Placing Storage Energies for Enhancing Small-Signal Stability of Converter-Based-Renewable Systems

Storage energies (SEs) have the flexibility of bi-directional power regulation, so they have been integrated into the power system via power electronic converters to reduce the power fluctuations introduced by converter-based renewables (CBRs), such as solar and wind. However, converter-based SEs may interact with CBRs through the power network, which increases the complexity and difficulty of the phase-lock-loop (PLL)-induced small-signal stability analysis in multi-CBR systems, especially in weak grids. In this context, it remains unclear how the placement of SEs influences the PLL-induced small-signal stability, particularly when the SEs absorb active power from grids. To fill this gap, this paper analyzes the impact of SEs on the PLL-induced small-signal stability in multi-converter systems from the perspective of grid strength and proposes a method for optimally placing SEs to enhance the small-signal stability. First, the analytic results reveal that when the SEs absorb active power from the power grid, they can enhance grid strength and thus the PLL-induced small-signal stability; moreover, the degree of system stability improvement depends on the location of SE placement. On this foundation, a grid-strength-based method is proposed for the PLL-induced small-signal stability improvement via SE placements. The proposed method is validated based on three test systems. This paper provides an effective way of better understanding the interaction among SEs and CBRs through power network, and coordinating the placements of SEs in future converter-dominated power systems.