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Munchen, Germany

Knezevic J.M.,BMW Peugeot Citroen GmbH | Katic V.A.,University of Novi Sad
Electronics | Year: 2012

The aim of this paper is to present a comparison of some popular methods for online harmonic estimation. The wellknown methods Descrete Fourier Ttransform (DFT), Enhanced Phase Locked Loop (EPLL), Adaptive Notch Filter (ANF) and method based on Extended Kalman Filter (EKF) are simulated and compared. The methods are compared in critical phases, such as the fast change of harmonic amplitudes and the change of the system frequency. Source

Fleckenstein M.,BMW Peugeot Citroen GmbH | Fischer S.,TU Darmstadt | Bohlen O.,BMW Peugeot Citroen GmbH | Baker B.,TU Dresden
Journal of Power Sources | Year: 2013

A new approach of Thermal Impedance Spectroscopy (TIS) is introduced for thermal characterization of battery cells. It examines the transfer behavior between internal heat generation and resulting battery surface temperature in the frequency domain. Compared to previously published TIS methods the internal heat generation forced by electrical operation can be determined without any previous knowledge or assumptions on the electric/electrochemical behavior of the battery cell. The complete procedure is demonstrated by the TIS-application on a cylindrical High-Power Li-Ion cell. By the use of a thermal battery model, its theoretical transfer function can be fitted to the TIS-measurement results in the Nyquist-Plot. Consequently, the specific heat capacity and the heat conductivity of the cell's jelly roll can be derived. A comparison of the exemplary operated TIS to conventional thermal characterization methods shows a difference of 5% in the heat capacity and 12% in the heat conductivity determination. Future improvements on the experimental setup are suggested in order to reach a higher measurement accuracy and additionally, the systematic advantages of the easy to operate and non-destructive TIS-method are presented. © 2012 Elsevier B.V. All rights reserved. Source

Paul S.,BMW Peugeot Citroen GmbH | Diegelmann C.,BMW Peugeot Citroen GmbH | Kabza H.,University of Ulm | Tillmetz W.,Center for Solar Energy and Hydrogen Research
Journal of Power Sources | Year: 2013

In this article, a new simulative approach that can determine ageing inhomogeneities in lithium-ion battery systems is outlined. The proposed method is based on a thermal electric ageing model of an entire battery system and the Monte Carlo Method. This method considers temperature inhomogeneities caused by active cooling within the battery system as well as cell spread and ageing spread caused by tolerances in the cell production. Each cell in the battery system model is represented by its own thermal electric cell model, having an initial capacity, initial internal resistance, ageing rate and thermal connection to the cooling system. In the experimental part of this research work, a battery system consisting of 96 lithium-ion cells based on the LiFePO4-technology was tested to investigate the capacity fade during a cycle life test. The results show that discrepancies in cells ageing within the battery system are a consequence of cell-to-cell spread and different loading of the cells, caused by temperature and SoC inhomogeneities within the battery system. Furthermore, the article will evince the gain of accuracy by using a battery system instead of a previous single cell approach for life prediction. © 2012 Elsevier B.V. All rights reserved. Source

Fleckenstein M.,BMW Peugeot Citroen GmbH | Bohlen O.,BMW Peugeot Citroen GmbH | Baker B.,TU Dresden
26th Electric Vehicle Symposium 2012 | Year: 2012

The occurrence and simulative reconstruction of local aging inhomogeneities in Li-ion cells caused by temperature gradients are described, which typically result from active battery cooling in automotive applications. The interactions of thermal, electrical and degradation behaviour are investigated on a prismatic Li-ion cell of 60Ah capacity comprising a graphite / NCM/LMO-blend system. Therefore a transient 3D thermal FVM model combined with a 3D impedance based FNM-model is implemented in order to consider thermal-electrical inhomogeneities. The model is validated by thermal measurements on operated Li-ion cells that are prepared with 8 internal thermocouples inside the jelly roll of the battery. For degradation investigations a weighted charge throughput cycle life model is discretized analogue to the thermal-electrical model. Temperature, current rate and SoC swing are each considered by an aging stress pre-factor. The aging model is exemplary parameterized by five isothermal cycle-life tests. The simulative results show the inhomogeneous capacity loss and impedance rise inside the battery cells with thermal gradient for two aging scenarios. As a result, also temperature and current density distributions inside the cell changes over lifetime. According to both aging indicators, a Li-ion battery cell with temperature gradient comprises an aging relevant temperature that equates the volumetric averaged jelly roll temperature plus 10% of the maximum temperature difference in the jelly roll. Source

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