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.

Transient and steady-state short-circuit currents in rectifiers for DC traction supply

Abstract: This paper presents some significant extension and analytical formalization of the knowledge on transient and steady-state short-circuit currents in DC traction systems. Electrical supply substations (ESSs) in modern metrorail and railway DC systems are equipped with 6- and 12-pulse diode bridge rectifiers. Large existing plants are equipped with 6-pulse converters, but the 12-pulse option is preferred in the design of new plants in the parallel configuration. Such a converter presents a good compromise between number and voltage/current rating of semiconductor devices, complexity and rating of transformers, DC-side voltage ripple, and AC-side current harmonic content. In this paper, the author considers the features of 6- and 12-pulse conversion units in terms of transient and steady-state short-circuit currents on zero fault impedance, accurate determination of the transient DC short-circuit current is important for correct rating and tuning of protection devices and power equipment (high-speed circuit breakers, isolator switches, switchgears, DC-busbars, etc.). An analytical solution of the short-circuit behavior is given for zero fault impedance currents: phase currents of the transformer, transient short-circuit DC current, approximate expression of the DC short-circuit current, and accurate expression of the steady-state DC short-circuit current. The general calculation method used in the paper is extensible to any conversion unit with a double secondary transformer.

Radio-frequency impedance measurements using a tunnel-diode oscillator (TDO) technique

Abstract: A resonant method based on a tunnel-diode oscillator (TDO) for precision measurements of relative impedance changes in materials, is described. The system consists of an effective self-resonant LC-tank circuit driven by a forward-biased tunnel diode operating in its negative resistance region. Samples under investigation are placed in the core of an inductive coil and impedance changes are determined directly from the measured shift in resonance frequency. A customized low temperature insert is used to integrate this experiment with a commercial Model 6000 Physical Property Measurement System (Quantum Design). Test measurements on a manganese-based perovskite sample exhibiting colossal magneto-resistance (CMR) indicate that this method is well suited to study the magneto-impedance in these materials.

Impedance shaping of three-phase grid-parallel voltage-source converters

Abstract: This paper presents techniques to shape the output impedance of three-phase voltage-source converters (VSC) used as inverters for grid integration of renewable energy and energy storage devices. The objective is to avoid harmonic resonance and other unintended interactions between the inverter and the grid impedance. For this purpose, the inverter is modeled by a positive-sequence and a negative-sequence output impedance. Shaping of the inverter output impedance is achieved through changes to various inverter control functions, including grid synchronization and current control. The trade-off between grid compatibility and inverter control performance is also discussed. Experimental results from a multi-converter system test-bed are presented to validate the analyses.

Analysis of stacked microstrip patches with a mixed potential integral equation

Abstract: A method based on the mixed potential integral equation for the analysis of flat microstrip antennas in a double-layer substrate is presented. The method is used to compute the input impedance of a stacked patch configuration. This structure permits a larger bandwidth and may also provide dual-frequency operation. The Green's functions are discussed in detail, and numerical results are obtained for the propagation constant of the dominant surface wave. Theoretical and experimental results are compared for a dual-frequency and a broadband stacked patch antenna. Theoretical results for the input impedance are in good agreement with measurements. The difference between theoretical and experimental results for the resonant frequency is less than 4.5% in all cases. >

Indirect current monitoring via voltage and impedance monitoring

Abstract: Electrical circuitry for monitoring the current flow through resistance elements on the leading edge of an aircraft wing or horizontal stabilizer. The resistance elements are individually and sequentially activated for heating to thereby effect a de-icing or anti-icing function. The non-activated elements are sensed by the circuitry to determine inferentially if there is a predetermined current flow through the heating elements to achieve the intended de-icing or anti-icing function.