arXiv subjects

Mark O'Malley

Publications and source records attributed to Mark O'Malley.

8 recordsLinked to original sources

arXiv2026

Jacobian Voltage Stiffness Metric -- A Measure of Grid-Forming Capability and System Strength in IBR-Dominated Grids

As power systems transition toward inverter-based resource (IBR)-dominated grids, traditional system strength definitions and metrics are becoming increasingly inadequate to characterize upcoming stability challenges. Emerging definitions characterize system strength in terms of "voltage source behind impedance (VSBI)" characteristics. Similarly, Grid-ForMing (GFM) IBRs are expected to contribute voltage stiffness by exhibiting near-constant VSBI characteristics in the (sub-)transient time frame. To quantify VSBI characteristics as a measure of system strength or grid-forming capability, this paper proposes the Jacobian Voltage Stiffness Metric (JVSM), derived from the frequency-domain Jacobian. JVSM provides a measure of both small-signal voltage magnitude and phase-angle stiffness. JVSM is demonstrated to serve as a compliance criterion for evaluating the VSBI characteristics of GFM IBRs. When applied for grid strength assessment, it more effectively identifies small-signal stability problems than state-of-the-art strength metrics. The proposed JVSM is validated through electromagnetic transient simulation case studies using the National Laboratory of the Rockies (NLR, formerly NREL) and WECC-approved industry-standard GFM IBR models and on a modified IEEE 39-bus system.

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arXiv2026

Parameterizing Operating-Point-Dependent IBR Using Coherent Operating Regions for Sub-synchronous Oscillation Analysis

Analysis of sub-synchronous oscillations (SSO) in IBR-dominated grids relies on frequency scan-based estimation of black-box IBR models at selected operating points. Since IBRs may operate over a wide range of operating conditions, frequency responses obtained at a limited number of operating points may not adequately represent the dynamics required for system-level SSO analysis. Accurate parameterization of operating-point-dependent IBR dynamics is challenging due to the heterogeneous dynamic behaviors that may arise across the operating space. This paper addresses this challenge by analytically characterizing the conditions that give rise to discontinuous and non-smooth variations in IBR dynamics. Leveraging these insights, a geometric representation based on singular value decomposition is used to identify coherent operating regions and partition the operating space into dynamically consistent regions. Within each region, the operating-point dependence of the IBR frequency response is accurately captured using simple linear regression. The proposed framework is validated on a modified IEEE 39-bus system. Results demonstrate that the parameterized IBR frequency responses accurately reconstruct system-level dynamics at the prevailing operating condition, enabling frequency-response and modal analysis without repeated system-level frequency scans.

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arXiv2026

Frequency-Domain Compliance Assessment of Grid-Forming Devices

Grid-ForMing Inverters (GFMIs) are expected to provide voltage stiffness to the grid. Explicitly, system operators (SOs) and regulators expect GFMIs to behave like a "voltage source behind impedance (VSBI)" in the (sub)-transient time frame. SOs assess this VSBI characteristic of GFMIs during compliance by defining a pass-fail time-domain criterion. This is done by evaluating the GFMIs' active (or reactive) power/current response to step changes in voltage phase (and magnitude) at its terminals. However, this approach is prone to errors due to poorly defined measurement specifications for very fast (less than a cycle) transients. To address this, this work proposes a compliance criterion for the VSBI characteristic of GFMIs in the frequency domain based on elements of the frequency-domain Jacobian. The compliance criterion is defined in terms of the minimum expected P(s)/\theta(s) and Q(s)/V(s) Bode plot characteristics across a specific frequency range. The equivalence between the time-domain and frequency-domain criteria is established. The proposed method is demonstrated by assessing the compliance of generic NLR (formerly NREL) GFMI models in PSCAD. Furthermore, the impact of GFMI compliance on the small-signal stability of the IEEE 39-bus bulk-power system is demonstrated.

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arXiv2026

Spatial Characterization of Sub-Synchronous Oscillations Using Black-Box IBR Models

Power systems with high penetration of inverter-based resources (IBRs) are prone to sub-synchronous oscillations (SSO). The opaqueness of vendor-specific IBR models limits the ability to predict the severity and the spread of SSO. This paper demonstrates that black-box IBR models estimated through frequency-domain identification techniques, along with dynamic network model can replicate the actual oscillatory behavior. The estimated IBR models are validated against actual IBR models in a closed-loop multi-IBR test system through modal analysis by comparing closed-loop eigenvalues, and participation factors. Furthermore, using output-observable right eigenvectors, spatial heatmaps are developed to visualize the spread and severity of dominant SSO modes. The case studies on the 11-bus and 39-bus test systems confirm that even with the estimated IBR models, the regions susceptible to SSO can be identified in IBR-dominated power systems.

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arXiv2026

Equivalent Circuit Modeling of Grid-Forming Inverters in (Sub)-Transient Time-Frame

The widely accepted definition of grid-forming (GFM) inverter states that it should behave as a (nearly) constant voltage source behind an impedance by maintaining a (nearly) constant internal voltage phasor in the sub-transient to transient time frame. Some system operators further mandate permissible ranges for this effective impedance. However, these specifications do not clearly define the location of the internal voltage source, and no systematic method exists to quantify its effective impedance for a black-box GFM model. To address this, we first compare the transient responses of an ideal voltage source and a GFM to show that an idealistic GFM maintains a (nearly) constant voltage across the filter capacitor, rather than at the inverter switches. Then we propose a systematic method to quantify the effective impedance of a GFM from its black-box model using frequency-domain admittance plots. Using standard PSCAD GFM models developed by NLR (formerly NREL), we demonstrate that the GFM's equivalent impedance model captures the sub-transient response and static voltage stability limit accurately. Further, replacing the GFM with the proposed equivalent circuit model in the modified IEEE-39 bus system is shown to reproduce the small-signal stability characteristics with reasonable accuracy.

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arXiv2025

A Fair, Flexible, Zero-Waste Digital Electricity Market: A First-Principles Approach Combining Automatic Market Making, Holarchic Architectures and Shapley Theory

This thesis presents a fundamental rethink of electricity market design at the wholesale and balancing layers. Rather than treating markets as static spot clearing mechanisms, it reframes them as a continuously online, event driven dynamical control system: a two sided marketplace operating directly on grid physics. Existing energy only, capacity augmented, and zonal market designs are shown to admit no shock robust Nash equilibrium under realistic uncertainty, instead relying on price caps, uplift, and regulatory intervention to preserve solvency and security. In response, the thesis develops a holarchic Automatic Market Maker (AMM) in which prices are bounded, exogenous control signals derived from physical tightness rather than emergent equilibrium outcomes. The AMM generalises nodal and zonal pricing through nested scarcity layers, from node to cluster to zone to region to system, such that participant facing prices inherit from the tightest binding constraint. Nodal and zonal pricing therefore emerge as special cases of a unified scarcity propagation rule. Beyond pricing, the AMM functions as a scarcity aware control system and a digitally enforceable rulebook for fair access and proportional allocation under shortage. Fuel costs are recovered through pay as bid energy dispatch consistent with merit order, while non fuel operating and capital costs are allocated according to adequacy, flexibility, and locational contribution. Large scale simulations demonstrate bounded input bounded output stability, controllable procurement costs, zero structural waste, and improved distributional outcomes. The architecture is climate aligned and policy configurable, but requires a managed transition and new operational tools for system operators and market participants.

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arXiv2024

Maintaining reliability while navigating unprecedented uncertainty: a synthesis of and guide to advances in electric sector resource adequacy

The reliability of the electric grid has in recent years become a larger concern for regulators, planners, and consumers due to several high-impact outage events, as well as the potential for even more impactful events in the future. These concerns are largely the result of decades-old resource adequacy (RA) planning frameworks being insufficiently adapted to the current types of uncertainty faced by planners, including many sources of deep uncertainty for which probability distributions cannot be defensibly assigned. There are emerging methodologies for dealing with these new types of uncertainty in RA assessment and procurement frameworks, but their adoption has been hindered by the lack of consistent understanding of terminology related to RA and the related concept of resilience, as well as a lack of syntheses of such available methodologies. Here we provide an overview of RA and its relationship to resilience, a summary of available methods for dealing with emerging types of uncertainty faced by RA assessment, and an an overview of procurement methodologies for operationalizing RA in the context of these types of uncertainty. This paper provides a synthesis and guide for both researchers and practitioners seeking to navigate a new, much more uncertain era of power system planning.

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arXiv2024

Embracing Fairness in Consumer Electricity Markets using an Automatic Market Maker

As consumer flexibility becomes expected, it is important that the market mechanisms which attain that flexibility are perceived as fair. We set out fairness issues in energy markets today, and propose a market design to address them. Consumption is categorised as either essential or flexible with different prices and reliability levels for each. Prices are generated by an Automatic Market Maker (AMM) based on instantaneous scarcity and resource is allocated using a novel Fair Play algorithm. We empirically show the performance of the system over 1 year for 101 UK households and benchmark its performance against more classical approaches.

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