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Extracting an electric vehicle (EV) charger's input impedance with the analytical model (white-box approach) or the frequency sweep (black-box approach) is limited by the parameter confidentiality or the measurement noise, respectively. To overcome these challenges, a gradient-descent (GD) optimization-based gray-box modeling approach is proposed. To start with, a sensitivity study on the analytical impedance model of an EV charger with a typical controller is carried out to identify the influential frequency range per controller and circuit parameter. On top of that, given an EV charger with unknown control and circuit information, a GD optimization-based algorithm for multiple parameter estimation is designed to identify the unknown controller and circuit parameters based on the measured impedance, by assuming the EV charger is using the typical controller. Then, an analytical input impedance of the black-box EV charger can be obtained. Moreover, the low-accuracy issue commonly encountered when estimating multiple parameters with GD optimization is mitigated with the proposed algorithm. Compared to pure frequency sweep, the proposed approach achieves a higher accuracy for the coupling impedance and a comparable accuracy for the diagonal impedance. The effectiveness of the proposed approach is validated by experimental results., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., DC systems, Energy conversion & Storage

High-voltage direct current (HVDC) systems linked to AC grids with converters are promising energy transmission systems. These systems present complex AC- and DC-side dynamic interactions. Impedance-based stability studies have recently been proposed to assess DC-side dynamics from DC-side characterization of voltage source converters (VSCs) considering AC-side dynamics. However, the existing approaches used for stability studies in VSC-HVDC systems do not completely model VSCs because they do not consider together the VSC delay, the grid voltage feedforward filter, and all the d- and q-reference current controls. Moreover, these approaches are analytically characterized from dq-real space vectors (less related to circuit theory than dq-complex space vectors), and some work with simple AC grids. The main contribution of this paper is a detailed and complete DC admittance model of VSCs from dq-complex space vectors, which considers the VSC delay, feedforward filter, and d- and q-reference current controls, and also a general AC grid. The proposed model can be used for DC-side stability studies in VSC-HVDC systems considering AC grid dynamics. The capabilities and drawbacks of impedance-based stability methods for DC-side stability assessment were analyzed, and the positive-net-damping criterion was validated as a robust approach. The model was validated by PSCAD/EMTDC simulations and applied to a stability study in a VSC-HVDC system., info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2021-2023/PID2021-123633OB-C33/ES/Estabilidad de microrredes formadas por agrupaciones de clusters, Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant, Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energia, Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.b - Per a 2030, ampliar la infraestructura i millorar la tecnologia per tal d’oferir serveis d’energia moderns i sos­tenibles per a tots els països en desenvolupament, en particular els països menys avançats, els petits estats insulars en desenvolupament i els països en desenvolupament sense litoral, d’acord amb els programes de suport respectius, Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura, Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.4 - Per a 2030, modernitzar les infraestructures i reconvertir les indústries perquè siguin sostenibles, usant els recursos amb més eficàcia i promovent l’adopció de tecnologies i processos industrials nets i racionals ambiental­ment, i aconseguint que tots els països adoptin mesures d’acord amb les capacitats respectives, Postprint (published version)

Metal alloy catalysts (e.g., Pt-Co) are widely used in fuel cells for improving the oxygen reduction reaction kinetics. Despite the promise, the leaching of the alloying element contaminates the ionomer/membrane, leading to poor durability. However, the underlying mechanisms by which cation contamination affects fuel cell performance remain poorly understood. Here, we provide a comprehensive understanding of cation contamination effects through the controlled doping of electrodes. We couple electrochemical testing results with membrane conductivity/water uptake measurements and impedance modeling to pinpoint where and how the losses in performance occur. We identify that (1) ∼44% of Co2+ exchange of the ionomer can be tolerated in the electrode, (2) loss in performance is predominantly induced by O2 and proton transport losses, and (3) Co2+ preferentially resides in the electrode under wet operating conditions. Our results provide a first-of-its-kind mechanistic explanation for cation effects and inform strategies for mitigating these undesired effects when using alloy catalysts.

The Advanced Light Source Upgrade (ALS-U) is a 4th generation diffraction-limited soft x-ray radiation source, consisting of a new accumulator ring (AR) and a new storage ring (SR). In both rings coupling-impedance driven instabilities need careful evaluation to ensure meeting the machine's high-performance goals. This paper presents the workflow followed in building the impedance models and the beam-stability analysis based on those models. We follow the commonly accepted approach of separating the resistive-wall and the geometric parts of the impedance; the former is obtained by analytical formulas, the latter by numerical electro-magnetic codes (primarily CST Studio software) with perfectly-conducting boundary conditions. Impedance budgets are established and pseudo-Green functions calculated to be used in beam dynamics studies. We also present various ways to cross-check simulation results for reliable impedance modeling. Finally, the crucial single-bunch instability current thresholds for various operation modes are determined and discussed.

Metal alloy catalysts (e.g., Pt-Co) are widely used in fuel cells for improving the oxygen reduction reaction kinetics. Despite the promise, the leaching of the alloying element contaminates the ionomer/membrane, leading to poor durability. However, the underlying mechanisms by which cation contamination affects fuel cell performance remain poorly understood. Here, we provide a comprehensive understanding of cation contamination effects through the controlled doping of electrodes. We couple electrochemical testing results with membrane conductivity/water uptake measurements and impedance modeling to pinpoint where and how the losses in performance occur. We identify that (1) ∼44% of Co2+ exchange of the ionomer can be tolerated in the electrode, (2) loss in performance is predominantly induced by O2 and proton transport losses, and (3) Co2+ preferentially resides in the electrode under wet operating conditions. Our results provide a first-of-its-kind mechanistic explanation for cation effects and inform strategies for mitigating these undesired effects when using alloy catalysts.

The Advanced Light Source Upgrade (ALS-U) is a 4th generation diffraction-limited soft x-ray radiation source, consisting of a new accumulator ring (AR) and a new storage ring (SR). In both rings coupling-impedance driven instabilities need careful evaluation to ensure meeting the machine's high-performance goals. This paper presents the workflow followed in building the impedance models and the beam-stability analysis based on those models. We follow the commonly accepted approach of separating the resistive-wall and the geometric parts of the impedance; the former is obtained by analytical formulas, the latter by numerical electro-magnetic codes (primarily CST Studio software) with perfectly-conducting boundary conditions. Impedance budgets are established and pseudo-Green functions calculated to be used in beam dynamics studies. We also present various ways to cross-check simulation results for reliable impedance modeling. Finally, the crucial single-bunch instability current thresholds for various operation modes are determined and discussed.

The frequency coupling and low-frequency oscillations are common challenges faced by PFC converters in data centers. To reveal their mechanism, this paper proposes the systematic harmonic state space (HSS) modeling of the single-phase PFC converters and conducts the stability analysis on that basis. The HSS model is based on the linear time-periodic (LTP) theory, which can accurately reveal the frequency-coupling interactions. Besides, the developed HSS model is validated by the frequency scan. The stability analysis is performed and is shown to be consistent with the simulation results. In addition, a SISO equivalent impedance model of the single-phase PFC converters is proposed considering the frequency-coupling dynamics and the interaction with grid impedance, based on the MIMO impedance model derived from the HSS modeling. © 2022 IEEE., QC 20230307

The stability of a power electronics system can be assessed by means of the impedance-based stability criterion. Impedance modeling is a useful tool to analyze the effect of different circuit parameters and control schemes on the behavior of a converter. Modeling the input impedance of a power electronics converter is often successful when having full knowledge of the converter topology, the circuit parameters, and the parameters and implementation of the control system. However, due to the proprietary nature of voltage source converter-based high voltage direct current systems, their exact control structure is often concealed. This complicates the calculation of the impedance of a modular multilevel converter, known for its complex internal dynamics. This paper proposes a method to estimate the impedance of a modular multilevel converter with partially black-boxed converter control. A discussion on partitioning the control system into open and closed parts is made, and the results are verified with simulations in time and frequency domains., QC 20230118

This article presents a small-signal model for power-electronics converters that use a typical control structure in wind energy applications: the double synchronous reference frame current control. The article considers the presence of unbalanced currents and voltages, and analyzes their impact on the frequency couplings of the converter. In addition, it is revealed that, in the presence of negative-sequence voltage synchronization, the converter presents an additional coupling at -2f_1-f_p., DC systems, Energy conversion & Storage

In this paper, harmonic stability of a back-to-back modular multilevel converter based voltage source converter high voltage direct current system is analyzed. These systems are prone to ac- and dc-side resonances and interactions between the converter and its interconnected systems. The stability of the system can be predicted by the impedance based stability criterion, which requires the modeled or measured converter impedance. The analysis in this paper focuses on interoperability when the converters employ different control schemes in order to utilize the inherent damping properties of the sum capacitor voltage balancing control loops., Part of proceedings: ISBN 978-1-6654-3554-3QC 20220502

This article presents a small-signal model for power-electronics converters that use a typical control structure in wind energy applications: the double synchronous reference frame current control. The article considers the presence of unbalanced currents and voltages, and analyzes their impact on the frequency couplings of the converter. In addition, it is revealed that, in the presence of negative-sequence voltage synchronization, the converter presents an additional coupling at -2f_1-f_p., DC systems, Energy conversion & Storage

The DC-side floating capacitors in the floating power modules of power converters are subject to high voltage fluctuation, due to the presence of reactive harmonic components. Utilizing passive capacitors, as done in traditional methods, helps reduce the DC-bus voltage ripple but makes the system bulky. An active capacitor can be integrated with the floating H-bridge power modules to remove the effect of the ripple powers on the DC bus. The auxiliary circuit, which is much smaller in size compared to an equivalent passive capacitor, helps increase the power density of the system. This work focuses on the analysis of power components, and the extension of the active capacitor to the Perturbation Injection Unit (PIU), in which the DC side is highly distorted by multiple harmonic components. A control scheme is proposed to compensate for these multiple harmonics and balance the DC-link voltage in the active capacitor. Also, an equivalent DC-bus impedance model is introduced, which is more accurate than that in existing works. Simulation studies and evaluation of the design have verified the effectiveness of the active capacitor solution.

This work investigates the noise reduction effect of extended tube liners which have the potential to shift the resonance to lower frequencies as compared with the conventional perforated liner which is constrained by the quarter-wavelength rule. In order to better utilize this technique for duct noise control, the surface impedance of the extended tube liner has to been known. However, existing models are mainly applicable to the normal incidence case and the influence of grazing flow effect is often ignored. In the current paper, an impedance model is developed based on the transfer matrix method and the grazing flow effect on the surface impedance is taken into account in terms of the end corrections. To examine the validity of the proposed model, liner samples are tested on a flow duct facility and the liner impedances are obtained from an impedance eduction method. The proposed model shows a reasonable agreement with the educed data. Then, geometry parameters including extended tube length, hole diameter and grazing flow speed are investigated. It is found that the frequency for maximum attenuation is shifted to lower frequency for a longer extended tube or smaller hole diameter but it is nearly unchanged with respect to the grazing flow speed., QC 20210218

The DC-side floating capacitors in the floating power modules of power converters are subject to high voltage fluctuation, due to the presence of reactive harmonic components. Utilizing passive capacitors, as done in traditional methods, helps reduce the DC-bus voltage ripple but makes the system bulky. An active capacitor can be integrated with the floating H-bridge power modules to remove the effect of the ripple powers on the DC bus. The auxiliary circuit, which is much smaller in size compared to an equivalent passive capacitor, helps increase the power density of the system. This work focuses on the analysis of power components, and the extension of the active capacitor to the Perturbation Injection Unit (PIU), in which the DC side is highly distorted by multiple harmonic components. A control scheme is proposed to compensate for these multiple harmonics and balance the DC-link voltage in the active capacitor. Also, an equivalent DC-bus impedance model is introduced, which is more accurate than that in existing works. Simulation studies and evaluation of the design have verified the effectiveness of the active capacitor solution.

Electrical lines, also known as wirelines, are commonly used for well intervention techniques to increase flow of oil and gas wells that can be executed during a low service time. Previous studies show the importance of this electrical conductor for power delivery as well as communication purposes. Nevertheless, a validated model and its parameters of this channel are still missing. This papers outlines a geometrical approach to estimate the electrical dynamic behavior for wireline types used in the field with results supported by four different types of validation. The proposed method proves to capture the wireline dynamic behavior characteristics and is particular accurate in modeling the capacitive element within 5 %.

The Mode Merging Design Method (MMDM), a theoretical design method further developed based on the Cremer concept, for non-locally reacting liners with porous materials is first proposed and established. The acoustic properties of such non-locally reacting liners are determined by the combined action of porous materials in the chamber and perforated plate adjacent to porous backing and grazing flow, which are described by the Delany & Bazley (DB)-like models and the combined Guess & Kirby-Cummings (Guess-KC) impedance model in this study, respectively. According to the structure characteristics of bulk liner, the porous chamber depth Lc and flow resistivity σ, are selected to be optimized to maximize the sound attenuation at a target frequency when a single circumferential mode is incident. In the spirit of the mode merging theory, the eigen equation and the branch point equation for this physical problem are derived, from which the merging double eigenvalue/mode can be solved, in turn, the optimum chamber depth Lc and flow resistivity σ can be simultaneously determined, which can produce theoretically maximum sound attenuation. Then, a Finite Element (FE) sound propagation model is established to validate the liner design of theoretical optimization by MMDM. The accuracies of the eigen-analysis method, the DB model, the Guess-KC model and the FE model are validated through several benchmark cases. Further, the MMDM is applied in four design cases of bulk liners with finite length, and the results indicate that the MMDM can accurately aim at a given condition of grazing flow Ma, circumferential mode order m and target frequency f to effectively optimize the structural parameters for actual bulk liners. Finally, an optimality analysis performed through two concrete cases demonstrates that the MMDM can avoid locally optimal solution and successfully find optimal structures for an infinite non-locally reacting liner, thus producing the maximum sound atte, QC 20200423

A semi-empirical impedance formula of a circular orifice under grazing flow is derived, based on a linearized potential flow model. The effect of boundary layer is considered by introducing the convection speed of vorticity which is assumed to be a function of the dimensionless boundary layer thickness. Asymptotic expression of the impedance at low Strouhal number is acquired by the method of perturbation, while the impedance at large Strouhal number can be well approximated by that without grazing flow. The model predictions achieve reasonable agreement with the data available in a previous experimental investigation., QC 20200622

The size of electrodes in bio-chemical sensors has shrunk quickly in recent years. The high impedance from polarizable microelectrodes brings new challenges to the sensor design. On the other hand, non-polarizable electrodes, such as Ag/AgCl electrodes, could have lower impedance at the low bio-signal frequency band. Thin-film Ag/AgCl electrode is commonly used as reference electrode. In this work, the electrochemical processes governing the impedance profile of thin film Ag/AgCl microelectrodes are systematically studied. New models are established for circuit parameters of thin film Ag/AgCl microelectrodes based on the new findings. The models are verified extensively with impedance measurements. © 2019 Elsevier Ltd

The size of electrodes in bio-chemical sensors has shrunk quickly in recent years. The high impedance from polarizable microelectrodes brings new challenges to the sensor design. On the other hand, non-polarizable electrodes, such as Ag/AgCl electrodes, could have lower impedance at the low bio-signal frequency band. Thin-film Ag/AgCl electrode is commonly used as reference electrode. In this work, the electrochemical processes governing the impedance profile of thin film Ag/AgCl microelectrodes are systematically studied. New models are established for circuit parameters of thin film Ag/AgCl microelectrodes based on the new findings. The models are verified extensively with impedance measurements. © 2019 Elsevier Ltd

The size of electrodes in bio-chemical sensors has shrunk quickly in recent years. The high impedance from polarizable microelectrodes brings new challenges to the sensor design. On the other hand, non-polarizable electrodes, such as Ag/AgCl electrodes, could have lower impedance at the low bio-signal frequency band. Thin-film Ag/AgCl electrode is commonly used as reference electrode. In this work, the electrochemical processes governing the impedance profile of thin film Ag/AgCl microelectrodes are systematically studied. New models are established for circuit parameters of thin film Ag/AgCl microelectrodes based on the new findings. The models are verified extensively with impedance measurements. © 2019 Elsevier Ltd

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Aeronautical ground lighting (AGL) systems assist aircraft pilots in airport operations. These systems are singlephase series circuits where constant current regulators (CCRs) feed luminaires with an adjustable rms current. CCRs are voltage source converters (VSCs) which may cause harmonic resonance instabilities when their control interacts with poorly damped resonances in the 0.75 - 2.5 kHz range. The paper studies these instabilities from the impedance-based representation of AGL systems which are grid-connected VSC systems much simpler than the usual systems analyzed in the literature. This offers the possibility of contributing with a comprehensive stability assessment. Approximate expressions of the CCR and AGL circuit equivalent admittances are given to assess system stability. A comprehensive overview of the influence of AGL system parameters on harmonic resonance instabilities is presented and several recommendations on the AGL system components and CCR parameters are proposed to improve stability. Additionally, an active damping solution based on virtual conductances is analyzed. The expressions of the CCR admittance and some of the recommendations on CCR and AGL system parameters contribute to stability studies of grid-connected VSC systems. Matlab/Simulink and PSCAD/EMTDC simulations of a 68 luminaire AGL system illustrate the contributions of this paper. Field measurements support the stability study., Postprint (author's final draft)

The concept of IC engine downsizing is a well-adapted industry standard, enabling better fuel conversion efficiency and the reduction of tailpipe emissions. This is achieved by utilizing different type of superchargers. As a consequence, the additional charger noise emission, at the IC engine inlet, can become a problem. In order to address such problem, the authors of this work have recently proposed a novel dissipative silencer for effective and robust noise control of the compressor. Essentially, it realizes an optimal flow channel impedance, referred to as the Cremer impedance. This is achieved by means of a straight flow channel with a locally reacting wall consisting of air cavities covered by an acoustic resistance, e.g., a micro-perforated panel (MPP). In this paper, an improved optimization method of this silencer is presented. The classical Cremer impedance model is modified to account for mean flow dependence of the optimal wave number. This modified model leads to significantly different impedance values compared to the classical model and consequently, the high damping of the classical model (hundreds of dB/m) is further increased. Moreover, the modeling herein, is performed by solving the convective wave equation, vital for accounting mean flow effects. The presented model is finally validated by experimental results included in the paper., QC 20161205

The final report for Diagnosis and Prognosis of Filament Wound Components Subject to Combined Loads Using Nonlinear Signal Processing of Standing and Traveling Waves is presented here in the form of a journal article. This article summarizes the approach, test procedures, analysis methods, results, and conclusions associated with the study of frequency domain techniques for characterizing helmet and helmet padding performance through nondestructive evaluation. Upon approval, this article will be submitted to an appropriate journal for publication consideration., The original document contains color images.

Optical membranes are currently pursued for their ability to replace the conventional mirrors that are used to correct wave front aberration and space-based telescopes. Among some of the many benefits of using optical membranes, is their ability to considerably reduce the weight of the structure. As a secondary effect, the cost of transportation, which is of great interest in space applications, is reduced as well. Given the low density of these thin-film membranes, the lower end dynamics play a greater significant role than their rigid plate-like counterparts in achieving functional mirrors. Space-based mirrors are subjected to a series of disturbances. Among those encountered are thermal radiation, debris impact, and slewing maneuvers. Thus, dynamic control is essential for the adequate performance of thin-film membrane mirrors. With this in mind, the work described herein aims to improve the performance of optical membranes with an innovative, acoustical control approach to suppress vibration of optical membranes backed by an air cavity. This is achieved by using a centralized acoustic source in the cavity as the method of actuation. The acoustic actuation is of great interest since it does not mass load the membrane in the conventional way, as most methods of actuation would. To achieve this end goal, two structural-acoustic coupled models are developed to describe the dynamics of a pressurized optical membrane system. This is done through an impedance based modeling approach where the subsystems are modeled individually, and then coupled at the interface. The control of the membrane is implemented using a positive position feedback approach. The theory is also extended to positive velocity and positive acceleration feedback. Three experiments are carried out to validate the models previously mentioned. Successful implementation of a control experiment is also accomplished leading to considerable attenuations in the coupled membrane's dynamics.