Output impedance

About: Output impedance is a research topic. Over the lifetime, 11185 publications have been published within this topic receiving 134949 citations.

New synchronization method for thyristor power converters to weak AC-systems

Abstract: An improved approach to obtaining good zero-voltage-crossing signals is presented. These signals are subsequently used as synchronization signals for a phase-controlled thyristor power converter. Detection of accurate zero crossings is possible even when there are large frequency changes, sudden load changes, or large commutation overlap angles. The improved accuracy in the integrity of the zero crossing is obtained by reconstructing a voltage representing the AC source voltage. This voltage is determined from the distorted thyristor converter input voltage, the converter input current, and an online identification of the source impedance using a microcontroller-based adaptive algorithm. The improvement provided by the new zero crossing detection scheme is verified experimentally. >

Shared-bus current sharing parallel connected current-mode DC to DC converters

Abstract: A power system consisting of parallel connected current-mode power converters combined with a voltage error signal on a shared-bus used in common for controlling all of the power stages for improved consistency, reliability, and performance in both transient and steady states. Near uniform current sharing is achievable without sacrificing the voltage regulation performance. The improved system offers faster settling time under step loads, consistent small signal characteristics and large signal responses regardless of mismatches of components values such as reference voltages, and reduced output impedance variations in magnitude and phase even during various modes of operation.

Multi-frequency EIT system with radially symmetric architecture: KHU Mark1.

Abstract: We describe the development of a multi-frequency electrical impedance tomography (EIT) system (KHU Mark1) with a single balanced current source and multiple voltmeters. It was primarily designed for imaging brain function with a flexible strategy for addressing electrodes and a frequency range from 10 Hz–500 kHz. The maximal number of voltmeters is 64, and all of them can simultaneously acquire and demodulate voltage signals. Each voltmeter measures a differential voltage between a pair of electrodes. All voltmeters are configured in a radially symmetric architecture in order to optimize the routing of wires and minimize cross-talk. We adopted several techniques from existing EIT systems including digital waveform generation, a Howland current generator with a generalized impedance converter (GIC), digital phase-sensitive demodulation and tri-axial cables. New features of the KHU Mark1 system include multiple GIC circuits to maximize the output impedance of the current source at multiple frequencies. The voltmeter employs contact impedance measurements, data overflow detection, spike noise rejection, automatic gain control and programmable data averaging. The KHU Mark1 system measures both in-phase and quadrature components of trans-impedances. By using a script file describing an operating mode, the system setup can be easily changed. The performance of the developed multi-frequency EIT system was evaluated in terms of a common-mode rejection ratio, signal-to-noise ratio, linearity error and reciprocity error. Time-difference and frequency-difference images of a saline phantom with a banana object are presented showing a frequency-dependent complex conductivity of the banana. Future design of a more innovative system is suggested including miniaturization and wireless techniques.

High impedance, low polarization, low threshold miniature steriod eluting pacing lead electrodes

Abstract: A small diameter, unipolar or bipolar, atrial or ventricular transvenous or epimyocardial pacing lead with a porous, platinized, steroid eluting cathode electrode exhibiting an effective surface area in the range of 0.1 to 4.0 mm 2 , preferably 0.6 to 3.0 mm 2 , provides low stimulation thresholds in the range of 0.5 volts, 0.5 milliseconds, very high pacing impedance (800 to 2,000 Ω), relatively low polarization, good to excellent sensing, and adequately low source impedance. The high pacing impedance prolongs the longevity of pacing pulse generators and allows for the miniaturization of their components. The low thresholds allow large safety factors at low applied voltages, which also contribute to increased battery longevity.

MIMO-Identification Techniques for Rapid Impedance-Based Stability Assessment of Three-Phase Systems in DQ Domain

Abstract: Grid impedance and the output impedance of grid-connected inverter are important parameters for the operation of grid-connected systems, such as solar, wind, and other distributed-generation resource systems. The impedance mismatch between the grid and the interfacing circuit often generates harmonic resonances that lead to reduced power quality and even instability. Since the impedances usually vary over time as a function of many parameters, online measurements are required for stability assessment and adaptive control of the inverters. Several methods have been proposed for quick, accurate measurements of impedances, but the use of multiple-input multiple-output (MIMO) identification techniques have not been considered. Applying the MIMO techniques, different components of the inverter output impedance or grid impedance can be simultaneously measured during a single measurement cycle. Therefore, the operating conditions of the system can be kept constant during the measurements, and the overall measurement time is significantly reduced. This paper shows the use of orthogonal binary sequences to simultaneously measure the “d” and “q” components of grid-connected inverter output impedance and/or grid impedance. Experimental results based on a three-phase grid-connected inverter are presented and used to demonstrate the effectiveness of the proposed methods.