Implementation of a battery back-up system for generator set downsizing

A battery back-up system coupled to a micro-grid network through a two-level inverter/rectifier module has been designed and implemented. The local grid is primarily supplied by one diesel generator set (genset) and the battery back-up system can be connected to the grid if required. The two-level inverter/rectifier module consists of six insulated-gate bipolar transistors (IGBTs) distributed in three legs with their anti-parallel diodes respectively. The system operates in three modes: charging, paralleling and stand-alone. Depending on the operation mode, the two-level IGBT module acts as rectifier or as an inverter. When the system is operating in the charging mode, the two-level module acts as an active rectifier and its output is used to charge the two battery packs, which are connected in series. In the charging mode, the batteries are firstly charged in current mode and then in voltage mode to maintain the charge. These batteries are used to supply the system when it is operating in the paralleling or stand-alone mode. In the stand-alone mode, the system is capable of maintaining the output voltage when operating in unbalanced load conditions.