Digital Battery Management Design for Point-of-Load Applications with Cell Balancing

In portable devices, such as notebook computers and tablet personal computers, one or more battery strings with multiple lithium-ion (Li-ion) cells have been used since long. Life cycle and safety of the Li-ion battery strings are crucial aspects. A battery management system (BMS) is required for monitoring the status of each cell and balancing their state of charge (SoC). However, most conventional cell equalizers provide only cell monitoring and equalization functions. In this article, a parallel architecture is presented that not only achieves battery cell equalization but also is capable of providing voltage regulation for point-of-loads (POLs). In the proposed equalizer, several isolated dc-dc converters are constructed. The input terminal of each converter is connected to a battery cell, and the output terminals are connected to one point for the poststage POLs. A battery voltage acquirement system is built for SoC estimation. A central BMS controller is realized using a field-programmable gate array to receive sensed signals and control all the functions. The entire system is verified using the experimental results for a battery string involving three NCR 18650B Li-ion cells connected in series.