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Lithium-ion (Li-ion) batteries are an important component of energy storage systems used in various applications such as electric vehicles and portable electronics. There are many chemistries of Li-ion battery, but LFP, NMC, LMO, and NCA are four commonly used types. In order for the battery applications to operate safely and effectively, battery modeling is very important. The equivalent circuit model (ECM) is a battery model often used in the battery management system (BMS) to monitor and control Li-ion batteries. In this study, experiments were performed to investigate the performance of three different ECMs (1RC, 2RC, and 1RC with hysteresis) on four Li-ion battery chemistries (LFP, NMC, LMO, and NCA). The results indicated that all three models are usable for the four types of Li-ion chemistries, with low errors. It was also found that the ECMs tend to perform better in dynamic current profiles compared to non-dynamic ones. Overall, the best-performed model for LFP and NCA was the 1RC with hysteresis ECM, while the most suited model for NMC and LMO was the 1RC ECM. The results from this study showed that different ECMs would be suited for different Li-ion battery chemistries, which should be an important factor to be considered in real-world battery and BMS applications.

In the current paper, ion transport parameters in poly (vinyl alcohol) (PVA) based solid polymer electrolyte were examined using Trukhan model successfully. The desired amount of lithium trifluoromethanesulfonate (LiCF3SO3) was dissolved in PVA host polymer to synthesis of solid polymer electrolytes (SPEs). Ion transport parameters such as mobility (μ), diffusion coefficient (D), and charge carrier number density (n) are investigated in detail using impedance spectroscopy. The data results from impedance plots illustrated a decrement of bulk resistance with an increase in temperature. Using electrical equivalent circuits (EEC), electrical impedance plots (ZivsZr) are fitted at various temperatures. The results of impedance study demonstrated that the resistivity of the sample decreases with increasing temperature. The decrease of resistance or impedance with increasing temperature distinguished from Bode plots. The dielectric constant and dielectric loss values increased with an increase in temperature. The loss tangent peaks shifted to higher frequency region and the intensity increased with an increase in temperature. In this contribution, ion transport as a complicated subject in polymer physics is studied. The conductivity versus reciprocal of temperature was found to obey Arrhenius behavior type. The ion transport mechanism is discussed from the tanδ spectra. The ion transport parameters at ambient temperature are found to be 9 × 10−8 cm2/s, 0.8 × 1017 cm−3, and 3 × 10−6 cm2/Vs for D, n, andμ respectively. All these parameters have shown increasing as temperature increased. The electric modulus parameters are studied in an attempt to understand the relaxation dynamics and to clarify the relaxation process and ion dynamics relationship.

The ultrasonic frequency radial vibration of an elastic thin spherical shell composed of isotropic materials is studied, the frequency equation of its vibration is deduced, and the equivalent circuit is obtained. The finite element software COMSOL is used to verify the obtained analytical theory, and the calculated results are basically consistent with the theoretical calculated values. The relevant conclusions provide references for the application of spherical shell structure in related fields.

Circuit analysis of frequency selective surfaces is reviewed with the aim to underline range of validity of different models and their advantages in terms of simplicity and physical insight. The circuit approach is based on an equivalent representation of the FSSs with series or shunt connections of inductances and capacitances. Dense non-resonant periodic surfaces (i.e.: grid or patch arrays) can be analyzed analytically by computing the values of inductors or capacitors via the homogenization theory. As the lattice period increases with respect to the operating wavelength or the element shape becomes resonant, a fully analytical circuital approach fails, in particular, in the presence of thin substrates. However, simple circuit approaches can still be employed by deriving lumped parameters values via a quick pre-processing and then generalizing them. The results are accurate up to the resonant frequency region of the element. By including an additional lumped element it is possible, taking into account the effect of the first high order Floquet harmonic. The multi-mode formulation is also able to catch the highly nonlinear response of FSS screens in the grating lobe region provided that the current profile of the element does not change significantly.

The growing complexity of electrical systems requires advanced analysis tools to optimize the design time and resources. While many circuit simulators exist, they often lack the flexibility needed for real-world applications. In this context, our paper develops practical approaches to building Thévenin and Norton equivalent diagrams by means of modern software facilities which overpass the capabilities of common commercial circuit simulators. They use the symbolic computation of two simulation tools developed by our research team. The proposed algorithms are not limited by the operation behavior of the analyzed systems, being usable in both DC and AC circuits, as well as in transients. The developed method facilitates and speeds up the complex analyses required by repeated simulations specific to the modern design process. Three case studies are discussed to prove the efficiency of the developed algorithms. They cover real DC and AC applications, respectively. The results obtained using the Thévenin and Norton equivalent diagrams were validated through analyses of the initial systems.

Nondestructive testing of plant roots is a hot topic in recent years. The traditional measurement process is time-consuming and laborious, and it is impossible to analyze the state of plant roots without destroying the sample. Recent studies have shown that as an excellent nondestructive measurement method, although electrical impedance spectroscopy (EIS) has made great achievements in many botanical research fields such as plant morphology and stress resistance, there are still limitations. This review summarizes the application of EIS in plant root measurement. The experiment scheme, instrument and electrode, excitation frequency range, root electrical characteristics, equivalent circuit, and combination of EIS and artificial intelligence (AI) are discussed. Furthermore, the review suggests that future research should focus on miniaturization of measurement equipment, standardization of planting environment and intelligentization of root diagnosis, so as to better apply EIS technology to in situ root nondestructive measurement.

A single-cell tri-band composite right/left-handed (CRLH) resonant antenna is presented. The antenna is designed on a single-layer coplanar waveguide-fed based on the T-junction discontinuity equivalent circuit. The proposed antenna provides compact size, easy fabrication process, multi-band feature and higher efficiency in comparison with the previously reported CRLH resonant antennas. The single-cell CRLH resonant antenna is fabricated and the measurements are consistent with the simulation result.

The power system is experiencing a higher penetration of renewable energy generations (REGs). The short circuit ratio (SCR) and the grid impedance ratio (GIR) are two indices to quantify the system strength of the power system with REGs. In this paper, the critical short circuit ratio (CSCR) is defined as the corresponding SCR when the system voltage is in the critical stable state. Through static voltage stability analysis, the mathematical expression of the CSCR considering the impact of GIR is derived. The maximum value of CSCR is adopted as the critical value to distinguish the weak power system. Based on the static equivalent circuit analysis, it is proved that the CSCR is still effective to evaluate critical system strength considering the interactive impact among REGs. Finally, we find that the GIR can be neglected and the SCR can be used individually to evaluate the system strength when SCR>2 or GIR>5. The correctness and rationality of the CSCR and its critical value are validated on ADPSS.

Solid-state supercapacitors (SSCs) consist of porous carbon electrodes and gel-polymer electrolytes and are used in novel energy storage applications. The current study aims to simulate the impedance of SSCs using a clearly defined equivalent circuit (EC) model with the ultimate goal of improving their performance. To this end, a conventional mathematical and a physicochemical model were adapted. The impedance was measured by electrochemical impedance spectroscopy (EIS). An EC consisting of electrical elements was introduced for each modeling approach. The mathematical model was purely based on a best-fit method and utilized an EC with intuitive elements. In contrast, the physicochemical model was motivated by advanced theories and allowed meaningful associations with properties at the electrode, the electrolyte, and their interface. The physicochemical model showed a higher approximation ability (relative error of 3.7%) due to the interface impedance integration in a more complex circuit design. However, this model required more modeling and optimization effort. Moreover, the fitted parameters differed from the analytically calculated ones due to uncertainties in the SSC’s microscale configuration, which need further investigations. Nevertheless, the results show that the proposed physicochemical model is promising in simulating EIS data of SSCs with the additional advantage of utilizing well-reasoned property-based EC elements.

With rapid transportation electrification worldwide, lithium-ion batteries have gained much attention for energy storage in electric vehicles (EVs). State of power (SOP) is one of the key states of lithium-ion batteries for EVs to optimise power flow, thereby requiring accurate online estimation. Equivalent circuit model (ECM)-based methods are considered as the mainstream technique for online SOP estimation. They primarily vary in their basic principle, technical contribution, and validation approach, which have not been systematically reviewed. This paper provides an overview of the improvements on ECM-based online SOP estimation methods in the past decade. Firstly, online SOP estimation methods are briefed, in terms of different operation modes, and their main pros and cons are also analysed accordingly. Secondly, technical contributions are reviewed from three aspects: battery modelling, online parameters identification, and SOP estimation. Thirdly, SOP testing methods are discussed, according to their accuracy and efficiency. Finally, the challenges and outlooks are presented to inspire researchers in this field for further developments in the future.