Microgrids as a resilience resource and strategies used by microgrids for enhancing resilience

Boosting the resilience of power systems is one of the core requirements of smart grid. In this paper, an integrated resilience response framework is proposed, which not only links the situational awareness with resilience enhancement, but also provides effective and efficient responses in both preventive and emergency states. The core of the proposed framework is a two-stage robust mixed-integer optimization model, whose mathematical formulation is presented in this paper as well. To solve the above model, an algorithm based on the nested column-and-constraint generation decomposition is provided, and computational efficiency improvement techniques are proposed. Preventive response in this paper considers generator re-dispatch and topology switching, while emergency response includes generator re-dispatch, topology switching and load shedding. Several numerical simulations validate the effectiveness of the proposed framework and the efficiency of the solution methodology. Key findings include the following: 1) in terms of enhancing power grid resilience, the integrated resilience response is preferable to both independent preventive response and independent emergency response; 2) the power grid resilience could be further enhanced by utilizing topology switching in the integrated resilience response.

Integration of Preventive and Emergency Responses for Power Grid Resilience Enhancement

Transportable energy storage systems (TESSs) have great potential to enhance resilience of distribution systems (DSs) against large area blackouts. A joint post-disaster restoration scheme for TESS and generation scheduling in microgrids (MGs) and network reconfigurations is proposed to minimize the total system cost, including customer interruption cost, generation cost, and TESS related costs. A temporal–spatial TESS model which is related to both transportation networks and DSs is proposed to represent the difference between TESS and ESS in terms of flexibility and cost reduction of ESS sharing among MGs. The proposed restoration problem is formulated as a mixed-integer linear programming with considering various network and TESS constraints. The proposed model and scheme are tested in a modified 33-bus test system with three MGs and four TESSs. The results verify that a distribution system with TESS is more resilient compared with conventional ESS because of the benefit from total cost reduction.

https://dr.ntu.edu.sg/bitstream/10356/89545/2/Transportable%20Energy%20Storage%20for%20More%20Resilient%20Distribution%20Systems%20With%20Multiple%20Microgrids.pdf

Transportable Energy Storage for More Resilient Distribution Systems With Multiple Microgrids

A robust security-constrained unit commitment (robust SCUC) model is proposed in this paper to enhance the operational reliability of integrated electricity-natural gas system (IEGS) against possible transmission line outages. In this work, adjustable capability of natural gas contract is considered to avoid dramatic changes in real-time gas demand. Distributed natural gas storage is also included to smooth out power system demand curve and further improve operational efficiency at normal state and during contingencies. Nonlinear and nonconvex natural gas flow functions are relaxed into second-order cone (SOC) constraints, then the SOC-based column and constraint generation method is adopted to solve the proposed two-stage robust convex optimization problem. In this iterative method, the security-check subproblem feeds back worst case constraints to the first-stage master problem, until no violated scenarios can be detected. Simulations tested on 6-bus-6-node and 118-bus-10-node IEGS with natural gas storage show that the proposed storage model is effective in the robust SCUC solution for IEGS considering possible N − k contingencies with limited natural gas adjustments.

Robust Constrained Operation of Integrated Electricity-Natural Gas System Considering Distributed Natural Gas Storage

The frequency of extreme events (e.g., hurricanes, earthquakes, and floods) and man-made attacks (cyber and physical attacks) has increased dramatically in recent years. These events have severely impacted power systems ranging from long outage times to major equipment (e.g., substations, transmission lines, and power plants) destructions. This calls for developing control and operation methods and planning strategies to improve grid resilience against such events. The first step toward this goal is to develop resilience metrics and evaluation methods to compare planning and operation alternatives and to provide techno-economic justifications for resilience enhancement. Although several power system resilience definitions, metrics, and evaluation methods have been proposed in the literature, they have not been universally accepted or standardized. This paper provides a comprehensive and critical review of current practices of power system resilience metrics and evaluation methods and discusses future directions and recommendations to contribute to the development of universally accepted and standardized definitions, metrics, evaluation methods, and enhancement strategies. This paper thoroughly examines the consensus on the power system resilience concept provided by different organizations and scholars and existing and currently practiced resilience enhancement methods. Research gaps, associated challenges, and potential solutions to existing limitations are also provided.

/pdf/power-system-resilience-current-practices-challenges-and-3p0fxnyf6d.pdf

Power System Resilience: Current Practices, Challenges, and Future Directions

The decline of system inertia due to the increasing displacement of synchronous units by renewable units has introduced a major challenge on the frequency dynamics management of a power system. This paper discusses how fast-response battery energy storages can be used to maintain the frequency dynamic security. Immediately following a generation loss, the injections of batteries are adjusted instantly to ensure minimum power imbalance in the system. This control strategy is included in a novel formulation of the frequency dynamics constrained unit commitment, in which the impact of wind uncertainty is dealt with using interval-based optimization. The reformulation-linearization technique is applied to reformulate the original nonlinear model as a mixed-integer linear programming problem. Case studies on a six-bus system and the modified RTS-79 system demonstrate that the proposed method guarantees frequency security while still preserving economy without curtailing wind generation.

Frequency Dynamics Constrained Unit Commitment With Battery Energy Storage

With the fast development of information and communication technologies and wide application of them into power systems, our grids have evolved into cyber-physical systems. Due to this transformation, it becomes urgently significant to analyze the interactions between the cyber network and the physical network and optimize the operation of the well-known smart grid, especially for emergency response. In this paper, we propose a cyber-constrained optimal power flow model for the emergency response of smart grids. The proposed model takes into account the impacts of cyber networks upon power grids, and vice versa. However, the above model is highly nonlinear and the curse of dimensionality will occur even when we model intermediate systems explicitly, thus we further propose an extended maximum flow method as a solution. We conduct simulation studies on two standard IEEE test systems, and the results have proved the effectiveness of the proposed model and the efficiency of the solution methodology. This paper highlights the importance of redesigning a resilient operational paradigm from the cyber-physical point of view.

Cyber-Constrained Optimal Power Flow Model for Smart Grid Resilience Enhancement

Frequency dynamics constrained unit commitment with battery energy storage

/pdf/system-resilience-enhancement-smart-grid-and-beyond-1drtru3tef.pdf

Gang Huang

Papers

Integration of Preventive and Emergency Responses for Power Grid Resilience Enhancement

Frequency Dynamics Constrained Unit Commitment With Battery Energy Storage

Cyber-Constrained Optimal Power Flow Model for Smart Grid Resilience Enhancement

Frequency dynamics constrained unit commitment with battery energy storage

System resilience enhancement: Smart grid and beyond