Showing papers by "Chen-Ching Liu published in 2018"
••
TL;DR: A resiliency-based methodology that uses microgrids to restore critical loads on distribution feeders after a major disaster is proposed, resulting in a strategy that uses generators on the Washington State University campus to restore service to the Hospital and City Hall in Pullman.
Abstract: Microgrids can act as emergency sources to serve critical loads when utility power is unavailable. This paper proposes a resiliency-based methodology that uses microgrids to restore critical loads on distribution feeders after a major disaster. Due to limited capacity of distributed generators (DGs) within microgrids, dynamic performance of the DGs during the restoration process becomes essential. In this paper, the stability of microgrids, limits on frequency deviation, and limits on transient voltage and current of DGs are incorporated as constraints of the critical load restoration problem. The limits on the amount of generation resources within microgrids are also considered. By introducing the concepts of restoration tree and load group, restoration of critical loads is transformed into a maximum coverage problem, which is a linear integer program (LIP). The restoration paths and actions are determined for critical loads by solving the LIP. A 4-feeder, 1069-bus unbalanced test system with four microgrids is utilized to demonstrate the effectiveness of the proposed method. The method is applied to the distribution system in Pullman, WA, resulting in a strategy that uses generators on the Washington State University campus to restore service to the Hospital and City Hall in Pullman.
318 citations
••
TL;DR: A state-of-the-art survey of the most relevant cyber security studies in power systems and a demonstration is provided to show how the proposed defense systems can be deployed to protect a power grid against cyber intruders.
308 citations
••
TL;DR: This paper will present a method of using end-use loads equipped with grid friendly appliance controllers to facilitate the switching operations between multiple microgrids; operations that are necessary for optimal operations when islanded for resiliency.
Abstract: Changes in economic, technological, and environmental policies are resulting in a re-evaluation of the dependence on large central generation facilities and their associated transmission networks. Emerging concepts of smart communities/cities are examining the potential to leverage cleaner sources of generation, as well as integrating electricity generation with other municipal functions. When grid connected, these generation assets can supplement the existing interconnections with the bulk transmission system, and in the event of an extreme event, they can provide power via a collection of microgrids. To achieve the highest level of resiliency, it may be necessary to conduct switching operations to interconnect individual microgrids. While the interconnection of multiple microgrids can increase the resiliency of the system, the associated switching operations can cause large transients in low inertia microgrids. The combination of low system inertia and IEEE 1547 and 1547a-compliant inverters can prevent multiple microgrids from being interconnected during extreme weather events. This paper will present a method of using end-use loads equipped with grid friendly appliance controllers to facilitate the switching operations between multiple microgrids; operations that are necessary for optimal operations when islanded for resiliency.
62 citations
••
TL;DR: By solving the MDP models, the optimal strategies (action policies) of both the attacker and defender can be obtained and the cyber security status of a substation can be evaluated within varied time frames.
Abstract: Cyber intrusions to substations are critical issues to a power grid, which must be defended and mitigated. Essentially, to better understand a cyber intrusion, reconnaissance activities should be modeled. Then, strategies of cyber attacker and defender can be studied, which help to identify substations vulnerable to cyber-attacks. In this paper, a successful intrusion is regarded as a probabilistic event related to reconnaissance activities. Its probability can be approximated by the Poisson distribution of the number of vulnerabilities discovered by the attacker. Furthermore, models of intrusion and defense in competition for control of the substations are proposed using Markov decision process (MDP). Key characteristics of target substation, attacker and defender are considered for determining probabilistic state transitions related to intrusion and defense actions. Thus, by solving the MDP models, the optimal strategies (action policies) of both the attacker and defender can be obtained. With these optimal strategies, the cyber security status of a substation can be evaluated within varied time frames. The case study validates the proposed models and method, including time-based strategies of the attacker and defender.
58 citations
•
Wichita State University1, University of Nevada, Reno2, University of Oklahoma3, University of Idaho4, Virginia Tech5, Michigan State University6, Electric Power Research Institute7, University of Utah8, Texas A&M University9, Washington State University10, Durham University11, Delft University of Technology12
TL;DR: The objective of this paper is to define the three-layer model and report a generalized framework for combined reliability modeling and evaluation for power system planning and operations.
Abstract: Power system operation considering an increasingly complex cyber infrastructure may be one of the key factors of the next generation power systems. The effective operation of a power system in a massively deployed cyber network environment will be affected by cyber network reliability. Therefore, it is vital not only to understand the operation of a cyber network and its reliability, but also it is critical to integrate the interdependency of cyber and power systems into power system planning and operations. This requires a three-layer approach to reliability modeling and evaluation. The cyber and power layers are interconnected by the information layer. The objective of this paper is to define the three-layer model and report a generalized framework for combined reliability modeling.
17 citations
••
TL;DR: Three educational modules allow students to learn the concepts of a cyber–physical system and an electricity market through an integrated testbed through industrial level visualization in an industry-grade distribution management system.
Abstract: At Washington State University, a modern cyber–physical system testbed has been implemented based on an industry-grade distribution management system (DMS) that is integrated with remote terminal units, smart meters, and a solar photovoltaic array. In addition, the real model from the Avista Utilities distribution system in Pullman, WA, is modeled in DMS. The proposed testbed environment allows students and instructors to utilize these facilities for innovations in learning and teaching. For power engineering education, this testbed helps students understand the interaction between a cyber system and a physical distribution system through industrial level visualization. The testbed provides a distribution system monitoring and control environment for students. Compared with a simulation-based approach, the testbed brings the students’ learning environment a step closer to the real world. The educational modules allow students to learn the concepts of a cyber–physical system and an electricity market through an integrated testbed. Furthermore, the testbed provides a platform in the study mode for students to practice working on a real distribution system model. This paper describes the new educational modules based on the testbed environment. Three modules are described together with the underlying educational principles and associated projects.
15 citations
•
TL;DR: Numerical tests on a modified IEEE 37-bus feeder demonstrate that the proposed mixed-integer linear program (MILP) takes less than four seconds to handle random outages of 1–5 lines.
Abstract: Increasing emphasis on reliability and resiliency call for advanced distribution system restoration (DSR). The integration of grid sensors, remote controls, and distributed generators (DG) brings about exciting opportunities in DSR. In this context, this work considers the task of single-step restoration of a single phase power distribution system. Different from existing works, the devised restoration scheme achieves optimal formation of islands without heuristically pre-identifying reference buses. It further facilitates multiple DGs running within the same island, and establishes a coordination hierarchy in terms of their PV/PQ operation modes. Generators without black-start capability are guaranteed to remain connected to a black-start DG or a substation. The proposed scheme models remotely-controlled voltage regulators exactly, and integrates them in the restoration process. Numerical tests on a modified IEEE 37-bus feeder demonstrate that the proposed mixed-integer linear program (MILP) takes less than four seconds to handle random outages of 1-5 lines. The scalability of this novel MILP formulation can be attributed to the unique use of cycles and paths on the grid infrastructure graph; the McCormick linearization technique; and an approximate power flow model.
11 citations
••
16 Apr 2018TL;DR: This paper purposes a method for developing a time-series distribution power-flow model using text-based AMI load data which may contain calculation failures, and provides ways to deal with had data.
Abstract: The electric distribution system is becoming more complex with increasing visibility, and a variety of control devices for voltage and power factor control. These advancements provide improved observability of system status and let the operator control the system in more efficient ways. Smart meters are measurement devices that allow the operator to acquire accurate information about the end consumers, and state of the system. Smart meters provide the opportunity to revisit traditional distribution system models in an effort to improve them with more accurate information. Smart meter data enables the creation of time-varying load based distribution system models, enabling testing of various control algorithms. This paper purposes a method for developing a time-series distribution power-flow model using text-based AMI load data which may contain calculation failures. As a test case, a real distribution feeder is modeled in the open source distribution software GridLAB-D, with seasonal loading scenarios. The results are verified by DMS data obtained from the utility. The proposed method does not require GIS data for creating distribution system model. and also provides ways to deal with had data.
9 citations
•
TL;DR: In this paper, a two-layer, four-level distributed control method for networked microgrid (NMG) systems, taking into account the proprietary nature of microgrid owners, is presented.
Abstract: This paper presents a two-layer, four-level distributed control method for networked microgrid (NMG) systems, taking into account the proprietary nature of microgrid (MG) owners. The proposed control architecture consists of a MG-control layer and a NMG-control layer. In the MG layer, the primary and distrib-uted secondary control realize accurate power sharing among distributed generators (DGs) and the frequency/voltage reference following within each MG. In the NMG layer, the tertiary control enables regulation of the power flowing through the point of common coupling (PCC) of each MG in a decentralized manner. Furthermore, the distributed quaternary control restores system frequency and critical bus voltage to their nominal values and ensures accurate power sharing among MGs. A small-signal dynamic model is developed to evaluate dynamic performance of NMG systems with the proposed control method. Time-domain simulations as well as experiments on NMG test systems are performed to validate the effectiveness of the proposed method.
7 citations
••
01 Sep 2018TL;DR: A bilateral Transactive Energy coordination framework is developed to manage the grid participants’ trading activities and the results indicate the effectiveness of the proposed mechanism and the approach to achieve optimal bilateral transactions.
Abstract: The power grid is being transformed from a system with centralized fossil-fuel-based generation and passive customers into the one with a large-scale deployment of distributed energy resources (DERs) and proactive customers. At the distribution level, centralized and decentralized market constructs have been proposed; however, these methods are not well suited for the coordination of a large number of DERs and responsive loads. In this paper, a bilateral Transactive Energy coordination framework is developed to manage the grid participants’ trading activities. The proposed method consists of long-term bilateral transactions, an optimal social welfare based real-time adjustment stage, and a settlement phase. The IEEE 123 node distribution feeder is used to validate the proposed method. The results indicate the effectiveness of the proposed mechanism and the approach to achieve optimal bilateral transactions.
3 citations
••
TL;DR: In this article, a decision-making method to determine the optimal restoration strategy coordinating multiple sources to serve critical loads after blackouts is proposed, where the objective is maximizing the number of loads restored, weighted by their priority.
Abstract: When a major outage occurs on a distribution system due to extreme events, microgrids, distributed generators, and other local resources can be used to restore critical loads and enhance resiliency. This paper proposes a decision-making method to determine the optimal restoration strategy coordinating multiple sources to serve critical loads after blackouts. The critical load restoration problem is solved by a two-stage method with the first stage deciding the post-restoration topology and the second stage determining the set of loads to be restored and the outputs of sources. In the second stage, the problem is formulated as a mixed-integer semidefinite program. The objective is maximizing the number of loads restored, weighted by their priority. The unbalanced three-phase power flow constraint and operational constraints are considered. An iterative algorithm is proposed to deal with integer variables and can attain the global optimum of the critical load restoration problem by solving a few semidefinite programs under two conditions. The effectiveness of the proposed method is validated by numerical simulation with the modified IEEE 13-node test feeder and the modified IEEE 123-node test feeder under plenty of scenarios. The results indicate that the optimal restoration strategy can be determined efficiently in most scenarios.