Real-Time Grid Impedance Measurement in E-STATCOM Using Orthogonal Optimized Pulse Patterns

Abstract

Accurate grid impedance knowledge is essential for the stable and adaptive operation of energy-storage-equipped STATCOMs (E-STATCOMs) in converter-dominated power systems with high penetration of renewable energy and dynamic loads. This paper proposes a real-time grid impedance measurement method based on orthogonal optimized pulse patterns (OPP) excitation, where the timing of signal level transitions is optimized to concentrate harmonic energy at selected frequencies. Unlike conventional discrete-time perturbation signals, such as pseudo-random binary sequences, the proposed continuous-time OPP signals preserve their spectral properties during implementation, enabling predictable frequency-domain behavior and more efficient excitation. The method is validated using a power hardware-in-the-loop (PHIL) setup under both grid-following and grid-forming control modes. Experimental results demonstrate accurate impedance estimation over the critical frequency range of approximately 60 Hz to 1 kHz, which is most relevant for stability analysis and control design, while maintaining robust performance under both nominal and weak grid conditions. These results confirm that the proposed OPP-based approach enables fast, reliable, and practically implementable real-time grid impedance measurement for E-STATCOM applications.