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LISTE DES PUBLICATIONS Journal papers
G. Chicco and J. Sumaili Akilimali, "Renyi entropy-based classification of daily electrical load patterns" IET Proceedings: Generation, Transmission and Distribution, in Press. Abstract :
Keywords :
F. Spertino and J. Sumailia Akilimali, "Are manufacturing I-V mismatch and reverse currents key factors in large photovoltaic arrays ?” IEEE Transactions on Industrial Electronics, in Press. Abstract : In this paper, two factors typical of large photovoltaic (PV) arrays are investigated: one is the current–voltage (I–V) mismatch consequent to the production tolerance; the other is the impact of reverse currents in different operating conditions. Concerning the manufacturing I–V mismatch, the parameters of the equivalent circuit of the solar cell are computed for several PV modules from flash reports provided by the manufacturers. The corresponding I–V characteristic of every module is used to evaluate the behavior of different strings and the interaction among the strings connected for composing PV arrays. Two real crystalline silicon PV systems of 8 × 250 kW and 20 kW are studied, respectively. The simulation results reveal that the impact of the I–V mismatch is negligible with the usual tolerance, and the insertion of the blocking diodes against reverse currents can be avoided with crystalline silicon technology. On the other hand, the experimental results on I–V characteristics of the aforementioned arrays put into evidence the existence of a remarkable power deviation (3%–4%) with respect to the rated power, linkable to the lack of measurement uncertainty in the manufacturer flash reports. Index Terms :
E. Carpaneto, G. Chicco, and J. Sumaili Akilimali, "Loss Partitioning and Loss Allocation in Three-Phase Radial Distribution Systems with Distributed Generation" IEEE Transactions on Power Systems, Vol 23, No 3, 1039–1049, August 2008.
Abstract : In this paper, the concepts related to loss partitioning among the phase currents in three-phase distribution systems are revisited in the light of new findings identified by the authors. In particular, the presence of a paradox in the classical loss partitioning approach, based on the use of the phase-by-phase difference between the input and output complex power, is highlighted. The conditions for performing effective loss partitioning without the occurrence of the paradox are thus established. The corresponding results are then used to extend the branch current decomposition loss allocation method for enabling its application to three-phase unbalanced distribution systems with distributed generation. Several numerical examples on a three-phase line with grounded neutral and on the modified IEEE 13-node test system are provided to assist the illustration and discussion of the novel conceptual framework. Index Terms : Distributed generation, distribution systems, loss allocation, loss partitioning, losses, paradox, unbalanced systems.
E. Carpaneto, G. Chicco, and J. Sumaili Akilimali “Characterization of the loss allocation techniques for radial systems with distributed generation” Electric Power System Research, Vol. 78, No. 8, 1396–1406, August 2008. Abstract : In the restructured electricity industry, meaningful loss allocation methods are required in order to send correct signals to the market taking into account the location and characteristics of loads and generations, including the local sources forming the distributed generation (DG). This paper addresses the issues related to loss allocation in radial distribution systems with DG, with a three-fold focus. First, the key differences in the formulation of the loss allocation problem for radial distribution systems with respect to transmission systems are discussed, specifying the modeling and computational issues concerning the treatment of the slack node in radial distribution systems. Then, the characteristics of derivative-based and circuit-based loss allocation techniques are presented and compared, illustrating the arrangements used for adapting the various techniques to be applied to radial distribution systems with DG. Finally, the effects of introducing voltage-controllable local generation on the calculation of the loss allocation coefficients are discussed, proposing the adoption of a “reduced” representation of the system capable of taking into proper account the characteristics of the nodes containing voltage-controllable DG units. Numerical results are provided to show the time evolution of the loss allocation coefficients for distribution systems with variable load and local generation patterns. Keywords : Distribution system; Distributed generation; Loss allocation; Circuit-based techniques; Derivative-based methods; Bus impedance matrix; Bus admittance matrix; Voltage-controllable units
E. Carpaneto, G. Chicco, and J. Sumaili Akilimali, “Branch Current Decomposition Method for Loss Allocation in Radial Distribution Systems with Distributed Generation”, IEEE Transactions on Power Systems, Vol. 21, No. 3, 1170–1179, August 2006. Abstract : The allocation of the system losses to suppliers and consumers is a challenging issue for the restructured electricity business. Meaningful loss allocation techniques have to be adopted to set up appropriate economic penalties or rewards. The allocation factors should depend on size, location, and time evolution of the resources connected to the system. In the presence of distributed generation, the variety of the power flows in distribution systems calls for adopting mechanisms able to discriminate among the contributions that increase or reduce the total losses. Some loss allocation techniques already developed in the literature have shown consistent behavior. However, their application requires computing a set of additional quantities with respect to those provided by the distribution system power flow solved with the backward/forward sweep approach. This paper presents a new circuit-based loss allocation technique, based on the decomposition of the branch currents, specifically developed for radial distribution systems with distributed generation. The proposed technique is simple and effective and is only based on the information provided by the network data and by the power flow solution. Examples of application are shown to confirm its effectiveness. Index Terms : Branch current decomposition, distributed generation, distribution systems, losses, loss allocation.
Conference Proceedings
F. Spertino, P. Di Leo, J. Sumaili Akilimali, “Optimal configuration of module connections for minimising the shading effect in multi-rows PV arrays”, Proc. 24th European Photovoltaic Solar Energy Conference, Hamburg, Germany, September 2009. Abstract : In large grid-connected PV systems it is a normal condition to accept periodic shading among the rows in the morning and in the evening. In fact, the designer does not take into account this shading when he decides the module connections in the strings, the number of modules per string and the arrangement, according to the longest side of the modules, in horizontal or vertical direction. This paper discusses, by suitable comparisons, various cases of shading pattern in PV arrays from multiple viewpoints: power profiles in clear days with 15-min time step, daily energy as a monthly average value for clear and cloudy days. The simulation results prove that, with simple structure of the array and important amount of shading, it is better to limit the shading effect within one string rather than to distribute the shading on all the strings: the gains are higher than 10% in the worst month and 1% on yearly basis. Contrary, with more complex structure of the array and low amount of shading, it is practically equivalent to concentrate or to distribute the shading on all the strings. Finally, in the simulation conditions the impact of the shading losses on yearly basis is limited to 1-3%. Keywords : Shading, Energy Performance , Simulation
J. Sumaili Akilimali, F. Spetino, H. Andrei and G. Chicco, “Characterization of the PV array parameters from the transient charge of a capacitor”, Proc. 6th Japanese-Mediterranean Workshop on Applied Electromagnetic Engineering for Magnetic, Superconducting and Nano-Materials, JAPMED’6, Bucharest, Romania, July 2009. Abstract : PV systems are becoming more and more largely sized. In small systems, the effects of stray or parasitic parameters are relatively low. When the systems size increases, the effect of additional capacitive and inductive parameters can become more relevant. The classical model of PV cell/module is based on the single exponential or double exponential representation of the PV cell/module behavior in which the parasitic parameters are ignored. The effects of the parasitic parameters can be visualized on the basis of experimental results gathered by the transient charge of an external capacitor connected to the terminals of a PV generator. The cumulative effect of stray capacitance charged in the initial conditions is clearly visible as a current spike. Moreover, an oscillation occurs in the current waveform, indicating the presence of some inductive components. This paper aims to determine the parameters of a model containing the parasitic parameter effects from the results of fast sampling of the voltage and current waveforms during the transient charge of an external capacitor. Specific numerical examples taken from real cases are provided in order to make a comparison among different PV arrays. F. Spertino, P. Di Leo, J. Sumaili Akilimali, “Assessment of energy production and comparison among different configurations of grid connected PV systems” Proc. 23rd European Photovoltaic Solar Energy Conference, Valencia, Spain, September 2008.
E. Carpaneto, G. Chicco and J. Sumaili Akilimali, “Three-phase loss partitioning in unbalanced distribution system branches” Proc. International Symposium of Electrical Engineering, ISEE 2007, Targoviste, Romania, in Scientific Bulletin of the Electrical Engineering Faculty, Valahia, University of Targoviste, 15–20, October 2007. Abstract : The technique of loss partitioning among the phase currents in three-phase distribution systems is revisited in the light of new concepts that highlight the presence of a paradox in the power-based loss partitioning. The IEEE 4-node test system is used in order to assist the illustration of the concepts presented. Index Terms : Three-phase unbalanced systems, paradox, losses, loss partitioning.
F. Spertino, J. Sumaili Akilimali and G. Zubi, "PV Grid parity in Italy" Proc. 22nd European Photovoltaic Solar Energy Conference, Milano, September 2007. Abstract : The PV technology covers the micro to the mega generation, but still has relatively high cost. In recent years the PV market has experimented significant growth, especially in Germany and Japan, thanks to ambitious subvention programs. This growth has been above all in the decentralized on-grid application. The advantage of applying PV close to consumer is that the technology has to compete with the electric grid price and not with the power plant generation cost: Grid Parity is the keyword. Although the sustainability, the low environmental impact, the energy independence and energy security are enough reasons to apply PV, a sustainable PV market requires that grid parity is on sight, so that subventions are just the instrument to achieve the PV emancipation. In Europe Italy will be probably the first country to achieve grid parity, because some conditions lead to that: high electric energy prices, high solar irradiation values, so as a huge market. This scenario will be studied and represented with numbers in this paper on hand of a detailed PV kWh cost calculation. Thereby, the regional irradiation differences are taken into account, so as the decreasing PV installation price and the increasing grid electricity cost. The objective is to predict when grid parity will be achieved and how much Italy can rely on PV. Keywords : Grid Parity, Economic Analysis, Cost Reduction
E. Carpaneto, G. Chicco and J. Sumaili Akilimali, "Application of the circuit-based loss allocation techniques to radial distribution systems" Proc. VI World Energy System Conference, WESC 2006, Torino, Italy, July 2006. Abstract : This paper presents some specific aspects concerning the application of the “circuit-based” techniques for allocating losses in radial distribution systems. The attention is focused on the role of the node of connection to the transmission network, the singularity of the bus admittance matrix and on a possible paradox occurring when the resistive and reactive components of the bus impedance matrix coefficients are used for the purpose of loss allocation, thus illustrating the ways for eliminating the occurrence of the paradox. Various loss allocation techniques are compared by considering a simple illustrative test system. Keywords : Distribution systems, losses, circuit based loss allocation, bus admittance matrix, bus impedance matrix.
E. Carpaneto, G. Chicco and J. Sumaili Akilimali, "Computational aspects of the marginal loss allocation methods for distribution systems with distributed generation" Proc. 15th IEEE Mediterranean Electrotechnical Conference, MELECON 2006, Benalmádena (Málaga), Spain, May 2006. Abstract: This paper highlights some specific aspects concerning the computational techniques for performing distribution system loss allocation including the impact of the distributed generation. The aspects addressed include the approximations related to the nearly-quadratic dependence of the total losses on the load power and the treatment of the voltage-controllable local generation. Examples showing the time evolution of the loss allocation coefficients with variable load and generation patterns are provided. Keywords : Distribution system losses, distributed generation, loss allocation, marginal methods. | ||||
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