Equivalent 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

A Frequency Up-Conversion Piezoelectric Energy Harvester Shunted to a Synchronous Electric Charge Extraction Circuit.

A frequency up-conversion piezoelectric energy harvester (FUC-PEH) consists of a force amplifier, a piezoelectric stack, a low-frequency oscillator (LFO), and a stop limiter. The force amplifier generates the amplification of stress on the piezoelectric stack. The LFO, comprising a spring and a mass block, impacts the stop limiter during vibration to induce high-frequency oscillations within the piezoelectric stack. In this paper, we represent and simplify the FUC-PEH as a lumped-parameter model based on piezoelectric material constitutive equations and structural dynamic theories. Using the electromechanical analogy, we developed an equivalent circuit model (ECM) of the FUC-PEH. A parametric study was performed to investigate the impact of system parameters, such as spring stiffness and concentrated mass, on the FUC-PEH performance. The collision-induced amplitude truncation (AT) effect enlarges the operation bandwidth. ECM simulations show that low-frequency input excitation is converted into a high-frequency output response, enhancing the energy conversion efficiency. Furthermore, we aimed to improve the FUC-PEH's performance using a synchronous electric charge extraction (SECE) circuit. Using the ECM approach, we established a system-level model that considers the electromechanical coupling behavior. The simulation results provide insights into the performance of FUC harvesters with SECE circuits and offer valuable design guidance.

Graphene ribbons based THz toxic gas sensing

In this paper, an optical chemical sensor is proposed to detect some toxic gases such as Methane (CH4), Nitrogen (N2), Nitrogen dioxide (NO2), and Carbon monoxide (CO). This type of chemical sensor consists of graphene ribbons and Kapton materials as sensing elements. Also, exploits electromagnetic properties such as absorption in terms of signal transducing. These kinds of small-scale, flexible architectures and advanced detection techniques are in demand to identify toxic gases as well. To develop the proposed chemical sensor, this study describes the structure in the aspect of an equivalent circuit model (ECM) mathematically, while the full-wave simulation (FEM) is performed as the reference. Acceptable agreement between the ECM and FEM simulations is shown while an interesting tuning capability against external stimulation is obtained. It should be noted that the ECM approach is performed in just a few seconds while the FEM simulation takes more than 3 h to produce results. In addition, the maximum error is around the second absorption peak and is less than 4%.The main contribution of this work is introducing a simple structure to distinguish several toxic gases in the sub-THz gap (0.1–2 THz). Additionally, ample simulations are performed to verify the sensor's reliability. According to the simulation results, the proposed meta-structure can appropriately show different peak frequencies and even different numbers of absorption peaks against different concentrations of toxic gases. Additionally, due to the ultra-thin nature of the graphene and the flexibility of the Kapton, the proposed sensor can be wearable while it is considered non-invasive testing.

Development of a Fast Running Equivalent Circuit Model with Thermal Predictions for Battery Management Applications

Equivalent circuit modelling (ECM) is a powerful tool to study the dynamic and non-linear characteristics of Li-ion cells and is widely used for the development of the battery management system (BMS) of electric vehicles. The dynamic parameters described by the ECM are used by the BMS to estimate the battery state of charge (SOC), which is crucial for efficient charging/discharging, range calculations, and the overall safe operation of electric vehicles. Typically, the ECM approach represents the dynamic characteristics of the battery in a mathematical form with a limited number of unknown parameters. Then, the parameters are calculated from voltage and current information of the lithium-ion cell obtained from controlled experiments. In the current work, a faster and simplified first-order resistance–capacitance (RC) equivalent circuit model was developed for a commercial cylindrical cell (LGM50 21700). An analytical solution was developed for the equivalent circuit model incorporating SOC and temperature-dependent RC parameters. The solution to the RC circuit model was derived using multiple expressions for different components like open circuit voltage (OCV), instantaneous resistance (R0), and diffusional parameters (R1 and C1) as a function of the SOC and operating temperature. The derived parameters were validated against the virtual HPPC test results of a validated physics-based electrochemical model for the voltage behavior. Using the developed RC circuit model, a polynomial expression is derived to estimate the temperature increase of the cell including both irreversible and reversible heat generation components. The temperature predicted by the proposed RC circuit model at different battery operating temperatures is in good agreement with the values obtained from the validated physics model. The developed method can find applications in (i) onboard energy management by the BMS and (ii) quicker evaluation of cell performance early in the product development cycle.

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

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.

Numerical Simulation and Equivalent Circuit Model of Multi-Band Terahertz Absorber Composed of Double-Sided Graphene Comb Resonator Array

Multi-band terahertz (THz) absorber based on a non-symmetric double-sided graphene comb resonator array is designed and simulated by the finite element method (FEM) in CST Software. Then, an equivalent circuit model (ECM) based on admittance with a fast MATLAB code is proposed to analyze the absorber in the THz region. The admittance-based ECM approach could be used for any metamaterial absorber containing one layer of resonators sandwiched between two dielectric slabs and backed by a metal layer consisting of a layer of resonators with a thickness much smaller than the minimum wavelength in the considered wavelength range. The proposed absorber is dynamically tunable with a one-layered resonator array. It has strong linear dichroism (LD) response of 98% and the frequency range of 0.7-5 THz with absorption > 96%: two absorption bands for TE mode and three for TM mode. The proposed absorber can be used in polarization-sensitive devices and systems in the THz region. The ECM model of the metastructure was derived to provide an efficient approach to analyzing the performance of the absorber. The FEM simulation results are in good agreement with the ECM ones.

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.

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.

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

Broadband single-layer reflectarray antenna loaded with meander-delay-lines for X-band applications

In this work, delay-lines loaded broadband reflectarray antenna is proposed for X-band applications. The array cells contain slotted square patch and quad meander delay-lines. The slotted square patch elements are combined with delay-lines to increase the reflection phase range. A smooth linear phase variation of 650° is realized through varying the length of delay-lines. The reflectarray unit element resonant behavior is observed through an equivalent circuit model approach. The reflectarray antenna is simulated and measured on a low-cost FR-4 substrate. A 23 × 23 elements reflectarray antenna is designed and simulated using a hybrid finite element boundary integral (FEBI) method. The proposed reflectarray antenna offers a measured gain of 25 dBi and 52.8% aperture efficiency for 10 GHz frequency band. The cross-polarization levels and side-lobe-levels and in E and H-plane are less than −35 dB and −22 dB respectively. Moreover, a measured 3-dB gain bandwidth of 29% and 1-dB gain of 19.5% is realized for the proposed reflectarray antenna.

Event-Driven Coulomb Counting for Effective Online Approximation of Li-Ion Battery State of Charge

Lithium-ion batteries are deployed in a range of modern applications. Their utilization is evolving with the aim of achieving a greener environment. Batteries are costly, and battery management systems (BMSs) ensure long life and proper battery utilization. Modern BMSs are complex and cause a notable overhead consumption on batteries. In this paper, the time-varying aspect of battery parameters is used to reduce the power consumption overhead of BMSs. The aim is to use event-driven processing to realize effective BMSs. Unlike the conventional approach, parameters of battery cells, such as voltages and currents, are no longer regularly measured at a predefined time step and are instead recorded on the basis of events. This renders a considerable real-time compression. An inventive event-driven coulomb counting method is then presented, which employs the irregularly sampled data information for an effective online state of charge (SOC) determination. A high energy battery model for electric vehicle (EV) applications is studied in this work. It is implemented by using the equivalent circuit modeling (ECM) approach. A comparison of the developed framework is made with conventional fixed-rate counterparts. The results show that, in terms of compression and computational complexities, the devised solution surpasses the second order of magnitude gain. The SOC estimation error is also quantified, and the system attains a ≤4% SOC estimation error bound.

Investigation of graphene fractal frequency selective surface loaded terahertz absorber

The voyage of the research in terahertz (THz) technology has an intriguing application in terahertz detection, and the graphene absorbers have dramatically enhanced the effectivity, and the efficiency in its performance. Though, there is a need of wide angle insensible, polarization angle insensible, broadband terahertz metamaterial absorber (TMA) with reduced design complexity. Hence, in this research an effort has been carried out to develop such TMA with equivalent circuit modelling approach. A massive − 10 dB reflection coefficient (RC) bandwidth of 2.66 THz (1.08–3.74 THz) has been obtained by the proposed TMA device with two significant peaks of − 19.48 dB and − 14.5 dB at 1.32 THz and 3.44 THz, respectively. The oblique incidence stability of the device has been verified by investigating the effect of wave incidence angle, and wave polarization angle in RC characteristic. Further, the physics behind the absorption has been systematically illustrated along with three different absorption mechanism, i.e., input-impedance matching mechanism, wave interference phenomena, and induced current model, that attest the Unprecedented absorption results. Moreover, the electrical parameters of the device (i.e., effective electric permittivity, and effective magnetic permeability) have been extracted to analyze the metamaterial behavior of the device. The results are good enough to explore the potential of the TMA for THz sensing applications.

Tunable Extraordinary Transmission through a Graphene-Covered Hole Array: an Analytical Equivalent-Circuit Modeling Approach

We study two-dimensional (2D) hole arrays drilled into a perfect conductor slab covered with a graphene sheet. Such arrays support the extraordinary transmission of electromagnetic waves and allow tunability via graphene properties. We investigate the effect of graphene on transmission spectra by proposing an accurate analytical circuit model for the structure, where the graphene contributes an admittance component at the interface. The model demonstrates how extraordinary transmission can be tuned via the graphene conductivity. We study the free-standing structure, where the hole array is covered by a graphene sheet on both sides of the conductor slab, and a substrate-bound hole array covered by graphene on the exposed slab surface. The results are compared to full-wave simulations, yielding good agreement. In addition, thanks to the proposed circuit model, we demonstrate a polarization-independent perfect absorber by tuning the surface conductivity of graphene.