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... 

Due to several advantages, three-phase Dual Active Bridge (DAB) converter is widely used in numerous applications nowadays. On the other hand, this converter is very vulnerable to Transistor Open-Circuit Fault (TOCF). Therefore, a fault-tolerant (FT) scheme has been proposed in this paper to solve the problem. First, normal and faulty conditions are investigated, and according to the results, a fault-diagnosis (FD) approach is introduced. Using the outcomes of FD unit, a new post-fault strategy is proposed for the converter. The FD method is based on the DC component of transformer phase currents, and the basis of FT technique is shedding the faulty phase. Some benefits of the proposed... 

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  

Multilevel converters are mainly used in high power applications (usually more than a few hundred kW). It is therefore important that they can continue working under faulty condition. In this paper, a new method is proposed to improve performance of CHB inverter under faulty condition. The proposed method will be compared with existing methods in term of voltage availability. The converter is simulated in Simulink and the results are provided. These results confirm the effectiveness of the proposed scheme, and are in accordance with the theoretical results  

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 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... 

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, the short-circuit fault in three-phase quasi-Z-source inverter (q-ZSI) is analyzed and a linear model is proposed for the short-circuit analysis. The proposed model is based on the state space equations of the system. By using this model, the most critical situation during short-circuit fault is recognized; the maximum reaction time for the protection system could be estimated and elements that are prone to failure are identified as well. The analysis is categorized into two groups, leg fault and switch fault. The linear model is confirmed by simulation of 1kw three-phase q-ZSI. © 2017 IEEE