M.M. Dawoud

Null steering in phased arrays by controlling the element positions

Null steering methods usually involve costly and complicated amplitude and/or phase control systems. A technique is presented for null steering based on the element position perturbations. The technique frees the phase shifters to be used solely for steering the main beam toward the direction of the desired signal. It also removes the limitations of the other techniques by independently steering the main beam and the nulls to arbitrary independent directions. This technique is also capable of obtaining sidelobe cancellation and wideband signal rejection. >

Optimal AGC tuning with genetic algorithms

Abstract This paper deals with the application of genetic algorithms for optimizing the parameters of conventional automatic generation control (AGC) systems. A two-area nonreheat thermal system is considered to exemplify the optimum parameter search. A digital simulation is used in conjunction with the genetic algorithm optimization process. Several integral performance indices, or cost functions, are considered in the search for the optimal AGC parameters. The work is further extended to include the use of more elaborate feedback control strategies, such as the proportional-plus-integral type, within the decentralized frame. The results reported in this paper have not been obtained before and they demonstrate the effectiveness of the genetic algorithms in the tuning of the AGC parameters.

Design of superdirective arrays with high radiation efficiency

Superdirective arrays have been considered unrealizable due to the high elemental currents required and their sensitivity to small variations in amplitude and phase. A new approach to superdirective array design based on polynomials which optimize radiation efficiency has been devised. An example of the optimization procedure is given for a 2-wavelength 11-element array, and the sensitivities of radiation patterns optimized for directivity and for radiation efficiency are compared. The relationship between radiation efficiency and the number of elements within a given array length is investigated, and an optimum number is proposed. Finally, the variation of radiation efficiency with beamwidth reduction of optimally filled arrays of different lengths is given.

Occupational exposure assessment for power frequency electromagnetic fields

Exposure assessment is the determination or estimate of the magnitude, frequency of occurrence, and rate of exposure of an individual or a group to an environmental agent. The agents of interest in this case are the electric and magnetic fields (EMF) in the extreme low-frequency range that includes the power frequency of 50/60 Hz. There are an increasing concern that exposure to EMF may be associated with biological and health effects. This concern has prompted numerous measurement projects and the development of instrumentation, methodologies, and exposure models and simulations. This paper identifies the status of EMF exposure assessment research related to occupational exposures. It draws the recent results to emphasize the unique aspects of EMF exposures in the home and utilities environments, and highlights the research needs. The intensities of electromagnetic fields have been measured under power transmission and distribution lines, at substations and industrial plants and near various electric devices including domestic electrical equipment. The field intensities have been related to the exposure time (duration of staying) in the different areas and have been compared with the internationally established standards. The data presented are useful for understanding the levels of electromagnetic fields that can be encountered in various places and also for estimating possible occupational and residential exposure levels.

Underground cable magnetic field simulation and management using new design configurations

This paper addresses one of the most important sources of magnetic fields: underground power cables. New design configurations for one, two, three and four cables per phase are presented from a magnetic field perspective. Different management techniques are studied in detail. Judicious placement of cable phases in multiconductor lines to reduce the field effect is implemented by computer modeling and simulations. The state-of-the-art magnetic field simulation package PCFIELD developed by EPRI is used to quantify and present the tool used to manage the field values. The new design configuration cases are very useful from a magnetic field point of view and have low cost schemes that can be easily implemented.

Tuning of AGC of interconnected reheat thermal systems with genetic algorithms

This paper deals with the application of genetic algorithms for optimizing the automatic generation control (AGC) systems. An integral controller and a proportional-plus-integral controller are considered. A two-area reheat thermal system is considered to exemplify the optimum parameter search. A digital simulation is used in conjunction with the genetic algorithm optimization process. The integral of the square of the error and the integral of time-multiplied absolute value of the error performance indices are considered in the search for the optimal AGC parameters. The results reported in this paper demonstrate the effectiveness of the genetic algorithms in the tuning of the AGC parameters.

Implementation of shielding principles for magnetic field management of power cables

Adverse health effects due to magnetic fields is a matter of great concern and has been widely debated in recent years. Managing these fields is a challenge to researchers. One of the important sources of magnetic fields is power cables. Different management techniques have been studied. In this paper, passive shielding schemes are implemented to manage the magnetic fields of power cables. The various shielding schemes can be separated into two broad categories: shielding subject and shielding source. Both schemes are implemented in this paper. Passive shielding schemes are found to be the most powerful technique as the reductions obtained are sometimes as high as 97-98%. This scheme is a costly one, should be used only in assigned locations, and as such, there has to be a trade-off between the cost and the level for reduction desired and the health desired and the health hazards.

Tuning of power system stabilizers using genetic algorithms

Abstract Several techniques exist for developing optimal controllers. This paper investigates the tuning of power system stabilizers (PSS) using genetic algorithms (GA). A digital simulation of a linearized model of a single-machine infinite bus power system at some operating point is used in conjunction with the genetic algorithm optimization process. The integral of the square of the error and the time-multiplied absolute value of the error performance indices are considered in the search for the optimal PSS parameters. In order to have good damping characteristics over a wide range of operating conditions, the PSS parameters are optimized off-line for a selected set of grid points in the real power (P)-reactive power (Q) domain. The optimal settings thus obtained can then be stored and retrieved on-line to update the PSS parameters based on measurements of the generator real and reactive power. Time domain simulations of the system with GA-tuned PSS show the improved dynamic performance under widely varying load conditions.

Magnetic field management techniques in transmission underground cables

Magnetic field management is concerned with the minimization of the effects of such fields on the public health, without sacrificing the effectiveness or reliability of the power system. The essential management techniques used for the underground transmission cables comprise geometry manipulation phase placement, and source shielding. In this paper, the simulation results of the standard recommended stack, triangular and flat configurations are presented. The simulations have been carried out for single and three phase cables. The resulting fields for different depths have been evaluated and compared. The results led to the conclusion that judicious placement of phases is a very powerful management technique to reduce the magnetic field as cost has not been changed. The appropriate phase placements corresponding to minimal field values are obtained.

Null steering in scanned linear arrays by element position perturbations

Null steering in scanned linear arrays by element position perturbations is presented. A new method has been devised to improve the performance of such arrays based on the null only steering criterion, Changes to the main array parameters, such as beam width and sidelobe levels, are kept to a minimum. The results show the superiority of this new method, especially when applied to phased arrays.