System and method for controlling multi-frequency of multiple microgrids based on back-to-back converter

The present invention relates to a system to control multi-frequency of multiple microgrids based on a back-to-back converter, which is to control a frequency of each microgrid within each allowance through a multifunctional back-to-back (BTB) voltage source converter (VSC) including a rectifier and an inverter connected to a link point of the microgrid, and to compensate and improve power quality to solve power quality lowering of each microgrid when degradation of the power quality occurs. The system comprises a standalone or off-grid microgrid which includes one or more distributed power sources and energy storage devices; and a BTB VSC which is composed of a rectifier unit, and an inverter unit to share a common DC link between the rectifier unit and the inverter unit, and links multiple standalone microgrids through an AC line so as to perform multi-frequency control by considering a load quality level of each microgrid.