Equivalent Circuit Model Research Articles

A comprehensive equivalent circuit model of Li-ion batteries for SOC estimation in electric vehicles based on parametric sensitivity analysis

A comprehensive equivalent circuit model of Li-ion batteries for SOC estimation in electric vehicles based on parametric sensitivity analysis

Analysis, modeling and design of piezoelectric-capacitive hybrid micromachined ultrasonic transducer

Abstract This paper proposes a spring-mass-damper model for a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer (HMUT) in immersion. Based on this model, a dual-force actuation mode is identified, where piezoelectric micromachined ultrasonic transducer (PMUT) and capacitive micromachined ultrasonic transducer (CMUT) are strongly coupled to achieve enhanced sensitivity. In order to design HMUT efficiently, an electro-mechanical-acoustical equivalent circuit model (ECM) is constructed and then the round-trip gain is calculated to demonstrate its pulse-echo response. The ECM calculations results align with those of finite element model (FEM) simulations, showing a relative deviation less than 4%. In the design cases, the transmit sensitivity of HMUT is twice that of PMUT and more than five times that of CMUT. The receive sensitivity of HMUT is 1% lower than that of CMUT, but an order of magnitude larger than that of PMUT. The round-trip gain of the HMUT is at least 24.9 dB higher than that of PMUT and 14.1 dB higher than that of CMUT. These results demonstrate the potential of HMUT in surpassing bulk piezoelectric ultrasonic transducers in pulse-echo imaging. Furthermore, the impact of cell pitch on the pulse-echo response of HMUT arrays is characterize.

Investigation into the impedance, dielectric behavior, and conductivity within p-silicon/n-nanocrystalline iron disilicide heterojunctions and equivalent circuit model in relation to temperature

The p-Si/n-nanocrystalline FeSi2 heterojunctions constructed through facing-targets sputtering were characterized for impedance under various frequencies and temperatures of between 160−400 K. Imaginary and real impedance plots for all temperatures demonstrated single semicircular arc with negative temperature dependency. From the arc, a circuit model equivalent to electrode resistance serially connected to several loops, each consisting of a parallel circuit comprising a resistance//constant phase element (Q), corresponding to the crystallite, crystallite boundary, and interface. All resistances increased with decreasing temperatures, while the Q values decreased but behaved as ideal capacitors for all temperatures. The dielectric constants versus increasing temperature demonstrated a linear increase. At 300 K and 1 MHz, the dielectric constant was 24.5 with 0.1 loss tangent, denoting its possible usage for filtration and storage. The alternating-current conductivities disclosed that direct-current conductivities increased as the temperature increased. The exponents from Jonscher's fit were 1 or less around 180 K and the values beyond 1 at higher temperatures, indicating the shift from long transitional transport to localized hopping transport. The activation energy based on conductivities was higher than the one based on relaxation times, implying that excess charge led to more energy requirements for transportation.

Applicability assessment of equivalent circuit-thermal coupling models on LiFePO4 batteries operated under wide-temperature and high-rate pulse discharge conditions

In military scenario, high-power lithium iron phosphate (LFP) batteries are frequently used under wide-temperature and high-rate pulse discharge conditions. An accurate electro-thermal coupling model (ETCM) is crucial for the safe operations. Equivalent circuit-thermal coupling model (ECTCM), which combines equivalent circuit model (ECM) and lumped thermal model, is the most widely used type of ETCM in applications. However, the applicability of ECTCM under wide-temperature and high-rate pulse discharge conditions is not clear. To assess the applicability of ECTCM under these special conditions, this study establishes six typical ECTCMs and accurately identify their corresponding model parameters. Then, these models are tested under high-rate pulse discharge conditions from -40oC to 50oC. The results indicate that ECTCMs are effective for pulse discharge at ambient and high temperatures, but not suitable for low-temperature conditions below 0oC. When the temperature is below 0oC, the pulse discharge voltage of the batteries can not be accurately simulated by ECTCMs. This work provides guidance for electro-thermal coupling modeling under high-rate pulse discharge conditions, and also points out the direction for the development of high-precision ETCM capable of handling wide-temperature and high-rate pulse discharge in the future.

Impacts of Quadrature-axis Equivalent Circuit Model of Turbine Generator on Simulation Results of Frequency Change in Grid Fault

Impacts of Quadrature-axis Equivalent Circuit Model of Turbine Generator on Simulation Results of Frequency Change in Grid Fault

Discrete-time Luenberger observer design for Lithium-ion battery state-of-charge with stability guarantee

State-of-charge (SOC) estimation is particularly important as it provides information about the remaining energy capacity of the battery, allowing for better planning and utilization. Accurate SOC estimation is challenging because it cannot be directly measured from the battery. Instead, it is estimated by analyzing measurable variables such as current and voltage. To address this challenge, a discrete-time observer-based SOC estimation approach is proposed in this paper. This approach utilizes a second-order equivalent circuit model and a piecewise linear approximation to represent the relationship between SOC and open circuit voltage (OCV). The proposed observer-based approach utilizes these models to estimate the SOC with assured asymptotic stability under specific assumptions to simplify the design process. Simulations in Python are conducted to evaluate the performance of the designed observer. In the simulations, the SOC estimation under various conditions, such as model uncertainty, disturbances, and measurement noise, is also covered. In addition, three different observer gains are considered in the simulations. Lastly, simulation studies indicate that the estimated SOC values converge to the real SOC values, with some different behavior depending on the regarded situations.

A Generalized and Efficient Equivalent Circuit Model for Frequency Selective Surfaces

Owing to their excellent intuitiveness and simplicity, equivalent circuit models (ECMs) are widely used to investigate and design frequency selective surfaces (FSSs). However, the generalization and accuracy of ECM has been a contentious issue, especially with regard to the requirement for analyzing diverse and numerous FSSs versus the restrictions applied to it. To address this problem, a generalized and efficient equivalent circuit model (GE-ECM), characterized by the feasibility of dealing with multiple sizes, broadband, and large oblique incidences, is proposed in this study to design FSSs and analyze their electromagnetic performance. In contrast to related works, gap and width factors are accounted for in the proposed GE-ECM to recalibrate the reactance and susceptance of the physical model, respectively. Additionally, normalized sizes of structure periods are introduced to further extend its generalization. Good agreement is achieved between the frequency responses of the GE-ECM and the electromagnetic software CST. Furthermore, excellent adaptation to multiple sizes and broadband is achieved from 0 GHz to 20 GHz, with the average relative error of the resonant frequency being only 1.19% for all sizes. Fabrication and measurements were conducted to verify the practicability of the proposed GE-ECM, with all results confirming its accuracy and universality in interpreting electromagnetic performance, thus establishing a reliable theoretical guideline for designing more complex FSSs.

Modeling of Microstrip line Gap Discontinuity on Multilayer Substrate

In this paper, the modeling of microstrip line gap discontinuity on multilayer semiconductor substrate is presented. The reflection coefficient and transmission coefficient are computed from the equivalent lumped circuit model of microstrip line gap discontinuity. The lumped circuit elements- capacitance, inductance and resistance are calculated using closed-form expressions in term of the gap discontinuity, width of microstrip line and dielectric substrate thickness. Static Spectral Domain Analysis (SDA) method is used to compute characteristic impedance of microstrip line.

Advanced integration of bidirectional long short-term memory neural networks and innovative extended Kalman filter for state of charge estimation of lithium-ion battery

The state of charge (SoC) of a battery is a crucial monitoring indicator for battery management systems and it helps to assess how much further an electric vehicle can travel. This work proposes a novel approach for predicting battery SoC by developing a closed-loop system that integrates a bidirectional long short-term memory neural network with an innovative algorithm-extended Kalman filter. A second-order equivalent circuit model is selected, and its parameters are computed using the variational and logistic map cuckoo search approach. Further, an Extended Kalman filter is combined with an innovation algorithm to update process noise in real-time, and a bidirectional long short-term memory neural network takes the input from the Extended Kalman filter and gives the compensated error value for the final SoC estimation. 75% of dynamic stress test data from the Extended Kalman filter is used for training purposes, remaining data sets are used for testing purposes. The addressed algorithm is validated by evaluating its performance in comparison to individual algorithms and various combined approaches. Empirical analysis demonstrates that the proposed model achieves a root mean square error of 0.11 % and mean absolute error of 0.1 % positioning it as a valuable tool for battery management systems.

A dual-band reflective polarizer based meta-surface with higher angular stability for C and X-band applications

A reflective dual-band linear-to-circular polarizer for C and X-band application is presented. The proposed elliptical Frequency Selective Surface (FSS) is capable of enhancing the polarization control and minimizes the cross-polarization compared to traditional circular or square geometries. The linear-to-circular polarization is achieved through two elliptical apertures, where each shape generates orthogonal modes with a 90° phase shift. The inner element targets higher frequencies while the outer element handles lower frequencies, enabling efficient polarization conversion across both bands. The proposed unit cell comprises 14 mm × 14 mm and is fabricated on Rogers RT5880 substrate. It exhibits a reflective polarizer at a center frequency of 7.70 GHz with a bandwidth of (7.64–7.76 GHz) and other at 9.42 GHz with a bandwidth of (9.27–9.57 GHz), respectively. In the proposed FSS, the 7.70 GHz exhibits LH-CP, and RH-CP conversion is provided at 9.42 GHz. In addition, an axial ratio of the FSS of (< 3 dB) demonstrated a circular polarization with a polarization conversion ratio (PCR) of 99.9%. In addition, an equivalent circuit model (ECM) of a reflective polarizer has been verified. Furthermore, angular stability of the FSS can be achieved at various incident angles at 0°, 30°, 60°, and 90°. The polarization conversion operates in frequency bands of C-/X, suitable for wireless systems, radar systems, electromagnetic shielding, and satellite communications.

Exploring the synaptic response of reactive Mn electrodes based TiO2 resistive switches

Mn/TiO2/Mn devices, prepared by reactive sputtering and photolithography techniques, were characterized by analyzing their current–voltage (I-V) dependence, non-volatile memory properties, and artificial synapse behavior. The detailed study of its I-V characteristics allowed for highlighting the main conduction mechanisms involved in the electrical transport through the Mn-TiO2 junctions and determining an equivalent circuit model. These results show that the oxidation of metallic Mn electrodes and the application of electrical pulses produce a complex scenario associated with a highly inhomogeneous oxygen vacancy distribution. The resistance hysteresis switching loops were determined, as well as the synaptic-like weight depreciation and potentiation, revealing a linear dependence of the reset voltage as a function of the amplitude of the set voltage and a quasi-linear variation of the conductance with the number of applied pulses. Simulations based on spiking neural network architecture, considering different updates of the synaptic weights, were trained to learn handwriting patterns. Notably, those based on the linear learning rule of the Mn/TiO2/Mn devices outperformed others with increasing non-linear behavior, demonstrating both high recognition and noise tolerance factors, further highlighting the robustness of this approach.

Compact metasurface antenna for Sub-6 GHz applications with isolated n77/n78 bands using CSRR

Abstract A compact (0.35 λ0× 0.35 λ0 where λ0 is free space wavelength at the lower resonance frequency 3.50 GHz) bio-inspired tulip flower-shaped antenna (TFSA) is proposed. A double negative (DNG) metamaterial complementary split ring resonator (CSRR) is introduced near the feed in the hybrid triangular-circular patch which inserts a notch-band (4.20-4.38 GHz) in the wide bandwidth (3.15-7.05 GHz) and makes the antenna response dual-band. Consequently, this results in in-band interference reduction in 5G-Sub-6 GHz applications. A slotted FSS is placed at a distance of 28.507 mm beneath the monopole-reduced ground of the antenna to enhance the reduced gain from 4.39 dBi to 7.22 dBi. A further gain is improved to 12.84 dBi by placing a full copper surface (0.35 λ0× 0.35 λ0) as the reflector layer is placed below FSS at 1.6 mm. Finally, prototyped TFSA with FSS and reflector model achieve a dual bands reflection coefficient response (3.15-4.20 GHz): n77/n78, and (4.38-7.03 GHz): n46/n47/n96/n102/n79. The antenna reflection coefficient is tested using Keysight 14 GHz FieldFox Microwave Analyzer N9916A, and radiation patterns in the E-plane and H-plane are measured using an 18 GHz anechoic chamber. The comparison of simulated results with measured results is found an excellent match in bandwidth and with shapes of gain radiation patterns. The reflector and FSS jointly make the radiation pattern strong in the E-plane above the TFSA radiator. The antenna is well suited for n77/n78 (3.30-4.20 GHz), n79(4.40-4.99 GHz), n46 (5150-5925MHz), n47 (5855 – 5925MHz), n96/n102 (5925-6425MHz), 5.8 GHz HiperLAN, WiMAX 3.5GHz applications. An electrical equivalent circuit model of the proposed TFSA antenna is presented and validated using ADS software.&amp;#xD;

Fault Diagnosis of Lithium-Ion Batteries Based on the Historical Trajectory of Remaining Discharge Capacity

In recent years, the number of safety accidents in new-energy electric vehicles due to lithium-ion battery failures has been increasing, and the lithium-ion battery fault diagnosis technology is particularly important to ensure the safe operation of electric vehicles. This paper proposes a method for lithium-ion battery fault diagnosis based on the historical trajectory of lithium-ion battery remaining discharge capacity in medium and long time scales. The method first utilizes the sparrow search algorithm (SSA) to identify the parameters of the second-order equivalent circuit model of the lithium-ion battery, and then estimates the state of charge (SOC) of the lithium-ion battery using the extended Kalman filter (EKF). The remaining discharge capacity is estimated according to the SOC, and finally the feature vectors are used to diagnose the faults using box plots on the medium and long time scales. Experimental results verify that the root mean squared error (RSME) and mean absolute error (MAE) of the proposed SOC estimation method are 0.0049 and 0.0034, respectively. This method can accurately identify the faulty single cell in a battery pack with low-capacity single cells and promptly detect any abnormalities in the single cell when a micro-short circuit fault occurs.

A magnetic equivalent circuit model for segmental translator linear switched reluctance motor

Because of exclusive characteristics of Switched Reluctance Motor (SRM) particularly simple and robust structure and high reliability, it can be a good choice for many industrial applications. In terms of structure and performance principles, the Linear Switched Reluctance Motor (LSRM) is similar to rotary SRM (RSRM) and therefore their advantages are identical. The Segmental Translator Linear Switched Reluctance Motor (STLSRM) is a special type of LSRMs that can produce a higher thrust density in comparison to the simple type of LSRM. One of the most important models for predicting the characteristics of electric machines is the model based on the Magnetic Equivalent Circuit (MEC), which can be used to predict the performance characteristics of machines. Although the STLSRM has significant advantages, no MEC model has been introduced for it so far. With the aim of predicting the static and dynamic characteristics of this motor, a new analytical model based on MEC method is developed in the present paper. In addition to simplicity, the developed model has acceptable accuracy and speed. The proposed model is utilized for a three-phase STLSRM and different static and dynamic characteristics of the motor including static flux-linkage, static force, instantaneous current waveform and instantaneous thrust waveform are predicted. To validate these obtained simulation results, they are compared with those derived from the Finite Element Method (FEM).

Using the Transversal Admittance to Understand Organic Electrochemical Transistors.

The transient behavior of organic electrochemical transistors (OECTs) is complex due to mixed ionic-electronic properties that play a central role in bioelectronics and neuromorphic applications. Some works applied impedance spectroscopy in OECTs for understanding transport properties and the frequency-dependent response of devices. The transversal admittance (drain current vs gate voltage) is used for sensing applications. However, a general theory of the transversal admittance, until now, has been incomplete. The derive a model that combines electronic motion along the channel and vertical ion diffusion by insertion from the electrolyte, depending on several features as the chemical capacitance, the diffusion coefficient of ions, and the electronic mobility. Based on transport and charge conservation equations, it is shown that the vertical impedance produces a standard result of diffusion in intercalation systems, while the transversal impedance contains the electronic parameters of hole accumulation and transport along the channel. The spectral shapes of drain and gate currents and the complex admittance spectra are established by reference to equivalent circuit models for the vertical and transversal impedances, that describe well the measurements of a PEDOT:PSS OECT. New insights are provided to the determination of mobility by the ratio between drain and gate currents.

A Novel LCLC Parallel Resonant Circuit for High-Frequency Induction Heating Application

A Novel LCLC Parallel Resonant Circuit for High-Frequency Induction Heating Application

Computational simulation of alternating current (AC) impedance of hardened cement mortar

The present study proposes a novel methodology for simulating the AC impedance of hardened cement mortar, through the technology of micro computed tomography based finite element analysis (μCT-based FEA). Three-dimensional (3D) physical meso-scale structure of hardened cement mortar is first segmented into multicomponent phases of air void, cement paste, sand aggregate, and interfacial transition zone (ITZ) considered with different thicknesses. Then, the real structure of mortar after discretization is subjected to current harmonic perturbations to acquire its AC impedance spectra. Compared to traditional impedance measurement, the proposed simulation approach avoids the influence of external electrode and hence improves the characterization of cementitious electrochemical system in its true state. The simulated complex impedance presents a depressed high-frequency loop and varies with the increasing ITZ thickness in the range of 26.6 to 106.4 μm. The numerical impedance plots are fitted to a theoretical equivalent circuit model of Rs(RctQ) consisting of bulk ionic resistance (Rs), charge transfer resistance (Rct) at the solid/liquid interface, and non-Debye capacitance (Q). The changes in mesostructure of cement mortar with the thickened ITZs can be captured by a linear reduction of Rs, a non-linear decrease of Q, and a limited increase of Rct. Based on the electrochemical impedance modelling, the study establishes the mathematical relationship between the defect's volume (air voids plus ITZ) and the model's parameters (Rs or Rct) for prediction of material deterioration.

Revealing Relationship Between In Situ Impedance and Lithium Plating Onset Based on Lithium–Graphite Half-Cells

Lithium plating may occur during charging, especially at high rates or overcharging conditions for lithium-ion batteries (LIBs), which would cause battery capacity degradation and even trigger thermal runaway. Thus, it is essential to detect lithium plating onset during the charging processes. Electrochemical impedance can reveal the dynamic electrode properties of the battery, which is promising for use in battery management systems for the online detection of lithium plating onset. In this article, the impedance at 1 Hz is measured during the over-discharge and fast discharge processes using lithium–graphite half-cells. For half-cells, the variation in graphite electrode potential vs. Li/Li+ during discharging is directly recorded. An equivalent circuit model is proposed and adopted to estimate the real lithium plating reaction overpotential, which is deemed the thermodynamic indicator of lithium plating and is used as validation for the detection of lithium plating onset. Through the auxiliary validation of the estimation of lithium plating overpotential and the shape of incremental capacity curves, the relationship between impedance changes at specific frequency and the lithium plating onset is revealed. The results lay a good foundation for proposing the online diagnostic method of lithium plating onset based on the in situ impedance.

Nitrous oxide abatement and valorization in an ammonia-fueled SOFC stack – Nitric oxide and electricity production

Nitrous oxide (N2O) is a harmful gas that strongly impacts climate change. Several strategies for denitrification have been addressed, where the use of solid oxide fuel cells (SOFCs) has been demonstrated to be attractive for N2O reduction and simultaneous electricity production. The reduction of N2O to N2 is studied for the first time at the cathode of an SOFC, where ammonia is supplied to the anode as fuel. A diluted ammonia stream is particularly interesting since it is normally available in HNO3 plants – the most important concentrated source of N2O emission – and is carbon-free. The combined reduction of N2O with the oxidation of NH3 allows the production of nitric oxide (NO) at the anode, a valuable precursor for HNO3 production.This work uses a commercial SOFC stack comprehending six cells, equipped with membrane electrode assemblies of LSM-CGO ‖ yttria-stabilized zirconia (YSZ) ‖ YSZ-NiO. Electrochemical Impedance Spectroscopy (EIS) was successfully employed to characterize the stack performance. Data were analyzed by combining a Distribution Function of Relaxation Times (DFRT) and Equivalent Circuit Models (ECMs), for different operating conditions, namely in terms of temperature and fuel feed composition. Three major processes were identified at the anode: one related to the adsorption/desorption of reactants on the surface of the electrocatalyst, a diffusion process of charge carriers/intermediate species to the triple phase boundary (TPB), and a charge-transfer process at the TPB. The electrochemical production of nitric oxide (NO) was investigated, and a 20 % selectivity towards NO production and an energy stack efficiency of 88 % was obtained. Overall, the current work provides a critical first step toward using SOFC to perform efficient N2O electroreduction using diluted ammonia as fuel.

Constructing high-performance and versatile liquid–solid triboelectric nanogenerator with inflatable columnar units

Abstract The use of water resources for energy generation has become increasingly prevalent, encompassing the conversion of kinetic energy from streams, tides, and waves into renewable electrical power. Water energy sources offer numerous benefits, including widespread availability, stability, and the absence of carbon dioxide and other greenhouse gas emissions, making them a clean and environmentally friendly form of energy. In this work, we develop a droplet-based liquid–solid triboelectric nanogenerator (LS-TENG) using sophisticatedly designed inflatable columnar structures with inner and outer dual-electrodes. This device can be utilized to harvest both the internal droplet-rolling mechanical energy and the external droplet-falling mechanical energy, capable of being assembled into various structures for versatile applications. The design incorporates a combined structure of both internal and external TENG to optimize output performance via multiple energy harvesting strategies. The internal structure features a dual-electrode columnar-shaped LS-TENG, designed to harvest fluid kinetic energy from water droplets. By leveraging the back-and-forth motion of a small amount of water within the air column, mechanical energy can be readily collected, achieving a maximum mass power density of 9.02 W·Kg−1 and an energy conversion efficiency of 10.358%. The external component is a droplet-based LS-TENG, which utilizes a double-layer capacitor switch effect elucidated with an equivalent circuit model. Remarkably, without the need for pre-charging, a single droplet can generate over 140 V of high voltage, achieving a maximum power density of 7.35 W·m−2 and an energy conversion efficiency of 22.058%. The combined LS-TENG with a sophisticated inflatable columnar structure can simultaneously collect multiple types of energy with high efficacy, exhibiting great significance in potential applications such as TENG aeration rollers, inflatable lifejacket, wind energy harvesting, TENG tents, and green houses.