Showing papers on "Equivalent circuit published in 2018"

Frequency-Selective Rasorber With Interabsorption Band Transparent Window and Interdigital Resonator

Abstract: A novel frequency-selective rasorber (FSR) is proposed in this paper which has a nearly transparent window between two absorption bands. The FSR consists of a resistive sheet and a bandpass frequency-selective surface (FSS). The impedance conditions of absorption/transmission for both the resistive sheet and the bandpass FSS are theoretically derived based on equivalent circuit analysis. The insertion loss of FSR at the resonant frequency of lossless bandpass FSS is proven to be only related to the equivalent impedance of the resistive sheet. When the resistive sheet is in parallel resonance at the passband, a nearly transparent window can be achieved regardless of lossy properties. An interdigital resonator (IR) is designed to realize parallel resonance in the resistive element by extending one finger of a strip-type interdigital capacitor to connect the two separate parts of the capacitor. The IR is equivalent to a parallel LC circuit. Lumped resistors are loaded around the IR to absorb the incident wave at lower and upper absorption bands. With the bandpass FSS as the ground plane, the absorption performances at both the lower and upper bands around the resonant frequency are improved compared to a metal-plane-backed absorber structure. The FSR passband is designed at 10 GHz with an insertion loss of 0.2 dB. The band with a reflection coefficient below −10 dB extends from 4.8 to 15.5 GHz. A further extension to dual-polarized FSR is designed, fabricated, and measured to validate the proposed design.

Investigation of Multimodal Electret-Based MEMS Energy Harvester With Impact-Induced Nonlinearity

Abstract: This paper presents an electret-based MEMS energy harvester synergizing the advantages of multi-modal structure and impact mechanism for broad operating bandwidth. The device with a volume of 295 mm3 comprises an electret-based primary subsystem for power generation and an electrode-free auxiliary subsystem for frequency tuning. The tiny auxiliary subsystem helps to induce close resonances with comparable outputs at low excitations, as well as introduces impact-based nonlinearity to drive the first resonant peak upward and further approach the second one at elevated excitations. The experimental results demonstrate that at an excitation of 12.8 m/ $\text{s}^{2}$ , the 3-dB bandwidth of the first peak is increased from 20.4 to 60.4 Hz and a low frequency ratio of 1.15 between the two peaks is achieved. The two degree-of-freedom resonant structure with impact-based nonlinearity is systematically investigated through an equivalent circuit representation. An electrical equivalent circuit model of the proposed device with impact mechanism is derived. The circuit simulation confirms the nonlinear behavior of the system, and reveals the mechanism of peak shifting and bandwidth enhancing dynamics. [2017-0207]

A Reconfigurable Broadband Polarization Converter Based on an Active Metasurface

Abstract: We propose an active metasurface whose functionalities can be dynamically switched among linear-to-linear, linear-to-elliptical, and linear-to-circular polarization conversions in a wideband. The active metasurface is composed of butterfly-shaped unit cells embedded with voltage-controlled varactor diodes. By controlling the bias voltage of the varactor diodes, the electromagnetic responses of the proposed metasurface can be tailored, leading to reconfigurable polarization conversions. The simulation results reveal that with no bias voltage, the proposed metasurface is able to reflect linear-polarization waves to cross-polarization waves in the frequency range from 3.9 to 7.9 GHz, with a polarization conversion ratio of over 80%; however, at the bias voltage of −19 V, the metasurface is tuned to be a circular polarization converter in a wideband from 4.9 to 8.2 GHz. Moreover, two equivalent circuits along the $x$ - and $y$ -directions are developed to elucidate the tunable mechanism. The experimental results are in a good agreement with the simulation results obtained from commercial software and from the equivalent circuit model.

Core Losses Analysis of a Novel 16/10 Segmented Rotor Switched Reluctance BSG Motor for HEVs Using Nonlinear Lumped Parameter Equivalent Circuit Model

Abstract: In this paper, a new nonlinear lumped parameter equivalent circuit model is proposed to calculate the core losses of a novel 16/10 segmented rotor switched reluctance motor (SSRM) for belt-driven starter generators. The model investigates the hysteresis, eddy current and anomalous losses by using the method of energy conservation. Four parameters are introduced in the proposed model to consider the effects of saturation and leakage flux in SSRM. They are the incremental leakage inductance, the incremental equivalent winding resistance, the incremental magnetizing inductance, and the incremental equivalent core-loss resistance. This model can overcome the hysteresis effects of winding resistance and leakage inductance on the current, and improve the accuracy of the parameters. To illustrate the advantages of the proposed model, an experiment platform is developed. Experimental results show that the proposed model can significantly improve the calculation accuracy of core losses of the SSRM. The accuracy is better than the conventional Epstein frame method. The proposed core-loss model and analysis method can be applied to other kinds of switched reluctance motors.

A New Method for Fitting Current–Voltage Curves of Planar Heterojunction Perovskite Solar Cells

Abstract: Herein we propose a new equivalent circuit including double heterojunctions in series to simulate the current–voltage characteristic of P–I–N planar structure perovskite solar cells. This new method can theoretically solve the dilemma of the parameter diode ideal factor being larger than 2 from an ideal single heterojunction equivalent circuit, which usually is in the range from 1 to 2. The diode ideal factor reflects PN junction quality, which influences the recombination at electron transport layer/perovskite and perovskite/hole transport layer interface. Based on the double PN junction equivalent circuit, we can also simulate the dark current–voltage curve for analyzing recombination current (Shockley–Read–Hall recombination) and diffusion current (including direct recombination), and thus carrier recombination and transportation characteristics. This new model offers an efficacious and simple method to investigate interfaces condition, film quality of perovskite absorbing layer and performance of transport layer, helping us further improve the device efficiency and analyze the working mechanism.

Locating the Source of Events in Power Distribution Systems Using Micro-PMU Data

Abstract: A novel method is proposed to locate the source of events in power distribution systems by using distribution-level phasor measurement units , a.k.a., micro-PMUs. An event in this paper is defined rather broadly to include any major change in any component across the distribution feeder. The goal is to enhance situational awareness in distribution grid by keeping track of the operation (or misoperation) of various grid equipment, assets, distribution energy resources, loads, etc. The proposed method is built upon the compensation theorem in circuit theory to generate an equivalent circuit to represent the event by using voltage and current synchrophasors that are captured by micro-PMUs. Importantly, this method makes critical use of not only magnitude but also synchronized phase angle measurements, thus, it justifies the need to use micro-PMUs, as opposed to ordinary RMS-based voltage and current sensors. The proposed method can work with data from as a few as only two micro-PMUs. The effectiveness of the developed method is demonstrated through computer simulations on the IEEE 123-bus test system, and also on micro-PMUs measurements from a real-life 12.47 kV test feeder in Riverside, CA. The results verify that the proposed method is accurate and robust in locating the source of different types of events on power distribution systems.

A 2.5-D Angularly Stable Frequency Selective Surface Using Via-Based Structure for 5G EMI Shielding

Abstract: A novel broadband bandpass frequency-selective surface (FSS) designed for fifth generation (5G) EMI shielding is proposed in this paper. This new design employs the vertical vias into the 2-D periodic arrays, and such a single 2.5-D periodic layer of via-based structure is demonstrated to produce a highly stable angular response up to 60° for both TE and TM polarizations. By cascading two layers of such 2.5-D periodic arrays, the proposed FSS is able to obtain a broad passband as well as the wide out-of-band rejection. Moreover, it has a quite sharp band edge between the passband and the specified stopband. A corresponding equivalent circuit model (ECM) is further developed for better analysis of the operating principle. Finally, a prototype working at the center frequency of around 28 GHz is fabricated and measured. The main novelty of this paper is introducing the 2.5-D concept into designing a wideband FSS, and further reduce the unit size as well as improve the angular stability. Favorable agreement is achieved among the 3-D full-wave simulation, ECM and measurement. All these results demonstrate that the proposed FSS is a good candidate for 5G EMI shielding.

Analytical and Experimental Investigations of Omnidirectional Wireless Power Transfer Using a Cubic Transmitter

Abstract: In recent years, wireless power technology has been promoted for recharging systems for portable devices that are used in everyday life. The conventional technology used for this purpose, which is based on magnetically coupled resonators, has provided promising results but is limited in range and direction at the receiving terminal. In this paper, we propose an omnidirectional wireless power transfer (WPT) system with a novel cubic transmitter to achieve relatively high efficiency. Specifically, a single power source is utilized to drive the current of the transmitter without phase and current control methodology. Energy delivery is transmitted to the receiver through magnetic resonant coupling in the medium-range WPT mode. In addition, an equivalent circuit model of a coupling two-coil system is derived and mathematically analyzed. The efficiency of the proposed omnidirectional WPT system depending on the various distances between the transmitter and the receiver, as well as the transmitter structure, is evaluated via analysis and implementation. Finally, practical experimental results from the resonant coupling system confirm the theoretical analysis of the cubic transmitter and the omnidirectional power transfer capability, which demonstrate approximately 60% power transfer efficiency.

Dual-Polarized Bandpass and Band-Notched Frequency-Selective Absorbers Under Multimode Resonance

Abstract: Two novel dual-polarized frequency-selective absorbers (FSA) are proposed based on two-layered structures under multimode resonances Each FSA consists of a two-layered metal structure with an air gap in the middle At the top layer, a hybrid resonator is applied to generate a wide absorption band and a stop/passband At the bottom layer, two different types of structures are separately applied to perform the opposite senses of bandpass and band-notched filtering for the final FSAs Moreover, the design strategies were examined using the corresponding equivalent circuit models The resultant absorbers have the thickness of only approximately $008~\lambda _{L}$ at the lowest operating frequencies and exhibit wide operating bands of over 100% To demonstrate this approach, two prototypes of the proposed absorbers were fabricated and tested, and reasonable agreement between the simulation results and experimental data was obtained

Reconfigurable Linear-to-Linear Polarization Conversion Metasurface Based on PIN Diodes

Abstract: A reconfigurable linear-to-linear polarization conversion metasurface (Re-PCM) based on positive-intrinsic-negative (PIN) diodes is proposed, which can be reconfigured between the conversion mode and the reflection mode by switching the loaded PIN diodes. The unit cell of the Re-PCM consists of two slotted metal square rings and bias lines, which are all etched on a substrate backed by a metal ground. In the conversion mode, the Re-PCM reflects linearly polarized incident waves with 90° polarization rotation. The simulated results show that the polarization conversion ratio is more than 88% over 3.39–5.01 GHz for x -polarized and y -polarized normally incident waves. In the reflection mode, it exhibits total reflection characteristic like a metal plate. The magnitude of co-polarization reflection is over −1 dB from 3.83 to 4.74 GHz. The physical mechanism and equivalent circuit of the Re-PCM are analyzed. To validate the simulation, a prototype of the Re-PCM is fabricated and measured. Reasonable accordance between the simulated and measured results is obtained.

Double-Layer Circuit Analog Absorbers Based on Resistor-Loaded Square-Loop Arrays

Abstract: Based on the equivalent circuit model, it is demonstrated that five resonances can occur within the absorption band of a circuit analog absorber containing two lossy layers. The lossy layers are composed of resistor-loaded square-loop and double-square-loop arrays. In the absence of a dielectric skin, an initial design with four resonances observed from its reflectivity exhibits a simulated bandwidth ratio (BWR) of 1:8.45 for at least 10 dB absorption. To facilitate physical implementation of the wideband absorber, a modified design is proposed to compensate the effect of parasitic parameters of actual resistors on reflectivity. It is shown through measurement that an operating BWR of 1:8.78 is achieved with the reflectivity smaller than −10 dB under normal incidence. The total thickness of the absorber prototype is only 0.096 λ at the lowest operating frequency. The agreement between simulation and measurement validates the proposed design.

Low-Profile Dual-Polarization Frequency-Selective Rasorbers Based on Simple-Structure Lossy Cross-Frame Elements

Abstract: The low-profile dual-polarization frequency-selective rasorbers with very simple structures are investigated. Based on an equivalent circuit model, the operating principle and design method are first studied. One rasorber using lossy cross-frame elements and double-square loops is then proposed, which exhibits two absorption bands at the two sides of one passband. Moreover, the rasorbers with reduced cell size are further developed to stabilize the angular response. Under normal incidence, an insertion loss of about 0.26 dB is obtained at 4.25 GHz, the fractional bandwidth for reflection less than −10 dB is over 100%, and the thickness is around ${\text{0.1}}\,\lambda _{L}$ . For demonstration, the rasorber prototypes are fabricated and measured, while reasonable agreements are observed accordingly.

Polarization-Insensitive Broadband Multilayered Absorber Using Screen Printed Patterns of Resistive Ink

Abstract: Design and implementation of a broadband polarization-insensitive multilayered microwave absorber using resistive ink has been presented here. The proposed absorber is constructed using layers of resistive surface where each layer consists of periodic arrangement of resistive patterns printed on a low-cost FR4 sheet using resistive ink. Due to the multilayered nature, the proposed absorber shows broadband absorption having simulated reflection coefficient less than $-$ 10 dB in the frequency range from 2.00 to 18.50 GHz under normal incidence, which covers the entire S, C, X, and Ku bands with the smallest thickness of 0.082 $\lambda _L$ (at lowest operating frequency of the absorption band) as compared to the state-of the-art absorbers. In order to validate the proposed absorber, the equivalent circuit model has also been presented. The equivalent circuit model shows good match with the proposed absorber. The proposed absorber is experimentally verified and the experimental results shows good agreement with the simulated results.

Equivalent circuit model parameters extraction for lithium ion batteries using electrochemical impedance spectroscopy

Abstract: Numerical modelling is the method by virtually testing and verifying the functionality of a specific product or component. The primary goal is to get approximate results of how the system behaves in a given time and environment. We are able to accept a certain numerical error from a real experiment, thus significantly speeding up part of the development of the device. In the field of electrochemistry of lithium-ion accumulators, several variants of numerical models have been proposed that yield satisfactory results in modelling certain physical fields of these batteries (electric field, temperature field, current field).

State of Charge-Dependent Polynomial Equivalent Circuit Modeling for Electrochemical Impedance Spectroscopy of Lithium-Ion Batteries

Abstract: Electrochemical impedance spectroscopy (EIS) is used not only to give a thorough understanding of reaction kinetics and transport mechanisms in lithium-ion batteries (LIBs), but also to provide a promising nondestructive tool for state of charge (SOC) estimation. Although various equivalent circuit models (ECMs) have been proposed to model impedance spectra, the impact of SOC on circuit parameters is often neglected in these models. In this study, the nonlinear relationship between circuit parameters and SOC is explicitly characterized using analytical polynomial functions. The effect of polynomial order is systematically investigated by means of fitting and prediction accuracy, in which the prediction performance is evaluated using leave-one-out cross-validation (LOOCV) method. The EIS measurements of a 20-A·h commercial LIB are performed to demonstrate the effectiveness of the proposed model. The results show that a seventh-order polynomial function is sufficiently high to capture the nonlinear effect of SOC on circuit parameters. Moreover, the LOOCV prediction performance of the polynomial function-based ECM is probably better than that of a common interpolation-based ECM.

State of Charge Estimation of Lithium-Ion Batteries Over Wide Temperature Range Using Unscented Kalman Filter

Abstract: With the development of electric vehicles in recent years, lithium-ion batteries have been widely used. Accurate state of charge (SOC) estimation plays an important role in the safety of electric vehicles. Since the temperature has the significant influence on charge and discharge performance of the battery, it is critical to achieve accurate SOC estimation over the wide temperature range. In this paper, a polymer ternary lithium-ion battery is focused, and a Thevenin equivalent circuit model with temperature compensation is established. The validity of the established battery model was verified by the dynamic stress test. On this basis, the ternary lithium-ion battery SOC was estimated using the unscented Kalman filter (UKF). The New European Driving Cycle is used to verify the effectiveness of the proposed algorithm. The simulation and experimental results show that the established Thevenin equivalent circuit model with temperature compensation can accurately represent the battery dynamics. Based on this model, the SOC was estimated using the UKF and the maximum errors are within 3%. Therefore, the proposed SOC estimation method is verified to be effective and robust.

Design-Oriented Modelling of Axial-Flux Variable-Reluctance Resolver Based on Magnetic Equivalent Circuits and Schwarz–Christoffel Mapping

Abstract: Axial flux variable reluctance (AFVR) resolvers have substantial benefits that make them suitable for motion control drives. However, they suffer from insufficient accuracy, especially in high-accuracy applications. Hence, optimizing the AFVR resolver structure is necessary for improving its commercial usage. However, its accurate modelling needs three-dimensional (3-D) time stepping finite element analysis (TSFEA) that is computationally expensive and unsuitable for co-usage with optimization algorithms. The aim of this paper is to establish an accurate, yet computationally fast, model suitable for optimal design of AFVR resolvers. The working of the proposed model is based on magnetic equivalent circuit (MEC) and conformal mapping, which are in turn based on Schwarz–Christoffel mapping. The model uses conformal mapping to calculate reluctances that are used in MEC for calculating magnetic fluxes linkages, inductances, and induced voltages. Then, the induced voltages are used for calculating angular position. The results of the proposed model are compared with those of 3-D TSFEA. Finally, the experimental prototype is used to evaluate the developed analytical model.

A Comprehensive Analysis of Short-Circuit Current Behavior in PMSM Interturn Short-Circuit Faults

Abstract: This paper presents a detailed analysis of short-circuit current behavior during interturn short-circuit faults in permanent magnet synchronous machines (PMSMs) by considering the short-circuit contact resistance. For this purpose, an finite element analysis (FEA)-based equivalent circuit model is developed to understand the circulating current behavior in the shorted turns. Various fault resistance and number of shorted turn combinations are examined at different torque and speed levels. To include saturation due to high fault currents, the inductance matrix of faulty machine is created in FEA environment and incorporated into the equivalent circuit model as four-dimensional lookup tables. In order to take loop responses into account, the model is controlled through field oriented control (FOC) with closed speed and current loops. An experimental setup is built to verify the simulation results using a PMSM with several winding taps. It is shown that the experimental results and the simulations are quite consistent with each other. The findings from this study are essential to predict fault severity, develop mitigation techniques and determine the safe operating area for faulty machines.

A comprehensive study of 2:1 internal-resonance-based piezoelectric vibration energy harvesting

Abstract: This work exploits a 2:1 internal resonance mechanism to enhance broadband vibration energy harvesting. It is achieved by adding a properly tuned auxiliary oscillator to the primary energy harvesting oscillator coupled by a nonlinear magnetic force. A theoretical study is conducted on the nonlinear dynamic and energy harvesting performance of the proposed harvester by various analytical approximations, and the accuracy of these analytical models is investigated. Given harmonic base excitation, the output voltage frequency response is derived by the multi-scale method and harmonic balance method (HBM), which are then verified by equivalent circuit simulations and experiments. The necessity of taking into account the zeroth-order harmonic component in the HBM is verified and discussed. The HBM result without this component and the multi-scale method fail to accurately predict the nonlinear dynamic behaviour. With the validated HBM model and the equivalent circuit model, key features of internal resonance are revealed by investigating modal interaction and saturation phenomena under varying excitation. By and large, the operational bandwidth of the vibration energy harvester is enlarged due to the 2:1 internal resonance.

Fault Current Analysis of Type-3 WTs Considering Sequential Switching of Internal Control and Protection Circuits in Multi Time Scales During LVRT

Abstract: As Type-3 wind turbine (WT) has already become a typical type of highly penetrated power sources in modern power systems, characterizing its properties during grid fault is a basic requirement for system analysis. However, many significant factors have not been considered in the existing analytical methods and results, such as various switching of internal control and protection circuits in low voltage ride through (LVRT) solutions. In this paper, performance of Type-3 WT during LVRT is first illustrated and summarized as the sequential switching characteristic in multi time scales, viz., instant control, ac control, dc voltage control, and rotor speed control time scales. Thus, for magnitude drops in stator voltage, a mathematical model is proposed to understand this characteristic and fault current analysis's features. Then, an analytical method, based on the operational inductance, is proposed so that fault current components, with the sequential switching considered, can be depicted with a unified and simple analytical expression. By identifying magnitude of symmetrical current, the transient and steady-state equivalent circuits of Type-3 WT are proposed to estimate momentary current and electrical power approximately. Finally, analytical results are verified by comparisons with real-time simulation results of a detailed 1.5 MW WT model in RT-LAB.

Characterisation and Modeling of Gallium Nitride Power Semiconductor Devices Dynamic On-State Resistance

Abstract: Gallium nitride high-electron-mobility transistors (GaN-HEMTs) suffer from trapping effects that increases device on-state resistance ( $R_\mathrm{DS(on)}$ ) above its theoretical value. This increase is a function of the applied dc bias when the device is in its off state, and the time which the device is biased for. Thus, dynamic $R_\mathrm{DS(on)}$ of different commercial GaN-HEMTs are characterised at different bias voltages in the paper by a proposed new measurement circuit. The time-constants associated with trapping and detrapping effects in the device are extracted using the proposed circuit and it is shown that variations in $R_\mathrm{DS(on)}$ can be predicted using a series of RC circuit networks. A new methodology for integrating these $R_\mathrm{DS(on)}$ predictions into existing gallium nitride-high-electron-mobility transistors models in standard SPICE simulators to improve model accuracy is then presented. Finally, device dynamic $R_\mathrm{DS(on)}$ values of the model is compared and validated with the measurement when it switches in a power converter with different duty cycles and switching voltages.