Improving Power System Stability by Designing Supplementary Controller of HVDC Using Real Genetic Algorithm Abstract: This paper investigates the ability of Real Genetic Algorithm (RGA) in designing supplementary controller of High Voltage Direct Current (HVDC) link to damp the power system oscillation. A conventional lead-lag structure is considered for the supplementary controller. The aim of the proposed control strategy is to choose the best controller parameters in such a way that the dominant eigenvalues of the closed-loop system are shifted to the left-hand side of s- plane as far as possible. Also, the binary version of genetic algorithm (BGA) is used to design a supplementary controller for HVDC. The characteristic convergence and time simulation results show that both versions of GA have good capability in solving the problem but RGA gives better results. Keywords: Real genetic algorithm, binary genetic algorithm, power system stability, dynamic stability, HVDC. 1 Introduction HVDC links has been widely applied in power transmission for a number of years and have provided utilities around the world with important technical solutions to a wide range of transmission needs due to their excellent and flexible control ability. Direct Current transmission can be between independent systems or between points within a system. By DC link power flow can be controlled precisely and very rapidly. By controlling its power transfer, the DC link can help the system operator to dictate the power flows in the adjacent ac lines. Also, by rapidly changing its power transfer, it can improve ac system stability. It can damp out post- disturbance swings. It can act as a voltage regulator by switching its reactive power banks or by adjusting control angles to absorb more or less reactive power. Therefore, HVDC links can be effectively used for damping electromechanical oscillations, stabilizing power swings, reducing the life-fatigue effects of Sub-Synchronous Resonance (SSR), etc. The development of Voltage Source Converter (VSC) technology (used for instance in HVDC Light interconnections) can improve also the network voltage compensation and the transmission grid load-ability, reducing the risks of voltage instability and collapse [1-7]. Since, their contributions to the damping of system oscillations are of great importance for achieving satisfactory system performance, in this paper a supplementary controller is designed for a HVDC link. Despite the potential of modern control techniques, intelligent control is used to design a conventional lead-lag structure. BGA is used to design supplementary controller of HVDC in [8-10]. Saeid Haidari, Malihe M. Farsangi and Hossein Nezamabadi-pour Electrical Engineering Department of Shahid Bahonar University, Kerman mmaghfoori@mail.uk.ac.ir, nezam@mail.uk.ac.ir Intelligent Systems Scientific Society of Iran Intelligent Systems Scientific Society of Iran ﻫ ﺸ ﺳﻴﺴﺘﻤﻬﺎي ﻛﻨﻔﺮاﻧﺲ ﺘﻤﻴﻦ ﻫﻮﺷﻤﻨﺪ، 9 - 7 ﺷﻬﺮﻳﻮر1386 ﻣﺸﻬﺪ ﻓﺮدوﺳﻲ داﻧﺸﮕﺎه، First Joint Congress on Fuzzy and Intelligent Systems Ferdowsi University of Mashhad, Iran 29-31 Aug 2007