System Impedance Research Articles

Damping in Compliant Actuation: A Review

Compliant actuator technology aims at building robots capable of physically interacting with humans and the environment, matching the versatility and capacity of biological systems. Recently, it underwent a significant evolution with the introduction of damping to improve performance. Such development reflects several aspects, including energy saving and oscillation mitigation. However, large damping values tend to increase the system impedance, worsening robot resilience and human safety during impacts. That suggests the importance of a correct tradeoff.

Characterization of high impedance of multilayer coplanar waveguide transmission line design for integration with nanodevices

Terahertz technology has recently attracted the attention of the researchers due to its wide range of applications such as security and military, biomedicine and health care, astronomy and biology. There are many scrutinized research papers among the terahertz applications with nanodevices such as self-switching devices. They need monolithic microwave integrated circuits for integration. It is evident that the system impedance of transmission lines is 50 Ω. However, the main limitation of self-switching diodes is high level of impedance in megaohms which is a huge value and is not so easy to implement. Paper focuses on the design and simulation of the coplanar waveguide transmission line structures with higher impedance by applying multilayer technology for the integration with self-switching diodes. Using multilayer technology in design allows wide range of impedances. Two approaches have been targeted such that meets all the requirements of integration with nanodevice. First approach is a widening the gap of the polyimide dielectric layers used in the fabrication of these components. Several design structures have been considered such as positioning the location of signal and grounds contacts with respect to the position of the dielectric layers. As the result the highest characteristic impedance of about 90 Ω was achieved at operating frequency of 110 GHz. Secondly, novel coplanar waveguide transmission line structure was investigated where the V – shape structure was joined with the signal elevated structure. The terahertz application research may effect on high data transmission rate of no less than 10 GBit/s and thereby in increase of traffic volume.

Beraprost Sodium for Pulmonary Hypertension in Dogs: Effect on Hemodynamics and Cardiac Function.

Simple SummaryPulmonary hypertension is a potentially life-threatening disease among dogs that is characterized by increased pulmonary arterial pressure and pulmonary vascular resistance. In veterinary medicine, a phosphodiesterase-5 inhibitor such as sildenafil is the most common drug used to treat pulmonary hypertension. However, the availability of sildenafil is limited because of its high cost, difficulty in obtaining the drug in some areas, and potential inter-individual variability in the response to sildenafil therapy. Beraprost sodium is one of the most common drugs used to treat pulmonary hypertension in humans. However, little is known about its efficacy in dogs with pulmonary hypertension. In this study, beraprost sodium showed significant pulmonary and systemic vasodilation without any adverse effects in sixteen dogs with pulmonary hypertension. Additionally, echocardiographic improvements in cardiac function and pulmonary and systemic circulation were observed. These results emphasize the potential efficacy of beraprost sodium in treating canine pulmonary hypertension.Pulmonary hypertension (PH) is a fatal condition that affects many dogs. In humans, PH is often treated with beraprost sodium (BPS). However, the effectiveness of BPS for canine PH has not been established. This study aimed to evaluate the clinical and cardiovascular response of BPS in canine patients with PH of various causes. Sixteen dogs with PH (post-capillary PH, n = 8; pre-capillary PH, n = 8) were included. BPS was continuously administered twice daily at 15 µg/kg. All dogs underwent echocardiography, including speckle-tracking analysis and blood pressure measurement, before and after BPS administration. Continuous BPS administration (range: 13.2–22.0 µg/kg) significantly decreased the pulmonary and systemic vascular impedance and increased left and right ventricular myocardial strain. In dogs with post-capillary PH, BPS administration caused no significant worsening of the left atrial pressure indicators. No side effects of BPS were observed in any dog. BPS also improved cardiac function and pulmonary circulation through pulmonary vasodilation, suggesting that BPS may be an additional treatment option for canine PH of various causes. Particularly, BPS increased left ventricular function and systemic circulation without worsening the left heart loading condition in dogs with post-capillary PH.

Research on Evaluation Method of Electric Vehicle Wireless Charging Interoperability Based on Two Parameter Representation

The interoperability of wireless charging for electric vehicles refers to the radio energy transmission that meets the performance and function requirements of different manufacturers and different models of electric vehicles on the premise of meeting the relevant requirements. If it fails to meet the requirements, the wireless charging system of electric vehicles has difficulty to realize interconnection and low charging efficiency, Therefore, how to evaluate the interoperability is a key issue in the promotion of electric vehicle wireless charging. In this paper, an interoperability evaluation method based on two parameters is proposed. The interoperability impedance plane is constructed by the system detuning coefficient A. The comprehensive evaluation of different compensation networks and coupling coils is realized; the power characteristic impedance ε is obtained by analyzing and calculating the relationship between the transmission power of the system while the system impedance, and the transmission power evaluation of the wireless power transmission system is realized. At the same time, according to simulation and experiment, it was verified that A meets the interoperability requirements when A is in the range of (−0.62, 0.62) in the aligned position and (−0.75, 0.75) in the offset position. When the input voltage is 200 V, when ε satisfies 0.1925 ≥ ε > 0.0925, the system WPT2 power level transmission interoperability requirements are met. The method in this paper can guide the interoperability evaluation of electric vehicle wireless charging.

Pengaruh Total Harmonic Distortion Terhadap Power Factor Pelanggan Rumah Tangga 900 – 2200 VA Dusun Tujuh Bubung Kepulauan Bangka Belitung

The high content of harmonics in an electric power system can cause several disturbances to the system, such as increasing power losses in the system, causing various damage to electrical equipment, and causing the use of electrical energy to be ineffective. Harmonics is caused by the operation of non-linear electrical loads. The interacting harmonic currents with the supply system impedance distorts the supplier's output current and voltage which in turn adversely affects the loads connected to the system and the supply itself. This study aims to analyze the quality of THD in Bubung Tujuh Hamlet, Sangku Village. In this study, THD measurements were carried out and analyzed the effect of harmonics on the power factor using a linear regression test. The results of the measurement and analysis of THDV ranged from 1.0% - 6.8%, with the final analysis of THDV still meeting the set standard of 5%. THDI ranged from 2.3% - 66.7% with the final analysis THDI did not meet the standard. THD of the village's electrical system is still at the standard limits set and THD(V) effect on PF.

Small Signal Stability Analysis of a Microgrid in Grid-Connected Mode

Microgrid stability issues are classified into three categories: transient, voltage, and small signal stability (SSS). Small variations in the load demand and small perturbations in the control system and line impedance parameters can cause instability, which can be avoided by performing an SSS analysis. This paper focuses on investigating the impact of line impedance and passive filter parameters on the stability of a MG in grid-connected mode. Therefore, a MG system was represented mathematically, before performing an SSS analysis that calculated the stability margin of the MG parameters. A sensitivity analysis was performed to determine those parameters highly participating in the SSS. The mathematical results were validated using the simulation results, which were obtained using MATLAB Simulink.

Travelling wave fault location approach for MMC-HVDC transmission line based on frequency modification algorithm

Travelling wave (TW) fault location principle is widely utilized on actual power transmission line, which shows better fault location performance than conventional algorithms. But, considering the TW fault location principle is generally implemented using TW front arrival times and transmission velocities, the fault location accuracy is high influenced by frequency distortion. Meanwhile, modular multilevel converter (MMC) based high-voltage direct-current (HVDC) transmission line has more complex boundary characteristic required to be researched. Therefore, in order to acquire better fault location performance, a novel TW fault location approach for MMC-HVDC transmission line is proposed based on frequency modification algorithm. Firstly, the frequency modification algorithm of TW front is studied. Secondly, the detailed calculation principle of system impedance and transmission line’s wave impedance is proposed. Thirdly, the novel TW fault location principle based on modified frequency spectrum is described. Eventually, via PSCAD/EMTDC simulation software, a typical ±400 kV simulation system is constructed to validate the performance of proposed TW fault location principle under the influences of fault type, fault location and grounding resistor issues.

Decaying DC Offset Current Mitigation in Phasor Estimation Applications: A Review

Decaying DC (DDC) offset current mitigation is a vital challenge in phasor current estimation since it causes malfunctioning/maloperation of measurements and protection systems. Due to the inductive nature of electric power systems, the current during fault inception cannot change immediately and it contains a transient oscillation. The oscillatory component acts similar to an exponential DC signal and its characteristics depend on the X/R ratio of the system, fault location, and fault impedance. DDC attenuates accurate phasor estimation, which is pivotal in protection systems. Therefore, the DDC must be eliminated from the fault current (FC) signal. This paper presents an overview of DDC mitigation methods by considering different groups—before the discrete Fourier transform (pre-DFT), after the discrete Fourier transform (post-DFT), the least square-based (LS-based), and other methods. Through a comprehensive review of the existing schemes, the effects of noise, harmonics, multiple DDCs (MDDCs), and off-nominal frequency (ONF) on the accuracy of DDC estimation, were recognized. A detailed discussion (along with some simulation results) are presented to address the main advantages/disadvantages of the past studies. Finally, this paper presents a few suggestions for future researchers, for researchers to investigate more implementable solutions in this field.

Stability Enhancement of Grid-Connected Inverters Using Weighted Average Current Control Method

Among different factors that threaten the stability of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered inverters in grid-tied mode, the variation of grid impedance and computational delay in digital systems are the most important ones. Often, a control system based on either the inverter- or grid-side current and a combination of impedance estimation and delay compensation methods are used to deal with these challenges. Such control systems are quite effective; however, they often involve a quite high implementation complexity. Especially, computational and pulsewidth modulation delay causes a critical frequency, which may deteriorate the stability conditions in grids with varying grid impedance. To deal with this challenge, a robust approach based on a weighted average current control method is proposed in this article. The suggested control system employs the point of common coupling voltage as a control variable, which increases the system stability in weak grids. Thus, the control system does not need any delay compensation or grid impedance estimation methods, which in turn simplifies the control system. The effectiveness of the proposed method is examined using the experimental results in different case studies.

Impedance Variation and Learning Strategies in Human-Robot Interaction.

In this survey, various concepts and methodologies developed over the past two decades for varying and learning the impedance or admittance of robotic systems that physically interact with humans are explored. For this purpose, the assumptions and mathematical formulations for the online adjustment of impedance models and controllers for physical human-robot interaction (HRI) are categorized and compared. In this systematic review, studies on: 1) variation and 2) learning of appropriate impedance elements are taken into account. These strategies are classified and described in terms of their objectives, points of view (approaches), and signal requirements (including position, HRI force, and electromyography activity). Different methods involving linear/nonlinear analyses (e.g., optimal control design and nonlinear Lyapunov-based stability guarantee) and the Gaussian approximation algorithms (e.g., Gaussian mixture model-based and dynamic movement primitives-based strategies) are reviewed. Current challenges and research trends in physical HRI are finally discussed.

Low-Frequency Oscillation Analysis of Virtual-Inertia-Controlled DC Microgrids Based on Multi-Timescale Impedance Model

Virtual inertia and damping control (VIDC) improves the stability of DC microgrid (DC-MG). However, the potential positive feedback aggravates low-frequency oscillation induced by the interaction insides control loops, which is explained and solved in this paper. The multi-timescale impedance modelling framework is established to clarify stability mechanism of VIDC and the low-frequency oscillation of VIDC controlled DC-MG. Control loops of different timescales are visualized as independent <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">loop virtual impedance</i> (LVI) elements to form an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">impedance circuit</i> considering the constant power load (CPL), rather than an all-in-one impedance as the external dynamic representation of power converters. Concrete impedance analysis is performed on LVI to reveal the impedance-shaping effect of control loops intuitively, the physical impedance nature of control parameters and the interaction among different timescale, which illustrates the stability mechanism of VIDC. The low-frequency oscillation ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> impedance interaction) in voltage- and inertia-loop is elaborated by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> circuits of LVIs. The potential instability factors, resulting in poor damping against voltage oscillation, are also revealed. Thus, dynamic stability enhancement method is further proposed to compensate for the negative damping caused by positive feedbacks of VIDC and CPL, and super-capacitor is added to alleviate rapid voltage changes. Accordingly, the passivity property of system impedance is strengthened and the stability can be evaluated by Nyquist plot. Finally, the simulation and experiment results have validated the low-frequency oscillation analysis and stability enhancement method.

Stability Modeling of a Three-Terminal MMC-HVDC Transmission System

Multi-terminal modular multilevel converter (MMC) power transmission is the current development trend in DC transmission. However, owing to its fast control and dynamic characteristics, it may interact with the other inductive devices or the grid and cause stability issues. This paper describes the use of the impedance analysis method in the frequency domain to analyze system stability. First, the multi-harmonic linearization method is used to model the impedance of a three-terminal MMC system. To make the model more accurate, the modeling considers the effect of frequency coupling caused by an asymmetric controller and the AC sampling site position. This paper then proposes an equivalent method of the grid impedance for the three-terminal system that can accurately judge the stability of the grid-connected system when the AC side is coupled. This work provides a theoretical basis for the prediction and suppression of the oscillation of MMC grid-connected system with coupling on the AC side. Finally, a three-terminal MMC model is built in Matlab/Simulink and the Nyquist stability criterion is used to verify the correctness of the analysis.

Investigation of the Effect of Different Facts Devices on Stability in Case of Asymmetric and Symmetrical Fault Condition in Two-Machine System

Many methods have been developed for the control and stability of electrical energy systems. As a result of the researches, more complex systems are produced for electricity generation, transmission and distribution. New modern systems are developed which are capable of changing power flow parameters such as voltage, impedance, power angle, frequency, and power transmission capacity in transmission systems. In this context, the effects of static elements to be connected in parallel or in series to the stability of power system stability studies is one of the most important fields of study of electrical science. In this study, the effects of STATCOM and SVC, one of these shunt flexible AC devices, on the stable operation of the system in case of symmetrical or asymmetric fault situations that may occur in the transmission system are examined in matlab / simulink environment. This study showed that STATCOM provides superior control than SVC and maintains the stability of the system in case of any failure.

Electrochemical Impedance Spectroscopic Investigation of Vanadium Redox Flow Battery

The kinetics of redox reactions relevant to vanadium redox flow battery (VRFB) is investigated using voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a three-electrode configuration and in a VRFB setup (two-electrode configuration). Impedance spectra are recorded in the VRFB setup with equimolar concentration of V5+/V4+ and V3+/V2+ solutions as positive and negative electrolytes, respectively (full-cell; asymmetric feed system); with an equimolar V5+/V4+ electrolyte on both sides (symmetric feed system 1); and also with V3+/V2+ electrolyte on both sides (symmetric feed system 2). Impedance of the full-cell VRFB (recorded with asymmetric feed system) is comparable to the sum of the half of the impedance of symmetric feed systems (of V5+/V4+ and V3+/V2+ electrolytes) at open circuit potential (OCP). Impedance and voltammograms recorded in the three-electrode configuration using Vulcan XC-72 modified rotating disk electrode, and the impedance recorded in the two-electrode full-cell configuration unequivocally confirms that the V5+/V4+ redox reaction limits the VRFB performance. The optimal performance of the VRFB with the in situ treated carbon felt compressed to 47% is ∼389 and ∼336 mW cm−2 with 5 and 25 cm2 cell area, respectively.

Impedance Properties of Multi-Optrode Biopotential Sensing Arrays.

Recording and monitoring electrically-excitable cells is critical to understanding the complex cellular networking within organs as well as the processes underlying many electro-physiological pathologies. Biopotential recording using an optical-electrode (optrode) is a novel approach which has potential to significantly improve interface-instrumentation impedance mismatching as recording contact-sizes become smaller and smaller. Optrodes incorporate a conductive interface that can sense extracellular potential and an underlying layer of liquid crystals that passively transduces electrical signals into measurable optical signals. This study investigates the impedance properties of this optical technology by varying the diameter of recording sites and observing the corresponding changes in the impedance values. The results show that the liquid crystals in this optrode platform exhibit input impedance values (1 MΩ - 100 GΩ) that are three orders of magnitude higher than the corresponding interface impedance, which is appropriate for voltage sensing. The automatic scaling of the input impedance enabled within the optrode system maintains a relatively constant ratio between input and total system impedance of about one for sensing areas with diameters ranging from 40 µm to 1 mm, at which the calculated signal loss is predicted to be <1%. This feature preserves the interface-transducer impedance ratio, regardless of the size of the recording site, allowing development of passive optrode arrays capable of very high spatial-resolution recordings.

Intra-breath changes in respiratory mechanics assessed from multi-frequency oscillometry measurements

Objective. Recent studies in respiratory system impedance (Zrs) with single-frequency oscillometry have demonstrated the utility of novel intra-breath measures of Zrs in the detection of pathological alterations in respiratory mechanics. In the present work, we addressed the feasibility of extracting intra-breath information from Zrs data sets obtained with conventional oscillometry. Approach. Multi-frequency recordings obtained in a pulmonology practice were re-analysed to track the 11 Hz component of Zrs during normal breathing and compare the intra-breath measures to that obtained with a single 10 Hz signal in the same subjects. A nonlinear model was employed to simulate changes in Zrs in the breathing cycle. The values of resistance (R) and reactance (X) at end expiration and end inspiration and their corresponding differences (ΔR and ΔX) were compared. Main results. All intra-breath measures exhibited similar mean values at 10 and 11 Hz in each subject; however, the variabilities were higher at 11 Hz, especially for ΔR and ΔX. The poorer quality of the 11 Hz data was primarily caused by the overlapping of modulation side lobes of adjacent oscillation frequencies. This cross-talk was enhanced by double breathing frequency components due to flow nonlinearities. Significance. Retrospective intra-breath assessment of large or special data bases of conventional oscillometry can be performed to better characterise respiratory mechanics in different populations and disease groups. The results also have implications in the optimum design of multiple-frequency oscillometry (avoidance of densely spaced frequencies) and the use of filtering procedures that preserve the intra-breath modulation information.

Assessment of the Grid Safety Values for Substation Grounding Grid Design Parameters in Vertical Two-Layer Soil Structure

Typically, the impact of the structure of vertically layered soil on the grounding behavior is not considered while designing a substation grounding system. Therefore, it will result in poor grounding designs due to computed inaccurate grid safety values. Besides, no comparative analysis of the grounding design parameters’ impact on the grounding grid systems’ behavior and protection level between vertical and horizontal two-layer soil structures is presently available. Computing and analyzing the grounding behavior of apparent soil resistivity installed in a vertical two-layer soil structure is more challenging than in a horizontal two-layer soil. There are many other parameters to consider, such as the distance ‘a’ between the test electrodes and the angle ‘β’ between the perpendicular line to the soil boundary and the location of the test electrodes. One of the important findings of the assessment shows that the influence of vertically layered soil on grid impedance, step, and touch voltages of a grounding system is insignificant compared to a homogeneous and horizontally layered soil structure. The current flow is affected by an entire grounding grid placed in a specified layer of soil with a specific resistivity for horizontally layered soil. In contrast, soil boundaries separate a grounding grid with various resistivities for vertically layered soil. The outcome of this work is crucial in helping the engineers to understand the behavior of grounding systems in diverse soil conditions and tropical climates.

Investigation of Beraprost Sodium on Cardiac Function and Hemodynamics in Canine Models of Chronic Pulmonary Hypertension.

Pulmonary hypertension (PH) is a life-threatening disease in dogs characterized by increased pulmonary arterial pressure (PAP) and/or pulmonary vascular resistance. No study has evaluated the utility of Beraprost sodium (BPS) in dogs with PH. This study aimed to evaluate the effect of BPS on cardiac function and hemodynamics and examine the optimal dose of BPS in canine models of chronic embolic PH. In this prospective crossover study, three doses of BPS (5, 15, and 25 μg/kg, twice a day) were examined in eight canine models of chronic embolic PH. All model dogs underwent invasive PAP measurement, echocardiography, and non-invasive systemic blood pressure measurement before and after continuous administration of oral BPS for 1 week. No side effects of BPS were observed in any dog during the study. All doses of BPS significantly decreased systolic PAP and pulmonary vascular impedance. Additionally, systemic vascular impedance significantly decreased with 15 and 25 μg/kg of BPS. The right ventricular stroke volume and longitudinal strain significantly decreased with all doses of BPS. The left ventricular stroke volume and circumferential strain decreased with 15 μg/kg BPS. BPS was well-tolerated in this study. A dose-dependent vasodilating effect on pulmonary vessels was observed in canine models of chronic PH. Additionally, 15 μg/kg BPS showed a balanced vasodilating effect on systemic and pulmonary vessels. Furthermore, with a decrease in systemic and pulmonary vascular impedance, the left and right ventricular functions were significantly improved. Our results suggest that BPS may be useful in the treatment of canine PH.

Novel travelling wave fault location principle based on frequency modification algorithm

Travelling wave (TW) fault location principle is widely utilized on actual power transmission line, which has higher fault location accuracy than conventional algorithms. But, considering the TW fault location principle is generally implemented using TW front arrival time and transmission velocity, the fault location accuracy is high influenced by frequency distortion. Therefore, in order to enhance the fault location accuracy, a novel TW fault location principle is proposed based on frequency modification algorithm. Firstly, the frequency modification algorithm of TW front is studied. Secondly, the detailed calculation principle of system impedance and transmission line’s wave impedance is proposed. Thirdly, the novel TW fault location principle based on modified frequency spectrum is described. Eventually, via PSCAD/EMTDC simulation software, a typical 500kV simulation model is constructed to validate the robustness of proposed TW fault location principle against fault type, grounding resistor and fault initial angle issues.

One-kilojoule pulsed-power generator for laboratory space sciences.

This paper reports on the assembly of a compact, low-cost, pulsed-power facility used for plasma studies. The construction uses two modules placed on opposite sides of the test chamber to minimize the system impedance and improve access to test samples. The stored energy is 1 kJ with a peak current of 135 kA and a 1592 ns quarter-period time. Up until now, an imploding conical-wire array has been studied by using time-integrated (visible) imaging, and time-resolved laser imaging, providing a measure of the plasma jet speed in the range of 170 km/s. Our future plans will continue to investigate high-energy-density plasmas that are relevant to the space environment, fusion, and spectroscopy.