EV BMS with Distributed Switch Matrix for Active Balancing, Online Electrochemical Impedance Spectroscopy, and Auxiliary Power Supply

A distributed switch matrix is proposed that enables balancing of series-connected groups of battery cells in a pack through dc-dc converters. The switch matrix is used to develop a multi-function electric vehicle Battery Management System (BMS) that features active cell balancing, online electrochemical impedance spectroscopy, and 12V auxiliary bus power supply. The BMS is designed for 6S2P, 88Ah custom liquid-cooled modules. A prototype system is demonstrated using a 1S2P, 0.5mΩ nominal impedance battery unit. Bidirectional active balancing operates at 2.5A while power is exchanged with the auxiliary bus. The 88Ah battery impedance is measured from 11 to 2000Hz for a varying range of temperatures. Based on a Monte-Carlo battery pack simulation under randomised cell capacity imbalance, an estimated 20% average increase in usable pack capacity can be achieved with active balancing engaged.