This document describes a design for a five-level photovoltaic (PV) inverter that uses a unipolar phase disposition pulse width modulation (PWM) technique. A fuzzy logic controller is applied to enhance the performance of the inverter. Simulation results using MATLAB/Simulink show that the total harmonic distortion (THD) of the output current is reduced when using the fuzzy controller compared to other modulation techniques. The fuzzy controller helps produce a sinusoidal output current at near unity power factor for different modulation indices to improve power transfer from the PV system to the grid.

1. International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982 Volume-4, Issue-2, Feb.-2016
Design Of Unipolar Phase Disposition Technique Connected To Five-Level PV Inverter Employing Fuzzy Control
116
DESIGN OF UNIPOLAR PHASE DISPOSITION TECHNIQUE
CONNECTED TO FIVE-LEVEL PV INVERTER EMPLOYING FUZZY
CONTROL
1
B.VIKRAM ANAND, 2
RAKESH SAHU, 3
AMRIT KU PANIGRAHI, 4
RATI RANJANSABAT
1,2,3,4
Asst Professor Department of Electrical Engineering, GIET, GUNUPUR,
E-mail: 1
ursvicky52@gmail.com, 2
rakeshrit@gmail.com, 3
amritkumar2306@gmail.com, 4
hodeee@giet.edu)
Abstract- This paper offers a simple five-level inverter topology for grid-connected PV systems with unipolar phase
disposition pulse width-modulated (PWM) technique. This technique uses two reference signals instead of single reference
whose magnitude is equal to each other with an offset corresponding to the magnitude of the triangular carrier signal to
generate the PWM signals for the IGBT’s. The inverter compromises much less harmonic distortion and can function at
near-unity power factor. It utilizes twofold reference signals and a carrier signal to produce PWM switching signals. The
circuit topology and operating principle of the proposed inverter were analysed in detail. A FUZZY-LOGIC control is
applied to enhance the performance of the inverter. MATLAB/SIMULINK results designate that the THD of the Fuzzy
Controller Circuit shows the better performance.
Keywords- Photo-voltaic system, five level inverter, fuzzy controller, unipolar phase disposition PWM, THD.
I. INTRODUCTION
At present, a wide interest has been developed in
renewable energy sources on one hand and the
initiation for deregulation of the utilities also
improved on the other hand. Together these
developments are at ease with power electronics
systems as a core enabling expertise. For example,
renewable energy sources like wind , solar and fuel
cells all require power-conditioning systems to
provide the necessary interface with the utility and
also to match the electrical characteristics of the
sources with the actual requirements of the loads
and/or the utility.
In these power-conditioning units, inverters are
everywhere heard for its conversion of fixed dc to ac
power i.e., from the dc power generated by some of
renewable energy sources to ac power required for the
load or utility. In general, two-level voltage source
inverters have been widely used. However, an
increase in the number of high power applications has
led to the development of multilevel inverters. In
addition to higher power ratings, multilevel inverters
produce better quality output voltages which thus
improve drive efficiency. Despite of the improvement
in output quality of voltages and currents, multilevel
inverters ahead of the three-level inverter have not
been considered due to the increase in design and
control complexity as the number of levels increases.
Thus, the three-level inverter has gathered its attention
as it produces better quailtated output waveforms over
the two-level inverter with only a minor increase in
complexity [1], [2].
However, these multilevel inverters alone cannot give
pure sinusoidal waveforms due to the further presence
of harmonics.
To overwhelm this limitation, this paper grants newly
developed unipolar phase disposition technique to a
five-level PWM inverter whose output voltage can
be characterized in the following five levels:
zero,+1/2Vdc, Vdc, , -1/2V dc , and -V dc . This
inverter topology practices two reference signals, in
its place of one reference signal, to produce PWM
signals for the IGBT’s. Together these reference
signals V ref1and Vref2are alike to each other,
except for an offset value corresponding to the
largeness of the carrier signal V carrier, as shown
inFig.1.
Fig.1 Carrier and reference signals
Since the inverter is castoff in a PV system, a
Fuzzy control scheme is active to retain the output
current sinusoidal and to obligate high dynamic
routine under swiftly changing atmospheric
circumstances and to uphold the power factor at
near unity[3]. Simulation results are obtainable to
validate the planned inverter configuration.
II. INVERTER DESIGN AND PWM CONTROL
IMPLEMENTATION
The planned five level inverter operations is explained
in Fig.2. This inverter accepts a full-bridge
configuration with a supplementary circuit. PV is
linked to the inverter through a dc–dc Boost converter.

2. International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982 Volume-4, Issue-2, Feb.-2016
Design Of Unipolar Phase Disposition Technique Connected To Five-Level PV Inverter Employing Fuzzy Control
117
Fig.2 Five level inverter
In the meantime the planned inverter is cast-off in
a grid-connected PV system, utility is preferred in
place of load. The dc–dc boost converter is second-
hand to boost up the collected voltage Vin to be
further than 2 of grid voltage magnitude Vg to
guarantee power flow starting from the PV to the
grid.
A smoothing inductor Lf is designed to riddle the
current injected into the grid. The injected current
necessity be sinusoidal with little harmonic bias. In
order to produce almost pure sinusoidal current,
unipolar phase disposition PWM is used for its
most effective approaches. This unipolar phase
disposition PWM is obtained by comparing a high
frequency carrier with a low frequency undirected
sinusoid, which acts as the modulating or reference
signal. The carrier has a continual period;
consequently, the IGBT’ sensures fixed switching
frequency. The switching instant is dogged from the
crossing of the carrier and the modulating signal.
Fig.3 Supreme five-level inverter output voltage .
III. OPERATIONAL PRINCIPLE OF THE
PROPOSED INVERTER
As PV arrays are cast-off as input voltage bases, the
voltage shaped by the array sis recognized as V arrays.
V arrays advanced by a dc–dc boost Converter to
surpass 2Vg. The voltage from corner to corner the
dc-bus capacitors is identified as V pv [4,5]. The
operational principle of the planned inverter is to
produce five level output voltage, i.e., 0, +V/2,
+V , -V /2, and -V. Suitable switching control of
the auxiliary circuit can create half level of PV.
Supply voltage, i.e., +V/2, +V pv, -V /2. Two
reference signals V ref1 and V ref2 will gross turns to
be related with the carrier signal at a suitable time.
When V ref1 overdoes the peak amplitude of the
carrier signal V carrier, V ref2 will be related with
the carrier signal until it touches zero. On this
point ahead, V ref1 proceeds over the comparison
process pending until it exceeds V carrier. This will
central to a switching design required for the IGBT’s,
as shown in Fig. 4. Switches S1–S3 will be switching
at the speed of the carrier signal frequency, whereas
S4 and S5 will function at a frequency corresponding
to the fundamental frequency[6]. Table I exemplifies
the level of Vinv during S1–S5 switch on and off.
Fig.4 switching pattern for the single-phase five-level inverter
IV. CONTROLALGORITHM AND
IMPLEMENTATION
The feedback controller implemented in this process
employs the FUZZY algorithm as shown in Fig., the
current inoculated into the grid, also identified as
grid current Ig, is detected and fed back to a
comparator which relates it with the reference
current Iref. Iref is attained by detecting the grid
voltage and adapting it to reference current and
multiplying it with fixed m. This is to guarantee
that Igis in phase with grid voltage Vg and to operate
at nearer-unity power factor[7,8,9]. One of the
difficulties in the PV generation systems is the
quantity of the electric power produced by solar
arrays always changing with weather disorders, i.e.,
the concentration of the solar radiation.
TABLE I: Inverter Output Voltage throughout S1-
S5 Switch ON and OFF
A maximum power point tracking (MPPT)
technique or algorithm, which devises quick-
response characteristics and is talented to make

3. International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982 Volume-4, Issue-2, Feb.-2016
Design Of Unipolar Phase Disposition Technique Connected To Five-Level PV Inverter Employing Fuzzy Control
118
respectable use of the electric power generated in
any weather conditions, is looked-for to solve the
above mentioned problem. Constant mis obtained
from the MPPT algorithm. The perturb band observe
algorithm is preferred to quote the maximum power
from PV arrays and distribute it to the
inverter[10,11].Here, the instantaneous current error
signal is fed to a FUZZY controller and the integral
period in the FUZZY controller improves the
tracking by reducing the immediate error between
the reference current signal and the actual current
signal. The subsequent error signal u which
customs Vref1 and V ref2 is compared with a
triangular carrier signal and crossings are wanted
to produce PWM signals for the inverter IGBT
switches[12].
Fig.5 Five level inverter employing FUZZYLOGIC control.
The Trapezoidal sum calculation is used to convert
the integral term into the discrete time domain as
it is the most up-front technique. The proportional
term is straight used without approximation. The
Simulation result aimed at five level inverter for
grid connected PV system
Fig.7 Simulink implementation of five level inverter
Fig.7Inverter voltage (Vinv) and grid current (Ig) for various values of modulation M. (a) Vinvfor modulationM<0.5. (b) Igfor
modulation M <0.5. (c) Vinv for modulation M >1.0. (d) Igfor modulation M >1.0. (e) Vinvfor modulation0.5 ≤ M ≤ 1.0. (f) Igfor
modulation 0.5 ≤ M ≤ 1.0.

4. International Journal of Industrial Electronics and Electrical Engineering, ISSN: 2347-6982 Volume-4, Issue-2, Feb.-2016
Design Of Unipolar Phase Disposition Technique Connected To Five-Level PV Inverter Employing Fuzzy Control
119
Table II: THD Analysis Table
V. SIMULATION RESULTS
In direction to prove that the planned inverter can be
practically realized in a PV system, simulations are
accomplished by expending MATLAB SIMULINK.
It also benefits to confirm the unipolar phase
disposition PWM switching strategy which then can
be executed. It comprises of two reference signals
and a triangular carrier signal. Both the reference
signals are related with the triangular carrier signal to
produce PWM switching signals for the IGBT
switches As mentioned earlier, the modulation index
M determine the shape of the inverter output voltage
Vinv and the grid current Ig. Fig.7displaysVinv and
Igfor different values of M.
The dc-bus voltage is fixed at 400 V (>√2Vg; in this
instance, Vg is 240 V) in order to inoculate current
into the grid. Fig. 7(a) shows that Vinv is a smaller
amount than √2Vg due to M being fewer than 0.5.The
inverter ought not operate at this condition as the
current will be inoculated from the grid into the
inverter, rather than the PV system inoculating the
current into the grid, as expose din Fig. 7(b). Over
modulation condition, which occurs atM >1.0, is
shown in Fig. 7(c). It takes a flat top at the peak of
the positive and negative cycles for both the reference
signals exceed the maximum amplitude of the carrier
signal. This causes Ig to have a flat portion at the
topmost of the sine waveform, as shown in Fig. 7(d).
To enhance the power shifted from PV arrays to the
grid, it is indorsed to operate at 0.5 ≤ M ≤ 1.0. Vinv
and Igfor best efficient condition are shown in Fig.
7(e) and (f), correspondingly. As Igis virtually a pure
sine wave, the THD can be reduced and also can be
compared with that under other values of M.
Table III: PV Multilevel Inverter Specifications
and Controller Parameter
CONCLUSION
This paper offered a multilevel inverter for PV
submission. It employs two reference signals and a
carrier signal to produce PWM switching signals. The
circuit operation and modulation law of the planned
inverter were worked out and explained in detail. A
FUZZY control is executed to improve the
performance of the inverter. MATLAB/SIMULINK
results show that the THD of the Fuzzy Controller
Circuit is much reduced. Moreover, both the grid
voltage and the grid current are in phase at almost-
unity power factor.
REFERENCES
[1] Effect of Flaying Capacitors on Improving the 4 Level
Three-Cell Inverter; KelaiaiaMounia Samira,
LabarHocine, BounayaKamel, and KelaiaiaSamia;
International Scholarly and Scientific Research
& Innovation 3(6) 2009;page(s):1360-1364.
[2] Hysteresis Current Controller based Transformerless Split
Inductor-NPC - MLI for Grid Connected PV- System;
R.latha*, C.Bharatiraja, R.Palanisamy, sudeepbanerji,
SubhransuSekhar Das, International Conference on
DESIGN AND MANUFACTURING 2013 (IConDM
2013), Procedia Engineering 64 ( 2013 ) 224 – 233
[3] Analysis of THD in Three phase PWM Inverter Drive with
Diode Neutral point method using Dual-Stage Common
mode filter-A simulation work; Dr.Manjesh and Ananda A
S; International Journal of Conceptions on Electronics and
Communication Engineering, Vol. 2, Issue. 1, June’ 2014,
Page(s):19-22.
[4] NPC-H Bridge Multilevel Inverter using Third Harmonic
Injection; Babitha T Abraham, Anish Benny; International
Journal of Advanced Research in Electrical, Electronics
and Instrumentation Engineering, Vol. 3, Special Issue 5,
December 2014,pp.174-181.
[5] V. G. Agelidis, D. M. Baker, W. B. Lawrance, and C. V.
Nayar, “A multilevel PWM inverter topology for
photovoltaic applications,” in Proc. IEEE ISIE,
Guimarães, Portugal, 1997, pp. 589–594.
[6] S. Kouro, J. Rebolledo, and J. Rodriguez, “Reduced
switching-frequency modulation algorithm for high-power
multilevel inverters,” IEEE Trans. Ind. Electron., vol. 54,
no. 5, pp. 2894–2901, Oct. 2007.
[7] S. J. Park, F. S. Kang, M. H. Lee, and C. U. Kim, “A new
single-phase five level PWM inverter employing a
deadbeat control scheme,” IEEE Trans. Power Electron.,
vol. 18, no. 18, pp. 831–843, May 2003.
[8] L. M. Tolbert and T. G. Habetler, “Novel multilevel
inverter carrier-based PWM method,” IEEE Trans. Ind.
Appl., vol. 35, no. 5, pp. 1098– 1107,Sep./Oct. 1999.
[9] CHUEN CHIEN LEE“Fuzzy Logic in Control System:
Fuzzy Logic Controller-Part 1,” IEEE Trans..
[10] A. Nabae and H. Akagi, “A new neutral-point clamped
PWM inverter,” IEEE Trans. Ind. Appl., vol. IA-17, no. 5,
pp. 518–523, Sep./Oct. 1981.
[11] Performance Evaluation of Various Unipolar SPWM
Strategies of Trinary DC Source Multilevel Inverter;
V.Arun, B.Shanthi, A.Bharathi; International Journal
of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 6, December 2012,pp.458-462.
[12] Three Phase MulticarrierPWM Switched Cascaded
Multilevel Inverter as Voltage Sag
Compensator;AASRI conference on Power and
Energy sytems, AASRI Procedia 2 ( 2012 ) 282 – 287.