Showing papers on "Equivalent circuit published in 2021"

A comprehensive equivalent circuit model for lithium-ion batteries, incorporating the effects of state of health, state of charge, and temperature on model parameters

Abstract: The equivalent circuit model (ECM) is a battery model often used in the battery management system (BMS) to monitor and control lithium-ion batteries (LIBs). The accuracy and complexity of the ECM, hence, are very important. State of charge (SOC) and temperature are known to affect the parameters of the ECM and have been integrated into the model effectively. However, the effect of the state of health (SOH) on these parameters has not been widely investigated. Without a good understanding of the effect of SOH on ECM parameters, parameter identification would have to be done manually through calibration, which is inefficient. In this work, experiments were performed to investigate the effect of SOH on Thevenin ECM parameters, in addition to the effect of SOC and temperature. The results indicated that with decreasing SOH, the ohmic resistance and the polarization resistance increase while the polarization capacitance decreases. An empirical model was also proposed to represent the effect of SOH, SOC, and temperature on the ECM parameters. The model was then validated experimentally, yielding good results, and found to improve the accuracy of the Thevenin model significantly. With low complexity and high accuracy, this model can be easily integrated into real-world BMS applications.

Impedance Spectroscopy of Metal Halide Perovskite Solar Cells from the Perspective of Equivalent Circuits.

Abstract: Impedance spectroscopy (IS) provides a detailed understanding of the dynamic phenomena underlying the operation of photovoltaic and optoelectronic devices. Here we provide a broad summary of the application of IS to metal halide perovskite materials, solar cells, electrooptic and memory devices. IS has been widely used to characterize perovskite solar cells, but the variability of samples and the presence of coupled ionic-electronic effects form a complex problem that has not been fully solved yet. We summarize the understanding that has been obtained so far, the basic methods and models, as well as the challenging points still present in this research field. Our approach emphasizes the importance of the equivalent circuit for monitoring the parameters that describe the response and providing a physical interpretation. We discuss the possibilities of models from the general perspective of solar cell behavior, and we describe the specific aspects and properties of the metal halide perovskites. We analyze the impact of the ionic effects and the memory effects, and we describe the combination of light-modulated techniques such as intensity modulated photocurrent spectroscopy (IMPS) for obtaining more detailed information in complex cases. The transformation of the frequency to time domain is discussed for the consistent interpretation of time transient techniques and the prediction of features of current-voltage hysteresis. We discuss in detail the stability issues and the occurrence of transformations of the sample coupled to the measurements.

Constrained Ensemble Kalman Filter for Distributed Electrochemical State Estimation of Lithium-Ion Batteries

Abstract: This article proposes a novel model-based estimator for distributed electrochemical states of lithium-ion (Li-ion) batteries. Through systematic simplifications of a high-order electrochemical–thermal coupled model consisting of partial differential-algebraic equations, a reduced-order battery model is obtained, which features an equivalent circuit form and captures local state dynamics of interest inside the battery. Based on the physics-based equivalent circuit model, a constrained ensemble Kalman filter (EnKF) is pertinently designed to detect internal variables, such as the local concentrations, overpotential, and molar flux. To address slow convergence issues due to weak observability of the battery model, the Li-ion's mass conservation is judiciously considered as a constraint in the estimation algorithm. The estimation performance is comprehensively examined under a wide operating range. It demonstrates that the proposed EnKF-based nonlinear estimator is able to accurately reproduce the physically meaningful state variables at a low computational cost and is significantly superior to its prevalent benchmarks for online applications.

60-GHz Compact Dual-Mode On-Chip Bandpass Filter Using GaAs Technology

Abstract: A 60-GHz compact dual-mode on-chip bandpass filter (BPF) is presented using gallium arsenide (GaAs) technology. To demonstrate the working mechanism of the proposed BPF, an LC equivalent circuit model is conceived and analyzed for further investigation of the transmission poles and zeros. Finally, a prototype of the BPF is fabricated and tested to validate the proposed idea, whose simulated and measured results are in good agreement. The measurements show that it has a center frequency of 58.7 GHz with a bandwidth of 18.4%, and the minimum insertion loss within the passband is 2.42 dB. The chip size, excluding the feedings, is about 0.158 mm $\times0.344$ mm.

Busbar Design and Optimization for Voltage Overshoot Mitigation of a Silicon Carbide High-Power Three-Phase T-Type Inverter

Abstract: The silicon carbide (SiC) devices have faster switching speed than that of the conventional silicon (Si) devices, which however may cause excessive device voltage overshoot. Larger gate resistance can help to restrain the overshoot, it however slows down the switching speed and increases switching losses. There are other methods that can mitigate the voltage overshoot, e.g., using low-inductance busbars, adding snubber circuits, etc. In this article, the busbar design for a 250-kW SiC three-level T-type inverter is investigated. The current commutation loops (CCLs) are first analyzed using a single-phase equivalent circuit. Then the detailed busbar design methods, especially a 3-D busbar design concept, are proposed to select the optimal stacking order for the multilayer laminated busbar and to address constraints posed by the physical terminal arrangements of SiC modules and dc-link capacitors. The stray inductance in each CCL is extracted via a finite element analysis and validated on the actual inverter busbar prototypes using an impedance analyzer. To further minimize the busbar stray inductance, a hybrid busbar structure with printed circuit board based buffer circuit using high-frequency decoupling capacitors is designed and evaluated in this article. Finally, the effectiveness of the designed busbars as well as the buffer circuit are validated using experimental studies.

Online EIS and Diagnostics on Lithium-Ion Batteries by Means of Low-Power Integrated Sensing and Parametric Modeling

Abstract: This article presents a compact measurement system for electrochemical impedance spectroscopy (EIS) on lithium-ion battery (LIB). The system is composed of a vector impedance analyzer (VIA) and state parameter estimation. The VIA architecture is based on delta–sigma digital-to-analog and analog-to-digital conversions to achieve the compactness, low-power consumption, and high resolution required to be potentially integrated within a battery cell. The estimation of state parameters is based on equivalent circuit models and the solution of nonlinear optimization problems. The proposed measurement system aims at the integration of complex measurement features directly into the battery cell to allow online and real-time diagnostic of the battery cell. A prototype of the compact measurement system was realized to assess the proposed approach. Experimental results are provided and validated by comparison with a reference laboratory instrument, showing good agreement. The VIA prototype is experimentally tested in both the online monitoring and aging monitoring of a commercial LIR2032 LIB cell. The modeling approach is applied to the experimental data provided by the VIA prototype, showing a good fit of the data. Moreover, parameters of the equivalent circuit models are extracted from the experimental data provided by the VIA prototype and identify trends related to the state of charge of the battery.

Wide-Angle Broadband Rasorber for Switchable and Conformal Application

Abstract: A novel wide-angle and broadband rasorber is presented incorporating several advances. To broaden the bandwidth, we introduce a new type of frequency selective surface (FSS) in the bottom layer of the rasorber. This strategy increases the upper and lower absorption bandwidths while reducing the insertion loss at transmission window. Furthermore, a new top resistive layer is proposed via the loading of electric field coupled resonator elements on a cross-dipole structure. The proposed design offers both, an angularly stable performance and a thin structure that can be fabricated on a single dielectric substrate. To enable switchability, p-i-n diodes are employed and a reconfigurable rasorber/absorber is designed where a new concept of “lossy/lossless” top layer is investigated and established as the best choice among other switchable designs. Equivalent circuit models are constructed for both active and passive designs to provide physical insight into their operation. Finally, to enable deployment of the rasorber over curved geometries, these advances are incorporated into a conformal structure. Three separate prototypes are fabricated and good agreement is obtained between design predictions and experimental results.

Highly Sensitive Phase-Variation Dielectric Constant Sensor Based on a Capacitively-Loaded Slow-Wave Transmission Line

Abstract: This paper presents a highly sensitive phase-variation sensor for dielectric constant measurements based on a capacitively-loaded periodic slow-wave transmission line. Such line is implemented in microstrip technology, and the loading capacitors are formed by closely spaced rectangular patches. The sensing area of the device is delimited by the region occupied by the capacitive patches, where the material under test (MUT) must be located. The presence of the MUT modifies the coupling capacitance between adjacent patches, thereby producing a variation in the electrical length, or phase of the transmission line, which is the output variable. A detailed analysis of the equivalent circuit model of the unit cell, useful for design purposes, is carried out in the paper. Based on such analysis, a prototype device sensor is designed and fabricated. It is demonstrated in the paper that the sensitivity of the proposed sensor is by far superior to the one achieved in an ordinary meandered line with similar sensing area. Thus, the proposed slow-wave structure constitutes a good alternative to meandered lines for the implementation of phase-variation sensors with simultaneously high sensitivity and compact size.

State of charge estimation with the adaptive unscented Kalman filter based on an accurate equivalent circuit model

Abstract: The accurate estimation of the state of charge (SOC) plays an important role in optimizing the energy management of electric vehicles. To improve the estimation accuracy of SOC, this study proposes a SOC estimation method with the adaptive unscented Kalman filter (AUKF) based on an accurate equivalent circuit model. First, combined with the n-RC equivalent circuit model, the relationship curve between SOC and open-circuit voltage (OCV) is fitted via parameter identification. Next, the accuracy advantage of the n-RC model is proven by comparing and analyzing the voltage response curves of different n-RC models and several common equivalent circuit models. Moreover, the accuracy of the n-RC model becomes higher with the increasing n. Then the numerical validation experiments are established based on the AUKF algorithm, and the constant current discharge experiment, hybrid pulse experiment, robustness verification experiment are carried out. Finally, to effectively evaluate this estimation approach, in addition to setting up a control group experiment based on the extended Kalman filter (EKF) algorithm and unscented Kalman filter (UKF) algorithm. The experiment results show that, compared with the other two algorithms, the SOC estimation method based on AUKF is more accurate.

Magnetic Equivalent Modeling of Stator Currents for Localized Fault Detection of Planetary Gearboxes Coupled to Electric Motors

Abstract: Stator current modeling for defective planetary gearboxes based on magnetic equivalent circuits (MEC) is conducted in this article. A lumped parameter torsional model of the motor-planetary gearbox coupling system is established to obtain the nonlinear time-variable torsional response of the rotor numerically. An MEC model of an induction motor is established by connecting the equivalent flux tubes with nodes. After considering the time-variable rotor torsional response, the nonlinear magnetic field intensity of the iron material, and magnetic saturation, an iterative numerical integration method is presented to solve the MEC model. Both a finite element analysis and dynamic tests on a planetary gearbox driven by an induction motor are carried out for verification. Based on these, the fault characteristic components in the stator current spectra are, respectively, identified when the tooth chipping defect appears at sun/planet/ring gears. Fault-related frequencies are essentially represented by the combinations between the meshing frequency, sun/planet/ring gear fault passing frequency, its harmonics, and the power supply frequency. Owing to the electromechanical coupling effect, high-order harmonics of the power supply frequency also participate in the fault-related frequencies of the planet and ring gears. By quantitatively analyzing the influence of chipping size on the amplitudes of fault characteristic frequencies, suitable spectra for planetary gearbox condition monitoring are recommended.

Study on a New Power Frequency Capacitive Voltage Transducer for Gas Insulated Substations Based on Capacitive Voltage Division

Abstract: The IVT for power frequency is an essential facility in the power system. Due to the requirement for high-voltage insulation, the sensing part of the conventional IVTs is bulky and costly. The purpose of this article is to propose a new voltage measurement method based on capacitive voltage divider for GIS. The equivalent circuit of the measurement method is built. The numerical simulation model for the measurement system is built based on the actual size of GIS with rated voltage of 220 kV. And FEM is employed to analyze the transfer relation and the accuracy of the proposed measurement method. The experiments are conducted in the laboratory and at an actual GIS platform, respectively. The transfer relation between the applied voltage and the induced voltage is obtained. Compared with conventional IVTs, the dimension of the measurement system is very small. Due to the low voltage of the sensing part, the insulation problem of the sensing part is avoided. And due to simple structure and linear characteristics, the transfer relation of the proposed measurement system can be obtained with high accuracy.

An Enhanced Equivalent Circuit Model with Real-Time Parameter Identification for Battery State-of-Charge Estimation

Abstract: This paper introduces an efficient modeling approach based on Wiener structure to reinforce the capacity of the classical Equivalent Circuit Models (ECMs) in capturing the nonlinearities of Lithium-ion (Li-ion) batteries. The proposed block-oriented modeling architecture is composed of a simple linear ECM followed by a static output nonlinearity block, which helps achieving a superior nonlinear mapping property while maintaining the real-time efficiency. The observability of the established battery model is analytically proven. This paper also introduces an efficient parameter estimator based on extended-kernel iterative recursive least squares algorithm for real-time estimation of the parameters of the proposed Wiener model. The proposed approach is applied for state-of-charge (SoC) estimation of 3.4 Ah 3.6 V NMC-based Li-ion cells using the extended Kalman filter (EKF). The results show about 1.5% improvement in SoC estimation accuracy compared with the EKF algorithm based on second-order ECM. A series of real-time tests are also carried out to demonstrate the computational efficiency of the proposed method.

Ultrawideband Frequency-Selective Absorber Designed With an Adjustable and Highly Selective Notch

Abstract: In this article, the working mechanism of a wideband absorber designed with an adjustable and highly selective notch band is studied, in which the narrow notch band is independently controlled by the lower lossless layer of the absorber, whereas the upper lossy layer loaded with lumped resistors realizes absorption. We present two instances with geometrically controlled and electrically controlled notch bands, respectively. Without decreasing absorption performance, the notch position can be flexibly adjusted throughout the entire frequency band by simply modifying the dimension of the lossless frequency-selective surface (FSS) or changing the capacitance of the varactor, i.e., using geometric control or electrical control. The narrow notch band allows two wide absorption bands to be retained on both sides; therefore, good stealth performance is still guaranteed. Equivalent circuit models (ECMs) are proposed to further explain the principle. The frequency-domain simulation, ECM, time-domain simulation, and experimental results are in good agreement and validate the adjustability and high selectivity of the notched absorbers. At the end of this article, an FSA-backed monopole antenna is simulated and measured, which clearly illustrates that these FSAs can serve as the ground plane for antennas and realize out-of-band RCS reduction.

A Broadband, Wide-Angle Scanning, Linear-to-Circular Polarization Converter Based on Standard Jerusalem Cross Frequency Selective Surfaces

Abstract: A broadband and wide-angle scanning linear polarization (LP)-to-circular polarization (CP) converter based on a dual-layer structure is presented. The elementary cell is composed of conventional Jerusalem crosses (JCs). The design procedure is based on transmission line circuit model and on full-wave simulations. The proposed equivalent circuit has been generalized to include the oblique incidence in the model. Simulated results demonstrate a 24% axial ratio bandwidth for an incidence angle $\theta = \pm 50^{\circ }$ in both x z and y z planes. The proposed converter provides a unique combination of wide bandwidth, thin profile, and stable response with respect to the angle of incidence. It can be integrated into any LP antenna system to generate CP without significantly affecting the antenna performances.

A S-type bistable locally active memristor model and its analog implementation in an oscillator circuit

Abstract: In this paper, a S-type memristor with tangent nonlinearity is proposed. The introduced memristor can generate two kinds of stable pinched hysteresis loops with initial conditions from two flanks of the initial critical point. The power-off plot verifies that the memristor is nonvolatile, and the DC V-I plot shows that the memristor is locally active with the locally active region symmetrical about the origin. The equivalent circuit of the memristor, derived by small-signal analysis method, is used to study the dynamics near the operating point in the locally active region. Owing to the bistable and locally active properties and S-type DC V-I curve, this memristor is called S-type BLAM for short. Then, a new Wien-bridge oscillator circuit is designed by substituting one of its resistances with S-type BLAM. It finds that the circuit system can produce chaotic oscillation and complex dynamic behavior, which is further confirmed by analog circuit experiment.

Parameter Identification and State-of-Charge Estimation for Lithium-Ion Batteries Using Separated Time Scales and Extended Kalman Filter

Abstract: With the development of new energy vehicle technology, battery management systems used to monitor the state of the battery have been widely researched. The accuracy of the battery status assessment to a great extent depends on the accuracy of the battery model parameters. This paper proposes an improved method for parameter identification and state-of-charge (SOC) estimation for lithium-ion batteries. Using a two-order equivalent circuit model, the battery model is divided into two parts based on fast dynamics and slow dynamics. The recursive least squares method is used to identify parameters of the battery, and then the SOC and the open-circuit voltage of the model is estimated with the extended Kalman filter. The two-module voltages are calculated using estimated open circuit voltage and initial parameters, and model parameters are constantly updated during iteration. The proposed method can be used to estimate the parameters and the SOC in real time, which does not need to know the state of SOC and the value of open circuit voltage in advance. The method is tested using data from dynamic stress tests, the root means squared error of the accuracy of the prediction model is about 0.01 V, and the average SOC estimation error is 0.0139. Results indicate that the method has higher accuracy in offline parameter identification and online state estimation than traditional recursive least squares methods.

A Polarization-Insensitive Band-Notched Absorber for Radar Cross Section Reduction

Abstract: A polarization-insensitive broadband absorber with a notch band characteristic has been presented for radar cross section (RCS) reduction applications. The proposed design is a three-layered structure, consisting of metal-printed substrate layers separated by air spacers. The top layer is a resistor-loaded convoluted cross-dipole geometry that results in a wideband absorption. The band-notch response is achieved by careful design of a square loop in the middle layer, and the bottom layer is a complete metal ground. The overall structure exhibits two discrete absorption bands (having absorptivity above 90%) over the frequency ranges of 2.12 to 4.15 GHz and 6.08 to 9.58 GHz, whereas a reflective behavior is obtained from 4.3 to 5.65 GHz. The proposed geometry has several novel features, such as compact topology (with unit cell size of 0.137 λL, λL being the lowest operating wavelength), low profile, polarization-insensitivity, and wide operating bandwidth of 127.52%, unlike the existing band-notched absorbers. By deriving an equivalent circuit model and several parametric variations, the performance of the proposed absorber has been qualitatively analyzed. A sample prototype has also been fabricated and reasonable agreement among the circuit analysis, simulation response, and measured result is obtained under normal incidence.

Physics-Based Modeling of Parasitic Capacitance in Medium-Voltage Filter Inductors

Abstract: This article proposes a general physics-based model for identifying the parasitic capacitance in medium-voltage (MV) filter inductors, which can provide analytical calculations without using empirical equations and is not restricted by the geometrical structures of inductors The elementary capacitances of the MV inductor are identified, then the equivalent capacitances between the two terminals of the inductor are derived under different voltage potential on the core Further, a three-terminal equivalent circuit, instead of the conventional two-terminal equivalent circuit, is proposed by using the derived capacitances Thus, the parasitic equivalent capacitance between the terminals and the core are explicitly quantified Experimental measurements for parasitic capacitances show a good agreement with the theoretical calculations

A Novel Miniaturized Strong-Coupled FSS Structure With Excellent Angular Stability

Abstract: In this article, a novel miniaturized concept named strong-coupled frequency selective surface (SC-FSS) with excellent angular stability is presented. First, a conceptual design of SC-FSS is introduced, where the resonant frequencies are insensitive to almost all incident angles. A corresponding equivalent circuit model is developed to interpret the operating principle and formulate relevant design equations with an error of 0.2%. Furthermore, an ultraminiaturized and ultrathin band-stop structure with a unit cell size of λ 0/35 and thickness of 0.26 mm ( λ0 /578) is designed and fabricated to verify this concept. Analysis and experiment show that the proposed band-stop SC-FSS structure can work stably at 2 GHz for both TE and TM modes, even when the incident angle varies from 0° to 84°. The measurement results are consistent with those obtained by full-wave simulations and the equivalent circuit model, which fully demonstrates that the concept of SC-FSS can be widely used in designing antenna reflectors, electromagnetic interference shielding, and angle-insensitive absorbers.

State of power estimation of lithium-ion battery based on fractional-order equivalent circuit model

Abstract: State of power (SOP) is an important parameter to characterize the power performance of lithium-ion battery. Different from State of Charge (SOC), SOP estimation assumes that the battery is operated in extreme working condition, so higher accuracy and robustness are required for the battery model. In this study, the fractional-order equivalent circuit model is adopted to estimate SOP, which takes SOC, voltage, and current of the battery as constraints with the fractional-order calculus. Through the estimation results analysis under the FUDS and DST driving cycles, the general guidelines of the SOP constraint process are summarized: the discharge SOP is sequentially constrained by current, voltage, and SOC, and when the current changes frequently, the hybrid constraint is easy to be generated; the constraint process of charge SOP is opposite. Besides, novel experiments are designed separately to verify the SOP estimation results under SOC, voltage, and current constraints. The experimental results show that the maximum error of SOP estimation results is 1.34%, which proves that the SOP estimation based on the fractional-order model provides high estimation accuracy.

On the Design of Wideband Absorber Based on Multilayer and Multiresonant FSS Array

Abstract: In this letter, a novel and effective design method for multilayer and multiresonant absorbers is proposed. The two-layer absorber is composed of two resistor-loaded square loop frequency selective surface (FSS) arrays printed on the Rogers 4003 dielectric substrate and a backed metal plane. Equivalent circuits for two-layer absorbers with resistive sheets and resonant FSSs are proposed, analyzed, and further improved to provide great insight into the existence of the four resonances and ultrawide bandwidth. In the equivalent circuit model, the substrate is transformed to a parallel admittance and a positive susceptance is introduced in the whole operation band, which contributes to an extra resonance. After the measurement of a fabricated sample, a fractional bandwidth of 171.2% is obtained for at least 10 dB reflection reduction, with a total thickness of only 0.087λL (wavelength at the lowest absorption frequency). The good agreement between the calculated, simulated, and measured results validates the designed absorber.

Modelling of supercapacitors based on simplified equivalent circuit

Abstract: The need for energy storage devices especially in renewable energy applications has increased the use of supercapacitors. Accordingly, several supercapacitor models have been proposed in previous researches. Nevertheless, most of them require an intensive test to obtain the model parameters. These may not be suitable for an initial simulation study, where a simple model based on the datasheet is required to evaluate the system performance before building the hardware prototype. A simplified electrical circuit model for a supercapacitor (SC) based on the voltage-current equation is proposed in this paper to address this issue. This model doesn't need an intensive test for accuracy. The structural simplicity and decent modelling accuracy make the equivalent electrical circuit model very suitable for power electronic applications and real-time energy management simulations. The parameters of the proposed model can be obtained from the datasheets value with a minimum test requirement. The experimental method to provide the parameters of the supercapacitor equivalent circuit is described. Based on the proposed method, the supercapacitor model is built in Matlab/ Simulink, and the characteristics of equivalent series resistance (ESR) measurement and cycle life are compared with datasheets. The simulation results have verified that the proposed model can be applied to simulate the behaviour of the supercapacitor in most energy and power applications for a short time of energy storage. A supercapacitor test circuit is given to test the charge and discharge of supercapacitor modules. The experimental results are suitable for simulation results.

Design and Analysis of a High-frequency CLLC Resonant Converter with Medium Voltage insulation for Solid-State-Transformer

Abstract: The isolated DC/DC converter is the key component in high-frequency medium-voltage solid-state transformer. This paper presents a comprehensive design of a CLLC converter, including the design of transformer and resonant tank. The transformer insulation is designed to pass the partial discharge and applied voltage test. And its impact on transformer leakage inductance, as well as the resonant converter characteristic is discussed. Also, the transformer is optimized based on loss and volume trade-off. Then the relation of zero voltage switching (ZVS) condition and circuit parameters and load condition is derived from equivalent circuit. The impact of magnetizing inductance, leakage inductance, MOSFETs junction cap, and characteristic factor Q on ZVS condition is revealed. Finally, this paper provides a guidance to select dead-time appropriately and demonstrates the design on a 200kHz converter with 1.6kV input and 1.1kV output, and achieves a peak efficiency of 98.9%.

High-Electrification Performance and Mechanism of a Water-Solid Mode Triboelectric Nanogenerator.

Abstract: With the advantages of superior wear resistance, mechanical durability, and stability, the liquid-solid mode triboelectric nanogenerator (TENG) has been attracting much attention in the field of energy harvesting and self-powered sensors. However, most reports are primarily observational, and there still lacks a universal model of this kind of TENG. Here, an equivalent circuit model and corresponding governing equations of a water-solid mode TENG are developed, which could easily be extended to other types of liquid-solid mode TENGs. Based on the first-order lumped circuit theory, the full equivalent circuit model of water-solid mode TENG is modeled as a series connection of two capacitors and a water resistor. Accordingly, its output characteristics and critical influences are examined, to investigate the relevant physical mechanism behind them. Afterward, a three-dimensional water-solid TENG array constructed from many single-wire TENGs is fabricated, which can not only harvest tiny amounts of energy from any movement of water, but also can verify our theoretical predictions. The fundamentals of the water-solid mode TENG presented in this work could contribute to solving the problem of electrical phenomena on a liquid-solid interface, and may establish a sound basis for a thorough understanding of the liquid-solid mode TENG.

Comparison of methods for finding the capacitance of a supercapacitor

Abstract: A carbon-based supercapacitor is usually associated with a capacitance such that the user can access its ability to store electrical charge. Three different measurement methods or variations thereof are typically employed to find the capacitance; galvanostatic charging, cyclic voltammetry and impedance spectroscopy. These three methods may give rather different capacitances, which must be interpreted with care. Here, it is discussed how one can extract consistent capacitance values from measurements obtained with the three techniques, to be interpreted within a single dynamic equivalent circuit. Different methods are compared in order to demonstrate where systematic errors occur, and how and under which conditions they can be removed. The extension of the methods presented here to pseudocapacitors utilizing both Faradaic and non-Faradaic charge storage is also briefly discussed.

Incorporating the Dynamic Threshold Voltage Into the SPICE Model of Schottky-Type p -GaN Gate Power HEMTs

Abstract: The threshold voltage ( V TH) of an enhancement-mode Schottky-type p -GaN gate high-electron-mobility transistor (HEMT) is found to have a special dependence on the drain bias. The device commonly requires higher gate voltage to switch on the transistor from a high-drain-voltage off -state than what is expected from the static device characteristics. The reason behind the dynamic V TH has been proved to be the floating p -GaN layer, where charges could be stored and further influence V TH under different drain bias. In this article, a SPICE-compatible equivalent circuit model is presented according to the structure of Schottky-type p -GaN gate HEMTs. It features a floating node to imitate the charge storage process within the gate stack. Compared to conventional models, the proposed model could accurately predict the dynamic V TH characteristics and switching behaviors of power electronics circuits, where Schottky-type p -GaN gate HEMTs are deployed as power transistors. The phenomena related to the dynamic V TH, including the disappearance of Miller plateau, the overestimated false-turn- on problem, and the higher reverse conduction loss are evaluated with a half-bridge circuit and the merits of the proposed model are verified.