Battery evaluation and battery management system

Various kinds of lithium batteries were evaluated in the Battery Evaluation Lab at Univ. Massachusetts, Lowell. The battery types evaluated were lithium cobalt oxide (ion type), lithium iron phosphate, lithium cobalt oxide (polymer type). Evaluations included gravimetric and volumetric energy density, gravimetric and volumetric power density, fast chargeability, realistic road test performance and life cycle. The effect of temperature on all characteristics was also evaluated.;It was found that the lithium cobalt oxide (ion type) cell were unsuited for high power applications such as electric vehicles. While the cell initially had the specified energy density, the power density (both charging and discharging) was inadequate. Furthermore, the ion-type lithium cobalt cell showed poor cycle life.;The polymer type lithium cobalt oxide cell and the lithium iron phosphate cell both demonstrated good performance on all applied tests. Cycle life, energy density, power density and temperature tolerance were all adequate for electric vehicle applications.;It was also found that over-charging lithium cells is a fire hazard and that to use an electric vehicle with lithium batteries, a battery management system must be used to avoid hazardous conditions.;Towards that end, a battery management system was designed, fabricated and tested at the Battery Evaluation Lab at UML.;The pros and cons of various types of Battery Management Systems are discussed. The virtues of power resistors, "flying" capacitors, multi-winding transformers, zener diodes, individual chargers and voltage clamps are discussed. The salient requirements of a full function battery management system are listed.;A battery management system based on current shunt / voltage clamp-type equalization scheme is described in detail. Battery management system sub-components of computer interface module (Master Controller), Battery Interface (Remote Unit), Current Shunt (Voltage Clamp) and battery charger are presented.;Several experiments to demonstrate the practicality and efficacy of the battery management system are described.