Comparison of Stabilization Methods for Fixed-Speed Wind Generator Systems

Static Synchronous Compensator (STATCOM), Pitch control system, Braking Resistor (BR), and Superconducting Magnetic Energy Storage (SMES) have recently been reported as stabilization methods for fixed-speed wind generator systems. although the individual technologies are well documented, a comparative study of these systems has not been reported so far. This paper aims to fill in the gap, and provides a comprehensive analysis of these stabilization methods for fixed-speed wind generator systems. The analysis is performed in terms of transient stability enhancement, controller complexity, and cost. a novel feature of this work is that the transient stability analysis of wind generator system is carried out considering unsuccessful reclosing of circuit breakers. Simulation results demonstrate that the SMES is the most effective means of transient stability enhancement and minimization of both power and voltage fluctuations, but it is the most expensive device. The STATCOM is a cost-effective solution for transient stability enhancement and minimization of voltage fluctuations. The BR is the simplest in structure and a cost-effective solution for transient stability enhancement. The pitch controller is the cheapest one, but its response is much slower than that of other devices

Effects of a Smaller Unit Cell Planar EBG Structure on the Mutual Coupling of a Printed Dipole Array

A new smaller unit-cell planar electromagnetic bandgap (EBG) structure is proposed on low dielectric constant low-cost substrate (TMM: epsilon(r) = 4.5, thickness = 25 mils) that has a stopband frequency at around 4 GHz. The proposed structure when placed in between a two-element printed dipole array results in over 13-dB reduction in mutual coupling and a significant improvement in antenna return loss bandwidth and gain pattern

Wireless Power Transmission to a Buried Sensor in Concrete

The feasibility of sending wireless power to a buried sensor antenna within concrete was studied. a receive patch rectenna with 75.8% conversion efficiency was designed for operation at 5.7 GHz. The received DC power at the rectenna was measured within dry and wet concrete samples with various cover thicknesses and air-gaps. For the rectenna buried within 30 mm of the concrete, the received DC power was 10.37 mW, which was, about 70% of the received DC power in free-space

A Miniature Implanted Inverted-F Antenna for GPS Application

A miniature implanted Hilbert inverted-F antenna design at the 1.575 GHz; global positioning system (GPS) frequency is proposed, which can be used to track the location of its user, e.g., the elderly with declining mental capacity (alzheimer\u27s disease). A detailed parametric study of the antenna design is performed by considering it to be implanted within a human muscle model. The effects of the substrate, superstrate, and the nearby muscle tissue on antenna performance are carefully investigated. A laboratory prototype of the antenna was built and tested within a muscle equivalent fluid indicating good VSWR performance. Finally the said antenna when placed within the tissue equivalent fluid was also tested to track GPS satellites with the help of a low noise amplifier (LNa). Such field measurements demonstrate that the antenna can easily lock into six or more satellites which are more than enough to determine the location of a person

Miniature Circularly Polarized Rectenna with Reduced Out-of-Band Harmonics

Wireless embedded sensors are becoming increasingly important for many safety critical applications. Sensor batteries or capacitors must be charged as needed in order to achieve high data rate communications. A miniature circularly polarized rectenna operating at 5.5 GHz is introduced which, with the help of an integrated band-reject filter, reduces out-of-band harmonic emission significantly. The rectenna has a conversion efficiency of 74% with more than 50 dB out-of-band harmonic suppression at 11 GHz

A Reconfigurable Stacked Microstrip Patch Antenna for Satellite and Terrestrial Links

A reconfigurable stacked microstrip patch antenna is proposed. The antenna operates at an upper frequency f(u) with a broadside pattern, 7.5-dBi right-hand circularly polarized gain, and 15.8% bandwidth. At a lower frequency f(1), the antenna operates as a planar inverted-F antenna (7.3% bandwidth and 3.9-dBi peak gain) with the main beam directed close to the horizon. Switching between the two regimes of operation is achieved using p-i-n diodes. antenna operation in the upper frequency hand is suitable for low-earth-orbit or medium-earth-orbit satellite communications, and in the lower frequency band, the antenna is useful for terrestrial land-mobile or other wireless applications

A Miniature Energy Harvesting Device for Wireless Sensors in Electric Power System

A novel energy harvesting device called the energy coupler is proposed which can provide power to small wireless sensors in a power system. The energy coupler when coupled electromagnetically to a nearby current carrying conductor scavenges ac power from the conductor. The proposed energy coupler converts the harvested ac power into dc using a passive voltage multiplier circuit. The design of the energy coupler is such that the dc power obtained is adequate to charge a miniature 1.2-V rechargeable battery. It is demonstrated that the energy coupler is capable of delivering 10 mW of dc power to a 50-Ω load. An analytical model is also presented which agrees well with measurement results within a margin of error of 10%

Ultrasonic and thermo-kinetic characterization of curing epoxy resin

This study combines cure kinetics modelling and thermal and ultrasonic cure monitoring to characterize the cure state of a complex commercial modified epoxy thermosetting system of industrial importance containing two epoxies, diethylene triamine hardener, external catalyst, aliphatic reactive diluent, and mica. Both catalyst and reactive diluent in the formulation of two epoxy resin mixture keep this complex system odd from others and to some extent a new one to report cure kinetics to the best of our knowledge. The cure was monitored using differential scanning calorimetry (DSC) and broadband ultrasonic techniques over a group of isothermal cure temperatures within corresponding acceptable time scales. The sensitivities of both techniques to the chemical, physical, and mechanical changes associated with each part of the cure was discussed comprehensively and critically together with an inspection of the similarities between them coupled with qualitative and quantitative correlations. An in depth details analysis of the chemical cure kinetics of the investigated system was presented utilizing the model free iso-conversional method coupled with the light of physics of advanced kinetics research. The modelling of the calorimetric cure kinetics of the epoxy system under study was developed utilizing the empirical approach of fitting of the experimental data to various kinetic models. The best fit model which best possibly describe the non-typical autocatalytic cure behaviour of the resin system and predicts the reaction course was evaluated and analyzed in details. Utilization of the maximum attained conversion at a specific curing temperature enables this model to most closely simulate the curing reaction under both chemical controlled and diffusion controlled conditions with almost a reasonable degree of satisfaction over the entire range of conversion and temperature studied without the a priori need of a glass transition temperature model. The non-conventional autocatalytic effect and prediction of the trimolecular catalysis mechanism of the curing reaction was found to be manifested in temperature dependence of reaction orders, which was elucidated and justified. In comparison to other epoxy resins without reactive diluents, the analysis of our data shows that most possibly, the reactive diluent increased the maximum value of calorimetric conversion and reaction rate, reduced the viscosity, while the values of activation energy and process parameters remained within the typical values of epoxy formulations and the crosslink density was unaffected. The performance of each particular model tested was discussed along with their comparisons. Implementing diffusion factor in conventional models some useful information associated with the diffusion controlled kinetics related to our data were explored. The cure kinetics was also analyzed from both kinetic and thermodynamic viewpoint in the context of Horie model. This approach we employed, is, to some extent uncommon, can contribute towards a new way of characterization and the critical understanding of the cure reaction from the microkinetic standpoint providing information of the effect of reactive diluent on kinetics, regarding reaction pathways, kinetic homogeneity I inhomogeneity associated with reaction phase and the properties of the end product which are important to monitor and ultimately control the cure to attain desired properties in the end material. A TTT diagram of the cure process of this system was also constructed. The ultrasonic compression wave velocity was demonstrated to be the most interesting and potential parameter for monitoring and characterizing the cure process at all stages which provided with the information of degree of mechanical property development and can detect gelation and vitrification that occur during cure. Therefore, ultrasonic velocity measurement could be exploited for non-destructive on-line process control in an industrial environment. It was demonstrated that ultrasonic compression wave velocity can be used as a predictor of calorimetric conversion measurements and thus can be used to track chemical reaction online which is of potential importance for cure monitoring. Though system specific, the methodology we utilized, at least in part, constitutes a novel way of quantifying the degree of cure of a commercial epoxy thermoset network from ultrasonic longitudinal velocity measurements which is interesting and promising. It was found that the DSC is much more sensitive to changes occurring at the early stages of the cure but is relatively insensitive to the changes occurring at the latter stage. Ultrasonic compression wave velocity shows a better sensitivity at the end of the cure. It was also demonstrated that ultrasonic compression wave attenuation, real and imaginary parts of compression modulus, ultrasonic loss tangent and associated central relaxation time, also provided information of the material state and the cure process as well. The end of cure ultrasonic data, in general, provide a convenient assessment of final product quality

Wideband Smaller Unit-Cell Planar EBG Structures and Their Application

A new low-cost smaller unit-cell planar electromagnetic bandgap (ERG) structure operating at the lower GHz frequencies (below 6 GHz) is proposed. ERG structures based on this new geometry are designed on a number of commonly available substrates. Characteristics of such structures, such as bandgap and reflection phase profile are analyzed. a simple empirical model is proposed to predict the surface wave stopband frequency of the proposed ERG structure. Finally, a low-profile dipole antenna is designed and tested for operation on the ERG structure