Charging/discharging of battery energy storage system using 3-phase transformer

A battery energy storage system comprising:

• a plurality of battery boxes provided with a plurality of battery packs, wherein each of the plurality of battery boxes is connected to each other in parallel;
• a plurality of power converter systems respectively connected to the plurality of battery boxes to selectively charge or discharge the plurality of battery boxes through alternating current supplied from an external power source device;
• a transformer disposed between the external power source device and the plurality of power converter systems, the transformer being directly connected in series to each of the plurality of power converter systems by a respective terminal;
• a controller controlling the plurality of power converter systems to selectively charge or discharge the plurality of battery boxes, the controller being directly connected to nodes located at the respective terminal between each of the plurality of power converter systems and the transformer;
• and
• a monitor device configured to display a connection state between the plurality of battery boxes and the plurality of power converter systems,
• wherein the transformer is connected directly between the monitor device and the controller,
• wherein the transformer has exactly three sets of windings to stably supply the alternating current to the plurality of power converter systems,
• wherein the plurality of power converter systems are connected to each other in parallel, and
• wherein each of the plurality of power converter systems is connected in series to the plurality of battery boxes and is configured to individually charge or discharge each of the plurality of battery boxes or to charge or discharge all of the plurality of battery boxes.