Authors

Optimization Models for Islanded Micro-Grids: A Comparative Analysis between Linear Programming and Mixed Integer Programming

Alberto Dolara, Francesco Grimaccia, Giulia Magistrati, Gabriele Marchegiani

Energies 2017, 10(2), 241 // 16 February 2017

"This paper presents a comparison of optimization methods applied to islanded micro-grids including renewable energy sources, diesel generators and battery energy storage systems. In particular, a comparative analysis between an optimization model based on linear programming and a model based on mixed integer programming has been carried out. The general formulation of these models has been presented and applied to a real case study micro-grid installed in Somalia. The case study is an islanded micro-grid supplying the city of Garowe by means of a hybrid power plant, consisting of diesel generators, photovoltaic systems and batteries. In both models the optimization is based on load demand and renewable energy production forecast. The optimized control of the battery state of charge, of the spinning reserve and diesel generators allows harvesting as much renewable power as possible or to minimize the use of fossil fuels in energy production.”

Performance Analysis of a hybrid micro-grid in Somalia

Alberto Dolara, Elisa Donadoni, Sonia Leva, Giulia Magistrati, Gabriele Marchegiani

IEEE PES PowerTech 2017 // 2017

This paper presents a data analysis of an islanded diesel-PV-battery system, placed in Somalia. Operation of each generator is observed, concerning the most relevant performance indicators. Analysis is carried out during the first 11 months of operation, from November 2015 to September 2016. Investigations are divided into two periods, according to a significant load variation due to the connection of a new distribution line to the power plant. Thus, a comparison on load demand sharing among generators is realized between the two periods. In conclusion, benefits in terms of fuel consumption, CO2 emissions and money savings are presented.

Distributed storage for provision of ancillary services to the main grid: project PRESTO

S. Nassuato, G. Magistrati, G. Marchegiani, D. Falabretti, M. Delfanti, M. Merlo

Energy Procedia, vol. 99, pp. 182-193 // November 2016

This paper presents the three-year PRESTO research project (2013-2015). PRESTO is a self-funded project developed by the Department of Energy of Politecnico di Milano in cooperation with FIAMM Storage, Elvi Energy and MCM Energy Lab (an Italian spin-off). Within the project, experimental tests and numerical simulations were performed in order to evaluate the effectiveness of an Energy Storage System (ESS) in the provision of ancillary services to the main grid. This paper focuses specifically on the experimental and numerical analyses carried out in the project to develop an innovative control law for the primary frequency regulation, able to maximize the performances of the regulating service and effectively manage the ESS state of charge.

Optimal Management Algorithm for Battery Energy Storage System Included in an Islanded Micro-Grid

Alberto Dolara, Giulia Magistrati, Francesco Grimaccia and Gabriele Marchegiani

16th International Conference on Environment and Electrical Engineering (EEEIC) // 7-10 June 2016

This work proposes an optimization method for the management of a Battery Energy Storage System (BESS) integrated in an islanded Micro-Grid, including Renewable Energy Systems (RESs) and generators burning fossil fuels. The optimized control of the battery State of Charge (SOC) allows to get the BESS available as much as possible to support the RES power production, hence minimizing the use of fossil fuels. The optimization of the BESS is based on load demand and RES production forecast. The Optimization Algorithm that has been adopted is the Linear Programming, using the method of the Interior Point.

Hybrid micro-grid experimental application in Tanzania

M. S. Carmeli, M. Mauri, C. Brivio, P. Guidetti, S. Mandelli, M. Merlo, R. Perini, G. Marchegiani, D. Rosati

2015 International Conference on Clean Electrical Power (ICCEP) // 16-18 June 2015

This paper is intended to introduce the project Energy4Growing that aims at studying and setting up a hybrid micro-grid to supply power to a school in rural Tanzania. It describes the results of the early project actions which concerned in: (i) analysing the actual school power supply system through locally metered data; (ii) developing the first step of a new electro-mechanical model which addresses the simulation of operation and dynamics within an off-grid power system; (iii) validating the new model. In particular the paper focuses on describing the development and the first step implementation of the new modelling approach which address: (i) voltage and frequency analyses over medium term period by means of simplified electromechanical models of power sources and power electronics, (ii) the analysis of different dispatch strategies and their consequence on voltage and frequency trends, (iii) the effects of dispatch strategies on the energy performances of particular components such as battery bank or dump loads. The new approach has also been applied in modelling the current school power supply system.

Technical Strategies for Voltage Power Regulation in LV Distribution Networks

M. Delfanti, L. Frosio, G. Monfredini, M. Merlo, C. Rosati, D. Rosati, G. Marchegiani

Distributed Generation and Alternative Energy Journal, vol. 30, no.4, pp. 7-14 // 1 January 2015

We report the integration of a novel voltage regulation strategy in the inverter control algorithm for Dispersed Generation (DG) applications. The adoption of a decentralized voltage control based on local curves allows the voltage profile to be controlled at the Point of Common Coupling (PCC) of the generators and, therefore, the capacity of existing distribution networks to host more generation from renewables. The work is focused on a low voltage distribution network and both the reactive power modulation and the real power curtailment are considered in the proposed local strategy. Both numerical and experimental analysis are necessary in order to test and validate the proposed voltage control strategy. Firstly, the performances of the proposed control are tested by a numeral analysis and the impact on both the electrical system and the inverter apparatus is evaluated. Secondly, the benefit of the control strategy is analysed by experimental analysis in a test facility to verify the feasibility of voltage regulation in a real feeder.

Hybrid distributed generation system for a rural village in Africa

M. S. Carmeli, P. Guidetti, M. Mancini, S. Mandelli, M. Mauri, M. Merlo, R. Perini, G. Tomasini, G. Marchegiani, D. Rosati

3rd Renewable Power Generation Conference (RPG 2014), pp. 1-6 // 24-25 September 2014

Nowadays the use of distributed generating systems, which use a renewable energy source, has experienced a fast development. Moreover, their intrinsic intermittent nature can be overcome using hybrid systems which combine more energy sources. This paper proposes the study and design of a hybrid generation system able to cover the energy needs of a school in a rural village in Africa (Tanzania), combining renewable and/or alternative sources and storage systems. The final results consist in the definition of an electric grid architecture suitable to interface renewable and energy needs in the most reliable way, exploiting advanced regulation and control techniques.

Harmonic Analysis of Output Filters for Grid Connected Converters in Battery Energy Storage Systems

Alberto Dolara, Giulia Magistrati, Riccardo Zich, Luisa Frosio and Gabriele Marchegiani

16th International Conference on Harmonics and Quality of Power (ICHQP) // 25-28 May 2014

Battery Energy Storage Systems, as well as many distributed generation systems, use voltage source inverter as interface with the grid. These converters require a filtering section to reduce current harmonics injected to the grid. Usually, harmonic filter is a series inductance connected between grid and inverter. Higher order filters can provide better harmonic attenuation at lower switching frequency and reduce filter size, with potential benefits for high power applications. This paper deals with the sizing and the frequency response of three different harmonic filters suitable to reduce the ripple in the grid current waveform. Dynamic simulations of a 100 kW Battery Energy Storage System highlight the better performance of high order filters.

A novel mechanical hardware in the loop platform for distributed generation systems

M. S. Carmeli, F. Castelli-Dezza, M. Mauri, G. Marchegiani

Distributed Generation and Alternative Energy Journal, vol. 28, no. 3, pp. 7-27 // 24 September 2013

The growing number of distributed generation (DG) plants has emphasized the need to perform tests before the plants begin to operate. DG systems are complex enough that setting up of an experimental phase requires high costs and efforts. Moreover, renewable energy sources are intrinsically intermittent as they vary randomly with the time of day, the season and the weather. Consequently, the possibility of emulating the behavior of the whole renewable generation system in a real time environment, where a part of the real system, the natural energy source, is replaced by a real time computer simulation allows one to test the actual system in all the operating conditions, optimizing the control strategy before its service entrance, overcoming the randomness of renewable energy sources. This article proposes a mechanical hardware in the loop approach applied to a renewable energy generating system, where the whole drive (control, power electronics and electric machine) is tested and the mechanical part is simulated in real time environment. The problem of emulating the inertial torque, which can have a significant high value, is solved through an approach that relaxes the high dynamic requirements of the electrical drive that emulates the mechanical part. The hardware in the loop test bench emulates two energy sources (hydro and wind). In addition, a control strategy that emulates the inertial torque is implemented. An experimental phase in which different energy sources are modeled and emulated in a real time environment is presented as well. The underlying hardware-in-the-loop energy source emulation and experimentation scheme is shown to accurately represent real systems performance, under various control strategies and varying operating conditions.

Parallel-connected photovoltaic inverters: Zero frequency sequence harmonic analysis and solution

M. S. Carmeli, M. Mauri, L. Frosio, A. Bezzolato, G. Marchegiani

International Journal of Emerging Electric Power Systems, vol. 14, no. 2, pp. 199-2016 // 30 May 2013

High-power photovoltaic (PV) plants are usually constituted of the connection of different PV subfields, each of them with its interface transformer. Different solutions have been studied to improve the efficiency of the whole generation system. In particular, transformerless configurations are the more attractive one from efficiency and costs point of view. This paper focuses on transformerless PV configurations characterised by the parallel connection of interface inverters. The problem of zero sequence current due to both the parallel connection and the presence of undesirable parasitic earth capacitances is considered and a solution, which consists of the synchronisation of pulse-width modulation triangular carrier, is proposed and theoretically analysed. The theoretical analysis has been validated through simulation and experimental results.

Centrali ibride, tecniche di controllo per la gestione di micro reti intelligenti

L. Frosio, C. Rosati, G. Marchegiani, I. Mazzucco

Automazione e Strumentazione, 84-88.pdf // April 2013

Le centrali ibride, elemento chiave per poter realizzare e controllare le microreti ad alta penetrazione di Fonti Energetiche Rinnovabili, richiedono tecniche di controllo specifiche. In questo articolo si presenta una panoramica sulle varie modalità di controllo degli inverter di interfaccia delle centrali ibride e sulle diverse architetture di microrete che si possono realizzare. Si presentano inoltre alcuni risultati sperimentali ottenuti su una microrete a potenza ridotta sulla quale sono state implementate diverse strategie di controllo.

Control strategies and configurations of hybrid distributed generation systems

M. S. Carmeli, F. Castelli-Dezza, M. Mauri, G. Marchegiani, D. Rosati

Renewable Energy, vol. 41, pp. 294-305 // May 2012

Nowadays the use of distributed generating systems, which use a renewable energy source, has experienced a fast development. Moreover, their intrinsic intermittent nature can be overcome using hybrid systems which combine more energy sources. This paper discusses the main topologies which can be adopted for a general hybrid generation system and it focuses on a particular hybrid system which combines two different energy sources, evidencing high level and local level power flow control strategies in both stand-alone and grid connected operation. A full experience in the realization of a hybrid plant which uses an internal combustion engine with cogeneration functionalities and solar source, installed in Delebio, Italy is then presented. System design aspects, with particular attention to the possible topologies and power flow control strategies, are analyzed. After the analysis of the design aspects, experimental results of the real plant are reported.

Reduction of high frequency zero sequence harmonics in parallel connected PV-inverters

A. Bezzolato, M. S. Carmeli, L. Frosio, G. Marchegiani, M. Mauri

Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) // 15 September 2011

High power photovoltaic plants are usually constituted of the connection of different photovoltaic subfields, each of them with its interface transformer. Different solutions have been studied to improve the efficiency of the whole generation system. In particular, transformerless configurations are the more attractive one from efficiency and costs point of view. This paper focuses on transformerless photovoltaic configurations characaterised by the parallel connection of interface inverters. The problem of zero sequence current due to both the parallel connection and to the presence of undesirable parasitic earth capacitances is considered and a solution, which consists on the synchronisation of PWM triangular carrier is proposed and theoretically analysed. The theoretical analysis has been validated through simulation and experimental results.

Reduction of motor overvoltage fed by PWM AC drives using a universal model

A. Bezzolato, M. S. Carmeli, L. Frosio, G. Marchegiani, M. Mauri

Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011) // 15 September 2011

High power photovoltaic plants are usually constituted of the connection of different photovoltaic subfields, each of them with its interface transformer. Different solutions have been studied to improve the efficiency of the whole generation system. In particular, transformerless configurations are the more attractive one from efficiency and costs point of view. This paper focuses on transformerless photovoltaic configurations characaterised by the parallel connection of interface inverters. The problem of zero sequence current due to both the parallel connection and to the presence of undesirable parasitic earth capacitances is considered and a solution, which consists on the synchronisation of PWM triangular carrier is proposed and theoretically analysed. The theoretical analysis has been validated through simulation and experimental results.

Design and analysis of a Medium Voltage DC wind farm with a transformer-less wind turbine generator

Maria Stefania Carmeli; Francesco Castelli-Dezza; Gabriele Marchegiani; Marco Mauri; Daniele Rosati

XIX International Conference on Electrical Machines (ICEM 2010) // 25 October 2010

In recent years, the interest in offshore wind farms has been increased significantly. One of the reasons of this development is the less perceived environmental cost of an offshore wind farm with respect to an in-land one, especially for new installations where big turbines are preferred. However, they have also the advantage of an increased and more constant wind speed, leading to higher and more constant production of electrical power. For these kinds of wind farms a pure DC system could be an interesting and cost effective solution. This paper describes an innovative Medium Voltage Direct Current electrical grid system (MVDC) for wind farms, based on transformer-less wind turbines. An accurate analysis is presented and the proposed solution has been validated through a simulation and experimental phase performed on a low voltage prototype.

Reduction of motor overvoltage fed by PWM AC drives using a universal model

F. Castelli-Dezza; M. M. Maglio; G. Marchegiani; D. F. Ortega; D. Rosati

XIX International Conference on Electrical Machines (ICEM 2010) // 25 October 2010

An induction motor model construction and the validation of the model response to a filtering technique is analyzed in this paper. The filter is connected to the rotating machine terminals in order to suppress overvoltages due to the long cables and high frequency pulses of the inverter. With the help of high frequency measurements made by the authors on a 1.1kW induction motor, an accurate simulation with Matlab Simulink™ based on differential mode analysis, is made. The simulation shows realistic results for the determination of the filter parameters among different values of rise time and cable length.

MVDC connection of offshore wind farms to the transmission system

M. S. Carmeli; F. Castelli-Dezza; D. Rosati; G. Marchegiani; M. Mauri

2010 International Symposium on Power Electronics Electrical Drives Automation and Motion (SPEEDAM) // 09 August 2010

This paper describes an innovative Medium Voltage Direct Current electrical grid system (MVDC) for wind farms, based on transformer-less wind turbines, equipped with modular, multilevel converter (M2LC). A comparison between this MVDC system and a traditional MVAC one has been done using EECC (Electrical Energy Conversion Cost) index in order to evaluate the competitiveness of this solution for an offshore wind farm in the Mediterranean Sea.

Hybrid PV-CHP distributed system: Design aspects and realization

M. S. Carmeli; F. Castelli-Dezza; G. Marchegiani; M. Mauri; L. Piegari; D. Rosati

2009 International Conference on Clean Electrical Power // 25 August 2009

The use of distributed generating systems, which use a renewable energy source, has experienced a fast development. Moreover, their intermittent nature can be overcome using hybrid systems which combine more energy sources. This paper discusses a full experience in the realization of a hybrid plant which uses an internal combustion engine with cogeneration/trigeneration functionalities and solar source, installed in Delebio, Italy. System design aspects, with particular attention to the possible topologies and power flow control strategies are analyzed. After the analysis of design aspects, some simulations are presented to validate the proposed solution and finally experimental results of the real plant are reported.

Hardware in the Loop (HIL) test bench for small-scale Distributed Generation systems

Marco Mauri; Francesco Castelli Dezza; Gabriele Marchegiani

2008 IEEE International Symposium on Industrial Electronics // 18 November 2008

The test procedure of electrical drives for Distributed Generation (DG) systems generally requires the installation of dedicated prototypes on site: this is an expensive, time and power consuming procedure. In recent years, the availability of high performance calculation platforms has made possible to perform these tests using Hardware in the Loop (HIL) test benches before the plant installation. A HIL environment allows reducing costs and saving time because an implementation error can be easily identified and it is possible to test fault conditions in a safety way. This paper presents a general HIL test bench for DG electrical drive testing. Experimental results emulating different DG sources and plant have been provided to validate the approach.

Advanced control strategy for PQ improvement in PV systems without energy storage device

M. S. Carmeli; F. Castelli Dezza; R. Faranda; G. Marchegiani; M. Mauri

2008 International Symposium on Power Electronics, Electrical Drives, Automation and Motion // 29 July 2008

The use of distributed generating systems based on renewable energy sources has experienced a significant development in the last years. This paper focuses its attention on those based on photovoltaic systems. The intrinsic intermittent nature of this kind of renewable source implies the use of storage to accommodate fluctuations. The present paper proposes a hybrid solution in which photovoltaic source and gas engine are both present without storage device. With this configuration a new control technique can be used to maximizes system efficiency in both grid connection and stand alone operation mode.

A novel small-scale variable speed hydropower emulator using an inverter-controlled induction motor

Marco Mauri; Francesco Castelli Dezza; Gabriele Marchegiani

2007 European Conference on Power Electronics and Applications // 04 January 2008

The test procedure of an electrical drive control generally requires connecting the control to the power converter, the motor and the load. This is an expensive, time and power consuming procedure especially when it is necessary to test new control algorithms or architectures as often happen in renewable energy generation power plants. This paper introduces a low power emulator of a Small Hydropower generator used to develop and test the power quality functions of a universal digital controller for distributed generation systems.

Universal digital controller for power quality and distributed generation systems

M. S. Carmeli; F. C. Dezza; R. Faranda; G. Marchegiani; M. Mauri

International Symposium on Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM 2006) // 05 July 2006

The paper introduces a complete study of a flexible digital control device for a very large number of low voltage power systems with functions of power quality (PQ) and/or distributed generation (DG). The novel aspect of the device is its hardware and software architecture: a modular and object oriented approach allows a high ability in adaptation to different power system topologies. In this work the authors have investigated various DG systems (wind turbine, photovoltaic generators, gas powered generating set) and different functionalities of the grid interface inverter (grid connected or stand alone operation mode). The proposed control strategy allows the definition of the power flows in order to optimize the energy source exploitation.