High-frequency Input Impedance Research Articles

A novel fault monitoring method based on impedance estimation of power line communication equipment

Due to the close relationship between power grid fault and impedance, there is a significant defect in the use of power line communication (PLC) equipment to monitor and locate power grid faults, which is the lack of real-time impedance information. Therefore, this study proposes a new fault monitoring method based on impedance estimation of power line communication equipment. The channel frequency response (CFR) obtained from the PLC receiver is used to estimate the high-frequency input impedance to monitor and locate the ground fault of the power grid in real time. Firstly, based on the multi-conductor transmission line theory, bottom-up channel modeling method and impedance estimation technology, the basic principles of fault monitoring and location methods are clarified. Then, modeling and analysis of cables in different situations are carried out, and the characteristics of the factors affecting the impedance in CFR are extracted by variational modal decomposition (VMD), and the estimation results of impedance are obtained by inversion analysis. Based on this, the impedance change and machine learning algorithm are used to track and identify the abnormal state of the power line to achieve high-sensitivity positioning of the cable fault. The simulation results show that the method has a good identification effect on high and low impedance cable fault, and has a better effect on low resistance fault monitoring. The fault location error is less than 2.13%, and has a good positioning accuracy.

Measurement of IGBT High-Frequency Input Impedance in Short Circuit

Insulated-gate bipolar transistors (IGBTs) operated in short circuit become instable in certain driving and load conditions. The induced oscillations can compromise robustness and reliability of the entire power converter. The stability of the device inserted in a real system can be analyzed using the theory of linear oscillators that requires the knowledge of input or output impedance of the device in real operating conditions. In this paper, we present an experimental procedure for measuring in pulsed mode the small-signal impedance of a power device biased in any test conditions. The small-signal input impedance of a 650-V 20-A IGBT operated in short circuit has been measured as a function of the frequency. This input impedance has been used to extract the stability map of the IGBT in short circuit, which allows us to easily predict the test conditions where the IGBT becomes instable. The validity of this stability map has been confirmed by a large-signal time-domain characterization of the IGBT operated in short circuit. The proposed technique is very useful to design driving circuit able to avoid instable operations.

High frequency input impedance modeling of low-voltage residential installations - influence on lightning overvoltage simulations results

The overvoltage level of a system is strongly dependent on the connected loads and with more precise models, better and more reliable simulation results are obtained. This paper presents the input impedance characteristics, measured over a wide range of frequencies, of various actual low-voltage residential installations. The measured frequency responses were fitted by effective RLC models and a general model was also developed. The range of frequencies considered in the study, nearly d.c. up to 5 MHz, allows the use of these models for lightning or switching studies. It is also presented overvoltage simulations, using different residential installations models presented in the paper, of a distribution network subjected to lightning surges on the medium voltage circuit.

A simple formula for the high frequency input impedance of the circular thin wire loop antenna

A formula is derived for the high frequency input impedance of a circular thin wire loop antenna. It allows for fast simulations, because it involves little numerical work, contrary to the previous models. A closed form is given for the first time, which can be written in a circuit simulator, for matching near the loop's second resonance. Simulation results compare well with published data, in the case of a thin wire.

High-frequency input impedance characterization of dielectric films for power-ground planes

Broadband impedance characterization of high dielectric constant (high-k) films was performed using a coaxial test fixture configuration. The presented coaxial test fixture and broadband measurement methodology of impedance for high-k films minimizes systematic uncertainties by reducing the interconnection inductance and improving the calibration procedure. In the APC-7 configuration, the technique enables accurate evaluation of impedance at frequencies of 100 MHz to 10 GHz with resolution of 0.01 /spl Omega/. The electrical characteristic of high-k films was found to be consistent with a capacitive load without significant contribution from the circuit inductance that typically dominates the high-frequency response. The experimental data and numerical simulations showed that high-k organic-ceramic composite materials could considerably suppress resonant behavior of the power-ground planes. It was found that high-k organic resins filled with ferroelectric ceramic powders exhibit a high-frequency dielectric loss that increases with increasing volume fraction of the ceramic component. The dielectric dispersion and the corresponding dielectric loss of organic-ceramic hybrid materials can serve as an effective mechanism for suppressing the resonant standing waves in power-ground planes.

High-frequency respiratory input impedance measurements in infants assessed by the high speed interrupter technique.

High-frequency input impedance (Z(f)) measurements, including antiresonances, provide useful noninvasive information on airway geometry and especially airway wall mechanics in the canine and human adult respiratory system. A knowledge of airway wall mechanics would be particularly important in understanding flow limitation phenomena in infants. High-frequency Z(f) has not been measured in infants above 256 Hz, because the high impedance of the infantile respiratory system would be expected to result in low amplitudes of oscillatory flow at higher frequencies. The aim of this study was to develop a technique to measure high-frequency Z(f) in infants and to elucidate the nature of the antiresonance phenomena in the Z(f) spectrum in infants. Z(f) was measured from 32-900 Hz during rapid airflow interruption by the high-speed interrupter technique (HIT) in 18 infants (aged 24-149 weeks) with wheezing disorders. The HIT enables the excitement of higher flow amplitudes at high frequencies using a pseudostep forcing function. In all infants Z(f) showed a mean (SD) first antiresonance (far,1) of 172 (35) Hz (real part of Z(f) at far,1 (Z(f)re(far,1)): 4.9 (1.1) kPa x L(-1) x s) and in five infants a second antiresonance (far,2) of 564 (51) Hz (Z(f)re(far,2): 2.0 (0.7) kPa x L(-1) x s). The antiresonances were found to be related to wave propagation in the airways (acoustic antiresonances), because they increased by a factor of approximately 2 when He-O2 was inhaled. This implies that far,1 and its harmonics are a function of airway wall compliance. In conclusion, the first and second antiresonances may be helpful in understanding flow limitation in wheezing disorders in infants, because flow limitation is related not only to airway diameter but also to airway wall compliance.

Differences in airway wall compliance as a possible mechanism for wheezing disorders in infants

High-frequency input impedance measurements (Z(f)) provide useful noninvasive information on airway geometry and especially airway wall mechanics in the canine and human adult respiratory system. Using the high-speed interrupter technique (HIT), we have shown that it is possible to measure high-frequency Z(f) in infants up to 900 Hz, including antiresonant phenomena which are known to be related to wave propagation velocity. This implies that the first antiresonant frequency (far,1) is a function of airway wall compliance. Since, airway wall mechanics are particularly important for the flow limitation phenomena, we wondered whether we could find evidence that airway wall properties were important for the occurrence of flow limitation during incremental methacholine challenge in infants. We measured Z(f) from 32-900 Hz and maximal flow at functional residual capacity (V'maxFRC) by the rapid chest compression technique in 10 infants (aged 36-81 weeks) with wheezing disorders. far,1 increased significantly at very low doses of mch before any decline could be detected in V'maxFRC. We hypothesize that these changes in far,1 are determined by mch-induced decrease in airway wall compliance. High-speed interrupter technique in combination with rapid chest compression technique can be used to study developmental differences in airway function (particularly of airway wall properties) and their contribution to airway disease and response to bronchodilator therapy in infants.

Human respiratory impedance from 8 to 256 Hz corrected for upper airway shunt

Respiratory input impedance (Zrs) was measured from 8 to 256 Hz in 10 healthy subjects by a method that eliminated the shunt impedance of extrathoracic airway walls. It consisted of combining the data obtained with a pressure input at the mouth (standard method, Zst) and with a pressure input around the head (Zhg) Zrs = Zst.(Zp + Zhg)/(Zp + Zst) where Zp is the impedance of the mouthpiece and pneumotachograph. Large quantitative differences were observed between Zrs and Zst, demonstrating that the standard method is unreliable at such frequencies. The real part of Zrs increased from 2.6 +/- 0.8 cmH2O.l-1.s at 8 Hz to a maximum of 38 +/- 19 cmH2O.l-1.s at 158 +/- 49 Hz. The imaginary part exhibited a maximum of 19 +/- 8 cmH2O.l-1.s at 126 +/- 38 Hz, a resonance at 157 +/- 43 Hz, and a minimum of lambda 19 +/- 16 cmH2O.l-1.s at 185 +/- 45 Hz. The data were analyzed with five models featuring alveolar gas compressibility; tissue resistance, inertance, and compliance; and different representations of the airways with lumped and distributed parameters. All except the simplest (lumped frequency-dependent resistance) fitted the data equally well, but none provided reliable estimates of gas compliance. Three models gave a consistent description of the airway in terms of equivalent rigid tubes (cross-sectional area 3.5-3.7 cm2, length 47-51 cm). We conclude that high-frequency input impedance could prove useful in exploring the airways but not the peripheral lung.

Frequency dynamics of arterial autoregulation.

In anesthetized dogs the low-frequency input impedances (0.001 to 0.1 Hz) of different arterial beds were measured. The following arteries were perfused with blood by a servocontrolled pump in different experiments: Femoral, renal, superior mesenteric, and circumflex branch of the left coronary artery. Step and sinusoidal flow changes were used as input patterns. Furthermore, in the femoral artery the high-frequency input impedance was calculated from pulsatile pressure and flow. The pressure reactions to flow changes were interpreted by assuming a lead-lag autoregulatory control system consisting of two opposing components. The time constants of the two components were found to have characteristic values in different arterial beds and may vary depending on the condition of the experiment. The magnitude of the response usually depends on the mean perfusion pressure, indicating a nonlinear behaviour of the system. Furthermore in the renal artery a characteristic delayed pressure increase was observed after short flow impulses. It is interesting to compare the general pattern of the pressure reaction to the input flow with the force response to stretch which, according to the literature, can be observed in certain striated muscle preparations. The mechanisms underlying the autoregulatory reactions described in this study appear to be, at least in part, a general feature of contractile tissues.