Legal Liability of Professional Engineers: The Case of a Fire at a Shopping Center

In this paper, the authors discuss the legal liabilities of the professional engineer as both the engineer of record of a project and the construction site manager. In particular, this paper analyzes the case of a fire at an end-user MV/LV substation of a shopping center in Italy, occurred a few years after maintenance works on the electrical installation. The professional engineer who had designed and overseen the construction of the substation was accused of criminal negligence. The authors through the examination of applicable technical standards, as well as of safety regulations, demonstrate that the professional engineer had acted diligently and that there was no ground for the neglige…

Grid-Following and Grid-Forming MODELS in ATP-EMTP for Power Systems Simulation

The paper presents the models of grid-following and grid-forming converters in the software ATP-EMTP for power systems simulation. The models are developed using the MODELS language, they are described in details discussing all issues and aspects related to the implementation, and they are also shared as open source models. The models are validated with a simulation-based approach, comparing the results with the models developed in MATLAB/Simulink and in NEPLAN, considering both the phasor RMS and EMT time domains, and thus performing a comprehensive cross-platform and cross-domain validation. In line with the spirit of the ATP software and community, the models of grid-following and grid-f…

Studio di fattibilità e progettazione preliminare di dimostratori di reti elettriche di distribuzione per la transizione verso reti attive. Report 2 – Simulazioni e valutazioni di progetto per gli scenari selezionati

No-Load Energization of Very Long EHV Mixed Overhead-Cable Lines

On the de-energization of over-head low-voltage lines under high-impedance fault conditions

Downed distribution conductors in overhead distribution systems, may not be a concern for equipment, but greatly challenge the safety of persons, as well as the integrity of properties. Upstream overcurrent protective devices may not be able to detect the magnitudes of fault currents resulting from these high-impedance faults. Even though protective devices capable to detect such faults have been available on the market, not all the utilities have equipped their stations with these products, likely due to the costs. In this paper, the authors formalize the problem, and propose a possible cost-effective solution for the low-voltage over-head lines with neutral wire. Such solution includes a …

Forensic Analysis of Fire in a Substation of a Commercial Center

In this article, the authors discuss the legal liabilities of the professional engineer as both the engineer of record of a project and the construction site manager. In particular, this article analyzes the case of a fire at the end-user medium voltage–low-voltage (MV–LV) substation of a shopping center in Italy, which occurred a few years after the maintenance works on the electrical installation. The professional engineer who had designed and overseen the construction of the substation was accused of professional negligence. The authors through the examination of applicable technical standards, as well as of safety regulations, demonstrate that the professional engineer had acted diligen…

Transition of a Distribution System towards an Active Network. Part I: Preliminary Design and Scenario Perspectives

In an European perspective, the focus of Smart Grids initiatives (SET Plan - Strategic Energy Technology Plan) is strictly linked with the main commitment to achieve the goals of the Climate and Energy Package 20-20-20, at the light of the three main pillars of the European energy policy: competitiveness, sustainability and security of supply. Smart grid technologies will enable load levelling of the electrical grid, allowing a power company to run cleaner power sources - such as hydroelectric, wind, or solar - while reducing the need to use carbon-emitting gas, coal, or oil plants to meet peak demand. In this framework the proposed paper refers about the technical economical feasibility st…

Transient behaviour of a “mixed” overhead-cable EHV line under lightning events

Recently, in many countries have been undergone or are planning links with AC extra-high voltage (EHV) underground cables. Cable lines offer the possibility of a reduced environment impact and for this reason they are often the only alternative for the reinforcement or the expansion of power system accepted by public opinion. The coexistence of overhead and cable line in the so called ¿mixed¿ lines, however, raises several questions regarding their behaviour both in steady state and in transient. The purpose of this work is to investigate the transient behaviour of a mixed overhead-cable EHV line under lightning events, describing the effects of the following overvoltages on the system. The…

Synthetic Inertia Impact on Inter-Area Oscillations of the Continental Europe Power System

The overall kinetic energy reduction due to increasing share of converter-interfaced generation (CIG) has been investigated so far by several works for systems of different types and sizes. The so called synthetic inertia is one of the most common and reviewed solutions to the issue of system inertia reduction. The paper investigates the effects of synthetic inertia as frequency service provided by the CIG sources for the Continental Europe (CE) synchronous area using a detailed large scale dynamic model. The model - provided in the basic form by the System Protection & Dynamics (SP&D) group of the ENTSOE - is properly developed substituting a determined amount of synchronous machin…

Ancillary Services in the Energy Blockchain for Microgrids

The energy blockchain is a distributed Internet protocol for energy transactions between nodes of a power system. Recent applications of the energy blockchain in microgrids only consider the energy transactions between peers without considering the technical issues that can arise, especially when the system is islanded. One contribution of the paper is, thus, to depict a comprehensive framework of the technical and economic management of microgrids in the blockchain era, considering, for the first time, the provision of ancillary services and, in particular, of the voltage regulation service. When more PV nodes are operating in the grid, large reactive power flows may appear in the branches…

Improving angle stability by switching shunt reactors in mixed overhead cable lines. An Italian 400 kV case study

Stringent environmental constraints make the construction of new transmission overhead lines more and more difficult. Alternatively, today it is possible to use cable lines for high (HV) and extra-high (EHV) voltage systems. The configuration of the so-called mixed lines can create some problems in the operation of the electrical system, both during steady-state and transient conditions. In particular, the system stability is one of the main concerns when analyzing the dynamic response of power systems. In this paper, the study of angular stability of a system containing a mixed line is presented: a specific control logic applied to the shunt reactors of the mixed line is proposed as improv…

A Cost-Effective Solution for Clearing High-Impedance Ground Faults in Overhead Low-Voltage Lines

Downed distribution conductors in overhead distribution systems may not be a concern for equipment but greatly challenge the safety of persons, as well as the integrity of properties. Standard overcurrent protective devices may not be able to detect the magnitudes of currents resulting from high-impedance ground faults. Sophisticated relays able to detect high-impedance ground faults have been available to electric utilities. However, their implementation is rather uncommon, especially in developing countries, most likely due to their costs. In this paper, the authors formalize the problem, and propose a possible cost-effective solution for low-voltage overhead lines with neutral wire. This…

Generalized power-angle control for grid-forming converters: A structural analysis

Several control schemes have been recently proposed and studied as grid-forming controls for power converters. In all these schemes, the power-angle control loop is the part which defines the fundamental capabilities of the grid-forming control: that control loop governs in fact the inherent synchronization mechanism of the power converter, the power sharing with the other generation sources in the system and the oscillatory characteristics of the converter-based resource. This article introduces a general formulation for the power-angle control characterizing the grid-forming concept for power converters. The generalized power-angle control is based on a polynomial fraction formulation, an…

Transient stability assessment of SMIB System with Mixed overhead-cable line – Sensitivity analysis

Synchronizing Interactions Between Different Types of Grid-Forming Converters in Smart Grids

The work investigates the transient synchronizing interactions between different types of grid-forming controls. Two well-known grid-forming schemes are implemented and considered for analysis: a droop-based control and a swing-based control. The two controls are examined for a temporary loss of synchronism. The analysis is performed considering two different conditions for the grid interconnecting the converters: a resistive-inductive grid and a mainly inductive grid. The first case corresponds to actual conditions in low and medium voltage applications. The second case is realized with the implementation of a virtual reactance in the grid-forming control scheme. The analysis of the result…

A Simulation Analysis for Assessing the Reliability of AC/DC Hybrid Microgrids - Part I: Underground Station and Car Parking

This paper reports the results of a simulation study with the aim of evaluating the capability of two portions of a hybrid AC/DC MV/LV network of maintaining their operation in off-grid mode during the loss of the main AC grid due to a failure. In particular, the study aims to verify, in the case of islanded operation of the two microgrids, the continuity of the electricity service by exploiting the local generation plants, Energy Storage Systems (ESSs), and other flexible resources managed by suitable algorithms in different energy scenarios. The analysis was carried out considering two microgrids: an underground station and a car parking with Electric Vehicles (EVs). For assessing the per…

Energy Management System in Grid-Connected Small Scale AC/DC Microgrids Including Renewable Sources and Flexible Loads

The growth of small scale microgrids with diverse distributed generations has drawn attention to their effective energy management. In this paper, for various energy scenarios, an energy management system is adopted to minimize the energy purchased by a hybrid AC/DC microgrid from the upstream grid due to high peak-hour energy prices and maximise generation from renewable sources, while adjusting the most optimal charge/discharge control strategies for flexible loads such as electric vehicles and storage systems, and the supply of non-controllable loads. In addition, peak shaving is simultaneously implemented in this proposed model without considering minimum power deviation as an objective…

Inter-area oscillations in the 500-kV Vietnamese power system

The paper presents the study of the 500-kV Vietnamese power system. The oscillatory response of the system is analyzed both with a modal analysis and a time domain analysis. The 500-kV system of Vietnam is modeled in details, including all the power plants with the corresponding regulators. The model is developed in collaboration with the Institute of Energy Science IES-VAST of Vietnam and it is validated with the data provided by the National Load Dispatch Centre (NLDC) of Vietnam. The simulation results reveal a clear identification of potential inter-area oscillations between North and South of the Country. A worsening of the observed phenomenon should be considered as possible, especial…

Impact of RES penetration on the frequency dynamics of the 500 kV vietnamese power system

The increase of renewable energy sources (RES) typically operating as converter-interfaced generation (CIG) is progressively causing a significant change of power systems operation paradigm. The reduction of the overall available kinetic energy and the consequent impact on the dynamic response of the system is a relevant issue currently under investigation in academic and industrial scopes. The work analyzes the impact of different CIG penetration in the three areas of the 500 kV Vietnamese power system, North, Center and South. The system is modified substituting conventional synchronous generation with converter-interfaced generation. The models of power converters and corresponding contr…

Grid-Forming Converters in Weak Grids – The Case of a Mediterranean Island

The existing power network of a Mediterranean island is used as test bed for the study of grid-forming converter dynamics in weak grid conditions. The control scheme adopted for the converter falls in the category of the so called virtual synchronous machines (VSM). Particular attention is committed to the interaction between the converter controls and the synchronous machines dynamics. Time delays typically associated to measurements and filters are considered in the study, and included in the system model with a specific mathematical approach. Time-domain simulations show the occurrence of oscillatory instability in the system, with VSM and synchronous machines swinging against each other…

Power System Oscillations with Different Prevalence of Grid-Following and Grid-Forming Converters

The oscillatory behaviour of the power system is an aspect that is significantly affected by the increasing integration of converter-based generation sources. Several works address the impact of non-synchronous generation on the operation of the system from different points of view, but only a few studies focus on power-frequency oscillations with a prevalence of generation sources interfaced through power electronics. A lack of research can be found in particular in the comparative analysis of the two main control strategies for power converters, namely grid-following and grid-forming. The article aims to contribute to this direction, starting from a theoretical analysis of the two control…

DEMAND Project: An algorithm for the assessment of the prosumers’ flexibility

Demand side aggregation represents an important opportunity for ancillary services provision due to the potential that the coordinated management of distributed resources has on affecting power systems' operation. In this framework, the Aggregator has a main role and takes on different relationships with the other actors of the power system, usually becoming a mediator between the prosumers and the distribution system operator. The DEMAND project introduces a new point of view in demand side aggregation by proposing a new framework where the Aggregator is no more needed and prosumers can share and combine their flexibility in a new aggregation platform called Virtual Aggregation Environment…

Dynamic Control of Static Converters for the Transition from Grid-on to Grid-off Operation of AC/DC Microgrids

In this paper, specific control logics defined for generators, controllable loads and electric energy storage systems are illustrated in order to improve the reliability of AC/DC hybrid microgrids in their grid-off operation following failure events such as short-circuits, line breaks, sudden disconnections of generating units or loads, etc. After defining specific control schemes, these were modelled in a digital environment and finally tested with dynamic simulations. Finally, the paper highlights the role of virtual synchronous machine control for the self-healing capacity of islanded hybrid microgrids.

Angle Stability Improvement by Switching Shunt Reactors in Mixed Overhead-Cable Lines

Effects of Demand Side Management on the Operation of an Isolated LV Microgrids

The work presents the results of a study regarding the impact of Demand Side Management actions on flexible loads distributed at the domestic end-users' facilities in an isolated low voltage microgrid. Aim of the research study is to evaluate how the implementation of local control actions on the end-user's side can impact on the operation of the isolated microgrid. The Demand Side Management is applied by each domestic user to optimize the operation of its own resources following well-defined operative steps. The study is carried out implementing a suitable model of the microgrid in Neplan environment, while the daily controlled load profiles of the end-users are evaluated using the Montec…

Effects of COVID19 pandemic on the Italian power system and possible countermeasures

Abstract The paper analyses the dramatic effects of the first wave of the COVID-19 pandemic on the Italian power system, considering the impacts on load and generation, market issues and ancillary services provision. During the period between March and May 2020, the Italian scenario was considered as exemplary due to the large reduction of loads and thermal generation caused by the hard lockdown across the Country. Italy has experienced the most severe effects of pandemic in terms of increase of death rates and of pressure on the health system as well as severity of the countermeasures. As a domino effect, the total lockdown of one of the most industrialized countries in the world has creat…

Impact of the high share of converter-interfaced generation on electromechanical oscillations in Continental Europe power system

This study investigates the effects of converter-interfaced generation integration on the dynamic response of the power system of Continental Europe. The system is analysed with a large-scale dynamic model of the entire synchronous area, considering different instantaneous integration percentages of converter-interfaced generation across the system. The study focuses on the reduction of the overall available kinetic energy and the impact on frequency dynamics and system oscillations. The dynamic model of the system originally provided by ENTSO-E is further developed according to a specific methodology, replacing a determined amount of synchronous generation and introducing a corresponding a…

Flexibility Services to Minimize the Electricity Production from Fossil Fuels. A Case Study in a Mediterranean Small Island

The design of multi-carrier energy systems (MESs) has become increasingly important in the last decades, due to the need to move towards more efficient, flexible, and reliable power systems. In a MES, electricity, heating, cooling, water, and other resources interact at various levels, in order to get optimized operation. The aim of this study is to identify the optimal combination of components, their optimal sizes, and operating schedule allowing minimizing the annual cost for meeting the energy demand of Pantelleria, a Mediterranean island. Starting from the existing energy system (comprising diesel generators, desalination plant, freshwater storage, heat pumps, and domestic hot water st…

Modeling of a Smart Grid System Using Real Time Data οn Neplan

The Institute for Energy and Transport (IET) is one of the seven institutes of the Joint Research Centre, which is a Directorate-General of the European Commission. IET is based both in Petten, the Netherlands, and Ispra, Italy, and has a multidisciplinary team of around three hundred academic, technical and support staff members. The mission of IET is to provide support to European Union policies in order to ensure sustainable, safe, secure and efficient energy production, distribution and use. The Energy Security Unit (ESU) is part of IET based in Petten and Ispra. A research action set up within this unit is devoted to studies on smart electricity systems (SES) and operates a Smart Grids…

On the Impact of Heat Pumps Electric Load on the Power Consumption of Lampedusa

The present paper reports the results of a simulation study regarding the impact of the adoption of heat pumps for domestic hot water production in the island of Lampedusa (Italy). In the study, it has been assumed to replace electric storage water heaters with heat pumps at every dwelling of the about four thousand domestic end-users of the island and, in addition, to control the heat pump operation in order to enhance some parameters that characterize the quality of the generation and distribution system of the island (power peak, energy losses and voltage drop). According to the results of the simulations, while the replacement of electric storage water heaters with heat pumps is able to…

Inertial response of isolated power networks with wind power plants

The constant increase of power generation provided by renewable energy source (RES) power plants is causing a progressive reduction of the overall inertia of the power systems. Especially in the case of small, isolated power networks, the replacement of conventional generation plants with RES power plants can affect significantly the frequency response of the system. The critical low-inertia conditions can be improved by the introduction of specific additional controls to the RES power converters. These control schemes are known as “synthetic inertia” or “virtual inertia” controls. The paper analyzes the impact of a derivative-based inertial control on a small, isolated power system, with a…

Analysis and simulations of the primary frequency control during a system split in continental europe power system

The occurrence of system separations in the power system of Continental Europe has been observed in recent decades as a critical event which might cause power imbalances higher than the reference incident specified per system design, representing an actual challenge for the stability and safe operation of the system. This work presents an analysis and simulations of the primary frequency control in the Continental Europe synchronous area in conditions of system separation. The adopted approach is based on fundamental aspects of the frequency-containment reserve process. The analysis takes an actual event into consideration, which determined the separation of the system in January 2021. The …

New Energy Corridors in the Euro-Mediterranean Area: The Pivotal Role of Sicily

The present paper deals with the new opportunities deriving from the interconnections of the European and North African transmission systems. In order to achieve a single international market for electricity exchanges, interconnections between networks in different countries are becoming increasingly important and Sicily, for its geographical position in the middle of the Mediterranean Sea, will undoubtedly play an important role as an electrical bridge between Europe and the North Africa in the near future. The paper, presenting the actual electro-energetic context of Tunisia, reports the new important interconnection already realized in South Italy (in particular in Sicily) and describe t…

FROM FUEL BASED GENERATION TO SMART RENEWABLE GENERATION: PRELIMINARY DESIGN FOR AN ISLANDED SYSTEM. PART I: TECHNICAL ISSUES AND FUTURE SCENARIOS

The subject addressed in this paper is the analytical study of the transition of the energy generation system for a real MV/LV distribution system from a ‘fuel based’ one to a distributed and smart ‘renewables based’ one. The paper outlines the technical issues related to such transition from one type of system to the other. The study is carried out for a real islanded MV/LV distribution network located in the Island of Pantelleria. The economical issues regarding the above transition are focused in a companion paper.

Blockchain for power systems:Current trends and future applications

Abstract Today, the blockchain is synonymous of technological innovation, being recognized among the 10 top strategy technologies in 2018 by the consulting company Gartner, it is more and more adopted in different sectors. However, the initial enthusiasm around this technology is going beyond the peak of inflated expectations, towards more stable applications in money transactions, cryptocurrencies and Digital Commodity Exchanges. Essentially, misguided efforts, the overuse of blockchain, and the Bitcoin's price drop have been the main reasons for this decay in expectations. Nevertheless, the exploitation of the blockchain technology in the power systems area appears largely underexplored, …

Building Automation and Control Systems and Electrical Distribution Grids: A Study on the Effects of Loads Control Logics on Power Losses and Peaks

Growing home comfort is causing increasing energy consumption in residential buildings and a consequent stress in urban medium and low voltage distribution networks. Therefore, distribution system operators are obliged to manage problems related to the reliability of the electricity system and, above all, they must consider investments for enhancing the electrical infrastructure. The purpose of this paper is to assess how the reduction of building electricity consumption and the modification of the building load profile, due to load automation, combined with suitable load control programs, can improve network reliability and distribution efficiency. This paper proposes an extensive study on…

Analysis of a Fast Reserve Unit Behaviour with Additional Modular Synthetic Inertia Control

The paper presents the results of a theoretical study on the behaviour of a battery storage system operated as a Fast Reserve Unit and equipped with additional synthetic inertia control. The Fast Reserve Unit is assumed connected to the transmission system of Sicily, operated as an isolated grid in order to show more clearly the effect of the Fast Reserve Unit intervention during a power imbalance. The unit is controlled also to provide synthetic inertia with a conventional control scheme and with a new scheme proposed by the authors and named “Modular Synthetic Inertia”. The latter has been conceived for offering a modular response as a function of the Rate of Change of Frequency, to avoid…

An original control strategy of storage systems for the frequency stability of autonomous grids with renewable power generation

This work examines the operation of the autonomous power system of a geographical island assuming the integration of significant generation shares from renewable energy sources and the installation of the required storage systems. The frequency stability of the system is investigated considering different operating conditions, in terms of load demand and renewable power generation. The main focus of the work is an original control strategy specifically designed for power converters interfacing storage units to the grid. The proposed strategy is based on an extended frequency droop control, which selects specific droop settings depending on the operating mode—charge or discharge—of the stora…

Electrical Safety Analysis in the Presence of Resonant Grounding Neutral

The resonant grounding is one of the possible methods of the system neutral grounding for the medium voltage distribution. IEEE standards do define this grounding configuration, but important advantages and drawbacks of the resonant grounding might not be fully known, due to its rather uncommon application in North America. On the other hand, resonant grounding in Europe is imposed by the increased requirements for power quality, especially for medium-voltage (MV) industrial users, imposed to electric utilities by regulatory authorities, with the purpose to protect the interests of users and consumers. Level of the continuity of the service, magnitude and phase of ground-fault currents, mag…

A Simulation Analysis of VSM Control for RES plants in a Small Mediterranean Island

The paper presents an application of Virtual Synchronous Machine control for managing inverter-interfaced renewable energy sources in a small Mediterranean island not supplied by the main grid. In the proposed analysis, the island's renewables-based generators area assumed interfaced to the grid by voltage source converters with a swing controller and a vector-current controller with two different options for the reference current for regulating the voltage at the Point of Common Coupling and the active power output. The system, modeled in PScad environment, allows to verify the response of the renewables-based generators with VSM control in the presence of a fault in the grid.

A Simulation Analysis for Assessing the Reliability of AC/DC Hybrid Microgrids - Part II: Port Area and Residential Area

This paper reports the second part of a simulation study with the aim of evaluating the ability of two portions of a hybrid AC/DC MV/LV network in maintaining their operation in off-grid mode during the loss of the main AC grid due to a failure. In particular, this paper follows a dual purpose: first, it analysis two microgrids in a residential area and a port zone capability of operating in islanded mode, applying a probabilistic approach, while there is different energy use cases, and second is to evaluate some reliability indicators.

STUDI DI TRANSITORI ELETTROMECCANICI ED ELETTROMAGNETICI PER LINEE MISTE DI TRASMISSIONE AEREOCAVO

Impact of Demand Response Control Logic on Isolated Island's Distribution Networks

The work presents the results of a study regarding the impact of some Demand Response control logics on an isolated distribution network. The proposed control is divided into precise steps in which the coordination between the general aggregator controller and the single local Energy Management Systems is developed and illustrated with details. The control is applied to the flexible loads and to the storage systems of photovoltaic plants installed at the end-users' houses and connected to the network. The study is carried out delivering a suitable network model of the island's system, with the implementation of load profiles for all the loads of the network for a total simulation time of 24…

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…

A Methodology for Exploiting Smart Prosumers’ Flexibility in a Bottom-Up Aggregation Process

The electrical power system is evolving in a way that requires new measures for ensuring its secure and reliable operation. Demand-side aggregation represents one of the more interesting ways to provide ancillary services by the coordinated management of a multitude of different distributed resources. In this framework, aggregators play the main role in ensuring the effectiveness of the coordinated action of the distributed resources, usually becoming mediators in the relation between distribution system operators and smart prosumers. The research project DEMAND recently introduced a new concept in demand-side aggregation by proposing a scheme without a central aggregator where prosumers ca…

Short-circuit Calculations in Hybrid AC/DC Microgrids

In this paper, the issues related to short-circuit calculations in hybrid AC/DC microgrids are discussed. The reference standard for short-current calculations in DC systems is the IEC 61660, which provides a mathematical formulation of the problem. The standard only includes radial DC grids and does not consider a more complex system, such as meshed DC systems or a hybrid AC/DC microgrid. This paper proposes a generalized approach that can be used independently of the characteristics of the hybrid system. The proposed approach is applied to two test microgrids and the results are compared with those obtained simulating the same grids with Neplan 360.

Frequency dynamics of power systems with temporally distributed disturbances

Abstract The frequency dynamics and stability of power systems is essentially affected by nature and characteristics of the disturbances occurring in the system. Conventionally, frequency transients are examined assuming a single disturbance applied at a given time. However, actual incidents in the power systems can be generally composed of a temporal sequence of events, and thus characterized by multiple power imbalances of different magnitudes and time offsets. The consideration of the effects of the temporal distribution of power imbalances is important for two main reasons: the impact on the frequency dynamics of the system in terms of frequency metrics such as minimum instantaneous fre…

Evaluation of the optimal renewable electricity mix for Lampedusa island: The adoption of a technical and economical methodology

Abstract Worldwide, the majority of small islands not connected to the main grid is still dependent on fossil fuels. From an economic and environmental point of view, this condition is no more sustainable given the high costs for electricity generation and the high level of pollutant emissions. Furthermore, the dependence on fossil fuel represents a risk for the security of the supply of several small developing Countries since they are obliged to import those resources from foreign Countries. The introduction of renewable energy sources in small islands represents a valid solution to solve these problems. In this context, the paper investigates the case of Lampedusa, a small Italian island…

Stability Analysis in a Vietnam Small Island for the Deployment of a Nearshore Wave Power Plant

The requirement for a more sustainable energy mix is promoting the spreading of technologies supplied by renewable sources. However, the introduction of unprogrammable energy sources in small electrical grids could jeopardize the stability of the entire system. In this context, the paper analyses a small island in Vietnam, assessing the effects due to the installation of a new power plant supplied by sea wave energy. While the installation of this technology could represent a great opportunity to reduce the local energy dependence, on the other side the quality of the supply could be worsened. Solutions are assessed to allow a good network service.

A Comparison between RMS and EMT Grid-Forming Implementations in MATLAB/Simscape for Smart Grids Dynamics

The article presents a comparison between phasor RMS and EMT models for grid-forming converters. The specific aspects related to the implementation in Simscape Electrical of MATLAB/Simulink are discussed for both RMS and EMT time-domains. The comparison between the different implementations is performed with the simulation of two widely studied grid-forming schemes, the virtual synchronous machine and the power-synchronization control. The simulation-based comparison examines transient phenomena with different characteristics and time scales, including frequency transients, phase jumps and short-circuit events. Specific indications regarding limitations and suitability of grid-forming model…

A decentralized load control architecture for smart energy consumption in small islands

Abstract In this paper we propose the adoption of Overgrid, a new decentralized load control architecture, for balancing the energy production variations introduced with the adoption of renewable sources, facilitating and improving the smart energy retrofit. The system is presented and applied for managing the aggregated daily load profile of a community of domestic end-users in the island of Lampedusa, Italy, exploiting the load profiles gathered in a real measurement campaign. The Overgrid Demand Response (DR) architecture is used for managing the residential flexible loads, estimating the aggregated power demand without any centralized server and creating a virtual “community” of smart b…

An Analysis of the Intertial Response of Small Isolated Power Systems in Presence of Generation from Renewable Energy Sources

Renewable Energy Sources are posing critical issues related to the mining of power systems stability, essentially due to a decrement of the inertial response during system's contingencies. As a consequence, to preserve the security and the reliability of the system, it is necessary to adopt new frequency adjustments mechanisms. This issue becomes particularly critical in isolated power systems, like those of small islands not supplied by the main grid, in the case of high shares of production from unpredictable renewabies such as photovoitaic and wind sources. In this framework, the present work deals with the analysis of the variation of the inertia time constant of a small island in vario…

Damping Provision by Different Virtual Synchronous Machine Schemes

The adoption of virtual synchronous machine (VSM) schemes for the control of power converters is gaining more and more attention both in academia and industry. The VSM control strategies fall into the category of grid-forming converter controls, and they are intended for a range of different applications, providing specific services and different kinds of support to the grid. The paper investigates the possibility of damping provision to the system by VSM power converters. Different schemes are considered and compared, showing the opportunity of the investigated solutions through combined modal and time domain analyses. A specific modification of the power synchronization loop is recognized…

Critical Assessments of the Potential for Integrating Renewable Energy into Isolated Grids on Vietnamese Islands: The Case of the An-Binh Grid

Renewable electricity for off-grid areas is widely seen as one of the top choices in supporting local economic development in most countries, and so is Vietnam. Over the years, many isolated networks using renewable energy sources have been deployed for off-grid areas in Vietnam. However, the use of these energy sources in Vietnam’s isolated networks is still facing many challenges due to its infancy here. The issues of reliability and vulnerability of these networks are not given the expected attention. Another challenge is that the issues of the operational security of these systems could also be negatively affected by the variable nature of renewable sources, including static and dynamic…

Sustainable Energy Supply in Vietnam

The steep growth of electricity demand in Vietnam (11% per year on average since 2006) calls for a deep rethinking of the Vietnamese electrical power system. Its topological structure indeed may not be well suited for a deep penetration of renewable energy sources and a predictable increase of reactive industrial loads. The Vietnamese power system is described and a few analytical methods are considered for its study both in steady state and in dynamic conditions in different scenarios. The power system simulation software Neplan is used for the implementation of the system’s model and the performing of the dynamic analysis.

A General Methodology for Short-circuit Calculations in Hybrid AC/DC Microgrids

In this paper, the issues related to short-circuit calculations in hybrid AC/DC microgrids are discussed. The reference standard for short-current calculations in DC systems is the IEC 61660, which provides a mathematical formulation of the problem. The standard only includes radial DC grids and does not consider a more complex system, such as meshed DC systems or a hybrid AC/DC microgrid. This paper proposes a generalized approach that can be used independently of the characteristics of the hybrid system. The proposed approach is applied to four test microgrids with different distributed sources and number of nodes and the results are compared with those obtained simulating the same grids …

Fundamental Analysis of Grid-Forming Converters Enhanced with Feedforward Controls

The grid-forming control for power converters can be enhanced by proper feedforward terms included in the active power control loop. Two basic structures are identified, the feedforward angle and the feedforward frequency. The formal analysis of the transfer functions reveals a structural similarity. The two schemes exhibit however a fundamental difference in their transient capabilities. The grid-forming controls are characterized with the introduction of two specific factors, for the direct assessment of the inertia and the damping which can be provided by the grid-forming converter. The sensitivity analysis of the two feedforward schemes indicates that the enhancement of the transient pe…

Extension and Tuning of Virtual Synchronous Machine to Avoid Oscillatory Instability in Isolated Power Networks

The risk of oscillatory instability introduced by virtual synchronous machines (VSM) control in isolated power networks is investigated. The considered control is a common scheme widely studied in literature, in several configurations and for different case studies. The impact of the VSM control on the system stability is examined for the existing power network of a Mediterranean island. The VSM control is implemented within the power converters interfacing the energy storage systems (ESS) installed in the network. Simulations and analysis show the occurrence of oscillatory instability in the system, with the ESS-VSM and the synchronous machines of the network progressively swinging against…

Primary Frequency Control in the Power System of Continental Europe including the Dynamics of the HVDC Link France-Great Britain

The paper presents a study of primary frequency control within the power system of Continental Europe (CE) including the dynamics of the high voltage direct current (HVDC) link between France and Great Britain (GB). The large-scale dynamic model of the CE system originally provided by ENTSO-E is extended with a more detailed representation of the whole HVDC interconnection. The dynamics of the GB synchronous area is also considered in the analysis, implementing a system equivalent suitable for primary frequency control studies. The opportunity of frequency containment reserve exchange between the two areas through the link is also investigated, considering supplementary frequency controls w…

Grid-forming converters. A critical review of pilot projects and demonstrators

Grid-forming control can be a useful solution for all dynamic issues in weak grids and for providing ancillary services. It represents the new frontier in modern power electronics, responding to the needs of power systems more and more rich in renewables and, for this reason, with lower inertia. Today, the research on grid-forming is mainly oriented to propose new and more effective control schemes and to evaluate their performances with simulation tools, but few works in the literature focus on the results of on-field experimentation. Therefore, this paper aims to provide a comprehensive review of grid-forming pilot projects and demonstrators developed worldwide. The work describes the mai…

A simulation study for assessing the impact of energy storage systems for Fast Reserve with additional synthetic inertia control on the Continental Europe synchronous area

This article shows the results of a simulation study on the application of battery storage systems for providing fast frequency regulation (the so-named Fast Reserve) with additional synthetic inertia control. The aim of the study is to assess the impact of the extension of the regulation provided by the FRUs to all the Continental Europe synchronous grid, with the same power proportions of the first Italian FRU auction. The simulations are conducted in two different scenarios: a base one related to 2020 and a future one related to 2040 and based on ENTSO-E projections for load and generation. The results show that, for the reference incident of 3000 MW, the frequency quality parameters in …

Power Grid Integration and Use-Case Study of Acid-Base Flow Battery Technology

There are many different types of energy storage systems (ESS) available and the functionality that they can provide is extensive. However, each of these solutions come with their own set of drawbacks. The acid-base flow battery (ABFB) technology aims to provide a route to a cheap, clean and safe ESS by means of providing a new kind of energy storage technology based on reversible dissociation of water via bipolar electrodialysis. First, the main characteristics of the ABFB technology are described briefly to highlight its main advantages and drawbacks and define the most-competitive use-case scenarios in which the technology could be applied, as well as analyze the particular characteristi…

System Stability of a Small Island's Network with Different Levels of Wind Power Penetration

The reduction of the inertial response of the generation system has been one of the main obstacles to the penetration of high sharing of renewable energy sources in islanded systems. This issue can be solved thanks to innovative control that makes wind turbines able to provide the so-named synthetic inertia. The paper investigates some scenarios with different levels of wind power penetration in a small island whose grid is not supplied by the main grid, by the use of the software NEPLAN 360, simulating the wind power plants accordingly to the standard IEC 61400-27. The aim of the paper is to assess the maximum level of penetration in the island of wind generation, with traditional control …

Sensitivity Analysis and Frequency Dynamics of Grid-Connected Converters with Virtual Inertia

For the participation in the frequency control of the system, power converters can be controlled with different strategies and methods, sharing the common concept of virtual inertia capability. In this work, a sensitivity analysis of two main categories of converter controls with virtual inertia is presented. The considered schemes are a grid-following current vector control with additional virtual inertia block and a grid-forming control scheme based on virtual synchronous machine concept. A proper basis for the comparison is first assessed providing an analytical correlation between the control parameters of the two schemes. For the two control strategies, the sensitivity analysis of the …

Frequency Dynamics in Fully Non-Synchronous Electrical Grids: A Case Study of an Existing Island

The operation of a power system with 100% converter-interfaced generation poses several questions and challenges regarding various aspects of the design and the control of the system. Existing literature on the integration of renewable energy sources in isolated systems mainly focuses on energy aspects or steady-state issues, and only a few studies examine the dynamic issues of autonomous networks operated with fully non-synchronous generation. A lack of research can be found in particular in the determination of the required amount of grid-forming power, the selection of the number and rated power of the units which should implement the grid-forming controls, and the relative locations of …