Effects of inertia distribution on regional frequency heterogeneity

Heterogeneous inertia distribution can result in large regional frequency deviations and inter-area oscillations that exceed protection limits configured based on system-wide averaged performance. This paper examines how the spatial distribution of inertia affects frequency heterogeneity. Along with varying inertia distribution, variations in generator turbine-governor control and network topology are studied to make the results more generalisable across wide-ranging operating conditions. An investigation into the effects of different fast frequency response (FFR) schemes on frequency heterogeneity is also presented. The frequency heterogeneity is quantified by calculating cosine similarity between regional frequency trajectories. The key results are obtained using a two-area model and verified using a mixed AC/DC power system. A key finding is that the localness of regional frequency is independent of the inertia of a specific area, nor of the total system inertia. The inertia ratio, described as the ratio of the disturbance area inertia to that of the non-disturbance area, is shown to have a strong correlation with frequency heterogeneity. This correlation is shown to be very robust to changes in generator dynamics and network topology. Providing derivative FFR within the disturbance area always demonstrates benefits regarding frequency heterogeneity inhibition, whereas droop scheme typically introduces deterioration in frequency heterogeneity.