(Invited) Management Systems for Lithium-Ion Batteries

Abstract

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 also 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, the effects of cell capacity imbalance, whether present from the start, or evolved over time, must be mitigated. This paper 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 has the ability to interrupt current and disconnect the battery if limits are exceeded. 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.