JEE(IEB) Online
Journal of Electrical Engineering (JEE), Vol. EE 31, No. I & II, December 2004
The Institute of Engineers, Bangladesh (IEB)
(Print issue of December 30, 2004)
Updated : January 31, 2005
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Base Transit Time of a Bipolar Transistor with Gaussian Base Doping Profile
Touhidur Rahman, Md. Ziaur Rahman Khan and M. M. Shahidul Hassan
Abstract :
In this work, an analytical expression for base transit time tb of a modern high-speed npn bipolar transistor with gaussian base profile is obtained. The doping dependence of mobility, bandgap narrowing effect and carrier velocity saturation at the base edge of the collector-base junction are incorporated in finding tb. The collector current density, Jn, and minority carrier stored charge per unit area, QnB, are separately expressed as a function of the injected electron density n(0) in the base in order to find tb. The modeling of Jn, QnB and tb is essential for the design of high-speed bipolar transistor. The base transit time calculated analytically is compared with numerical results in order to demonstrate the validity of the assumptions made in deriving the expression. The closed form expressions for collector current density and base transit time offer a physical insight into device operation and are a useful tool in device design and optimization.
[PDF Full-Text, 183 KB]
Evaluating the Web Search Engines Quality: Point of User View
Mollah Muhammad Towhidul Hoque
Abstract :
This paper presents an evaluating method of the Web search engines quality. A large number of experts and organizations in the world are engaged in development and updating the methods for evaluating the quality of search engines. Unfortunately, there is no standardization for the methods of evaluating the quality of search engines, both nationally and internationally. The evaluation of the quality of Web search engines not only enables informed consumer choice but also assists and encourages search engine operators to improve their standard of service. Since many search engines claim to be using novel techniques, effectiveness comparisons between these engines and systems employing published methods are potentially of interest to the Information Retrieval research community. Experimental results demonstrate that the offered method is less expensive and is of less labour-consuming procedure, than all earlier known methods.
[PDF Full-Text, 238 KB]
Performance Parameters in GPRS Based Traffic with Data and Voice Integrated Transmission
Mohammad Rakibul Islam, Mohammad Ismat Kadir, Mohammed Nazrul Islam and Shaikh Mostafa Al Masum
Abstract :
General Packet Radio Service (GPRS) is a new bearer service for Global System for Mobile (GSM) that greatly improves and simplifies wireless access to Packet Data Networks (PDN). We have presented an analytical model to analyze the performance of different sharing strategies in the circuit switched voice and packet switched data networks. We have compared the blocking probability, throughput and average delay time for these strategies. In the fixed sharing strategy, these traffic parameters show better performance for lower traffic. However, for higher traffic the partial sharing strategy turns out to be the best solution. The Partial sharing scheme also shows better performance than the complete sharing scheme in case of higher traffic.
[PDF Full-Text, 167 KB]
Adaptive Fuzzy-Artificial Neural Network Based Speed Controller of DC Motor Drive
Mohammed Golam Sarwer, Md. Abdur Rafiq and B.C. Ghosh
Abstract :
This paper introduces a DC motor drive system with a fuzzy-artificial neural-network controller. First, a neural network-based architecture is described for fuzzy logic control. The characteristic rules and their membership functions of fuzzy systems are represented as the processing nodes in the neural network structure. Then, the fuzzy rules and input-output of the system are tuned by the supervised gradient descent learning algorithm. The performance of the proposed controller is evaluated under various operating conditions. The controller is shown to be robust, adaptive and capable of learning.
[PDF Full-Text, 256 KB]
AC Voltage Regulation by Switch Mode Buck-Boost Voltage Controller
P. K. Banerjee, M. A. Choudhury and Golam Toaha Rasul
Abstract :
Voltage sag is a serious power quality problem affecting domestic, industrial and commercial customers. Voltage sags may either be decrease or increase in the magnitude of system voltage due to faults or change in loads. In this paper a switch mode AC Buck- Boost regulator is proposed to maintain voltage across a medium size domestic appliance constant during long period of voltage deviation from the rated value. Such deviation may occur due to change in load or change in input voltage due to voltage sag of the system itself.
[PDF Full-Text, 417 KB]
The FMM-MoM Method for Solving Electromagnetic Scattering Problem
N. M. Alam Chowdhury, Mohammad Shahed Akond and Md. Shahid Ullah
Abstract :
In this paper, a new method is proposed for the numerical analysis of electromagnetic scattering problem, which compromises between Fast Multipole Method (FMM) and Method of Moments (MoM). This method saves memory usage as well as computational (CPU) time requirement by matrix sparsity as done in FMM. It also improves the accuracy level by using the concept of MoM in the non-zero elements of the sparse matrix. Thus, the number of operations in this method is also optimized between the operations of FMM and MoM. Proposed method is implemented on infinitely long perfectly conducting body. Numerical results are verified with the solution of same problem by using FMM and MoM. The minimum storage memory requirements and CPU time savings of the proposed method are also verified with the existing methods.
[PDF Full-Text, 235 KB]
Theory, Design and Simulation of a Distribution STATCOM for Mitigation of Voltage Sag and Elimination of Harmonic
Noor Izzri Abdul Wahab, Norman Mariun, Azah Mohamed and Mohibullah
Abstract :
This paper describes the theory, design and simulation of a 12-pulse Distribution STATCOM on an 11kV distribution system. The distribution STATCOM (D-STATCOM) is one of the custom power (CP) family which also includes dynamic voltage restorer (DVR), solid state fault current limiter (SSFCL), active filters and solid state transfer switch (SSTS). Custom power offers customer with no power interruptions, tight voltage regulation, low harmonic voltage and acceptance of fluctuating and non-linear loads without effect on the terminal voltage. The D-STATCOM, which consists of a thyristor-based voltage source inverter, uses advanced power electronics to provide voltage stabilization, flicker suppression, power factor correction, harmonic control and a host of other power quality solutions for both utility and industrial applications. In this paper however, the concern will be mitigating voltage sags on the 11kV distribution system and reduction of harmonics generated by the device. The D-STATCOM simulations are done by using the PSCAD/EMTDC version 3.0.7 electromagnetic transient program.
[PDF Full-Text, 661 KB]
Sliding Mode Speed Controller of a DC Motor Drive
Mohammed Golam Sarwer, Md. Abdur Rafiq and B.C. Ghosh
Abstract :
This paper presents a separately excited DC motor speed control scheme using sliding mode control technique. The mathematical model suitable for sliding mode control is derived. A straight-line switching surface is proposed, and a controller is designed to guarantee that the operation on sliding surface is reached and sustained. The simulation results and experimental results are presented. The performance of the proposed controller is evaluated under various operating conditions and compared with conventional PI controller.
[PDF Full-Text, 230 KB]
Comparative Study of Wiener-Hopf Solution and LMS Algorithm for Adaptive Noise Cancellation of Noisy Speech
Rishad Ahmed Shafik and AHM Razibul Islam
Abstract :
The performance of Wiener-Hopf and Least Mean Square (Online and Batch) methods are considered for recovering the desired signal buried under noise using adaptive noise cancellation techniques. A reference signal and a desired signal are available. To combat the noisy environment an adaptive noise cancellation filter is developed. This filter tries to converge in least mean square sense to the optimal Wiener-Hopf solution to filter the noise from the signal. In the analysis part the weight and learning tracks are shown. Effects of leakage and effects of interchanging the primary and reference inputs to the adaptive filter are also discussed. In the end a comparison is drawn on intelligibility of the recovered signal from both the methods.
[PDF Full-Text, 752 KB]
TCP Friendly Rate Control Protocol Performance with Many Flows
Mohammad Nazmul Ahsan and Md. Saifur Rahman
Abstract :
The TCP-Friendly Rate Control Protocol (TFRC), is a rate-based end-to-end congestion control protocol. TFRC uses a model for steady state Transmission Control Protocol (TCP) throughput to limit the sending rate and assure fair behaviour against competing flows. Instead of reacting to single congestion events (in the form of packet loss) like TCP, the TFRC protocol changes its sending rate in response to the loss rate, sampled over a certain amount of time. While TFRC achieves the same long-term throughput as a conformant TCP flow, its short-term sending rate is more stable. This makes the protocol suitable for traffic where sudden rate changes are undesirable (e.g. video or audio streams). In the last several years extensive research have been done on TCP-Friendly Protocols and it shows that TFRC is able to share a bottleneck or congested router’s bandwidth fairly with competing TCP flows. But all the research so far done uses a simulated test-bed or real life internet where number of flows are limited. In this paper we show the performance of TFRC with a large number of flows and found some discrepancies with previous research outcome. It is shown that TFRC is a scalable protocol though at very high loss rate, its fairness performance degrades.
[PDF Full-Text, 241 KB]
Close-loop Control System of a Three-phase Induction Motor using Fuzzy Approach
Md. Nurul Islam and M. Bashir Uddin
Abstract :
In this paper, it is proposed to control the speed of a three-phase induction motor by microcomputer with flux control. To estimate flux, the system needs to sample line current and speed and solve first order simultaneous differential equations. But complications arise with the numerical solution of differential equations. Also uniform and periodic sampling technique necessary to solve differential equation is almost complicated due to hardware limitation. Hence Fuzzy-mapping technique is proposed to make computation efficient in real time system. Triangular modulation of the inverter is used in control system. But the software to implement triangular modulation on the basis of comparison of carrier wave with modulating signal has many limitations. A new simplified analytical equation formulated based on certain approximations without loss of accuracy is used to determine the switching points of a three-phase inverter.
[PDF Full-Text, 489 KB]
MHD Retrofit
Scheme for Efficiency Enhancement of Thermal Power Plants : A Case Study
Mohibullah, Norman Mariun, Noor Izzri Abdul Wahab, Mohd. Liakot Ali
Abstract :
Around 68% of electrical energy is generated by thermal power plants in India. These power plants run at very poor efficiency of 15-30% depending upon the season of the year. The over all efficiency of each unit of Harduaganj thermal power plants near Aligarh India, is given for different years and found to be quite low around 18 % as an average. Efficiency of a proposed unit of Magneto Hydro Dynamics (MHD) channel of 20 MW (BHEL) is calculated and this channel is retrofitted as topper unit with Harduaganj thermal power plant which is used as trailer unit. The overall efficiency of this retrofit scheme is calculated and being reported in this paper. It is seen that the efficiency increases by more than 50% of its existing value. This can be further enhanced if larger size of MHD generator is used. This scheme enhances the efficiency, conserve coal and the pollution caused by thermal power plant is also reduced to a great extent. When the technology is matured ,it will conserve coal which is a limited amount and expected that world reserves will be 80 % over by the year 2250.
[PDF Full-Text, 195 KB]
For more information :
Editor
Journal of Electrical Engineering
The Institute of Engineers, Bangladesh
Headquarters : Ramna, Dhaka – 1000, Bangladesh
&
Professor
Dept. of Electrical & Electronic Engineering
Dhaka University of Engineering & Technology (DUET), Gazipur
Gazipur – 1700, Bangladesh.
Phone : +880-2-9264021 Ext. 302, Fax : +880-2-9261234
Email: [email protected]
Updated : January 31, 2005