###### Abstract  
Low frequency oscillations in large power systems may result in system instability under large disturbances. Power system stabilisers (PSS) play an effective role in damping these low frequency oscillations by injecting a modulating signal in the excitation loop of a synchronous machine. A new metaheuristic optimisation algorithm termed the sine cosine algorithm (SCA) was proposed for optimising PSS controller parameters to obtain an optimal solution with the damping ratio as an objective function. The SCA technique was examined on a single machine infinite bus (SMIB) system under distinct loading situations and matched with a moth flame optimisation technique and evolutionary programming to design a robust controller of PSS. The simulation was accomplished using a linearised mathematical model of the SMIB. The performance of a designed lead lag-controller of PSS was demonstrated using eigenvalue analysis with simulations, showing promising results. The dynamic performance was validated with respect to the damping ratio, the eigenvalue's location in the s-plane and rotor angle deviation response to demonstrate system stability. low frequency oscillation; damping controller; objective function; metaheuristic optimization techniques; power system stabilizer; eigenvalues; single machine infinite bus system +
Footnote †: journal: Applied  
of angle stability, transmission line power carrying capacity, and load equipment efficiency. The input to PSS is either the rotor speed or frequency, or power. or a combination of the two. The damping and synchronising performance of the synchronous generator excitation system depends on the selection and proper tuning of the parameters of the PSS and AVR controllers. The design of the PSS controller parameters requires the finding of the objective function with a linearised model and the use of suitable metaheuristic optimisation techniques. Metaheuristic optimisation techniques are used to optimise the controller's parameters by finding the maximum or minimum value of an objective function, which are some of the accomplished targets in this work [1,4]. Proper modelling of a system and damping controller devices are required to damp oscillations and improve and maintain the angle stability of a power system. Different schemes, such as PSS, flexible alternating current transmission system (FACTS), and coordination control, have been used for damping. The PSS lead lag controller, with the excitation system of the machine, controls the output power by delivering the supplementary synchronising torque, which is in phase with speed eccentricity to damp the required low frequency oscillations and improve power system stability [1,4]. PSS is the preferred method for improving power system stability by damping low frequency oscillations [5,6]; its design for multimachine by using local measurements [7]; and for the tuning of its parameters by combining transfer function-eigenfunction [8]. Different types of FACTS devices--shunt, series, shunt-series and series-series--have been used to damp low frequency oscillations in power systems through an appropriate design of controllers by inserting or absorbing reactive power. FACTS shunt devices, namely, static VAR compensators (SVC) [9,10] and static synchronous compensators (STATCOM), are used for damping low frequency oscillations and to increase angle stability [9,11]. The literature also includes a damping performance analysis [12], a dynamic control strategy to improve the power flow capabilities [13], and an enhancement of low voltage ride-through capability in power systems [14]. In coordination control, the use of PSS and FACTS devices with effective coordination amongst controllers is combined to damp both types of low frequency oscillations in an electrical power system: namely, local and inter modes. The coordination control design for SVC, STATCOM, thyristor-controlled series capacitor (TCSC) and PSS [11,12,15,16] and of PSS and series capacitive reactance compensators (SCRC) and TCSC are used to enhance damping [15,17].