IRANIAN JOURNAL OF ELECTRICAL AND COMPUTER ENGINEERING (IJECE)
Year:2004 | Volume:3 | Issue:2|Papers Count:14

This paper presents and compares two different methods using in the forecasting of wind power turbine (WPT) outputs. These two forecasting methods, which utilize different types of input to forecast the output of WPT, are the Meteorology Forecasting Method (MFM) and the Observational Forecasting Method (OFM). The MFM determines the unit output from the forecasted wind speed at the WPT installation site, using the input from a composite data set created from the original annual-hourly weather data. Three different techniques can be used in MFM to forecast the wind speed, and the best result is selected for conversion calculation of the output of WPT. OFM, however, forecasts the unit output based on five observed annual-hourly data obtained from the operation of target WPT. Two different techniques can be used in the OFM simulation. The results from these techniques for each method are compared and the best one will be used for the final forecast of the WPT outputs. This paper presents and compares the forecasting results of WPT output obtained from MFM and OFM. Furthermore, in order to increase the result precision and decrease the forecast error, a new composite data system is also developed and proposed.The methodologies proposed in this paper will be very useful for designers, planners and operators of the wind power turbines

This paper proposes an advanced structure of Super-conducting Magnetic Energy Storage using a PWM Current Source Inverter by adopting a robust method based on the fuzzy set theory for generate the modulation index and the shift angle, which allowed the active and reactive powers exchange control in the four quadrants. Two independent fuzzy controllers are assigned, one for the angular speed control and the other for the terminal voltage control.However, the fuzzy control methodology which has ever been reported has many problems, since structure and choosing of fuzzy rules, membership function and parameters in fuzzy controller are determined by trial and error depending on computer simulations and skilled person(s) intuition. In this paper, we introduce a learning control that is developed by synthesizing several basic ideas from fuzzy set and control theory, self-organizing control and conventional adaptive control. This provides the motivation for adaptive fuzzy control where the focus is on the automatic on-line synthesis and tuning of fuzzy controller parameters. Simulation results show that the proposed learning control is able to ensure the transient stability of power system under various fault conditions and significant disturbances.

Modeling of generalized unified power flow controller (GUPFC), based on the static consideration, and has been presented in this paper used for power flow control.A Newton-Raphson load flow program has been developed which includes comprehensive control facilities and yet exhibits very strong convergence characteristics. The injection model, which is used to locate GUPFC suitably in the power system, is incorporated into an existing Newton-Raphson load flow algorithm in polar coordinate. The modified Jacobian matrix and power mismatch equations are deduced based on the injection model of GUPFC to control active and reactive powers and voltage magnitude in any combination or to control none of them. Test results are presented on IEEE 30- bus system, which demonstrate the effectiveness of the proposed method.

One of the power quality concerns that have received most attention is the problem of harmonics which are generated by widely dispersed single phase nonlinear loads.Such loads cause harmonic distortion of voltages and currents in a power distribution system. In order to fully understand the problem of harmonic distortion, an effective means of identifying the harmonic patterns generated by different types of nonlinear loads is considered. This paper presents the application of fractal analysis for analyzing various harmonic current waveforms generated by typical nonlinear loads such as personal computer, fluorescent lights and uninterruptible power supply. The fractal technique provides both time and spectral information of the nonlinear load harmonic patterns. The analysis results shows that the various harmonic current waveforms can be easily identified from the characteristics of the fractal features. This investigation proves that the fractal technique is a useful tool for identifying harmonic current waveforms and forms a basis towards the development of the harmonic load recognition system.

We report measurements of the temperature at different times during the arcing period of an experimental model of a sand-filled, high-voltage, high breaking capacity fuse. The cylindrical fuse-holder, containing a single-strand of uniform silver fuse-element, is tested at 6 kV, 50 Hz, and 1.25 kA prospective current is passed through it to generate the fuse arc. An optical fiber is used to carry light from the fuse arc to a spectrograph which is used to isolate spectral lines of interest. The spectrum is recorded by an intensified photodiode array. By gating the image intensifier in front of the diode array a complete spectrum is recorded in several microseconds. By varying the timing of the gate pulse the arc spectrum can be obtained at any desired time during the arcing period. The arc temperature is determined from the relative intensities of Si II spectral lines. The arc temperature was found to be around 20,000 °K.

Stark broadening of the Si II doublet at 504.1 nm and 505.6 nm has been used to estimate the electron density in two model silica-sand-filled high-voltage, high breaking capacity fuses. For a 240 mm long fuse which successfully interrupted a test circuit set up to deliver a 4.5 kA prospective current, the electron density fell from ~ 2x10 cm-3 shortly after arc initiation to ~ 1x 1018 cm-3 just before current zero for a 112 mm long fuse and a prospective current of 1.25 kA the electron density was ≤=1x10 cm-3 for the duration of the arc.

This paper presents harmonic analysis of power quality disturbances in scale-frequency domain. A suitable scheme has been proposed for power signal analysis using orthonormal harmonic basis functions with compact support. These basis functions are band-pass in nature. One can choose filter center frequencies easily. It has been shown that the respective band-pass filter outputs are associated with harmonics of the distorted power signal under consideration.Hence, the present scheme may be useful for harmonic analysis of power quality disturbances. Moreover, this technique provides a precise scale-frequency analysis.

This paper will purpose a beat recognition algorithm using discrete wavelet coefficients and fuzzy hybrid neural network. Cardiac beats have been detected from differential of compressed wavelet coefficients by Linear Approximation Data Transfer (LADT) algorithm and adaptive thresholds. The variance and sum of the squared wavelet coefficients and the R-R ratio of successive beats have been applied to the self organizing subnetwork connected in cascade with a multi layer perceptron as final classifier.The c-means and Gustafson-Kessel algorithms have been applied for the self-organizing layer. Potential of the method was examined using MIT_BIH arrhythmia database. Results show high detection (99.43%) and high sensitivity (99.65%) on 59864 detected beats and 100% sensitivity and specificity on premature beat recognition.

A genetic based algorithm for deconvolution of Printed Circuit Board (PCB) thermal images is presented.The deconvolution of thermal images is modeled as an optimization problem, whose cost function is to be minimized based on mechanics of natural selection and genetics. The proposed algorithm can be configured with all available apriori information to speedup the solution computation. The paper presents the results for deconvolution using the proposed genetic algorithm and its utility in PCB infrared thermal testing.

Embedding of a digital watermark in an electronic document is proving to be a feasible solution for copyright protection and authentication purposes. In this paper, we present an innovative scheme of perceptually shaping watermark to the cover images. A watermark is generally embedded in the selected coefficients of the transformed image using a carefully chosen watermarking strength. Choice of a good watermarking strength, to perceptually shape the watermark according to the cover image is crucial to make a tradeoff between the two conflicting properties, namely: robustness and imperceptibility of the watermark. Traditionally, a constant watermarking strength obtained from spatial activity masking and heuristics has been used for all the selected coefficients during embedding. We consider this tradeoff as an optimization problem and have investigated an evolutionary optimization technique to find optimal/near-optimal perceptual shaping function for DCT based watermarking system. The new scheme provides an excellent tradeoff between the robustness and imperceptibility and is image adaptive. Improved resistance to attacks, especially against JPEG compression of quality 7% and Gaussian noise of variance 17000 has been observed.

This paper presents a new approach for power quality analysis using a phase corrected wavelet transform (PCWT). The local spectral information of the wavelet transform can, with slight modification, be used to perform local cross-spectral analysis with very good time resolution. The ‘phase correction’ absolutely references the phase of the wavelet transform to the zero time point, thus assuring that the amplitude peaks are regions of stationary phase. The excellent time-frequency resolution characteristic of the PCWT makes it an attractive candidate for analysis of power system disturbance signals. Several power quality problems are analyzed using PCWT and it clearly demonstrates the advantages of PCWT in detecting, localizing and classifying the power quality problems.

A digital domain design of cascaded ladder WDFs using simple design parameters is presented. This special class of filters uses first order sections that are cascaded to realize N-order lowpass or highpass filters with tunable 3-dB cut-off frequency. To obtain the design parameters, the correspondence between the adaptor coefficient and the digital domain transfer function is shown. The transfer function is then used to derive the equations for the tunable coefficients in terms of the required cut-off frequency and filter order. The resulting structures are highly modular requiring the same type of adaptor throughout the structure. In addition, the number of coefficients required is minimal and is equal to the order of the filter.

Based on the various components involved in the structure of fuzzy logic controllers, this study provides an indepth examination of the different features and disadvantages of commonly used defuzzification methods. Then based on this examination, and taking into account the compatible assignment of the logical connectives, inference rules as well as membership functions (MFs), a superior defuzzification technique is described and justified. It is shown that this technique integrates the defuzzification problem into the global structure of fuzzy controllers. It also helps the designer achieve his design objectives in a simple and systematic manner. Another defuzzification strategy, which falls within the general framework of this study, is also given and commented upon. It is shown that this strategy satisfies properties which should be possessed by a desired defuzzification method, and also shares important features with the former one. Further, a recent defuzzification-based methodology for the systematic data-driven design of fuzzy controllers is outlined.

This paper considers the problem of stabilizing a class of linear time-invariant large-scale systems composed of a number of subsystems using several local dynamic output feedback controllers. For this problem, a sufficient condition on each closed-loop individual subsystem is derived under which the decentralized controller composed of the local controllers designed for individual subsystems, achieves stability for the overall system. This condition is used to convert the decentralized stabilization problem to a set of the H∞ disturbance rejection subproblems.