IRANIAN JOURNAL OF ELECTRICAL AND COMPUTER ENGINEERING (IJECE)
Year:2004 | Volume:3 | Issue:1|Papers Count:12

This paper presents the derivation of three transient models for analysis and simulation of Wind Power Turbine (WPT) based on the theory of asynchronous induction generator. They may be used for determining the operational characteristics of WPT in normal and abnormal operation. The models are derived by using current, magnetic linkage and electromagnetic potential as variables; they are applicable to simulation of WPT and Wind Power System (WPS). The application of derived models is illustrated by using one of the models, the electromotive-force model to simulate the operation performance of a 150 kW WPT. The simulation results enable engineers or designers to have insight on the behavior of the WPT in operation.

The low voltage power networks in developing countries like Tanzania are designed without taking into consideration their application in data communication. In order to use them for data communication, powerline channel models have been developed and analysed in order to understand the factors that will affect the transmission. In this paper transfer characteristics of powerline channel from power users to primary substation have been modeled and analyzed. Simulation results show that the signal in PLC environment attenuates more with interconnections, which needs to be amplified/regenerated within a few meters.

This paper deals with a modern approach of controlling the power flow in AC transmission lines. The control and distribution of power flow in two parallel transmission lines can be implemented by applying one of the flexible AC transmission system (FACTS), which is static compensator (STATCOM) device. The STATCOM device is installed on one line of the two parallel transmission lines to design the controllers for such a system using Electromagnetic Transients Program (EMTP). The closed-loop STATCOM system as a terminal line voltage regulator is designed with two types of controllers, PI with gain scheduling and fuzzy logic. The dynamic performance of the two controllers is tested and compared. It is found that, the fuzzy logic controller forces the system to settle to the steady state value faster than the PI controller with gain scheduling. The fuzzy logic controller is robust; it has a fast response during disturbance and parameters variation. Whereas, the PI controller with gain scheduling has a higher overshoot percentage during transient behavior. Tuning the PI controller with gain scheduling is time consuming and difficult in EMTP, it has a limited range of changing the operating voltage condition due to the tuning difficulty. In the other hand, the fuzzy logic controller can be tuned much faster. Finally, It is claimed that the fuzzy logic controller is a better choice for the STATCOM system compared to the PI controller with gain scheduling.  

This paper describes the behavior of ReMica material Relanex during accelerated thermal stress. Samples were stressed at temperature 186oC. Polarization processes were observed due to direct voltage application. Absorption curves were measured and the isothermal relaxation current analysis was realized. Also capacitance and loss factor development was monitored.

The main objective of this paper is to construct a distributed environment through which the load flow solutions of multi-area power systems can be monitored and controlled. A single-server/multi-client architecture which enables the neighboring power systems to access the remote load flow server at any time, with their respective data and to get the load flow solutions from the remote server has been proposed. An RMI (Remote Method Invocation) based distributed environment has been implemented in such a way that for every specific period of time, the remote server obtains the system data simultaneously from the neighboring power systems which are the clients registered with the remote load flow server and the load flow solutions from the server have been sent back to the respective clients. The load flow server creates a new thread of control for every client’s request and hence complete distributed environment is exploited.

This paper uses the simulated annealing algorithm to solve a unique staff workload scheduling problem present in a school that has about 250 academic staff and 4000 students. This paper also examines and compares various types of cooling schedules. Five types of cooling schedules, namely, geometric ratio, hybrid geometric function with reheating, quadratic equation, Huang’s equation and improved quadratic equation are tested for the scheduling problem. For each cooling schedule, ten test runs are conducted. The results show that the hybrid geometric function with reheating, whose value is directly proportional to the cost function, yields best results to the problem.

Diffraction of electromagnetic waves by a media containing periodic changes of characteristics is widely used in many optical devices and processing methods. Usually diffractive structures contain periodic changes of relative electric permittivity. In this article, we have analyzed electromagnetic wave interaction with a media containing periodic changes of both relative electric permittivity, and relative magnetic permeability. Most of this work is based on using transfer matrix approach and rigorous coupled wave method for analysis of both TE and TM polarizations. Our analytical formulation proves the possibility of polarization insensitivity in diffractive behavior of these structures under specific relationship between harmonic contents of electric permittivity and magnetic permeability.

Dropping probability of handoff calls and blocking probability of new calls are two important QoS measures for cellular networks. Since the dropping probability of handoff calls is more important, call admission policies are used to maintain the upper bound of dropping probability of handoff calls. The fractional guard channel policy (FG) is a general call admission policy and includes most prioritized channel allocation schemes such as guard channel (GC), limited fractional guard channel (LFG), and uniform fractional channel policy (UFC) policies. Since the input traffic is not a stationary process and its parameters are unknown a priori, the optimal value of UFC parameter is not known in advance and possibly varies as traffic conditions change. In this paper, we propose two adaptive algorithms based on learning automata for finding the optimal value of UFC parameter. To evaluate the proposed algorithms, the computer simulations are conducted. The simulation results show that for some range of input traffic, the performance of the proposed algorithms is close to the performance of the uniform fractional channel policy which knows the traffic parameters a priori.

An algorithm has been developed for the simultaneous measurement of the fetal and maternal heart rates from the maternal abdominal electrocardiogram during pregnancy and labor. The algorithm is based on digital filtering, adaptive thresholding, statistical properties in the time domain and differencing of local maxima and minima. The technique has been developed through a combination and modification of earlier techniques making it suitable for ambulatory monitoring. Eighteen volunteers at various weeks of gestation were studied for the fetal heart rate detection. The computation complexity is such that the developed algorithm can extract both maternal and fetal heart rates in real-time utilizing a single-lead configuration.

The main idea of this paper is to present the Principal Component Analysis (PCA) approach in order to reduce dimensionality of measured data for three-dimensional impedance tomography. The reconstruction method is based on the inverse mapping with the aid of the Multi Layer Perceptron neural network. The inverse problem solution provides the identification of the radius and the position of the object placed inside the cylindrical tank.

This paper proposes a synthesized method of a minimum variance adaptive control (MVAC) system to control the cutting force of the Computerized Numerical Control (CNC) turning machine. In this system a linearized state-space model for the CNC turning machine is derived, and a model reference adaptive system (MRAS), which includes the cutting force as a controlled output and the feed rate as a control input, is implemented. The deterministic autoregressive moving average (DARMA) model with auxiliary input is introduced to cope with any disturbances of the controlled system. The parameters of the DARMA model are obtained using the structure of a lattice adaptive control system. The robustness of the proposed controller copes with any changes in depth of cut and/or the cutting speed. These changes are embedded in the linearized model of the CNC machine and are considered as system parameters. Extensive computer simulations are made to prove the applicability of the proposed controller for controlling the cutting force over different operating conditions.

This paper presents two different kinds of regulating control strategies for the angular velocity of a rigid body model with two torque actuators. The first strategy presents piece-wise constant, states dependent feedback control laws. The method is based on the construction of a cost function V (not a Lyapunov function), which is sum of two semi-positive definite functions 1 V and 2 V. The semipositive definite function 1 V is dependent on the first m state variables which can be steered along the given vector fields and 2 V is dependent on the remaining m n - state variables which can be steered along the missing Lie brackets. The values of the functions 1 V and 2 V allow in determining a desired direction of system motion and permit to construct a sequence of controls such that the sum of these functions decreases in an average sense. The second strategy presents a time-varying feedback law based on the model reference approach, where the trajectory of the extended system is chosen as the model reference trajectory. The controllers are designed in such a way that after each time period T, the trajectory of the rigid body model intersects the trajectory of the model reference which can be made asymptotically stable. The proposed feedback law is as a composition of a standard stabilizing feedback control for a Lie bracket extension of the original system and a periodic continuation of a specific solution to an open loop control problem stated for an abstract equation on a Lie group.