Aleksandar Dimitrovski

Boundary load flow solutions

The load flow is one of the most fundamental tools used in power system analysis. The need for a load flow approach, which would incorporate uncertainty into the solution process, has been long recognized. The boundary load flow finds solutions given uncertain nodal powers. Here, a new concept for finding accurate boundary load flow solutions given fuzzy/interval numbers is presented. Extending an idea from probabilistic load flow, an optimization procedure for implicitly defined functions is introduced. Test systems are used for performance evaluation and comparison between the new method and extant methods that give approximate solutions.

Time Synchronization Attack in Smart Grid: Impact and Analysis

Many operations in power grids, such as fault detection and event location estimation, depend on precise timing information. In this paper, a novel Time Synchronization Attack (TSA) is proposed to attack the timing information in smart grid. Since many applications in smart grid utilize synchronous measurements and most of the measurement devices are equipped with global positioning system (GPS) for precise timing, it is highly probable to attack the measurement system by spoofing the GPS. The effectiveness of TSA is demonstrated for three applications of phasor measurement unit (PMU) in smart grid, namely transmission line fault detection, voltage stability monitoring and event locationing. The validity of TSA is demonstrated by numerical simulations.

Design and Implementation of a Real-Time Off-Grid Operation Detection Tool from a Wide-Area Measurements Perspective

Real-time situational awareness tools are of critical importance to power system operators, especially during emergencies. The availability of electric power has become a linchpin of most post-disaster response efforts, because public and private sector services depend upon it. Knowledge of the scope and extent of facilities impacted, as well as the duration of their dependence on backup power, enables emergency response officials to plan for contingencies and provide a better overall response. Based on the measurement data acquired by the frequency disturbance recorders deployed in the North American power grids, an off-grid detection method is proposed and implemented. This method monitors the critical electrical loads and detects the transition of these loads from an on-grid operation to an off-grid operation, during which the loads are fed by an uninterrupted power supply or a backup generation system. The details of the detection algorithm are presented, and some case studies and off-grid detection scenarios are also provided to verify the effectiveness and robustness. This paper also presents the real-time implementation of this method and several effectively detected off-grid situations. Moreover, two visualization tools are developed to display the real-time system operation condition in an intuitive manor.

A Cross-Layer Defense Mechanism Against GPS Spoofing Attacks on PMUs in Smart Grids

Recent investigations have revealed the susceptibility of phasor measurement units (PMUs) to the time synchronization attack by spoofing its global positioning system (GPS). This paper proposes a cross-layer detection mechanism to fight against simultaneous attacks toward multiple PMUs. In the physical layer, we propose a GPS carrier-to-noise ratio (C/No) based spoofing detection technique. We apply the patch-monopole hybrid antenna to two GPS receivers and compute the difference between the standard deviation of each receivers C/No. The priori probability of spoofing is calculated from the distributions of the difference. A counter is embedded in the physical layer to identify the most suspicious PMU. In the upper layer, the spoofing attack is considered similarly to the bad data injection toward the power system. A trustworthiness evaluation, which is based on both the physical layer information and power grid measurements, is applied to identify the PMU being attacked. An experiment has been carried to validate the proposed algorithm.

Communication Infrastructure Design in Cyber Physical Systems with Applications in Smart Grids: A Hybrid System Framework

This paper provides a survey on communications in CPS and a tutorial of a unified framework, i.e., hybrid system featured by the co-existence of discrete and continuous system states, for the design of communication infrastructure in cyber physical system (CPS). First, CPS with communication infrastructure is modeled as a hybrid system, in which the discrete system state is the mode of the communication infrastructure while the continuous system state is the state of the physical dynamics. The dynamical system can be considered as being switched among multiple modes corresponding to the discrete system state. Then, the communication infrastructure design is converted to the problems of mode provisioning and scheduling. This framework is applied in the context of smart grid as a special example of CPS and is shown to achieve good performance via numerical simulations.

Impact of Wind Generation Uncertainty on Generating Capacity Adequacy

This paper addresses the issue of generating capacity adequacy in power systems with considerable share of wind generation. It shows on a hypothetical example derived from the WECC system (western US interconnection) how different percentages of wind penetration affect this adequacy. For this purpose, the popular LOLP-loss of load probability (or more accurately, LOLE-loss of load expectation) is used as an objective, probability based, index. It is compared to reserve margin, another popular, deterministic index. Two systems with the same reserve margin or largest unit reserve can have very different risks of being unable to serve the load. It is shown that this discrepancy exacerbates as wind penetration increases

An interdisciplinary approach to long-term modelling for power system expansion

This article describes an interdisciplinary approach to computer modelling of large-scale power systems over a long-term horizon. The goal is to simulate the interplay between the economic, technical and environmental factors in the system. Our approach is illustrated with a model based on data from the Western Electric Coordination Council (WECC). We present simulations to show the change in the WECC system over 20 years. We explain the challenge of simulating short-term behaviour such as hourly wholesale electricity prices within the longer-term model. The usefulness of the model is illustrated by showing simulated impacts on the WECC system due to a market for carbon allowances. This research demonstrates the importance of simulation models that are designed for interactive use by policymakers, engineers and researchers.

Combating time synchronization attack: a cross layer defense mechanism

A novel time synchronization attack (TSA) on wide area monitoring systems in smart grid has been identified recently. A cross layer detection mechanism is proposed to combat TSA in this paper. In the physical layer, we propose a G PS carrier carrier to noise ratio (C/No) based spoofing detection technique. In addition, a patch-monopole hybrid antenna is applied to receive GPS signal. By computing the standard deviation of the C/No difference from two GPS receivers, the a priori probability of spoofing detection is fed to the upper layer, where power system state is estimated and controlled. A trustworthiness based evaluation method is applied to identify the PMU being under TSA. Both the physical layer and upper layer algorithms are integrated to detect the TSA, thus forming a cross layer mechanism. Experiment is carried out to verify the effectiveness of the proposed TSA detection algorithm.

Applications of saturable-core reactors (SCR) in power systems

The study of the saturable-core reactor (SCR) can be traced back to 1900s. Although commonly used in electronic circuit applications, SCR has seldom been used in power system applications. In recent years, power engineers have raised interest in exploring applications of SCR in power systems. The SCR is low-cost and durable. Its nature of using the magnetic field as control medium makes it more familiar and, perhaps, more easily accepted by power utilities. In this paper, the basic concept of SCR and some existing or potential applications of SCR in power systems are introduced. A project on the R&D of a SCR-based power flow controller has been funded by the U.S. Department of Energy (DOE) and conducted by the Oak Ridge National Laboratory (ORNL), the University of Tennessee-Knoxville, and Waukesha Electric Systems, Inc. since early 2012. Some technical details of the project are presented and some preliminary results are highlighted.

Data Traffic Scheduling for Cyber Physical Systems With Application in Voltage Control of Distributed Generations: A Hybrid System Framework

The design of the communication infrastructure in cyber physical systems (CPSs) is of key importance since it conveys information from sensors to controllers. Scheduling in the medium access control layer, i.e., the selection of active communication links, plays an important role in improving efficiency of communication in CPS. Different from traditional scheduling algorithms designed for pure data communication networks, the scheduling in CPS is for the purpose of optimizing the physical dynamics and needs to be designed with awareness of the dynamics. In this paper, the scheduling problem in CPS is fitted into the framework of the hybrid systems, in which different selections of links correspond to different dynamic modes. Both centralized and distributed scheduling algorithms are designed. The proposed algorithms are also applied in the background of voltage control of distributed generations (DGs). Numerical simulations show that the proposed framework and algorithms achieve good performances.