A battery model for monitoring of and corrective action on lead-acid EV batteries

With the oil crisis in the early 1970s an intensive development of electric vehicles, i.e. passenger cars, delivery vans, and buses was initiated. Already in an early stage of the demonstration phase it became quite clear that the lead-acid battery, more precisely the battery pack, requires more attention than can be provided by simple meters for current, voltage, and ampere-hours. This led to the requirement for a sophisticated monitoring system, which should be extended to a supervisory system. The author discusses the main objectives of the supervisory system and the algorithm for determining the residual capacity. Weak cells or modules may be called those with a capacity significantly lower than the average or those with extremely high self discharge, e.g. due to internal shorts. They may be supported by energy transfer either full battery or from modules via DC/DC converters. The pros and cons as well as hardware cost and reliability implications of these methods is discussed. The actual power which can be transferred depends on the state of charge as well as on the actual load on the full battery and also on the capacity deficit of the modules to be assisted. An applicable algorithm is demonstrated.<>