The penetration of inverter-based power plants (IBPPs), such as large-scale photovoltaic (PV) power plants (LPPPs), is ever increasing considering the merits of renewable energy power plants (REPPs). Given that IBPPs are added to power systems or replaced by conventional power plants, they should undertake the most common tasks of synchronous generators. The low-frequency oscillation (LFO) damping through the power system stabilizers (PSSs) of synchronous generators is regarded as one of the common tasks in power plants. This paper proposes an optimal fractional-order proportional-integral-derivative (FOPID) controller implemented in the control loop of IBPPs for LFO damping in power systems. For this purpose, the last version of the generic dynamic model for renewable technologies (GDMRT) is used, which was released by the Western Electricity Coordinating Council (WECC) and Electric Power Research Institute (EPRI). In addition, an LPPP is studied as a case study. The FOPID controller is optimally tuned using the particle swarm optimization (PSO) algorithm in order to produce effective LFO damping. Finally, the performance of this controller is simulated and investigated in a two-area test system, showing the better performance of the LPPP for LFO damping by using the proposed optimal FOPID controller compared to the optimal lead-lag controller and optimal PID controller.

Load frequency control in power systems introduces as one of the most important items in order to supply reliable electric power with good quality. The goals of the Load Frequency Control (LFC) are to maintain zero steady state errors in a two area interconnected power system. To achieve this goal a fast controller with having no steady-state error will be necessary to be included in power systems. In this paper a new genetic algorithm based method is presented to obtain optimal gains of this controller included in two-area interconnected power system. Simulation results in comparison with correspondence methods confirm the efficiency of proposed method through fastdamping steady-state deviations in power and frequency with presence of step load disturbance.

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