Circuit Model Approach Research Articles

A Fast Matrix Solver for Linear Boundary-Value Problem in the PEM Fuel Cell Impedance Model

A core physics-based model for PEM fuel cell impedance reduces to the numerical solution of a boundary value problem for two coupled, linear, complex–valued ordinary differential Eqs. with variable coefficients. We report a matrix formulation of a previously developed recurrent method for the fast numerical solution of this problem. This formulation does not require iterations and it utilizes only elementary functions and 4 × 4 matrix products, resulting in one to two orders of magnitude faster code compared to the standard Python boundary–value problem solver. This significantly improves the computational speed of the physics-based impedance model, making it competitive with the popular equivalent circuit modeling approach. The numerical calculation of cell impedance is demonstrated based on the model that includes proton transport in the catalyst layer and oxygen transport in the catalyst and gas-diffusion layers. Least–squares fitting of a real experimental spectrum shows that the matrix solver returns the cell transport parameters 50 times faster than the classic boundary–value problem solver.

Dynamic Modeling and Validation of a Fuel Cell-Based Hybrid Power System for Zero-Emission Marine Propulsion: An Equivalent Circuit Model Approach

Dynamic Modeling and Validation of a Fuel Cell-Based Hybrid Power System for Zero-Emission Marine Propulsion: An Equivalent Circuit Model Approach

Modification of the In-Wheel Motor Housing and Its Effect on Temperature Reduction

This research proposes a novel cooling system to minimize the external rotor type of electric motor temperature by installing fan blades (wafters) on the inner housing of the electric motor. Fan blades (wafters) are made by printing using 3D printer technology and using polylactic acid (PLA) as the material. Wafters are then installed on an in-wheel motor with a power of 1500 W, having 48 poles and 52 slots. The study included thermal simulation and experimental techniques to ascertain how fan blades (wafters) affected the electric motor’s thermal properties. The motor rotated at 500 rpm during the experimental test with no load condition. The temperature of the electric motor is known using an infrared thermal imager. Using Ansys Motor-CAD 15.1 software, thermal modeling employs the lumped circuit model approach. Thermal simulation results show almost the same results as the experimental test results. Applying wafters on the in-wheel motor housing significantly reduces the winding temperature by 3.047 °C or experiences a temperature reduction of 4.34%. Using wafters in the in-wheel motor housing also speeds up the stable state temperature of the electric motor by 9 min compared to in-wheel motors without wafters.

Insights into Non-uniform Aging Effects on Broadband Dielectric Behaviors for High-voltage XLPE Cable Insulation: A Novel Fractional-order Circuit Modeling Approach

Insights into Non-uniform Aging Effects on Broadband Dielectric Behaviors for High-voltage XLPE Cable Insulation: A Novel Fractional-order Circuit Modeling Approach

Manipulating electromagnetic waves on graphene-based optical device with mixer application: equivalent circuit model approach

Manipulating electromagnetic waves on graphene-based optical device with mixer application: equivalent circuit model approach

A transistor model for the cystic fibrosis transmembrane conductance regulator

In this paper we present a transistor circuit model for cystic fibrosis transmembrane conductance regulator (CFTR) that seeks to map the functional form of CFTR both in wild type and mutants. The circuit architecture is configured so that the function, and as much as possible the form, faithfully represents what is known about CFTR from cryo-electron microscopy and molecular dynamics. The model is a mixed analog-digital topology with an AND gate receiving the input from two separate ATP-nucleotide-binding domain binding events. The analog portion of the circuit takes the output from the AND gate as its input. The input to the circuit model and its noise characteristics are extracted from single-channel patch-clamp experiments. The chloride current predicted by the model is then compared with single-channel patch-clamp recordings for wild-type CFTR. We also consider the patch-clamp recordings from CFTR with a G551D point mutation, a clinically relevant mutant that is responsive to therapeutic management. Our circuit model approach enables bioengineering approaches to CFTR and allows biophysicists to use efficient circuit simulation tools to analyze its behavior.

Investigation of Six-Phase Surface Permanent Magnet Machine With Typical Slot/Pole Combinations for Integrated Onboard Chargers Through Methodical Design Optimization

This article presents an analytical magnetic equivalent circuit (MEC) modeling approach for a six-phase surface-mounted permanent magnet (SPM) machine equipped with fractional slot concentrated winding (FSCW) for integrated onboard chargers. For the sake of comparison, the selected asymmetrical six-phase slot/pole combinations with the same design specifications and constraints are first designed based on the parametric MEC model and then optimized using a multiobjective genetic algorithm (MOGA). The commercial BMW i3 design specifications are adopted in this article. The main focus of this study is to achieve optimal design of the SPM machine considering both the propulsion and charging performances. Thus, a comparative study of the optimization cost functions, including the peak-to-peak torque ripple and core losses under both motoring and charging modes and electromagnetic forces (EMFs) under charging, is conducted. In addition, the demagnetization capability in the charging mode and the overall cost of the employed machines are optimized. Since the average propulsion torque is crucial in electric vehicle (EV) applications, it is maintained through the design optimization process. Furthermore, finite element (FE) simulations have been carried out to verify the results obtained from the analytical MEC model. Eventually, the effectiveness of the proposed design optimization process is corroborated by experimental tests on a 2-kW prototype system.

Improved Configuration Proposal for Axial Reluctance Resolver Using 3-D Magnetic Equivalent Circuit Model and Winding Function Approach

Resolver is a position sensor that is widely employed in motor servo systems under harsh working conditions. In this article, a novel axial flux resolver with a fractional-slot sinusoidal distributed winding configuration is developed, which has the advantages of a simple structure and convenient mass production. Sinusoidal distribution winding expands the optional range of pole–slot combinations, and its harmonic suppression capability is proposed and verified by the winding function approach (WFA). Furthermore, the magnetic equivalent circuit (MEC) model is formulated to analyze the impact of structural parameters on the induced voltage envelope, through which the optimal parameters on the resolver are developed. In terms of computation time and accuracy, the results of the MEC model under healthy and eccentric conditions are compared with the finite-element method (FEM). In addition, the antiaxial offset capability of the half-wave resolver is illustrated and verified. The effectiveness and superiority of the proposed resolver are illustrated and verified based on numerical simulations and experimental tests.

SPICE-Compatible Equivalent Circuit Models for Accurate Time-Domain Simulations of Passive Photonic Integrated Circuits

Passive photonic integrated circuits (PICs) can be easily characterized in the frequency-domain, but their accurate time-domain performance evaluation is a hurdle for system-level designers, especially when dealing with resonant circuits having highly dispersive behavior, such as ring resonators. In this paper, a new equivalent circuit modeling and simulation approach is proposed, based on the Complex Vector Fitting algorithm, able to perform accurate and robust time-domain simulations of passive PICs directly in standard SPICE simulators. The proposed modeling technique starts from scattering parameters of passive PICs, and is able to capture linear and high order dispersion, backscattering, and wavelength dependent effects. Considering the different nature of optical and electronic signals, a novel concept of equivalent voltage and current for optical waveguides is proposed to simplify the optical to electronic ports conversion and to make it possible to connect and terminate the equivalent circuit models as needed in SPICE simulators, natively supporting bidirectional signal propagation in a waveguide. This work provides a precise and reliable solution to evaluate time-domain characteristics of passive PICs and to access any internal nodes within a circuit, such as the signals inside a ring resonator. Three examples of time-domain simulations of passive PICs in commercial SPICE simulators are presented to demonstrate the flexibility and advantages of the proposed technique.

A hybrid circuit breaker with fault current limiter circuit in a VSC-HVDC application

A conventional hybrid circuit breaker (HCB) is used to protect a voltage source converter-based high voltage direct current transmission system (VSC-HVDC) from a short circuit fault. With the increased converter capacity, the DC protection equipment also requires a regular upgrade. This paper adopts a novel type of HCB with a fault current limiter circuit (FCLC), and focuses on the responses of voltage and current during DC faults, which are associated with parameter selection. PSCAD/EMTDC based simulation of a three-terminal VSC-HVDC system confirms the effectiveness and value of HCB with FCLC, by using an equivalent circuit modelling approach. Laboratory experimental tests validate the simulation results. The peak fault current is reduced according to the current limiting inductor (CLI) increase, and can be isolated more quickly. By adopting parallel metal oxide arrester (MOA) with the main branch of HCB, voltage stresses across the breaker components decrease during transient and continuous operation, and less energy needs to be dissipated by the MOA. The remnant current for all cases is transmitted to power dissipating resistor (PDR) in the final stage, and the fault current is reduced to the lowest possible value. When the current from the main branch is transferred to the FCLC branch, transient voltage spikes occur, while smaller PDR is required to absorb current in the final stage.

Ambiguity in induced polarization time constants and the advantage of the Pelton model

The perceived differences between two popular relaxation models (referred to here as the “Cole-Cole model” and the “Pelton model”), along with their corresponding time constants, have been a source of confusion in recent spectral induced polarization (SIP) literature. These differences complicate comparisons among experimental results recorded by different researchers. A circuit model approach is adopted to better understand the differences among these relaxation models. Either relaxation model can fit SIP data sets equally well, the sole difference corresponds to the relaxation time that varies for the impedance and admittance formulations of the circuit models. The reporting of time constants from a common relaxation model will advance petrophysical investigations of the controls on SIP measurements when exploring databases compiled from previously published data sets.

Two new broadband and tunable terahertz pyramid patch/disk absorbers based on graphene metasurface

In this work, an efficient circuit model of functional thin-film graphene-assisted metamaterial devices with exploiting transmission line theory is presented. The design is done by the usage of a MATLAB code analytically and the numerical results are obtained by the Finite Element Method (FEM) to verify the accuracy and validity of the circuit model approach. This paper proposes two new broadband graphene metasurface absorbers at terahertz frequencies. At first, a metasurface absorber consisting of pyramid graphene patches separated by dielectric layers is introduced. For most absorber applications, the bandwidth of the absorber is one of the most remarkable metrics. The obtained normalized absorption bandwidth for this absorber is 83.85 % for 90 % absorption with a bandwidth of 4.57 THz. To attain broad frequency bandwidth, we design the metasurface absorber consisting of disk graphene and extract its circuit model. There is good agreement between the results of the circuit model and those of the full-wave simulations. Also, the obtained normalized absorption bandwidth is 82.57 % for 90 % absorption with a bandwidth of 4.74 THz. The suggested method is easy and general, so we can apply it to the design and the simulation of other subwavelength structures in the wide frequency range from terahertz (THz) to visible regions.

A tunable broadband THz absorber using periodic arrays of graphene disks

PurposeA wide band perfect THz absorber is presented in this work. The structure includes two layers of graphene disks on the silicon dioxide dielectric layer while a golden plate is placed at the bottom to act as a fully reflecting mirror against THz waves. According to the simulations, the device is robust enough to show independent operation versus layers thicknesses variations, chemical potentials mismatches and changing of electron relaxation time. The designed THz absorber in this work is an appropriate basic block for several applications in THz optical systems such as sensors, detectors and modulators.Design/methodology/approachThe layers in the proposed device are modeled via passive circuit elements and consequently, the equivalent circuit of the device is calculated. Leveraging the developed equivalent circuit model (ECM) and impedance matching concept, the proposed device is designed to perfect absorption with 4.7 THz bandwidth that possesses over 90% absorption. Ample simulations are performed using MATLAB (ECM) and CST (finite element method) to verify the superior performance of the device. According to the simulations, the device is robust enough to show independent operation versus layers thicknesses variations, chemical potentials mismatches and changing of electron relaxation time.FindingsThis work reports a wideband THz absorber, composed of two graphene layers. This paper considers the circuit model representation for two different layers of the device. For a unique structure, a highly tunable response versus chemical potential is obtained. The circuit model approach and impedance matching theory are exploited to reduce computational time regarding conventional approaches.Originality/valueA wide band absorber in THz band is presented. Leveraging circuit model approach and impedance matching theory, the design procedure is simplified regarding CPU time and memory requirements compared to conventional methods. Detailed calculations and ample simulations verify the performance excellency of the device to absorb THz incident waves in 2–6.5 THz frequencies. Also, the robustness of the device is investigated versus parameters mismatches like layers thicknesses and chemical potentials values. According to the simulations and absorption response, the proposed device is an appropriate block to be used in THz optical systems such as detectors, imaging systems and optical modulators.

Significance of fault-current-limiters and parameters optimization in HVDC circuit breakers for increased capacity of VSC-HVDC transmission networks application

The voltage and current ratings of the voltage source converter (VSC) based high voltage direct current (HVDC) transmission line projects have increased over the years. It testifies the increasing popularity of VSC-HVDC technology. Since the long-distance, VSC-HVDC transmission lines are more exposed to commonly appearing short circuit faults; thus, protection equipment with increased fault-current handling capability is required. The DC circuit breakers (DCCBs), with or without fault current limiters (FCLs), can effectively handle the fault-current. The variations in VSC-HVDC projects’ ratings and their impact for DCCB with FCL and without FCL are thoroughly analysed in this paper. The paper further includes an in-depth discussion on DCCBs with FCL and without FCL. An equivalent circuit modelling approach is used for simulation analysis of three case studies under the influence of these breakers to analyse current behaviour; the case studies include the Zhoushan HVDC Project, Xiamen HVDC Project, and Zhangbei-I HVDC Project. All these projects have different capacities in terms of their power, voltage, and current ratings. For DCCBs, this paper includes a detailed analytical model to understand the fluctuations in the size of fault-current limiting components (in DCCBs) for increased fault-current handling requirements. The simulation results using PSCAD/EMTDC and MATLAB are presented to verify different aspects of this study. A small scale laboratory prototype is also developed to validate the performance of DCCB with and without FCL. Based on theoretical, simulation, and experimental validations, it is substantiated that for increased VSC-HVDC projects’ ratings, DCCB with FCL can perform better compared to conventional DCCB without FCL.

A Comprehensive Circuit Modeling Approach for Self-Sustained Capacitively Coupled Microwave Plasmas

A circuit modeling approach for self-sustained capacitively coupled microwave plasmas is introduced and validated in this article. The model solves the particle balance equation using a novel circuit optimization scheme to calculate the plasma parameters like electron density, sheath thickness, and electron temperature for a given input power, operating frequency, gas type, and pressure. While the existing models capture the ohmic loss in the bulk plasma region, the proposed model also takes into account power required to sustain plasma which proves to be considerable for higher electron densities. The model is rigorously validated using experimental results from two cases—one resonant and one non-resonant—both with self-sustained microwave plasma. As the post-processing results, other discharge parameters like sheath and plasma voltages as well as plasma reduced field are calculated. The proposed modeling approach can substantially simplify design and analysis of capacitively coupled microwave plasmas.

Traveling Wave Effects in Microwave Quantum Photonics

Traveling wave effects are increasingly exploited in microwave and terahertz quantum devices to implement novel functionalities and obtain improved performance. A suitable quantum circuit modeling approach is discussed for Josephson and bulk-material kinetic inductance traveling-wave parametric amplifiers enabling broadband, quantum-limited amplification. As another example, a multi-domain simulation approach for novel terahertz quantum cascade laser structures exploiting microwave and optical co-propagation effects is presented.

Modified small‐signal behavioral model for GaN HEMTs based on support vector regression

A novel, modified small signal behavioral modeling methodology for gallium nitride (GaN) high electron-mobility transistors (HEMTs), based on the support vector regression (SVR) technique, is presented in this paper. Compared with the classic equivalent small-signal circuit model, the proposed model adds an error correction technique, which is developed using SVR techniques. The proposed model maintains accuracy across a broad frequency range, from 1 GHz to 10 GHz. The verification is performed through comparisons with measured multibias S-parameter data performed on an 8 × 125 μm GaN HEMT device with a 0.25 μm gate feature size. The modified model shows a significant improvement in S-parameter prediction accuracy when compared with the classic equivalent circuit modeling approach.

Effects of Effluent Stream Composition and Competing Reactions Effect on Wastewater Nitrate Reduction in a Photoelectrochemical Device

More than 80% of nitrogen-contaminants are present in the form of nitrates in point sources of wastewater, including municipal wastewater effluents, ion-exchange brines, low-level nuclear wastes and in power generation. Wastewater nitrates represent an untapped source for the recovery of nutrients, value-added chemicals, and energy. Nitrates can be reduced to form ammonia, which can be used as a fertilizer or fuel, and nitrous oxide, which is a powerful oxidizer for the combustion and supercharging applications. Depending upon the source of the wastewater, the concentration of nitrates present in these streams can vary significantly. Ion-exchange brines and low-level nuclear wastes have large nitrate concentrations, on the order of > 0.1 M, whereas municipal and power generation effluents are more dilute (0.1 mM). However, the effect of varying contaminant concentrations and the competing redox reactions have not been quantified for these systems.In this study, a photoelectrochemical device is proposed to transform wastewater nitrates into ammonia, coupled with water oxidation. We expand on a previously developed numerical model to include the effects of the reacting nitrate species concentrations and the competing redox reactions on the solar-to-chemical efficiencies and nitrogen-removal rates. Notably, we implemented an equivalent circuit modeling approach to account for the influences of the competing reactions and the concentration-dependent mass-transfer limiting current densities. Model results predict that for a single light-absorber and a nitrate concentration of 100 mM, the optimal solar-to-chemical efficiency is 7% and the nitrogen recovery rate (as NH3) is 260 gN m-2 day-1. Oxygen reduction is more dominant as a competing reaction than hydrogen reduction at the cathode. However, this reduction is mass-transfer limited even while assuming an air-saturated (1 atm) device and therefore didn’t impact the performance significantly. Modeling results are complemented by experimental measurements of the effects of nitrate concentrations on the operating current densities and the rates of product formation with copper and platinum electrodes at the cathode and anode respectively.

Analysis and Design of General Printed Circuit Board Metagratings With an Equivalent Circuit Model Approach

An accurate equivalent circuit model (ECM) for general multiwire multiorder printed circuit board (PCB) metagratings (MGs) is developed. The effective impedances of the grating wires are modeled as lumped loads in the ECM. The numerous propagating Floquet harmonics supported by the grating are modeled as circuit ports. Based on the desired field transformation for the MG, a set of required scattering parameters for its ECM is derived. The equivalent lumped loads are subsequently optimized to realize these parameters, which is analogous to shaping the diffraction pattern of the MG to match the desired functionality. Within this framework, it is possible to encode multiple functions into a single device by simultaneously optimizing all relevant entries of the ECM scattering matrix. Using the proposed technique, an angle-multiplexed multifunctional MG is designed and investigated.

Electrochemical and Dynamic Characterization of a 6-Cell Solid Oxide Cells Stack in Steam Electrolysis and Steam and Carbon Dioxide Co-Electrolysis

High temperature steam electrolysis and co-electrolysis of steam and carbon dioxide for hydrogen and syngas production is gaining attention for its potential to play a key role in the production of renewable fuels and for long-term energy storage. Unlocking a longer lifetime and lower costs for these systems is required if they are to be widely deployed. In this work, we consider a 6-cell Solid Oxide Cell (SOC) short-stack, manufactured by SOLIDpower S.p.a. (Italy), that has been installed and tested at UC Irvine. The short-stack is installed in a test bench that maintains the operating temperature in a controlled range of 650-850°C, via an electric furnace. The cells are characterized by an 8 mol% Y2O3 stabilized Zirconia (YSZ) electrolyte (8 ± 2 μm) supported on a conventional porous Ni/YSZ anode electrode (240 ± 20 μm). The cathode electrode is comprised of a composite of metallic perovskite Sr-doped LaMnO3 (LSM) and oxide-ion electrolyte YSZ (40 ± 10 μm). The active area of each cell is 80 cm2.The aim of the study is the experimental characterization of the short-stack via electrochemical and dynamic techniques to: i) characterize stack performance in steady-state; ii) investigate single cell degradation and interdependencies between adjacent cell operating conditions to determine stack degradation; and iii) determine characteristic time responses of thermal, fluid-dynamic and electrochemical phenomena. The experiments are conducted for both steam electrolysis and co-electrolysis of steam and carbon dioxide. The experimental electrochemical methods employed include chronopotentiometry, electrochemical impedance spectroscopy and current interrupt. Moreover, fluid-dynamic step response and thermal ramp dynamic response of the stack are evaluated to achieve a better understanding of the effect of an operating control system on local fuel starvation and local temperature hot spot regions, which are possible contributors to increased degradation.Preliminary results show unequal degradation rates for the six cells under thermal cycles (which put stack under continuous switching between exothermic and endothermic operating modes). The unequal degradation rates of the cells were investigated and are possibly related to unequal flow distribution within the stack. Degradation rates were below 1% for thirty consecutive thermal cycles for operation in steam electrolysis. Responses that included fluid-dynamic step step changes allowed determination of the fluid-dynamic and thermal time constants associated with preheating flows introduced to the stack of the order of 200 to 300 seconds, depending on the step size. The evaluation of the fluid-dynamic and thermal response allowed decoupling of the thermal capacitance of the stack and that associated with the furnace and piping, via an equivalent circuit model approach. This has led to an ability to estimate the amount of heat produced by the stack when operating in exothermic conditions and the absorbed heat from the furnace when operating in endothermic (sub-thermoneutral voltage) conditions. Figure 1