The influence of GUPFC FACTS device on small signal stability of the electrical power systems D.B. Valle ⇑ , P.B. Araujo Avenida Prof. José Carlos Rossi, 1370, 15385-000 Ilha Solteira, São Paulo, Brazil article info Article history: Received 5 June 2013 Received in revised form 23 September 2014 Accepted 10 October 2014 Available online 4 November 2014 Keywords: Electric power system FACTS GUPFC Small-signal stability Supplementary stabilizers abstract In this paper a power injection model is presented for the Generalized Unified Power Flow Controller (GUPFC), which facilitates its representation in the electric power system (EPS). This model of the GUPFC device becomes an attractive option to be implemented in power flow and optimal power flow programs. An efficient structure for the GUPFC control system is also presented in the article. This can be used to represent the dynamics in both stability analysis of small perturbations, which is the focus of this work, and in transient stability analysis (large disturbances) of the EPS. Considering the most basic GUPFC con- figuration, the proposed structure can control four active and reactive power flows in two lines, the volt- age at the common installation bus; addition to these characteristics inherent in the GUPFC, this device can provide damping for the electromechanical oscillations of the EPS, as a POD (Power Oscillation Damp- ing) controller is coupled to the control loop. Simulations are performed on one multimachine test sys- tem, whose results are analyzed and discussed in this paper, in order to analyze the performance of the power injection model and its proposed control structure in the damping of oscillations. Ó 2014 Elsevier Ltd. All rights reserved. Introduction Faced with a scenario of high electric energy demand due to an increasing population and to economic development, the construc- tion of new power stations and the expansion of the transmission grid is becoming of increasing importance to meet the needs which, in general, are growing constantly. Moreover, since the beginning of the century, the political, economic and, in particular, environmental restrictions are becoming one of the greatest chal- lenges for researchers, conservationists, government officials and communities worldwide. With the goal of trying to delay emergency situations with the need of new power lines, by making existing transmission systems more efficient, FACTS (Flexible AC Transmission System) devices have emerged as an alternative, giving greater flexibility to the transmission system which until recently was ’’inflexible’’ in respect to the invariability of its parameters. These devices may intervene not only in the capacity and control of transmission (improved facilities to import/export power), but also exert a sig- nificant influence on the dynamic and transitional performance of EPS [1]. This paper analyzes the performance of GUPFC FACTS devices to improve stability related to small perturbations of EPS. For this, the Power Sensitivity Model (PSM) is used to represent the EPS [2], due to the ease of including new dynamic devices, as for example, the dynamic model of the control structure of the GUPFC, EPS control- lers (power system stabilizers – PSS) and the POD device. A power injection model was used to represent the GUPFC in the power flow, which is one of the contributions of this work. As will be dis- cussed in more detail, both the proposed power injection model of the GUPFC and the control system structure gave positive results when applied in one multimachine test system. Analyzes of the results obtained will be made during the course of this work. GUPFC power injection model This section presents a model of the GUPFC power injection. For this, Fig. 1 shows a GUPFC device connected between three buses (i, j and k) of the EPS. In Fig. 1 the three voltage source converters (VSCs) are based on GTOs (Gate Turn-Off Thyristors) and have identical configurations as well as operating principles, but their functions differ by the way that they are connected to the EPS [3]. VSCs are connected to the AC system via coupling transformers which are connected to each other via a common DC link [4]. As shown in Fig. 2, the converters in series, VSC2 and VSC3, are represented by two http://dx.doi.org/10.1016/j.ijepes.2014.10.012 0142-0615/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: danilodovalle@gmail.com (D.B. Valle). Electrical Power and Energy Systems 65 (2015) 299–306 Contents lists available at ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes