International Journal of Energy
E-ISSN: 1998-4316
Volume 9, 2015
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 9, 2015
Title of the Paper: Dynamic Control of a PMSG Wind System for Time-Variable Wind Speed by Imposing the DC Link Current
Authors: Ciprian Sorandaru, Sorin Musuroi, Gheza-Mihai Erdodi, Doru-Ionut Petrescu
Pages: 38-43
Abstract: This paper presents a method for controlling a wind system, - wind turbine (WT) + permanent magnet synchronous generator (PMSG) – in order to reach an energetically optimal operation at a time-variable wind speed. Wind speed and instantaneous mechanical angular speed of the PMSG impose the generator load value in the energetically optimal region. By energy balance measurements done by speed and power measurements, the generator load is obtained so that the system has been brought into the energetically optimal region. It analyzes the maximum power operation in a WT by changing the load to the generator, while the wind speed significantly varies over time. The coordinates of the maximum power point (MPP) changes over time and they are determined by the values of the wind speed and mechanical inertia. Not always wind system can be lead in a timely manner in the MPP. The speed variation of the wind speed and the inertia value are two fundamental elements on which the MPP operation depends. By prescribing the amount of DC link current, Icc, the main circuit of the converter can achieve a simple and useful system tuning WT + PMSG. Operation control method in the optimal energy region of the WT is based on the value of Icc current, which is calculated from wind speed and instantaneous mechanical angular speed, MAS.
Title of the Paper: Method for Determination of Minimum Fluidization Velocity of Polydisperse Mixtures in Running Unit with Fluidized Bed
Authors: Oleg Milovanov, Rafail Isemin, Sergey Kuzmin, Alexander Mikhalev, Valentin Konyakhin, Dmitry Klimov
Pages: 31-37
Abstract: The aim of this article is to develop an experimental method for determining the minimum fluidization velocity for multi-solid beds, which are a mixture of two polydisperse beds in a case where particles constituting each bed differ greatly in shape and size from the particles of the other bed. It is shown that the known methods for determining the minimum fluidization velocity by the change of pressure drop in a bed at increasing (or decreasing) the velocity of gas blown through a bed are not applicable to multi-solid beds. It is suggested determining the minimum fluidization velocity for multi-solid beds using the curves of changes of root-mean-square deviation of pressure fluctuations in a bed at increasing or decreasing the velocity of gas blown through a bed. The proposed method allows determining the minimum fluidization velocity in the running unit without bed deposition that is very important for the control of technological processes, which are accompanied by a change in granulometric composition of a bed (sintering, particles crushing, etc.).
Title of the Paper: Optimization of Capacitive and Resistive Field Grading Devices for Cable Joint and Termination
Authors: George Greshnyakov , Simon Dubitskiy, Nikolay Korovkin
Pages: 24-30
Abstract: Grading the electric field in the reinforced insulation of cable joint and termination is one of the key problem in building reliable high voltage cable power lines. There a two basic ways to solve this problem. In high voltage system mostly capacitive grading is used, which employs specially profiled stress-cone of a two-component rubber. Jojnts and terminations for low to medium voltage commonly employs resistive field grading using the cylindrical grading element with relatively high, often field-dependent conductivity. In this paper we discuss the optimization of both stress-cone and resistive grader by means of FEA modelling of electric field. We also discuss which dielectric properties should have the resistive field grader for using with cable joints of higher voltage.
Title of the Paper: Grid Connected Wind Energy Conversion Systems Control Strategies
Authors: Lata Gidwani
Pages: 20-23
Abstract: In this paper the grid interconnection issues of AC-DC-AC inverter interfaced wind energy conversion system have been dealt. The feed-in power to the grid in Wind Energy Conversion Systems (WECS) shows always a high fluctuation resulting in power quality problems. These problems clearly show that there is a strong need for controlling various stages of WECS, such as generator control, converter control, and inverter control. This paper presents an overview of various control strategies applied to WECS. A model is discussed and its control strategy offers a proper tool for smart grid performance optimization. A rule-based fuzzy logic controller to control the output power of a pulse width modulated (PWM) inverter used in a standalone wind energy conversion scheme (SAWECS) is also discussed. Space vector pulse-width modulation (SVPWM) has been widely employed for the current control of three-phase voltage source inverters (VSI). Emphasis is placed on introducing the control techniques followed by a description of methodologies adopted.
Title of the Paper: Refinement of Underground Power Cable Ampacity by Multiphysics FEA Simulation
Authors: Simon Dubitsky, George Greshnyakov, Nikolay Korovkin
Pages: 12-19
Abstract: The maximum current in underground cable line is limited by the rated temperature of conductor and insulation. The standard method for ampacity calculation in accordance the IEC 60287 standard is quite accurate for individual power lines laid in accordance to standard practice. However, when multiple power lines should be placed together in a limited space, it is necessary to consider the electromagnetic and thermal influence of cables to each other. The increase of losses due to mutual influence of cables may be greater than is commonly believed. It is shown that the use of electromagnetic and thermal FEA simulation successfully solves this problem not only in the context of research, but also in the engineering practice. The FEA-based approach and the software tool is proposed for calculation ampacity of underground cable lines. The electromagnetic FEA simulations can also assess the electromagnetic environment near power lines and quantitatively evaluate the effect of magnetic shielding. The proposed method can be used in cases where the standard IEC 2087 calculation gives unreliable results due to unusual cable line formation, inhomogeneous soil, presence of metallic or concrete supports and other difficulties.
Title of the Paper: Hybrid Bat Algorithm for Solving Reactive Power Problem
Authors: K. Lenin, B. Ravindhranath Reddy, M. Suryakalavathi
Pages: 7-11
Abstract: Real power loss reduction plays a significant role in power system operation and control. Ahybrid bat algorithm (HBA)is proposed to reduce the real power loss. Swarm Intelligence based bat algorithm has been hybridized with differential evolution strategyto solvethe problem. The main objective of the problem is to minimize the real power loss. HBA algorithm is used to find the optimal settings of generator bus voltage, transformer tap settings and reactive power of shunt compensator. The proposed HBA algorithm has been validated on standard IEEE 30 bus system. The results have been compared to other heuristics methods and the proposed algorithm converges to best solution.
Title of the Paper: Field-Circuit Model of the Resistive Welding Load and the Welding Power Source for Reducing Power Consumption and Electromagnetic Noise
Authors: L. Sakhno, O. Sakhno, S. Dubitsky
Pages: 1-6
Abstract: Resistance welding machines with inverter power sources are considered. The equivalent scheme of the welding load for resistance butt flash welding is proposed, which based on the experimental analysis of physical processes in the flashing zone. The model was used for the AC analysis of the input current and the welding circuit in application to the inverter power unit for a steel pipe flash butt welder. The equivalent circuit of the three-winding transformer is proposed, where the primary and secondary windings are coupled by the coefficient of mutual induction on the leakage flux. Self and mutual leakage inductances of the transformer are calculated and optimized by means of 2D FEA simulation. Electromagnetic processes in welding machines are modeled in time domain with P-Spice simulation. The above model was used for optimization of the invertor based welding power supply. The results of time domain simulation of the welding power source were confirmed experimentally.
