Optimization and Coordination of Damping Controls for Optimal Oscillations Damping in Multi-Machine Power System Mahdiyeh Eslami 1 , Hussain Shareef 2 , Azah Mohamed 2 Abstract – This paper proposes a novel optimization technique for simultaneous coordinated designing of power system stabilizer (PSS) and static VAR compensator (SVC) as a damping controller in the multi-machine power system. PSO and chaos theory is hybridized to form a chaotic PSO (CPSO), which reasonably combines the population-based evolutionary searching ability of PSO and chaotic searching behavior. The coordinated design problem of PSS and SVC controllers over a wide range of loading conditions are formulated as a multi-objective optimization problem which is the aggregation of the two objectives related to the damping ratio and damping factor. The proposed damping controllers are tested on a weakly connected power system. The effectiveness of the proposed controllers is demonstrated through the eigenvalue analysis and nonlinear time-domain simulation. The results of these studies show that the proposed coordinated controllers have an excellent capability in damping power system inter- area oscillations and enhance greatly the dynamic stability of the power system. Moreover, it is superior to both the manually coordinated stabilizers of the PSS and the SVC damping controller. Keywords: Chaotic, PSO, PSS, SVC, Coordinated Design I. Introduction Power system stability problem has been receiving a great deal of attention over the years. Electric power system becomes more heavily loaded and system damping is weakened due to environmental and economic pressures. Electro-mechanical oscillations happen more often than before, and inadequate damping of these oscillations will limit the capacity to transmit power. These oscillations may be very weakly damped in some cases, resulting in mechanical fatigue at the machines and unacceptable power variations across the important transmission lines. Due to this cause, the use of the controllers to provide better damping for these oscillations is of utmost importance [1], [2]. Request of power system stabilizers (PSSs) has become the first measure to increase the system damping. In some cases, if the utilization of PSS cannot provide enough damping for inter-area power swing, flexible AC transmission systems based (FACTS) damping controllers are alternative efficient resolutions. FACTS are designed to overcome the limitations of the present mechanically controlled power systems and enhance power system stability by applying reliable and high-speed electronic devices. Usually, the FACTS devices are utilized in power system to supply fast continuous control of power flow in the transmission system by changing the impedance of transmission lines, by controlling voltages at critical buses, or by controlling the phase angles between the ends of transmission lines. One of the promising FACTS devices is the Static VAR Compensators (SVC) which is a shunt compensation component and it can rapidly regulate its susceptance to supply dynamic reactive compensation and maintain the bus voltage in power system. SVC with damping controller is effective to increase damping of electro-mechanical modes (inter-area). However, the SVC controllers will likely to react differently with other damping controllers (e.g. PSS) in a power system. The interaction among stabilizers may increase or degrade the damping of the particular modes of rotor oscillation. This problem may happen especially after the clearance of a critical fault, with FACTS devices used in the same area. Interactions between damping controllers can adversely influence the rotor damping of generators and under weakly interconnected system conditions; it can even cause dynamic instability and restrict the operating power range of the generators. To improve overall system performance, many researches focus on the coordination between PSSs and FACTS controllers [3]– [6]. Some of these methods are based on the complex nonlinear simulation, while the others are based on the linearized power system model. However, linear methods cannot properly capture the complex dynamics of the system, especially during the critical faults. This develop difficulties for tuning the SVC damping controller and PSS in that the controllers tuned to provide the desired performance at a small signal condition do not guarantee acceptable performances in the event of large disturbances [7].