Showing papers on "Equivalent circuit published in 2019"

Dual-Polarized Band-Absorptive Frequency Selective Rasorber Using Meander-Line and Lumped Resistors

Abstract: A novel dual-polarized band-absorptive frequency selective rasorber (FSR) is proposed in this communication. The FSR is constructed by two-layer cascaded printed circuit boards, in which meander-line square loops with and without lumped resistors loaded on the top and bottom surfaces of the two substrates. Its operating principle is analyzed, and an accurate equivalent circuit model is presented. A prototype has been fabricated, assembled, and measured. The measured absorption band is from 4.8 to 6.81 GHz (34.6%), with a thickness of $\lambda _{\mathrm {a}}$ /8 at 4.8 GHz. Moreover, it is almost transparent to electromagnetic waves below 1.54 GHz. The measurement results achieve a good agreement with the simulated results, which verifies the effectiveness of the design.

Robust Power Flow and Three-Phase Power Flow Analyses

Abstract: Robust simulation is essential for reliable operation and planning of transmission and distribution power grids. At present, disparate methods exist for steady-state analysis of the transmission (power flow) and distribution power grid (three-phase power flow). Due to the nonlinear nature of the problem, it is difficult for alternating current power flow and three-phase power flow analyses to ensure convergence to the correct physical solution, particularly from arbitrary initial conditions, or when evaluating a change (e.g., contingency) in the grid. In this paper, we describe our equivalent circuit formulation approach with current and voltage variables, which models both the positive sequence network of the transmission grid and three-phase network of the distribution grid without loss of generality. The proposed circuit models and formalism enables the extension and application of circuit simulation techniques to solve for the steady-state solution with excellent robustness of convergence. Examples for positive sequence transmission and three-phase distribution systems, including actual 75k+ nodes Eastern Interconnection transmission test cases and 8k+ nodes taxonomy distribution test cases, are solved from arbitrary initial guesses to demonstrate the efficacy of our approach.

Brains Are Made of Memristors.

Abstract: This exposition shows that the potassium ion-channels and the sodium ion-channels that are distributed over the entire length of the axons of our neurons are in fact locally-active memristors. In particular, they exhibit all of the fingerprints of memristors, including the characteristic pinched hysteresis Lissajous figures in the voltage-current plane, whose loop areas shrink as the frequency of the periodic excitation signal increases. Moreover, the pinched hysteresis loops for the potassium ion-channel memristor, and the sodium ion-channel memristor, from the Hodgkin-Huxley axon circuit model are unique for each periodic excitation signal. An in-depth circuit-theoretic analysis and characterizations of these two classic biological memristors are presented via their small-signal memristive equivalent circuits, their frequency response, and their Nyquist plots. Just as the Hodgkin-Huxley circuit model has stood the test of time, its constituent potassium ion-channel and sodium ion-channel memristors are destined to be classic examples of locally-active memristors in future textbooks on circuit theory and bio-physics.

Ionic-to-electronic current amplification in hybrid perovskite solar cells: ionically gated transistor-interface circuit model explains hysteresis and impedance of mixed conducting devices

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.

An Optically Transparent Broadband Microwave Absorber Using Interdigital Capacitance

Abstract: In this letter, an optically transparent broadband microwave absorber has been developed. The proposed geometry is constructed of the patterned resistive films of an indium-tin-oxide on flexible substrates, such that the structure exhibits broadband absorptivity (above 90%) from 4 to 17.20 GHz (covering C, X, and Ku bands). The novelty of the design lies in leveraging the properties of interdigital capacitance to achieve wide absorption (fractional bandwidth of 124.53%), angular stability, as well as optical transparency compared to the earlier reported broadband absorbers. Moreover, the structure has been extensively investigated through deriving an equivalent circuit model and studying surface current distributions. Experimental validation of the fabricated prototype has also confirmed the potential use of resistive film based broadband absorbers in several applications.

Self-Inductance-Based Metal Object Detection With Mistuned Resonant Circuits and Nullifying Induced Voltage for Wireless EV Chargers

Abstract: In this paper, a metal object detection (MOD) system, a kind of foreign object detection (FOD), which is based on mistuned resonant circuits and utilizes the variation of self-inductance of a sensing pattern, is newly proposed for wireless electric vehicle (EV) chargers. The sensing pattern that consists of multiple loop coil sets is mounted on the transmitting (Tx) pad of an EV charger, where a loop coil set has two coils connected in series with the opposite polarity to cancel out the induced voltage generated by the Tx coil. Variation of self-inductance of the loop coil set is detected by a parallel-resonant circuit, driven by a current source and operating at near 1 MHz, in order to enhance the resolution of the proposed MOD system. To increase the detection sensitivity of the proposed MOD system, instead of an exact resonant frequency, a mistuned operating frequency near the –3 dB point is utilized for the parallel-resonant circuit. In this way, the proposed MOD system can detect very small metal objects regardless of their position and orientation on the Tx coil without any blind zone. Through simulations and experiments, it is found that the proposed MOD system detects not only horizontal but also standing upright metal objects. A prototype MOD system, operating at 85 kHz to satisfy the standard J2954, was fabricated to verify its feasibility. The results showed that output voltage change of the proposed MOD system becomes 22.7% for a piece of the aluminum foil of 3 × 3 cm2 and 40.9% for 100 Korean Won coin.

Analysis of the Current Electric Battery Models for Electric Vehicle Simulation

Abstract: Electric vehicles (EVs) are a promising technology to reduce emissions, but its development enormously depends on the technology used in batteries. Nowadays, batteries based on lithium-ion (Li-Ion) seems to be the most suitable for traction, especially nickel-manganese-cobalt (NMC) and nickel-cobalt-aluminum (NCA). An appropriate model of these batteries is fundamental for the simulation of several processes inside an EV, such as the state of charge (SoC) estimation, capacity and power fade analysis, lifetime calculus, or for developing control and optimization strategies. There are different models in the current literature, among which the electric equivalent circuits stand out, being the most appropriate model when performing real-time simulations. However, impedance models for battery diagnosis are considered very attractive. In this context, this paper compares and contrasts the different electrical equivalent circuit models, impedance models, and runtime models for battery-based EV applications, addressing their characteristics, advantages, disadvantages, and usual applications in the field of electromobility. In this sense, this paper serves as a reference for the scientific community focused on the development of control and optimization strategies in the field of electric vehicles, since it facilitates the choice of the model that best suits the needs required.

An electrical equivalent circuit model of a lithium titanate oxide battery

Abstract: A precise lithium-ion battery model is required to specify their appropriateness for different applications and to study their dynamic behavior. In addition, it is important to design an efficient battery system for power applications. In this investigation, a second-order equivalent electrical circuit battery model, which is the most conventional method of characterizing the behavior of a lithium-ion battery, was developed. The current pulse procedure was employed for parameterization of the model. The construction of the model was described in detail, and a battery model for a 13 Ah lithium titanate oxide battery cell was demonstrated. Comprehensive characterization experiments were accomplished for an extensive range of operating situations. The outcomes were employed to parameterize the suggested dynamic model of the lithium titanate oxide battery cell. The simulation outcomes were compared to the laboratory measurements. In addition, the proposed lithium-ion battery model was validated. The recommended model was assessed, and the proposed model was able to anticipate precisely the current and voltage performance.

Adaptive Forgetting Factor Recursive Least Square Algorithm for Online Identification of Equivalent Circuit Model Parameters of a Lithium-Ion Battery

Abstract: With the popularity of electric vehicles, lithium-ion batteries as a power source are an important part of electric vehicles, and online identification of equivalent circuit model parameters of a lithium-ion battery has gradually become a focus of research. A second-order RC equivalent circuit model of a lithium-ion battery cell is modeled and analyzed in this paper. An adaptive expression of the variable forgetting factor is constructed. An adaptive forgetting factor recursive least square (AFFRLS) method for online identification of equivalent circuit model parameters is proposed. The equivalent circuit model parameters are identified online on the basis of the dynamic stress testing (DST) experiment. The online voltage prediction of the lithium-ion battery is carried out by using the identified circuit parameters. Taking the measurable actual terminal voltage of a single battery cell as a reference, by comparing the predicted battery terminal voltage with the actual measured terminal voltage, it is shown that the proposed AFFRLS algorithm is superior to the existing forgetting factor recursive least square (FFRLS) and variable forgetting factor recursive least square (VFFRLS) algorithms in accuracy and rapidity, which proves the feasibility and correctness of the proposed parameter identification algorithm.

SIW-Based Leaky-Wave Antenna Supporting Wide Range of Beam Scanning Through Broadside

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.

Unified Load-Independent ZPA Analysis and Design in CC and CV Modes of Higher Order Resonant Circuits for WPT Systems

Abstract: This article proposes a general unified methodology for arbitrary higher order resonant circuits. With the proposed methodology, the equivalent circuits and the general resonant methods of the higher order resonant circuit are presented to realize the load-independent constant current (CC) and constant voltage (CV) outputs at two different load-independent zero phase angle (ZPA) frequencies. In addition, the corresponding regularized mathematical models of the constant output current and voltage and the purely resistive input impedances in CC and CV output modes are derived. All compensation topologies in both inductive and capacitive power transfer (CPT) systems have the essence of higher order resonant circuits. It means that the proposed methodology can be applied to investigate the load-independent output and input characteristics of any inductive power transfer (IPT) and CPT topologies. A 3.3-kW $LCC$ -series-compensated IPT system for electric vehicles (EVs) was designed and manufactured to verify the theoretical analysis. The system operating frequencies in both the CC output with ZPA and the CV output with ZPA are in compliance with the SAE J2954 standard.

Novel Multifunctional Reconfigurable Active Frequency Selective Surface

Abstract: In this paper, a multifunctional active frequency selective surface (MAFSS) is presented based on the switching responses of active components. The proposed structure comprises periodic arrays of metallic patterns imprinted on both sides of an FR4 substrate on which p-i-n diodes are embedded with parallel feed networks. The novelty of the design lies in its multifunctional characteristics with independent control of the biasing states (ON/OFF) of the diodes mounted on opposite layers. This leads to four different working states (dual bandpass for OFF–OFF state, single-band absorber for OFF–ON state, single-bandpass for ON–OFF state, and reflector for ON–ON state) being facilitated by the proposed reconfigurable AFSS. Furthermore, the effects of the design parameters and active components on multifunctional responses are extensively analyzed by deriving equivalent circuit models. Even though the topology is polarization sensitive, multiple dividable working functions (transmission, absorption, and reflection) have been realized in single geometry, unlike the earlier reported designs. The proposed structure has also been fabricated, and the measured responses show reasonable agreement with the simulated results under normal incidence. An MAFSS with such diverse characteristics is an essential element for regulating electromagnetic wave propagation in manifold applications.

Switchable Broadband Dual-Polarized Frequency-Selective Rasorber/Absorber

Abstract: This letter presents a switchable dual-polarized frequency-selective rasorber/absorber at low microwave frequency based on double-layered metallic resonant structure array loaded with lumped elements. It consists of an absorbing layer and a bandpass frequency-selective surface layer loaded with PIN diodes, sandwiched with an air-spacer between them. The operating principle is analyzed with the help of an equivalent circuit model. By biasing the PIN diodes on or off , it can be easily switched between the rasorber and absorber modes. When in the rasorber mode, it exhibits a passband at 1.6 GHz with 1.7 dB insertion loss between two neighboring absorption bands. While switched to the absorber mode, it achieves more than 80% absorptivity ranging from 0.8 to 3.4 GHz, corresponding to a fractional bandwidth of 124%. The total thickness is less than 8% of the free-space wavelength at the lowest operating frequency. A prototype of the proposed structure is fabricated and measured, where reasonable agreements between simulations and measurements are observed.

Severity Estimation of Interturn Short Circuit Fault for PMSM

Abstract: This paper presents a novel method to estimate the number of shorted turns in a permanent magnet synchronous machine (PMSM) following the detection of interturn short-circuit (ITSC) fault and its location. In this proposed method, PMSM is excited through a low sinusoidal voltage at standstill condition to obtain the winding resistance and synchronous inductance by current response. It is shown that the ITSC fault introduces variation in the current response, which can be used to calculate the number of shorted turns under zero fault resistance assumption. Using this practical procedure, the fault severity can be estimated directly in a straight-forward manner. In other words, the severity estimation for a given machine can be done without complex machine modeling or experiments on ITSC prototype with multiple taps. The findings in this paper are essential for a comprehensive solution including fault mitigation algorithms and postfault operations. In order to verify the findings, a three-phase equivalent circuit model supported by finite element analysis results is used to take saturation and space harmonics into account. In addition, experimental results are presented to demonstrate the validity and practicability of the severity estimation.

Octave Bandwidth Doherty Power Amplifier Using Multiple Resonance Circuit for the Peaking Amplifier

Abstract: This paper presents a broadband Doherty power amplifier (DPA) design with an octave bandwidth based on a new load network consisting of a quasi-lumped impedance transformer for the carrier amplifier, a multiple resonance circuit for the peaking amplifier, and a broadband post-matching network. The quasi-lumped impedance transformer and the multiple resonance circuit were designed based on accurate equivalent circuits for internal components inside the packaged transistor. Based on power bandwidth analysis, optimum susceptance provided by the multiple resonance circuit at the peaking amplifier, was obtained. The proposed broadband DPA was designed using 45 W gallium–nitride high electron mobility transistor for both carrier and peaking amplifiers. For continuous-wave signals in frequency range of 0.9 to 1.8 GHz, the implemented broadband DPA exhibited a drain efficiency of 54.2% to 73.4% at peak output power of 49.7 to 51.4 dBm and a drain efficiency of 41.7% to 58.0% at output back-off of 6 dB. For the down-link long-term evolution signal with a channel bandwidth of 10 MHz and a peak-to-average power ratio of 6.5 dB, a drain efficiency of 41.3% to 57.4% and an adjacent channel leakage power ratio of −22.5 to −30.2 dBc at an average output power of 43.2 to 449 dBm were achieved at an octave bandwidth.

Broadband Frequency-Selective Rasorber With Varactor-Tunable Interabsorption Band Transmission Window

Abstract: In this paper, we present a frequency-selective rasorber with tunable transmission window located within the absorption band. The rasorber maintains a low reflectivity, which is less than −10 dB in broadband during the tuning process. An equivalent circuit model is provided as a guideline for the tunable rasorber design. Based on the model, a varactor-tunable rasorber composed of three stacked metallic layers is constructed and investigated. These layers include a frequency selective surface (FSS) loaded with resistors and varactors, a wire grid and a varactor-loaded bandpass FSS. The wire grids in the middle and bottom layers in combination with metallic vias provide the bias and grounding for the varactors, respectively. This configuration avoids using two separated bias networks for varactors on different layers, thus, averting undesirable responses associated with having more bias grids. A tunable rasorber prototype was fabricated and measured, showing that the passband can be tuned from 2.2 to 3.3 GHz by changing bias voltage from 4 to 22 V, with an insertion loss between 6.6 and 3.3 dB. A wide low-reflectivity band under normal incidence for double polarizations from 1.9 to 5.4 GHz is realized. This tunable rasorber has promising applications in broadband stealth facilities with integrated hopping communication functionality.

Online parameters identification and state of charge estimation for lithium-ion capacitor based on improved Cubature Kalman filter

Abstract: Lithium-ion capacitor is a hybrid electrochemical energy storage device which combines the merits of lithium-ion battery and electric double-layer capacitor. The precise state of charge estimation is essential to utilize lithium-ion capacitor efficiently. In this paper, the electrical characteristics of lithium-ion capacitor have been studied and the corresponding equivalent circuit model is established. Then, an adaptive square root cubature Kalman filter with variable forgetting factor recursive least square has been proposed to achieve state of charge estimation at each sampling step. The proposed method identifies the model parameters and noise statistics in real time, leading to obtain accurate SOC estimation even if the method is initialized with inaccurate parameters. Estimations under four working conditions are quantitatively studied, the experimental results show that the proposed method has better performance and the corresponding maximum root mean square error is controlled within 1%. Furthermore, the verification of robustness illustrates that the proposed method remains stability and acceptable accuracy when external interference and inaccurate initial SOC are included.

The Equivalent Circuit Approach for the Electrical Diagnostics of Dielectric Barrier Discharges: The Classical Theory and Recent Developments

Abstract: Measurements of current and voltage are the basic diagnostics for electrical discharges. However, in the case of dielectric barrier discharges (DBDs), the measured current and voltage waveforms are influenced by the discharge reactor geometry, and thus, interpretation of measured quantities is required to determine the discharge properties. This contribution presents the main stages of the development of electrical diagnostics of DBDs, which are based on lumped electrical elements. The compilation and revision of the contributions to the equivalent circuit approach are targeted to indicate: (1) the interconnection between the stage of development, (2) its applicability, and (3) the current state-of-the-art of this approach.

Understanding the validity of impedance and modulus spectroscopy on exploring electrical heterogeneity in dielectric ceramics

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.

Design and Analysis of Printed Lossy Capacitive Surface-Based Ultrawideband Low-Profile Absorber

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.

Circular-Polarized Substrate-Integrated-Waveguide Leaky-Wave Antenna With Wide-Angle and Consistent-Gain Continuous Beam Scanning

Abstract: Circularly polarized (CP) antennas are in high demand for use in future wireless communications. To advance the development of CP substrate-integrated-waveguide (SIW) leaky-wave antennas (LWAs) with the intent to meet this demand, a novel benzene-ring-shaped slot-loaded LWA with partially reflecting wall (PRW) vias is investigated and verified to realize wide-angle continuous beam scanning with consistent gain. The dispersion features of slot-loaded SIW LWAs with PRW vias are theoretically explored using an equivalent circuit model. The CP radiation feature is investigated numerically utilizing the E- and H-field distributions of an initial design and its equivalent magnetic currents. The results of these studies are used to demonstrate that improved CP performance over a wide-angle scan range can be attained with a change from a standard slot shape to a benzene-ring-shaped slot. The resulting benzene-ring-shaped slot-loaded CP SIW LWA was optimized, fabricated, and measured. The measured results verify that a CP beam was continuously scanned through a wide angle from backward to forward directions with a consistent gain. The prototype exhibits a continuous 97.1° CP beam scan with a gain variation between 8 and 11.3 dBic when the source frequency is swept from 9.35 to 11.75 GHz.

Open-Switch Fault-Tolerant Operation of a Two-Stage Buck/Buck–Boost Converter With Redundant Synchronous Switch for PV Systems

Abstract: In photovoltaic systems, dc–dc converters have been identified as one of the most critical and challenging subsystem in terms of failure rate. Thus, this paper proposes fault-tolerant operation of a two-stage buck/buck–boost converter under open-circuit switch failure. Remedial actions are efficient in any failure of one of the two switches of the converter. Here, a new unified approach is considered, for the overall fault-tolerant operation of the two stages of the converter. The fault-tolerant circuit we propose lies on performing redundancy by implementing the equivalent synchronous switch for the two main switches of the two stages, in offline mode. The fault-tolerant circuit results from the basic two-stage buck/buck-boost converter and its equivalent circuit with a synchronous switch, merged together to form the new dc–dc fault-tolerant circuit. Therefore, postfault operation at full power can also be performed. By using a switch fault management unit with reduced complexity, inserted between the control block and the switches, we have designed an unified, efficient, and optimized fault-tolerant control, suitable in both healthy and postfault operations. Some selected experimental tests, which all confirm the good performances of the proposed fault-tolerant approach, are presented and discussed.

Cascaded Graphene Frequency Selective Surface Integrated Tunable Broadband Terahertz Metamaterial Absorber

Abstract: The quest of novel materials and structures to design an efficient absorber for realizing wave trapping and absorption at terahertz (THz) frequencies is an open topic. But the design of a thin, wideband, and tunable THz absorber is still an arduous job. Hence, in this paper, a hybrid THz metamaterial absorber integrated with a cascaded graphene frequency selective surface (FSS), with ultra-high absorbance over a wide frequency range is designed using an analytical equivalent circuit model. Such an approach provides a feasible way to optimize the device by interrelating the effective electromagnetic and circuit parameters with the unit cell dimensions of FSS. A systematic study and critical analysis over a wide range of device parameters including graphene chemical potential and FSS design variables is demonstrated. A peak dip in reflection coefficient of -30.27 dB is observed at 2.94 THz for an optimal device with a chemical potential (μ c ) of 0.38 eV (μ c1 ), and 0.25 eV (μ c2 ) in the range of 0.1-4.0 THz. The cascaded FSS configuration results in the unique anti-reflection-based absorption phenomena, which is responsible for the achievement of -10 dB absorption bandwidth of 2.34 THz (0.85-3.19 THz). In addition, the frequency-dependent effective permittivity, permeability, and impedance is extracted using reflection data, in order to understand the device physics. Such ultra-thin and broadband absorbing device architecture may confer potential application perspectives in THz sensing, imaging, and detection.