Mitigation of Voltage Sag for Power Quality Improvement Using DPFC System

Mitigation of Voltage Sag for Power Quality Improvement Using DPFC System Page 25
International Journal for Modern Trends in Science and Technology
ISSN: 2455-3778 |Volume No: 02 | Issue No: 01 | January 2016
Mitigation of Voltage Sag for Power Quality
Improvement Using DPFC System
Dr.L.V.Narasimha Rao
Professor ,Department of EEE, Priyadarshini Institute of Technology & Science,
Chintalapudi, Guntur (Dt),Andhra Pradesh
Article History ABSTRACT
Received on: 15-01-2016
Accepted on: 20-01-2016 A new control scheme to improve and maintain the power quality of
an electrical power system by design of distributed power flow
controller. Generally, In case of modern power utilities have problems
like challenges in growth of electricity in case of non-linear loads in grid
connected systems. In this paper, we introduced a new FACTS method
i.e. distributed power flow controller which is similar to other series-
shunt controller types. This DPFC method is also used like UPFC to
mitigate voltage sag and swell as a power quality issue. In DPFC, we
eliminate the common dc link capacitor and instead of single three
phase series converter it has three individual single phase converters.
In this paper the control circuit is designed by using series referral
voltages, branch currents. The evaluated values are obtained by using
MATLAB/SIMULINK.
Published on: 26-01-2016
Keyword
DPFC ,
UPFC
FACTS,
matlab/simulink
Copyright © 2015 International Journal for Modern Trends in Science and Technology
All rights reserved.

I. INTRODUCTION
Because of power demand grows dramatically,
and extension in transmission and generation is
restricted with the rigid environmental constraints
and the limited availability of resource. But in case
of transfer of power from the generation units to
the utility customers, the term power quality is a
measure of how the elements affect the system as a
whole[1]-[2]. From consumer point of view, the
power quality issue is concentrated about current,
voltage or frequency deviation which causes the
failure of power[3]-[4]. For solving such type of
power quality problem a new method based on the
power electronic based equipment’s such as flexible
alternating current transmission system (FACTS)
and custom power devices (DVR) which are used in
both transmission and distribution control,
respectively, should be developed. But, the majority
of problems transmission lines are such as sag
(voltage dip), swell (over voltage) and
interruption[5]-[6]. To mitigate this type of power
quality problems, the utilization of FACTS devices
such as unified power flow controller (UPFC) and
static synchronous compensator (STATCOM) can
be helpful. In this paper we introduce a new
method like distributed power flow controller
(DPFC) which has similar configuration to UPFC
structure[7]-[8]. The DPFC has a combination of
parallel converter and multiple series converters
which is used to balance the transmission line
parameters, such as bus voltage, line impedance,
and transmission angle[9]-[10].
II. WORKING OF DPFC
The DPFC consists of parallel and series connected
converters. The parallel converter is similar as a
STATCOM, while the series converters employ the
D-FACTS concept such as DVR. Each converter
within the DPFC is independent and has a separate
DC link capacitor to provide the required DC
voltage. Illustration. 1 shows the structure of single
machine system with DPFC. The control capability
of the Unified power flow controller is given by the
back-to-back connection between the shunt and
the series converters with DC link, which allows
the active power to exchange freely. To ensure that
the DPFC has the same control capability as the
UPFC device, a method that allows the exchange of
active power between converters without DC link is
the prerequisite. Therefore, it is allows to exchange
the active power through the AC terminals of the
converters.
Fig 1: Basic Configuration of DPFC
A. Advantages of DPFC:
The Distributed Power Flow Controller has the
following advantages in comparison with UPFC,
such as:
 More capability to control. The DPFC can
control all parameters of transmission line
such as, impedance, load angle and voltage
magnitude.
 High efficiency. The series converters
redundancy increases the DPFC reliability
during converters operation.
 It means, if one of series converters fails,
the others can continue to work. Least
Economy.
III. CONTROLL CIRCUIT OF DPFC
According to illustration 2 the DPFC has
three types of control strategies: i.e. Main
controller, DVR controller and Static controller.
Fig 2: Control Diagram of DPFC

These three controllers are explained as follows:
A. Central Controller:
The central controller is used to control dvr and
static controllers by generation of referral signals
(like series voltages and currents).
B. Series Controller:
The main purpose of this series controller is to
maintain the voltage of capacitor of its own
converters and to generate series voltages at the
natural frequency. This controller requires inputs
as series capacitor voltages, line voltages and
reference capacitor voltages in direct and
quadrature axis frame. Generally, these series
controllers has first order low pass and third order
band pass filters to create natural and 3rd order
harmonic currents. The control structure for series
controller is shown in figure 3.
Fig 3: Block Diagram for Series Controller
IV. SHUNT CONTROLLER
. The control diagram of the shunt converter is
shown in figure 4. Main aim of the shunt control is
to insert a 3rd harmonic current into the
transmission line to provide active power for the
dvr converters. The static converter have three
phase converter which is back to back connected
with single phase converter. In this the three phase
converter absorbs active power from grid and
controls Dc voltage of capacitor between this
converters
Fig 4: Control Diagram for Shunt Controller
V. SIMULATION RESULTS
The case study, for voltage dip condition is
implemented in a single machine system and
analyzed observations are shown below. The
experimental diagram is implemented by basic
diagram which is shown in figure 5.
Fig 5: Structure of DPFC
In this system the time duration for this fault is
500ms to 1500ms. The three phase fault causes
observable voltage sag during this time as shown in
figure 6. The voltage sag values is about 0.65 per
unit and the mitigation of voltage sag by DPFC is
shown in figure 7
.
Fig 6: Simulation results for voltage sag condition
Fig 7: Simulation results for mitigation of Voltage sag
with DPFC system
After creating the fault the load current swell
around 0.2 per unit. The simulation results of load
current in case of swell condition and mitigation of
current are shown in figure 8 and figure 9.

Fig 8: Simulation results for current swell condition
Fig 9: Simulation results for mitigation of current swell
with DPFC system
Fig 10: simulation results for active and reactive powers
VI. CONCLUSION
In this paper we implemented a new
concept for controlling power quality problems by
Distributed Power Flow Controller device. The
proposed concept of the DPFC approach is
mathematically formulated and analyzed for voltage
dips and their mitigations for a three phase source
with linear load. The experimental results of DPFC
show the effectiveness of DPFC in power quality
enhancement as compared to all other FACTS
devices.
REFERENCES
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Mitigation of Voltage Sag for Power Quality Improvement Using DPFC System

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