Evaluation of State-of-Charge Indicator Approaches for EVs

Studies of battery management systems (BMS), including state-of-charge (SOC) algorithms, were performed in the Battery Test and Vehicle Dynamometer Laboratories at the INEL. The test and evaluation of the SOC algorithms indicated that the capacity rate dependent and adaptive approaches to determining battery SOC yielded RMS errors between the indicated and actual states-of-charge of less than 10% if battery temperature and aging effects were not dominate. The BMS tested were not sufficiently accurate and reliable to permit their use as the primary means of charge control during the various INEL test programs. Considerable progress has been made in the development of BMS, but further work is needed before the systems can be used with confidence in either the charge or discharge modes without careful attention from the user.