Topic
Output impedance
About: Output impedance is a research topic. Over the lifetime, 11185 publications have been published within this topic receiving 134949 citations.
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05 Nov 2015
TL;DR: Based on a review of existing measurement methods, the paper presents an extended measurement method, which is able to address both harmonic levels and harmonic current emission limits, and the application is illustrated by two example measurements in different low voltage grids.
Abstract: Harmonic levels and their propagation in the power system are mainly determined by the network harmonic impedance. It is also an essential parameter for the calculation of harmonic current emission limits. Different methods for measuring the network harmonic impedance have been developed in the last decades, but all of them assume that the impedance is constant within a cycle at fundamental frequency, which is true in case of passive elements only. As nowadays most of the equipment in low voltage grids contains power electronics including rectifier circuits, network harmonic impedance will vary within a half cycle of power frequency. As more and more equipment operates with switching frequencies of several ten kHz, knowledge about the network harmonic impedance in the frequency range up to 150 kHz is also of significant importance. Based on a review of existing measurement methods, the paper presents an extended measurement method, which is able to address both, above mentioned issues. The application of the method is illustrated by two example measurements in different low voltage grids.
46 citations
01 Jan 2000
TL;DR: In this paper, a power electronic circuit is used to inject a small current disturbance onto the energized power network, and the measurements of the disturbance current and resultant voltage transient are used to identity impedance.
Abstract: This paper describes a method for on-line measurement of power system impedance to source. The method employs a power electronic circuit to inject a small current disturbance onto the energised power network, and the measurements of the disturbance current and resultant voltage transient are used to identity impedance. Simulation results demonstrate the effectiveness of the technique for identification of the impedance of transmission lines and linear loads. An alternative data processing technique is introduced in order to address the measurement problems associated with nonlinear loads. This technique is also illustrated using simulation.
46 citations
Patent•
19 Aug 1996TL;DR: In this article, the reactance component of the impedance is modeled as a resistor in series with a capacitor, and a response voltage is measured across the load to estimate a transfer function between them, which results in estimation of the actual resistance and capacitance components of the true impedance.
Abstract: Impedance across a load, such as a pair of face-to-face electrodes and/or a patient's transthoracic and transmyocardial impedance, respectively, is modeled as a resistor in series with a capacitor, wherein the reactance component of the impedance equals 2 π*frequency/capacitance. A reference square wave voltage is applied to the load in series with a selected load resistor, and a response voltage is measured across the load. Both the reference voltage and the response voltage are then used to estimate a transfer function between them. Equating this transfer function to a resistor-capacitor circuit model results in estimation of the actual resistance and capacitance components of the true impedance. Alternately, the impedance may be measured with a high current load, such as during a defibrillator discharge. In this case, the voltage input and outputs are sampled at a much faster rate for the resistance component estimation, with the capacitance initialization adapted for the specific type of defibrillator waveform input.
46 citations
TL;DR: A fully differential (zero common-mode voltage) op amp has been developed which has low output impedance, but unlike source-follower output stages, it has a large output swing, namely, 8 V/sub p-p/ for 1-k Omega load and a 5-V supply.
Abstract: A fully differential (zero common-mode voltage) op amp has been developed which has low output impedance, but unlike source-follower output stages, it has a large output swing, namely, 8 V/sub p-p/ for 1-k Omega load and a 5-V supply. The output stage, which is a combination of common-source and source-follower stages, is driven by the two complimentary outputs of the differential-output input stage. A continuous-time common-mode feedback circuit has been used, which due to the op amp's low output impedance, causes negligible open-loop gain (95 dB) degradation. Floating compensation capacitors are used in order to reduce the capacitance value and, hence, the area (490 mil/sup 2/). >
46 citations
TL;DR: In this paper, the authors proposed a power-dependent impedance surface, which consists of a lattice of modified slotted mushroom-like cells loaded with varactor diodes and lumped circuits.
Abstract: Impedance surfaces are artificially designed periodic structures that support surface waves. This paper presents a novel concept of a nonlinear impedance surface, whose impedance increases with the surface wave power. The proposed surface consists of a lattice of modified slotted mushroom-like cells loaded with varactor diodes and lumped circuits. The circuits are designed to sense the incoming surface wave power and feed back the signal to control the bias of the varactors, which eventually tunes the surface impedance. Such proposed power-dependent impedance surface has been demonstrated by a prototype consisting of $4 \times 10$ cells. It is observed from the experiments that as the power varies from 16 to 27 dBm, the surface exhibits a surface impedance range as much as j385 to j710 $\Omega$ . This characteristic enables the surface to be potentially useful in self-trapping surface-wave waveguide, power-dependent beam-steering antenna reflector, and other nonlinear applications.
46 citations