Essam A. Al-Ammar

Finite-Width Magnetic Mirror Models of Mono and Dual Coils for Wireless Electric Vehicles

Improved magnetic mirror models (IM3) for mono and dual coils with a finite width and infinite permeability are proposed in this paper. By introducing a mirror current, which is located at the same distance from a source current but with a smaller magnitude than the source current, the magnetic flux density of the mono and dual coils can be determined in a closed form. The ratio of the mirror current and source current is identified as a function of the width of the core plate and the distance between the source current and core plate, as rigorously derived from finite-element method simulations. Applying the proposed IM3 to the mono and dual coils used for wireless electric vehicles, the magnetic flux density over an open core plate is analyzed and its maximum points on the plate are found, which is crucial in the design of the coils to avoid local magnetic saturation. Furthermore, the magnetic flux density when a pick-up core plate is positioned over a primary core plate is also analyzed by introducing successive mirror currents. The proposed magnetic mirror models were extensively verified by experiments as well as site tests, showing quite promising practical usefulness.

Distributed Generation Using Indirect Matrix Converter in Reverse Power Mode

Indirect matrix converter (IMC) is an alternative for ac/ac energy conversion, usually operated with a voltage stepped-down gain of only 0.866. For applications like distribution generation where voltage-boost functionality is required, the traditional style of operating the IMC is therefore not appropriate. Like most power converters, the operation of the IMC can surely be reversed to produce a boosted gain, but so far its relevant control principles have not been discussed. These challenges are now addressed in this paper with distributed generation suggested as a potential application. Simulation and experimental results for validating various performance aspects of the proposed control schemes can be found in a later section of this paper.

Experimental study and design of smart energy meter for the smart grid

The demand for energy is increasing as a result of the growth in both population and industrial development. To improve the energy efficiency, consumers need to be more aware of their energy consumption. In recent years, utilities have started developing new electric energy meters which are known as smart meters. A smart meter is a digital energy meter that measures the consumption of electrical energy and provides other additional information as compared to the traditional energy meter. The aim is to provide the consumer and supplier an easy way to monitor the energy. Smart meters are considered a key component of the smart grid as these will allow more interactivity between the consumers and the provider. Smart meters will enable two-way and real-time communication between the consumers and the provider. Considering the increase of electricity demand in Saudi Arabia, smart meters can decrease the overall energy consumption. This paper presents the development of a GSM and ZigBee based smart meter. This meter can measure the energy and send the information to the service provider, who can store this information and notify the consumer through SMS messages or through the internet.

Design of energy band alignment at the Zn1−xMgxO/Cu(In,Ga)Se2 interface for Cd-free Cu(In,Ga)Se2 solar cells

The electronic band structure at the Zn(1-x)Mg(x)O/Cu(In(0.7)Ga(0.3))Se(2) interface was investigated for its potential application in Cd-free Cu(In,Ga)Se(2) thin film solar cells. Zn(1-x)Mg(x)O thin films with various Mg contents were grown by atomic layer deposition on Cu(In(0.7)Ga(0.3))Se(2) absorbers, which were deposited by the co-evaporation of Cu, In, Ga, and Se elemental sources. The electron emissions from the valence band and core levels were measured by a depth profile technique using X-ray and ultraviolet photoelectron spectroscopy. The valence band maximum positions are around 3.17 eV for both Zn(0.9)Mg(0.1)O and Zn(0.8)Mg(0.2)O films, while the valence band maximum value for CIGS is 0.48 eV. As a result, the valence band offset value between the bulk Zn(1-x)Mg(x)O (x = 0.1 and x = 0.2) region and the bulk CIGS region was 2.69 eV. The valence band offset value at the Zn(1-x)Mg(x)O/CIGS interface was found to be 2.55 eV after considering a small band bending in the interface region. The bandgap energy of Zn(1-x)Mg(x)O films increased from 3.25 to 3.76 eV as the Mg content increased from 0% to 25%. The combination of the valence band offset values and the bandgap energy of Zn(1-x)Mg(x)O films results in the flat (0 eV) and cliff (-0.23 eV) conduction band alignments at the Zn(0.8)Mg(0.2)O/Cu(In(0.7)Ga(0.3))Se(2) and Zn(0.9)Mg(0.1)O/Cu(In(0.7)Ga(0.3))Se(2) interfaces, respectively. The experimental results suggest that the bandgap energy of Zn(1-x)Mg(x)O films is the main factor that determines the conduction band offset at the Zn(1-x)Mg(x)O/Cu(In(0.7)Ga(0.3))Se(2) interface. Based on these results, we conclude that a Zn(1-x)Mg(x)O film with a relatively high bandgap energy is necessary to create a suitable conduction band offset at the Zn(1-x)Mg(x)O/CIGS interface to obtain a robust heterojunction. Also, ALD Zn(1-x)Mg(x)O films can be considered as a promising alternative buffer material to replace the toxic CdS for environmental safety.

Transfer function analysis using STFT for improvement of the fault detection sensitivity in transformer impulse test

Insulation of transformer windings may shift as a result of short circuit current or impact during transportation. The shift modifies the dielectric space between the layers of the windings and may cause an insulation breakdown, leading to a complete transformer failure. As transformers are very costly to replace, it is important that their condition determined accurately without having to dismantle the apparatus to visually inspect it. Testing of winding insulation is performed by using the standard impulse test, via applying fast Fourier transform (FFT) to analyze the transformer state (healthy or faulty) in the frequency domain, as a transfer function (TF). Nonetheless, one of the shortcomings of the FFT is that it cannot be used with non-stationary signals. Voltage and current waveforms in the transformer are treated as nonstationary signals, especially when there is a fault. In addition, FFT does not give any information on the time at which a frequency component occurs. To obtain better signature analysis and to increase the detection sensitivity, this paper suggests a new method using short time Fourier transform (STFT) in the transfer function analysis. It is hoped that this high resolution method will help to reduce the subjective judgments of technicians when making decisions about changes in the winding structure of the transformer.

Optimal allocation and sizing of Distributed Generation in distribution networks using Genetic Algorithms

This paper addresses the optimization problem of integration of Distributed Generation (DG) in distribution networks. Three Genetic Algorithms (GAs) have been developed to minimize the power losses of the system. The First GA enables the optimal sizing of the DG units given their locations. Alternatively, the second GA determines the optimal locations of the DG units assuming equal sizes of the units. The third GA enables the determination of both optimal sizes, on discrete values, and optimal locations. The results prove the effectiveness of the developed genetic algorithms in finding the optimal penetration level and optimal locations and sizes of the DG units to yield minimum losses of the system.

Analysis of a PWM voltage source inverter with PI controller under non-ideal conditions

Apart from the traditional pulse-width modulation (PWM) or SPWM voltage source inverters (VSI), the proposed VSI with a Proportional integral current controller (PI VSI) offers superiority. They include instantaneous current control and wave shaping, fixed inverter switching frequency independent of the output frequency resulting in only known harmonics, and free-running carrier operation. A modeling approach to proposed PI VSI is introduced. A design example of the VSI power circuitry is presented. The PI controller design is discussed. Finally the VSI load current is verified for harmonic contents and instantaneous current control capabilities, under normal, unbalanced, load outage and load short-circuit conditions.

The consumer rationality assumption in incentive based demand response program via reduction bidding

Because of the burgeoning demand of the energy, the countries are finding sustainable solutions for these emerging challenges. Demand Side Management is playing a significant role in managing the demand with an aim to support the electrical grid during the peak hours. However, advancement in controls and communication technologies, the aggregators are appearing as a third party entity in implementing demand response program. In this paper, a detailed mathematical framework is discussed in which the aggregator acts as an energy service provider between the utility and the consumers, and facilitate the consumers to actively participate in demand side management by introducing the new concept of demand reduction bidding (DRB) under constrained direct load control. Paper also presented an algorithm for the proposed framework and demonstrated the efficacy of the algorithm by considering few case studies and concluded with simulation results and discussions.

Demand response in Saudi Arabia

Demand Response is a useful tool to limit the maximum demand thereby reducing the need of peak power generation units which are normally less efficient and operational for only small time interval. DR enables consumers to manage their consumption according to the available generation which means electric supply is generation oriented rather than demand oriented. Considering the challenges facing Saudi Arabia in electrical sector, demand response initiative can be very beneficial. This paper describes various demand response methods in general followed by the simulation of variable price structure and incentive based methods for possible DR implementation.

Framework for Identification of Power System Operating Security Regions

Power system operation aims, in principle, at maintaining reliable and secure supply of electricity while minimizing the total cost of operation. In theory, there are two main objec-tives that could be considered, namely the maximization of system security and the minimization of total operating cost of supplying energy. In practice, however, the security requirements are included as constraints rather than formulating the problem as a security maximization mandate. The system security constraints are in fact boundaries that surround all possible operating modes (scenarios) of the power system. In other words, these boundaries form the feasible operating domain in the parameter space spanned by vari-ous operating variables within which the system can safely be operated. For a given operating scenario, the associated security level is measured by the “distance” (for example, the Euclidean norm) of the operating point from the security region boundary. This paper presents a novel framework for identification and representation of operating security regions in power systems as well as evaluation of security levels associated with different operating scenarios. While the concepts and principles presented are general, the work of this the paper is confined to the interpretation of the security boundary in terms of system stability criteria. Of course, the framework presented is applicable quite as well to other criteria that may be considered.