Prof. Dr.-Ing. Karl-Ragmar Riemschneider
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Working Group Wireless Battery Cell Sensors and Distributed Battery Monitoring
Large batteries with multi-cell structure are a key technology for sustainable energy systems in smart grids and for electric vehicles. The knowledge of the state of each battery cell ensures an optimized cycle control and lifetime utilization. The lifetime aging often leads to diverging states of charge and health of each cell. These differences result in evident uncertainities, if the battery is observed as whole unit. Precise and dense measurements from each cell are necessary to over-come this “blackbox-observation”.
The approach of our research group is to use data of voltage and temperature delivered from in-telligent sensors which are directly mounted inside the cells. Pressure and electrochemical pa-rameters are planed objectives of research. These raw data are pre-processed in low-power and low-effort microcontrollers as parts of the sensors. The communication from cell sensor to a battery control unit utilizes dedicated wireless techniques. Wireless communication without cables is very robust. Moreover, wireless solutions do not have the major problem of large voltage potential levels up to several hundred volts because of serial connected cells. The large voltages are in an expensive contrast to the millivolt resolution requirements of the state observer models in modern batteries technologies.
The short and stable geometric distances between cell sensors and battery control unit is advan-tageous and allows to implement very low cost and energy efficient wireless receivers and trans-mitters, which can be completely integrated in microelectronic chips. The engineering research aims to deliver flexible classes of sensor devices. Very different battery models have to be supported. A battery monitoring and control langue (BMCL) describes the distributed information structure of the data acquisition and modeling system. The language consists for example of con-trol commands, measurement data messages and distributed or centralized functions.
Balancing of ‘weak’ and ‘strong’ cell capacities using effectors (switchable current paths) as parts of the sensors will need undiscovered decision models. The state of health (SOH) significantly profits of the well balanced states of charge (SOC) of the cells. Similar situation is given for a probably necessary parallel arrangement of cells, due to the uncertainty of volatile currents between aged cells.
The ongoing research project BATSEN (Wireless Cell Sensors for Vehicle Batteries) is supported by the BMBF and six companies of automotive and battery industry since 2010.
Our industrial project partners are Still GmbH Hamburg (electrical forklifts), Volkswagen AG Wolfsburg (automotive), Bertrandt AG Wolfsburg (automotive development), Coilcraft Inc. UK/US (electronic components), OMT/ECC Luebeck (battery producer and electrochemial systems), Fey Elektronik Sevetal (battery and electronic systems). As synergetic background we are also involved in a magnetic sensors and signal processing project in co-operation with NXP Semiconductors and in the european project electromobility NSR Interreg IV.
The working group is notably focused to application oriented and engineering-minded approaches In close co-operation with our partners.
As part of the graduate school the Ph.D. candidate will contribute to the activities of battery sen-sors and state observation and modeling. The practical research work is planed as close collabo-ration in the existing team of professors, research engineers as Ph.D. candidates and experi-enced laboratory engineers, industrial experts and a group of master and bachelor students.
First demonstrators and experiments with our battery sensor systems have promising results. Positive feedback from experts as well as international patents and patent applications are available. It is strongly expected that the experience is applicable to the field of dedicated battery management for the smart grid technology.