International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 10 | Oct -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 354 Design and Analysis of Power System Stabilizer and Unified Power Flow Controller for Enhancements of Transient Stability Shegaw Melak Akele 1 , Dr.T.R. Jyothsna 2 1 PG student, EEE Department, Andhra University (A), Andhra Pradesh, India 2 Professor, EEE Department, Andhra University (A), Andhra Pradesh, India -----------------------------------------------------------------------------***---------------------------------------------------------------------------- Abstract— Modeling and analysis of AVR, PSS and UPFC in SMIB system for the transient stability enhancement and improvement of power transfer capability have been done in this paper. The effects of UPFC, AVR and PSS controller evaluated under different case studies, namely by step changing reference voltage, infinity bus voltage, mechanical torque and introducing short circuit fault into the system has been made. In all cases the response of rotor angle, slip, excitation voltage, and electrical torque were simulated. The control strategies of UPFC are in phase voltage control, quadrature voltage control, quadrature current control, real current control and phase angle control, but in this paper except phase angle control the leftovers were implemented. Key Words: SMIB, AVR, PSS, UPFC, Shunt injected current; Series injected Voltage, Transient Stability. 1. INTRODUCTION The available power generating plants are often placed in distant locations for economic, environmental and safety reasons. Additionally, modern power systems are highly interconnected. Sharing of generation reserves, exploiting load diversity and economy gained from the use of large, efficient units without losing stability, reliability and quality of the system. The stability of the power system implies that all its generators remain in synchronism through normal and abnormal operation conditions. Transient stability arises when a large disturbance such as a loss of generation, load or transmission line takes place in the power system. It is becoming a major factor in planning and day to day operations and there is a need for fast online solutions of transient stability to predict any possible loss of synchronism and to take the necessary measures to restore the stability. Recently varies controller device are designed to damp these oscillations and to improve the system stability, which are found in modern power system, but conventional control and FACTS device still an alternative solution. The main objectives of excitation system are to control the field currents of synchronous machine. The field current is controlled to regulate the terminal voltage of the machine. And also, the basic functions of power system stabilizer are to add damping to the generator rotor oscillations by controlling its excitations using auxiliary stabilizing signals [12]. To provide damping the stabilizer must produce a component of electrical torque in phase with the rotor speed deviations. Unified Power Flow Controller (UPFC) is one of the important members of Flexible AC Transmission System(FACTS) family. It is a combination of Static Synchronous Compensator (STATCOM) and Static Series Compensator (SSSC) [2], [6], [10]. These two are coupled via a common DC link, to allow bidirectional flow of real power between the series output terminals of the SSSC and the shunt output terminals of the STATCOM, and are controlled to provide simultaneous real and reactive series line compensation without an external electric energy source [11]. The schematic of UPFC is shown in Fig-1. The UPFC consists of two branches. The series branch consists of a voltage source converter which injects a voltage in series through a transformer. Since the series branch of the UPFC can inject a voltage with variable magnitude and phase angle it can exchange real power with the transmission line [9]. The shunt branch is required to compensate for any real power drawn/supplied by the series branch and the losses. If the power balance is not maintained, the capacitor cannot remain at a constant voltage. Control VSC 2 VSC 1 Shunt transformer Series Transformer Transmission line VDC Fig-1: The Schematic diagram of UPFC As shown in Fig-1 the two converters are operated from a common DC link provided by a DC storage capacitor. VSC2 is used to inject the required series voltage via an injection transformer. The real power exchanged at the terminals of the series transformer is converted by the converter into DC power which appears at the DC link as positive or