A series active power filter based on a sinusoidalcurrent-controlled voltage-source inverter

A series active power filter working as a sinusoidal current source, in-phase with the mains voltage, has been developed and tested. The amplitude of the fundamental current in the series filter is controlled through the error signal generated between the load voltage and a pre-established reference. The control allows an effective correction of power factor, harmonic distortion and load voltage regulation. Compared with previous methods of control developed for series active filters, this method is simpler to implement because it is only required to generate a sinusoidal current, in-phase with the mains voltage, the amplitude of which is controlled through the error in the load voltage. The proposed system has been studied analytically and tested using computer simulations and experiments. In the experiments, it has been verified that the filter keeps the line current almost sinusoidal and in-phase with the line voltage supply. It also responds very quickly under sudden changes in load conditions, reaching its steady-state in about two cycles of the fundamental     

Monte Carlo simulations of homogeneous upconversion in erbium-dopedsilica glasses

Quenching of Er³⁺ ions by homogeneous energy-transfer upconversion in high-concentration erbium-doped silica glasses has been theoretically investigated, The results indicate that at Er³⁺ concentrations of 1.0-2.0·10²⁶ m^-3 or below, the kinetic limit of strong migration is not reached, and hence the widely accepted quadratic upconversion model is not generally valid. Nevertheless, the results offer an explanation of the experimental observations of quadratic upconversion. Furthermore, it has been shown that at a given population inversion, the quenching rate depends on the rate of exchange of the excited Er³⁺ ions by emission and absorption     

Optical imaging of anatomical maps derived from magnetic resonanceimages using time-independent optical sources

Presents a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed     

A probabilistic method for the design of power grounding systems

An improved multivariable, probabilistic method for the safety analysis of power grounding systems is presented. The application of this method is demonstrated in four examples. The first three examples illustrate the practical evaluation of one new and two existing substation grounding grids when the substation is connected to an overhead distribution system. The fourth example ascertains the relative impact of a difference between the S curve of IEC Publication 479 and Dalziel's equation for the allowable body current used in ANSI/IEEE Std 80-1986 on the validity of an exposure model based on the requirements of Std 80. In this example, the statistical data on ground faults have been taken from actual system records. Further possible refinements of the exposure model are discussed     

Assessing Environmental Risks: Lessons From Superfund

This essay analyzes the use of risk assessment in Superfund, the controversial American hazardous waste cleanup programme. We argue that risk assessment has been used in three ways in discussing policy options in this programme: as a metric for assessing performance; as a means for resolving conflicts; and as a tool for comparing different environmental initiatives. Use of risk reduction as an analytical tool in European efforts to clean up hazardous waste sites is discussed. We conclude that while risk assessment has potential utility for each of these applications, there are also accompanying technical and political difficulties.     

The influence of trigger configurations and laminate lay-up on the failure mode of composite crush cylinders

In this paper the results are presented of a test program on the energy absorption of composite cylinders loaded in compression. The influence of the laminate lay-up and of the trigger configuration were determined. Two different failure modes for the different laminates and triggers were observed: a splaying mode and a fragmentation mode. The splaying mode is more efficient in absorbing energy. The failure mode did not change during the crushing process.     

Cable insulation density profile determined from ultrasonicvelocity measurements

Density results obtained on the same cable sample with a column and from ultrasonic measurements are reported. A calibration curve relating ultrasonic velocity and cable insulation density is given for PE and crosslinked PE (XLPE) cables. The limits and advantages of deducing density profiles of cable insulation using a focused, ultrasound beam rather than the more time-consuming column measurements are discussed     

Adaptive control of siso plants with unmodelled dynamics

In this paper we pursue a twofold aim. First we want to simplify the complexity of the classical Monopoli's scheme, the so-called ‘Augmented error signal control scheme’. Then we also wish to cope with the realistic situation in which the presence of unmodelled dynamics has to be taken into account. This latter problem has been faced in the literature by suitably modifying the adaptation mechanism in order to avoid undesired phenomena as well as to obtain an attractive stability region for the state trajectories starting from any point in a predefined initial condition set. In our case the necessity of introducing any sort of modification in the adaptation mechanism is completely avoided, but we still obtain asymptotic stability of the output error signal.     

Sensorless speed measurement using current harmonic spectralestimation in induction machine drives

This paper proposes a sensorless speed measurement scheme that improves the performance of transducerless induction machine drives, especially for low-frequency operation. Speed-related harmonics that arise from rotor slotting and eccentricity are analyzed using digital signal processing. These current harmonics exist at any nonzero speed and are independent of time-varying parameters, such as stator winding resistance. A spectral estimation technique combines multiple current harmonics to determine the rotor speed with more accuracy and less sensitivity to noise than analog filtering methods or the fast Fourier transform. An on-line initialization routine determines machine-specific parameters required for slot harmonic calculations. This speed detector, which has been verified at frequencies as low as 1 Hz, can provide robust, parameter-independent information for parameter tuning or as an input to a sensorless flux observer for a field-oriented drive. The performance of the algorithm is demonstrated over a wide range of inverter frequencies and load conditions     

Application of evolutionary programming to transient andsubtransient parameter estimation

This paper presents an artificial intelligence approach of using evolutionary programming to estimate the transient and subtransient parameters of a generator under normal operation. The estimation using evolutionary programming is compared with that using a corrected extended Kalman filter. The comparisons with both simulation and micromachine test results show that evolutionary programming is robust to search the real values of parameters even when the data are highly contaminated by noise, while with the extended Kalman filter, the estimation tends to diverge with such data