A robust contactless capacitive communication link for high power battery systems

Large Li-ion battery systems are being used in a growing number of applications. Due to lack of standards and various requirements, the battery systems have to be specifically designed for each application. This need for a specific design also affects the battery monitoring circuit. In order to reduce design effort, distributed battery monitoring systems integrated into the cells were proposed. Economies of scale allow these circuits to be produced at low cost per unit as they will be needed in every single battery cell. One of the major challenges of the distributed battery monitoring concept is the communication link for the monitoring circuits: it has to be robust, reliable, and easy to install. As a possible solution, a capacitively coupled data transmission link for a battery system consisting of up to 100 smart battery cells is investigated by simulation and experiment. Relevant influence factors of the physical implementation on a capacitive voltage divider determining the transmitted data signal are identified and evaluated, considering application specific constraints. As a result, a suitable signal conditioning circuit using frequency shift keying (FSK) modulation is proposed and experimental results obtained with a prototype implementation of the proposed circuit are presented.