Bidirectional Contactless Power Transfer System
Expandable from Unidirectional System
Soichiro Nakadachi*, Shigeru Mochizuki*, Sho Sakaino*, Yasuyoshi Kaneko*, Shigeru Abe*, Tomio Yasuda***Saitama University, Saitama, Japan**Technova Inc., Tokyo, Japan
S12mm235@mail.saitama-u.ac.jp
Abstract— Contactless power transfer (CPT) systems withprimary series and secondary parallel capacitors (SP topology)
are useful for charging electric vehicles. However, SP topology
is not suitable for bidirectional power transfer. This paper
introduces a novel SPL topology for bidirectional CPT systems
that is realized by adding an inductor and an inverter to the SP
topology. The 3kW and 160mm gap bidirectional test results
show that the efficiency of G2V is 92.5%, and the efficiency of
V2G is 93.4%, which are approximately equal to the efficiencyof the unidirectional SP topology system of 93.1%.

I.

INTRODUCTION

The development and commercialization of plug-in
hybrid electric vehicles (PHVs) and electric vehicles (EVs)are being actively pursued due to environmental concerns
and rising oil prices. Both PHVs and EVs currently requirea physical connection to power supplies by electric cables
for battery charging.
In recent years, contactless power transfer (CPT)systems have been developed as a new battery charging
method in which the battery can be charged simply by
parking the cars in a predefined position. Although CPT
systems have been researched extensively, most of thesesystems are unidirectional grid (home) to vehicle (G2V)
power transfer systems [1-4].
Current charging methods using electric cables (with afocus on large EV batteries) have been researched
extensively for use in bidirectional power transfer systems,
which can also transfer power from the vehicle to the home
(V2H or V2G). These systems use the EV batteries asenergy storage for homes, movable power supplies, andemergency power supplies. Similarly, CPT systems should
also accommodate bidirectional power transfer.
Madawalara et al. [5] proposed a point-to-multipoint
bidirectional CPT system that allows for bidirectional powertransfer by operating the primary and secondary inverters
and controlling the phase between these inverters. They
used a CPT system with primary parallel and secondary
parallel capacitors (PP topology).
The other method for controlling the power is byoperating only the transmitter side inverter and using thereceiver side inverter as a rectifier. As for the capacitor
topology, series and series capacitors (SS topology) [6, 7]
and series and parallel capacitors (SP topology) areapplicable.
The SS topology can easily transfer the powerbidirectionally due to its symmetrical circuit. However, theSS topology has immittance converter characteristics [8];that is, if the input voltage is constant, the output current isconstant. This is not suited for keeping the battery voltage
constant during the final stage of charging.
On the other hand, the SP topology has the idealtransformer characteristics: if the input voltage is constant,the output voltage is constant. This is suited for precise
charge control of Li-ion batteries. Moreover, the secondary
voltage of the transformer is kept low compared to that for
the SS topology, since it is desirable to avoid high voltages
inside a car. However, in V2G, the square voltage waveformof the inverter causes a problem: a large harmonic current
flows into the parallel capacitor at the secondary side.
In this paper, we propose a novel SPL (SP plus L)
topology that resolves this problem and has goodcharacteristics. The SPL topology achieves bidirectional
power transfer by adding an inductor (LS) to the SP topology
and by changing the CS value slightly. The SPL topology
allows bidirectional power transfer with high efficiency andsimplifies the control of inverters by operating only one sideof the inverter. The SPL topology also has an excellent
feature where the primary and secondary voltages become
equal between G2V and V2G if the same rated power istransferred at maximum efficiency. This means that thecapacity (KVA) of the bidirectional system’s inverter isalmost equal to that of the unidirectional system’s inverter
and rectifier.
II.

BIDIRECTIONAL CONTACTLESS POWER TRANSFERSYSTEM

A. System configuration
Figure 1(a) shows a schematic diagram of theconventional unidirectional CPT system using the SP(a) Unidirectional CPT system
Figure 2. Equivalent circuit of SP topology.

mutual reactance x'0 (=ω0l'0) and a leakage reactance x2(=ω0l2), the secondary parallel capacitor CP is given by1(1) 0 L2  xP  x0  x2
0 C P
The primary series capacitor C'S ( = a2CS) is determined as(b) Bidirectional CPT system
Figure 1. CPT systems.

topology. The 50Hz/60Hz AC power is converted to highfrequency 50kHz~150kHz AC power by the inverter at the
primary side, transferred to the secondary side through acontactless power transformer, and then converted into DC
power to charge the battery.
Figure 1(b) shows the proposed bidirectional CPT systemusing the SPL topology. The extension procedure is asfollows:･Change the rectifier in the primary side to a bidirectional
PWM rectifier.
･Change the CS value in the primary side slightly.
･Add an inductor (LS) to the secondary side.
･Change the rectifier in the secondary side to an inverter.
The primary and secondary inverters can be used as rectifiers
by turning all switching devices (e.g., IGBT and FET) off.
By operating the transmitting side inverter as a normal
inverter and the receiving side inverter as a rectifier, thissystem can control the power transfer direction.
B. SP topology (series and parallel resonant capacitor
topology)
Figure 2 shows a detailed equivalent circuit for the SP
topology. It consists of a T-shaped equivalent circuit inwhich the primary series capacitor CS, the secondary parallel
capacitor CP, and a resistance load RL have been added. The
battery and rectifier located in the vehicle are approximatedas RL, whose value is determined as RL=VIN22/PL, where VIN2
is the secondary voltage, and PL is the secondary power. The
primary values are converted into secondary equivalentvalues by a turn ratio (a=N1/N2) and are represented by theprime symbol. The winding resistances (r'1 and r2) and theferrite core loss (r'0) are considerably lower than the mutualand leakage reactance (x'0, x'1, and x2) at the resonant
frequency. Therefore, r'1, r2, and r'0 can be omitted in thecircuit for the analysis.
To achieve resonance with the self-reactance of thesecondary winding ω0L2, which is equivalent to adding a1

0 C S xS  x1 

x0 x2x0  x2

(2)

The input-output characteristic of the SP topology can be
expressed by the F matrix as
0  VIN2 VΙΝ1  ab I    0 1 / ab  I   IN2  IN1  N a  1
N2
b

x0  (3)x0  x2 

Equation (3) indicates that the equivalent circuit for atransformer with these capacitors is the same as an idealtransformer with a voltage ratio of ab at the resonant
frequency. The b is almost equal to the coupling coefficient kof the contactless transformer. The voltage ratio between the
primary and secondary sides (VIN2/VIN1) can be set to any
value by selecting a (=N1/N2) corresponding to k. However,in the SP topology, V2G is not allowed because of the large
harmonic current flowing through CP.
C. SPL topology (series and parallel resonant capacitor
plus L topology)
The SPL topology is a novel circuit topology that can beobtained by adding an inductor LS to the SP topology andsolves the issue of harmonic current. Figure 3 shows adetailed equivalent circuit for the SPL topology. The valuesof CS and CP are determined by (6) and (7) to achieve
resonance with the self-reactance of the connected side
winding.
1(6)
 0 L1  xS  x0  x1
0 CS
1(7)
 0 L2  xP  x0  x2
0 C P
Here, L1 and L2 are the self-inductances of the primary andsecondary windings, respectively. Since (7) is the same as(1), the value of CP does not need to be changed if it is usedin the SPL topology. The value of the added inductor LS isgiven by (8) to be the same value as L2(8)LS  L2
When CS, CP, and LS are determined as (6)-(8), and the
input-output characteristics of the SPL topology in G2V canbe expressed by an F matrix as

RL max G 2V x0  x2 2
x0

r1
r2

(16)

Similarly, in V2G, the efficiency of the contactless
power transformer ηV2G (=PIN1/PIN2) is expressed by
 21
RL I IN
(17)


V 2G

 21  r2 I 22  RL I IN
 21
r1I IN

The relationship between V2, I2, VIN2, and IIN2 is given by(a) G2V x0  x 2
V2   x0
I    2   j 1

x0


 jx0 V  
  IN 1 
0   I IN 1 


(18)

Equation (18) can also be expressed as
I2   j(b) V2G

Figure 3.

Equivalent circuit of SPL topology.

0  VIN2 VΙΝ1  ab I    0 1 / ab  I   IN2  IN1  N a  1
N
2


b

x0 

x0  x2 V 2 G 

D. Condition for maximum efficiency operation
In the SPL topology, RL should be appropriately selected
to operate at maximum efficiency. The efficiency of thecontactless power transformer ηG2V (=PIN2/PIN1) is expressedby equation (9) because r0 is sufficiently smaller than r1 andr2 to be ignored in this analysis.
2
RL I IN
(11)
2


2
 21  r2 I 22  RL I IN
r1I IN
2

Here, the resistance of inductor (Ls) is ignored as well. The
relationship between V2, I2, VIN2, and IIN2 is given by1
j x0  x2 V2  (12)
 VIN 2 1I 
I   j0 2 IN 2  x0  x 2
Equation (12) can also be expressed as
I2  jVIN 2
I R
 j IN 2 L
x0  x2
x0  x2,

I2
I IN 2

2

 RL  
 x0  x2 

2

(13)

Equation (14) is obtained by substituting I'IN1=IIN2/b
developed from (9) and (13) into (11).
 G 2V 

RL
RL2r
RL  r2
 122
x0  x2  b(14)Equation (14) shows that ηG2V depends on the value of RL.
The maximum efficiency in G2V (ηmaxG2V) is obtained when
RL=RLmaxG2V is expressed by(15)
1
 max G 2V 
2
1
x0

RLmaxG2V is given by

r1r2

2

 R 
I2
  L 
1
I IN x0 2

(19)

Then, equation (20) is obtained by substituting (19) into
(17).

(9)
Equation (9) is the same as (3). Thus, the input-output
characteristics of the SPL and SP topologies are expressedby the same F matrix, which is equivalent to an idealtransformer with a voltage ratio of ab.

G 2V

VIN 1I  R
  j IN 1 L ,
x0
x0

RL

 R 
RL  r1  r2  L 
 x0 2

(20)

Thus, the maximum efficiency in V2G (ηmaxV2G) and thevalue of RLmaxV2G, which maximizes ηV2G, are expressed by
1
2
1
r1r2
x0

(21)

r
1
RL max V 2G  x0 1
2
r2
a

(22)

 max V 2G 

RL max V 2G In the case of G2V, the value of RL should be selected as
RL= RLmaxG2V from equation (16), and in the case of V2G,
the value of RL should be selected as RL= RLmaxV2G fromequation (22). Since the value of RL is also determined by
the load voltage VL and the load power PL as RL=VL2/PL, thetransformer is usually designed to be RLmax=RL=VL2/PL. In
the case of a bidirectional system, it is desirable that
RLmaxG2V and RLmaxV2G have the almost same value.
E. Power characteristic at maximum efficiency operationin both G2V and V2GThe bidirectional CPT system requires high efficiency
and a comparable voltage level in both power directions(G2V and V2G). In the following, we present therelationship between the output power, the primary voltage(VIN1), and the secondary voltage (VIN2) at the maximum
efficiency.
Equations (15) and (16) can be expressed by (24) and(25) using k and Q as defined in (23).
L
L
M
(23)
k
, Q1  0 1 , Q2  0 2
L1 L2

 max G 2V 

r1

1
2
1
1
k Q1Q2r2(24)

TABLE I.

SP(G2V)
RLmax

ηmax

RLmax Qηmax Q

V'IN1,I'IN1

RLmax AND ηmax OF EACH TOPOLOGYSPL(G2V）b r2

x0  x2 2

1
2r2
1 r1
1
1
x0  x2 b 2 r2

1
2
1
r1r2
x0

1
2
1
r1r2
x0

r2 Q2
k

Q2
Q1

a 2 kr1 Q1Q2

1
2
1
1
k Q1Q21
2
1
1
k Q1Q2

r2 Q2
k

x0

Q2
Q1

1
2
1
1
k Q1Q2rQ
RL max G 2V  2 2
k

r1
r2

a 2 x0

Q2
Q1

1
2
1
1
k Q1Q2

R V 2Gr  R
1
RL max G 2V  2 x0 1  L max2V 2G  L max.
br2ba 2b 2

Figure 4.

2
RL max G 2V  VIN2(G2V)
PG2V .

RLG 2V 

PV 2G



2

-jxP

RLG2V

Regulation of voltage ratio added reactance.

F.
(25)

(26)

Adjustment of the secondary voltage by inserting C
and L
The voltage ratio (VIN1/VIN2) can be adjusted easily bychanging the self-inductance of the secondary winding L2.
This means that the voltage ratio can be adjusted byinserting C or L between the secondary winding and CP.
Figure 4 shows a detailed equivalent circuit for the SPL
topology when C or L are inserted. Here, xα is the reactanceof C or L. When the values of CP and LS are determined as(33), the input-output characteristics ηmax and RLmax in eachdirection can be expressed by (34)-(37)1(33)
  L  x  x  x  x  x
0 C P(28)

 ab  RL max G 2V  RL max V 2G

(31)
Equation (31) shows that the primary and secondary
voltages do not change between G2V and V2G if the same
rated power is transferred at maximum efficiency. This is an
excellent feature of the SPL topology and means that thecapacity (KVA) of the bidirectional system’s inverter isalmost equal to the capacity of the unidirectional system’s
inverter and rectifier.
RLmaxQ and ηmaxQ in each direction expressed using k and
Q are shown in Table I. The values of ηmaxQ are found to beequal in the two topologies (SP and SPL). Note that the

S

P

L

0

2


0  V IN 2c   I IN 2 ab 
1 max G 2V   max V 2G 
2
1
r1r2
x0

RL max G 2V 

(30)

2

0



 ab
VIN 1   c
I    IN 1   0


(29)

For the case in which PV2G = PG2V and VIN2 = VIN2(G2V),
RLG2V is derived as follows:
IN 2 G 2V 

jxL

±jxα

k 2 Q1On the other hand, the equivalent resistance in V2Gwith the output power PV2G (=PIN1) in G2V is expressed
as follows:
RLV 2G  VIN2 1 PV 2G  abVIN2 2 PV 2G

jx2

approximation expressed by equation (32) is used to
calculate RLmaxQ and ηmaxQ for the SP topology.
1 Q2
(32)
 1

When the efficiency is maximum in G2V, the secondary
voltage VIN2(G2V), the output power PG2V (=PIN2), andRLmaxG2V satisfy the following relationship:

abV 

r2
jx'0

RL max V 2G  kr1 Q1Q2
(27)
where r'1=r1/a2.
Considering (16) and (22), the relationship between
RLmaxG2V and RLmaxV2G is given by



r'1

r1
r2

Similarly, in V2G, (21) and (22) can be expressed by (26)and (27),
 max V 2G 

jx'1

-jx'S

SPL(V2G）

x0  x2  12 r1  1

VIN2,IIN22
c 2 x0  x2  r1
r, RL max V 2G  x0 1
x0
r2
r2
x  x2  xc 0x0  x2

(34)

(35)
(36)
(37)

Here, c is the step up or step down ratio defined by (37).
When L is inserted to increase L2, xα is positive. On theother hand, when C is inserted to decrease L2, xα is negative.
Equations (34)-(37) show that the voltage ratio (VIN1/VIN2)
can be also changed by c. In addition, ηmax does not change
based on whether L or C is inserted.
III.

EXPERIMENTAL RESULTS

In order to verify the performance of the proposed SPL
topology, a 3kW bidirectional CPT test was conducted. In
addition, a 3kW unidirectional CPT test with the SP
topology was also carried out to compare its performancewith that of the SPL topology. In the test, the inverter
frequency was 50kHz, and the value of RL was selected toTABLE III.

EXPERIMENTAL RESULTS(NORMAL POSITION)
G2V

V2G

RL [Ω]

17.5

10

SP(G2V)
15

RLmax [Ω]

10.9

8.0

12.9

(a) G2V

VIN1 [V]

201.6

173.1

184.1

(a)

VIN2 [V]

202.5

193.5

183.2

VIN2/VIN1

1.00

1.12

1.00

PIN1 [W]

3319

3067

3314

PIN2 [W]

3069

3284

3084

η [%]

92.5

93.4

93.1

ηmax [%]

97.1

97.1

97.1

(b) V2G
Figure 5.

Experimental circuit.

(a)

200V

VIN1

200V

VIN1

40A

IIN1

40A

IIN1

200V

VIN2

200V

VIN2

40A

IIN2

40A

IIN2

0
Figure 6.

Photgraph of transformer.

10 20 30 40 50
Time [s]0

10 20 30 40 50
Time [s](a) G2VTABLE II.

(b) V2G

PARAMETERS OF TRANSFORMER

Freq [kHz]50

L1 [µH]

144.8

Gap [mm]160

L2 [µH]

6.0

N1

20

CS [µF]

0.070

N2

4

CP [µF]

1.697

k

0.170

LS [µH]

6.0

maximize the efficiency in the SPL (G2V and V2G) and SP
topologies.

B. Characteristics of normal position
First, the result of the 3kW bidirectional CPT test in thenormal position is described. The test condition was a gap
length of 160mm with no misalignment. The test results areshown in Table III and Figure 7. Table III shows the test
results for the SP’s G2V, the SPL’s G2V, and V2G. The
efficiency in the SPL topology (ηG2V or ηV2G) wasapproximately 93% when the output power was 3 kW, which
is nearly equal to the SP topology (ηSP) efficiency of 93.1%.
The reason why the efficiency of V2G was higher than the

VIN1

40A

IIN1

200V

VIN2

40A

IIN2

0

10 20 30 40 50
Time [s](c) SP topology (G2V)

Figure 7.

Experimental waveform of SPL topology.

100



A. A contactless power transformer and experimental
circuitFigure 5 shows the experimental circuits for eachdirection (G2V and V2G). Figure 6 shows the 3kWtransformer used in the bidirectional CPT test [9]. Table IIshows the transformer parameters at the normal position (agap length of 160mm and no misalignment).

200V

90

80
0

G2V calculated value
V2G calculated value
SP calculated value
G2V experimental result
V2G experimental result
SP experimental result

1020RL [

Figure 8.

Transformer efficiency with load change.

30

TABLE IV. EXPERIMENTAL RESULTS WITH CHANGE IN POSITION AND AIR GAP
positionx [mm]

0

100

0

0

y [mm]

0

0

200

0

0

gap [mm]

160

160

160

120

200

direction

G2V

V2G

G2V

V2G

G2V

V2G

G2V

V2G

G2V

RL [Ω]

17.5

10

17.5

10

17.5

10

17.5

10

17.5

10

VIN1 [V]

201.6

173.1

154.7

173.5

139.2

173.7

285.6

173.7

148.9

173.7

V2G

267.4

VIN2 [V]

202.5

193.5

202.5

313.6

202.7

299

202.3

135.2

202.5

VIN2/VIN1

1.00

1.12

1.31

1.81

1.46

1.72

0.71

0.78

1.36

1.54

PIN1 [W]

3319

3067

3430

3067

3499

3068

3257

3068

3453

3068

PIN2 [W]

3069

3284

3067

3483

3071

3455

3070

3232

3071

3401

η [%]

92.5

93.4

89.4

88.0

87.8

88.8

94.2

94.9

88.9

90.2

100

100

90



100





0

90

G2V
V2G
SP(G2V)80
120 140 160 180 200
gap [mm](a) Change in gap length

90
G2V
V2G
SP(G2V)

G2V
V2G
SP(G2V)
80
0

20

40 60
x [mm]

80

100(b) Change in forward direction

Figure 9.

80
0

20

40

60

80

100 120 140 160 180 200
y [mm](c) Change in lateral direction

Efficiency with change in position and air gap.

efficiency of the SP topology is considered to bemeasurement error.
Figure 7 shows the input and output voltage and current.
The primary and secondary voltages were almost coherent,
which demonstrates that the SPL topology has thecharacteristics of an ideal transformer in both directions. In
Figure 7(a), there are LC oscillations around the instances ofvoltage switching. This oscillation appears when the current
IIN2 becomes discontinuous.
C. Characteristics with resistance-load change
Figure 8 shows the experimental efficiency when RL ischanged and the curves of calculated value are derived from
(14) and (20). Here, the value of RL is calculated from the
input voltage VIN1, VIN2 of the full-bridge rectifier and thepower running through it. Since the theoretical efficiency
ignores the core loss, the theoretical efficiencies are higher
than the experimental efficiencies, and the difference
corresponds to the core loss. Both efficiencies show the samecharacteristics.
During battery charging, the battery voltage is almost
constant. Therefore, Figure 8 represents the change inefficiency when the charging power is changed.
D. Characteristics with change in gap length andmisalignment
In the contactless power transfer system for EVs,misalignment of the transformer due to the driver’s skill andthe change in the gap length from the car's weight isinevitable. The coupling factor k depends on the relative
position between the primary and secondary transformers,
and the efficiency decreases with a decrease in k.
Table IV shows the test results when a change in gap
length and forward / lateral misalignment occurred. Here, xis the forward direction, and y is the lateral direction of thecar.
Figure 9 shows the efficiency when the gap length andmisalignment are changed. The efficiency of the SPL
topology is almost the same as that of the SP topology
E. Frequency characteristics of SPL topology
Because CPT systems have a resonance circuit, it isnecessary to know the characteristics of the circuit when the
inverter frequency is changed. Figure 10 shows thefrequency characteristics of the impedance of the SPL circuitwith load from the output terminal of the inverter. Here, theimpedance is calculated from the measured parameters of thetransformer. If the frequency is changed in the range of ±2%(±1kHz), the absolute value of the impedance changes
slightly in both G2V and V2G.

80

90

60

45

40

0

20

|Z| -45

REFERENCES

[deg]

|Z|

[1]

[2]

[3]


0
30

40

-90
50
60 70 80 90 100
freqency [kHz]

[4]
[5]

G2V
[6]

20

90

15

45

[7]

10

[deg]

|Z|

(a)

0

[8]

|Z| -45

5
0
30


40

Figure 10.

-90
50
60 70 80 90 100
freqency [kHz](b) V2G
Frequency characteristics of Z

IV.

CONCLUSION

We proposed a novel SPL topology for a bidirectional
contactless power transfer system. The SPL topology is
expandable from the SP topology by adding an inductor to
the secondary side, changing the primary capacitor value,
and replacing the secondary rectifier with an inverter.
The input / output characteristics of the SPL topology are
equal to those of an ideal transformer with a turn ratio of b
for the SP topology. The power transfer control enables
bidirectional power transfer (G2V and V2G) with highefficiency at the rated power.
The 3kW bidirectional test results show that theefficiency of the SPL topology in G2V is 92.5%, and theefficiency of the SPL topology in V2G is 93.4%, which areapproximately equal to the efficiency of the unidirectional
SP topology of 93.1%.
The proposed SPL topology can be used not only forvehicles but also for other CPT systems. We hope that thiswill allow a wider range of applications of bidirectional CPT
technology.

[9]

Yuichi Nagatsuka, N. Ehara, Y. Kaneko, S. Abe, and T. Yasuda“Compact Contactless Power Transfer System for Electric Vehicles”
IPEC2010-Sapporo pp. 807-813(2010)
M. Chigira, Y. Nagatsuka, Y. Kaneko, S. Abe, T. Yasuda, andA.Suzuki “Small-Size Light-Weight Transformer with New Core
Structure for Contactless Electric Vehicle Power Transfer System”
ECCE2011-PHOENIX pp. 260-266(2011)
M. Budhia, G. Covic, and J. Boys “Development of a Single-Sided
Flux Magnetic Coupler for Electric Vehicle IPT Charging Systems”,
IEEE Trans. Ind. Electron., Vol. 60, No. 1, January 2013, pp. 318328
G. Covic and J. Boys, “Inductive Power Transfer”, Proc IEEE, Vol.
101, No. 6, June 2013, pp. 1276-1289
U. K. Madawala and D. J. Thrimawithana, “A Bidirectional Inductive
Power Interface for Electric Vehicles in V2G Systems”, IEEE Trans.
Ind. Electron., Vol. 58, No. 10, pp. 4789-4796 (2011)
C.-S. Wang, G. Covic, and O. H. Stielau “General Stability Criterions
for Zero Phase Angle Controlled Loosely Coupled Inductive Power
Transfer Systems” in Proc. IEEE IECON’01, vol. 2, 2001, pp. 10491054.
Y. Jang, and M. M.Jovanovic “A Contactless Electrical Energy
Transmissin System for Portable- Telephone Battery Chargers” IEEE
Trans. Ind. Electron., Vol. 50, No. 3, June 2003, pp. 520-527
H. Irie, and T. Yabuuchi “High-Frequency Constant-Current Power
Supply in Noncontact Energy Transfer System Using Immittance
Conver” Electrical Engineering in Japan, Vol. 158, No. 3, 2007, pp.
81-89
H.Takanashi, Y. Kaneko, S. Abe, and T.Yasuda "A Large Air Gap 3
kW Wireless Power Transfer System for Electric Vehicles"
ECCE2012, North Carolina, pp.269-274 (Sep 15-20 2012)