Jorge Varela Barreras

Datasheet-based modeling of Li-Ion batteries

Researchers and developers use battery models in order to predict the performance of batteries depending on external and internal conditions, such as temperature, C-rate, Depth-of-Discharge (DoD) or State-of-Health (SoH). Most battery models proposed in the literature require specific laboratory test for parameterization, therefore a great majority do not represent an appropriate and feasible solution. In this paper three easy-to-follow equivalent circuit modeling methods based only on information contained in a commercial Li-Ion cell manufacturers datasheet are presented and validated at steady state, comparing simulation results and manufacturers curves. Laboratory results are included in order to demonstrate the accuracy of parameters estimation. Results of each method are presented, compared and discussed for a Kokam SLPB 120216216 53Ah Li-Ion cell.

An Advanced HIL Simulation Battery Model for Battery Management System Testing

Developers and manufacturers of battery management systems (BMSs) require extensive testing of controller Hardware (HW) and Software (SW), such as analog front-end and performance of generated control code. In comparison with the tests conducted on real batteries, tests conducted on a state-of-the-art hardware-in-the-loop (HIL) simulator can be more cost and time effective, easier to reproduce, and safer beyond the normal range of operation, especially at early stages in the development process or during fault insertion. In this paper, an HIL simulation battery model is developed for purposes of BMS testing on a commercial HIL simulator. A multicell electrothermal Li-ion battery (LIB) model is integrated in a system-level simulation. Then, the LIB system model is converted to C code and run in real time with the HIL simulator. Finally, in order to demonstrate the capabilities of the setup, experimental results of BMS tests over a certain set of exemplary cases are shown.

Multi-Objective Control of Balancing Systems for Li-Ion Battery Packs: A Paradigm Shift?

While a great number of battery balancing circuit topologies have been proposed, the unique control objective typically pursued is equalization of single cell charge. However, a balancing circuit could offer potentially more control features, especially with topologies able to provide bidirectional power flow control. This has not been explored yet in literature or at least not with enough thoroughness. Thus, in addition to charge balancing, up to three more objectives could be pursued simultaneously. Firstly, virtual resistance control, in order to provide dynamic compensation for variations in terminal cell voltage. Secondly, thermal management, to achieve a more uniform temperature distribution within a battery pack. Third, on-board diagnosis or fault detection tools, e.g. to perform characterization tests or to identify and even isolate problematic cells. In this paper, this issue is discussed and evaluated for a battery pack made up of 48 large format Li-Ion cells in series in a e-mobility application. Simulation results demonstrate the technical feasibility of this newly defined concept.

Influence of Li-Ion Battery Models in the Sizing of Hybrid Storage Systems with Supercapacitors

This paper presents a comparative study of the influence of different aggregated electrical circuit battery models in the sizing process of a hybrid energy storage system (ESS), composed by Li-ion batteries and supercapacitors (SCs). The aim is to find the number of cells required to propel a certain vehicle over a predefined driving cycle. During this process, three battery models will be considered. The first consists in a linear static zeroeth order battery model over a restricted operating window. The second is a non-linear static model, while the third takes into account first- order dynamics of the battery. Simulation results demonstrate that the adoption of a more accurate battery model in the sizing of hybrid ESSs prevents over-sizing, leading to a reduction in the number of cells of up to 29%, and a cost decrease of up to 10%.

Functional analysis of Battery Management Systems using multi-cell HIL simulator

Developers and manufacturers of Battery Management Systems (BMSs) require extensive testing of controller HW and SW, such as analog front-end (AFE) and performance of generated control code. In comparison with tests conducted on real batteries, tests conducted on hardware-in-the-loop (HIL) simulator may be more cost ant time effective, easier to reproduce and safer beyond the normal range of operation, especially at early stages in the development process or during fault simulation. In this paper a li-ion battery (LIB) electro-thermal multi-cell model coupled with an aging model is designed, characterized and validated based on experimental data, converted to C code and emulated in real-time with a dSpace HIL simulator. The BMS to be tested interacts with the emulated battery pack as if it was managing a real battery pack. BMS functions such as protection, measuring of current, voltage and temperature or balancing are tested on real-time experiments.

Development of software and strategies for Battery Management System testing on HIL simulator

In comparison with tests conducted on real Li-ion batteries, Battery Management System (BMS) tests conducted on a Hardware-In-the-Loop (HIL) battery simulator may be more cost and time effective, more flexible and traceable, easier to reproduce and safer beyond the normal range of operation. This is particularly the case of tests at early stages in the development process or during fault simulation. However, the use of a HIL battery simulator requires the development of software (SW) and strategies for testing. While the possibilities are immense, it should be noted that the greater the level of complexity of the tests, the higher the demands for ad hoc development of SW and strategies. With regard to the latter, there is not a universal definition and there are different points of view. Therefore different strategies may be followed, which can be classified into many different ways according to the testing level, methods or processes. The aim of this paper is both to introduce the theoretical principles of BMS testing and to present a practical approach to develop ad hoc SW and strategies for BMS testing at system level on a commercial HIL simulator.

Evaluation of a Novel BEV Concept Based on Fixed and Swappable Li-Ion Battery Packs

In this paper a novel battery electric vehicle (BEV) concept based on a small fixed and a big swappable li-ion battery pack is proposed in order to achieve: longer range, lower initial purchase price and lower energy consumption at short ranges. For short ranges the BEV is only powered by the relatively small fixed battery pack, without the large swappable battery pack. In this way the mass of the vehicle is reduced and therefore the energy consumed per unit distance is improved. For higher ranges the BEV is powered by both battery packs. This concept allows the introduction of subscription-based ownership models to distribute the cost of the large battery pack over the vehicle lifetime. A methodology is proposed for the analysis and evaluation of the proposed concept in comparison with a direct owned non swappable single pack BEV, proving that significant improvements on city fuel economy (up to 20 %) and economic benefits are achievable under several scenarios. These results encourage further study of battery swapping service plans and energy management strategies.

An improved parametrization method for Li-ion linear static Equivalent Circuit battery Models based on direct current resistance measurement

During many years, battery models have been proposed with different levels of accuracy and complexity. In some cases, simple low-order aggregated battery pack models may be more appropriate and feasible than complex physic-chemical or high-order multi-cell battery pack models. For example: in early stages of the system design process, in non-focused battery applications, or whenever low configuration effort or low computational complexity is a requirement. The latter may be the case of Electrical Equivalent Circuit Models (EECM) suitable for energy optimization purposes at a system level in the context of energy management or sizing problem of energy storage systems. In this paper, an improved parametrization method for Li-ion linear static EECMs based on the so called concept of direct current resistance (DCR) is presented. By drawing on a DCR-based parametrization, the influence of both diffusion polarization effects and changing of Open-Circuit Voltage (OCV) are virtually excluded on the estimation of the batterys inner resistance. This results in a parametrization that only accounts for pure ohmic and charge transfer effects, which may be beneficial, since these effects dominate the battery dynamic power response in the range of interest of many applications, including electro-mobility. Model validation and performance evaluation is achieved in simulations by comparison with other low and high order EECM battery models over a dynamic driving profile. Significant improvements in terms of terminal voltage and power losses estimation may be achieved by a DCR-based parametrization, which in its simplest form may only require one short pulse characterization test within a relatively wide range of SoCs and currents. Experimental data from a 53 Ah Li-ion pouch cell produced by Kokam (Type SLPB 120216216) with Nickel Manganese Cobalt oxide (NMC) cathode material is used.

Tvindkraft: Implementing a 500 kW 21-IGBT-based frequency converter for a 1.7 MW wind power conversion system

The 54-meter-high Tvindkraft windmill was built by a group of volunteers during 1975-1978, as an argument for renewable energy sources as well as an argument against nuclear power. At that time it was the worlds biggest windmill. So far, Tvindkraft has been running for 35 years, proving that a well-constructed wind turbine is a sustainable approach to renewable energy utilization. This paper deals with the analysis, simulation, implementation and experimental testing of a new 500 kW 21-IGBT-based frequency converter that will run in parallel with the former 12-Thyristor-based frequency converter to fully utilize the capacity of the windmill. Simulations and experimental results are presented side-by-side to verify the proper functionalities of the frequency converter described in this paper.

Results of Screening over 200 Pristine Lithium-Ion Cells

This paper presents and analyses results from simplified screening tests conducted on more than 200 large format Kokam NMC lithium-ion pouch cells at their beginning of life. Such data are not common in the literature. The cells were sandwiched between two large heat sinks for testing, which was conducted using an automated dis/charge test system and thermal chambers. Analysis of the screening data gives valuable quantitative information, but also qualitative insights into the nature of cell-to-cell variations and the complex interactions between battery temperature, capacity, voltage or internal resistance. In this paper, statistical results show that the cells under test present small cell- to-cell differences in capacities and internal resistances at their beginning-of-life. For example, the relative standard deviation is below 0.4 % for the capacities and 2.5 % for the pure ohmic plus polarization resistances. However, these differences may be enhanced by system level issues, and exacerbated over time by complex degradation mechanisms.