Simulation of DVR by using Ultra Capacitor to Analysis of THD with and without Dc-Dc Converter

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 11 | Nov -2017 www.irjet.net p-ISSN: 2395-0072
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Simulation of DVR by Using Ultra Capacitor to Analysis of THD with and
without Dc-Dc Converter
Pravin G. Bhende1, Mr.Saurabh H. Thakare2, Dr.Vijay.G.Neve3
1P.G. Student, Department of Electrical Engineering, Padm.Dr.V.B.Kolte COE,Malkapur,M.S., India
2Asst.Professor, Department of Electrical Engineering, Padm.Dr.V.B.Kolte COE,Malkapur,M.S., India
3HOD, Department of Electrical Engineering, Jagadambha COE & Technology,Yavatmal,M.S., India
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Abstract- Issues related to power quality have become more
critical in recent times due to the increased penetration of
renewable into the power grid. Voltage sags and swells are
amongst the most important issues associated with a power
grid, and extensive research has been directed towards the
mitigation of these issues. The quality of the power may be
improved by using power conditioning equipment. To protect
sensitive load from the effect of voltage disturbance on the
distribution feeder the Dynamic voltage restorers (DVR) are
used. In the DVR control strategies the absence of a buck-
boost converter in some of the existing DVR systems
necessitates energy storage of high voltage rating. Ultra
capacitors (UCAP) have typical characteristics such as low
energy density and high power density for the mitigation of
voltage sag and swell The DVR system discussed in this paper
has a bidirectional buck-boost converter and an ultra-
capacitor as the energy storage device This paper presents an
enhance DVR topology suitable for delivering extended
mitigation for PQ problems. In the proposed DVR, Ultra-
Capacitor is used as an energy storage device as it provides
extravagant power in a short interval of time due to thismany
advantages it offers over the conventional battery, has been
used as the active source for the DVR This paper presents
modeling and simulation of a DVR for power quality problems
and Compare the THD for Voltage Sag and Swell when Ultra
Capacitor connected to the series inverter via with and
without Dc-Dc converter. All the simulation work is done in
MATLAB software.
Key words: Dynamic Voltage Restorer (DVR), Ultra-
capacitor (UCAP), Voltage sag/swell, PI controller, DC-
DC Converter.
1. INTRODUCTION
In recent years , the term powerqualityreferstothe
characterization of the quality of power being delivered to
the customer premises in terms of certain indices like the
magnitude and frequency of voltage, waveform shape etc.
Power quality has turn into major issues by way of the
beginning of power electronics devices, whose behavior is
most responsive to the power quality problems. In the
production industries, load devicesutilizespower electronic
based controllers which are fast responding to pitiable
voltage quality and will be in OFF mode if the source voltage
is lowered and may mis-operate in many methods if
harmonic distortion of the source voltage is much more.
Power quality issues is an incidence evident as unwanted
voltage, current or frequency, the performance is operation
failure or miss operation of user device.Muchofthismodern
load equipment itself uses electronic switching devices
which then can contribute to poor network voltage quality.
With a fast increasing technology in industrial sector,
electrical companies are observing more stipulating
demands on the power quality from the power consumers
and the association of the universal financial system has
advanced in the direction of globalization and the gain
boundaries of a lot of tricks be likely to reduced. The
improved compassion of the huge amount of work like
(industrial, Services and even residential) to power quality
issues makes the accessibility of electric power system with
excellence a essential feature for competitiveness in each
sector. Some of the salient power quality issues include
voltage sags/swells, harmonics, long term voltage
disruptions etc. Switching of loads and capacitor banks,
faults or short circuits in the powersystem,startingcurrents
of large machines and many such occurrences may manifest
as power quality issues. A surveyconducted byInternational
Energy Agency lists voltage sag asthemostimportantpower
quality issue to be dealt with Voltage sag/swell is a
momentary dip/rise in voltage from 0.9 - 0.1 p.u (sag)/1.1–
1.8 p.u (swell) of the nominal rms value. Typically the
duration of voltage sags or swells can lie anywhere between
half cycle to one minute.
There are many FACTS devices or power
conditioning devices are introduced to minimize different
power quality problem to improve the power quality of the
electrical power. With the help of these devices we are
capable to reduce the problems related to power quality.
This paper presents the two simulation model of integrated
UCAP based DVR with and without Dc-Dc converter. UCAPs
have high power density and low energy density ideal
characteristics for effective compensation of PQ problems
such as voltage sag and voltage swell investigating the high
quality of power in the distributed power generation.

2. DYNAMIC VOLTAGE RESTORER (DVR)
The DVR (Dynamic Voltage Restorer) model is shown inFig-
1. It consists of the Insulated gate bipolar transistor (IGBT),
its gate driver, filter circuit consists of the inductance and
capacitor and an isolation transformer.
Fig- 1: Basic Model of DVR
The key purpose of a DVR is the protection of
sensitive loads from power quality problemssuchasvoltage
sag and swell. If a fault arises on the transmission lines, DVR
injects a series voltage and pre-fault value is obtained by
compensating the load voltage. The injected voltage of the
DVR connected in series can be written as
VDVR=Vload+ZTHIL-VTH (1)
Where, Vload is the required load voltagemagnitude, ZTHisthe
load impedance, IL is the load current and VTH is the source
voltage during sag and swell condition.
The load current can be calculated by given formula,
IL= (2)
In order to provide dynamic voltage restoration, there are
various methods available to control the inverter connected
in series. The control method requires the use of the
proportional and integral controller.Theoutputsignal ofthe
PI controller is directly proportional to the sequence of
measured actuating error signal and its time. The transfer
function is given by,
Transfer Function=(K1 /s)+KP
Power quality problem includes voltage sag and
swell are generated at the load terminals by inducing the
fault. The sensing of load voltage takes place and is passed
through the sequence analyzer and its amplitude is
compared with a reference voltage (Vref). In order to
maintain the base voltageacrosstheloadterminals,theIGBT
inverter is controlled by using PI controller. Using DVR, the
compensation is achieved by either injecting or absorbing
the real and reactive power into the system. The main
disadvantage of DVR states that it can supply only limited
amount of real power during compensation. For effective
compensation to take place, DVR can be connected through
the energy storage device.
3. ULTRA-CAPACITOR (UCAP)
The specifics of ultra capacitor construction are dependent
on the application and use of the ultra capacitor. The
materials may differ slightly from manufacturer or due to
specific application needs. The ultra capacitor is consist of a
positive electrode, a negative electrode and separator
between these two electrodes. The assembly of the ultra
capacitors can vary from product to product. This is due in
part to the geometry of the ultra capacitor packaging. UCAP
can be divided into three categories according to the energy
storage mechanism namely Double-LayerCapacitor,organic
polymer electrode Ultra-capacitor and metal oxide super
capacitor. Double layerCapacitorisshowninfollowingFig-2.
Fig- 2: Ultra-Capacitor Model
While charging, the Positive attracts electrolyte anion and
negative attracts cation. When discharging, it can release
all stored energy instantly. UCAP is mainly suitable for
short term high power application.
4. Bidirectional Dc–Dc Converter And Controller
Like a battery, A UCAP cannot be connecteddirectly
to the dc-link of the inverter, as the voltage profile of the
UCAP varies as it discharges energy. Therefore, here is a
need to integrate the UCAP system through a bidirectional
dc–dc converter, which maintains a stiff dc-link voltage, as
the UCAP voltage decreases while discharging andincreases
while charging. The model of the bidirectional dc–dc
converter and its controller are shown in Fig-3, where the
input consists of three UCAPs connected in series and the
output consists of a nominal load to prevent operationatno-
load, and the output is connected to the dc-link of the

inverter. The amount of active power support required by
the grid during a voltage sag eventisdependentonthedepth
and duration of the voltage sag, and the dc–dc converter
should be able to withstand this power during the discharge
mode. The dc–dc converter should also be able to operate in
bidirectional mode to be able to charge or absorb additional
power from the grid during voltage swell event.
Fig-3. Model of the bidirectional dc–dc converter and its
controller.
In this paper, the bidirectional dc–dc converter acts
as a boost converter while discharging powerfromtheUCAP
and acts as a buck converter while charging the UCAP from
the grid. A bidirectional dc–dc converter is required as an
interface between the UCAP and the dc-link since the UCAP
voltage varies with the amount of energy discharged while
the dc-link voltage has to be stiff. Average current mode
control, which is widely is used to regulate the output
voltage of the bidirectional dc–dcconverterinboth buck and
boost modes while charging and dischargingtheUCAPbank.
This method tends to be more stable when compared to
other methods such as voltage mode control and peak
current mode control. Average current mode controller is
shown in Fig. 3, where the dc-link and actual output voltage
Vout is compared with the reference voltage Vref and the
error is passed through the voltage compensator C1(s),
which generates the average reference current Iucref.When
the inverter is discharging power into the grid during
voltage sag event, the dc-link voltage Vout tends to go below
the reference Vref and the error is positive; Iucref is positive
and the dc–dc converter operates in boost mode. When the
inverter is absorbing power from the grid during voltage
swell event or charging the UCAP, Vout tends to increase
above the reference Vref and the error is negative; Iucref is
negative and the dc–dc converter operates in buck mode.
Therefore, the sign of the error between Vout and Vref
determines the sign of Iucref and thereby the direction of
operation of the bidirectional dc–dc converter. The actual
UCAP current (which is also the inductor current) Iucisthen
compared to the average reference current Iucref and the
error is then passed through the current compensator C2(s).
The compensator transfer functions, which provide a stable
response, are given by,
C1 (s) = 1.67 +
C2 (s) = 3.15 +
5. PROPOSED WORK
Fig- 4: Block diagram of Integrated UCAP-DVR without
Dc-Dc Converter
The block diagram of the without Dc converter
UCAP-DVR system is shown in Fig-4. It consists of three
phase series inverter, UCAP energy storage deviceandthree
phase isolation transformer connected to distribution Grid.
The three phase supply voltage of 415 V,50 Hz is connected
to the sensitive load in both the block diagram.
Fig- 5: Block diagram of Integrated UCAP-DVR with Dc-Dc
Converter
Fig-5. shows the block diagram of the integrated
UCAP-DVR system. It consists of three phase series inverter,
a bidirectional DC-DC converter connected with UCAP
energy storage device and three phase isolationtransformer
connected to distribution Grid. In both the system the three
phase voltage source inverter which acts as a power stage is
connected in series to the grid and is responsible for the
voltage sag and swell compensation. In Fig-4. the energy
storage device i.e. UCAP is connected directly totheinverter

circuit vice versa in Fig-5. the energystoragedevicei.e.UCAP
is connected to the inverter via Dc-Dc Buck Boost Converter
because to maintain stiff Dc voltage to the inverter.
And the various Simulation results of this two
system are discussed and shown in results section
6. SIMULATION/EXPERIMENTS RESULTS
The simulation of the UCAP-DVR with and without
DC-DC converter is carried out in MATLAB/Simulink for a
415 V, 50Hz system. Fig-6. shows the simulation model of
three phase DVR Circuit with DC-DC converter and Fig-7.
shows the simulation model of UCAP-DVR without Dc-Dc
converter and three phase RL load are connected. Between
three phase ac supply and load an injection transformer
having 1:1 turn’s ratio is connected. Primary of transformer
is connected in series with load, while its secondary is
connected to the invertercircuit.ThreeVImeasurements are
connected at source side, load side and DVR side, so that
these voltages are used to see the waveforms on scope.
Voltage of the DC storage device is 300volts. SPWM control
technique is used in the DVR in both the model to stimulate
the sag and swell.
Fig-6: Simulation model of Three phase DVR with Dc-Dc
Converter
Fig-7: Simulation model of Three phase DVR without Dc-
Dc Converter
6.1 Case study: Voltage sag compensation
At the power frequency sag is a decrease for durations from
0.5 cycle to 1 minute in between 0.1 and 0.9 pu in rms
voltage or current. The system model with 20% voltage sag
created in 0.2s to 0.3s in three phase voltageasshowninFig-
8(a). When the three phase supply voltage sag is produce at
0.2s to 0.3s the DVR activated suddenly in milliseconds to
compensate load voltage and injectthelostsagvoltagetothe
load voltage side to maintain the magnitude constantduring
voltage sag condition as shown in Fig-8(c).
a) Source Voltage
b) Injected Voltage
c) Load Voltage
Fig-8: Simulation results for voltages Sag Condition
(a) Source voltage (b) Injected DVR Voltage (c)Load
voltage
6.2 Case study: Voltage Swell compensation
A swell is defined as, at the power frequency for
durations from 0.5 cycle to 1 minuteanincrease between 1.1
pu and 1.2 pu in rms voltage or current. In this simulation
20% voltage swell are created in three phase at 0.2s to 0.3s
as shown in Fig-9(a). When voltage swell are produced in
0.2s to 0.3s the DVR is activated and inject the missing
voltage as shown in Fig-9(c).
Here UCAP-DVR absorbed the active power from the
grid during voltage swell event through the bidirectional
converter and the inverter. It can be observed that, the
magnitude of the source voltage is reduced due to the
injected voltage, but the load voltage remains constant and

thus the voltage sag event canbecompensated.Similarly,the
magnitude of source voltage has increased due to the
injected voltage, but the load voltage remains constant and
thus the voltage swell can be compensated.
a) Source Voltage
b) Injected Voltage
c) Load Voltage
Fig-9: Simulation results for voltages Swell Condition
(a) Source voltage (b) Injected DVR Voltage(c) Load
voltage.
Thus, the voltage sag and swell problems are
compensated effectively by the use of Integrated of UCAP
with DVR.
6.3 Case study: Voltage harmonics Compensation
The supply system is designed to operate (termed
the fundamental frequency; usually 50 or 60 Hz)at which
The Harmonics are sinusoidal voltages or currents having
frequencies that are integer multiples of the frequency.
Generally on the power system, Harmonic distortion
originates in the nonlinear characteristics of devices and
loads. Harmonic distortion levels are described by the
complete harmonic spectrum with magnitudes and phase
angles of each individual harmonic component. It is also
common to use a single quantity, the total harmonic
distortion(THD), as a measure of the effective value of
harmonic distortion.
Fig-10:THD for UCAP-DVR without Dc-Dc Converter
during Voltage sag
Fig-11:THD for Integrated UCAP-DVR with Dc-Dc
converter during Voltage sag
Fig-10 & Fig-11. Shows the stimulated THD for the
integrated Ultra capacitor connected to the DVR via Dc-Dc
converter.
Fig-12:THD for UCAP-DVR without Dc-Dc converter
during Voltage swell

Fig-13:THD for Integrated UCAP-DVR with Dc-Dc
converer during Voltage swell
Fig-12 & Fig-13. Shows the stimulated THD for the
Ultracapacitor connected to the DVR without Dc-Dc
converter.
Thus, some distortion may be seen in compensated
voltage is specified in the Total harmonic distortionanalysis.
The voltage sag and swell event in terms of THD for the
integrated UCAP-DVR with Conveter is shown in Fig-10 and
Fig-11. The comparisonoftotal harmonic distortion between
the conventional DVR where UCAP is directly connected to
the Series Inverter and the proposed system i.e. Integrated
UCAP-DVR where UCAP is connected to the Series Inverter
via Dc-Dc Converter is shown in Table-1.
Table -1: THD Comparison
System THD for Voltage Sag
THD for Voltage
Swell
Conventional UCAP-
DVR(Without Dc-Dc
converter)
9.56% 6.50%
IntegratedUCAP-DVR 0.23% 0.13%
Chart-1:The comparison for Two DVR System
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Simulation of DVR by using Ultra Capacitor to Analysis of THD with and without Dc-Dc Converter

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