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World Academy of Science, Engineering and Technology 24 2006

Optimal Sizing of SSSC Controllers to Minimize Transmission Loss and a Novel Model of SSSC to Study Transient Response
A. M. El-Zonkoly
Unified Power Flow Controller (UPFC), etc., bus voltages, line impedances and phase angles in the power system can be regulated rapidly and flexibly. Thus, FACTS can facilitate the power flowcontrol, enhance the power transfer capability, decrease the generation cost, and improve the security and stability of the power system. In previous work, researches concentrated on locating and sizing of different types of FACTS devices in order to maximize the power transfer considering networks with variable loads. The problem was formulated as an optimization problem and was solved using differentmethods such as using iterative techniques, MATLAB optimization routines or Genetic Algorithm (GA) [2-4]. In this paper, the problem of sizing of SSSC controllers is formulated as an optimization problem with the objective of minimizing the transmission losses in a network with unchanged loads. The problem is solved using PSO method, which is fast and simple if compared with GA technique and alsogive promising results. In order to calculate the power losses and check the system operating constraints such as voltage profile, a load flow model is used. A modified load flow model, based on the existing Newton-Raphson load flow algorithm, is introduced in [5]. That model was modified to represent the UPFC devices. In this paper, this model is further modified in order to include the SSSCdevices presented into the network. The proposed algorithm is tested using the IEEE 14 bus system at different levels of loading and the results are presented. Further more, to have the ability to study the transient response of an SSSC device under different operating conditions of the power system, a novel model of SSSC controller is proposed. The model was simulated using PSB and Simulinksoftware. A small, two-area test system is used to verify the validity of the proposed model. II. OPTIMAL SIZING OF SSSC DEVICES BASED ON PSO A. Static Synchronous Series Compensator (SSSC) The SSSC is one of the most recent FACTS devices for power transmission series compensation. It can be considered as a synchronous voltage source as it can inject an almost sinusoidal voltage of variable andcontrollable amplitude and phase angle, in series with a transmission line. The injected voltage is almost in quadrature with the line current. A small part of the injected voltage that is in phase with the line

Abstract—In this paper, based on steady-state models of Flexible
AC Transmission System (FACTS) devices, the sizing of static synchronous series compensator (SSSC) controllers in transmissionnetwork is formed as an optimization problem. The objective of this problem is to reduce the transmission losses in the network. The optimization problem is solved using particle swarm optimization (PSO) technique. The Newton-Raphson load flow algorithm is modified to consider the insertion of the SSSC devices in the network. A numerical example, illustrating the effectiveness of the proposedalgorithm, is introduced. In addition, a novel model of a 3phase voltage source converter (VSC) that is suitable for series connected FACTS a controller is introduced. The model is verified by simulation using Power System Blockset (PSB) and Simulink software.

Keywords—FACTS, Modeling, PSO, SSSC, Transmission loss
reduction.

I. INTRODUCTION N today’s highly complex and interconnected powersystems, there is a great need to improve electric power utilization while still maintaining reliability and security. While power flows in some of the transmission lines are well below their normal limits, other lines are overloaded, which has an overall effect on deteriorating voltage profiles and decreasing system stability and security. Because of all that, it becomes more important to control the...