Energy storage system

An energy storage system comprising:

• a battery container comprising:
• sub-battery containers comprising battery racks;
• and
• a master battery container comprising:
• battery racks comprising battery modules;
• a system battery management system (BMS) configured to monitor states of, and to control operations of, the battery racks of the master battery container and the sub-battery containers;
• a master programmable logic controller (PLC) configured to monitor a state of the master battery container, to transmit a monitoring result to the system BMS, and to transmit data to, or receive data from, the system BMS;
• a first switch configured to be controlled by a switching control signal from the master PLC based on a request from the system BMS to control electrical connection between one or more of the battery racks and the PCS;
• and
• a second switch configured to be controlled by a switching control signal of the system BMS to control electrical connection between one or more of the battery modules and the first switch;
• and
• a power conversion system (PCS) configured to:
• convert direct current power from the battery container into alternating current power, and transmit the alternating current power to a power system;
• and
• convert alternating current power from the power system into direct current power, and transmit the direct current power to the battery container
• wherein the system BMS and the master PLC are further configured to transmit and receive data via a contact communication method.