Electrical Engineering Department

Nowadays power quality is one of the crucial issues in power systems. Among power quality issues, harmonics caused by nonlinear loads are of great importance as causing great problems in power systems such as malfunction of electrical devices, efficiency reduction as well as reduction of effective lifetime of electrical devices. Electric railways utilizing thyristor rectifiers in order to control speed consume enormous lead current and inject huge harmonic to the grid. In order to eliminate harmonic and compensate reactive power in electric railways, it is proper to use hybrid filters. Hybrid filters are a combination of active and passive filters. Regarding the way active and passive filters are connected in hybrid filters, they have different structures. In this paper, harmonic model of electric railway as well as some of the hybrid filters configurations are evaluated and their performance in electric railways are simulated in MATLAB/SIMULINK. Finally, performances of different configurations are compared to demonstrate their advantages and disadvantages in reducing current total harmonic distortion (THD).

In DC-electrified railway systems, rails are used to navigate trains as well as providing the returning path of train's electric current to the traction power substation (TPS). Due to electrical resistance of rails and the conductivity between rail and ground, a part of train returning current to the TPS permeate in the ground which causes different problems like increasing of rails potential that increase of rails potential leads to death hazards for the train station personnel and stray current increment causes metal's corrosion and decrease of their lifetime. Therefore, surveying electric railway system in order to know the unfavorable effects of rails potential and stray currents is an essential matter. In this paper, effect of control methods on stray current and rail potential amount and analysis of this current with Finite Element Method (FEM) is presented.

In electric railways, thyristor rectifiers are used in order to control the speed. As a consequence in addition to substantial input lead current, an enormous amount of harmonics is injected into the grid. To avoid such harmonics as well as reactive power compensation, reactive power hybrid filters consisting of active and passive filters are utilized. Hybrid filters have several different structures. Since electric railway has a non-linear and variable nature, a novel hybrid filter structure is designed that compensates reactive power and eliminates harmonics to attain desired harmonic level regarding the conventional allowable harmonics level standards. The designed filter model is simulated in MATLAB/SIMULINK and then applied to a harmonic model of an electric railway.

Thyristor rectifiers are widely used in electric railways in order to control the speed. As a consequence of their usage in addition to substantial input lead current, an enormous amount of harmonics is injected into the grid. To avoid such harmonics as well as reactive power compensation, reactive power hybrid filters consisting of active and passive filters are utilized. Regarding different passive and active filters connection in a hybrid filter, various configurations of hybrid filters are possible. Each of these configurations has different functionality in harmonic elimination and reactive power compensation. Since electric railway has a non-linear and variable nature, a novel hybrid filter structure is designed that compensates reactive power and eliminates harmonics to attain desired harmonic level regarding the conventional allowable harmonics level standards. The designed filter model is simulated in MATLAB/SIMULINK and then applied to a harmonic model of an electric railway. Since electric railways are single phase loads, specific three-phase to two-phase transformers are required to feed the load. To attain such purpose, an adaptive transformer is utilized in this paper. The proposed model has properly overcome the deficiencies of active and passive filters as well as demonstrating an appropriate performance in the reduction of total harmonic distortion (THD).

In urban electric railway transit systems, rails are used to navigate trains, as well as to provide the returning path of the train's electric current to the traction power substation (TPS). Due to electrical resistance of rails and the rail-to-ground conductivity, a part of the train's returning current to the TPS flows into the ground, which is called stray current, which causes different problems such as an increase of rail potential. In this regard, a model of an electric train with a TPS, running rail, and third rail is simulated in MATLAB/Simulink. In the simulated model, the amounts of stray currents in different soil types, with and without collection mats, are compared. Afterward, to calculate the amount of stray current in the presence of the stray current control method considering different soil types through finite-element (FE) method (FEM), a UIC54 rail with insulated fastening equipment is modeled in FEMM 4.2 and analyzed with 2-D FEM. Finally, a comparison of efficiency of stray current collection mats in different soil models for both simulation in MATLAB/Simulink and FEM is also presented. The obtained results verify the accuracy of the simulated and modeled system in real conditions of electric railways.

This paper presents a probabilistic optimal power flow (POPF) algorithm considering different uncertainties in a smart grid. Different uncertainties such as variation of nodal load, change in system configuration, measuring errors, forecasting errors, and etc. can be considered in the proposed algorithm. By increasing the penetration of the renewable energies in power systems, it is more essential to consider the stochastic nature of wind power generation units. In this study, probability density function (PDF) of wind speed has been considered as Weibull. The proposed algorithm is based on point estimation method. In order to show the effectiveness of the proposed algorithm it has been applied to IEEE 14-bus test case power system. Simulation results show the effectiveness and precision of the proposed algorithm.

Imbalance between generation and consumption in each instant can result in frequency
instability. A storage device that responds quickly to changes and is capable
of energy injection or consumption in a microgrid (MG) can improve frequency stability.
The Flywheel Energy Storage System (FESS) has this characteristic. In this
paper, a detailed model of the FESS is presented, and its control strategies for frequency
regulation are proposed and discussed. The field oriented control is used
for machine‐side convertor control of FESS. Two MG islanding scenarios and the
performance of the proposed control strategy are studied by MATLAB/Simulink.
The simulation results show good FESS performance with regard to frequency
changes in the MG.