MODARES TECHNICAL AND ENGINEERING
Year:2009 | Volume:- | Issue:34 (SPECIAL ISSUE ON ELECTRICAL ENGINEERING)|Papers Count:10

We present a detailed analysis of the static tuning characteristics of three section tunable distributed Bragg reflector (DBR) laser. The analysis is based on the transfer matrix method (TMM), transmission line and scattering theory. The key feature of the analysis is the use of modified oscillation condition. With the exact oscillation condition, the static tuning characteristics such as threshold current, output power, oscillating wavelength are obtained and the effects of a discontinuity at the active-passive interface and also the manufacturing imperfections on the device characteristics are investigated.

Speech emotion can add more information to speech in comparison to available textual information. However, it will also lead to some problems in speech recognition process.In a previous study, we depicted the substantial changes of speech parameters caused by speech emotion. Therefore, in order to improve emotional speech recognition rate, in a first step, the effects of emotion on speech parameters should be evaluated and in the next steps, emotional speech recognition accuracy be improved through application of suitable parameters. The changes in speech parameters, i.e. formant frequencies and pitch frequency, due to anger and grief were evaluated for Farsi language in our former research. In this research, using those results, we try to improve emotional speech recognition accuracy using baseline models. We show that adding parameters such as formant and pitch frequencies to the speech feature vector can improve recognition accuracy. The amount of improvement depends on parameter type, number of mixture components and the emotional condition.Proper identification of emotional condition can also help in improving speech recognition accuracy. To recognize emotional condition of speech, formant and pitch frequencies were used successfully in two different approaches, namley decision tree and GMM.

In SCPC-DAMA satellite networks, the baseband RRC pulse shaping is utilized to reduce the bandwidth and Inter Symbol Interference (ISI). But the variation in carrier's envelope, which expands the spectrum and ultimately increases the bandwidth, causes ISI and Quadrature Channel Crosstalk CQCc). The goal of this paper is to introduce a method to shape baseband RRC pulses, in order to make a nearly constant carrier envelope. We have introduced and implemented an algorithm to limit the amplitude variation of each pulse to generate constant amplitude RRC pulses at the input of modulator. Matlab simulation and hardware experiments show that OQPSK modulation and this pulse shaping method, can improve BER about 2dB.

Induction heating is widely used in metal industry for melting or heating thin slabs in a continuous casting plant. The wide application is based on good efficiency, high production rate and non-polluting conditions. For designing a parallel resonant induction heating system, calculating the capacitance for the resonant circuit is important, because its value affects resonance frequency, output power, power quality factor, heating efficiency and power factor.In this paper, phase controlled rectifier and H-bridge inverter are modeled. Then a method of finding an optimal value for the capacitance under voltage constraint is presented. This value is selected for maximizing output power of an induction heater, while minimizing the power loss of capacitor at the same time. For this purpose, the role of equivalent series resistance in the choice of capacitance value is significantly recognized. In this regard, the heating coil and the load of induction heating are modeled at first, and then the optimal value of capacitance is selected. Finally a complete model of heater and its power is simulated and effectiveness of the proposed method is verified.

Deregulation policy has caused some changes in the concepts of power systems reliability assessment and enhancement. In this paper, generation reliability is considered, and a method for its assessment using intelligent systems is proposed. Also, because of power market and generators' forced outages stochastic behavior, Monte Carlo simulation is used for reliability evaluation. Generation reliability, merely focuses on interaction between generation complex and load. Therefore, in this research, based on market type and its concentration, reserve margin, and various future times, a Neuro-Fuzzy system is proposed for evaluation of generation reliability which is valid and usable for all kinds of power pool markets. Finally, the proposed method is assessed on IEEE-Reliability Test System; and generation reliability indices of various markets are evaluated with different reserve margins and different load levels.

In this paper, power system restoration in the presence of SVC and TCSC in partial outage conditions is considered and a new method for maximum load restoration using different control variables is presented. Control variables are tap of transformers, generation rescheduling and operating points of FACTS devices. Objective function is restored load (to be maximized) and constraints are voltage magnitudes in buses, carrying load in lines and power generation limits in generators. Also SPA limits in voltage angles in both sides of circuit breakers before closing are considered. With respect to the number of control variables, optimization is done using Genetic Algorithm with IEEE-118bus network as the test system.

Electric arc furnaces (EAFs) are unbalanced, nonlinear and time varying loads, which can cause many problems in the power system quality. In steel industries, the two arc furnaces often perform in parallel and stand on a single bus, which surely deteriorate the power quality. In this paper, in order to study and analyze the harmful effects of parallel operation of EAFs, first, a three phase arc furnace model, which can simulate all the operational conditions of EAFs are simulated based on Hyperbolic- Exponential Model. In this process, in order to perform exact analysis of EAFs, effects of arc furnace transformer and the mutual inductance of the flexible cables are also considered. In the next step, in order to improve the power quality indices, the TSC and TCR/FC compensators are designed optimally and then simulated. Finally, the simulation results that are accomplished by PSCAD/EMTDC software show the validity of the proposed method in the entire power systems.

Thyristor-Controlled Series Compensator (TCSC) is one of the electric power lines sense compensators. TCSC increases transmission system capacity and improves system dynamic and voltage stability. Several controllers have been proposed, but most of them generally improve one of TCSC capabilities. In this paper a TCSC robust controller is designed based on Nonlinear Quantitative Feedback Theory (QFT). This controller improves both of small signal and transient stability of power system.

It is shown in [1] that the optimal downlink radio resource allocation for non-realtime traffic in cellular CDMNTDMA networks can be mapped to a Multi-dimensional Multiple-choice Knapsack Problem (MMKP) which is NP-hard. In this correspondence we propose a heuristic algorithm with polynomial time complexity for this problem. Numerical results indicate significant computational performance improvement in comparison to existing heuristic algorithms for MMKP.