Optimal Damping of Oscillation in Multi-machine Power System by Renewable Energy Effects H. A. Shayanfar * Center of Excellence for Power System Automation and Operation, College of Elect. Eng., Iran University of Science and Technology, Tehran, Iran O. Abedinia Electrical Engineering Department, Semnan University, Semnan, Iran N. Amjady Electrical Engineering Department, Semnan University, Semnan, Iran hashayanfar@yahoo.com, oveis.abedinia@gmail.com, n_amjady@yahoo.com Abstract— In this paper a robust Power System Stabilizer (PSS) is proposed based on inverse additive perturbation in a power system with wind farms. For this purpose a new algorithm of Harmony Search (HS) with Fuzzy Mechanism (FM) is proposed to achieve robustness of proposed controller strategy which is formulated based on an enhancement of system robust stability margin. To demonstrate the capability of proposed technique, ten machine 39 buses power system of New England is presented as a case study. The achieved results demonstrate the superiority of proposed technique in comparison of conventional PSS. Keywords: HS, Fuzzy controller, PSS, Multi-machine. NUMENCLUTURE δ Rotor angle ω Rotor speed P m Mechanical input power P e Electrical output power E' q Internal voltage behind x' d E fd Equivalent excitation voltage T e Electic torque T' do Time constant of excitation circuit K A Regulator gain T A Regulator time constant v ref Reference voltage v Terminal voltage I. Introduction In power system, the Low Frequency Oscillations (LFOs) are related to the small signal stability are detrimental to the goals of maximum power transfer and power system security. Once the adjustment of using damper windings on the generator rotors and turbines to control these oscillations was found to be satisfactory, the stability problem was thereby disregarded for some time [1]. But, as power systems began to be operated closer to their consistency limits, the weakness of a synchronizing torque among the generators was distinguished as a major cause of system instability [2]. Automatic Voltage Regulators (AVRs) helped to improve the steady-state stability of the power systems, but transient stability started a concern for the power system operators. The addition of a supplementary controller into the control loop, such as the introduction of Power System Stabilizers (PSSs) to the AVRs on the generators, supplies the means to reduce the inhibiting effects of low frequency oscillations [3]. In the recent years, renewable electrical energy such as wind power generations, have achieved a significant level of penetration in the power systems due to infinite availability and low impact to environment. However, wind power generation is staggering in nature. Matching the supply and the demand is often a problem. The power output fluctuations from wind power generations cause a problem of low frequency oscillation, deteriorate the system stability and make the power system operation more difficult. The power frequency and the tie-line power deviations persist for a long term. In this status, the governor system may no longer be capable to absorb the frequency fluctuations due to its slow response [4]. Actually, several plants prefer to employ conventional lead-lag structure PSSs, due to the ease of online tuning and reliability [5]. However, the revenue of these controllers doesn’t have good behavior in different load conditions. So, different intelligent algorithms have been introduced to optimal tuning of the PSSs parameters such as Ant Colony (AC) [6], Genetic Algorithm (GA) [7], Particle Swarm Optimization [8], Artificial Bee Colony [9] and etc. Accordingly, this paper proposes a new algorithm of Harmony Search (HS) to solve the mentioned problem. * Correspanding Author. E-Mail Address: hashayanfar@yahoo.com (H. A. Shayanfar)