# International Journal of Energy

**ISSN: 1998-4316
Volume 11, 2017**

Notice: As of 2014 and for the forthcoming years, the publication frequency/periodicity of NAUN Journals is adapted to the 'continuously updated' model. What this means is that instead of being separated into issues, new papers will be added on a continuous basis, allowing a more regular flow and shorter publication times. The papers will appear in reverse order, therefore the most recent one will be on top.

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**Volume 11, 2017**

Title of the Paper: **Studies Regarding the Use of Renewable Energy Sources to Produce Electricity**

Authors: **Lepadatescu B., Nedelcu Anisor**

Pages: **50-53**

Abstract: Due to prolonged use of wind turbines they must be characterized by high reliability. This can be achieved through a rigorous design, appropriate simulation and testing and proper construction. The reliability prediction and analysis of these systems will lead to identify critical components, increase operating time, minimizing failure rate and minimizing maintenance costs. The Monte-Carlo simulation of parameters of helical wind turbine with vertical axis includes elements of reliability theory and notions of probability and statistical inferences. To estimate the produced energy by wind turbine, an evaluation approach based on Monte Carlo simulation model is developed which permits us to estimate the probability of minimum and maximum parameters. In our simulation process we used triangular distributions. The case study consists on determination of statistical parameters of assumed distribution, in order to estimate the reliability and unreliability functions, probability density function (pdf) and hazard rate (failure rate) of the helical wind turbine with vertical axis. Based on experimental tests, it was calculated the variation of power produced for different wind speed, respectively it was calculated the Weibull distribution of wind probability and the power which is generated. The analysis of experimental results indicates that this type of wind turbine at low wind speed is more efficient than other wind turbine with horizontal axis and with three blades.

Title of the Paper: **Analytical Methods of Destabilizing Factors of Improving the Technical Systems Efficiency**

Authors: **A. Zhilenkov, A. Nyrkov, S. Chernyi, S. Sokolov**

Pages: **46-49**

Abstract: According to the Navy Register rules, ship electrical power system voltage fluctuations within ±10% of the nominal voltage are admissible if not lasting longer than 5 seconds; longer fluctuations are admissible if they are within ±5% of the nominal voltage. For the operation of a rotational speed Automatic Control System with a sliding-mode regulator, there is no need to identify the diesel and propeller parameters; however, one needs a quantitative assessment of the limits within which such parameters could change. To implement the algorithm of such sliding-mode regulator, it is enough to control the rotational speed deviation for the specified value

Title of the Paper: **Hydrogen Production by Steam Reforming of Methanol over Copper Catalysts Prepared by Using the Sol-Gel Method - Effect of Metal Addition -**

Authors: **Kaoru Takeishi, Hiromitsu Suzuki**

Pages: **41-45**

Abstract: We have already reported that Cu(10 wt.%)/SiO2 catalyst prepared by using the sol-gel method is excellent catalyst for hydrogen production by methanol steam reforming. Zn, Pd, Au, Pt, Ir, Re, Rh, Ru, Ag, Cr, Mn, Fe, Co, Ni, Mo, Sn were added to the Cu/SiO2 catalyst on the way of its sol-gel preparation process and Cu-M(9-1 wt.%)/SiO2 catalysts were prepared using the sol-gel method, respectively. These catalysts were tested for hydrogen production by methanol steam reforming, respectively. Cu-Zn(9-1 wt.%)/SiO2 catalyst prepared using the sol-gel method is the most excellent catalyst for hydrogen production by methanol steam reforming at 350 oC. On the other hand, low temperature methanol steam reforming system is needed for waste heat recovery around 200 oC. For this purpose, Cu-Pd(9-1 wt.%)/SiO2 catalyst prepared using the sol-gel method is most excellent among the catalysts, while the Cu-Zn(9-1 wt.%)/SiO2 catalyst produces 1/10 amount of H2 that of hydrogen produced at 350 oC.

Title of the Paper: **Study and Experimental Test of Combined Harvesting Technologies to Increase the Efficiency of Solar Energy Devices**

Authors: **Massimo Viscardi, Romeo Di Leo**

Pages: **27-40**

Abstract: The present work focuses its attention about the need of implementation of an energy recovery system for a renewable energy device as photovoltaic cells. In a specific way the present paper is addressed to the evaluation of a potential use of Peltier cells to recover waste heat of PV, using the Seedback effect, and the opportunity to recovery the vibrational energy of the PV cell surface when it is subject to the effect of rain drops. An overview of Peltier cells, mainly focused on their functionality, properties and possible applications, is initially presented. The results of an extensive experimental test campaign is then presented; these tests have mainly been dedicated to the evaluation of Peltier cells properties in the electrical conversion of heating energy produced and/or not dissipated during the photovoltaic phenomena in siliceous PV cells. The second part of the work is focuses on a first study for a piezoelectric harvesting system, finalized to obtain electrical energy from the kinetic energy of rainy precipitation; a renewable energy source not really considered until now. After a state of art of the harvesting systems from environmental energy, linked to vibrations, using piezoelectric structures, and of piezoelectric harvesting systems functioning with rain, authors propose an analysis of the fundamental features of rainy precipitations for the definition of the harvesting system. An electro-mechanical model for the simulation of performance of the unit for the energetic conversion, composed by three blocks, is proposed. The model is used for a simulation campaign to perform the final choice of the more suitable piezoelectric unit, available on the market, which will be adopted for the realization of the “Piezo Roof Harvesting System”.

Title of the Paper: **A Predictive Current Control Strategy for a Naturally-Commutated Converter Using a Finite-State Machine Model**

Authors: **VÄ±ctor Guerrero, Jorge Pontt, Marcelo Vasquez, Manuel Olivares**

Pages: **19-26**

Abstract: Predictive current control methods for forced-commutated converters, e.g., voltage source inverter, are well documentated and they perform very well compared with the classical solutions, i.e., hysteresis control and proportional-integral controllers with pulsewidth modulation. This paper presents a strategy to implement a predictive control technique for a naturally-commutated converter, e.g., multipulse cycloconverter. This strategy uses a discrete-time model of the system to predict the future value of the load current for all possible output voltages of the converter. Since in a naturally-commutated converter the possible output voltages are dynamic and they depend on the present switching state of every semiconductor of the converter, these output voltages must be obtained from a mathematical model (finite-state machine) of the converter. The proposed current control strategy is tested. The simulation and experimental results show that a predictive control strategy can be used not only in applications with forced-commutated converters but also with naturally-commutated converters showing good electric performance.

Title of the Paper: **Comparative Characteristics, Analysis, Mathematical Model and Simulation of Selected Energy-Electronic Converters of Modern Aircraft in Line with the Concept of a More Electric Aircraft MEA/ AEA**

Authors: **L. Setlak, R. Kowalik**

Pages: **7-18**

Abstract: The work deals with the issues of modern architecture power supply compatible with the trend of more electric aircraft in the field of energy-electronic power electronics systems PES (Power Electronics Systems), both civil aircraft "classical" companies Airbus and Boeing aircraft (A-320, B-767) and military Lockheed Martin (F-16) as well as a more civil aircraft/ fully electric MEA/ AEA (A-380 and A-350XWB, B-787) and military JSF (Joint Strike Fighter) F-35 and F-22 Raptor. The subject, and also the aim of this paper is to make a comparative characteristics of selected elements of power electronic converters, which are multi-pulse rectifiers (6- and 12- pulse) or (18- and 24- pulse) used on modern aircraft with 48- pulse rectifier, presenting them analysis and mathematical models, and based on the above, the analysis and draw practical conclusions in the field of advanced power electronic power systems PES according to the concept aircraft more/ fully electric (MEA/ AEA). The idea behind this concept is to replace conventional key air devices, circuits and systems, electrical power, pneumatic, hydraulic and mechanical - devices, circuits and systems fed one kind of energy, namely electricity.

Title of the Paper: **Parameters’ Optimisation Methods for the Electrostatic Discharge Current Equation**

Authors: **Vasiliki C. Vita, George P. Fotis, Lambros Ekonomou**

Pages: **1-6**

Abstract: In the current international standard IEC 61000-4-2 the equation describing the electrostatic discharge current needs a further investigation in order to describe the measured current accurately. In the current paper two different optimization methods are presented that have been developed in order to calculate the parameters of the electrostatic discharge current equation. The first method uses a quasi-Newton optimization algorithm, while the second one uses genetic algorithms and constitutes an extension of a methodology that has been used in a previous research work. Electrostatic discharge current data obtained from real measurements are also used in this work in order to compare them with the results obtained from the two proposed methods in an effort to prove their efficiency and accuracy. The proposed methods are extremely useful in the ESD studies, since an accurate electrostatic discharge current equation is an indispensable requirement for the description of the ESD generators in simulation programs.