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.

Low-Frequency Stability Analysis of Single-Phase System With dq -Frame Impedance Approach—Part I: Impedance Modeling and Verification

Abstract: The utilization of a large number of power electronic converters in the high-speed railway system results in the low-frequency instability for the single-phase vehicle-grid system. In order to probe into the problem, the impedance-based approach is adopted. This paper focuses on the dq -frame impedance modeling and verification of the single-phase converters in the electric multiple units. The closed-loop input impedance modeling methods for both single converter and interleaved converters considering the second-order generalized integrator-based phase-locked loop (PLL) are put forward. Then, the dq -frame impedance measurement method for single-phase systems based on the Hilbert transform is proposed, and the modeling approach is verified by the frequency-domain simulations on the switching models. The good agreement of the model and simulation illustrates that the modeling method is suitable and accurate enough until half of the switching frequency. It is elucidated that the single-phase rectifier's impedance has the off-diagonal characteristic and the negative-impedance characteristic on the dd channel at low frequencies. Moreover, both the current and voltage controls have influences on the negative impedance shaping, while PLL does not.

Eddy current loss measuring sensor, thickness measuring system, thickness measuring method, and recorded medium

Abstract: A thickness measuring system comprises: an eddy current loss measuring sensor having an exciting coil for receiving a high frequency current to excite a high frequency magnetic field to excite an eddy current in a conductive film, and a receiving coil for outputting the high frequency current which is influenced by an eddy current loss caused by the eddy current; an impedance analyzer for measuring the variation in impedance of the eddy current loss measuring sensor, the variation in current value of the high frequency current or the variation in phase of the high frequency current on the basis of the high frequency current outputted from the receiving coil; an optical displacement sensor for measuring the distance between the conductive film and the eddy current loss measuring sensor; and a control computer including a thickness calculating part for calculating the thickness of the conductive film on the basis of various measured results of the impedance analyzer and optical displacement sensor, and the eddy current loss measuring sensor further has a ferrite member surrounding the exciting coil and the ferrite member has an opening in the bottom surface portion thereof for allowing the exciting coil to be exposed.

Harmonic impedance measurement using three-phase transients

Abstract: In this paper, a technique is presented for measuring the harmonic impedances of an unbalanced three-phase distribution feeder. The technique uses transients in bus voltages and feeder currents generated by several close-trip operations of the shunt capacitor bank. The work is based on the assumption that the impedance of the feeder does not change over time during which the switching operations are performed. Mathematical development of the technique is verified with the laboratory and the field tests. The technique provided good measurements of the harmonic impedances up to 1.5 kHz for the given capacitor sizes. Statistical indices were developed to assess the accuracy of the estimated impedance values.

A new method of on-line grid impedance estimation for PV inverter

Abstract: The recent increase in photovoltaic (PV) installations calls for new and better power quality requirements with respect to connection to the grid supply. Therefore, different methods are typically used for continuous grid monitoring, usually by using external devices. In this paper a new method for on-line measuring the grid impedance is presented. The presented method requires no extra hardware being accommodated by typical PV inverters, sensors and CPU, to provide a fast and low cost approach of on-line impedance measurement. By injecting a noncharacteristic harmonic current and measuring the voltage grid response it is possible to evaluate the grid impedance. Practical test on an existing PV inverter validate the new method.

Energy harvesting from vibration using a piezoelectric membrane

Abstract: In this paper we investigate the capability of harvesting the electric energy from mechanical vibrations in a dynamic environment through a unimorph piezoelectric membrane transducer. Due to the impedance matrices connecting the efforts and flows of the membrane, we have established the dynamic electric equivalent circuit of the transducer. In a first study and in order to validate theoretical results, we performed experiments with a vibrating machine moving a macroscopic 25 mm diameter piezoelectric membrane. A power of 1.8 mW was generated at the resonance frequency (2.58 kHz) across a 56 kQ optimal resistor and for a 2 g acceleration.