Voltage Sharing With Series Output Connected Battery Modules in a Plug-and-Play DC Microgrid

This article presents output voltage sharing among series output connected battery power modules (BPMs) in plug-and-play (PnP) dc microgrids with a wide bus voltage range. The system provides active cell balancing and interfaces cells to the bus voltage through series output connected BPMs. A cell current sensor is utilized to achieve both state-of-charge regulation and output voltage sharing. To improve microgrid modularity, the battery pack behaves as a current source. A current-dependent droop between the individual output voltages and input currents is used to facilitate series output connected voltage sharing with bidirectional power flow, simple control, and smooth transitions between charge and discharge regions. Experimental results are reported for a 3 kWh 1C-rate prototype consisting of two parallel 24 V subsystems, with five series output connected BPMs in each subsystem. Each BPM consists of three battery cells and three 100 W dc-dc converters.