Performance Results for a Universal Lithium Ion Battery Management System

The advantages of lithium-based batteries over lead acid batteries have created great interest in developing safe and cost effective drop-in replacements. To achieve the required cost effectiveness and safety of the battery, Battery Management Systems (BMS) are critical to avoid over-charging, over-discharging, and continuously and accurately determining the State of Charge (SOC), State of Health (SOH), and State of Life (SOL) of the battery. In a program funded through a U.S. Army–TARDEC SBIR, the authors developed and tested a military-grade BMS that includes: (1) a Kalman Filter-based SOC estimation algorithm with better than 5% accuracy; (2) continuous cell monitoring to avoid over-charging or over-discharging; (3) active and passive cell balancing; (4) an innovative, low cost, and high-accuracy current sensing method; and (5) vehicle-level communication capability. Our BMS uses a modular, universal architecture that supports any lithium-based chemistry, pack size, or configuration. This is particularly important when multiple packs are series connected to achieve high voltage. This paper presents our design approach, test data which validate performance expectations, and our plans for integrating this BMS with an emerging class of 6T format batteries for U.S. Army tactical vehicle starting and Silent Watch energy storage needs. INTRODUCTION Lithium-based batteries promise excellent performance in terms of lifetime, energy density, and power density. However, they require careful management to avoid personnel injury and equipment damage. Consequently, there is extreme interest in developing an accurate Battery Management System (BMS) to take advantage of the positive attributes of lithium-based chemistries without sacrificing flexibility and safety. However, the lack of proper BMS standardization and inaccurate state estimation algorithms has hampered the widespread adoption of lithium chemistries in spite of their advantages. In this paper we describe our BMS and present results that show that we can: (1) provide State of Charge (SOC) estimation accuracy to better than 5%; (2) provide a universal architecture that is adaptable to other chemistries, capacities and formats; (3) actively balance the series cells in a pack; and (4) enable operation over a wide range of temperatures. The primary application that we Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.