Showing 13–24 of 256 results
A New Heuristic Algorithm for Unit Commitment Problem
Large scale power syرایگان!
Large scale power systems Unit Commitment (UC) is a complicated, hard limit, mixed integer combinatorial and nonlinear optimization problem with many constraints. This paper presents an innovative and effective solution based on modification of the Harmony Search (HS) Algorithm to solve the strategic planning of Generating unit’s commitment. The proposed algorithm is easy in application compared to the other Evolutionary Methods (EM) and has a high capability in reaching to optimal solution with reasonable time. The proposed method is tested using the reported problem data sets. Simulations were down for daily unit commitment. The results are compared with previous reported articles results. Numerical results show the efficiency and improvement of the solution in cost and execution time compared to the results of the other powerful heuristic optimization algorithms.
A Novel and Fundamental Approach towards Field and Damper Circuit Parameter Determination of Synchronous Machine
In this era of advanرایگان!
In this era of advanced computing where complex algorithms and expensive approaches are used to determine the machine parameters of a synchronous machine, this paper proposes a novel, economical and yet fundamental approach towards estimation of the d- and q-axis field and damper circuit parameters of a low/medium power wound-field synchronous machine. The proposed novel methodology employs fundamental voltage, current, flux linkage relationships of the 3-phase wound-field synchronous machine in a-b-c reference frame theory. Firstly, the proposed methodology has been explained in detail using analytical equations and then employed to determine the aforementioned parameters of a small laboratory synchronous machine. Other equivalent circuit parameters have been determined using conventional tests. Further validation of the proposed methodology was performed using two other larger machines with different nameplate ratings. Moreover, the aforementioned parameters of the larger machines were also experimentally determined using IEEE standard tests. Finally, a comparison of the results obtained employing the conventional and the proposed methodologies were performed and the proposed methodology has been established to be valid as the results are in close agreement.
A Novel Hybrid Network Architecture to Increase DG Insertion in Electrical Distribution Systems
Distribution networks will experience a deep mutation concerning their planning and operation rules due to the expected increase of distributed generation (DG) interconnection to the grid. Indeed, the opening of the electricity market or the growing global concern for environmental issues will lead to a massive development of DGs. Yet, a too large amount of DGs could raise technical problems on distribution networks which have not been planned to operate with bi-directional power flow. The existing solutions to solve marginal DG connections could be no longer relevant. The distribution network definitely has to evolve towards a smarter and more flexible network. Two possible ways to reach this goal are through new architectures and developing intelligent systems. This paper focuses on new architectures and operating modes. The traditional radial distribution network could accept more DGs by introducing appropriately specific loops. A new hybrid structure enabling the coexistence of the radial and meshed operation is proposed. It is equipped with autonomous circuit-breakers and automated switches that improve its reliability. A heuristic algorithm is also proposed to build this new architecture while ensuring the equality of consumers with respect to the continuity of service and while minimizing the global cost.
A Novel Protective Scheme to Protect Small-Scale Synchronous Generators Against Transient Instability
Installation of smalرایگان!
Installation of small generators in distribution networks has been increased recently due to its various benefits. One of the important issues related to these distributed generators is the effect of system faults on their transient stability. Due to the low inertia constant of the small-scale generators and the slow operation of the distribution networks’ protective relays, transient instability is quite probable for these generators. In this paper, the dynamic behavior of small-scale synchronous generators to the system faults and its sensitivity to the system parameters are investigated. Then, a practical protective method using theexisting overcurrent and undervoltage relays is proposed, and its advantages and disadvantages are pointed out. Next, based on the obtained information from sensitivity analysis, a novel protective relay is proposed to protect the generators against instability. The proposed relay uses a generator active power to determine the appropriate time to disconnect the generator. Simulation results confirm the secure operation and robustness of the proposed relay against system transients. In addition, the proposed algorithm complies with the generator fault-ride-through requirements.
A Phase-Domain Synchronous Machine Model With Constant Equivalent Conductance Matrix for EMTP-Type Solution
Interfacing machine models in either nodal analysisbased (EMTP-like) or state variable-based transient simulation programs play an important role in numerical accuracy and computational performance of the overall simulation. As an advantageous alternative to the traditional qd models, a number of advanced phase- domain (PD) and voltage-behind-reactance machine models have been recently introduced. However, the rotor-positiondependent conductance matrix in the machine–network interface complicates the use of such models in EMTP. This paper focuses on achieving constant and efficient interfacing circuit for the PD synchronous machine model. It is shown that the machine conductance matrix can be formulated into a constant submatrix plus a time-variant submatrix. Eliminating numerical saliency from the second term results in a constant conductance matrix of the proposed PD model, which is a very desirable property for the EMTP solution since the refactorization of the network conductance matrix at every time step is avoided. Case studies demonstrate that the proposed PD model represents a significant improvement over other established models used in EMTP while preserving the accuracy of the original/classical PD model.
A review of solar photovoltaic technologies
Global environmental concerns and the escalating demand for energy, coupled with steady progress in renewable energy technologies, are opening up new opportunities for utilization of renewable energy resources. Solar energy is the most abundant, inexhaustible and clean of all the renewable energy resources till date. The power from sun intercepted by the earth is about 1.8 × 1011 MW, which is many times larger than the present rate of all the energy consumption. Photovoltaic technology is one of the finest ways to harness the solar power. This paper reviews the photovoltaic technology, its power generating capability, the different existing light absorbing materials used, its environmental aspect coupled with a variety of its applications. The different existing performance and reliability evaluation models, sizing and control, grid connection and distribution have also been discussed.
A self-organized structure for mobility management in wireless networks
The objective of thiرایگان!
The objective of this work is to analyse performance of unstable mobile nodes with selforganization structures in Delay Tolerant Networks (DTN). This process enables the nodes to utilize their power fairly, and ensures that the links are established between nodes and used to improve the connectivity. In this paper two approaches are proposed: 1. Self-Healing (SH) and 2. Unstable Topology Structure (UTS) approaches based on localized computations. The proposed work is proven with simulations by analysing node degree, coverage area and Quality of Service (QoS) parameters. The performance of the work is analysed in a network simulator with mathematical models.
A simple power factor calculation for electrical power systems
The accurately and fرایگان!
The accurately and fast estimation of Phase Difference (PD) is required between the voltage and current of an AC electrical power system to calculate the Power Factor (PF) for defining how effectively the electrical energy is converted into the useful form. Many complex methods based on difficult mathematical equations are presented by the researchers to estimate the PD. In this study, a new and simple algorithm derived by using the trigonometric functions is proposed for PD estimation to calculate PF of a power system. With this method, the fast-time and unaffected by distorted sinusoids of PD estimation are carried out by decreasing the number of mathematical equations. The performance of the proposedmethod is evaluated under the various system conditions by performing the simulation case studies. The results of these studies are given to verify its effectiveness under the distorted system conditions.
A Single-Phase Voltage Sag Generator for Testing Electrical Equipments
This paper describesرایگان!
This paper describes a transformer-based voltage sag generator (VSG) suitable to evaluate the susceptibility of electrical equipment to voltage sag. The built VSG utilized one auto-transformer and two solid state relays (SSRs) to provide nominal voltage and sag voltage to the load. The switch statuses of two SSRs are controlled by nominal voltage and sag voltage duration signal produced by electronic circuits. The VSG operating result shows that it enables effective control of sag magnitude, duration, beginning and ending points on output voltage wave. If needed, it can work as a voltage swell generator and a voltage interruption generator. By supplying high voltage (HV) transformer from the primary side, the VSG also can provide HV sag, swell, and interruption. The presented VSG is easier to set up in the lab, and the construction cost is much lower than buying VSG products at the current market.
A study of the variation of synchronous machine parameters due to saturation: a numerical approach
This paper shows theرایگان!
This paper shows the variation of the fundamental parameters of synchronous machine two-axis equivalent circuits due to magnetic saturation. The different magnetic states of the machine are obtained using finite- element magnetostatic solutions. This way the permeability patterns of the saturable parts of the machine can be stored and used in a specially designed finite-element program that outputs the standstill frequency response (SSFR) of the machine. A hybrid genetic algorithm, capable of finding global extrema is then applied to obtain the parameters of two equivalent circuit structures for the d-axis. The process is repeated for each magnetic state, so that the variation of parameters can be seen. The magnetic states of the machine are validated by comparing the measured open-circuit characteristic with the one calculated from the finite- element model. In order to validate the d-axis equivalent circuit parameters identified, they have been adopted in the simulation of a synchronous machine short-circuit and the results obtained have been compared to those calculated by a transient finite-element program.
A survey on coverage and connectivity issues in wireless sensor networks
A wireless sensor neرایگان!
A wireless sensor network (WSN) is composed of a group of small power-constrained nodes with functions of sensing and communication, which can be scattered over a vast region for the purpose of detecting or monitoring some special events. The first challenge encountered in WSNs is how to cover a monitoring region perfectly. Coverage and connectivity are two of the most fundamental issues in WSNs, which have a great impact on the performance of WSNs. Optimized deployment strategy, sleep scheduling mechanism, and coverage radius cannot only reduce cost, but also extend the network lifetime. In this paper, we classify the coverage problem from different angles, describe the evaluation metrics of coverage control algorithms, analyze the relationship between coverage and connectivity, compare typical simulation tools, and discuss research challenges and existing problems in this area.
A UPFC MODEL FOR DYNAMIC STABILITY ENHANCEMENT
While the controllabرایگان!
While the controllability of the line power flow by unified power flow controller (UPFC) has been recognised, only very limited information is available concerning the quantitative control of the UPFC to provide additional damping during system oscillations. This paper presents a current injection model of UPFC which is suitable for use in power system stability studies. To use the current injection model on dynamic stability studies, a proper control method is necessary. It is proposed that the shunt compensation of UPFC is controlled to maintain the system bus voltage and the two components of UPFC series voltage, which are in phase and quadrature with the line current, are controlled in coordination by Strip Eigenvalue Assignment method. The eigenvalue analysis and time domain simulation results show that the proposed model and control method can substantially improve the dynamic stability of the power system.