Velin Kounev

Advanced Metering and Demand Response communication performance in Zigbee based HANs

Using IEEE 802.15.4 and Zigbee for home area networks (HANs) in the Smart Grid is becoming an increasingly prominent topic in the research area. As the standard designed for low data rate and low cost wireless personal area networks, IEEE 802.15.4 is widely employed in the construction of home sensor networks to assist with real-time environment information. For the purposes of Smart Grid the Zigbee Alliance has defined new Smart Energy Profile Protocol that leverages the existing TCP and HTTP protocols. In this paper, we provide an overview of the Smart Grids Advanced Metering Infrastructure (AMI) and Demand Response (DR) functionalities, and the communication requirement they pose for the new SEP protocol. The discussion is followed by an evaluation of the theoretical performance bounds of the new architecture based on a analytical model. We conclude, by extending the model to account for WiFi interference which is expected to be present in home and office environments.

A Secure Communication Architecture for Distributed Microgrid Control

Microgrids are a key component in the evolution of the power grid. Microgrids are required to operate in both grid connected and standalone island mode using local sources of power. A major challenge in implementing microgrids is the communications and control to support transition from grid connected mode and operation in island mode. Here, we propose a secure communication architecture to support microgrid operation and control. A security model, including network, data, and attack models, is defined and a security protocol to address the real-time communication needs of microgrids is proposed. The implementation of the proposed security scheme is discussed and its performance evaluated using theoretical and co-simulation analysis, which shows it to be superior to existing protocols.

Automatic evaluation of information provider reliability and expertise

Q&A social media have gained a lot of attention during the recent years. People rely on these sites to obtain information due to a number of advantages they offer as compared to conventional sources of knowledge (e.g., asynchronous and convenient access). However, for the same question one may find highly contradicting answers, causing an ambiguity with respect to the correct information. This can be attributed to the presence of unreliable and/or non-expert users. These two attributes (reliability and expertise) significantly affect the quality of the answer/information provided. We present a novel approach for estimating these user’s characteristics relying on human cognitive traits. In brief, we propose each user to monitor the activity of his peers (on the basis of responses to questions asked by him) and observe their compliance with predefined cognitive models. These observations lead to local assessments that can be further fused to obtain a reliability and expertise consensus for every other user in the social network (SN). For the aggregation part we use subjective logic. To the best of our knowledge this is the first study of this kind in the context of Q&A SNs. Our proposed approach is highly distributed; each user can individually estimate the expertise and the reliability of his peers using his direct interactions with them and our framework. The online SN (OSN), which can be considered as a distributed database, performs continuous data aggregation for users expertise and reliability assesment in order to reach a consensus. In our evaluations, we first emulate a Q&A SN to examine various performance aspects of our algorithm (e.g., convergence time, responsiveness etc.). Our evaluations indicate that it can accurately assess the reliability and the expertise of a user with a small number of samples and can successfully react to the latter’s behavior change, provided that the cognitive traits hold in practice. Furthermore, the use of the consensus operator for the aggregation of multiple opinions on a specific user, reduces the uncertainty with regards to the final assessment. However, as real data obtained from Yahoo! Answers imply, the pairwise interactions between specific users are limited. Hence, we consider the aggregate set of questions as posted from the system itself and we assess the expertise and realibility of users based on their response behavior. We observe, that users have different behaviors depending on the level at which we are observing them. In particular, while their activity is focused on a few general categories, yielding them reliable, their microscopic (within general category) activity is highly scattered.

A microgrid co-simulation framework

Microgrids have been proposed as a key piece of the Smart Grid vision to enable the potential of renewable energy generation. Microgrids are required to operate in both grid connected and standalone island mode using local sources of power. A major challenge in implementing microgrids is the communications and control to support transition to and from grid connected mode and operation in island mode. Microgrids consists of two interdependent networks, namely; the power distribution and data communication networks. To accurately capture the overall operation of the system, we propose a co-simulation model driven by embedded power controllers. Further, we propose a novel co-simulation scheduler taking into account events from both the power and communication network simulators, as well as the timing of each embedded controllers execution loop to adaptively synchronize both simulators efficiently. The approach ensures minimal synchronization error while still providing the ability to simulate extended operational scenarios. The numerical results illustrate the novelty of the propose co- simulation to study the microgrid power and communication networks interactions, and the effect on the power stability.

Reliable Communication Networks for Smart Grid Transmission Systems

In this paper, we discuss the communications reliability requirements posed by the smart power grid with a focus on communications in support of wide area situational awareness. Implementation of wide area situational awareness relies on both transmission substation networks and wide area optical networks. We study the reliability of a sample communications network of the California Power Grid and find that its reliability falls short of proposed requirements. To overcome this issue, we consider the problem of designing the substation network and the wide area network to meet the reliability requirements while minimizing the network cost. For the wide area network design problem, we propose two alternate design approaches, namely: (1) following the power lines and (2) a mesh based design interconnecting the nodes. For the first approach we develop two greedy iterative heuristics and a heuristic integer linear programming (H-ILP) model using minimum cut-sets for network reliability optimization. The greedy iterative algorithms outperform the H-ILP approach in terms of cost, but require a larger amount of computing resources. Both proposed models are in fact complementary and thus provide a framework to optimize the reliability of smart grid communications networks restricted to following the power lines. In the second approach a greenfield mesh network method is proposed based on starting with a minimum spanning tree which is then augmented through a greedy heuristic into a mesh. Comparative numerical results show that the reliable mesh design has advantages in terms of the number of links and total link distance needed.

An effective algorithm for computing all-terminal reliability bounds

The exact calculation of all-terminal reliability is not feasible in large networks. Hence estimation techniques and lower and upper bounds for all-terminal reliability have been utilized. Here, we propose using an ordered subset of the mincuts and an ordered subset of the minpaths to calculate an all-terminal reliability upper and lower bound, respectively. The advantage of the proposed new approach results from the fact that it does not require the enumeration of all mincuts or all minpaths as required by other bounds. The proposed algorithm uses maximally disjoint minpaths, prior to their sequential generation, and also uses a binary decision diagram for the calculation of their union probability. The numerical results show that the proposed approach is computationally feasible, reasonably accurate and much faster than the previous version of the algorithm. This allows one to obtain tight bounds when it not possible to enumerate all mincuts or all minpaths as revealed by extensive tests on real-world networks.

Analysis of an Offshore Medium Voltage DC Microgrid Environment - Part II: Communication Network Architecture

The microgrid is a conceptual solution proposed as a plug-and-play interface for various types of renewable generation resources and loads. The high-level technical challenges associated with microgrids include (1) operation modes and transitions that comply with IEEE1547 and (2) control architecture and communication. In Part I, the emphasis is on the design of an electrical control architecture for an offshore oil drilling platform powered by wind generation. Engineering a distributed control system having safety critical features, requiring real-time performance is challenging. In this follow-up article we introduce the communication framework for the microgrid scenario under investigation. In all communication networks, scholastic delays and performance are inherent. The only feasible approach is to put bounds on the random processes, qualitatively define the worst cases, and build the distributed control system to be resilient enough to tolerate those behaviors. This is the approach taken by this paper. We propose a communication architecture, discuss performances requirements of the sub-systems, and layout network solutions meeting those specifications.

Analysis of an offshore medium voltage DC microgrid environment — Part I: Power sharing controller design

The AC microgrid is proposed as a plug-and-play interface for various types of renewable generation resources. The fundamental microgrid requirements include the capability of operating in islanding mode and/or grid connected modes. The high-level technical challenges associated with microgrids include (1) operation modes and transitions that comply with IEEE1547 and (2) control architecture and communication. Proposed control layers and respective functions have been defined in the microgrid literature. These layers include the primary, secondary and tertiary control. In this work, the focus is on the design of a power management secondary control for an offshore DC microgrid serving induction motor drives. The power is managed through a secondary controller to adjust the power delivered through bidirectional DC/DC converters, which intertie with the inverters connected to the machine loads. Simulations in Matlab/Simulink demonstrate the system performance under a mechanical torque step change for one motor drive unit with other conditions fixed. Part I of the concept emphasizes the electrical layout and part II, a communication layout of the offshore platform is described.

On smart grid communications reliability

In this paper, we discuss the communications reliability requirements posed by the smart power grid with a focus on communications in support of wide area situational awareness. Implementation of wide area situational awareness relies on both transmission substation networks and wide area optical networks. We study the reliability of a sample communications network of the California Power Grid and find that its reliability falls short of proposed requirements. To overcome this issue, we consider the problem of designing the network to meet the reliability requirements while minimizing the network cost. Therefore, we propose two greedy iterative heuristics and a heuristic integer linear programming (H-ILP) model using minimum cut-sets for network reliability optimization. The greedy iterative algorithms outperform the H-ILP approach in terms of cost, but require a larger amount of computing resources. Both proposed models are in fact complementary and thus provide a framework to optimize the reliability of smart grid communications networks.

An algorithm for computing all-terminal reliability bounds

The exact calculation of all-terminal reliability is not feasible in large networks. Hence estimation techniques and lower and upper bounds for all-terminal reliability have been utilized. We propose using an ordered subset of the mincuts and an ordered subset of minpaths to calculate an all-terminal reliability upper and lower bound, respectively. The advantage of the proposed approach results from the fact that it does not require the enumeration of all mincuts or all minpaths as required by other bounds. The performance of the algorithm is compared with the first two Bonferroni bounds, for networks where all mincuts could be calculated. The results show that the proposed approach is computationally feasible and reasonably accurate. Thus allowing one to obtain bounds when it not possible to enumerate all mincuts or all minpaths.