Charge Estimation Of Lithium-ion Batteries Research Articles

Improved unscented Kalman filter for state of charge estimation of lithium-ion battery with one-step randomly measurement loss and inaccurate noise covariance matrices

Accurate state of charge estimation is of great significance for optimizing the management of lithium batteries. Due to the influence of actual environmental factors, random measurement loss and inaccurate noise covariance matrices will appear in the estimation process. Especially when the two situations occur at the same time, the estimation of SOC will be seriously affected. Thus, an improved unscented Kalman filter is presented to solve the above problems in this paper. First, the state space model of nonlinear system is constructed, which can fully reflect one-step random measurement loss, and the nominal noise covariance matrix is used to reflect the uncertainty. Second, as the prior probability density function of the parameters, the Beta prior and inverse Wishart prior are used in the derivation of the joint probability density function. Finally, these parameters are derived based on variational Bayesian theory, the updated state vector is obtained. Simulation results shows that the proposed method can deal with random measurement loss and inaccurate noise covariance matrices and the high accuracy in dynamic stress test and federal urban driving schedule.

State of charge estimation for lithium-ion batteries based on improved barnacle mating optimizer and support vector machine

Precise state of charge (SOC) estimation is essential for battery management systems. The improved barnacle mating optimizer-support vector machine (IBMO-SVM) model is proposed and used for SOC estimation of lithium-ion batteries. (1) The cubic chaotic mapping, hyperbolic sinusoidal conditioning factor, and Gauss-Cosey variation are introduced to improve the barnacle mating optimizer (BMO) to obtain the improved barnacle mating optimizer (IBMO); (2) The convergence performance of IBMO is verified by comparing with other five intelligent optimization algorithms under several test functions; (3) IBMO-SVM is created by using IBMO to optimize the search for support vector machine (SVM) parameters; and (4) IBMO-SVM is used for SOC estimation of lithium-ion batteries and the estimation results are analyzed by multiple evaluation indexes. The proposed model's root mean squared error (RMSE) and mean absolute percentage error (MAPE) are 0.0042 and 0.61 %, and its R-square (R2) is 0.9994, outperforming the four comparison models. The SOC estimation methodology proposed in this study is highly accurate and reliable, and it provides advantages for improving the battery management system.

An optimized long short-term memory-weighted fading extended Kalman filtering model with wide temperature adaptation for the state of charge estimation of lithium-ion batteries

Accurate state of charge (SOC) estimation at different operating temperatures is essential for the reliable and safe operation of battery management systems (BMS) for lithium-ion batteries in electric vehicles (EVs). In this paper, an optimized long-short-term memory-weighted fading extended Kalman filtering (LSTM-WFEKF) model with wide temperature adaptation is proposed as a temperature-conditioned model for SOC estimation. Firstly, the input datasets are categorized based on the operating temperatures for EVs in the United States Advanced Battery Consortium manual: cold (−10 °C), normal (25 °C), and hot (50 °C) temperatures and optimized with an attention mechanism for faster training of the LSTM model to cross-train and test to specifically study the effects of temperature on the SOC estimation through a transfer learning mechanism. Secondly, the SOC estimated by the LSTM model is input into a WFEKF method, which introduces adaptive weighing and fading factors to correct, denoise, and optimize the final SOC for each temperature variation under complex working conditions. Finally, the results show that the training and testing temperatures have distinctive SOC effects using the LSTM model. Also, the proposed LSTM-WFEKF model estimates the SOC with overall best mean absolute error (MAE), root mean square error (RMSE), and R-squared (R2) values of 0.0697%, 0.0784%, and 99.9965%, respectively, under different temperatures and complex working conditions, which is optimal compared to other existing models. Based on the MAE, RMSE, and R2 values under different operating temperatures and complex working conditions, this paper concludes that the 25 °C training dataset ensures a more accurate SOC estimation. Meanwhile, the −10 °C and 50 °C training datasets cause more and less noisy estimates, respectively. The proposed LSTM-WFEKF model has wide temperature and working condition adaptability for real-time BMS applications in EVs.

Bayesian information criterion based data-driven state of charge estimation for lithium-ion battery

Accurate state of charge (SOC) estimation is essential for the safe and reliable operation of Li-ion batteries. To solve the problem of poor generalisation caused by over-fitting, this paper presents a combination algorithm based on feature selection to estimate battery SOC. Firstly, a portion of the features is extracted from the extended Kalman filtering (EKF) results. It forms the set of features to be selected with four other measured features. Secondly, the optimal feature subset is adopted by designing a wrapped feature screening framework based on the Bayesian information criterion (BIC). Finally, the selected combination of features is adopted to train the support vector regression (SVR) model, which is applied to the battery SOC estimation. The experimental results reveal that the combination strategy of EKF and SVR improves the accuracy of SOC estimation. The optimal SVR model based on the feature selection criterion shows better generalisation. Better estimation results in four driving conditions are achieved, and the root-mean-square error of the battery SOC estimation is decreased by at least 64.1 % and 56.5 % compared to the EKF algorithm and SVR algorithm driven by full feature, respectively.

State of Charge Estimation of Lithium-Ion Battery for Electric Vehicles under Extreme Operating Temperatures Based on an Adaptive Temporal Convolutional Network

The accurate estimation of state of charge (SOC) under various conditions is critical to the research and application of batteries, especially at extreme temperatures. However, few studies have examined the SOC estimation performance of estimation algorithms for several types of batteries under such conditions. In this study, a new method was derived for SOC estimation and a series of experiments were conducted covering five types of lithium-ion batteries with three kinds of cathode materials (i.e., LiFePO4, Li(Ni0.5Co0.2Mn0.3)O2, and LiCoO2), three test temperatures, and four real driving cycles to verify the proposed method. The test temperatures for battery operation ranges from −20 to 60 °C. Then, an adaptive machine learning (ML) framework based on the deep temporal convolutional network (TCN) and Coulomb counting method was proposed, and the structure of the estimation model was designed through the Taguchi method. The accuracy and generalizability of the proposed method were evaluated by calculating the estimation errors and their standard deviations (SDs), its average errors showed a decline of at least 49.66%, and its SDs showed a decline of at least 45.88% when compared to four popular ML methods. These traditional ML methods performed poor accuracy and stability at extreme temperatures (−20 and 60 °C) when compared to 25 °C, while the proposed adaptive method exhibited stable and high performances at different temperatures.

State of charge estimation for lithium-ion batteries based on fractional order multiscale algorithm

The accuracy of state of charge (SoC) plays a critical role in lithium-ion batteries management system, whereas it gradually reduces as ohmic internal resistance growing and maximum available capacity decreasing with battery aging, which is still an open and challenging problem in SoC estimation. To tackle this issue, a multi-scale estimation algorithm is proposed by incorporating fractional order adaptive extended Kalman filter and variable forgetting factor recursive least square (FOAEKF-VFFRLS). Firstly, in order to describe the physicochemical reactions inside battery accurately, a fractional order model of lithium-ion battery with its discrete form is introduced, and the resistor-capacitor (RC) values as well as the order of capacitors are obtained by employing ant colony algorithm (ACA). Secondly, for enhancing SoC estimation accuracy, a fractional order adaptive extended Kalman filter algorithm (FOAEKF) is proposed to continuously modify the noise statistical characteristics while utilizing observation data information. Thirdly, to predict ohmic internal resistance and maximum available capacity for battery, a variable forgetting factor recursive least square algorithm (VFFRLS) is established based on the fact that forgetting factor determined by individual data error would be suddenly changes in the case of inaccurate or perturbed data. Besides, to further improve the accuracy of SoC estimation, a multi-scale estimation approach is proposed in light of the slow variation of battery internal resistance and the fast change of SoC. Finally, through comparative experiments, it is proved that the proposed approach has comprehensive strengths. First, the minimum root mean square error (RMSE) of SoC estimation error is controlled within 0.52 %. Second, terminal voltage error is kept small while limiting SoC errors within narrow ranges. Third, favorable robustness in terms of SoC estimation is achieved despite SoC initial value is mis-initialized.

State of charge estimation of lithium-ion battery based on improved forgetting factor recursive least squares-extended Kalman filter joint algorithm

In order to solve the problem that forgetting factor recursive least squares (FFRLS) is prone to abnormal jitter and even divergence under complex working conditions, improved forgetting factor recursive least squares based on dynamic constraint and parameter backtracking is proposed. A joint algorithm of improved forgetting factor recursive least squares and extended Kalman filter (EKF) is used to estimate the state of charge (SOC) of lithium-ion battery. Firstly, parameters of Thevenin equivalent circuit model are identified on-line by the improved FFRLS considering dynamic constraint and parameter backtracking, and then the SOC of lithium-ion battery is estimated by extended Kalman filter. The results show that the improved forgetting factor recursive least squares has high accuracy of battery model parameters identification and the joint algorithm also has high accuracy and robustness of SOC estimation under dynamic stress test (DST) condition, the maximum absolute SOC estimation error is 2.49 % and the average absolute SOC estimation error is 1.39 %.

A Novel Bias Compensated Recursive Least Squares and Multi Innovation Unscented Kalman Filtering Algorithm Method for Accurate State of Charge Estimation of Lithium-ion Batteries

A Novel Bias Compensated Recursive Least Squares and Multi Innovation Unscented Kalman Filtering Algorithm Method for Accurate State of Charge Estimation of Lithium-ion Batteries

A hybrid neural network model with improved input for state of charge estimation of lithium-ion battery at low temperatures

Lithium-ion batteries have been used in all aspects of life for environmental and resource reasons. The accurate estimation of the state of charge (SOC) ensures the proper operation of the battery. However, few methods have focused on the problem of SOC estimation at low temperatures. A hybrid method based on the CNN-BWGRU network is proposed in this paper. The method optimizes the influence of battery information on the results through a “multi-moment input” structure and the bidirectional network. The convolutional neural network (CNN) is used to learn the feature parameters in the input. The bidirectional weighted gated recurrent unit (BWGRU) can improve the fitting performance of the network at low temperatures by changing the weights. The proposed network has a strong generalization capability, estimation accuracy, and robustness. SOC estimation is performed under different conditions to verify the plausibility of the network. The experimental results show that the method has higher accuracy and stability than other networks. In addition, the proposed method can overcome the effect of different initial SOC on the estimation results. Therefore, the CNN-BWGRU network provides a new method in battery SOC estimation while providing helpful guidance for safe and stable battery operation in natural environments.

State of Charge Estimation of Lithium-Ion Batteries Using Stacked Encoder-Decoder Bi-Directional LSTM for EV and HEV Applications.

Energy storage technologies are being used excessively in industrial applications and in automobiles. Battery state of charge (SOC) is an important metric to be monitored in these applications to ensure proper and safe functionality. Since SOC cannot be measured directly, this paper puts forth a novel machine learning architecture to improve on the existing methods of SOC estimation. This method consists of using combined stacked bi-directional LSTM and encoder–decoder bi-directional long short-term memory architecture. This architecture henceforth represented as SED is implemented to overcome the nonparallel functionality observed in traditional RNN algorithms. Estimations were made utilizing different open-source datasets such as urban dynamometer driving schedule (UDDS), highway fuel efficiency test (HWFET), LA92 and US06. The least Mean Absolute Error observed was 0.62% at 25 °C for the HWFET condition, which confirms the good functionality of the proposed architecture.

An optimized relevant long short-term memory-squared gain extended Kalman filter for the state of charge estimation of lithium-ion batteries

Accurate state of charge (SOC) estimation of lithium-ion batteries by the battery management system (BMS) plays a prominent role in ensuring their reliability, safe operation, and acceptable durability in smart devices, electric vehicles, etc. In this paper, the effect of the training and testing working conditions on the accuracy of the SOC using a long short-term memory (LSTM) network is studied through transfer learning. Then, a relevant attention mechanism is introduced as a data optimizer for faster training of the LSTM network to establish a relevant LSTM (RLSTM). Finally, the SOCs estimated by the RLSTM are independently input with the working current to an extended Kalman filter (EKF) and a proposed squared gain EKF (SGEKF) method to iteratively denoise and optimize the accuracy of the final SOC under the three complex working conditions. The results show that the SOC estimation accuracy is influenced by the training and testing working conditions using the LSTM network, which provides a technique for accurate SOC estimation. Also, the established RLSTM network is computationally efficient for accurate SOC estimation. Moreover, the proposed hybrid RLSTM-SGEKF model has an overall maximum mean absolute error, mean squared error, root mean squared error, and mean absolute percentage error values of 0.35299%, 0.0017448%, 0.41765%, and 2.34403%, respectively, under the three complex working conditions. The proposed hybrid RLSTM-SGEKF model is optimal, robust, and computationally efficient for accurate SOC estimation of lithium-ion batteries for real-time BMS applications.

State of charge estimation for lithium-ion batteries using gated recurrent unit recurrent neural network and adaptive Kalman filter

The state of charge (SOC) is one of the most important monitoring states for the battery management system. It is still a challenge to estimate the battery SOC accurately and stably. The conventional model-based filtering methods may cause inaccurate SOC estimation in application due to the high dependence on accurate battery model. And the emerging methods based on machine learning often have the problem of estimated SOC fluctuation when the current fluctuates greatly. To solve these problems, this paper proposes a robust and efficient combined SOC estimation method, GRU-AKF, which combines the gated recurrent unit recurrent neural network (GRU-RNN) and the adaptive Kalman filter (AKF). Firstly, the GRU-RNN is used to establish a mapping model between the battery measured variables and SOC in the full temperature range, and to achieve the SOC pre-estimation. Then, an AKF is employed to filter the output SOC of the GRU-RNN for reducing the fluctuation in pre-estimated SOC. Finally, the accurate and stable estimated SOC is obtained. In the experiments, the LiFePO4 battery datasets at various temperatures are used to validate the SOC estimation performance and generalization ability. Specifically, the root mean square error is less than 1.3% and 5.8%, and the maximum error is less than 2.2% and 7.7% for the unknown data at positive and negative temperatures, respectively. By comparing with other methods of the same type, the proposed method is demonstrated to be superior in SOC estimation performance and computation efficiency, especially it has excellent performance in initial SOC convergence ability.

Improved Algorithm Based on AEKF for State of Charge Estimation of Lithium-ion Battery

Improved Algorithm Based on AEKF for State of Charge Estimation of Lithium-ion Battery

State of Charge Estimation for Lithium-Ion Batteries Using Simple Recurrent Units and Unscented Kalman Filter

Accurate estimation of the state of charge plays a very important role in ensuring the safe and effective operation of battery lithium-ion batteries and is one of the most important state parameters. However, the estimation method of state of charge has various limitations, so it is of great significance to improve the accuracy and calculation speed of the method. In this article, we propose an improved recurrent neural network model to estimate lithium-ion battery state of charge. Simple recurrent units are used to replace the traditional recurrent neural network basic unit or long short-term memory unit, and the computation speed is improved by implementing parallel processing. Finally, the prediction results of the model are fed into an unscented Kalman filter module to remove the interference of noise on the prediction. This article studies the prediction accuracy and speed of Samsung INR 18650-20R and INR 18650-25R under various ambient temperatures, initial state of charge values, and electric vehicle drive cycles. The results show that the proposed method can obtain accurate state of charge estimation results in the INR 18650-20R data set. For different temperatures and initial SOC, the root mean square error is less than 0.015 and 0.016, and the prediction speed is about 30% higher than that of long short-term memory. In the INR 18650-25R data set, for three different driving cycles, the root mean square error is less than 0.034, and the average test speed is about 2.7s, which proves the effectiveness of this method in estimating accuracy and speed.

Adaptive Exponentially Weighted Extended Kalman Filtering for State of Charge Estimation of Lithium-ion Battery

Adaptive Exponentially Weighted Extended Kalman Filtering for State of Charge Estimation of Lithium-ion Battery

Towards efficient state of charge estimation of lithium-ion batteries using canonical correlation analysis

State of charge (SOC) estimation plays an important role for lithium-ion batteries indicating the remaining charge during a cycle. The deep networks adopt the complicated network structure with a large number of parameters, which are sophisticated and lack generality. This paper presents a novel and facile data-driven method based on canonical correlation analysis (CCA) for battery SOC estimation. Firstly, CCA is demonstrated in a regression form and given with an optimizing algorithm for battery SOC estimation. Then the offline training results are followed by the Kalman filter (KF) for online error correction. Finally, a robust canonical correlation analysis (RCCA) is proposed for noise corruption on the input data. Simulation results on different dynamic profiles show the effectiveness of RCCA compared with CCA with improved accuracy by 40% for input noise, and the final results of RCCA with KF achieve root mean squared error (RMSE) of 0.71%. The proposed method achieves superior results in accuracy under input noise and is also computationally efficient with less training time compared with other methods.

State of charge estimation of lithium-ion batteries using adaptive neuro fuzzy inference system

A battery’s state of charge (SOC) is used to assess its residual capacity. It is a very important parameter for the control of the electric vehicle (EV). The objective of this paper is to estimate the SOC of a lithium-ion battery (LIB) using an adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) because SOC of a battery must be estimated from measurable battery parameters such as current, voltage or temperature. Two intelligent SOC estimation methods are compared according to their suitability and accuracy. ANN estimation is more precise and perfectly represents the experimental data.

State of charge estimation of lithium-ion battery under time-varying noise based on Variational Bayesian Estimation Methods

Non-linear filters such as UKF, CKF are often used to estimate the State of Charge (SoC) of lithium batteries, but the premise is that the noise is Gaussian noise, but the actual noise cannot be Gaussian noise, such as the process noise or measurement noise changed with time, which will affect the estimated effect. In this paper, a second-order battery model is established, and the Kalman filter is used to identify the model parameters, and then three methods are used to obtain the SOC-OCV mapping curve. Next, to improve the performance of SoC estimation under the influence of time-varying measurement noise or process noise, the idea of Variable Bayesian iteration is introduced into the nonlinear filter to obtain the Variable Bayesian unscented Kalman filter and the Variable Bayesian square-root cubature filter. Then the two methods are used to estimate the SoC under four working conditions, two temperatures, and two kinds of covariance time-varying noise. Experimental results show that the proposed method can effectively improve the estimation performance of SoC, and the SOC-OCV mapping curve used in this paper is more stable.

Hybrid Methods Using Neural Network and Kalman Filter for the State of Charge Estimation of Lithium-Ion Battery

With the increasing carbon emissions worldwide, lithium-ion batteries have become the main component of energy storage systems for clean energy due to their unique advantages. Accurate and reliable state-of-charge (SOC) estimation is a central factor in the widespread use of lithium-ion batteries. This review, therefore, examines the recent literature on estimating the SOC of lithium-ion batteries using the hybrid methods of neural networks combined with Kalman filtering (NN-KF), classifying the methods into Kalman filter-first and neural network-first methods. Then the hybrid methods are studied and discussed in terms of battery model, parameter identification, algorithm structure, implementation process, appropriate environment, advantages, disadvantages, and estimation errors. In addition, this review also gives corresponding recommendations for researchers in the battery field considering the existing problems.

A Novel BCRLS-BP-EKF Method for the State of Charge Estimation of Lithium-ion Batteries

A Novel BCRLS-BP-EKF Method for the State of Charge Estimation of Lithium-ion Batteries