Showing papers on "Electrical impedance published in 2019"
TL;DR: The proposed topolectrical Chern circuit features an admittance bulk gap fully tunable via the resistors used in the INICs, along with a chiral voltage boundary mode reminiscent of the Berry flux monopole present in the admittance band structure.
Abstract: We propose an electric circuit array with topologically protected unidirectional voltage modes at its boundary. Instead of external bias fields or Floquet engineering, we employ negative impedance converters with current inversion (INICs) to accomplish a nonreciprocal, time-reversal symmetry-broken electronic network we call a topolectrical Chern circuit (TCC). The TCC features an admittance bulk gap fully tunable via the resistors used in the INICs, along with a chiral voltage boundary mode reminiscent of the Berry flux monopole present in the admittance band structure. The active circuit elements in the TCC can be calibrated to compensate for dissipative loss.
208 citations
TL;DR: The harmonic state-space (HSS) modeling approach is first introduced to characterize the multiharmonic coupling behavior of the MMC, and small-signal impedance models are developed based on the proposed HSS model of theMMC, which are able to include all the internal harmonics within the M MC, leading to accurate impedance models.
Abstract: The small-signal impedance modeling of a modular multilevel converter (MMC) is the key for analyzing resonance and stability of MMC-based power electronic systems. The MMC is a power converter with a multifrequency response due to its significant steady-state harmonic components in the arm currents and capacitor voltages. These internal harmonic dynamics may have great influence on the terminal characteristics of the MMC, which, therefore, are essential to be considered in the MMC impedance modeling. In this paper, the harmonic state-space (HSS) modeling approach is first introduced to characterize the multiharmonic coupling behavior of the MMC. On this basis, the small-signal impedance models of the MMC are then developed based on the proposed HSS model of the MMC, which are able to include all the internal harmonics within the MMC, leading to accurate impedance models. Besides, different control schemes for the MMC, such as open-loop control, ac voltage closed-loop control, and circulating current closed-loop control, have also been considered during the modeling process, which further reveals the impact of the MMC internal dynamics and control dynamics on the MMC impedance. Furthermore, an impedance-based stability analysis of the MMC-high-voltage direct current connected wind farm has been carried out to show how the HSS-based MMC impedance model can be used in practical system analysis. Finally, the proposed impedance models are validated by both simulation and experimental measurements.
188 citations
TL;DR: In this paper, a 400-nm-thick platelet of crystalline ZY-LiNbO 3, narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear-wave bulk acoustic resonances (XBARs), by utilizing lateral electric fields oriented parallel to the crystalline Y-axis and parallel to plane of the platelet.
Abstract: In a free-standing 400-nm-thick platelet of crystalline ZY-LiNbO
3
, narrow electrodes (500 nm) placed periodically with a pitch of a few microns can eXcite standing shear-wave bulk acoustic resonances (XBARs), by utilising lateral electric fields oriented parallel to the crystalline Y
-axis and parallel to the plane of the platelet. The resonance frequency of ~4800 MHz is determined mainly by the platelet thickness and only weakly depends on the electrode width and the pitch. Simulations show quality-factors (
Q
) at resonance and anti-resonance higher than 1000. Measurements of the first fabricated devices show a resonance Q
-factor ~300, strong piezoelectric coupling ~25%, (indicated by the large Resonance-antiResonance frequency spacing, ~11%) and an impedance at resonance of a few ohms. The static capacitance of the devices, corresponds to the imaginary part of the impedance ~100 Ω. This device opens the possibility for the development of low-loss, wide band, RF filters in the 3-6 GHz range for 4th and 5th generation (4G/5G) mobile phones. XBARs can be produced using standard optical photolithography and MEMS processes. The 3rd, 5th, 7th, and 9th harmonics were observed, up to 38 GHz, and are also promising for high frequency filter design.
111 citations
TL;DR: The generalized distribution of relaxation times (GDRT) analysis as mentioned in this paper was proposed for complex superposed impedance spectra that include ohmic, inductive, capacitive, resistive-capacitive, and resistiveinductive effects.
Abstract: Impedance spectroscopy is a universal nondestructive tool for the analysis of the polarization behavior of electrochemical systems in frequency domain. As an extension and enhancement of the standard impedance spectroscopy, the distribution of relaxation times (DRT) analysis was established, where the spectra are transferred from frequency into time domain. The DRT helps to analyze complex impedance spectra by identifying the number of polarization processes involved without prior assumptions and by separating and quantifying their single polarization contributions. The DRT analysis, as introduced in literature, claims to be a model-free approach for the characterization of resistive-capacitive systems. However, a data preprocessing step based on impedance models is often required to exclude non-resistive-capacitive components off the measured impedance spectra. The generalized distribution of relaxation times (GDRT) analysis presented in this work is dedicated to complex superposed impedance spectra that include ohmic, inductive, capacitive, resistive-capacitive, and resistive-inductive effects. The simplified work flow without preprocessing steps leads to a reliable and reproducible DRT analysis that fulfills the assumption of being model-free. The GDRT is applicable for the analysis of electrochemical, electrical, and even for non-electrical systems. Results are shown for a lithium-ion battery, a vanadium redox flow battery, and for a double-layer capacitor.
98 citations
TL;DR: To address the unbalanced and harmonic power sharing issue among parallel inverters caused by feeder impedance mismatch in islanded microgrids, an adaptive virtual impedance control method is proposed based on the injection of an extra small ac signal (SACS) in the output voltage of each inverter.
Abstract: To address the unbalanced and harmonic power sharing issue among parallel inverters caused by feeder impedance mismatch in islanded microgrids, an adaptive virtual impedance control method is proposed based on the injection of an extra small ac signal (SACS) in the output voltage of each inverter. Similar to the principle of active power–frequency droop, the frequency of the injected signal droops with the output unbalanced and harmonic power, while the active power produced by the injected SACS is detected to adjust the virtual impedance at the fundamental negative sequence and selected harmonic frequencies, which will tune the distribution of unbalanced and harmonic power in the system. When the injected SACSs of each inverter synchronize with each other and reach a common frequency in steady state, the virtual impedance of each inverter will be matched to each other for evenly sharing the unbalanced and harmonic power. This proposed method requires neither communication links among parallel inverters nor feeder impedance information. Furthermore, the control parameter design method based on modeling and stability analysis of the proposed control structure is discussed in detail. Finally, simulation and experimental results are provided to validate the effectiveness of the proposed scheme.
95 citations
TL;DR: In this paper, an analytical impedance model is developed for capturing the interactions between the dc-link voltage control and ac current control of converters, which enables to identify different stability impacts of the dc link voltage control in the rectifier and inverter operation modes.
Abstract: This paper addresses the stability issues caused by the dc-link voltage control of grid-connected voltage-source converters. An analytical impedance model is developed first for capturing the interactions between the dc-link voltage control and ac current control of converters, which enables to identify different stability impacts of the dc-link voltage control in the rectifier and inverter operation modes of converters. The impedance model is further transformed from the $dq$ -frame to the $\alpha \beta $ -frame, which allows characterizing the frequency-coupling effects of the dc-link voltage control dynamics. The impedance-based analysis reveals that the dc-link voltage control may cause low-frequency oscillations in the rectifier mode and high-frequency oscillations in the inverter mode. Case studies on the rectifier and inverter operation modes are presented, and subsequently validated by using time-domain simulations and experimental tests. The close correlations between the measured results and theoretical analysis demonstrate the effectiveness of the impedance model and stability analysis.
94 citations
TL;DR: The capacitor-current proportional-integral (PI) positive feedback active damping method is proposed that can ensure a positive equivalent resistance almost within the Nyquist frequency, i.e., the full controllable frequency range.
Abstract: Capacitor-current-feedback active damping has been widely used in LCL -type grid-connected inverters. However, the damping performance is deteriorated due to the negative equivalent resistance resulted by the digital control delays, and thus the grid-connected inverter is apt to be unstable under the grid impedance variation. To address this issue, this paper proposes the capacitor-current proportional-integral (PI) positive feedback active damping method that can ensure a positive equivalent resistance almost within the Nyquist frequency, i.e., the full controllable frequency range. In theory, the proposed damping method can be implemented by feeding back the capacitor current through a PI function. However, the integral term will continuously accumulate the noise and dc bias arising from the feedback signal. To overcome this drawback, a more practical implementation solution is drawn in this paper. Furthermore, a straightforward design procedure is presented for the convenience of selecting the proper controller parameters. With the proposed damping method and its practical implementation, high inverter robustness against the grid impedance variation can be achieved. Experiments are performed on a 6-kW prototype and the experimental results are in well agreement with the theoretical expectations.
89 citations
TL;DR: In this article, the perovskite-contact interfaces are described as transistors which couple ionic charge redistribution to energetic barriers controlling electronic injection and recombination, revealing an amplification factor between the out of phase electronic current and the ionic current.
Abstract: Mobile ions in hybrid perovskite semiconductors introduce a new degree of freedom to electronic devices suggesting applications beyond photovoltaics. An intuitive device model describing the interplay between ionic and electronic charge transfer is needed to unlock the full potential of the technology. We describe the perovskite-contact interfaces as transistors which couple ionic charge redistribution to energetic barriers controlling electronic injection and recombination. This reveals an amplification factor between the out of phase electronic current and the ionic current. Our findings suggest a strategy to design thin film electronic components with large, tuneable, capacitor-like and inductor-like characteristics. The resulting simple equivalent circuit model, which we verified with time-dependent drift-diffusion simulations of measured impedance spectra, allows a general description and interpretation of perovskite solar cell behaviour.
87 citations
TL;DR: In this paper, the Warburg impedance of Li-ion cells at very low frequencies down to 0.1 µmHz was investigated using electrochemical impedance spectroscopy (EIS).
Abstract: In this work we investigate the Warburg impedance of Li-ion cells at very low frequencies down to 0.1 mHz. Three different Li-ion cells are used, two 18650-type and one pouch cell of 80 Ah. The measurements are conducted with electrochemical impedance spectroscopy (EIS). The open circuit voltage is measured separately to enable a correction due to voltage hysteresis effects. It is found that the Warburg impedance does not only dependent on the state of charge (SoC) but also on the SoC setting current, the rest time after SoC setting, the sinusoidal excitation amplitude and the charge and discharge history of the cell. It is assumed that the reason for these dependencies are the hysteresis of the open circuit voltage as well as the hysteresis of the cell thickness.
80 citations
TL;DR: In this article, a frequency-selective rasorber (FSR) with dual-band transmission and wideband absorption property is proposed, which is a two-layer structure composed of a lossy resistive sheet at the top and a lossless bandpass frequency selective surface (FSS) at the bottom, separated by an air spacer.
Abstract: A novel frequency-selective rasorber (FSR) with dual-band transmission and wideband absorption property is proposed in this letter. The FSR is a two-layer structure composed of a lossy resistive sheet at the top and a lossless bandpass frequency-selective surface (FSS) at the bottom, separated by an air spacer. The element of the resistive sheet is a lumped-resistor-loaded metallic dipole with a dual-resonance structure inserted in the center. The dual-resonance structure is realized by three different series LC structures in parallel, based on the Foster reactance theorem. There are two impedance poles between the three impedance zeros of the series LC circuits, where two transparent windows can be obtained for the lossy resistive sheet. The bandpass FSS is a simple dual-band FSS by etching two slots with different shapes and dimensions in a metallic plane. The FSR has realized two transmission bands at 7.7 and 12.6 GHz, and the band with | S 11| < −10 dB is 3.7–11.1 GHz. The design has been validated by full-wave simulation and experimental measurement.
77 citations
TL;DR: In this article, the authors reviewed the techniques available for matching the electric impedance of piezoelectric sensors, actuators, and transducers with their accessories like amplifiers, cables, power supply, receiver electronics and power storage.
Abstract: Any electric transmission lines involving the transfer of power or electric signal requires the matching of electric parameters with the driver, source, cable, or the receiver electronics. Proceeding with the design of electric impedance matching circuit for piezoelectric sensors, actuators, and transducers require careful consideration of the frequencies of operation, transmitter or receiver impedance, power supply or driver impedance and the impedance of the receiver electronics. This paper reviews the techniques available for matching the electric impedance of piezoelectric sensors, actuators, and transducers with their accessories like amplifiers, cables, power supply, receiver electronics and power storage. The techniques related to the design of power supply, preamplifier, cable, matching circuits for electric impedance matching with sensors, actuators, and transducers have been presented. The paper begins with the common tools, models, and material properties used for the design of electric impedance matching. Common analytical and numerical methods used to develop electric impedance matching networks have been reviewed. The role and importance of electrical impedance matching on the overall performance of the transducer system have been emphasized throughout. The paper reviews the common methods and new methods reported for electrical impedance matching for specific applications. The paper concludes with special applications and future perspectives considering the recent advancements in materials and electronics.
TL;DR: In this article, a substrate integrated waveguide-based leaky-wave antenna with wide beam scanning is presented to mitigate open stopband (OSB), which can scan from −49° to +69° through broadside because of wide impedance matching.
Abstract: In this letter, a substrate integrated waveguide-based leaky-wave antenna with wide beam scanning is presented to mitigate open stopband (OSB). The unit cell of this proposed antenna consists of a longitudinal slot and a post placed oppositely offset from the center line. By introducing inductive post along with the longitudinal slot in each unit cell, the OSB is suppressed resulting in continuous beam scanning. An equivalent circuit of the proposed unit cell is developed to explain the impedance matching technique used here to suppress OSB. Dispersion diagram is also used to analyze this seamless scanning. This antenna can scan from –49° to +69° through broadside because of wide impedance matching. Finally, the antenna is prototyped and experimentally verified. Measured results are in accord with simulated results. This antenna provides maximum gain of 14.2 dBi and low level of cross polarization.
TL;DR: In this article, the authors proposed a multi-point impedance technique, involving impedance measurement on three characteristic frequency points and being able to separate ohmic, contact and solid electrolyte interphase resistances.
TL;DR: In this article, a symmetrical E-shaped patch antenna with multimode resonance is proposed for 5G broadband millimeter-wave (mmWave) applications, where a longitudinal slot is etched on the patch surface to change the original E-field distribution of the TM20 mode without affecting that of TM10 mode.
Abstract: A symmetrical E-shaped patch antenna with multimode resonance is proposed for 5G broadband millimeter-wave (mmWave) applications. A longitudinal slot is etched on the patch surface to change the original E-field distribution of the TM20 mode without affecting that of the TM10 mode. This etching also tunes the resonance frequencies of these two modes to be sufficiently close to each other. Therefore, the antenna is able to realize good impedance performance within the wide designated bandwidth. Moreover, two transverse slots are etched to suppress undesirable modes, but the slots have a small effect on the current distribution of the two designed modes. Thus, the antenna is able to realize a stable radiation pattern and low cross-polarization within the whole operating band. The proposed patch antenna is designed, fabricated, and measured around the $Ka$ -band. The fabricated prototype achieves a wide impedance bandwidth of 45.4%. The simulated total efficiency of the proposed antenna is more than 85.0%. The proposed broadband symmetrical E-shaped patch antenna has a very simple structure and great electrical performance and is a very attractive candidate for 5G mmWave applications.
TL;DR: The effectiveness of the virtual inductance control strategy in weak grids is first proved through closed-loop transfer function analysis and then the system's root locus analysis to determine the stability region of the system versus the grid impedance.
Abstract: In this paper, a feedforward virtual inductance control strategy is developed for the stability of voltage source inverters (VSIs) in weak grids. A weak grid is characterized by a low short-circuit ratio and a low inertia constant, in which VSIs become susceptible to voltage distortions and instability. The proposed feedforward virtual inductance term is integrated into the current control loops of grid-tied VSIs. In this paper, the effectiveness of the virtual inductance control strategy in weak grids is first proved through closed-loop transfer function analysis and then the system's root locus analysis to determine the stability region of the system versus the grid impedance. The developed virtual inductance controller is also verified through laboratory experiments for different weak grid scenarios.
TL;DR: A microfluidic device combining the IFC and EIS techniques for single-cell electrical property measurement using hydrodynamic constriction to passively trap single cells, and uses coplanar electrodes to obtain the impedance spectrum of the trapped cell via EIS and discrete impedance data points of the passing cells via IFC is presented.
Abstract: Single-cell impedance measurement is a label-free, noninvasive method for characterizing the electrical properties of single cells. At present, though widely used for impedance measurement, electric impedance flow cytometry (IFC) and electric impedance spectroscopy (EIS) are used alone for most microfluidic chips. In this paper, we present a microfluidic device combining the IFC and EIS techniques for single-cell electrical property measurement. The device uses hydrodynamic constriction to passively trap single cells and uses coplanar electrodes to obtain the impedance spectrum of the trapped cell via EIS and discrete impedance data points of the passing cells via IFC. Through experiment, we verified the individual functionality of IFC and EIS respectively, by revealing through IFC the impedance magnitude difference and quantifying through EIS the area-specific membrane capacitance and cytoplasm conductivity of the three types of cancer cells. We also demonstrated the complementarity of IFC and EIS, which holds for a wide range of the flow rate. We envision that the strategy of combining IFC and EIS provides a new thought in the efforts to enhancing the efficiency of electrical property measurement for single cells.
TL;DR: A novel voltage stabilization and power sharing control method based on the virtual complex impedance is investigated to achieve accurate power sharing without the impact of hardware parameters variations and to improve the voltage quality.
Abstract: Microgrid (MG) usually operates in medium/low-voltage systems, where the line impedance parameters are mainly resistive, and traditional P–f / Q–U droop control is no longer applicable. When the virtual complex impedance method is adopted, the resistance component of line impedance can be counteracted by a virtual negative resistance. Unfortunately, the improper design of the virtual negative resistance will result in an unstable system due to the problem of line impedance parameter drift and estimation error. According to the line parameters characteristics of the off-grid MG with medium/low voltage, the P–U / Q–f droop control is adopted in this study, where the virtual complex impedance composed of a virtual negative inductance and a virtual resistance is introduced in the control loop. The virtual negative inductance is used to reduce the power coupling caused by the inductive component of the system impedance. The virtual resistance is implemented to enhance the resistive component and adjust the impedance matching degree for raising the accuracy of power sharing. However, the power sharing is still affected by the system hardware parameters; meanwhile, the voltage deviation caused by the droop control and the virtual impedance exists. In this study, a novel voltage stabilization and power sharing control method based on the virtual complex impedance is investigated to achieve accurate power sharing without the impact of hardware parameters variations and to improve the voltage quality. Moreover, the small-signal model of the inverter-based off-grid MG with the proposed controller is established, which can be utilized to analyze the stability and dynamic performance of the system. Meanwhile, the control parameters can be sequentially determined. Analysis shows that the strategy is robust against the line-impedance parameter drift and the estimation error and has a large stability margin and fast dynamic-response speed. Finally, numerical simulations and experimental results are provided to verify the effectiveness of the proposed control method in comparison with traditional frameworks.
TL;DR: This paper presents a complete design methodology of a Class-E inverter with a loosely coupled transformer under zero-voltage switching conditions, and Saber simulations and experimental results are given to validate the soft-switching capabilities over a wide range of the coupling coefficient and load resistance.
Abstract: This paper presents a complete design methodology of a Class-E inverter with a loosely coupled transformer under zero-voltage switching conditions. At a selected maximum coupling coefficient, the inverter satisfies both zero-voltage switching (ZVS) and zero-derivative switching (ZDS) conditions to achieve a high efficiency. As the coupling coefficient is decreased from its maximum value to zero, the inverter satisfies the ZVS condition over a wide range of load resistance. The proposed method absorbs the magnetizing inductance and the leakage inductance into the inverter topology. The closed-form expressions for all the Class-E inverter parameters are derived in terms of the coupling coefficient, including: 1) input impedance of the transformer with a complex load impedance; 2) equivalent phase of the resonant circuit for both nominal and suboptimum operations; and 3) slope of the switch voltage waveform. The relationship between the voltage slope and the coupling coefficient is introduced, which indicates the proximity of the operating point from ZVS and ZDS conditions. A design example of the Class-E inverter is presented to achieve both ZVS and ZDS, at an optimum coupling coefficient of 0.77, and ZVS condition for any coupling coefficient lower than 0.77 and over a wide range of load resistance. Saber simulations and experimental results are given to validate the soft-switching capabilities over a wide range of the coupling coefficient and load resistance. The theoretical results were in good agreement with Saber simulations and experiments.
TL;DR: In this article, the root mean square (RMS) of open-circuit voltage in a rotary freestanding TENG with the capacitive impedance load used in high voltage field, where the dielectric barrier discharge (DBD) microplasma as an example, was explored.
TL;DR: A gray-box method that, with basic assumptions about the control structure of the wind energy conversion system (WECS), can estimate the parameters of its controllers and ensures the stability of the system by retuning only the critical controller parameters is proposed.
Abstract: Estimation of critical control parameters is a desirable tool feature for stability analysis and impedance shaping of high voltage dc (HVdc) connected wind farms. Accurate estimation of such parameters would be enabled by access to detailed models, which is not always the case in real wind farms. Industrial secrecy is one of the main factors hindering the access to such models. This paper proposes a gray-box method that, with basic assumptions about the control structure of the wind energy conversion system (WECS), can estimate the parameters of its controllers. The method is based on the measurements of frequency domain equivalent impedance combined with nonparametric impedance identification used in the solution of an inverse problem. The method makes possible to specify which part of the equivalent WECS impedance has a major impact on the stability of the system and according to this, reshape the impedance to enforce stability. Once the critical controller bandwidth is identified with this method, an instability mitigation technique is proposed based on reshaping the impedance by retuning the critical controllers of the interconnected converters. In order to avoid interaction between the HVdc rectifier and the WECS inverter, the controllers of both converters need to be retuned in such a way that the q -axis impedance magnitude of the HVdc system is kept lower than the q -axis impedance magnitude of the wind farm at the frequency of the phase-locked loop bandwidth. The results show that the method ensures the stability of the system by retuning only the critical controller parameters.
TL;DR: A systematic design procedure for the optimal selection of the PI controller of the PLL is presented, which guarantees the steady-state performance and dynamic response of the ACHMI system.
Abstract: This paper analyzes the influence of phase-locked loop (PLL) on the stability of LCL -type single-phase grid-connected asymmetrical cascaded H-bridge multilevel inverter (ACHMI) with synchronous reference frame proportional-integral (SRF-PI) grid current control under weak grid scenarios The ACHMI system is composed of power stage circuit and control system, where the control system contains the dual-loop current control strategy established in the hybrid reference frame, the SRF-PLL, and the hybrid modulation method employed to synthesize the multilevel output voltage The small-signal model of the whole ACHMI system is first established by using a simple step-by-step derivation method, and then, the small-signal analysis method is adopted to linearize the ACHMI, which is then utilized to derive the impedance model of the ACHMI system Furthermore, an improved impedance stability criterion is derived, which is then employed to analyze the system stability By using this criterion, the stability of the ACHMI can be evaluated with the variation of the bandwidth of PLL, the output power factor angle of the ACHMI, and the amplitude of the grid current reference signal under weak grid conditions In this paper, a systematic design procedure for the optimal selection of the PI controller of the PLL is presented, which guarantees the steady-state performance and dynamic response of the ACHMI system With this design method, the dual-loop current control and PLL can be taken into account simultaneously when analyzing the stability margin of the ACHMI Finally, the simulation and experimental results from a down-scaled grid-connected ACHMI prototype system are provided to confirm the validity of theoretical analysis
TL;DR: In this paper, a modified equivalent circuit which is in accordance with practical dielectric responses in not only modulus and impedance spectra but also Dielectric spectroscopy is presented.
Abstract: Combined modulus and impedance spectra are widely employed to explore electrical inhomogeneity and carriers' behaviors in dielectric ceramics based on equivalent circuit. However, discrepancies are found between practical dielectric responses and widely proposed equivalent circuits. Taking ZnO varistor ceramics as an example, a low-frequency dielectric relaxation, which can be detected in practical dielectric spectroscopy, is overlooked in simulated dielectric spectroscopy based on the proposed equivalent circuit according to modulus and impedance spectra. Therefore, equivalent circuits are frequently incomplete because the real low-frequency dielectric response is unable to be characterized from them. The problem originates from debatable understanding of frequency responses in modulus and impedance spectra. The low-frequency peak in modulus spectroscopy is proved originating from DC conductance instead of a real dielectric relaxation and the involvement of DC conductance component makes a low-frequency dielectric relaxation unable to be characterized in modulus spectroscopy. Therefore, improved dielectric spectroscopy eliminating the component of DC conductance is proposed and a clear peak corresponding to the low-frequency dielectric relaxation appears. In addition, a modified equivalent circuit which is in accordance with practical dielectric responses in not only modulus and impedance spectra but also dielectric spectroscopy is presented.
TL;DR: The impedance characteristics of the full-bridge rectifier at MHz and their influence under the series–series, parallel– series, series–parallel, and parallel-parallel compensation topologies are discussed.
Abstract: The spatial freedom of wireless power transfer (WPT) systems can be improved using a high operating frequency such as several megahertz (MHz). In the conventional compensations the load of the coupling coils is usually assumed to be pure resistive. However, in MHz WPT systems this assumption is not accurate anymore due to the nonneglectable rectifier input reactance. This paper discusses the impedance characteristics of the full-bridge rectifier at MHz and their influence under the series–series, parallel–series, series–parallel, and parallel–parallel compensation topologies. An undesirable nonzero phase (i.e., none unity power factor) is shown to exist at the primary input port, which leads to decreased power transfer capability. In order to minimize this negative effect, the compensation capacitors are optimally designed, and the series–series topology is found to have the smallest phase under load and coupling variations. Finally, an experimental 6.78 MHz system is built up to verify the optimized design of the compensation capacitors. The results show that the average nonzero phase is effectively reduced together with the improved power factor from 0.916 to 0.982.
TL;DR: A mirror-frequency impedance modeling and measurement approach of single-phase VSCs in the stationary frame based on harmonic linearization is proposed and results indicate that the mirror- frequency impedance model considering the dc-link voltage control is more accurate and better captures the cross-coupling dynamics of V SCs.
Abstract: The impedance-based stability analysis of single-phase voltage source converters (VSCs) emphasizes the precise impedance modeling. Considering the complexity of $dq$ -frame impedance modeling and measurement, this paper proposes a mirror-frequency impedance modeling and measurement approach of single-phase VSCs in the stationary frame based on harmonic linearization. First, the mirror frequency definition is put forward and the dynamics of the second-order generalized phase-locked loop considering the mirror-frequency effects is validated by simulations. Next, the impedance model considering the mirror-frequency effects and dc-link voltage control loops is compared with the conventional one-dimension impedance model and a mirror-frequency impedance measurement method is presented, which are verified by experiments on the hardware-in-the-loop platform. The results indicate that the mirror-frequency impedance model considering the dc-link voltage control is more accurate and better captures the cross-coupling dynamics of VSCs. Finally, the different bandwidths of dc-link voltage control loops and different capacitances are designed to study the impacts of dc-link voltage control loops and ripples on impedance. The experiments and impedance-based analysis illustrate that the wider bandwidth of dc-link voltage control loops or the less capacitance with high dc-link voltage ripple will expand the frequency range of negative impedance in the low frequency.
TL;DR: In this article, the ACE1 active complex electrode (ACE1) electrical impedance tomography system for single-ended phasic voltage measurements is presented, which allows reconstruction of conductivity and permittivity images.
Abstract: The design and performance of the active complex electrode (ACE1) electrical impedance tomography system for single-ended phasic voltage measurements are presented. The design of the hardware and calibration procedures allows for reconstruction of conductivity and permittivity images. Phase measurement is achieved with the ACE1 active electrode circuit which measures the amplitude and phase of the voltage and the applied current at the location at which current is injected into the body. An evaluation of the system performance under typical operating conditions includes details of demodulation and calibration and an in-depth look at insightful metrics, such as signal-to-noise ratio variations during a single current pattern. Static and dynamic images of conductivity and permittivity are presented from ACE1 data collected on tank phantoms and human subjects to illustrate the system’s utility.
TL;DR: In this paper, an ultrawideband low profile absorber is designed using printed lossy capacitive surface on a ground-backed substrate, which is shown to be polarization insensitive and capable of reducing radar cross section for all the reflection angles in both monostatic and bistatic scenarios.
Abstract: In this communication, an ultrawideband low-profile absorber is designed using printed lossy capacitive surface on a ground-backed substrate. Simple guidelines are proposed to design the absorber using the impedance analysis of its equivalent circuit model. The 10 dB reflection reduction for 120% fractional bandwidth from 3 to 12 GHz is achieved by generating three resonances using a single element in the unit cell. The thickness at the lowest cutoff frequency of the proposed absorber is thus obtained as $0.080\lambda _{L} (\lambda _{L} $ is the wavelength at the lowest cutoff frequency). It is shown that the proposed absorber is polarization insensitive and capable of reducing radar cross section for all the reflection angles in both monostatic and bistatic scenarios. To manufacture the absorber, commercially available low-cost resistive ink, Y-shield HSF 74 is used. The measurement results are provided to validate both the full-wave and circuit simulated results.
TL;DR: In this article, the radiated electromagnetic interference generated by isolated power converters is analyzed using a general radiation model for the converters, and the predicted radiated electric field of the dual active bridge converter is predicted from the developed model.
Abstract: To analyze the radiated electromagnetic interference generated by isolated power converters, this paper proposes a technique to develop a general radiation model for the converters. The radiated electric field can be predicted from the developed model. The interaction between the impedance of the converter and the undesired antenna in the converter's power delivery paths is explored in detail based on the developed model. Moreover, a dual active bridge converter is taken as an example to demonstrate the developed modeling technique based on the converter's topology. The radiated electric field of the dual active bridge converter is predicted from the developed model. Experiments are conducted to validate the developed model and the predicted interaction between the converter impedance and the undesired antenna impedance in the power delivery paths.
TL;DR: In this article, a novel high voltage conversion ratio (HVCR) bidirectional CLTC resonant dc-dc converter was proposed, which can achieve zero voltage switching in all load ranges.
Abstract: This paper presents a novel high voltage conversion ratio (HVCR) bidirectional CLTC resonant dc–dc converter. Based on inductor-inductor-capacitor (LLC), series resonant converter, and capacitor-inductor-inductor-capacitor (CLLC), the novel CLTC structure is proposed. With the use of auxiliary transformer and extra resonant capacitor, a CLTC resonant dc–dc converter can achieve zero voltage switching in all load ranges. Also, CLTC has a good gain characteristic with high power load. In this study, a review of the statuses for the isolated HVCR bidirectional converters is made. The operating principle of a bidirectional power flow in two directions is analyzed in details. In addition, by changing ac output resistance, a modified fundamental harmonic analysis (FHA) method makes the calculated gain curve more accurately than traditional FHA. Also, voltage and current stresses of power switches and resonant capacitors are given. A parameter optimization method is proposed to minimize the impedance angle of CLTC, which corresponds to less reactive power and turn-off current. The optimal parameters show advantages in voltage and current stresses. Moreover, power losses are analyzed in this study, showing advantage of CLTC in efficiency. At last, the experimental results based on a 5-kW prototype converter are presented to validate the theoretical analyses.
TL;DR: A new single-stage high boost quasi-Z-source inverter based on the active switched Z-impedance network that provides higher voltage boost factor, draws continuous input current, and shares the same ground between the input source and the bridge inverter.
Abstract: This paper deals with a new single-stage high boost quasi-Z-source inverter based on the active switched Z-impedance network. The proposed inverter provides higher voltage boost factor, draws continuous input current, and shares the same ground between the input source and the bridge inverter. Compared with the traditional enhanced boost (quasi-)Z-source inverters (EB-ZSI/EB-qZSI), for two less inductors, one less capacitor, and one additional active switch used at the impedance network, the output voltage boost factor of the proposed inverter is twice as much as the EB-ZSI and EB-qZSI, which implies that it can use a very higher modulation index to provide improved quality output waveforms. Besides, for obtaining the same dc–ac output voltage gain, the proposed method has lower active switching voltage stress, lower passive component voltage ratings, and lower shoot-through current stress with lower input current ripple. The operation theory analysis, power loss calculation, simulation results, and performance comparison with other high boost impedance source inverters are presented. To verify the operating theory of the proposed inverter, a laboratory prototype based on the TMS320F28335 DSP was constructed and tested with 60 V dc input and ac 110 Vrms phase output. Finally, both simulations and the experimental results confirmed that the proposed inverter has high boost voltage inversion capability.
TL;DR: Simulation results show that the proposed control strategy can reduce circulating current effectively as well as improve power sharing accuracy and adjust to the equivalent feeder impedance, which provides accurate and quick response to load changes and line impedance mismatches.
Abstract: Among parallel inverters in islanded microgrid, circulating current originated by output impedance mismatches and output voltage differences cannot be neglected. Conventional droop control and fixed virtual impedance control are sensitive when the load changes. In this paper, the concept of equivalent feeder is proposed to cover the mismatch of external feeder impedance. The differences of external inductor, local load, and transmission line among parallel inverters are considered. Based on equivalent feeder impedance calculation, an aggregated control strategy of improved droop control and adaptive virtual impedance control is introduced. To improve power sharing accuracy, the equivalent feeder voltage drop of each inverter is calculated and compensated to the reference voltage of droop control. Conventional virtual impedance control is defective to cope with sudden load perturbations, especially when local loads exist. In this regard, the adaptive virtual complex impedance control can adjust to the equivalent feeder impedance, which provides accurate and quick response to load changes and line impedance mismatches. Simulation results show that the proposed control strategy can reduce circulating current effectively as well as improve power sharing accuracy.