Abstract
This paper proposes a new methodology for coordinated voltage support in distribution networks with large integration of distributed generation and microgrids. Given the characteristics of the LV networks, it is shown that traditional control strategies using only reactive power control may not be sufficient in order to perform efficient voltage control. Therefore, microgeneration shedding must also be employed, especially in scenarios with extreme microgeneration penetration. An optimisation tool based on a meta-heuristic approach was developed to address the voltage control problem. In addition, neural networks were employed in order to decrease computational time, thus enabling the use of the tool for online operation. The results obtained revealed good performance of this control approach.

Abstract
In this paper, a proposal for an ancillary services (AS) market framework addressing voltage control in multi-microgrid systems is presented. This var market proposal for MV distribution systems can be adopted to involve Distributed Generation (DG) units and microgrids in AS provision. In the approach that was developed each player is given the opportunity to submit its bid to the var market and the market settlement is performed using an Optimal Power Flow (OPF) formulation in order to minimize the price of reactive power purchased by the Distribution System Operator (DSO). This market is based on var capacity use and runs daily after the scheduling of the generation units for a period of operation of one clay.

Abstract
This 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 meta-heuristic 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. Copyright (C) 2010 John Wiley & Sons, Ltd.

Abstract
The expected growth of Distributed Generation (DG) penetration in distribution systems will fundamentally alter both planning and operating procedures of Distribution Network Operators (DNO). This means that distribution networks can no longer be considered as a passive appendage to the transmission network and should be explored actively to take full advantage of the capabilities of DG units available and avoid technical problems (such as line overloading or poor voltage profiles) resulting from massive integration of this type of sources. Presently, when the capacity of the generation, transmission and distribution systems is exceeded, the traditional utility response is expanding or reinforcing existing circuits through large investments in power transformers, substations or distribution feeders. However, in some situations such as in congested metropolitan areas these actions can have prohibitive costs or simply be impossible due to space restrictions, for instance. Although current investment costs of many solutions for energy storage remain extremely high, recent developments and advances in both energy storage technologies and power electronic interfaces are opening new doors to the inclusion of Energy Storage Systems (ESS) as a potentially viable solution for modern power applications, including their use in distribution network planning and operation. This paper presents a heuristic approach for siting and sizing of ESS in distribution networks in order to maximize the capacity of DG that can be integrated in the grid without bringing technical problems to network operation. The proposed methodology enables a technical and economical comparison between a strategy based on ESS deployment and exploitation and typical traditional DNO grid reinforcement strategies. Several technologies for ESS were considered, each one with different costs and technical characteristics. The proposed methodology was validated using a real Portuguese Medium Voltage (MV) distribution network.

Abstract
Under normal operating conditions, a MicroGrid (MG) is interconnected with the Medium Voltage (MV) network. However, planned or unplanned events like maintenance or faults in the MV network, respectively, may lead to MG islanding. In order to deal with islanded operation and even black start following a general blackout, an emergency operation mode must be envisaged. Two possible control strategies were investigated and are described in this paper in order to operate a MG under emergency mode. A sequence of actions for a well succeeded black start procedure, involving microgeneration units, has also been identified contributing for an increase in distribution network reliability.