Method for controlling a reactive power flow in a hybrid energy storage system

A method for actively controlling an output voltage of a first energy storage system connected to a second energy storage system The method can comprise providing at least one power flow demand value of at least one phase load and/or a phase grid; providing an output voltage measurement value and a current measurement value of the second energy storage system; calculating a power-flow-demand current value of the second energy storage system based on the at least one power flow demand value and the output voltage measurement value; calculating a control output voltage value of the first energy storage system based on the power-flow-demand current value and the current measurement value of the second energy storage system; modulating the control output voltage value into at least one control signal; and controlling the output voltage of the first energy storage system based on the at least one control signal.