Abstract—Now I. Introduction A. Introduction This Today, lots of

Abstract—Now a day’s electrical
equipment’s are more receptive to power quality problems.  In power system there may be oscillation in
power quality at the sensitive load due to faults and switching operation of
breakers. This interruption results in breakdown of the equipment which
connected at load side. In this paper, a bidirectional power electronic
transformer based three phases four wires Dynamic Voltage Restorer (DVR)
structure is projected to inject required series voltage to the electric power
system in such a way that continuous sinusoidal voltage is seen at load side at
heavy fault occurrences also main power quality problems like voltage sag and
swell are deliberate. The PET-Power Electronic Transformer is a power
transformer which has the advantage of increasing the frequency to reduce the
overall size of transformer and hence this system delivers the extreme cost
effective solution to alleviate the above problems which required by customer.
So in MATLAB simulation model, this PET based DVR for load side protection
against voltage disturbance is investigated which shows that power quality at
load side improved with greater controllability and reliability.

Keywords—PET,
DVR; SPS; Power Quality

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I.      Introduction

A. Introduction

      This
Today, lots of attention on Power Quality problems as they affect lots of
sensitive end-users including industrial and commercial electrical consumers.
From Studies it is clear that voltage sags, transients and momentary
interruptions constitute 92% of all the PQ problems occurring in the distribution
power system. In fact, voltage sags always have a huge threat to the industry
and still 0.25s voltage sag is long enough to interrupt a manufacture process
resulting in enormous financial losses. According to depth and duration time,
voltage sags are commonly classified. Typical sag can be a drop to between 10%
and 90% of the rated RMS voltage and has the time duration of half cycles to 1
min. According to the data presented in majority of the sags recorded are of
depth no less than 50%. But deeper sags with long duration time obviously
cannot be ignored as they are more unbearable than shallow and short-duration
sags to the sensitive electrical consumers. Power distribution systems; ideally
provide their customers with a continuous flow of energy at pure sinusoidal
voltage at the tapered magnitude level and frequency. But in practice, power
systems specially the distribution systems, have numerous nonlinear loads which
considerably affect the quality of power supplies. As a result of the nonlinear
loads at the utility, the pureness of the waveform of supplies is lost and
hence this starts producing many power quality problems. With the increasing
use of non-linear loads and complexity of the network, the power system network
faces challenges to deliver quality power to the consumers. In this paper we describe the effectiveness of dynamic voltage restorer
(DVR) in order to alleviate voltage sags and swells in low voltage distribution
systems, required by customer. DVR is a rapid, flexible and resourceful
solution to power quality problems which has great importance today in all
modern environments. One of the major concerns in electricity industry today is
power quality troubles. So, Dynamic voltage restorer (DVR) can provide the
worthwhile solution to mitigate voltage sag by establishing the appropriate
voltage quality level, necessary.

B. Problem
Definition

Electric power
which delivered is affected by many different factors at the distribution
network which has to be compensated to improve the quality as well as quantity
of power been delivered.

C. Objectives of the work

1. Detection of voltage sag/swell in the power system network.

2. To mitigate the power quality issue using DVR and its behavioral
study.

3. To select the best suitable control technique for DVR.

4. To control the device in order to obtain desired performance. 9

D. Outline of paper

This paper is
arranged in following diverse sections. In section 1 we give a brief introduction
of the system with problem definition and objectives. The Section 2 gives
explanations of various reviews of different research papers. In section 3 we explained
Dynamic Voltage Restorer (DVR) with its various components in detail. Then in section 4 we give simulation
work with its results and finally we conclude and lay out the future work.

                                                                                                                                                      
II.    Literature Review

 

A vast number of publications have been
addressed the voltage sag compensation. The numerous researchers have
investigated all the topics associated to Dynamic Voltage Restorer (DVR) by
including the compensation strategy, the circuit topology, the components
design, the control circuit, the filter design and the detection of the sag. So
in this below paragraphs we gave a brief literature review on the mitigation of
voltage sag and its associated scheme.

In this paper 1 author explain
reviews of various articles with advantages and disadvantages of each possible
configuration and control techniques pertaining to DVR are presented. As, power
quality requirement is one of the most essential issues for power companies and
to their customers. For an industrial customer, the voltage sag and swell is
very rigorous problem which requires attention for its compensation. So, there
are various methods for the compensation of voltage sag and swell in which one
of the most popular methods of sag and swell compensation is DVR-Dynamic
Voltage Restorer, which is used in both low voltage and medium voltage
applications. Also, compensation strategies and controllers have been presented
in this literature, which aims at fast response, accurate compensation and low
costs. Finally it’s clear that this review help the researchers to select the optimum
control strategy and power circuit configuration for DVR applications.

In this paper 2 discuss and
proposed a new control algorithm for the DVR to regulate the load terminal
voltage during sag, swell in the voltage at the Point of Common Coupling. This
proposed work is based on Synchronous Reference Frame theory along with PI
controller which is used for the generation of reference voltages for a Dynamic
Voltage Restorer (DVR). Also, the control of the DVR is implemented through
used of derived reference load terminal voltages. Finally, it concludes that
the proposed control scheme is simple to design. The simulation results are taken
by MATLAB as its Simulink and Sim Power System (SPS) toolboxes to verify the
performance of the proposed scheme.

In this paper 3 author mainly
focus and deals with terminology and assorted issues related to Power Quality
problems. This problem mainly occurs in voltage sags, swells, harmonics,
surges, sustained over voltage and under voltage originated from power system
can often damage etc. This focal incident of voltage sag and harmonics
disturbed in power quality improvement and which is overcome by custom power
device called as Dynamic Voltage Restorer (DVR) that installed stuck between
the source voltage and sensitive load. Through MATLAB/SIMULINK software
performance improvement of the DVR based PI with Fuzzy Logic Controller is in
both balance and unbalance conditions of voltages.

Today end-users of domestic
as well as industrial customers of the public electric distribution networks,
high quality energy is essential. The quality of electric power is
characterized by the measurement and the analysis of the electric disturbances
which make it possible to understand the origin of the disturbances, to
evaluate their impact and then find the most suitable solution as either
economically or technically. This paper 4 introduces the probable relevance of the
evolution of the intervention function of a DVR as a new method to reduce and
attenuate the numerous electric defects in voltage influencing the quality of
energy supply.

As DVR-Dynamic Voltage Restorer is a
convention power device used to correct the voltage sag by injecting voltage as
well as power into the system. The mitigation capability of these devices is
mainly influence by the maximum load; power factor and maximum voltage dip to
be compensated. Voltage Dips on a feeder is significant assignment for DVR
system operation and appropriate desired voltage sag compensation. So in this
paper 6
main focus is projected to incorporate the amount of DC energy storage depends
on voltage dip, which available in a convenient manner for DVR power circuit.

In this paper 7 author described
DVR principles and voltage restoration methods for balanced and unbalanced
voltage sags and swells in a distribution system. Voltage sags and swells in
the medium and low voltage distribution grid are considered as most frequent
type of power quality problems based on studies of power quality. This impact
on sensitive loads which ranges from load disruptions to substantial economic
losses up to millions of dollars. For this purpose, different solutions
developed to protect sensitive loads against such disturbances but among them
the DVR is the most efficient and effective solution that includes lower cost,
smaller size and its dynamic response to the disturbance. Finally, simulation
results present illustration and understanding of the performance of DVR under
voltage sags/swells conditions.

The DVR is a power electronic based
device which is fast, flexible and efficient solution to voltage sag problem.
In this paper 8 author give an overview of the DVR and its functions, configurations,
components, compensating strategies and control methods are reviewed as well as
the device capabilities and limitations. The DVR offers a three-phase
controllable voltage source, whose voltage vector adds to the source voltage
during sag event to restore the load voltage to pre-sag conditions.

                                                                                                                              
III.   Dynamic Voltage Restorer (DVR)

A Dynamic Voltage Restorer is a recently
proposed series connected solid state device that injects voltage into the
system in order to regulate the load side voltage. It is normally installed in
a distribution system between the supply and critical load feeder. The basic
structure and Circuit diagram of a DVR is shown in below fig.1.
and fig.2. respectively as,

Fig. 1. Basic Structure of DVR

 

Fig. 2.Circuit Diagram of A DVR

 

The various
components constitute by DVR are, i) Energy Storage Unit: Energy
stored in DC form. Super capacitors, Flywheels, superconducting magnetic energy
storage and Batteries can be used as energy storage devices. Main Purpose – to
supply necessary energy to the VSI via a DC link for the generation of injected
voltages. ii) Capacitor: A large DC
capacitor is used in DVR to ensure a proper input DC voltage to Inverter. iii) Voltage Source Inverter (VSI): Inverter system is used to convert dc storage
into ac. It is a power electronic system which consists of a storage device and
switching device, which can generate a sinusoidal voltage at any required
frequency, magnitude and phase angle from dc storage. iv) Voltage Injection
Transformers: The AC voltage supplied by VSI is stepped up by using injection
transformer to the desired voltage level. It is a specially designed
transformer that attempts to limit the coupling of noise and also transforms
energy from the primary side to the secondary side. v) Passive Filters: It converts the inverted pulse width modulation
(PWM) waveform into a sinusoidal waveform. It is achieved by eliminating the
unwanted harmonic components generated VSI action. Higher orders harmonic
components distort the compensated output voltage. Also it filters out the
harmonics present in the output of the VSI which kept either at the inverter
side or at the HV side of the transformer. vi) By-Pass Switch: It is used to protect
the inverter from High current in the presence of unwanted conditions.  At a time of a fault or a short circuit, DVR
changes it into the bypass condition where the VSI inverter is protected
against over current flowing through the power semiconductor switches. vii)
Control
circuit: It steadily observe the system and its function is to detect any
disturbance in the system done by comparing the supply voltage with reference
voltage and based on that  generate the
switching command signals for VSI in order to generate the compensating voltage
by DVR.

                                                                                                                                                
IV.   Simulation & Results

A.   
Simulation work

In the simulation model, the DVR is connected
in series with the load which is supplied by the source voltage VRMS. The
injecting transformer is connected in each line to insert the compensating
voltage in the line. Injecting transformer is fed by voltage source inverter
with DC bus voltage Vdc. The scope is connected at output to show the results
waveforms. The below fig. 3. Shows
the simulation model of DVR as,

Fig.3. Simulation model of DVR

In this controlling
circuit as shown in below fig. 4., Three Dimensional Space Vector Pulse Width
Modulation (3DSVPWM) technique is used. Here value at load side and reference
value get compared and proportional to the above deference the pulse get
generated by this modulation technique. The deferent blocks are used like abc
to dq0 transformation, three phases PLL, alpha beta to abc.

Fig.4. Control
System Diagram

B.   
 Simulation Results

Fig.5. shows the simulation
results under balanced voltage sag condition. In this case, 50% voltage sag has
been considered for each phases. Utility voltage, injected voltage & load
voltage is restored to the nominal condition (before sag occurrence) after a
time lower than a half cycle.

Fig.5.
Simulation results under Balanced Sag

Fig.6. shows the simulation results under
unbalanced voltage sag condition with the values of 60%, 50% & 40% on
phases a,b respectively.

 

 

Fig.6.
Simulation results under Un-balanced Sag

 

In other case
the DVR performance is investigated under balanced & Unbalanced Voltage
Swell. Fig.7. shows the performance of Dvr Under 50% Balance Voltage Swell
conditions.

 

 

Fig.7
Simulation results under Balanced Swell

 

The result of un-balanced swell are shown in fig.8. In this case the three phase terminal voltages with unbalanced swell
of  60%, 50% & 40% on phase a, b& c are considered,
respectively. as can be
seen, also under swell condition, the load voltage is restored to its nominal
value.

 

 Fig.8. Simulation results
under Un-balanced Swell

 

Fig. 9. Shows the simulation results of the proposed
DVR under harmonic polluted utility voltage. It is clear that the load voltage
remains balanced & sinusoidal even when such condition is occurred for
utility voltage.

Fig.9. Simulation
results under Harmonic Polluted utility Voltage

 

The below table 1 shows
utility voltage with or without PET base DVR is given as,

TABLE I: OBSERVATION
TABLE

 

Without PET base DVR

With PET base DVR

Utility Voltage Before Fault (At 0.01 sec)

415 volt

415 volt

Utility Voltage at the time of Fault (At 0.06 sec)

250 volt

415 volt

Utility Voltage at the time of Fault (At 0.04 sec)

560 volt

415 volt

 

Conclusion

To improve power quality at utility
side, there are some effective methods. In this paper, the voltage sag and swell mitigation using a
device called power electronic transformer based DVR is presented. Voltage
unbalance under both balanced and unbalanced condition is considered and
simulation results are shown. Modelling and compensating technique used by DVR
for compensating such unbalance are also presented. The 33kv/11kv Distribution
Substation was taken for study of system with and without PET based DVR at
Rahata. The simulation result shows that DVR compensate sag and swell
effectively and provide good voltage regulation. From this structure point of view, the main
advantage of the proposed DVR is low volume & weight due to use PET. In future by considering the enhanced
functionality and flexibility of PET, the added cost can be easily justified.

References

 

1     Anita
Pakharia, Manoj Gupta, “Dynamic Voltage Restorer for Compensation of Voltage
Sag and Swell: A Literature Review”, International Journal of Advance in Engineering
& Technology, Vol. 4, Issue 1, pp.347-355, July 2012.

2     Himadri
Ghosh, Pradip Kumar Saha, “Design and Simulation of a Novel Self Supported
Dynamic Voltage Restorer (DVR) for Power Quality Improvement”, International
Journal of Scientific Engineering
Research, Vol. 3, Issue 6, pp 1-6, June2012.

3     Mahmoud
A. El-Gammal, Amr Y. Abou-Ghazala, “Dynamic Voltage Restorer for Voltage Sag
Mitigation”, International Journal on Electrical Engineering and Informatics,
Volume-3, Number 1, pp 1-11, March 2011.

4     M.
N. Tandjaouli, C. Benachabia, “Sensitive Loads Voltage Improvement Using
Dynamic Voltage Restorer”, International Conference on Electrical Engineering
and Informatics, Bandung, Indonesia, 17-19 July 2011.

5    
E. Babaei ,M.
FarhadiKangarlu, “Voltage quality improvement by a dynamic voltage restorer
based on a direct three-phase converter with fictitious DC link,” IET Generator
Transmission Distribution, vol. 5, Iss. 8, pp. 814–823, 2011.

6     H.P.
Tiwari and Sunil Kumar Gupta, “Dynamic Voltage Restorer against Voltage Sag”,
International Journal of Innovation, Management and Technology, Vol. 1, No. 3, ISSN:
2010-0248, August 2010.

7     C.
Benachaiba and B. Ferdi, “Power Quality Improvement Using DVR”,  American Journal of Applied Sciences 6 (3):
396-400, ISSN 1546-9239, © 2009 Science Publications.

8     Mahmoud
A. El-Gammal1, Amr Y. Abou-Ghazala2, and Tarek I. El-Shennawy, “Dynamic Voltage
Restorer (DVR) for Voltage Sag Mitigation”, International Journal on Electrical
Engineering and Informatics ? Volume 3, Number 1, 2011.

9     Kiran
P. Varade, P. C. Tapare,and C. Veeresh, “Enhancement of Power Quality using
Power Electronics Transformer based DVR, “International Journal of Science
Technology Management and Research”, Vol. 2, Issue 5, 2017.

 

 

 

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