Impedance Converter Research Articles

Underwater low frequency subwoofer systems

Experiments with a gas-filled adiabatic bubble resonator of large diameter have shown that it is an efficient emitter of low-frequency seismic waves. The resonator has a single resonant frequency with a narrow bandwidth. The internal acoustic resonant structure changes the frequency response of the entire source and makes it possible to expand its bandwidth. An internal Helmholtz resonator converts the system into a double resonant system with a wide bandwidth. The bass-reflex resonator separates the pressure in front and behind the speaker cone, and the speaker works as an internal monopole driver. Any other known loudspeaker enclosure design can be used to create the desired multi-pole frequency response. A specific of the underwater enclosure is that it is loaded into the inner chamber of the bubble resonator. The bubble resonator works as an efficient impedance converter, matching the impedance of the internal resonant system to the water radiation impedance. Examples of various systems and the results of their tests in water are considered. Experiments have shown that a gas-filled underwater bubble covered with an elastic membrane and driven by an audio subwoofer can achieve source levels of 180–185 dB re 1 μPa@1 m over a wide frequency band.

Design and analysis of isolated high step-up Y-source DC/DC resonant converter for photovoltaic applications

ABSTRACT This paper presents the design and analysis of an isolated high step-up Y-source DC/DC converter for photovoltaic systems. At high switching frequencies, the conventional impedance source converter (ISC) experiences higher switching losses. To mitigate this, a high gain soft-switched frequency-modulated Y-source DC/DC converter is proposed. Here, soft switching is implemented on the Y-source impedance converter by creating quasi-resonance during a shoot-through instant. Thus, quasi-resonance occurs by an LC resonant tank, and it is formed using a resonant capacitor and leakage inductance of a transformer. It ensures that all the active switches are turned off with zero current switching (ZCS) and the voltage stress on each switch is much lower than the output voltage with lower turn-off voltage spikes. Thus, it eliminates the need for a snubber circuit. The output voltage is regulated by frequency modulation with the ON period of all four active switches kept constant. The converter can also deliver a continuous input current (CIC) and high voltage gain with a small shoot-through duty ratio . The galvanic isolation of the converter helps to eliminate the leakage current issues and safety hazards faced by the non-isolated counterparts. The proposed topology has all the inherent characteristics of a typical impedance source DC/DC converter with higher conversion efficiency over a wide range of output loads. The proposed converter achieves 96.46% of full load efficiency. Finally, a 200W prototype is built and tested in the laboratory to verify the converter design and performance.

Inertia and Grid Impedance Emulation of Power Grid for Stability Test of Grid-Forming Converter

The virtual synchronous generator (VSG) control is a promising solution for the grid-forming converters to enhance the inertia of the converter-based power grid. The virtual inertia and output impedance of the VSG are the important behaviors to be focused. However, the virtual inertia of grid-forming converters may cause active power oscillation due to the interaction with the power inertia of grid through the low-frequency band grid impedance. Besides, the resonance can be also triggered by the interaction between middle-frequency impedance of power grid and output impedance of converter. In order to test the stability of grid-forming converter, accurate emulation of grid behaviors from more aspects, including inertia and impedance under wider frequency ranges, is becoming critical. This article proposes a grid emulation method to mimic the inertia and impedance characteristics of power grid, targeting for the stability test of grid-forming converter under multifrequency bands. A high-switching-frequency converter and a low-switching-frequency converter are adopted in the proposed emulator structure to achieve both high capability in respect to control bandwidth and power level. Moreover, the virtual impedance control is integrated with the VSG control to emulate the line impedance and inertia within relatively wider frequency ranges. The realization of virtual impedance is achieved without derivation terms nor low pass filter. Finally, the performance of the proposed emulator is verified by various simulations and experimental measurements.

Simultaneous quantitative detection of hematocrit and hemoglobin from whole blood using a multiplexed paper sensor with a smartphone interface.

We report a highly accurate single-step label-free testing technology for simultaneous and independent hematocrit (Hct) and hemoglobin (Hb) level detection from a drop of whole blood by employing a disposable paper strip sensor interfaced with a portable impedimetric device. The paper strip is fabricated by in situ automated printing of a customized electrode template on the non-glossy side of a commercially available photo paper substrate followed by graphite deposition. The integrated platform device technology additionally includes a compact detection cum readout unit comprising a high precision impedance converter system that combines an on-board frequency generator with an analog-to-digital converter evaluation board, collectively interfaced with a central processor, calibration circuit, and smartphone. Employing a dispensed blood sample volume of 25 μL, the device is shown to have a sensitivity of 92 Ω/Hct and 287 Ω/Hb at an optimal frequency of 57 kHz. The respective linear response regimes appear to be wide enough to cover physiologically relevant limits, with excellent stability and reproducibility. Validation with clinical samples reveals limits of detection of Hct and Hb levels as low as 4.66% and 1.89 g dL-1, respectively, which are beyond the quantitative capability of commonly used affordable point of care test kits. The envisaged paradigm of rapid, robust, highly accurate, energy-efficient, simple, user-friendly, multiplex portable detection, obviating any possible ambiguities in interpretation due to common artefacts of colorimetric detection technologies such as optical interference with the image analytical procedure due to the inherent redness of blood samples and background illumination, renders this ideal for deployment in resource-limited settings.

A low‐cost and high‐performance self‐trigger method for high‐voltage transient measurement

AbstractStable triggering of acquisition devices is critical to accurately measure electromagnetic transients, especially for very fast transient overvoltages (VFTOs). A highly stable and low‐cos t self‐trigger method for transient measurement is proposed. An integrated low‐voltage arm module was developed to synchronously realise the triggering and VFTO measurement. The trigger branch was developed using a high‐pass filter. This component obtained the high‐frequency component of the VFTO to trigger the oscilloscope. The trigger branch was integrated with the measurement branch through an impedance converter. An attenuator was implemented before the impedance converter to avoid overvoltage damage to the chip. The circuit parameters of the attenuator were optimised to alleviate the disturbance of the measurement branch. The calibration results demonstrated that the ±1 dB bandwidth of the measurement branch in this system ranged from 11.8 Hz to 105 MHz. The low cutoff frequency of the trigger branch was 710 Hz. The VFTO waveforms generated by the operation of a disconnector in a real 252 kV gas insulated switchgear were measured using the proposed system. The test results verified that the self‐trigger measurement system can provide stable trigger signals and accurately measure the VFTO waveforms.

A broadband active damping method for high-frequency resonance suppression in MMC-HVDC system

Negative damping in modular multilevel converter (MMC) impedance may lead to high-frequency resonance (HFR) in MMC-high-voltage direct current systems. The existing solution is based on amplitude attenuation by digital filters. However, filters have weak amplitude attenuation and obvious phase shifts in the attenuation band, resulting in the transfer of negative damping. The system still has a risk of HFR when grid condition is changed. This study proposed a broadband active damping method based on phase compensation to address this limitation. The embedding position and scheme of the phase compensation controller are optimally designed through impedance-based analysis. By tuning parameters correctly, the negative damping of MMC is eliminated over a wide frequency range (500–2000 Hz). Thus, the proposed method performs better in HFR suppressing under varying grid conditions. In addition, considering the harmonic amplification problem caused by the differential link, an inertia link and a proportional link are further employed to increase high frequency impedance magnitude. Time-domain simulations in MATLAB/SIMULINK verify the effectiveness of the proposed method.

Parasitic Effects on Electrical Bioimpedance Systems: Critical Review.

Parasitic capacitance represents the main error source in measurement systems based on electrical impedance spectroscopy. The capacitive nature of electrodes' impedance in tetrapolar configuration can give origin to phase errors when electrodes are coupled to parasitic capacitances. Nevertheless, reactive charges in tissue excitation systems are susceptible to instability. Based on such a scenario, mitigating capacitive effects associated with the electrode is a requirement in order to reduce errors in the measurement system. A literature review about the main compensation techniques for parasitic capacitance was carried out. The selected studies were categorized into three groups: (i) compensation in electronic instrumentation; (ii) compensation in measurement processing, and (iii) compensation by negative impedance converters. The three analyzed methods emerged as effective against fixed capacitance. No method seemed capable of mitigating the effects of electrodes' capacitance, that changes in the frequency spectrum. The analysis has revealed the need for a method to compensate varying capacitances, since electrodes' impedance is unknown.

Settling-Angle-Based Stability Analysis for Multiple Current-Controlled Converters

This letter proposes a settling-angle-based stability criterion, as the extension of determinant-based general Nyquist criterion, to facilitate the stability analysis of nonminimum phase power systems with multiple current-controlled converters. Using only the phase information of converter impedance in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dq$</tex-math></inline-formula> -frame, the proposed stability criterion can accurately demonstrate the system stability and identify resonance sources according to the settling angles of the overall system and its subsystems, which are validated by simulation and control hardware-in-the-loop results.

Interfacial skin modes at a non-Hermitian heterojunction

We uncover a non-Hermitian skin mode in which the eigenmodes of a nonreciprocal topoelectrical (TE) heterojunction circuit array are localized at the heterojunction interface under both open boundary condition (OBC) and periodic boundary condition (PBC). This is in marked contrast to the conventional non-Hermitian skin effect (NHSE) in homogenous non-Hermitian systems that exists under OBC but vanishes in PBC. The interfacial non-Hermitian skin effect is induced when two non-Hermitian circuit chain segments with dissimilar NHSE decay lengths are cascaded together. It is shown analytically that the interfacial NHSE decay rates are directly associated with the asymmetric intracell couplings in the TE segments. Such nonreciprocal directional couplings can be realized in practical circuits by means of negative impedance converters with current inversion (INIC). In contrast to the conventional NHSE in homogeneous systems, the TE heterojunction circuit allows for a voltage profile localized at the interface, that is independent of the boundary conditions and whose decay length can be modulated by circuit parameters. Finally, the results presented are general and applicable to other analogous non-Hermitian platforms such as photonic and condensed matter nanoscale systems.

Grounded Meminductor Emulator Using Operational Amplifier-Based Generalized Impedance Converter and Its Application in High Pass Filter

This paper exhibits a grounded meminductor emulator designed using an operational amplifier generalized impedance converter (GIC) and a memristor. One of the resistors of GIC has been judiciously replaced by memristor to convert active inductor circuit into meminductor emulator circuits. For the proposed grounded meminductor emulator, pinched hysteresis loops of up to 5kHz have been produced. The simulation findings were obtained using the LTspice simulation tool. The pinched hysteresis loops are shrinking when the frequency is varied from 100 Hz – 5 kHz. A high pass filter has also been constructed and simulated using the proposed meminductor emulator to validate its performance.

An Adaptive Element-Level Impedance-Matched ASIC With Improved Acoustic Reflectivity for Medical Ultrasound Imaging.

This paper presents an active impedance matching scheme that tries to optimize electrical power transfer and acoustic reflectivity in ultrasound transducers. Leveraging negative capacitance-based impedance matching would potentially improve the bandwidth and electrical power transfer while minimizing acoustic reflection of transducer elements and improve uniformity while reducing acoustic crosstalk of transducer arrays. A 16-element transceiver front-end is designed which employs an element-level active capacitive impedance cancellation scheme using an element-level negative impedance converter. The ASIC fabricated in 180-nm HVBCD technology provides high-voltage pulses up to 60 V consuming 3.6 mW and occupying 2.5 mm2. The front-end ASIC is used with a 1-D capacitive micromachined ultrasonic transducer (CMUT) array and its acoustical reflectivity reduction and imaging capabilities have successfully been demonstrated through pulse-echo measurements and acoustic imaging experiments.

DVCC Based (2 + α) Order Low Pass Bessel Filter Using Optimization Techniques

This paper proposes the design and analysis of (2 + α) order low pass Bessel filter using different optimization techniques. The coefficients of the proposed filter are obtained by minimizing the error between transfer functions of (2 + α) order low pass filter and third-order Bessel approximation using simulated annealing (SA), interior search algorithm (ISA), and nonlinear least square (NLS) optimization techniques. The best optimization technique based on the error in gain, cut-off frequency, roll-off, passband, stopband, and phase is chosen for designing the proposed filter. The stability analysis of the proposed filter has also been done in W-plane. The simulated responses of the best optimized proposed filter are attained using the FOMCON toolbox of MATLAB and SPICE. The circuit realization of 2.5 order low pass Bessel filter is done using two DVCCs (differential voltage current conveyors), one generalized impedance converter (GIC) based inductor, and one fractional capacitor. The proposed filter is implemented for the cut-off frequency of 10 kHz using a wideband fractional capacitor. Monte Carlo and noise analyses are also performed for the proposed filter. The MATLAB and SPICE results are shown in good agreement.

Hybrid electromagnetic shunt damper with Coulomb friction and negative impedance converter

Electromagnetic shunt damper (EMSD) offers flexible tunability of linear damping. The low damping force-to-mass ratio of the EMSD, however, hinders those applications which require large damping force. Adding a negative impedance shunt in EMSD circuit can increase its damping force and broaden its effective frequency range at the expense of causing possible instabilities in the control circuit. On the other hand, Coulomb friction damper (FD) can offer a higher damping force-to-mass ratio than EMSD but it is difficult to be precisely controlled due to its nonlinear characteristics and excessive frequency sensitivity. This paper examines, both theoretically and experimentally, two types of hybrid dampers: one combining an EMSD and a Coulomb friction damper (EMSD+FD), and the other EMSD with a voltage negative impedance converter (EMSD+VNIC). Through proper control of the additional damping arising from FD and VNIC, the problem of unstable ESMD+VNIC and the excessive frequency sensitivity of the FD are alleviated. A prototype of EMSD+VNIC+FD is built and tested. The damping force provided by the FD in the prototype is varied by adjusting the normal force applied by a compression spring, while that from the EMSD+VNIC is controlled by adjusting the shunt circuit impedance with a variable resistor. The maximized tunability of the two enhancement methods provides a ninefold increase of the tunable damping range and a sixfold increase of the damping force-to-mass ratio of the EMSD. The proposed EMSD+VNIC+FD is finally applied and tested experimentally to achieve H∞ optimization of a ground-hooked dynamic vibration absorber for the minimization of resonant vibration of a single-degree-of-freedom system.

An Impedance Converter-Based Probe Characterization Method for Magnetic Materials’ Loss Measurement

As an essential component in power applications, magnetic cores and their design play an important role in achieving high efficiency and high power density. Accurate measurement of the core loss is important for inductor and power converter optimization. Loss measurement depends on exactly determining the phase angle between the voltage and the current. However, measurement errors can be introduced due to the discrepancies in propagation delays in the voltage and current sensors. In addition, the propagation delay is frequency-dependent but has a large influence in the MHz range and above. Previously, several methods have been proposed to compensate for this discrepancy, but they are time-consuming and can result in large measurement errors. In this article, a characterization method for core loss based on a vector network analyzer (VNA) and an impedance converter is proposed to accurately measure the phase discrepancies between voltage and current sensors. The proposed method is experimentally verified up to 15 MHz with a three-coil test setup.

Impedance Characteristics and Harmonic Analysis of LCL-Type Grid-Connected Converter Cluster

This study addresses the output impedance model of the LCL-type grid-connected converter considering the dead-time effects and the digital control delay. The model shows that the digital control delay will affect the accuracy of the output impedance of the grid-connected converter, and the dead-time effects are only equivalent to superimposing a disturbance voltage on the original output impedance model. The derived output impedance model is verified by comparing it with the switching model in the PSIM simulation environment. The harmonic interaction between converter cluster and utility grid is modeled and analyzed based on the output impedance model. A combined harmonic suppression strategy is incorporated into every converter control scheme to suppress the harmonic interaction. Simulation results are presented to demonstrate the correctness of harmonic interaction analysis and the effectiveness of the proposed suppression strategy.

Impedance-Based Stability Analysis of DAB Converters With Single-, Double-, or Cooperative Triple-Phase-Shift Modulations and Input LC Filter

The impedance-based criterion has turned out to be a very effective tool for the stability analysis of the dual active bridge (DAB) converter with its input LC filter. While the input impedance of the DAB converter is highly dependent on the modulation methods, the influences of the modulation methods on the input impedances of the DAB converters are still not clear. To close this gap, three typical modulation methods of DAB converters, traditional single-phase-shift (SPS), dual-phase-shift (DPS) and the emerging cooperative triple-phase-shift (CTPS) modulation, are studied in this paper. First, the full-order input impedance models of the DAB converter with these modulation methods are derived for the first time. Second, based on the developed models, the impacts of these modulation schemes on the DAB input impedances are revealed. An interesting phenomenon is found that the open-loop impedances of SPS-DAB and DPS-DAB converters present the characteristics of the parallel-connected inductor and capacitor, while the open-loop impedance of CTPS-DAB converter presents the resistor characteristics. Third, the optimal modulation scheme for system stability is investigated. Finally, the theoretical analysis has been validated by the experimental results.

Analysis, Design and Realization of Negative Impedance Converter Circuit with Current Feedback Operational Amplifier

Analysis, Design and Realization of Negative Impedance Converter Circuit with Current Feedback Operational Amplifier

Multi-orbital topolectrical circuit for topological quantum states

Remarkable progress has been made in using electric circuits as a powerful platform to realize a plethora of exotic topological quantum states, even of higher orders and/or dimensions. So far the proposed circuits are restricted to a single-orbital tight-binding model with different lattices. Here, we introduce the concept of a multi-orbital topolectrical circuit and construct practical LC circuits to demonstrate its superiorities. As a proof of concept, we assemble two sets of inductors in one plaquette to simulate a (px, py )-orbital model within a two-dimensional hexagonal lattice. In the presence of spin–orbit coupling, as generated by mixing voltage degrees of freedom, a quantum spin Hall (QSH) state emerges with spin-resolved edge modes propagating along the boundary in the time domain. Implementation of negative impedance converters (NICs) with nonreciprocal links transforms the circuit into a quantum anomalous Hall (QAH) state. Remarkably, we demonstrate that QSH/QAH states can be reversibly switched by tuning the resistance of NIC, and an experimental observable-edge distance ratio is proposed to facilitate the phase transition detection. This work provides an exciting playground for exploring multi-orbital physics in topolectrical circuits, paving the way for future applications in nanoelectronics, telecommunications, signal processing and quantum computing.

A Triple-Band Microstrip Antenna with a Monopole Impedance Converter for WLAN and 5G Applications

In this study, a triple-band microstrip antenna with compact size and simple structure is proposed for WLAN and 5G applications. The radiating element consists of a circular patch, a Y-shaped patch, and a monopole impedance converter. In order to obtain the desired operating bands, the monopole impedance converter is inserted between the circular patch and Y-shaped patch. The proposed antenna can work in the frequency range of 2.38∼2.53 GHz, 3.29∼4.11 GHz, and 4.72∼5.01 GHz, with the corresponding peak gains of 4.09 dBi (2.4 GHz), 2.95 dBi (3.5 GHz), and 4.01 dBi (4.9 GHz), respectively. The measures’ results are in approximate agreement with the simulated values, which shows that the proposed compact antenna can offer omnidirectional radiation, appropriate gains, and sufficient bandwidths.

Study of Operational Amplifier Test Procedure and Methods

In this paper, we present about the study of operational amplifier test procedure and methods. Operational Amplifiers (Op-amps) are one of the most widely used building blocks for analog and mixed-signal systems. They are employed from dc bias applications to high-speed amplifiers and filters. General purpose op-amps can be used as buffers, summers, integrators, differentiators, comparators, negative impedance converters, and many other applications. The two-pole model widely used in the test analysis to assess the parameters of an op amp is not accurate and may be unsuitable for gain boosting op amp designs. A more complex model with more than two poles may require tedious analysis and a large amount of calculation. Most reported op amp measurement methods require a complicated test circuit, delicate calibration, and sophisticated test instrumentation. The practical bench test of the open loop gain along with other op amp characteristics are addressed alsoin this paper.