Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

Magnet temperature estimation in surface PM machines using high frequency signal injection

Abstract: This paper proposes a method to estimate the magnet temperature in surface PM machines (SPMSM) using high frequency carrier signal injection. The injection of a high frequency signal, superimposed on the fundamental excitation, allows the estimation of the stator transient impedance, which is a function of both the stator and rotor impedances. The temperature of the magnets is shown to have a significant weight on the overall stator transient impedance, from which it can be estimated. The high frequency carrier signal is injected intermittently in order to minimize potential adverse effects on the normal operation of the machine. The paper first explains the physics behind the magnet temperature dependence. Then the principles of the method as well as its practical implementation are discussed. Experimental verification of the method is provided.

Multi-frequency imaging and modelling of respiratory related electrical impedance changes.

Abstract: Two studies concerning multi-frequency impedance measurements are presented. The first uses tetrapolar measurements made on the thorax and the second electrical impedance tomography images, also made from the thorax. The way in which the impedance and the changes in impedance with ventilation depend upon frequency are investigated using Cole-Cole modelling and also a physiological model of lung tissue. There is an excellent fit to the Cole-Cole model, and the results show that it should be possible to identify tissue on the basis of the impedance spectrum and the spectrum of the changes in impedance during breathing.

AC impedance spectroscopy: a new equivalent circuit for titania thick film humidity sensors

Abstract: The variation of the electrical signal with humidity in ceramic sensors is originated by the chemical and physical sorptions of water molecules existing in the atmosphere. The aim of the work described in the present paper is to establish an equivalent electrical circuit for the case of two titania thick-film samples. It is shown, at least for the temperature of 23 ◦ C, that the same type of circuit represents adequately these two samples for various relative humidities. Chemisorption and physisorption are responsible for the different charge transport mechanisms – ion hopping, ion diffusion and electrolytic conduction. Complex impedance data were obtained at the temperature of 23 ◦ C and various relative humidities, in the frequency range 0.1 Hz–40 MHz. The best and simpler circuit representation we found, which gives the best fitting for the Cole–Cole and Bode plots, consists of two RC parallel circuits in series with two constant-phase elements (CPEs). The values of the electrical components are tabled and, as an example, the Cole–Cole and Bode plots fitting obtained for one of our samples, the sample B, for 87.5% RH, in the frequency range 0.1 Hz–40 MHz is shown. © 2004 Elsevier B.V. All rights reserved.

An efficient implementation of surface impedance boundary conditions for the finite-difference time-domain method

Abstract: An efficient way to implement the surface impedance boundary conditions (SIBC) for the finite-difference time-domain (FDTD) method is presented in this paper. Surface impedance boundary conditions are first formulated for a lossy dielectric half-space in the frequency domain. The impedance function of a lossy medium is approximated with a series of first-order rational functions. Then, the resulting time-domain convolution integrals are computed using recursive formulas which are obtained by assuming that the fields are piecewise linear in time. Thus, the recursive formulas derived here are second-order accurate. Unlike a previously published method [7] which requires preprocessing to compute the exponential approximation prior to the FDTD simulation, the preprocessing time is eliminated by performing a rational approximation on the normalized frequency-domain impedance. This approximation is independent of material properties, and the results are tabulated for reference. The implementation of the SIBC for a PEC-backed lossy dielectric shell is also introduced. >

A Case Study on the Application of the Nyquist Stability Criterion as Applied to Interconnected Loads and Sources on Grids

Abstract: As the penetration of complex grid-connected devices, such as power electronic inverters, increases, so too does the complexity of analyzing system stability. A graphical application of the Nyquist stability criterion is presented that indicates how an individual load and source each contribute to the closed-loop system grid eigenvalues. The case study is not limited to particular impedance forms or scenarios like the more common complex torque coefficient method or passivity theory method. From the individual frequency responses of the load and source impedances, the graphical technique indicates how each impedance contributes to the system stability. Examples are provided that successfully indicate the cause of instability for a digitally controlled voltage source inverter (VSI) operating as a microgrid, with a current source inverter as a load. A second example is provided that identifies the potential instability of a VSI running an induction machine. A 42-kW inverter system is used to confirm the findings, showing a close correlation with the theoretical analysis.