Incorporation of FACTS Controllers in Newton Raphson Load Flow for Power Flow Operation, Control and Planning: A Comprehensive Survey
Abstract-
This paper presents a comprehensive survey ofincorporation of FACTS controller such as SVC, TCSC,SSSC, STATCOM, UPFC, and IPFC devices in Newton-Raphson load flow (NRFL) for power flow control. Thepurpose of this paper is to present a comprehensive surveyof various FACTS controllers are incorporated in loadflow analysis for different point of view such as optimalpower flow control, planning and operations of large-scalepower system networks. Authors strongly believe that thissurvey article will be very much useful to the researchersfor finding out the relevant references in the field ofoptimal power flow control of FACTS Controllers inmulti-machine power systems.Index Terms:- Flexible A.C. Transmission system(FACTS), FACTS controllers, TCSC, SVC, SSSC,STATCOM, UPFC, IPFC, Newton-Raphson Load Flowalgorithms (NRFL), load flow analysis, optimal powerflow (OPF) control.
I.INTRODUCTION
THE power flow equations are non-linear algebraicequations and for which explicit solutions are notpossible. These equations can be solved by iterativetechniques. Historically, the first algorithm for power flowproblem, employing the Gauss-Siedel method, using Ybuswas reported by Ward and Hale in 1956. The Gauss-Siedelmethod has minimum storage requirement but has slowerconvergence, and in some studies fails to converge. Even tothis day this method is still used when the system size is notvery large. In 1961, Van-Ness and Griffins SuggestedNewton’s using Gaussian elimination that has the advantageof superior convergence characteristics. In 1963, Sato andTinny introduced the concepts of optimally orderedelimination for the solution of large, sparse systems andshowed such methods to be very efficient. Later in 1967,Tinney and Hart showed that by the use of optimally orderedGaussian elimination and special programming techniquesboth the storage requirement and computing speed aredrastically reduced by Newton’s method. For systems having200 buses or more this method is inevitably used. Newton-Raphson method with quadratic convergence characteristicshas become popular for general purpose power flow study formost electric utilities.In 1963, Brown et al. develop a method which employed thesystem bus impedance matrix Zbus for power flow solution.This method of power flow solution has excellentconvergence characteristics, is not sensitive to initial values ofthe voltage profile, and can process negative impedance(series compensation of lines). However, this suffers from thedisadvantage that the bus impedance matrix Zbus is a fullmatrix and requires very large computer memory. This barrierwas overcome by applying diakoptics. However, this barrierhas how become insignificant as the present day computershave very large storage capacity.In 1972, B. Stott suggested approximations in Newton-Raphson method by decoupling MW-frequency and MVARvoltageloops in the power system. A simplified version ofdecoupled method known as the fast decoupled method, withfaster convergence characteristics, was suggested by B. Stottand O. Alsac in 1974. Subsequently, more work on the fastdecoupled method, for faster convergence, was reported.Load flow or power flow analysis is the determination ofcurrent, voltage, active power and reactive volt-amperes atvarious points in a power system operating under normalsteady-state or static conditions. Load flow studies are madeto plan the best operation and control of the existing system aswell as to plan the future expansion. The prior informationserves to minimize the system losses and to provide a checkon the system stability.There are several methods proposed in literatures for loadflow analysis with incorporated FACTS controllers in multimachinepower systems from different operating conditionsviewpoint. There are three methods such as a Gauss Sidelmethod, Newton Raphson Methods, and Fast DecoupleMethods for load flow analysis with incorporated FACTScontrollers from different operating conditions in multimachinepower systems for optimal power flow control. TheNewton Raphson Methods have been proposed in literaturesincludes for Series FACTS controllers [1]-[6], Shunt FACTScontrollers [7]-[11], Series-Shunt FACTS Controllers [12]-[41].This paper is organized as follows: Section II presents thereview of various FACTS controllers incorporated withNewton-Raphson load flow in multi-machine power systemsfor different point of view. Section III presents the summaryof the paper. Section IV presents the conclusions of the paper.
II. CLASSIFICATION OF FACTS CONTROLLERS
A. Series FACTS Controllers
Reference [1], the optimal power flow (OPF) model has beendeveloped and analyzed with Thyristor Controlled SeriesCompensator (TCSC) for practical power networks usingNewton’s optimization technique. The minimization of totalsystem real power losses is an objective with controlling thepower flow of specified transmission lines. The proposedmodel has considered the optimal settings generators,transformers and TCSC devices. The optimal transmissionlosses and corresponding generation schedules with optimalTCSC setting parameters for different case studies have alsobeen reported in literature. The proposed model convergesvery fast and independent of initial conditions. The proposedalgorithm can he applied to larger systems and do not sufferwith computational difficulties.Reference [2], has been suggested to develop a steady-statemathematical model of the new generation of powerelectronic-based plant components presently emerging as aresult of the newly developed concept of FACTS, namelyTCSC. The modeling is carried out in the phase domainconsidering the TCSC physical structure. A poly phase powerflow program based on Newton Algorithm is developed inorder to implement the proposed model in literature. Analysisof the TCSC performance is carried out in both balanced andunbalanced power network operating conditions. This kind ofanalysis will allow quantifying the many economical andtechnical benefits this technology promises, as well asexamining the applicability and functional specifications ofthe controller.G. R. Kumar et al. [3], has been introduced the problem ofreactive power compensation is viewed from two aspects:load compensation and voltage support. Voltage support isgenerally required to reduce voltage fluctuation at a giventerminal of a transmission line. In this literature the OPFmodel has been developed and analyzed with TCSC andStatic var Compensator (SVC) for practical power networksusing Newton’s optimization technique. The optimaltransmission losses and corresponding generation scheduleswith optimal TCSC and SVC setting parameters for differentcase studies have also been reported in literature. Theperformance of the proposed algorithm has been reported withsingle and multiple TCSC and SVC devices with contingencyanalysis and do not suffer with Computational difficulties inthe literatures.In [4], the steady state modeling of Static SynchronousCompensator (STATCOM) and TCSC for power flow studieshas been presented. STATCOM is modeled as a controllablevoltage source in series with impedance and firing anglemodel for TCSC used to control active power flow of the lineto which TCSC is installed. Proposed model for TCSC takesfiring angle as state variable in power formulation. Tovalidate the effectiveness of the proposed models of NewtonRaphson Method Algorithm was implemented to solve powerflow equations presence of STATCOM and TCSC.Xiao-Ping Zhang, et al. [5], has been suggested the staticsynchronous series compensator (SSSC) is one of the recentlydeveloped FACTS controllers. The SSSC coupled with atransformer is connected in series with a transmission line.This literature describes a multi control functional model ofthe SSSC for power flow analysis, which can be used forsteady state control of one of the following parameters: 1) theactive power flow on the transmission line; 2) the reactivepower flow on the transmission line; 3) the voltage at the bus;and 4) the impedance (precisely reactance) of the transmissionline. Furthermore, the proposed model can also take intoaccount the voltage and current constraints of the SSSCdevice. The detailed implementation of such a multi-controlfunctional model in Newton power flow algorithm ispresented in literature. A special consideration of theinitialization of the variables of the SSSC in power flowanalysis is also proposed.R. Jalayer et al. [6], the load flow problems have always beenan important issue in power system analysis and requireproper modeling of system components is reported. In thisregard FACTS controllers are modern devices that theirmodeling specially the series type is a challenging topic. Thisliterature describes a three-phase model for Distributed StaticSeries Compensator (DSSC) based on extending the SSSCmodel in Newton power flow algorithms. To extend the SSSCmodel the following two differences must be considered;three completely independent phases and the existence ofseveral modules in a DSSC system.


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