Authors

Electricity market. Is the design really obsolete?

Giuseppe Artizzu

www.qualenergia.it // february 2014

In the Italian electricity system outlined there is the hypothesis that the closure of part of the thermoelectric capacity would compromise system security. It would be better to leave the reserve margin to drop and see if commodity prices return to levels compatible with ensuring the system. An article by Giuseppe Artizzu. Until three years ago, the time profile of the equilibrium price in the market followed the electric load curve faithfully. By 2012 the photovoltaics had brought a gradual but systematic reduction of price in the central hours of the day, preceded and followed by two short spikes in the early morning and late afternoon, also helped by migrating to those times of the programmable power production. In substance the hourly price curve doesn’t follow the load but the residual load, i.e. the portion not covered by intermittent sources at zero marginal cost.

The big bluff of oil companies

Giuseppe Artizzu

www.huffingtonpost.it // february 2014

The Eni media campaign focuses on the emergency of a competitive European industry, penalized by gas and electricity which is much more expensive than in the United States. The problem is real, but there are also real doubts about the sustainability of a model founded on cheap hydrocarbons. Besides this, what is striking is the unscrupulousness with which Eni, alone among the big oil companies, has chosen to play a controversial match. The leaders of the company have taken a position contrary to community strategies of decarbonisation, claiming them to be ineffective, a high cost to the economy and a potential injury to the security of supply. The economical alternative, according to Eni, would be the American choice in favor of shale gas, which means drilling in Europe and renewing the pacts with historical suppliers like Algeria and Russia.

The american energy model is not a model

Giuseppe Artizzu

www.huffingtonpost.it // january 2014

Americans are paying a third of the cost of gas in Europe, and half of that of electricity. The America of Bush and Obama is an enlightened energy model, to be imported to this side of the Atlantic. The numbers are not far from reality, but this conclusion is somewhat hasty. That Scaroni and his colleagues pester the European press with slogans is understandable, however the Ministers of Industry being their sounding board is not. This is a brief recent American history, : in the past decade the soaring prices of oil and gas has made it for the first time economically exploitable, with innovative technologies and known reserves of non-conventional hydrocarbons. Money, skills and infrastructure, combined with private ownership of the subsoil, triggered a typical American rush to deposit: within a few years, the seemingly irreversible decline of gas production has turned into a boom, shortly followed by an oil production boom too.

Modeling and control of low voltage flexible units for enhanced operation of distribution feeders

P. Raboni, H. Weihao, S. K. Chaudhary, and Z. Chen

IECON 2013 - 39th Annual Conference of the IEEE, 2013, pp. 7469-7474 // 13 November 2013

In some networks Distributed Generators (DGs) are phasing out conventional power plants in terms of power production but still large efforts are required for providing ancillary services. In this paper the usage of fast response units like a Micro Turbines (MT) and a stationary Electric Vehicle Battery (EVB) is proposed for providing primary regulation in grid connected mode and for hierarchically manage an islanded LV distribution feeder. The unit models are described and a novel EVB model directly based on manufacturer's data is proposed and evaluated comparing its performances with SimPowerSystems library block. Moreover a voltage dependant power term is applied to the Voltage-Source Converter (VSC) control scheme of the EVB for improving the performances of the islanded feeder. The control is tested in case of under frequency and consequent load shedding occurring at the residential feeder of CIGRE C6.04.02 benchmark network.

An OFF-GRID Base Station Powered By Sun Wind, and Water

S. Bian, X. Wang, M. Congiatu

Intelec 2013, Hamburg, Germany // 13 - 17 October 2013

With the fast deployment of mobile network the energy consumption is increasing at the same time. The Radio Access Network may occupy more than 60% total energy consumption of a mobile operator. How to improve the energy efficiency of the Base Stations is vital important. The renewable energy is now widely used to power the Base Stations and usually the Lead Acid Batteries are used to be the energy storage. In this paper a new hybrid pure renewable energy system for BTS is introduced. The Site is powered only by the Sun Wind, and Water. The most innovative technology is that a water electrolyzer and PEM hydrogen fuel cell is integrated together with solar panel and wind turbine as the energy storage system replacing the legacy lead acid batteries. This made the BTS can work totally off-grid and zero carbon emission.

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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.

Dispersed generation to provide ancillary services: AlpStore project

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

International Conference on Clean Electrical Power (ICCEP), pp. 133-138 // 29 August 2013

In the future, electrical systems should be able to integrate all users at the same time and guarantee power quality, stability and safety over time. The integration of renewable energy sources leads to new issues involving the intermittence of this generation typology. A high penetration of intermittent power plants will reduce the capability of the system to overcome critical events (e.g. frequency oscillations and voltage profile perturbation). This work presents new regulation schemes/functions developed in the AlpStore project framework, devoted to managing dispersed generation in order to provide ancillary services to the main grid. The work developed can be split into two main items: reactive injection regulation and frequency control regulation. The first regulation is devoted to increasing the Hosting Capacity of the distribution grid (i.e. it results to be a local control), whereas the latter aims to guarantee the energy balance of the national electric grid (i.e. it could be classified as a grid control).

Commercial bills are cut with the carbon tax

Giuseppe Artizzu

www.huffingtonpost.it // august 2013

In 2012 the electric bills have been loaded wth 10 and a half billion euros of incentives for renewable energy sources. Who benefits is who works in the green industry, at least indirectly. I do not intend to defend the reasons for incentives, nor stigmatize mistakes. I will look at the facts: the average charge in a bill is over 4 cents per kilowatt hour. Aside from second homes and families with high consumption, users most affected are small and medium-sized enterprises. On the other hand there are a number of exempted consumers like those of railways and a number of big businesses. Cutting bills is a cornerstone of the relaunch of the industrial sector. But the proposals, from a further opening of the gas market, the modification of charges between categories of users, the extension of charges of auto consumption (a blatant stupidity), have limited the short-term impact. If you want to make a big difference then you need to act with a direct cut of the administration part of the bill: the rational way to do this is to transfer the renewable energy incentivation costs , with the introduction of a carbon tax.

Gas bills are falling – thanks to who?

Giuseppe Artizzu

www.huffingtonpost.it // june 2013

“In a scenario of strong contraction of the demand for energy, the new system of balancing introduced by the authorities in December 2011 has contributed -along with other regulatory interventions and recent European rules on transport capacity allocation and congestion management- to lowering the spread in the rest of Europe”. The spread which the energy authority has spoken about is the one that reflects the difference between the price of gas in Italy and across the borders. In recent months the differential has fallen dramatically, until becoming inverted: recently our wholesale price has often been lower than average European prices. The authority, for its part, has implemented a series of measures to reflect this reality in detail, which we have seen in our bills.

Reduction method for active distribution networks

P. Raboni and Z. Chen

2013 IEEE Grenoble, 2013, pp. 1-6 // 20 June 2013

On-line security assessment is traditionally performed by Transmission System Operators at the transmission level, ignoring the effective response of distributed generators and small loads. On the other hand the required computation time and amount of real time data for including Distribution Networks also would be too large. In this paper an adaptive aggregation method for subsystems with power electronic interfaced generators and voltage dependant loads is proposed. With this tool may be relatively easier including distribution networks into security assessment. The method is validated by comparing the results obtained in PSCAD® with the detailed network model and with the reduced one. Moreover the control schemes of a wind turbine and a photovoltaic plant included in the detailed network model are described.

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.

Methods to detect and mitigate catalyst support carbon corrosion in PEM fuel cells

Denis Bona, Francesco Pedrazzo, Ilaria Rosso, Dennis E. Curtin, Elena M. Tresso

International Workshop on characterization and quantification of MEA degradation processes, Grenoble, France // 26 - 27 September 2012

Carbon black based electrodes are generally recognized as state of art for PEM fuel cell technology due to the high performance achieved with relatively low Pt content. However, the catalyst carbon support is prone to carbon oxidation. This leads to loss of catalyst area and overall performance, as well as higher mass transport loss due to an increased flooding tendency. This phenomenon is particularly severe when the fuel cell experiences repetitive start-stop cycles. Therefore, specific countermeasures against catalyst layer carbon oxidation are required, especially for automotive and backup power applications, where the startup/shutdown rate is considerably high. The authors evaluated a basic design that uses a stack shunt. A properly modified control protocol, which includes the stack shunt, is able to avoid high cathode potential peaks, which are known to accelerate catalyst carbon support corrosion and its negative effects. During two separate durability tests, one adopting the shunt design and another using non-protected shutdown, a 24-cell stack was subjected to continuous starts and stops for several months and its performance constantly monitored. Results show that when the shunt is used, there is a 37 percent reduction in the voltage degradation rate for each startup/shutdown cycle, and a two-fold increase in the number of startup/shutdown cycles before an individual cell reached the specified “End of Life” voltage criteria. Furthermore, ex-situ FE-SEM analysis revealed cathode catalyst layer thinning, an indication that the emerging degradation mechanism is the catalyst support carbon corrosion, as expected. This provides further support that the constant voltage degradation rate typically experienced in PEMFCs can be attributed primarily to the catalyst support carbon corrosion rate. The proposed shunt protocol is very cost-effective and does not require any substantial changes in the system. For this reasons, its adoption is recommended as a viable method to decrease the catalyst support carbon corrosion rate and extend the operating life of the PEMFC stack.

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Intelligent control for a DC micro-grid system

M. Martino, Y. F. Quinones, P. Raboni, and Z. Chen

Universities Power Engineering Conference (UPEC), 2012 47th International, 2012, pp. 1-5 // 7 September 2012

This paper presents the dynamic response of a DC - micro-grid (DC-MG) controlled in master-slave mode. The benefits of the micro-grids (MGs) are the low cost in terms of power electronics converters and the high reliability and quality, even in case of loss connection to the transmission system. A DC-MG in fact can survive in standalone mode if properly managed. The considered system is made by a photovoltaic array (PV), a wind turbine (WT), a gas engine (GE) and an energy storage system (ESS). The DC-MG behavior is analyzed in different scenarios to demonstrate the efficacy of the control for all the units, especially in case of variable weather conditions with different DC loads. Thus the voltage level of the system and the power flow are shown, out of a detailed description of the power electronic interfaces featuring the distributed generators (DGs).

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.

Identification of the best power plant layout for large offshore wind farms connected via VSC-HVDC links

F. Careri, C. Genesi, P. Marannino, M. Montagna, P. Raboni, S. Rossi, et al.

Energy Market (EEM), 2011 8th International Conference on the European, 2011, pp. 281-287. // 27 May 2011

The overall purpose of this paper is to find out the best choice in terms of generator technology for large offshore wind farms connected to the EHV network by means of VSC-HVDC transmission: besides the traditional benefits compared with HVAC and line commutated HVDC, this technology allows variable frequency operation, in order to increase the overall production of the wind farm. Two different types of generators - Squirrel Cage Induction Generator (SCIG) and Doubly-Fed Induction Generator (DFIG) - are compared in variable frequency operation: the related power plant layouts are analyzed, for different wind speed conditions, by means of a slightly modified version of an online optimization algorithm. The resulting programs are coded in MATLAB® environment and some tests are carried out.

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.