Source--Grid Coupling in Power System Oscillations: Observational Equivalence, Feedback Detectability, and Modal Interaction

Electrical Engineering and Systems Science > Systems and Control
[Submitted on 17 Sep 2026]
Title:Source--Grid Coupling in Power System Oscillations: Observational Equivalence, Feedback Detectability, and Modal Interaction
View PDF HTML (experimental)Abstract:The conventional distinction between forced and natural oscillations treats the oscillation source as external to a fixed power-system boundary. This paper develops a coupling-aware dynamical interpretation by explicitly accounting for the directionality of source-grid coupling. It examines when prescribed forcing and a one-way autonomous source are observationally equivalent, and when grid measurements can distinguish the presence of grid-to-source feedback. Matched interface signals yield exact equivalence under the same deterministic grid initial-value problem and measurement map. Bidirectional feedback enables source-grid eigenvalue interaction in the augmented autonomous model, while a reduced two-mode model shows that the interaction depends jointly on loop coupling and complex modal separation. The resulting framework establishes source-grid coupling directionality as a feedback-based dynamical boundary and clarifies when feedback can be inferred from grid-side measurements and why weak feedback may remain unresolved. Simulation studies on a two-area system demonstrate feedback detection within a calibrated source family, while source-model mismatch can be confounded with feedback. A WECC 243-bus system study demonstrates feasibility on a large system and shows that feedback detection need not require exact candidate selection.
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Facts Only

* The paper examines the distinction between forced and natural oscillations.
* It develops a coupling-aware dynamical interpretation accounting for source-grid coupling directionality.
* Matched interface signals yield exact equivalence under identical deterministic grid initial-value problems and measurement maps.
* Bidirectional feedback enables source-grid eigenvalue interaction in the augmented autonomous model.
* A reduced two-mode model shows that interaction depends on loop coupling and complex modal separation.
* The framework establishes source-grid coupling directionality as a feedback-based dynamical boundary.
* Grid measurements can distinguish grid-to-source feedback presence.
* Simulation studies on a two-area system demonstrated feedback detection within a calibrated source family.
* A WECC 243-bus system study showed feasibility of feedback detection without exact candidate selection.

Executive Summary

The research explores the distinction between forced and natural oscillations in power systems by incorporating the directionality of source-grid coupling into dynamical models. The study investigates when prescribed forcing and autonomous sources are observationally equivalent, and whether grid measurements can detect feedback from the source to the grid. The findings indicate that matched interface signals lead to exact equivalence under specific conditions defined by the deterministic grid problem and measurement map. Bidirectional feedback allows for interaction between source-grid eigenvalues in an augmented model. A reduced two-mode model suggests that this interaction depends on both loop coupling and modal separation. The framework establishes source-grid coupling directionality as a dynamical boundary for feedback inference, noting that weak feedback might remain unresolved. Simulation results on a two-area system demonstrate the feasibility of detecting feedback within a calibrated source family, although source-model mismatch can obscure the presence of feedback. A large system study on a WECC 243-bus system confirms the feasibility of feedback detection without requiring an exact candidate selection for the source.

Full Take

The work probes the fundamental ambiguity in interpreting power system dynamics by formalizing the role of coupling directionality. The core tension lies between mathematical equivalence (matched signals) and physical observability (detectability via measurements). The implication for system assessment is that standard separation into 'forced' versus 'natural' modes may be insufficient when feedback paths exist; the system state requires modeling the causality of energy flow, not just the magnitude of oscillation. The limitation identified—where source-model mismatch confounds feedback detection—suggests that observational equivalence in measurement space does not automatically translate to physical certainty regarding the underlying causal structure. This suggests that grid monitoring must integrate a framework where coupling directionality is an explicit dynamical variable rather than an external assumption, pushing research toward defining necessary and sufficient conditions for inferring bidirectional causality from unilateral measurements. The finding on large systems suggests that practical monitoring can achieve this demarcation even without perfect knowledge of the source dynamics, highlighting the resilience of observational techniques despite underlying model imperfections.

Sentinel — Human

Confidence

The text exhibits the high technical density and logical structuring characteristic of academic research, suggesting a human author operating within established scientific discourse.

Signals Detected

Varied sentence structure and technical vocabulary consistent with academic writing.

High internal logical flow; the abstract clearly builds a theoretical argument leading to specific mathematical/system implications.

References formal concepts (eigenvalue interaction, dynamical boundary) without relying on vague attribution.

Claims are specific to a technical research context; no overt signs of LLM-generated narrative fluff.

Human Indicators

Use of highly specialized, dense mathematical and systems science terminology without unnecessary explanatory hedging.

The structure follows the standard, complex logical progression expected in a peer-reviewed abstract.