0000000000051544
AUTHOR
M. L. Di Silvestre
Robust Multi-Objective Optimal dispatch of Distributed Energy Resources in Micro-Grids
Modern distribution systems are implemented through micro grids: small power networks where generation is close to consumption and ICT supports the coordinated management of the different energy resources. In such systems, the central control unit manages energy dispatch from the different sources according to different criteria (technical, economical and environmental) and takes care of tertiary regulation. Such optimization for the tertiary regulation is performed with a time interval that typically is of 24 hours. This is due to the fact that it is necessary to take into account the charge and discharge cycles of storage systems. On the other hand, such long time leads to large errors in…
Optimizing droop coefficients for minimum cost operation of islanded micro-grids
This paper shows how minimum cost energy management can be carried out for islanded micro-grids considering an expanded state that also includes the system's frequency. Each of the configurations outputted by the energy management system at each hour are indeed technically sound and coherent from the point of view of generation-consumption balancing by exploiting a frequency dependent load flow algorithm. A Glow-worm Swarm Optimization (GSO) algorithm carried out in a 24 hour time frame provides optimized results. A test has been carried out for a residential PV-Storage-Microturbine islanded micro-grid to show the feasibility as well as the efficiency of the proposed approach and results ar…
A modified IEEE 802.11 protocol for reliable data transmission in automated power distribution systems
A high level of power quality in distribution networks is obtained by means of a diagnostic software, that establishes on-line the status of the network, by elaborating the measured data. An efficient telecommunication system is necessary, from whose reliability depends the security of the timely interventions on the network in case of fault. In the paper, after a brief examination of the diagnostic method, the telecommunication system is examined. The WiFi system has been considered most suitable, for its economy, for the diagnostic service, besides it is not suitably reliable for how it is managed by the IEEE 802.11 protocol for this application. In this work a new protocol derived by the…
Analysis of the efficacy of a WiFi architecture for the management of medium voltage distribution systems
The paper illustrates the interventions for improving security of a WiFi communication system applied in the automatic management of a Medium Voltage network. The management system fails if the data measured at the secondary substations can’t flow regularly. In this paper the security of the transmission as function of the action range of the radio channel, on the data sending time of the IEEE 802.11 protocol, and of the out of use of a WiFi node. Then, a modified IEEE 802.11 protocol is described, for making secure the transmission in presence of a high number of WiFI nodes. Finally, a probabilistic analysis in presented for analyzing the problem from an economical point of view.
A methodology for assessing the impact of salinity gradient power generation in urban contexts
Abstract The paper proposes a methodology to assess the potential impact of salinity gradient power technology in urban contexts. The idea to employ such energy source in urban contexts derives from the observation that, among the energy districts outputs, low-salinity treated wastewater can be used to produce electricity if a suitable source of high salinity feed (seawater of a salt-works) is also available. The methodology uses the HOMER software for assessing the district’s electric energy production, consumption and exchange with the main grid. Then, starting from the total gross surface and the number of inhabitants of the district, some possible realistic scenarios characterized by di…
Frequency constrained optimal Power Flow based on Glow-worm Swarm Optimization in Islanded Microgrids
This work presents an application of a swarm optimization method to solve the optimal power flow problem taking into account the constraints of frequency and line ampacity in three-phase islanded Microgrids. Each generation unit is equipped with a Power Electronics Interface. In the considered formulation, the droop control parameters are considered as variables to be adjusted by a higher control level, while the frequency is kept in rated bounds. Another typical constraint for OPF formulation, the max ampacity of each line, is also considered. Two case studies with different dimensions and electrical features have been considered and the obtained results show the efficiency of the proposed…
Nonlinear droop control for minimum power losses operation in islanded microgrids
In this work, a modified primary regulation technique is proposed to control one of the inverter interfaced units feeding an islanded microgrid. The proposed approach employs an off-line minimum losses Optimal Power Flow, OPF, to extract a lookup table for the composition of the droop curve. Simulations prove that generators reach an operating point that corresponds to a minimum loss operation for the relevant power flow distribution. Since OPF has been implemented with frequency and voltage dependent models, the results of the modified droop are stable and also energy efficient. Further studies will address further analysis on systems showing different R/X ratio and modeling of more genera…
A generalized methodology for distribution systems faults identification, location and characterization
Service continuity is of basic importance in the definition of the quality of the electrical energy, for this reason, the research in the field of faults diagnostic for distribution systems is spreading ever more. In this paper, a new methodology for diagnostic management of automated distribution systems is presented. The technique is based on the solution of a circuital model of the electrical system resulting from the composition of distributed parameters quadripoles. The solution gives as a result the identification of the type of fault, of its characteristic parameters and location. The paper shows an application to line to line grounded and ungrounded faults in which also its precisio…
Current and Voltage Behaviour During a Fault in a HV/MV System: Methods and Measurements
When a single line to ground fault happens on the MV side of a HV/MV system, only a small portion of the fault current is injected into the ground by the ground-grid of the faulty substation. In fact the fault current is distributed between grounding electrodes and MV cables sheaths. In systems with isolated neutral or with resonant earthing this may be sufficient to provide safety from electric shock. Experimental measurements were performed on a real MV distribution network: a real single line to ground fault was made and fault currents were measured in the faulty substation and in four neighbouring substations. In this paper the problem of fault current distribution is introduced, the te…
Multi-objective strategies for management and design of distributed electric storage systems in a Mediterranean island
The paper proposes an analytical study about the design and operation of distributed Electrical Storage Systems(ESS) in an active distribution network supplying a Mediterranean island, according to different criteria. The approach is based on the application of a multi-objective optimization algorithm (NSGA-II) that outputs a set of optimized schedules of the ESS in different configurations when operated according to different criteria (minimum energy losses in the grid, total generation cost, greenhouse gas emissions, limiting the fluctuations of the generation from fossil fuel plants). Moreover the variability of the voltage profile has been investigated also by a comparison with a refere…
An Advanced Numerical Model in Solving Thin-Wire Integral Equations by Using Semi-Orthogonal Compactly Supported Spline Wavelets
Abstract—In this paper, the semi-orthogonal compactly sup- ported spline wavelets are used as basis functions for the efficient solution of the thin-wire electric field integral equation (EFIE) in frequency domain. The method of moments (MoM) is used via the Galerkin procedure. Conventional MoM directly applied to the EFIE, leads to dense matrix which often becomes computation- ally intractable when large-scale problems are approached. To overcome these difficulties, wavelets can be used as a basis set so obtaining the generation of a sparse matrix; this is due to the local supports and the vanishing moments properties of the wavelets. In the paper, this technique is applied to analyze elec…
Efficient modeling of a combined overhead cable line for grounding-system analysis
Simple compact models for combined overhead-cable lines supplying a substation are presented as an extension of a previous paper for grounding system analysis. The overhead line section can be equipped with uniform or combined ground wires, whereas the cable line section can consist of coated metal sheathed cables, with/without intermediate grounding, or uncoated metal sheathed cables in continuous contact with the earth. Besides the calculation of the earth current at the faulted substation, the proposed modeling method allows the evaluation of the leakage current at the transition station, where cables are connected to the overhead line, as well as at critical overhead line towers. In thi…
Simplified hybrid PD model in voids: Pattern validation
The purpose of the present work is to show the validation of a new model to simulate the physical phenomenon of partial discharge (PD) produced in air voids inside insulating epoxy resin. The model has been developed on the basis of a new approach that combines the known circuit model of three capacitors with a model used to describe the behavior of the ionized channel inside of the inclusion during the discharge phenomenon, short-circuiting the capacity that represents the void. The approach is based on time-variable conductance of the void, subjected to multistress conditions: voltage, temperature and pressure. The new approach has been developed from a time variable conductivity model us…
Improved primary regulation for minimum energy losses in islanded microgrids
In this paper, an improved primary regulation is proposed for grid forming units supplying islanded microgrids. A minimum losses Optimal Power Flow is run off-line to devise the operating set points composing the primary regulation curve. In this way, after load perturbations, generators can reach an optimized operating point for a given and unique minimum losses energy flows distribution. The idea is to skip the hierarchical control architecture and provide a feasible and optimized operating point. A case study over 24 hours shows the effectiveness of this new approach as well as the improved operation quality of the system.
Energy efficient operation in smart grids: optimal management of shiftable loads and storage systems
In this paper, the authors analyze the impact of the participation of customers to the sustainable implementation of energy rational strategies in microgrids. The management of shiftable loads is compared to the control of real and reactive storage systems in smart grids. An optimization algorithm is used as analysis tool to assess the impact of such control variables in different conditions. The results clearly indicate that if shiftable loads are of suitable size, they have a more promising as tools to both reduce losses and to flatten the peak load through the HV/MV bus. Many tests have been carried out on a real experimental MV system in the area of Rome Italy.
An Energy Blockchain, a Use Case on Tendermint
The recent advances in distributed energy systems require new models for exchanging energy among prosumers in microgrids. The blockchain technology promises to solve the digital issues related to distributed systems without a trusted authority and to allow quick and secure energy transactions, which are verified and cryptographically protected. Transactions are approved and subsequently recorded on all the machines participating in the blockchain. This work demonstrates how users, which are nodes of the energy and digital networks, exchange energy supported by a customized blockchain based on Tendermint. We focus on the procedures for generating blocks and defining data structures for stori…
The Global Grounding System: Definitions and guidelines
The present paper presents the preliminary results of the ongoing Italian METERGLOB project on the contribution given by the exposed conductive parts to a Global Grounding System. One of the expected results of METERGLOB is to carry out guidelines for the identification of a Global Grounding System. These guidelines must be defined on the basis of the definitions and methods present in the current international standards on grounding and safety. In the paper some definitions and elements to be taken into account for the identification of a Global Grounding System are given.
A statistic approach of cables ageing in MV lines on thermal and electrical combined stress
The paper introduces a methodology that through a probabilistic characterisation of load for MV network, and implementing a life model for combined electric and thermal stresses, simulates the process of ageing of the insulating materials evaluating the expected life time of the cable. Such evaluation is necessary to the possibility of assuming less restrictive thermal overloading limits on electrical cables, with the consequential increase on reserve that cables could offer. A numerical example is reported to better explain the methodology
On the hazardous situations due to the presence of HV/MV substations in urban areas
The paper focuses on the hazardous situations that can rise in urban areas in case of earth fault inside a High Voltage/Medium Voltage station. IEEE and IEC/EN Standards and technical documents are examined and discussed, in order to propose some practical guidelines for a safe integration of such installations in contexts characterized by the presence of low voltage systems and not trained persons.
Applicational Aspects of a New Diagnostic Methodology for Fault Location in MV Networks: Problems, Solutions and Improvements
The electrical energy market liberalization has encouraged utilities to make new investments at distribution level so as to attain higher quality levels. Service continuity is one of the aspects of greater importance in the definition of the quality of the electrical energy, for this reason, the research in the field of faults diagnostic for distribution systems is spreading ever more. The Authors have just developed a new methodology for diagnostic management of automated distribution systems. The technique is based on the use of circuital models of the electrical system resulting from the composition of quadripoles. In this paper, after a brief description of the proposed approach, the is…
A simulation model for electromagnetic transients in lightning protection systems
This paper deals with the evaluation of electromagnetic transients in a lightning protection system (LPS). A field approach is used, based on the numerical solution of a modified version of the thin-wire electric field integral equation in the frequency domain. Time profiles of interesting electromagnetic quantities are computed by using a discrete fast Fourier transform algorithm. The model takes into account coupling effects among aerial parts and ground electrodes in order to correctly estimate the quantities which can determine electromagnetic hazard inside the LPS; transient touch and step voltages can be easily evaluated also taking into account the human body presence on the soil sur…
A study on the assessment of the production costs curves in micro-grids
In micro-grids, due to their small scale, there is commonly only one power supplier. A competitive wholesale market hardly exists, so the question about how to consider market issues for small producers within micro-grids arises. On the other hand, the specific features of micro-grids where load and generated power hardly find a balance, require that customers take part to regulation issues, also using demand-response (DR) programs. In this paper, price responsive (PR) policies and their programs are discussed to answer this question. A case study of a micro-grid with one micro-turbine and two photovoltaic (PV) generators is analyzed to assess the overall production cost in order to build a…
A Holistic Vision of Smart Cities: An Opportunity for a Big Change
The depletion of energy resources on the one hand, and the population growth on the other, forced the society at all levels (local, national and international) to turn its attention to the identification of new forms of protection of the environment and the waste reduction for a new eco-sustainable way of living. The process of massive urbanization already in place, exacerbated by the movement of large masses of people in search of a more human form of life, is putting severely under test the livability within our cities, bringing out the inefficiency of existing management and organization models. Daisaku Ikeda said: “Certainly, the density of urban populations means that problems are conc…
A multi-agent system reinforcement learning based optimal power flow for islanded microgrids
In this paper, a distributed intelligence algorithm is used to manage the optimal power flow problem in islanded microgrids. The methodology provides a suboptimal solution although the error is limited to a few percent as compared to a centralized approach. The solution algorithm is multi-agent based. According to the method, couples of agents communicate with each other only if the buses where they are located are electrically connected. The overall prizing system required for learning uses a feedback from an approximated model of the network. Based on the latter, a distributed reiforcement learning algorithm is implemented to minimize the joule losses while meeting operational constraints…
Minimum power losses by using droop coefficients regulation method with voltage and frequency constraints in islanded microgrids
In this paper, a droop coefficients regulation methodology is proposed for an islanded microgrid to optimize the power losses. Based on the P-f and Q-V relations to adjust the droop coefficients at every loading condition, the optimized operating set point generates minimum power losses operation while satisfying the constraints of voltage and frequency limitation. A 9-bus case study is here implemented to show the effectiveness of this new approach as well as the improved operation quality of the system.
Multi-objective optimized management of electrical energy storage systems in an islanded network with renewable energy sources under different design scenarios
The subject addressed in this paper is the definition of some strategies for the design and the optimaized management of EES (Electrical Energy Storage) systems, for an existing islanded distribution network supplying the Island of Pantelleria (Italy) in the Mediterranean Sea. In the paper the authors have drawn interesting conclusions through the application of an efficient MO (multi-objective) optimization algorithm, the NSGA-II, minimizing the energy losses in the grid, the total electricity generation cost and the greenhouse gas emissions. The results obtained for different installation scenarios of the EES are presented and discussed, putting into evidence the technical, environmental …
A New Protection Strategy for Electrical Distribution Systems
In this paper, the authors propose a new protection strategy for electrical Medium Voltage distribution networks, based on a distributed intelligence system composed of a central unit and of many local processing units. The distributed intelligence system can precisely identify and locate faults in suitably limited times. Each local processing unit is composed of a data acquisition system and a data analysis system. The first allows the accurate reconstruction of the fundamental using only 1.5 cycles of under fault transient electrical quantities. The second performs suitably precise on-line fault diagnosis based on the data provided by the data acquisition module. The data acquisition algo…
Influence of LV neutral grounding on global earthing systems
International Standards define a Global Earthing System as an earthing net created interconnecting local Earthing Systems (generally through the shield of MV cables and/or bare buried conductors). In Italy, the regulatory authority for electricity and gas requires distributors to guarantee the electrical continuity of LV neutral conductor. This requirement has led to the standard practice of realizing “reinforcement groundings” along the LV neutral conductor path and at users’ delivery cabinet. Moreover, in urban high-load scenarios (prime candidates to be part of a Global Earthing System), it is common that LV distribution scheme creates, through neutral conductors, an effective connection…
A practical method to test the safety of HV/MV substation Grounding Systems
The adequacy of a Grounding System (GS) to the safety conditions has to be periodically tested by measurements. The test methods and techniques used to verify the electrical characteristics of the GS include the measurements of step and touch voltages. The goal of the test is to verify that touch voltage and step voltage remain below a safe value in all the zones of the installation. The measurements can present some operational difficulties. The purpose of this paper is to present the procedure, step-by-step, of a practical method of measuring touch/step voltages in grounding systems located in urban or industrial areas with reduced accessibility. The suggested method uses auxiliary curren…
Wavelet-based efficient simulation of electromagnetic transients in a lightning protection system
In this paper, a wavelet-based efficient simulation of electromagnetic transients in a lightning protection systems (LPS) is presented. The analysis of electromagnetic transients is carried out by employing the thin-wire electric field integral equation in frequency domain. In order to easily handle the boundary conditions of the integral equation, semiorthogonal compactly supported spline wavelets, constructed for the bounded interval [0,1], have been taken into account in expanding the unknown longitudinal currents. The integral equation is then solved by means of the Galerkin method. As a preprocessing stage, a discrete wavelet transform is used in order to efficiently compress the Fouri…
A Feasibility Study for the Transition to Electric Mobility in the Island of Favignana
The energy transition and climate neutrality are a short time scenario as climate concerns are rising fast. Small islands are natural microgrids in which the energy transition is subjected to economic and regulatory constraints and highly challenged by technical issues. As a first step, the Mediterranean island of Favignana has been considered in this study, to assess how electric mobility could impact the power system. According to the plans from the local decision makers, the island is moving towards a full public electric mobility in the near term, also due to the participation in the BloRin project. For this reason, a feasibility study about the technical and environmental impact of ele…
An analysis methodology to evaluate the contribution to electrical security given by bare buried conductors in a system of intertied earthing grids
The paper presents an analysis methodology for a single-line-to-ground fault, occurring at a secondary MV/LV substation in a power network formed by a HV/MV station, feeding, through a MV tri-phase cable line, N MV/LV substations whose earth electrodes are interconnected by bare buried conductors. In the preliminary explanation of the methodology, earth buried conductors are studied in their double function of earth electrodes and connection elements between earthing grids, both in absence and in presence of other interfering conductors. Subsequently analyzed is, with a distributed parameters approach, the system constituted by an earth buried conductor and a MV tri-phase cable line. The eq…
On the effects of HV/MV stations on global grounding systems
The METERGLOB project has faced the issue of the identification of Global Grounding Systems. One of the main point of the problem is to define if an interconnection of single grounding systems gives place to a Global Grounding System in any condition and for every kind of ground fault. This paper focuses the attention on what happens in the case of single line to ground fault inside a HV/MV station whose ground electrode is connected to the cable' shields of the MV lines outgoing the station and supplying the secondary substations of a given area.
Voltage Profile Improvement for Soc Son's Low-Voltage Grid with High Penetration of PV Systems by Optimizing the Location of SVC Devices
This paper presents a method that is applied to optimize the placement of Static VAR compensators in a real low-voltage grid in the Vietnamese territory. In this way, the voltage profile of the distribution grid turns to be improved. A heuristic method, the Binary Particle Swarm Optimization, is used to find a solution to this problem within the Matlab environment. A case study that considers a high penetration of rooftop PV systems in a branch of Soc Son distribution grid is implemented to show the efficiency of the optimization method for this specific application.
An efficient diagnostic technique for distribution systems based on under fault voltages and currents
Service continuity is one of the major aspects in the definition of the quality of the electrical energy, for this reason the research in the field of faults diagnostic for distribution systems is spreading ever more. Moreover the increasing interest around modern distribution systems automation for management purposes gives faults diagnostics more tools to detect outages precisely and in short times. In this paper, the applicability of an efficient fault location and characterization methodology within a centralized monitoring system is discussed. The methodology, appropriate for any kind of fault, is based on the use of the analytical model of the network lines and uses the fundamental co…
A new methodology for distribution systems faults identification, location and characterization
PurposeIdentify a new methodology for fault characterization, identification and location in electrical distribution systems, based on the use of matrix algebra.Design/methodology/approachThe developed diagnostic methodology is based on a high precision analytical model of the network using a distributed parameters representation.FindingsTest results have proved the approach to be efficient and precise, while providing a generalized quadripolar model of a line affected by the most common kinds of fault.Research limitations/implicationsGeneralization to a greater number of fault cases, experimental tests.Practical implicationsUtilities are quite interested in such items, since the new requir…
A new architecture for Smart Contracts definition in Demand Response Programs
The present paper shows the possibility to use a smart contract for defining a distributed Demand Response mechanism. The use of the blockchain and smart contracts for the Demand Response mechanism allows the creation of an automatic system, where network users can communicate with the DSO to provide their flexibility. The blockchain ensures that the same information is shared among the users of the grid, while preserving user privacy. The DSO notifies the request to increase or reduce the load in a given period of the day using channels, a native abstraction of Hyperledger Fabric. The smart contract computes the support provided by each user to fulfill the requested load adaptation and aut…
Interconnections criteria of grounding grids in global grounding systems
A Global Grounding System is defined as the combination of local grounding systems, obtained by their interconnection, which ensures, thanks to their proximity, that no dangerous touch voltages can arise. The interconnection of grounding systems via the armors of the MV cables, between secondary substations and HV/MV stations is herein analyzed to verify the effects on touch voltages in ground-fault conditions. In particular, two main issues are discussed: 1) the transfer of dangerous voltages to secondary substations, due to ground-faults occurring at the HV/MV station; 2) the reduction in the magnitude of the ground potential rise due to ground-fault conditions at secondary substations, t…
Improving the energy efficiency of an islanded distribution network using classical and innovative computation methods
The paper presents the analysis of some potentially suitable actions for reducing the energy losses of an islanded Medium Voltage distribution network, with the aim of improving electricity distribution efficiency. For this purpose, four actions are considered: 1) increasing the network's rated voltage; 2) reactive power compensation through static capacitor banks; 3) reactive power compensation through switchable capacitor banks; 4) installation of distributed photovoltaic (PV) generation. The first two measures are typically taken into account by the distribution system operators and can be examined by means of classical design methods, whereas the latter two more innovative actions are t…
Energy Management Systems and tertiary regulation in hierarchical control architectures for islanded microgrids
In this paper, the structure of the highest level of a hierarchical control architecture for micro-grids is proposed. Such structure includes two sub-levels: the Energy Management System, EMS, and the tertiary regulation. The first devoted to energy resources allocation in each time slot based on marginal production costs, the latter aiming at finding the match between production and consumption satisfying the constraints set by the EMS level about the energy production in each time slot. Neglecting the efficiency of the different energy generation systems as well as that of the infrastructure for electrical energy distribution, the problem dealt with by the EMS sub-level is linear and can …