State-of-Charge Balancing With Parallel and Series Output Connected Battery Power Modules

This article presents a new state-of-charge (SOC) balancing method with parallel and series output connected battery power modules (BPMs) in an active battery management system (BMS.) To increase both the battery pack and system-level modularity, the BMS controls the average SOC of the entire battery pack by regulating the input currents of all BPMs to a common reference. A balancing loop introduces input current offsets to regulate all cells SOCs. The BMS functions are distributed between a central controller for battery pack SOC regulation, and a module controller that regulates the input current of the individual BPMs. Experimental results are presented on a 1.5 kWh 1C-rate prototype with five series output connected battery bricks. Each battery brick consists of three parallel output connected BPMs, which employ three battery cells and three 100 W dc/dc converters.