Stability Enhancement for Multi-machine Power System by Optimal PID Tuning of Power System Stabilizer using Particle Swarm Optimization ANANT OONSIVILAI and BOONRUANG MARUNGSRI Alternative and Sustainable Energy Research Unit, Power and Control Research Group School of Electrical Engineering, Institute of Engineering, Suranaree University of Technology Muang District, Nakhon Ratchasima, 30000, THAILAND Email: anant@sut.ac.th, bmshvee@sut.ac.th Abstract: - This paper demonstrates the superior effectiveness of utilizing the artificial search technique to ascertain parameters optimization of power system stabilizer (PSS), contemplating proportional-integral- derivative controller (PID) for a multi-machine power system, compared to the customary Ziegler-Nichols method. As the PID - PSS parameters are also tuned by the Ziegler-Nichols method at the same operating point. Its effectiveness is presented using four machines power system. Acquire settings of PID - PSS which meliorate damping frequency of system are optimized by minimizing an objective function using Particle Swarm Optimization, an artificial search technique. The results convey eminent efficiency of the proposed PSO based PID controller. Key-Words: - Power system stabilizer, PID tuning, Multi-machine power system, Particle Swarm Optimization, Artificial intelligent search technique 1 Introduction Recently, electricity demands are increasingly in every electric utility around the world. Modern power system control requires a continuous balance between electrical generation and a varying load demand, while maintaining system frequency and voltage levels. The use of high performance excitation systems is essential for maintaining steady state and transient stability of modern synchronous generators and provides fast control of the terminal voltage. It is well known that each generator in an interconnected power system is supported by two major control loops. These loops are: Automatic Generation Control (AGC) which is responsible for power balancing, and Automatic Voltage Regulator (AVR) which regulates the terminal voltage by controlling the excitation. Since the development of interconnection of electric power systems, there have been spontaneous system oscillations at low frequencies in the order of several cycles per seconds. These oscillations may cause operating constraints depending on their magnitude and location in system, and are classified as local mode oscillations that oscillate in the range 0.8 to 3 Hz, inter-machine mode oscillations that oscillate in the range 0.3 to 1 Hz , and inter-area mode oscillations that oscillate in the range 0.1 to 0.7 Hz. These slow oscillations could continue to grow causing system separation. It is well known that these oscillations are due to lack of sufficient damping of the slow mechanical modes of the systems. The desired additional damping is provided by a supplementary control loop known as Power System Stabilizer (PSS) [1]. A PSS stabilizer provides a supplementary control signal to the AVR loop for excitation control. This signal improves the transient behavior of the generator and provides a damping for the slow mode oscillations. This results in an enhancement of transient stability limit. The most commonly used PSS, referred to as conventional PSS(CPSS), is a fixed parameter analog type device with lead-lag compensation, wash out, and amplifier gains, which are limited and may lose effective damping robustness for overall operation. The conventional PSS is widely used in power systems, contributing to enhancing power system dynamic stability. A PSS uses several local measurements and, perhaps, remote telemetries measurements to augment Stability by supplementary excitation control. A PSS has input signals from speed deviation (Δω), accelerating power (ΔP a ), actual generator speed deviation and reactive power (ΔP g , WSEAS TRANSACTIONS on POWER SYSTEMS Anant Oonsivilai and Boonruang Marungsri ISSN: 1790-5060 465 Issue 6, Volume 3, June 2008