Sharif Digital Repository

The effects of laser field and laser pulse width on the dissociation probability of C-H bond of CH4 have been investigated. Calculation of time dependent Schrödinger equation by grid spectral method is carried out and it is produced optimistic results in comparison to the earlier Quasi-classical calculations. The results show that there is an excellent match with experimental data. In this work, a number of results in the emerging field of laser with intensity of I = 8 × 1013 W cm-2 and pulse duration of 100 fs are presented. The present modulated field leads to more than 20% improvement in the dissociation probability  

This paper presents an effective hybrid optimal modulation technique for a cascaded H-bridge (CHB) multilevel inverter. The introduced method is generalized optimal pulsewidth modulation, which can be extended to any m-level CHB multilevel inverter operating at any switching frequency. The presented hybrid optimal modulation strategy includes the pattern exchange and optimal modulation techniques. In the optimal modulation technique, the hybrid interior-point algorithm, which is more flexible and efficient than conventional optimization techniques, is applied. The proposed hybrid optimal modulation strategy yields balanced units' output fundamental voltages, and low total harmonic distortion... 

LLC-LC resonant converter is a suitable circuit topology to design switched-mode power supplies for wide-output-voltage and wide-output-load applications. In this paper, a design procedure is introduced to optimize this converter. Unlike soft switching techniques for pulse width modulated converters, which usually apply an active auxiliary circuit to reduce switching losses and EMI, in the proposed converter, not only such circuits are not used, but also all of the parasitic elements are merged to the converters main components. Zero-voltage switching (ZVS) operation is realized for all power devices under all operating conditions. Thus, this converter is a suitable choice for... 

Harmonic pollution minimisation in voltage-source programmed pulse-width modulation (PPWM) inverters is defined as a time-limited optimisation problem in real-time applications with variable DC sources. In order to obtain minimum total harmonic distortion (THD) as the objective function, shuffled-frog-leaping algorithm (SFLA) is modified and employed to calculate the switching angles and compared with non-linear programming as a traditional optimisation method. In addition, particle swarm optimisation and three of its modified versions as popular evolutionary optimisation algorithms are employed to ensure the capability of the proposed optimisation method. Moreover, modified sinusoidal PWM... 

In this paper, a novel reduced switch cascaded transformer multilevel inverter is proposed. In this structure, a new structure is replaced with conventional H-bridge inverter. It consists of four high frequency switches, two line frequency switches, and two transformers which can be assembled in one core with a specific winding connection. This topology can produce 5 or 7 voltage levels depending on transformers turns ratio. The simplicity and modularity are its advantages compared to the existing structures. Beside these advantages, due to its similarity with H-Bridge converter, it is possible to use a modified technique based on conventional phase shift pulse width modulation to generate... 

In this paper a novel soft switching three-phase pulse width modulation (PWM) rectifier is proposed. Various switching state sequences of a three-phase three-switch buck-type unity power factor rectifier are reviewed and the operation modes of the converter are explained and analyzed. The converter operates under zero current switching (ZCS) condition. 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 to be turned off; so, switching losses in the converter are reduced. The auxiliary circuit consists of two auxiliary switches and a resonant inductance-capacitance circuit connected to the auxiliary... 

This paper is dealing with single phase PWM rectifier parameter optimization. A control loop has been designed to attain a suitable output DC voltage with minimum ripple, input current with minimum harmonic and maximum input power factor. In this paper these parameters have been optimized by using Genetic algorithm. To verify the effectiveness of proposed optimization, different simulations have been done. The simulation results prove that the proposed system working good  

This paper introduces a high efficiency AC voltage regulator based on an AC/AC buck converter cascaded by a transformer in series with the input voltage. The AC/AC converter uses an overlap time in the gate signals to solve the commutation problem. Non-use of any snubber circuits and current sensors leads to lower cost, smaller size and simpler hardware. The converter generates only the compensation term which results in smaller switches and, thus, lower cost. Simulation and experimental results verify the performance of the proposed topology  

In this paper, optimal control strategy is applied to parallel three-phase inverters using SVPWM technique. The three-phase system is transformed to a synchronous-stationary frame, suitable cost functions are defined, and the switching schemes are determined for the inverters. The control strategy minimizes the circulating current between the inverters, therefore, proper load sharing scheme is achieved. Simulations are performed for steady state and load change operation, and the results which show the suitability of the controller are provided. ©2009 IEEE  

Random pulse width modulation (RPWM) technique has been employed to generate the control signals of Vienna-type rectifier. This technique is compared to two conventional techniques (Hysteresis-band and ramp comparison with fix frequency carrier signal). Simulation results are illustrated for three approaches. The results verify significantly reduction of high frequency harmonics magnitude; and consequently overcome electromagnetic interference (EMI) problem in this active type of rectifier. ©2009 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 (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