J Electr Eng Technol Vol. 9, No. 6: 1873-1881, 2014 http://dx.doi.org/10.5370/JEET.2014.9.6.1873 1873 PSSs and SVC Damping Controllers Design to Mitigate Low Frequency Oscillations Problem in a Multi-machine Power System Mohsen Darabian † and Abolfazl Jalilvand* Abstract – This paper deals with the design of multi-machine power system stabilizers (PSSs) and Static var compensator (SVC) using Modified shuffled frog leaping algorithm (MSFLA). The effectiveness of the proposed scheme for optimal setting of the PSSs and SVC controllers has been attended. The PSSs and SVC controllers designing is converted to an optimization problem in which the speed deviations between generators are involved. In order to compare the capability of PSS and SVC, they are designed independently once, and in a coordinated mode once again. The proposed method is applied on a multi-machine power system under different operating conditions and disturbances to confirm the effectiveness of it. The results of tuned PSS controller based on MSFLA (MSFLAPSS) and tuned SVC controller based on MSFLA (MSFLA SVC) are compared with the Strength pareto evolutionary algorithm (SPEA) and Particle swarm optimization (PSO) based optimized PSS and SVC through some performance to reveal its strong performance. Keywords: Modified shuffled frog leaping algorithm (MSFLA), PSS and SVC design, Multi machine power system, Strength pareto evolutionary algorithm (SPEA), Particle swarm optimization (PSO). 1. Introduction Owing to the environmental and economic pressures, electric power system becomes more heavily loaded and system oscillations are increased. Inadequate damping of these oscillations will restrict the power transfer capability. The conventional PSS (CPSS) is widely utilized to enhance the system damping. In some cases, if the utilization of PSS cannot provide sufficient damping for inter-area power swing, Flexible AC transmission systems (FACTS) devices are substitute effectual solutions. The principle of these FACTS devices is to regulate the reactance and voltage. SVC is the most popular FACTs device utilized to improve the reliability of power systems [1]. It has different capability to improve the operation of power systems by mitigating network loss, providing voltage regulation, compensating active power, improving transient stability, limiting short circuit currents and damping the power system oscillation [2]. The system damping can be enhanced by incorporating supplemental damping controller. Numerous schemes have been documented for PSS and SVC parameters optimization to improve the damping of power system oscillations. Genetic algorithms (GA) [3], Tabu search (TS) [4], simulated annealing [5] evolutionary programming [6] have been proposed to design PSS parameters. In [7], an adaptive network based fuzzy inference system (ANFIS) is used to improve the power system damping via SVC. In [8], a new scheme is proposed to find optimal location of SVCs to increase power system stability. In order to increase power system stability, a new scheme based on wide area signals via SVC is suggested in [9]. A BFOA algorithm is used in [10] to design SVC parameters in a single machine infinite bus system. In [11], a pade approximation technique is suggested to design of SVC with delayed input signal. In [12], a hybrid scheme is used to simulate power systems equipped with SVC. A simultaneous tuning of a PSS and a SVC controller based on GA is represented in [13]. The adjusted design of PSSs and SVC based on probabilistic theory is described in [14]. In [15], the decentralized modal control technique is applied to pole placement in multi- machine power system using FACTS devices. In [16], an extensive evaluation is performed on PSS and FACT device independently as well as in a coordinated mode. In this paper, the problem of PSS and SVC design is formulated as an optimization problem and MSFLA is used to solve it. The objective is to improve the stability of the multi-machine power system, subjected to the disturbance. The capability of the proposed MSFLAPSS and MSFLASVC is tested on a multi-machine power system under different operating conditions in comparison with the PSO [17] and SPEA [18] based tuned PSS and SVC through proper value analysis, nonlinear time simulation and some performance indices. Results evaluation shows that the proposed method achieves significant improvement for stability performance of the system under different operating conditions and is superior to the other methods. The paper is sets out as follows: Section 2 presents the † Corresponding Author: Dept. of Electrical Engineering, Univerity of Zanjan. Zanjan, Iran. (m.darabian@znu.ac.ir) * Dept. of Electrical Engineering, Univerity of Zanjan. Zanjan, Iran. (ajalilvand@znu.ac.ir) Received: Febuary 3, 2013; Accepted: July 16, 2014 ISSN(Print) 1975-0102 ISSN(Online) 2093-7423