Ana-Irina Stroe

Operation of a Grid-Connected Lithium-Ion Battery Energy Storage System for Primary Frequency Regulation: A Battery Lifetime Perspective

Because of their characteristics, which have been continuously improved during the last years, Lithium-ion batteries have been proposed as an alternative viable solution to present fast-reacting conventional generating units to deliver the primary frequency regulation service. However, even though there are worldwide demonstration projects, where energy storage systems based on Lithium-ion batteries are evaluated for such applications, the field experience is still very limited. In consequence, at present, there are no very clear requirements on how the Lithium-ion battery energy storage systems should be operated, while providing frequency regulation service and how the system has to reestablish its state of charge (SOC) once the frequency event has passed. Therefore, this paper aims to investigate the effect on the lifetime of the Lithium-ion batteries energy storage system of various strategies for reestablishing the batteries’ SOC after the primary frequency regulation is successfully delivered.

Degradation behaviour of Lithium-ion batteries based on field measured frequency regulation mission profile

Energy storage systems based on Lithium-ion batteries have been proposed as an environmental friendly alternative to traditional conventional generating units for providing grid frequency regulation. One major challenge regarding the use of Lithium-ion batteries in such applications is their cost competitiveness in comparison to other storage technologies or with the traditional frequency regulation methods. In order to surpass this challenge and to allow for optimal sizing and proper use of the battery, accurate knowledge about the lifetime of the Lithium-ion battery and its degradation behaviour is required. This paper aims to investigate, based on a laboratory developed lifetime model, the degradation behaviour of the performance parameters (i.e., capacity and power capability) of a Lithium-ion battery cell when it is subjected to a field measured mission profile, which is characteristic to the primary frequency regulation service.

An Overview and Comparison of Online Implementable SOC Estimation Methods for Lithium-Ion Battery

With the popularity of electrical vehicles, the lithium-ion battery industry is developing rapidly. To ensure battery safe usage and to reduce its average lifecycle cost, accurate state of charge (SOC) tracking algorithms for real-time implementation are required for different applications. Many SOC estimation methods have been proposed in the literature. However, only a few of them consider the real-time applicability. This paper classifies the recently proposed online SOC estimation methods into five categories. Their principal features are illustrated, and the main pros and cons are provided. The SOC estimation methods are compared and discussed in terms of accuracy, robustness, and computation burden. Afterward, as the most popular type of model-based SOC estimation algorithms, seven nonlinear filters existing in literature are compared in terms of their accuracy and execution time as a reference for online implementation.

Performance model for high-power lithium titanate oxide batteries based on extended characterization tests

Lithium-ion (Li-ion) batteries are found nowadays not only in portable/consumer electronics but also in more power demanding applications, such as stationary renewable energy storage, automotive and back-up power supply, because of their superior characteristics in comparison to other energy storage technologies. Nevertheless, prior to be used in any of the aforementioned application, a Li-ion battery cell must be intensively characterized and its behavior needs to be understood. This can be realized by performing extended laboratory characterization tests and developing Li-ion battery performance models. Furthermore, accurate performance models are necessary in order to analyze the behavior of the battery cell under different mission profiles, by simulation; thus, avoiding time and cost demanding real life tests. This paper presents the development and the parametrization of a performance model for a commercially available 13Ah high-power lithium titanate oxide battery cell based on laboratory-performed extended characterization tests.

Degradation Behavior of Lithium-Ion Batteries Based on Lifetime Models and Field Measured Frequency Regulation Mission Profile

Energy storage systems based on Lithium-ion (Li-ion) batteries have been proposed as an environmentally friendly alternative to traditional conventional generating units for providing grid frequency regulation. One major challenge regarding the use of Lithium-ion batteries in such applications is their higher cost-in comparison with other storage technologies or with the traditional frequency regulation methods-combined with performance-degradation uncertainties. In order to surpass this challenge and to allow for optimal sizing and proper operation of the battery, accurate knowledge about the lifetime of the Li-ion battery and its degradation behavior is required. Thus, this paper aims to investigate, based on a laboratory developed lifetime model, the degradation behavior of the performance parameters (i.e., capacity and power capability) of a Li-ion battery cell when it is subjected to a field measured mission profile, which is characteristic for the primary frequency regulation service.

Evaluation of different methods for measuring the impedance of Lithium-ion batteries during ageing

The impedance represents one of the most important performance parameters of the Lithium-ion batteries since it used for power capability calculations, battery pack and system design, cooling system design and also for state-of-health estimation. In the literature, different approaches are presented for measuring the impedance of Lithium-ion batteries and electrochemical impedance spectroscopy and dc current pulses are the most used ones; each of these approaches has its own advantages and drawbacks. The goal of this paper is to investigate which of the most encountered impedance measurement approaches is the most suitable for measuring the impedance of Lithium-ion batteries during ageing.

An overview of online implementable SOC estimation methods for Lithium-ion batteries

With the popularity of Electrical Vehicles (EVs), Lithium-ion battery industry is also developing rapidly. To ensure the battery safety usage and reduce the average lifecycle cost, accurate State Of Charge (SOC) tracking algorithms for real-time implementation are required in different applications. Many different SOC estimation methods have been proposed in the literature. However, only few of them consider the real-time applicability. This paper reviews the recently proposed online SOC estimation methods and classifies them into five categories, that is, Coulomb Counting methods (CCMs), Open Circuit Voltage methods (OCVMs), Impedance Spectroscopy Based Methods (ISBMs), Model Based methods (MBMs) and ANN Based methods (ANNBMs). Then, their principal features are illustrated and the main pros and cons are given. After that, SOC estimation methods are compared in terms of their accuracy, robustness, and computation burden. Finally, some conclusions are drawn.

Comparison of lithium-ion battery performance at beginning-of-life and end-of-life

Abstract In this paper, a comparison between the performance of a Lithium-ion battery at beginning-of-life (BOL) and at two increased degradation levels is presented. The capacity, internal resistance, and open circuit voltage of a 13 Ah high-power Lithium-ion battery had been measured at BOL for different temperatures, C-rates, and state-of-charge (SOC) levels. Then, two battery cells were aged at two different cycle aging conditions until they lost 40% and 60% of their initial capacity, respectively. At that moment, the two battery cells were removed from the aging processes and were subjected to characterization measurements similar to the ones performed at BOL. The obtained results shown that besides the expected capacity fade and internal resistance increase, there is a dramatic change in the variation of the battery performance parameters with the temperature, C-rate, and/or SOC, between a fresh cell and the two heavily degraded cells.

Lithium-ion battery dynamic model for wide range of operating conditions

In order to analyze the dynamic behavior of a Lithium-ion (Li-ion) battery and to determine their suitability for various applications, battery models are needed. An equivalent electrical circuit model is the most common way of representing the behavior of a Li-ion battery. There are different circuit models proposed and various techniques for parameterization of these models available in literature. Nevertheless, in this paper a second order equivalent circuit is proposed and the current pulse technique is used for its parameterization. This study shows results of extensive experimental characterization tests performed for a wide range of operating conditions (temperature, load current and state-of-charge) on a commercial available 13Ah high-power lithium titanate oxide battery cell. The obtained results were used to parametrize the proposed dynamic model of the battery cell. To assess the accuracy of the proposed dynamic model, simulation results are presented and compared against laboratory measurements, performed for different conditions.