AC-AC modular multilevel converter; Distribution system; Medium frequency transformer; Solid-state transformer AC-AC power converters; Electric power systems; Electric power transmission networks; Energy resources; Power control; Power converters; Power quality; Renewable energy resources; Conventional transformer; Coupling transformers; Distribution systems; Medium frequency transformer; Medium-voltage distribution systems; Modular multilevel converters; Power quality compensators; Solid state transformer (SST); Electric power system interconnection