In-vehicle battery management for high-volume applications

Battery management systems (BMS) have been introduced into series production in some vehicles recently. Together with new electric and/or powertrain features, battery management will have to migrate into high-volume applications. This paper characterizes drivers and demands for BMS in such vehicles. Concepts are reviewed for functional separation and communication between BMS and other vehicle components. It is shown that the concept of state-of-charge (SOC) and state-of-health (SOH), inherited from stationary and traction batteries, in general does not provide the information needed. Especially for lead/acid batteries, the dynamic power availability critically depends on the short-term charge/discharge history not covered by the SOC/SOH concept. An alternative concept (state-of-function, SOF) is proposed as a standard interface for a wide variety of BMS functionalities, effectively decoupling battery-related from vehicle-related functions. It can thus achieve a good compromise between application-specific functionality and cost-efficient commonality. Application of the SOF concept is demonstrated in a case study, namely a stop/start vehicle with regenerative braking and a 14 V single-battery system. It is shown that impedance-based measurements can significantly improve prediction of dynamic battery behavior, because it continuously and directly senses the SOF associated to the stop/start function.