Impedance Model Research Articles

Adaptive positioning method for ball head based on impedance control

PurposeComponent positioning is an important part of aircraft assembly, aiming at the problem that it is difficult to accurately fall into the corresponding ball socket for the ball head connected with aircraft component. This study aims to propose a ball head adaptive positioning method based on impedance control.Design/methodology/approachFirst, a target impedance model for ball head positioning is constructed, and a reference positioning trajectory is generated online based on the contact force between the ball head and the ball socket. Second, the target impedance parameters were optimized based on the artificial fish swarm algorithm. Third, to improve the robustness of the impedance controller in unknown environments, a controller is designed based on model reference adaptive control (MRAC) theory and an adaptive impedance control model is built in the Simulink environment. Finally, a series of ball head positioning experiments are carried out.FindingsDuring the positioning of the ball head, the contact force between the ball head and the ball socket is maintained at a low level. After the positioning, the horizontal contact force between the ball head and the socket is less than 2 N. When the position of the contact environment has the same change during ball head positioning, the contact force between the ball head and the ball socket under standard impedance control will increase to 44 N, while the contact force of the ball head and the ball socket under adaptive impedance control will only increase to 19 N.Originality/valueIn this paper, impedance control is used to decouple the force-position relationship of the ball head during positioning, which makes the entire process of ball head positioning complete under low stress conditions. At the same time, by constructing an adaptive impedance controller based on MRAC, the robustness of the positioning system under changes in the contact environment position is greatly improved.

Investigation of Nondestructive and Noncontact Electrical Characterization of GaN Thin Film on ScAlMgO4 Substrate Using Terahertz Time‐Domain Spectroscopic Ellipsometry with Characteristic Impedance Analytical Model

Semiconductor evaluation methods frequently require sample processing and carry the risk of defects and property changes. Therefore, nondestructive and noncontact electrical property measurement techniques are necessary. Terahertz time‐domain spectroscopic ellipsometry (THz‐TDSE) can simultaneously estimate the electrical properties and film thickness of a sample. However, whether this method can simultaneously determine electrical properties and film thickness for semiconductor thin films of 1 μm or less remains unclear. This study uses THz‐TDSE to evaluate the electrical properties and film thickness of a GaN thin film (≈0.8 μm thick) on a ScAlMgO4 substrate. Using the conventional analysis based on Fresnel's formula (FR model), which is used in the field of optics, uniquely determining the electrical properties and film thickness is not possible owing to multiple optimal solutions. Therefore, a model combining the characteristic impedance model used in the radio‐wave region with the FR model is employed in the analysis. The obtained values of electrical properties of the GaN thin film evaluated using THz‐TDSE are consistent with those using Hall effect measurement. Moreover, the film thickness is consistent with that measured from the cross‐sectional transmission electron microscopy observation.

Acoustic effect of wire mesh liners subjected to grazing flow

The wire mesh liner usually possesses a better acoustic linearity to flow than perforated liners, but it still lacks an impedance model. So, the grazing flow effect of the mesh liner is studied experimentally herein. It reveals that, relative to perforated liners, the mesh liner has qualitatively similar but quantitatively weakened trends in the grazing flow resistance Rg and reactance Xg. As a mesh occurs or as the mesh becomes finer on the flow-saturated perforated surface, Rg is suppressed gradually especially at high frequencies, by lowering its sinking segment, delaying its increasing segment, and decreasing its increasing slope. Furthermore, the effect of a fine mesh can be superimposed with that of a larger orifice diameter dp on lowering the sinking and delaying the increasing, but the former can weaken the effect of the latter on increasing the slope. On another aspect, Xg can also be suppressed evidently by a fine mesh. By contrast, a tested liner with a fine mesh embedded in the middle of perforated plates rather than on the surface exhibits no such a suppressing effect on Rg. Accordingly, a more complete impedance model of the mesh-on-perforated-surface liner considering the grazing flow, mesh type and frequency is established.

Recent advances in the CERN PS impedance model and instability simulations following the LHC Injectors Upgrade project

Transverse instability growth rates in the CERN Proton Synchrotron (PS) are studied thanks to the recently updated impedance model of the machine. Using this model, macroparticle tracking simulations were performed with a new method well-suited for the slicing of short wakes, which achieves comparable performance to the originally implemented method while reducing the required number of slices by a factor of 5 to 10. Furthermore, dedicated beam-based measurement campaigns were carried out to benchmark the impedance model. Until now, beam dynamics simulations based on this model underestimated instability growth rates at injection energy. Thanks to a recent addition to the impedance model, namely the kicker magnets' connecting cables and their external circuits, the simulated instability growth rates are now comparable to the measured ones even when neglecting the impact of the space charge force. Finally, the space charge force is included in simulations and its impact on the instability growth rate and intra-bunch motion is studied.

Current Sharing Analysis and Evaluation of Parallel DC-Link Capacitors in Vehicle Motor Drive

In electric vehicle inverter systems, the DC-link capacitor bank becomes a critical obstacle to high power density due to its large volume. DC-link capacitor bank commonly adopts a multi-core parallel structure. The challenges exist in the current sharing of parallel capacitor cores because of the imbalance of stray parameters in the busbars. A current sharing analysis method aiming at thermal stress for capacitor banks in high-power-density inverters based on the characteristic matrix is proposed in this paper. First, the design basis of DC-link capacitors is given theoretically. Then, the complex coupling impedance model between multiple ports on capacitor busbars is mathematically derived by the matrix method, revealing the current resonance phenomenon of parallel capacitor cores affected by stray parameters. Next, three capacitor banks are evaluated by the proposed current sharing model. The influence of capacitor core arrangement and terminal position on current sharing is explored, which can guide capacitor banks’ high-power-density structure and heat dissipation design. Finally, an experimental platform is built with customized capacitor samples. The experimental results are consistent with the analysis results of the model, verifying the proposed method.

On the Proper Use of a Warburg Impedance

Recent battery papers commonly employ interpretation models for which diffusion impedances are in series with interfacial impedance. The models are fundamentally flawed because the diffusion impedance is inherently part of the interfacial impedance. A derivation for faradaic impedance is presented which shows how the charge-transfer resistance and diffusion resistance are functions of the concentration of reacting species at the electrode surface, and the resulting impedance model incorporates diffusion impedances as part of the interfacial impedance. Conditions are identified under which the two model formulations yield the same results. These conditions do not apply for batteries.

Efficient water-related failure detection in PEM fuel cells: Combining a PEMFCs fractional order impedance model with FFT-PWM techniques and artificial neural network classification

Water management and early detection of faults in proton exchange membrane fuel cells (PEMFCs) are among the most critical constraints that limit the optimal spread of this type of energy. Consequently, it is necessary to enhance the reliability and durability of PEMFCs by developing an approach to diagnose and identify water failure modes. This paper proposes an effective and simple method to detect, diagnose, and classify various water failure modes in PEMFCs using a hybrid diagnostic approach. This approach combines the PEMFC fractional order impedance model (FOIM) with fast Fourier transform pulse width modulation (FFT-PWM) techniques and artificial neural network pattern recognition (ANN-PR) classification. The results show an accurate match between the electrochemical impedance spectroscopy (EIS) experimental data, the Nyquist impedance spectra of FOIM, and the FFT-PWM algorithm as a proposed alternative technique to EIS measurements. Learning of ANN-PR was performed using the frequency spectrum amplitude (FSA) database of the voltage and current signals produced by the PEMFCs FOIM DC/DC boost converter, which was generated using the FFT-PWM algorithm. The ANN-PR achieved low values for error accuracy, with the Low Square Error and Learning Error reaching 6.676 × 10−19 and 1.888 × 10−16, respectively. The elements inside the confusion matrix and the rest of the matrices confirm that the proposed model's accuracy, precision, recall, and high F1 score reached 100%. Furthermore, all predictions made by the ANN-PR model were consistently accurate across all areas of failure detection. Overall, the proposed method helps in analyzing, diagnosing, and classifying fuel cell failure modes such as flooding and drying, which may simplify the health assessment of PEMFC.

Transfer force perception skills to robot‐assisted laminectomy via imitation learning from human demonstrations

AbstractA comparative study of two force perception skill learning approaches for robot‐assisted spinal surgery, the impedance model method and the imitation learning (IL) method, is presented. The impedance model method develops separate models for the surgeon and patient, incorporating spring‐damper and bone‐grinding models. Expert surgeons' feature parameters are collected and mapped using support vector regression and image navigation techniques. The imitation learning approach utilises long short‐term memory networks (LSTM) and addresses accurate data labelling challenges with custom models. Experimental results demonstrate skill recognition rates of 63.61%–74.62% for the impedance model approach, relying on manual feature extraction. Conversely, the imitation learning approach achieves a force perception recognition rate of 91.06%, outperforming the impedance model on curved bone surfaces. The findings demonstrate the potential of imitation learning to enhance skill acquisition in robot‐assisted spinal surgery by eliminating the laborious process of manual feature extraction.

Design of Interleaved Winding for Multilayer Planar Inductor and Its Application in Reducing Current Ringing of LLC Resonant Converter

To enhance the power density of LLC resonant converters, multilayer planar inductors are required. However, multilayer planar inductors have high parasitic capacitance, which may cause inductor current ringing in LLC resonant converters, leading to EMI problems. In this paper, it is found that by using interleaved winding inductors, compared with traditional winding inductors, the parasitic capacitance of multilayer planar inductors is reduced, which can reduce current ringing, without sacrificing power density and increasing manufacturing complexity. The method used to analyze current ringing is to establish an impedance model, and the parasitic capacitance of the interleaved winding inductors is verified by FEM simulations. The analysis is validated in an LLC resonant converter prototype.

An acoustic impedance design method for tubular structures with broadband sound insulations and efficient air ventilation

In this research, we proposed an acoustic impedance-based design method to increase the soundproofing bandwidths and maintain efficient air ventilation for tubular structures consisting of hollow air-flowing channels. This research has great potential to provide design guidelines based on an acoustic impedance model and even/odd mode analysis for hollow-tube ventilated devices containing resonance and antiresonances. We introduced a thin ventilated structure with a subwavelength thickness of 0.107 λ where λ corresponds to the lowest frequency within the filtering bandwidth, a 19.4 % cross-section open for air passage, and a 10 dB fractional bandwidth of 110.2 % (i.e., 90 % sound energy is blocked), which is broader than that of a conventional Fano-like structure of 44.7 %. To experimentally verify the proposed approach, two prototypes, including lateral-coupled and longitudinal-coupled devices, were designed, fabricated with 3D printing, and experimentally characterized via a commercial-available impedance tube system. The simulations matched the measurements and demonstrated the 10 dB fractional bandwidth of 65 % and 91.5 % and ventilation efficiencies of 21.4 % and 33.4 %, respectively. The main contribution of this work is that the proposed approach can be adopted for lateral or longitudinal coupled ventilated structures with broadband sound insulations and lower the effects of resonance-induced sound transmissions. Besides, the proposed acoustic-impedance model can significantly save the required tremendous computational resources and time compared to FEM simulations. Moreover, the proposed lateral and longitudinal ventilated structures are expected to benefit broadband sound filtering and noise reduction for thin panel or tubular silencers

High-frequency characteristics of multilayer graphene nanoribbon interconnects: Exploring the implications OF SKIN effect

A study is undertaken to explore the frequency-dependent traits of crosstalk delay (X-D), crosstalk noise area (X-NA), and the mean time to failure induced by electromigration (EM-MTF) in interconnects constructed from lithium-doped multilayer graphene nanoribbon (Li-MLGNR) and their optimized counterparts, known as optimized Li-MLGNR (O-LiMLGNR) interconnects. The analysis is based on the skin depth and impedance model incorporating scatterers and the finite thickness of the interconnect. The obtained high-frequency impedance and performance characteristics reveals that O-LiMLGNR outperforms Li-MLGNR, rough copper, and mixed carbon nanotube bundle in terms of X-D, X-NA, and EM-MTF. Subsequently, the performance of O-LiMLGNR, limited by process and temperature variations, is analyzed at high frequencies under the influence of skin-effect. As a result of variations in process parameters and temperature, the O-LiMLGNR exhibits an increase in variations of X-D and X-NA, accompanied by a reduction in variation of EM-MTF as the frequency increases.

Small Disturbance Stability Analysis of Onshore Wind Power All-DC Power Generation System Based on Impedance Method

The Onshore Wind Power All-DC Generation System (OWDCG) is designed to integrate with renewable energy sources by modifying the grid structure. This adaptation supports the grid infrastructure and addresses the challenges of large-scale wind power AC collection and harmonic resonance during transmission. Crucially, small disturbance stability parameters are essential for ensuring the system’s stable operation. Unlike conventional power systems, the OWDCG exhibits strong coupling between subsystems, accentuating the small disturbance stability issue due to the dynamic nature of its converter control system. The impedance method facilitates the decomposition of such systems into subsystems, offering insights into the destabilization mechanism through the lens of negative impedance contribution. This approach is conducive to conducting small disturbance stabilization analyses. To tackle this issue, the initial step involves deriving the input and output equivalent impedance models of the subsystem, considering the topological structure, control features, and operational dynamics of the OWDCG. Subsequently, the impact of circuit and control parameters on the system’s impedance characteristics and small-disturbance stability is examined through Bode diagrams and Nyquist curves. This analysis identifies critical parameters for small-disturbance stability, guiding the stable operation and parameter optimization of the OWDCG. The analysis highlights that the main control strategies for stability are the Modular Multilevel Converter (MMC) DC voltage control and the inner-loop current control gain. Validation of the theoretical findings is achieved through simulation results using PSCAD/EMTDC.

Dual-frames-impedance-based analysis of dynamic phase difference effect on grid-forming converter with different power synchronization controls

The grid-forming converters (GFMs) have been widely employed to support the power grid. Yet, the phase difference effect (PHE) caused by active power control (APC) on the system's design and stability is still inexplicable. This paper comprehensively investigates the PHE in the GFM under six APCs in terms of the developed impedance models. We observed that GFM exhibits nearly equal dq-frame impedance across six APCs when the PHE is disregarded. However, when accounting for PHE, the impedance of GFM with P-δ droop-based APCs differs significantly from that with P-ω droop- and virtual synchronous generator (VSG)-based APCs. Additionally, the sequence impedance of GFM with P-ω droop- and VSG-based APCs appears to be largely decoupled, whereas P-δ droop-based APCs introduce substantial sequence impedance coupling. Stability and coupling analyses indicate that the P-δ droop-based GFM must work in a weaker grid for stable operation compared to other APC-based GFM. Furthermore, the resulting frequency coupling leads to a higher amplitude of the coupled frequency (2f1-f) than the dominant frequency (f). Lastly, theoretical analysis is verified by experiments, providing new insights into the future research and design guidelines of GFM.

Stability enhancement control strategy for grid-connected wind power system based on composite feedforward damping

The stability of grid-connected wind power system (GCWPS) is prone to deteriorate due to the impedance interaction between wind turbines and the weak grid. For purpose of finding out the cause of power oscillation and effectively improving the stability of GCWPS under weak grid, firstly of all, a frequency coupling impedance model (FCIM) for GCWPS is established. Through analyzing the impedance characteristic of GCWPS, a significant coupling effect between GCWPS impedance and grid impedance in the middle-low frequency region under weak grid is observed, which is easy to cause power oscillation. For purpose of restraining the power oscillation of GCWPS under weak grid, this paper proposes an oscillation suppression strategy based on composite feedforward damping. Virtual damping is incorporated into the feedforward loop to rectify the impedance characteristic curve of GCWPS. Then, a FCIM of GCWPS that adopts the proposed oscillation suppression strategy is established, and the stability analysis demonstrates that the proposed strategy effectively enhances the GCWPS stability under weak grid. Additionally, compared with conventional control strategy, GCWPS exhibits enhanced adaptability to the increased output power and phase-locked loop (PLL) bandwidth under weak grid. Finally, experiments are undertaken to evidence the feasibility of the proposed oscillation suppression strategy.

Stability analysis and improved control of voltage source converters based on impedance models in weak grids

Stability analysis and improved control of voltage source converters based on impedance models in weak grids

Analysis of Factors Affecting Sub-Synchronous Oscillation in Doubly-Fed Wind Power Grid-Connected System Based on Impedance Sensitivity and Research on Suppression Strategy

Aiming at the matter of sub-synchronous oscillation (SSO) of the doubly-fed induction generator (DFIG) series compensation capacitors grid connection, a SSO suppression strategy based on adding damping controllers in rotor-side converter (RSC) is put forwarded. Considering the control parameters of power and current control loops of RSC, the equivalent impedance model of DFIG series compensation grid connection (SCGC) is established, and then combined with the equivalent RLC resonant circuit of the system, the mechanism and factors of SSO are analyzed by impedance method. Calculating the impedance sensitivity of the system impedance to parameters by sensitivity analysis method, so as to identify the leading factor affecting the SSO characteristics of wind power system. Combined with the stability criterion of system impedance characteristics, the parameters are adjusted to meliorate system stability. Based on the leading factor affecting the SSO and the mechanism of the SSO, the damping controllers are added in the RSC to supply positive damping for the system to eliminate the negative damping brought by the RSC and rotor resistance, thus suppressing the SSO of the system. The validity of the put forwarded suppression strategy is proved through PSCAD/EMTDC simulation.

Theories derived from Haissinski equation and their applications to electron storage rings

As a stationary solution of the Vlasov–Fokker–Planck equation, the Haissinski equation predicts the equilibrium line density of a bunch that circulates in a storage ring for a given wake function. This paper shows that some equations regarding the centroid shift of the bunch, the peak position of the bunch profile, bunch length, and the impedance from the bunch profile can be derived from the Haissinski equation in a self-consistent manner. Specifically, a generalized quadratic equation for potential-well bunch lengthening is derived to accommodate any arbitrary impedance model (that is, the impedance spectrum under consideration can take any form). This expands upon Zotter’s cubic equation, which is primarily applicable to inductive impedance. The equations derived in this paper are tested using computed impedance models for some electron storage rings, showing machine-dependent properties of impedance effects. We conclude that these equations can be employed in electron storage rings to effectively bridge the gap between impedance computations and beam-based measurements.

Equivalence of Impedance Participation Analysis Methods for Hybrid AC/DC Power Systems

Participation analysis based on whole-system impedance models enables the root-cause stability analysis of large-scale power systems when state-space models are unavailable. To extend participation analysis to the hybrid AC/DC system, especially for the interlinking converter, this paper proposes two complementary methods, namely the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">direct method</i> and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">indirect method</i> . The direct method treats the interlinking converter as hybrid AC-DC port apparatus and the participation factor can be defined with the terminal hybrid AC-DC impedance matrix correspondingly. As for the indirect method, system equivalence can be made at the AC or DC terminal of the interlinking converter when impedance models within subsystems are unavailable such that preliminary knowledge of systems can be simplified. Importantly, the equivalence of these two methods on the observability of system components is revealed through theoretical analysis. The proposed impedance participation analysis methods are illustrated with a 4-bus hybrid AC/DC system, a modified 28-bus hybrid AC/DC system and a modified 96-bus hybrid AC/DC system. Numerical calculations and time-domain simulations are performed to validate the theoretical analysis.

Research on DC Voltage Stability Control of Railway Power Conditioner Based on Impedance Matching Principle

When the Railway Power Conditioner (RPC) is used to solve the power quality problem of the electrified railroad, the DC impedance will have a negative impedance characteristic during the bidirectional transmission of RPC power, and this negative impedance characteristic will affect the accuracy of RPC power compensation, cause the fluctuation of RPC DC bus voltage, and affect the effect of negative sequence current management on the grid side. In view of the above problems, this paper proposes an RPC control strategy based on the impedance matching principle, which optimizes the negative impedance characteristics into positive impedance characteristics by the cooperative control of DC voltage and power, increases the phase angle margin of the system, improves the stability and dynamic performance of DC voltage under the bidirectional flow of RPC power, and improves the effect of grid-side negative sequence current management. Firstly, this paper performs small-signal modeling of the DC-side port impedance and analyzes its impedance characteristics. Secondly, the working principle of the RPC control strategy based on the impedance matching principle is analyzed. Finally, the proposed control strategy is effectively verified by building a simulation model and an experimental platform.

A Comprehensive Stability Assessment System for EV DC Charging Station Based on Multitimescale Impedance Model

The existing all-in-one impedance-based stability analysis only qualitatively reveal the instability factors by the graphic Nyquist criterion while the stability margin is not considered. In this article, a design-oriented multiattribute and multidimensional based comprehensive assessment system (MAMD-CAS) is proposed to evaluate the stability quantitatively and guide the parameter design as well as ensure the desired dynamic response and stability margin. This MAMD-CAS mainly includes the loop-gain-based multi-timescale impedance estimation to analyze the low-frequency oscillation (LFO), phase margin (PM) calculation of different timescales and dynamic performance indicators as the time-domain quantitative expression of impedance estimation. In detail, the multi-timescale impedance model is established and its loop-gain representation is deduced to implement the impedance estimation. Combined with the known PM, the influence of the parameters on dynamic performance and stability margin can be comprehensively evaluated, then the conflict between dynamic performance and stability margin is explored. It is found that the voltage-loop parameters do not have the coupling problem between dynamic performance and stability margin while <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vir</sub> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">svr</sub> present a conflicting effect between the inertia-loop LFO dynamic performance and stability margin and their interaction affects the severity of inertia-loop LFO. The appropriate control parameters can be thus selected for a good stability margin while suppressing the impedance peak. This MAMD-CAS analysis result is verified by simulation and experiment and this assessment system provides theoretical fundamental for the online stability monitor of multi-timescale power electronics system.