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A graphical method is extended to and applied for visual inspection of solution patterns (region of complex natural frequencies sn) in the complex s-plane for dispersive materials characterized by the Debye and Lorentz models. These patterns are in the form of exponential decay and C-shaped profiles for the Debye and Lorentz models, respectively. Their forms are observed to be affected (e.g., moving left/right) in different manners with a variation of dispersion parameters. This method, thanks to its visual inspection capability, can help in analyzing/synthesizing filters and frequency-selective surfaces. [ABSTRACT FROM AUTHOR]

We propose a powerful graphical method for evaluating the natural complex frequencies and amplitudes of the layered structures for their electromagnetic characterization. Its advantage is to show a pattern of the location of the natural complex frequencies so that it would be possible to examine how they can move for a possible error in the measurement system. The method is validated by a two-layered structure by comparing the natural complex frequencies and amplitudes computed by the proposed method and the inverse Fourier transform. It has been applied to monitor the effect of noise in a measurement system. [ABSTRACT FROM AUTHOR]

Symmetrical and unsymmetrical voltage sags are a major cause of energy loss in induction motors affecting the efficiency and longevity of the motor. A comprehensive and novel graphical method to determine energy loss during unsymmetrical sags is proposed. The energy is computed using torque–speed characteristics of the induction motor. Due to unbalance in the voltages during unsymmetrical sags, oscillations are observed in torque–speed characteristics. Throughout these oscillations, motor torque and speed attain extreme values. Area under the curve of torque and speed during oscillation is computed using MATLAB/Simulink simulation, which is a measure of the output power during unsymmetrical sags. The sag duration is measured to compute the energy loss. The analytical expression to assess output power of an induction motor during unsymmetrical sag is derived. The graphical results are validated using analytical calculations. Graphical representation is easy and faster to construct than analytical methods; in addition, the graphical method proposed makes it easier to assess the comparative magnitudes. Assessment of energy loss provides a useful tool for optimal injection of energy for sag mitigation techniques. [ABSTRACT FROM PUBLISHER]

This paper presents an optimal scheme of excitation capacitor to decrease the capacity of static excitation controller (SEC) for dual stator-winding induction generator (DWIG) system applied in wind power generation. The investigations into reactive excitation power released by the excitation capacitor and SEC illustrate that the optimal excitation capacitor is not only related to generator parameters, speed range, and load, but also affected by wind turbine power curve. Based on the objective of minimizing the capacity of SEC, several methods are employed here to select an appropriate excitation capacitor. Through the analysis of DWIG control mechanism and model of SEC in the stator-voltage-orientation synchronous d– q frame, a decoupling control strategy using the space vector modulation is obtained. On the basis of this, the simulation and experimental works from the prototype of 18-kW six/three-phase DWIG wind power system are carried out to verify the optimal scheme. The results demonstrate the correctness and effectiveness of this optimization scheme. [ABSTRACT FROM AUTHOR]

In order to minimize the quantity of superconducting wire used in superconducting High Gradient Magnetic Separation (HGMS) systems, we developed two computational techniques to simulate the magnetic field created by superconducting solenoids: a detailed numerical model and a simplified graphical method. The numerical model is used as a standard of comparison to evaluate the accuracy of the graphical method. The evaluated error in the graphical determination of superconducting wire volume was less than 4.6% in hypothetical HGMS systems for purifying dissolved fission products in nuclear reprocessing. Compared with the case where an HGMS filter and a superconducting solenoid have the same length, our optimization technique shows that a large amount of wire reduction is possible. [ABSTRACT FROM AUTHOR]