Showing papers by "Chen-Ching Liu published in 2015"

Toward a resilient distribution system

Abstract: Resiliency with respect to extreme events, such as a major hurricane, is considered one of the key features of smart distribution systems by the U.S. Department of Energy (DOE). In this paper, approaches to resilient distribution systems are reviewed and analyzed. Three important measures to enhance resiliency, i.e., utilization of microgrids, distribution automation (DA), and vulnerability analysis, are discussed. A 4-feeder 1069-node test system with microgrids is simulated to demonstrate the feasibility of these measures.

SCADA modeling for performance and vulnerability assessment of integrated cyber–physical systems

Abstract: Summary On top of the power infrastructure reside information and communication technology (ICT) layers for monitoring and control of the grid. The cyber and power systems together form a complex structure, which is referred to as a cyber–physical system (CPS). If the power system's observability and controllability are compromised due to communication and cyber security problems, the grid can be exposed to catastrophic events. As a result, there is a great need to model the interactions between ICT and power grids. This paper proposes a new model and simulation platform for the supervisory control and data acquisition (SCADA) system of an integrated CPS. SCADA performance is assessed based on communication time delays. Methods to model cyber intrusions and assess the CPS security are proposed. The success rates for unauthorized access and control of power devices are computed. The impact on the grid is evaluated and the attack with the highest efficiency is identified. The proposed method is tested with the IEEE 39-bus system on a SCADA testbed. Copyright © 2013 John Wiley & Sons, Ltd.

A co-simulation environment for integrated cyber and power systems

Abstract: Due to the development of new power technologies, cyber infrastructures have been widely deployed for monitoring, control, and operation of a power grid. Information and Communications Technology (ICT) provides connectivity of the cyber and power systems. As a result, cyber intrusions become a threat that may cause damages to the physical infrastructures. Research on cyber security for the power grid is a high priority subject for the emerging smart grid environment. A cyber-physical testbed is critical for the study of cyber-physical security of power systems. For confidentiality, measurements (e.g., voltages, currents and binary status) and ICT data (e.g., communication protocols, system logs, and security logs) from the power grids are not publicly accessible. Therefore, a realistic testbed is a good alternative for study of the interactions between physical and cyber systems of a power grid.

Coordinating generation and load pickup during load restoration with discrete load increments and reserve constraints

Abstract: After a major outage happens, the independent system operator, transmission owners (TOs), generation owners (GOs), and distribution owners (DOs) should coordinate control actions to restore the power system timely and reliably. This study proposes a methodology to establish load restoration plans for the coordination among these participants. This methodology models the load restoration as a multi-stage decision-making process. At each stage, a mixed-integer nonlinear load restoration model (MINLR) is formulated to maximise load pickup subject to AC power flow and reserve constraints. Comprehensive load characteristics are considered in this model. The solution of the MINLR model provides power set points for GOs/TOs and load pickup amount for DOs. A complete load restoration plan is obtained by solving a series of MINLR models. To solve MINLR models efficiently, a branch-and-cut solver is constructed by identifying efficient cutting planes and a reliable problem-specific branching method. The applicability of cutting planes is proven. This methodology is tested using a 24-bus system with 170 interrupted load increments, and a 118-bus system with 637 interrupted load increments. The simulation results show that the proposed methodology can be efficiently applied to aid restoration participants pickup load increments within the TO’s islands, while maintaining adequate reserve margins.

Reliability analysis of distribution systems considering service restoration

Abstract: Distribution system restoration (DSR) is intended to restore service to interrupted customers by a sequence of switching operations. An effective DSR strategy reduces interruption duration and consequently enhances reliability of distribution systems. In this paper, a systematic method is proposed for reliability analysis of smart distribution systems with DSR technique and remote control capability. The spanning tree search algorithm is used to generate optimal DSR schemes that restore the maximal amount of load with a minimal number of switching operations. Switching sequence is decided by a set of rules. Breadth-first search technique is used to determine the restoration time for customers. A 4-feeder 1069-node unbalanced test system with microgrids, developed by Pacific Northwest National Laboratory (PNNL), is simulated to demonstrate the effectiveness of the proposed method.

Cyber-Physical Security Testbed for Substations in a Power Grid

Abstract: The physical system of the power grids relies on the cyber system for monitoring, control, and operation. As a result, the reliable operation of power grids is highly dependent on the associated cyber infrastructures. The integrated cyber and physical system of power grids creates a large and complex infrastructure. Due to the high penetration of Information and Communications Technology (ICT), Supervisory Control And Data Acquisition (SCADA) systems are highly interconnected with one another, resulting in higher vulnerability with respect to cyber intrusions. Recent reports indicate that cyber-attacks are increasingly likely for the critical infrastructures, e.g., control centers, nuclear power plants, and substations. These attacks may cause significant damages on the power grid. Cyber security research for the power grid is a high priority subject for the emerging smart grid environment.

Risk assessment framework for power control systems with PMU-based intrusion response system

Abstract: Cyber threats are serious concerns for power systems. For example, hackers may attack power control systems via interconnected enterprise networks. This paper proposes a risk assessment framework to enhance the resilience of power systems against cyber attacks. The duality element relative fuzzy evaluation method is employed to evaluate identified security vulnerabilities within cyber systems of power systems quantitatively. The attack graph is used to identify possible intrusion sce- narios that exploit multiple vulnerabilities. An intrusion response system (IRS) is developed to monitor the impact of intrusion scenarios on power system dynamics in real time. IRS calculates the conditional Lyapunov exponents (CLEs) on line based on the phasor measurement unit data. Power system stability is predicted through the val- ues of CLEs. Control actions based on CLEs will be suggested if power system instability is likely to happen. A generic wind farm control system is used for case study. The effectiveness of IRS is illustrated with the IEEE 39 bus system model.

Decision support for restoration of interconnected power systems using tie lines

Abstract: Existing system restoration strategies are primarily based on operators’ experience with no specific decision support tools. Restoration of interconnected grids in Europe is decentralised; restoration planning is limited to within the area of control for each national transmission system operator (TSO). Although coordination of restorative actions between TSOs is encouraged, few agreements exist. This study proposes a decision support methodology for system operators and restoration planners for restoration of interconnected grids. Solutions to optimal and coordinated utilisation of tie lines (TLs) are proposed. The proposed tool facilitates collaboration between TSOs affected by wide area blackouts. The decision support tool allows to adaptively develop restoration strategies based on system conditions, available resources and operating constraints. Optimisation algorithms are proposed to determine the optimal utilisation of TLs and/or black-start (BS) units to crank non-BS units. Optimal power flow problems are formulated for utilisation of TLs. They offer solutions for neighbouring TSOs to determine the extent to which TLs can be used without violating constraints. The proposed decision support tool is tested with IEEE 39-bus system.

Distributed underfrequency load shedding using a multi-agent system

Abstract: Underfrequency load shedding (UFLS) is critical for mitigation of large disturbances on a power grid. There are centralized and distributed UFLS methods. In this paper, the proposed distributed methodology uses a multi-agent system (MAS). The framework and classification of agents are presented. Steps for monitoring, estimation, and distributed computation are developed, implemented, and tested in a testbed environment. A comparison has been performed to show that the performance and capability of load shedding can be enhanced by the multi-agent scheme.

Intelligent physical security monitoring system for power substations

Abstract: Power substations are vulnerable with respect to malicious physical attacks. Various types of sensors and technologies are developed for enhancing the physical security of critical infrastructures. In this paper, the proposed intelligent substation physical security monitoring (ISPSM) system uses a multi-agent system (MAS) with the distributed Kalman filtering (DKF) algorithm. The system architecture and computational methods are presented. In addition, industry experience is considered. Data collected from a drill and computer simulations is used for validation of the proposed ISPSM system.

Improving Distribution Resiliency with Microgrids and State and Parameter Estimation

Abstract: ............................................................................................................................................ iii Acknowledgments ............................................................................................................................... v Acronyms and Abbreviations ...........................................................................................................vii 1.0 Introduction ................................................................................................................................ 1 1.1 Traditional Mitigation ........................................................................................................ 1 1.2 Distribution Resiliency ....................................................................................................... 1 2.0 Microgrids as a Resiliency Resource .......................................................................................... 3 2.1 Previous Work .................................................................................................................... 3 2.2 Asset Feasibility ................................................................................................................. 3 2.2.1 Dynamic considerations .......................................................................................... 4 2.2.2 Distribution line and transformer in-rush ................................................................ 7 2.2.3 Resilience-Oriented Service Restoration and Reconfiguration ............................. 11 2.2.4 Nomograms ........................................................................................................... 19 2.3 Consolidated approach ..................................................................................................... 22 3.0 Distribution-level State Estimation and Parameter Estimation ................................................ 25 3.1 Background and Introduction ........................................................................................... 25 3.2 Data and Measurements in Distribution Systems ............................................................. 28 3.3 Distribution System State Estimation............................................................................... 29 3.3.1 Weighted Least Squares Formulation for Distribution System State Estimation . 29 3.3.2 Simulation Studies ................................................................................................. 34 3.3.3 Case 6: IEEE 8500 Node Test System .................................................................. 38 3.4 Distribution System Parameter Estimation ...................................................................... 39 3.4.1 Methods ................................................................................................................. 40 3.4.2 Simulation Studies ................................................................................................. 42 3.5 Conclusions and Future Work .......................................................................................... 47 4.0 Conclusions .............................................................................................................................. 48