During the last few years generation from renewable energy sources (RESs) has grown considerably in European electrical networks. Transmission system operators are greatly concerned about the impact of RESs on the operational security and efficiency of their networks and more in general of the ENTSO-E interconnected system. Grid codes are to be revised in order to harmonise the rules regarding the connection of RES power plants. A main issue concerns frequency control: frequency is greatly affected by RESs intermittency and its deviations must be limited as much as possible in order to guarantee a suitable level of power quality. To improve frequency stability, in the future, Grid codes could extend frequency control requirements also to RES units, whereas today they are applied only to conventional power plants. Energy storage systems can be a possible solution to increase the flexibility and performance of RES power plants: they allow generators to modulate their power injections without wasting renewable energy. In this paper, the authors studied the suitability of extending frequency control to RES units integrating them with energy storage systems. In particular, the paper focuses on the impact of frequency control on the storage lifetime by analysing the power charge/discharge in response to real frequency oscillations.

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This paper describes the possible evolution of Italian distribution system in facing the growing penetration of Dispersed Generation (DG), in the perspective of smart grids.As for the Italian system, after discussing the Hosting Capacity of MV distribution networks, it is recognized that some challenges are to be faced due to the increasing amount of DG. Even though current technology provides satisfactory solutions to manage this new situation, loss-of-mains protection (LOM) is one of the most critical issues to be faced, at least for the Italian system. Only an intelligent use of Information and Communication Technology (ICT) will overcome the current limitations and make possible a larger DG penetration without hindering system security.Milano Wi-Power is a project undertaken by Politecnico di Milano dealing with the critical aspects of the communication systems applied to distribution networks. The specific goal is to test and validate, both through simulations and field trials, possible communication systems able to connect primary substations with DG units along the network.

The development of the Dispersed Generation (DG) in Distribution Networks (DN) requires new planning and operational tools. The Distribution Company takes the role of the Distribution System Operator (DSO) that has to manage the network from many points of view; in particular, DSOs need advanced tools to manage DNs with respect to security, reliability and quality constraints, and to improve the Hosting Capacity (HC) of the system. To fulfill these goals, it is necessary to estimate the state of the network in different operating conditions, also considering the DG. Moreover, the new standard framework requires that the DG provides, among others, reactive support. The paper presents the preliminary results of the INGRID 2 project, which is the product of the collaboration among Politecnico di Milano, SIEMENS SpA and Università degli Studi di Milano and represents a tool developed to answer the above mention needs of the DSO.Index Terms--Smart grid, Distribution networks, Distribution System Operator. I. INTRODUCTIONThe Ingrid project was started in 2010 thanks to a collaboration among Politecnico di Milano, University of Milan and Siemens SpA. The goals are to develop new tools for DSO Control Center useful for both off-line analysis and real-time operations. In the first part of the project, the attention was put on the data exchange problem with existing SCADA system [1]-[3]. Moreover, power flow (PF) and short-circuit computational tools were developed. In this context, it was also necessary to overcome the problem related to the estimation of real and reactive power consumptions of the customers connected to the MV system. In particular, starting from standard profiles of different customers, the real and reactive power for each hour is estimated according to the energy consumption of the customer in the last year. In this context, the Ingrid tool needs to be implemented in a server that manages all data exchange among different components and users.Moreover, the information given by the power flow and short-circuit solutions allow to implement new procedures in order to improve the generation units operation; in this way, the capacity of the existing system to host further generator injection will increase [4]. In particular, in Ingrid project new approaches about the reactive support management of DG are developed; it represents one of the most critical issues that impacts on the hosting capacity of the distribution grid.

The presence of Dispersed Generation (DG) in LV distribution networks affects voltage profiles along distribution feeders, specifically over-voltages may occur at the DG Point of Common Coupling. This study focuses on a voltage control system that exploits DG units in order to mitigate overvoltage violations. The proposed approach is based on a local-corrective control strategy that modulates the reactive power injected/absorbed by the DG power plants. A chronological analysis is carried out on an annual basis to assess the performance of the control laws proposed and the sensitivity of the LV network characteristics on voltage regulation, i.e., the effectiveness of the LV reactive injections regulation model. From the results obtained by extensive numerical simulations it can be pointed out that the local-corrective regulation approach is a viable solution useful to increase the Hosting Capacity (HC) of existing networks, without the need for complex new infrastructures that entail huge investments. Finally, a novel DG coordination procedure is proposed, this approach has been designed in order to minimize the communication channel requirements, i.e., to allow coordinated voltage control without requiring complex real time apparatus and calculations (measurements, state estimation, Optimal Power Flow, etc.), considered to be impractical for LV grid applications.