The interaction among inverter-based resources (IBRs) and power network may
cause small-signal stability issues, especially in low short-circuit grids.
Besides, the integration of static synchronous compensators (STATCOMs) in a
multi-IBR system for voltage support can deteriorate small-signal stability.
However, it is still challenging to understand the impact mechanism of STATCOMs
on IBR-induced oscillation issues and to design STATCOMs' control for damping
these oscillation issues in a multi-IBR system, due to complex system dynamics
and varying operating conditions. To tackle these challenges, this paper
proposes a novel method to reveal how STATCOMs influence IBR-induced
oscillation issues in a multi-IBR system from the viewpoint of grid strength,
which can consider varying operating conditions. Based on this proposed method,
we find critical operating conditions, wherein the system tends to be most
unstable; moreover, we demonstrate that robust small-signal stability issues of
the multi-IBR system with STATCOMs can be simplified as that of multiple
subsystems under critical operating conditions, which avoids traversing all
operating conditions and establishing system's detailed models. On this basis,
an adaptive control-parameter design method is proposed for STATCOMs to ensure
system's robust small-signal stability under varying operating conditions. The
efficacy of proposed methods is validated by a 39-node test system