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Continuously changing electricity demand and intermittent renewable energy sources pose challenges to the operation of power systems. An alternative to reinforcing the grid infrastructure is to deploy and manage distributed energy storage systems. In this work, a micro-energy market is proposed for smart domestic energy trading in the low-voltage distribution systems in the context of high penetration of photovoltaic systems and battery energy storage systems. In addition, a micro-balancing market is proposed to address the congestions due to unforeseen energy imbalance. Centralised and decentralised management strategies are simulated in real time, based on generation and demand forecasts. In addition, electric vehicles are also simulated as potential storage solutions to improve grid operation. A techno-economic evaluation informs key stakeholders, in particular grid operators on strategies for a sustainable implementation of the proposed strategies. The results show that the micro-energy market reduces the energy cost for all grid users by 4.1–20.2%, depending on their configuration. In addition, voltage deviation, peak electricity demand and reverse power flow have been reduced by 12.8%, 7.7% and 85.6% respectively, with the proposed management strategies. The micro-balancing market has been demonstrated to keep the voltage profile and thermal characteristic within the set limit in case of contingency.

Multi-Energy Microgrids (MEMGs) offer great opportunities for enhancing energy systems efficiency and penetration of renewable energy sources (RESs). By coupling traditionally independent electrical and thermal networks with binding components such as Combined Heat and Power (CHP) units, system operators can benefit from higher energy utilization efficiency. However, MEMGs' operation is severely compromised by uncertainties existing in RES generation and electric loads, which can never be perfectly predicted. This affects considerably the MEMG day-ahead dispatch and poses major challenges on how to maintain reliable operating conditions. This work proposes a coordinated dispatch strategy to minimize the operating costs of a network-constrained MEMG consisting of combined electrical and thermal distribution networks when multiple uncertain parameters are considered. To capture uncertainty variability, the operation method was modeled as a stochastic programming problem. Moreover, the Monte Carlo sampling technique was used to generate a large number of random scenarios. The proposed stochastic operation method was tested on a 14-bus system to find the optimal day-ahead scheduling operation. A feasibility check of the stochastic and deterministic methods was then carried out based on a new set of uncertainties realizations. Results indicated the proposed operation model to minimize the operating costs and guarantee strong robustness against uncertainties' realizations.

The continuous increase of Renewable Energy Sources (RESs) connected to distribution networks requires a careful review of the current regulatory framework to enable the provision of Ancillary Services (ASs) by these small-scale units. One of the envisaged options for coordinating Transmission System Operators (TSOs) and Distribution System Operators (DSOs) is the agreement and regulation of a scheduled power profile at the Primary Substation (PS). This means assigning the balancing responsibility to DSOs and, consequently, reducing the unpredictability of the power exchanges with the upstream transmission grid. The paper proposes a novel procedure for the management of Distributed Energy Storages (DESs) in order to provide ASs to both the DSO (local regulation of distribution network and congestion management) and the TSO (control of the power profile at the PS). The methodology, based on a sliding time window approach, evaluates the actual availability of each storage unit in providing ASs, assigns a scheduled profile and corrects it during the real-time operation. In addition, for each DES, the scheduled State of Charge (SoC) is restored in accordance with network constraints. Simulations on a realistic case study network are carried out considering randomly perturbed power profiles for both loads and generators. Benefits associated with storage coordination (power exchange management at the PS and support to DSO in voltage regulation and congestion resolution) are evaluated and discussed.

The paper discusses preliminary results of an extensive survey of residential load users in an urban area. This work is part of a wider collaboration between University of Padova and AGSM aiming to analyze the Medium and Low Voltage electrical distribution network, i.e. to characterize existing loads and to define realistic future scenarios considering new resources satisfying sustainable energy policies, e.g., an increased penetration of electricity in final energy uses and the electrical mobility. The first part of the study focused on residential end-users, which represent the customer category with the highest diffusion in LV grids, with the aim of characterizing the actual utilization degree of the existing electrical infrastructure and providing a suitable estimate of end-users’ energy consumption growth trend for network planning purposes.

The diffusion of distributed energy resources in distribution networks requires new approaches to exploit the users&rsquo, capabilities of providing ancillary services. Of particular interest will be the coordination of microgrids operating as an aggregate of demand and supply units. This work reports a model predictive control (MPC) application in microgrids for the efficient energy management of energy storage systems and photovoltaic units. The MPC minimizes the economic cost of aggregate prosumers into a prediction horizon by forecasting generation and absorption profiles. The MPC is compared in realistic conditions with a heuristic strategy that acts in a instant manner, without taking into account signals prediction. The work aims at investigating the effect that different types of energy tariffs have in enhancing the end-users&rsquo, flexibility, based on three examples of currently applied tariffs, comparing the two storage control modes. The MPC always achieves a better solution than the heuristic approach in all considered scenarios from the cost minimization point of view, with an improvement that is amplified by increasing the energy price variations between peak and off-peak periods. Furthermore, the MPC approach provides a cost saving when compared to the case considering a microgrid endowed with only photovoltaic units, in which no storage is installed. Findings in this work confirm that storage units better perform when some knowledge of future demand and supply trends is provided, ensuring an economic cost saving and an important service for the overall community.

With the increase of the distributed generation, the development of distribution networks able to operate detached from the bulk grid has become possible. However, these islanded distribution networks lead to several issues to be dealt with, including the stability, the efficient generation profile scheduling and the procurement of balancing services. This paper proposes an optimal network management scheme capable of obtaining the power profiles of all users connected to the network for a given time frame. This scheme, based on a double negotiation phase, aims to minimize the social cost for the coverage of the overall demand, keeping the network within its technical operating limits. The impact of Multi-Energy Storage Systems (MESS) in the cost of providing these services is assessed by considering the technical limits of the specific users. Finally, the proposed control scheme has been tested on four different scenarios, with increasing MESS penetration level, demonstrating to be able to reduce the social cost associated with the re-dispatching by exploiting the services offered by the Battery and Thermal Energy Storage Systems.

Passive distribution networks are rapidly transforming to active networks due to ever growing penetration of mainly renewable distributed energy resources. The integration of these resources has positive impact from environmental perspective but their penetration has raised serious issues on secure and reliable operation of a network, owing to their intermittent and not dispatchable output. To maintain an optimal operation of a network, extensive research studies have been carried out under the theme of network management. This paper discusses the concept of losses management, which falls under the same theme, in active distribution networks. The methods related to modelling of such systems and end-users, numerical tools required for system analysis, active network management schemes for losses minimization and fair losses allocation to passive and active consumers are reported and investigated. Therefore, the aim of this paper is to provide a concise yet comprehensive comparison of the most recently proposed losses management approaches and strategies.

Under emergency conditions, portions of medium-voltage (MV) networks can be locally supplied for a significantly long time period by moveable generating units connected to the low-voltage (LV) side of a standard distribution transformer, which in this case operates as a step-up transformer. It is, therefore, necessary to ensure a proper operation which must include the detection of any possible faulty condition. When the MV network portion is operated with isolated neutral (as it is usually the case), a reliability issue arises for earth faults detection by the protection system, due to the negligible capacitive fault current values. In this work, possible detection methods are identified through analytical and numerical simulations and two promising solutions are proposed, i.e. the intentional earthing of one phase conductor and the connection of a suitable neutral forming transformer with earthed neutral terminal, both operated at the MV side of the MV/LV transformer.

The growth of distributed energy resources (DER) connected at distribution network level and the current legislation concerning the participation of DER to the energy and ancillary services markets, are a huge opportunity to get flexibility services from these resources but at the same time a great challenge from the technical point of view. According to the latest indications from EU Directives, demand response and generation flexibility are encouraged in order to meet network balancing needs, but a new actor is required: the aggregator. This new participant has the duty to aggregate consumption and generation in order to offer flexibility products in the ancillary services market, while ensuring the technical feasibility and assuring revenues for its clients and itself. This work focuses on the structure and the business model of aggregators and discusses the technical implication that such role has on the distribution network.

The urban development of our cities has often made overhead power lines, almost always pre-existing, closely affected by the presence of new infrastructure and residential homes. The following questions arise from this aspect: “Is it possible to think of new overhead power lines arrangements, built with innovative solutions, with lower environmental impact compared to traditional solutions?” Further “were all this possible, what would the specific features and problems of these solutions be? And finally, as regards the magnetic field emission, “what would the performance of these overhead line innovative solutions be like, compared to the underground cable solution?” The above questions stimulated the research and application feasibility of “low magnetic field” technical solutions, traditional and innovative, described in this paper.

In many countries, in the last years, there has been a wide spread of Distributed Generation (DG) from renewable sources at MV and LV level. The distribution network is eventually changing from a passive structure to an active protagonist of a dynamic, low carbon and reliable energy market. On the other hand, this change could lead to a power quality depletion and to threats to the safety of the network itself. In this work, a concurrent control strategy is proposed to coordinate the prosumers with the aim of improving the reliability of the distribution network. The control scheme is based on an adaptive-area-based method and a multi-conductor Power Flow. In this way, it is possible to monitor the voltage unbalance among the phases while managing voltage and current magnitudes.

Many planning and operation studies that aim at fully assessing and optimizing the performance of the distribution grids, in response to the current trends, cannot ignore grid limitations. Modelling the distribution system, by including the electrical characteristics of the network (e.g., topology) and end user behaviors, has become complex, but essential, for all conventional and emerging actors/players of power systems (i.e., system and market operators, regulators, new market parties as service providers, aggregators, researchers, etc.). This paper deals with a methodology that, starting from publicly available open data on the energy consumption of a region or wider area, is capable to obtain reasonable load and generation profiles for the network supplied by each primary substation in the region/area. Furthermore, by combining these profiles with territorial and socio-economic information, the proposed methodology is able to model the network in terms of lines, conductors, loads and generators. The results of this procedure are the synthetic networks of the real distribution networks, that do not correspond exactly to the actual networks, but can characterize them in a realistic way. Such models can be used for all the kind of optimization studies that need to check the grid limitations. Results derived from Italian test cases are presented and discussed.

The large penetration of distributed energy resources (DERs), especially photovoltaic (PV), in low-voltage (LV) distribution grids has raised the concern of unintentional islanding operations. The probability of unintentional islanding is increased mainly due to the newly introduced standards with extended frequency and voltage thresholds and the additional grid support functions, such as active and reactive power regulation using P/f and Q/V droop characteristics. Moreover, islanding operation due to faulty events at the medium-voltage (MV) distribution level may be dangerous in the presence of automatic reclosing procedure leading to out-of-phase reconnections. In this paper, an analysis of this phenomena is provided using simplified generator and load models. Simulation results based on MATLAB and DIgSILENT tools on a simplified LV distribution network are reported together with experimental results on a lab-scale prototype.

The significant growth of embedded generation in distribution systems is leading network operators to reconsider some of the prescriptions for losses minimization. Analyzing the operating conditions of small-scale generators connected to Low Voltage (LV) networks is becoming more and more important. Since LV customers are mostly single-phase connected, the time shifting between load and generation power profiles is likely to increase both voltage unbalance and power losses. Recently revised grid codes focus on the involvement of distributed generators in the network management, and this feature needs to be taken into account in the power losses evaluation. In this paper, some of the controls applicable to embedded generators are considered in a real case LV distribution system, and their effects on annual network losses, referring to real customers’ power profiles, are investigated.

The deployment of Electric Vehicles (EVs) is continuously increasing on a global scale due to governmental commitments to ensure energy security, decarbonisation and address environmental concerns, by phasing out Internal Combustion Engine (ICE) vehicles. However, if charging is not appropriately controlled, massive EV penetration can lead to significant challenges for local distribution systems. In this context, this paper presents a new extensive tool, based on a Matlab/Simulink platform, to model distribution networks and analyse the impacts of charging of EVs, generation from local Renewable Energy Sources (RES) and the use of smart grid technologies to mitigate these impacts. The tool models the geographical locations of the distribution substations and the nodes where local loads, RES and EV charges may be connected. It allows the user to study the operational framework of current and future distribution networks and enables techno-economic assessment to be made. The modelling tool simulates the daily basis operation of any low-voltage (LV) distribution grid, considering the interaction with both consumers and local RES. This is done by evaluating key system performance measures, such as nodal voltages, line currents and transformer overloading. A user-friendly Graphical User Interface (GUI) facilitates the flexible management of the input parameters. The tool was applied to analyse an existing UK LV distribution network, to demonstrate the feasibility of smart charging and V2G (Vehicle to Grid) technology and the advantages over uncontrolled charging. This paper presents the outline of the modelling tool and the results of investigation of the different scenarios considered in this research.

In the last decades, strengthening the high voltage transmission system through the installation of new overhead power lines has become critical, especially in highly developed areas. Present laws concerning the human exposure to electric and magnetic fields introduce constraints to be considered in both new line construction and existing systems. In the paper, a technique for passive magnetic field mitigation in areas close to overhead power lines is introduced, fully modelled and discussed through a parametric analysis. The investigated solution, which basically consists in approaching line conductors along the span making use of rod insulators, is applicable on both existing and under-design overhead lines as an alternative to other mitigating actions. Making use of a 3-dimensional representation, the procedure computes both positions of phase conductors and forces acting on insulators, towers, conductors and compactors, with the aim of evaluating the additional mechanical stress introduced by the compactors. Finally, a real case study is reported to demonstrate and quantify the benefits in terms of ground magnetic field reduction achievable by applying the proposed solution, in comparison to a traditional configuration. Furthermore, using compactors to passively reduce the magnetic field is simple to be applied, minimally invasive and quite inexpensive as regards to alternative mitigating actions.

The proliferation of Distributed Energy Resources (DERs) in the Distribution Network (DN) has affected the optimal operation of the grid due to multiple technical issues such as voltage rise, reverse power flow, voltage unbalance, islanding etc. Therefore, optimal management of DERs is becoming a key research area to improve the system power quality. In this context, several active network management schemes have been proposed to mitigate the issues associated with DERs integration into the grid and ultimately reduce the network power losses. This paper provides a comprehensive review of these schemes along with a discussion on the network modelling and load profiling. Further, it also reports the possible future research areas in the field of losses management.

The increasing penetration of distributed generation has lead international authorities to integrate the rules for the connection of active end-users to distribution networks. Thus, power regulating functions aiming at supporting the voltage and frequency stability of the main grid have been recently introduced in European grid codes. In this paper, the consequences of adopting such regulating functions have been examined in detail. In particular, the risk of uncontrolled islanding on a Medium Voltage network with increasing amount of embedded generation connected to Low Voltage subsystems has been studied. Both existing regulating requirements, such as active and reactive power modulation according to locally measured frequency and voltage, and additional stabilizing functions, such as Inertia Emulation and Fast Voltage Support, have been investigated. Results of dynamic simulations, carried out making use of DIgSILENT PowerFactory 2016 software, demonstrate the interactions between stabilizing functions, generators protection systems and network automatic reclosing procedures.

The ever-growing penetration of local generation in distribution networks and the large diffusion of energy storage systems (ESSs) foreseen in the near future are bound to affect the effectiveness of interface protection systems (IPSs), with negative impact on the safety of medium voltage (MV) and low voltage (LV) systems. With the scope of preserving the main network stability, international and national grid connection codes have been updated recently. Consequently, distributed generators (DGs) and storage units are increasingly called to provide stabilizing functions according to local voltage and frequency. This can be achieved by suitably controlling the electronic power converters interfacing small-scale generators and storage units to the network. The paper focuses on the regulating functions required to storage units by grid codes currently in force in the European area. Indeed, even if such regulating actions would enable local units in participating to network stability under normal steady-state operating conditions, it is shown through dynamic simulations that they may increase the risk of unintentional islanding occurrence. This means that dangerous operating conditions may arise in LV networks in case dispersed generators and storage systems are present, even if all the end-users are compliant with currently applied connection standards.

As a consequence of the increasing penetration of distributed generation from renewable energy sources into power systems, international authorities have provided the rules for the connection of active end-users to distribution networks. Power regulating functions have been recently introduced in European grid codes aiming to support voltage and frequency stability. In this paper, the effects of the adoption of such regulating functions have been widely examined, emphasizing the risk of uncontrolled islanding on a Medium Voltage network as the amount of static generators connected to Low Voltage subsystems increases. The study investigates the performances of both existing regulating requirements, such as active and reactive power modulation according to local frequency and voltage, and the additional contribution of further stabilizing functions, such as Inertia Emulation and Fast Voltage Support. Furthermore, the interaction between power regulating rules, generators protection systems and automatic reclosing procedures applied by the Distribution System Operator to circuit breakers at sending end of Medium Voltage feeders, are investigated. The presented results, carried out making use of DIgSILENT PowerFactory software, well demonstrate the correlation between regulating functions applied to generators and the islanding phenomenon.

Distribution networks are increasingly hosting embedded generators, most of them converting renewable energy primary sources. These units are usually interfaced with the main network by means of static power converters. Grid codes have recently introduced stabilizing functions to engage distributed plants in supporting the main system stability during network events and consequent voltage/frequency perturbations. The paper highlights the risk of unintentional islanding, which may be concrete depending on the embedded plant operating conditions, the load characteristics and the stabilizing functions main settings. Firstly, the stabilizing effect of rotating loads is demonstrated. Secondly, the positive impact of the recently introduced intentional delay on the reactive power response in the case of voltage variations is studied. Non-detection zones in terms of generator active and reactive power are reported as final results with reference to different scenarios.

Power flow analysis of distribution networks incorporating LV consumer representation needs to be cognizant of an unbalanced load structure and the grounding network between the consumer and network operator (TNC-S earthing). In this paper, the asymmetrical 3-phase (and neutral) power flow problem is solved by a correction current injection methodology applied to a system represented by a complex admittance matrix. The correction current injection technique is adopted to adjust the power exchange of shunt elements, whose nominal admittances are included in the system admittance matrix, through suitable fringing currents in the iteration process. This methodology offers an improved and more robust alternative for asymmetrical network scenarios under unbalanced power flow conditions when compared to the standard power flow methodologies, such as the Newton–Raphson or the forward–backward sweep approaches. These well-known methods may encounter convergence issues as a consequence of the specific consumer/network earthing arrangements especially when they need to be defined throughout the network. The algorithm presented here has been applied to a 4-wire representation of a suburban distribution network within Dublin city, Ireland, which incorporates consumer connections at single-phase (230 V N). The analysis presented uses the correction-current injection power flow algorithm in conjunction with the network model to consider the impact of distributed wind and solar (PV) generation systems ( DwG and DpvG respectively), for a range of load profiles.

The recent growing diffusion of dispersed generation in low voltage (LV) distribution networks is entailing new rules to make local generators participate in network stability. Consequently, national and international grid codes, which define the connection rules for stability and safety of electrical power systems, have been updated requiring distributed generators and electrical storage systems to supply stabilizing contributions. In this scenario, specific attention to the uncontrolled islanding issue has to be addressed since currently required anti-islanding protection systems, based on relays locally measuring voltage and frequency, could no longer be suitable. In this paper, the effects on the interface protection performance of different LV generators’ stabilizing functions are analysed. The study takes into account existing requirements, such as the generators’ active power regulation (according to the measured frequency) and reactive power regulation (depending on the local measured voltage). In addition, the paper focuses on other stabilizing features under discussion, derived from the medium voltage (MV) distribution network grid codes or proposed in the literature, such as fast voltage support (FVS) and inertia emulation. Stabilizing functions have been reproduced in the DIgSILENT PowerFactory 2016 software environment, making use of its native programming language. Later, they are tested both alone and together, aiming to obtain a comprehensive analysis on their impact on the anti-islanding protection effectiveness. Through dynamic simulations in several network scenarios the paper demonstrates the detrimental impact that such stabilizing regulations may have on loss-of-main protection effectiveness, leading to an increased risk of unintentional islanding.

The ever growing penetration of Distributed Energy Resources (DERs), involving both conventional and renewable technologies, is changing the power system face. International Standards are being revised for including new requirements for DERs such as wider voltage amplitude and frequency protection thresholds and new local P=f and Q=V power regulation. This scenario has led to an increasing concern about the problem of uncontrolled islanding on distribution networks. The purpose of this paper is to describe a hardware in the loop (HIL) test-bed, where the effects of the DER inverter control actions and of the physical interface protection systems (IPSs) on the unintentional islanding can be addressed. The analysis has shown that the frequency measurement under transient conditions is very important, influencing the P=f DER control action and the IPS tripping. Thus, the preliminary results on the HIL test-bed suggest the need of standardization for the frequency measurement. This solution would be of fundamental importance to predict system behavior of distribution network having large DER diffusion and its protection system during unintentional islanding and other transient conditions.

National and internationals grid codes define the connection rules for passive and active users, guaranteeing the electrical power system stability and safety. Recently, the increasing diffusion of Distributed Generators from Renewable Energy Sources, mainly interfaced through electronic converters, has called for a drastic review of traditional approaches to distribution network operation. As a consequence, new regulating functions, aiming to support network stability by regulating local units power flows, have been defined, and others are under investigation. The paper discusses the role of existing and proposed stabilizing actions in terms of unintentional islanding identification, according to the Low Voltage interface protection characteristics.

This paper concerns the quantification of the costs that a distributor must support to enable the new market scheme and the participation of new potential competitors to the ancillary service market. Starting by available open data and GIS the value of distributed resources and active demand in the market for system services has been assessed. Representative models of the network beyond the TSO/DSO interface have been developed in order to evaluate the operation extra-costs for solving contingencies. The impact on the flexibility (quantity) potentially offered by a distribution network and on the price of the bids in the ancillary service market has been calculated by applying the proposed methodology to real world cases.

A regulatory effort is expected to be undertaken in the next years in order to foster the transition towards “smart grids”. In this view, the ancillary services market framework needs to change in order to cater for the possible contribution coming from distribution networks. Recently, the Italian Authority for Electricity, Gas and Water proposed three new market models aiming at exploiting the contribution of the resources connected to distribution networks for the ancillary services provision to the bulk grid. In this context, storage systems could enhance significantly the availability of ancillary services meanwhile allowing a better management of distribution networks. This paper aims at investigating the possible contribution of storage units in the ancillary services provision by distribution networks.

Nowadays, renewable energy sources feed significant shares of energy demand, resulting in a reduction of market energy price but also a significant increase of expenditures for ancillary services due to inherent not complete predictability and programmability. Thus loads and generation in the distribution network are more and more required to play an active role in supporting grid stability by participating to ancillary service markets, either directly or through aggregators. The paper presents a novel procedure to estimate distribution networks capabilities to support grid stability, by making use of synthetic representation of HV/MV substations and their relevant distribution networks with a GIS based clustering procedure. The impact of active distribution networks to the bulk ancillary service market is then evaluated by applications to the Italian electric system and by assuming different regulatory frameworks for transmission/distribution network market interactions.

The paper presents the results of a critical analysis of the most important prediction methods of radio-interference and acoustic noise produced by power transmission lines available in the technical literature. A code has been implemented in the MATLAB environment to improve the quality of the predictions, and the results of a preliminary validation of the tool are presented. Particular attention is given to the applicability to non-conventional geometries of the lines.

As the process of deregulation of the electric utility industry proceeds, the importance of power quality is increasing. A fundamental aspect of power quality is the continuity of power supply that is the absence of momentary, temporary and sustained power interruptions. In this paper a network reconfiguration strategy is proposed which allows the distribution network to separate into a certain number of autonomous islands, supplied by local distributed generation, in case of permanent fault within the grid. Intentional islanding of portions of the grid is automatically carried out with an adaptive network reconfiguration depending upon the local generation/load state at the time of outage.

The electromagnetic environment related to electric power installations is typically evaluated by numerical integration methods. Numerical techniques, although powerful, are not well suited for assessing the dependence of the field strength on electric and geometric parameters. In this paper, a fast procedure to analytically evaluate power-line magnetic fields, based on complex vectors, is proposed. The use of complex algebra greatly simplifies analytical calculations compared to other approaches proposed in literature, allowing also complex conductor arrangements to be taken into account. A general formula for the magnetic-field intensity of any multiphase single-circuit line configuration is obtained. An expression for practical three-phase line configurations is simply derived as a particular case of the general formula. The proposed approach is then extended successfully to double-circuit lines, taking the load differences between circuits into account. Approximate formulas are validated by comparing magnetic flux density values with those computed from the general expression.

Distributed Generation in Low Voltage grids has raised the concern of unintentional islanding and its probability has increased due to the newly introduced standards for generators, which in particular impose wider frequency and voltage ranges and active and reactive power support capabilities using of P/f and Q/V droop characteristics. Anti-islanding protections that each inverter is equipped with, may fail to detect the grid transition and so uncontrolled islanding operation may appear. This operation may be dangerous especially in presence of automatic reclosing procedure, because of possible out of phase reconnections. In this paper, the temporary unintentional islanding operation (e.g. below 600 ms) is studied considering the effects of P/f and Q/V droop characteristics of generators and their response times. A potential increase of such phenomenon will be shown with simulations and experimental results.

The spreading of electrical vehicles leads to a positive impact on the mobility field from the ecological, economical and efficiency point of view. Unfortunately this diffusion is also potentially capable of negative reverberations on distribution and transmission networks, since EVs can be considered as a new load category. Rather than preventing this virtually negative situation, it is possible for the grid to take advantage of the capabilities of EVs' batteries to implement ancillary services: for this reason the proposed vehicle's battery charger is designed to operate with bidirectional power flow (implementing V2G - Vehicle to Grid- and G2V -Grid to Vehicle- modes). The target is pursued through grid manager request towards grid connected EVs. If the power flow's direction and amount is enabled by the EV controller (depending on the SOC of the battery), the control system acquires the reference signal, which is the network sinusoidal voltage wave. This synchronization between the device and the grid is followed by the battery charger's modulation of a voltage sine wave with a certain amplitude and phase displacement with respect to the reference signal, in order to reach the desired working point which provides ancillary services to the grid. This paper analyses both the control strategy and the profiles of the transient states that take place when the switch between working points is request.

In many countries different technical rules have been introduced in order to integrate the DG units in the medium voltage (MV) and low voltage (LV) distribution network. New standards state requirements for all generators, included inverter based ones, imposing a Fault Ride Through (FRT) philosophy and new active and reactive power regulation actions with the aim of maintaining the transmission system stability at the level it was with traditional rotating generators, or even increasing it. These technical rules may not be fully compliant with the automatic reclosing cycle usually performed from the CB at the beginning of MV feeders and/or with the automatic procedure of faulty section selection and supply restore to healthy ones. In this paper the effects of DG units connected at MV and LV voltage level in relation to different fault conditions are analyzed. The possibility of temporary uncontrolled islanded operations are investigated in order to evaluate the role of new Standards or Regulatory or Law requirements in the automatic reclosing procedure and MV network automation.

The analysis of unintentional islanding in distribution grids with a large penetration of renewable energy sources is of increasing interest due to the recently introduced requirements of P/f and Q/V supporting capabilities of Distributed Energy Resources (DERs) and the wider frequency and voltage ranges, DERs should be able to operate with, before protection tripping. DER anti-islanding protections, if present, may fail to detect this grid transition and so uncontrolled islanding operation may appear. Since this operating mode may be dangerous for the electric network operation and may cause damages for the grid equipment, in this paper the increase of its risk due to P/f and Q/V droop characteristics of generators is addressed. Analytic results are initially derived for the steady-state unintentional islanding operation and then they are validated on a laboratory-scale grid setup. The proposed investigation will show that the risk of permanent unintentional islanding increases introducing P/f or Q/V droop regulation and that such risk is maximum including both the P/f and Q/V droop regulations, rather than only one of them.

Nowadays grid connected renewable energy sources have reached a level that was not even conceivable just few years ago with serious concerns on power systems’ stability and security. The Italian TSO and the Italian regulatory authority for electricity, gas and water system (AEEGSI) pioneered this field, and imposed the participation of distributed generation (DG) into voltage and frequency regulation for reducing the risk of loosing significant power generation during frequency transients. Smart grids are the next step towards DG integration. In 2010, the AEEGSI demonstration phase on smart grids was designed according to an input based incentive scheme and a competitive selection process in order to award a limited number of projects. According to AEEGSI resolution ARG/elt 39/10, the selected smart grid demonstration projects did benefit from an extra remuneration of capital cost (a 2% extra WACC in addition to the ordinary return) for a period of 12 years. All projects are now in the rollout phase and the first data are going to be collected from the field in a real world environment. This paper gives a brief description of the projects and adds information about the selection criteria that allowed identifying what are the benefits that the system stakeholders should expect by the innovation of distribution operation and planning. Furthermore, the procedure used to define a regulatory environment suited for smart grids is described. The main idea is to define the fundamentals of a fair and transparent regulation mechanism based on different levels of smartness and on the identification of some suitable indicators that allow the AEEGSI to establish the expected performances of novel smart grids and, consequently, to define penalties and/or rewards for DSOs. With the aid of some examples the role of indicators is showed. Finally, it must be remarked again that the SG projects are in progress and field data are not yet disposable. This is the reason why the numerical simulations reported in this paper have been developed on a reference network that can represent the behaviour of some of the real SG networks relevant to the projects; such simulations have been performed in order to better quantify the benefits that the stakeholders of the system should expect. When the projects will enter the operation phase the field data collected after the new operational approach will be collected and can be used to verify the simulations hypothesis assumed.

In order to supply warning discharge lamps installed atop towers, the insulation of ground wires in HV and EHV can be used. The paper describes a simplified yet efficient matrix procedure which allows both to compute the capacitive induced voltages and to determine the equivalent circuit supplying such non-linear loads. In addition, the waveform of the conduction currents and voltages and the average power on the lamps are determined by a fast analytical procedure. The analytical results have been compared with laboratory experimental results giving a really good agreement.

The large penetration of Distributed Energy Re- sources (DERs), especially PhotoVoltaic (PV), in Low Voltage (LV) distribution grids has raised the concern of unintentional islanding operations. The probability of unintentional islanding is increased due to the newly introduced standards with extended frequency and voltage thresholds and additional grid support functions, such as active and reactive power regulation using P/f and Q/V droop characteristics, which can make ineffective the anti-islanding provisions each PV is equipped with. Moreover, islanding operation due to faulty events at the Medium Voltage (MV) distribution level may be dangerous in presence of auto- matic reclosing procedure leading to out of phase reconnections. In this paper, an analysis of this phenomena is provided using a simplified characterization of the generators and the loads. Simulation results based on Matlab and DIgSILENT tools on a simplified LV distribution network are reported together with preliminary experimental results on a lab-scale prototype.

The modern power systems have recently increased the interest in distributed generation (DG) technologies due to, fuel cost uncertainties, environmental constraints, and increasing power consumption with shortage of transmission capacities. Distributed generation (DG) using clean and renewable energy in power supply system have attracted serious attention. Many developing countries are adopting distributed generation (DG) technologies for their power systems expansion planning. Solar Energy is one of the most promising, nonpolluting, free source of energy. Libya is a developing country located in North Africa, most of the country's land area is desert which is wealthy in solar radiation income, found to be one of the most reliable and consistent solar energy resources. Despite of this energy resource this area (southern part) of Libya experiences permanent outages which may last for days in certain occasions. This paper investigates the implementation of distributed generation using solar energy resource to improve security of supply to these areas and emphasizes other benefits on power quality and economics.

The interest of unintentional islanding operation has recently grown in Low Voltage (LV) distribution grids because of the large penetration of Distributed Energy Resources (DERs), especially the ones based on the PhotoVoltaic (PV) energy source. The probability of unintentional islanding is increased also due to the newly introduced standards with extended frequency and voltage limits before the PV protection trips and due to the large number of PV generators, which can make ineffective the anti-islanding provisions each PV is equipped with. Moreover, interconnection standards of DERs require some additional grid support functions, such as active and reactive power regulation using P/f and Q/V droop characteristics, which can further increase the probability of unintentional islanding. In this paper, an analysis of this phenomena is provided using a simplified static and dynamic characterization of the generators and the loads. Simulation results based on Matlab and DIgSILENT tools on a simplified LV distribution network are reported together with preliminary experimental results on a lab-scale prototype.

The paper studies a medium voltage-low voltage transformer with a decoupled on load tap changer capability on each phase. The overall objective is the evaluation of the potential benefits on a low voltage network of such possibility. A realistic Danish low voltage network is used for the analysis. The load profiles are characterized by using single phase measurement data on voltages, currents and active powers with a 10 minutes resolution. Different scenarios are considered: no tap action, three-phase coordinated tap action, single phase discrete step and single phase continuous tap action. The effectiveness of the tapping capability is evaluated by comparing the Voltage Unbalance Factor and the voltage levels on the neutral cable.

Due to the significant growth of distributed generators connected to the distribution networks, these systems might reach their technical limits requiring new investments. Since a large number of such units is interfaced with inverters to the grid, several research works proposing strategies to coordinate DERs in regulation schemes have been presented. In this work, a distributed control strategy is proposed to coordinate the active users with the aim of increasing the system's Hosting Capacity. In particular, the paper presents a scenario in which a multitude of DER with storage capabilities, are connected to the grid and able to provide network services responding to power exchange requests.

In the last twenty years the Distributed Generation (DG) increased till a high level that introduced several issues to the classical management system of distribution networks. In many countries different technical rules have been introduced in order to integrate the DG units in the medium voltage (MV) and low voltage (LV) distribution network. New standards state requirements for all generators, included inverter based ones, imposing a Fault Ride Through (FRT) philosophy and new active and reactive power regulation actions with the aim of maintaining the transmission system stability at the level it was with traditional rotating generators, or even increasing it. These technical rules may not be fully compliant with the automatic reclosing cycle usually performed from the CB at the beginning of MV feeders and/or with the automatic selection procedure of faulty section selection and supply restore to healthy ones. In this paper the effects of DG units connected at MV and LV voltage level in relation to different fault conditions are analysed. The possibility of temporary uncontrolled islanded operations are investigated in order to evaluate the role of new Standards or Regulatory or Law requirements in the automatic reclosing procedure and MV network automation.

This paper presents some of the results of a three-year research project entitled ATLANTIDE, which is aimed at developing a comprehensive digital archive of reference models of Italian distribution networks, including forecasted load and generation development evolving towards future smart grid scenarios. The paper focuses on the models developed for harmonic penetration studies and on how the results of these models can be included in the multi-objective optimization approach used by the Distribution Management System model developed in ATLANTIDE.

The increasing number of inverter-based Distributed Generator (DG) units connected to both MV and LV distribution networks can be used as a resource in order to overcome some emergency conditions. The presence of different inverter-based DG units could introduce issues regarding the management of intentional islanded networks, therefore reliable inverter control strategies for islanded operation assume an essential role. In this paper an inverter operating scheme has been implemented suitable in presence of networks supplied by a single DG or multiple DGs and for both grid tie and grid off operation. This inverter control scheme has been modeled and tested through detailed dynamic simulations in LV and MV islanded networks. Moreover the dynamic behavior of the proposed inverter control strategy has been studied and analyzed in light of the recently issued Italian connection grid codes for active users. The results show that the control scheme allows operation of intentional islanded networks supplied by single or multiple DG units. In case of multiple DG units, simulations show that, grid connection rules influence the dynamic of islanding operations depending on the power balance existing before the islanding forming.

The increasing penetration of Distributed Generation (DG) in distribution electrical systems may cause alteration of voltage profiles on the lines. Traditionally, distribution networks with radial configuration are designed as a passive top-down architecture where voltage regulation is mainly performed by an On-Load Tap Changer (OLTC) transformer located at the Primary Substation. Therefore it becomes rather difficult to compensate lines radiating out from the same bus-bar where some of these are subject to overvoltages due to the power injection by DGs connected whereas others are subject to voltage drops due to the presence of passive loads only. A first step in regulation and managing the voltage levels, in order to be consistent with the contingent needs of the network, may be a decentralized local control strategy performed by the DG units, however better results will be obtained with a coordinated OLTC intervention. In this paper an OLTC control strategy, based on only few remote measurements, is proposed. This procedure allows the tap changer controller to infer the state of network node voltages and to act accordingly. The performance of the proposed control method is demonstrated through simulations on a realistic MV distribution network.

The increasing diffusion of embedded generators on distribution systems leads to the idea of managing portions of the network operating in islanded mode for overcoming emergency conditions. To this aim, it becomes essential to have reliable control strategies for the different types of generator and loads. In this paper some issues regarding the dynamic control of frequency and voltage in MV islanded networks supplied by inverter interfaced DGs are investigated. The aim is to identify opportunities and constraints in light of national regulatory provisions on active power reduction and reactive power compensation. Appropriate models for the inverters control have been developed and systematic simulations of a realistic network switching to islanding operation have been performed.

Power flow analysis of distribution networks incorporating Low Voltage (LV) consumer representations needs to be cognisant of both a highly unbalanced load structure as well as the provision of the grounding network between the consumer and grid operator (TN-C-S earthing). In this paper, the asymmetrical 3-phase (plus neutral) power flow problem is solved by a correction current injection method using a complex Y matrix approach in consideration of a representative Irish urban distribution network. This methodology offers a much improved and more robust alternative for ill-conditioned asymmetrical network scenarios compared to the standard power flow methodologies such as the Newton-Raphson methods or the forward-backward sweep approach (which encounters convergence issues as a consequence of the complex earthing arrangements). The model refers to a 4-wire representation of a suburban distribution network within Dublin city, Ireland, which incorporates consumer connections at single-phase (230V-N). Investigations relating to a range of network issues are presented. More specifically, network issues considered include voltage unbalance/rise and the network neutral earth voltage (NEV) for increasing levels of micro/small wind generation technologies with respect to a modeled urban wind resource.

The number of small power Distributed Generation (DG) units connected to the distribution networks has increased particularly for photovoltaic (PV) applications. According to recently issued Italian standards, each DG unit is allowed to participate in the active and reactive power regulation, using specifically defined P-f and Q-V droop characteristics. Furthermore, these standards have introduced wider frequency and voltage thresholds allowed during normal operation of DG units. Therefore the risk of unintentional islanding operations is expected to increase, due to the possibility of the DG units to supply the loads with a wider voltage and frequency range without the protections interventions. In this paper, the impact of the loads' voltage and frequency dependence on the isolated grid's frequency and voltage deviation, during unintentional islanding operations, has been considered. The system has been modeled and analyzed through detailed dynamics simulations. The results show that, using a classical grid-connected inverter control system, the loads' voltage and frequency dependence may play a crucial role in determining the unintentional islanding operation and possible failure of the protections intervention.