Catalin Gavriluta

In this paper we propose an approach for automatically building real-time emulations of large scale cyber-physical energy systems. An end-to-end methodology is presented, starting from the system description, continuing with automatic model and interface generation, and finally completing with deployment and real-time execution. The intended target use of the proposed solution is the validation of massively distributed smart-grid software applications. The goal is to provide an automated testing framework that can be integrated in modern software development tool-chains. In this manner, complex software ecosystems that act on critical infrastructure can be exhaustively evaluated and validated before being deployed in the field. A prototypical implementation is also presented. This relies on a commercially available real-time simulator whose digital interfacing capabilities were extended in order to meet our automation requirements. As a showcase we consider the problem of generator dispatch using a distributed optimal power flow algorithm. For this example application we consider two test scenarios: one consisting of a smaller network where 13 software agents are deployed, and a larger one involving 123 software agents. Using the proposed framework, scaling the test setup is automated, considerably reducing the required time and errors that typically appear during this process.

The Electromagnetic Time Reversal (EMTR) method has been receiving a lot of attention in the last years as an effective method to localize faults in electrical grids by analyzing transient signals induced by the fault. In this paper we first underline some of the limitations of EMTR when applied in real networks. Then, we propose a new metric based on spectrum similarity between the recorded signal and the fault-to-sensor frequency response of the network. Unlike similar approaches in the literature, this metric requires no information regarding the fault instant. Afterwards, we argue the need of multiple sensors to address the limitations of fault observability in complex network topologies. A novel algorithm for optimal sensor placement is introduced, which uses observability indices to determine the most effective sensor locations. This ensures maximum fault detection coverage, even in networks characterized by significant characteristic impedance variations between overhead lines and underground cables. Extensive simulations on two real medium-voltage distribution networks consisting of 32 and 161 buses respectively, are performed to illustrate the effectiveness and scalability of the proposed approach.

In this article, a distributed hierarchical control framework with coordinated secondary and tertiary levels is proposed for islanded microgrids (MGs). The structure and functionality of each agent are formulated to process simultaneously the secondary control and TC in a peer-to-peer communication network. First, the distributed secondary control is proposed for restoring system frequency/voltage while providing power sharing considering droop coefficients and upper level power dispatch orders. Then the distributed TC minimizes the network power loss in the islanded MG by using alternating direction method of multipliers (ADMM) algorithm. The multiagent system is designed to cover both control levels for cyber–physical implementations. A laboratory cyber–physical MG platform has been built to validate the proposed control framework in real-time and hardware-in-the-loop conditions. A six-bus three-DG MG is implemented on the platform and the experimental results validate the effectiveness of the proposed method.

Distributed control and optimization strategies are a promising alternative approach to centralized control within microgrids. In this paper, a multi-agent system is developed to deal with the distributed secondary control of islanded microgrids. Two main challenges are identified in the coordination of a microgrid: (i) interoperability among equipment from different vendors; and (ii) online re-configuration of the network in the case of alteration of topology. To cope with these challenges, the agents are designed to communicate with physical devices via the industrial standard IEC 61850 and incorporate a plug and play feature. This allows interoperability within a microgrid at agent layer as well as allows for online re-configuration upon topology alteration. A test case of distributed frequency control of islanded microgrid with various scenarios was conducted to validate the operation of proposed approach under controller and power hardware-in-the-loop environment, comprising prototypical hardware agent systems and realistic communications network.

Virtual primary frequency regulation (VPFR) is a coordinated demand and generation response, which is proposed to counteract post-disturbance frequency fluctuations and deviations. But meanwhile, it also influences oscillation stability. VPFR's continuity, slope and response time are three characteristics that have large influences on oscillation stability. Due to uncertainties of these characteristics, VPFR's influences are nondeterministic and random. In order to analyze them, first, VPFR is modeled and combined with existing models of power systems for eigenvalue analysis. The repeated LHS method is developed to more efficiently sample uncertainties. Eigenvalue analysis is repeatedly made for each sampling to estimate mean values of participation factors and distributions of damping ratios for critical modes. The former indicate where VPFR increases system damping, where not. The latter show the influences of regulation parameters on damping ratios for VPFR at a selected location. Utilizing this statistical information, system operators can select VPFR's locations and parameters through price signals to improve system damping. Two test cases on a 16-generator, 68-bus system show that VPFR implemented in this way can improve oscillation stability as well as frequency stability. Finally, VPFR's performance is further investigated with motor-type loads.

This paper deals with the hierarchical control architecture of meshed multi-terminal dc (MTDC) networks. The key difference with previous works is that the customarily adopted centralized secondary control is replaced by a fullydistributed, agent-based approach, in which the nodes of the network cooperate and self-coordinate in order to bring the network to an optimal operating state. The paper covers the theoretical aspects and shows how, by setting the problem as a general consensus problem and by making use of modern optimization techniques such as the alternating direction of multipliers (ADMM), the optimal power flow (OPF) problem of a dc grid can be solved in a distributed manner. The proposed method is validated on a network with 27 nodes obtained by properly adapting a 30 bus ac network.