Input Admittance Research Articles

Mixed Lumped and Distributed Circuits in Wideband Bandpass Filter Application for Spurious-Response Suppression

Mixed lumped and distributed circuits (MCs) have been analyzed and applied in a wideband bandpass filter (BPF) synthesis procedure for spurious-response suppression. First, an MC is proposed and compared with the conventional commensurate line. With the even–odd mode analysis, the MC is decomposed into an inverter and the shunt stubs on the two sides, which finds its lowpass equivalent circuit. Then, constant and frequency mapping functions, simply formed by two basis functions, are derived to link the MC and its lowpass equivalent circuit. With this technique, the lowpass prototype filter can be mapped to its BPF counterpart. Finally, the BPF design variables are obtained by comparing the input admittances of the even/odd mode in the MC or the shunt stubs to the basis functions. A fifth-order ladder type BPF has been implemented following the proposed procedure. The experimental results accurately predict both wide passband and spurious-response rejection band.

Investigation of subsynchronous control interaction in DFIG-based wind farms connected to a series compensated transmission line

The aim of this paper is to investigate the risk for subsynchronous control interaction (SSCI) in doubly-fed induction generator (DFIG) based wind farms connected to series-compensated transmission lines. For this purpose, a detailed analytical model of the frequency-dependent input admittance of the DFIG is derived. The developed admittance model is then used to get insights on the frequency characteristic of the DFIG wind turbine generator unit. In particular, the power-dissipation properties of the DFIG are used to identify those control parameters and operating condition that mainly impact the behaviour of the wind turbine in the subsynchronous frequency range. The admittance model of the wind farm together with the impedance model of the series-compensated transmission line are used to identify the risk for SSCI. Through the use of the Generalized Nyquist Criterion, it is shown that the closed-loop bandwidth of the current controller that regulates the rotor current has a major detrimental impact on the stability of the system. Furthermore, results show that the active power set-point and the level of series compensation also play an important role on the overall system’s stability. Time-domain simulations are conducted to validate the theoretical findings.

Realization of Multiple Concurrent Beams With Independent Circular Polarizations by Holographic Reflectarray

A multibeam radiator with each beam possessing independent polarization is developed by a single-feed holographic reflectarray (RA) antenna without using any optimization algorithms. Regardless of wave polarization, the relation between the electromagnetic properties of the antenna aperture (henceforth referred to as “hologram”) and impinging wave properties can be described by the holographic technique. For the practical implementation of such a hologram, we used a subwavelength metallic patch with anisotropic properties to satisfy the input admittance distribution of the hologram. In doing so, a fast numerical method, fundamentally inspired by the method of moments, is employed to calculate the input admittance of the element for all angles of incidence. This technique significantly speeds up the design process. Finally, as a typical case, a simple circularly polarized RA with four-beam radiation pattern was manufactured and tested at 13 GHz. The measured results showed that the aperture efficiency of 45.8%, cross-polarization discrimination of higher than 25 dB, 1 dB drop gain, 3 dB axial ratio bandwidths of 19.23% and 18.26%, sidelobe level of below −17 dB, and peak gain of around 19.43 dBi for each beam were obtained.

Robust Admittance Shaping Approach to Grid Current Harmonic Attenuation and Resonance Damping

This paper presents a novel grid current control of a grid-connected voltage source converter with an LCL filter. The proposed control method uses an $\mathcal {H}_\infty$ synthesis method to shape the input admittance of the converter, to track a given current reference, and/or to limit the controller actuation at different frequency ranges. The converter admittance is shaped, both in magnitude and phase, following a model reference defined by the designer in the frequency domain. By specifying a low admittance magnitude reference, the optimization algorithm will obtain a controller that actively damp the filter resonance and attenuate/reject the grid voltage oscillations, either in a wide frequency range or concentrated at the main harmonic frequencies. Additionally, the proposed controller design methodology takes advantage of its admittance phase shaping capability to improve the system robustness in front of grid uncertainties and minimizing converter impact over grid stability due to its positive-real nature. The synthesized controller only measures the grid current and voltage to achieve the aforementioned results, reducing the number of sensors (and their associated cost) required for its implementation. Experimental results illustrate the correct behavior of the closed-loop system with the designed controller in time and frequency domain.

Impedance-Based Harmonic Instability Assessment in a Multiple Electric Trains and Traction Network Interaction System

This paper presents an impedance-based method to systematically investigate the interaction between multiple trains and a traction network, focusing on evaluating the harmonic instability problem. First, the interaction mechanism of the multitrain and the traction network is represented as a feedback interconnection of the two subsystems, i.e., an equivalent output impedance of the traction network and an equivalent input admittance of the multitrain. Then, the harmonic instability is evaluated through a series of pole-zero diagrams drawn from the closed-loop transfer matrix of the multitrain and network system. The interaction system is unstable, and the harmonic instability will happen if there are some high-frequency poles of the closed-loop system locating in the right-half plane. This method is used for analyzing the harmonic instability phenomena, the characteristics, influential factors, and potential mitigation schemes. The theoretical results are further validated by the simulations and experiments.

In2O5Sn based transparent gate recessed channel MOSFET: RF small-signal model for microwave applications

This paper discusses the small signal RF model of Transparent Gate Recessed Channel (TGRC) MOSFET using a 3D TCAD device simulator. Small signal model is studied in terms of microwave parameters such as S (scattering) parameters, Z (impedance) parameters, Y (admittance) parameters, and h (hybrid) parameters with an aim to analyze the behavior of TGRC MOSFET at microwave frequency. All the results of TGRC-MOSFET have been compared with Conventional Recessed Channel (CRC) MOSFET having aluminum as gate metal electrode. Modeled results have also been compared with simulation results and found good agreement with the 3D-simulation results. Moreover, it is perceived from the results that 99.4% enhancement in the input impedance of TGRC-MOSFET and input admittance is improved by 32.9% in the proposed device (TGRC-MOSFET) in comparison to CRC-MOSFET. It has also been observed that the transit (cut-off) frequency (fT) and maximum oscillator frequency (fMAX) enhances significantly by 42.85% and 123% respectively in TGRC MOSFET owing to the remarkable reduction in intrinsic capacitances. Results reveal that the proposed device design improves the small signal behavior thus, may provide detailed insight to RF engineers for microwave applications and testing of RF ports.

Holographic-Inspired Multibeam Reflectarray With Linear Polarization

In this paper, a novel systematic method based on the holographic theory to design a reflectarray (RA) antenna is presented. According to the holographic technique, one can record features of electromagnetic waves impinging on a specific surface and then, whenever needed, reconstruct each of them. We exploit this property to design a single-feed RA with a multibeam linearly polarized pattern without using any iterative method such as optimization algorithms in the design process. At first, various kinds of interferograms along with related input admittance distributions are introduced according to the polarization and number of radiated beams. Afterward, a simple subwavelength metallic patch as a scalar admittance unit cell is employed to implement the input admittance distribution of the interferograms. Moreover, a fast analytical method, which is fundamentally inspired by the method of moments, has been employed to calculate the input admittance of the utilized element. Finally, as a typical case, an 18 cm $\times $ 18 cm linearly polarized RA with a two-beam radiation pattern has been manufactured and tested at 15 GHz. The sidelobe level, cross-pol, and efficiency of the antenna are found −26 dB, lower than −10 dB, and 47.2%, respectively, which meet the expectations.

Electric Vehicle Fast-Charging Station Unified Modeling and Stability Analysis in the dq Frame

The electric vehicle fast-charging station is an important guarantee for the popularity of electric vehicle. As the fast-charging piles are voltage source converters, stability issues will occur in the grid-connected fast-charging station. Since the dynamic input admittance of the fast-charging pile and the dynamic output impedance play an important role in the interaction system stability, the station and grid interaction system is regarded as load-side and source-side sub-systems to build the dynamic impedance model. The dynamic input admittance in matrix form is derived from the fast-charging pile current control loop considering the influence of the LC filter. Similarly, the dynamic output impedance can be obtained similarly by considering the regional power grid capacity, transformer capacity, and feed line length. On this basis, a modified forbidden region-based stability criterion is used for the fast-charging station stability analysis. The frequency-domain case studies and time-domain simulations are presented next to show the influence of factors from both the power grid side and fast-charging pile side. The simulation results validated the effectiveness of the dq frame impedance model and the stability analysis method.

A finite element approach for the calculation of self and mutual radiation impedances of resonators.

A simulation method relying on the finite and infinite element techniques and a post-processing routine is introduced in this paper for the calculation of self and mutual radiation impedances of horns and acoustical resonators. The proposed procedure can be applied for the evaluation of the frequency dependent coupling impedance matrix of an arbitrary number of ducts in an arbitrary geometrical arrangement. The resulting impedance matrix can be utilized in a one-dimensional low-frequency waveguide model in order to calculate the input impedance or admittance function of the system. The applicability and usefulness of the proposed methodology is demonstrated by multiple simulation cases.

Analytical Derivation of the AC-Side Input Admittance of a Modular Multilevel Converter With Open- and Closed-Loop Control Strategies

This paper deals with the derivation of the ac-side input admittance of a grid-connected modular multilevel converter (MMC) under both open- and closed-loop ac-side current control strategies. The contribution of the internal dynamics of the MMC on the input admittance depends on the type of ac-side controllers implemented. For this reason, the input admittance is first derived with the MMC operating in open loop on the ac side. The results are then modified to include various ac-side controllers in order to analyze the impact of the internal dynamics of the MMC on the total input admittance. Based on the findings, recommendations are given on modeling the input admittance of the MMC. Finally, the derived analytical models are verified using a detailed switching model of the MMC in the frequency domain.

Analytical derivation of the DC‐side input admittance of the direct‐voltage controlled modular multilevel converter

The input admittance of a converter, connected to other dynamic subsystems, is a useful tool to investigate whether poorly damped oscillations or even unstable conditions might occur at certain frequencies. This is of interest in applications employing the modular multilevel converter (MMC), where the internal dynamics of the converter and the increased number of control loops greatly affect the MMC’s dynamic behaviour, compared to other types of converters. In this paper, the dc-side input admittance of the direct-voltage controlled MMC is derived analytically and verified via small-signal perturbation in a detailed nonlinear time-domain simulation model. The MMC’s input admittance is parametrically studied and compared to the dc-side input admittance of an equivalent two-level converter.

Transient and Steady-State Response of a Fractional-Order Dynamic PV Model Under Different Loads

In this paper, a fractional-order dynamic model of the photovoltaic (PV) solar module is introduced. Dynamic modeling of PV solar modules is useful when used in switching circuits and grid-connected situations. The dynamic elements of the proposed model are a fractional-order inductor and capacitor of two independent orders which allow for two extra degrees of freedom over the conventional dynamic model. The step response and transfer function of the load current are investigated for different orders under resistive and supercapacitor loading conditions. Closed-form expressions for the time response of the load current at equal orders of capacitor and inductor are derived. Stability analysis of the load current transfer function is carried out for different orders and loading conditions. The regions for pure real and pure imaginary input admittance scenarios are calculated numerically for both resistive and supercapacitor load cases. It is found that the order of the inductor has a dominant effect on the responses. As a proof of concept, the model is fitted to experimental data to show its flexibility in regenerating the actual response. The fitted fractional-order model response is compared to optimized integer-order ones from literature showing noticeable improvement.

VSC Input-Admittance Modeling and Analysis Above the Nyquist Frequency for Passivity-Based Stability Assessment

The interconnection stability of a grid-connected voltage-source converter can be assessed via the dissipative properties of its input admittance. In this paper, the modeling of the current control loop is revisited with the aim to improve the accuracy of the input-admittance model above the Nyquist frequency of the converter control system. Particular care is taken in the modeling of the pulsewidth-modulation and sampling processes. It is shown that, in order to eliminate the risk for destabilization of poorly damped grid resonances, dissipativeness of the input admittance is desirable not only for frequencies below, but also above, the Nyquist frequency. Validation is made by simulations and experiments.

Fluid-Structure Finite-Element Modelling and Clinical Measurement of the Wideband Acoustic Input Admittance of the Newborn Ear Canal and Middle Ear.

The anatomical differences between the newborn ear and the adult one result in different input admittance responses in newborns than those in adults. Taking into account fluid-structure interactions, we have developed a finite-element model to investigate the wideband admittance responses of the ear canal and middle ear in newborns for frequencies up to 10kHz. We have also performed admittance measurements on a group of 23 infants with ages between 14 and 28days, for frequencies from 250 to 8000Hz with 1/12-octave resolution. Sensitivity analyses of the model were performed to investigate the contributions of the ear canal and middle ear to the overall admittance responses, as well as the effects of the material parameters, measurement location and geometrical variability. The model was validated by comparison with our new data and with data from the literature. The model provides a quantitative understanding of the canal and middle-ear resonances around 500 and 1800Hz, respectively, and also predicts the effects of the first resonance mode of the middle-ear cavity (around 6kHz) as well as the first and second standing-wave modes in the ear canal (around 7.2 and 9.6kHz, respectively), which may explain features seen in our high-frequency-resolution clinical measurements.

Chinchilla middle ear transmission matrix model and middle-ear flexibility.

The function of the middle ear (ME) in transforming ME acoustic inputs and outputs (sound pressures and volume velocities) can be described with an acoustic two-port transmission matrix. This description is independent of the load on the ME (cochlea or ear canal) and holds in either direction: forward (from ear canal to cochlea) or reverse (from cochlea to ear canal). A transmission matrix describing ME function in chinchilla, an animal commonly used in auditory research, is presented, computed from measurements of forward ME function: input admittance YTM, ME pressure gain GMEP, ME velocity transfer function HV, and cochlear input admittance YC, in the same set of ears [Ravicz and Rosowski (2012b). J. Acoust. Soc. Am. 132, 2437-2454; (2013a). J. Acoust. Soc. Am. 133, 2208-2223; (2013b). J. Acoust. Soc. Am. 134, 2852-2865]. Unlike previous estimates, these computations require no assumptions about the state of the inner ear, effectiveness of ME manipulations, or measurements of sound transmission in the reverse direction. These element values are generally consistent with physical constraints and the anatomical ME "transformer ratio." Differences from a previous estimate in chinchilla [Songer and Rosowski (2007). J. Acoust. Soc. Am. 122, 932-942] may be due to a difference in ME flexibility between the two subject groups.

H∞current controller for input admittance shaping of VSC-based grid applications

This paper presents a current controller that shapes, in the frequency domain, the input admittance of voltage-source converters connected to the grid. The controller is obtained by means of a H ∞ synthesis procedure, which minimizes the difference between the application closed-loop input admittance and a model-reference defined by the designer. This formulation achieves good accuracy in both modulus and phase. The proposed methodology allows the fulfilment of other current control objectives, such as current tracking, by defining frequency regions where each objective is desired. Experimental results show the good response of the proposed controller, both in frequency and time domain.

Stability Analysis and Stability Enhancement Based on Virtual Harmonic Resistance for Meshed DC Distributed Power Systems with Constant Power Loads

This paper addresses the stability issue of the meshed DC distributed power systems (DPS) with constant power loads (CPLs) and proposes a stability enhancement method based on virtual harmonic resistance. In previous researches, the network dynamics of the meshed DC DPS are often ignored, which affects the derivation of the equivalent system impendence. In addition, few of them have considered the meshed DC DPS including multiple sources with voltage-controlled converters and CPLs. To tackle the aforementioned challenge, this paper mainly makes the following efforts. The component connection method (CCM) is employed and expanded to derive the stability criterion of the meshed DC DPS with CPLs. This stability criterion can be simplified to relate only with the network node admittance matrix, the output impendences of the sources, and the input admittances of the CPLs. A virtual harmonic resistance through the second-order generalized integrator (SOGI) is added in the source with the voltage-controlled converter to lower the peak of the source output impendence, which can enhance the stability of the meshed DC DPS. The effectiveness of the proposed stability criterion and stability enhancement method are verified by nonlinear dynamic simulations.

Design of compact diplexer with novel matching network using cascaded quadruplet filters

ABSTRACTThis letter reports a new kind of matching network to design diplexer. The matching network is comprised by two open‐circuited and one short‐circuited transmission lines. By properly adjusting the input admittance of the matching network, each channel of the diplexer can be designed independently. Therefore, the diplexer can be easily realized by the connection of different bandpass filters without further tuning. Moreover, the proposed matching network occupies little place, and thus the size of the diplexer is mostly determined by the filters. Systematic design procedure for the network is fully presented in this letter. To illustrate the concept, a diplexer is designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:315–318, 2017

Power delivery to a piezoelectric transducer embedded in an elastic body by acoustic waves

ABSTRACTWe studied the transmission of power to a piezoelectric transducer embedded in an elastic body by acoustic waves. A four-layer mechanics model was constructed. A theoretical analysis was performed using the equations of linear piezoelectricity and elasticity. The input admittance, the output voltage and the efficiency of the power transmission structure were calculated. It was shown that significant energy transmission can be produced at a few resonant frequencies. The effects of various physical and geometric parameters were examined. The performance of the structure is sensitive to these parameters and design optimization is necessary for effective power transmission. It was found that the location of the piezoelectric transducer inside the elastic body does not matter much. As long as the strain in the transducer is large and does not change its sign along the transducer thickness, a significant output can be received.

Finite-Element Modelling of the Acoustic Input Admittance of the Newborn Ear Canal and Middle Ear.

Admittance measurement is a promising tool for evaluating the status of the middle ear in newborns. However, the newborn ear is anatomically very different from the adult one, and the acoustic input admittance is different than in adults. To aid in understanding the differences, a finite-element model of the newborn ear canal and middle ear was developed and its behaviour was studied for frequencies up to 2000Hz. Material properties were taken from previous measurements and estimates. The simulation results were within the range of clinical admittance measurements made in newborns. Sensitivity analyses of the material properties show that in the canal model, the maximum admittance and the frequency at which that maximum admittance occurs are affected mainly by the stiffness parameter; in the middle-ear model, the damping is as important as the stiffness in influencing the maximum admittance magnitude but its effect on the corresponding frequency is negligible. Scaling up the geometries increases the admittance magnitude and shifts the resonances to lower frequencies. The results suggest that admittance measurements can provide more information about the condition of the middle ear when made at multiple frequencies around its resonance.