JOURNAL OF FACULTY OF ENGINEERING (UNIVERSITY OF TABRIZ)
Year:2005 | Volume:32 | Issue:3 (40) ELECTRONICS|Papers Count:8

In this paper a method for analyzing the role of the intruder and automatic exploration of possible attack scenarios in cryptographic protocols is presented. In the presented method, the intruder’s capability for eavesdropping the protocol messages and using them to masquerade the protocol principals by means of a set of inference capabilities is modeled. Furthermore, the existence of a proper attack strategy as a general capability of an intelligent intruder for designing the attack scenario is considered in the model. The intruder strategy is based on finding proper instances of the protocol execution as a source of obtaining necessary attack information. Two important properties of the cryptographic protocols (i.e. secrecy and authentication) can be analyzed using the presented method. To show the strength of the presented method, formal specification of the Woo-Lam authentication protocol and the way of finding an attack scenario against it is described as a sample.

This paper presents the design of a novel method for improvement of the operation of distance relays during capacitive voltage transformer transients using artificial neural network. The proposed module uses voltage and current signals to learn the hidden relationship existing in the input patterns. Simulation studies are preformed and the influence of changing system parameters, such as fault resistance and source impedance is studied. Details of the design procedure and the results of performance studies with the proposed relay are given in the paper. Performance studies show that the neural networks improve the operation of distance relays during capacitive voltage transformer transients and reduce the effects of system variables such as fault resistance, source impedance and decaying DC offset on the decision made by the distance relay.

An induction motor driving controller, with the aim of the reduction of energy consumption and minimum input power, has been developed. The shaft torque is calculated using the rotor flux and torque current component and then it is applied into the control system. For the purpose of energy saving, the magnetizing current is so determined that the required torque is produced at a maximum efficiency. A current regulator ensures the adaptability of the actual magnetizing current with its reference value; this results in the production of a stable torque at any desired load torque, even during the transient periods. According to simulation results, this controller can be suitable for drive systems of elevators and electric vehicles.

The development and use of FACTS devices for power transmission system has led to the application of these controllers to improve the stability of power systems. This paper discusses the optimal control of static compensator (STATCOM) to improve transient stability. To demonstrate the ability of the proposed control strategy, it has been applied on a single machine and multi machine power systems. Different modes of operation of compensator regarding the modulation of active and reactive power has been considered. In multi machine system, since the control signal based on the state variable is not available at the compensator bus, the derivative of an electric quantity derived from local measurement has been utilized.

Magnetic field distribution in railgun structure is the effective factor that determines its efficiency. This field distribution is affected by rails and armature geometry and dimensions. This paper investigates how the rails dimensions and spaces affect the magnetic field distribution, magnetic flow density and inductance gradient (L'). L' plays an important role in the performance of an Electromagnetic Launcher (EML), and it determines directly the force that accelerate projectile. A finite element method is discussed to simulate two dimensional railgun in this study. Finally L' for various dimensions are tabulated and compared with values obtained from other methods.

UPQC (Unified Power Quality Conditioner) is an advanced custom power device, which can be used in the case that the load is non-linear and the system supply voltage is distorted simultaneously. It consists of a series and shunt Voltage Source Converter (VSC) whit a common DC link. The shunt VSC is mainly intended for conditioning the current flowing from a load into the network and series VSC is mainly used to protect sensitive loads against power quality problems caused by disturbances in supply system.  In this paper, a new control strategy for the UPQC is proposed. This control strategy is based on two different methods; the Instantaneous Power Balance Method and Synchronous Reference Frame Method. These two methods have been used earlier independently. Each of them has merits and demerits. To overcome their drawbacks, the instantaneous power balance methods have been applied to the shunt VSC and synchronous reference frame method has been applied to the series VSC of UPQC. The simulation results of UPQC in a typical distribution system, carried out by PSCAD/EMTDC, verify the performance improvement of UPQC. It is shown that using this combination of control strategy, the power quality problems in distribution systems can be solved easily.