Abstract: Voltage Restorer (DVR) with bidirectional power electronic

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Abstract: A three phase four wire Dynamic Voltage Restorer (DVR) with
bidirectional power electronic transformer structure is proposed to inject
required compensating series voltage to the electric power system in such a way
that continuous sinusoidal voltage is seen at load side ever at heavy fault
occurrences at utility side. The Proposed structure is composed of a three
phase four- leg inverter, three single phase high frequency transformers, three
cyclo converters and high frequency harmonic filter that are connected to the
utility. Three dimensional space vector modulation (3DSVM) methods is used for
pulse generation. Fourth added wire enables the DVR to compensate unbalance
voltage disturbance that are customer power quality problems in electrical
utility. In this paper proposed DVR performance was studied via
simulation results. This simulation results validated the satisfying operation
of the proposed DVR

Keywords: PET, DVR; 3DSVM; Power Quality.

INTRODUCTION

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Power
quality is one of major problems in the today’s scenario. It has become
important with the introduction of complex devices, whose performance is very
sensitive to the quality of power supply. Power quality problem is an
occurrence developed as a nonstandard voltage, current or frequency that
results in a failure of end use equipments. Some of the major problems dealt
here is the power sag and swell. This paper describes the effectiveness of
using dynamic voltage restorer (DVR) in order to mitigate voltage sags and
swells in low voltage distribution systems. Dynamic Voltage Restorer can
provide the most cost effective solution to mitigate voltage sags and swells
that is required by customer. The Dynamic Voltage Restorer (DVR) is a rapid,
flexible and resourceful solution to power quality problems.

Power
quality is of great importance in all modern environments where electricity is
involved, power quality can be essentially influenced by an important factor
like quality service. One of the major concerns in electricity industry today
is power quality problems. Presently, most of the power quality problems are
due to different fault conditions. These conditions cause voltage sag, voltage
swell, transients, voltage interruption and harmonics. These problems may cause
the apparatus tripping, shutdown commercial, domestic and industrial equipment,
and miss process of drive system. Dynamic voltage restorer (DVR) can provide
the lucrative solution to mitigate voltage sag by establishing the appropriate
voltage quality level, necessary. It is recently being used as the active solution
for mitigation of power quality problems.

 

.

LITERATURE REVIEW

 

Design and study of DVR is presented
in 1-5. It gives an overview of DVR control scheme and its modelling. It
shows that DVR provide efficient voltage restoration capability. The basic structure
and the operating principle of DVR are shown. Different compensation technique
of DVR is discussed.

Different control technique commonly
used for Voltage Source Inverter (VSI) is presented in 6-10. Different
control scheme is shown and are discussed. The performance of various
techniques are evaluated and compared.

The performance evaluation of DVR
with Sinusoidal Pulse Width Modulation (SPWM) and Space Vector Pulse Width
Modulation (SVPWM) is presented in 11-14. Two PWM based control techniques
are shown to control the VSI. SVPWM technique is compared with SPWM technique
and shows that SVPWM has better DC utilisation and lesser harmonics are
produced as compared SPWM.

Simulation of SVPWM and its
application in three phase inverter is presented in 15-16. The paper gives an
idea of SVPWM algorithm and its simulation. The simulation result shows that
SVPWM techniques are best suited for high power applications.

New scheme to control the two level
VSI is presented in 17. Detailed study of one of the SVPWM scheme i.e. seven
segment space vector modulation (SVM) is done. Determination and realization of
different switching states, sector value calculation, approximation of
reference voltage vector and switching time calculation for linear modulation
range is discussed.

SVPWM based DVR is presented in
18-21. In this control algorithm in which the three phase supply, is
converted into synchronously rotating d-q reference frame. The d-component
gives information for depth of sag and q-component tells us about phase shift
information. The error generated is given to SVPWM for DVR operation.

 

Dynamic voltage restorer (DVR) provide the worthwhile solution to
mitigate voltage sag by establishing the proper voltage quality level,
necessary.1 It is recently being used as the active solution for mitigation
of power quality problems.

 

PROPOSED WORK-:

Dynamic voltage restorer (DVR) provide the worthwhile solution to
mitigate voltage sag by establishing the proper voltage quality level,
necessary.1 It is recently being used as the active solution for mitigation
of power quality problems.

 

 

Figure 1: Basic Structure of A DVR

 

Basic
principal of DVR is to transfer the voltage sag compensation value from DC side
of the inverter to the injected transformer after filter. The compensation
capacity of a particular DVR depends on the maximum voltage injection
capability and the active power that can be supplied by the DVR. When DVR’s
voltage disturbance occurs, active power or energy should be injected from DVR
to the distribution system A DC system, which is connected to the inverter
input, contains a large capacitor for storage energy. It provides reactive
power to the load during faulty conditions. When the energy is drawn from the
energy storage capacitors, the capacitor terminal voltage decrease. Therefore,
there is a minimum voltage required below which the inverter of the DVR cannot
generate the require voltage thus, size and rating of capacitor is very
important for DVR power circuit.

The proposed DVR is shown in Fig. 2. The
purpose of control scheme is to maintain the load voltage at a desired value.
In order to control the three-phase four-wire inverter, 3DSVM method is used
that has some advantages such as more efficiency, high DC link voltage
utilization, lower output voltage THD, less switching and conduction losses,
wide linear modulation range, more output voltage magnitude and its simple
digital implementation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                            
Fig. 2. Three-Phase Four-Wire DVR

 

 

Ø  The main objectives of this Proposed system are:-

 

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

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

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

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

 

 

SIMULATION & RESULTS

 

In
this section, the proposed system in Fig. 2 is simulated in PSCAD-EMTDC. It
should be noted that the series transformers are operating in the linear region.
Fig. 3 shows the simulation results under unbalance voltage sag condition with
the values of 60%, 50% and 40% on phases a, b, and c, respectively. As can be
seen, under such conditions Fig. 3.(a), the DVR injects unbalance voltage Fig.
3.(b) in such a way that the load voltage Fig. 3.(c) remains balanced and
sinusoidal and doesn’t sense the voltage sag. Fig. 5.2 shows the simulation
results under balance voltage sag condition. It is clear that the load voltage
is restored to the nominal condition (before sag occurrence) after a time lower
than a half cycle.

 

 

3. Unbalanced
voltage sag, (a) utility voltages (b) injected voltages (c) load voltages

 

 

 

 

 

“.

                                                        
4. Balanced sag
(a) utility voltages (b) injected voltages (c) load voltages

 

 

 

As can be seen, the load
voltage remains continuously balanced and sinusoidal.

The THD values of utility
voltages and load voltages compensated are given in TABLE. The THD of the load
voltage is less than 3% that lays in the criterion reported in IEEE
standards  5l9-l99222.

Voltage

THDa

THDb

THDc

Utility Voltage

%38.87

%32.02

%4l.66

Load Voltage

%2.28

%l.9l

%2.37

 

CONCLUSION

 

The
proposed DVR performance was studied via simulation results. This simulation
results validated the satisfying operation of the proposed DVR.

 

                 According to the results, DVR
injects appropriated series voltage during utility voltage disturbance and
maintains the load voltage at desired value. Also the THD values of the load
voltage are less than the standard values.

 

 

REFERENCES

 

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