Sharif Digital Repository

New advances in technology of mobile computers along with advent of wireless and mobile networking bring new capabilities, applications and concerns to the computer world. In this paper, we discussed on file sharing requirements in a mobile environment. Then, we proposed an architecture that supports mobility of hardware, data and software over the environment. Finally a sample implementation of the suggested architecture is presented. © 2005 by Knowledge Systems Institute Graduate School  

In this paper a novel T type scheme for 1-phase direct ac/ac converters is proposed. In this topology, frequency changing takes place directly (without common DC voltage bus) through three converters that are connected in a T structure. Unity power factor and precise output voltage regulation is achieved through appropriate control of these three converters. H-bridge converters are implemented, as the basic unit, in each branches of T to make the proposed converter. The converter is controlled such that the average active power of each H-bridges remains zero. So capacitors are implemented in DC links of H-bridges. In comparison to conventional back-to-back converters, life time of each... 

The number of humidity outputs on the cap of a cylindrical capacitance sensor is optimized by designing three different probes with direct and indirect windows. The time interval is measured within which 30- 70 % humidity can influence the dielectric constant and conductivity of the capacitance when exposed to a range of relative humidity. It is then compared with a simple set-up including a simplified equivalent circuit. The direct probes had four and double outputs on the window of the cylindrical capacitive sensor while the indirect probe had a thin plastic layer only. We observed that the dielectric constant and its conductivity depend closely to the humidity outgoing pathway and also to... 

New advances in mobile-computer technology, together with the advent of wireless networking, introduce new requirements, capabilities and concerns to the computer science and industry. In this paper, we discuss the special requirements of file sharing in mobile environments. Then our proposed architecture for mobile file sharing (MobFish) is presented. Finally, we present an implementation of the proposed architecture based on its special design tactics. © 2006 by Knowledge Systems Institute Graduate School. All rights reserved  

In this paper, the Line-Modulated Fixed Off-Time method is used as the current control strategy for a Power Factor Corrector (PFC) pre-regulator. A zero voltage switching PWM (ZVS-PWM) auxiliary circuit is configured to perform ZVS in the switches. Soft commutation of the main switch is achieved without additional current stress. A significant reduction in the total conduction loss is achieved, since the circulating current for the soft switching flows only through the auxiliary circuit and a minimum number of switching devices are involved in the circulating current path .The proposed rectifier uses a single converter instead of the conventional configuration composed of a four-diode... 

Recent developments in improving lighting efficiency and cost reduction of LED's have caused them to be a suitable alternative for the current lighting systems. In this paper a novel off-line structure is proposed to drive LED's. The proposed circuit has a high power factor and high efficiency and a long lifetime. To increase the life time of the converter, the proposed circuit doesn't use any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode (TM) Flyback converter in order to have power factor correction (PFC). A Buck converter is added to the third winding of the Flyback transformer in order to create two paths for the electrical power. DC power... 

In this study, a novel T-type topology for single-phase direct AC/AC conversion is proposed. In this topology, frequency changing takes place directly (without common DC voltage bus) through three converters that are connected in a T structure. Unity input power factor and precise output voltage and frequency regulation is achieved through appropriate control of these three converters. H-bridge converters can be used in each branch of T to make the proposed converter. The converter is controlled such that the average active power of each H-bridge remains zero. Therefore, capacitors are implemented in DC links of H-bridges. Moreover, using half-bridge converters, instead of H-bridge ones, for... 

In this paper, a fast and practical method is proposed for open-circuit (OC) fault diagnosis (FD) in a three-phase quasi-Z-source inverter (q-ZSI). Compared to the existing fast OC FD techniques in three-phase voltage-source inverters (VSIs), this method is more cost-effective since no ultra-fast processor or high-speed measurement is required. Additionally, the method is independent of the load condition. The proposed method is only applicable to Z-source family inverters and is based on observing the effect of shoot-through (SH) intervals on the system variables during switching periods. The proposed algorithm includes two consecutive stages: OC detection and fault location identification.... 

In this paper, a fast and practical method is proposed for open-circuit (OC) fault diagnosis (FD) in a three-phase quasi-Z-source inverter (q-ZSI). Compared with the existing fast OC FD techniques in three-phase voltage source inverters, this method is more cost-effective since no ultrafast processor or high-speed measurement is required. Additionally, the method is independent of the load condition. The proposed method is only applicable to Z-source family inverters and is based on observing the effect of shoot-through intervals on the system variables during switching periods. The proposed algorithm includes two consecutive stages: OC detection and fault location identification. When both... 

Serious and challengeable role in markets of low power supplies for cellular phones and other small portable devices is expected for single fuel cell in future. Single fuel cell voltage level is extremely low in comparison with its output current. According to the extremely low level of the voltage, a suitable dc/dc boost converter must be used for increasing the voltage. In this paper, a model for a single fuel cell is presented and the effect of external load variation and changing of reactant pressure on cell performance is investigated. Moreover, a predictive voltage controller for boost convertor of PEM fuel cell is presented, simulated and validated using MATLAB/Simulink. The results... 

In this paper a single stage structure is proposed for realizing a three-phase unity power factor rectifier. This topology utilizes a forward/flyback transformer to allow the high-frequency isolation. The principle of the operation and the applied control concept is discussed. Space vector modulation is used in order to achieve unity power factor and to have the output voltage be regulated. Furthermore, the system transient is analyzed during turn-on and a novel method is applied to the control system in order to limit inrush current during startup. The proper operation of the soft-start method is confirmed by numerical simulation of a 6KW, 380V/48Vdc. The stability of the closed-loop as... 

In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through (SH) states in a quasi-Z-source inverter (q-ZSI), increase the amplitude of high order harmonics of CMV. In this paper, by using the modulation technique based on odd PWM (OPWM) and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. IEEE  

In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through states in a quasi-Z-source inverter (q-ZSI) increase the amplitude of high-order harmonics of CMV. In this paper, by using the modulation technique based on odd pulse width modulation and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. ©... 

Molecular dynamics simulations were employed to both estimate the solubility of nonelectrolyte solids, such as acetanilide, acetaminophen, phenacetin, methylparaben, and lidocaine, in supercritical carbon dioxide and understand the underlying molecular-level driving forces. The solubility calculations involve the estimation of the solute's limiting activity coefficient, which may be computed using conventional staged free-energy calculations. For the case of lidocaine, wherein the infinite dilution approximation is not appropriate, we demonstrate how the activity coefficient at finite concentrations may be estimated without additional effort using the dilute solution approximation and how... 

In this paper a novel soft switching isolated buck rectifier is proposed. Various switching state sequences of a three-phase three-switch buck-type unity power factor rectifier are reviewed and the value of switching power loss in each state transition is investigated. The switching power loss of the converter is decreased by using zero current switching (ZCS) method. The operation modes of the converter are explained and analyzed. By using an auxiliary circuit with a simple method of energy recovery, the current is diverted away from the main power switches before they are turned off; so, switching losses in the converter are reduced. In this topology, the power transformer has only the... 

In this letter, the problem of source localization using time difference of arrival (TDOA) is investigated. Then, a closedform two-stage solution is proposed based on estimation of the range nuisance parameter in the first stage and refinement of initial solution in the next stage. The proposed solution is shown analytically and verified by simulations to be an efficient estimate, which can attain the CRLB performance under mild Gaussian noise assumption. This method is able to locate the source with the minimum number of sensors required for N-dimensional localization. Numerical simulations demonstrate significant performance improvement of the proposed method compared with the... 

In this study, an algebraic closed-form method for jointly locating the target and refining the antenna positions in multiple-input-multiple-output radar systems is proposed. First, a set of linear equations is formed by non-linear transformation and nuisance parameters elimination, and then, an estimate of the target position is obtained by employing a weighted least-squares estimator. To jointly refine the target and antenna positions, the associated error terms are estimated in the sequence. The proposed method is shown analytically and confirmed by simulations to attain the Cramér-Rao lower bound performance under small-error conditions. Numerical simulations are given to support the... 

In this paper, a novel solution for the problem of joint moving target and antenna localization in the distributed multiple-input multiple-output (MIMO) radar systems is proposed. The localization problem in the presence of antenna location uncertainty is formulated as a maximum likelihood (ML) estimation problem, which is then recast into convex form by defining some auxiliary variables and applying semidefinite relation (SDR) technique. Next, an algebraic closed-form estimator is proposed to jointly estimate the target and the antennas error terms and refine their uncertain values. The proposed method is shown analytically and verified by the numerical simulations to be an efficient... 

The leakage current originated from the fluctuations of the common-mode voltage (CMV) is an issue in a transformerless grid-connected photovoltaic (PV) system. In this paper, a modified space vector modulation based on the Fourier transform analysis is proposed to reduce the leakage current in a three-phase quasi-Z-source inverter (qZSI). The CMV harmonic content in a qZSI contains low and high-frequency harmonics which cause safety and EMI problems respectively. By implementing the proposed modulation in a three-phase qZSI, the low-frequency harmonics of the CMV are mainly reduced. The distribution of the high-frequency harmonics is also modified in a way they can be simply filtered....