System Impedance Research Articles

Sequence component direction element based on power frequency variation

Unlike the relatively stable network structure of the transmission and distribution network, under the new distribution network, resulting in errors in the impedance tuning of the fault directional element, misjudgment of the fault directional element, and a decrease in sensitivity. For this reason, this paper proposes a sequence component adaptive fault directional element based on power frequency variation. The sequence impedance amplitude is calculated through the measured values of the voltage sequence component and the current sequence component of the relay location. Then the phase angle of the setting impedance is determined according to various sequence components in the system. It improves the problem that the setting impedance of power frequency distance directional element is greatly affected by the amplitude and phase angle fluctuation of distribution system impedance and line impedance. The reliability and stability of the sequence component adaptive fault directional element based on the power fresquency variation are verified by Matlab simulation.

Pregled metoda za eliminisanje uticaja sistemske smetnje u aktivnom visokonaponskom postrojenju

In this paper, practical and conceptual problems related to the way of suppressing or eliminating the influence of interference (at a frequency of 50 Hz) in an active high-voltage power facility are discussed. The problem is relevant in the context of measuring the safety characteristics of the grounding system: grounding system impedance, touch voltage and step voltage. The paper gives an evolutionary overview of title methods. The review focuses on the characteristic problems and shortcomings of individual methods. Also, the basic characteristics of the author's FSM (Frequency Shift Method) method, which guarantees precise control of interference, are elaborated. In this sense, the FSM method is the basis for accurate and economical measurement of the safety characteristics of the grounding system.

Impulse Oscillometry as a measure of airway dysfunction in Sarcoidosis.

Background:Sarcoidosis is a systemic inflammatory granulomatous disease which commonly affects intrathoracic lymph nodes, lung parenchyma and airways.Objectives:To measure respiratory impedance using Impulse Oscillometry (IOS) in patients with pulmonary sarcoidosis and compare the parameters with healthy controls.Methods:Patients diagnosed with sarcoidosis (n=28); and age and gender matched healthy controls (n=17) were recruited. Lung volumes and capacities were measured by spirometry and respiratory system impedance was assessed using Impulse Oscillometry System (IOS). Measurements were performed before and 15 minutes after inhalation of a short acting bronchodilator. The IOS and spirometric parameters were compared between two groups and correlated. ROC curve analysis was also performed to identify the IOS parameters which can discriminate between sarcoidosis and healthy controls.Results:Resistance at 5 and 20 Hz (R5 and R20), small airway resistance (R5-R20), resonant frequency (FRes) and area of reactance (AX) were significantly higher in Sarcoidosis subjects compared with controls. Reactance at 5 and 20 Hz (X5 and X20) were significantly lower in sarcoidosis. FEV1 (% predicted) and FVC (% predicted) were significantly lower in patients with sarcoidosis while FEV1/FVC ratio and peak expiratory flow rate (PEF) values were comparable. Post bronchodilator inhalation, there was improvement in airway resistance and reactance, but no significant changes observed in spirometric parameters. R5, X5 and R5-R20 are promising parameters to discriminate sarcoidosis from healthy controls.Conclusion:Increased airway resistance is a better indicator of airway involvement than airflow limitation by spirometry in pulmonary sarcoidosis.

Power System Impedance Estimation Using a Fast Voltage and Current Changes Measurements

Equivalent power system impedance is an important electrical quantity from many points of view. Areas in which this parameter plays an important role include, in particular: Voltage stability analysis, power quality, or fault condition analysis. Power system impedance estimation in real operation conditions can be performed by one of the non-invasive methods described by different authors. This paper aims to investigate and compare seven different methods for power system impedance estimation based on voltage and current variations measurement. After a brief description of selected methods, these methods were applied for power system impedance estimation in the case of two simple simulation tests and then in the case of three real measured data. Voltage and current changes used for power system impedance estimation in real conditions were measured in high voltage (HV) and medium voltage (MV) substations feeding steel mill with the electric arc furnace (EAF) operation. As the results presented in this paper have shown, not all of the methods analyzed are suitable for determining the power system impedance based on the fast step changes of voltage and current that occur, for example, during an EAF operation. Indeed, some of the tested methods were originally designed to determine the power system impedance from changes in voltages and currents recorded at steady state.

The characteristic acoustic impedance of the thermodynamic ideal system and its “excess” for a non-ideal mixture

The characteristic acoustic impedance is sometimes discussed in terms of molecular interactions in liquid mixtures. Commonly, the mole-fraction-weighted average of the characteristic impedances of the pure components of the mixture serves as a reference function for the impedance deviation. The latter is sometimes called an “excess”. Such deviations, however, lack physical meaning. In the paper, the thermodynamic correct formulae for the characteristic impedance of the thermodynamic ideal mixture were reported and discussed. In these formulae, the isobaric thermal expansibilities and the heat capacities of pure components are considered. Four examples illustrate substantial differences between the specific impedance deviations calculated in the conventional and thermodynamic correct manner.

Investigation of dielectric behavior in Ni0.7-xZn0.3MxFe2O4 (M=Mn/Co/Cu) ferrites by impedance spectroscopy

The electrical characteristics of the Mn/Co/Cu-substituted Ni–Zn ferrites prepared using the citrate technique have been explored in detail by ac impedance spectroscopy. Measurements between temperatures (373K–523 K) were observed over a broad frequency range of 100 Hz–1 MHz. Maxwell and Wagner's model was used to analyze the frequency dependence of dielectric parameters. Dielectric loss tangent versus frequency plots show relaxation peaks due to the coincidence of the frequency of charge hopping between the localized state and the outer field. The Cole-Cole curve was designed to investigate the complex impedance of the current systems. Two semicircles corresponding to the grain and grain boundary were observed. The investigation of the electrical modulus includes the electrical relaxation of the non-Debye form. The substitution of Ni ions by Mn/Co/Cu ions indicates a major improvement in the dielectric characteristics of Ni − Zn ferrite. The Ni–Zn–Cu ferrite series displays the best dielectric properties suggesting the capability of this series to be suitable for high-frequency devices.

Rapid Multivariable Identification of Grid Impedance in DQ Domain Considering Impedance Coupling

Identifying grid impedance at the point of common coupling is essential for the adaptive control and the online stability analysis of grid-connected converters. A balanced three-phase system is commonly modeled by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> components in the synchronous reference frame. In identification of the synchronous reference-frame impedance components, errors may occur due to the coupling of the system impedances; for example, a measurement injection that is intended to perturb only the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> -channel current may also perturb the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -channel current, thus distorting the impedance measurements. Traditionally, sequentially performed measurements, where different injections are performed one after another at the same frequencies, have been required to tackle the impedance coupling. However, the sequential measurements are prone to changes in the operating conditions between the measurements. This article proposes a method to simultaneously obtain all the grid-impedance components within a single measurement cycle with no coupling effect. In the method, two orthogonal binary injections are simultaneously injected into the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> current references of the inverter controller. Then, a frequency-domain interpolation technique is applied to adjust the measured current and voltage responses. As a result, the impedance coupling is avoided in the measured grid impedance. The proposed technique is validated by experimental measurements.

Methodology of solution for the distribution network reconfiguration problem based on improved harmony search algorithm

The topology of power distribution systems can be modified by altering the status of sectional and tie switches for load management and protection, while maintaining the required network radiality. Several effective optimisation algorithms and graph theory-based techniques for system radiality detection have been proposed in specialised literature to solve the distribution network reconfiguration problem, usually seeking to achieve power loss reductions and voltage profile improvements. This work aims to contribute to this line of research and its novelties are composed of proposing as solution method a methodology based in an enhanced version of harmony search metaheuristic called improved harmony search algorithm, and a new simple and effective system impedance matrix based process to detect islanding of nodes as a strategy to meet radiality constraint. The proposed methodologies were applied to 33-bus, 84-bus and 118-bus distribution networks known from technical literature, aiming to total active power loss minimisation. As comparison between methods, a key focus in analysis of results is related to discuss some advantages and effectiveness of improved harmony search over original harmony search algorithm to attain optimal radial topologies.

Assessing system impedance based on data regrouping

Assessing system impedance based on data regrouping

200W급 철도 분기부 유도 발열 히팅장치의 임피던스를 고려한 설계 연구

동절기 철도 교통시스템에서 열차의 진행방향으로 선로를 전환시키는 분기기가 적설과 결빙으로 인하여 오작동 할 수 있고 이는 열차 지연 및 사고를 유발한다. 이를 예방하기 위하여 현재 국내에는 전열선을 이용한 분기부 히팅장치가 설치되어 있으나 오래된 기술로 여러가지 단점을 가진다. 본 논문에서는 기존의 방식보다 효율성이 높은 유도발열 방식을 이용한 200W급 히팅장치를 3D 유한요소법을 이용하여 설계 및 제작하였다. 제작된 히팅장치 시작품의 임피던스를 측정하였고 200W의 전력을 히팅장치에 공급하였다. 하지만 PCB 코일의 전류밀도[A/㎟]를 초과하게 되는 낮은 임피던스 값이 측정되었고 이는 PCB 코일의 과전류 인가로 인한 파손을 유발하기 때문에 히팅장치의 파손 예방을 위한 임피던스 조정이 필요하게 되었다. 따라서 임피던스 조정을 위한 PCB코일 구조 변경 설계 방향을 제안한다.

Failure of SCS MR-Conditional Modes Due to High Impedance: A Review of Literature and Case Series.

IntroductionMagnetic resonance imaging (MRI) conditional modes are a novel feature for certain Food and Drug Administration (FDA)-approved spinal cord stimulation (SCS) devices. However, there is a paucity of literature around the limitation of MRI-conditional modes (“MRI safe”), specifically in clinical scenarios where urgent MRIs may be needed. One such limitation is load impedance, referring to the circuit’s resistance to the current being generated by the system. High impedance can limit the MRI-conditional mode capability, presenting potential harm to a patient undergoing an MRI or make an MRI unable to be completed.MethodsThree cases were identified, and informed consent was obtained. All information was obtained via retrospective chart review.ResultsIn this case series of three patients where MRI-conditional SCS systems were unable to be placed in “MRI safe” settings, preventing timely MRI study completion in the setting of high impedance, all three were required to undergo alternative imaging including CT scans, and two patients ultimately had the system explanted and one chose to be re-implanted after completion of scans.ConclusionThis case series highlights the need for further investigation of impedance in SCS systems and potential limitations for future MRI usage. The review of literature of impedance in SCS shows both device- and physiologic-related etiologies for changes in impedance that warrant consideration by the implanting physician.

An Impedance Matching Method for LC Passive Wireless Sensors

This paper presents an impedance matching method for increasing the readout distance of an inductor-capacitor (LC) passive wireless sensor. When the impedance of the LC sensor system is equal to that of the measurement system, there is no reflection between the LC sensor system and the measurement system, which maximizes signal-to-noise ratio and readout distance. Complex impedance matching networks at the readout port of the LC sensor system have been analyzed and simulated. The matching capacitor at the readout port is required to change with the sensing capacitor in the LC sensor in order to maintain the same resonant frequency in both readout port and LC sensor. The matching resistor at the readout port has been analyzed and optimized. A varactor-based capacitor was inserted as the matching capacitor, which can be controlled by a DC voltage so that the resonant frequency of the readout port can be scanned within the full range of resonant frequency in the LC sensor. A capacitive humidity sensor constructed from a planar spiral inductor and an interdigital capacitor was used here to demonstrate the proposed impedance matching method. It shows that the readout distance under the impedance matching is 1.5 times as long as that without the impedance matching. The impedance matching analysis gives in-depth insight into the LC sensor system behavior, and the results presented here suggest that the impedance matching method may be utilized the long distance readout of the scaled LC sensor application based on the S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> measurement.

Unbalanced responsibility division considering renewable energy integration

A reasonable division of the unbalanced contribution is the premise of responsibility division and mitigation. As a large amount of renewable energy integrates into the power system, the disturbance of the system increases and the system impedance is no longer much smaller than the load impedance. The traditional unbalanced responsibility division method is difficult to calculate accurately. This study proposes a new method for calculating unbalanced contribution, which can effectively avoid the limitations of traditional methods. The robust independent component analysis is used to estimate the equivalent source signal. The sparse component analysis method is used to construct the screening criterion to screen the equivalent source signals to obtain estimated signals that are more in line with the real source signals. Then the equivalent negative sequence impedance of upstream and downstream is calculated, and the unbalanced responsibility is divided. This method is still effective when the system impedance is not much different from the load impedance. At the same time, the calculation accuracy is high and the anti-interference ability is strong. Simulation and field test verify the correctness and effectiveness of the proposed method.

Real-time flow impedance evaluation method for ultra-fast early detection of aneurysmal diseases

ObjectiveA novel method to measure the real-time input flow impedance of thoracic aorta aneurysm (TAA) was developed. MethodsThe fundamental of real-time input flow impedance was described. The simultaneously measured blood pressure and volumetric flow rate were obtained and used for the calculation. The input flow impedance was then presented in its complexed format: real and imaginary; modulus and phase in the time domain. ResultsUnique features of real-time input flow impedance were extracted to correlate with the TAA formation. It showed that the trough of modulus located at the end of each cardiac cycle has different values, which are proportional to the sizes of TAAs. ConclusionsA real-time input flow impedance of the cardiovascular system was presented in this paper. We postulate that the proposed fluid mechanics model has the potential to analyze the pathomechanics of aneurysmal diseases in real-time.

Altered airway mechanics in the context of obesity and asthma.

The obesity epidemic is causing a rise in asthma incidence due to the appearance of an obesity-specific late-onset nonallergic (LONA) phenotype. We investigated why only a subset of obese participants develop LONA asthma by determining how obesity, both alone and in combination with LONA asthma, affects the volume dependence of respiratory system impedance. We also determined how obesity and asthma affect impedance during and following challenge with the PC20 dose of methacholine. We found during passive exhalation that all obese participants, in contrast to lean controls and lean asthmatics, experienced similarly profound elevations in lung elastance as they approached functional residual capacity. We also found, however, that the LONA asthmatics had a greater negative dependence of airway resistance on lung volume over the middle of the volume range compared with the other groups. Methacholine challenge with the PC20 dose led to comparable changes in respiratory system impedance in the four study groups, but the doses themselves were substantially lower in both obese and lean asthmatic participants compared with obese and lean controls. Also, the obese LONA asthmatics had higher breathing frequencies and lower tidal volumes postchallenge compared with the other participants. Taken together, these results suggest that all obese individuals experience substantial lung collapse as they approach functional residual capacity, presumably due to the weight of the chest wall. It remains unclear why obese LONA asthmatics are hyperresponsive to methacholine while obese nonasthmatic individuals are not.NEW & NOTEWORTHY Why only a subset of severely obese subjects develop late-onset nonallergic (LONA) asthma remains unknown, although it is widely assumed that compression of the lungs by the chest wall is somehow involved. We show that lung compression is common to obese individuals both without asthma and with LONA asthma but that those with LONA asthma may have increased airway wall compliance and possibly also a reduced ability to recruit collapsed lung.

Predictive Control Based DC Microgrid Stabilization With the Dual Active Bridge Converter

Dual-active-bridge (DAB) enabled dc microgrids stabilization is investigated in this article. DAB has two control objectives: load current regulation and the dc-bus voltage stabilization. In multiobjective control applications, the conventional proportional integrator (PI)-based controllers face challenges in the control loop coordination. The saturation of the loops largely deteriorate the control performance. Moreover, the system impedance has to be measured before designing the active damping control. In this article, a moving discretized control set—model predictive control (MDCS-MPC) is proposed for DAB. The proposed MDCS-MPC is inherently a good choice for multiobjective control. It provides several advantages, such as a good tradeoff between two control objectives and adaptive performance on system impedance. The evaluation and comparison of the proposed MDCS-MPC and PI are carried out. Experiments on a 270–270V, 20 kHz, 1 kW DAB converter are conducted to verify the theoretical claims.

Application of dual-stage exhaust system using an expansion chamber and resonator for formula SAE

Typical vehicle mufflers utilize a series of expansion chambers and resonators to reduce engine noise. Both components behave like acoustic filters by changing the impedance of the exhaust system. Expansion chambers act as low-pass filters, which mitigate noise above a cut-off frequency determined by the geometry of the chamber. Meanwhile, resonators target specific frequencies to attenuate like a notch-filter. The present work explored tuning a muffler system containing an expansion chamber and a resonator to reduce engine noise of a Formula SAE racecar. The exhaust system design was completed using custom MATLAB scripts, Ricardo WAVE, and iterative prototyping. After determining the frequencies where the engine produced maximum sound output, the components were fabricated to damp the amplitude of the offending frequencies. The transmission loss of the prototype exhaust system was tested in an anechoic chamber by measuring the frequency responses of each separate component and the entire system. Based on this experimentation, the exhaust system had an expected overall transmission loss of 45 dB. Installed on the vehicle, the operational transmission loss was 18 dB. This discrepancy is likely due to operational conditions that could not be replicated in the laboratory experiment, such as increased temperature and gas flow.

Harmonic effects optimization at a system level using a harmonic power flow controller

Increase of nonlinear loads in industries has resulted in high levels of harmonic currents and consequently harmonic voltages in power networks. Harmonics have several negative effects such as higher energy losses and equipment life reduction. To reduce the levels of harmonics in power networks, different methods of harmonic suppression have been employed. The basic idea in all of these methods is to prevent harmonics from flowing into a power network at customer sides and the point of common coupling (PCC). Due to the costs, none of the existing mitigating methods result in a harmonic-free power system. The remaining harmonic currents, which rotate in a power network according to the system impedances, may not necessarily result in an optimum harmonic power flow in terms of harmonic undesirable results such as harmonic losses or harmonic over voltage/current due to possible resonances. This paper proposes a new method to control the flow of the remaining harmonics at a power system level such that the effects of harmonics such as losses are optimized. This task is achieved by the use of series active power filters controlled in a different manner from their conventional methods. In this new application, the series active power injects a controlled harmonic voltage into a power system (e.g., a line, transformer, or other elements) to control the harmonic current (power) flow such that the overall performance of the power system is improved in terms of harmonic effects. The series active power filter in this new application is named as harmonic power flow controller (HPFC). In this paper, the theory, structure, applications, and the basics of the control method of a HPFC are described. To investigate the effects of the HPFC on the power network harmonics, an HPFC is used in the 14-busbar IEEE test system. To make the proposal more practical, an HPFC is designed for Iran north-west transmission system to alleviate the harmonic problem in this region. Simulations are carried out to show the effectiveness of the HPFC. Simulation results show that the HPFC can control the harmonic currents (power) and voltage consequently. In this paper, several control algorithms for an HPFC are also considered to achieve the desired harmonic voltages levels.

Intratracheal budesonide/surfactant attenuates hyperoxia-induced lung injury in preterm rabbits.

Recent clinical trials have shown improvements in neonatal outcomes after intratracheal administration of a combination of budesonide/surfactant (ITBS) in infants at risk of bronchopulmonary dysplasia. However, the effect of ITBS on lung function and alveolar structure is not known. We aimed to determine the effect of ITBS on lung function, parenchymal structure, and inflammatory cytokine expression in a relevant preterm animal model for bronchopulmonary dysplasia. Premature neonatal rabbits were administered a single dose of ITBS on the day of delivery and exposed to 95% oxygen. Following 7 days of hyperoxia, in vivo forced oscillation and pressure-volume maneuvers were performed to examine pulmonary function. Histological and molecular analysis was performed to assess alveolar and extracellular matrix (ECM) morphology, along with gene expression of connective tissue growth factor (CTGF), IL-8, and CCL-2. ITBS attenuated the functional effect of hyperoxia-induced lung injury and limited the change to respiratory system impedance, measured using the forced oscillation technique. Treatment effects were most obvious in the small airways, with significant effects on small airway resistance and small airway reactance. In addition, ITBS mitigated the decrease in inspiratory capacity and static compliance. ITBS restricted alveolar septal thickening without altering the mean linear intercept and mitigated hyperoxia-induced remodeling of the ECM. These structural changes were associated with improved inspiratory capacity and lung compliance. Gene expression of CTGF, IL-8, and CCL-2 was significantly downregulated in the lung. Treatment with ITBS shortly after delivery attenuated the functional and structural consequences of hyperoxia-induced lung injury to day 7 of life in the preterm rabbit.

Microelectrode Combinations of Gold and Polypyrrole Enable Highly Stable Two‐electrode Electrochemical Impedance Spectroscopy Measurements under Turbulent Flow Conditions

AbstractAn electrochemical impedance spectroscopy (EIS) sensor design is proposed based on a standard interdigitated electrode layout in which the smaller working electrode consists of gold (Au) whereas the larger combined counter and reference electrode is coated with a porous layer of polypyrrole (PPy) doped with polystyrene sulfonate (PSS) (PPy : PSS). Each electrode material was first characterized by EIS in a standard 3‐electrode setup with subsequent spectra fitting by a modified Randles equivalent circuit. The differences in the spectra obtained by the PPy : PSS coated electrodes can be explained by an increased electroactive surface area due to the porous polymer film. The changes in morphology of the film are discussed with respect to the evolution of the elements of the electric equivalent circuit. When applying the Au/PPy : PSS electrode combination to a standard 2‐electrode arrangement, the enlarged highly electroactive surface area of the PPy : PSS coating lowers the interfacial impedance in a way that mainly the gold working electrode contributes to the overall system impedance. Therefore, obtaining reproducible EIS signals depends only on the electrode's open‐circuit potential (OCP) and on additional adsorption events at the gold electrode/electrolyte interface. We present a protocol for microelectrode coating with PPy : PSS, which enables highly stable 2‐electrode EIS experiments without the need of a reference electrode. This combination is believed to be very useful if an integration of sensing electrodes inside Micro Total Analysis Systems is aspired.