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\def\makelabel##1{\upshape ##1}}% } {\end{list}\end{raggedright}} \newenvironment{specHead}[2]% {\vspace{20pt}\hrule\vspace{10pt}% \phantomsection\label{#1}\markright{#2}% \pdfbookmark[2]{#2}{#1}% \hspace{-0.75in}{\bfseries\fontsize{16pt}{18pt}\selectfont#2}% }{} \def\TheFullDate{2016-01-15 (revised: 15 January 2016)} \def\TheID{\makeatother } \def\TheDate{2016-01-15} \title{Simulation and Analysis of Power Quality Improvement using Multilevel Unified Power Quality Conditioner} \author{}\makeatletter \makeatletter \newcommand*{\cleartoleftpage}{% \clearpage \if@twoside \ifodd\c@page \hbox{}\newpage \if@twocolumn \hbox{}\newpage \fi \fi \fi } \makeatother \makeatletter \thispagestyle{empty} \markright{\@title}\markboth{\@title}{\@author} \renewcommand\small{\@setfontsize\small{9pt}{11pt}\abovedisplayskip 8.5\p@ plus3\p@ minus4\p@ \belowdisplayskip \abovedisplayskip \abovedisplayshortskip \z@ plus2\p@ \belowdisplayshortskip 4\p@ plus2\p@ minus2\p@ \def\@listi{\leftmargin\leftmargini 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\textcolor{GJMediumGrey}{\rule{\textwidth}{2pt}} \vskip16pt \textcolor{GJBlue}{\large\bfseries\abstractname\space} }{% \vskip8pt \textcolor{GJMediumGrey}{\rule{\textwidth}{2pt}} \vskip16pt } \usepackage[absolute,overlay]{textpos} \makeatother \usepackage{lineno} \linenumbers \begin{document} \author[1]{G. Annapurna} \author[2]{G. Tulasiram Das} \affil[1]{ G. Narayanamma Institute of Technology and Science (for women)} \renewcommand\Authands{ and } \date{\small \em Received: 14 December 2015 Accepted: 4 January 2016 Published: 15 January 2016} \maketitle \begin{abstract} Unified Power Quality Conditioner (UPQC) is an effective device to solve the power quality problems. The UPQC is a combination of series and shunt filters which simultaneously compensate load voltage and source current imperfections. This paper presents harmonic mitigation using three level Neutral Point Clamped inverter based Unified Power Quality Conditioner. The use of three level Neutral Point Clamped converters allows a better performance of equipment by reducing harmonics and the ripple of the generated oltages and currents. The performance of UPQC in the reduction of harmonics is evaluated when employed with Multi carrier based SPWM and three level novel SVPWM techniques. Simulation results based on MATLAB/SIMULINK are presented to verify the effective compensation of harmonics using the two different modulation techniques. \end{abstract} \keywords{active filters, neutral point clamped converters, total harmonic distortion, power quality, SVPWM.} \begin{textblock*}{18cm}(1cm,1cm) % {block width} (coords) \textcolor{GJBlue}{\LARGE Global Journals \LaTeX\ JournalKaleidoscope\texttrademark} \end{textblock*} \begin{textblock*}{18cm}(1.4cm,1.5cm) % {block width} (coords) \textcolor{GJBlue}{\footnotesize \\ Artificial Intelligence formulated this projection for compatibility purposes from the original article published at Global Journals. However, this technology is currently in beta. \emph{Therefore, kindly ignore odd layouts, missed formulae, text, tables, or figures.}} \end{textblock*} \let\tabcellsep& \section[{I. Introduction}]{I. Introduction}\par he increased use of non-linear loads deteriorate power system voltage and current waveforms as they inject harmonics into the system. This results in increased losses, lower efficiency, failure of equipment etc. in the power system. Apart from voltage and current harmonics, voltage sag, voltage swell, voltage outage also can lead to poor quality of power \hyperref[b0]{[1]}. Harmonic compensation and voltage regulation have become more important as imbalance in the voltage and presence of harmonics have been serious issues. Hence, there is a great need to mitigate these power quality issues.\par The introduction of advanced power electronics technology has led to the development of active power filters which are viable solution to these power quality problems \hyperref[b0]{[1,}\hyperref[b1]{2]}.\par The general arrangement of Unified power quality conditioner is shown in Fig. {\ref 1}. The main function of a UPQC is to compensate voltage and current harmonics.\par The UPQC combines series and shunt active filters with a common dc link. The series active filter suppresses voltage distortions while the shunt filter Author ?: e-mail: gootyanu@gmail.com cancels current distortions such that this combination allows simultaneous compensation of voltages and currents supplied to the sensitive load to see that they are sinusoidal and balanced. Fig. {\ref 1} : General configuration of UPQC Multilevel inverters play an important role in the reduction of harmonic content in the voltages and currents. The multilevel inverters can synthesize high output voltage from smaller voltage levels and thus the current ripples and voltage harmonics are reduced. The UPQC presented in this work consists of three level converter topology \hyperref[b2]{[3,}\hyperref[b3]{4]}. The performance of UPQC can be optimized because of reduction in the size of passive components and transformers \hyperref[b3]{[4]}. \section[{II. The Upqc Controller}]{II. The Upqc Controller}\par The UPQC controller is composed of PLL circuit, Reference Voltage Algorithm and Reference Current Algorithm \hyperref[b3]{[4,}\hyperref[b4]{5,} {\ref 6]}.\par The PLL circuit has the system voltages Vab and Vcb i.e (Vab =Vas -Vbs, Vcb = Vcs -Vbs) as inputs and the outputs are the signals Pll\textunderscore a, Pll\textunderscore b and Pll\textunderscore c as shown in Fig. {\ref 2}. \section[{Fig. 2 : The synchronizing ciruit}]{Fig. 2 : The synchronizing ciruit}\par The PLL circuit guarantees the load voltages and source currents to be balanced sinusoidal waveforms at fundamental frequency.\par The reference current control strategy is shown in Fig. \hyperref[fig_0]{3}. The reference currents algorithm control block determines six reference currents (i aref1, i bref1, i cref1 ) and (i aref2 ,i bref2 ,i cref2 ) by using the outputs of PLL (Pll-a,Pll-b,Pllc) , the DC link voltages (V dc1 ,V dc2 ) and the load currents (I al, I bl ,I cl ) as inputs. The shunt active power filter will then synthesize the reference currents. The "reference voltage algorithm" shown in Fig. \hyperref[fig_1]{4} calculates, the reference voltages (V aref , V bref , V cref ) by using system input voltages (V as , V bs , V cs ) and PLL outputs(pll-a, pll-b, pll-c) that will be synthesized by the series power converter. \begin{quote} .\end{quote} \section[{III. Switching Strategy of Three Level Converters}]{III. Switching Strategy of Three Level Converters}\par In order to illustrate the switching control technique applied to the series and shunt active power converters, a basic three level NPC (Neutral Point Clamped ) topology as shown in Fig. {\ref 5} is used \hyperref[b6]{[7,}\hyperref[b7]{8]}. \section[{Fig. 5 : Three level Neutral point clamped converter}]{Fig. 5 : Three level Neutral point clamped converter}\par Each leg has four switching devices connected in series. As an example, phase "a" is considered to explain the behavior of the circuit.\par The output of the inverter can take three voltage levels based on the switching states of the devices. The output Va is positive when switches S1a and S2a are ON, it is negative when S3a and S4a are turned ON, and it is '0' when switches S2a and S3a are ON. The switching states of the devices and the corresponding output voltages with respect to the dc mid-point are indicated in the following Table {\ref I}.\par The switching strategy of the series active filter is shown in Fig 6 {\ref .} In this technique, the reference signal is compared with measured signal, the error is amplified and processed by PWM generator to obtain Va\textunderscore PWM. This signal is compared with two triangular waves of different limits having unit magnitude. The switching control strategy of the shunt active converter is shown in In this work, Phase Disposition multicarrier scheme is applied to Sinusoidal PWM. In this modulation, the reference sine wave is compared with the level shifted carrier triangular waves for producing the pulses. For a three level inverter, two triangular carrier waves of same frequency and amplitude are compared with the reference wave. The plane is divided into 6 triangular major sectors numbered I to VI each of 60 0 of fundamental cycle. There are 4 minor sectors within each major sector such that 24 minor sectors are there in the plane.\par The vertices of these minor sectors represent the voltage vectors. In the above plane, V0 is the zero voltage vector, large voltage vectors are represented by V13, V14, V15, V16, V17, V18 and V7, V8, V9, V10, V11, V12 are the medium voltage vectors. To determine the location of the command vector V* in a given major sector, first space vector phase angle' ?' is calculated and then sector is determined. The determination of major sector is done as follows:\par Table I : Determination of major sector \section[{Range of '? '}]{Range of '? '}\par Major sector number0 ? ? < 60 0 I 60 ? ? < 120 0 II 120 ? ? < 180 0 III 180 ? ? < 240 0 IV 240 ? ? < 300 0 V 300 ? ? < 360 0 VI\par Let us consider space vector diagram of sector I as shown in Fig . {\ref 9}. It contains 4 minor triangles D1, D7, D13 and D14. The reference vector can be located in any of these 4 regions, where each region is limited by three adjacent vectors.\par If the triangular sector where the command vector lies is defined by vectors Vx, Vy, and Vz assuming their durations Tx, Ty, and Tz respectively and Tx + Ty + Tz = Ts ,then V*= Vref can be synthesized by Vx, Vy, and Vz as follows : (?/6