a novel control method for transformerless h bridge cascaded statcom with excellent dyna
DESCRIPTION
ABSTRACT:This work proposes a novel technique in transformerless STATCOM design based on the HBridge converter star topology. The proposed method jointly implementing current control loops and also the DC voltage control loops. The current control loops and also the DC voltage control loops are designed based on the four parts like passivity based control, overall voltage control, Clustered balancing control,. Individual balancing control. The current loop control, a non linear controller based on the passivity based control theory is used in this cascaded structure STATCOM for the first time. The dc capacitor voltage control ,overall voltage control is realized by adopting proportional resonant (PR) controller. Clustered balancing control is obtained by using active disturbances rejection controller (ADRC). Individual balancing control is achieved by shifting the modulation wave vertically which can be easily implemented in FPGA .The proposed system is providing good dynamic performanTRANSCRIPT
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
All Rights Reserved © 2016 IJORAT 1
A NOVEL CONTROL METHOD FOR
TRANSFORMERLESS H BRIDGE
CASCADED STATCOM WITH
EXCELLENT DYNAMIC
PERFORMANCE Liza.V
1, S.Nirosha Devi
2, S.Usha Rani
3
123Student, Dept of EEE ,FRANCIS XAVIER ENGINEERING COLLEGE, Tamilnadu, India
ABSTRACT:This work proposes a novel technique in transformerless STATCOM design based on the H-
Bridge converter star topology. The proposed method jointly implementing current control loops and also
the DC voltage control loops. The current control loops and also the DC voltage control loops are
designed based on the four parts like passivity based control, overall voltage control, Clustered balancing
control,. Individual balancing control. The current loop control, a non linear controller based on the
passivity based control theory is used in this cascaded structure STATCOM for the first time. The dc
capacitor voltage control ,overall voltage control is realized by adopting proportional resonant (PR)
controller. Clustered balancing control is obtained by using active disturbances rejection controller
(ADRC). Individual balancing control is achieved by shifting the modulation wave vertically which can be
easily implemented in FPGA .The proposed system is providing good dynamic performance while
compared with the conventional STATCOM topology because of its robust procedure.
KEYWORDS :PR-Proportional Resonant, ADRC-Active Disturbances Rejection Controller
I. INTRODUCTION
Power Generation and Transmission is a
complex process, requiring the working of many
components of the power system in tandem to
maximize the output. One of the main components
to form a major part is the reactive power in the
system. It is required to maintain the voltage to
deliver the active power through the lines. Loads
like motor loads and other loads require reactive
power for their operation. To improve the
performance of ac power systems, we need to
manage this reactive power in an efficient way and
this is known as reactive power compensation.
There are two aspects to the problem of reactive
power compensation: load compensation and
voltage support. Load compensation consists of
improvement in power factor, balancing of real
power drawn from the supply, better voltage
regulation, etc. of large fluctuating loads. Voltage
support consists of reduction of voltage fluctuation
at a given terminal of the transmission line. Two
types of compensation can be used: series and
shunt compensation. These modify the parameters
of the system to give enhanced VAR compensation.
In recent years, static VAR compensators like the
STATCOM have been developed. These quite
satisfactorily do the job of absorbing or generating
reactive power with a faster time response and
come under Flexible AC Transmission Systems
(FACTS). This allows an increase in transfer of
apparent power through a transmission line, and
much better stability by the adjustment of
parameters that govern the power system i.e.
current, voltage, phase angle, frequency and
impedance.
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
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As power demand increases in many parts
of the world , power transmission needs to be
developed, as well. The FACTS devices are used in
power system to enhance the system utilization,
power transfer capacity and power quality for ac
system interconnections, STATCOM is utilized at
the point of common connection to absorb or inject
the required reactive power, through which the
voltage quality of PCC is improved. Now a days
many topologies are used in the STATCOM. One
of the topology is H-bridge cascaded STATCOM
has been widely used in high power applications.
The H –bridge STATCOM leads to following
applications like high efficiency, quick response
speed, small volume, minimal interaction with the
supply grid and individual phase control ability.
II. PROPOSED SYSTEM
A.BLOCK DIAGRAM
The below block diagram shows the
control algorithm for H – bridge cascaded
STATCOM . The whole control algorithm mainly
consist of parts , namely ,passivity based control,
overall voltage control, clustered balancing control.
The three parts are achieved in DSP. The current
loop control, a non linear controller based on the
passivity based control theory is used in this
cascaded structure STATCOM for the first time.
The dc capacitor voltage control ,overall voltage
control is realized by adopting proportional
resonant (PR) controller. Clustered balancing
control is obtained by using active disturbances
rejection controller (ADRC).
Fig 1: Control block diagram for the 10 KV 2
MVA H-bridge cascaded STATCOM
.
B. PWM GENERATOR
The PWM Generator block generates
pulses for carrier-based pulse width modulation
(PWM) converters using two-level topology. The
block can be used to fire the forced-commutated
devices (FETs, GTOs, or IGBTs) of single-phase,
two-phase, three-phase, two-level bridges or a
combination of two three-phase bridges.The pulses
are generated by comparing a triangular carrier
waveform to a reference modulating signal. The
modulating signals can be generated by the PWM
generator itself, or they can be a vector of external
signals connected at the input of the block. One
reference signal is needed to generate the pulses for
a single- or a two-arm bridge, and three reference
signals are needed to generate the pulses for a
three-phase, single or double bridge.
The amplitude (modulation), phase, and
frequency of the reference signals are set to control
the output voltage (on the AC terminals) of the
bridge connected to the PWM Generator block.
Pulse width modulation (PWM) is a method of
changing the duration of a pulse with respect to the
analog input. The duty cycle of a square wave is
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
All Rights Reserved © 2016 IJORAT 3
modulated to encode a specific analog signal level.
This pulse width modulation tutorial gives you the
basic principle of generation of a PWM signal. The
PWM signal is digital because at any given instant
of time, the full DC supply is either ON or OFF
completely.PWM method is commonly used for
speed controlling of fans, motors, lights, pulse
width modulation controller etc. These signals may
also be used in varying intensities for approximate
time-varying of analogue signals. Below you can
see the pulse width modulation generator circuit
diagram (pulse width modulator) using op amp.
PWM is employed in a wide variety of
applications, ranging from measurement and
communications to power control and conversion.
C. PASSIVITY BASED CONTROL
To better understand the passivity concept
and passivity-based control (PBC), we need to
leave behind the notion of state of a system and
think of the latter as a device which interacts with
its environment by transforming inputs into
outputs. From an energetic viewpoint we can define
a passive system as a system which cannot store
more energy than is supplied by some “source”,
with the difference between stored energy and
supplied energy, being the dissipated energy.
Passivity is a fundamental property of
many physical systems which may be roughly
defined in terms of energy dissipation and
transformation. It is an inherent Input-Output
property in the sense that it quantifies and qualifies
the energy balance of a system when stimulated by
external inputs to generate some output. Passivity
is therefore related to the property of stability in an
input-output sense, that is, we say that the system is
stable if bounded “input energy” supplied to the
system, yields bounded output energy. This is in
contrast to Lyapunov stability which concerns the
internal stability of a system, that is, how “far” the
state of a system is from a desired value. In other
words, how differently a system behaves with
respect to a desired performance
Passivity based control is a methodology which
consists in controlling a system with the aim at
making the closed loop system, passive. A section
is also devoted to a wide class of physical
passive systems: the Euler-Lagrange (EL) systems
and their passivity-based control.
Figure 2: Block diagram of PBC
Consider the above figure the following set of
voltage and current equations can be derived:
𝐿 𝑑𝑖𝑎𝑑𝑡
= 𝑢𝑠𝑎 − 𝑢𝑎 − 𝑅𝑖𝑎 − − − − − (3.1)
𝐿 𝑑𝑖𝑏𝑑𝑡
= 𝑢𝑠𝑏 − 𝑢𝑏 − 𝑅𝑖𝑏 − − − − − −(3.2)
𝐿 𝑑𝑖𝑐𝑑𝑡
= 𝑢𝑠𝑐 − 𝑢𝑐 − 𝑅𝑖𝑐 − − − − − −(3.3)
Where R is the equivalent series resistance
of the inductor.
Applying the d-q transformations ,the equations in
d-q axix are obtained
𝐿 𝑑𝑖𝑑𝑑𝑡
= −𝑅𝑖𝑑 + 𝜔𝐿𝑖𝑞 + 𝑢𝑠𝑑 − 𝑢𝑑 − − − (3.4)
𝐿 𝑑𝑖𝑞
𝑑𝑡= −𝜔𝐿𝑖𝑑−𝑅𝑖𝑞 + 𝑢𝑠𝑞 − 𝑢𝑞 − − − (3.5)
Where ud and uq are d-axis and q axis
components corresponding to the three-phase
STATCOM cluster voltages, ua,ub and uc. Usd
and usq are those corresponding to the three- phase
grid voltages usa,usb and usc. Whenthe grid
voltages are sinusoidal and balanced , usq is always
zero because usa is aligned with d-axis.
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
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To apply PBC method the above equation
is transformed in to the form of EL, system model
in this paper. EL system model is one of the
important part of the non linear PBC theory and an
effective modelling technology. It defines the
energy equation by setting the general variable and
harness the known theorem that can be used to
analyses the dynamic performance to deduce the
dynamic equations.
D. OVERALL VOLTAGE CONTROL
As the first level control of the dc
capacitor voltage balancing, the aim of the overall
voltage control is to keep the dc mean voltage of all
converter cells equalling to the dc capacitor
reference voltage. The common approach is to
adopt the conventional PI controller which is
simple to implement. However, the output voltage
and current of H-bridge cascaded STATCOM are
the power frequency sinusoidal variables and the
output power is the double power frequency
sinusoidal variable, it will make the dc capacitor
also has the double power frequency ripple voltage.
So the reference current which is obtained in the
process of the overall voltage control is not a
standard dc variable and it also has the double
power frequency alternating component and it will
reduce the quality of STATCOM output current.
Figure 3: Block diagram of overall
voltage control.
To resolve the problem, this paper adopts
PR controller for the overall voltage control. The
gain of PR controller is infinite at the fundamental
frequency and very small at the other frequency.
Consequently, the system can achieve the zero
steady state error at the fundamental frequency. By
setting the
Cut off frequency and the resonant frequency of PR
controller appropriately, it can reduce the part of
ripple voltage in total error, decrease the reference
current distortion which is caused by ripple voltage
and improve the quality of STATCOM output
current. Moreover, the dynamic performance and
the dynamic response speed of the system also can
be improved. In particular, during the start up
process of STATCOM, the much larger dc voltage
overshoot can be restrained effectively.
PR controller is composed of a
proportional regulator and resonant regulator. Its
transfer function can be expressed as
Gpr s = kp +2kr ωc s
s2+2ωc s+ω02 ----------- (3.7)
where kp is the proportional gain coefficient. kr is
the integral gain coefficient. wc is the cutoff
frequency. Wo is the resonant frequency. Kr
influences the gain of the controller but the
bandwidth. With kr increasing, the amplitude at the
resonant frequency is also increased and it plays a
role in the elimination of the steady state error. wc
influences the gain of the controller and the
bandwidth. With wc increasing, the gain and the
bandwidth of the controller are both increased. This
paper selects kp=0.05, kr=10,wc=3.14 rad/s and
wo=100pie as the controller parameters.
E. CLUSTERED BALANCING CONTROL
The purpose of the clustered balancing
control is to keep the dc mean voltage of three
cascaded converter cells in each cluster equal to the
dc mean voltage of the three clusters. The clustered
balancing control as the second level control of the
dc capacitor voltage balancing , the purpose is to
keep the dc mean voltage of 12 cascaded converter
cells in each cluster equalling the dc mean voltage
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
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of the three clusters. ADRC is adopted to achieve
it.
Figure 4: Block diagram of clustered
balancing control.
The block diagram of the
clustered balancing control with the simplified
ADRC. When ADRC receives the reference
voltage udc* and the real-time detected value of the
dc mean voltage ukdc ( k = a,b,c ) of 12 cascaded
converter cells in each cluster, it will trace the
reference voltage rapidly with TD and obtain the
tracking signal v1 by filtering. Then, by subtracting
the tracking signal v1 from the state estimation
signal of the dc capacitor voltage z1 , the control
deviation command €1 the system voltage is
calculated. €1 is used as the input signal of
NLSEF. Finally, the active adjustment control
current ▲ik ( k = a,b, c ) of the clusteredbalancing
control is achieved by subtracting the disturbance
estimate signals which obtained in ESO from the
output result of NLSEF.
F. INDIVIDUAL BALANCING CONTROL
The individual control becomes necessary
because of the different cells have different losses.
The aim of the individual balancing control as the
third level control is to keep each of 12 dc voltages
in the same cluster equalling to the dc mean voltage
of the corresponding cluster. It plays an important
role in balancing 12 dc mean capacitor voltages in
each cluster
Fig 5: Block Diagram of Individual Balancing
Control
Figure shows the block diagram of the
individual balancing dc-capacitor voltage control. It
forms an active power between the ac voltage of
each bridge cell and the corresponding cluster
current.
G. CIRCUIT DIAGRAM
Figure shows the circuit configuration of
the 10 kV 2 MVA star-configured STATCOM
cascading 12 H-bridge PWM converters in each
phase and it can be expanded easily according to
the requirement. By controlling the current of
STATCOM directly, it can absorb or provide the
required reactive current to achieve the purpose of
dynamic reactive current compensation.
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
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Figure 6: Circuit diagram of the
experimental system.
The power switching devices working in ideal
condition is assumed. usa , usb and usc are the
three-phase voltage of grid. a u , b u and c u are the
three-phase voltage of STATCOM. isa ,isb and isc
are the three-phase current of grid. ia , ib and ic are
the three-phase current of STATCOM. ila , ilb and
ilc are the three-phase current of load. Udc is the
reference voltage of dc capacitor. C is the dc
capacitor. L is the inductor. Rs is the
H. SIMULATION OF PROPOSED SYSTEM
The proposed method describes most
widely used linear control schemes are PI
controllers. In to regulate reactive power, only a
simple PI controller is carried out. In through a
decoupled control strategy, the PI controller is
employed in a synchronous d–q frame. Thus, a
number of intelligent methods have been proposed
to adapt the PI controller gains such as particle
swarm optimization neural networks and artificial
immunity. A dc injection elimination method called
IDCF is proposed to build an extra feedback loop
for the dc component of the output current.
To verify the correctness and effectiveness
of the proposed methods, the experimental platform
is built according to the second part of this paper.
Two H-bridge cascaded STATCOMs are running
simultaneously. One generates the set reactive
current and the other generates the compensating
current that prevents the reactive current from
flowing into the grid. The experiment is divided
into two parts: the current loop control experiment
and the dc capacitor voltage balancing control
experiment. In current loop control experiment, the
measured experimental waveform is the current of
a-phase cluster and it is recorded by the
oscilloscope. In dc capacitor voltage balancing
control experiment, the value of dc capacitor
voltages are transferred into DSP by signal
acquisition system and they can be recorded and
observed by CCS software in computer. Finally,
with the exported experimental data from CCS,
experimental waveform is plotted by using
MATLAB.
With the proposed control method, the
reactive current is compensated effectively. The
error of the compensation is very small. The
residual current of the grid is also quite small. The
phase of the compensating current is basically the
same as the phase of the reactive current. The
waveforms of the compensating current and the
reactive current are smooth and they have the small
distortion and the great sinusoidal shape. When
STATCOM is running in over load state (about 1.4
times current rating), due to the selected IGBT has
been reserved the enough safety margin,
STATCOM still can run continuously
and steadily. The over load capability of
STATCOM is improved greatly and the operating
reliability of STATCOM in practical industrial
field is enhanced effectively.
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
All Rights Reserved © 2016 IJORAT 7
Figure 7: Simulation model of proposed system.
I.SIMULATION RESULT
This chapter will investigate the results
of the proposed model. Simulated
results of the project are shown and
discussed.
Fig 8: Result for Real Power from
Genaration
The figure shows the simulation result
for power from generation
Fig 9:Result for Reactive Power from
Generation
This figure shous the simulation
result for reactive power from
generation.
Fig 10: Result for Real Power
from STATCOM
This above figure shows the
simulation result for Real Power
from STATCOM
2
V DC
1
PF Source PI
Vpcc
Vdc
Vabc
Vinv
Ipcc
Iabc
Iinv
Vpcc*
Vdc*
Vabc*
Vinv *
Ipcc*
Iabc*
Iinv *
fi lter concept
A
B
C
A
B
C
a
b
c
A
B
C
a
b
c
A B C
a b
c
A
B
C
a
b
c
A B C
A B C
out
Q f rom Gen
Q Demand at Load
P f rom Gen
P Demand at Load
PF at Source
PF at load
P f rom STATCOM
Q f rom StTATCOM
Subsystem3
In1
ANGLE
Conn4
Conn5
Conn6
Subsystem1
VPcc
V DC in
Subsystem
Statcom V & I3
Statcom V & I2
Reference2
Reference1
Real P From Gen
Real P Demand
Reactive Q drawn from Gen
Reactive Q Demand
Q STATCOM
PFat Load
PF at Source
P STATCOM
VDC
Goto1
Vabcc
Iinvv
Vinvv
Ipccc
VDCC
Vpcc
Iabc
RealPI
ReactivePI
Vdc2
From20
Vabc
Vdc1
From19
Vdc
From18
I_mul
V_mul
Vdc
From15
Vpcc
From14
Vpccc
Iabcc
I_inv
V_inv
Ipcc
VDC0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
0
0.5
1
1.5
2
Time(sec)
voltage(v
)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Time(sec)
voltage(v
)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
Time(sec)
voltage(v
)
source_power_factor
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
All Rights Reserved © 2016 IJORAT 8
Fig 11: Result for Reactive
Power from STATCOM
This above figure shows the simulation
result for reactive power from
STATCOM
Fig 12 : Result for Real Power
Demand at Load
The above figure shows the
simulation result for real power
demand at load.
Fig 13 : Result for Reactive Power
Demand at Load
This above figure shows the
simulation result for reactive power
demand at load.
Fig 14 Result for Source Votage
This above figure shows the
simulation result for source voltage.
Fig 15: Result for source current
This above figure shows
the simulation result for source
current.
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
Time(sec)
voltage(v
)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0.05
0.1
0.15
0.2
0.25
Time(sec)
pow
er(w
)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0.05
0.1
0.15
0.2
0.25
time(sec)
pow
er(w
)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1
-0.5
0
0.5
1
Time(sec)
voltage(v)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1.5
-1
-0.5
0
0.5
1
1.5
Time(sec)
current(am
p)
source_power_factor
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
All Rights Reserved © 2016 IJORAT 9
Fig 16 : Result for Load Voltage
This above figure shows
the simulation result for load
voltage.
Fig 17: Result for Load Current
This above figure shows
the simulation result for load
current.
Fig 18: Result for Inverter Voltage
This above figure shows the
simulation result for Inverter
Voltage.
Fig 19: Result for
Inverter current This above figure shows the simulation
result for inverter current.
Fig 20: Result for DC Voltage
This above figure shows the simulation
result for DC Voltage
Fig 21: Result for H Bridge
Cascaded Input Voltage
The above figure shows the
simulation result for H Bridge
Cascaded input voltage.
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1
-0.5
0
0.5
1
Time(sec)
voltage(v)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Time(sec)
current(am
p)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1
-0.5
0
0.5
1
Time(sec)
voltage(v)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1.5
-1
-0.5
0
0.5
1
1.5
Time(sec)
current(am
p)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
200
400
600
800
1000
Time(sec)
voltage(v)
source_power_factor
0.475 0.48 0.485 0.49 0.495 0.5-1500
-1000
-500
0
500
1000
1500
Time(sec)
voltage(v
)
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
All Rights Reserved © 2016 IJORAT 10
Fig 22: Result for Load Power
Factor
This figure shows the
simulation result for load power factor.
Fig 23: Result for Source Power
Factor
This above figure shows the
simulation result for source power
factor.
Fig 24: Resut for Total Harmonic
Distortion
CONCLUSION
This paper has addressed a
transformerless STATCOM model
based on multi level H bridge converter
with star topology. This paper has
analyzed the fundamentals of
STATCOM based on multilevel H-
bridge converter with star
configuration. And then, the actual H-
bridge cascaded STATCOM rated at 10
kV 2 MVA is constructed and the novel
control methods are also proposed in
detail. The proposed methods has the
following characteristics: A PBC
theory based nonlinear controller is
first used in STATCOM with this
cascaded structure for the current loop
control, and the viability is verified by
the experimental results. The PR
controller is designed for overall
voltage controland the experimental
result proves that it has better
performance in terms of response time
and damping profile compared with the
PI controller. The ADRC is first used
in H-bridge cascaded STATCOM for
clustered balancing control
and the experimental results verify that
it can realize excellent dynamic
compensation for the outside
disturbance.
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50.707
0.7071
0.7072
0.7073
0.7074
0.7075
Time(sec)
pow
er(w
)
source_power_factor
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50.942
0.944
0.946
0.948
0.95
0.952
0.954
0.956
0.958
Time(sec)
pow
er(w
)
source_power_factor
International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 3, MARCH 2016
All Rights Reserved © 2016 IJORAT 11
ACKNOWLEDGMENT
First of all we would like to thank the
almighty for giving me sound health
throughout my paper work. This research
was supported/partially supported by our
college. We thank our staffs from our
department who provided insight and
expertise that greatly assisted the research,
although they may not agree with all of the
interpretations/conclusions of this paper
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