This paper presents a new hierarchical approach to deal with the problem of controlling frequency and active power generation of a medium voltage network comprising several microgrids and distributed generation sources operated in islanded mode. The hierarchical approach described here should be cost effective and capable of dealing with large numbers of distributed microsources and performing tasks related to coordinated frequency control.

SUMMARYLarge scale integration of distributed generation of both medium and low voltage (LV) networks can be achieved by exploiting the Multi-MicroGrid (MMG) concept, a new distribution system architecture comprising a hierarchical control system, which allows the coordination among distributed generation units and MicroGrids (MGs) and therefore the operation of such a system in islanded mode. After a general blackout the MMG capabilities can also be used to provide service restoration in distribution systems. A new procedure for MMGs black start is then addressed in this paper. A sequence of control actions is defined and evaluated through numerical simulations. Fully automation of the entire MMG black start procedure is discussed along the paper. The results obtained demonstrate the feasibility of the proposed sequence of control actions and highlight some accomplishments that should be considered in order to successfully restore the MMG service, ensuring system stability and power quality.

SUMMARYThis paper addresses the extension of the microgrid concept, following a massive integration of these active cells in power distribution networks, by adopting a coordinated management strategy together with distributed generation units directly connected to the medium voltage distribution network. In order to achieve this, a technical and commercial management scheme must be developed for coordinated control of a distribution system with multi-microgrids, which should take into account the specific technical capabilities and characteristics of each type of generating source. In particular, tools for coordinated voltage support and frequency control, as well as for state estimation have been developed for this type of network. Concerning voltage support, a new methodology exploiting an optimization tool based on a metaheuristic approach was developed. For state estimation, two approaches were considered: multi-microgrid state estimation and fuzzy state estimation. Regarding frequency control, the hierarchical structure of the multi-microgrid is exploited to deal with the transition to islanded operation and load following in islanded operation. All these tools have proved to be efficient in managing the multi-microgrid system in normal interconnected mode and, in case of the frequency control, in islanded operation.

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This paper presents a decentralized architecture for the islanding operation of distribution grids with large volume of distributed generation. This architecture involves the definition of network blocks which share the responsibility of frequency control. The control block abstraction was particularly designed to support the transition from regular grids to smart grids. In addition, the control schemes were developed using an agentbased paradigm. Hence, an agent-based simulation platform was implemented using libraries from the Java Agent Development Framework (JADE). The control schemes were evaluated using a test system with different sorts of distributed energy resources and modeled in the EUROSTAG environment. Simulation results show the effectiveness of the control architecture when different failure events are applied to the test system.