V EV battery. During V2G operation this part is
replace by a dc power supply.
Fig. 10 shows experimental results of G2V operation for
900W power output and corresponding switching frequency of
the inverter is 46.6 kHz. The duty cycle of the inverter devices
is kept fixed to 0.52. Fig. 10a shows the profiles of the voltage
across and current through the coils. It is clear that the TC and
RC get almost pure sinusoidal voltage and current. Fig. 10b
shows voltage profiles of TC side tank network. From these
waveforms, it is clear that inverter output voltage, Vi is a
fraction of TC voltage (V1) where Vi directly determines the
switch voltage rating of the current-fed converter. Thus, this is
a major advantage of the proposed converter over simple
parallel LC tank at TC side that inverter switches get lower
voltage stress. It is clear that this is achieved because of the
presence of the series capacitor Cs.
Fig. 9. Photograph of 1.2kW experimental set-up.
v1
i1
i2
v2
v1
vs
vi
vi
-i2
vr
ii S1
vS1+vS3
vi
ii
S1
(a) (b)
(c) (d)
ZVS at device turn-on
Fig. 10. Experimental results of G2V operation at fs=46.6 kHz, Po=900W,
Vo=325V (a) TC and RC currents and voltages, i1 [10A/div], v1 [1.0 kV/div], i2
[10A/div], v2 [1.0 kV/div]; (b) Voltage across TC side tank components, v1, vi, vs [500V/div]; (c) Voltages and currents at inverter output and rectifier input, vi
[500V/div], ii [5A/ div], vr [100V/div], i2 [10A/ div]; (d) ZVS turn on of switch
S1, vs2+vs4 [500V/div], vi [500V/div], ii [5A/ div].
Fig. 10c shows the profiles of ac side voltages and currents of
both side converters during G2V operations. From these results
it is clear that the power factor of the TC side converter is
slightly lagging and this is suitable for ZVS turn-on of the
switches. Also RC side rectifier voltage and current profiles
are in the same phase and this ensures soft recovery of the
diodes D5 and D6. Fig. 10d confirms ZVS turn-on of the TC
side inverter switches because of lagging power factor
operation. At the instant when S1or S2 is turned-on, the
voltage across the corresponding leg switches i.e. S1-S3 or S2-
S4 are slightly negative. Switches S3 or S4 blocks this voltage
and switches S1 or S2 are turned-on at zero voltage.
Fig. 11 shows experiment results of G2V operation for
975W at switching frequency of 50 kHz. From [30], it is clear
that this operating region is in leading power factor region.
0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2682793, IEEETransactions on Industry Applications
Fig. 11 validates this operation and the inverter switches S1
and S2 experience soft-switching at turn-off due to leading
power factor at inverter output. This operation is significant if
the inverter switches are selected as IGBTs to ensure zero turn
off loss. Fig. 12 shows efficiency curve for G2V operation.
The transmitter and receiver coil unloaded coupling factors are
250 and 200, respectively i.e. the internal resistances are 0.26Ω
and 0.32Ω, respectively. At rated load, coil-to-coil power loss
is around 4.8% of rated power. This forms more than 60% of
overall power loss. Therefore, major efficiency improvement is
possible by using optimum sized and shaped coils.
(a) (b)
(c) (d)
v1
i1
i2
v2
v1
vs
vi
vi
-i2
vr
ii S1
ii
S1
vS1+vS3
vi
Soft switching at turn-off
Fig. 11. Experimental results of G2V operation at fs=50 kHz, Po=975W,
Vo=325V (a) TC and RC currents and voltages, i1 [10A/div], v1 [1.0 kV/div], i2 [10A/div], v2 [1.0 kV/div]; (b) Voltage across TC side tank components, v1, vi,
vs [500V/div]; (c) Voltages and currents at inverter output and rectifier input, vi
[500V/div], ii [5A/ div], vr [100V/div], i2 [10A/ div]; (d) ZVS turn on of switch
S1, vs2+vs4 [500V/div], vi [500V/div], ii [5A/ div].
Fig. 13 and 14 shows the experimental results of V2G
operations for 950W and 760W power fed back to grid and
corresponding switching frequencies are 55.5 kHz and 57.5,
kHz respectively. During V2G operation, the vehicle side
voltage doubler circuit operates as voltage-fed inverter with a
fixed duty cycle 0.5. Both the Fig. 13a and 14a shows that the
coil voltages and currents are almost harmonic free. Fig. 13b
and 14b shows the voltage profiles of TC (V1), series capacitor
(Vs), and parallel capacitor (Vi). Form these results, it is clear
that parallel capacitor voltage, Vi is a fraction of TC voltage,
V1. Since, the voltage Vi directly determines the voltage rating
of the converter switches; therefore, the proposed topology is
capable of reducing switch voltage during V2G operation.
Fig. 12. Efficiency curve for G2V operation.
(a) (b)
(c) (d)
v1
i1
i2
v2
vi
-i2
vr
ii
v1
vs
vi
S5
id
vS5
-i2
vr
ZVS at device turn-on
Fig. 13. Experimental results of V2G operation at fs=55.5 kHz, Po=950W,
Vo=325V (a) TC and RC currents and voltages, i1 [10A/div], v1 [1.0 kV/div], i2
[10A/div], v2 [1.0 kV/div]; (b) Voltage across TC side tank components, v1, vi, vs [500V/div] id [2A/div]; (c) Voltages and currents at inverter output and
rectifier input, vi [500V/div], ii [5A/ div], vr [200V/div], i2 [5A/ div]; (d) vs5
[200V/div], vr [200V/div], i2 [10A/ div].
(a) (b)
(c) (d)
v1
i1
i2
v2
vi
-i2
vr
ii
v1
vs
vi
S5
id
vS5
-i2
vr
ZVS at device turn-on
Fig. 14. Experimental results of V2G operation at fs=57.5 kHz, Po=760W,
Vo=325V a) TC and RC currents and voltages, i1 [10A/div], v1 [1.0 kV/div], i2
[10A/div], v2 [1.0 kV/div]; (b) Voltage across TC side tank components, v1, vi, vs [500V/div] id [2A/div]; (c) Voltages and currents at inverter output and
rectifier input, vi [500V/div], ii [5A/ div], vr [200V/div], i2 [10A/ div]; (d)
Voltages and currents at inverter output and rectifier input, vs5 [200V/div], vr [200V/div], i2 [10A/ div].
Fig. 15. Efficiency curve for V2G operation.
50
60
70
80
90
100
400 600 800 1000 1200
Eff
icie
ncy
in
%
Power output in watt 70
75
80
85
90
95
100
400 600 800 1000 1200
Eff
icie
ncy
in
%
Power Output in watt
0093-9994 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2017.2682793, IEEETransactions on Industry Applications
From Fig. 13c and 14c, it is clear that the ac side voltage and
current profiles of TC side converter are in the same phase due
to uncontrolled rectification. Also, ac side voltage and current
profiles of voltage doubler is slightly lagging and this is
suitable for ZVS turn-on of the switches S5 and S6. Fig. 13d
and 14d shows the ZVS turn-on of inverter switch S5. Similar
to switch S5 switch S6 also turns on at zero voltage.
Fig. 15 shows efficiency curve for V2G operation. Similar
to G2V operation, the wireless coil-to-coil power transfer loss
contributes major power loss in the converter circuit. The
proof-of-concept hardware is not optimized for packaging,
volume, and components. Therefore, the obtained efficiency is
close to 92%. Compare with the maximum reported efficiency
95% [31]-[32], this converter efficiency is less. Efficiency can
be farther improved by using improved quality and shaped
coils. The experimental results match closely with the
analytically predicted waveforms.
V. CONCLUSIONS
The contribution and focus of this paper is to propose,
analyze, and develop a new power electronics system for
wireless power transfer with G2V and V2G capability. A new
current-fed topology with bidirectional ability and current-
sharing and voltage doubling features has been proposed. The
proposed topology is analyzed with a new series-parallel CLC
tank network. The proposed tank network reduces the device
rating of grid side devices and permits the use of devices with
low on-state resistance and cost compared to traditional series
LC tank. Bidirectional inductive WPT is designed and
developed using proposed current-fed circuit and CLC tank
configuration. This is the first attempt to implement
bidirectional IPT with current-fed circuit and CLC tank and
demonstrate G2V and V2G operation. Keeping inverter output
power factor lagging, soft-switching turn-on of the inverter
switches is always ensured irrespective of load variation.
Complete mathematical analysis and systematic design is
reported. However, coils or magnetics design is not the focus
of the paper. Experimental results verify the reported analysis
and design and demonstrate the operation and performance.
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Suvendu Samanta (S’16) received the B.E. degree from
IIEST Shibpur (formerly Bengal Engineering and
Science University), Howrah, India, in 2009 and the M.Tech. degree from Indian Institute of Technology
Kanpur, India, in 2013, both in Electrical Engineering.
He is presently working towards the PhD degree in the Department of Electrical and Computer Engineering
(ECE), Concordia University, Montreal, QC, Canada. He
was with Coal India Ltd. as operation and maintenance engineer of Electrical and Mechanical section from 2009-2011. Also from April 2014-April 2016 he
worked as research Engineer in the ECE department, National University of
Singapore, Singapore. His research interests include modeling and control of power electronic converters especially in wireless power transfer applications.
Akshay Kumar Rathore (M’05 - SM’12) received the M.Tech. degree from the Indian Institute of
Technology (BHU), Varanasi, India, in 2003. He
received the Ph.D. degree from the University of Victoria, Victoria, BC, Canada, in 2008. He had two
subsequent Postdoctoral Research Appointments with
the University of Wuppertal, Germany, and University of Illinois at Chicago, IL, USA. From
November 2010 to February 2016, he was an
Assistant Professor in the Department of Electrical and Computer Engineering, National University of Singapore, Singapore. He is currently an Associate
Professor at the Department of Electrical and Computer Engineering,
Concordia University, Montreal, QC, Canada. He has published more than 160 research papers in international journals and conferences including 55 IEEE
Transactions. His research is mainly focused on current-fed converters and
multilevel inverters. He is leading the area of current-fed power electronics and contributed to analysis, design, and development of new classes of
current-fed soft-switching converters.
Dr. Rathore is an Associate Editor of IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, IEEE TRANSACTIONS ON INDUSTRIAL
ELECTRONICS, IEEE TRANSACTIONS ON TRANSPORTATION
ELECTRIFICATION, IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, and IEEE JOURNAL OF EMERGING SELECTED TOPICS IN
POWER ELECTRONICS. Dr. Rathore is Editor-in-Chief of IEEE Industrial
Electronics Technology News (ITeN). He is Paper Review Chair of IEEE Transactions on Industry Applications for Industrial Automation and Control.
He is a Distinguished Lecturer and Executive Board Member-at-Large of IEEE
Industry Applications Society. He received the Gold Medal during his M.Tech. degree for securing highest academic standing among all electrical engineering
specializations. He was a recipient of University Ph.D. Fellowship, NSERC
research assistantship and Thouvenelle Graduate Scholarship during his PhD. He received 2013 IEEE IAS Andrew W. Smith Outstanding Young Member
Achievement Award and 2014 Isao Takahashi Power Electronics Award.
Duleepa J. Thrimawithana (M’09) received his BE
in Electrical Engineering (with First Class Honors) in 2005 and his Ph.D. in power electronics in 2009
from The University of Auckland, Auckland, New
Zealand. From 2005 to 2008, he worked in collaboration with Tru-Test Ltd. in Auckland as a
Research Engineer in the areas of power converters
and high-voltage pulse generator design. He joined the Department of Electrical and Computer
Engineering at The University of Auckland in 2009
where he currently works as a Senior Lecturer. He also serves as the Chairman of the Joint Chapter of IEEE Industrial Electronics and Industrial Applications
Society, New Zealand (North). He has co-authored over 100 international
journal and conference publications, and holds 8 patent families on wireless power transfer technologies with several pending. In recognition of his
outstanding contributions to engineering as an early career researcher, Dr.
Thrimawithana received the Jim and Hazel D. Lord Fellowship in 2014. His main research areas include wireless power transfer, power electronics and
renewable energy.