Battery energy storage system and method therefor

A method for a battery energy storage system (BESS) comprising a power converter system (PCS), at least one sensor, and a plurality levels of controller distributed in the BESS, the method comprising:

• charging/discharging, via the PCS, a battery including at least one battery module by using a superimposed control signal in which an electrochemical impedance spectra (EIS) reference signal for a state of health (SOH) evaluation of the battery is superimposed on a control signal for charging/discharging the battery, wherein the EIS reference signal has a frequency selected for EIS;
• detecting, via at least one sensor, response data of the battery in the charging/discharging by the superimposed control signal;
• wherein the respective levels of controller are in communication with each other and the response data of the battery are accessible to the respective levels of controller, and
• wherein the SOH evaluation of the battery is conducted in such a dynamic manner that the response data of the battery is processed at any level of controller to obtain a result for the SOH evaluation.