Search

The paper describes the control and protection strategies of a device conceived to improve Power Quality in Low Voltage (LV) electrical distribution grid. The device, studied in the frame of the research project “DRYSMES4GRID”, acts as an active filter, compensating load harmonics and network disturbances (voltage dips and micro-interruptions) thanks to a Superconducting Magnetic Energy Storage system (SMES).The control logics are presented with a particular focus on detecting and overcoming overload or internal and external fault condition. The effectiveness of the proposed control strategies has been investigated in ATPdraw simulation environment, using a detailed network and device model.

The boosting progress of HVDC (High Voltage Direct Current) technology developed for transmission grid applications can be exploited for distribution network needs as well. This has made raise a growing interest on the development of MVDC (Medium Voltage Direct Current) technology. The present paper provides an overview of the ongoing developments related to HVDC (High Voltage Direct Current) and MVDC (Medium Voltage Direct Current) in Italy. Particular attention is paid to HVDC projects and to MVDC studies that have been conducted in the latest years in Italy.

This paper assesses the development of a novel solid-state MVDC breaker and current limiter. Matlab/Simulink simulations are used as benchmark, then Real Time Control Hardware In the Loop (CHIL) simulations are performed. Same control algorithm is implemented into a microcontroller by using two different software languages: C and MicroPython. In both cases, high performances are achieved by using fast features like hardware interrupts and low level assembler code. Results are then compared in terms of simplicity, ease and speed of implementation and code readability, very important in fast prototyping activity.

This work presents the optimization process of real time control equipment for a Medium Voltage Direct Current (MVDC) static switch-limiter device. Description of the control strategy and its implementation into a microcontroller programmable board are described. System performances have been analyzed by real time Control Hardware in The Loop (CHIL) simulations. Initial results did not match expected performances. Control has been optimized by hardware and software features, like interrupt routines and low-level programming. Final tests showed a substantial improvement of system performances, like speed response and current limitation accuracy.

This work aims to investigate about integration of a Dual Active Bridge converter (DAB) developed for MV distribution lines into a traction system of an urban metro railway. Equipment is fed by 1500 V DC catenary and supplies active/passive loads at low voltage (750 V DC), providing galvanic insulation for safety reasons. Operation at very maximum voltage limits (up to 2 kV DC) and in case of MV drops and fluctuations have been simulated, focusing on system stability, control and proper sizing of passive filters to interface the converter with a storage device.

The design of an interface device for interconnecting a SMES (Superconducting Magnetic Energy Storage) to a LV distribution grid is carried out, in order to demonstrate the feasibility of a SMES for achieving, with the same device, power quality and critical load protection functions. The work is developed inside a three-year research project, called DRYSMES4GRID, funded by the Italian Minister of Economic Development and sees the cooperation of five partners (companies, universities, and research institutes). The aim of the project is to demonstrate the feasibility of the SMES (500 kJ/200 kW) in the short/medium term at competitive cost based on Magnesium Diboride (MgB2). In particular, in this article, after a brief state of art of the SMES applications for the grid, the design and the control logics of the DC/DC chopper for the power modulation of the energy stored in the SMES and of the threephase AC/DC inverter are shown. The activities are mainly based on digital simulations to evaluate the performances of this device in a LV distribution grid in presence of linear and non-linear loads, considering in particular the peak shaving function, while the device is connected to the mains, and the islanding operation condition after the detection of a voltage dip.

This paper addresses the meshing of distribution networks through MVDC (Medium Voltage Direct Current) links, based on VSCs (Voltage Source Converters), as a viable solution to manage critical network conditions, i.e. overloads or the connection of large loads to the existing distribution system. In this paper the impact of MVDC links on distribution networks was evaluated with OPF (Optimal Power Flow) analyses either for a test distribution network and a real case study provided by Unareti SpA (an Italian Distribution System Operator - DSO). For the real case study, fault studies to check the adequateness of the existing protection systems to the proposed meshed network configuration were performed.

This work studies the possibility of controlling HVDC (High Voltage Direct Current) systems to support the primary frequency regulation of the traditional rotating generators; in particular, the paper presents how to provide the synthetic inertia function by means of the energy stored into the HVDC connection itself. Simulations on a two-terminal grid have been performed, implementing a synthetic inertia model based on a classic frequency-derivative grid controller. Simulations show that HVDC can support the grid inertia as long as a good frequency derivative measurement is available and proper DC capacitors are given.

The increasing use of grid connected power electronic systems generates a set of interference phenomena between those devices and distribution grids. Power electronic systems are both sensitive to voltage disturbances and sources of disturbances, such as current harmonic distortion, voltages unbalance and flicker. Such phenomena motivated the study of a system named Open Unified Power Quality Conditioner, based on power electronic converters, used for the improvement of the Power Quality level in low voltage distribution grids. The study, mainly theoretical, has addressed the issue of compensators coordination under different operating conditions.

A three-year research project, called DRYSMES4GRID, was recently funded by the Italian Minister of Economic Development, Italy. The project, which involves five Italian partners (companies, universities, and research institutes), is aimed to demonstrate the feasibility of cost-competitive SMES based on magnesium diboride (MgB2) with a cryogen-free cooling by means of the manufacturing and the testing of a demonstrator with an objective rating of 500 kJ/200 kW. This rating is deemed suitable for disclosing the critical technological aspects of all components in view of practical applications. A further goal of the project is the assessment of the technical and economic benefits that the SMES can bring to real-world electric grids. The general outline and technical objectives of the project are presented in this paper. Preliminary design assumptions and results concerning the MgB2 coil and the power condition system are also discussed. © 2018 IEEE.

A Shunt Active Power Filter (SAPF) employable in a Low Voltage distribution grid four-wires model is presented. The use of this device helps to improve Power Quality compensating harmonic currents, reactive power and current unbalances of a disturbing loads. Each compensating function can be activated or disabled according to the specific requirements of the application. A selective harmonic compensation is also possible, in order to avoid possible resonances at specific frequencies. A current hysteresis modulation with predictive calculation of threshold bands achieving fixed switching frequency is adopted for a fast dynamic response. The compensation performance of the proposed active power filter and the associate control scheme under steady state and transient conditions is demonstrated through digital simulations.

This paper presents a protection scheme for a medium voltage dc (MVDC) link, that meshes three different MVAC distribution grids through ac/dc power converters. The proposed scheme includes active current limiters, hybrid circuit breakers and a communication layer for the coordination of these protection devices and power converters (logic selectivity). Active current limiters, installed just after dc bulk capacitors of each power converter, ensure fault current limitation in order to protect the power converters until the fault clearance by dc grid protections. The coordination logic among the protection devices is described in this paper, together with notes on the design of those devices. In case of communication failure, the proposed scheme could not guarantee logic selectivity, but it is anyway able to clear the fault. The effectiveness of the proposed protection strategy is validated in a fast transients simulation environment, using detailed model of power electronic converters.

The paper is focused on the possible influence that some network characteristics (i.e. network configuration, type of neutral operation, geographical area, lines and cable length...) and environmental phenomena (lighting) may have on voltage dip performance in Medium Voltage (MV) networks. The investigation has been performed by applying both correlation techniques and Multiple Linear Regression analysis (MLR) on the voltage dips collected along several years of monitoring by the Italian MV network monitoring system QuEEN. As to the network characteristics and environmental factors used in the performed analysis they are referred to the data supplied in the past for the monitoring system and to the lighting data provided by the Italian lightning location system SIRF. The percentage contribution of each network and environmental factor to the voltage dips statistic, irrespective of the other parameters, have been evaluated by multiple linear regression methods. The results of these analysis confirm that the overhead line length has got a significant influence on the phenomena while cable lines length has, as expected, only a negligible effect. The influence of lightning seems to be not so critical as expected and this happen also with the neutral type of operation while voltage dips performances depend, in a non-negligible way, on the belonging to a geographical area.

Local control of Distributed Energy Resources (DER) in microgrids usually relies on droop algorithm in order to ensure stability to the system in islanded operation. Conventional and reverse droop control are applied respectively to Voltage Control Mode (VCM) inverters and to Current Control Mode inverters (CCM). In low-voltage microgrid, traditional P-ω and Q-V droop characteristic is subject to the power coupling and could lead to unstable operating conditions due to dependence of load on the voltage and on the frequency. Therefore P-V and Q-ω droop characteristic, named resistive droop, is used in simulations and in experimental tests to show its effectiveness for a stable and decoupled regulation of islanded LV microgrid.

Reporting and analysis procedures play an important role in power quality monitoring systems especially for long term surveys. As far as voltage dips are concerned, the network voltage dip performance can be effectively described in many different ways depending on the aims of the data presentations at both site and system level. The paper deals with network dip performance different representation methods focussing in particular on the way of presentation proposed by the working group UIE/CIGRE’/CIRED C4.110. This method has been applied to the Italian 2009 voltage dips statistic as acquired by the Italian power quality monitoring system named QuEEN. Contour charts have been drawn for both different percentage of the monitoring sites and voltage dips types.

La ricerca ripercorre la storia della tipografia-editrice e libreria Pirola di Milano, dalla fondazione dell'attivitŕ nel 1781 alle vicende del recente Novecento. Nello specifico, si sono analizzate le proposte ottocentesche dell'azienda, entro una parabola che spazia dalle pubblicazioni di servizio alla produzione teatrale alle edizioni scolastiche e pedagogiche.

This paper evaluates the economic sustainability of different premium power park (PPP) solutions – derived from two prototypes and a theoretical solution – and completes a previous technical analysis of the same PPP solutions. All of these are utility-provided solutions that improve the quality of the electricity delivered at medium voltage (MV) level. We calibrate the study on the potential customers of a PPP, which are MV users sensitive to power quality (PQ) events and badly served. As to PQ events, accidental interruptions and voltage dips are concerned. We evaluate the direct costs caused by PQ events through original and simple cost models developed using different approaches. Even though until today PPPs have not proved to be a winning idea, the results prospect possible future applications of this idea as a consequence of the increasing penetration of dispersed generation, maturation of renewables and developments of energy storage technologies.

One of the main issues concerning the Inverter based Distributed Generators (DGs) is the possibility that inverters could feed parts of the public grid, even when the grid is disconnected from the main power system. Such a condition, that is called unwanted island, is potentially critical both for safety and for consumers' operations. In order to avoid unwanted islands, it's mandatory equipping the generating plant with an Interface Protection (IP) which has to detect the islanding condition and, in this case, to disconnect the generator from the public grid. Several methods for identifying island condition have been proposed, both passive and active, each one characterized by its pros and cons. The standard IEC 62116 was promulgated with the aim of regulating a test procedure to evaluate the IP effectiveness of PhotoVoltaic (PV) inverters independently from the island detection method implemented. The paper discusses the test procedure proposed by the standard IEC 62116 and presents some experimental activities developed by RSE spa, aimed at the assessment of test feasibility and effectiveness.

New problems concerning the distribution grid protection system arise from the large diffusion of installed distributed energy resources. In particular, unwanted trips, unwanted island operations and worsening of power quality are the main issues coming from the interactions among active networks and grid protections. A possible new protection scheme, which can be employed in active networks, is proposed and discussed in the paper. Logic selectivity is implemented introducing communications among grid and distributed generator systems protections. Digital simulations confirm the suitability of the proposed solution for a large set of grid faults.

The paper presents three different approaches for the control of grid connected inverters for Permanent Magnet Wind Generators. Their performances in facing grid unbalances are compared through digital simulations. For each control scheme, three alternative Fault Ride Through (FRT) strategies are considered and tested. From simulations, it emerges that, in addition to control expedients, some hardware devices are required for satisfying FRT requirements.