Modeling of Hybrid 5-Level Cascaded H-Bridge Based
Dynamic Voltage Restorer
Haritha A, V.R Vithal & T. Deva Raju
Department. of EEE
Sree Vidyanikethan Engineering College, Tirupati.
distribution system is internally generated by the
restorer without AC passive reactive components. The
real power exchanged at the restorer output AC
terminals is provided by the restorer input DC terminal
from an external energy source or energy storage
system. In August 1996, Westinghouse Electric
Corporation installed world’s first dynamic voltage
restorer in Duke Power Company’s 12.47 kV
substations in Anderson, South Carolina. This was
installed to provide protection to an automated rug
manufacturing plant. Prior to this connection, the
restorer was first installed at the Waltz Mill test facility
near Pittsburgh for the full power tests [1]. Faults at
either the transmission or distribution level may cause
voltage sag or swell in the entire system or a large part
of it. Also, under heavy load conditions, a significant
voltage drop may occur in the system. Voltage sags can
occur at any instant of time, with amplitudes ranging
from 10 – 90% and a duration lasting for half a cycle to
one minute [2].
Abstract - This type of converter is suitable for high voltage
and high power applications. This multilevel inverter has
ability to synthesize waveforms with better harmonics
spectrum. This paper deals with modelling and simulation
of five- level inverter based Dynamic Voltage Restorer
(DVR). The control of DVR that injects a voltage in series
with a distribution feeder is presented. DVR is a power
electronic controller that can protect sensitive loads from
disturbances in supply system. There are numerous
topologies has been introduced and widely studied for
utility and drive application. In this work a study of 5-level
inverter controlled with DVR technique. MATLAB
software is used for simulate the 5-level inverter controlled
with DVR technique.
Keywords: MATLAB Simulink, 5- level Inverter, Series
Compensation, Dynamic Voltage Restorer (DVR).
I.
INTRODUCTION
The Fig. 1 shows the series connection of a
Dynamic Voltage Restorer (DVR) between the utility
source and loads, through a coupling transformer.
A power electronic converter based series
compensator that can protect critical loads from all
supply side disturbances other than outages is called a
dynamic voltage restorer. The restorer is capable of
generating or absorbing independently controllable real
and reactive power at its AC output terminal. This
device employs solid state power electronic switches in
a pulse width modulated (PWM) inverter structure. It
injects a set of three phase AC output voltages in series
and synchronism with the distribution feeder voltages.
Conventionally, the series voltage Vo is injected
through a coupling transformer, whose main functions
are to provide voltage boosting (Vo/Vo’ > 1) and
electrical isolation between the phases. Usage of a
transformer, however, has the disadvantage of making
the DVR bulky and costly, the other disadvantages, as
summarized in [3]. To overcome these disadvantages,
has proposed the series/parallel connection of
semiconductor switches, or H -bridges, to develop high
voltage DVR (HVDVR), which can be connected
directly to the utility grid without a coupling
transformer.
The amplitude and phase angle of the injected
voltages are variable there by allowing control of the
real and reactive power exchange between the device
and the distribution system. The DC input terminal of
the restorer is connected to an energy source or an
energy storage device of appropriate capacity. The
reactive power exchanged between the restorer and the
This study begins by analyzing different topological
possibilities for implementing the HVDVR with the
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main aim of designing a reliable custom power
conditioner. The next letter next presents an open-loop
control scheme with Posicast compensator incorporated
for damping transient voltage oscillations at the instant
of voltage injection (an issue which has not been
actively investigated for DVR) [4]. The Posicast-based
open-loop control is subsequently improved by adding a
parallel multifeedback-loop control path to give twodegrees-of-freedom in control tuning. This feedback
path uses the P+resonant compensator to force the
steady-state voltage error to zero, hence, enhancing the
DVR load voltage regulation performance [5]. All
principles presented have been verified in Matlab/
Simulinks simulation using a cascaded five level
inverter
Fig.2 One phase leg of an inverter with (a) two levels,
(b) three levels, and (c) n levels
Fig. 2 shows a schematic diagram of one phase leg
of inverters with different numbers of levels, for which
the action of the power semiconductors is represented
by an ideal switch with several positions. A two-level
inverter generates an output voltage with two values
(levels) with respect to the negative terminal of the
capacitor [see Fig. 2(a)], while the three-level inverter
generates three voltages, and so on. Considering that m
is the number of steps of the phase voltage with respect to
the negative terminal of the inverter, then the number of
steps in the voltage between two phases of the load k is
k=2m+1
and the number of steps in the phase voltage of a threephase load in wye connection is
p=2k-1
Fig.1: System Configuration With Dynamic
Restoration
The term multilevel starts with the three-level
inverter introduced by Nabae et al. [4]. By increasing
the number of levels in the inverter, the output voltages
have more steps generating a staircase waveform, which
has a reduced harmonic distortion. However, a high
number of levels increases the control complexity and
introduces voltage imbalance problems
Voltage
II. MULTILEVEL INVERTERS
The multilevel voltage source inverters have unique
structure therefore output reach high voltages with low
harmonics without the use of transformers or seriesconnected synchronized switching devices. The main
function of the multilevel inverter is to synthesize a
desired voltage wave from several levels of dc voltages.
Three different topologies have been proposed for
multilevel inverters: diode-clamped (neutral-clamped)
[4]; capacitor- clamped (flying capacitors) [1], [5], [6];
and cascaded multi cell with separate dc sources [1],
[7]–[9]. In addition, several modulation and control
strategies have been developed or adopted for multilevel
inverters including the following: multilevel sinusoidal
pulse width modulation (PWM), multilevel selective
harmonic elimination, and space-vector modulation
(SVM).
Due to this reason, multilevel inverters provide the
high power required of a large electric drive. As we try
to increase the number of levels, the synthesized output
waveform has more steps, which produces a staircase
waveform that approaches a desired waveform. Also,
due to more steps are added to the waveform, the
harmonic distortion of the output wave decreases,
approaching zero as the number of levels increases. As
the number of levels increases, the voltage that can be
extended by summing multiple voltage levels. Due to
the structural property of the multilevel inverter no
voltage sharing problems are encountered by the active
devices [6].
The most attractive features of multilevel inverters
are as follows.
1) They can generate output voltages with extremely
low distortion and lower dv/dt
2) They draw input current with very low distortion.
3) They generate smaller common-mode (CM)
voltage, thus reducing the stress in the motor
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ITSI Transactions on Electrical and Electronics Engineering (ITSI-TEEE)
bearings. In addition, using sophisticated
modulation methods, CM voltage can be eliminated
[8].
DVR is a device that injects a dynamically
controlled voltage Vinj in series to the bus voltage by
means of ac booster transformer as depicted in Fig.3
There are three single phase booster transformers
connected to a three phase converter with energy storage
system and control circuit [8]. The amplitudes of the
three injected phase voltages are controlled such as to
eliminate any detrimental effects of a bus fault to the
load voltage VL (t). This means that any differential
voltage caused by transient disturbances in the ac feeder
will be compensated by an equivalent voltage generated
by the converter and injected on the medium voltage
level through the booster transformer.
4) They can operate with a lower switching frequency
2.1 Dynamic Voltage Restorer
A DVR is a power-electronic controller that can
protect sensitive loads from disturbances in the supply
system. It is connected in series with a distribution
feeder and is capable of generating or absorbing real and
reactive power at its ac terminals. The basic principle of
a DVR is simple: by inserting a voltage of required
magnitude and frequency, the DVR can restore the loadside voltage to the desired amplitude and waveform
even when the source voltage is unbalanced or distorted.
Usually a DVR is connected to protect sensitive loads
during faults in the supply system. DVR has become
popular as a cost effective solution for the protection of
sensitive loads from voltage sags. Implementations of
the DVR have been proposed at both a low voltage (LV)
level, as well as a medium voltage (MV) level and give
an opportunity to protect high power sensitive loads
from voltage sags .The basic operational principle of the
DVR is to inject an appropriate voltage in series with
the supply through an injection transformer when
voltage sag is detected at the point of common coupling
(PCC). Loads that are connected downstream are thus
protected. Fig.3 is designed to mitigate voltage sags on
lines feeding sensitive equipment. Viable alternative to
uninterruptible power systems (UPS's) and other
utilization voltage solutions to the voltage sag problem. .
DVR consists of energy storage unit, PWM inverter, and
injection transformer as shown in Fig.3
For most of the time the DVR has, virtually,
"nothing to do," except monitoring the bus voltage. This
means it does not inject any voltage (Vinj = 0)
independent of the load current. Therefore, it is
suggested to particularly focus on the losses of a DVR
during normal operation. Two specific features
addressing this loss issue have been implemented in its
design, which are a transformer design with low
impedance and the semiconductor devices used for
switching. An equivalent circuit diagram of the DVR
and the principle of series injection for sag
compensation are depicted in Fig. 4(a) and phasor
diagram is shown in Fig.4 (b).
Fig. 4(a): Equivalent Circuit Diagram
Fig. 4(b) : Phasor Diagram
Fig. 3: Typical Model of DVR
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ITSI Transactions on Electrical and Electronics Engineering (ITSI-TEEE)
III. OPERATION OF DVR
In normal conditions, the DVR operates in stand-by
mode. However, during disturbances, nominal system
voltage will be compared to the voltage variation. This
is to get the differential voltage that should be injected
by the DVR in order to maintain supply voltage to the
load within limits. The amplitude and phase angle of the
injected voltages are variable, thereby allowing control
of the real and reactive power exchange between the
DVR and the distribution system. The DC input terminal
of a DVR is connected to an energy storage device of
appropriate capacity. As mentioned, the reactive power
exchange between the DVR and the distribution system
is internally generated by the DVR without AC passive
reactive components. The real power exchanged at the
DVR output ac terminals is provided by the DVR input
DC terminal by an external energy source or energy
Storage system.
Fig. 5: First Half Cycle Of The Quarter-Wave
Symmetric Waveform
The output voltage level is zero from wt = 0 to wt =
α1. At wt = α1, the output voltage level is changed from
zero to +V1, and from +V1 to +(V1+V2) at wt = α2.
The process will be repeated until wt = π/2, and the
output voltage level becomes +V1 +V2+…+V(S1)+VS. Then, in the second quarter, the level of output
voltage will be decreased to +V1 +V2+…+V(S-1) at wt
= π-αS. The process will be repeated until wt = π-α1 and
output voltage becomes zero again. In the second half of
the waveform, the process will be repeated all of
previous steps except the amplitude of the dc sources
change from positive to negative. The next period will
then repeat the same cycle.
IV. MULTILEVEL CONCEPT
Recent advances in power electronics have made
the multilevel concept practical. In fact, the concept is
so advantageous that several major drives manufacturers
have obtained recent patents on multilevel power
converters and associated switching techniques. It is
evident that the multilevel concept will be a prominent
choice for power electronic systems in future years,
especially for medium-voltage operation. Multi-level
inverters are the modification of basic bridge inverters.
They are normally connected in series to form stacks of
level.
5. 5- LEVEL INVERTER
The proposed multilevel inverter for five level
inverter is shown in fig.6. The inverter consists of eight
switches and two DC separate sources with the load. By
switching the GTO at appropriate firing angle, and
obtained the five level output voltage. GTO is good for
high voltage performance.
The Multilevel Concept And Notation
A multilevel inverter can be defined as a device that
is capable to produce a stepped waveform.
The first half cycle of the quarter-wave symmetric
waveform is depicted in Fig. 5.
The topological structure of multilevel inverter
must cope with the following points.
1.
It should have less switching devices as far as
possible.
2.
It should be capable of enduring very high input
voltage such as HVDC transmission for high power
applications.
3.
Each switching device should have lower switching
frequency owing to multilevel approach.
Fig.6: Circuit diagram of Five Level Proposed Inverter
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5.1 SWITCHIN STATES FOR THIS CIRCUIT
DVR without LC filter
Switching states of the circuit shows that which
switch will be on at a particular time. All the five
different switching states are shown in table. Switching
states of the circuit shows that which switch will be ON
at a particular time interval. Two cascade inverter
different switching states are shown in table. GTO is
used for switching, because GTO have high voltage
rating.
S1
S2
S3
S4
S5
S6
S7
S8
OUTPUT
VOLTAGES
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
V1
0
0
0
0
1
0
0
1
V2
0
1
1
0
0
0
0
0
-V1
0
0
0
0
0
1
1
0
-V2
5.2. SIMULATION RESULTS
Fig.7. simulation circuit of dvr with out LC filter
Fig. 6a: Five level inverter with RL load
Fig. 7a: Voltage across external,load-1and load-2
Fig. 7b: RMS voltage
Figure 6b. Output with filter
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VI. CONCLUSION
The simulation of the five level inverter controlled
with DVR technique is successfully done using with
pulse width modulation technique. The circuit modelling
and simulation of dynamic voltage restorer (DVR)
using cascaded five level inverter. However, under input
disturbances noise is present in the response
characteristics. Multilevel cascade inverter with separate
dc sources has been proposed for sensitive load.
Simulation results have shown that with control strategy
that operate the switches at fundamental frequency.
DVR structure is studied and the corresponding results
are presented. The heating is reduced since the
harmonics in the output of cascaded inverter are less.
The simulation is based on the assumption of balanced
load and single phase circuit model is considered. The
simulation results are in line with the predictions.
Fig. 7c: RMS load current
5.3. SIMULATION CIRCUIT OF FIVE LEVEL
INVERTER CONTROLLED WITH DVR
VII. FUTURE WORK
The work presented over here is essentially
theoretical and analytical in nature. It is felt that the
required modification in design details needed in five
level inverter controlled with DVR as proposed in the
present work will be advantage to future designers of
such systems. The detail simulink model can be used
with modifications for achieving an optimization in the
design.
VIII. REFERENCES
[1]
N.H.Woodley, L.Morgan and A.Sundaram,
“Experience with an inverter-base dynamic
voltage restorer,” IEEE Trans. Power Delivery,
Vol. 14, No.3, pp.1181-1185, 1999.
[2]
IEEE Std. 1159 – 1995, “Recommended Practice
for Monitoring Electric Power Quality”.
[3]
Li, B.H., S.S. Cho and D.M. Vilathgamuwa,
2002. Transformerless
Dynamic
Voltage
Restorer. Proc. Instit. Elec. Eng. Gener. Transm.
Distrib., 149(2): 263-273.
[4]
Hung, J.Y., 2003. Feeedback control W ith
Posicast. IEEE Trans. Ind. Electron., 50: 94-99.
[5]
Zmood, D.N., D.G. Holmes and G. Bode,
2001.Frequency domain analysis of three phase
linear current regulators. IEEE Trans. Ind.
Applicat., 37: 601-610.
[6]
Leon M. Tolbert, F. Z. Peng, T. G. Habetler,
“Multilevel converters for large Electric Drives”
[7]
A.Ghosh and A.Joshi, “A new approach to load
balancing and power factor correction in power
distribution system,” IEEE Trans. on Power
Delivery, Vol.15, No.1, pp.417-422, 2000.
Fig. 8(a) : Five Level Inverter Controlled with DVR
Fig. 8(b): Output Voltage across External load-1 and
load-
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[8]
S. J. Finney, A. M. Massoud, and B. W.
Williams, “A comparison of Three-level
converters versus twolevel converter for low
voltage drives, traction and utility application”, in
11th International Conference on harmonics and
power Quality, 2004.
[9]
H.P. Tiwari, Sunil Kumar Gupta, “Dynamic
Voltage Restorer Based on Load Condition”,
International Journal of Innovation, Management
and Technology, Vol. 1, No. 1, April 2010
[10]
Mohammed El Gamal Ahmed Lotfy G. E. M.
Ali, “Firing Approach for Higher Levels of Diode
Clamped Multi-Level Inverters”, Proceedings of
the 14th International Middle East Power
Systems Conference
[11]
Paisan
Boonchiam
and
Nadarajah
Mithulananthan, “Understanding of Dynamic
Voltage
Restorers
Through
MATLAB
Simulation”, Int. J. Sc. Tech.,Vol. 11, No. 3, JulySeptember 2006.
[12]
Arindam Ghosh and Gerard Ledwich,
“Compensation of Distribution System Voltage
Using DVR” IEEE Transactions on Power
Delivery, vol. 17, NO. 4, October 2002.
[13]
Arindam Ghosh, Amit Kumar Jindal, and
Avinash Joshi, “Design of a Capacitor-Supported
Dynamic Voltage Restorer (DVR) for
Unbalanced and Distorted Loads”, IEEE
Transactions on Power Delivery, vol. 19, NO. 1,
January 2004.
[14]
John Godsk Nielsen, Michael Newman, Hans
Nielsen, and Frede Blaabjerg, “Control and
Testing of a Dynamic Voltage Restorer (DVR) at
Medium Voltage Level”, IEEE Transactions on
Power Electronics,vol. 19, NO. 3, MAY 2004.
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