arXiv subjects

Dominic Groß

Publications and source records attributed to Dominic Groß.

At least 19 recordsLinked to original sources

arXiv2026

Dynamic droop specifications for Grid-Forming Inverter-Based Resources

The large-scale retirement of synchronous generators requires additional capabilities from inverter-based resources (IBRs) to ensure the stability and reliability of power grids. With the heterogeneous controls of IBRs, it is especially important to understand their behavior on the grid. This work proposes a simple data-enabled dynamic model to capture the small-signal dynamics of IBRs and formulate specifications for grid-forming (GFM) IBRs. The dynamic droop model is complementary to well-studied impedance models and extends the common definition of steady-state droop coefficients to dynamic droop coefficients that fully characterize the IBR small-signal response below the nominal line frequency (e.g., subsynchronous oscillations). We propose bounds on the gain and phase of the dynamic droop coefficients to encode minimum requirements for GFM IBRs to promote interoperability and minimize adverse interactions. The resulting specifications also provide some insights into the much-debated question of how to certify an IBR as GFM. Moreover, we also provide dynamic droop specifications for frequency control ancillary services that, e.g., clarify and generalize the notion of an IBR inertia response. Finally, common grid-following (GFL) and GFM controls as well as original equipment manufacturer (OEM) models are used to illustrate the results and showcase the use of dynamic droop coefficients as a tool to screen IBR dynamics for potential adverse interactions.

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arXiv2026

Transient Stability of Offshore Energy Hubs

Offshore energy hubs (OEHs) use grid-forming modular multilevel converters (MMCs) to enable large-scale offshore wind integration and multi-terminal HVDC operation. In HVDC-connected offshore wind farms and OEHs, the offshore grid-forming HVDC converters absorb active power from an offshore AC grid supplied by the wind farms and convert it to DC power for transmission to the onshore grid. Converter current limiting under different fault types in this setting is an understudied topic in the literature, which mostly focuses on power-injecting converters. This paper proposes a unified current-limiting strategy that combines a variable virtual impedance (VVI), based on a smooth threshold function, with a novel virtual-power (VP) mechanism derived from the power dissipated in the virtual resistance. The VVI ensures current limitation during fault-induced overcurrents while preserving voltage-source behavior, whereas the VP mechanism adds a compensating power term into the synchronization loop, enabling automatic power redistribution among converters. P-delta analysis further shows that a more resistive VVI can improve the transient stability of power-absorbing converters, while the proposed VP mechanism further enlarges the stability margin. EMT simulations validate that the combined VVI-VP strategy limits fault currents, maintains synchronism during severe faults, and achieves coordinated post-fault power sharing in fully converter-based OEHs.

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arXiv2026

Holistic Grid-Forming Control to Enhance the Frequency Support from HVDC-Connected Offshore Wind Power Plants

To address the frequency stability challenges posed by the rising penetration of power electronics in power systems, HVDC-connected offshore wind power plants (OWPPs) are increasingly expected to provide inertial response and frequency containment reserve (FCR). In this paper, an improved holistic grid-forming (GFM) control is proposed, aiming to enhance the frequency support by coordinating the GFM controls implemented at all AC and DC terminals of an HVDC-OWPP system, without requiring communication. Firstly, the model of a typical HVDC-OWPP system is developed for control design. Accordingly, the proposed controllers are formulated, followed by an analytical tuning method, where the upper bound of the bandwidth at each AC or DC terminal is identified. Finally, simulations are conducted to verify the functionality and compare the performance with that of representative control configurations. The results show that the proposed holistic GFM control achieves faster response and thus more effective frequency support, while the utilization of the inherent energy storage of each converter is minimized, thereby supporting a new design philosophy for converter control in converter-dominated systems.

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arXiv2026

Input-Output Specifications and Dynamic Droop Coefficients: Stability and Performance Conditions for Grid-Forming IBRs

This paper proposes dynamic stability and performance conditions for grid-connected inverter-based resources (IBRs). To this end, we extend the notion of steady-state droop coefficients to dynamic droop coefficients to capture the small-signal dynamics of IBRs and synchronous generators (SGs). Notably, the dynamic droop coefficients can be obtained from input-output data collected at the unit's (e.g., IBR or SG) point of interconnection without requiring prior knowledge of IBR internals or controls structure. To obtain frequency stability conditions, this IBR model is combined with a lightweight dynamic transmission network model that accounts for uncertainty of line dynamics. The resulting stability conditions are highly scalable and, given a few key network parameters, can be verified at the unit level. To make the conditions practical and offer intuitive and illustrative interpretations, we map the frequency stability conditions to bounds on the Bode plot of the dynamic droop coefficient for two broad types of IBR responses. Moreover, our specifications on the dynamic droop coefficient (i) translate basic frequency control ancillary services into verifiable requirements, and (ii) provide insights into the much-debated question of how to certify an IBR as grid-forming (GFM). The results are illustrated using dynamic droop coefficients obtained using detailed simulations of GFM and GFL IBRs as well as SGs.

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arXiv2026

Stability and convergence of multi-converter systems using projection-free power-limiting droop control

In this paper, we propose a projection-free power-limiting droop control for grid-connected power electronics and an associated constrained flow problem. In contrast to projection-based power-limiting droop control, the novel projection-free power-limiting droop control results in networked dynamics that are semi-globally exponentially stable with respect to the set of optimizers of the constrained flow problem. Under a change to edge coordinates, the overall networked dynamics arising from projection-free power-limiting droop control coincide with the projection-free primal-dual dynamics associated with an augmented Lagrangian of the constrained flow problem. Leveraging this result, we (i) provide a bound on the convergence rate of the projection-free networked dynamics, (ii) propose a tuning method for controller parameters to improve the bound on the convergence rate, and (iii) analyze the relationship of the bound on the convergence rate and connectivity of the network. Finally, the analytical results are illustrated using an Electromagnetic transient (EMT) simulation.

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arXiv2026

Improving Stability Margins with Grid-Forming Damper Winding Emulation

This work presents (i) a framework for certifying small-signal frequency stability of a power system with line dynamics and heterogeneous bus dynamics, (ii) a novel reduced-order model of damper windings in synchronous machines, and (iii) a proportional-derivative (PD) damper winding emulation control for voltage-source converters (VSCs). Damper windings have long been understood to improve the frequency synchronization between machines. However, the dynamics of the damper windings are complex, making them difficult to analyze and directly emulate in the control of VSCs. This paper derives a reduced-order model of the damper windings as a PD term that allows grid-forming controls for VSCs to emulate their effect on frequency dynamics. Next, a framework for certifying small-signal frequency stability of a network with heterogeneous bus dynamics is developed that extends prior results by incorporating line dynamics. Finally, we analytically demonstrate that PD damper winding emulation can improve the stability of grid-forming converter controls. These results are validated with electromagnetic-transient (EMT) simulation.

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arXiv2025

Constraint-Aware Grid-Forming Control for Current Limiting

This work develops a constraint-aware grid-forming (GFM) control that explicitly accounts for current limits and modulation limits within the GFM oscillator dynamics generating the GFM voltage reference (i.e., phase angle and magnitude). Broadly speaking, the voltage reference generated by the constraint-aware GFM control minimizes the deviation from conventional unconstrained GFM droop control, while respecting current and modulation limits. The resulting GFM control achieves fast current limiting while preserving transient stability, e.g., exhibiting infinite critical clearing time. To develop the control, we first characterize and analyze the set of converter voltages that do not result in constraint violations. Next, an efficient algorithm for projecting voltages onto the feasible set is developed. Subsequently, these results are used to restrict the dynamics of GFM droop control to the set of feasible voltages. Finally, detailed simulation studies and hardware experiments are used to illustrate and validate the response to short-circuit faults and phase jumps.

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arXiv2025

Frequency Domain Stability Conditions for Hybrid AC/DC Systems

In this article, we investigate small-signal frequency and DC voltage stability of hybrid AC/DC power systems that combine AC and DC transmission, conventional machine- based generation, and converter-interfaced generation. The main contributions of this work are a compact frequency domain representation of hybrid AC/DC systems and associated stability conditions that can be divided into conditions on the individual bus dynamics and conditions on each DC network. The bus- level conditions apply to a wide range of technologies (e.g., synchronous generators, synchronous condensers, grid-forming renewables and energy storage). Moreover, the system-level conditions establish that hybrid AC/DC systems combining a wide range of devices are stable independently of the network topology provided that the frequency response of converters on each DC network is sufficiently coherent relative to the network coupling strength. Additionally, we develop and validate a novel reduced- order damper winding model for multi-machine systems.

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arXiv2025

Dynamic Modeling, Analysis, and Validation of Dual-Port Grid-Forming Control for Hybrid AC/DC Systems

This work investigates the transient and dynamical behavior of hybrid AC/DC systems using dual-port grid-forming (GFM) control. A generalized modeling framework for hybrid AC/DC networks is first introduced that accounts for converter, control, and network circuit dynamics and arbitrary network topologies. This modeling framework is applied to low-voltage networks to analyze the performance of dual-port grid-forming (GFM) control. The results demonstrate that active damping by dual-port GFM control is effective at improving the transient response and mitigating oscillations. In contrast, the steady-state response characteristics can be adjusted independently with minimal impact on damping characteristics. The dynamic model and results are validated through hardware experiments for three prototypical system architectures. Furthermore, we demonstrate that low-voltage DC distribution interfaced by AC/DC converters using dual-port GFM control, can serve both as the sole interconnection between AC distribution systems and in parallel to an AC connection, thereby enhancing the operational flexibility of low- and medium-voltage distribution networks.

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arXiv2025

Networked dynamics with application to frequency stability of grid-forming power-limiting droop control

In this paper, we study a constrained network flow problem and associated networked dynamics that resemble but are distinct from the well-known primal-dual dynamics of the constrained flow problem. Crucially, under a change of coordinates, the networked dynamics coincide with primal-dual dynamics associated with the constrained flow problem in edge coordinates. Next, we show that, under mild feasibility assumptions, the networked dynamics are globally asymptotically stable with respect to the set of optimizers of its associated constrained flow problem in nodal coordinates. Subsequently, we apply our stability results to establish frequency stability of power-limiting grid-forming droop control. Compared to conventional grid-forming droop control, power-limiting droop control explicitly accounts for active power limits of the generation (e.g., renewables) interfaced by the converter. While power-limiting droop control has been demonstrated to work well in simulation and experiment, analytical results are not readily available. Moreover, we (i) show that the converter frequencies synchronize to a common synchronous frequency for each grid-forming converter, (ii) characterize the synchronous frequency in the case of converters operating at their power limit, and (iii) establish that power-limiting droop control exhibits power-sharing properties similar to conventional unconstrained droop control. Finally, the analytical results are illustrated using an Electromagnetic transient (EMT) simulation.

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arXiv2024

Black Start Operation of Grid-Forming Converters Based on Generalized Three-phase Droop Control Under Unbalanced Conditions

This paper focuses on the challenging task of bottom-up restoration in a complete blackout system using Grid-forming (GFM) converters. Challenges arise due to the limited current capability of power converters, resulting in distinct dynamic responses and fault current characteristics compared to synchronous generators. Additionally, GFM control needs to address the presence of unbalanced conditions commonly found in distribution systems. To address these challenges, this paper explores the black start capability of GFM converters with a generalized three-phase GFM droop control. This approach integrates GFM controls individually for each phase, incorporating phase-balancing feedback and enabling current limiting for each phase during unbalanced faults or overloading. The introduction of a phase-balancing gain provides flexibility to trade-off between voltage and power imbalances. The study further investigates bottom-up black start operations using GFM converters, incorporating advanced load relays into breakers for gradual load energization without central coordination. The effectiveness of bottom-up black start operations with GFM converters, utilizing the generalized three-phase GFM droop, is evaluated through electromagnetic transient (EMT) simulations in MATLAB/Simulink. The results confirm the performance and effectiveness of this approach in achieving successful black start operations under unbalanced conditions.

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arXiv2024

Input-Output Specifications of Grid-Forming Functions and Data-Driven Verification Methods

This work investigates interoperability and performance specifications for converter interfaced generation (CIG) that can be verified using only input-output data. First, we develop decentralized conditions on frequency stability that account for network circuit dynamics and can be verified using CIG terminal dynamics and a few key network parameters. Next, we formalize performance specifications that impose requirements on the CIG disturbance response. A simple data-driven validation method is presented that enables verification of the interoperability and performance specifications for CIG using input-output data from a two-node system. Data obtained from electromagnetic transient (EMT) simulations are used to illustrate the proposed approach and the impact of key parameters such as inner control loop gains, network coupling strength, and controller bandwidth limitations.

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arXiv2023

Three-phase grid-forming droop control for unbalanced systems and fault ride through

In this work, we investigate grid-forming (GFM) control for dc/ac voltage source converters (VSC) under unbalanced system conditions and unbalanced faults. To fully leverage the degrees of freedom of VSCs, we introduce the concept of generalized three-phase GFM control that combines individual GFM controls for every phase with a phase balancing feedback. The proposed control allows trading off voltage and power unbalance under unbalanced conditions, enables current limiting for each phase during unbalanced faults, and reduces to positive sequence GFM droop control in balanced systems. High-fidelity simulations are used to illustrate the properties of the control.

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arXiv2022

Frequency shaping control for weakly-coupled grid-forming IBRs

We consider the problem of controlling the frequency of low-inertia power systems via inverter-based resources (IBRs) that are weakly connected to the grid. We propose a novel grid-forming control strategy, the so-called frequency shaping control, that aims to shape the frequency response of synchronous generators (SGs) to load perturbations so as to efficiently arrest sudden frequency drops. Our solution relaxes several existing assumptions in the literature and is able to navigate tradeoffs between peak power requirements and maximum frequency deviations. Finally, we analyze the robustness to imperfect knowledge of network parameters, while particularly highlighting the importance of accurate estimation of these parameters.

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arXiv2022

Grid-forming control of three-phase and single-phase converters across unbalanced transmission and distribution systems

In this work, we investigate grid-forming control for power systems containing three-phase and single-phase converters connected to unbalanced distribution and transmission networks, investigate self-balancing between single-phase converters, and propose a novel balancing feedback for grid-forming control that explicitly allows to trade-off unbalances in voltage and power. We develop a quasi-steady-state power network model that allows to analyze the interactions between three-phase and single-phase power converters across transmission, distribution, and standard transformer interconnections. We first investigate conditions under which this general network admits a well-posed kron-reduced quasi-steady-state network model. Our main contribution leverages this reduced-order model to develop analytical conditions for stability of the overall network with grid-forming three-phase and single-phase converters connected through standard transformer interconnections. Specifically, we provide conditions on the network topology under which (i) single-phase converters autonomously self-synchronize to a phase-balanced operating point and (ii) single-phase converters phase-balance through synchronization with three-phase converters. Moreover, we establish that the conditions can be relaxed if a phase-balancing feedback control is used. Finally, case studies combining detailed models of transmission systems (i.e., IEEE 9-bus) and distribution systems (i.e., IEEE 13-bus) are used to illustrate the results for (i) a power system containing a mix of transmission and distribution connected converters and, (ii) a power system solely using distribution-connected converters at the grid edge.

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arXiv2022

Power-balancing dual-port grid-forming power converter control for renewable integration and hybrid AC/DC power systems

In this work, we investigate grid-forming (GFM) control for dc/ac power converters in emerging power systems that contain ac and dc networks, renewable generation, and conventional generation. We propose a novel power-balancing GFM control strategy that simultaneously forms the converter ac and dc voltage (i.e., dual-port GFM), unifies standard grid-following (GFL) and GFM functions, and is backwards compatible with conventional machine-based generation. Notably, in contrast to state-of-the-art control architectures that use a mix of grid-forming and grid-following control, dual-port GFM control can be used independently of the converter power source or network configuration. Our main contribution are stability conditions that cover emerging hybrid ac/dc networks as well as machines and converters with and without controlled power source, that only require knowledge of the system topology. Finally, a detailed case study is used to illustrate and validate the results.

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arXiv2022

Unified Grid-Forming Control of PMSG Wind Turbines for Fast Frequency Response and MPPT

In this work we present a novel dual-port grid-forming control strategy, for permanent magnet synchronous generator wind turbines with back-to-back voltage source converters, that unifies the entire range of functions from maximum power point tracking (MPPT) to providing inertia and fast frequency response without explicit mode switching between grid-following and grid-forming control. The controls impose a well-defined AC voltage at the grid-side converter (GSC) and the machine-side converter (MSC) AC terminals and explicitly stabilize the DC-link capacitor voltage through both GSC and MSC. The wind turbine's kinetic energy storage and curtailment are adjusted through a combination of implicit rotor speed control and pitch angle control and directly determine the operating mode and level of grid support. Moreover, we provide analytical small-signal stability conditions for a simplified system and explicitly characterize the relationship between control gains, curtailment, and the wind turbines steady-state response. Finally, a detailed simulation study is used to validate the results and compared the proposed control with state-of-the-art MPPT control.

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arXiv2022

Dual-port grid-forming control of MMCs and its applications to grids of grids

This work focuses on grid-forming (GFM) control of Interconnecting Power Converters (IPCs) that are used to interconnect multiple HVAC and HVDC subgrids to form a grid of grids. We introduce the concept of dual-port GFM control that leverages the ability of Modular Multilevel Converters (MMCs) to simultaneously form its AC and DC terminal voltage and present two dual-port GFM MMC controls. We provide analytical results and high-fidelity simulations that demonstrate that (i) dual-port GFM control is more resilient to contingencies (i.e., line and generator outages) than state-of-the-art single-port GFM control, and (ii) unlike single-port GFM control, dual-port GFM control does not require assigning grid-forming and grid-following (GFL) roles to the IPC terminals in grids of grids. Finally, we provide an in-depth discussion and comparison of single-port GFM control and the proposed dual-port GFM controls.

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