Majlesi Journal of Energy Management
Volume:4 Issue: 4, Dec 2015

Given the growing use of wind power plants in the power supply and the importance of power quality in the electrical networks, the stability in wind energy conversion systems in an error condition and even after eliminating the faults is needed. The disturbances which enter into the system cause the strong oscillations and these oscillations immediately should be removed after error clearing in order to stabilize the system. In this paper, we compare the transient stability in the wind turbine by using fixed-speed induction generator and doubly fed induction generator, in the present of a fault and after clearing the fault. In this paper, we also compare the voltage and the power generated profile oscillations. The case analysis on a wind farm is connected to an infinite bus and it has been done by using the software environment MATLAB / Simulink.

In this paper dynamics of a vapour bubble generated due to a local energy input inside a vertical rigid cylinder and in the absence of buoyancy forces is investigated. Different ratios of the diameter of the rigid cylinder to the maximum radius of the bubble are considered. The Boundary Integral Equation Method is employed for numerical simulation of the problem. Results show that during the collapse phase of the bubble inside a vertical rigid cylinder, two liquid micro jets are developed on the top and bottom sides of the vapour bubble and are directed inward. Results also show that existence of a deposit rib inside the vertical rigid cylinder slightly decreases the life time of the bubble. It is found that by increasing the ratio of the cylinder diameter to the maximum radius of the bubble, the rate of the growth and collapse phases of the bubble increases and the life time of the bubble decreases.

Considering that nowadays has occurred to a widely application of distributed generation in distribution systems, it is necessary to investigation of problems and issues that may arise the distribution system. In this paper the main issue is to investigate the effect of random load behavior of distribution system on enhancement of system loadability in presence of DG units. The results show that random load behavior how and how much will affect on improved system loadability. To do these investigations, at first the optimized place for installing DG has been specified in certain load condition using Genetic Algorithm, and its effect on loadability is investigated. Then network loads has taken randomly and the results are obtained and investigated for this case too. Moreover, in certain load condition, effect of number of DG and type of generation capability of real and reactive power (due to the fact that some types of DG can only generate and inject real power) has been studied and best one is specified.

In this study, numerical analysis of the effect of external flow turbulence and aspect ratio of building on the amount of opening discharge coefficient in natural ventilation is reviewed by modeling. The solution is the use of computational fluid dynamics (CFD) approach by Fluent Software and to understand taken properly of the result of numerical solution, the result of experimental solution that had been obtained by others is used. All the obtained results are gotten in three-dimensional space assuming steady state flow and incompressible fluid. Turbulent model was used is standard k-ε that has the most accommodation with experimental results. At the end of the study, this conclusion was reached that the amount of opening discharge coefficient is increased by increasing the number of Reynolds in opening and with increasing the width to length ratio of building the amount of discharge coefficient decreases. Finally, it is concluded that by increasing of the turbulence of external flow, discharge coefficient decrease.

Generation of electrical energy in order to minimizing cost is one of the main issues in modern power networks. Economic dispatch is the most proper solution which leads to an optimal and effective programming for generative units which takes the utility grid’s constraints and factors into account. The present study investigates the economic load dispatch problem, using an imperialist competitive algorithm while considering valve point loading effect. To portray the efficiency of the proposed method, the algorithm is applied to two popular test systems in the area including 13 and 40 thermal units. The obtained results are compared to those of other algorithms which indicates the efficiency and priority of the proposed algorithm in solving economic load dispatch problem.

Development of distributed generations’ (DGs) technologies and their continuous increasing penetration has recently lead to a great tendency toward these resources, among which photovoltaic (PV) generations in power distribution systems are of great importance. Being cost-effective, PV resources which are directly connected to utility grids are studied in this paper where a new adaptive hysteresis current controller for single-phase single-stage PV central inverters is presented. The proposed scheme can be utilized in a diverse scope of PV technologies. Simulation results indicate that the suggested strategy improves the efficiency of the system by reducing the total harmonic distortion of the injected current to the grid; and, in addition to having the output current in phase with the voltage of the utility grid it is able to control switching frequency and to inject the current into power grid with good power quality. The simulated model of the system is developed in SIMULINK/MATLAB environment. The proposed scheme is found effective in obtaining the desired goal when the switching frequency is adequately high which leads to the synchronization of power grid voltage and inverter current and near to unity power factor.

Phase Unbalance in distribution networks is one of the unavoidable problems that results from presence of single-phase charges and diversity of consumption among customers. This paper aims to study unusable capacity in distribution transformers due to phase Unbalance through proposing a new coefficient for estimating their capacity. In this study, the primary reasons which lead to Unbalance in transformers have been studied, then unusable capacity in transformers and phase Unbalance index have been formulated, and finally, real results on two posts related to Ardabil electricity distribution network have been evaluated, information corresponded to sample posts has been acquired through installing data logger machine, type TDL 104 for a week and using hour-to-hour sampling method. The results form machine have been analyzed using Matlab software, and then related diagrams have been drawn and also comparison among them has been done. Finally, the effect of phase Unbalance in estimating transformers’ capacity has been proposed by a coefficient.