Battery management systems (BMS) for large Li-ion batteries are, of themselves, complex systems. The complexity starts with voltage measurement for individual cells. Large batteries may have 96, 192, or more, series connected cells, so requiring complex wiring harnesses. The high noise environment provides additional challenges for wiring and also analog front end and analog to digital conversion system design. For safety, and to help with state-of-charge (SOC) estimation, temperature sensors must be located throughout the battery. A computational infrastructure estimates SOC for each cell. The estimate is typically based on cell voltage, measured current, estimated cell resistance, integrated current and temperature. Additionally, cell capacity imbalance, whether present from the start or evolved over time, must be corrected.

This talk will attempt to provide some insight into BMS design for mass-produced large batteries. The applications, whether for electric vehicles (EV) or stationary storage, are generally safety critical, so placing additional demands on the BMS. Typically, the BMS also manages the interaction between the battery and the remainder of the system. It sets limits for allowed charge and discharge currents and can interrupt current and disconnect the battery if limits are exceeded. This area will also be addressed, with a particular focus on fusing challenges for EV applications. Power transfer of 500 kW or more may be required. Depending on the application this may be for only a few seconds, or it may be indefinite. In additional to safety, reliability is also critical. For example, the many required cell connections must remain intact for the intended service life of the installation. This will be addressed, touching also on design of the overall battery pack.