IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 6, Issue 6 (Jul. - Aug. 2013), PP 54-63 www.iosrjournals.org www.iosrjournals.org 54 | Page Low Frequency Oscillations Damping by UPFC with GAPOD and GADC-voltage regulator Dakka. Obulesu 1 , Dr. S.F. Kodad 2 , Dr. B.V Sankar Ram 3 1 Asso Professor, Department of Electrical & Electronics Engg., VEMU.I.T.,P.Kothakota, Chittoor dist, Andhra Pradesh-517325, India. 2 Principal, Krishna Murthy Institute of Technology and Engineering, Hyderabad, India. 3 Director, Admissions, J.N.T.U.H, Hyderabad, India. Abstract: Low frequency oscillations(LFO) are inevitable characteristics of power system which affect the transmission line transfer capability and the system stability. In this paper, a new POD controller with DC- voltage regulator based on genetic algorithm is proposed for the UPFC for damping low frequency oscillations. The effectiveness of the proposed controller has been tested on a SMIB(double-line) power system in comparison with PSOMSF DC-voltage regulator under different operating conditions. The construction and implementation of this controller is fairly easy, which can be useful in real world power system. Keywords : UPFC, Multi-Stage Fuzzy Controller (MSF), GAPOD (Genetic Algorithms based Power oscillation damping), PSO based MSF (PSOMSF), GA DC-voltage regulator. I. INTRODUCTION The large-scale power system interconnection is intended to make electric energy generation and transmission more economical and reliable. The economic aspect is manifested through the drastic reduction of spinning reserve or the standby generating capacity for maintenance or emergency use, from 25% or more of the total capacity a few decades ago to much less in the modern electric power systems. The reliability of the interconnected system is enhanced by virtue of the capability of transferring power readily from one area to other within the system. The large-scale power system interconnection caused many new dynamic power system problems to emerge which include the low-frequency oscillations of the interconnected large electric power systems. The low-frequency oscillations are due to the lack of damping of the mechanical mode of the system. A better utilization of the existing power systems to increase their capacities and controllability by installing FACTS devices becomes imperative. Due to the present situation, there are two main aspects that should be considered in using FACTS devices. The first aspect is the flexible power system operation according to the power flow control capability of FACTS devices. The other aspect is the improvement of transient and steady-state stability of power systems. FACTS devices are the right equipment to meet these challenges. The Unified Power Flow Controller (UPFC) is regarded as one of the most versatile devices in the FACTS device family which has the ability to control power flow in the transmission line, improve the transient stability, mitigate system oscillation and provide voltage support. It performs this through the control of the in- phase voltage, quadrate voltage and shunts compensation due to its mains control strategy [1]. In [2] N. Tambey, M.L. Kothari suggested that the addition of a conventional supplementary controller to the UPFC is an effective solution to the problem. However, an industrial process, such as a power system, contains different kinds of uncertainties due to continuous load changes or parameters drift due to power systems highly nonlinear and stochastic operating nature. As a result, a fixed parameter controller based on the classical control theory such as PI or lead-lag controller is not certainly suitable for the UPFC damping control methods. Thus, it is required that a flexible controller be developed. In [3-6] authors P.K. Dash, S. Mishra, B C. Pal, et al. suggested Artificial neural networks method and robust control methodologies to cope with system uncertainties to enhance the system damping performance using the UPFC. However, the parameters adjustments of these controllers need some trial and error. Also, although using the robust control methods, the uncertainties are directly introduced to the synthesis, due to the large model order of power systems the order resulting controller will be very large in general, which is not feasible because of the computational economical difficulties in implementing. The fuzzy controller has a number of distinguished advantages over the conventional one. It is not so sensitive to the variation of system structure, parameters and operation points and can be easily implemented in a large-scale nonlinear system. The most attractive feature is its capability of incorporating human knowledge to the controller with ease. This approach provides the FL systems better functionality, performance, adaptability, reliability and robustness. The most dynamic area of fuzzy systems research in the power systems has been the stability enhancement and assessment [7-8].