Pak. J. Biotechnol. Vol. 13 (special issue on Innovations in information Embedded and communication Systems)
Pp. 474- 477 (2016)
MODELLING AND CONTROL DESIGN OF THREE PHASE-FOUR WIRE UPQC FOR
POWER QUALITY IMPROVEMENT
Iswarya R1 and Jayashree S2
Dept. of EEE, SNS college of Technology, Coimbatore, Tamilnadu, India
Ishwarya.pse@gmail.com1; jayaa1974@gmail.com2
ABSTRACT
Unified power quality conditioner is the combination of series active power filter and shunt active power
filter. The purpose of series Active power filter is to compensate source side distortions. Purpose of using shunt
active power filter is to compensate load side distortions. The neutral current flow is considered to be major
distortion in distribution system.Inorder to harmony the load current and neutral current flow, three phase four
wire distribution is used. Fourth leg is used in the shunt part of the inverter for neutral flow current. Unbalance is
considered to be serious issue in transmission and distribution system. By using UPQC above problem can be
overcome. Hysteresis controller is mainly used to control the gating pulses of the inverter. The simulation results
based on MATLAB/Simulink are presented to show the effectiveness of the balanced load current in three phase
four wire distribution.
IndexTerms: Active power filter (APF), four-leg voltage-source inverter (VSI) structure, three-phase fourwire(3P4W) system, unified power quality conditioner (UPQC)
I. INTRODUCTION
The Use Of refined equipment/loads at transmission
and distribution level has increased considerably in
recent years due to the reinforcement in the semiconductor device technology. The equipment needs
clean power in order to function properly. At the same
time, the switching transaction of these devices generates current harmonics resulting in infected distribution system. The power-electronics-based devices
have been used to swamped the major power quality
problems [1]. To provide a balance, jazz-free, and
constant magnitude power to sensitive load and, at the
same time, to restrict the harmonic, instability, and
reactive power appealed bytheload and hence to make
the overall power distribution system more vigorous,
the unified power quality conditioner (UPQC) is one
of the prime solutions [6–11].A three-phase four-wire
(3P4W) distribution system can be accomplished by
providing the neutral conductor along with the three
power lines from generation station or by forwarding
a delta-star (Δ–Y) transformer at distribution level.
The UPQC installed for 3P4W application generally
deal with 3P4W supply [9].This paper proposes a new
topology/structure that can be accomplished in
UPQC-based applications, in which the series
transformer neutral used for series inverter can be
preowned to accomplish a 3P4W system even if the
power supplied by utility is three phase three-wire
(3P3W).This new functionality using UPQC could be
effective in future UPQC based distribution systems.
The instability load currents are very common and yet
an significant problem in 3P4W distribution system.
This paper deals with the instability load current
problem with a new control approach, in which the
radical active powers demanded by each phase are
computed first, and these active powers are then re
posited equally on each of the phases. Thus, the proposed control strategy makes the instability load
currentsas completely balanced source currents using
UPQC. The prospective 3P4W distribution system
realized from prevailing 3P3W UPQC-based system
is discussed in Section II.The prospective control
strategy for balancing the unbalanced load currents is
elucidated in Section III section IV explains control
strategy The simulation results are given in Section V,
and finally, Section VI concludes this paper.
II. PROPOSED 3P4W DISTRIBUTION SYSTEM
UTILIZING UPQC
Generally, a 3P4W distribution system is accomplished by providing a neutral conductor along with
three power conductors from generation station or by
outlining a three-phase Δ–Y transformer at distribution level. Fig. 1 shows a 3P4W network in which the
neutral conductor is yielded from the generating
station itself, whereas Fig 2 shows a 3P4W distribution network considering a Δ–Y transformer. Assume
aplant site where three-phase three-wire UPQC is
already installed to protect a sensitive load and to
restrict any entry of distortion from load side toward
utility as shown in Fig. 3.
Fig 1 3-Phase four wire distribution system (neutral is
provided by generating station)
Fig 2 3 P4W distribution (neutral is provided by-Y
transformer
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Pak. J. Biotechnol. Vol. 13 (special issue on Innovations in information Embedded and communication Systems)
Pp. 474- 477 (2016)
used in order to take few samples for taking reference
value. Positive sequence extraction is taken from load
for the generation of output pulses. Both the actual
and reference value is taken from the circuit block
itself for the purpose of simplification of circuit.
Hence hysteresis is advance method of controlling
gating pulse of the inverter. The neutral current is
taken as a input for the fourth leg inverter in order to
avoid sending back to the source. This prevents
distortion of the source and hence circuit is protected.
Fig 3 3P3W distributed system with UPQC
If we want to upgrade the system now from 3P3W
to 3P4W due to installation of some single-phase
loads and if the distribution transformer is close to the
plant under consideration, utility would provide the
neutral conductor from this transformer without major
cost involvement. In certain cases, this may be a
costly solution because the distribution transformer
limits, drawn by nonlinear loads, to control the power
distribution system harmonic pollution. At the same
time, the use of refined equipment/load has increased
significantly, and it needs clean power for its proper
operation. Therefore, in future distribution systems
and the plant/load centers, application of UPQC
would be common. Fig. 4 show the proposed novel
3P4W topology. Recently, the utility service providers
are putting more and more restrictions on current total
harmonic distortion (THD).At the same time, the use
of refined equipment/load has increased significantly,
and it needs clean power for its proper operation.
Therefore, in future distribution systems and the
plant/load centers, application of UPQC would be
common. Fig. 4 shows the proposed novel 3P4W
topology.
As shown in Fig. 3, the UPQC should necessarily
consist of three-phase series transformer in order to
connect one of the inverters in the series with the line
to function as a controlled voltage source. If we could
use the neutral of three-phase series transformer to
connect a neutral wire to realize the 3P4W system,
then 3P4W system can easily be achieved from a
3P3W system (Fig. 4).
The neutral current, present if any, would flow
through this fourth wire toward transformer neutral
point. This neutral current can be compensated by
using a split capacitor topology [2,9,10] or a four-leg
voltage-source inverter (VSI) topology for a shunt
inverter [2,11]. The load on the 3P4W system, the
current drawn from the utility can be unbalanced. In
this paper, a new control strategy is proposed to
compensate the current unbalance present in the load
currents by expanding the concept of single phase p–q
theory [5, 6]. According to this theory, a signal phase
system can be defined as a pseudo two-phase system
by givingπ/2 lead orπ/2 lag, i.e., each phase voltage
and current of the original three-phase system can be
considered as three independent two-phase systems.
These resultant two- phase systems can be represented
inα–β coordinates, and thus, the p–q theory applied
for balanced three-phase system [3] can also be used
for each phase of unbalanced system independently.
Fig 4 Proposed system
III. GENERATION OF REFERENCE COMPENSATOR CURRENTS UNDER UNBALANCED
AND DISTORTED VOLTAGES
In this equation, plavg is the average load power,
Ploss denotes the switching losses and ohmic losses in
actual compensator,and it is generated using a capacitor voltage PI controller. The term Plavg is obtained
by using moving average filter of one cycle window
of time Tin seconds. The term  is the desired phase
angle between the source voltage and current
i*fa = ila - i*sa = ila –
+
(1)
i*fb = ilb - i*sb = ilb –
+
(2)
i*fc = ilc - i*sc = ilc –
+
(3)
IV.UPQC CONTROLLER
The hysteresis controller is used for controlling gating
pulses of the inverter. Actual value is compared with
the reference value. By using reference current
generation pulses are generated. The gating pulse of
the circuit is controlled by hysteresis controller. DC
link capacitor voltage is controlled by PI controller.
Actual and reference value is compared and given to
the inverte Moving active filter is used in order to take
few samples for taking reference valuer Positive
sequence extraction is taken from load for the
generation of output pulses. Both the actual and
reference value is taken from the circuit block itself
for the purpose of simplification of circuit. Hence
hysteresis is advance method of controlling gating
pulse of the inverter. The neutral current is taken as a
input for the fourth leg inverter in order to avoid
sending back to the source. This prevents distortion of
the source and hence circuit is protected
V.SIMULATION RESULTS
The UPQC should necessarily consist of
three-phase series transformer in order to connect one
of the inverters in the series with the line to function
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Pak. J. Biotechnol. Vol. 13 (special issue on Innovations in information Embedded and communication Systems)
Pp. 474- 477 (2016)
as a controlled voltage source. If we could use the
neutral of three-phase series transformer to connect a
neutral wire to realize the 3P4W system, then 3P4W
system can easily be achieved from a 3P3W
system.The neutral current, present if any, would flow
through this fourth wire toward transformer neutral
point. This neutral current can be compensated by
using a split capacitor topology or a four leg voltage
source inverter (VSI) topology for a shunt inverter.
OUTPUT WAVEFORM
Fig 5 Pulse generation model
The above model explains the control block diagram
of UPQC with hysteresis controller. The gating pulse
of the circuit is controlled by hysteresis controller.
Fig 6 Overall Simulink Model
The UPQC should consist of three-phase series
transformer in order to conjoin one of the inverters in
the series with the line to function as a stabled voltage
source. If we could use the neutral of three-phase
series transformer to co-joina neutral wire to
accomplish the 3P4W system, then 3P4W system can
easily be achieved from a 3P3W system.Theneutral
current, present would flow through this fourth wire
toward transformer neutral point. This neutral current
can be compromised by using a split capacitor
topology or a four leg voltage source inverter (VSI)
topology for a shunt inverter
Fig (a) Before Compensation and (b) After compensation
VI CONCLUSION
This paper presents control and performance of UPQC
intended for installation on a transmission line with
the help of hysteresis controller. A control system is
simulated in unbalanced condition with series inverter
and shunt four leg inverter.
Simulation results show the effectiveness of UPQC
in active filteringand controlling unbalance in voltage
and current through the line.AC voltage regulation
and power factor of the transmission line also
improved.
PROPOSED SYSTEM PARAMETERS
VALUES
SYSTEM
QUANTITIES
REFERENCES
System voltages 230V(line to neutral),50 Hz
Zla=34+j47.5,Zlb=81+j39.6,Zlc=31.5+j70.9
Linear load
Shunt VSI
Cdc=2200µF,Lf=26Mh,Rf=1
parameters
Series VSI
Cse=80µF,Lse=5 Mh
parameters
Series interfacing 1:1,100V and 700 VA
transformer
PI controller gains KP =6,Ki=5.5
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