Showing 7 results for Ramezani
A.vahedi, M.ramezani,
Volume 1, Issue 2 (April 2005)
Abstract
Dc excitation of the field winding in a synchronous machine can be provided by
permanent magnets. Permanent magnet synchronous machine (PMSM) can offer simpler
construction, lower weight and size for the same performance, with reduced losses and higher
efficiency. Thanks to the mentioned advantages these motors are widely used in different
application, therefore analysis and modeling of them, is very important. In this paper a new, fast
and simple method is presented to study performance of a PMSM connected to the converter.
For this purpose, average-value modeling and related analytical relations which leads to the
desired characteristics such as electromagnetic torque, dc current and dc voltage is presented
and applied to PMSM & converter system. The advantage of this model lie in reduction of
computation time compares to the other dynamic models while keeping accuracy quite
acceptable. This model is applicable for studying the steady-state performance of systems as
well as dynamic performance.
M. Aliramezani, Sh. Mohammad Nejad,
Volume 8, Issue 2 (June 2012)
Abstract
In this paper, a novel design of all-solid photonic bandgap fiber with ultra-low
confinement loss is proposed. The confinement loss is reduced remarkably by managing the
number of rods rings, up-doping level, pitch value, and rods diameters. Moreover, the
designed PCF shows ultra-flattened dispersion in L- and U-band. Furthermore, a new
design, based on introducing of an extra ring of air holes on the outside of the all-solid
bandgap structure, is then proposed and characterized. We demonstrate that it significantly
reduces the fiber diameter to achieve negligible confinement loss. The validation of the
proposed design is carried out by employing a two dimensional finite difference frequency
domain with perfectly matched layers.
M. R. Ramezani-Al, A. Vahidian Kamyad, N. Pariz,
Volume 11, Issue 2 (June 2015)
Abstract
Uncertain switched linear systems are known as an important class of control systems. Performance of these systems is affected by uncertainties and its stabilization is a main concern of recent studies. Existing work on stabilization of these systems only provides asymptotical stabilization via designing switching strategy and state-feedback controller. In this paper, a new switching strategy and a state-feedback control law are designed to exponentially stabilize Uncertain Discrete-Time Switched Linear Systems (UDSLS), considering a given infinite-horizon cost function. Our design procedure consists of three steps. First, we generalize the exponential stabilization theorem of nonlinear systems to UDSLS. Second, based on the Common Lyapunov Function technique, a new stabilizing switching strategy is presented. Third, a sufficient condition on the existence of state-feedback controller is provided in the form of Linear Matrix Inequality. Besides, convergence rate is obtained and the upper bound of the cost is calculated. Finally, effectiveness of the proposed method is verified via numerical example.
F. Amanifard, N. Ramezani,
Volume 12, Issue 3 (September 2016)
Abstract
The article presents the transients analysis of the substation grounding systems and transmission line tower footing resistances which can affect to the back-flashover (BF) or overvoltage across insulator chain in an HV power systems by using EMTP-RV software. The related transient modeling of the grounding systems is based on a transmission line (TL) model with considering the soil ionization. In addition, different configuration of grounding system have been simulated to calculated the BF, including number of vertical grounding rod, length of rod, point of lightning current injection into the grounding grid and using two depth design of grounding system where the surface of substation under consideration is very small orit is necessary to bury the grounding grid in the rocky media, occasionally. The simulation results have shown that how the mentioned parameters can considerably affect inception of BF, and suitable design of grounding system can reduce damages caused by lightning.
M. Esmaeilzadeh, I. Ahmadi, N. Ramezani,
Volume 14, Issue 2 (June 2018)
Abstract
Distributed generation (DG) has been widely used in distribution network to reduce the energy losses, improve voltage profile and system reliability, etc. The location and capacity of DG units can influence on probability of protection mal-operation in distribution networks. In this paper, a novel model for DG planning is proposed to find the optimum DG location and sizing in radial distribution networks. The main purpose of the suggested model is to minimize the total cost including DG investment and operation costs. The operation costs include the cost of energy loss, the cost of protection coordination and also the mal-operation cost. The proposed DG planning model is implemented in MATLAB programming environment integrated with DIgSILENT software. The simulation results conducted on the standard 38-bus radial distribution network confirm the necessity of incorporating the protection coordination limits in the DG planning problem. Additionally, a sensitivity analysis has been carried out to illustrate the significance of considering these limits.
Y. Fattahyan, N. Ramezani, I. Ahmadi,
Volume 18, Issue 3 (September 2022)
Abstract
Using doubly-fed induction generator (DFIG) based onshore wind farms in power systems may lead to mal-operation of the second zone (Z2) of distance protection due to the uncertain number of available wind turbines on the one hand and the function of DFIGs control system to maintain the bus voltage on the other hand. In such cases, variable injected current by the wind farm causes distance relay fall in trouble to distinguish whether the fault point is in the Z2 operating area or not. In the current study, an adaptive settings scheme is proposed to determine the Z2 setting value of distance relays for such cases. The proposed method is based on the adaptive approach and the settings group facility of the commercial relays. The proposed method applies the k-means clustering approach to decrease the number of setting values calculated by the adaptive approach to the number of applicable settings group in the distance relay and uses the Particle Swarm Optimization (PSO) algorithms to achieve the optimum setting values. The high accuracy of the proposed method in comparison with other methods, suggested in the literatures, is shown by applying them to the IEEE 14-bus grid.
Nabiollah Ramezani, Mohsen Shahnazdoost Kilvaei,
Volume 21, Issue 1 (March 2025)
Abstract
In this paper, a novel method is presented that can accurately estimate the Thevenin equivalent circuit parameters of an external power system by RTUs. The presented method is based on the simultaneous measurements of the desired points in the boundary system, which includes the bus voltage amplitude, the current amplitude of the boundary transmission lines, as well as active and reactive power, and is continuously active until the Thevenin equivalent circuit model would be available online. The practical application of the proposed method is related to online monitoring and control of wide-area power systems as well as their development design. Also, the innovation of the method is the accurate estimation of the Thevenin equivalent circuit model from part of the power network where information is not available. In the proposed method, an additional measurement and the least squares method are used to eliminate measurement errors in order to accurately estimate the parameters of the equivalent circuit model. In order to avoid providing the wrong equivalent circuit model due to external system changes, a method is presented that can track the correct system changes to continuously monitor the disturbances. The proposed method performance has been implemented and validated by DigSILENT software.
