The electricity infrastructure is a critical lifeline system and of utmost importance to our daily lives. Power system resilience characterizes the ability to resist, adapt to, and timely recover from disruptions. The resilient power system is intended to cope with low probability, high risk extreme events including extreme natural disasters and man-made attacks. With an increasing awareness of such threats, the resilience of power systems has become a top priority for many countries. Facing the pressing urgency for resilience studies, the objective of this paper is to investigate the resilience of power systems. It summarizes practices taken by governments, utilities, and researchers to increase power system resilience. Based on a thorough review on the existing metrics system and evaluation methodologies, we present the concept, metrics, and a quantitative framework for power system resilience evaluation. Then, system hardening strategies and smart grid technologies as means to increase system resilience are discussed, with an emphasis on the new technologies such as topology reconfiguration, microgrids, and distribution automation; to illustrate how to increase system resilience against extreme events, we propose a load restoration framework based on smart distribution technology. The proposed method is applied on two test systems to validify its effectiveness. In the end, challenges to the power system resilience are discussed, including extreme event modeling, practical barriers, interdependence with other critical infrastructures, etc.

Battling the Extreme: A Study on the Power System Resilience

Optimal scheduling of thermal-wind-solar power system with storage

Optimal daily generation scheduling of large hydro–photovoltaic hybrid power plants

Active power dispatch and reactive power optimization problems are usually handled separately in active distribution systems, aiming at minimizing the total generation cost or transmission losses. However, the separate optimization cannot achieve a global optimum scheme in distribution system operations. Moreover, the significant relationship between the active power and reactive power may pose great challenges to distribution system operations due to the uncertain nature of load demands and intermittent renewable energy resources. In this paper, using the branch flow model-based relaxed optimal power flow, we formulate a robust coordinated optimization problem for active and reactive powers as a mixed integer second-order cone (SOC) programming problem. Furthermore, in order to address the uncertainties, a two-stage robust optimization model is proposed to coordinate the on load tap changer ratios, reactive power compensators, and charge–discharge power of energy storage system to find a robust optimal solution. Then the column-and-constraint generation algorithm is applied to solve the proposed robust two-stage optimization model. In the relaxed optimal power flow, a stricter cut is added to speed up the computation process of the SOC relaxation in order to guarantee the exactness for representative cases, such as those with high penetration of distributed energy resources. Numerical results based on the 33-bus and 69-bus systems verify the effectiveness of the proposed method.

Robust Coordinated Optimization of Active and Reactive Power in Active Distribution Systems

Allocation of ESS by interval optimization method considering impact of ship swinging on hybrid PV/diesel ship power system

A fast and effective service restoration method is proposed for medium-voltage distribution system with distributed generators by combining intentional islanding of distributed generators with network reconfiguration to maximize restoration of out-of-service loads. The whole process is divided into four stages: 1) matching islanding schemes; 2) restoration of network connectivity and distributed generators; 3) network reconfiguration; and 4) optimization of load shedding. Whether the last three stages are executed or not depends on violations of operational constraints. In accordance with the topological feature of distribution system, a new concept of fundamental loop matrix is presented and applied in detecting out-of-service areas, restoration of network connectivity, and network reconfiguration. Simulation studies on the PG&E 69-bus system shows the effectiveness of the proposed approach.

A Multi-Stage Restoration Method for Medium-Voltage Distribution System With DGs

An interval optimization based day-ahead scheduling scheme for renewable energy management in smart distribution systems

Self-healing is a key characteristic and goal of smart grid, which is based on the classification of the operating states of the power system. With views to the differences between the distribution and transmission system in terms of the operation model and structural features, an essential difference can appear in the classification of operating states between these two systems. According to the characteristics of distribution system with distributed generations (DGs), a new method based on hierarchical classification is proposed to classify the operating states of distribution system with DGs. In this method, several important performances reflecting the operating conditions of distribution system are regarded as critical attributes, including external stability, reliability, integrity, and economy. Moreover, different transition paths and control targets in different states are proposed to demonstrate the effectiveness of the classification method, which aim at the safety and reliability of the distribution system operation. Finally, a control strategy based on state classification is presented to support the decision-making for the self-healing distribution system. A case study demonstrates the feasibility and effectiveness of the classification method for the operating states of distribution system.

Assessment Method and Indexes of Operating States Classification for Distribution System With Distributed Generations

The power failure models are a key to understand the mechanism of large scale blackouts In this letter, the similarity of blackouts in interconnected power grids (IPGs) and their subgrids is discovered by the fractal characteristics analysis to simplify the failure models of the IPG The distribution characteristics of blackouts in various subgrids are demonstrated based on the Kolmogorov–Smirnov (KS) test The fractal dimensions (FDs) of the IPG and its subgrids are then obtained by using the KS test and the maximum likelihood estimation The blackouts data in China were used to demonstrate the similarity of distribution characteristics and FDs of the IPG and its subgrids The results are consistent with the development of the power grids

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Fractal Characteristics Analysis of Blackouts in Interconnected Power Grid

Since distributed energy resources (DERs) can provide capacity in distribution system, distribution network reinforcement interacts with DER planning (DERP) for meeting load growth. This article proposes the coordination of distribution network reinforcement and DER planning in competitive market. The model is formulated as a multi-stage programming. In first stage, distribution companies (DISCOs) and DER aggregators (DERAs) make bidding plans for network reinforcements and DERP. In second stage, DSO checks the network security. If the check fails, DSO sends capacity signals to DISCOs and DERAs for more capacities. In third stage, the distributed market is cleared by DSO’s optimal operation problem and distribution locational marginal price (DLMP) is returned to DERAs as price signal. An iterative algorithm is proposed to solve the multi-stage model. The algorithm embodies the process of information interaction among DISCOs, DERAs, and DSO, where DISCOs and DERAs compete in capacity market under DSO’s supervision. Numerical results on IEEE 33-system and an actual 141-bus system demonstrate that the proposed model coordinates distribution network reinforcement and DERP in competitive market.

Feng Wang

Papers

A Multi-Stage Restoration Method for Medium-Voltage Distribution System With DGs

An interval optimization based day-ahead scheduling scheme for renewable energy management in smart distribution systems

Assessment Method and Indexes of Operating States Classification for Distribution System With Distributed Generations

Fractal Characteristics Analysis of Blackouts in Interconnected Power Grid

Coordination of Distribution Network Reinforcement and DER Planning in Competitive Market