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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{2013-01-15 (revised: 15 January 2013)} \def\TheID{\makeatother } \def\TheDate{2013-01-15} \title{Improvement of Power System Stability by using SVC with Cascade PID Controller} \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 \topsep 2\p@ plus1\p@ minus1\p@ \parsep 2\p@ plus\p@ minus\p@ \itemsep 1pt} } \makeatother \fvset{frame=single,numberblanklines=false,xleftmargin=5mm,xrightmargin=5mm} \fancyhf{} \setlength{\headheight}{14pt} \fancyhead[LE]{\bfseries\leftmark} \fancyhead[RO]{\bfseries\rightmark} \fancyfoot[RO]{} \fancyfoot[CO]{\thepage} \fancyfoot[LO]{\TheID} \fancyfoot[LE]{} \fancyfoot[CE]{\thepage} \fancyfoot[RE]{\TheID} \hypersetup{citebordercolor=0.75 0.75 0.75,linkbordercolor=0.75 0.75 0.75,urlbordercolor=0.75 0.75 0.75,bookmarksnumbered=true} \fancypagestyle{plain}{\fancyhead{}\renewcommand{\headrulewidth}{0pt}} \date{} \usepackage{authblk} \providecommand{\keywords}[1] { \footnotesize \textbf{\textit{Index terms---}} #1 } \usepackage{graphicx,xcolor} \definecolor{GJBlue}{HTML}{273B81} \definecolor{GJLightBlue}{HTML}{0A9DD9} \definecolor{GJMediumGrey}{HTML}{6D6E70} \definecolor{GJLightGrey}{HTML}{929497} \renewenvironment{abstract}{% \setlength{\parindent}{0pt}\raggedright \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]{Pranoy Kumar Singha Roy} \author[2]{G.K.M. Hasanuzzaman} \author[3]{Md. Moniruzzaman} \affil[1]{ } \renewcommand\Authands{ and } \date{\small \em Received: 11 December 2012 Accepted: 1 January 2013 Published: 15 January 2013} \maketitle \begin{abstract} In power system, one most crucial problem is maintaining system stability. The main reasons for occurring stability problem in the system is due to the fault occurs in the system. In this paper the effect of SVC on voltage stability is investigates using cascade Proportional Integral Differential controller.SVC is a shunt type FACTS device which is used in power system primarily for the purpose of voltage and reactive power control. The cascade PID controller parameters has been selected by using Tyreus-Luyben settings method for primary loop controller and modified Ziegler-Nichols method for secondary loop controller. Cascade control is mainly used to achieve fast rejection of disturbance before it propagates to the other parts of the plant.PID controller in cascade architecture is the best choice compared to conventional single loop control system for controlling nonlinear processs. The primary controller is used to calculate the setpoint for the secondrary controller. The effect of fault on line with SVC and SVC with supplementary controller is also investigates. In this paper, A power system network is considered which is simulated in the phasor simulation method & the network is simulated in three steps; without SVC , With SVC but no externally controlled, SVC with cascade PID. The result of the Simulation shows that SVC with cascade PID controllers are more effective to enhance the voltage stability and increases power transmission capacity of a power system .The power system oscillations is also reduced with controllers in compared to that of without controllers. So with cascade PID controllers the system performance is greatly enhanced. \end{abstract} \keywords{svc, voltage regulator, cascade propotional integral differential controller, matlab simulink.} \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[{Introduction}]{Introduction}\par he challenge facing power system engineers today is to use the existing transmission facilities to greater effect {\ref [1]} . Power system should retain its synchronism during and after all these kind of disturbances. Therefore the transient stability is an important security in power system design. So FACTS has come to help the power system engineer {\ref [2]}\hyperref[b1]{[3]} . The SVC is one of the important FACTS devices whose effectiveness for voltage control is well known. The AC power transmission system has diverse limits, classified as static limits and dynamic limits \hyperref[b2]{[4]}\hyperref[b3]{[5]} .Traditionally, fixed or mechanically switched shunt and series capacitors, reactors and synchronous generators were being used to enhance same types of stability augmentation {\ref [6]} . For Authors ? ? ?: Department of EEE, Rajshahi University of Engineering \& Technology Rajshahi-6204, Bangladesh. e-mails: pronoy331@yahoo.com, g.kibria82@yahoo.com, mdmonir.eee08@gmail.com many reasons desired perfor-mance was being unable to achieve effectively. A static VAR compensator (SVC) power compensation on high voltage transmission networks and it can contribute to improve the voltage profiles in the transient state and therefore, it can improve the qualities and performances of the electric services {\ref [6]} . An SVC can be controlled externally by using properly designed different types of controllers which can improve voltage stability of a large scale power system \hyperref[b4]{[7]} . However, in this study, With a view to get better performance, A new PID has been designed \& proposed for SVC to injects V qref externally for the improvement of power system stability. The dynamic nature of the SVC lies in the use of thyristor devices (e.g. GTO, IGCT) {\ref [6]} . Therefore, thyristor based SVC with PID controllers has been used to improve the performance of 2-machine power system. \section[{II.}]{II.} \section[{Control Concept of SVC}]{Control Concept of SVC}\par An SVC is a controlled shunt susceptance(B) which inject reactive power (Q net ) into thereby increasing the bus voltage back to its net desired voltage level. If bus voltage increases, the SVC will inject less (or TCR will absorb more) reactive power, and the result will be to achieve the desired bus voltage[Fig. \hyperref[fig_0]{1}]. Here, +Q cap is a fixed capacitance value, therefore the magnitude of reactive power injected into the system, Q net , is controlled by the magnitude of -Q ind reactive power absorbed by the TCR. The basis of the thyristor controlled reactor (TCR) which conduct on alternate half-cycles of the supply frequency. If the thyristors are gated into conduction precisely at the peaks of the supply voltage, full conduction results in the reactor, and the current is the same as though the thyristor controller were short circuited. SVC based control system is shown in Fig. \hyperref[fig_0]{1} {\ref [6]} . for secondary loop controller. Cascade control is mainly used to achieve fast rejection of disturbance before it propagates to the other parts of the plant.PID controller in cascade architecture is the best choice compared to conventional single loop control system for controlling nonlinear processs. \section[{III. SVC V-I characteristics}]{III. SVC V-I characteristics}\par In voltage regulation mode (the voltage is regulated within limits as explained below). b). In VAR control mode (the SVC susceptance is kept constant). From V-I curve of SVC, From Fig. \hyperref[fig_1]{2} \hyperref[b1]{[3]}, V=V ref +X s .I,: In regulation range(-Bc max