System Impedance Research Articles

The study of the harmonic impedance measurement

Harmonic impedance of system is the important parameter for the harmonic suppression and it is also useful to the design of filter, circuit analysis, et al. Generally, a controllable harmonic perturbation is used and injected into the target circuit port, and then harmonic impedance can be captured by the corresponding harmonic voltage and current. In this paper, a circuit design of harmonic impedance measurement is proposed, in which each functional modules is comprised of analogue circuit, and it can generate a controllable current disturbance into the target system. The system impedance is calculated by using the current and the corresponding voltage, which are captured by the data acquisition circuits. By using the PSCAD, a simulation of measurement circuit is established. In simulation, the measuring results are coincident with the theoretical value, which validate the effectiveness of the circuit design.

Design of passivity‐based stabilized control of grid‐connected inverter system with LCL filter

AbstractInstabilities due to mutual interactions between inverters and grid impedance are observed sometimes. This paper proposes a new stabilization method, which improves the output frequency impedance characteristics, satisfying the Nyquist stability criterion. The principle is that the output impedance is designed to be passive with the feedfoward loop characteristics and the system is stable even for an unknown grid system impedance. The design principle for the proposed stabilization method is described and investigated and validated on the basis of simulation and experimental results.

Factors Associated With High-Voltage Impedance and Subcutaneous Implantable Defibrillator Ventricular Fibrillation Conversion Success.

The ability to predict defibrillation efficacy at the time of subcutaneous implantable cardioverter-defibrillator implantation without the need to induce ventricular fibrillation might eliminate the need for defibrillation testing. The purpose of this study was to determine the association of high-voltage impedance and system implant position on ventricular fibrillation conversion success with a submaximal 65-J shock. In the subcutaneous implantable cardioverter-defibrillator IDE study (Investigational Device Exemption), a successful conversion test required 2 consecutive ventricular fibrillation conversions at 65 J in either shock vector. Chest radiographs were obtained after implantation. Patients with imaging and impedance data were included. Suboptimal device position was defined as an inferior electrode or pulse generator or electrode coil depth >3 mm anterior to the sternum. Absence of suboptimal positional parameters was defined as appropriate position. Conversion success rate was calculated among all 65-J tests. Of 314 patients who underwent subcutaneous implantable cardioverter-defibrillator implantation, 282 patients were included in this analysis. There were 637 inductions to test defibrillation at 65 J. Sixty-two conversion failures (9.7%) occurred in 42 (14.9%) patients. Lower body mass index and lower shock impedance were associated with higher conversion success rate, whereas white race was associated with lower conversion success rate. Suboptimal position was more common in obese patients. Inferior electrode and greater distance between the lead and sternum were associated with a higher impedance. When appropriate system position was achieved, conversion failure was not associated with high body mass index. Subcutaneous implantable cardioverter-defibrillator shock efficacy is associated with system position and high-voltage system impedance. A high impedance is associated with inferiorly placed pulse generator and electrode system, inadequate coil depth, and a lower rate of defibrillator success. URL: https://www.clinicaltrials.gov . Unique identifier: NCT01064076.

Using circuit elements to represent the distributed parameters of a grounding system under lightning strokes

This work presents a proposal to represent electrical grounding systems directly in the time domain. The advantage in using this type of representation is that voltage and current are better understood in this domain, and the model can easily be inserted into conventional software such as the Alternative Transient Program (ATP). The proposed method is applied to horizontal electrodes, vertical rods and grounding grids. The grounding is initially modelled in the frequency domain to obtain harmonic impedance, which is then represented by means of an approximation in the time domain, by passive elements (resistors, inductors and capacitors) associated in series and/or parallel. Validation was achieved by comparing the results with those obtained using the TLM (transmission line model), the HEM (hybrid electromagnetic model) and technical literature. The TLM and HEM were used to obtain the harmonic impedance of the grounding systems, but any other model could have been used, since this process has no effect on the proposed method, making the proposed method very versatile and attractive.

Within-breath changes in respiratory system impedance in children with cystic fibrosis.

The aim of this study was to assess within-breath respiratory system impedance by the forced oscillation technique (FOT) in children with cystic fibrosis (CF) and relate it to the underlying lung disease. Thirty-three children with CF (median [range] age 12.0 [6-17] years) underwent FOT at 8 Hz during tidal breathing, multiple breath nitrogen washout (LCI), spirometry (FEV1), body plethysmography (RV/TLC), and magnetic resonance imaging (MRI). FOT outcomes included: mean inspiratory, expiratory, and whole breath resistance (R8INSP , R8EXP , R8TOT ) and reactance (X8INSP , X8EXP , X8TOT ), and the differences between X8INSP and X8EXP (ΔX8). Morphological changes were evaluated by MRI using CF-specific morphological scores. Spearman correlation was performed to examine the correlation between FOT indices and other parameters. FEV1 was negatively correlated with R8EXP (r = -0.52, P = 0.002) and ΔX8 (r = -0.55, P = 0.001), and positively correlated with and X8EXP (r = 0.56, P < 0.001). RV/TLC was positively correlated with R8EXP (r = 0.43, P = 0.013), and ΔX8 (r = 0.54, P = 0.001) and negatively correlated with X8EXP (r = -0.54, P = 0.001). We found poor correlation between FOT parameters and LCI and no correlation between FOT parameters and MRI scores. In children with CF, changes in within-breath FOT parameters are consistent with peripheral obstruction and dynamic airway compression, while they are not associated with ventilation heterogeneities and morphological alterations.

Low frequency sound absorption by compliant Helmholtz resonators

A traditional Helmholtz resonator is a rigid-walled cavity and an open neck, which result in one acoustic resonance. In this study, a soft-walled cavity with an open neck, a compliant Helmholtz resonator, is investigated for broadband and large absorption of sound at low frequencies. By applying the soft materials, the dynamics of the compliant walls and the material impedance are coupled to the acoustic pressure filed in the cavity. Thus the impedance of the compliant resonator system as seen by an incident acoustic wave is determined by the interaction of the wall dynamics, material properties, and acoustic domain. Compared to a traditional Helmholtz resonator with the same geometric dimensions, the compliant Helmholtz resonator exhibits multiple resonances with large absorption of sound. In addition, strategic design of the structural composition and the material selection leads to resonant behavior at frequencies lower than the conventional Helmholtz resonance. Through exploring an analytical model developed to characterize the resonator, the threshold on material and structural compliance to yield traditional Helmholtz behavior is also illuminated.

Inhibition effect of dissolved organic matter in secondary-treated municipal wastewater on corrosion of N80 carbon steel

Abstract Secondary-treated municipal wastewater (MWW) is the alternative water source in recirculating cooling water systems. Municipal wastewater treatment plant (WWTP) effluent was collected and four fractions including hydrophobic acidic (HPOA), hydrophobic alkaline (HPOB), weakly hydrophobic (WHPO) and hydrophilic (HPI) organics were isolated from the effluent by using DAX-8/XAD-4 resin. We used potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) to investigate corrosion characteristics of N80 carbon steel in the different water samples and control samples. In contrast with control samples, the corrosion rate of N80 carbon steel decreased 41%, 23%, 18% and 4% in the presence of HPOA, HPOB, WHPO and HPI, respectively. The results were further confirmed by the EIS test. In the presence of the four fractions (especially HPOA), the radius of the semicircle in the Nyquist plot was much larger than that for the control samples, which indicated that the impedance in the EIS test of the HPOA sample was much higher than that of the control sample. The dissolved organic matter (DOM) could adsorb onto the surface of the electrode and form a protective film, which could inhibit electron transfer and increase the electrochemical impedance of the electrochemical test system.

A Novel Controlled Frequency Band Impedance Measurement Approach for Single-Phase Railway Traction Power System

The accurate information of the wide-bandwidth impedance versus the frequency is urgently needed for evaluating the system resonances, instabilities, and operations of the railway traction power system (TPS), and to avoid/control the harmonic resonance and oscillation issues. As the system topology and detailed parameters of the TPS are not fully known even timely varying, we have to obtain the detailed wide-bandwidth impedance information through exciting the harmonic disturbance into the system, and then, calculating the response information. Therefore, a controlled wide-bandwidth impedance measurement approach is presented in this paper, in which, a butterfly-type disturbance circuit and chirp pulsewidth modulation signal model are incorporated to generate the desired controlled-bandwidth harmonics with a high aggregation as well as the average amplitude. Impedance measurement results of the proposed approach have been validated through both simulation and experiment. Considering the measured errors, the proposed method is efficient in testing the wide-bandwidth impedance of the single-phase railway traction system.

A Novel Voltage Stabilization and Power Sharing Control Method Based on Virtual Complex Impedance for an Off-Grid Microgrid

Microgrid (MG) usually operates in medium/low-voltage systems, where the line impedance parameters are mainly resistive, and traditional P-f/Q-U droop control is no longer applicable. When the virtual complex impedance method is adopted, the resistance component of line impedance can be counteracted by a virtual negative resistance. Unfortunately, the improper design of the virtual negative resistance will result in an unstable system due to the problem of line impedance parameter drift and estimation error. According to the line parameters characteristics of the off-grid MG with medium/low voltage, the P-U/Q-f droop control is adopted in this study, where the virtual complex impedance composed of a virtual negative inductance and a virtual resistance is introduced in the control loop. The virtual negative inductance is used to reduce the power coupling caused by the inductive component of the system impedance. The virtual resistance is implemented to enhance the resistive component and adjust the impedance matching degree for raising the accuracy of power sharing. However, the power sharing is still affected by the system hardware parameters; meanwhile, the voltage deviation caused by the droop control and the virtual impedance exists. In this study, a novel voltage stabilization and power sharing control method based on the virtual complex impedance is investigated to achieve accurate power sharing without the impact of hardware parameters variations and to improve the voltage quality. Moreover, the small-signal model of the inverter-based off-grid MG with the proposed controller is established, which can be utilized to analyze the stability and dynamic performance of the system. Meanwhile, the control parameters can be sequentially determined. Analysis shows that the strategy is robust against the line-impedance parameter drift and the estimation error and has a large stability margin and fast dynamic-response speed. Finally, numerical simulations and experimental results are provided to verify the effectiveness of the proposed control method in comparison with traditional frameworks.

Investigation of the Interactions between Electrodes in Li4Ti5O12 – Based Batteries with Complementary Surface Analysis Techniques (XPS, SAM, ToF-SIMS)

Li4Ti5O12(LTO)-based negative electrode for lithium-ion batteries is of interest for electrical vehicles due to its safety, low cost and cycling stability [1]. In this study, the effect of the positive electrode on the electrochemical performances of LTO electrodes, in relation with the Solid Electrolyte Interphase (SEI) properties, has been investigated [2]. Full cells LTO/LiNi3/5Co1/5Mn1/5O2 (NMC) and LTO/LiMn2O4 (LMO) were cycled at 40°C over 100 cycles and the electrodes were analyzed by XPS, Scanning Auger Microscopy (SAM) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) after one and 100 cycles (figure 1). Moreover, LTO/LTO symmetrical cells were also analyzed in order to be free of the positive electrode impact. For each system, LTO electrodes are homogeneously covered by surface layers since the first cycle which induces an irreversible capacity loss. This latter is more important for LTO/LMO compared to LTO/NMC and LTO/LTO. Both SEI layers are composed of organic (polyethylene oxides, oxalates) and inorganic species (LiF, phosphates and fluorophosphates) but in different proportions and with different 2D and 3D spatial distributions: fluorine species are detected deeper in the electrode than organic species and in higher quantities for LTO/LMO for instance [3]. Moreover, the SEI is thicker on the LTO electrode when cycled versus LMO compared to NMC and contains small amounts of manganese, homogeneously spread over the surface and deeply inserted in the SEI, which entails an increase of the system impedance. In conclusion, a thick SEI associated with the presence of metallic species could alter the passivating role of the SEI and explain the less efficient electrochemical performance of LTO/LMO cells. [1] Tarascon et al. Nature 2001, 414, 359–367. [2] El Ouatani et al. Journal of The Electrochemical Society, 156(6): A468, 2009. [3] Nicolas Gauthier et al. Journal of The Electrochemical Society, 165(13): A2925-A2934, 2018. Figure 1

Vibration Performance Analysis of a Mining Vehicle with Bounce and Pitch Tuned Hydraulically Interconnected Suspension

The current investigations primarily focus on using advanced suspensions to overcome the tradeoff design of ride comfort and handling performance for mining vehicles. It is generally realized by adjusting spring stiffness or damping parameters through active control methods. However, some drawbacks regarding control complexity and uncertain reliability are inevitable for these advanced suspensions. Herein, a novel passive hydraulically interconnected suspension (HIS) system is proposed to achieve an improved ride-handling compromise of mining vehicles. A lumped-mass vehicle model involved with a mechanical–hydraulic coupled system is developed by applying the free-body diagram method. The transfer matrix method is used to derive the impedance of the hydraulic system, and the impedance is integrated to form the equation of motions for a mechanical–hydraulic coupled system. The modal analysis method is employed to obtain the free vibration transmissibilities and force vibration responses under different road excitations. A series of frequency characteristic analyses are presented to evaluate the isolation vibration performance between the mining vehicles with the proposed HIS and the conventional suspension. The analysis results prove that the proposed HIS system can effectively suppress the pitch motion of sprung mass to guarantee the handling performance, and favorably provide soft bounce stiffness to improve the ride comfort. The distribution of dynamic forces between the front and rear wheels is more reasonable, and the vibration decay rate of sprung mass is increased effectively. This research proposes a new suspension design method that can achieve the enhanced cooperative control of bounce and pitch motion modes to improve the ride comfort and handling performance of mining vehicles as an effective passive suspension system.

Behaviour of the electrochemical intrgrator on the basis of solid electrolyte in galvanoharmonic charging mode

Behaviour of the Electrochemical integrator on the basis of Solid Electrolyte is studied in the galvanoharmonic charging mode. The possibility of application of simpler and more graphic calculation technigue and separation of impedance of electrochemical systems into active and reactive components is shown. The plotting of the dependences of the active and reactive impedance components on ac freguency was used to find the values of parameters of the studied equivalent electric cuircuits.

A Novel Stability Analysis Approach for the Gird-connected Wind Generator Based on Impedance Ratio Criterion

A novel stability analysis approach is proposed for a gird-connected Wind generator system based on the impedance criterion, which can consider the dynamic characteristics of permanent magnet synchronous generator (PMSG). Firstly, the stability analysis criteria for the grid connected power system with electronic converters is deduced based on the impedance stability analysis principle. Secondly, the small signal model of a PMSG with consideration of the dynamic characteristics of PMSG is established by the state-space equation of PMSG, and the output impedance of a grid-connected PMSG system is derived. On this basis, the stability analysis method for the gird-connected PMSG is obtained. Numerical simulation are performed to validate the proposed control method.

The Role of Airway Shunt Elastance on the Compartmentalization of Respiratory System Impedance.

An inverse model consisting of two elastic compartments connected in series and served by two airway conduits has recently been fit to measurements of respiratory impedance in obese subjects. Increases in the resistance of the distal conduit of the model with increasing body mass index have been linked to peripheral airway compression by mass loading of the chest wall. Nevertheless, how the two compartments and conduits of this simple model map onto the vastly more complicated structure of an actual lung remain unclear. To investigate this issue, we developed a multiscale branching airway tree model of the respiratory system that predicts realistic input impedance spectra between 5 and 20 Hz with only four free parameters. We use this model to study how the finite elastances of the conducting airway tree and the proximal upper airways affect impedance between 5 and 20 Hz. We show that progressive constriction of the peripheral airways causes impedance to appear to arise from two compartments connected in series, with the proximal compartment being a reflection of the elastance of upper airway structures proximal to the tracheal entrance and the lower compartment reflecting the pulmonary airways and tissues. We thus conclude that while this simple inverse model allows evaluation of overall respiratory system impedance between 5 and 20 Hz in the presence of upper airway shunting, it does not allow the separate contributions of central versus peripheral pulmonary airways to be resolved.

New Results for Battery Impedance at Very Low Frequencies

In search of an equivalent circuit model for rechargeable batteries, many authors start with a measurement of battery impedance, spanning what is presumed to be the frequency range of interest. Various networks have been suggested in the literature to account for the measured impedance characteristic. Most incorporate two or more resistors, at least one capacitor, some include at least one Warburg element, and more recently “constant phase elements”(CPE), otherwise identified as fractional-derivative capacitors. Networks that are more successful at reproducing the measured impedance have from five up to tens of degrees of freedom. The frequency range upon which most models are based extends only to 1mHz. This is surprising since many batteries see a daily or longer usage cycle, corresponding to a frequency of ≈ 11.6 μHz or lower. We show in this manuscript that the most-cited impedance measurement instrument, and one of the few that can operate below 1mHz, can be unreliable at and below this boundary. We present a novel impedance measurement algorithm robust against the issues present while measuring the impedance of electrochemical systems to as low as 1 μHz. Next, we present reliable impedance data extending to a lower frequency limit of 10 μHz. A remarkable characteristic appears at the lower frequencies, suggesting a surprisingly simple and elegant equivalent circuit consisting of a single fractional capacitor. A new model is proposed, which requires only four parameters to predict the measured impedance as a function of frequency.

Time-Variant In-Circuit Impedance Monitoring Based on the Inductive Coupling Method

In-circuit impedance extraction of a time-variant electrical system is essential for real-time condition monitoring purpose. This paper looks into the design consideration of real-time in-circuit monitoring for a time-variant system based on inductive coupling approach and discrete Fourier transform in a moving window. By using two clamped-on-type inductive probes, the proposed setup eliminates the need of voltage sensors to measure the terminal voltages of system-under-monitoring (SUM) and, hence, eliminates direct electrical contact with the SUM. Therefore, it facilitates ease of mounting and disassembly. Experimental results show that with careful design consideration, the proposed method has the ability to measure the in-circuit impedance of a time-variant system in real time, which facilitates useful inputs for early detection of abnormality of the monitored electrical system that is time variant in nature.

A Flexible Wireless Power Transfer System With Switch Controlled Capacitor

Wireless power transfer (WPT) with a switch-controlled capacitor (SCC) is proposed in this paper for compensating load impedance which is related to the coupling coefficient of coils and the load variations. In general, the power supply in the WPT system is desired to output constant voltage under varied load impedance. In the proposed WPT system, the resonant capacitor in the primary side is replaced by an SCC and only diode full-bridge rectifier in the secondary side is used. The SCC realizes adjustable capacitor which makes it flexible to control the capacitance. At the same time, the modulation of the SCC aims to guarantee an inductive input impedance of the WPT system, achieving soft switching and reducing the high switching losses of the high-frequency inverter. In order to verify the feasibility of the proposed method, mathematical analysis, and experimental validations have been thoroughly performed. The experiment results show that the WPT system maintains a stable output voltage by through the regulation of the SCC according to the load variations.

Oscilometría de impulso. Recomendaciones y procedimiento

The Impulse Oscillometry System (IOS) is a lung function test that assesses the respiratory system impedance (Z) at different frequencies of oscillation. From the Z we can get the resistance Z (R) and reactance (X) that are the forces that must be overcome so that the air can be moved in and out of the respiratory system. By the results of the IOS is possible to know, indirectly, if the functional pattern is compatible with bronchial obstruction or restriction. The IOS is particularly useful in those patients with bronchial obstruction symptoms that have a normal spirometry, or, for uncooperative patients in testing effort dependent. Although there are international guidelines for carrying out the IOS, this document is intended to guide the clinician about the advantages and usefulness of the IOS and facilitate their implementation by describing the procedure that has been standardized in our laboratory. Finally, we propose a simple strategy on the clinical interpretation of the test.

Frequency superimposed energy bifurcation technology for a hybrid microgrid

A conventional microgrid comprising both ac and dc components undergoes a significant power loss during the multistage conversion process. To overcome the problem of reduced efficiency in a conventional microgrid, a significant attention has been drawn towards the structure of the hybrid ac/dc microgrid. The precise power management in a hybrid microgrid is relatively complicated due to the presence of the dc sub-grids in the architecture. In dc sub-grids, the converter power can only be controlled by regulating the output voltage. However, the computation of the reference voltage turns out to be a challenging task due to the system resistance. The complexity further increases as the line resistances associated with the interlinking converter differs. Addressing this issue, to implement an efficient power management strategy in a dc sub-grid, a superimposed virtual frequency based control variable is proposed in this work. The proposed control variable remains unaffected by the system impedance which helps to attain an efficient power bifurcation. The study extensively evaluates the maximum exchanged power, storage utilisation factor, and circulating power among the multiple interlinking converters. The proposed strategy efficiently manages the bidirectional power flow between the ac and dc sub-grids.

Engineering organic electrochemical transistor (OECT) to be sensitive cell-based biosensor through tuning of channel area

The barrier integrity of epithelial tissue is crucial to many physiological functions in multicellular organisms. Hence, several scientific techniques, such as epithelial voltohmmeter (EVOM) and electric cell-substrate impedance sensing (ECIS), were developed to assess barrier function for in vitro assays. Organic electrochemical transistor (OECT), in particular, outperforms many biosensors because of its multiple advantages such as high transconductance, mixed ionic-electronic conductivity and high biocompatibility. Despite its extensive application in cell impedance sensing, little was reported on how its geometrical dimensions would affect the device performance and quality of cell-based measurement. In this work, OECTs in different dimensions were fabricated and characterized. Specifically investigated were their time and frequency responses towards the presence of epithelial cells (i.e. tightly packed colorectal adenocarcinoma cell line caco-2 and a novel leaky nasopharyngeal carcinoma cell line NPC43). Results show that the sensitivity of cell-based measurement is closely related to the impedance of the whole cell-OECT system. The performance of cell-based sensor would be affected by the tightness of target cell and can be tuned by controlling the active area of OECT.