Robust Input/Output Signal Selection for WADCs: Comparing Independent and Parallel Operation with Local PSSs

The integration of wide-area damping controllers (WADCs) with local Power System Stabilizers (PSSs) has traditionally been considered a standard approach for enhancing power system stability. Nevertheless, whether a WADC operates independently or in parallel with local PSSs, the effectiveness of the controller critically depends on the selection of robust input/output signals. The robustness of these signals may differ between the two configurations, as the presence of local PSSs operating in parallel has the potential to influence signal dynamics and thereby affect robustness. This paper presents the first systematic investigation of the impact of local PSSs on the robustness of WADC signal selection by comparing independent WADC operation with the conventional parallel PSS/WADC configuration. A residue-based methodology is proposed, incorporating both magnitude and phase angle variations to evaluate robustness across multiple operating conditions. The proposed methodology is validated on two well-known benchmark systems. Results show that the presence of local PSSs can introduce significant phase angle inconsistencies, leading to variations that compromise the robustness and effectiveness of the selected input/output signals. The findings provide new insights into signal selection for wide-area damping control and challenge the conventional assumption that parallel operation with local PSSs is always beneficial.