RC Equivalent Circuit Research Articles

The measurement and analysis for Open Circuit Voltage of Lithium-ion Battery

In this paper, charging and discharging characteristic of Lithium-ion Battery is studied. The relationship between open circuit voltage and model parameters is analyzed based on RC equivalent circuit model. Charging and discharging characteristic of a brand of Lithium-ion battery was tested. By fitting the terminal voltage data, the OCV-SOC curve was compared with the actual OCV-SOC curve. The analysis results show that the deviation between the fitting curve and the actual curve is within the effective range.

State of Charge Estimation for Lithium-Ion Batteries Based on Temperature-Dependent Second-Order RC Model

Accurate estimation of battery state of charge (SOC) is of great significance for extending battery life, improving battery utilization, and ensuring battery safety. Aiming to improve the accuracy of SOC estimation, in this paper, a temperature-dependent second-order RC equivalent circuit model is established for lithium-ion batteries, based on the battery electrical characteristics at different ambient temperatures. Then, a dual Kalman filter algorithm is proposed to estimate the battery SOC, using the proposed equivalent circuit model. The SOC estimation results are compared with the SOC value obtained from experiments, and the estimation errors under different temperature conditions are found to be within ±0.4%. These results prove that the proposed SOC estimation algorithm, based on a temperature-dependent second-order RC equivalent circuit model, provides accurate SOC estimation performance with high temperature adaptability and robustness.

RC equivalent circuit model of lumped parameters for lithium ion batteries in electric vehicles

RC equivalent circuit model of lumped parameters for lithium ion batteries in electric vehicles

Application of ac impedance as diagnostic tool – Low temperature electrolyte for a Li-ion battery

In this report, we study the impact of the solid electrolyte interphase (SEI) of lithium ion batteries (LIB) on low temperature performance in 3-electrode pouch cells with electrochemical impedance spectroscopy. Two kinds of electrolytes are used for the comparison purpose. One is chosen as the best low temperature electrolyte (1.0 M LiPF6 in ethylene carbonate (EC)/ethyl methyl carbonate (EMC)/dimethyl carbonate (DMC) at a certain ratio) developed in our laboratory by design of experiment method. The other electrolyte used is state-of-art baseline electrolyte (1.0 M LiPF6 in 3 EC/7 EMC). Electrochemical impedance of cathode, anode and the complete cell is measured in various states of aging, charge, and temperature conditions. Our results show that majority of the full cell impedance arises from anode SEI. Cathode SEI has very small impedance. Approximately 75% of full cell impedance is from anode and rest is from cathode. The impedance data are fitted by RC equivalent circuit model to extract various parameters of interfacial phenomena. Also, the data are analyzed by using the relation between the impedance, its distribution of relaxation times (DRT), and the time constants. Conclusively, the high rate performance of a LIB in low temperature depends on the kinetics of the electrochemical process rather than the value of polarization resistance.

Comparative analysis to determine the accuracy of fractional derivatives in modeling supercapacitors

SummaryIn this paper, we study a supercapacitor model represented by an equivalent RC circuit considering five different types of derivatives: Caputo, Caputo‐Fabrizio, and Atangana‐Baleanu fractional derivatives and the conformable and integer‐order derivatives. A set of experimental data from six commercial supercapacitors are used to estimate the parameter values for each derivative model by applying interior point optimization. The results show that the most accurate approach is achieved with the conformable derivative followed by the Caputo fractional derivative.

A New Analysis Way of Three-Phase Switched Capacitor Converter

The paper presents the theoretical analysis way of the switched capacitor converter (SCC). The main goal of this research is to suggest the analysis way of three-phase SCC. A common SCC operates by two phases; charging phase and discharging phase. Therefore, state-space averaging model or slow and fast switching limit (S-FSL) model has been suitable. Although the four-terminal equivalent model can cover all situation including three-phases cases, this model does not include the parameter of frequency and capacitance. Therefore, the four-terminal model has a weakness. In this situation, we selected the Fibonacci sequence SCC operated by three-phase as the target circuit, which topology has been proved to have higher efficiency, small size in the previous research. In the paper, we suggest the new analysis way of the three-phase SCC by combination of the four-terminal equivalent model and RC circuit model from each loop equation of the equivalent circuits of the SCC. By using the suggested way, it is possible to analyze the three-phase SCC, deriving the effect of the load, operation frequency and duty ratio variation. In order to verify the feasibility and the cogency of the suggested analysis way, comparative analysis is implemented by SPICE simulations. The error in the load regulation between the suggested way and the simulation result is negligible. Through this result, we establish the foundation of the analysis of the three-phase SCC.

Adaptive Forgetting Factor Recursive Least Square Algorithm for Online Identification of Equivalent Circuit Model Parameters of a Lithium-Ion Battery

With the popularity of electric vehicles, lithium-ion batteries as a power source are an important part of electric vehicles, and online identification of equivalent circuit model parameters of a lithium-ion battery has gradually become a focus of research. A second-order RC equivalent circuit model of a lithium-ion battery cell is modeled and analyzed in this paper. An adaptive expression of the variable forgetting factor is constructed. An adaptive forgetting factor recursive least square (AFFRLS) method for online identification of equivalent circuit model parameters is proposed. The equivalent circuit model parameters are identified online on the basis of the dynamic stress testing (DST) experiment. The online voltage prediction of the lithium-ion battery is carried out by using the identified circuit parameters. Taking the measurable actual terminal voltage of a single battery cell as a reference, by comparing the predicted battery terminal voltage with the actual measured terminal voltage, it is shown that the proposed AFFRLS algorithm is superior to the existing forgetting factor recursive least square (FFRLS) and variable forgetting factor recursive least square (VFFRLS) algorithms in accuracy and rapidity, which proves the feasibility and correctness of the proposed parameter identification algorithm.

Model Parameters Online Identification and SOC Joint Estimation for Lithium-Ion Battery Based on a Composite Algorithm

The purpose of this paper is to discuss how to solve the problem of on-line identification of model parameters of Li-ion battery and on-line estimation of SOC. Based on the matlab/simulink platform, a first-order RC equivalent circuit model of the battery is built, and a joint estimation algorithm of the model parameters and SOC of the lithium ion battery is designed based on the dynamic model, which is compared with the single adaptive Kalman filter algorithm (AEKF). The simulation results show that the proposed joint estimation algorithm can make effective online estimation and update of the battery model parameters and SOC. The average estimation error of SOC is less than 2.8%, the estimation accuracy is higher than that of adaptive Kalman filter, and its robustness level is relatively high.

Epitaxial Thin Films as a Model System for Li-Ion Conductivity in Li4Ti5O12.

Using an epitaxial thin-film model system deposited by pulsed laser deposition (PLD), we study the Li-ion conductivity in Li4Ti5O12, a common anode material for Li-ion batteries. Epitaxy, phase purity, and film composition across the film thickness are verified employing out-of-plane and in-plane X-ray diffraction, transmission electron microscopy, time-of-flight mass spectrometry, and elastic recoil detection analysis. We find that epitaxial Li4Ti5O12 behaves like an ideal ionic conductor that is well described by a parallel RC equivalent circuit, with an ionic conductivity of 2.5 × 10-5 S/cm at 230 °C and an activation energy of 0.79 eV in the measured temperature range of 205 to 350 °C. Differently, in a co-deposited polycrystalline Li4Ti5O12 thin film with an average in-plane grain size of <10 nm, a more complex behavior with contributions from two distinct processes is observed. Ultimately, epitaxial Li4Ti5O12 thin films can be grown by PLD and reveal suitable transport properties for further implementation as zero-strain and grain boundary free anodes in future solid-state microbattery designs.

Loss Simulation by Finite-Element Magnetic Field Analysis Considering Dielectric Effect and Magnetic Hysteresis in EI-Shaped Mn–Zn Ferrite Core

Loss Simulation by Finite-Element Magnetic Field Analysis Considering Dielectric Effect and Magnetic Hysteresis in EI-Shaped Mn–Zn Ferrite Core

Nonlinear dynamic modeling of ultrathin conducting polymer actuators including inertial effects

Trilayer conducting polymer (CP) actuators are potential alternatives to piezoelectric and electrostatic actuators due to their large strain, and recently demonstrated operation at hundreds of Hertz. However, these actuators exhibit nonlinear electrical and mechanical properties as a function of their oxidation state, when operated over their full strain range, making it more challenging to accurately predict their mechanical behavior. In this paper, an analytical multi-physics model of the CP actuators is proposed to predict their nonlinear dynamic mechanical behavior. To demonstrate the accuracy of the model, a trilayer actuator composed of a solid polymer electrolyte sandwiched between two poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes was fabricated and characterized. This system consists of an electrical subsystem represented by an RC equivalent circuit, an electro-mechanical coupling matrix, and a mechanical subsystem described by using a rigid finite element method. The electrical conductivity and the volumetric capacitance, an empirical strain-to-charge ratio, and Young’s modulus of the actuator as a function of the PEDOT electrode charge state were also implemented into the model, using measured values. The proposed model was represented using a bond graph formalism. The concordance between the simulations and the measurements confirmed the accuracy of the model in predicting the nonlinear dynamic electrical and mechanical response of the actuators. In addition, the information extracted from the model also provided an insight into the critical parameters of the actuators and how they affect the actuator efficiency, as well as the energy distribution including dissipated, stored, and transferred energy. These are the key parameters for designing, optimizing, and controlling the actuation behavior of a trilayer actuator.

A set-membership algorithm based parameter identification method for lithium-ion batteries

The accuracy of lithium-ion battery model is one of the most important factors that affects the applicability of power battery in electrical vehicles. Based on the traditional forgetting factor recursive least square (FFRLS) method, the random noise should be subjected to the normal distribution of zero mean and zero covariance, which, however, is very difficult to be satisfied in practical application. In this paper, based on the first-order RC equivalent circuit model, the identification of lithium-ion battery model parameters is performed by using the set-membership identification algorithm with unknown but bounded noise. The model parameters are identified by the set-membership algorithm with the experimental data of UDDS test on the NCM battery module. Experiments and simulation results show that the new method can simulate the dynamics of battery well, it can keep terminal voltage error within 1%, alongside with the root mean square error(RMSE) improved up to 8% compared with the FFRLS, which verifies the feasibility and the effectiveness of the new method, as well as providing data support for accurate estimation of battery state.

Lithium-ion battery modeling and parameter identification based on fractional theory

To effectively use and manage lithium-ion batteries and accurately estimate battery states such as state of charge and state of health, battery models with good robustness, accuracy and low-complexity need to be established. So the models can be embedded in microprocessors and provide accurate results in real-time. Firstly, this paper analyzes the electrochemical impedance spectrogram of lithium-ion battery, and adopts impedance elements with fractional order characteristics such as constant phase element and Warburg element to improve the second-order RC integer equivalent circuit model based on the fractional calculus theory. Secondly, a fractional-order equivalent circuit model of lithium-ion battery is established, which can accurately describe the electrochemical processes such as charge transfer reaction, double-layer effect, mass transfer and diffusion of lithium-ion battery. Thirdly, based on the mixed-swarm-based cooperative particle swarm optimization, parameter identification of the fractional-order equivalent circuit model is conducted using the federal city driving schedule experimental data in the time domain. The simulation results show that the model has higher accuracy and better robustness against different driving conditions, different SOC ranges and different temperatures than the second-order RC equivalent circuit model. The SOC estimation accuracy based on the fractional-order equivalent circuit model of lithium-ion battery is validated.

Dielectric constant measurement using atomic force microscopy of dielectric films: a system theory approach

A technique was developed to measure dielectric constant at microscale based on the system theory approach using an atomic force microscopy (AFM), this makes possible the electrical characterization of dielectric materials using an optimized instrumentation. This technique is capable of measuring capacitance on either metallic contact–insulator–metallic contact or metallic contact–insulator with the AFM tip as the upper contact, the dielectric constant can be calculated from these results. The technique compares the frequency response between the input voltage and the output voltage of an equivalent RC-circuit (resistance–capacitance) in the frequency range 1 Hz–60 kHz. This comparison is analyzed using a transfer function model and a least-squares process to get the time constant involved in this kind of circuit, facilitating the implementation of this technique with any atomic force microscopy equipment. Additionally, the measurements can be carried out in a single point or in a mapping. The measurements were carried out on two hybrid films, PMMA–TiO\(_{2}\)–SiO\(_{2}\) and PMMA–TiO\(_{2}\)–BT, which were prepared by sol–gel technique and deposited on indium tin oxide (ITO)-coated glass substrates. The results obtained with this technique agreed with conventional measurements that use commercial capacitance–voltage analyzer, and indicated that dielectric constant is 11.31 for PMMA–TiO\(_{2}\)–SiO\(_{2}\), and 15.41 for PMMA–TiO\(_{2}\)–BT.

A Novel Battery State of Charge Estimation Method Based on a Super-Twisting Sliding Mode Observer

A novel method for Li-ion battery state of charge (SOC) estimation based on a super-twisting sliding mode observer (STSMO) is proposed in this paper. To design the STSMO, the state equation of a second-order RC equivalent circuit model (SRCECM) is derived to represent the dynamic behaviors of the Li-ion battery, and the model parameters are determined by the pulse current discharge approach. The convergence of the STSMO is proven by Lyapunov stability theory. The experiments under three different discharge profiles are conducted on the Li-ion battery. Through comparisons with a conventional sliding mode observer (CSMO) and adaptive extended Kalman filter (AEKF), the superiority of the proposed observer for SOC estimation is validated.

Overview of Lithium-Ion Battery Modeling Methods for State-of-Charge Estimation in Electrical Vehicles

As a critical indictor in the Battery Management System (BMS), State of Charge (SOC) is closely related to the reliable and safe operation of lithium-ion (Li-ion) batteries. Model-based methods are an effective solution for accurate and robust SOC estimation, the performance of which heavily relies on the battery model. This paper mainly focuses on battery modeling methods, which have the potential to be used in a model-based SOC estimation structure. Battery modeling methods are classified into four categories on the basis of their theoretical foundations, and their expressions and features are detailed. Furthermore, the four battery modeling methods are compared in terms of their pros and cons. Future research directions are also presented. In addition, after optimizing the parameters of the battery models by a Genetic Algorithm (GA), four typical battery models including a combined model, two RC Equivalent Circuit Model (ECM), a Single Particle Model (SPM), and a Support Vector Machine (SVM) battery model are compared in terms of their accuracy and execution time.

Electrical Conduction of Ba(Ti0.99Fe0.01)O3−δ Ceramic at High Temperatures

BaTiO3 and Ba(Ti0.99Fe0.01)O3−δ ceramics with dense microstructure have been synthesized by a solid-state reaction method, and their electrical conduction investigated by broadband electrical impedance spectroscopy at frequencies from 0.05 Hz to 3 × 106 Hz and temperatures from 200°C to 400°C. Compared with BaTiO3, the real part of the permittivity and the phase-transition temperature of Ba(Ti0.99Fe0.01)O3−δ decreased. Relaxation peaks appeared in the curves of the imaginary part of the permittivity as a function of frequency. With increase in frequency, the peaks gradually shifted towards higher frequency and their height increased. Conductivity was closely related to frequency and temperature. Frequency-dependent conductivity was analyzed using the Jonscher double power law. Compared with BaTO3, Ba(Ti0.99Fe0.01)O3−δ exhibited high impedance at given frequency and temperature. Impedance Cole–Cole plots displayed two semicircles, which could be well fit using two parallel RC equivalent circuit models. The conductivity activation energy was found to be around 1 eV. For Ba(Ti0.99Fe0.01)O3−δ, the electrical modulus curve versus frequency displayed two peaks.

Lifetime estimation of IGBT modules for MMC-HVDC application

Modular multilevel converters (MMCs) usually work in harsh operating environments due to their compact layouts and adverse mission profiles, which accelerate the thermomechanical fatigue process in insulated-gate bipolar transistor modules (IGBTs). Accurate lifetime estimation is desired to conduct reliability prediction and develop maintenance policies. This paper presents an analytical approach to estimating the lifetimes of IGBTs for MMC-HVDC application based on the thermal cycles, which are influenced by the transmission power profile and ambient temperature profile. The structure and operating principle of MMCs are studied to develop an analytical model for computing the IGBT power loss. A thermal equivalent network in the form of a Foster model is adopted to link the power losses and junction temperature. Next, an RC equivalent circuit analytical method for characterizing the fundamental-frequency thermal cycles, developed using electrothermal analogy theory, is proposed. The rainflow counting algorithm is applied to extract the low-frequency thermal cycles from the annual junction temperature data computed at every minute. The Bayerer model is employed to predict the IGBTs lifetime. Finally, the lifetime distribution, mission profiles and comparison of different IGBTs are analyzed via case studies.

Physical Interpretations of Nyquist Plots for EDLC Electrodes and Devices

Electrochemical impedance spectroscopy (EIS) consists of plotting so-called Nyquist plots representing negative of the imaginary versus the real parts of the complex impedance of individual electrodes or electrochemical cells. To date, interpretations of Nyquist plots have been based on physical intuition and/or on the use of equivalent RC circuits. However, the resulting interpretations are not unique and have often been inconsistent in the literature. This study aims to provide unequivocal physical interpretations of electrochemical impedance spectroscopy (EIS) results for electric double layer capacitor (EDLC) electrodes and devices. To do so, a physicochemical transport model was used for numerically reproducing Nyquist plots accounting for (i) electric double layer (EDL) formation at the electrode/electrolyte interface, (ii) charge transport in the electrode, and (iii) ion electrodiffusion in binary and symmetric electrolytes. Typical Nyquist plots of EDLC electrodes were reproduced numerically for d...

Design of dynamic genetic memory.

In electronic systems, dynamic random access memory (DRAM) is one of the core modules in the modern silicon computer. As for a bio‐computer, one would need a mechanism for storage of bio‐information named ‘data’, which, in binary logic, has two levels, logical high and logical low, or in the normalised form, ‘1’ and ‘0’. This study proposes a possible genetic DRAM based on the modified electronic configuration, which uses the biological reaction to fulfil an equivalent RC circuit constituting a memory cell. The authors implement fundamental functions of the genetic DRAM by incorporating a genetic toggle switch for data hold. The results of simulation verify that the basic function can be used on a bio‐storage module for the future bio‐computer.