Due to the higher proportion of non-synchronous power resources in microgrids, adequate frequency regulation supports are required to maintain acceptable system frequency stability. As one of the sources for frequency regulation support in microgrid operation, via proper droop controller operations, wind energy conversion systems (WECS) could deliver kinetic energy stored in their turbines to the grid when needed. However, as the system inertia becomes smaller, the droop controller's response to system disturbances could cause the WECS to resonate with the grid and lead to torsional stress and fatigue damage in the WECS drivetrain. To protect the WECS against such damage, a resonance damper based on pole-zero cancellation technique is proposed in this paper. Simulation results depict the possible resonance phenomenon, and the reduction of undesired fatigue damage by the proposed damper retrofitted to the droop controller while improving the overall frequency regulation. Sensitivity analysis results are also provided to verify its robustness for practical applications.

Microgrids are designed to ensure reliability and quality of power supply. Reliable islanding transition is key to maintain uninterrupted supply of power to critical loads. Current islanding transition schemes assume fast response from local energy resources to establish secure islanding; however, such fast response systems are often expensive. Analysis of historical events shows that the islanding event, at most instances, can be predicted; by exploiting this feature, this paper proposes an adaptive optimal defense mechanism to establish secure islanding, without acquiring fast response energy resources. The dynamics involved in the islanding transition are incorporated into the search for optimal defense measures by using ‘simulation optimization” technique. A comparison between no defense approach and with defensive approach for the scenario when the islanding occurs demonstrates the effectiveness of the proposed adaptive defensive approach. The application of the adaptive defensive approach can help improve system performance. Sensitivity analyses are conducted to suggest improvements to reduce the operation cost of proposed defense plan.

The transition to a sustainable energy future will result in greater dynamics of aggregated power generation and demand in distribution networks. A vast network with limited real-time measurements presents challenges in comprehensively monitoring the system status and responding promptly to localized disturbances. Sparse signal reconstruction techniques based on affine-constrained rank minimization have been proposed to estimate distribution feeder states with a few measurements, which are presumably well-suited for contexts with very limited observability. Although previous studies on matrix completion-based distribution system state estimation (MCDSSE) have demonstrated acceptable node voltage estimation performance, their effectiveness in estimating branch flow states, to monitor line and transformer loading, remains unproven in the literature. This study assesses the consistency between estimated system states obtained using a variant of the MCDSSE method and actual branch flows and node injection powers to judge the method’s applicability in distribution system monitoring with limited available measurements. The test results confirm that solving a low-rank minimization problem does not enable MCDSSE to recover a realistic AC solution in areas with insufficient measurements, and show that degenerate solutions and multiplicity appear to occur frequently. To leverage its advantage in providing complete solution of the system states, based on operator-defined visibility requirements, four fidelity-monitoring-driven MCDSSE meter placement methods were tested to enhance its acceptability for system monitoring with affordable additional measurements. Numerical examples highlighting practical implications are provided.

Net-load variability and uncertainty in high renewable penetration networks have imposed new challenges to the system operators; adequate ramping, restart, and wider frequency and voltage operation capabilities provided by responsive resources are required to preserve acceptable service quality. Flexibility indicators and resource requirement constraints are proposed for unit commitment studies to address fast net-load variations. However, there is a gap in demonstrating the application of proposed flexibility indicators to determine the required minimum cost flexibility reserves to maintain desired operational performance. To address this issue for system operation planning purposes, a two-stage corrective flexibility constrained unit commitment (FCUC) formulation supported by a data-driven scheme for uncertainty quantification of flexibility shortage driven under and over frequency events is proposed. The first stage unit commitment (UC) is solved with relaxed flexibility constraints to determine the nominal resource schedules. A statistical test is used to determine if the second stage UC is needed. The second stage UC is solved with tighter flexibility constraints. A procedure to quantify the additional flexibility resources needed in the second stage UC to achieve adequate frequency regulation performance with lower operational costs is presented. Test results under various operation scenarios and comparisons with previous flexibility deployment methods illustrate the effectiveness of the proposed method. Test results indicate that in certain situations, flexible resources should remain online and be prioritized against less flexible (although cheaper) resources. The costs incurred by the additional system flexibility required to maintain good frequency control performance can be evaluated.