فصلنامه فنی و مهندسی مدرس
پیاپی 38 (زمستان 1388)

The higher frequency transient signals generated as a result of a power system fault or disturbance provide the basis for an alternative approach to power system containing connectors and cables result in unsuitable operation of the system. However one major challenge is the need to ensure that the transients to be neutralized by electromagnetic compatibility (EMC) issues and cabling routes. This paper proposes novel method for optimal cable routings and connectors; a combinatorial design Algorithm, to choose the best path when two or more physical paths are available. The best path from EMC point of view can be chosen based upon various criteria such as monetary cost minimization, voltage drop and quality (electromagnetic compatibility) parameters. This paper initially provides a numerical 2D and 3D resolution of the problems of radiation generated by current sources. The approach is based on the finite element method (FEM) associated with absorbing boundary conditions. The presented model makes it possible to consider wave propagation and their effects in heterogeneous mediums in transient which can be applied in EMC for the simulation of radiation. First, the formulations of the electromagnetic problem are detailed. The simulation results are used for the cabling routes with respect to undesirable field distribution in the specified regions. Finally by the use of AHP optimal routes for cabling based upon the above mentioned criteria are chosen. The proposed method is successfully implemented on two different types of power systems, "high voltage substation and current injection system".

In trading electrical energy in deregulated power systems, violation of operation constraints such as transmission lines flow limits is possible. These conditions have been called “congestion”. One of the most important responsibility of Independent System Operator (ISO) is congestion management in a manner that all the system equipments be operated in their nominal ranges. In this paper, using topological generation distribution factor, participation of each generator in power flow in each line is calculated. Then, by means of decomposition of nodal price and mentioned factor, the effect of generation in each bus on the locational marginal price in all buses of the system are calculated. And the congestion price is calculated based on re-dispatch in constant demand. In this paper a new method is introduced to dedicate congestion price to each generator and by this method a fair congestion cost allocation is implemented. The method has been tested on IEEE 24-bus test system and the results have been demonstrated.

In this paper a macroeconomic approach is derived to develop a long run electricity demand model to analyze the main factors affecting electricity demand in the Islamic Republic of Iran. According to the definition of a demand function, electricity demand, in general, is determined by some main factors including gross domestic product (GDP), prices, etc. This paper, by analyzing the specific political and economical conditions in the Iran, introduces electricity intensity and a dummy variable WAR into the electricity demand forecasting model. A binary dummy variable, WAR is applied to correct the model (between the years 1980-1988 during the Iran and Iraq war). In this study, two popular econometric techniques namely unit root test and cointegration model is derived for modeling the electricity demand. Cointegration is established between kWh and, respectively, GDP, electricity price, electricity intensity, and WAR as a dummy variable. The results show that although GDP is still the most important factor for electricity demand, electricity demand is negatively related to efficiency improvement and tariffs in Iran.

In this paper, optimum location of power system stabilizers in order to damp inter-area oscillations has been investigated by using modal series method. Nonlinear effects grow in dynamical behaviors of heavily loaded stressed power systems significantly. Hence linear based methods and techniques no longer present clear and exact response of the systems. In this article by defining new nonlinear participation factors and a nonlinear interaction index in modal series frame, location of PSS is determined and its effectiveness has been analyzed. For two various operating conditions, low and high stress cases proper site of the controller is determined by using both the conventional methods such as mode shapes, participation factors and residues in one side and the proposed nonlinear participation factors in modal series frame in other side. The obtained results are compared with each other and with nonlinear time domain simulations. Studies carried out on IEEE 50-generator test case system and selected machines to locate PSS by modal series method are validated by time domain simulations. Also nonlinear interaction index shows increasing of nonlinear interaction between fundamental modes of the system when PSS placement has been selected properly and its design has been done well. This shows a high influence of PSS on damping inter-area oscillations and improving system oscillatory stability. Nonlinear time domain simulation shows that improper selection of PSS location may result in poor performance of system and deterioration of oscillatory response of the system. =

In this paper, in order to detect the number of transmitting antenna in MIMO communication systems, it is proposed that the techniques such as AIC & MDL, which have been primarily designed so as to detect the number of Gaussian sources, are applied. Then a hypothesis testing based method for recognizing the type of modulation in MIMO communication systems with block orthogonal codes is suggested; in which in order to reduce the complexity of the traditional methods, simpler likelihood functions for testing hypotheses are applied. Furthermore, because in all modulation scheme detection methods, a proper estimation of channel gain (channel matrix) is required; in this paper, a new and efficient method based on SAGE iterative algorithm for estimation of channel matrix in MIMO communication system with space-time block codes is proposed. At the end of this paper, the performance and effectiveness of all proposed modules are separately and jointly analyzed by numerical simulations.

This paper presents a fuzzy search controller approach along with the look-up tables, to optimize the efficiency of a pump-induction motor drive. The induction motor and the converter are modeled based on thermal loss; and for modeling the pump and the hydraulic system, which are non-linear and relatively complicated, the neural network is used. In the designed system, in order to optimize the efficiency of the pump and the hydraulic system, the amount of outflow is controlled by adjusting the pump’s rotating speed. Meanwhile by choosing the suitable switching frequency of the inverter and feeding the motor by proper amount of voltage and frequency, the loss amount of the drive system is minimized. Simulation results show that the proposed controller improving the efficiency of the drive system under flow-changing conditions, as well as it has improved the problems that existed in some of the classical efficiency optimization approaches, such as the slowness of the converging, and the oscillation around the optimal point.

This paper deals with the electromagnetic scattering of plane wave by a randomly rough surface. Scattering mechanism is extracted in backscattered alignment or mono-static radar, made up of a non periodic mesh array of finite number of rectangular sloped surfaces. By the Kirchhoff approximation, the total scattering components are calculated for several different numbers of slopes, relative dielectric constants, correlation length, and height deviation of surface and incident angle. Then eigenvector target decomposition method (EV-TDT) is applied for calculating covariance matrix eigenvectors and then estimate of entropy and scattering mechanism and then target classification. As results, for SAR data sets which supported from European space agency (ESA) data provider, polarimetric signatures of randomly rough dielectric surface such as entropy and scattering mechanism, extracted and their results are compared to theoretical results.

Transmission expansion planning (TEP) is one of the most important parts in power systems. Restructuring of power system has changed the traditional planning objectives and introduced new challenges in the field of TEP. In this new environment, the comprehensive and precise design based on electricity market criteria in planning horizon is indispensable. In this paper a new algorithm is proposed for dynamic transmission expansion planning in deregulated environment. In this method, investment cost and operation cost are considered as market based economic criteria, and average load curtailment cost in contingencies is considered as a reliability criterion from market player's viewpoint. Congestion cost is also used as a competition index between market participants. The combination of Genetic Algorithm (GA) and fuzzy satisfying method is used for solving TEP problem. At last the proposed method has been tested on 8-bus network and IEEE 30-bus network.

In this paper, the effective parameters in access time of a low earth orbit (LEO) satellite, in a ground user, are studied and outcome of each one is estimated on it. Then the total access time of a single LEO satellite has been maximized. For this purpose, the inclination angle of orbit, to the equator, has been optimized in various satellite altitudes and ground station’s latitudes. The obtained results, once considered along with the power supply issue, give a comprehensive vision for LEO satellite orbit design. Then the satellite access to the sun, as the energy source, has also been evaluated. Simulations have been done by the satellite tool kit (STK) software.

Increasing real time services in multimedia environments has initiated a new phenomenon in data communication. This paper analyzes delay in multimedia environments focusing on multi-point to point communication [1]. We separate the playtime delay in a point-to-point transmission and propose an optimization scenario for each part. It is proved that sum of the normalized path delay for point-to-point connections is invariant and based on this property, the playtime for delay-sensitive media has been minimized. We have shown that in transmission media, priority queuing is an effective solution where in the receiver side, waiting time for playtime scheduling and queuing discipline are two main factors. It is shown that there is a compromise between packet loss and packet departure time in the receiver side where the acceptable packet loss can adjust the playtime delay adaptively. Theoretical analysis for priority assignment, queuing technique and performance evaluation in different classes of queuing with different playtime scheduling are given.