In recent years a multitude of events have created a new environment for the electric power infrastructure. The presence of smallscale generation near load spots is becoming common especially with the advent of renewable energy sources such as wind power energy. This type of generation is known as distributed generation (DG). The expansion of the distributed generators-(DGs-) based wind energy raises constraints on the distribution networks operation and power quality issues: voltage sag, voltage swell, voltage interruption, harmonic contents, flickering, frequency deviation, unbalance, and so forth. Consequently, the public distribution network conception and connection studies evolve in order to keep the distribution system operating in optimal conditions. In this paper, a comprehensive power quality investigation of a distribution system with embedded wind turbines has been carried out. This investigation is carried out in a comparison aspect between the conventional synchronous generators, as DGs are widely in use at present, and the different wind turbines technologies, which represent the foresightedness of the DGs. The obtained results are discussed with the IEC 61400-21 standard for testing and assessing power quality characteristics of grid-connected wind energy and the IEEE 1547-2003 standard for interconnecting distributed resources with electric power systems.
Owing to the increasing penetration of renewable energy resources in the electric grids, the need for systematic studies of the impact of wind power on voltage, synchronous (angle) and frequency stability of the grid is encouraged. Unlike the massive literatures for stability issues with conventional energy resources, the corresponding research efforts for Wind Energy Conversion Systems (WECS) are still highly demanded. In this paper, a comprehensive methodology for realizing an efficient, versatile and accurate modeling for grid-integrated WECS for transient stability studies is explored. Details for representing the wind aerodynamics, drive trains, wind generators in addition to other conventional synchronous generators with its control mechanisms are outlined. The presented study is conducted with the known IEEE 3-generator, 9-bus power system network as a simulation example. Some explanation cases are illustrated examining the system voltage, angle and frequency stability.
Harmonic analysis is an important application for analysis and design of distribution systems. It is used to quantify the distortion in voltage and current waveforms at various buses for a distribution system. However such analysis has become more and more important since the presence of harmonic-producing equipment is increasing. As harmonics propagate through a system, they result in increased power losses and possible equipment lossof-life. Further equipments might be damaged by overloads resulting from resonant amplifications. There are a large number of harmonic analysis methods that are in widespread use. The most popular of these are frequency scans, harmonic penetration and harmonic power flow. Current source (or current injection) methods are the most popular forms of such harmonic analyses. These methods make use of the admittance matrix inverse which computationally demand and may be a singular in some cases of radial distributors. Therefore, in this paper, a new fast harmonic load flow method is introduced. The introduced method is designed to save computational time required for the admittance matrix formation used in current injection methods. Also, the introduced method can overcome the singularity problems that appear in the conventional methods. Applying the introduced harmonic load flow method to harmonic polluted distribution systems embedded shunt capacitors which commonly used for losses minimization and voltage enhancement, it is found that the shunt capacitor can maximize or minimize system total harmonic distortion (THD) according to its size and connection point. Therefore, in this paper, a new proposed multi-objective particle swarm optimization "MOPSO" for optimal capacitors placement on harmonic polluted distribution systems has been introduced. The obtained results verify the effectiveness of the introduced MOPSO algorithm for voltage THD minimization, power losses minimization and voltage enhancement of radial distribution systems.
The relaxation time of a physically based nonquasi-static (NQS) MOSFET model [l] is investigated with emphasis to the empirical approach used in BSIM3v3 NQS model. The 5042 S parameters of a l.Oym RF MOSFET are determined using our model in SPICE and compared to those obtained experimentally. A high-frequency OTA is designed and realized in a modern RF CMOS technology. The circuit is then analyzed and simulated to study the validity of the €IF performance of our model in contrast to the available BSIM3v3 NQS and QS MOSFET models. Our NQS model has provided realistic simulation results, which meet our expectations based on analysis and theory. NOTATION Effective channel length of a MOSFET. Effective channel width of a MOSFET.Effective mobility of channel carriers.Gate oxide capacitance per unit area. Zero-bias overlap capacitance per unit area.Threshold voltage. DC gate-to-source voltage.DC drain-to-source voltage.Vd,,,, Saturation drain-source voltage ( Vgs -vfh ).
R,,Elmore resistance. E Os Strong inversion surface potential.Elmore coefficient of the channel RC network.
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