arXiv subjects

Taha Saeed Khan

Publications and source records attributed to Taha Saeed Khan.

4 recordsLinked to original sources

arXiv2026

Human-on-the-loop Resilient Control of InverterBased Resources Under Actuator Degradation

This paper proposes a human-on-the-loop resilient control architecture for grid-supporting inverter-based resources (IBRs) operating under actuator degradation. Conventional fault-tolerant control and adaptive control strategies each face notable limitations in this setting: active FTC depends on fast, accurate fault detection and isolation, leaving it vulnerable to misdiagnosis of incipient or ambiguous degradation, while passive FTC tends toward overly conservative operation. Adaptive controllers face a related problem as they typically assume sufficient control authority, but when actuator degradation erodes that authority, the adaptive law may misinterpret tracking errors, leading to parameter drift, performance loss, or instability. To overcome these limitations, the proposed framework embeds human supervisory judgment directly into the control loop, detecting subtle off-nominal behavior, validating or overriding controller parameters, and adjusting operational objectives when conditions exceed the modeled fault space. Two new metrics underpin this resilient decision-making: Generation Reserve Capacity (GRC), which quantifies remaining inverter capacity available for future contingencies, and Controlled Performance Degradation (CPD), which allows temporary, deliberate performance relaxation to preserve overall system operability. A human-selected resilience tuning parameter, μ, governs the trade-off between immediate tracking accuracy and long-term operational readiness. A stability analysis of the proposed HOTL μ-mod adaptive controller is presented. The approach is also validated through simulations of a grid-connected inverter under sequential actuator degradation. Results show that the proposed architecture preserves control reserves, prevents actuator saturation, and achieves superior voltage regulation compared with conventional adaptive control and FTC methods.

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arXiv2026

Power Flow Solvability with Volt-Var Controlled Inverter-Based Resources

This paper establishes a sufficient condition for guaranteeing power flow solvability in distribution grids with inverter-based resources (IBRs) operating under IEEE 1547 compliant Volt-Var control. While designed to improve voltage profiles, reactive power injection can drive the system toward its operational limits. Under these stressed conditions, any further incremental reactive power injection can trigger voltage collapse, the point at which a power flow solution ceases to exist. In this paper, by leveraging a phasor-based voltage representation, the power flow equations with Volt-Var control are developed in the complex fixed point form, enabling a compact formulation and the rigorous application of fixed-point theorems. Addressing the challenges posed by the non-holomorphicity of the complex power flow equations due to the Volt-Var function's dependence on voltage magnitude, the solvability conditions are then developed using the Brouwer fixed-point theorem. The proposed conditions are validated through simulations on distribution test feeders, with a primary focus on their application to real-time decision-making for voltage regulation services.

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arXiv2025

Global Frequency Reference Tracking as an Oscillation Suppression Mechanism in VSM Primary Control: A Coupled-Oscillator Study

Synchronization in power systems is traditionally achieved through physical network coupling, whereby inverter-based resources (IBRs) and synchronous machines converge to a common frequency via oscillatory swing dynamics. In conventional operation, secondary control acts on a slow time scale and is typically engaged only after the primary dynamics have largely settled. As a result, in the absence of an explicit global reference, disturbances can induce prolonged transients and large phase excursions. This work considers a setting in which the total active power balance is known and maintained at all times, and proposes a control architecture for virtual synchronous machine (VSM) based inverters in which all units track a broadcast global frequency reference. Under this assumption, synchronization is transformed from a mutual oscillator locking problem into a reference tracking problem. Using a second order swing network model, we show that embedding a simple proportional integral (PI) frequency controller can significantly improves transient behavior. A washout mechanism ensures that the additional control action vanishes in steady state, thereby preserving network determined power sharing. Simulations on a three oscillator network demonstrate reduced frequency overshoot, elimination of underdamped oscillations, and lower angular stress compared to conventional open loop synchronization, highlighting the effectiveness of a global frequency reference as a coordination mechanism for grid-forming inverter networks.

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arXiv2025

Least Squares based Estimation of Thevenin Equivalent in Noisy Distribution Grid

This work presents a novel approach that synergizes the extremum seeking method with an online least squares estimation technique to accurately estimate Thevenin equivalent circuit being seen at each node in distribution grids. Thevenin's theorem offers a simplified representation of electrical networks, critical for the effective monitoring, control, and optimization of grid operations. However, real-time identification of Thevenin parameters, particularly impedance, poses significant challenges due to the dynamic nature of distribution grids. By integrating extremum seeking algorithms, which are adept at locating optima in dynamic systems without explicit model information, with the robustness of least squares estimation, we develop a novel methodology that continuously adapts to grid fluctuations. These fusion harnesses the strengths of both techniques: the extremum seeking method's non-model-based optimization capabilities and the least squares method's proficiency in estimating parameter value in a noisy environment. The result is a robust, adaptive algorithm capable of delivering reliable Thevenin parameter estimations in real-time. Our simulation results demonstrate the efficacy of the proposed method, showcasing its potential as a tool for enhanced grid management and resilience.

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