Primary Frequency Response Enhancement for Future Low Inertia Power Systems Using Hybrid Control Technique

Maintaining the stability of a conventional power system during under frequency events is partially dominated by a natural behavior called inertial response. Although a variable speed wind turbine (VSWT) is fundamentally deprived from such behavior, it was shown recently that it can virtually emulate this response, hence increasing its output power given to the grid to sustain the power balance. This paper reviews and analyzes the performance of four primary frequency control structures, and provides comparison between these controllers in terms of security indices. The results reflect the superiority of the inertia emulation controller and the droop control type in low and high wind speed respectively. To enhance the system frequency control response and take any inherent advantage of each controller, this paper proposes two novel controllers based on combination (hybridization) strategy between the four controllers. The results show that the combination between the inertia emulation controller and the de-loading controller will lead to reducing the rate of change of frequency (ROCOF) and raising the frequency nadir (FN) values. Finally, the role of each discussed controller in determining the correlations among ROCOF, FN and wind power penetration level are explored.