Abstract— Power quality is one of the major area of
concern in recent forty years both in transmission and distribution system. The
major fault occur in the system are voltage sag, voltage swell, harmonics,
voltage fluctuation etc. There are various custom power devices are used to
compensate such problems. In this paper we have discuss on the Multilevel
inverter based DVR which is used to protect the sensitive equipment such as
computer, printer from line fault such as voltage sag. The implementation of
the DVR in the distribution system is based on the multilevel inverter topology
against voltage sag. The system is used for the distribution system for single
phase 230V supply. This paper represent the Simulink modal of multi level
inverter based DVR system which can compensate the voltage sag. All result are
shown in the MATLAB software and Result shown that, the multilevel inverter can
compensate voltage sag problem more effectively & improve voltage
Keywords-Power Quality,Multilevel inverterMLI,Voltage sag, DVR,Simulation
model, Matlab Simulation.
The common characteristics in most of the electronics apparatus is
they are very sensitive to the voltage variation. Now a days the use of power
electronics devices,computer,printer etc. can create power quality issue. Among
those power quality issue the most of them is related to the voltage such as
voltage sag, voltage swell etc. As there are many custom power devices has been
used to compensate such problems. Dynamic voltage restorer is one of the device
that can be capable of generating and absorbing active and reactive power in
distribution system against the voltage sag1.For that dc-dc converter is
used, by adjusting the thedc-dc input voltage according to range of voltage
sag.so the control technique is effective & simple.
Voltage sag are the frequent problem in distribution system. So for that
FACT devices such as static series compensator can be used2. This device
inject the missing voltage in the distribution system.
In recent year cascade multilevel
inverter has gained attention because of its advantages in high voltage,also it
has low harmonic distortion. The number of stages has been used in case of
multilevel inverter.the output waveform is in staircase form, that can be 3
There are the different topologies are used in multilevel inverter
such as diode clamp,flying capacitor, cascade multilevel inverter. The diode
clamp method split dc bus in required levels & bulk capacitor connected in
series. Flying capacitor topology is more flexible but controlling method is
more complex for high power lines. cascade inverter used the separate dc source
so that higher number of voltage levels can produce3.
The operation of DVR in the different
fault condition. The simulink is made of 5 level multilevel inverter based DVR,
where the POD control techniques are used & Diode clamp topology has been
The cascade H-bridge based
interline dynamic voltage restorer show that its performance is based on the
load power factor. while DVR is connected in series with the distribution
feeder. The two cascade H- bridge inverter injects voltage with low
distortion5.the results are observe in PSCAD software.
There are different compensation
techniques are used for injection of voltage in case of DVR such as pre sag, in
phase, phase advance compensation. The voltage magnitude are consider for
injection of the voltage in the system6.
Simulation modal has been done
for the closed loop and open loop system, where the PQ theory has been used to
to generate reference voltage7. Z source converter has been implemented for
the various power conversions for that impedance circuit presented8. The
simulink is done to show its effectiveness.
Dynamic voltage restorer is one of the device that can be capable of
generating and absorbing active and reactive power in distribution system
against the voltage sag. From using Multilevel inverter, the output voltage
waveform obtained is in staircase waveform but at the same time increased in
voltage levels can create circuit complexity. Multilevel inverter based DVR
provide the compensation of the voltage sag with less voltage stress. So
harmonic profile of the system gets improved.
DVR & MULTILEVEL INVERTER
i)DYNAMIC VOLTAGE RESTORER:
The power quality issue like voltage sag, voltage
swell, harmonics are more intense disturbances. To avoid this disturbances the
various custom power devices are used.DVR is one of the devices used to
compensate the voltage sag. It is device that is connected between the source
and load at point of common coupling, to regulate load side voltage.
Fig.1. Block diagram of DVR
basic DVR consist of the parts such as battery charging circuit which charges
the source of energy after sag compensation. voltage source converter is
provide sinusoidal voltage by using power electronic switches. Filter provide
the voltage of voltage source converter with acceptable level. Transformer is
used basically injection type which inject the compensating voltage in the
ii) MULTI LEVEL INVERTER TOPOLOGY:
inverter basically used of number of electronics switches such as MOSFET, GTO
etc. Sometimes capacitor, flying clamp diode can be used to obtain higher
number of stepped waveform. By introducing the concept of Multilevel inverter
the output voltage stress become reduce also harmonic profile improved.
the types of multilevel inverter:
Multilevel inverter using flying
Diode clamp multilevel inverter.
1) Cascade multilevel inverter:
Cascade multilevel topology often used.
It is always have separate dc source so it is efficient because it does not
require any capacitor or diode clamp. In this method the soft switching could
be used to avoid bulky and losses due to capacitor diode switching snubber
2)Multilevel inverter using flying capacitor:
The building block of capacitor clamp
circuit is known as the flying capacitor multilevel inverter. By applying the
suitable combination of capacitor the balancing of capacitor is possible. For
this method the number of bulky capacitor clamp are required.
3)Diode clamp multilevel inverter:
This type of inverter uses the diode to
produce the different voltage levels. It is having disadvantage of the real
power flow control is difficult to do also for higher number of voltage levels
diode clamp required in large number.
III. SIMULATION MODEL
model of multilevel inverter is shown, which includes the multilevel inverter
in which two MOSFET bridge circuit are cascade two each other. Each one of the
MOSFET circuit consist of the four MOSFET switches. In first bridge they are
denoted as the S1,S2,S3,S4. In second bridge they label as T1,T2,T3,T4. Three
unknown variables are given to the embedded function they are u, V cap, I load.
Each switches given the variables to stored gate signal whether 0 for OFF
&1 for ON. According to this manner the switching pattern are given to
Fig.2.Simulink model of
Fig.3. MLI based DVR
model shown is for 230V, 50 Hz supply. When the voltage sag is occur in the
system then multilevel inverter provide the voltage during sag period which is
around 0.4 second to 0.8 second. The DVR suddenly operate to compensate load
voltage. We can observe this waveform in scope connected on the load side.
this paper different simulation models with simulation results for power
quality disturbances are developed in matlab software that are capable to
simulate various power quality disturbances at distribution and utility
levels.The models for power quality disturbances like transients,voltage swell,voltage
unbalance,voltage sag, harmonics, interruption,voltage notch and voltage fluctuation.
These simulation models serve as a first step in analysis of power quality
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