NASHRIYYAH -I MUHANDISI -I BARQ VA MUHANDISI -I KAMPYUTAR -I IRAN, A- MUHANDISI -I BARQ
Year:2009 | Volume:7 | Issue:1|Papers Count:11

This paper presents a new multiobjective model for optimal placement of distributed generation sources in electric distribution network under load and market price uncertainties that finds out the non-dominated multiobjective solutions corresponding to the simultaneous minimization of economic cost, technical risks, and economical risk due to uncertainties. Fuzzy sets theory is used to model the uncertainties. The proposed model is solved using a specialized genetic algorithm as the optimization tool. The performance of the proposed approach is assessed and appreciated by case study on a typical distribution network.

In this paper a new configuration of unified power quality conditioner (UPQC) is proposed. In this new configuration, by adding a series converter in an adjacent feeder, the abilities of the UPQC are enhanced. The proposed configuration can be applied to adjacent feeders to compensate for supply voltage and load current imperfections on the main feeder and fully compensation of supply voltage imperfections, especially interruption, on other feeder. In this configuration two series and one shunt converters are used which all are voltage source converters (VSC). All VSCs are connected back to back on the DC side and shared a common DC-link capacitor. The proposed configuration offers the following advantages: 1) Power transfer between two adjacent feeders for sag/swell and interruption compensation. 2) Using one shunt VSC for current compensation in main feeder and voltage regulation of common DC link capacitor between all VSCs. The simulation results obtained in PSCAD/EMTDC on a two bus/two feeder system show the effectiveness of the proposed configuration as well as the adopted control system.

Due to uncertainties in system modeling as well as system parameters, current excitation systems are unable to perform quite satisfactorily over a wide range of operating conditions. In this paper a QFT-based excitation robust control is proposed which the above mentioned uncertainties are, somehow, considered. The Horowitz second method is employed in the design of the nonlinear QFT controller.

Phase angle between the currents measured at the two ends of a protected transmission line could be highly affected by load current component for high resistance internal faults. As a result, the phase comparison protection (PCP) scheme might fail to recognize these kinds of faults. In this paper a new approach is proposed to enhance the accuracy of PCP scheme to detect such kind of faults. The fault component of current signal is reconstructed using the estimation of load component of the current signal under fault condition. Therefore, the proposed method eliminates the phase angle difference due to the load component. The pre-fault current of the line is used as the estimation of the load current component during the fault condition. It is shown that this approximation enhances the performance of PCP scheme for high resistance faults. It also increases the accuracy of classifying fault type due to increase of the sensitivity of fault detection units. The proposed method is simulated for a test system and is examined for various fault conditions. Obtained results show major improvement in the performance of PCP scheme.

Congestion management is deal with in this paper. The algorithm proposed is based on active and reactive power dispatches of critical nodes, determined from a detailed sensitivity analysis. The electricity market considered is a hybrid model, in which firm transmission rights may also be observed. The proposed algorithm is assessed and its capabilities evaluated for a typical test system.

In this paper a new steady state modeling of unified power flow controller (UPFC) is proposed. Using this model, factors that affect the objective function of electricity market as a result of UPFC installation in power grid has been decomposed into four components, including line series impedance increase, shunt reactive power compensation, in-phase component of series voltage and quadrature component of series voltage. An UPFC has been placed in different points of a test system and impact of each component on objective function of electricity market has been measured by simulation and compared with results from analytical method. Both active and reactive locational marginal prices are calculated and their relation with settings of UPFC series part has been studied.

This paper addresses the problem of speech enhancement in wavelet domain. After decomposition of noisy signal into wavelet sub-bands, an adaptive thresholding process is applied on wavelet coefficients. In the proposed technique, small threshold value and hard thrsholding function are used in sub-bands with high speech energy; vice versa, in sub-bands with low speech energy, large threshold value and soft thresholding function are employed. For other sub-bands (between above two extreme cases for speech energy), we use an adaptive thresholding function that is actually between soft- and hard-thresholding functions. The threshold value and thresholding function are determined by a parameter related to the ratio of speech and noise powers in each sub-band. Our extensive experiments show the superiority of proposed method in removing the background noise and reduction of speech distortion. It was also shown that both wavelet tree structure and wavelet type affect on the performance of speech de-noising system.

In the design of mobile cellular networks, the option of methods for location management of mobile users and updating this location is very important. In general, numerous methods of location management could be classified in two different categories named static and dynamic. Analysis and studies show that the second category imposes less computational load onto network. One of the algorithms in dynamic case is based on distance which has better performance compared to other algorithms which are based on time or movement. The important point in this technique is the calculation of cellular distance by mobile unit (MS). Because MSs could receive only cell codes or cell identification (cell ID) by BTSs, in this technique the mobile unit should be able to calculate the cellular distance from these codes (ID). In this paper the authors propose a method for cell ID assignment based on real geographic location of BTS in GPS system. The achieved IDs are then used for applying the distance based method for location management. We have also tested the performance of this method by simulation of a real cellular network in city of Yasuj, province of Kohkiluyeh in Iran.

In this paper, experimental modeling of two-dimensional discrete systems with ARMA structure is considered. Therefore two-dimensional model order selection and parameter estimation problems are proposed. This method shows that the information of AR and MA orders are implicitly contained in two different correlation matrices and the AR and MA orders of the 2-D ARMA model can be independently determined before parameter estimation.The two-dimensional model is assumed to be causal, stable, linear, and spatial shift-invariant with quarter plane (QP) support. Numerical Simulations are presented to show the good performance and effectiveness of the proposed method in two-dimensional discrete system with ARMA structure.

Nonlinear behavior of the power amplifiers in satellite transmitters causes a lot of errors in digital image transmission. So, even by using a moderate linearizer, the bit error rate (BER) will greatly improve. In this paper, the particle swarm optimization has been used as an effective method with good conversion speed. Effects of an optimized cubic linearizer on digital image transmission are evaluated. The simulations results for the bit error rate as a function of signal to noise ratio (SNR), third order intercept point (TOI), and noise figure (NF) of low noise amplifier (LNA) are compared with each other.

The performance of video transmission over wireless channels is limited by the channel noise. Thus many error resilient tools have been incorporated into the MPEG-4 video compression method. In addition to these tools, the unequal error protection (UEP) technique has been proposed to protect the different parts in a MPEG4 video packet with different channel coding rates based on the rate compatible punctured convolutional (RCPC) codes. However, it is still not powerful enough to achieve a high visual quality over the wireless networks. To provide more robust MPEG-4 video transmission over wireless channels, this paper proposes a modified unequal error protection (MUEP) approach based on the content of the video scene. In proposed technique, channel coding rates for motion section of the video packet are determined based on the motion of the video scene. Experimental results show that the proposed technique enhances both subjective visual quality and PSNR about 1.5 dB, comparing to the traditional UEP method.