Energy and Power Engineering, 2013, 5, 534-539
doi:10.4236/epe.2013.54B102 Published Online July 2013 (http://www.scirp.org/journal/epe)
Study Hybrid Compensation Cophase Tr action Power
Supply System Schemes for High-Speed and Heavy Haul
Electrical Railway with V Connection Transformer
Yankun Xia, Qunzhan Li, Yuanzhe Zhao, Xiaohan Liu, Hao Wu, Yang Zhou
School of Electrical Engineering, Southwest Jiaotong University, Chengdu, Sichuan, China
Received March, 2013
ABSTRACT
In order to solve negative phase sequence problem of V connection transformer in the high speed and heavy haul elec-
trical railway of China, the hybrid compensative co-phase traction power supply system which based on passive and
active compensation is proposed. Firstly, there construction and capacity distribution are analyzed, and the compensa-
tion current of active equipment is gave; Second, the feature of the hybrid compensative schemes are discussed. In the
end, the related simulation results have confirmed the effectiveness of the compensation schemes in this paper.
Keywords: V Connection Transformer; Hybrid Compensation; Negative Phase Sequence; Cophase Power Supply
System
1. Introduction
Chinese electrified railway used single-phase power fre-
quency AC power supply mode; relative to the three-
phase power system is an asymmetry of power supply.
There is the problem of negative sequence. As we all
know, the negative sequence will bring a range of haz-
ards for generator and protection devices.
To reduce the negative sequence, the high-speed and
overload electrified railway traction transformer uses the
V connection transformer. Two single-phase power of
the secondary side of the transformer turns in provide
energy to locomotives load, commonly known as
split-phase power supply. V connection transformer has
simple structure, low manufacturing costs, but can reduce
half of the negative sequence current caused by the load
at most. In the future, along with the increase of
high-power electric locomotive power and increase of
transport capacity lines, negative sequence caused by
high-speed and heavy-duty electric railway will deterio-
rate further. Then one three- phase to single-phase sym-
metrical power supply system (also known as co-phase
power supply system) which applying to electric railway
eliminates the negative sequence is of great significance
to enhance the development of high-speed and heavy
load of electrified railway carrier.
In [1, 2] earlier proposed the cophase power supply
scheme based on Passive symmetrical compensation, in
[3-6] proposed cophase power supply scheme based on
active compensation. The cost is low of the former, but
the poor dynamic performance; the latter is real-time, but
the cost is high. Combine the features of both, the litera-
ture [7-11], passive and active hybrid integrated com-
pensation was proposed. At the same time, compensation
characteristics and capacity configuration are discussed,
but they did not cancel the secondary side of the trans-
former commutation link. In [12] first proposed a hybrid
compensation scheme based on the balance of the trans-
former, but mainly for the general speed electrified rail-
way transformer, and is not suitable for
Chinese high-speed and heavy load electrified railway.
In [13, 14] were explored with V/v wiring active cophase
and split phase compensation capacity of the power sup-
ply scheme and the optimization problem.
On the basis of the above study, V connection trans-
former hybrid compensation scheme was proposed for
Chinese high-speed and heavy-duty electric railway. In
the end, the related simulation result is provide to dem-
onstrate the good performance for compensating nagative
sequence.
2. Passive Symmetrical Compensation
Cophase Power Supply Based on V
Connection Transformer
Passive compensation cophase power supply system
structure based on V connection traction transformer
shown in Figure 1.

Y. K. XIA ET AL. 535
In Figure 1 only b ports is the power supply por t. Ac-
cording to Steinmetz compensation principles [15], nega-
tive sequence caused by any single-phase load can be
componented by capacitive and reactance components.
Without considering the load reactive, only need to set
compensation capacitor in port a, set the compensation
reactance in the port the ab. Corresponding two ports
compensation capacity are
1
1
1
=3
1
=3
ca
cab
SP
SP
P1 is the load active power.
System positive sequence and negative sequence
compensation schematic diagram are shown in Figure 2.
The total capacity of the compensation is 1
2
=3 SP . If
the load contains a reactive component, it need to con-
figure port b capacitance or inductance reactive power
compensation. Electrified railway of high-speed and
overload has high power factor which is closed to 1. Not
to consider the impact of the locomotive load reactive
power, we only analysis active power.
bL
i
L
I

a
u
b
u
A
i
C
i
B
i
Figure 1. Passive cophase power supply system based on V
connection.
()

A
U
b
u
a
u
bL
i 60
()
()
bLa
i
Ca
i
ab
u
()
Figure 2. Positive and negative sequence diagram with
compensation.
Passive compensation only need to invest capacitance,
inductance element, the one-time investment of compen-
sation system is small. However, due to the capacitance
and inductance difficult dynamic continuous adjustment,
usually passive compensation is only suitable for small
changes in load occasions. In the case of large load
changes, the method is difficult to meet the requirements
of real-time compensation, and easily leads to under-
compensat ion or over- compens ation.
3. Active Compensation Cophase Power
Supply Based on V Connection
Transformer
Active power compensation is developed on the basis of
modern power converter which can transmit active and
reactive power. Active cophase power supply system
structure shown in Figure 3, the two sets of single-phase
power flow controller (PFC) common intermediate DC
voltage. In AC side, respectively, the port a and port b
are the link port of PFC.
Known from the literature [9,13], if the V connection
transformer wiring to achieve the cophase power supply,
it requires single-phase power compensation device to
transfer a half load active power 0.5P1 from the port a
to port b, and simultaneously at the port a and the port b
compensates reactive component. Corresponding port
compensation capacity is
22
11
1
31
=0.5)()
63
1
=3
ca
cb
SPP
SP
（1 P
At this time the total capacity is the same to passive
compensation, it is 1
2
=3 SP .
bL
i
L
I

a
u
b
u
A
i
B
i
C
i
Figure 3. Active cophase power supply system based on V
connection.

Y. K. XIA ET AL.
536
The primary side and the secondary side voltage and
current vector relationship shown in Figure 4(a), the
corresponding compensated positive sequence and nega-
tive sequence vector is shown in Figure 4(b).
Figure 5 shows primary three-phase side of the nega-
tive sequence component is 0 through PFC compensation.
The active compensation basic principle is as follows:
Vocabulary primary side of the A phase voltage is
=2cos( )
AA
uU t

the secondary side of the transformer powered arms vol-
tage
a
=2cos(- )
6
a
uU t


bb
=2cos(- )
2
uU t

 (1)
The load current
11
()2 sin()()
Lh
it I tit   (2)
n
2
()2 sin()
h
n
itInt n






is the harmonic components of the load current.
The instantaneous power of the load
11
11
()() ()(1cos2)
sin2() ()
LLp
qh
ptutit UIt
UItuti t





 (3)
11 111
cos, sin.
pq
IIII 1


A
U
B
U
C
U
b
u
a
u
30
bL
i
Figure 4. Voltage and current vectors.
cbL
i
caC
i
()

A
U
B
U
C
U
b
u
a
u
bL
i
aL
i
60
()
()()

()
cbL
i
caC
i
Figure 5. Positive and negative sequence diagram with
compensation,
Fully compensated case of the negative sequence, the
arms provide a current effective value 1
12
23
I

, and
then multiplied by the corresponding sync voltage signal
2cos( )t

and 2
2cos( -)
3
t

 . So the arms current
instantaneous value
1
b1
2
i=cos( )
3
22
i=cos( -)
3
3
aIt
It



(4)
The arms current contains the active and reactive cur-
rent component. The corresponding compensation cur-
rent commands are
c1
cb 1
2
i=i-i=cos()i
3
22
i=i=cos( -)
3
3
aaL L
b
It
It




(5)
Obviously the port b included the reactive and har-
monic current components caused by the locomotive load.
Firstly, PFC device calculate the compensation current
and
ica
b
ic. Secondly, PFC compensate the negative
sequence component in a timely using the modulation
mode control algorithm and the current track manner,
thus eliminating the negative sequence.
Active compensation can compensate load power re-
quired in real-time according to the changes in load
power, but there is a high cost of compensating device.
Therefore it is necessary to research active compensation
device capacity minimized to reduce the compensation
system works investment.
4. Hybird Cophase Compensation
Such as the first two sections, if we can combine the
characteristics of passive compensation and active com-
pensation, using the compensation to reduce the capacity
of active compensation device and using active compen-
sation to speed up real-time. Then we constitute a hybrid
compensation which will achieve compensation system
investment minimum. The hybird compensation has two
compensation schemes.
4.1. The First Hybird Compensation Scheme
The scheme as shown in Figure 6, is the combination of
passive compensation and active compensation together.
In port ab and ports b respectively access to the reactor
and the capacitor, and in the port a and the port b access
to PFC.
Assumed that K is constant, in order to achieve the
symmetrical compensation, passive compensation in-

Y. K. XIA ET AL. 537
vestment capacity is S1, and active device input capacity
is S2
11
21
2
=k
3
2
=(1)
3
SP
SkP 
k[0,1]
Obviously the scheme inputs a major change capacity
weight of passive and active compensation, does not
change the total capacity of the whole co mpensation sys-
tem inputs
4.2. The Second Hybird Compensation Scheme
Inspired by the active compensation, the second hybrid
compensation scheme is shown in Figure 7. The passive
compensation device and active compensation device
connecte to the port a and port b. PFC device transfers
half active power of load. Passive compensates reactive
component in two ports. Under the conditions of fully
compensated, passive compensation invested capacity S1
and active device input capacity S2
bL
i
L
I

a
u
b
u
A
i
B
i
C
i
Figure 6. The first mode of hybird cophase power supply
system.
bL
i
L
I

a
u
b
u
A
i
B
i
C
i
Figure 7. The second mode of hybird co phase power supply
system.
The passive and active compensation capacity ratio is
fixed in this scheme, the total input capacity will reach
1.577P1. PFC compensation current in two port are
1
1
2
b2
i=2sin( -30)
i=-2sin( -90)
I
ca
I
c
t
t




4.3. Hybrid Compensation Characteristics
1) By the preceding sections that the total capacity of
purely passive compensation and the pure active com-
pensation device are equal 1
2
=3. In the first hybrid
compensation, the total capacity remain
SP
1
2
=3, but
the scheme two will result in a significant increase in
total capacity. Obviously from saving the entire system
capacity point of view, the first sch eme is better than the
second.
SP
2) Two hybrid options, the power factor of the three-
phase system is not affected, because the capacity of the
passive capacitive and reactance is equal.
3) Due to the high speed and heavy load electric lo-
comotives with regenerative function, when the locomo-
tive in the regeneration conditions, locomotive current
flow traction transformer. At this condition, negative
sequence produced by locomotives and passive devices
compensation is superimposed, resulting in deterioration
of the negative sequence. Then it need greater active
compensation device to compensate. In order to reduce
the capacity requirements of the active devices, passive
compensating means should as far as possible through
the switching switch out of operation in the regenerative
brake of the locomotive, and then the active device ca-
pacity demand remains 1
2
=3 SP
.
5. Simulation Analysis
In order to validate the correctness of the principle of
hybird cophase compensation schemes, simulation in
Matlab/simulink platform is done. Side of power system
voltage is 220 kV. Traction network rated voltage is 27.5
kV. The PFC device uses a single-phase back-to- back
structure. The step-down transformer voltage ratio is
27500:930. The intermediate DC side voltage of PFC is
set to 3000 V. Control system uses voltage and current
double closed-loop structure. Locomotive load is consid-
ered as constant power source.
Figure 8 shows in the port b locomotive load active
power is 10 MW. Taken passive compensation degree k
= 0.5, the current imbalance is 50% when only a passive
compensation, the capacitance and reactance capacity are
the 2.887 MVA; then implementation of the active com-
pensation, two-port active capacity are 2.887 MVA in
a-phase and b-phase port. The basic balance of the
three-phase side current imbalance is 0. Compensation
device total input capacity is 11.548 MVA.

Y. K. XIA ET AL.
538
0.80.82 0.840.86 0.88 0.9
-2
0
2x 10
5
u/V
t/s
BC
A
The first side voltage
0.80.82 0.84 0.86 0.880.9
-50
0
50
i/A
t/s
A
B
C
The first side current without compensation
0.80.82 0.840.86 0.880.9
-50
0
50
i/A
t/s
A
BC
The first side current in passive compensation
0.80.82 0.840.86 0.88 0.9
-50
0
50
i/A
t/s
ABC
The first side current in hybird compensation
Figure 8. First side current with and without compensation
in the first mode.
Figure 9 shows the A phase current is 0, the B phase
and C phase current at the same magnitude in not any
compensation. The current imbalance degree is up to
100%.When we use PFC transferring 5 MW power from
a phase to b phase, the current imbalance degree change
to 50%. Then implementation 2.887 MVA. In a-phase
and b-phase port, the current imbalance degree reduces to
0.Compensation device total input capacity is also 11.548
MVA.
Simulation analysis shows that by the above two
schemes. Hybrid schemes provid e a good solutio n for the
high-speed and overloading electrified railway power
quality control. At the same time, the simulation proves
the correctness of the theory in this paper.
6. Conclusions
The hybrid compensation schemes are proposed in this
paper based on V co nnection transformer, combinin g the
principle of passive and active compensation techniques.
0.80.82 0.840.86 0.880.9
-2
0
2x 10
5
u/V
t/s
BC
A
The first side voltage
0.80.82 0.840.86 0.88 0.9
-50
0
50
i/A
t/s
A
B
C
The first side current without compensation
0.80.82 0.840.86 0.880.9
-50
0
50
i/A
t/s
AB
C
The first side current in active compensation
0.80.820.840.86 0.88 0.9
-50
0
50
i/A
t/s
ABC
The first side current in hybird compensation
Figure 9. First side current with and without compensation
in the second mode.
The schemes provide a new way to save investment and
optimize the compensation device capacity. Simulation
results demonstrate the feasibility of the program.
The schemes are not only suitable for high-speed and
heavy load electrified railway, also applied to conven-
tional speed electrified railway V connection transformer
power supply.
REFERENCES
[1] C. Y. Liu, “Power Transformer Design Methods and
Practice,” Liaoning: Liaoning Science and Technology
Press, 2002, pp. 32-35．
[2] Q. Z. Li and J. M. He, “Electrified Feeding System with-
out Phase Exchange and Symmetrical Compensation
Technology,” Automation of Electrical Power Systems,
Vol. 20, No. 4, 1996, pp. 9-11．
[3] Q. Z. Li, “Electrified Railway Power Quality Analysis
and Control,” Chengdu：Southwest jiaotong university
press, 2011, p. 2.

Y. K. XIA ET AL.
539
[4] K. S. Yu and S. J. Zhou, “Electrified Railway Power Sup-
ply and Power Quality,” Beijing：China electric power
press, 2011, 2.
[5] X. F. Zhang, S. B. Gao, Q. Q. Qian, et al., “A Novel Co-
phase Traction Power Supply System Based on Imped-
ance Matching Balance Transformer and AT Power Sup-
ply Mode,” Journal of the China Railway Society, Vol. 8,
2006, pp. 32-37.
[6] G. Wei, Q. Z. Li, J. Huang and J. Zhou, “A New Cophase
Traction Power Supply System,” Automation of Electrical
Power Systems, Vol. 32, No. 10, 2008, pp. 80-83．
[7] D. Q. Qiu, Q. Z. Li, F. L. Zhou, et al., “Comprehensive
Power Quality Control of Electric Railway Based on
Back to Back SVG,” Electric Power Automation Equip-
ment, Vol. 30, No. 6, 2010, pp. 36-39.
[8] D. Q. Qiu, Q. Z. Li and J. X. Yu, “Compensation Princi-
ple of Hybrid Power Quality Conditioner for Electric
Railways and Capacity Analysis,” Electric Power Auto-
mation Equipment, Vol. 32, No. 10, 2012, pp. 59-64.
[9] L. Fang, A. Luo, X. Y. Xu, et al., “A Novel Power Qual-
ity Compensator for High-speed Electric Railway,”
Transactions of China Electrotechnical Society, Vol. 25,
No. 12, 2010, pp. 167-174．
[10] C. L. Zeng, A. Luo, F. J. Ma, et al., “A Novel Powerqual-
ity Compensation System for High-speed Railway and Its
Parameter Design,” Power System Technology, 2011，
Vol. 35, No. 10, pp. 64-69．
[11] F. J. Ma, A. Luo, X. Y. Xu, et al., “High-power Hybrid
Power Quality Compensation System in Electrified Rail-
way,” Transactions of China Electrotechnical Sociey，
2011, Vol. 26, No. 10, pp. 93-102．
[12] F. L. Zhou, Q. Z. Li and D. Q. Qiu, “Co-phased Traction
Power Supply System Based on Hybird Compensation,”
Journal of the China Railway Society, 2012, Vol. 34, No.
1, pp. 19-23.
[13] G. Wei, “Cophase traction power supply system based on
V connection,” Electric Power Automation Equipment,
2010，Vol. 30, No. 12, pp. 60-65．
[14] C. P. Wu, A. Luo, et al., “Integrative Compensation
Method of Negative Phase Sequence and Harmonic for
High-speed Railway Traction Supply System with V/v
Transformer,” Proceedings of the CSEE, 2010, Vol. 30,
No. 16, pp. 111-117．．
[15] Q. Z. Wan, G. P. Zhu, J. Y. Chen, et al., “Optimum De-
sign of Compensation Capacity for Balancing the Single
Phase Traction Load,” Automation of Electric Power Sys-
tems, Vol. 32, No. 8, 2008, pp. 93-97.