The voltage stability margin (VSM) is an important indicator to access the voltage stability of the power system. In this paper, Flexible AC transmission systems (FACTS) DEVICES like static synchronous compensator (STATCOM), static synchronous series compensator (SSSC), and unified power flow controller (UPFC) have been deployed to enhance the VSM of the power system. The placement of the FACTS DEVICES is decided based on contingency raking. For the top five critical contingencies, the most severe bus is selected based on bus voltage stability criticality index and degree centrality methods. The critical line is decided based on the values of the line stability index, fast voltage stability index, and line stability factor. The STATCOM and shunt part of the UPFC are placed at the critical bus, whereas the SSSC and series part of the UPFC are placed at the critical line for enhancing voltage stability. The proposed method for voltage stability enhancement using FACTS DEVICES is tested and validated on the IEEE-14 bus system and the NRPG-246 bus system at different system loading scenarios. The impact of the placement of FACTS DEVICES is validated in terms of VSM improvement.

This paper presents a sequential based Newton-Raphson power flow algorithm for reliable and efficiently handling power systems with embedded FACTS (Flexible AC Transmission Systems) DEVICES. Computation and control of power flow in power systems with embedded FACTS DEVICES appear to be fundamental for power system analysis and planning purposes. A power injection model for conventional FACTS DEVICES such as SVC (Static Var Compensator) and TCSC (Thyristor Controlled Series Capacitor) as well as modem FACTS DEVICES such as STATCOM (Static Series Compensator) SSSC (Static Synchronous Series Compensator) and UPFC (Unified Power Flow Controller) is derived. Also a power injection model of conventional HVDC (High Voltage Direct Current) is obtained. Then a sequential power flow algorithm (two step algorithm) is adopted. The proposed injection models and sequential power flow algorithm have been programmed and systematically tested in a number of systems. The results of Ward-Hale network are reported which clearly illustrates the Capabilities and generalization of the proposed algorithm.

This paper presents a novel optimization based methodology to allocate Flexible AC Transmission Systems (FACTS) DEVICES in an attempt to improve the previously mentioned researches in this field. Static voltage stability enhancement, voltage profile improvement, line congestion alleviation, and FACTS DEVICES investment cost reduction, have been considered, simultaneously, as objective functions. Therefore, multi-objective optimization without simplification has been used in this paper to find a logical solution to the allocation problem. The optimizations are carried out on the basis of location, size and type of FACTS DEVICES. Thyristor Controlled Series Compensator (TCSC) and Static Var Compensator (SVC) are utilized to achieve the determined objectives. The problem is formulated according to Sequential Quadratic Programming (SQP) problem in the first stage. This formulation is used to accurately evaluate static security margin with congestion alleviation constraint incorporating voltage dependence of loads in the presence of FACTS DEVICES and estimated annual load profile. The best trade-off between conflicting objectives has been obtained through Genetic Algorithm (GA) based fuzzy multi-objective optimization approach, in the next stage. The IEEE 14-bus test system is selected to validate the allocated DEVICES for all load-voltage characteristics determined by the proposed approach.

Distributed flexible ac transmission system (D-FACTS) is a light-weight version of FACTS, which it is easily allocated and costs less than flexible ac transmission system (FACTS) DEVICES. They have potential benefits to improve the system stability and improvement in power quality in microgrid (MG). The integration of distributed energy sources, loads, electrical energy storage DEVICES, and electronic power DEVICES, as well as the operation of microgrids in connected or island-connected modes has expanded their use. It is a small main grid that can generate electricity when disconnected from the main network. In addition, microgrids reduce the high investment costs required to upgrade the network. The application of DFACTS DEVICES for improving the microgrid operation has been investigated by some researches. This paper provides a review of impact and role of various DFACTS DEVICES in the function of microgrids, which has been reported in recent years in various pieces of the literature. DFACTS DEVICES with their properties are described. Finally, a useful reference and framework for the study is provided for future expansion of DFACTS DEVICES so as to improve the performance of the microgrid.

Given the high costs of investment for transmission network development and the key role of transmission networks in restructured space, using FACTS DEVICES is crucial. In this paper, the optimal Placement of FACTS in transmission networks is investigated. In the proposed method, the objective function is defined for loss reduction a. Average models available in references are used for modeling FACTS DEVICES. The multi-objective harmony search algorithm is used for problem-solving. This algorithm has good speed in the convergence of non-linear problems. In the numerical studies section, the problem is solved in two different scenarios with the presence of different types of FACTS DEVICES. Results of numerical studies indicate that FACTS DEVICES can have a considerable impact on loss reduction.