AC/DC Frequency-Dependent Power Flow Jacobian: Quantifying Grid Support and Stability Implications

TL;DR

The work addresses the risk that AC-side, band-limited analyses of grid-forming converters may misrepresent their impact on power system stability.It introduces an extended AC/DC frequency-dependent Jacobian by linking the admittance model $\boldsymbol{Y}(j\omega)$ to the FD-JB $\boldsymbol{J}(j\omega)$, enabling cross-domain stability assessment.A unified analysis framework and benchmark test system are proposed to evaluate system support, integration stability, and stabilizing effects under DC and AC weak-grid conditions.Case studies with a modular multilevel converter show that stronger AC-side support does not necessarily translate to improved stability, underscoring the need for holistic, cross-domain stability analysis in AC/DC grid design.

Abstract

This letter proposes an AC/DC frequency-dependent power flow Jacobian analysis to identify the system support capabilities. In addition, the analyses reveal that system support capabilities do not necessarily enhance the system stability margin, suggesting that technical requirements of narrow-frequency-band and AC-side focused specifications may not lead to the expected performance of GFM.

Figures (5)

• Figure 1: Unified analysis framework with a benchmark test system to test the system support capabilities, system integration stability, and stabilizing effects.
• Figure 2:
• Figure 3: EMT results of system support and weak-grid integration tests.
• Figure 4: EMT results of DC side stabilizing effects where DC weak-grid with $|Z_{s,dc}|$ increases at 1s and 6s.
• Figure 5: EMT results of AC side stabilizing effects where AC-weak grid with $|Z_{s,ac}|$ increases at 1s and 6s.