VRLA battery rapid charging under stress management

This paper discusses an approach for closed-loop charge control of valve-regulated lead-acid (VRLA) batteries used in telecommunication standby power applications. This is an alternative to conventional preprogrammed, configuration-driven charge control. The developed approach uses the battery´s response to the supplied charge to control the recharge process. In this way, only the energy that can be absorbed by the battery in the desired recharge operation is dealt with. Hence, excessive energy that causes battery stress, or lack of energy that slows the charging process is avoided. Two main sources of recharge stress are identified: (a) thermal stress, and (b) charge saturation stress. A charge control algorithm based on thermal management and charge saturation avoidance is suggested. The algorithm utilizes a fuzzy state-of-charge estimation model that derives the state of charge from real-time parameters. This in turn calculates the maximum recharge rate that maintains the battery´s thermal rise within permissible limits.