Overview
This study investigates the small-signal stability of centralized energy storage systems (CESSs). The analysis specifically compares grid-following (GFL) and grid-forming (GFM) control strategies within these systems. Focus areas include bidirectional power flow and the aggregation of multiple energy storage systems (ESSs).
Research Context
Centralized energy storage systems involve complex dynamics, particularly when comprehensive GFL and GFM control loops are considered. The research addresses the issues arising from these complex dynamics. It emphasizes understanding the stability characteristics to inform the design and integration of such systems.
Approach
The research methodology involves simplifying high-order dynamics in CESSs by employing a virtual damping method. This simplification focuses on the dominant oscillation mode. Damping analysis was conducted to assess the dynamic characteristics. The study also examined damping sensitivity to various parameters. Conclusions are validated through modal analysis and time-domain simulations.
Findings
- CESSs utilizing a single type of control (either GFL or GFM) exhibit dynamic superimposition characteristics.
- As the number of ESSs increases, the damping of GFM-CESSs improves.
- Conversely, as the number of ESSs increases, the damping of GFL-CESSs decreases.
- The damping of GFM-CESSs is more sensitive to bidirectional power flow and to all control loops.
- The damping of GFL-CESSs is more sensitive to the d-axis control loop.
- GFM-CESSs are suggested as preferable for large-scale integration scenarios.
- However, GFM-CESSs are limited in scenarios characterized by significant power reversal.
- If GFL and GFM controls are hybridized within CESSs, the ratio of GFM-CESSs should be constrained.
- This constraint is necessary to avoid instability that can arise from modal resonance between GFL-CESSs and GFM-CESSs.
- Implementing GFM-CESSs necessitates considering scenario limitations, rather than exclusively pursuing maximal integration under hybrid conditions.
Why This Matters
The findings indicate specific dynamic behaviors and limitations for different control strategies in centralized energy storage systems. Understanding these characteristics is critical for the stable integration of such systems, particularly in scenarios involving large-scale deployment or hybrid control schemes. The study provides guidance on controller selection and integration ratios to avoid instability.