Bernhard Schweighofer

Modelling of high power automotive batteries by the use of an automated test system

In order to estimate the field of application for an electrical energy storage, its performance at different operating conditions has to be measured and evaluated. An automated test system has been designed to speed up measurement and to ensure reproducible measurement conditions. The paper focuses on the performance of this test system and on measured data. Based on this data, a battery model of a NiMH cell is parameterized and the obtained results are discussed.

Automatic Antenna Tuning Unit to Improve RFID System Performance

Systems for radio-frequency identification (RFID) realize a bidirectional wireless communication between a reader device and cheap passive tags (e.g., an RFID chip with an antenna printed on badges for access-control systems) in the near field of an antenna. This paper deals with the automatic and fast tuning of the resonant reader antennas in the widely used 13.56-MHz frequency band, resulting in a performance improvement and an increased read/write range. A novel RFID reader system is proposed with a tuning transformer for the automatic adjustment of the resonant circuit center frequency. This is achieved by shifting the magnetic operating point (i.e., the biasing direct-current (dc) magnetization) of a Ni-Zn ferrite transformer by means of an additional dc winding. The operation principle and the performance potential of this device are demonstrated by measurements on a prototypical RFID system.

Measurement and simulation framework for throughput evaluation of narrowband power line communication links in low-voltage grids

High-data-rate narrowband Power Line Communication (PLC) is a prominent candidate for smart grid communications in the low-voltage grid at low operational costs. However, the power-line channel is fairly harsh in terms of time-variance, frequency selectivity, and observable impulsive and narrowband noise sources. These unpredictable phenomena motivate selective measurement campaigns in addition to common channel modeling. While previously published measurement studies were fairly limited in duration, we report on a measurement setup for capturing power-line channels over weeks and show measurement results highlighting day-dependent channel effects on selected communication links. Furthermore, previous performance simulations are typically based on simplified channel models and limited in terms of the detail level at the physical layer or lack a consideration of higher-layer protocol overhead. We present a novel simulation methodology which is based on detailed physical-layer simulations exploiting measured, time-varying channel data, and incorporates protocol overhead models for transport-layer throughput estimation. Exemplary simulation results include the newest, commercially available narrowband PLC standards in their latest version, that is ITU-T G.9903 (G3) and G.9904 (PRIME), as well as IEEE 1901.2.

An accurate model for a lead‐acid cell suitable for real‐time environments applying control volume method

The accurate simulation of battery cells is of growing interest in automotive industry especially in hybrid vehicle technology. Conventional lumped parameter models are not able to predict the battery voltage accurately. Thus models describing the physics of the battery cell are searched. In this paper a model consisting of six partial differential equations is proposed, which predicts the state of charge (SOC) and the battery voltage for given charge and discharge current densities.

Fast and accurate battery model applicable for EV and HEV simulation

The need to reduce fuel consumption, minimize emissions, and improve levels of safety, comfort, and reliability is expected to result in a much higher demand for electric power in future cars. In order to develop the needed control algorithms and to optimize the required components some kind of virtual prototype environment is needed. Even so for most components good models already exist, an adequate model for the battery is still missing. However, this is needed since the battery has a large impact on the efficiency of the total system. Therefore this work presents a battery model applicable for EV and HEV simulations.

Magnetic DC-Properties of LTCC-Ferrite Material and Their Temperature Dependence

Low temperature co-fired ceramic (LTCC) technology allows to create 3-D ceramic devices from tapes with different electrical and magnetic properties. Recently ferrimagnetic materials became available as LTCC tapes. To magnetically characterise the ferritic LTCC material we have realised ring samples using ESL 40012 LTCC-tapes. The ring core fabrication process and the sample preparation are described in detail. The quasi-static B(H) curve has been measured by inductive methods, and its dependence on temperature between room temperature and the Curie temperature is shown.

Selection of Magnetic Materials for Bearingless High-Speed Mobile Flywheel Energy Storage Systems

Beside a higher amount of reactive power and a lower power to weight ratio compared with other machine types, the switched reluctance motor (SRM) features robustness, low cost, failure tolerance, and a wide operation temperature range. With additional power electronics and construction effort, the SRM can be operated as a bearingless drive. This is important to increase the lifetime of bearings in vacuum since their lubrication is difficult. In this paper, the technical potential of this particular motor topology to produce torque and radial force is evaluated based on finite element simulations. Additionally, the estimated hysteresis and eddy current losses during the normal and bearingless drive operation depending on the selected soft magnetic materials are evaluated.

Method for the Measurement of Transient Magnetic AC Properties of Soft Ferrites

NiZn-ferrite materials are commonly used soft ferrites in all sorts of devices utilizing ferrimagnetic properties in a frequency range up to several tens of megahertz. Manufacturer data sheets of material properties usually contain values for the initial permeability for a given amplitude of the flux density for different frequencies, and some numbers for the loss factor. Strictly, these values are reasonable for steady-state processes with harmonic excitations only. Informations about the transient behavior of the material are contained in a single (dis)accommodation factor, if present at all. The phenomena of (dis)accommodation or generally the change of the magnetic properties with time are explained by the magnetic aftereffect (MAE). We describe a measurement system to characterize the transient magnetic properties of ferrite rings, and present some results for a commercial ferrite torus. In contrast to measurement systems working with impedance analyzers (LCR-meter) or with resonant circuits, our system gives results with a much higher time resolution. The behavior of the material can be determined almost from the very first beginning of the excitation.

Magnetism Versus LiFePO 4 Battery’s State of Charge: A Feasibility Study for Magnetic-Based Charge Monitoring

In recent years, lithium ion batteries have become wide-spread energy sources for various battery-powered applications. In particular, LiFePO4 batteries are increasingly used for high-power automotive and storage applications. Unfortunately, the state of charge (SOC) is not uniquely determined by measuring just the LiFePO4 batterys open-circuit voltage. However, an alternative approach for SOC determination is introduced by investigating the batterys magnetic susceptibility. This is motivated by the iron atoms magnetic state in the LiFePO4 cathode material, which changes during charging and discharging. The magnetic susceptibility of differently charged battery samples will be investigated to correlate the magnetic moment with the SOC in view of a new sensor concept.

Improving kinetic energy storage for vehicles through the combination of rolling element and active magnetic bearings

The demand for short term energy storage providing high power for electric and hybrid-electric vehicles is increasing dramatically. Stationary flywheel energy storage systems (FESS) are established as uninterruptible power supply (UPS) and represent an emerging market. In contrast, mobile FESS are currently only used in few applications such as motor sports. To enable a wider use in personal and public transportation the lifespan of the flywheels bearings needs to be increased significantly. This paper presents an alternative approach to extend the lifespan of the flywheels bearings by using a combination of rolling element and active magnetic bearings (CREAMB).