Available at: https://digitalcommons.calpoly.edu/theses/1392
Date of Award
MS in Electrical Engineering
A high performance battery management system (BMS) for large capacity cells was designed, built, and tested in a cycle of three revisions. The BMS was designed for use in applications where the battery pack configuration is unknown: parallel, series, or any combination. Each of the cells is equipped with its own battery management system to allow a peer-to-peer mesh network to monitor the safety of the cell. The BMS attached to each cell also is equipped with a 25A DC/DC converter to perform active balancing between cells in a string. This converter can transfer charge to (or from) a cell of higher potential and a cell of lower potential at the same time. The balancing circuit has a peak efficiency of 85.3%. The system draws only 53mA while balancing at 25A helping to increase low current performance. The system draws just under 5mA over all while active. Each BMS is equipped with one current sensor, which can measure ±800A with a second ±120A current range. Additionally, the board is equipped with coulomb counting to provide a better understanding of each cell.
While this design has many great features, lack of full software support makes many of the subsystems dependent on user interaction to use. As a result, the design is not fully complete. Additionally, last minute design changes on the final revision resulted in detrimental effects to the accuracy of many of the analog circuits including the current sensing features.