1) The team has performed the correlation analysis between the wide-area oscillation modes obtained from the PMU data and the load/generation, which shows that the increase of renewable energy source (RES) penetration level in WI has a significant impact on the damping ratio of NS-A mode. Fig. 1 gives an example of the correlation analysis between the solar, wind, load and the North-South Mode A damping ratio.
Fig. 1 Correlation analysis between the solar, wind, load and the North-South Mode A damping ratio.
2) The team has performed the model-based wide-area oscillation trend analysis for the WI, which shows that the increase of RES penetration level in WI has a significant impact on the damping ratio of NS-A mode. Renewable generation was increased significantly system-wide (up to 70%) by replacing synchronous generators with fully-converter based plants. Fig. 2 shows renewable generation in different areas and system-wide for 13 different simulation cases. Fig. 3 shows that, with the increasing of system-wide renewable penetration level, the North-South mode A damping ratio decreases.
Fig. 2 Renewable generation in different areas and system-wide for different simulation cases.
Fig. 3 North-South modes A damping ratio vs. system-wide renewable generation penetration level.
3) We have performed the small signal eigenvalue analysis for the full-WECC system model with SSAT tools and obtain a lot of useful results that could explain the previous findings for the trending of the WECC wide-area oscillation modes with respect to high penetration of inverter-based renewable generation. The main takeaways from the model-based small-signal eigenvalue analysis are (a) increased penetration of inverter-based renewable generation sources can result in the change of frequency and damping ratio of wide-area oscillation modes; (b) trends observed in the damping ratio of the wide-area oscillation modes could be explained by the change in the participation factors and/or mode shapes of remaining synchronous generator in the system.
For example, the following Fig. 4 shows that, when the renewable penetration level increases from 10% (case-0) to 40% (case-6) system wide, the damping ratio of the wide-area oscillation mode NS-A does not change too much, as the participation factors of the remaining online synchronous generators do not change too much. However, the Fig. 5 shows that when the renewable penetration level continuous to increase from 45% (case-7) to 70% (case-12) system wide, the damping ratio of the wide-area oscillation mode NS-A decreases significantly, since the participation factors of the remaining online synchronous generators change a lot.
Fig. 4 Participation factors of online synchronous generators for the renewable penetration level increases from 10% (case-0) to 40% (case-6) system wide.
Fig. 5 Participation factors of online synchronous generators for the renewable penetration level increases from 45% (case-7) to 70% (case-12) system wide.