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

This paper is focused on output voltage sharing among series-connected battery modules in an active battery management system (BMS) for a plug-and-play (PnP) DC micro-grid where the output voltage may vary in a wide range. In the considered active balancing system, battery cells are interfaced to the bus voltage through series connected step-up DC/DC converters. A cell current sensor is utilized to achieve BMS objectives, including state-of-charge (SOC) regulation, as well as output voltage sharing. To improve microgrid modularity, the battery pack behaves as a current source. A current-dependent droop between the individual output voltages to the input current is used to facilitate voltage sharing, which reduces the overall system cost and complexity by eliminating the need for an output current sensor in each DC/DC converter. Results of experimental validation are reported for a 1.5 kW experimental prototype system consisting of five series-connected modules, each module consisting of three battery cells and three DC/DC converters.